AU2012201264B2 - A safety mechanism for a coupler for coupling an accessory to a dipper arm - Google Patents

Abstract

Disclosed is a coupler and safety mechanism therefor, for coupling an accessory to a 5 dipper arm of a vehicle such as an excavator. In one form, there is disclosed a quick hitch coupler for coupling an accessory to a dipper arm of a back actor, the quick hitch coupler comprising: a body member adapted for coupling to the dipper arm; a fixed engagement means mounted on the body member for engaging a first one of a 10 pair of coupling pins mounted on the accessory; a moveable engaging means mounted on the body member for engaging a second one of the pair of coupling pins of the accessory; the moveable engagement means being moveable between an engaged state with the moveable engagement means engaging the second coupling pin while the fixed 15 engagement means engages the first coupling pin for coupling the accessory to the coupler, and a disengaged state for disengaging the second coupling pin; a latching means co-operable with the fixed engagement means for retaining the first coupling pin of the accessory engaged in the fixed engagement means, the latching means being alternatively operable in a latched state co-operating with the fixed 20 engagement means for retaining the first coupling pin in the fixed engagement means, and an unlatched state for releasing the first coupling pin from the fixed engagement means; a first biasing means for biasing the latch into the latched state; a drive means acting between the moveable engagement means and the latch for urging 25 the moveable engagement means between the engaged state and the disengaged state, and for urging the latch from the latched state to the unlatched state against the biasing action of the biasing means when the moveable engagement means is in the disengaged state; and characterised by the coupler further comprising: a safety means comprising at least one second biasing means coupled to the moveable 30 engagement means, the second biasing means urging the moveable engagement means into the engaged state. "~'17-. -V J 'DO c-

Description

Regulation 3.2 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant: Geith International Ltd Actual Inventors: Martin McCormack Tony McKeown Address for Service: C/- MADDERNS, GPO Box 2752, Adelaide, South Australia, Australia Invention title: A SAFETY MECHANISM FOR A COUPLER FOR COUPLING AN ACCESSORY TO A DIPPER ARM The following statement is a full description of this invention, including the best method of performing it known to us.

2 Title A safety mechanism for a coupler for coupling an accessory to a dipper arm 5 Field of the Invention The present invention relates to a safety mechanism for a coupler for coupling an accessory to a dipper arm of a back actor of, for example, an earth working apparatus, and in particular a coupler of the type generally referred to as a quick hitch coupler. 10 Background to the Invention Coupling devices for coupling accessories to a hydraulically operated arm of an excavator are well known. These devices typically are used to attach different types of 15 attachments to a dipper arm of an excavator, for example to attach different sizes of buckets or a jack hammer or other such implements to the excavator. The coupling device (also commonly referred to as a "coupler" or "quick hitch") is usually releasably attachable to both the (dipper) arm of the excavator and the 20 accessory. The coupler is adapted for attachment to the arm, and normally would remain on the arm and be utilised to interchangeably work different attachments on the arm. A coupler typically includes a body member which is adapted for coupling to the dipper arm, and a pair of engagement members for releasably engaging a pair of spaced apart 25 first and second coupling pins located on the accessory. One of the engagement members is moveable while the other engagement member is fixed. The moveable engagement member typically is moveable relative to the fixed engagement member between an engaged state, with the pair of engagement members co-operating with each other for engaging the first and second coupling pins of the accessory for coupling the 30 accessory to the dipper arm, and a disengaged state for disengaging the coupling pins for releasing the accessory from the dipper arm. Typically, the moveable one of the engagement members is either slideable or pivotally carried in the body member and is moveable between the engaged and disengaged states by a hydraulic ram. However, any other drive means could equally well be used instead of a hydraulic ram, such as a 3 mechanical drive means. The engagement members most usually are formed by a set of jaws, typically at least two jaws. It will be appreciated that should the hydraulic fluid supply to the hydraulic ram driving 5 the moveable engagement member fail when the moveable engagement member is in the engaged position, it may cause the moveable engagement member to return to its disengaged state. As a result, safety mechanisms may be associated with the engagement members in order to prevent the accidental release of an accessory from the coupler should such a failure occur. 10 The safety mechanism for the fixed engagement member may be provided by a biasing means which biases the fixed engagement member towards engagement with the first coupling pin of the accessory. This can for example take the form of a spring, which acts through the hydraulic ram which drives the moveable engagement member to its 15 disengaged state to bias the fixed engagement member into the engaged position. Typically this safety mechanism can only be retracted by being actively driven by this ram. Therefore, the safety mechanism ensures that the fixed engagement member is biased towards the first coupling pin should a loss of pressure occur in the ram. 20 It will be appreciated that a safety mechanism should ideally also be associated with the moveable engagement member, in order to prevent the moveable engagement member from moving towards the disengaged state should a loss of pressure occur in the ram. One known means of implementing this safety mechanism is by providing a hook on the outer edge of the jaws of the moveable engagement member, such as for example the 25 hook described in UK Patent No. GB 2 205 299 in the name of J. Balemi. Should the moveable engagement member move towards the disengaged state due to a sudden loss of hydraulic pressure in the ram driving the moveable engagement member, the second coupling pin should move onto the hook, which then acts as a seat to retain the second coupling pin in contact with the moveable engagement member. Accordingly, the hook 30 is intended to secure the second coupling pin in a safe position should a hydraulic failure occur, by preventing the second coupling pin from swinging free of the moveable engagement member and allowing the accessory to rotate dangerously.

