Patent Publication Number: US-2023151581-A1

Title: Coupling apparatus

Description:
PRIORITY 
     The present application is related to, and claims the priority benefit of, Great Britain patent application serial no. 2116534.5, filed Nov. 17, 2021, the contents of which are incorporated herein directly and by reference in their entirety. 
     BACKGROUND 
     The invention to which this application relates is a coupling apparatus. 
     Coupling apparatus for use in attaching a dipper arm of an excavator to various accessories are well known. The couplers are used to attach buckets of various sizes, or other construction implements, to the dipper arm for subsequent use. The couplers are usually provided to be detachably attachable to both the dipper arm and the accessory which is to be used. Usually, the coupler remains on the dipper arm and the various accessories are attached, detached, interchanged as required. The attachment between the coupler and the accessory typically involves the provision of a pair or parallel coupling pins fixed on the accessory, which then connect or otherwise engage with respective engaging members on the coupler. In most common configurations, a pair of engaging members is provided on the coupler, one of which is fixed in place with the other being movable. The fixed engaging member usually contacts one of the coupling pins first, in an engaging position, and subsequently the second engaging member will then move into position engaging the second coupling pin and securing the accessory to the coupler. 
     The fixed engaging member usually includes a latch or other blocking member associated with it to retain the coupling pin in position, and the movable engaging member is usually hydraulically operated. However, there are some disadvantages to such configurations, for example, wherein the hydraulic operation may fail owing to a leak or failure to provide hydraulic fluid to the hydraulic ram. The movable engaging member may then fail to engage properly and the associated coupling pin may be inadvertently released. The weight of the accessory may then be such that the coupling pin held by the fixed engaging member and latch may simply overcome the biasing strength of the latch under gravity, leading to complete release of the accessory from the coupler and consequently potentially causing a serious accident. 
     There is therefore a need to provide a coupling apparatus which has improved safety features which prevents or substantially reduces the possibility of accidental or inadvertent release of accessories from the coupler. 
     BRIEF SUMMARY 
     It is therefore an aim of the present invention to provide an improved coupling apparatus which overcomes the aforementioned problems associated with the prior art. 
     According to a first aspect of the invention there is provided a coupling apparatus for coupling an attachment to a dipper arm of a machine, the apparatus including:
     a coupler body;   a first, fixed engaging means mounted on the coupler body for engaging a first coupling pin of the attachment, in use;   a latch member associated with and pivotable with respect to the first, fixed engaging means between latched and unlatched positions;   a locking member pivotable about a pivot point between first and second positions, and provided in mechanical communication with the latch member;   wherein the latch member includes an aperture located therethrough, and said locking member includes a trunnion member or other such protrusion located thereon, extending into or through the aperture of the latch member and engaging the same such that when said locking member is in the first position, the latch member is in the latched position, and when said locking member is moved to the second position, the trunnion member moves the latch to the unlatched position.   

     Typically, the coupling apparatus includes second, movable engaging means mounted on the coupler body for engaging a second coupling pin of the attachment, in use. Preferably, said second, movable engaging means is movable between an engaged position wherein it engages the second coupling pin as the first, fixed engaging means engages the first coupling pin, in use, and a disengaged position. 
     In one embodiment, said latch member includes a pivot point located at or near a first, proximal end thereof. 
     In one embodiment, the aperture of the latch member is located at or near a second, distal end thereof. 
     Typically, said latch member is biased to the latched position by biasing means. In one embodiment, said biasing means are provided as a torsion spring member. Typically, said torsion spring member is located about the pivot point of the latch member. 
     Typically, biasing means are also provided associated with the locking member, biasing the same to the first position. Typically, said biasing means are provided located at the pivot point of the locking member. Preferably, said biasing means are provided in the form of a torsion spring member. 
     In one embodiment, the aperture of the latch member is formed as a slot. Typically, the trunnion member is movable within and/or along the slot. 
     Preferably, the path movement of the trunnion member on the locking member is provided to be at an angle relative to the slot when the latch member is in the latch position. Such an arrangement ensures that while the trunnion member moves within the confines of the slot, its path of movement as the locking member moves will consequently move the latch member from the latched position to the unlatched position, and back again as the direction of movement is reversed. 
     In one embodiment, the slot is formed as a substantially V-shaped slot within the latch member. Typically, when the locking member is provided in the first position and the latch member is consequently in the latched position, the trunnion member rests at an apex of the V-shaped slot. 
     Typically, as the locking member is movable from the first position to the second position, the trunnion member is movable along the first length of the V-shaped slot to a distal end thereof, thereby moving the latch member form the latched position to the unlatched position. 
