WO1995015449A1 - One-way gear mechanisms - Google Patents

Abstract

A gear mechanism capable of selectively permitting motion in one direction whilst preventing it in another is formed from gearwheel (12), locking wheel (14) and a pinion (15). The wheels (12, 14) are mounted co-axially and each has a stub axle projecting therefrom. The gear wheel is slightly larger than the locking wheel, and each wheel has widely spaced narrow teeth (13, 15) which intermesh alternately, the locking wheel teeth projecting axially between the gear wheel teeth (13). The pinion (16) which also has widely spaced teeth is arranged to engage with the teeth (13) of the gear wheel (12). Wheels (12 and 14) may be locked together to form a composite wheel, having spaces to receive the teeth of the pinion (16). Such a wheel will only be permitted to rotate in one direction, in which the gear wheel teeth will engage and rotate the pinion teeth. In the other direction, the pinion teeth will slide strike the locking wheel teeth and prevent rotation of the composite wheel. If the gear wheel (12) and locking wheel (14) are permitted to rotate slightly with respect to one another, and arrangement is produced which will permit motion to be transferred from one stub axle to the other, but not in the other direction.

Description

ONE-WAY GEAR MECHANISMS

This invention relates to gear mechanisms, and in particular to such mechanisms arranged to allow motion, whether translational or rotational, in one direction or sense but not in another.

Known apparatus of this type includes the simple ratchet mechanism. Here, a ratchet wheel is provided which has a series of indentations or projections with which a pawl attached to the body of the mechanism may engage. The arrangement is such that the pawl, which is generally resiliently or gravity biased towards the ratchet wheel, will prevent the wheel turning in one direction. In the other direction the indentations or projections are able to move past the pawl and motion is transferred only when the ratchet wheel turns in this direction.

Analogous mechanisms are also known in linear- motion systems. In such systems a rack may be provided having a series of recesses in which a pawl may engage in a manner very similar to that discussed above.

A common and well-known application of the rotary type of ratchet mechanism is in a bicycle free-wheel hub. The purpose of a free-wheel is to allow the bicycle to coast without the pedals being turned, for example, when going down hill. The mechanism is arranged such that when the ratchet wheel is rotated clockwise with respect to the body (ie. the hub) , which occurs when the pedals are moving the bicycle, then the pawl engages with the ratchet wheel. However, when the cycle is coasting and pedals are not moving, or the pedals are moving more slowly than is necessary to accelerate the bicycle, the ratchet wheel rotates anti¬ clockwise with respect to the hub and therefore the pawl does not engage with the ratchet. It is also known to use ratchet mechanisms in which the driving direction is reversible. This may be achieved by providing a pair of pawls which have portions for engaging with the ratchet wheel which are mirror-images of each other and therefore engage when the ratchet wheel turns in opposite directions. All that is required is to disable one of the pawls in order to allow drive to occur in only one direction. This may be achieved by connecting both pawls together and mounting them on a central pivot so that moving one towards the ratchet wheel moves the other away. Reversible direction ratchets have many applications, for example in wrenches or screwdrivers. In these examples the provision of a reversible ratchet enables the tool to be used for both tightening and removing fastenings such as screws or bolts.

Although these mechanisms are long-established they do have certain disadvantages. In particular, the pawl is generally biased by a small spring which is liable to lose its resilience over time or even to be dislodged. Furthermore, the ingress of dirt may block the movement of the pawl and prevent it from properly engaging with the ratchet wheel. Similar problems exist in the context of linear systems.

According to a first aspect of the invention there is provided a gear mechanism comprising first and second intermeshing members arranged to be moveable relative to each other, the members having meshing surfaces profiled such that relative motion between the members is allowed in only one direction.

Thus there is provided a one-way motion mechanism which avoids the use of potentially unreliable pawls and springs. Only two moving parts are required - the first and second intermeshing members - and these may be continuously enmeshed. This avoids a problem of ratchet type systems that the pawl may fail properly to engage with the ratchet wheel. This aspect of the invention is applicable to rotary or linear systems. Thus, the first member may be, for example, a gearwheel or a rack respectively. The second member may be a gearwheel or pinion in either case.

There are various ways in which the invention may be achieved. One way is to provide hooked teeth on one of the members and a corresponding profile to teeth on the other member around which the hooks may catch. If the hooks are generally shaped like a letter "J" then as the hook portion moves leftwards it will engage around a tooth on the other member, rather than simply strike it as in the case of conventional gears. Further movement will be prevented since the teeth cannot disengage. Motion in the other direction (so that the J-shaped teeth move to the right) will be allowed because the teeth of the other member will be struck by the "plain" side of the hooked teeth. Therefore they will not become interlinked.

A disadvantage of the above approach is that large forces may be exerted on the hook-portions which may lead to failure. Thus, in a preferred embodiment there is provided motion transfer apparatus comprising a first member having periodically arranged meshing regions cooperating with periodically arranged meshing projections on a second member, each of the meshing regions comprising a first portion for receiving a projection of the second member and a second portion for engaging the projection so that relative motion between the first and second members in one direction may be effected, and means being provided for preventing relative motion in the opposite direction, characterised in that each of the meshing regions has a third portion for blocking engagement with the projection and serving as the means for preventing said relative motion in the opposite direction.

In certain embodiments of the invention the first member comprises a toothed gearwheel or rack, wherein the teeth have three portions arranged sequentially along the meshing surface of the gearwheel or rack, the first such portion being a tooth receiving portion, the second being a tooth engaging portion and the third being a tooth blocking portion; and wherein the second member comprises a gearwheel having teeth of similar pitch to those of the first member and which may be received in the tooth receiving portion of the first member. However, it is not essential that the first member is toothed. As will be described later, the portions may be formed by, for example, providing recesses or apertures in the member.

In the case of toothed apparatus, the teeth of one member may freely drive the other in one direction, but in the other direction motion is blocked as the teeth of the second member strike the tooth blocking portions of the first member, rather than engaging in the receiving portions. The greater the force applied in an attempt to cause rotation, the more firmly locked together will be the members. The forces acting on the teeth are compressive and therefore this mechanism is very strong.

In the case of a rotary system it is convenient for the first member to be a gearwheel and for the teeth to be provided around its circumference in the usual manner. Preferably, each of the three parts of the teeth subtend a similar angle from the axis of the gearwheel. The three portions of the teeth may conveniently be formed across the whole width of the- gearwheel which makes the wheel simple to produce. However, this is not essential provided that the second member has teeth of sufficient width to engage with each portion. The tooth receiving portions are of sufficient size to receive the teeth of the second member in the manner of a normal gearwheel. Preferably, the tooth engaging portions are similar to the teeth of the second member and they project further than the other portions from the first gearwheel. The blocking portion is a region of the tooth which extends sufficiently far from the axis of the first gearwheel to partially, but not fully, engage with the second member.

The gearwheel forming the second member has teeth of similar pitch to the first gearwheel in order to engage in the receiving portions of the first gearwheel. In the preferred embodiment discussed above in which the three portions of the gearwheel teeth subtend similar angles it follows that the pitch of the teeth on the second member should be about three times their width (in the circumferential direction) . Thus, preferably the second member has narrow, widely spaced gearteeth compared to a standard gearwheel.

It is possible for both gearwheels to be of similar size, but, in order to form a compact mechanism, the second member may be in the form of a small pinion.

In the case of a liner-motion apparatus the rack is treated in a directly analogous way to the first gearwheel discussed above. In other words it may be through of as a 'straightened out' portion of the circumference or part of a gearwheel of infinite diameter. Thus, preferably the three portions are of similar width in the linear direction.

It is also possible to apply the teachings of the present invention to provide a selectable-direction one¬ way motion device. Thus, in a preferred embodiment of the invention there is further provided means for varying the profile of one of the intermeshing members. In this manner the direction in which relative rotation of the members is permitted may be varied, thereby allowing the apparatus to be used in situations where a switchable, ratchet-type effect is required, such as in socket spanners. In addition, heavy-duty versions of the apparatus may be produced for use in transmissions, for example for use in motor vehicles.

An example of the latter kind is to replace or supplement the conventional differential found in the axles of most motor vehicles with a switchable-direction one-way mechanism in or associated with each driven wheel. This approach is advantageous because if there is no differential, or the differential is locked it is easier to drive over slippery ground. This is because, although the drive wheels would be permitted to exceed their driven speed (eg. when cornering) they would not be permitted to turn at a lower speed than that at which they were driven. Therefore, the known problem of differentials allowing one wheel on an axle to spin whilst the other remains stationary is avoided.

