GB2492850A - Hitch coupler - Google Patents

Abstract

A hitch coupler (100) for a mechanical excavator or similar equipment comprises a body portion (110) having a fixed jaw (112) formed integrally with the body portion. The hitch coupler comprises an engagement mechanism for attaching and detaching the hitch coupler to the carrying bars (12, 14) of an attachment (10). The engagement mechanism comprises sliding jaw (118) and a locking member (120), each mounted for sliding engagement within the body portion, coupled by a double-acting actuator (122) and spring mechanism comprising a helical spring (132) mounted on a telescopic former (134). The engagement mechanism may be switched between a first condition in which the actuator is retracted and the locking member is clear of the fixed jaw, and a second condition in which the actuator is extended, the locking mechanism cooperates with the fixed jaw to retain a carrying bar of an attachment therein, and the moveable jaw engages another carrying bar of the attachment. The spring mechanism is biased to prevent disengagement of an attachment with the hitch coupler in the event of failure of the actuator.

Description

HITCfl COUPLER The invention relates to hitch couplers for usc with mechanical excavators, earth-movers, diggers, backhoe loaders, skid steer loaders and similar equipment.

A mechanical excavator typically has an articulated mechanical arm, the remote end of which carries some sort of attachment, for example a digging bucket, pneumatic drill etc. for performing a desired operation. the attachment is typically releasably attached to the remote end of the mechanical arni by means of a hitch coupler provided at the remol:e end of the niechanical arm Generally, an attachment such as a digging bucket is provided with a pair of carrying bars extending laterally across the width direction of the attachment and mutually displaced along the length direction of the attachment. A hitch coupler has a pair ofjaws, at least one of which may be extended and retracted with respect to the other by use of control means located IS within the operating cab of a mechanical excavator. An operator of a mechanical excavator is thus able to release a particular attachment, and attach another attachment, by suitable control of the mechanical arm and the hitch coupler effected from within the cab of the excavator without need for any assistance, and particularly without manual intervention at the remote end of the mechanical arm.

Movement of the jaw, or jaws, or hitch coupler is typically effected by a hydraulic actuator mounted in or on the hitch coupler because such an actuator may be incorporated into the overall hydraulic system of a mechanical excavator, which includes actuators for manipulating the mechanical arm of the excavator. This presents a safety problem in that, in the absence of some sort of safety mechanism, failure of (he hydraulic actuator of the hitch coupler can lead to an attachment simply detaching from the end of the mechanical arm and falling to the ground. Falling attachments have been known to kill people working on the ground near mechanical excavators. Certain safety features are known in the prior art for insuring against hydraulic faiLure in a hitch coupler. One such feature is the use of a mechanical pin which is hammered into position behind the moveable jaw(s) of a hitch coupler after engagement with an attachment. Tins has the disadvantage that manua[ intervention is required outside the operating cab of a mechanical excavator. It has been known for operators of mechanical excavators to dispense with use of such a pin due to bad weather conditions, or for other reasons. Sonic hitch couplers provide for one bar of an attachment to be locked into one, fixed, jaw on engagement with the attachment, for example by a Latch mechanism (see for example published international application WO 2009/064203) or by means of an cxtcnsion on a xnoveablc jaw (sce for example published international application WO 2009/050445). Aliliough such acluators can prevent complete detachment of an attachment in the event of a loss of hydraulic pressure in the hitch coupler, an attachment may nevertheless swing dangerously about one carrying bar thereof in such an event. There is therefore still a significant safety hazard involved in using such hitch couplers.

The present invention provides a hitch coupler comprising: (a) a body portion providing a fixed jaw integrated with the body porl.ion; and (b) an engagement mechanism comprising: (i) a moveable jaw, having a jaw opening in a direction generally anti-parallel to that of the jaw opening of the fixed jaw; (ii) a locking member; (iii) a double-acting actuator mechanism; and (iv) a spring mechanism: wherein the actuator mechanism is arranged to switch the engagement mechanism between a first condition whereby the fixed and inoveable jaws have a first separation and a second condition whereby said jaws have a second separation and the locking member cooperates with the fixed jaw to prevent removal of a carrying bar of an attachment when the carrying bar is present in the fixed jaw, and wherein the spring mechanism tends to bias the engagement mechanism to the second condition.