     Preferably, the provision of a second length of the V-shaped slot permits pivoting movement of the latch member, while the locking member and trunnion member remain in their respective first positions, to a deadlock position, wherein the trunnion member is located at a distal end of the second length of the V-shaped slot, preventing further movement of the latch member. 
     The provision of such a deadlock position provides the apparatus of the present invention with an additional and improved safety feature should the coupling begin to falter, preventing unwanted or accidental full release of the accessory from the coupling apparatus. For example, if for whatever reason the movable engaging means failed to engage with or inadvertently disengaged from the second coupling pin, the weight of the accessory would then be borne by the fixed engaging means entirely. In some examples in the prior art, there then becomes a real danger that the weight of the accessory may overcome the biasing force afforded to a latch provided with the fixed engaging means, allowing the accessory to fully detach, fall and potentially cause serious accident. In the present invention, if the weight or movement of the accessory is such that the first coupling pin is urged to move out from the fixed engaging means, this movement begins to urge the latch member against its biasing force about its own pivot point. However, the locking member and hence the trunnion member are stationary in the first position and so the latch member may only be moved as far as the second length of the V-shaped slot and trunnion member will permit. As the trunnion member engages the distal end of the V-shaped slot, this creates a deadlock position preventing any further movement of the latch member and, consequently, prevents release of the first coupling pin from the fixed engaging means and hence detachment of the accessory from the coupling apparatus. 
     In one embodiment, the coupling apparatus is provided to be hydraulically operable. Typically, drive means are provided to affect movement of the movable engaging means and the locking member. Preferably, said drive means are hydraulically operated. 
     Typically, said drive means comprises a hydraulically operable dual piston rod members. 
     In a preferred embodiment, said drive means includes a body portion, first piston and piston rod members, and second piston and piston rod members. 
     Typically, the first piston rod member engages with and drives movement of the movable engaging means. Further typically, said movement is linear movement, along a longitudinal axis of the first piston rod member. 
     Typically, the second piston rod member engages with and drives movement of the locking member. Further typically, said movement is linear movement, of the second piston rod member, along a longitudinal axis thereof, which drives pivoting movement of the locking member about its pivot point, in use. Consequently, pivoting movement of the locking member causes movement of the latch member between the latched and unlatched position. 
     In one embodiment, pivoting movement of the locking member may cause arcuate movement of the trunnion member, such that the trunnion member moves within the aperture of the latch member, moving it between the latched and unlatched positions. 
     In one embodiment, the body portion of said drive means comprises a manifold, a first piston chamber and a second piston chamber. Typically, said first and second piston chambers locate with and/or through the manifold. 
     In one embodiment, the manifold further includes ports, valves and feed means for the introduction and flow of first and second bodies or volumes of hydraulic fluid into and through the drive means. Typically, the first and second bodies or volumes of hydraulic fluid are provided to affect hydraulic movement of the first and second piston members and piston rod members. 
     In one embodiment, said first and second piston members are located in respective first and second piston chambers of the body portion, and said first and second piston rod members are linearly movable along longitudinal axes thereof, extending from and retracting towards/into the respective first and second piston chambers. 
     Typically, retraction of the first piston and piston rod member serves to move the movable engaging means from an engaged position to a disengaged position. Conversely, extension of the first piston and piston rod member serves to move the movable engaging means from a disengaged position to an engaged position. 
     In one embodiment, the movable engaging means are biased to the engaged position by biasing means. Preferably, said biasing means is provided in the form of one or more compression spring members. Typically, said compression spring member is arranged coaxially with the first piston rod member. Further typically, retraction of the first piston rod member is against and overcomes the biasing force of the compression spring member. 
     In one embodiment, extension of the second piston and piston rod member serves to move/pivot the locking member from the first position to the second position, and consequently move the latch member from the latched position to the unlatched position. Conversely, retraction of the second piston and piston rod member serves to move/pivot the locking member from the second position to the first position, and consequently move the latch member from the unlatched position to the latched position. 
     Typically, the first piston rod member includes attachment means at a distal end thereof for attachment to the movable engaging means. 
     Typically, the second piston rod member includes attachment means at a distal end thereof for attachment to the locking member. In one embodiment, said attachment is at an end of the locking member spaced apart from the trunnion member. Preferably, said attachment is at an opposing side of the pivot point from the trunnion member. 
     In one embodiment, the manifold includes a first port and feed means provided of the introduction and flow of a first body or volume of fluid. Typically, the manifold further includes a second port and feed means provided of the introduction and flow of a second body or volume of fluid. 
     In one embodiment, the first piston chamber includes a first fluid receiving portion and a second, separate fluid receiving portion. Typically, said first and second fluid receiving portions are separated by and provided either side of the first piston member. 