4 However, under some circumstances, it has been found that the hook of the moveable engagement member does not manage to achieve its intended purpose. For example, should the excavator operator continue to work extensively with an accessory coupled to the coupler, the shock forces exerted during the digging operation in certain 5 orientations may result in the second coupling pin losing contact with the hook, such that the second coupling pin swings out of contact with the moveable engagement member, while the first coupling pin is retained in the fixed engagement member through the biasing action of the spring associated with the safety mechanism of the fixed engagement member. This is particularly likely to occur when the coupler is in a 10 vertical position, with gravity acting on the moveable engagement member to move it downwards and away from the second coupling pin. It will be appreciated that if this loss of contact between the second coupling pin and the moveable engagement member were to occur when the accessory is in an elevated state with a person standing beneath it, the accessory could swing and impact with the person, thus leading to fatal injuries. 15 Object of the Invention The present invention is directed towards providing a quick hitch coupler with a safety mechanism associated with the moveable engagement member that overcomes the 20 disadvantages of existing quick hitch couplers, in particular by preventing the coupler from disengaging in potentially dangerous circumstances. The invention is also directed towards providing a safety mechanism associated with the moveable engagement member of a quick hitch coupler that is suitable for use in the 25 extreme operating conditions associated with an excavator. Such operating conditions include dirt ingress, as well as impact from stones, clay and concrete. The invention is also directed towards providing a safety mechanism associated with the moveable engagement member of a quick hitch coupler that can also be safely installed 30 onto and removed from the quick hitch coupler. The invention is also directed towards providing a safety mechanism associated with the moveable engagement member of a quick hitch coupler which can be used with variable 5 pin centre quick hitch couplers i.e. those couplers which can accommodate accessories of varied spacing between the first and second coupling pins. Summary of the Invention 5 The present invention provides a quick hitch coupler for coupling an accessory to a dipper arm of a back actor, the quick hitch coupler including: a body member adapted for coupling to the dipper arm; a fixed engagement means mounted on the body member for engaging a first one of a pair of coupling pins mounted on the accessory; 10 a moveable engaging means mounted on the body member for engaging a second one of the pair of coupling pins of the accessory; the moveable engagement means being moveable between an engaged state with the moveable engagement means engaging the second coupling pin while the fixed engagement means engages the first coupling pin for coupling the accessory to the 15 coupler, and a disengaged state for disengaging the second coupling pin; a latching means co-operable with the fixed engagement means for retaining the first coupling pin of the accessory engaged in the fixed engagement means, the latching means being alternatively operable in a latched state co-operating with the fixed engagement means for retaining the first coupling pin in the fixed engagement 20 means, and an unlatched state for releasing the first coupling pin from the fixed engagement means; a first biasing means for biasing the latch into the latched state; a drive means acting between the moveable engagement means and the latch for urging the moveable engagement means between the engaged state and the 25 disengaged state, and for urging the latch from the latched state to the unlatched state against the biasing action of the biasing means when the moveable engagement means is in the disengaged state; and wherein the coupler further includes: at least two safety means each including at least one further biasing means coupled to the moveable engagement means, wherein the secondary biasing means is for 30 urging the moveable engagement means into the engaged state. The movement of the drive means to urge the moveable engagement means to the disengaged state may move the secondary biasing means against its respective urging action from a first state to a second state. 35 6 The respective secondary biasing means of said at least two safety means may be a compression spring, and the first state is an uncompressed state and the second state is a compressed state. 5 Said at least two safety means may further include: a supporting means located internally of the further biasing means and extending beyond the ends of the further biasing means, the supporting means connected to the body member; and an abutment member in contact with the further biasing means, the abutment 10 member connected to the moveable engagement means and the supporting means, wherein movement of the drive means to urge the moveable engagement means towards the disengaged state causes the abutment member to move along the length of the supporting means so as to move the further biasing means in contact with the abutment member from the uncompressed state to the compressed state. 15 For each of said at least two safety means the abutment member may further include a connecting member, and wherein the connecting member is connected to the moveable engagement means by means of an aperture provided in the moveable engagement means. 