It is possible to vary the profile of one or both of the meshing members in order to reverse the drive- direction of the apparatus. However, preferably one of the members is not altered. This reduces mechanical complexity and thereby increases the reliability of the apparatus. For the purposes of the following discussion it is assumed that only the first member has its profile varied.

There are numerous ways in which this effect may be achieved. For example, in the apparatus described above employing J-shaped hooked teeth, the hook-portion of the teeth may be pivotable in order to reverse the direction in which the hooks point, thereby reversing the direction in which they will become interlocked with the other member. However, it is particularly preferred to use apparatus of the embodiment described previously having receiving, engaging and blocking portions. In order to change the drive direction of this type of apparatus it is necessary to change the sequence of the portions along the meshing surface. There are many ways in which this can be done, but it has been found particularly convenient to keep all the portions of one type fixed and to swap over the remaining two. For example the engaging portions may be fixed in place whilst the positions of the blocking and receiving portions may be changed.

One way to achieve this is to provide the first member with a main body forming the major portion of the wheel or rack. Projecting from the body are the engaging portions of the teeth which are themselves narrow, widely spaced teeth (eg. pitch of three times tooth width) . Connected to the body are a series of movable members which form the blocking portions. These may be placed between the teeth projecting from the body or alongside the body, provided that they can engage with the teeth of the second member. Thus, by moving the movable members from positions on one side of the space between the engaging portions of the teeth to the other has the effect of reversing the positions of the receiving and blocking portions.

The movable portions may all be separate, but preferably the first member comprises a body with projections forming the engaging portions of a series of gear teeth and a further member adjacent to, or interlocked with, the body, wherein the further member has a series of projections which provide the blocking portions (as defined previously) , and the further member is displaceable, relative to the body in order to change the sequence of the blocking engaging and receiving portions of the teeth and thereby reverse the drive direction of the mechanism.

As discussed previously, the present invention is applicable to both linear and rotary systems. In the case of rotary systems, the body is preferably in the form of a disc, wheel, or ring and the further member is a second disc or wheel parallel to, and co-axial with, the first. The discs or wheels are preferably of similar diameter in order that the blocking portions on the second disc may be mounted on the circumference of that disc in line with the engaging portions on the circumference of the first disc.

It is important that the second member (typically a pinion) is able to engage both discs or wheels. This may be achieved by providing a pinion of sufficient width to engage adjacent, but non-overlapping discs, or by arranging the body and further member so that they interlock. In the latter case, the blocking portions may comprise lateral projections from the second disc which fit between the engaging portions on the first member, leaving a space which forms the receiving portion. Relative movement between the body and further member causes the blocking portions to move relative to the engaging portions and in so doing, reverse the positions of the blocking and receiving portions. For example, a blocking portion may initially be provided at the left hand side of a gap between two widely spaced narrow teeth forming adjacent engaging portions. Thus, the order of the portions from left to right is engaging, blocking, receiving, engaging. This may be changed, by moving the blocking portion rightwards, to engaging, receiving, blocking, engaging, thus changing the drive direction. It will be appreciated that as the two discs are interlocked, no further apparatus is required to restrict the relative movement of the discs.

On the other hand, separate restricting mechanism is preferably provided when non-interlocking discs are employed. This may be in the form of, for example, a pin in one disc engaging with a slot in the other or, if the discs are mounted on co-axial axles, a pin and a suitably shaped hole to receive it may be provided in the respective axles.

In the case of linear mechanisms, directly analogous constructions are possible so that there may be interlocking or non-interlocking strips side by side to form the first member (eg. a rack) . As in the rotary case, the second member (eg. a pinion) must be capable of engaging both parts of the rack simultaneously.

Another construction is to provide the rack in the form of two strips, one on top of the other and a pinion above both. In this embodiment each strip is provided with slots spaced to match the pitch of the teeth of the pinion, and the strips are able to move in their longitudinal direction relative to each other. This movement is constrained so that the slots are always at least partially overlapping in order to provide a through-hole large enough to receive a pinion tooth. It will be appreciated that this provides the three portion arrangement discussed previously. The through-hole is the receiving portion and the adjacent portion of the lower strip visible through the hole in the first is the blocking portion. The engaging portion is provided by the part of the upper strip next to the through-hole. Movement of the strips with respect to one another changes the position of the hole (ie. the receiving portion) with respect to the other portions. The pinion is arranged to rotate freely when the rack is moved in one direction and the teeth pass through the through- holes. In the opposite direction the teeth will strike the blocking portions (ie. the upper surface of the lower strip) and movement will be prevented.

This approach is also applicable to rotary systems. For example the first member could comprise a disc with a series of slots cut into its rim, and an annulus with corresponding slots cut through it could be provided around the outside of the disc to form the second member. The apparatus would engage a pinion in the manner described previously and the disc and annulus could be moved relative to each other to change the drive direction.

In all of the above described mechanisms it is possible to increase the strength and reliability of operation by providing a plurality of members which mesh with the first member. For example a number of identical pinions may be provided around the circumference of a disc, or along the length of a rack forming the first member. In many common applications of the rotary mechanism described previously there will be further provided a housing or mounting on which the first and second members are rotatably mounted. The housing could, for example form the body of a freewheel unit. In this case, projecting from an aperture in the housing would be an axle connected to the first member and arranged to rotate therewith. Thus, there will be one direction in which the axle may be rotated in which body and axle will be locked together and another in which they are not. The latter is the "freewheeling" mode. A small lever or other means may be provided in the switchable- direction embodiments in order to change the direction of permitted motion and thereby change the drive direction. This should preferably be associated with a locking mechanism so that the components stay in the desired configuration.

It is, however, also useful to arrange the apparatus such that one or more pinions may be moved in a rotary, or reciprocating manner, around the outside of a larger wheel forming the first member. For example, one or more pinions could each be connected to a source of reciprocating motion such as a piston. As the pinion moves back and forth around the circumference of the larger gear wheel intermittent rotary motion would be produced. If two or more pinions are each connected to suitably phased sources of linear motion then continuous motion may be produced. Of course, the larger gearwheel may be arranged as discussed previously to be selectable in its drive direction.

Preferably the pinions are constrained to move around the circumference of the first member by rotatably mounting them on arms which are themselves rotatably mounted co-axially with the first member.

One application of this principle is in continuously-variable-ratio transmissions. It is known to provide this type of transmission by converting rotary motion to reciprocating linear motion and then back to rotary motion. The gear-ratio may be varied by changing the amplitude of the reciprocating motion.

It is known, for example to provide a disc or "swashplate" on the end of a rotary axle, the angle of the plane of the disc with respect to the axle being variable. A number of rods are arranged parallel to the axle and in abutment with the disc, so that rotation of the disc causes the rods to reciprocate. The rods are in turn connected, typically via a hydraulic circuit to a further disc and axle arrangement which operates in the reverse manner to the first. Variation in the angle of the first disc changes the amplitude of oscillation of the rods which in turn controls the speed of rotation of the second disc and this in turn controls the speed of the output shaft to which it is connected.

As discussed above, the present invention provides an apparatus which can be employed to convert reciprocating motion to continuous rotary motion. In order to provide a continuously variable transmission it is necessary to provide further apparatus which can produce variable amplitude reciprocating linear motion. This may be achieved by connecting a source of reciprocating motion (eg. a piston) to an axle having a crank in which the crank offset is variable. Preferably the crank offset is provided by connecting two axles by a crank arm pivoted at each end to the respective axles. The axles may be laterally offset from each other within the limits imposed by the crank arm. Thus if the axles are axially aligned, rotation of one will rotate the other along the same axis. However, when the axles are laterally offset, rotation of one axle along its length will cause the other to describe a circular path, thus providing a combination of rotational and translational motion. The maximum diameter of circle (and therefore maximum amplitude of linear motion) will occur when the crank arm is perpendicular to each axle. Linear motion may be provided from the circular motion produced by the crank arrangement by, for example, rotatably connecting the second axle to a slotted member which is restrained to move in a plane. The slotted member may have a plurality of slots which radiate from the point where the axle is connected. In these slots run rollers mounted co-axially with the pinions which engage the gearwheel. The pinions are preferably mounted on arms and these arms are rotatably mounted on the gearwheel axle. Thus the pinions move around the gearwheel in a planetary manner. Circular motion of the slotted member, produced by the crank arm, allows the rollers to move along the slots and as they do so the pinions are caused to reciprocate in a planetary manner around the gearwheel. If a plurality of pinions are provided and appropriately located, at least one of the pinions will move around the gearwheel in one direction and one in the other direction. Thus, one will engage the gearwheel, thereby turning it, and another will be freewheeling. If more than two pinions are provided (e.g. four) then reliability will be improved and the motion will be smoother.