     Preferably, the first fluid receiving portion is located at a proximal end of the first piston chamber and the second fluid receiving portion is located at a distal end of the first piston chamber. 
     In one embodiment, the second piston chamber includes a first fluid receiving portion and a second, separate fluid receiving portion. Typically, said first and second fluid receiving portions are separated by and provided either side of the second piston member. 
     Preferably, the first fluid receiving portion is located at a distal end of the second piston chamber and the second fluid receiving portion is located at a proximal end of the second piston chamber. 
     Typically, as the first body or volume of fluid is injected or otherwise introduced into and through the first port and feed means, fluid fills the respective first fluid receiving portions of the first and second piston chambers, thereby causing extension of the first piston and piston rod member, and retraction of the second piston and piston rod member. 
     Typically, as the second body or volume of fluid is injected or otherwise introduced into and through the second port and feed means, fluid fills the respective second fluid receiving portions of the first and second piston chambers, thereby causing retraction of the first piston and piston rod member, and extension of the second piston and piston rod member, and forces the first body or volume of fluid back out of the manifold through the first port and feed means. 
     In one embodiment, valve means are provided associated with the first port. Typically, said valve means are provided to prevent return flow of the first body or volume of fluid through the first port, unless forced by pressurised injection or introduction of a second body or volume of fluid through the second port and feed means. 
     In one embodiment, valve means are provided associated with the second port. Typically, said valve means are provided to prevent return flow of the second body or volume of fluid through the second port, unless forced by pressurised injection or introduction of a first body or volume of fluid through the first port and feed means. 
     In one embodiment, movement of the locking member from the first position to the second position and consequently movement of the latch from the latched position to the unlatched position is arranged to occur subsequent to, and not simultaneously with, at least a first stage of movement of the movable engaging means from the engaged position to at least a partially disengaged position. 
     Typically, said partially disengaged position may be a position wherein the first piston and piston rod members are retracted from a fully extended position, but are not in a fully retracted position. Such an arrangement may provide a movement region wherein if the movable engaging means fails to properly engage the second coupling pin, the latch member may still remain in the latched position, preventing full detachment of the accessory from the coupling apparatus. 
     In another embodiment of the present invention, the coupling apparatus is provided to be manually operable. Typically, said coupling apparatus is manually operable such that movement of second, movable engaging means between engaged and disengaged positions is achieved by manual operation. 
     In one embodiment, said movable engaging means includes:
     a body portion having first and second opposing ends, wherein the first end thereof engages the second coupling pin;   a shaft portion extending outwardly from the second end; and   one or more drive portions extending outwardly from the second end, parallel to but separate from the shaft portion.   

     Typically, the shaft portion is arranged to extend into a first end of a housing or cowling body, located within the body of the coupling apparatus. Preferably, said housing is fixed in position within the body of the coupling apparatus. 
     Preferably, the housing is provided as a substantially elongate member having first and second opposing ends, and a cavity extending therethrough. 
     In one embodiment, the shaft portion is arranged to extend into the first end of the housing and is linearly movable within the cavity along a longitudinal axis of the housing. 
     In one embodiment, a screw member is provided, extending into the second end of the housing. Typically, a screw thread is provided on an outer wall or surface of the screw member. 
     Typically, the shaft portion comprises a cavity located therein, extending towards an opening at a distal end of the shaft portion. Typically, an interior wall or surface of the cavity of the shaft portion includes a screw thread, extending from the opening inwardly of the cavity along at least part of the length of the shaft portion. 
     Preferably, the screw member is rotatable about a longitudinal axis thereof and is threadedly engaged with the shaft portion. Typically, the outer wall or surface of the screw member is threadedly engaged with the interior wall or surface of the cavity of the shaft portion. 
     Typically, rotational movement of the screw member about its longitudinal axis causes linear movement of the shaft portion and hence the movable engaging means, between engaged and disengaged positions. 
     In one embodiment, a distal end or ends of the one or more drive portions is/are arranged to engage the locking member as the movable engaging means is moved from the engaged position to a disengaged position. 
     In one embodiment, as the movable engaging means are moved from an engaged position to a disengaged position via rotational movement of the screw member, in use, the distal end or ends of one or more drive portions engage the locking member, moving the locking member from the first position to the second position, and consequently moving the latch from the latched position to the unlatched position. 
     Conversely, as the movable engaging means are moved towards the engaged position, the one or more drive portions disengage the locking member allowing the locking member to move from the second position to the first position and consequently the latch member from the unlatched position to the latched position. 
