A Coupler for Coupling an Attachment to a Dipper Arm

Abstract

A quick hitch coupler for coupling an attachment to a dipper arm of an excavator, the quick hitch coupler comprising: (a) a body member adapted for coupling to the dipper arm, (b) a fixed engaging jaw mounted on the body member for engaging a first one of a pair of coupling pins mounted on the attachment, (c) a movable engaging jaw mounted on the body member for engaging a second one of the pair of coupling pins of the attachment, the movable engaging jaw being movable between an engaged state with the movable engaging jaw engaging the second coupling pin while the fixed engaging jaw engages the first coupling pin for coupling the attachment to the coupler, and a disengaged state for disengaging the second coupling pin, (d) a latch co-operable with the fixed engaging jaw for retaining the first coupling pin of the attachment engaged in the fixed engaging jaw the latch being alternately operable in a latched state co-operating with the fixed engaging jaw for retaining the first coupling pin in the fixed engaging jaw, and an unlatched state for releasing the first coupling pin from the fixed engaging jaw, (e) an urging means for urging the latch into the latched state, (f) a release block being movable on (and relative to) a guide, the release block being movable on the guide between a non-active position in which the latch remains in the latched state and an active position where the release block abuts against the latch to move the latch from the latched state to the unlatched state against the urging action of the urging means, (g) a drive means generating an amount of displacement: (i) for moving the movable engaging jaw from the engaged state to the disengaged state, and (ii) for moving the release block on the guide from the non-active position to the active position.
The drive means generates an amount of displacement for moving the movable engaging jaw but the release block is not moved and a second stage where the drive means generates an amount of displacement for moving the movable engaging jaw above a threshold amount where the release block is moved.

Claims

1-23. (canceled)

24. A quick hitch coupler for coupling an attachment to a dipper arm of a machine, the quick hitch coupler comprising: a body member adapted for coupling to the dipper arm, a fixed engaging jaw mounted on the body member for engaging a first one of a pair of coupling pins mounted on the attachment, a movable engaging jaw mounted on the body member for engaging a second one of the pair of coupling pins of the attachment, the movable engaging jaw being movable between an engaged state with the movable engaging jaw engaging the second coupling pin while the fixed engaging jaw engages the first coupling pin for coupling the attachment to the coupler, and a disengaged state for disengaging the second coupling pin, a latch co-operable with the fixed engaging jaw for retaining the first coupling pin of the attachment engaged in the fixed engaging jaw the latch being alternately operable in a latched state co-operating with the fixed engaging jaw for retaining the first coupling pin in the fixed engaging jaw, and an unlatched state for releasing the first coupling pin from the fixed engaging jaw, an urging means for urging the latch into the latched state, a release block being movable on and relative to a guide, the release block being movable on the guide between a non-active position in which the latch remains in the latched state and an active position where the release block abuts against the latch to move the latch from the latched state to the unlatched state against the urging action of the urging means, a drive means generating an amount of displacement: for moving the movable engaging jaw from the engaged state to the disengaged state, and for moving the release block on the guide from the non-active position to the active position.

25. A quick hitch coupler according to claim 24 having a first stage where the drive means generates an amount of displacement for moving the movable engaging jaw but the release block is not moved and a second stage where the drive means generates an amount of displacement for moving the movable engaging jaw above a threshold amount where the release block is moved.

26. A quick hitch coupler according to claim 24 comprising attenuation means arranged to impart to the release block an amount of displacement that is attenuated relative to the amount of displacement generated by the drive means.

27. A quick hitch coupler according to claim 24 comprising biasing means arranged to act against the displacement generated by the drive means.

28. A quick hitch coupler according to claim 27 wherein the biasing means acts as attenuation means to impart to the release block an amount of displacement that is attenuated relative to the amount of displacement generated by the drive means.