It has also been found that certain embodiments of the invention have a further highly useful property. In the case of the selectable direction rotary one-way motion apparatus having two discs or similar structures forming the first member in which relative rotational motion of the two discs is restricted to that necessary to switch the drive direction, it will be realised that, any greater movement of one disc will move the other with it. Thus if a shaft is connected to each disc motion may be transferred from one shaft to the other. (The shafts may be arranged on opposite sides of the first member or they may be arranged co-axially on the same side.) However, the rotation of the first member is restricted by its engagement with the second member as discussed previously, so, for a given relative position of the two discs, when fixed in that position the first member will rotate in only one direction relative to the second member. However, if the two discs are permitted to move freely within the limited range of movement permitted, the apparatus may be arranged such that the relative movement happens before movement of the whole first member. In this way the action of turning one of the discs may change the drive direction. It has been found that turning one disc will always cause the mechanism to switch into the mode which allows rotation in that direction relative to the pinion and turning the other always switches the mechanism into the mode which prevents motion in that direction.

This property has been described, for purposes of clarity, in the context of a first member formed of discs. It is equally applicable when wheels, rings etc. are employed.

The linear switchable direction one-way mechanisms discussed previously also have a similar property. Their operation is directly analogous to that described in the case of the rotary mechanisms and so will not be described here in detail. Suffice it to say that, for example, in the embodiment comprising a pinion and two slotted strips, moving one strip in either direction will cause both strips to move freely past the pinion, whereas moving the other will lock-up the mechanism.

This mode of operation is believed to contain inventive matter and therefore viewed from a further aspect the invention provides a motion controlling means having a body, an input shaft and an output shaft, the shafts being interconnected to move together via a switchable one-way motion mechanism mounted on the body, wherein the input shaft is capable of movement relative to the body in two directions and the mechanism is arranged such that motion applied to the input shaft in one of said directions causes the mechanism to switch into a condition which allows movement of the input and output shafts in the direction of applied motion, but motion applied to the output shaft causes the mechanism to switch into a condition which prevails movement of the output shaft in the direction of applied motion.

Such apparatus is particularly useful in situations where rotary or linear motion is to be transmitted from a source to an object without the object being able to transmit motion back to the source. For example in winches it is essential that rotation of a motor or hand crank can freely turn the winch in order to raise or lower a load. However, if there is a direct connection between the source of motion (motor or hand crank etc. ) and the winch, then failure of the source of motion would result in the load being dropped with potentially serious consequences. Providing apparatus according to the present invention between the source and the winch allows the source to turn freely to raise or lower the load, but if the source fails or is removed, then the apparatus will lock the winch. An analogous linear- motion application is in the provision of apparatus according to the invention in mechanism used to hold windows open. If the body of the apparatus is fixed to the window frame and the shaft (eg. one of the strips in the appropriate embodiment) is connected to the window, movement of the other shaft will open or close the window, but movement of the window, say caused by the wind, will be blocked.

Although it is possible to use other one-way mechanisms to provide the invention these would be complex since a separate mechanism would be needed to cause the direction-switching effect. Therefore, preferably the mechanisms are as described previously herein in which the switching effect is inherent. Thus, for example, stub-axles or co-axial axles may be connected to each disc etc. of rotary apparatus to form the shafts or, in the linear-motion embodiments, the ends of the strips themselves may form the shafts. The invention also extends to another type of mechanism for permitting rotary motion in one direction relative to a body and not in the other.

Thus, according to a still further aspect of the invention there is provided apparatus for permitting rotational motion in one direction and preventing it in another comprising a body on which are rotatably mounted a driven gear, a following gear in mesh with the driven gear and a jamming member, the following gear being arranged to move into engagement with the jamming member whilst remaining in mesh with the driven gear only when rotary motion is applied to the driven gear in one direction, thereby preventing rotation of the driven gear in that direction.

It has been found that this aspect of the invention provides an extremely strong and reliable mechanism which does not require potentially fragile components such as springs.

Preferably the jamming member comprises a further following gear driven by the driven gear. In this case, as the two following gears move towards each other, their adjacent teeth will be moving in opposite directions. This will cause the entire mechanism to lock solidly when they intermesh. The greater the rotational force applied to the driven gear, the more tightly the three gears will intermesh.

To further strengthen the apparatus further following gears and jamming members (preferably also following gears) may be added around the circumference of the driven gear. Thus, in a preferred embodiment a driven gear is surrounded by four following gears in two pairs. Rotation of the driven gear in one direction causes the following gears to rotate, whilst remaining radially spaced from each other. Rotation in the opposite direction causes the pairs of following gears to intermesh, thereby jamming the mechanism solidly. A preferred manner of mounting the following gears is for one of each pair to be rotatably mounted in a fixed position on the body and for the other to be mounted on axle fitted in an arcuate slot, so that the axle may move from one side of the slot to the other, thus allowing the following gear to move around the circumference of the body.

In order to improve the strength and reliability of the apparatus it is preferred to provide the body within an outer shell through which passes an axle on which the driven gear is mounted. In addition, the axle(ε) mounted in arcuate grooves on which the following gear(s) is/are mounted are received in holes or bearings in the shell. In this way, as the mechanism locks or unlocks in response to rotation of the axle, the body moves relative to the shell.

This aspect of the invention may be applied in many situations in which a very strong and reliable ratchet- effect is required, such as free-wheels in bicycles. If the shell is made circular and of appropriate size it may form a wheel itself. For example, such a wheel may be provided in roller skates in order to allow to state to push forward against the ground. Normal skating would be unaffected since the wheels would be arranged to free-wheel in the forward direction.

Certain embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:-

Figure 1 is a section of a first gear mechanism according to the invention;

Figure 2 is a plan view of the mechanism of Figure

1;

Figures 3 and 4 are partial plan views of the mechanism of Figure 1 illustrating the operation of the mechanism;

Figure 5 is a section of a second gear mechanism according to the invention;

Figure 6 is a plan view of the mechanism of Figure 5 ;

Figures 7 and 8 are partial plan views of the mechanism of Figure 5 illustrating the operation of the mechanism;

Figure 9 is a plan view of a third gear mechanism;

Figure 10 is a section of the mechanism of Figure 9;

Figure 11 is a similar view to Figure 9 showing the mechanism in an alternative configuration;

Figures 12 and 13 are plan views of a fourth gear mechanism according to the invention illustrating alternative configurations;

Figures 14 to 16 are sections of the mechanism of Figures 12 and 13 illustrating its operation;

Figure 17 is a section of a fifth gear mechanism according to the invention;

Figures 18 and 19 are plan views of the mechanism of Figure 17 illustrating the operation of the mechanism;

Figure 20 is a plan view of a component of the mechanism of Figures 17 and 18;

Figure 21 is an elevation, partly in section, of a sixth mechanism according to the invention;

Figure 22 is a partial section of the mechanism of Figure 21;

Figure 23 is a section along the line X-X of Figure 21;

Figure 24 is a similar view to Figure 23 illustrating the mechanism in a different position,-

Figure 25 is a section along the lines Y-Y of Figure 21.

Figures 1 to 4 illustrate a first gear mechanism 10. Two parallel support plates 11 are provided each having a central aperture in which bearings 19 and 20 are provided coaxially. Between the support plates there are located a gear wheel 12 and a locking wheel 14. These wheels have respective stub axles 17 and 18 which are journaled in bearings 19 and 20 respectively. In this manner, a stub axle projects outwardly from each support plate, the axles 17 and 18 being coaxial.

A blind bore is provided along the axis of each stub axle in which a connecting rod 30 is inserted. This forms a friction fit within the bore of the gear wheel axle and journals in the bore of the locking wheel axle 18 so that relative rotational movement between the gear wheel and locking wheel is permitted.

