GB2523836A - Mechanical linkage and trigger assembly for a coupling member for a detachable tow ball - Google Patents

Abstract

A mechanical linkage 202 for a detachable tow ball comprises a housing 2, a shuttle 8 movable relative to the housing between a first position and a second position and an actuation shaft 26. The actuation shaft includes first and second interface lugs (121,122, fig 6C) which cooperate with first and second interface slots 101,102 on the shuttle. Rotation of the actuation shaft in a first direction drives the shuttle in the direction from its second position to its first position. When the shuttle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, an abutment section of the second interface lug contacts an abutment section of the shuttle and prevents the shuttle from reaching its first position. The mechanical linkage may comprise a handle 24 that is releasably connectable to the actuation shaft. The handle may be disposed at a position off the rotational axis of the actuation shaft. The actuation shaft may comprise interface lugs and slots configured to meshingly engage to form a rack and pinion mechanism, where each interface lug includes an arcuate portion which is substantially in the shape of a segment of a cylinder.

Description

MECHANICAL LINKAGE AND TRIGGER ASSEMBLY FOR A COUPLING MEMBER

FOR A DETACHABLE TOW BALL

The present invention relates to a mechanical linkage of the kind that may be used, for example, in operation of a detachable tow ball. The present invention also relates to a trigger assembly for a coupling member of the kind that may be used, for example, in operation of a detachable tow ball.

In some circumstances, attaching a traditional tow bar to a vehicle may be deemed undesirable. For instance, some drivers feel that the tow ball (to which a trailer, caravan or the like can be connected for towing) projecting from the back of their vehicle is unsightly or inconvenient when not in use. In such circumstances, a tow bar with a detachable tow ball may be preferable. As with traditional tow bars, a tow bar with a detachable tow ball requires a mounting assembly to be fitted to the vehicle. Unlike traditional tow bars however, the tow ball can be removed from the mounting assembly when not required, and re-attached when towing is to take place. This allows the rear of the vehicle to be returned to its original shape and appearance when desired.

An automatic detachable tow ball is a detachable tow ball that locks into place automatically when it is positioned correctly with respect to a mounting assembly of the tow bar. Most current automatic detachable tow balls utilise a coupling shaft on the tow ball, which is inserted into a collar on the mounting assembly of the tow bar. When the shaft is inserted into the collar a trigger mechanism on the shaft releases a sprung shuttle, usually in the form of an elongate bolt, which drives one or more coupling elements to project from the shaft into corresponding recesses in the collar, securing the tow ball to the mounting assembly. To detach the tow ball again, the sprung shuttle is withdrawn, most commonly by rotating a handle connected to the shuttle via a rack and pinion. This allows the coupling element(s) to be withdrawn back into the shaft, releasing the tow ball from the collar.

Most presently available automatic detachable tow balls utilise either ball-type or lever-type trigger mechanisms. In either mechanism, prior to release of the shuttle a latch member is positioned to lie partially in a bore in the shuttle and partially in a bore in the housing of the shaft, preventing relative movement of the shuttle and the shaft. When the shaft of the tow ball is introduced into the collar of the mounting assembly, the collar moves a latch release member, which disturbs the latch member and releases the shuttle.

In the case of a ball-type trigger mechanism the latch member is a ball bearing, and the latch release member is another ball bearing received within the above bore in the shaft housing. A spring is positioned in the bore in the shuttle, and acts to push the latch ball bearing outwards from this bore. The latch member being urged outwards within the bore in the shuttle pushes the latch release ball bearing outwards within the bore in the housing so that it projects beyond the surface of the shaft. The collar of the mounting assembly has an internally frustro-conical mouth which acts on the latch release ball bearing when the shaft is inserted into the collar, forcing the latch release ball bearing deeper into the bore in the housing. This forces the latch ball bearing deeper into the bore in the shuttle (against the bias of the spring) at which point the shuttle is free to move. When the shuttle is retracted and the shaft removed from the collar, once the bore in the shuttle is re-aligned with the bore in the housing, The laTch ball bearing (under action of the spring) moves back outwards so that it is partially received in each bore. This pushes the latch release ball bearing outwards, so that it projects from the surface of the shaft once again.

In a lever-type trigger mechanism the latch release member takes the form of a lever which is pivotably attached to the base of the shaft and projects alongside the shaft. The latch member is a rod which projects from the lever (to which it is pivotally attached), through the bore in the housing and into the bore in the shuttle. A spring is positioned to urge the lever to pivot towards the shaft, which in turn urges the latch rod to move deeper into the bore in the shuttle. The collar of the mounting assembly has an externally frustro-conical tip which runs between the lever and shaft as the shaft is inserted into the collar. The frustro-conical tip of the collar therefore acts to cam the lever away from the shaft during insertion, against the bias of the spring, thereby retracting the rod from the bore in the shuttle. When the rod has been withdrawn completely from the bore in the shuttle, the shuttle is free to move and deploy the coupling elements. When the shuttle has been retracted and the shaft removed from the collar, once the bore in the shuttle is re-aligned with the bore in the housing, the rod can move back into this bore and the lever can rotate back towards the shaft (under action of the spring).

Detachable tow balls of either design conventionally utilise a rack & pinion mechanism to retract the shuttle. The end of the shuttle furthest from the coupling elements is provided with an array of teeth which form the rack, and the housing has a rotary actuation shaft positioned perpendicular to the shuttle. The shaft has an operating handle on one end, and on the other end has gear wheel which forms the pinion and meshes with the teeth of the rack on the shuffle. Rotating the handle in a first direction rotates the pinion, which moves the rack and thus retracts the shuttle. Similarly movement of the shuttle to its deployed position, under action of the spring, causes the pinion and thus the handle to rotate in a second rotational direction.

One disadvantage of this rack and pinion mechanism is that it is susceptible to thieves trying to detach the tow ball. In this regard, thieves try to withdraw the sprung shuttle by rotation of the operating handle. Alternatively, or additionally, thieves may try and apply force directly to the shuffle to forcibly move the shuttle, from its deployed position to its retracted position.

Furthermore, accidental knocking of the handle can cause an inadvertent retraction of the shuttle that releases the tow ball.

Accordingly, it is commonplace to include a lock mechanism on the handle. A key is used to selectively extend and retract a plunger of a lock. In the extended position the plunger projects from the handle into the shaft of the tow ball, preventing relative rotation between the handle and the shaft. However, such a lock mechanism can be overcome by force (for instance by pushing the vehicle over a curb), urging the handle to rotate and retracting the shuttle. In addition, providing such a locking mechanism adds complexity and weight to the detachable tow ball and adds to the cost of its manufacture.

Currently known designs also attempt to address the problem of accidental knocking causing an inadvertent retraction of the shuttle by providing an arrangement in which it is necessary to push, or pull, the handle before it can be rotated to retract the shuttle.

However, such an arrangement adds complexity and weight to the detachable tow ball and adds to the cost of its manufacture. In addition, it is necessary for the push/pull retraction to be accommodated at the rack and pinion interface. This requires the handle to be close to the shuttle, i.e. at the base of the shuttle housing. With the handle in this position, it can be difficult for an operator to turn the handle.

Furthermore, conventional rack and pinion mechanisms must utilise relatively high numbers of teeth in order for the rack to remain meshed with the pinion throughout the range of motion of the mechanism. Forming so many teeth on the rack and pinion can therefore require relatively expensive and/or time consuming manufacturing steps, thereby increasing the cost of manufacture of such devices. Further, relatively tight dimensional tolerances are required for conventional gear teeth to mesh correctly.

In addition, one disadvantage of both mechanisms is that the utilisation of springs can complicate the assembly process. For instance, in the case of a tow bar with a ball-type trigger, the latch ball bearing must be forced into the bore in the shuttle, against the bias from the spring, and held in place while the shuttle is inserted into the housing. Similarly, in a tow bar with a lever-type mechanism it may be necessary to force the shaft and lever together, against the bias of the spring, while inserting the pivot pin which connects the lever and shaft. Such operations can be fiddly and/or necessitate the use of an assembly jig, increasing production times. In addition, it can be dangerous for assembly processes to require components to be placed in a spring-biased state before being restrained. For instance, in a ball-type tow ball if an assembly worker slips while holding the latch ball bearing in place in the bore in the shuttle, the ball bearing and/or spring may be ejected at speeds sufficient to cause eye injury. In addition, tow bars utilising a lever-type trigger can be bulky in the region of the shaft, which can make attaching the detachable tow ball to a vehicle difficult and may even preclude use on vehicles with limited space between the rear bodywork and the chassis.

Furthermore, both the coupling balls and the latch release balls are prevented from being completely ejected out of the external mouths of the bores in which they are received, by slightly narrowed throats at the external mouths of the bores. Assembly of current designs therefore requires the coupling balls and the latch release balls to be inserted into their respective bores from within the tow ball shaft, through the longitudinal bore in the shaft in which the shuttle is received. This is a fiddy and time-consuming process. In addition, it is relatively complex and time-consuming to manufacture the respective bores in the shuttle such that they have narrowed throats at their external mouths.

It is an object of various aspects of the present invention to mitigate or obviate one or more of the aforesaid disadvantages, and/or to provide an improved or alternative mechanical linkage, detachable tow ball assembly or tow bar assembly.

According to a first aspect of the present invention there is provided a mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuttle receivable within the housing and movable relative to the housing, along a shuttle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it is rotatable; the actuation shaft comprising first and second interface lugs spaced substantially circumferentially about the actuation shaft, and the shuttle comprising first and second interface slots spaced along the shuttle axis; the interface lugs and slots being engageable so as to couple the motion of the shuttle along the shuttle motion axis and the rotation of the actuation shaft; wherein the interface slots and lugs are arranged such that when the actuation shaft is rotated in a first direction, to drive the shuttle in the direction from its second position to its first position, the first interface lug engages a first section of a surface of the shuffle that defines the first interface slot, driving the shuffle in said direction and the second interface lug engages at least a section of a surface of the shuttle that defines the second interface slot such that the shuffle is driven to its first position; and when the shuffle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, a second section of the surface of the shuffle that defines the first interface slot engages the first interface lug and rotatably drives the actuation shaft such that an abutment section of the second interface lug contacts an abutment section of the shuttle and thereby prevents the shuttle from reaching its first position.

This is advantageous in that, in normal use, the shuttle may be moved from its second position (e.g. a deployed position) to a first position (e.g. a retracted position) by rotation of the actuation shaft, for example by a handle connected to the actuation shaft. In this case, the first and second interface lugs meshingly engage with the first and second interface slots so asia drive the shutTle to its first posiTion.

However, if a person (e.g. a thief) tries to apply a force directly to the shuffle to forcibly move the shuffle, from its second position (e.g. a deployed position) to a first position (e.g. a retracted position), the second interface lug does not meshingly engage with the second interface slot and the abutment section of the second interface lug contacts the abutment section of the shuttle, thereby preventing the shuttle from reaching its first position.

This prevents the unauthorised movement of the shuttle from its second position to its first position. Accordingly, where the mechanical linkage is used as part of a detachable tow ball, this prevents unauthorised removal of the tow ball by the application of a force directly to the shuttle so as to move the shuttle from its second position (e.g. a deployed position) to its first position (e.g. a retracted position).

In addition, it removes the need for a separate locking mechanism in order to prevent the shuttle from being forcibly moved from its second position to its first position by the application of a force directly to the shuttle.

Furthermore, the linkage utilising a relatively low number of interface lugs and slots may be advantageous in that it may further reduce or simplify the manufacturing steps required.

A surface of the shuttle that defines the second interface slot may comprise first and second opposed sections that extend from an open end of the second interlace slot, wherein the first section faces in the direction of the shuttle motion axis, in the direction from the first position to the second position of the shuttle and the second section faces in the direction of the shuttle motion axis, in the direction from the second position to the first position of the shuttle.

Preferably the first section of the surface that defines the first interface slot and the first and second sections of the surface that defines the second interface slot are spaced in the direction of the shuttle motion axis, and the second interface lug is spaced in the circumferential direction from the first interface lug such that when the actuation shaft is rotated in the first direction, to drive the shuttle in the direction from its second position to its first position, the first interface lug engages the first section of the surface of the shuttle that defines the first interface slot, driving the shuttle in said direction and the second interface lug engages the at least a section of the surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position; and the second section of the surface that defines the first interface slot and the first and second sections of the surface that defines the second interface slot are spaced in the direction of the shuttle motion axis, and the second interface lug is spaced in the circumferential direction from the first interface lug such that the when the shuffle is moved in the direction from its second position To its firsT posiTion, To rotatably drive the ac[uation shaft, the second section of the surface of the shuffle that defines the first interface slot engages the first interface lug and rotatably drives the actuation shaft such that the abutment section of the second interface lug contacts the abutment section of the shuttle and thereby prevents the shuttle from reaching its first position.

Preferably the respective first sections of the surfaces that define the first and second interface slots are spaced in the direction of the shuttle motion axis by a distance that is substantially equal to the circumferential distance between a surface of the first interface lug that engages the first section of the surface of the shuttle that defines the first interface slot and a surface of the second interface lug that engages the at least a section of a surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position; and the respective second sections of the surfaces that define the first and second interface slots are spaced in the direction of the shuttle motion axis by a distance that is less than the circumferential distance between a surface of the first interface lug that is engaged by the second section of the surface of the shuttle that defines the first interface slot and a circumferentially outer surface of the second interface lug.

The first interface lug and the first and second sections of the surface of the shuttle that define the first interface slot may be arranged such that when the first interface lug first engages the first section, the first and second interface lugs are in respective first positions along the shuttle motion axis relative to the shuttle and when the second section first engages the first interface lug, the first and second interface lugs are in respective second positions along the shuttle motion axis relative to the shuffle.

The first interface slot may have a length in the direction of the shuttle motion axis that is greater than the length of the second interface slot in the direction of the shuttle motion axis.

The first and second sections of the surface that defines the first interface slot may be spaced apart in the direction of the shuttle motion axis by a distance that is greater than the length of the first interface lug in the direction of the shuttle motion axis. In this respect, the first and second sections of the surface that defines the first interface slot may be spaced apart in the direction of the shuttle motion axis by a distance that is greater than the length of the first interface lug in the direction of the shuttle motion axis when the first interface lug first engages the first section of the surface of the shuttle that defines the first slot and/or when the second section of the surface of the shuffle that defines the first slot first engages the first interface lug.

The first and second sections of the second interface slot may be spaced apart in the direction of the shuffle motion axis by a distance that is substantially equal to the length of the second interface lug in the direction of the shuffle motion axis.

In this respect, the first and second sections of the surface that defines the second interface slot may be spaced apart in the direction of the shuttle motion axis by a distance that is substantially equal to the length of the second interface lug in the direction of the shuttle motion axis when the second interface lug engages the at least part of the surface of the shuffle that defines the second interface slot such that the shuttle is driven to its first position.

The first and/or second interface lugs may include an arcuate porton which is substantially in the shape of a segment of a cylinder. The arcuate portion of the first and second interface lugs may be of substantially the same radius.

The first and second sections of the surface that defines the first interface slot may be spaced apart in the direction of the shuttle motion axis by a distance that is greater than the radius of the arcuate portion of the first interface lug.

The first and second sections of the surface that defines the second nterface slot may be spaced apart in the direction of the shuffle motion axis by a distance that is substantially equal to than the radius of the arcuate portion of the second interface lug.

The actuation shaft may be biased to a rotational position such that when the shuttle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, the second section of the surface of the shuffle that defines the first interface slot so engages the first interface lug (the engagement of the lugs and slots as defined in the first aspect of the invention). The actuation shaft may be biased by a resilient member.

The arrangement of the interface slots and lugs may be such that when the actuation shaft is rotated in the first direction, to drive the shuffle in the direction from its second position to its first position, the second interface lug substantially meshes with the second interface slot. When the second interface lug substantially meshes with the second interface slot, the second interface lug may be at least partially received within the second interface slot and preferably it is substantially received within the second interface slot.

When the abutment section of the second interface lug contacts the abutment section of the shuttle, the second interface lug may not be received within the second interface slot.

In this regard, the second interface lug may be disposed externally to the second interface slot. Alternatively, when the abutment section of the second interface lug contacts the

B

abutment section of the shuttle, the second interface lug may be at least partially received, or only partially received, within the second interface slot.

The abutment section of the shuttle may comprise a surface of the shuttle. The abutment section of the shuttle may be substantially planar. The abutment section of the shuttle may be, or comprise, an edge of a surface of the shuttle.

The abutment section of the second interface lug and the abutment section of the shuttle may contact along a plane, or a line, thai has a normal that has at least a component in the direction of the shuttle motion axis. Preferably the normal has a component in both the direction of the shuttle motion axis and a direction substantially perpendicular to the shuttle motion axis.

The abutment section of the shuttle may comprise a section of a surface of the shuttle that forms the second interface slot and/or a surface of the shuttle external to the second interface slot.

The abutment section of the second nterface lug may comprise a surface of the second interface lug. The abutment section of the shuttle may be, or comprise, an edge of a surface of the second interface lug. The abutment section of the second interface lug may be substantially curved about an axis that is substantially perpendicular to the shuttle motion axis.

The actuation shaft and the shuffle may each comprise a first limit section arranged such that, at a certain rotational position of the actuation shaft as the actuation shaft rotates in the first rotational direction, the first limit section of the actuation shaft contacts the first limit section of the shuttle and thereby prevents any further rotation of the actuation shaft in the first rotational direction. The contact between the first limit section of the actuation shaft and the first limit section of the shuttle preferably prevents any further movement of the shuttle in the direction from the second position to the first position of the shuttle. Preferably the arrangement is such that the first limit section of the actuation shaft contacts the first limit section of the shuttle after the shuttle is driver to its first position by rotation of the actuation shaft in the first direction.

The interface lugs and slots may be arranged such that when the shuttle moves in the direction from its first position to its second position, the actuation shaft is rotated in a second rotational direction. The second rotational direction may be opposite to the first rotational direction.

The actuation shaft and the shuttle may each comprise a second limit section arranged such that at a certain rotational position of the actuation shaft as the actuation shaft rotates in the second rotational direction, the second limit section of the actuation shaft contacts the second limit section of the shuttle and thereby restricts any further rotation of the actuation shaft in the second rotational direction. The contact between the second limit section of the actuation shaft and the second limit section of the shuttle preferably prevents any further movement of the shuttle in the direction from the first position to the second position of the shuffle. Preferably the arrangement is such that the second limit section of the actuation shaft contacts the second limit section of the shuffle after the shuttle has reached its second position.

The shuffle may be biased towards its second position. The shuffle may be biased by a resilient member.

Any of the resilient members referred to above may be, for example, a spring, a leaf spring, Belleville washer, coil spring, volute spring, tensator spring, gas springs, elastomeric tubes, rods, sheets or blocks, etc. The first and/or second sections of the surface of the shuffle that defines the first interface slot may be, or comprise, an edge of the surface of the shuffle that defines the first interface slot.

The first section of the surface of the shuffle that defines the first interface slot may face in the direction of the shuttle motion axis, in the direction from the first position to the second position of the shuffle and the second section of said surface may face in the direction of the shuttle motion axis, in the direction from the second position to the first position of the shuffle.

The first and/or second sections may each comprise a first portion that extends from the open end of the first interface slot, is substantially planar and extends substantially in a plane that is oriented such that a normal to the plane has at least a component in a direction that is substantially parallel to the shuffle motion axis. The first portion may extend substantially in a plane that is substantially perpendicular to the shuttle motion axis.

The first and/or second sections may each comprise a second portion that extends from an end of the first portion that is distal to the open end of the first interface slot, to the base section of the first interface slot, wherein the second portion is substantially curved along its length in the direction from the first portion to the base section. The second portion may have substantially the same radius of curvature as the first interface lug.

The base section may be substantially planar. The base section may extend substantially in a plane that has at least a component in the direction of the shuffle motion axis. The base section may extend substantially in a plane that is substantially parallel to the shuffle motion axis.

The respective first and second sections of the surfaces of the shuffle that define the first and/or second interface slots may extend to a base section of the respective interface slot that forms a closed end of the slot.

The first and/or second sections of the surface that defines the second interference slot may be substantially planar and extend substantially in a plane that is oriented such that a normal to the plane has at least a component in a direction that is substantially parallel to the shuttle motion axis. The first and/or second sections may extend substantially in a plane that is substantially perpendicular to the shuttle motion axis.