29. A quick hitch coupler according to claim 24 wherein the drive means is an extendible actuator which instrokes in an instroke direction towards an instroked position and outstrokes in an outstroke direction towards an outstroked position, and wherein the displacement for moving the movable engaging jaw from the engaged state to the disengaged state, and for moving the release block on the guide from the non-active position to the active position is generated by the instroke action of the extendible actuator.

30. A quick hitch coupler according to claim 29 wherein biasing means biases the movable engaging jaw toward the engaged state against the instroke action of the extendible actuator.

31. A quick hitch coupler according to claim 24 wherein a first biasing means is provided on a first side of the release block and a second biasing means is provided on a second side of the release block.

32. A quick hitch coupler according to claim 31 wherein the second biasing means has a greater compressive strength than the first biasing means so as to attenuate the displacement of the release block.

33. A quick hitch coupler according to claim 31 wherein the first and second biasing means together act to urge the movable engaging jaw toward the engaged state against the action of the drive means.

34. A quick hitch coupler according to claim 31 wherein the displacement generated by the drive means displaces the release block by imparting the displacement to the first biasing means.

35. A quick hitch coupler according to claim 32 wherein the displacement generated by the drive means displaces the release block by imparting the displacement to the first biasing means and the second biasing means acts as attenuation means to impart to the release block an amount of displacement that is attenuated relative to the amount of displacement generated by the drive means.

36. A quick hitch coupler according to claim 31 wherein the first biasing means comprises a pair of springs and the second biasing means comprise a pair of springs.

37. A quick hitch coupler according to claim 24 wherein the guide on which the release block is movable extends from the movable engaging jaw to the fixed engaging jaw when the movable engaging jaw is the engaged state.

38. A quick hitch coupler according to claim 24 wherein the guide on which the release block is movable is a rail.

39. A quick hitch coupler according to claim 38 wherein the release block has a bore defined therein and is slidingly mounted on the rail with the rail extending through the bore, optionally wherein the release block has two bores defined therein and is slidingly mounted on a pair of rails with the rails extending through respective bores.

40. A quick hitch coupler according to claim 38 wherein the release block has a bore defined therein and is slidingly mounted on the rail with the rail extending through the bore.

41. A quick hitch coupler according to claim 38 including a biasing means and wherein the biasing means comprises at least one coil spring, and the coil spring is mounted on the rail with the rail extending through the centre of the coil spring.

42. A quick hitch coupler according to claim 41 wherein the biasing means comprises: a first coil spring, for example a first coil compression spring, provided on a first side of the release block and the first coil spring is mounted on the rail with the rail extending through the centre of the coil spring; and a second coil spring, for example a second coil compression spring, provided on a second side of the release block and the second coil spring is mounted on the rail with the rail extending through the centre of the coil spring.

43. A quick hitch coupler according to claim 24 wherein the guide on which the release block is movable is a rail and a bracket is provided on the movable engaging jaw which slides along the rail so that as the drive means generates an amount of displacement for moving the movable engaging jaw from the engaged state to the disengaged state, this displacement is transmitted along the rail to the release block, and is optionally transmitted along the rail by biasing means arranged to act against the displacement generated by the drive means.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

[0062] FIG. 1 is an exploded perspective view of a quick hitch coupler of the invention having a fixed engaging jaw for engaging a first one of a pair of coupling pins mounted on an attachment, and a movable engaging jaw mounted on the body member for engaging a second one of the pair of coupling pins of the attachment;

[0063] FIGS. 2 to 5 show a series of side sectional views of the quick hitch coupler of FIG. 1 moving from a working/engaged state (FIG. 2) in which it engages and retains an attachment (omitted for ease of illustration) for working the attachment and a release sequence (FIGS. 3 to 5) showing how it operates to safely release the attachment in a disengaged or release state (FIG. 5);

[0064] FIG. 6 shows a side view of a coupler of the invention in use attached to the dipper arm of a machine and with an attachment in the form of a bucket engaged correctly with the coupler;