20 For each of said at least two safety means each end of the supporting means may be secured to the body member. For each of said at least two safety means the supporting means may be secured to the 25 body member at one end by a securing means including a nut with a collar portion, wherein the supporting means is secured to the body member by locating the collar portion of the securing means within a receiving aperture provided on the body member. The receiving aperture may be provided on a cross plate member of the body member. 30 The supporting means may be secured at its other end to the body member within a recess provided on the body member. 35 Brief Description of the Drawings 7 Figure 1 is an outline perspective view of an earth working apparatus having a back actor mounted thereto and an excavator bucket hitched to a dipper arm of the back actor by a quick hitch coupler; 5 Figures 2a and 2b are cut-away side elevational views of the quick hitch coupler of Figure 1 when the moveable engagement member of the quick hitch coupler is in the engaged position; Figures 3a and 3b are cut-away side elevational views of the quick hitch coupler of 10 Figure 1 when the moveable engagement member of the quick hitch coupler is in the disengaged position; Figure 4 is a cut-away perspective view of the quick hitch coupler of Figure 1; 15 Figure 5a is a perspective view of the safety mechanism of the present invention; Figure 5b is an exploded view of the safety mechanism of Figure 5a; Figure 6a is a side elevational view of the safety mechanism of the present invention 20 prior to assembly to the quick hitch coupler of Figures 2a and 2b; Figure 6b is a perspective view of the safety mechanism of the present invention prior to assembly to the quick hitch coupler of Figures 2a and 2b; 25 Figure 7a is a cut-away side elevational view of the quick hitch coupler with the safety mechanism of the present invention assembled thereto when the coupler is in the disengaged position; Figure 7b is a perspective view of a portion of the coupler with the safety mechanism of 30 the invention assembled thereto when the coupler is in the disengaged position; 8 Figure 8a is a cut-away side elevational view of the quick hitch coupler with the safety mechanism of the present invention assembled thereto when the coupler is in the engaged position; and 5 Figure 8b is a perspective view of a portion of the coupler with the safety mechanism of the invention assembled thereto when the coupler is in the engaged position. Detailed Description of the Drawings 10 The present invention will now be described with the aid of the accompanying drawings. Figure 1 shows an earth working apparatus 1 which may be used with the quick hitch 15 coupler of the invention. The apparatus 1 includes a main housing 2 mounted on a sub housing 5 which is rotatably carried on a main chassis 3. A back actor arm 8 is mounted on the sub-chassis 5 and includes a boom 9 which is pivotally connected to the sub chassis 5 and extends upwardly therefrom. A dipper arm 10 is pivotally carried on the boom 9 for in turn pivotally carrying an accessory or attachment. The dipper arm 10 20 enables attachment of accessories by means of a pair of mounting linkages 22 extending from a connecting linkage 18 connected to its distal end. The mounting linkages 22 terminate in bushed bores for pivotally connecting an accessory to the dipper arm 10 through a pair of connector pins. 25 In order to provide a quicker and easier coupling of accessories to the dipper arm 10 than that which is possible through direct attachment of an accessory to the dipper arm 10, a quick hitch coupler 14 is used. The quick hitch coupler 14 is coupled to the dipper arm 10 by means of the mounting linkages 22. An accessory (such as a bucket) can then be coupled indirectly to the dipper arm 10 by means of the quick hitch coupler 14. 30 Referring now in particular to Figures 2 to 4, the quick hitch coupler 14 according to one embodiment of the invention includes a body member 35 formed by a pair of spaced apart side plates 36 of steel having a pair of fixed jaws 45 and a safety 9 mechanism 76, and a transversely extending connector plate 37, also of steel, extending between the adjoining side plates 36. A pair of connector members 38 and 39 extend between the side plates 36 for reinforcing the body member 35. In the described embodiment, the connector members are welded at opposing ends of the side plates 36, 5 with connector member 39 also connected to one end 96 of connector plate 37. The connector plate 37 is provided at its other end 97 with an upstanding cross plate member 87. The cross plate member 87 is provided with three spaced apart slotted apertures 88a, 88b, and 88c. Slotted aperture 88a and 88c are adapted for receiving the safety mechanism of the invention, as will be explained in further detail below. 10 A fitting plate 72 is coupled to each respective side plate 36 to enable the coupling of the quick hitch coupler 14 to the dipper arm 10. The connecting means for connecting the quick hitch coupler 14 to the dipper arm 10 and the mounting linkages 22 includes a pair of bushed bores 40 and 41, which extend through the respective fitting plates 72. 