The surface that defines the second interface slot may be, or comprise, an arcuate surface of complementary shape to the second interface lug. The arcuate surface may have substantially the same radius of curvature as the second interface lug. Such an arcuate surface may be beneficial in that it may increase the area of contact between the second interface lug and the second interface slot. This, in turn, may decrease the wear experienced by the linkage during use. The arcuate surface may be the base section of the surface that defines the second interface slot. The base section may be substantially curved along its length from the first to the second section.

The arcuate portion of an interface lug having a relatively large arc length may be beneficial in that it may spread the loading between it and the corresponding slot in the shuttle over a larger area. As such, the arcuate portion of the first and/or second interface lugs may have an arc length of over 20% of the circumference of the notional cylinder a segment of which the arcuate portion is substantially in the shape of. The arcuate portion of the first and/or second interface lug preferably has an arc length of over 30% of the circumference of the notional cylinder, and more preferably has an arc length of over 40% of the circumference of the notional cylinder.

The arcuate portion of the first and/or second interface lug may be substantially in the shape of a major segment of a cylinder. In other words, the arc length of said arcuate portion may be more than half the circumference of the notional cylinder a segment of which the arcuate portion is substantially in the shape of. For instance, said arcuate portion may have an arc length of more than 60% of the circumference of the notional cylinder, preferably more than 70% and more preferably more than 80%.

The arcuate portion of the first and/or second interface lug may define an arc radius for that interface lug, the arc radius being the radius of a notional cylinder a segment of which the arcuate portion is substantially in the shape of.

The first interface lug may be configured such that when the first interface lug engages the first section of the surface of the shuttle that defines the first slot, it is received within the first interface slot to a maximum depth of more than the length of the arc radius for that lug. Said maximum depth may be at least 1.3 times the arc radius, preferably at least 1.6 times the arc radius and more preferably at least 1.9 times the arc radius. Instead or in addition, said maximum depth may be less than 2.7 times the arc radius, preferably less than 2.4 times the arc radius and more preferably less than 2.1 times the arc radius.

The first interface lug may be configured such that when the second section of the surface of the shuttle that defines the first interface slot engages the first interface lug, the first interface lug is received within the first slot to a maximum depth of more than the length of the arc radius for that lug. Said maximum depth may be at least 1.3 times the arc radius, preferably at least 1.6 times the arc radius and more preferably at least 1.9 times the arc radius. Instead or in addition, said maximum depth may be less than 2.7 times the arc radius, preferably less than 2.4 times the arc radius and more preferably less than 2.1 times the arc radius.

The second interface lug may be configured such that when it engages the surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position, it is received within the second interface slot to a maximum depth of more than the length of the arc radius for that lug. Said maximum depth may be at least 1.3 times the arc radius, preferably at least 1.6 times the arc radius and more preferably at least 1.9 times the arc radius. Instead or in addition, said maximum depth may be less than 2.7 times the arc radius, preferably less than 2.4 times the arc radius and more preferably less than 2.1 times the arc radius.

The first and/or second interface slots may extend radially inwardly from an outer surface of the shuttle. The first and/or second interface slots may extend in the circumferential direction of the shuttle, preferably part way along the circumference of the shuttle.

The first and second interface lugs may be substantially identical.

When the shuttle is in its first and second positions it may be in a retracted position and a deployed position respectively.

The mechanical linkage may comprise at least one coupling element movable between a stowed position and a deployed position, the coupling element being movable to the deployed position under action of the shuttle moving to the second position and being movable to a stowed position under action of the shuttle moving to the first position.

The housing may be for insertion into a collar of a complementary coupling member and wherein the at least one coupling element is arranged such that when it is in the deployed position it projects substantially radially from the housing for receipt within the collar so as to prevent withdrawal of the housing from the collar and when it is in the stowed position it is received within the housing to an extent that allows withdrawal of the housing from the collar.

The mechanical linkage may comprise at least one latch member movable from an engaged configuration, in which the latch member retains the shuttle in the first position, to a released configuration, in which the latch member permits movement of the shuttle from the first position to the second position.

The mechanical linkage may comprise a handle that is connectable to the actuation shaft such that rotation of the handle rotates the actuation shaft and wherein the handle is releasably connectable to the actuation shaft.

This is advantageous in that the handle functions in the manner of a key, with the actuation shaft only being rotatable when the handle is connected to the actuation shaft.

Therefore, when it is not desired to rotate the actuation shaft, the handle may be removed from the actuation shaft and kept in an external secure location (e.g. on the owner of the tow ball assembly). The removable handle therefore acts to prevent thieves from trying to directly rotate the actuation shaft so as to move the shuffle to its retracted position and release the tow ball assembly. Accordingly, the above nterface lug and slot arrangement prevents thieves from applying a force directly to the shuffle so as to try and retract the shuttle and the removable handle prevents thieves from applying a rotational force directly to the actuation shaft of the shuffle to do this. The combination of these features therefore provides a very secure mechanical linkage.

Furthermore, since the handle may be removed when it is not necessary to retract the shuttle, this prevents accidental knocking of the handle and so prevents inadvertent detachment of the tow ball assembly.

Preferably when the handle is connected to the actuation shaft, rotation of the handle in a first and/or second rotational direction rotates the actuation shaft in its first and/or second rotational direction respectively.

The handle may be directly connectable to the actuation shaft. Alternatively the handle may be indirectly connectable to the actuation shaft, via one or more mechanical couplings, transmissions, connecting sections, etc. The handle may be connectable to the actuation shaft by a connecting section that is rotatably coupled to the actuation shaft, wherein the handle comprises a first formation and the connecting section comprises a second formation, the first and second formations being releasably engageable with each other such that when they are engaged, rotation of the handle rotates the connecting section, which rotates the actuation shaft. When the first and second formations are not engaged, rotation of the handle does not rotate connecting section, or actuation shaft.

The connecting section may be integrally formed with the actuation shaft.

Alternatively the connecting section may be formed separately to the actuation shaft and coupled to the actuation shaft. The connecting section may be directly rotatably coupled to the shaft, for example by being part of the shaft or attached to the shaft, or may be indirectly rotatably coupled to the shaft, for example via one or more mechanical couplings, transmissions, etc. Preferably the connecting section is rotatably mounted within the housing. The connecting section may be mounted to rotate co-axially with the actuation shaft.

Preferably the mechanical linkage is arranged to prevent a person from rotating the actuation shaft from outside of the housing when the handle is not connected to the connecting section.

The second formation may be an anti-tamper formation. In this regard, the second formation may be sized and dimensioned such that it is difficult for a person to gain a sufficient purchase on the second formation to rotate the connecting section.

Preferably the connecting section is rotatably mounted at least partially within a housing. The connecting section may form a close radial fit with the housing. In this regard, there is preferably only a relatively small radal clearance between the connecting section and the housing.

Preferably the housing at least partially covers the connecting section so as to prevent a person from rotating the actuation shaft from outside of the housing when the handle is not connected to the connecting section. Preferably the housing substantially covers the connecting section in an axial and/or circumferential direction of the connecting section. The housing may be part of the housing of the mechanical linkage. Alternatively, the housing may be separate to the housing of the mechanical linkage.

The first and second formations may be arranged such that they are releasably engageable with each other in a plurality of rotational positions of the handle relative to the connecting section. In this regard, the first and second formations may be arranged such that they have an order of rotational symmetry greater than one. Preferably the first and second formations are arranged such that they have an order of rotational symmetry greater than two, more preferably greater than three. Even more preferably the first and second formations are arranged such that they have an order of symmetry greater than five.

The first formation may be provided with a plurality of projections and/or recesses distributed circumferentially about the rotational axis of the handle and the seccnd formation may be provided with a plurality of recesses and/or projections distributed circumferentially about the rotational axis of the connecting section which are respectively engageable with the plurality of projections and/or recesses of the first formation such that the first and second formations are engageable in a plurality of rotational positions of the handle relative to the connecting section.

One of the first and second formations may form a plug and the other of the first and second formations may form a socket, with the first and second formations being releasably engageable by the plug being releasably receivable within the socket.

Preferably the second formation forms the socket, with the housing at least partially covering the socket in the axial and/or circumferential direction of the socket.

The plug and socket may each have a polygonal cross-sectional shape about its respective rotational axis.

At least one face of the plug may be provided with at least one projection or recess and at least one face of the socket may be provided with at least one recess or projection that is releasably engageable with the at least one projection or recess on the at least one face of the plug.

Preferably the at least one face ol the plug and socket is a plurality of said faces.

Preferably every face of the plug and socket is provided with said at least one recess or projection respectively.

Preferably each of the plug and socket each has a hexagonal cross-sectional shape about its rotational axis. It will be appreciated that the plug and socket may have any other suitable cross sectional shape, including cross-sectional shapes that are curved at least partly curved.

Preferably the handle comprises a gripping section attached to the first formation. The gripping section may be formed integrally with the first formation or may be formed separately to the first formation and attached to it.

The mechanical linkage may comprise a handle that is disposed at a position oft the rotational axis of the actuation shaft and is connected to the actuation shaft such that rotation of the handle rotates the actuation shaft.

This is advantageous in that allows the handle to be located a position in which it is easily operable, compared to if the handle was located proximal to the actuation shaft. Since the above arrangement of the interface lugs and slots removes the need for a handle that must be pushed or pulled, before it can be rotated, this removes the need for the handle to be close to the actuation shaft (e.g. to a rack and pinion interface), thereby allowing the handle to be disposed in such a position in which it is remote from the actuation shaft, i.e. off the rotational axis of the actuation shaft.

The handle may be connected to the actuation shaft by a mechanical connection. The mechanical connection may comprise a cable, rack and pinion connection, rotary gears, or any other suitable mechanical connection.

The mechanical connection may be at least partially housed within a housing.

Preferably the mechanical connection is substantially housed within a housing.

Alternatively, or additionally, the handle may be connected to the actuation shaft by an electrical connection, (e.g. by connection to an electrical switch which operates an actuator connected to the actuation shaft), by a magnetic connection (e.g. a magnetic gear), etc. The handle may be arranged to rotate about an axis that is offset from the rotational axis of the actuation shaft. The handle may be arranged to rotate about an axis that is substantially parallel to the rotational axis of the actuation shaft.

The handle may include a gripping portion. The gripping portion may have any suitable arrangement including a single lever and a multi-pronged arrangement.

According to a second aspect of the present invention there is provided a detachable tow ball assembly comprising a mechanical linkage according to The first aspect of the invention connected to a tow ball.

Such a detachable tow ball assembly may provide one or more of the advantages described in relation to the first aspect of the invention.

The mechanical linkage may be connected to the tow ball by a ball arm. Where the handle is disposed at a position off the rotational axis of the actuation shaft, the handle may be disposed on the ball arm. Preferably the handle is rotationally mounted to the ball arm.

The handle may be disposed closer to the tow ball than it is to the housing of the mechanical linkage. The handle may be disposed at least half of the length of the ball arm away from the housing of the mechanical linkage. The handle may be disposed at least two thirds of the length of the ball arm away from the housing of the mechanical linkage.

The handle may be disposed on the ball arm at a position substantially midway along the length of the ball arm between the housing of the mechanical linkage and the tow ball.

The handle may be releasably connectable to the actuation shaft, as defined above.

Alternatively, the handle may not be releasably connectable to the actuation shaft.

According to a third aspect of the present invention there is provided a tow bar assembly comprising a detachable tow ball assembly according to the second aspect of the invention.

Such a tow bar assembly may provide one or more of the advantages described in relation to the first aspect of the invention.

The tow bar assembly may comprse a mounting assembly comprising said complementary coupling member.

According to a fourth aspect of the invention there is provided a mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuttle receivable within the housing and movable relative to the housing, along a shuttle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it is rotatable; the shuttle being coupled to the actuation shaft such that the motion of the shuttle along the shuttle motion axis is coupled to the rotation of the actuation shaft; wherein the mechanical linkage comprises a handle that is connectable to the actuation shaft such that rotation of the handle in a first direction rotates the actuation shaft in its first rotational direction and wherein the handle is releasably connectable to the actuation shaft.

According to a fifth aspect of the present invention there is provided a detachable tow ball assembly comprising a mechanical linkage according to the fourth aspect of the invention connected to a tow ball.

According to a sixth aspect of the present invention there is provided a tow bar assembly comprising a detachable tow ball assembly according to the fifth aspect of the invention.

According to a seventh aspect of the invention there is provided a mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuttle receivable within the housing and movable relative to the housing, along a shuttle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it is rotatable; the shuttle being coupled to the actuation shaft such that the motion of the shuttle along the shuffle motion axis is coupled to the rotation of the actuation shaft; wherein the mechanical linkage comprises a handle that is disposed at a position off the rotational axis of the actuation shaft and is connected to the actuation shaft such that rotation of the handle rotates the actuation shaft.

According to an eighth aspect of the present invention there is provided a detachable tow ball assembly comprising a mechanical linkage according to the seventh aspect of the invention connected to a tow ball.

According to a ninth aspect of the present invention there is provided a tow bar assembly comprising a detachable tow ball assembly according to the eighth aspect of the invention.

According to a tenth aspect of the present invention there is provided a mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuffle receivable within the housing and movable relative to the housing, along a shuffle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it can rotate, wherein: the actuation shaft comprises a plurality of interface lugs spaced substantially circumferentially about the actuation shaft, and the shuttle comprises a plurality of interface slots spaced along the shuttle axis, the interface lugs and slots being configured to meshingly engage to form a rack and pinion mechanism; each interface lug includes an arcuate portion which is substantially in the shape of a segment of a cylinder.

Use of interface lugs with such arcuate portions may be beneficial in that it may allow each interface lug to undergo significant rotation while meshed with an interface slot. This may allow each lug to remain meshed with a slot over a greater range of motion of the shuttle and actuation shaft, which may allow the rack and pinion mechanism to be formed from a smaller number of lugs and slots than would be required if formed from conventional involute or cycloid teeth. Reducing the number of interface lugs and interface slots required to form the rack and pinion mechanism may reduce the extent and/or complexity of the manufacturing steps required to form it. This, in turn, may reduce production time and/or cost. In addition, the use of a smaller number of larger lugs, rather than fine arrays of teeth, may allow the mechanism to be manufactured to lower dimensional tolerances. For instance, while in conventional rack and pinion mechanisms the teeth must be machined, the actuation shaft may be cast with integral lugs and/or the shuttle may be cast with integral slots, which may be faster and/or cheaper.

The shuttle may be received in the housing in an enclosed channel or cavity, or in an open-sided void such as a groove. The shuttle is preferably slidably receivable within the housing. For the avoidance of doubt, the shuttle motion axis may be curved (for instance the shuttle may be slidable within an arcuate channel in the housing). The shuttle may be biased towards the second position, for instance by a spring.

All the interface lugs and/or interface slots may be substantially identical. In alternative embodiments, all but 1 of the lugs and/or slots, or all but 2 of the lugs and/or slots may be substantially identical. For instance, the interface slots may be provided in a linear array running along the shuttle, and all the slots may be substantially identical except for the slot at one or both ends of the array. Alternatively, the slots may all be different or they may have any other suitable configuration.

For the avoidance of doubt, reference to the actuation shaft' is not intended to limit the linkage to situations in which the actuation shaft functions as the input to the linkage and the shuttle as the output. Arrangements in which the shuttle is the input and the actuation is the output are also intended to be covered.

One or more of the interface slots may take the form of other types of voids than discrete notches. For instance, one of the interface slots may be formed by the space beyond the distal tip of the shuttle. As another example, the interface slots may be provided on a raised portion of the shuttle and slots may be formed by the space beyond one or both ends of the raised portion.

The actuation shaft may comprise 4 or fewer interface lugs. It preferably comprises precisely 3 interface lugs and more preferably comprises precisely 2 interface lugs.

The linkage utilising a relatively low number of interface lugs may be advantageous in that it may further reduce or simplify the manufacturing steps required.

The arcuate portion of an interface lug having a relatively large arc length may be beneficial in that it may spread the loading between it and the corresponding slot in the shuttle over a larger area. As such, the arcuate portion of at least one of the interface lugs may have an arc length of over 20% of the circumference of the notional cylinder a segment of which the arcuate portion is substantially in the shape of. The arcuate portion of said at least one interface lug preferably has an arc length of over 30% of the circumference of the notional cylinder, and more preferably has an arc length of over 40% of the circumference of the notional cylinder.

In one embodiment, the arcuate portion of at least one of the interface lugs is substantially in the shape of a major segment of a cylinder. In other words, the arc length of said arcuate portion may be more than half the circumference of the notional cylinder a segment of which the arcuate portion is substantially in the shape of. For instance, said arcuate portion may have an arc length of more than 60% of the circumference of the notional cylinder, preferably more than 70% and more preferably more than 80%.

The linkage may comprise substantially the same number of interface slots as interface lugs. Preferably, the linkage comprises exactly the same number of interface slots as interface lugs. Alternatively, the linkage may have more slots than lugs (such as is the case in most conventional rack and pinion mechanisms). As another alternative, the linkage may have more lugs than slots. For instance, the actuation shaft may have one or more lugs which are redundant in normal use. This may be useful in that during assembly of the linkage the actuation shaft may be inserted into the housing at an arbitrary angular position, rather than it needing to be inserted into the housing such that a particular lug meshes with a particular slot.

The arcuate portion of each interface lug may define an arc radius for that interface lug, the arc radius being the radius of a notional cylinder a segment of which the arcuate portion is substantially in the shape of, and at least one of the interface lugs may be configured to be received within at least one of the slots to a maximum depth of more than the length of the arc radius for that lug. Said maximum depth may be at least 1.3 times the arc radius, preferably at least 1.6 times the arc radius and more preferably at least 1.9 times the arc radius. Instead or in addition, said maximum depth may be less than 2.7 times the arc radius, preferably less than 2.4 times the arc radius and more preferably less than 2.1 times the arc radius.

At least one of the interface slots may have an arcuate surface of complementary shape to the or one of the interface lugs that it is configured to receive. Such an arcuate surface may be beneficial in that it may increase the area of contact between said lug and said slot. This, in turn, may decrease the wear experienced by the linkage during use.

The interface lugs and/or interface slots may be substantially evenly spaced.

Alternatively, the lugs and slots may be positioned with unequal spacing. For instance, the linkage may be provided with more lugs and slots in regions of the rack and pinion mechanism which are predicted to experience particularly high loads.

The actuation shaft may comprise a first limit surface positioned to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in a first limited direction.

The first limited direction may be the direction in which the actuation shaft must be turned in order to move the shuttle towards the first position, or may be the opposite direction.

Where no limit surface is present, the actuation shaft may be freely rotatable, or the motion of the linkage may be limited in any other suitable fashion (for example the movement of the shuttle may be limited rather than the movement of the actuation shaft).

Where the actuation shaft comprises a first limit surface, it may further comprise a second limit surface positioned to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in the opposite direction to the first limited direction.

The portion of the linkage contacted by the second limit surface may be the same as the portion contacted by the first limit surface.

Where no second limit surface is present, rotation of the actuation shaft in the opposite direction to the first limited direction may be unrestricted, or may be limited in any other suitable fashion.

The plurality of interface lugs may be movable along the actuation shaft axis between an actuable configuration and a non-actuable configuration with respect to the interface slots.

The non-actuable configuration is a configuration in which the interface lugs and interface slots cannot function as a rack and pinion mechanism. The lugs and slots being in the non-actuable configuration includes, but is not limited to, configurations in which no lug is meshed with a slot. Similarly, the lugs and slots being in the actuable configuration includes, but is not limited to, configurations in which at all times at least one of the lugs is meshed with at least one of the slots.

The interface lugs and slots may be moved between the actuable and non-actuable configurations by moving the whole actuation shaft (including the lugs) along its axis. As an alternative, the lugs, or a portion of the actuation shaft comprising the lugs, may move along the remainder of the shaft. As a further alternative, the lugs may be movable to the non-actuable position by radially retracting them within the actuation shaft.

In embodiments where the lugs are movable between actuable and non-actuable positions, and where the actuation shaft comprises at least a first limit surface, the linkage may or may not be arranged such that the first limit surface and/or second limit surface can contact said portion of the linkage only when the lugs and slots are in the actuable configuration.