In the event of failure of the double-acting actuator, the spring mechanism biases the engagement mechanism to the second condition in which the locking member cooperates with the fixed jaw of the hitch coupler so that a first carrying bar of an attachment may be retained therein and the inoveable jaw may be maintained in engagement with a second carrying bar of the attachment. Thus both carrying bars of an attachment remain locked ill respective jaws of the hitch coupler in the event of failure of the actuator mechanism. This means that the attachment not only remains attached to the hitch coupler in such an event, but does not swing dangerously from one carrying bar. A hitch coupler of the invention also has the advantage that the engagement mechanism is relatively simple compared to couplers which rely on pivoting jaws and/or latch mechanisms which are susceptible to fouling with debris, such as building rubble, cement etc and which arc morc complex and therefore more prone to malfunctioning. A further advantage is that one jaw of a hitch coupler of the invention is fixed and integrated with the body portion. The hitch coupler may be used so that the front carrying bar of a digging bucket is engaged with the fixed jaw and the rear carrying bar of the digging bucket is engaged with the moveable jaw. In this way, when digging trench for example, most stress is taken by the fixed jaw, which can be made very thick and strong by integration with the body portion. In certain hitch couplers of the prior an, both jaws are moveable by means of a single actuator, and digging operations therefore place significant stress on the actuator, making failure of the actuator more likely. In addition, a hitch coupler of the invention may be operated by a single control switch in the cab of a mechanical excavator, which means that an operator familiar with the mode of operation of a standard hitch coupler is able to use a hitch coupler of the invention without the need for additional training or instruction.

The respective jaw openings of the fixed and moveable jaws are generally anti-parallel meaning that they may face either generally towards each other, or alternatively.

generally away from each other. In the former case, when the engagement mechanism is in the first condition, the jaws are further apart than when the engagement mechanism is in the second condition. In the latter ease, the jaws are closer together when the engagement mechanism is in the first condition than when it is in the second condition. The latter case conforms to the jaw configuration of most hitch couplers; in this case the moveable jaw and the locking member may be coupled simply by the actuator mechanism and the spring mcuhanism.

Conveniently, the moveable jaw and the locking member are slidably mounted on the body for movement on a common axis. In other words the moveable jaw and the locking member are moved apart linearly along the common axis, in opposite directions, when the engagement mechanism is switched from the first condition to the second condition.

The respective positions of the locking member and of the moveable jaw when the engagement mechanism is in the first condition, and the position of the locking member when the engagement mechanism is in the second condition, are preferably defined by mechanical stops mounted on the body portion. This provides a simple scheme for defining the respective positions of the moveable jaw and the locking member with respect to the body portion when the engagement mechanism is in the first and second conditions.

A further mechanical stop is preferably provided on the body portion to define the maximum extent of movement of the moveable jaw with respect to the body portion in a direction away from the locking member. This prevents the actuator and spring mechanisms being over extended and potentially damaged it' the hitch coupler is misaligned with the carrying bars of an attachment during an attempt at picking up the attachment such that the moveable jaw misses one of the carrying bars, and can prevent the engagement niechanisni as a whole sliding with respect to the body portions so that the locking member moves out of cooperation with the fixed jaw.

In order reduce the possibility that the locking pin does not properly cooperate with the fixed jaw when the engagement mechanism is in the second condition, due to fouling with debris such as building rubble, cement etc., preferably the locking member has a portion extending in a direction generally orthogonal to the common axis along which the moveable jaw and the locking member move, said portion being spaced apart from the end of the locking member remote from the moveable jaw, and the mechanical stop which defines the position of the locking member when the engagement mechanism is in the second condition is arranged to contact said portion of the locking member. Any debris on the side of the locking member remote from the moveable jaw thus cannot prevent movement of the locking member into cooperation with the fixed jaw. The potential for the locking member to become fouled is further reduced if the locking member and the mechanical stop which defines its position when the engagement mechanism is in thc second condition have respective flat surfaces which remain in contact over the whole pitch of movement of the locking member. This prevents debris interposing itself between that stop and the locking member.