The gear wheel 12 and locking wheel 14 are of approximately similar diameters, the locking wheel being slightly smaller. Gear wheel 12 has gear teeth 13 which project radially in the usual manner. However, the teeth are unusually widely spaced for their size. In fact, the pitch of the teeth is about 3 times the width of the base of the teeth.

The locking wheel 14 has a main body in the form of a disc which is parallel to and slightly spaced apart from the gear wheel 12. At the circumference of the disc there are laterally projecting locking teeth 15 which are of the same pitch and maximum width as the gear teeth 13. The locking teeth 15 project from the body of the locking wheel 14 in the direction of the gear wheel 12 and are received in the spaces between the gear teeth 13 in a similar manner to that found in a dog clutch. However, because the pitch of the gear teeth and locking teeth is large compared to the width of the teeth, a significant degree of relative motion is possible between the gear wheel 12 and locking wheel 14. In addition, it will be noted that the locking wheel teeth 15 do not project radially as far as the gear teeth 13.

A further gear wheel, pinion 16, is provided between the support plates 11. It also has widely spaced narrow teeth and these have the same pitch as the gear teeth 13. The pinion 16 is mounted for rotation on axle 21 which is attached to the support plates 11. The axle 21 is received in holes in the support plates and, along with spacer posts (not shown) , serves to secure the support plates 11 together. The pinion 16 is arranged to engage with the teeth of the gear wheel 12 and locking wheel 14.

When the gear wheel and locking wheel are assembled as illustrated, it will be noted from Figure 2 that they provide a composite gear wheel with gaps which are sufficient to receive the teeth of the pinion 16.

The mechanism just described is capable of operation in two particular ways. In the first of these the mechanism operates as a selectable-direction ratchet arrangement. As discussed previously, it is possible for the gear wheel 12 and locking wheel 14 to move rotationally relative to one another. This motion is of course restricted by the interengagement of the gear teeth 13 and locking teeth 15. In Figure 3 the wheels are illustrated with the gear wheel 12 rotated clockwise as far as possible in relation to the locking wheel 14. If they are fixed in this orientation then the two wheels act as a single composite gear wheel. This gear wheel will rotate freely in the anti-clockwise direction. It will be noted from Figure 3 that if the composite gear wheel is turned anti-clockwise, tooth 22 of the gear wheel 12 strikes tooth 23 of the pinion 16 and thereby rotates the pinion in the clockwise direction. As the pinion rotates tooth 24 drops into space 25 in the composite wheel and as the composite wheel rotates further, the following tooth 26 will strike tooth 24 and so on. Thus, the composite gear may rotate freely in the anti-clockwise direction.

However, should there be an attempt to rotate the composite gear in the clockwise direction then this motion will be prevented. Because the teeth of the locking wheel 14 do not project radially as far as those of the gear wheel, if the pinion is aligned as illustrated in Figure 3, the locking gear tooth 29 will pass under pinion tooth 24 without striking it. The pinion 16 will therefore not be moved from the position in which it is illustrated in Figure 3 by the initial rotation of the composite gear wheel. As the composite wheel is rotated further, gear tooth 27 will strike the pinion tooth 23. However, the presence of locking tooth 28 blocks the path of pinion tooth 23 and thereby prevents the pinion from being rotated. As the pinion 16 cannot rotate, its tooth 23 blocks the path of gear tooth 27 and thereby prevents the composite wheel from rotating further. Thus the arrangement works as a ratchet in which only anti-clockwise rotation of the composite wheel is permitted.

The allowable direction of rotation may be reversed by aligning the wheels as illustrated in Figure 4. From this figure it will be noted that the gear wheel 12 has been rotated anti-clockwise as far as possible relative to the locking wheel 14. It will be seen from Figure 4 that if the wheels are fixed like this, anti-clockwise rotation of the composite wheel is thereby prevented in a manner similar to that described in respect of clockwise rotation previously. Clockwise rotation of the composite wheel is, however, permitted.

The second mode of operation of the mechanism will now be described. In this mode the gear wheel and locking wheel are allowed to move relative to each other and this allows motion to be transmitted in one direction along a shaft whilst preventing its transmission in the opposite direction. Thus, an effect is provided in which turning locking wheel stub axle 18 in either direction causes gear wheel stub axle 17 to rotate in the same direction and at the same speed, but directly rotating gear wheel stub axle 17 is not possible unless the locking wheel is turned at the same time.

Taking the arrangement• illustrated in Figure 3, if the locking wheel axle 18 is rotated in an anti- clockwise direction (as viewed in Figure 3) then the locking teeth 15 will engage with the gear teeth 13 and thereby drive the gear wheel in the same direction. It will be seen from Figure 3 that when rotation occurs in this direction the teeth of the pinion 16 are struck by the teeth of the gear wheel 12 and there is nothing to prevent the pinion from rotating. Thus, the mechanism operates in a similar manner to the ratchet mode discussed above in which anti-clockwise rotation is permitted.

If, on the other hand, the locking wheel 14 is rotated in the opposite direction it will initially move relative to the gear wheel 12 because the load or frictional force on the gear wheel 12 will resist its motion in the clockwise direction. Thus, the gear wheel 12 will remain immobile until the locking wheel 14 has rotated far enough for the locking teeth to engage the other side of the gear teeth as illustrated in Figure 4. As discussed previously in respect of the ratchet operation, this orientation allows the clockwise rotation of the composite gear. It will therefore be seen that it is possible to rotate the locking wheel axle 18 in either direction and for this motion to be transferred via the locking wheel 14 and gear wheel 12 to the gear wheel axle 17.

However, rotation of the gear wheel axle 17 in either direction without the corresponding rotation of the locking wheel axle 18 is not permitted. For example, if the gear wheel 12 and locking wheel 14 are in the configuration illustrated in Figure 3, clockwise rotation of gear wheel 12 will cause the mechanism to jam in the manner described previously in respect of ratchet operation because the locking wheel teeth will prevent the pinion from rotating. Alternatively, if there is an attempt to rotate gear wheel 12 in an anti¬ clockwise direction, then the gear wheel will firstly move relative to the locking wheel. This will result in the wheels being arranged as shown in Figure 4 and therefore the locking teeth will again prevent the pinion from rotating.

In summary, it will be seen that if the locking wheel is turned, the locking wheel teeth will push the trailing sides of the gear teeth and the leading sides of the gear teeth will strike the pinion teeth which will rotate the pinion without any interference. On the other hand, if the gear wheel is rotated then the gear teeth will push the trailing sides of the locking wheel teeth and the locking wheel teeth will obstruct the rotation of the pinon. In this way, rotational motion may be transmitted in one direction through the mechanism but resisted in the other direction. For example, the locking wheel axle may be attached to a motor and the gear wheel axle to a winch. Rotation of the axle by the motor in either direction will turn the winch in order to raise a load. However, should the motor fail, the weight of the load on the winch will lock the mechanism and prevent the load from falling.

Figures 5 to 8 illustrate a second mechanism which operates in a manner similar to the first. It is, however, structurally different because, rather than having locking wheel teeth which project between gear teeth, a locking wheel and gear wheel are provided side by side, both engaging wide following gears which correspond to the pinion.

The mechanism is supported by two support plates 51 which are held apart by spacers (not illustrated) . A gear wheel 52 and locking wheel 54 are disposed between the support plates in a co-axial manner. The gear wheel 52 is fixedly attached to gear wheel axle 57 which is journaled in an aperture in the left hand support plate (as illustrated in Figure 5) . Gear wheel axle 57 is hollow, having a central bore which receives one end of locking wheel axle 58. This axle is fixedly attached to the locking wheel 54 and is journaled in the right hand support plate 74. At the right hand end of the locking wheel axle is provided a first wheel 73 for turning the axle. At the opposite end, which is located within gear wheel axle 57, the locking wheel axle 58 is provided with a transverse slot 71. In this slot is located engaging pin 70 which passes diametrically through and is attached to gear wheel axle 57. A degree of play between the pin 70 and slot 71 is provided in order to allow a precise limited degree of relative rotational motion between the gear wheel axle 57 and locking wheel axle 58. A second wheel 72 is attached to the exterior of gear wheel axle 57.

The gear wheel 52 has teeth 53 which are narrow in comparison with their pitch, as in the first mechanism. Abutting gear wheel 52 is the locking wheel 14 which performs a similar function to the locking wheel 54, but in a slightly different manner. The locking wheel 54 has teeth 55 set at the same pitch as those of the gear wheel 52 but which are wider and considerably shorter and have flat, rather than pointed, tips. The diameters of the gear wheel and locking wheel are similar when measured from the base of the teeth.