     According to another aspect of the invention there is provided a coupling apparatus for coupling an attachment to a dipper arm of a machine, the apparatus including:
     a coupler body;   a first, fixed engaging means mounted on the coupler body for engaging a first coupling pin of the attachment, in use;   a second, movable engaging means mounted on the coupler body for engaging a second coupling pin of the attachment, in use, and movable between an engaged position wherein it engages the second coupling pin as the first, fixed engaging means engages the first coupling pin, in use, and a disengaged position;   a latch member associated with and pivotable with respect to the first, fixed engaging means between latched and unlatched positions; and   a locking member pivotable about a pivot point between first and second positions, and provided in mechanical communication with the latch member;   wherein hydraulically operated drive means are provided to affect movement of the second, movable engaging means and the locking member, said drive means including a body portion, first piston and piston rod members, and second piston and piston rod members, the first piston rod member engaging with and driving movement of the movable engaging means, and the second piston rod member engaging with and driving movement of the locking member.   

     Typically, movement of the first piston rod member and movable engaging means is linear movement, along a longitudinal axis of the first piston rod member. 
     Typically, movement of the second piston rod member is linear movement, along a longitudinal axis thereof, which drives pivoting movement of the locking member about its pivot point, in use. Consequently, pivoting movement of the locking member causes movement of the latch member between the latched and unlatched positions. 
     In one embodiment, the latch member includes an aperture located therethrough, and said locking member includes a trunnion member or other such protrusion located thereon, extending into or through the aperture of the latch member and engaging the same such that when said locking member is in the first position, the latch member is in the latched position, and when said locking member is moved to the second position, the trunnion member moves the latch to the unlatched position. 
     In one embodiment, pivoting movement of the locking member may cause arcuate movement of the trunnion member, such that the trunnion member moves within the aperture of the latch member, moving it between the latched and unlatched positions. 
     Typically, said latch member is biased to the latched position by biasing means. In one embodiment, said biasing means are provided as a torsion spring member. Typically, said torsion spring member is located about the pivot point of the latch member. 
     Typically, biasing means are also provided associated with the locking member, biasing the same to the first position. Typically, said biasing means are provided located at the pivot point of the locking member. Preferably, said biasing means are provided in the form of a torsion spring member. 
     In one embodiment, the body portion of said drive means comprises a manifold, a first piston chamber and a second piston chamber. Typically, said first and second piston chambers locate with and/or through the manifold. 
     According to a further aspect of the present invention, there is provided a coupling apparatus including:
     a coupler body;   at least first, fixed engaging means mounted on the coupler body for engaging a first coupling pin of the attachment, in use;   a latch member associated with and pivotable with respect to the first, fixed engaging means between latched and unlatched positions; and   a locking member pivotable about a pivot point between first and second positions, and provided in mechanical communication with the latch member;   wherein the locking member is movable by a driving force provided associated with the coupling apparatus.   

     Typically, the apparatus further includes a second, movable engaging means mounted on the coupler body for engaging a second coupling pin of the attachment, in use, and movable between an engaged position wherein it engages the second coupling pin as the first, fixed engaging means engages the first coupling pin, in use, and a disengaged position. 
     Typically, movement of the locking member from the first position to the second position serves to move the latch member from the latched position to the unlatched position. 
     In one embodiment, the driving force is provided as hydraulically operated drive means provided to affect movement of the second, movable engaging means and the locking member. 
     In another embodiment, the coupling apparatus is provided to be manually operable such that movement of a second, movable engaging means between engaged and disengaged positions is achieved by manual operation, and one or more drive portions are provided on the movable engaging means and arranged to engage the locking member as the movable engaging means is moved from the engaged position to a disengaged position, thereby moving the locking member from the first position to the second position, and consequently the latch member from the latched position to the unlatched position. 