The purality of interface lugs may be urged towards the non-actuable configuration.

For instance, the lugs (either alone or with all or part of the actuation shaft) may be urged to the non-actuable configuration by a spring. The lugs being urged to the non-actuable configuration may require them to be actively moved to the actuable configuration before the linkage will function. This may make the linkage less prone to accidental operation.

Where the lugs are movable between actuable and non-actuable configurations, the actuation shaft may have a first restraint surface positioned, when the interface lugs and interface slots are in the non-actuable configuration, to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in a first restrained direction.

The first restrained direction may be the direction in which the actuation shaft must be turned in order to move the shuttle towards the first position, or may be the opposite direction.

Where the actuation shaft also has a first limit surface, the first restrained direction may be the same direction as the first limited direction, or it may be the opposite direction.

Instead or in addition, the first restraint surface may be parallel to or contiguous with the first limit surface (and/or the second limit surface, where present).

Where no restraint surface is present, when the lugs and slots are in the non-actuable configuration the actuation shaft may be freely rotatable or the motion of the linkage may be limited in any other suitable fashion (for example the movement of the shuttle may be limited rather than the movement of the actuation shaft).

Where the actuation shaft has a first restraint surface, it may have a second restraint surface positioned, when the plurality of interface lugs is in the non-actuable configuration, to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in the opposite direction to the first restrained direction.

The portion of the linkage contacted by the second restraint surface may be the same as the portion contacted by the first restraint surface (and/or the portion contacted by the first limit surface and/or second limit surface, where present).

The second restraint surface may be parallel to or contiguous with the first restraint surface (and/or the first and/or second limit surface, where present).

Where no second restraint surface is present, when the lugs and slots are in the non-actuable configuration the actuation shaft may be freely rotatable in the opposite direction to the first restrained direction, or the motion of the linkage may be limited in any other suitable fashion.

The first and second restraint surfaces may be configured to substantially prevent rotation of the actuation shaft when in the plurality of interface lugs is in the non-actuable configuration.

Where the actuation shaft has at least a first limit surface and/or a first restraint surface, the portion of the mechanical linkage which the first limit surface and/or first restraint surface is configured to contact may be the shuttle.

According to an eleventh aspect of the present invention there is provided a detachable tow ball comprising a mechanical linkage according to the tenth aspect of the invention.

Such a tow ball may provide one or more of the advantages described in relation to the tenth aspect of the invention.

According to a twelfth aspect of the present invention there is provided a tow bar assembly comprising a detachable tow ball according to the eleventh aspect of the invention.

Such a tow bar may provide one or more of the advantages described in relation to the tenth aspect of the invention.

According to a thirteenth aspect of the invention there is provided a trigger assembly for a coupling member, the trigger assembly comprising: a housing; a shuttle receivable within the housing and movable between a first position and a second position relative to the housing; one or more coupling elements movable between a stowed position and a deployed position, the coupling elements being movable to the deployed position under action of the shuttle moving to the second position; and a first latch member movable from an engaged configuration, in whch the latch member retains the shuttle in the first position, to a released configuration, in which the latch member permits movement of the shuttle from the first position to the second position, wherein: the shuttle comprises a deployment member configured to move the coupling elements to the deployed position as the shuttle moves to the second position, and a latch-operation member movable relative to the deployment member between an active position and a passive position; and the latch-operation member or first latch member has a first cam surface contigured to couple the motion of the latch-operation member and the first latch member such that the latch-operation member moving from the passive position towards the active position moves the first latch member from the released configuration towards the engaged configuration, and such that movement of the first latch member from the engaged configuration towards the released configuration moves the latch-operation member from the active position towards the passive position.

Use of a latch-operation member coupled to the first latch member as described above may provide a trigger assembly which can be assembled more quickly and/or more easily. For instance, it may eliminate the need for a spring positioned to urge the first latch member to the engaged configuration, thereby avoiding the additional complexity of the assembly process that such a component may require.

The shuttle is preferably biased towards the second position, for instance by a spring.

The or each coupling element may be substantially spherical. The latch-operation member may be biased towards the active position, for instance by a spring or by its own weight.

The trigger assembly may further comprise a second latch member movable from an engaged configuration, in which the latch member retains the shuttle in the first position, to a released configuration, in which the latch member permits movement of the shuttle from the first position to the second position, wherein the second latch member or the latch-operation member has a second cam surface configured to couple the motion of the latch-operation member and the second latch member such that the latch-operation member moving from the passive position towards the active position moves the second latch member from the released configuration towards the engaged configuration, and such that movement of the second latch member from the engaged configuration towards the released configuration moves the latch-operation member from the active position towards the passive position.

Use of two latch members may provide a trigger assembly which is advantageously resistant to unintentional actuation. For instance, in the event of unintentional movement of one the latch members to the released configuration (such as by an accidental knock), the bolt may be retained in the first position by the other latch member.

The second cam surface of the latch-operation member may be contiguous with the first cam surface (for instance both may be portions of a flat or arcuate surface), and/or the first and second cam surfaces may be positioned substantially opposite to one another.

The trigger assembly may comprise a third latch member, and the third latch member or the latch-operation member may comprise a third cam surface.

Where the trigger assembly has a second latch member, the first and second latch members may be positioned on opposite sides of the shuttle. For instance, they may be positioned substantially radially opposite to one another. Alternatively or in addition, they may be axially and/or radially spaced from one another by any suitable amount.

The shuttle may be slidable within the housing along a shuttle motion axis. For example, the shuttle may take the form of an elongate bolt defining a longitudinal axis, received in a channel in the housing which is aligned with the longitudinal axis of the bolt.

Alternatively or in addition, the shuttle may be rotatable and/or pivotable, as well as or instead of being slidable, between the first and second positions.

The or each latch member may be configured, when in the released configuration, to couple the latch-operation member to the deployment member such that movement of one of said components causes movement of the other. This may allow the movement of one of these components to be brought about at least partially by movement of the other. For instance, the whole shuffle may be movable towards the second position by applying force to only the deployment member, and/or the whole shuttle may be movable towards the first position by applying a force only to the latch-operation member.

The housing may have one or more retention surfaces configures to hold the or each latch member in the released configuration when the shuttle is in the second position. For instance, where the shuffle is slidably received within a channel in the housing, a portion of the wall of the channel may form a retention surface. The retention surfaces may be configured to hold the or each latch member in the released configuration when the shuttle is in any position except the first position.

The latch-operation member may be slidable relative to the deployment member.

The latch-operation member may be rotatable and/or pivotable, as well as or instead of being slidable, relative to the deployment member.

Where the latch-operation member is slidable relative to the deployment member and the shuffle is slidable within the housing along a shuttle motion axis, the latch-operation member may be slidable in a direction substantially parallel to the shuffle motion axis.

At least a portion of the latch-operation member may be received within a cavity in the deployment member. For instance, where the latch-operation member is slidable relative to the deployment member it may be slidaby received in the cavity. The cavity may be partially open-sided, for instance it may be a groove or recess. Alternatively, the cavity may be fully enclosed, for instance it may be a through-bore or a blind bore.

The or each cam surface may be provided on the latch-operation member.

Alternatively, the or each cam surface may be provided on the or each latch member (for instance the or each latch member may have a radially inner pointed tip configured to act as a cam surface and bear against a projection provided on the latch-operation member). As another alternative, the trigger mechanism may have the first cam surface provided on the latch-operation member and a second cam surface provided on the second latch member.

Where the or each cam surface is provided on the latch-operation member, the latch-operation member may be elongate and the or each cam surface may be defined by a wall of a transverse notch in the latch-operation member. Where the latch-operation member has two cam surfaces, both cam surfaces may be defined by walls of by the same notch, or they may be defined by walls of different notches. Where they are defined by walls of the same notch they may or may not be defined by the same wall of that notch. The or each notch may be straight, or may be arcuate (for instance the or each notch may be a circumferential groove).

The or each latch member may be substantially prismic. For example, the or each latch member may be a cuboid, or a regular or irregular pentagonal prism, hexagonal prism or octagonal prism. Alternatively, the or each may be a prism of any other suitable type. For the avoidance of doubt, the term prismic' is intended to include oblique prisms and antiprisms, as well as right prisms. Any such prism may have one or more arcuate faces.

The or each latch member may be substantially cylindrical. For the avoidance of doubt, a latch member may be both substantially prismic and substantially cylindrical. For instance, it may be a prism where the base faces have a sufficient number of edges to be substantially circular.

Where the or each latch member is substantially prismic and/or substantially cylindrical, the edges round one or both base faces of the or each latch member may be filleted or chamfered.

The or each latch member may be received partially in a void in the shuttle and partially in a void in the housing when the latch member is in the engaged configuration, and be fully received within the void in the shuttle when the latch member is in the released configuration. In such arrangements, prismic or cylindrical latch members may be able to retain the shuttle in the first position (when in the engaged configuration) over a wider range of radial positions than spherical ones. For instance, if a cylindrical latch member only projected slightly out of the shuttle and into the housing it could still prevent movement of the shuttle, whereas a ball would be cammed back into the shuttle and the shuttle would be able to move.

One or more of said voids may be bores (such as radial bores).

The or each latch member may have a corresponding latch release member which, when the latch member is in the engaged configuration, lies adjacent to the latch member and projects from the housing such that disturbance of the latch release member moves the latch member from the engaged configuration to the released configuration.

The or each latch release member may be substantially spherical.

Where the trigger assembly has two latch members with corresponding latch release members, they may share a common latch release member or may each have a separate latch release member.

The or each latch release member may be received within a corresponding void in the housing. In arrangements where this is the case and where the or each latch member is received partially in a void in the shuttle and partially in a void in the housing when the latch member is in the engaged configuration and is fully received within the void in the shuttle when the latch member is in the released configuration, the or each latch release member may be received within the bore in the housing in which a portion of the corresponding latch member is received when said latch member is in the engaged configuration.

According to a fourteenth aspect of the invention there is provided a detachable tow ball comprising a trigger assembly according to the thirteenth aspect of the invention.

Such a tow ball may provide one or more of the advantages described in relation to the first arrangement useful for understanding the invention.

According to a fifteenth aspect of the invention there is provided a tow bar assembly comprising a detachable tow ball according to the fourteenth aspect of the invention.

Such a tow bar may provide one or more of the advantages described in relation to the first arrangement useful for understanding the invention.

The tow bar assembly may comprise a collar with an actuation surface, the actuation surface being arranged to move the or each latch member to the released contiguration when the trigger assembly of the detachable tow ball is inserted into the collar. The collar preferably has one or more voids configured to receive the coupling elements when the coupling elements are in the deployed position, thereby coupling the tow bar assembly and the collar.

According to a sixteenth aspect of the invention there is provided a trigger assembly for a coupling member, the trigger assembly comprising: a housing; a shuttle receivable within the housing and movable between a first position and a second position relative to the housing; a coupling element movable along a first bore in the housing between a stowed position and a deployed position in which the coupling element protrudes from an outer surface of the housing, through a mouth of the first bore; the shuttle comprising a deployment member configured to move the coupling element to the deployed position as the shuttle moves to the second position; a latch member movable from an engaged configuration, in which the latch member retains the shuttle in the first position, to a released configuration, in which the latch member permits movement of the shuffle from the first position to the second position; a latch release member at least partially received within a second bore in the housing, when the latch member is in the engaged configuration the latch release member is in a first position in which it lies adjacent to the latch member and protrudes from the outer surface of the housing, through a mouth of the second bore, such that disturbance of the latch release member from its first position to a second position moves the latch member from the engaged configuration to the released configuration; a retaining assembly arranged to retain the coupling element and/or the latch release member at least partially within the respective first or second bore by preventing it from passing completely through the mouth of the respective bore; wherein the retaining assembly is releasably attachable to the housing.

This is advantageous in that, because the retaining assembly is releasably attachable to the housing, it allows the latch release member or coupling element to be inserted into its respective bore without the retaining assembly being attached to the housing. The retaining assembly may then subsequently be attached to the housing, so as to retain the latch release member or coupling element within its bore.

This allows the latch release member or coupling element to be inserted into the respective bore from outside of the housing, through the mouth of the bore, before the retaining assembly is attached to the housing. This removes the need to insert the latch release member or coupling element into the respective bore trom the inside the housing, i.e. through a mouth of the bore at the inner surface of the housing. This simplifies and speeds up the assembly process and removes the need for assembly jigs. In addition, it allows the shapes of the first or second bores to be simplified, for instance they may simply be drilled through bores, since the narrowed throats have been eliminated.

The mouth of the respective bore is preferably disposed at an end of the bore proximal to the outer surface of the housing. The mouth of the respective bore may open into the outer surface of the housing.

Preferably the retaining assembly is releasably attachable to the housing from outside of the housing. In this respect, the retaining assembly is preferaby releasably attachable to the outer surface of the housing. The retaining assembly is preferably releasably mountable to the outer surface of the housing.

Preferably the retaining assembly protrudes into the first and/or second bore so as to prevent the coupling element and/or latch release member from passing completely through the mouth of the first and/or second bore respectively. Preferably the respective bore has a substantially circular cross-sectional shape and the retaining assembly protrudes into the bore in the radial direction of the bore. In this regard, the radial direction of the bore is substantially perpendicular to the axial direction of the bore.

The retaining assembly may be at least partially received within a cavity and/or bore in the housing. The bore may be the same as, or different to, the first and second bores in the housing. The cavity or bore may be adjacent to the first and/or second bores. The cavity or bore may extend into the first and/or second bores. The bore may extend in the radial direction of the housing. The cavity may be substantially annular.

The retaining assembly may comprise a first retaining member arranged to retain the coupling element at least partially within the first bore by preventing it from passing completely through the mouth of the first bore, wherein the first retaining member is releasably attachable to the housing.

Additionally, or alternatively, the retaining assembly may comprise a second retaining member arranged to retain the latch release member at least partially within the second bore by preventing it from passing completely through the mouth of the second bore, wherein the second retaining member is releasably attachable to the housing.

The first and/or second retaining member may comprise at least one clip. The at least one clip may be mountable to the outer surface of the housing. The at least one clip may be substantially annular, defining an internal surface within which the housing is received when the clip is mounted to the housing. The at least one clip may be at least partially received within an annular cavity in the outer surface of the housing. The at least one clip may be a circlip, or any other suitable clip. The at least one clip may be a plurality of said clips.

Alternatively, or additionally, first and/or second retaining member may comprise at least one fastener that is releasably engageable with said housing. The at least one fastener may be releasably engageable in said cavity or bore in the housing. The at least one fastener may be screwedly engageable in the housing. In this respect, the at least one fastener may be provided with a screw thread that is screwedly engageable with a screw thread provided in an inner surface of the housing. The at least one fastener may be a screw. The at least one fastener may be a plurality of said fasteners.

A head of the at least one fastener may protrude into the first and/or second bore so as to prevent the latch release member and/or the coupling element respectively from passing completely through the mouth of the first and/or second bore respectively. The head of the at least one fastener may taper radially inwardly from an outer end, that is distal to a shaft of the fastener, to an inner end that is proximal to a shaft of the fastener.

Preferably the retaining assembly is arranged to retain the coupling element at least partially within the first bore by preventing it from passing completely through the mouth of the first bore when the coupling element in its deployed position and/or to retain the latch release member at least partially within the second bore by preventing it from passing completely through the mouth of the second bore when the latch release member is in its first position.

Preferably the retaining assembly is arranged to retain both the coupling element and the latch release member within the respective first or second bore by preventing it from passing completely through the mouth of the respective bore.

Preferably the first retaining member is said at least one clip and the second retaining member is said at least one fastener.

Preferably the trigger assembly comprises a plurality of said coupling elements and the retaining assembly is arranged to retain each coupling element at least partially within a respective said first bore by preventing it from passing completely through the mouth of the respective bore. The retaining assembly may be comprise a clip that so retains each coupling element. The trigger assembly may comprise a plurality of said first and/or second retaining members each arranged to so retain a respective coupling element.

The trigger assembly may comprise a plurality of said latch members and said latch release members and wherein the retaining assembly is arranged to retain each latch release member at least partially within the respective bore by preventing it from passing completely through the mouth of the respective bore. The trigger assembly may comprise a plurality of said first and/or second retaining members each arranged to so retain a respective latch release member.

The or each latch release member may be substantially spherical.

The or each coupling element may be substantially spherical.

The, or each, latch member may be received partially in a bore in the shuttle and partially in a bore in the housing when the latch member is in the engaged configuration, and be fully received within the bore in the shuttle when the latch member is in the released configuration.

According to a seventeenth aspect of the invention there is provided a detachable tow ball comprising a trigger assembly according to the fourth arrangement useful for understanding the invention.

Such a tow ball may provide one or more of the advantages described in relation to the fourth arrangement useful for understanding the invention.

According to an eighteenth aspect of the invention there is provided a tow bar assembly comprising a detachable tow ball according to the seventeenth aspect of the invention.

Such a tow bar may provide one or more of the advantages described in relation to the fifteenth aspect of the invention.

Any of the features of any of the above aspects of the invention may be combined with any of the features of any of the other aspects of the invention.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cross-sectional front view of a detachable tow ball assembly and a collar of a complementary coupling member of a tow bar assembly useful for understanding the invention; Figure 2 is an enlarged cross-sectional front view of part of the detachable tow ball assembly and collar of figure 1 Figure 3 is a cross-sectional front view of a part of a detachable tow ball assembly comprising a mechanical linkage according to a first embodiment of the invenUon, with part of the mechanical linkage not shown for illustrative purposes; Figure 4 is an enlarged cross-sectional front view of the part of the detachable tow ball assembly circled in Figure 3; Figure 5 is an enlarged cross-sectional front view of the part of the detachable tow ball circled in Figure 3, with its components in a different configuration to that of Figure 4; Figures 6A-6C are each a side view of a portion of the mechanical linkage of the detachable tow ball assembly of Figures 3 to 5 (with a housing of the mechanical linkage omitted for illustrative purposes), illustrating in sequence where a shuttle of the mechanical linkage is driven from a second position to a first position by the rotation of an actuation shaft in a first rotational direction; Figures 7A-70 are each the same side view of the portion of the mechanical linkage shown in Figures 6A-6C, but illustrating in sequence where the actuation shaft is driven in the first rotational direction by a linear force applied to the shuffle in the direction from the second position to the first position of the shuttle.

Figure 8 is a perspective view of the portion of the mechanical linkage shown in Figures 6A to 70, in a position between those shown in Figures 6B and 60.

Figure 9 is an enlarged perspective view of the region circled A' in Figure 8; Figure 10 is a perspective view of the detachable tow ball assembly shown in Figures 3 to 5, showing a handle of the detachable tow ball assembly in a detached position; Figure 11 is an enlarged view of the region circled C' in Figure 10; Figure 12 is a perspective view of a socket section and part of an actuation shaft of the detachable tow ball assembly of Figure 10; Figure 13 is a front perspective view of a handle of the detachable tow ball assembly of Figure 10; Figure 14 is a rear perspective view of a handle of the detachable tow ball assembly of Figure 10; Figure 15 is perspective view of a detachable tow ball assembly according to a second embodiment of the invention; Figure 16 is a side view of a part of a mechanical linkage according to a further embodiment of the invention with part of the mechanical linkage not shown for illustrative purposes; Figure 17 is a rear view of the portion of a mechanical linkage of Figure 16; Figure 18 is a perspective view of the portion of the mechanical linkage of Figure 16; Figure 19 is a perspective view of part of the mechanical linkage of Figure 16; Figure 20 is another perspective view of the of part of the mechanical linkage of Figure 19; Figure 21 is a cross-sectional side view of the portion of the mechanical linkage of Figure 16; Figures 22A-22F are other cross-sectional side views of the portion of the mechanical lnkage of Figure 16, illustrating in sequence the retraction of the shuttle of the embodiment; Figure 23 is a further cross-sectional side view of the portion of a mechanical linkage of Figure 16; Figure 24 shows a cut-away perspective view of a mechanical linkage according to a further embodiment of the invention; Figure 25 shows a cross-sectional front view of the mechanical linkage of Figure 24; Figure 26 is an enlarged cross-sectional front view of the part of the detachable tow ball assembly circled A' in Figure 25; Figure 27 is a view corresponding to that of Figure 24 with its components in a different configuration to that of Figure 24; Figure 28 shows a cross-sectional front view of the mechanical linkage of Figure 27, and Figure 29 is an enlarged cross-sectional front view of the part of the detachable tow ball assembly circled A' in Figure 27.