Two identical following gears 56 are provided having axes parallel to the gear wheel and locking wheel axes and arranged to engage the gear wheel in diametrically opposite positions. The mechanism would in fact operate with only one of these following gears, but the provision of two increases the reliability. The following gears 56 have teeth of similar width, pitch and height to those of the gear wheel 52. However, the following gears are approximately twice as wide axially and extend across most of the space between the support plates 51. If the locking wheel 54 were not present, rotation of gear wheel 52 would mesh with and turn following gears 56 freely.

The outer diameter of locking wheel 54 is less than that of gear wheel 52, and therefore the teeth of the locking wheel do not mesh with the teeth of the following gears 56. However, as in the case of the first mechanism, they do project far enough to strike the tips of the teeth of the following gears.

The operation of the second mechanism is broadly similar to that of the first mechanism. As the teeth of the locking wheel 54 and gear wheel 52 do not themselves interengage, as in the case of the first mechanism, their relative positions are controlled by the engaging pin 70 and slot 71.

Figure 6 illustrates the mechanism when the locking wheel 54 has been rotated anti-clockwise as far as possible relative to the gear wheel 52 (as viewed in Figure 6) . It will be seen that if the gear wheel and locking wheel are fixed in their relative positions to form a composite gear then this gear may rotate freely in an anti-clockwise direction beacuse there is no obstruction to the engagement of the following wheel teeth with the leading side of the gear wheel teeth. However, if an attempt is made to rotate the composite gear in the clockwise direction, the teeth 55 of the locking wheel will obstruct the path of the teeth of the following gear 56 and thereby prevent clockwise rotation of the composite gear.

Figure 7 illustrates the arrangement of Figure 6 in which clockwise rotation has been attempted but is blocked by the interengagement of the following gear 56 with the teeth 55 of the locking gear. It will be seen that as gear tooth 60 pushes the pinion tooth 61, locking wheel tooth 62 blocks the path of the following wheel tooth 63. This prevents the following wheel from rotating, which in turn jams the composite gear.

Figure 8 illustrates the opposite effect in which the locking wheel 54 is rotated clockwise as far as possible with respect to the gear wheel and the composite gear thereby produced is capable of rotation in the clockwise, but not the anti-clockwise, direction. If anti-clockwise rotation of the composite gear is attempted, locking tooth 64 will block the path of following wheel tooth 65 which will in turn jam the composite gear.

Thus, a ratchet in effect is obtained in a manner similar to that of the first mechanism, the direction of permissible rotation being dependent upon the relative positions of the gear wheel 52 and locking wheel 54.

The second mechanism also provides a second mode of operation in which rotary motion may be transmitted in one direction but not the other. This is achieved in essentially the same manner as in the case of the first mechanism. Thus, when the locking wheel axle 58 is rotated in an anti-clockwise direction this will turn locking wheel 54. The locking wheel will rotate relative to the wheel 52 as far as is permitted by the engaging pin 70 and slot 71. This will result in the gear wheel and locking wheel being aligned as illustrated in Figure 6 which, as discussed previously, will permit anti-clockwise rotation of the gear wheel and locking wheel 54 and therefore also the gear wheel axle. Clockwise rotation of the locking wheel axle will initially rotate the locking wheel relative to the gear wheel and bring the gear wheel and locking wheel into the configuration illustrated in Figure 7 which permits clockwise rotation. In this way, rotary motion applied to the locking wheel axle in either direction may be transmitted to the gear wheel axle.

In contrast to the foregoing, when the gear wheel axle 57 is rotated in a clockwise direction this will bring it and the locking wheel 54 into the configuration illustrated in Figure 6 which, as discussed previously, prevents clockwise rotation. Similarly, anti-clockwise rotation of the gear wheel axle 57 will bring the gear wheel and locking wheel into the configuration illustrated in Figure 7 which prevents anti-clockwise rotation. Therefore, whichever way the gear wheel is turned, if the locking wheel is allowed to move relative to it, then rotary motion cannot be transmitted through the mechanism.

Figures 9 to 11 illustrate a third mechanism which is generally similar to the second mechanism. The most significant difference between them is that the third mechanism has axles projecting from only one side, with the gear wheel axle projecting through the centre of the locking wheel axle.

The mechanism is mounted on two support plates 151 and 152. Support plate 151 has mounted through its centre a cylindrical bearing 171 which provides a bearing surface 172 on the inside face of the support plate. In the centre of this is a locating pin (not shown) which serves to centralise the locking wheel axle as explained below. Support plate 152 has an aperture coaxial with bearing 171 which provides a clearance hole for locking wheel axle 158. The locking wheel axle is in the form of a cylindrical collar through which passes gear wheel axle 157, the arrangement being such that relative rotation is possible between the two axles. A small hole is provided in the centre of gear wheel axle 157 in which is located the pin on bearing 171.

Gear wheel 162 and locking wheel 154 are mounted on the appropriate axles between the support plates 151, 152. These wheels are similar in design to the corresponding components in the second mechanism except that they are in the form of thin discs rather than the more substantial cylinders of the second mechanism. The gear wheel 162 therefore has long thin but widely spaced teeth and the locking wheel 154 has shorter and wider teeth which do not project radially as far as those of the gear wheel.

The two wheels lie parallel and next to one another and are capable of limited relative rotational motion which is restricted by a pin and slot arrangement. As illustrated in Figure 9, locking wheel 154 is provided with a short arcuate slot 181 which cooperates with pin 180 projecting laterally from the gear wheel. The relative motion allowed by the arrangement corresponds to that permitted by the engaging pin and slot assembly of the second mechanism.

As in the case of the second mechanism, two following gears 116 are provided to engage with the locking wheel and gear wheel. These rotate about axles 121 which are fastened between support plates 151 and 152. The following gears 116 are formed from pairs of parallel discs 191 having a central tubular bearing and teeth in the form of pins 192 which connect the discs at evenly spaced points about their circumference.

Although the gear wheel axle and locking wheel axle both project from the same side of the mechanism, the device operates in the same manner as the second mechanism. Thus, as illustrated in Figure 11, when the locking wheel is rotated clockwise as far as possible relative to the gear wheel, if this orientation is fixed, then the composite gear thereby produced can only rotate in a clockwise direction. On the other hand, if the locking wheel 154 is rotated anti-clockwise as far as possible relative to the gear wheel 162 (Figure 9) and fixed in that position then the composite gear may only freely rotate in the anti-clockwise direction. In this way the selectable-direction ratchet effect is produced.

In addition, if the gear wheel and locking wheel are permitted to rotate relative to one another, restricted only by the pin and slot arrangement 180,131, then the one-way transmission effect is achieved. If the support plates 151, 152 are held firmly the locking wheel 158 axle may be turned freely and this will cause the gear wheel axle to rotate at the same speed. However, any attempt directly to rotate the gear wheel axle in either direction will jam the mechanism because the locking wheel teeth will obstruct the path of the following gear teeth, as in the second mechanism.

Figures 12 to 16 illustrate a fourth mechanism 200 which operates in a linear, rather than rotary, fashion. Two parallel and spaced apart support plates 201, 202 are provided secured together by bolts and spacers (not shown) . The support plates 201 and 202 are apertured to receive an axle 213 which passes perpendicularly between them. Rotatably mounted on this axle is a gear wheel 210 in form of a cylindrical collar having projecting pin-like teeth 211. Two studs 205 and 206 are provided attached to the support plate 202 projecting towards the other support plate 201. The bases of the studs are in line with the bottom of the collar portion of the gear wheel 210 (Figure 14) .

Between the support plates are two perforated strips, upper strip 220 and lower strip 221. These are supported by a pair of elongate side supports 208 (Figure 14) which sandwich the strips between themselves and the studs 205 and 206. One side support 208 is attached to each support plate 201,202 and there is a gap between the side supports 208 so as not to obstruct the teeth of the gear wheel 210 passing through the strips as will be discussed hereinafter.

A thin separator plate 207 having a large central slot is provided between the upper 220 and lower 221 strips. This has a bearing surface on each side which the strips side slide across and prevents the strips from contacting each other in the region of the support plates. The strips 220 and 221 are therefore held perpendicularly to the support plates 201,202 and, if the gear wheel 210 were removed would be able to slide smoothly and easily from left to right through the apparatus (as viewed in Figure 12) .