[0065] FIG. 7 shows a side view of a coupler of the invention in use attached to the dipper arm of a machine and with an attachment in the form of a bucket engaged only in the fixed engaging jaw illustrating a partially attached condition of the attachment;

[0066] FIG. 8 shows a side view of a coupler of the invention in use attached to the dipper arm of a machine and in a crowded position with an attachment in the form of a bucket engaged only in the fixed engaging jaw and illustrating a condition in which the movable engaging jaw is moved so that the rear of the movable jaw abuts against the second pin; and

[0067] FIGS. 9 to 11 show a series of side sectional views of the quick hitch coupler of FIG. 1 moving from a working/engaged state (FIG. 9) in which it engages and retains an attachment (omitted for ease of illustration) for working the attachment and a release sequence (FIGS. 9 to 11) showing how it operates when opening movement is jammed as movement of the drive means is impeded by debris;

DETAILED DESCRIPTION OF THE DRAWINGS

[0068] The present invention will now be described with reference to the accompanying drawings which illustrate but do not limit the invention.

[0069] With reference to FIGS. 1 to 8 a quick hitch coupler according to the invention and indicated generally by the reference numeral 1 releasably hitches an attachment in the form of a bucket 2 to the dipper arm 3. The quick hitch coupler 1 is described in detail below. The dipper arm is typically connected to a working machine such as an excavator/digger by a boom arm operated by boom operating rams. A dipper arm operating ram typically operates between the boom and the dipper arm. The movement of the quick hitch coupler 1 relative to the dipper arm 3 is controlled by a hydraulic ram. The operation of a boom and dipper arm of such earth working apparatus is well known to those skilled in the art, as is the attachment of a coupler to a dipper arm and it is not intended to describe this further.

[0070] A bushed bore extending through the dipper arm 3 at the distal end thereof accommodates a connector pin 4 for pivotally connecting the quick hitch coupler 1 to the dipper arm 3. A connector pin 5 is for connecting the quick hitch coupler 1 to an operating ram typically via a linkage.

[0071] A pair of coupling pins, namely, a first coupling pin 10 and a second coupling pin 11 are provided on the bucket 2, or indeed, on any other attachment to be connected to the dipper arm 3 for engagement with the quick hitch coupler 1 as will be described below.

[0072] The quick hitch coupler 1 of the invention comprises a body member 12 formed by a pair of spaced apart side plates 13 of steel and a transversely extending connector plate 14 (not shown in FIG. 1 for ease of showing other parts of the coupler 1) also of steel extending between the adjoining side plates 13. The side plates 13 each comprise a main side plate 13a and reinforcing side plates 13b and 13c welded together, however, for convenience the combination of the main and reinforcing side plates 13a, 13b and 13c are referred to as the side plates 13.

[0073] A pair of connector members 15 and 16 of steel plate extend between the side plates 13 at opposite ends of the side plates 13 for reinforcing the body member 12. The connector plate 14 and the connector members 15 and 16 are welded to the side plates 13.

[0074] A connecting means for connecting the quick hitch coupler 1 to a machine including a dipper arm 3 comprises a first pair of bushed bores 17 which extend through the respective side plates 13 and a second pair of bushed bores 18 which extend through the respective side plates 13. The bushed bores 17 in the side plates 13 are aligned with each other for engagement with the connector pin 5. The bushed bores 18 in the respective side plates 13 are aligned with each other for in turn alignment with the bushed bore through the dipper arm 3 for engagement with the connector pin 4. In this way the quick hitch coupler 1 can be connected to the dipper arm 3.

[0075] The side plates 13 define a pair of fixed jaws 20 for forming a fixed engaging means for engaging the first coupling pin 11 of the bucket 12. The jaws 20 define an open mouth 21 which faces outwardly of the quick hitch coupler 1 for receiving the (first) coupling pin 11.

[0076] A lock or latch 30 is pivotally mounted between the side plates 13. A pin 32 extends through bores 31 in the lock 30 and corresponding bores 19 in the side plates 13. A pair of locking rings 33 (only one shown in FIG. 1) respectively engage within grooves 34 to hold the pin 32 and lock 30 in place.