15 The bushed bores 40, 41 are aligned with each other for in turn aligning with the bushed bores in the mounting linkages 22 of the dipper arm 10 for engagement with the pair of connector pins for coupling the coupler 14 to the dipper arm 10. The side plates 36 define corresponding pairs of fixed jaws 45 for forming a fixed 20 engagement member for engaging the first coupling pin 30 of an accessory. The jaws 45 define an open mouth 47 which faces outwardly of the quick hitch coupler 14 for receiving the first coupling pin 30. Slotted aperture 88b of the cross plate member 87 is adapted for receiving one end 93 of 25 a spring 53. The other end 94 of spring 53 is loaded against the body 71 of a hydraulic ram. A pivoting latching means 50 formed by a pair of latches is mounted between and supported on the coupler body side plates 36 by a pivot pin 89a. A pair of linkage plates 90 are connected to each latch by means of another pivot pin 89b. The linkage plates 90 are also connected to trunnions 91 provided on the ram body 71. The latching means 50 30 is pivotal between its latched state, as illustrated in Figures 2a and 2b, where it co operates with the fixed jaws 45 for extending across the open mouth 47 defined by the jaws 45 for retaining the first coupling pin 30 within the jaws 45, and its unlatched state, as illustrated in Figures 3a and 3b, for releasing the first coupling pin 30 from the fixed 10 jaws 45 through the open mouth 47. Extension or retraction of the ram acts directly through the linkage plates 90 and into the latching means 50 to move the latching means 50 between its two states. The latching means 50 is further urged into the latched state by the spring force from spring 53 which acts on the linkage plates 90 indirectly through 5 the loading against the body 71 of the hydraulic ram and the cross plate member 87. A moveable engaging means is provided by a moveable engagement member 58. In one embodiment of the invention, this is provided by a wedge shaped plate. The moveable engagement member 58 is slideably carried in the body member 35, and is moveable 10 between an engaged state, as illustrated in Figures 2a and 2b, for engaging the second coupling pin 31 of an accessory, and a disengaged state, as illustrated in Figures 3a and 3b, for disengaging the second coupling pin 31 for releasing the accessory from the coupler 14. Slots 59 are provided in the side plates 36 for engagement with corresponding protrusions (not shown) in the moveable engagement member 58 to 15 guide the moveable engagement member 58 between the engaged and disengaged states with rectilinear motion. It will be appreciated that any other means of connecting the moveable engagement member 58 to the side plates 36 could equally well be used. For example, in an alternative embodiment, guide tracks could be mounted on the side plates for slideably engaging corresponding guide grooves on opposite sides of the 20 engagement member 58. A jaw 62 extending from the engagement member 58 defines with adjacent edges 63 of the respective side plates 36 an open mouth 64 for accommodating the second coupling pin 31 into and between the jaw 62 and the edges 63 of the side plates 36. The open 25 mouth 64 faces outwardly of the coupler 14 in a direction opposite to the direction in which the open mouth 47 defined by the fixed jaws 45 faces. The free end of the jaw 62 is provided with a hook 75, Accordingly, when the moveable engagement member 58 is in the engaged state the first and second coupling pins 30 and 31 are securely engaged between the fixed jaws 45 and the engagement member 58 respectively. 30 In the described embodiment of the invention, a drive means including the previously mentioned hydraulically operated double acting coupler ram acts between the moveable engagement member 58 and the latching means 50 for moving the latching means 50 11 between the latched and the unlatched states, and for urging the engagement member 58 between the engaged and disengaged states. The coupler ram includes the ram housing 71 and a piston rod 74 extending from the ram housing 71. It will be appreciated however that another drive means could equally well be used to perform the same 5 function, for example a mechanical drive means. The trunnions 91 extend transversely from one end of the ram housing 71 and slideably engage corresponding longitudinally extending guide grooves (not shown) in the side plates 36 for facilitating longitudinal movement of the trunnions 91, and in turn the ram 10 body 71 in the body member 35. The piston rod is connected to the moveable engagement member 58 for urging the moveable engagement member 58 between the respective engaged and disengaged positions. As previously mentioned, the trunnions 91 also engage corresponding latch linkage members 90 for urging the latching means 50 from the latched to the unlatched state against the action of the spring 53 after the 15 engagement member 58 has been urged by the ram from the engaged to the disengaged state. Accordingly, the ram co-operates between the moveable engagement member 58 and the linkage plates 90 and the latching means 50 for respectively operating the moveable engagement member 58 and the latching means 50. 