     According to a further aspect of the present invention, there is provided an excavator apparatus or vehicle, said apparatus or vehicle comprising a dipper arm and a coupling apparatus as described above attachable to a distal end of the dipper arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described with reference to the accompanying figures, wherein: 
         FIG.  1    illustrates a side-on cross-sectional view of a coupling apparatus in a first arrangement, according to an embodiment of the present invention; 
         FIG.  2    illustrates a side-on cross-sectional view of a coupling apparatus in a second arrangement, according to an embodiment of the present invention; 
         FIG.  3    illustrates the movement of a locking member and a latch member of a coupling apparatus from first and latched positions to second and unlatched positions, according to an embodiment of the present invention; 
         FIG.  4    illustrates a latch member of a coupling apparatus in a deadlock position, according to an embodiment of the present invention; 
         FIG.  5    illustrates perspective view of a body portion of a drive means for a coupling apparatus, in accordance with an embodiment of the present invention; 
         FIG.  6    illustrates a top-down cross-sectional view of a drive means including a body portion, first and second piston and piston rod members, according to an embodiment of the present invention; 
         FIG.  7    illustrates side-on and top-down views, respectively, of a hydraulically operated drive means for a coupling apparatus, in a first arrangement, according to an embodiment of the present invention; 
         FIG.  8    illustrates side-on and top-down views, respectively, of a hydraulically operated drive means for a coupling apparatus, in a second arrangement, according to an embodiment of the present invention; 
         FIG.  9    illustrates a side-on cross-sectional view of another coupling apparatus in a first arrangement, according to an embodiment of the present invention; 
         FIG.  10    illustrates a side-on cross-sectional view of another coupling apparatus in a second arrangement, according to an embodiment of the present invention; and 
         FIG.  11    illustrates perspective and cross-sectional views of a manually operable movable engaging means of a coupling apparatus, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring firstly to  FIGS.  1  and  2   , there is illustrated a coupling apparatus  1  for coupling accessories such as buckets and the like to a dipper arm of an earth-moving or excavating machine. The coupler  1  includes a main body portion  3 , the upper part of which includes attachment means  5  for connection with a dipper arm. The lower part includes attachment parts and mechanisms for connecting the coupler  1  to an accessory. There is provided a first, fixed engaging means in the form of a fixed jaw  7  which is formed integrally with the body  3 , and which is provided to receive a first coupling pin  9  of an accessory. In order to secure the first coupling pin  9  within the fixed jaw  7 , there is provided a pivotable latch  11  which is movable between a latched position, shown in  FIG.  1   , and an unlatched position, shown in  FIG.  2   . Movement of the latch  11  is enabled by the provision of a pivoting locking member  13 , which is pivotable about a pivot point  15  between a first position, shown in  FIG.  1   , wherein the latch  11  is in the latched position, and a second position, shown in  FIG.  2   , wherein the latch  11  has been moved to the unlatched position. The locking member  13  affects movement of the latch  11  via the provision of a trunnion  17 , which extends outwardly laterally from the locking member  13 , and extending into or through an aperture  19  formed in the latch  11 . Thus, pivoting movement of the locking member  13  causes movement of the trunnion  17  within the aperture  19 , which in turn moves the latch  11 . 
     The latch  11  is provided to be pivotable about a pivot point  21  located at a first, proximal end thereof, and biasing means in the form of a torsion spring  23  is also provided at that point in order to bias the latch  11  toward the latched position. The aperture  19  of the latch  11  is generally provided at an opposing, distal end of the latch  11 . Thus, as the locking member  13  is moved from its first position in  FIG.  1    to the second position in  FIG.  2   , this moves the latch  11  to the unlatched position against the biasing force of the spring  23 . Biasing means in the form of a further torsion spring  25  are provided with the locking member  13 , located at its pivot point  15  and biasing it to the first position. Thus, a driving force is required to move the locking member  13  from the first position to the second position, and consequently the latch  11  from the latched position to the unlatched position. 
     In a first embodiment of the present invention, the coupler  1  further includes a second, movable engaging means in the form of a sliding jaw  27 , which is arranged to receive a second coupling pin  29  of an accessory. The second coupling pin  29  is secured in place as the sliding jaw  27  is movable between an engaged position, shown in  FIG.  1   , and a disengaged position, shown in  FIG.  2   . In this embodiment, the driving force which is required to move the locking member  13  is also utilised to drive movement of the sliding jaw  27  between engaged and disengaged positions. The coupler  1  in this embodiment is provided as a hydraulically operable coupler  1 , wherein hydraulic drive means are provided to affect movement of the locking member  13  and the sliding jaw  27 , which will be discussed in more detail later. 