[0077] The latch 30 is pivotally carried on the pin 32. The latch 30 is urged into a latched state by urging means in the form of a (double) torsion spring 36 which is also mounted on pin 32. The torsion spring 36 acts between the latch 30 and the connector member 15.

[0078] The latch 30 is pivotal between a latched state illustrated in FIGS. 2 to 4 and FIGS. 6 to 8 co-operating with the fixed jaws 20 for extending across the open mouth 21 defined by the jaws 20 for retaining the (first) coupling pin 10 within the jaws 20, and an unlatched state illustrated in FIG. 5 for releasing the first coupling pin 10 from the fixed jaws 20 through the open mouth 21. As above the torsion spring 36 urges the latch 30 toward the latched state.

[0079] A pair of movable engaging jaws 40 are provided by a movable engagement member 41 is slideably carried in the body member 12. By virtue of movement of the movable engagement member 41 the engaging jaws 40 are slideable between an engaged state illustrated in FIGS. 2 to 4 and FIGS. 6 to 8 for engaging the second coupling pin 11 of the bucket 2, and a disengaged state illustrated in FIG. 5 for disengaging the second coupling pin 11 for releasing the bucket 2 from the coupler 1. Guide tracks 42 mounted on opposite sides of the movable engagement member 41 slideably engage corresponding guide grooves on the respective inside walls of the side plates 13. This track and groove arrangement is for guiding the movable engagement member 41 and thus the fixed jaws 40 between the engaged and disengaged states with rectilinear motion.

[0080] The jaws 40 extending from the movable engagement member 41 define an open mouth 44 for accommodating the second coupling pin 11 into and between the jaws 40. The open mouth 44 faces outwardly of the coupler 1 in a direction opposite to the direction in which the open mouth 21 defined by the fixed jaws 20 faces.

[0081] Accordingly, when the movable engagement member 41 and jaws 40 are in the engaged state the first and second coupling pins 10 and 11 are securely engaged between the fixed jaws 20 and the (movable engaging) jaws 40 respectively.

[0082] A drive means of the quick hitch coupler 1 comprising a hydraulically operated double acting ram 50 acts between the movable engagement jaws 40 and the latch 30 for urging the movable engagement jaw 40 between the engaged and disengaged states, and for moving the latch 30 between the latched and the unlatched states. The coupler ram 50 comprises a ram housing 51 and a piston rod 52 extending from the ram housing 51.

[0083] A pair of trunnions 54 extending transversely from one end of the ram housing 51 slideably engage corresponding longitudinally extending guide grooves 55 in the side plates 13 for facilitating longitudinal movement of the trunnions 54, and in turn the ram housing 51 in the body member 12. An end 56 of the piston rod 52 is connected to the movable engagement jaw 40 for urging the movable engagement jaw 40 between the respective engaged and disengaged positions. In particular a locking bolt 46 with a washer 47 extends through a bore 45 in the movable engaging jaw 40 so that the locking bolt attaches the movable engaging jaw 40 to the end 56 of the piston 52.

[0084] On the closed end 57 of the ram housing 51 is provided a stop 58. The stop 58 abuts against the latch 30 and prevents it from opening when the ram 50 is fully extended. This position of the stop 58 abutting the latch 30 is shown in FIGS. 2, 6 and 8. The stop 58 can be designed to engage within a socket 35 of the latch 30. This aids in preventing the latch 30 from unlatching. It will be appreciated that in FIGS. 2, 6 and 8 opening of the latch 30 is prevented by the resistance of the torsion spring 36 and also by the ram 50, and in particular stop 58, which abuts the latch 30 preventing it from opening. The tension in the torsion spring 36 is sufficiently strong to retain the latch 30 in the latched state unless the latch 30 is positively urged from the latched state by the release block 61. Furthermore, as mentioned above, in the fully extended position of the ram 50 the stop 58 on the ram 50 also prevents opening of the latch 30.