20 As explained above, the tension force in the compression spring 53 is sufficiently strong for retaining the latching means 50 in the latched state unless it is positively urged from the latched state by the ram. Accordingly, the ram co-operates with the spring 53 for controlling operation of the latching means 50. Thus, when the moveable engagement member 58 is in the engaged position engaging the second coupling pin 31 of an 25 accessory, and the fixed jaws 45 are engaging the first coupling pin 30, the piston rod 74 is extended from the ram housing 71, thereby retaining the moveable engagement member 58 in the engaged position and the latching means 50 in the latched position. In order to release the accessory from the coupler 14, the ram is initially operated for retracting the piston rod 74 into the ram housing 71. Because of the strong force in the 30 spring 53, the initial retraction of the piston rod 74 into the ram housing 71 urges the engagement member 58 from the engaged to the disengaged position. At that stage further movement of the engagement member 58 is no longer possible, and thus further retraction of the piston rod 74 into the ram housing 71 causes the latching means 50 to 12 be pivoted from the latched to the unlatched state, thus permitting disengagement of the first coupling pin 30 through the open mouth 47. For so long as the piston rod 74 is fully retracted within the ram housing 71, the 5 engagement member 58 is held in the disengaged state and the latching means 50 is held in the unlatched state. Initial movement of the piston rod 74 outwardly of the ram housing 71 causes the latching means 50 to be urged from the unlatched to the latched state by the spring 53. Once the latching means 50 is in the latched state, further outward movement of the piston rod 74 from the ram housing 71 causes the engagement 10 member 58 to be urged from the disengaged position to the engaged position. Should a sudden loss of hydraulic pressure occur in the ram when the coupler is in the engaged state coupling an accessory, the force of the spring 53 retains the latching means 50 in the latched state, and thus prevents the first coupling pin 30 from being 15 released from the fixed jaws 45. In addition, should the moveable engagement member move from the engaged position to the disengaged position because of the loss of pressure in the ram, the hook 75 on the moveable engagement member should act as a seat to retain the second coupling pin in contact with the moveable engagement member. Thus the hook 75 is intended to prevent the second coupling pin from 20 swinging free of the moveable engagement member and allowing the accessory to rotate dangerously. The description above is of a typical quick hitch coupler which would be well known to a person skilled in the art. However, as described in the background of invention 25 section, the present invention provides for additional safety means associated with the moveable engagement member in order to avoid the coupler disengaging in potentially dangerous circumstances, such as for example when supply pressure to the ram is interrupted and the ram check valve is malfunctioning. 30 Figures 5a and 5b shows the components of one embodiment of the safety means of the present invention, namely a pair of safety mechanisms 76. Each safety mechanism 76 includes a biasing means moveable between two states. In the described embodiment of the invention the biasing means is a compression spring 77 moveable between a 13 compressed and an uncompressed state. However, the spring could equally well be a tension spring, depending on the method of applying the force to the moveable engagement member 58 (i.e. either under compression or as a tension force). It should be understood that the term "uncompressed" as used throughout this patent specification 5 means a less compressed state, as it will be appreciated that the spring is never fully uncompressed, as there should be a pre-tension or pre-compression force maintained in order for the spring to provide a force at all times. A supporting means in the form of a rod 78 is located internally of the spring 77 substantially parallel to the spring's longitudinal axis such that each end of the rod 78 extends beyond the ends of the spring 10 when in its uncompressed state. An abutment member 79 abuts one end 80 of the spring 77. The abutment member 79 includes a main body 81 and a connecting member 82. The abutment member 79 is connected to the rod 78 by means of an aperture 98 defined within the main body 81 of 15 the abutment member 79, and is moveable in position along the length of the rod 78 with the spring 77 as it moves between its compressed and uncompressed states. A securing means 83 located adjacent to one end 85 of the rod 78 secures the rod 78 to the cross plate member 87 of the quick hitch 14. In the described embodiment, the securing means 83 takes the form of a nut that mates with external threads provided on the rod 20 78. The nut 83 includes a collar portion 93 for engagement with the receiving apertures 88a, 88c of the cross member 87 when the safety mechanism 76 is assembled within the quick hitch coupler 14. Each safety mechanism 76 is located in the body member 35 of the quick hitch coupler 25 14 such that the two safety mechanisms 76 extend in parallel along the length of each side plate 36, as shown in Figure 4. The safety mechanism 76 is secured to the body member 35 at three separate locations, as will be described below. Figures 6a and 6b show the safety mechanism in its state prior to assembly into position 30 in the quick hitch coupler 14. In this state, the nut 83 is rotated so that it is in contact with the abutment member 81 and the spring 77 is compressed. In order to assemble the safety mechanism 76 to the coupler, rod 78 is placed into the body member 35 so that it passes through the receiving aperture 88c of the cross plate member 87. When in this 14 position, the nut 83 is rotated on the external threads of the rod 78 to decompress the spring until the collar portion 93 of the nut 83 is seated within the receiving aperture 88c, thus securing the end 85 of the rod 78 of the safety mechanism 76 to the body