     As described above, movement of the locking member  13  between the first and second positions causes movement of the latch  11  as the trunnion  17  is movable within the aperture  19  of the latch  11 . The aperture is provided as a slot at or near the distal end of the latch  11 , with the trunnion  17  being movable within and/or along the slot. In practice, the path of movement of the trunnion  17  as the locking member  13  is moved about its pivot point  15  may be slightly arcuate and at an angle relative to the slot of the latch  11  when the latch  11  is in the latched position. Such an arrangement ensures that while the trunnion  17  moves within the confines of the slot, its path of movement as the locking member  13  moves will consequently move the latch  11  from the latched position to the unlatched position, and back again as the direction of movement is reversed. In a preferred embodiment, the aperture in the latch  11  is provided as a substantially V-shaped slot  19 , and as the locking member  13  is moved as described above from the first position to the second position, the trunnion  17  moves from a resting position at an apex  31  of the V-shaped slot  19 , along a first length of that V-shape to a distal end thereof  33 . This movement causes the latch  11  to pivot from a latch position, wherein the first coupling pin  9  is secured in the fixed jaw  7 , to an unlatched position, wherein the pin  9  may be freely released from the jaw. The stages of movement of the locking member  13 , trunnion  17  and latch  11  are shown in more detail in subsections a) through d) of  FIG.  3    as the latch  11  is moved from the latched position (subsection a)) to the unlatched position (subsection d)). The locking member  13  is pivoted by a driving force ensuring it pivots in the direction of Arrow A about the pivot point  15 . This causes the trunnion  17  to move in the direction of Arrow B and along the first length of the V-shaped slot  19  from the apex  31  to the end  33  of the first length, which causes the latch  11  to pivot about its pivot point  21  in the direction of Arrow C and releasing the first coupling pin  9 . 
     The latch  11  in preferred embodiments includes a substantially V-shaped slot  19 , as discussed above. The second length of the V-shape may be required in instances where the latch  11  is pivoted away from a fully latched position, while the locking member  13  is maintained in the first position. Consequently, the trunnion  17  will remain static and, as the latch  11  is pivoted - for example if the coupler  1  is oriented in such a way that gravity and the weight of the accessory attempts to remove the first coupling pin  9  from the fixed jaw  7  and overcomes the biasing force of the spring  23  - the second length of the V-shape moves along trunnion  17  such that the trunnion  17  rests at a distal end  35  of the second length of the V-shaped slot  19 . This prevents further pivoting movement of the latch  11 , creating, along with the end of the locking member  13 , a deadlock, ensuring the latch  11  is not moved to the unlatched position and ensures the first coupling pin  9  remains within the fixed jaw  7 . This is illustrated in  FIG.  4   , which shows the first coupling pin  9  moving in a direction of Arrow D within the fixed jaw  7 , but being prevented from being fully released by the latch  11  and locking member  13 , due to the latch  11  being moved into the deadlock position, wherein the trunnion  17  rests at the distal end  35  of the second length of the V-shaped slot  19 , preventing any further movement of the latch  11 . The provision of such a deadlock position provides the coupler  1  with an improved safety feature should the coupling begin to falter, preventing unwanted or accidental full release of the accessory therefrom. For example, if for whatever reason the sliding jaw  27  failed to engage with or inadvertently disengaged from the second coupling pin  29 , the weight of the accessory would then be borne by the fixed jaw  7  entirely. In some examples in the prior art, there then becomes a real danger that the weight of the accessory may overcome the biasing force afforded to a latch provided with the fixed jaw, allowing the accessory to fully detach, fall and potentially cause serious accident. In the present invention, if the weight or movement of the accessory is such that the first coupling pin  9  is urged to move out from the fixed  7 , this movement begins to urge the latch  11  against its biasing force about its own pivot point  21 . However, the locking member  13  and hence the trunnion  17  are stationary in the first position and so the latch  11  may only be moved as far as the second length of the V-shaped slot  19  and trunnion  17  will permit. As the trunnion  17  engages the distal end  35  of the V-shaped slot  19 , this creates the deadlock position preventing any further movement of the latch  11  and, consequently, prevents release of the first coupling pin  9  from the fixed jaw  7  and hence detachment of the accessory from the coupler  1 . 
     As mentioned above, in one embodiment of the present invention, the coupler  1  may be provided to be hydraulically operable, wherein hydraulic drive means  37  are provided to affect movement of the locking member  13  and the sliding jaw  27 . The hydraulic drive means  37  are provided in the form of a dual piston ram arrangement, broadly comprising a main body portion  39 , a first piston  41  and associated first piston rod  43 , and a second piston  45  and associated second piston rod  47 . The body  39  itself comprises a manifold block  49  a first piston chamber  51  and a second piston chamber  53 , wherein the piston chambers  51 ,  53  are generally located with and/or through the manifold block  49 . The manifold block  49  also includes various ports, valves and feed pipes for the introduction and flow of hydraulic fluid to cause movement of the pistons and associated piston rods, and will be discussed in more detail later.  FIG.  5    illustrates in a perspective view, the body portion  39  of the drive means, including the manifold block  49  and the first and second piston chamber  51 ,  53 .  FIG.  6    illustrates a top-down cross-section view of the drive means also including the first and second pistons and associated piston rods  41 ,  43 ,  45 ,  47 . The hydraulic drive means  37  is arranged such that the first piston rod  43  attaches to and drives linear movement of the sliding jaw  27 . The linear movement is along a longitudinal axis of the first piston rod  43 . The second piston rod  47  is provided attached to, and to drive movement of, the locking member  13 . Movement of the second piston rod  47  is linear along a longitudinal axis thereof. 