[0085] The quick hitch coupler 1 of the invention further comprises a motion delay or attenuation mechanism 60 while being imparted with the latch urging action, delays transmission of the latch urging action to the latch 30. The attenuation mechanism 60 has a latch urging action imparted to it by the drive means in the form of the ram 50. In particular, a release block 61 of the attenuation mechanism 60 has a latch urging action imparted to it by the ram 50. A hydraulic port block 53 on the ram housing 51, connects to the hydraulic system of the excavator for supplying hydraulic fluid to the hydraulic ram to power it both for extension and retraction in a manner conventional for a double-acting ram.

[0086] The release block 61 is slidable relative to the body member 12 as it is provided in a sliding arrangement on a pair of (rounded) rails, 63. The rails 63 have a first end 65 which engage within and extend through respective bores 64a in an endstop 64.

[0087] The respective ends 65 of the rails 63 extend though respective bores 48a in respective fixing brackets 48. The fixing brackets 48 are fixed to the movable engagement jaw 40 by locking bolts 49 which extend through respective bores 49a and engage with bores 43 in the movable engagement jaw 40. Pins 65 hold the respective ends 65 of the rails 63 in place relative to the body member 12.

[0088] The other ends 69 of the rails extend into bores 23 in connector member 15.

[0089] In this arrangement the endstop 64 and the rails 63 remain stationary while the movable engagement jaw 40 (by means of brackets 48) and the release block 61 are also slidable back and forth along the rails 63.

[0090] Also mounted on respective rails 63 are a pair of longer compression springs 67 on the same side of the release block 61 as the movable engagement jaw 40 and a pair of shorter compression springs 69 on the same side of the release block 61 as the fixed jaws 20.

[0091] The longer compression springs 67 are on the opposite side of the release block 61 to the pair of shorter compression springs 68. Thus a first biasing means is provided on a first side of the release block 61 and a second biasing means is provided on a second side of the release block 61.

[0092] The movable release block 61 is for abutting against the latch 30 to move the latch to an unlatched state.

[0093] It will be noted that for the ram 50 to instroke towards a retracted position it must pull movable engagement jaw in an instroke direction indicated by arrow I. To do so it must compress the springs 67 and 68 as will be described in more detail below.

[0094] The attenuation mechanism 60 delays transmission of the latch urging action to the latch 30 by delaying abutment of the movable release block 61 against the latch 30.

[0095] The (reversible) sequence for releasing the bucket 2 from the quick hitch coupler 1 by moving the movable engaging jaw from an engaged state (e.g. shown in FIG. 2) with the movable engaging jaw 40 engaging the second coupling pin while the fixed engaging jaw 20 engages the first coupling pin for coupling the attachment to the coupler, and a disengaged state (e.g. shown in FIG. 5) with the movable engaging jaw 40 disengaging the second coupling pin, and the latch 30 being alternately operable in a latched state co-operating with the fixed engaging jaw 20 for retaining the first coupling pin 10 in the fixed engaging jaw 20, and an unlatched state for releasing the first coupling pin 10 from the fixed engaging jaw 20, is shown in FIGS. 2 to 5. It will be appreciated that the reverse sequence from FIG. 5 to FIG. 2 can be used to couple to the bucket 2.

[0096] In FIGS. 2 to 5 the pins 10 and 11 and the bucket 2 are omitted for ease of illustration.

[0097] In FIG. 2 the ram 50 is fully extended or outstroked. In this configuration the movable engaging jaw 40 is in its fully engaged state for engaging pin 11. Furthermore the latch 30 is in its latched state co-operating with the fixed engaging jaw 20 for retaining the first coupling pin 10 in the fixed engaging jaw 20.

[0098] The piston rod 52 is fully extended and this has caused the ram housing 51 and in particular trunnions 54 to slide within body member 12 until the end 57 of the ram housing 51 and in particular the stop 58 on the ram housing 51, engages with or against the latch 30 preventing it from rotating about pin 32 and thus preventing it from unlatching.