The upper and lower strips are both perforated with elongated slots 222. These slots are of identical size and spacing on both strips. The two strips are secured together by loosely fitting pegs 230 and 231 located at opposite ends of the strips. Peg 231 passes through a slot in each strip and thereby restricts the relative longitudinal motion between the strips. Figure 12 illustrates the strips when the upper strip has been moved leftwards as far as possible with respect to the lower strip 221. It will be seen that, in effect, there is a series of round holes passing through the two strips arranged at the right hand side of each slot 222 in the upper strip 220. Peg 230 which is located at the opposite end of the strips from peg 231 is located in a normal size slot in the lower strip 221 and an oversize one in the upper strip 220. Thus, whilst this peg helps to hold the strips together it has no restricting effect on relative longitudinal motion.

The slots 222 are regularly spaced and correspond to the pitch of gear wheel 210. If the apparatus is considered with the lower strip 221 removed, the upper strip may be slid back and forth between the studs 205, 206 and the separator plate 208 and, as shown in Figure 14, will almost touch the circumference of the collar forming the body of gear wheel 210. As the upper strip is slid back and forth, the gear teeth 211 will be struck by the trailing ends of the slots in the upper strip 220. This will push the gear wheel around sufficiently for the next tooth to be engaged by the trailing end of the next slot. In this way the gear wheel 210 and upper strip 220 act as a pinion and rack respectively.

The lower strip 221 is further from the gear wheel 210 than the upper strip 220. As will be seen from Figure 14, this spacing is sufficient that lower strip 221 may pass back and forth without rotating gear wheel 210. However, the spacing is not so great that the lower strip cannot contact the teeth of the gear wheel 210 and, in fact, the only time at which contact does not take place is when the relative orientations of the teeth and strip are as illustrated in Figure 14. Figures 15 and 16 illustrate orientations in which the lower strip and gear teeth interact.

The operation of the present apparatus is, in effect, a linear analogue of the previously described mechanisms. Again, there are two modes of operation, a selectable ratchet and a one-way motion device. If the upper 220 and lower 221 strips are fixed in the orientation illustrated in Figure 12, that is with the upper strip moved leftwards relative to the lower strip, then the two strips may be considered as a single rod which is only free to move leftwards (viewed in Figure 12) . As the rod is moved leftwardly the trailing ends of the slots in the upper strip 220 engage and rotate the gear wheel 210. The gear wheel teeth 211 are pushed by the trailing edges of the slot and, as can be observed from Figure 12, this portion of the slot is unobstructed by the lower strip 211. Figure 16 shows a cross section through the apparatus in this configuration from which it will be noted that when the rod is moved leftwardly there is a clear space to receive a gear tooth 215 at the trailing (right hand) end of the slot 225 in the upper strip 220.

If, on the other hand, there is an attempt to move the rod to the right this will be resisted by the apparatus. This is because the opposite (left hand) ends of the slots become the trailing ends and, as can be clearly seen from Figures 12 and 16, these ends are obstructed by the lower strip 221. Therefore, as gear tooth 215 (Figure 16) attempts to drop into the trailing end of slot 225 it strikes portion 226 of the lower strip. Thus the lower strip prevents the gear wheel from rotating further. In addition, as the rod is moved rightwardly, the tooth 215 also strikes the trailing end of the slot 225 in the upper strip 210 and thereby prevents the upper strip, and therefore the entire rod, from moving further to the right.

The mechanism may also be arranged to permit movement of the rod in the opposite dirction. If the upper strip is moved rightwardly as far as possible with respect to the lower strip and fixed in that position then the device will allow movement of the rod to the right. This is illustrated in Figures 13, 14 and 15. From these figures it can be seen that the rod is free to move rightwardly since the left hand, trailing, ends of the slots in the upper strip 210 are clear, but motion in the leftwards direction will be prevented.

When the mechanism is to be operated in its second mode as a one-way motion device the upper 220 and lower 221 strips are permitted to move relative to each other, restricted only by the peg 231. If the upper strip is pulled to the right it will move relative to the lower strip (whose motion is restricted by friction) until the peg 231 engages with the end of its slot in the lower strip. When this occurs, the strips will be aligned as illustrated in Figure 13 so that the left hand sides of the slots in the upper strip 220 are clear. Since the lefthand ends of these slots are the trailing ends for rightward motion, the strips will move freely through the apparatus rotating the gear wheel. If the upper strip is then moved to the left it will initially move relative to the lower strip until again restrained by peg 231 thereby reaching the configuration illustrated in Figure 12. The right hand sides of the slots in the upper strip 220 are now the trailing ends and are clear of obstruction. The strips will now move freely to the left through the apparatus. It will therefore be seen that if the upper strip is moved in either direction it will cause both strips to move freely in that direction through the mechanism.

If it is the lower strip which is moved, it will firstly move relative to the upper strip. The effect of this is to block the trailing ends of the holes in the upper strip and therefore prevent motion in the same way as was described previously in respect of the ratchet operation. For example, if the lower strip 221 is moved rightwardly the strips will attain the configuration illustrated in Figure 12 from which it may be seen that the left hand edges of the slots in upper strip 210 are blocked by the lower strip 221. Thus, further rightward motion is prevented because the lower strip 221 will block the motion of the gear wheel teeth 211. An equivalent effect occurs when the lower strip is moved to the left since the strips will then attain the configuration illustrated in Figure 13. Thus, any attempt directly to move the lower strip results in the apparatus locking.

It will therefore be seen that the apparatus allows motion to be transferred from the upper strip to the lower strip, but not in the opposite direction. If it is desired to transfer motion from one end of the device to the other, but not in the reverse direction, then it is a simple matter to arrange for the upper strip to project outwardly at one end and the lower strip to project outwardly at the other, as shown in Figures 12 and 13. A source of linear motion may then be easily attached to the projecting end of the upper strip 220 and an object which is to be moved may be attached to the lower strip 221 at the opposite end. In this way, the source of motion may operate freely to move the object but motion of the object in either direction will be restrained unless it is caused by the source of linear motion.

Figures 17 to 20 illustrate a fifth mechanism 300 which operates as a one-way ratchet.

As may be seen from Figure 17, the mechanism has a body formed of two identical support plates 301 which are attached together by cylindrical spacers 302 which hold them in co-axial parallel alignment. Through the centres of the support plates 301 there is rotatably mounted an axle 304. A solid tyre 305 may be located around the periphery of the support plates 301 in order to form a wheel.

Between the two support plates is located a gear carrier 310. This is in the form of two carrier plates 311 (see Figure 20) which are rotatably mounted on axle 304 and which are held together by spacer pins 312. The carrier plates are in the form of discs with opposite cut-away portions 313 which allow the gear carrier to be received between the cylindrical spacers 302 (Figure 18) allowing some rotational movement with respect to the support plates 301.

In the centre of the gear carrier 310 is provided a drive gear 320 which is fixedly mounted on axle 304. Four similar gears 321-324 are provided on the gear carrier 310 disposed around the drive gear 320 and meshing with it. Driven gears 323 and 324 have integral axles which are rotatably mounted in apertures in the carrier plates 311. The axles are sufficiently short so that they do not project outside gear carrier 310. Movable driven gears 321 and 322 have longer integral axles which are mounted for rotation in apertures in the support plates 301. Slots 325 are provided in the carrier plates 311 around these axles. These permit the gear carrier 310 a degree of rotational movement relative to the support plates 301.

Figure 19 illustrates the arrangement of components when the gear carrier 310 is rotated anti-clockwise as far as possible in relation to the support plates 301. Figure 18 illustrates the effect of partial rotation of the gear carrier 310 in the opposite direction.

It will be noted from Figure 19 that the driven gears 321 to 324 are widely spaced and engaged only with the drive gear 320. If the drive gear is rotated anti¬ clockwise (as illustrated by the arrows in this figure) then each of the driven wheels will be rotated in the opposite direction. Thus, if the support plates 301 or a tyre 305 attached to them to form a wheel is held in place the axle 304 may freely rotate in an anti- clockwise direction and conversely if the axle is fixed, the wheel may freely rotate in a clockwise direction.