The probability of debris preventing the locking member reaching its proper position against the sLop due to the presence of debris is further reduced if the extending portion of the locking member consists of two or more sub-portions which together contact less than the whole width of the stop when the engagement mechanism is in tile second condition. Such an arrangement reduces the probability that debris between the locking member and the stop will prevent the locking member reaching its proper position when the engagement mechanism. is in the second condition, because the area of contact between the locking member and the stop is reduced cotnpared to the case where the extending portion of the locking member contacts the full width of tile stop when the engagement mechanism is in the second condition.

The locking member preferably has a portion having a flat surface which is substantially parallel to the common axis, and wherein the fixed law and the locking member are arranged such that said fiat surface may be brought into contact with a carrying bar of an attachment located in the fixed jaw wheti the engagement mechanism is in the second condition. This ensures that a force exerted on the locking member by a carrying bar located in the fixed jaw when the engagement mechanism is in the second condition is substantially normal to the common axis. The force therefore does not tend to move the locking member out of position and puts no addition stress on the actuator or spring mechanism.

The spring mechanism preferably comprises a helical spring formed around telescopic core, which can extend or retract as the engagement mechanism switches between the first and second conditions. The telescopic core prevents the helical spring from deforming significantly.

The double-acting actuator mechanism is preferably a double-acting hydraulic actuator, providing for incorporation within the overall hydraulic system of a mechanical excavator, digger, hackhoe loader etc. Where the spring mechanism is a helical spring aronnd a telescopic former, the actuator and spring mechanism may be arranged so that they lie in a plane which is substantially parallel to the cylindrical axes of the fixed and movablejaws. This provides for the hitch coupler to assume a low profile, which saves material and overall weight, and is especially beneficial for base couplers, in which a digging bucket or other attachment may be rotated out of the plane of movement of the mechanical arm of an excavator. The spring mechanism may comprise two helical springs each mounted on a respective telescopic core, the helical springs and the double-acting hydraulic actuator lying in a plane substantially parallel to the cylindrical jaw axes of the fixed and moveahlc jaws, and wherein the helical springs lie on respective sides of the actuator.

lhc mass of the inoveable jaw may be greater than that of the locking member so that when the engagement mechanism is switched from the first to the second condition, the locking member moves to cooperate with the fixed jaw prior to movement of the moveable jaw. In this way the hitch coupler may be made to behave in the same way as many hitch couplers of the prior art. If moveable jaw is required to move prior to movement of the locking member, it may be arranged to have a smaller mass than that of the Locking member.

A sceond spring mechanism may be provided, which second spring mechanism includes a spring having a first end coupled to the locking member and a second end coupled to a mechanical stop fixed to or formed integrally with the body portion, the second spring mechanism being arranged to bias the locking member into cooperation with the fixed jaw to prevent removal of a carrying bar of an attachment when the carrying bar is located in the fixed jaw. The second spring mechanism ensures that [lie locking mechanism remains in cooperation with the fixed law in the event of failure of both the actuator mechanism and the (first) spring mechanism. Although in such an event an attachment may swing from one of its carrying bars, the second spring mechanisni ensures that it does not become completely detached from the hitch coupler. The actuator mechanism may be a double-acting hydraulic actuator, the second spring mechanism comprising two springs which are mounted on respective telescopic formers and which couple the locking member to respective mechanical stops (or the same mechanical stop) mounted on or forrncd inicgrallv with the body portion of the hitch coupler. The hydraulic actuator and the two springs of the second spring mechanism may lie in a plane substantially parallel to the cylindrical jaw axes of the fixed and ntoveable jaws, each spring being disposed on a respective side of the hydraulic actuator.

Enibodiinents of the invention are described below with reference to the accompanying drawings in which: Figure 1 shows a vertical section through a hitch coupler of the invention cngagcd with a digging bucket; Figure 2 shows a perspective view of the underside (in normal operation) of the Figure 1 hitch coupler; Figures 3 & 4 show detailed perspective views of one end of the Figure hitch coup icr; Figures 5 to 8 illustrate steps in the engagement of the Figure I hitch coupler with a digging bucket or oilier attachment; Figures 9 & 10 show a perspective view and vertical section respectively of a low-profile hitch coupler of the invention; Figure 11 shows a perspective view of another low-profile hitch couplet of the invention; and Figures 12 & 13 show a vertical section and a perspective view respectively of another example iLitch coupler of the invention.