Figure 1 shows a cross-sectional view of an arrangement of an automatic detachable tow ball assembly 1 which is useful for understanding the invention. The tow baN assembly 1 of this arrangement utilises a ball-type trigger. It comprises a mechanical linkage 202 connected to a tow ball 200 by a ball arm 201 (see Figures 1 and 10).

The mechanical linkage 202 comprises a housing 2, a shuttle 8 received within the housing 2 and an actuation shaft 26.

The housing 2 comprises a base 3 and a shaft 4. The shaft 4 of the housing 2 is shaped to be inserted into a collar 6 of a mounting assembly (not visible) of a tow bar assembly (not shown) on the rear of a vehicle. The shuttle 8 comprises an elongate bolt slidably received within a channel 10 in the housing 2. The channel 10 defines a shuttle motion axis (i.e. an axis in the direction in which the shuttle 8 can slide), which in this case is parallel to the longitudinal axis of the shaft 4 (and also of the shuttle 8), that is to say vertical from the perspective of figure 1. The shuffle 8 is coaxial with the shaft 4 and is movable along the shuttle motion axis from a first (retracted) position, the position shown in figure 1, to a second (deployed) position in which from the perspective of figure 1 the shuttle is axially higher up the channel 10 in the shaft 4 (i.e. the shuffle is nearer the distal end of the shaft).

The shuffle 8 is biased towards the second position by a coil spring 12, held compressed between a shoulder 14 of the shuttle 8 and a shoulder 16 of the channel 10 in the housing 2.

The shaft 4 has three coupling elements 18, each of which is received in a bore (not visible) in the shaft 4.

The detachable tow ball assembly 1 has a latch member in the form of ball bearing 20, receivable in a radial bore 36 in the shuttle 8 and a radial bore 38 in the housing 2.

These components, in combination with the shuttle 8, form the trigger assembly of the detachable tow ball 1 and will be discussed in more detail below.

A rotary handle 24, on the end of an actuation shaft 26 which extends n a direction perpendicular to the shuffle 8, is connected to a toothed pinion 28. The pinion 28 is meshed with a toothed rack 30 on the bottom end of the shuffle 8, so that rotation of the handle 24 causes linear motion of the shuffle, and vice versa. A cavity 31 in the housing 2, within which the actuation shaft 26 is received, is sealed with a cap 33 to prevent ingress of water and dirt.

The tow ball assembly 1 has a lock 32, by which the user can manually prevent movement of the shuffle 8. More particularly, in this arrangement the lock 32 has a plunger (not visible) which can be extended so that it projects into the space below the shuttle 8 (from the perspective of figure 1). When so positioned, the plunger lies in the path of the shuttle 8 when the shuffle is moving from the second position to the first position, and can thereby prevent the shuffle reaching the first position. Preventing the shuffle reaching the first position prevents the coupling elements 18 from being moved to a stowed position (see below), which in turn prevents removal of the tow ball assembly 1 from the collar 6 (for instance by thieves or vandals).

Figure 2 shows the collar 6 and the components of the trigger assembly in more detail. The three coupling elements 18, which are substantially spherical, lie in an annular array in a plane normal to the longitudinal axis of the shaft 4 and shuffle 8. The coupling elements 18 are evenly spaced around the circumference of the shuffle 8 (and indeed around the circumference of the shaft 4) at intervals of 120 degrees. The shuffle 8 has a tapered tip 9, behind which is a frustro-conical section 11.

The coupling elements 18 are shown in a stowed position in figure 2. In the stowed position the coupling elements 18 lie flush with or beneath the outer surface of the shaft 4.

The coupling elements 18 can be radially displaced, moving them from the stowed position to a deployed position in which they project from the outer surface of the shaft 4. The collar 6 has corresponding and complementary shaped recesses 34 for receiving a portion of the coupling elements 18 when the coupling elements are in the deployed position, allowing the shaft to interlock with the collar to connect the detachable tow ball assembly ito a mounting assembly on a vehicle. The coupling elements 18 are movable to the deployed position by moving the shuttle 8 to the second position, as outlined below.

In Figure 2 the latch member 20 is shown in an engaged configuration. The latch member 20 is received partially in the radial bore 36 in the shuttle and partially in the radial bore 38 in the shaft 4. The bore 38 in the shaft 4 also contains the latch release member 22, which abuts the latch member 20 and projects from the outer surface of the shaft 4. The latch member 20 is movable to a released configuration by disturbing the latch release member 22 (in this case by depressing the atch release member, moving it towards the longitudinal axis of the shaft 4). When the latch member is in the engaged configuration, it being received partially in the shaft 4 and partially in the shuttle 8, the shuttle is prevented from moving from its first position to its second position. When the latch member 20 is in the released configuration it is fully received within the bore 36 in the shuttle 8, and the shuttle is therefore able to move, under the action of the spring 12, to its second position. When the shuttle 8 moves, it carries the latch member 20 with it. When the shuttle 8 is in the second position, a section of the wall of the channel 10 acts as a retention surface 37, which holds the latch member 20 in the bore in the shuttle 8 and prevents it moving to the engaged configuration. Indeed, in this embodiment, the retention surface 37 is positioned such that it holds the latch member 20 in the released configuration when the shuttle 8 is in any position which is not the first position (such as an intermediate position between the first and second positions).

The latch member 20 and latch release member 22 are both substantially spherical, and in fact the latch member is substantially identical to the latch release member. The latch member 20 is biased towards the engaged configuration. In this arrangement it is biased radially away from the longitudinal axis of the shuttle 8 by a coil spring (not visible) held compressed in the bore 36 between the end of the bore (not visible) and the latch member.

The bore 38 in the housing has a narrowed mouth 39 of smaller radius then the latch release member 22, thereby preventing the latch release member from being ejected from the shaft by the spring (or by gravity if the tow ball assembly 1 is turned sideways). Similarly, the coupling elements 18 are prevented from being ejected from the bores 19 by narrowed mouths 41. As discussed below, the collar 6 has an internally frustro-conical actuation surface 40.

The function of the detachable tow ball assembly 1 will now be described with reference to figures 1 and 2. As stated previously, when the latch member 20 is in the engaged configuration the shuttle 8 is prevented from moving to the second position (under action of the spring 12) by virtue of the latch member bridging the gap between the shaft 4 and shuttle B and preventing relative movement therebetween. To connect the removable tow ball assembly 1 to a mounting assembly (not visible), the shaft 4 is inserted into the collar 6 with the shuttle S in the first position. Conventionally, the collar 6 is positioned vertically so that the shaft 4 is inserted into it by moving the tow ball assemby 1 upwards from below the collar. When the shaft reaches the position shown in figures 1 and 2, the actuation surface 40 of the collar 6 contacts the latch release member 22. As insertion of the shaft continues, the actuation surface 40 disturbs the latch release member 22, camming it radially inwards. The latch release member 22, in turn, forces the latch member 20 radially inwards from the engaged configuration towards the released configuration. When the latch member 20 reaches the released configuration, that is to say when it is received fully within the bore 36 in the shuffle 8, the shuttle is released and begins to move to the second position due to the force provided by the spring 12. Due to the pinion 28 being meshed with the rack 30 on the shuttle 8, as the shuttle moves, the pinion 28 (and therefore the actuation shaft 26 and handle 24) is driven to rotate. The direction in which the actuation shaft 26 and handle 24 rotate under these circumstances will hereafter be referred to as a second rotational direction.

As the shuffle 8 moves towards the second position, the sides of its tapered tip 9 cam the coupling elements 18 outwards, urging them from the stowed position to the deployed position. Each coupling element 18 is then accommodated in a complementary recess 34 in the collar 6. The coupling elements 18 being received in complementary recesses 34 provides a centering action, as the sides of the recesses guide the coupling elements (and therefore the entire detachable tow ball assembly 1) into position as they move outwards.

When the coupling elements 18 reach the deployed position, the shuttle 8 reaches the second position. The spring 12 continues to urge the shuffle S towards the distal end of the shaft 4, but the shuffle is prevented from moving beyond the second position due to its frustro-conical section 11 being held wedged between the coupling elements 18. The frustro-conical section 11 being wedged between the coupling elements 18 (and being urged further between them by the spring 12) also maintains a clamping force on the coupling elements, securing them in the deployed position. With the shuffle 8 in the second position and the coupling elements 18 in the deployed position, the detachable tow ball assembly 1 is interlocked with the collar 6 of the mounting assembly (not visible) and is therefore secured to the vehicle to which the mounting assembly is attached.

To remove the detachable tow ball assembly 1, the handle 24 (and pinion 28) is rotated in a first rotational direction, which is the opposite direction to the second rotational direction. The pinion 28 is meshed with the rack 30 on the shuttle 8, therefore as the pinion rotates the shuttle is moved axially back to the first position against the bias of the spring 12.

When the shuttle 8 reaches the first position the bores 36, 38 are aligned so that the latch member 20, under action of the spring (not shown), returns to the engaged configuration. It re-enters the bore 38 in the shaft 4, securing the shuttle 8 in the first position. At this point, the handle 24 can be released by the user. The latch member 20 re-entering the bore 38 pushes the latch release member 22 (which is no longer in contact with the actuation surface 40) outwards so that it project from the housing 2 once again. Having moved the shuttle 8 to the first position, the coupling elements 18 are no longer urged to the deployed position and so the shaft 4 may be withdrawn from the collar 6. As the shaft 4 is withdrawn, the recesses 34 cam the coupling projections 18 radially inwards and back to the stowed position.

Fig 3 shows a cross-sectional view of an automatic detachable tow ball assembly according to a first embodiment of the invention, comprising a mechanica linkage 203 with part of the mechanical linkage not shown for illustrative purposes (the actuation shaft, housing and interface slots on the shuttle are omiffed for illustrative purposes). This embodiment is similar to the arrangement of figures 1 and 2, therefore only the differences will be described in detail. The same reference numerals are used to refer to the same features. The tow ball assembly 100, like the above arrangement, is shown with the shuffle 8 in the first position. Though the retraction mechanism of the embodiment employs a handle, an actuation shaft with interface lugs and a shuffle with interface slots, these are not shown in figure 3 and will be described subsequently. The cap 33 is included on figure 3 so as to indicate the location of these components.

Unlike the arrangement of figures 1 and 2, the shuffle 8 of the embodiment comprises two portions movable relative to one another. It has a latch-operation member 42 and a deployment member 44. The latch-operation member 42 is slidably received within a cavity 46 in the deployment member 44, and is movable relative to the deployment member between an active position and a passive position as outlined below (the latch-operation member 42 s shown in the active position in figure 3). In the embodiment, the cavity 46 defines the direction in which the latch-operation member can move relative to the deployment member 44, which in this case is coaxial with the shuffle motion axis. The spring 12 abuts the deployment member 44, but does not act directly on the latch-operation member 42. However, the relative movement of the latch-operation member 42 and deployment member 44 is limited by the latch members 20a, 20b (as described below), therefore the spring 12 still urges the entire shuttle 8 to the second position.

While the arrangement of figures 1 and 2 had a single latch member, received within a bore in the shuffle and acted on by a single latch release member 22 received in a single bore 38 in the housing, the embodiment has two sets of these components. Latch member 20a is received within radial bore 36a in the shuttle 8 and is acted on by latch release member 22a in radial bore 38a in the housing 2, and latch member 20b is received within radial bore 36b in the shuffle 8 and is acted on by latch release member 22b in radial bore 38b in the housing 2. Further, the channel 10 defines two retention surfaces 37a, 37b, each of which function as described above. Like the latch member of the above arrangement, latch member 20a of the embodiment is movable under action of latch release member 22a from an engaged configuration to a released configuration. Latch member 20b is movable similarly under action of latch release member 22b. This is described more fully below.

The circled area of figure 3 is shown in more detail in figures 4 and 5. In figure 4, the latch-operation member 42 is shown in the active position and each latch member 20a, 20b is in the engaged configuration. In figure 5, the latch-operation member 42 is in the passive position and the latch members 20a, 20b are each in the released configuration. In both figures, the shuttle 8 is shown in the first position. As shown more clearly in these figures, the latch members 20a, 20b are cylindrical. The edges round both base faces 47 of the cylinder are chamfered.

In the embodiment the bores 36a, 36b, within which the latch members 20a, 2Db are receivable, adjoin the cavity 46. In contrast with the above arrangement, where the latch member was received fully within the bore in the shuttle when in the released configuration, in the embodiment when a latch member 20a, 2Db is in the released configuration it is received partly in the corresponding bore 36a, 36b in the shuttle 8 and partially in the cavity in the deployment member 44 (in other words, the bores and cavity co-operatively form a void in the shuttle in which the latch members are received when in the released configuration). Similarly, in this embodiment when a latch member 20a, 20b is in the engaged configuration, it is not only received partially in a bore 36a, 36b in the shuffle and partially in a bore 38a, 38b in the housing 2 (as is the case for the latch member of the above arrangement), it also remains partially received in the cavity 46.

The latch-operation member 42 has a cam surface 48a, which is cooperatively positioned with respect to latch member 20a, and another cam surface 48b cooperatively positioned with respect to latch member 20b. The cam surfaces 48a, 48b and chamfered surfaces 50a, SOb on the latch members 20a, 20b form bearing surfaces and couple the motion of the latch-operation member 42 and latch members. If the latch-operation member 42 is moved to the active position, the cam surfaces 48a, 48b act on chamfered surfaces 50a, 50b and cam the latch members 20a, 20b outwards to the engaged configuration.

Similarly, if one or both of the latch members 20a, 20b are moved inwards to the released configuration the chamfered surfaces 50a, 5Db act on the cam surfaces 48a, 48b and cam the latch-operation member 42 to the passive position.

It is to be noted that in this embodiment the motion of the latch-operation member 42 is only coupled to that of the latch members 20a, 20b to the extent described above. For instance, movement of the latch-operation member 42 from the active position to the passive position does not move the latch members 20a, 20b to the released configuration, and movement of the latch members To the engaged configuration does not move the laTch-operation member towards the active position. Further, while each cam surface 48a, 48b couples the motion of the latch-operation member 42 and each latch member 20a, 20b in the manner described above, the motion of the two latch members are otherwise ndependent.

In particular, each latch member 20a, 20b is independently movable to the released configuration. In other words, though moving the latch-operation member 42 to the active position moves both latch members 20a, 20b to the engaged configuration, moving one of the latch members to the released configuration moves the latch-operation member to the passive position but does not move the other latch member to the released configuration.

This will be described in more detail below.

A method of operating the detachable tow ball assembly 1 of the embodiment will now be described with reference to figures 3-5. To attach the tow ball assembly 1 to the collar 6 mounted on a vehicle (not shown), the tow ball assembly should be in the configuration shown in figure 3, that is to say the shuttle 8 should be in the first position, the latch-operation member 42 should be in the active position and the latch members 20a, 20b should be in the engaged configuration. The shaft 4 of the tow ball assembly 1 is then inserted into the collar 6 If one of the latch release members 22a, 22b is disturbed while the shaft 4 is being presented to the collar, for instance if one of the latch release members is knocked against the bodywork of the vehicle while reaching under the vehicle with the tow ball assembly 1, the corresponding latch member 20a, 20b may be moved to the released configuration.

Though one of the latch members 20a, 20b moving to the released configuration would move the latch-operation member 42 to the passive position, as described above this would not move the other latch member to the released configuration. The shuttle 8 would therefore remain held in the first position, and insertion of the shaft 4 could continue. In contrast, in the arrangement of figures 1 and 2 if the latch release member was accidentally disturbed, the shuttle would be released and would move to the second position. This would prevent insertion of the shaft into the collar, and necessitate manual retraction of the shuttle before repeating the attempted insertion.

When the shaft 4 is inserted into the collar (not shown), the collar disturbs the latch release members 22a, 22b, camming them inwards (as described in relation to the arrangement of figures 1 and 2). This moves the latch members 20a, 20b to the released configuration, and therefore also moves the latch-operation member 42 to the passive position. Where one of the latch members 20a, 20b has already been moved to the released configuration by an accidental knock, insertion of the shaft 4 merely moves the other latch member to the released configuration. In this situation, as the latch-operation member 42 has already been moved to the passive position, movement of this latch release member from the engaged configuration to the released configuration does not bring about any further movement of the latch-operation member.

With both latch members 20a, 20b in the released configuration, the shuttle 8 is released and moves towards the second position under action of the spring 12. The spring 12 moves the deployment member 44 upwards (from the perspective of figures 3-5). With the latch members 20a, 20b in the released configuration, they act to prevent removal of the latch-operation member 42 from the cavity 46. The latch-operation member 42 is therefore pulled upwards along with the deployment member, and so the entire shuffle 2 moves towards the second position. Once the shuffle is no longer in the first position, the retention surfaces 37a, 37b hold the latch members 20a, 20b in the released configuration, which maintains this coupling between the latch-operation member 42 and the deployment member 44. When the shuttle 8 reaches the second position, the deployment member 44 moves the coupling elements 18 to the deployed position as described in relation to the arrangement of figures 1 and 2.

To release the coupling elements 18, allowing them to move to the released configuration so that the shaft 4 can be removed from the collar, the shuttle is retracted by pulling the latch-operation member downwards (from the perspective of figures 3-5). The mechanism by which this is performed will be described later. As the latch members 20a, 20b are held in the released configuration by the retention surfaces 37a, 37b, the coupling between the latch-operation member 42 and deployment member 44 is maintained.

Downward movement of the latch-operation member 42 therefore results in downward movement of the entire shuttle 8.

When the shuffle reaches the first position, the latch members 20a, 20b pass beyond the retention surfaces 37a, 37b and become aligned with the bores 38a, 38b in the housing 2. At this point the latch members 20a, 2Gb are free to be moved to the engaged configuration. The latch-operation member 42 being urged downwards (from the perspective of figures 3-5) with the deployment member 44 being urged upwards (from the perspective of figures 3-5) by the spring 12 causes the latch-operation member to be moved to the active position. This in turn moves the latch members 20a, 2Gb to the engaged configuration, at which point they enter the bores 38a, 38b in the housing 2 and thus hold the shuffle in the first position. Retraction of the latch-operation member 42 (and thus of the entire shuttle 8) can then cease.

In this embodiment, the bores 38a, 38b in the housing 2 have narrowed mouths 39a, 39b positioned so that the radial travel of the latch release members 22a, 22b is limited. The limited motion of the latch release members 22a, 22b prevents the latch members 20a, 20b from moving fully out of the cavity 46. This means that the latch members 20a, 20b cannot be moved fuly out of the path of The latch-operation member 42. They therefore act to limit the range of motion of the latch-operation member 42 relative to the deployment member 44, preventing them being detached from one another (i.e. preventing full withdrawal of the latch-operation member from the cavity 46). In this embodiment the latch-operation member 42 is also prevented from being separated from the deployment member 44 by the mechanical linkage by which the shuttle is retracted. The linkage prevents the latch-operation member from moving downwards any further once the shuttle B has reached the first position, as outlined below.

Figures 6A-6C are each a side view of a portion of the mechanical linkage 203 of the detachable tow ball assembly of Figures 3 to 5, illustrating in sequence the retraction of the shuttle 8 by the actuation shaft 26 of the mechanical linkage 203 being drivably rotated; The actuation shaft 26 is positioned substantially perpendicularly to the longitudinal axis of the shuttle 8. The actuation shaft 26 is connected to a detachable handle 204 (see Figure 10) by which the shaft 26 can be rotated by a user.

In terms of orientation, in this embodiment the mechanical linkage 203 and tow ball is arranged so that when the tow ball assembly 1 is positioned as shown in figure 3, the shuttle 8 is aligned vertically and the actuation shaft 26 runs horizontally with the end with the handle 204 on the right of the housing.

The shuttle S (in this case the latch-operation member 42) has first and interface slots 101, 102 that are provided towards a first end 110 of the shuttle 8 that is distal to the tip 9 of the shuffle 8. The first and interface slots 101, 102 are spaced along the shuttle motion axis. The first interface slot 101 is provided adjacent to the first end 110 of the shuttle B, with the second interface slot 102 provided on the opposite side of the first interface slot 101 to the first end 110 of the shuttle 8.