However, if the axle is rotated in a clockwise direction the driven gears will be turned anti¬ clockwise. Since gears 323 and 324 are mounted on the carrier plates 311 the action of the drive gear 320 upon them will impart a torque to the gear carrier 310 as a whole and cause it to move in a clockwise direction. Movement in this direction is possible because, as discussed above, the axles of the driven gears 321 and 322 which are attached to the support plates 301 pass through slots 327 in the carrier plates 311. These slots are arranged to allow the gear carrier 301 to rotate sufficiently for driven gears 323 and 324 to move into mesh with driven gears 321 and 322. Figure 18 illustrates the arrangement when the gears first come into contact in this manner. Further rotation of the gear carrier 310 will result in the gears becoming closely meshed.

Since all of the driven gears 321 to 324 are being driven to rotate in the same, anti-clockwise, direction it will be appreciated that when they come into contact with each other the mechanism will lock because the teeth of adjacent driven gears will be moving in opposite directions. Thus, if the axle (as viewed in Figure 19) is rotated in a clockwise direction, only a very small degree of movement, sufficient to rotate the gear carrier 310 to achieve the effect just described, will be possible before the mechanism jams solid and prevents further motion. Conversely, if the axle is fixed in position, anti-clockwise rotation of the assembly is prevented.

It will be noted that the further the axle is turned in the locking direction, the more tightly the gears will jam together, and the more securely locked the ratchet becomes. This mechanism is therefore suitable for use in situations where very high torques must be resisted.

Figures 21 to 25 illustrate a sixth mechanism 400 which operates as a continuously variable transmission.

The mechanism has a frame 401 having a flat base 402 which allows it to be securely placed on any suitable surface. At the left-hand side of the frame 401, as illustrated in Figure 21, is mounted a drive axle 411. This is journaled in a pair of ball bearing races 408 and 413 which hold it in a horizontal position. As well as being capable of rotary motion, the drive axle can also be slidably moved back and forth through the bearings.

A first bevel gear 409 is mounted on the drive axle 411 using a pin and slot arrangement to accommodate the linear motion of the drive shaft. An elongate slot 412 is provided in the drive axle 411 and this receives pin 414 which passes diametrically through and is attached to the hub of the first bevel gear. This allows the drive axle 411 to be moved back and forth through the bearings and the first bevel gear 409 whilst remaining in rotational engagement with that gear.

Meshing with the first bevel gear 409 is a second bevel gear 410 to which a drive shaft (not shown) is attached. The drive shaft is therefore perpendicular to the drive axle 411.

On the extreme left-hand end of the drive axle 411 there is rotatably mounted a control knob 407. At the opposite end there is provided an offset 416 to which a crank arm 415 is pivotally mounted by way of a pin 418.

The other end of crank arm 415 is connected to a further offset 417 on a short axle 421 which is rotatably mounted in the centre of the carrier 436 of a cross frame 435 which will be described below.

The cross frame carrier 436 is mounted on a parallel-bar arrangement 433 as illustrated in Figure 23. This comprises two smooth vertical steel rods 451 mounted on opposite sides of the frame 401 in a plane perpendicular to the drive axle 411. The vertical rods are connected at their upper ends by a horizontal tie 453. Slidably mounted on each vertical rod 451 are a pair of brass carrier frames 45 . These are connected by a second pair of smooth horizontal steel rods 452. Thus, the carrier frames 454 permit the horizontal rods to move up and down whilst holding them parallel to each other and perpendicular to the vertical rods 451.

Slidably mounted on the horizontal rods 452 is the cross-frame carrier 436 which is also made of brass. This may move in either direction along the horizontal rods 452. It will be realised that since the horizontal rods may in turn move up and down in relation to the vertical rods 451 the parallel-bar arrangement 433 therefore provides a means of supporting cross frame carrier 436 in a manner which permits it to move in any direction within a vertical plane.

As discussed above, the drive axle 411 may be slid back and forth through its bearings 408,413. Figure 22 illustrates the apparatus when the drive axle 411 has been moved fully to the left, ie. away from the centre of the apparatus. Since the parallel bar apparatus 433 only permits the cross frame carrier 436 to move in a vertical plane, the effect of moving the drive axle 411 away from the centre of the apparatus is to pull and thereby extend the crank arm 415 which in turn pulls the axle 421 of the cross frame carrier to its central position. In this position, the axle 421 and drive axle 411 are coaxial. Since the axle 421 is rotatably mounted within the cross frame carrier 436, rotation of the drive axle freely rotates axle 421 and has no further effect.

However, when the drive axle 411 is pushed in towards the centre of the apparatus, for example as illustrated in Figure 21, the crank arm 415 pushes axle 421 away from its central position with a result that the drive axle 411 and axle 421 are no longer coaxial. In this configuration, when the drive axle is rotated the axle 421 describes a circle centred on the axis of the drive axle 411. As discussed above, the parallel- bar arrangement 433 supports the cross frame carrier 436 thereby restraining it to move within a vertical plane. The arrows on Figure 23 illustrate a circular path in which the cross frame carrier may move. Figure 24 illustrates the cross frame assembly 430 after the crank arm has rotated 90° compared to Figure 23. It will be noted that the rotary motion of the cross frame carrier is in the form of a combination of vertical and horizontal translations and that the carrier always maintains its orientation with respect to the frame 401.

It will be appreciated that the further the drive axle is pushed in towards the centre of the apparatus, the greater will be the radius of the circle described by the motion of the cross frame assembly. The radius of that circle is, of course, continuously variable.

Fixedly mounted to the cross frame carrier 436 is a cross frame 435. This is a regular, cross shaped piece of brass in the form of the letter X. The arms of the cross are all equal in length and are radially spaced at 90° from each other. Slots 437 are provided from the centre of the cross to the tip of each arm for receiving rollers 438 (shown in phantom in Figure 23) . The rollers 438 are guided by the slots 437 so that they may move back and forth along the slots towards, and away from, the centre of the cross.

At the far right-hand side of the frame 401 there is a pair of ball bearing races (not shown) which support an output shaft 442. At the outermost end of the shaft there is mounted an output gear 443. On the other end is a gear wheel and ratchet assembly 450 which cooperates with the cross frame 435 in order to transfer motion from the drive axle to the output gear.

The gear wheel and ratchet assembly 450 has a pair of parallel wheels mounted on output shaft 442. These are gear wheel 436 which is fixedly mounted to the output shaft 442 and locking wheel 437 which is rotatably mounted on the shaft and interlinked with gear wheel 436 by means of a pin and slot arrangement. The two wheels form a composite gear and are of the same type as the locking and gear wheels of the third mechanism. The pin and slot arrangement also operates in precisely the same manner as in that mechanism. Thus, the gear wheel has a slightly larger outside diameter than the locking wheel and has widely spaced narrow teeth. It will, however, be noticed from the drawings that the wheels used in the present mechanism are much larger and have many more teeth than those in the third mechanism.

Four following gears 432 provided around the circumference of the gear wheel 436 and locking wheel 437. These are similar to following gears 116 of the third mechanism. The following gears 432 are rotatably mounted on axles 452. Each axle is mounted on a pair of elongate axle supports 453 which are rotatably mounted on the output shaft 442. Thus, the following gears 432 are able to move around the circumference of the gear wheel and locking wheel (see Figure 25) . At the end of each axle 452 furthest from output gear 443 there are rotatably mounted the rollers 438. Thus, there are four such rollers, one attached to each axle 452 and one of these roller is engaged in each slot 437 of the cross frame 435. The location of two such rollers is shown in phantom in Figure 21.

As discussed above, provided the apparatus is not arranged as in Figure 22, rotation of drive axle 411 will cause the cross frame 435 to translate following a circular path, the radius of which depends on how far crank arm 415 is extended. As the cross frame 435 moves, rollers 438 slide up and down the slots 437 in the arms of the cross frame 435. Since the following gears 432 are mounted on the same axles as the rollers 438 and these axles are constrained to move in arcuate paths by axle support 453, the result of the movement of the cross frame 435 is that the following gears 432 attempt to orbit in a planetary fashion around the circumference of the gear wheel 436 and locking wheel 437.

Since the gear wheel and ratchet assembly 450 is essentially a large version of the third mechanism, it will be appreciated that the following gears 432 may only freely orbit around the circumference of the wheels in one direction since in the other direction the locking wheel will block the path of the following gear teeth thereby preventing relative motion between the following gear and the composite gear. Thus, in the present mechanism, when the following gears cannot orbit around the circumference of the wheels, they will engage with them and turn the entire composite wheel about its axis.