Referring to Figures 1 to 4, a hitch coupler of rhe invention is indicated generally by 100 and comprises body portion 110 having a fixed cylindrical jaw 112 which is formed integrally with the body portion 110 and has a cylindrical jaw axis 113. The body portion 110 has a first 114 and second 116 pairs of apertures by which the hitch coupler 100 may be connected to the remote end of a mechanical excavator or similar equipment, so that the hitch coupler 100 may be rotated about an axis through the first pair 114 of apertures. The hitch coupler 100 further comprises a movable jaw 118 (having a cylindrical jaw axis 117) and a locking member 120 which are each mounted within, and for sliding engagement with, the body portion 110. Moveablc jaw 118 and locking member 120 are mounted for motion along a common axis 115. The fixed 112 and moveahle 11 8 jaws of the hitch coupler open in respecLive directions 111, 119 which are substantially anti-parallel and which are directed generally away from jaws 118. 112 respectively. The moveable jaw 118 and the locking tncrnbcr 120 are coupled together by a double-acting hydraulic actuator 122 and by a helical spring 132 mounted on a telescopic core 134. Mechanical stops 124, 126 define the limits of movement of the locking member 120 along the common axis 115 A mechanical stop 128 defines the limit of movement of the nioveable jaw 118 along the common axis in [lie direction of the ocking member 120. A further mechanical stop 130 attached to or formed integrally with the body portion 110 is provided on the body portion 110 to define the maximum extent of movement of the moveable Jaw 118 along the common axis in the direction away from the locking member 120 (i.e. general[y in the direction 119). The moveabk jaw ITS has a portion 125 which contacts the stop 130 to limit movement of the nioveable jaw 118, and of the engagement mechanism as whole, with respect to the body portion in the direction 119. In certain orientations of the hitch coupler, the stop 130 allows the actuator 122 to thrust against it to move the locking member 120 into cooperation with the fixed jaw 112. The double-acting hydraulic actuator 122 may be arranged to he controlled by a switch in the operating cab of a mechanical excavator comprising the hitch coupler 1 00. The actuator I 22 may conveniently be integrated into the overall hydraulic system of the mechanical excavator.

The moveable jaw 118, the locking nieLnher 120, the double-acting hydraulic actuator 122, the helical spring 132 and associated telescopic core 134 together comprise an eiigagenient mechanism allowing the hitch coupler 100 to be engaged and disengaged from an attachment. By suitable control of the actuator 1 22, the engagement mechanism may be switched between a first condition in which the moveable jaw 118 and locking member 120 have a lower separation, and a second condition in which the tuoveabie jaw 118 and locking member 120 have a higher separation and in which the locking member 120 cooperates with the fixed jaw 112 to prevent removal of a carrying bar located in the fixed jaw 112 (12 in Figure 1). In the first condition, the moveable jaw 118 and the locking meniber 120 rest against mechanical stops 128, 126 respectively, with the actuator 122 biasing the moveable jaw 118 and the locking member 120 towards each other against tEie force of the helical spring 134. Tn the second condition (shown in Figure 1), the actuator 122 biases the moveable jaw 118 and the locking member 120 apart, with the locking member 120 being forced against mechanical stop 124 and the moveable jaw being forced into engagement with the rear carrying bar 14 of the digging bucket 10 or other attachment. When the hitch coupler is engaged with an attachment such as the digging bucket 10, the helical spring 132 acts to bias the moveable aw 118 and the locking member 120 apart along the common axis 115 so that in the event of a loss of hydraulic pressure in the actuator 122, the movcable jaw 118 remains engaged with the rear carrying bar 14 and the locking member remains in cooperation with the fixed jaw 112 to prevent removal of the front carrying bar 12 therefrom.