member 35. The other end 86 of the rod 78 is connected to the body member 35 by 5 means of a recess (not shown) provided in connector member 38. Thus, the safety mechanism is now fully retained in the coupler body while maintaining an amount of pre-compression in the spring. The connecting member 82 of the abutment member 79 is also connected to the moveable engagement member 58 by means of an aperture provided in the moveable engagement member 58. This aperture can take the form of a 10 slot or hole 94. It will be appreciated that the same assembly process is applied to assemble the second safety mechanism 76 to the coupler 14, except that the second safety mechanism 76 is of course positioned within the other receiving aperture 88a of the cross plate member 15 87. The mounting of the safety mechanism as described above covers the full working range of the quick hitch coupler due to the compression range of the springs 77 in cooperation with the abutment member 79. As the moveable engagement member 58 travels 20 slideably across the full working range, it varies the compression ratio of the springs 77 to maintain an appropriate spring force on the moveable engagement member 58. During operation of the quick hitch, it will be understood that as the abutment member 79 of each safety mechanism 76 is affixed to the moveable engagement member 58, and 25 the abutment member 79 is in contact with spring 77, as the moveable engagement member 58 is driven by the piston rod 74 of the ram between the engaged and disengaged states, the driving force of the ram will overcome the force of the spring 77 so as to urge the spring 77 from its uncompressed state to its compressed state by the action of the abutment member 79 moving along the rod 78 in a direction away from its 30 end 85. Therefore, when the piston rod 74 is fully retracted within the ram housing 71, the engagement member 58 is held in the disengaged state and the spring 77 is in its compressed state, as shown in Figures 7a and 7b. Movement of the piston rod 74 outwardly of the ram housing 71 causes the spring 77 to be urged from its compressed 15 state to its uncompressed state, as shown in Figures 8a and 8b. As the uncompressed state of the spring 77 corresponds to when the moveable engagement member 58 is in its engaged state at its extreme extent of travel, should the hydraulic pressure to the ram fail when the moveable engagement member 58 is in its engaged state, the tension 5 forces of the spring 77 will continue to urge the moveable engagement member 58 towards its engaged state to retain the second coupling pin within the moveable engagement member 58. The safety means of the present invention provides numerous advantages over existing 10 safety systems, not only during operation of the coupler, but also at the initial stage of assembly of the safety means to the coupler. Firstly, the safety means of the present invention ensures that the second coupling pin is securely retained within the moveable engagement member 58 in the event of a sudden 15 loss of hydraulic pressure on the ram driving the moveable engagement member 58 in all positions of the coupler with respect to the dipper arm of an excavator. Furthermore, the safety means of the present invention can be safely and easily adjusted over a range of stroke dimensions, both while installed in the confines of the body 20 member 35 of the quick hitch coupler 14, and also when removed from the body member 35. The safety means of the present invention is therefore designed to operate on a coupler adapted to work across a wide range of variable pin centres. The safety means of the present invention also contains few component parts. As a 25 result, it provides the necessary robustness for the extreme operating conditions experienced by an excavator, as it will be appreciated that a complex multi component design is more likely to suffer damage, and ultimate failure in such working conditions. In addition, the fact that the safety means is driven by a hydraulic ram provides the requisite power to overcome work environment ingress. 30 In addition, it will be appreciated that in order to assemble or remove the safety means, the hydraulic oil pressure to the quick hitch must be removed. This means that it is not possible to provide any forces that would ensure that any potentially dangerous spring 16 force is not unleashed by the springs 77. It will be appreciated however that due to the functionality provided by the components of the safety mechanism 76, the springs 77 may be safely and securely compressed during assembly and removal of the safety means. In addition, the safety means may be easily assembled to the coupler body 35 by 5 means of the connecting plate 87. A detailed description of one or more preferred embodiments of the invention is provided above along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such 10 embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications, and equivalents. For the purpose of example, numerous specific details are set forth in the description above in order to provide a thorough understanding of the present invention. 15 The present invention may be practised according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured. 20 Throughout this specification and the claims that follow unless the context requires otherwise, the words 'comprise' and 'include' and variations such as 'comprising' and 'including' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 25 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge of the technical field.