     At a distal end of the second piston rod  47 , there is provided a clevis fastener  55  and pin  57  which attach to the locking member  13  through a slot  59  located in an end thereof. The arms of the clevis  55  extend around either side of the end of the locking member  13  and the clevis pin  57  extends through the slot  59 , providing mechanical attachment between the second piston rod  47  and the locking member  13 . While the rod  47 , clevis  55  and pin  57  move in a linear manner, the pivoting movement of the locking member  13  is enabled by forming the slot  59 , when the locking member  13  is in the first position, at an angle relative to direction of movement of the piston rod  47 . This is illustrated best in subsection a) of  FIG.  3   . As the piston rod  47  extends, the clevis pin  57  moves in a linear path but also within the slot  59  from a first end to a second end thereof. This causes pivoting movement of the locking member  13  and the angular orientation of the slot  59  changes as the pin  57  drives movement and moves to the second of the slot  59 , shown in stages in subsections a) through d) of  FIG.  3   . This extension of the second piston rod  47  thus pivots the locking member  13  from the first position to the second position and, consequently, moves the latch  11  from the latched position to the unlatched position. 
     The first and second pistons  41 ,  45  are located in their respective first and second piston chambers  51 ,  53  such that the piston rods  43 ,  47  are linearly movable along longitudinal axes thereof, extending from and retracting towards/into the respective first and second piston chambers  51 ,  53 . Retraction of the first piston rod  43  from an extended position serves to retract the sliding jaw  27 , moving it from an engaged position retaining the second coupling pin  29  in place to a disengaged position wherein the second coupling pin  29  may be released. Reverse movement, that is to say extension of the first piston rod  43 , therefore serves to move the sliding jaw  27  into the engaged position, retaining and securing the second coupling pin  29  in place. The sliding jaw  27  is biased towards the engaged position via the provision of a compression spring  61  which is located coaxially with the first piston rod  43  and located between a wall of the manifold block  49  and an abutting wall portion  63  of the sliding jaw  27 . Retraction of the first piston rod  43  overcomes the biasing force of the compression spring  61  to retract the sliding jaw  27 , moving it to a disengaged position, compressing the compression spring  61 . A distal end of the first piston rod  43  is provided to be fixedly attached to the sliding jaw  27 . More specifically, the end of the rod  43  is arranged to extend through an aperture in the abutting wall portion  63  of the sliding jaw  27  and a plate  65  is provided on the rod  43  to abut against the wall portion  63 . The distal end of the rod  43  includes a screw thread  67  around its outer surface and a locking nut  69  or similar may be screwed on, abutting against the opposing side of the wall portion  63 , securing the rod  43  to the sliding jaw  27 . 
     The manifold block  49  includes a first port  71  and associated feed pipes  73  for introducing a first body or volume of hydraulic fluid into the hydraulic drive means  37 . The introduction of the first body or volume of fluid, under pressure, serves to move the pistons and piston rods  41 ,  43 ,  45 ,  47  in a first direction. A second port  75  and associated feed pipes  77  are provided with the manifold block  49  for introducing a second body or volume of hydraulic fluid. The introduction of the second body or volume of fluid, under pressure, serves to move the pistons and piston rods  41 ,  43 ,  45 ,  47  in a second, opposing direction. Each of the piston chambers  51 ,  53  is separated into two distinct fluid receiving portions, the portions separated by the pistons  41 ,  45  in their respective chambers  51 ,  53 . The first piston chamber  51  includes first fluid receiving portion  79 , located at a proximal end of the chamber  51 , for receiving the first body or volume of hydraulic fluid therein, and a second fluid receiving portion  81 , located at a distal end of the chamber  51 , for receiving the second body or volume of hydraulic fluid therein. The second piston chamber  53  includes first fluid receiving portion  83 , located at a distal end of the chamber  53 , for receiving the first body or volume of hydraulic fluid therein, and a second fluid receiving portion  85 , located at a proximal end of the chamber  53 , for receiving the second body or volume of hydraulic fluid therein. This is illustrated best in  FIG.  6   . 