Figure 1 shows the hitch coupler 100 in an engaged condition (i.e. with the engagement mechanism in the second condition) such that front 12 and rear [4 carrying bars of a digging bucket 10 are engaged respectively with the fixed 112 and moveable 118 jaws of the hitch coupler 100. In Figure 1, the fixed jaw 112 is engaged with the front carrying bar 12 of the digging bucket 10 so that most of the stress on the hitch coupler 100 during digging is taken by the fixed jaw 112, thus reducing stress on the actuator 122 and increasing the mean. time between thilures for this compocent...In normal usc of' a digging bucket such as 10, the carrying bar 12 is closest to the operating cab of a mechanical excavator. It is therefore usually known as front carrying bar; the other carrying bar is known as the rear carrying bar 14.

Figures 5 to 8 illustrate steps for engaging the hitch coupler 100 with the digging bucket 10. In Figure 5, the lnteh coupler 100 is positioned close 10 thc digging bucket 10, which rests on the ground. and the engagement mechanism of the hitch coupler is set to the first condition. The fixed jaw 112 of the hitch coupler is engaged with the front carrying bar 12 of the digging bucket 10 by suitable control of the arm of a mechanical excavator to which the hitch coupler 100 is attached. The hitch coupler 100 is then rotated counter-clockwise so that the underside of the body portion 110 contacts the rear carrying bar 14 as shown in Figure 6. The engagement mechanism is then set to the second condition, i.e. the actuator 122 is operated to force the moveahie jaw 118 and the locking member 120 apart, so that the locking member 120 cooperates with the Fixed jaw 112 to retain the front carrying bar 12 and Ihe rnovcable jaw 118 engages the rear carrying bar 14 (Figure 7). The hitch coupler 100 is then fully engaged and the digging bucket may be picked up and used for digging operations (Figure 8). In the event of failure of the actuator 122, the helical spring 134 ensures that the moveable jaw 118 and the locking member 120 remain in position (i.e. in the second condition). The hitch coupler 100 thus ensures that the bucket 10 does not drop to the ground, and/or swing dangerously from one carrying bar, in the event of failure of the actuator 120.

Referring again to Figures 3 and 4, Figure 3 shows the locking member 1 20 when the engagement mechanism is in the second condition and Figure 4 shows the locking member 120 when the engagement mechanism is in the first condition. The position of the locking member 120 when the engagement mechanism is in the second condition is defined by the mechanical stop 124. The locking member 120 has a portion comprising two sub-portions 121, 123 which extend generally orthogonally to the common axis 115 along which both the moveable jaw 118 and the locking member 120 slide. These portions contact the mechanical stop 124 when the engagement mechanism is in the second condition. The mechanical stop 124 has a flat upper surface which is contact with a flat lower surface of the locking member 120 over the whole pitch of thc movcment of the locking member 120. This reduces the probability of debris (building rubble, cement etc) becoming trapped between the locking member 120 and the mechanical, stop 124 thus preventing the locking mcinber 120 reaching the position defined by the stop 124. Iho two sub-portions 121, 123 have a combined extent in the width direction of the hitch coupler 100 (substantially parallel to the cylindrical axes 113, 117 of the jaws 112, 118) which is less than the width of the stop 124. This arrangenient further reduces the probability of debris becoming trapped between the locking member 120 and the stop 124.

Figures 9 and 10 show a perspective view and a vertical section respectively of a second hitch coupler the invention which is indicated generally by 200. Parts of the hitch coupler 200 corresponding to parts of the hitch coupler 100 of Figures 1-8 are labelled by reference numerals differing by 100 from the reference numerals labelling the correspotiding parts in Figures 1-8. The hitch coupler 200 has a spring mechanism which comprises two springs 226A. 2268 each of which is mounted on a respective telescopic former (not shown). The helical springs 226A, 2268 and the actuator 222 are arranged so that they lie in a plane which is substani ially çarallel to the cylindrical jaw axes 213, 217 of the fixed 212 and moveable 218 jaws of the hitch coupler 200, i.e. they arc disposed generally in a plane across the width dimension of the hitch coupler 200. The helical springs 226A, 2268 caeh lie on a respective side of the actuator 222.