Each of the first and second interface slots 101, 102 are provided in a side wall of the shuttle 8 and extend from an open end, radially inwardly towards the shuttle motion axis shuttle 8, to a closed end. Each of the first and second interface slots 101, 102 has a generally U-shaped cross sectional shape about a longitudinal slot axis that extends in a plane that is substantially perpendicular to the shuttle motion axis. The first and second interface slots extend part way around the circumference of the shuttle 8. In this regard, the longitudinal axis of each slot 101, 102 is a generally curved about the shuttle motion axis.

The first interface slot 101 is defined by a surface 103 of the shuttle 8. The surface 103 has first and second sections 104, 105 that form opposed sides of the slot 101. The first and second sections 104, 105 extend from the open end of the first interface slot to a base section 106 that forms the closed end of the slot 101.

The first and second sections 104, 105 are spaced in the direction of the shuttle motion axis and are opposed to each other.

The first section 104 faces generally in the direcTion of the shuttle motion axis, in the direction from the first position to the second position of the shuttle 8. The second section faces generally in the direction of the shuttle motion axis, in the direction from the second position to the first position of the shuttle 8.

Each of the first and second sections 104, 105 comprises a first portion 108, 111 that extends from the open end of the slot to a second portion 109, 112 that extends from an end of the respective first portion 108, 111 distal to the open end, to a respective end of the base section 106 (see Figure 7A).

Each first portion 108, 111 is substantially planar and extends substantially in a plane that is substantially perpendicular to the shuttle motion axis.

Each second portion 109, 112 is substantially curved along its radial length (its length in the radial direction of the shuttle 8). It has substantially the same radius of curvature as the first interface lug (see below).

The base section 106 is substantialy planar and extends in a plane that is substantially parallel to the shuffle motion axis.

The second interface slot 102 is defined by a surface 107 of the shuttle 8. The surface 107 has first and second sections 113, 114 that form opposed sides of the slot 102 (see Figure 6C). The first and second sections 113, 114 extend from the open end of the second interface slot 102 to a base section 115 that forms the closed end of the slot 101.

The first and second sections 113, 114 are spaced in the direction of the shuttle motion axis and are opposed to each other.

Each of the first and second sections 113, 114 is planar and extends substantially in a plane that is substantially perpendicular to the shuttle motion axis. The first section 113 faces generally in the direction of the shuttle motion axis, in the direction from the first position to the second position of the shuttle 8. The second section 114 faces generally in the direction of the shuttle motion axis, in the direction from the second position to the first position of the shuttle 8.

The base section 115 is substantially curved along its length between the first and second sections 113, 114 and has substantially the same radius of curvature as the second interface lug (see below).

A section of the side wall of the shuttle 8 adjacent to the first section 114 of the surface 107 defining the second interface slot 102, on an opposite side to that of the first interface slot 101, forms a first limit surface 171 of a first limit section of the shuttle 8. A sectional the side wall of the shuttle 8 adjacent to the first portion 108 of the first section 104 of the surface 103 defining the first interface slot 101, on an opposite side to that of the second interface slot 102, forms a second limit surface 172 of a second limit section at the shuttle 8 (whose function will be described in more detail below).

As can be seen from figure 8, the actuation shaft 26 is generally elongate extending along a longitudinal axis. The actuation shaft 26 comprises a first section 161 for attachment to a connecting section 205 for connection to the handle 24 (see below). The first section 161 has a substantially semi-circular cross-sectional shape about the longitudinal axis. A second section 162 of the actuation shaft 26 extends axially from the end of the first section 161 distal to the handle 24 to a third section 163.

The actuation shaft 26 comprises first and second interface lugs 121, 122 spaced substantially circumferentially about the longitudinal axis of the actuation shaft 26. Each of the interface lugs 21, 122 extends along a longitudinal axis that is substantially parallel to the longitudinal axis of the actuation shaft 26. Each interface lug 121, 122 includes an arcuate portion 131, 132 in the shape of a segment of a cylinder. Each arcuate portion 131, 132 has a respective arcuate outer surface 133, 134.

In Figure 60 the arcuate portion 131 of the first interface lug is shown as a shaded region. In this embodiment, each arcuate porton 131, 132 is a major segment of a cylinder.

In other words, the arc length of said arcuate portion is more than half the circumference of the notional cylinder a segment of which the arcuate portion is substantially in the shape of.

Both the first and second interface lugs 121,122 are substantially identical.

The arcuate portions 131, 132 of the first and!or second interface lugs 121, 122 define a radius for that interface lug, the radius being the radius of a notional cylinder a segment of which the arcuate portion is substantially in the shape of.

The arcuate portion of an interface lug having a relatively large arc length may be beneficial in that it may spread the loading between it and the corresponding slot in the shuttle over a larger area.

The actuation shaft 26 further comprises a first limit section 141 and a second limit section 142 (see Figure GB). The first limit section 141 extends outwardly from an end of the arcuate portion 132 of the second interface lug 122. The second limit section 142 extends in a circumferential direction from a radially outer end of the first limit section 141.

An outer surface of the first limit section 141 is substantially planar and forms a first limit surface 151 of the actuation shaft 26. The second limit section 142 has a radially outer surface 153 that is an arcuate surface of substantially constant radius centred on the longitudinal axis of the actuation shaft 26. A circumferential end of the second limit section 142, that is distal to the first limit section 41, forms a second limit surface 152 of the actuation shaft 26. The second limit surface 152 is substantially curved and extends radially inwardly from the radially outer arcuate surface 153 to a radially inner arcuate surface 154 of the second limit section 142.

The third section 163 of the actuation shaft 26 is substantially cylindrical. An end of the third section 163 distal to be end of the second section 162 is connected to a rotational coil spring 164.

It is to be appreciated that the rotation of the actuation shaft 26 may drive the linear motion of the shuttle 8 along the shuttle motion axis and, conversely, the linear motion of the shuttle 8 may rotatably drive the actuation shaft 26.

The shuttle will be referred to as being driven by the actuation shaft where a rotational torque applied directly to the actuation shaft 26 (i.e. a rotational torque applied to the actuation shaft 26 other than that exerted by the shuttle 8 on the actuation shaft 26) drives the linear motion of the shuttle 8 in the direction of the shuttle motion axis.

Conversely, the actuation shaft 26 will be referred to as being driven by the shuttle 8 where a linear force applied directly to the shuttle 8 (i.e. a linear force applied to the shuttle 8 other than that exerted on the shuttle 8 by the actuation shaft) drives the rotation of the actuation shaft 26.

As will now be described, the first and second interface slots 101, 102 and the first and second interface lugs 121, 122 are arranged such that such that when the actuation shaft 26 is rotated in a first direction (which, when viewed in the direction shown in figures 6A to 6C is anti-clockwise, as shown by the arrow D) about its longitudinal axis, to drive the shuttle 8, the interface lugs 121, 122 and slots 101, 102 meshingly engage such that the shuttle 8 is driven from its second position to its first position.

Figures 6A-6C illustrate in sequence where the shuttle 8 is driven from its second position to its first position by the rotation of the actuation shaft 26 in said first rotational direction. In this regard, a rotational torque is applied directly to the handle 24 such that the actuation shaft 26 is rotated in the first rotational direction (D).

As shown in figures 6A and SB, as the actuation shaft 26 is rotated in the first rotational direction, the first interface lug 121 is received within the first interface slot 101. As it is received within the slot 101, a section 333 of the arcuate surface 133 of the first interface lug 121 contacts the first and second portions 108, 109 of the first section 104 of the surface 103 that defines the first interface slot 101. Because the second portion 109 is curved with substantially the same radius of curvature as the first interface lug 121, the first interface lug 121 forms a close fit with said first and second portions 108, 109 as it is received within the first interface slot 101 The engagement of the first interface lug 121 with said first and second portions 108, 109 of the first section 104 of said surface 103 acts to move the shuttle 8, along its shuttle motion axis, in the direction from the second position to the first position (which is in the downward direction as shown in figures 6A to 6C), against the bias of the spring 12.

The first section 104 of the first interface slot 101 and the first and second sections 113, 114 of the second interface slot 102 are spaced in the direction of the shuttle motion axis, and the second interface lug 122 is circumferentially spaced from the first interface lug 121 such that, as the actuation shaft 26 continues to rotate in the first direction and the shuttle 8 travels in the direction from its second position to its first position, the second interface lug 121 is substantially received within the second interface slot 102, as shown in figure 6C.

The first and second sections 113, 114 of the second interface slot 102 are spaced apart in the direction of the shuttle motion axis by a distance that is substantially equal to the length of the second interface lug 122 in the direction of the shuttle motion axis. In this respect, the first and second sections 113, 114 are spaced apart in the direction of the shuttle motion axis by a distance that is substantially equal to the length of the second interface lug 122 in the direction of the shuttle motion axis when the second interface lug 122 is received within the slot 102. The first and second sections 113, 114 are spaced apart in the direction of the shuttle motion axis by a distance that is substantially equal to the radius of the arcuate portion 132 of the second interface lug 122. Therefore, the second interface slot 102 forms a close fit with the second interface lug 122.

As the second interface lug 122 is received within the second interface slot 102, the first interface lug 121 passes out of the first interface slot 101.

As the second interface lug 122 is received within the second interface slot 102, a section 334 of the arcuate surface 134 of the second interface lug 122 engages the first section 113 and a portion of the base section 115 of the surface 107 that defines the second interface slot 102. This engagement acts to drive the shuttle 8 to its first position.

Accordingly, rotation of the actuation shaft 26 in the first rotational direction (D) drives the shuttle 8 from its first position to its second position.

The respective first sections 104, 113 of the surfaces that define the first and second interface slots 101, 102 are spaced in the direction of the shuttle motion axis by a distance that is substantially equal to the circumferential distance between the section 333 of the arcuate surface 133 surface of the first interface lug 121 that contacts the first section 104 of the first interface slot 101 and the section 334 of the arcuate surface 134 of the second interface lug 122 that engages the first section of the second interface slot 102.

As the actuation shaft 26 continues to rotate in the first rotational direction (D), its first limit surface 151 engages the first limit surface 171 of the shuttle 8. This prevents any further rotation of the actuation shaft 26 in the first rotational direction (D). This prevents over rotation of the actuation shaft 26 in the first rotational direction.

Figures 7A-7C illustrate in sequence where the actuation shaft 26 is driven in the first rotational direction by a linear force applied to the shuffle 8 in the direction from the second position to the first position of the shuttle 8.

The rotational spring 164 biases the actuation shaft 26 in a second rotational direction (which, when viewed in the direction shown in figures 7A to 7B is clockwise, as shown by the arrow B)) about its longitudinal axis. The second rotational direction (B) is opposite to the first rotational direction (D). The rotational spring 164 biases the actuation shaft 26 in the second rotational direction such that when it is not engaged by a surface of the shuttle 8, it occupies the rotational position shown in Figure 7A.

In this position, when a linear force (F) is applied to the shuttle 8 to move it in the direction from its second position to its first position, thereby rotatably driving the actuation shaft 26 in the first rotational direction, the second section 105 of the surface of the shuttle 8 that defines the first interface slot 101 engages a section 335 of the arcuate surface 133 of the first interface lug 121. This acts to rotate the actuation shaft 26 in the first rotational direction (D).

The respective second sections 105, 114 of the first and second interface slots 101, 102 are spaced in the direction of the shuttle motion axis by a distance that is less than the circumferential distance between the section 335 of the arcuate surface 133 of the first interface lug 121 that is engaged by the second section 105 of the first interface slot 101 and a circumferentially outer surface 336 of the second interface lug 122 (the section of the arcuate surface of the second interface lug that is outermost in the circumferential direction of the actuation shaft).

The first interface slot 101 has a length in the direction of the shuttle motion axis that is greater than the length of the second interface slot 102 in the direction of the shuttle motion axis.

Specifically, the first and second sections 104, 105 of the surface 103 that defines the first interface slot 101 are spaced apart in the direction of the shuttle motion axis by a distance that is greater than the length of the first interface lug 121 in the direction of the shuttle motion axis. In this respect, the first and second sections 104, 105 are spaced apart in the direction of the shuttle motion axis by a distance that is greater than the length of the first interface lug 121 in the direction of the shuttle motion axis when the first interface lug 121 first engages the first section 104, when the shuffle B is drive by rotation of the shaft 26 (and when the second section 105 first engages the first interface lug 121 when the shaft is rotatably drive by the shuttle 8). The first and second sections 103, 105 are spaced apart in the direction of the shuttle motion axis by a distance that is greater than the radius of the arcuate portion 131 of the first interface lug 121.

Accordingly, when the first interface lug 121 first engages the first section 104 (when the shuttle 8 is driven from its second position to its first position by the rotation of the actuation shaft 26 in said first rotational direction-see Figure SB) and when the second section 105 first engages the first interface lug 121 (where the actuation shaft 26 is driven in the first rotational direction by a linear force applied to the shuttle B in the direction from the second position to the first position of the shuttle 8-See Figure 7B), the second interface lug 122 (and the first interface lug 121) is at different positions along the shuttle motion axis relative to the second interface slot 102.

In this regard, as the actuation shaft 26 is driven in the first rotational direction by the linear force applied to the shuttle 8 in the direction from the second position to the first position of the shuffle 8, the second interface lug 122 is not received within the second interface slot 102. Instead, an abutment section 181 of the second interface lug 122 contacts an abutment section 182 of the shuttle 8 and thereby prevents the shuttle 8 from reaching its first position. The abutment section 181 of the second interface lug 122 is formed by a section of the arcuate surface 134 of the second interface lug 122. The abutment section 181 is substantially curved about an axis that is substantially perpendicular to the shuttle motion axis.

The abutment section 182 of the shuttle 8 comprises a section of the side wall of the shuttle 8 adjacent to the first section 114 of the surface 107 defining the second interface slot 102, on an opposite side of the second slot 102 to the first slot 101, and the edge formed by this section of said first section 114. Accordingly, in this embodiment, the abutment section 181 forms part of the first limit surface 171. The abutment section 182 of the shuttle 8 is substantially planar. The abutment section 181 of the second interface lug 122 and the abutment section 182 of the shuttle 8 contact along a plane that has a normal that has component in both the direction of the shuttle motion axis and a direction substantially perpendicular to the shuttle motion axis.

Accordingly, when the actuation shaft 26 is driven in the first rotational direction by a linear force applied to the shuttle 8 in the direction from the second position to the first position of the shuttle 8, the shuttle 8 is prevented from reaching its first position.

When both latch members 20a, 2Db are moved to the released configuration (as described above), the shuttle 8 is released and moves towards the second position under action of the spring 12. This acts to rotate the actuation shaft 26 in the second rotational direction (B). If the actuation shaft 26 is rotated in the second rotational direction, after the shuttle 8 has reached its second position, the second limit surface 152 of the actuation shaft 26 engages the second limit surface 172 of the shuttle 8. This prevents any further rotation of the actuation shaft 26 in the second rotational direction (B). This prevents over rotation of the actuation shaft 26 in the second rotational direction.

The first interface lug 121 is configured such that when it engages the first section 104 of the surface 103 of the shuffle 8 that defines the first slot 101, it is received within the first slot 101 to a maximum depth of more than the length of the radius for that lug 121. The first interface lug 121 is configured such that when the second section 105 of the surface 103 of the shuTtle 8 thaI defines the first interface slot 101 engages the firsT interface lug 121, the first interface lug 121 is received within the first slot 101 to a maximum depth of more than the length of the arc radius for that lug.

The second interface lug 122 is configured such that when it engages the surface 107 of the shuttle 8 that defines the second interface slot 102 such that the shuttle 8 is driven to its first position, it is received within the second interface slot 102 to a maximum depth of more than the length of the arc radius for that lug.

The above arrangement is advantageous in that, in normal use, the shuffle 8 may be moved from its second position (its deployed position) to its first position (its retracted position), so as to allow the shaft 4 to be withdrawn from the collar 6 (and therefore allow the tow ball 200 to be detached from the collar 6) by rotation of the handle 24 to rotate and actuation shaft 26 in the first rotational direction.

However, if a person (e.g. a thief) tries to detach the tow ball by applying a force directly to the shuttle 8 to forcibly move the shuttle 8 from its second position to its first position, the shuttle 8 is prevented from reaching its first position. This prevents the unauthorised movement of the shuttle S from its second position to its first position and therefore prevents unauthorised detachment of the tow ball 200 from the collar 6.

In addition, this removes the need for a separate locking mechanism in order to prevent the shuttle 8 from being forcibly moved from its second position to its first position by the application of a force directly to the shuttle 8.

Furthermore, the linkage utilising a relatively low number of interface lugs and slots may be advantageous in that it may further reduce or simplify the manufacturing steps required.

Referring now to Figures 10 and 11, the handle 204 of the mechanical linkage is releasably connectable to the actuation shaft 26 via a connecting section 205. The connecting section 205 is rotationally fixed to the actuation shaft 26 such that rotation of the connecting section 205 rotates the actuation shaft 26.

When the handle 204 is connected to the connecting section 205, rotation of the handle 204 in a first rotational direction rotates the connecting section 205 in a first rotational direction, which rotates the actuation shaft 26 in its first rotational direction and rotation of the handle in a second rotational direction (which is opposite to the first rotational direction) rotates the connecting section 205 in a second rotational direction which rotates the actuation shaft 26 in its second rotational direction. Accordingly, the handle 204 may be rotated in its first rotational direction to retract the shuttle 8 from its second position to its first position. Conversely, the rotation of the actuation shaft 26 in its first or second rotational directions rotates the handle 204 in its first or second rotational directions respectively.

In figures 10 and 11, the handle 204 is shown in a detached position, in which it is not connected to the actuation shaft 26. For the avoidance of doubt, when the handle 204 is not connected to the actuation shaft 26, rotation of the handle 204 does not cause rotation of the actuation shaft 26 (or vice versa).

Referring to Figures 12 to 14, the handle 204 comprises a gripping section 501 connected to a first formation in the form of a plug section 502. The plug section 502 is integrally formed with the gripping section 501.

The gripping section 501 has an outer surface 503 that extends generally in a circumferential direction about the rotational axis of the handle 204 in a generally undulating manner so as to form a six-pronged shape.

The plug section 502 is a generally elongate and extends in a length direction, along the rotational axis of the handle 204. The plug section 502 has a radially outer surface 504 that has a generally hexagonal cross sectional shape centred on the rotational axis of the handle 204. Each radially outer face 509 of the plug section 502 is substantially planar. The plug section 502 has a radially inner surface 505 that has a substantially circular cross-sectional shape centred on the rotational axis of the handle 204 so as to define a substantially cylindrical bore 507 that extends from a front face 508 of the plug section 502 to a rear face of the plug section 502 where it is closed by an inner surface of the gripping section 501.

Each radially outer face 509 is provided, substantially midway along the width of the face 509, with an elongate recess 510 that extends along a longitudinal axis from the front of the face 509, in a direction parallel to the rotational axis of the handle 204, to substantially midway along the axial length of the face 509. Each recess 510 has a substantially semi-circular cross-sectional shape about its longitudinal axis.

The connecting section 205 has an outer housing 206 that extends in a length direction from a front face 516 to a rear face 517 along its rotational axis and has a generally cylindrical radially outer surface 511 centred on the rotational axis of the connecting section 205 (which is the rotational axis of the actuation shaft 26). The housing 206 has a radially inner surface 512 that has a substantially hexagonal cross sectional shape centred on the rotational axis of the connecting section 205 to define a hexagonal bore that extends axially inwardly from the front face 516 of the housing 206, terminating before the rear face 517 such that the bore has a closed rear end.

Each face 519 of the inner surface 512 is provided substantially mid-way along its length with an elongate protrusion 520 that protrudes radially inwardly of the face and extends along a longitudinal axis from the front face 560, in a direction parallel to rotational axis of the connecting section 205, terminating inwardly of the rear face 517. Each protrusion 520 has a substantially semi-circular cross-sectional shape about its longitudina axis.