     Thus, as the first body or volume of hydraulic fluid is injected or otherwise introduced into and through the first port  71  and feed pipes  73 , fluid fills the respective first fluid receiving portions  79 ,  83  of the first and second piston chambers  51 ,  53 , thereby causing extension of the first piston  41  and piston rod  43 , and retraction of the second piston  45  and piston rod  47  - this arrangement is illustrated in subsections a) and b) of  FIG.  7    and corresponds with the arrangement of  FIG.  1   , wherein the sliding jaw  27  is in the engaged position, the locking member  13  is in the first position and consequently the latch  11  is in the latched position, such that both the coupling pins  9 ,  29  may be secured in place. As the second body or volume of fluid is subsequently injected or otherwise introduced into and through the second port  75  and feed pipes  77 , fluid fills the respective second fluid receiving portions  81 ,  85  of the first and second piston chambers  51 ,  53 , thereby causing retraction of the first piston  41  and piston rod  43 , and extension of the second piston  45  and piston rod  47 , also forcing the first body or volume of fluid back out of the manifold  49  through the first port  71  and feed pipes  73  - this arrangement is illustrated in subsections a) and b) of  FIG.  8    and corresponds with the arrangement of  FIG.  2   , wherein the sliding jaw  27  is in the disengaged position, the locking member  13  is in the second position and consequently the latch  11  is in the unlatched position, such that both the coupling pins  9 ,  29  may be released. Further, one or more valves are provided with the first and second ports  71 ,  75  and are used to prevent return flow of fluid through the associated port unless forced to do so by the pressurised introduction of fluid through the opposing port. That is to say, for example, after the first body or volume of fluid has been introduced through the first port  71  and feed pipes  73 , a valve  87  may be provided to prevent return flow of that fluid until the subsequent pressurised injection of the second body or volume of fluid through the second port  75  and feed pipes  77  overcomes the resistive force of the valve  87 . The valve  87  then likewise prevents the return flow of fluid through the second port  75  until the pressurised introduction of fluid through the first port  71 . 
     In another embodiment of the present invention, the coupler 1′ may be provided to be manually operable. That is to say, in this embodiment, the movable engaging means and driving means to operate movement is provided as a manually operable wedge lock and drive screw combination, movable between an engaged configuration, shown in  FIG.  9   , and a disengaged configuration, shown in  FIG.  10   . The movable engaging means is provided as a wedge lock  91  having a body portion  93  with first and second opposing ends. The first end  95  includes a wedge or taper section and engages the second coupling pin  29  when in the engaged configuration. A shaft  97  extends outwardly from the second end  99  of the wedge lock body  93 , and is arranged to extend into a first end of a housing or cowling  101 , located in a fixed position within the body  3  of the coupler 1′. One or more drive stems  103  are also provided to extend outwardly from the second end  99  of the wedge body  93 , parallel to but separate from the shaft  97 . The housing  101  is formed as an elongate body having first and second opposing ends with a cavity extending therethrough. The shaft  97  extends into the first end  105  of the housing  101  and is linearly movable within the cavity along a longitudinal axis thereof. A drive screw  107  is provided to extend into the second end  109  of the housing  101 , which has a screw thread  111  provided on an outer wall thereof. The shaft  97  has a cavity located therein which extends out towards a distal end of the shaft  97 . The interior wall of the cavity includes a screw thread  113  arranged to threadedly engage the screw thread  111  of the drive screw  107 , such that the drive screw  107  is rotatable about its longitudinal axis and rotation of the drive screw  107  causes linear movement of the shaft  97  and hence the wedge lock  91  as a whole, between engaged and disengaged positions. 
     As the wedge lock  91  is moved from an engaged position upon rotation movement of the drive screw  107 , a distal end of the drive stem or stems  103  subsequently engages an end or cam portion  115  of the locking member  13 , moving the locking member from its first position to its second position, which consequently causes movement of the latch  11  from its latched position to an unlatched position. The function features of the locking member  13 , latch  11 , trunnion  17  and V-shaped slot  19  in the manually operable embodiment of the present invention operate in the same manner as described above in the hydraulically operable embodiment, thereby also providing the deadlock arrangement, if required, as an additional safety feature of the coupler 1′. Conversely, as the drive screw is rotated in the opposite direction, the drive stem or stems  103  eventually disengage from the locking member  13 . The biasing torsion springs  23 ,  25  provided with the latch  11  and locking member  13  then serve to move the locking member  13  back to the first position and the latch  11  to the latched position. The wedge lock  91  continues to move away rom the locking member  13  and ultimately engages the second coupling pin  29 , securing the same in place. 
     The present invention therefore provides an improved coupler, in manually operable and hydraulically powered embodiments, having an additional safety feature preventing inadvertent opening of the latch  11  of the fixed jaw  7  resulting in premature release of the first coupling pin  9  and thus the accessory, potentially causing serious accident. The provision of a deadlock position, enabled via the provision of a V-shaped slot  19  in the latch  11  ensures the first coupling pin  9  is prevented from being released from the fixed jaw  7  inadvertently.