Figure 11 shows another hitch coupler 300 of the invention. The hitch coupler 300 has an engagement mechanism comprising a doubEe-acting actuator 322 and a spring mechanism comprising a single helical spring mounted on a telescopic core, the actuator 322 and spring mechanism again being disposed in a plane substantially parallel to the cylindrical jaw axes 313, 317 of the fixed 312 and moveable 318 jaws.

The hitch couplers 200, 300 have low profiles compared to the hitch coupler 100 of Figure 1. They are particularly useful for use with base couplers. They also have the advantage that the body portions 210, 310 require less material than the body portion of t.hc hitch coupler 100. They are therefore lighter and cheaper to manufacture (for a given density and material cost per unit mass).

The body portions 110, 210, 310 of any of t]ie hitch couplers 100, 200, 300 may be provided with an additional stop defining the position of the moveabie jaws 118, 218, 318 ill tile second conditions of the respective engagement mechanisms (i.e. in the directions away from the locking members 120, 220, 320). Such a slop prevents excessive movement of the moveable jaw 118, 218, 318 with respect to the body portion, which could lead to damage of the double-acting actuator and/or disconnection of tile moveable jaw from the body portion. This may occur it' the hitch coupler is not properly aligned to an attachment so that the moveabie jaw does not engage with a carrying bar of the attachment as intended (i.e. as shown in Figure 6), In any of the hitch couplers 100, 200, 300 the moveahie jaw has a greater mass than the locking member. This provides br' the locking member to typically move first when t]ie engagement mechanism is switched from the first condition to the second condition, and thus allows a carrying bar to be locked into position in the fixed jaw of coupler prior to engagement of the moveable jaw with a second carrying bar. In tElis way the hitch coupler can be made to operate in the same way as most known hitch couplers.A hitch coupler of the invention therefore has the advantage that an operator of a mechan!ca] excavator fitted with the hitch coupler may carry out tasks witboi.mt the need for any special knowledge/skill or particuiar training or instructions going beyond those needed for operating conventional hitch couplers.

Figures 12 and 13 show a vertical section and a perspective view respectively of a further example hitch coupler 400 of the invention. The hitch coupler 400 comprises a second spring mechanism comprising springs 429A, 429B whicit couple locking member 420 to respective mechanical slops 440A, 4403 mounted on or formed integrally with body portion 410. Springs 429A, 4293 are each mounted on a telescopic former and lie in a plane which contains double-acting hydraulic actuator 422 and which is substantially parallel to cylindrical axes 413, 417 of fixed 412 and inoveable 418 jaws of the hitch coupler 400. Springs 426A, 4263 tend to bias apart fixed 412 and moveablc 418 jaws. Should the hydraulic actuator 422 and the springs 426A, 42613 fail, springs 429A, 4293 of the second spring mechanism will operate to bias locking member 420 into cooperation with fixed jaw 112, preventing release of a carrying bar of attachment from. th.c fixed jaw 112. Thus, even though an attachment may swing from one carrying bar thereof, it will not completely detach from the hitch coupler 400 in such an event.

Claims (1)