A substantially cylindrical shaft 513 is disposed radially inwardly of the inner surface 512 and extends along a longitudinal axis that is co-axial with the rotational axis of the connecting section 205. The curved outer surface 514 of the cylindrical shaft 513 is spaced radially inwardly from the inner surface 512 of the housing 206 so as to define a cavity 515 between the outer surface of the shaft and the inner surface 512.

The cylindrical shaft 513 extends axially from a front face 530 that is coplanar with the front face 516 of the outer housing 206, to a rear face 518 disposed axially rearwardly of the rear face 517 of the housing 206. Accordingly the cylindrical shaft 513 protrudes rearwardly from the housing 206. The rear face 518 of the cylindrical shaft 513 is attached, and rotationally fixed to, to the first section 161 of the actuation shaft 26 by a D-shaped formation (not shown) on the rear face 518 that engages with a co-operating D-shaped formation (not shown) on the actuation shaft 26. Accordingly, rotation of the connecting section 205 rotates the actuation shaft 26 and vice-versa. This engagement also prevents the actuation shaft 26 and rear face 518 from separating. The rotational axis of the connecting section 205 is co-axial with the rotational axis of the actuation shaft 26.

The actuation shaft 26 and the connecting section 205 are rotatably mounted within a substantially cylindrical bore 521 in the housing 2 (see figure 11) defined by an nner surface 555 of the housing 2. The bore 521 is centred on the rotational axis of the actuation shaft 26 and extends axially inwardly from an outer face of the housing 2.

As the connecting section 205 rotates, its outer surface 511 rotates in close proximity to the inner surface of the housing 555. The inner surface 555 substantially surrounds and covers the outer surface 511 of the connecting section 205 in the circumferential and axial directions (relative to the rotational axis of the connecting section 205).

The outer housing 206 and the cylindrical shaft 513 together form a second formation in the form of a socket section. The plug section 502 and the socket section are arranged such that they are engageable with each other by the plug section 502 being received within the outer housing 206 of the connecting section 205.

In this regard, the hexagonal cross sectional shape of the inner surface 512 of the housing 206 has a complementary shape to that of the hexagonal cross sectional shape of the outer surface 504 of the plug section 502. In addition, the curved outer surface 514 of the cylindrical shaft 513 has a complementary shape to that of the cylindrical inner surface 505 of the plug section 502. Furthermore, each recess 510 in the plug section 502 has a complementary shape and position to that of each protrusion 520 on the inner surface 512 of the housing 206 of the connecting section 205.

Accordingly, the plug section 502 is slidably receivable within the radially inner surface 512 of the housing 206 of the connecting section 205. As the plug section 502 is received within the housing 206 each protrusion 520 of the connecting section 205 is received within a corresponding recess 510 in the plug section 502. In addition, the cylindrical shaft 513 of the connecting section 205 is received within the cylindrical bore 507 of the plug section 502.

When the plug section 502 is received within the connecting section 205 (the socket section), the plug section 502 is engaged with the connecting section 205 and is rotationally fixed relative to the connecting section 205, by virtue of the engagement of the respective hexagonal outer and inner surfaces and the protrusions 520 and recesses 510. Accordingly, rotation of the handle 204 acts to rotate the connecting section 205, which in turn rotates the actuation shaft 26. In this way, the handle may be rotated in a first rotational direction so as to rotate the actuation shaft 26 in its first rotational direction and therefore retract the shuttle 8 from its second position to its first position..

When it is not required to rotate the actuation shaft 26, the handle 204 can be disengaged from the connecting section 205 by slidably removing the plug section 502 out of the connecting section 205. As the plug section 502 is slidably removed from the housing 206, each protrusion 520 of the connecting section 205 is slidably removed from the corresponding recess 510 in the plug section 502. In addition, the cylindrical shaft 513 of the connecting section 205 is slidably removed from the cylindrical bore 507 of the plug section 502. The plug section 205 and the connecting section 205 are then disengaged and the handle 204 is not connected to the actuation shaft 26.

The mechanical linkage is arranged to prevent a person is rotating the actuation shaft 26 from outside of the housing 2 when the handle 204 is not connected to the connecting section 205. In this regard, as stated above, the outer surface 206 of the housing 206 of the connecting section 205 forms a close fit with the inner surface 555 of the housing 2 that defines the bore 521 and is substantially surrounded and covered by said inner surface 555, in the circumferential and axial directions. This acts to prevent access to the connecting section 205 so as to prevent rotation of the connecting section 205, other than by the engagement of the handle 204 with the connecting section 205.

The connecting section 205 is arranged such that it is difficult for a person to gain purchase on the connecting section 205. Access to the outer surface 206 of the connecting section 205 is prevented by the close radial fit with the housing 2, as stated above. Access to the cylindrical shaft 513 is prevented by there being a relatively small radial clearance between the curved outer surface 514 of the cylindrical shaft 513 and the radially inner surface 512 of the housing 206. In addition, the distance between the circumferentially adjacent protrusions 520 is relatively small, as compared to a person's fingers, so as to make it difficult for a person to gain purchase on the cylindrical shaft 513. In this way, the connecting section 205 acts as an anti-tamper formation.

The plug section 502 of the handle 204 and the connecting section 205 are arranged such that they are releasably engageable with each other in a plurality of relative rotational positions. In this regard, the plug section 502 and the connecting section 205 each have a rotational symmetry of the order of six, i.e. they have the same shape in six different rotational positions. Furthermore, every recess 510 in the plug section 502 is engageable with every protrusion 520 of the connecting section 205 and vice-versa. Accordingly, the plug section 502 is receivable within the connecting section 205, and is engageable therewith, in six different relative rotational positions.

This is advantageous in that it allows ease of engagement of the handle 204 with the connecting section 205 as the user only has to rotate the handle 204 relative to the connecting section 205 by a relatively small angle, if at all, before the plug section 502 is engageable with the connecting section 205.

The above arrangement of the removable handle 204 and connecting section 205 is advantageous in that the handle 204 functions in the manner of a key, with the actuation shaft 26 only being rotatable when the handle 204 is connected to the actuation shaft 26 by the connecting section 205. Therefore, when it is not desired to rotate the actuation shaft 26, the handle 204 may be removed from the actuation shaft 26 and kept in an external secure location (e.g. on the user). The removable handle 204 therefore acts to prevent thieves from trying to directly rotate the actuation shaft 26 so as to move the shuttle 8 to its retracted position and release the tow ball assembly. Accordingly, the above interface lug and slot arrangement prevents thieves from applying a force directly to the shuttle 8 so as to try and retract the shuttle 8 and the removable handle 204 prevents thieves from applying a rotational force directly to the actuation shaft 26 of the shuttle to do this. The combination of these features therefore provides a very secure mechanical linkage.

In addition, since the handle 204 may be removed when it is not necessary to retract the shuffle 8, this prevents accidental knocking of the handle 204 and so prevents inadvertent detachment of the tow ball assembly.

Furthermore, the arrangement of the handle 204 and the connecting section 205 provides an anti-tamper arrangement that acts to prevent rotation of the connecting section 205, and therefore of the actuation shaft 26, other than by the engagement with the handle 204.

In addition, the handle 204 may be easily and quickly engaged with the connecting section 205.

Referring now to figure 15 there is shown a perspective view of a detachable tow ball assembly 1000 according to a second embodiment of the invention. The detachable tow ball assembly 1000 is identical to be described above except in relation to the features described below and like reference numerals are used to like features.

Instead of the removable handle 204 a handle 900 is rotatably mounted to the tow ball arm 201, about a rotational axis 903. In the described embodiment, the handle 900 is not removable from the ball arm 201 (in the manner of the handle 204). The handle 900 comprises a gripping portion in the form of a single lever 901.

The handle 900 is connected to the actuation shaft 26 via a mechanical connection in the form of a cable 902 such that rotation of rotation of the handle 900 in a first rotational direction rotates the actuation shaft 26 in its first rotational direction and rotation of the handle 900 in a second rotational direction (which is opposite to the first rotational direction) rotates the actuation shaft 26 in its second rotational direction. Accordingly, the handle 900 may be rotated in its first rotational direction to retract the shuttle 8 from its second position to its first position. Conversely, the rotation of the actuation shaft 26 in its first or second rotational directions rotates the handle 900 in its first or second rotational directions respectively.

The cable 902 is an elongate cable that is attached to a point on the handle 900, that is of the rotational axis of the handle 900, to the actuation shaft 26 via a coupling member (not shown) that converts the linear movement of the cable, produced when the handle 902 is rotated, into rotational movement of the actuation shaft 26. The cable 902 passes into and out of the ball arm 201 and is at least partially housed within the ball arm 201.

The handle 100 is disposed at a position off the rotational axis 904 of the actuation shaft 26. In this respect, the rotational axis 903 of the handle 900 is disposed off the rotational axis 904 of the actuation shaft 26. The rotational axis 903 of the handle 900 is substantially parallel to the rotational axis of the actuation shaft 26. The handle 900 (specifically its rotational axis 903) is disposed on the ball arm 201 at a position substantially midway along the length of the ball arm 201 between the mechanical linkage 203 and the tow ball 200.

A cover (not shown) may be provided within the bore 521 in the housing 2 so as to cover prevent access to the actuation shaft 26.

Locating the handle 100 at a position off the rotational axis 904 of the actuation shaft 26 is advantageous in that allows the handle 900 to be located a position in which it is easily operable, compared to if the handle 900 was located proximal to the actuaton shaft 26.

Since the above described arrangement of the interface lugs and slots removes the need for a handle that must be pushed or pulled, before it can be rotated, this removes the need for the handle 900 to be close to the actuation shaft (e.g. to a rack and pinion interface), thereby allowing the handle 900 to be disposed in such a position in which it is remote from the actuation shaft 26, i.e. off the rotational axis 904 of the actuation shaft 26.

Figures 16-18 show a portion 52 of a mechanical linkage according to a further embodiment, in three different views. The mechanical linkage is identical to that of Figures 3 to 5, apart from the differences described below. Like references numerals are used to refer to like features.

The portion 52 shown comprises the shuttle 8 (only the latch-operation member 42 of which is shown), and an actuation shaft 26 positioned substantially perpendicularly to the longitudinal axis of the shuttle. Figures 1 6-18 show the actuation shaft 26 and shuttle 8 in the relative positions they would be in when the shuttle 8 was in the second position. The actuation shaft 26 has flats 54 for receipt of a knob (not visible) by which the shaft can be rotated by a user. In terms of orientation, in this embodiment the illustrated portion 52 is positioned within the tow ball (not visible) so that when the tow ball is positioned as shown in figure 3, the shuffle 8 is aligned vertically and the actuation shaft 26 runs horizontally with the end with the flats 54 on the right of the housing. It is to be noted that when the tow ball of figures 1 and 2 is viewed from this position the actuation shaft passes in front of the shuffle 8, whereas in the embodiment it passes behind the shuffle. The shuffle 8 (in this case the latch-operation member 42) has two transverse interface slots 58 which are spaced along the longitudinal axis of the shuffle.

Returning briefly to the trigger mechanism of the embodiment, from figures 16-18 it is apparent that the cam surfaces 48a, 48b are formed by walls of transverse notches 56a, 56b in the latch-operation member 42.

Figures 19 and 20 show the actuation shaft 26 in isolation. It has an actuable portion on the tip of the shaft 26 opposite to the end with the flats 54. The actuable portion 60 has two circumferentially-spaced interface lugs 62, each of which is aligned parallel to the actuation shaft 26. As described in more detail below, each interface lug 62 includes an arcuate portion in the shape of a segment of a cylinder. The actuable portion also has a first limit surface 64 and a second limit surface 66. The actuation shaft 26 also has a non-actuable portion 68 which is axially adjacent to the actuable portion 60. The non-actuable portion 68 defines a radial wall 70 at its longitudinally distal end (i.e. the end which meets the actuable portion 60), and an axial waIl 72 at its longitudinally proximal end (i.e. the end nearer the flats 54). It also defines a first restraint surface 74 and a second restraint surface 76. In this embodiment the first and second restraint surfaces 74, 76 are coplanar. Further, the second restraint surface 76 of the non-actuable portion 68 is contiguous with the second limit surface 66 of the actuable portion 60.

Referring to figures 16-20, the interface lugs 62 are movable along the axis of the actuation shaft 26 between an actuable configuration and a non-actuable configuration with respect to the interface slots 58 in the shuttle 8. In this embodiment, this is done by moving the entire actuation shaft 26 along its axis. Wth the actuation shaft 26 axially positioned so that the non-actuable portion 68 is aligned with the shuttle 8 (as shown in figures 17 and 18) the lugs 62 are in the non-actuable configuration, and when the actuation shaft is axially positioned so that actuable portion 60 is aligned with the shuttle, the lugs 62 are in the actuable configuration.

Figure 21 shows a section through the shuttle 8 and actuaTion shafT 26, in a plane which is perpendicular to the actuation shaft and which bisects the shuttle 8, with the non-actuable portion 68 aligned with the shuffle B (that is to say with the interface lugs 62 and interface slots 58 in the non-actuable configuration). With the components of the linkage in this configuration, the first and second restraint surfaces 74, 76 are positioned to substantially prevent rotation of the actuation shaft 26, thereby preventing and significant movement of the shuttle 8. If the actuation shaft 26 is urged to rotate in a first direction, in this case forwards' as defined above (i.e. the direction in which the shaft must be rotated to retract the shuttle 8, which is clockwise from the perspective of figure 21), the first restraint surface 74 contacts the shuttle B and prevents rotation of the actuation shaft. Similarly, if the shuttle 8 is urged downwards (from the perspective of figure 21) it urges the actuation shaft 26 to rotate forwards, but this is prevented by the first restraint surface 74 therefore no significant movement takes place. If the actuation shaft 26 is rotated in the opposite direction (backwards' as defined above), the second restraint surface 76 contacts the shuttle and prevents rotation of the actuation shaft. Similarly, if the shuttle 8 is urged upwards it urges the actuation shaft 26 to rotate backwards, but this is prevented by the second restraint surface 76 therefore no significant movement occurs.

It is to be noted that though figure 21 shows the lugs 62 and slots 58 in the non-actuable configuration, one of the lugs 62 extends over the non-actuable portion 68 as well as the actuable portion (not shown in figure 21), and is still received within one of the slots 58 in the shuttle. The portion of this lug 62 which extends over the non-actuable portion 68 acts as an anchor, preventing the shuttle 8 from moving axially while the lugs 62 and slots 58 are in the non-actuable configuration. It also acts as a guide member during axial movement of the shaft 26 (when the lugs 62 are moved between the actuable and non-actuable configurations), preventing the lugs from becoming misaligned with the slots 58 while in the non-actuable configuration.

When the interface lugs 62 and interface slots 58 are in the actuable configuration, they form a rack and pinion mechanism, whereby rotation of the actuation shaft 26 relative to the shuttle B causes linear motion of the shuttle relative to the actuation shaft (and linear motion of the shuttle causes rotational motion of the actuation shaft). This rack and pinion mechanism is used to retract the shuttle 8 from the second position to the first position, as illustrated in figures 22A-22F. Figure 22A shows the actuable portion 60 and shuttle 8 in the same relative positions as in figures 16-18 (but with the lugs 62 in the actuable configuration relative to the slots 58), i.e. with the shuttle 8 in the second position. The second limit surface 66 contacting the shuttle 8 prevents the actuation shaft from rotating any further backwards (and therefore prevents the shuttle moving any further upwards) in the same manner as is outlined above in relation to the second restraint surface 74.

In this embodiment, a spring (not visible) is wound round the actuation shaft 26 and held compressed between a wall (72 in figure 20) of the non-actuable section and a surface of the cavity in the housing (when the linkage is in situ in the tow ball). The spring acts to urge the actuation shaft 26 axially, thereby urging the interface lugs 62 to the non-actuable configuration.

To retract the shuttle 8 and move it along the shuttle motion axis towards the first position, the actuation shaft is forced against the bias of the spring (not visible) by pulling on the knob (not visible) so that the interface lugs 62 are moved to the actuable configuration.

The shaft 26 is then rotated forwards (i.e. clockwise from the perspective of Figures 22A- 22F), by rotating the knob. Figure 22B shows the relative positions of the actuation shaft 26 and shuttle once the actuation shaft has begun to rotate. At this point, the axial force applied to the actuation shaft 26 by the user to overcome the force from the spring can be removed, since the wall (71 in figures 17-19) contacts the shuttle 8 and prevents the lugs 62 and slots 58 from moving to the non-actuable configuration under action of the spring.

During the initial movement, the interface between the actuation shaft 26 and the shuttle 8 takes place entirely though one interface lug 62 (in this case the one nearest the second limit surface) and one interface slot 58 (in this case the one nearest the tip of the shuttle). Once the actuation shaft 26 and shuffle 8 have moved sufficiently, the other lug 62 enters the other slot 58. At this point, as shown in figure 22B, the interface between actuation shaft 26 and shuffle 2 takes place through both lugs 62 and both slots 58.

As the actuation shaft 26 continues to rotate and the shuttle 8 continues to move downwards (from the perspective of figures 22A-22F), the lug 62 through which the interface initially took place is withdrawn from the corresponding slot 58. This is shown in figure 22D.

Thereafter, the interface between actuation shaft 26 and shuffle 8 thereafter takes place entirely through the other lug 62 and slot 58. The actuation shaft 26 continues to rotate and the shuffle 8 continues to move towards the first position, as shown in figure 22E.

When the shuffle 8 reaches the first position, it is contacted by the first limit surface 64, as shown in figure 22F. The first limit surface 64 prevents any further forward rotation of the actuation shaft 26, and therefore prevents the shuffle 8 moving beyond the first position, in the fashion outlined above in relation to the first restraint surface 74. The shuffle 8 is then held in the first position by the latch members (not visible) of the trigger mechanism. When the shuttle 8 is released by the latch members and moves to the second position, the above process is reversed.

Figure 23 is an enlarged view of figure 22E, in which the arcuate porton 76 in the shape of a segment of a cylinder is highlighted on one of the interface lugs 62. The notional cylinder 78 of which the arcuate portion 76 is a segment is also shown. For the sake of clarity of the drawing, the arcuate portion 76 and notional cylinder 78 are both shown slightly smaller than actual size. In this embodiment, the arcuate portion 76 is a major segment of a cylinder. As shown more clearly in this diagram, both the interface lugs 62 are substantially identical, as are both the interface slots 58. Figure 23 also shows more clearly that each interface slot 58 has an arcuate surface 78 of complementary shape to its corresponding interface lug 62.

Fig 23 shows the actuation shaft 26 and shuttle 8 at the relative position in which one of the interface lugs 62 is received within its corresponding slot 58 to its maximum depth. In this embodiment the depth 82 to which the lug 62 is received within the slot 58 (which is shown slightly smaller than actual size) is substantially equal to twice the radius of the notional cylinder 78.

Referring now to Figures 24 to 29 there is shown a detachable tow ball assembly 1100 according to a further embodiment of the invention. The detachable tow ball assembly 1100 is the same as that of Figures 3 to 14 except for the differences described below and like reference numerals are used to refer to like features.

The detachable tow ball assembly 1100 comprises a retaining assembly comprising a first retaining member 1201 arranged to retain the coupling elements 18 at least partially within the respective bores 19 in the housing 2 by preventing the coupling elements 18 from passing completely through mouths 1202 (see Figure 1) of the respective bores 19, out of the housing 2.

The first retaining member 1201 is a substantially annular clip 1201. The clip 1201 is a circlip. The shaft 4 of the housing 2 is provided with an annular cavity 1203 that is centred substantially on the longitudinal axis of the shaft 4. The annular cavity 1203 extends radially inwardly from the outer surface of the shaft 4, terminating before it reaches a radially inner wall of the shaft 4. The clip 1201 is releasably mountable within the cavity 1203.

The annular cavity 1203 extends adjacent to the bores 19 and opens into the bores 19. When the clip 1201 is mounted within the cavity 1203 it extends into the bores 19 in a direction substantially perpendicular to the longitudinal axis of the bores.

This provides a blockage within the bores 19 that effectively reduces the cross-sectional area of the bores 19 presented to the coupling elements 18 respectively to less than the cross-sectional area of the coupling elements 18. This prevents the coupling elements 18 from passing completely through the mouths 1203 of the respective bores 19 from inside the housing 2 to outside the housing 2.