If one considers the motion of just a single following gear 432, if it is moved around the composite gear in the- direction in which the locking wheel blocks the path of its teeth then the composite gear will be turned in that direction.

If it is moved in the opposite direction then it will merely roll back along the circumference of the composite gear without engagement. The direction in which the free-wheeling effect occurs can be changed by altering the relative positions of the gear wheel and locking wheel, as in the other mechanisms.

As may be understood from Figures 23 to 25, the effect of moving the cross frame 435 in a particular direction is to move rollers 438 back and forth along slots 437 with the result that following gears 432 move back and forth around the circumference of the composite gear. The following gears 432 will not all move in the same direction around the composite gear and therefore at any given time, some will be free-wheeling and others serving to turn the composite gear. Since the following gears 432 will only engage with the composite gear when moving in the same given direction it follows that any movement of the cross frame 435 will result in the output gear turning in a single direction determined only by the relative positions of the gear wheel 436 and locking wheel 437. The nature of the motion of the cross frame has no effect on the direction in which the output gear 443 rotates. In fact, even if the motion of the drive axle 441 is oscillatory the output gear will still turn in the same single direction. Moreover, even moving the drive axle 411 in and out in a reciprocating manner will cause the output gear 444 to rotate in this same direction.

It may therefore be seen that any movement of the cross frame 435 will cause the output gear 432 to rotate because any such motion will cause the rollers 438 to move within their slots 437. This in turn, causes the following gears to move around the circumference of the composite gear. Since the following gears cannot all move in the same direction it follows that at least a pair of them will be engaged with the composite gear and will therefore rotate the output shaft 442.

A better understanding of the manner in which movement of the cross frame 435 causes rotation of the output gear 443 may be obtained by reference to Figure 25. This illustrates the gear wheel 436 and locking wheel 437 together with the four following gears 432. The cross frame 435 and axle supports 453 are shown in phantom. In this figure the cross frame 435 is positioned at approximately the upper limit of its travel as illustrated in Figure 23. If it is imagined that the crank arm 415 is rotated in an anti-clockwise direction by the drive axle 411, then the cross frame 435 will be moved to the left and downwards. As it does so, the rollers attached to following gears 460 and 461 will move towards the outside ends of their respective slots. This will cause gear wheel 461 to freely rotate in a clockwise direction and roll around the exterior of the composite gear. Following gear 460, on the other hand, will move in an anti-clockwise direction and, as may be seen from Figure 25 will be prevented from rolling around the circumference of composite gear 450 by the locking wheel 437. It may be seen from this Figure that the teeth of the following gear are blocked by the teeth of the locking wheel in precisely the same manner as in the case of the third mechanism. Since following gear 460 cannot roll around the outside of the composite gear it is therefore engaged with the composite gear and causes the composite gear to move in an anti-clockwise direction, as illustrated by the arrows in Figure 25. Thus, at this particular stage, following gear 460 drives the composite gear (and therefore the output gear 443) whilst following gear 416 effectively free-wheels.

At other points in the cycle, for example if the cross frame 435 is rotated in an anti-clockwise direction from the position illustrated in phantom in Figure 23, then following gears 460 and 461 will reverse their roles.

Returning to Figure 25, as the following gears 460 and 461 move as discussed above, following gears 462 and 463 will be moving along their respective slots towards the centre of the cross frame 435. This causes following gear 463 to move in a clockwise direction around the circumference of the composite gear and therefore it free-wheels. Following gear 462, however, moves in anti-clockwise direction and therefore engages with, and assists following gear 460 in driving, the composite gear.

It will be apparent from Figure 25 that the direction of motion of the composite gear is not determined by the direction of motion of the following gears, but by the relative positions of the gear wheel 436 and locking wheel 437 which determines the direction in which the following gears will free-wheel around the circumference, and when they will engage and thereby rotate the composite gear. The relative positions of the gear wheel and following wheel are constrained by a pin 471 attached to the locking wheel 437 which engages in a small slot 472 in the gear 436 (Figure 25) . This operates in precisely the same manner as the corresponding components in the third mechanism and by moving the wheels relative to one another between the two extreme positions permitted by the pin and slot, the drive direction may be changed.

The transmission ratio of the apparatus is varied by moving drive axle back and forth in order to alter the extension of crank arm 415. Figure 22 illustrates the crank arm at its maximum extension in which the drive axle 411 and axle 421 are coaxial, and therefore this is a neutral position since axle 421 will be rotated without moving the cross frame 435. However, if the drive axle is moved towards the position illustrated in Figure 21, then the crank arm 415 will cause the cross frame 435 to move in a circular manner. The further the crank moves from the neutral position, the more compressed will be the crank arm and therefore the greater will be the radius of the circle described by the motion of the axle 421. This, in turn, determines the speed at which output gear 443 rotates for a given speed of rotation of the drive axle 411. When the crank arm has move only slightly from the position illustrated in Figure 22, and the cross frame 435 describes only small circles, then each rotation of drive axle 411 will cause the following gears 432 to move back and forth only a small direction. This, in turn will only rotate the output shaft by small amount. On the other hand, when the crank arm is arranged as in Figure 21, the crank arm 415 will cause the cross frame 435 to move much further for each rotation of the drive axle 411. This causes following gears 432 to move much further and therefore turns the output shaft 442 by a larger amount.

It is therefore a simple matter to alter the transmission ratio of the device to any one of an infinite number of positions. Moreover, this may be done easily whilst the drive axle 411 is being rotated. Figure 21 illustrates a control knob 407 mounted via a bearing on the drive axle 411 and by pulling or pushing this knob the transmission ratio may be adjusted at any time.

Claims

Claims

1. Motion transfer apparatus comprising a first member having periodically arranged meshing regions cooperating with periodically arranged meshing projections on a second member, each of the meshing regions comprising a first portion for receiving a projection of the second member and a second portion for engaging the projection so that relative motion between the first and second members in one direction may be effected, and means being provided for preventing relative motion in the opposite direction, characterised in that each of the meshing regions has a third portion for blocking engagement with the projection and serving as the means for preventing said relative motion in the opposite direction.

2. A motion transfer apparatus as claimed in claim 2, wherein the first member comprises a toothed gearwheel or rack; wherein the teeth have three portions arranged sequentially along the meshing surface of the gearwheel or rack, the first such portion being a tooth receiving portion, the second being a tooth engaging portion and the third being a tooth blocking portion; and wherein the second member comprises a gearwheel having teeth of similar pitch to those of the first member and which may be received in the tooth receiving portion of the first member.

3. A motion transfer apparatus as claimed in claim 2, wherein the first member is a gearwheel having teeth provided on its circumference and each of the three parts of the teeth subtend a similar angle from the axis of the gearwheel.

4. A motion transfer apparatus as claimed in claim 3, wherein the tooth engaging portions are similar to the teeth of the second member and they project further than the other portions from the first gearwheel.

5. A motion transfer apparatus as claimed in claim 3 or 4, wherein the blocking portion is a region of the tooth which extends sufficiently far from the axis of the first gearwheel to partially, but not fully, engage with the second member.

6. A motion transfer apparatus as claimed in claim 3, 4 or 5, wherein the teeth in the second member have a pitch of about three times their width in the circumferential direction.

7. An apparatus as claimed in any preceding claim further comprising means for varying the profile of one of the intermeshing members.

8. An apparatus as claimed in claim 7, wherein dependent upon claims 2 to 6, wherein the sequence of the receiving, engaging and blocking portions on the first member may be varied.

9. An apparatus as claimed in claim 8, wherein the first member comprises a body with projections forming the engaging portions of a series of gear teeth and a further member adjacent to, or interlocked with, the body, wherein the further member has a series of projections which provide the blocking portions, and the further member is displaceable, relative to the body in order to change the sequence of the blocking engaging and receiving portions of the teeth and thereby reverse the drive direction of the mechanism.

10. An apparatus as claimed in claim 9, wherein the body is in the form of a first disc, wheel, or ring and the further member is a second disc or wheel parallel

- Al ¬ ls . An apparatus as claimed in claim 14, wherein the jamming member comprises a further following gear driven by the driven gear.

16. A gear mechanism comprising first and second intermeshing members arranged to be moveable relative to each other, the members having meshing surfaces profiled such that relative motion between the members is allowed in only one direction.

17. A gear mechanism as claimed in claim 16, wherein the first member is a gearwheel.

18. A gear mechanism as claimed in claim 16, wherein the first member is a rack.