[0099] Furthermore the release block 61 is spaced apart from the latch 30 so it does not act upon the latch 30. The release block is thus in a passive position.

[0100] The latch 30 is also being biased toward its latch position by the torsion spring 36.

[0101] FIG. 2 shows a working configuration of the quick hitch coupler 1, a configuration where the coupler is attached to an attachment and is ready to work.

[0102] FIG. 3 shows a first stage in the sequence. In FIG. 3 the operator has initiated a quick coupler release sequence.

[0103] It will be appreciated, that, as is desirable, the operator may have to first place the coupler and attachment in a position where release is possible such as a crowded position and with the attachment on the ground. To achieve this a control system such as is described in EP1637659 to Geith International the entire contents of which are incorporated herein by reference, may be employed. This ensures that the release sequence can only be initiated when the attachment is in a safe position for release.

[0104] As can be seen from FIG. 3 in this first stage as power is transmitted to the ram 50 to instroke, the piston rod 52 retracts into the ram housing 51. This has the effect of pulling ram housing 51, and end 57 thereof with stop 58, away from latch 30 by sliding of trunnions 54 within the body member 12. Movable engaging jaw 40 remains in the position shown in FIG. 2. The latch 30 remains in its latched position because of torsion spring 36. Release block 61 remains in the position shown in FIG. 2.

[0105] As can be seen from FIG. 4 as further power is transmitted to the ram 50 to instroke, the piston rod 52 further retracts into the ram housing 51. This has the effect of pulling ram housing 51, and end 57 thereof with stop 58, further away from latch 30 until the trunnions 54 reach their limit of movement. Once trunnions 54 reach their limit of movement the ram housing 51 no longer moves and instead piston rod 52 moves by retracting into the ram housing 51. Movable engaging jaw 40 is now pulled away from the position shown in FIG. 2 as guide tracks 42 slide within the body member 12. This in turn moves brackets 48 which compress springs 67 against release block 61. In turn release block 61 compresses springs 68. The net effect is that as the piston rod 52 further retracts into the ram housing 51 release block 61 is moved along rails 63 until it becomes active and it abuts latch 30. In FIG. 4 the latch 30 remains in its latched position because of torsion spring 36. Release block 61 abuts latch 30.

[0106] As can be seen from FIG. 5 as yet further power is transmitted to the ram 50 to instroke, the piston rod 52 further retracts into the ram housing 51. Movable engaging jaw 40 is now pulled further away from the position shown in FIG. 2 as guide tracks 42 slide within grooves 25 in the body member 12. This in turn moves brackets 48 which further compress springs 67 against release block 61. In turn release block 61 further compresses springs 68. The net effect is that as the piston rod 52 further retracts into the ram housing 51 release block 61 becomes active and it is moved along rails 63 until it opens latch 30. It does so by acting against and overcoming the biasing action of torsion spring 36.

[0107] Within this sequence it is only in the configuration of FIG. 5 that an attachment can be completely released from the quick hitch coupler 1.

[0108] It will be appreciated that by reversing the sequence from FIG. 5 to FIG. 2 an attachment can be coupled to a quick hitch coupler 1 of the invention.

[0109] FIG. 6 (partially) shows coupling pins 10 and 11 of a bucket 2 coupled to a quick hitch coupler 1 of the invention which is also shown attached to a dipper arm 3. (Hydraulic cylinders/linkage for attaching to pin 5 have been omitted for ease of illustration.)

[0110] FIGS. 7 and 8 show what happens when an operator unsuccessfully follows a coupling sequence. In this arrangement the operator has successfully coupled pin 10 within the fixed jaw 20. However the operator has missed pin 11 and has outstroked ram 50 to such a point that movable engaging jaw 40 has passed by pin 11. In summary the operator has missed catching the pin 11 with the movable engaging jaw 40 but movable engaging jaw 40 has now been extended too far and must be retracted in order to try again to couple to pin 11.