1. <claim-text>CLAIMS1. A hitch coupler comprising: a body portion providing a fixed jaw integrated with the body portion; an engagement mechanism comprising; a moveable jaw, having a jaw opening in a direction generally anti-parallel to that of the jaw opening of the fixed jaw; a locking member; a double-acting actuator mechanism and; a spring mechanism; wherein the actuator mechanism is arranged to switch the engagement mechanism between a first condition whereby the fixed and moveable jaws have a first separation and a second condition whereby said jaws have a second separation and the locking member cooperates with the fixed jaw to prevent IS removal of a carrying bar of an attachment when the carrying bar is present in the fixed jaw, and wherein the spring mechanism tends to bias the engagement mechanism to the second condition.</claim-text> <claim-text>2. A hitch coupler according to claim I wherein the jaw opening of each jaw faces away from the other jaw, and wherein the first separation of the fixed and moveabk jaws in the first condition of the engagement mechanism is less than the second separation thereof in the second condition of the engagement mechanism, and wherein the actuator mechanism and the spring mechanism each couple the moveable jaw to the locking member.</claim-text> <claim-text>3. A hitch coupler according to claim 2 wherein the moveable jaw and the locking member are slidably mounted on the body portion for movement on a common axis.</claim-text> <claim-text>4. A hitch coupler according to claim 3 wherein the respective positions of the locking member and of the moveable jaw when the engagement mechanism is in the first condition, and the position of the locking member when the engagement mechanism is in. the second condition, are defined by mcchanical stops mounted on the body portion.</claim-text> <claim-text>5. A hitch coupler according to claim 4 wherein the body portion further comprises a further mechanical stop defining the maximum extent of movement of the movable jaw with respect to the body portion in a direction away from the locking member.</claim-text> <claim-text>6. A hitch coupler according to any of claims 3 to S wherein the locking member has a portion extending in a direction generally orthogonal to said common axis, said portion being spaced apart from the end of the locking member remote from the moveabk jaw, and wherein the mechanical stop which defines Lhe position of the locking member when the engagement mechanism is in the second condition is arranged to contact said portion of the locking member.</claim-text> <claim-text>7. A hitch coupler accoiding to claim 6 wherein said niechanical stop and the locking member have respective flat surfaces which remain in contact over the whole pitch of movement of the locking member.</claim-text> <claim-text>8. A hitch coupler according to claim 6 or claim 7 whercin said portion of the locking member consists of two or more sub-portions which together contact less than the whole width of said mechanical stop, in a direction orthogonal thereto, when the engagement mechanism is in the second condition.</claim-text> <claim-text>9. A hitch coupler according to any of claims 3 to 8 wherein the locking member has a portion having flat surface which is substantially parallel to said common axis, and wherein the fixed jaw and the locking member are arranged such that said flat surface may be brought into contact with a carrying bar of an attachment located in the fixed jaw whcn the engagement mechanism is in the second condition.</claim-text> <claim-text>10. A hitch coupler according to any of claims 2 to 9 wherein the spring mechanism comprises a helical spring formed around a telescopic core.</claim-text> <claim-text>11. A hitch coupler according to any of claims 2 to 10 wherein the double-acting actuator mechanism is a double-acting hydraulic actuator.</claim-text> <claim-text>12. A hitch coupler according to claim 11 when dependent cii claim 10 wherein the helical spring and the double-acting hydraulic actuator lie in a plane substantially parallel to the cylindrical axes of the fixed and inoveable jaws.</claim-text> <claim-text>13. A hitch coupler according to claim 12 wherein the spring mechanism comprises two helical springs each mounted on a respective telescopic core, and wherein the helical springs and the double-acting hydraulic actuator lie in a plane substantially parallel to the cylindrical jaw axes of the fixed and nioveable jaws, and wherein the helical springs lie on respective sides of the actuator.</claim-text> <claim-text>14. A hitch coupler according to any of claim 3 to 13 wherein the inoveable jaw has a greater mass than the locking member.</claim-text> <claim-text>15. A hitch coupler according to any preceding claim further comprising a second spring mechanism which includes a spring having a first end coupled to the locking member and a second end coupled to a mechanical stop fixed to or formed integrally with the body portion, the second spring mechanism being arranged to bias the locking member into cooperation with the fixed jaw to prevent removal of a carrying bar of an attachment when the carrying bar is located in the fixed jaw.</claim-text> <claim-text>16. A hitch coupler according to claim 15 when dependent on claim 2, wherein the actuator mechanism comprises a double-acting hydraulic actuator coupling the moveable jaw to the locking member, and wherein the second spring mechanism comprises first and second springs each mounted on a respective telescopic former and coupling the locking member to a respective mechanica stop mounted on or formed integrally with the body portion, said actuator and said springs lying in a plane substantially parallel to the plane containing the cylindrical jaw axes of the fixed and mnoveable jaws and each spring being disposed on a respective side of said actuator.</claim-text> <claim-text>17. A hitch coupler substantially as described above with reference to Figures 1 to 1S A hitch coupler substantially as described above with reference to Figures 9 and 10.19. A hitch coupler subscancially as described above with reference to Figure 11.A hitch substantially as described above with reference to Figures 12 and 13.</claim-text>