Because the clip 1201 is releasably attachable to the housing 2, it allows the coupling elements 18 to be inserted into the respective bores 19 without the clip 1201 being attached to the housing 2, i.e. without the clip 1201 being received within the annular cavity 1203.

The clip 1201 may then subsequently be attached to the housing 2, i.e. by being received within bores l9so as to retain the coupling elements 18 within the bores 19.

This allows the coupling elements 18 to be inserted into the respective bores 19 from outside of the housing 2, through the mouths 1202 of the bores 19. This simplifies and speeds up the assembly process and removes the need for assembly jigs. In addition, it allows the shapes of the bores 19 to be simplified, for instance they may simply be drilled through bores.

In this respect, when assembling the tow ball assembly, the coupling elements 18 are inserted into the bores 19, from the outer surface of the shaft 4 through the mouths 1202 of the bores 19. The retaining clip 1201 is then attached to the housing by mounting it within the annular cavity 1203. This retains the coupling elements 18 within the bores 19 by preventing them from passing completely through the mouths of the bores 19.

Specifically, when the shuttle moves from first position, as shown in Figures 24 to 26, to its second position (Figures 27 to 29 shown the shuttle in a position just before it reaches its second position), the deployment member 44 moves the coupling elements 18 to the deployed position as described above. However, the retaining clip 1201 retains the coupling elements 18 within the bores 19 by preventing them from passing completely through the mouths of the bores 19.

The retaining assembly also comprises a pair of second retaining members 1205a, 1205b arranged to retain the latch release members 22a, 22b at least partially within the respective bores 38a, 38b in the housing 2 by preventing the latch release members 22a, 22b from passing completely through the mouth of the respective bore, out of the housing 2.

Each of the second retaining members is a screw 1205a, 1205b. Each screw 1205a, 1205b has a longitudinally extending shaft section 1206 that is provided at one end with a section of increased diameter to form a head 1207 of the screw 1205a, 1205b. The head 1207 of the screw 1205a, 1205b tapers radially inwardly from an outer end, that is distal to a shaft section of the screw, to an inner end that is proximal to the shaft of the screw.

Each screw 1205a, 1205b is releasably engageable within a respective respective radial bore 1210a, 1210b in the housing 2. Each bore 1210a, 1210b has a generally corresponding shape to that of the screw 1205a, 1205b that is received within the bore 1210a, 1210b. Each bore 1210a, 1210b, has an inner axial section that has a substantially circular cross-sectional shape of substantially constant diameter. Each bore 1210a, 1210b, has an outer axial section that is generally circular in cross sectional shape but is of a greater diameter than the diameter of the inner axial section.

Each screw 1205a, 1205b is inserted into the respective radial bore 1210a, 1210b, with its shaft section first. The head 1207 of each screw 1205a, 1205b is received within the outer axial section of the respective bore 121 Oa, 121 Ob.

Each screw 1205a, 1205b is provided with a threaded section, along its shaft that is engageable with a correspondingly threaded section of the respective radial bore 1210a, 1210b. Accordingly each screw 1205a, 1205b maybe releasably screwed within the respective radial bore 1210a, 1210b.

The radial bores 1210a, 121Db that receive the screws 1205a, 1205b are substantially parallel to, adjacent to and below the radial bores 38a, 38b in the housing 2 that receive the latch release members 22a, 22b. The outer axial sections of the radial bores 1210a, 1210b open into the radial bores 38a, 38b in the housing 2 respectively.

Furthermore, when the screws 1205a, 1205b are received in the radial bores 1210a, 1210b, the heads 1207 of the screws 1205a, 1205b extend into the radial bores 38a, 38b in the housing 2 respectively.

This provides a blockage within the radial bore 38a, 38b, that effectively reduces the cross-sectional area of the bores 38a, 38b presented to the latch release members 22a, 22b respectively to less than the maximum cross-sectional are of the latch release members 22a, 22b. This prevents the latch release members 22a, 22b from passing completely through the mouth of the respective radial bores 38a, 38b, out of the housing 2, when the latch release members 22a, 22b are in the first position (as shown in Figures 24 to 26).

Because the retaining screws 1205a, 1205b are releasably attachable to the housing, it allows the latch release members 22a, 22b to be inserted into the respective bores 38a, 38b without the retaining screws 1205a, 1205b being attached to the housing 2, i.e. without the retaining screws 1205a, 1205b being received within the radial bores 1210a, 1210b. The retaining screws 1205a, 1205b may then subsequently be attached to the housing, i.e. by being received within radial bores 1210a, 1210b so as to retain the latch release members 22a, 22b within the respective bores 38a, 38b.

This allows the latch release members 22a, 22b to be inserted into the respective bores 38a, 38b from outside of the housing 2, through the mouths of the bores 38a, 38b.

This simplifies and speeds up the assembly process and removes the need for assembly jigs. In additon, it allows the shapes of the bores 38a, 38b to be simplified, for instance they may simply be drilled through bores.

In this respect, when assembling the trigger assembly of the tow ball assembly, the latch release members are inserted into the respective bores 38a 38b, from the outer surface of the shaft 4 through the mouth end of the bore 38a, 38b. The retaining screws 1205a, 1205b are then screwedly engaged in the radial bores 1210a, 1210b so as to retain the latch release members 22a, 22b within the bores 38a, 38b by preventing them from passing completely through the mouths of the bores 38a, 38b.

In addition, the limited motion of the latch release members 22a, 22b, due to their abutment with the screws 1 205a, 1 205b prevents the latch members 20a, 20b from moving fully out of the cavity 46. This means that the latch members 20a, 20b cannot be moved fully out of the path of the latch-operation member 42. They therefore act to limit the range of motion of the latch-operation member 42 relative to the deployment member 44, preventing them being detached from one another (i.e. preventing full withdrawal of the latch-operation member from the cavity 46).

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined by the appended claims. For instance, the mechanical linkage of the above described embodiments may be utilised in a different context altogether (for instance it may be used in a pin tumbler door lock, to translate rotation of the plug into linear movement of the deadbolt). Alternatively, the mechanical linkage may be used in a non-automatic detachable tow bar assembly. For instance, the spring which biases the shuttle to the second position may be removed, resulting in the shuttle being movable only via manipulation of the handle.

Furthermore, the mechanical linkage may be used in an automatic detachable tow bar which uses a conventional trigger mechanism (such as those described in the introduction and in relation to the arrangement of figures 1 and 2) to retract the shuttle.

Either, or both, of the spring 12 and the coil spring 164 may be replaced by any suitable resilient member, including a leaf spring, Belleville washer, coil spring, volute spring, tensator spring, gas springs, elastomeric tubes, rods, sheets or blocks, etc. Though in the described embodiment a rotational spring 164 biases the actuation shaft 26 in a second rotational direction, it may be the case that the rotational spring is omitted. In this case, the actuation member 26 may be arranged such that when the shuttle 8 is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft 26 in the first rotational direction, the second section 105 of the surface of the shuttle that defines the first interface slot engages the arcuate surface 133 of the first interface lug 121. This may be, for example, by the weight distribution of the actuation shaft 26.

There may be a plurality of said first interface lugs and a plurality of said first interface slots respectively. In this regard, there may be a plurality of said first interface lugs circumferentially distributed around the actuation shaft and a set of respective said first interface slots distributed along the shuttle in the axial direction, wherein the interface slots and lugs are arranged such that when the actuation shaft is rotated in a first direction, to drive the shuttle in the direction from its second position to its first position, each first interface lug engages a respective first section of a surface of the shuttle that defines a respective first slot, driving the shuttle in said direction and the second interface lug engages the surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position, and when the shuttle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, respective second sections of the surfaces of the shuttle that define the first slots engage the first interface lugs and rotatably drive the actuation shaft such that an abutment section of the second interface lug contacts an abutment section of the shuttle and thereby prevents the shuttle from reaching its first position.

Alternatively, or additionally, there may be a plurality of said second interface lugs and a plurality of said second interface slots respectively. In this regard, there may be a plurality of said second interface lugs circumferentially distributed around the actuation shaft and a set of respective said second interface slots distributed along the shuttle in the axial direction, wherein the interface slots and lugs are arranged such that when the actuation shaft is rotated in a first direction, to drive the shuttle in the direction from its second position to its first position, the first interface lug engages the first section of the surface of the shuttle that defines the first interface slot, driving the shuttle in said direction and each second interface lug engages a respective surface that defines a respective said second interface slot such that the shuttle is driven to its first position, and when the shuttle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, the second section of the surface of the shuttle that defines the first interface slot engages the first interface lug and rotatably drives the actuation shaft such that an abutment section of each second interface lug contacts a respective abutment section of the shuttle and thereby prevents the shuttle from reaching its first position.

There may be a plurality of said first interface lugs and said first interface slots respectively and/or a plurality of said second interface lugs and said second interface slots respectively.

The plurality of said first and/or second interface lugs and the plurality of first and/or second interface slots may be distributed in any suitable arrangement.

The shuttle may be received in the housing in an enclosed channel or cavity, or in an open-sided void such as a groove. The shuttle is preferably slidably receivable within the housing. For the avoidance of doubt, the shuttle motion axis may be curved (for instance the shuttle may be slidable within an arcuate channel in the housing).

As the actuation shaft 26 rotates in the first direction, to drive the shuttle from its second position to its first position, the second interface lug 121 is substantially received within the second interface slot 102, as shown in figure SC. Alternatively, the second interface lug 121 may only be partially received within the second interface slot.

In the described embodiment each of the first and second portions 108, 111 * 109, 112 of the first and second sections 104, 105 of the first slot 101 is substantially planar and extends substantially in a plane that is substantially perpendicular to the shuttle motion axis.

Any or each of said portions 108, 111, 109, 112 may extend substantially in a plane that is oriented such that a normal to the plane has at least a component in a direction that is substantially parallel to the shuffle motion axis.

Similarly, the first and second sections 113, 114 of the second slot 102 may extend substantially in a plane that is oriented such that a normal to the plane has at least a component in a direction that is substantially parallel to the shuttle motion axis.

The arcuate portion of the first and/or second interface lugs 121, 122 may have an arc length of over 20% of the circumference of the notional cylinder a segment of which the arcuate portion is substantially in the shape of. The arcuate portion of the first and/or second interface lug preferably has an arc length of over 30% of the circumference of the notional cylinder, and more preferably has an arc length of over 40% of the circumference of the notional cylinder. The arc length is preferably more than 60% of the circumference of the notional cylinder, preferably more than 70% and more preferably more than 80%.

The first interface lug may be configured such that when the first interface lug engages the first section of the surface of the shuffle that defines the first slot, it is received within the first interface slot to a maximum depth of at least 1.3 times the arc radius, preferably at least 1.6 times the arc radius and more preferably at least 1.9 times the arc radius. Instead or in addition, said maximum depth may be less than 2.7 times the arc radius, preferably less than 2.4 times the arc radius and more preferably less than 2.1 times the arc radius.

The first interface lug may be configured such that when the second section of the surface of the shuttle that defines the first interface slot engages the first interface lug, the first interface lug is received within the first slot to a maximum depth of at least 1.3 times the arc radius, preferably at least 1.6 times the arc radius and more preferably at least 1.9 times the arc radius. Instead or in addition, said maximum depth may be less than 2.7 times the arc radius, preferably less than 2.4 times the arc radius and more preferably less than 2.1 times the arc radius.

The second interface lug may be configured such that when it engages the surface of the shuffle that defines the second interface slot such that the shuttle is driven to its first position, it is received within the second interface slot to a maximum depth of at least 1.3 times the arc radius, preferably at least 1.6 times the arc radius and more preferably at least 1.9 times the arc radius. Instead or in addition, said maximum depth may be less than 2.7 times the arc radius, preferably less than 2.4 times the arc radius and more preferably less than 2.1 times the arc radius.

In the described embodiment the plug section 502 is integrally formed with the gripping section 501. Alternatively, the plug section 502 may be formed separately to the gripping section 501 and attached to it.

In the described embodiment the handle 204 is connectable to the actuation shaft 26 by the connecting section 205. The handle 204 may be indirectly connectable to the actuation shaft 26 via one or more mechanical couplings, transmissions, connecting sections, etc. Alternatively, the handle 204 may be directly connectable to the actuation shaft 26.

In the described embodiment the connecting section 205 is formed separately from the actuation shaft 26 and is attached to the actuation shaft 26. Alternatively, the connecting section 205 may be integrally formed with the actuation shaft 26.

In the described embodiment the connecting section is directly rotatably coupled to the actuation shaft 26 by virtue of its attachment to the actuation shaft 26. Alternatively, the connecting section 205 may be indirectly rotatably coupled to the actuation shaft 26, for example via one or more mechanical couplings, transmissions, etc. in the described embodiment the connecting section 205 is received within the housing 2 of the mechanical linkage. Alternatively, the connecting section 205 may be received with a housing that is separate to that of the housing of the mechanical linkage.

In the described embodiment the handle 204 comprises a plug section 502 and the connecting section 205 forms a socket section. Alternatively, in a reciprocal arrangement, the handle 204 may comprise a socket section and the connecting section 205 may comprise a plug section that is receivable within the socket section so as to engage the handle 204 with the connecting section 205.

In the described embodiment, each of the connecting section 205 and the plug section 502 of the handle 204 has a hexagonal cross-sectional shape about its rotational axis. It will be appreciated that the connecting section 205 and the plug section 502 may have any other suitable cross sectional shape, including cross-sectional shapes that are curved at least partly curved.

In the described embodiment the handle 900 is connected to the actuation shaft 26 by a cable 902. Additionally, or alternatively, any other form of a mechanical collection may be used including a rack and pinion connection, rotary gears, or any other suitable mechanical connection.

The mechanical connection may be substantially housed within a housing, such as the ball arm 201.

Alternatively, or additionally, the handle 900 may be connected to the actuation shaft 26 by an electrical connection, (e.g. by connection to an electrical switch which operates an actuator connected to the actuation shaft), by a magnetic connection (e.g. a magnetic gear), etc. The gripping portion of the handle may have any suitable arrangement including a multi-pronged arrangement, such as that of the handle 204.

The handle 901 may be disposed closer to the tow balI 200 than it is to the housing 2 of the mechanical linkage. The handle 901 may be disposed at least half of the length of the ball arm 201 away from the housing 2 of the mechanical linkage. The handle 901 may be disposed at least two thirds of the length of the ball arm 201 away from the housing 2 of the mechanical linkage.

The handle 900 may be releasably connectable to the actuation shaft 26, as described for the handle 204.

Though in the mechanical linkage shown in Figures 16 to 23 one of the interface lugs extends over the non-actuable portion, in other embodiments there may be no lugs in this region of the actuation shaft. Instead or in addition, in other embodiments the non-actuable portion may not have restraint surfaces. For instance, it may be a simple cylinder, in which case the actuation shaft would freewheel' when the non-actuable portion was aligned with the shuffle.

Furthermore, the second limit surface and/or second restraint surface may be present but may not contact the shuffle in normal use. This would ensure that the shuffle would continue to be urged upwards by the spring when in the second position (this force not being counteracted by the rotation of the actuation shaft being prevented), therefore the coupling elements would continue to be urged outwards. This may provide a stronger and/or more stable coupling engagement with the collar.

Though in the mechanical linkage shown in Figures 16 to 23 each of the interface lugs is associated with a particular interface slot, in other embodiments each lug may be associated with two or more (where there are more than two) slots, and/or each slot may be associated with two or more lugs. For instance, the actuation shaft may comprise a substantially circular array of lugs each of which may be meshed with any of the slots in the shuttle.

Though in the described embodiments, when a latch member is in the engaged configuration it is received partially in the cavity in the deployment member, partially in a bore in the shuttle and partially in a bore in the housing, in other embodiments this may not be the case. For instance, the deployment member may be shaped so that the latch members only project into the cavity when in the released configuration. In such an arrangement, the shuttle retraction mechanism may be solely responsible for preventing separation of the deployment member and latch-operation member (or they may be allowed to separate and rejoin when required, or they may be prevented from separating in any other

suitable fashion).

As outlined above, in the described embodiments movement of the latch members to the engaged configuration does not cause movement of the latch-operation member to the active position. However, in other embodiments this may be the case. For instance, the trigger mechanism may have a resilient member positioned to urge the latch-operation member to the active position (such as a coil spring held compressed in the cavity in the deployment member). In such an arrangement movement of the latch members to the released configuration would move the latch-operation member to the passive position against the bias of the spring, and (both) the latch members being moved to the engaged configuration would cause the latch-operation member to move back to the active position under action of the spring. In a similar arrangement, the weight of the latch-operation member may be used in place of a spring to urge the latch-operation member to the active position. Arrangements where the latch-operation member is urged to the active position may be beneficial in that the latch members would be biased to the engaged configuration by the latch-operation member. As such, if one of the latch members was inadvertently moved to the released configuration (such as by a knock prior to insertion of the shaft, as described above) it would move the latch-operation member to the passive position, but then the latch-operation member would be moved back to the active position and so that latch member would be returned to the engaged configuration. This may provide an additional level of resistance to accidental triggering, as all the latch members would have to be in the released configuration simultaneously in order for the shuttle to be released.

Though in the described embodiments the first and second cam surfaces are provided on the latch-operation member, it is to be noted that the chamfered surfaces of the latch members also function as cam surfaces. As such, the described embodiments could also be considered to have the first and second cam surfaces provided on the first and second latch members, or one of the cam surfaces on one of the latch-operation member and the other on one of the latch members.

For the avoidance of doubt, reference herein to directions, axes and/or components being parallel is intended to include their being coaxial. Further, it is to be understood that any feature described herein in relation to one or more interface lugs or interface slots may apply to all the lugs or slots, or to some of them (for instance all but one or all but two of the lugs or slots).

In the above described embodiment the retaining assembly is used with the embodiment of the tow ball assembly shown in figures 3 to 6, i.e. where the tow ball assembly comprises the described latch-operation member 42. However, it will be appreciated that the retaining assembly may be used with the tow ball assembly shown in figures 1 and 2, i.e. where instead of the latch-operation member 42, there is a biasing member, e.g. a spring.

In addition, it will be appreciated that the retaining assembly does not necessarily require both the first and second retaining members 1201, 1205a, b, but may have either the first or second retaining assembly as desired.

The described and illustrated embodiment is to be considered as illustrative and not restrictive in character, it being understood that only a preferred embodiment has been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary. In addition, use of the term void' is intended to refer to the absence of material in a particular area, and includes (though not exclusively) features such as blind bores, through-bores, recesses and gaps.

Optional and/or preferred features as set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional and/or preferred features for each aspect of the invention are also applicable to any other aspects of the invention where appropriate.

Similarly, any of the features described in relation to an arrangement useful for understanding the invention may be applicable to one or more aspects of the invention.