[0111] Because of a control system of the invention the operator must now follow a release sequence by first placing the arm and bucket/coupler in a release position as shown for example in FIG. 8.

[0112] As can be seen from FIG. 8 the pin 11 has now become trapped or engaged behind a rear side 39 of the movable engaging jaw 40. This means that as the operator instrokes the ram 50 that instead of jaw 40 retracting, jaw 40 jams in place behind pin 11 and ram housing 51 slides along as trunnions 54 slide within the body member. This is the condition described above where in the coupler of European patent EP 1637659 this can cause the ram to pull open the latch and then the force of the rear side 39 of the movable engaging jaw 40 acting against the pin 11 would push pin out of jaw 20 thus allowing the attachment to be ejected unintentionally from the coupler.

[0113] However with the quick release coupler of the present invention and even if the condition shown in FIG. 8 arises the attachment will never be ejected unintentionally in this manner as the release block will not unlatch the latch in such circumstances.

[0114] FIGS. 9 to 11 show a series of side sectional views of the quick hitch coupler 1 of FIG. 1 moving from a working/engaged state (FIG. 9) in which it engages and retains an attachment (omitted for ease of illustration) for working the attachment and a release sequence (FIGS. 10 and 11 in particular) showing how it operates when opening movement is jammed as movement of the drive means is impeded by debris.

[0115] The coupler 1 is as described above. However in this case the sequence shows what happens when the trunnions 54 can no longer move due to debris 59 (indicated by hatching) within grooves 55.

[0116] As can be seen from FIG. 10 in this first stage as power is transmitted to the ram 50 to instroke, the piston rod 52 retracts into the ram housing 51. Because of the debris 59 the effect of pulling ram housing 51, and end 57 thereof with stop 58, away from latch 30 by sliding of trunnions 54 within the body member 12 does not occur. Instead the ram housing 51 does not move and the movable engaging jaw 40 moves. (This is in contrast to the normal sequence where there is no debris, for example as shown in FIG. 2, where the movable engaging jaw 40 remains in the position shown in FIG. 2 as movement of the trunnions is allowed.) In FIG. 10 the latch 30 remains in its latched position because of torsion spring 36. Release block 61 moves toward and abuts the latch 30 as shown in FIG. 10. (Again this in contrast to the normal sequence.) Movable engaging jaw 40 has now pulled away from the position shown in FIG. 9 as guide tracks 42 slide within the body member 12. This in turn moves brackets 48 which compress springs 67 against release block 61. In turn release block 61 compresses springs 68. The net effect is that as the piston rod 52 further retracts into the ram housing 51 release block 61 is moved along rails 63 until it becomes active and it abuts latch 30. Because of the jammed condition the release block has become active earlier than would otherwise occur. Also because of the jammed condition the ram housing 51, and end 57 thereof with stop 58, stays in position abutting latch 30 and preventing it from opening.

[0117] The coupler 1 is now operating to try to open the latch 30 and hold the latch 30 in a latched position at the same time which has the potential to cause overload forces.

[0118] As can be seen from FIG. 11 as further power is transmitted to the ram 50 to instroke, the piston rod 52 further retracts into the ram housing 51. This increases the opening force being applied to the latch 30 by the release block 61 but because of the jammed condition the ram housing 51, and end 57 thereof with stop 58, stays in position abutting latch 30 and preventing it from opening.

[0119] The net result is that because of the jammed condition the latch 30 does not open so the attachment cannot be released. The opening force being applied on the latch 30 by the release block 61 is resisted by the ram housing 51, and end 57 thereof with stop 58, stays in position abutting latch 30 and preventing it from opening. The opening force could potentially cause damage trying to move the latch 30 which is locked in position. Instead because of the use of the release block the opening force can be attenuated/dissipated taken by the biasing means.

[0120] The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0121] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.