Claims (11)

1. A quick hitch coupler for coupling an accessory to a dipper arm of a back actor, the quick hitch coupler including: 5 a body member adapted for coupling to the dipper arm; a fixed engagement means mounted on the body member for engaging a first one of a pair of coupling pins mounted on the accessory; a moveable engaging means mounted on the body member for engaging a second one of the pair of coupling pins of the accessory; 10 the moveable engagement means being moveable between an engaged state with the moveable engagement means engaging the second coupling pin while the fixed engagement means engages the first coupling pin for coupling the accessory to the coupler, and a disengaged state for disengaging the second coupling pin; a latching means co-operable with the fixed engagement means for retaining 15 the first coupling pin of the accessory engaged in the fixed engagement means, the latching means being alternatively operable in a latched state co-operating with the fixed engagement means for retaining the first coupling pin in the fixed engagement means, and an unlatched state for releasing the first coupling pin from the fixed engagement means; 20 a first biasing means for biasing the latch into the latched state; a drive means acting between the moveable engagement means and the latch for urging the moveable engagement means between the engaged state and the disengaged state, and for urging the latch from the latched state to the unlatched state against the biasing action of the biasing means when the moveable engagement means is 25 in the disengaged state; and wherein the coupler further includes: at least two safety means each including at least one further biasing means coupled to the moveable engagement means wherein the further biasing means is for urging the moveable engagement means into the engaged state. 30