Claims (98)

1. Claims 1. A mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuttle receivable within the housing and movable relative to the housing, along a shuttle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it is rotatable; the actuation shaft comprising first and second interface lugs spaced substantially circumferentially about the actuation shaft, and the shuttle comprisng first and second interface slots spaced along the shuttle axis; the interface lugs and slots being engageable so as to couple the motion of the shuttle along the shuttle motion axis and the rotation of the actuation shaft; wherein the interface slots and lugs are arranged such that when the actuation shaft is rotated in a first direction, to drive the shuffle in the direction from its second position to its first position, the first interface lug engages a first section of a surface of the shuffle that defines the first interface slot, driving the shuffle in said direction and the second interface lug engages at least a section of a surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position; and when the shuffle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, a second section of the surface of the shuttle that defines the first interface slot engages the first interface lug and rotatably drives the actuation shaft such that an abutment section of the second interface lug contacts an abutment section of the shuttle and thereby prevents the shuttle from reaching its first position.
2. 2. A mechanical linkage according to claim 1 wherein a surface of the shuttle that defines the second interface slot may comprise first and second opposed sections that extend from an open end of the second interface slot, wherein the first section faces in the direction of the shuttle motion axis, in the direction from the first position to the second position of the shuttle and the second section faces in the direction of the shuffle motion axis, in the direction from the second position to the first position of the shuffle.
3. 3. A mechanical linkage according to claim 2 wherein the first section of the surface that defines the first interface slot and the first and second sections of the surface that defines the second interface slot are spaced in the direction of the shuttle motion axis, and the second interface lug is spaced in the circumferential direction from the first interface lug such that when the actuation shaft is rotated in the first direction, to drive the shuttle in the direction from its second position to its first postion, the first interface lug engages the first section of the surface of the shuttle that defines the first interface slot, driving the shuttle in said direction and the second interface lug engages the at least a section of the surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position; and the second section of the surface that defines the first interface slot and the first and second sections of the surface that defines the second interface slot are spaced in the direction of the shuttle motion axis, and the second interface lug is spaced in the circumferential direction from the first interface lug such that the when the shuttle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, the second section of the surface of the shuffle that defines the first interface slot engages the first interface lug and rotatably drives the actuation shaft such that the abutment section of the second interface lug contacts the abutment section of the shuffle and thereby prevents the shuffle from reaching its first position.
4. 4. A mechanical linkage according to either of claims 2 or 3 wherein the respective first sections of the surfaces that define the first and second interface slots are spaced in the direction of the shuffle motion axis by a distance that is substantially equal to the circumferential distance between a surface of the first interface lug that engages the first section of the surface of the shuffle that defines the first interface slot and a surface of the second interface lug that engages the at least a section of a surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position; and the respective second sections of the surfaces that define the first and second interface slots are spaced in the direction of the shuttle motion axis by a distance that is less than the circumferential distance between a surface of the first interface lug that is engaged by the second section of the surface of the shuffle that defines the first interface slot and a circumferentially outer surface of the second interface lug.
5. 5. A mechanical linkage according to any preceding claim wherein the first interface lug and the first and second sections of the surface of the shuffle that define the first interface slot are arranged such that when the first interface lug first engages the first section, the first and second interface lugs are in respective first positions along the shuttle motion axis relative to the shuttle and when the second section first engages the first interface lug, the first and second interface lugs are in respective second positions along the shuttle motion axis relative to the shuttle.
6. 6. A mechanical linkage according to any preceding claim wherein the first interface slot has a length in the direction of the shuttle motion axis that is greater than the length of the second interface slot in the direction of the shuttle motion axis.
7. 7. A mechanical linkage according to any preceding claim wherein the first and second sections of the surface that defines the first interface slot are spaced apart in the direction of the shuttle motion axis by a distance that is greater than the length of the first interface lug in the direction of the shuffle motion axis.
8. 8. A mechanical linkage according to any preceding claim wherein the first and second sections of the second interface slot are spaced apart in the direction of the shuffle motion axis by a distance that is substantially equal to the length of the second interface lug in the direction of the shuttle motion axis.
9. 9. A mechanical linkage according to any preceding claim wherein the first and second interface lugs include an arcuate portion which is substantially in the shape of a segment of a cylinder.
10. 10. A mechanical linkage according to claim 9 wherein the arcuate portion of the first and second interface lugs is of substantially the same radius.
11. 11. A mechanical linkage according to either of claims 9 or 10 wherein the first and second sections of the surface that defines the first interface slot are spaced apart in the direction of the shuttle motion axis by a distance that is greater than the radius of the arcuate portion of the first interface lug.
12. 12. A mechanical linkage according to any of claims 9 to 11 wherein the first and second sections of the surface that defines the second interface slot are spaced apart in the direction of the shuffle motion axis by a distance that is substantially equal to than the radius of the arcuate portion of the second interface lug.
13. 13. A mechanical linkage according to any preceding claim wherein the actuation shaft is biased to a rotational position such that when the shuffle is moved in the direction from its second position to its first position, to rotatably drive the actuation shaft, the second section of the surface of the shuffle that defines the first interface slot so engages the first interface lug.
14. 14. A mechanical linkage according to any preceding claim wherein the arrangement of the interface slots and lugs is such that when the actuation shaft is rotated in the first direction, to drive the shuttle in the direction from its second position to its first position, the second interface lug substantially meshes with the second interface slot.
15. 15. A mechanical linkage according to any preceding claim wherein the abutment section of the second interface lug and the abutment section of the shuttle contact along a plane, or a line, that has a normal that has at least a component in the direction of the shuttle motion axis.
16. 16. A mechanical linkage according to any preceding claim wherein the actuation shaft and the shuffle each comprise a first limit section arranged such that, at a certain rotational position of the actuation shaft as the actuation shaft rotates in the first rotational direction, the first limit secticn of the actuation shaft contacts the first limit section of the shuffle and thereby prevents any further rotation of the actuation shaft in the first rotational direction.
17. 17. A mechanical linkage according to any preceding claim wherein the interface lugs and slots may be arranged such that when the shuttle moves in the direction from its first position to its second position, the actuation shaft is rotated in a second rotational direction and the actuation shaft and the shuffle each comprse a second limit section arranged such that at a certain rotational position of the actuation shaft as the actuation shaft rotates in the second rotational direction, the second limit section of the actuation shaft contacts the second limit section of the shuttle and thereby restricts any further rotation of the actuation shaft in the second rotational direction.
18. 18. A mechanical linkage according to any preceding claim wherein the shuffle is biased towards its second position.
19. 19. A mechanical linkage according to any preceding claim wherein the first section of the surface of the shuttle that defines the first interface slot faces in the direction of the shuffle motion axis, in the direction from the first position to the second position of the shuffle and the second section of said surface faces in the direction of the shuffle motion axis, in the direction from the second position to the first position of the shuttle.
20. 20. A mechanical linkage according to claim 19 wherein the first and second sections each comprise a first portion that extends from the open end of the first interface slot, is substantially planar and extends substantially in a plane that is oriented such that a normal to the plane has at least a component in a direction that is substantially parallel to the shuttle motion axis.
21. 21. A mechanical linkage according to claim 20 wherein the first and second sections each comprise a second portion that extends from an end of the first portion that is distal to the open end of the first interface slot, to the base section of the first interface slot, wherein the second portion is substantially curved along its length in the direction from the first portion to the base section.
22. 22. A mechanical linkage according to claim 21 wherein the second portion has substantially the same radius of curvature as the first interface lug.
23. 23. A mechanical linkage according to claim 2 or any of claims 3 to 22 when dependent on claim 2 wherein the first and second sections of the surface that defines the second interference slot are substantially planar and extend substantiaNy in a plane that is oriented such that a normal to the plane has at least a component in a direction that is substantially parallel to the shuttle motion axis.
24. 24. A mechanical linkage according to claim 9 or any of claims 10 to 23 when dependent on claim 9 wherein the surface that defines the second interface slot comprises an arcuate surface of complementary shape to the second interface lug.
25. 25. A mechanical linkage according to claim 9 or any of claims 10 to 24 when dependent on claim 9 wherein the arcuate portion of the first and/or second interlace lugs has an arc length of over 20% of the circumference of the notional cylinder a segment of which the arcuate portion is substantially in the shape of.
26. 26. A mechanical linkage according to claim 25 wherein the arcuate portion of the first and/or second interface lug is substantially in the shape of a major segment of a cylinder.
27. 27. A mechanical linkage according to claim 9 or any of claims 10 to 26 when dependent on claim 9 wherein the first interface lug is configured such that when the first interface lug engages the first section of the surface of the shuttle that defines the first slot, it is received within the first interface slot to a maximum depth of more than the length of the arc radius for that lug.
28. 28. A mechanical linkage according to claim 9 or any of claims 10 to 27 when dependent on claim 9 wherein the first interface lug is configured such that when the second section of the surface of the shuttle that defines the first interface slot engages the first interface lug, the first interface lug is received within the first slot to a maximum depth of more than the length of the arc radius for that lug.
29. 29. A mechanical linkage according to claim 9 or any of claims 10 to 28 when dependent on claim 9 wherein the second interface lug is configured such that when it engages the surface of the shuttle that defines the second interface slot such that the shuttle is driven to its first position, it is received within the second interface slot to a maximum depth of more than the length of the arc radius for that lug.
30. 30. A mechanical linkage according to any preceding claim wherein the first and second interface lugs are substantially identicaL
31. 31. A mechanical linkage according to any preceding claim comprising at least one couplng element movable between a stowed position and a deployed position, the couplng element being movable to the deployed position under action of the shuttle moving to the second position and being movable to a stowed position under action of the shuttle moving to the first position.
32. 32. A mechanical linkage according to claim 31 wherein the housing is for insertion into a collar of a complementary coupling member and wherein the at least one coupling element is arranged such that when it is in the deployed position it projects substantially radially from the housing for receipt within the collar so as to prevent withdrawal of the housing from the collar and when it is in the stowed position it is received within the housing to an extent that allows withdrawal of the housing from the collar.
33. 33. A mechanical linkage according to any preceding claim comprising at least one latch member movable from an engaged configuration, in which the latch member retains the shuttle in the first position, to a released configuration, in which the latch member permits movement of the shuttle from the first position to the second postion.
34. 34. A mechanical linkage according to any preceding claim comprising a handle that is connectable to the actuation shaft such that rotation of the handle rotates the actuation shaft and wherein the handle is releasably connectable to the actuation shaft.
35. 35. A mechanical linkage according to claim 34 wherein the handle is connectable to the actuation shaft by a connecting section that is rotatably coupled to the actuation shaft, wherein the handle comprises a first formation and the connecting section comprises a second formation, the frst and second formations being releasably engageable with each other such That when They are engaged, rotation of the handle rotates the connecting section, which rotates the actuation shaft.
36. 36. A mechanical linkage according to claim 35 wherein the connecting section is rotatably mounted within the housing.
37. 37. A mechanical linkage according to any of claims 34 to 36 wherein the mechanical linkage is arranged to prevent a person from rotating the actuation shaft from outside of the housing when the handle is not connected to the connecting section.
38. 38. A mechanical linkage according to any of claims 35 to 37 wherein the second formation is an anti-tamper formation.
39. 39. A mechanical linkage according to any of claims 35 to 38 wherein the connecting section is rotatably mounted at least partially within a housing and the connecting section forms a close radial fit with the housing.
40. 40. A mechanical linkage according to claim 39 wherein the housing at least partially covers the connecting section so as to prevent a person from rotating the actuation shaft from outside of the housing when the handle is not connected to the connecting section.
41. 41. A mechanical linkage according to claim 40 wherein the housing substantially covers the connecting section in an axial and/or circumferential direction of the connecting section.
42. 42. A mechanical linkage according to any of claims 35 to 41 wherein the first and second formations are arranged such that they are releasably engageable with each other in a plurality of rotational positions of the handle relative to the connecting section.
43. 43. A mechanical linkage according to claim 42 wherein the first and second formations are arranged such that they have an order of rotational symmetry greater than one.
44. 44. A mechanical linkage according to either of claims 42 or 43 wherein the first and second formations are arranged such that they have an order of rotational symmetry greater than five.
45. 45. A mechanical linkage according to any of claims 35 to 44 wherein the frst formation is provided with a plurality of projections and/or recesses distributed circumferentially about the rotational axis of the handle and the second formation is provided with a plurality of recesses and/or projectons distributed circumferentially about the rotational axis of the connecting section which are respectively engageable with the plurality of projections and/or recesses of the first formation such that the first and second formations are engageable in a plurality of rotational positions of the handle relative to the connecting section.
46. 46. A mechanical linkage according to any of claims 35 to 45 wherein one of the first and second formations forms a plug and the other of the first and second formations forms a socket, with the first and second formations being releasably engageable by the plug being releasably receivable within the socket.
47. 47. A mechanical linkage according to claim 46 wherein the plug and socket each have a polygonal cross-sectional shape about its respective rotational axis.
48. 48. A mechanical linkage according to any of claims 35 to 47 wherein the handle comprises a gripping section attached to the first formation.
49. 49. A mechanical linkage according to any preceding claim wherein the mechanical linkage comprises a handle that is disposed at a position off the rotational axis of the actuation shaft and is connected to the actuation shaft such that rotation of the handle rotates the actuation shaft.
50. 50. A mechanical linkage according to claim 49 wherein the handle is arranged to rotate about an axis that is offset from the rotational axis of the actuation shaft.
51. 51. A mechanical linkage according to either of claims 49 or 50 wherein the handle is arranged to rotate about an axis that is substantially parallel to the rotational axis of the actuation shaft.
52. 52. A mechanical linkage according to any of claims 49 to 51 wherein the mechanical connection is at least partially housed within a housing.
53. 53. A detachable tow ball assembly comprising a mechanical linkage according to any preceding claim.
54. 54. A tow bar assembly comprising a detachable tow ball assembly according claim 53.
55. 55. A mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuttle receivable within the housing and movable relative to the housing, along a shuttle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it is rotatable; the shuttle being coupled to the actuation shaft such that the motion of the shuttle along the shuttle motion axis is coupled to the rotation of the actuation shaft; wherein the mechanical linkage comprises a handle that is connectable to the actuation shaft such that rotation of the handle in a first direction rotates the actuation shaft in its first rotational direction and wherein the handle is releasably connectable to the actuation shaft.
56. 56. A mechanical linkage according to claim 55 wherein the handle is connectable to the actuation shaft by a connecting section that is rotatably coupled to the actuation shaft, wherein the handle comprises a first formation and the connecting section comprises a second formation, the frst and second formations being releasably engageable with each other such that when they are engaged, rotation of the handle rotates the connecting section, which rotates the actuation shaft.
57. 57. A mechanical linkage according to claim 56 wherein the connecting section is rotatably mounted within the housing.
58. 58. A mechanical linkage according to any of claims 55 to 57 wherein the mechanical linkage is arranged to prevent a person from rotating the actuation shaft from outside of the housing when the handle is not connected to the connecting section.
59. 59. A mechanical linkage according to any of claims 56 to 58 wherein the second formation is an anti-tamper formation.
60. 60. A mechanical linkage according to any of claims 56 to 59 wherein the connecting section is rotatably mounted at least partially within a housing and the connecting section forms a close radial fit with the housing.
61. 61. A mechanical linkage according to claim 60 wherein the housing at least partially covers the connecting section so as to prevent a person from rotating the actuation shaft from outside of the housing when the handle is not connected to the connecting section.
62. 62. A mechanical linkage according to claim 61 wherein the housing substantially covers the connecting section in an axial and/or circumferential direction of the connecting section.
63. 63. A mechanical linkage according to any of claims 56 to 62 wherein the first and second formations are arranged such that they are releasably engageable with each other in a plurality of rotational positions of the handle relative to the connecting section.
64. 64. A mechanical linkage according to claim 63 wherein the first and second formations are arranged such that they have an order of rotational symmetry greater than one.
65. 65. A mechanical linkage according to claim 64 wherein the first and second formations are arranged such that they have an order of rotational symmetry greater than five.
66. 66. A mechanical linkage according to any of claims 63 to 65 wherein the frst formation is provided with a plurality of projections and/or recesses distributed circumferentially about the rotational axis of the handle and the second formation is provided with a plurality of recesses and/or projectons distributed circumferentially about the rotational axis of the connecting section which are respectively engageable with the plurality of projections and/or recesses of the first formation such that the first and second formations are engageable in a plurality of rotational positions of the handle relative to the connecting section.
67. 67. A mechanical linkage according to any of claims 56 to 66 wherein one of the first and second formations forms a plug and the other of the first and second formations forms a socket, with the first and second formations being releasably engageable by the plug being releasably receivable within the socket.
68. 68. A mechanical linkage according to claim 67 wherein the plug and socket each have a polygonal cross-sectional shape about its respective rotational axis.
69. 69. A mechanical linkage according to any of claims 56 to 68 wherein the handle comprises a gripping section attached to the first formation.
70. 70. A detachable tow ball assembly comprising a mechanical linkage according to any of claims 55 to 69.
71. 71. A tow bar assembly comprising a detachable tow ball assembly according to claim 70.
72. 72. A mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuttle receivable within the housing and movable relative to the housing, along a shuttle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it is rotatable; the shuttle being coupled to the actuation shaft such that the motion of the shuttle along the shuttle motion axis is coupled to the rotation of the actuation shaft; wherein the mechanical linkage comprses a handle that is disposed at a position off the rotational axis of the actuation shaft and is connected to the actuation shaft such that rotation of the handle rotates the actuation shaft.
73. 73. A mechanical linkage according to claim 72 wherein the handle is arranged to rotate about an axis that is offset from the rotational axis of the actuation shaft.
74. 74. A mechanical linkage according to either of claims 72 or 73 wherein the handle is arranged to rotate about an axis that is substantially parallel to the rotational axis of the actuation shaft.
75. 75. A mechanical linkage according to any of claims 72 to 74 wherein the mechanical connection is at least partially housed within a housing.
76. 76. A detachable tow ball assembly comprising a mechanical linkage according to any of claims 72 to 75.
77. 77. A tow bar assembly comprising a detachable tow ball assembly according to claim 76.
78. 78. A mechanical linkage for a detachable tow ball, the linkage comprising: a housing; a shuttle receivable within the housing and movable relative to the housing, along a shuttle motion axis, between a first position and a second position; an actuation shaft rotatably receivable within the housing, the actuation shaft defining an actuation shaft axis about which it can rotate, wherein: the actuation shaft comprises a plurality of interface lugs spaced substantially circumferentially about the actuation shaft, and the shuttle comprises a plurality of interface slots spaced along the shuttle axis, the interface lugs and slots being configured to meshingly engage to form a rack and pinion mechanism; each interface lug includes an arcuate portion which is substantially in the shape of a segment of a cylinder.
79. 79. A mechanical linkage according to claim 78 wherein the actuation shaft comprises 4 or fewer interface lugs.
80. 80. A mechanical linkage according to claim 79 wherein the actuation shaft comprises precisely 2 interface lugs.
81. 81. A mechanical linkage according to any of claims 78 to 80 wherein the arcuate portion of at least one of the interface lugs is substantially in the shape of a major segment of a cylinder.
82. 82. A mechanical linkage according to any of claims 78 to 81 wherein the linkage comprises substantially the same number of interface slots as interface lugs.
83. 83. A mechanical linkage according to any of claims 78 to 82 wherein the arcuate portion of each interface lug defines an arc radius for that interface lug, the arc radius being the radius of a notional cylinder a segment of which the arcuate portion is substantially in the shape of, and at least one of the interface lugs is configured to be received within at least one of the slots to a maximum depth of more than length of the arc radius for that lug.
84. 84. A mechanical linkage according to any of claims 78 to 83 wherein at least one of the interface slots has an arcuate surface of complementary shape to the or one of the interface lugs that it is configured to receive.
85. 85. A mechanical linkage according to any of claims 78 to 84 wherein the interface lugs and/or interface slots are substantially evenly spaced.
86. 86. A mechanical linkage according to any of claims 78 to 85 wherein the actuation shaft comprises a first limit surface positioned to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in a first limited direction.
87. 87. A mechanical linkage according to claim 86 wherein the actuation shaft comprises a second limit surface positioned to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in the opposite direction to the first limited direction.
88. 88. A mechanical linkage according to any of claims 78 to 87 wherein the plurality of interface lugs is movable along the actuation shaft axis between an actuable configuration and a non-actuable configuration with respect to the interface slots.
89. 89. A mechanical linkage according to claim 88 wherein the plurality of interface lugs are urged towards the non-actuable configuration.
90. 90. A mechanical linkage according to claim 88 or 89 wherein the actuation shaft has a first restraint surface positioned, when the interface lugs and interface slots are in the non-actuable configuration, to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in a first restrained direction.
91. 91. A mechanical linkage according to claim 90 wherein the actuation shaft has a second restraint surface positioned, when the plurality of interface lugs is in the non-actuable configuration, to contact a portion of the mechanical linkage and thereby restrict rotation of the actuation shaft in the opposite direction to the first restrained direction.
92. 92. A mechanical linkage according to claim 91 wherein the first and second restraint surfaces are configured to substantially prevent rotation of the actuation shaft when in the plurality of interface lugs is in the non-actuable configuration.
93. 93. A mechanical linkage according to any one of claims 86, 87 and 90-92 wherein the portion of the mechanical linkage which the first and/or second limit surface, and/or the first and/or second restraint surface, is configured to contact is the shuttle.
94. 94. A detachable tow ball assembly comprising a mechanical linkage according to any of claims 78 to 93
95. 95. A tow bar assembly comprising a detachable tow ball according to claim 94.
96. 96. A mechanical linkage substantially as described herein with reference to the accompanying drawings.
97. 97. A detachable tow ball substantially as described herein with reference to the accompanying drawings.
98. 98. A tow bar assembly substantially as described herein with reference to the accompanying drawings.