2. The quick hitch coupler of Claim 1, wherein movement of the drive means to urge the moveable engagement means to the disengaged state moves the respective further biasing means of said at least two safety means against its respective urging action from a first state to a second state. 35

3. The quick hitch coupler of Claim 2, wherein the respective further biasing means of said at least two safety means is a compression spring, and the first state is an uncompressed state and the second state is a compressed state. 18

4. The quick hitch coupler of Claim 3, wherein said at least two safety means each further includes: a supporting means located internally of the second biasing means and extending beyond the ends of the further biasing means, the supporting means 5 connected to the body member; and an abutment member in contact with the further biasing means, the abutment member connected to the moveable engagement means and the supporting means, wherein movement of the drive means to urge the moveable engagement means towards the disengaged state causes the abutment member to move along the length of the 10 supporting means so as to move the further biasing means in contact with the abutment member from the uncompressed state to the compressed state.

5. The quick hitch coupler of Claim 4, wherein in each of said at least two safety means the abutment member further includes a connecting member, and wherein the 15 connecting member is connected to the moveable engagement means by means of an aperture provided in the moveable engagement means.

6. The quick hitch coupler of Claim 4 or Claim 5, wherein in each of said at least two safety means each end of the supporting means is secured to the body member. 20

7. The quick hitch coupler of Claim 6, wherein for said at least two safety means the supporting means is secured to the body member at one end by a securing means including a nut with a collar portion, wherein the supporting means is secured to the body member by locating the collar portion of the securing means within a receiving 25 aperture provided on the body member.

8. The quick hitch coupler of Claim 7, wherein the receiving aperture is provided on a cross plate member of the body member. 30

9. The quick hitch coupler of Claim 7 or Claim 8, wherein the supporting means is secured at its other end to the body member within a recess provided on the body member.

10. A quick hitch coupler substantially as described herein with reference to, and as 35 illustrated in Figure 4. 19

11. A safety means for a quick hitch coupler substantially as described herein with reference to, and as illustrated in Figures 5 and 6.