WO1991018716A1

WO1991018716A1 - Quick fastening device

Info

Publication number: WO1991018716A1
Application number: PCT/US1991/003556
Authority: WO
Inventors: Victor Yeou
Original assignee: Esco Corporation
Priority date: 1990-06-08
Filing date: 1991-05-24
Publication date: 1991-12-12
Also published as: AU8186791A

Abstract

Device for the quick fastening of a working tool (9, 110) on an arm of a machine, especially a public works machine, comprising a first part (1, 101) carried by an arm of the machine and second part (8, 109) fixed to the tool (9, 110). One of the first and second parts are equipped with first and second bearing members (6 or 106, 7 or 108), and the other part is equipped with hook-shaped first bearing elements (16, 117) adapted to receive the first bearing members (6, 106) and with inclined second bearing elements (17, 120) adapted to interact by wedging with the second bearing members (7, 108). One of the first and second parts also carry a locking member (31, 123) which interacts with a complementary locking member (12, 113) carried by the other part, after the engagement of the bearing members (6 or 106, 7 or 108). The locking members contributed to the wedging of the second bearing members in relation to the inclined second bearing elements (17, 120) to tightly secure the tool to the machine without play.

Description

QUICK FASTENING DEVICE

BACKGROUND OF THE INVENTION

The present invention relates to fastening devices for securing exca¬ vator buckets, or alternatively other working tools, to public works and con¬ struction machines, to machines used in mines and quarries, and to indus¬ trial and agricultural machines.

The known devices for fastening buckets to hydraulic diggers gener¬ ally comprise a first part carried by the arm of the machine and a second part integrally connected to the bucket. The two parts to be assembled are held in contact with each other by a conventional mechanical clamping system. However, when the machine is being used, the stresses of the dig¬ ging forces tend to increase the play in the assembly. Moreover, these known fastening devices have a relatively complex construction and take a relatively long time to implement. SUMMARY OF THE INVENTION

The object of the present invention is to overcome the disadvantages of the known fastening devices by providing a fastening device which has a simple, efficient construction, can be implemented quickly, and avoids the formation of play.

More specifically the device is designed to facilitate the quick fas¬ tening of a working tool to a machine, and in particular to a machine for public works. In general, the device comprises a first relatively elongated part carried by an arm of the machine and a second relatively elongated part integrally connected to the tool. The first and second parts are each provided with first and second cooperative bearing members. One part includes hook-shaped first bearing elements adapted to receive first bearing members of the other part. The one part also includes inclined second bearing elements adapted to interact by a wedging action with second bear¬ ing members of the other part. The first and second parts further carry cooperative locking members which interact with each other after the first and second bearing members have been positioned in bearing engagement. The locking members not only lock the parts together but also contribute to the wedging of the second bearing members relative to the inclined second bearing elements. The interaction between the first and second bearing members of the two parts and between the complimentary locking members constitute a plurality of contact zones between the first and the second parts of the device. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the aid of the descrip¬ tion which follows, given purely by way of example and made with refer¬ ence to the attached drawings, in which:

FIG. l is a side elevational view of the quick-assembly device accord¬ ing to the invention showing the two parts of the device before their assembly;

FIG. 2 is a view similar to that in FIG. 1 showing the front end of the first part of the device engaged in the hook-shaped ends of the slideway guides of the second part;

FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 5 of the device according to the invention in the assembled position;

FIG. 3a is a partial, cross-sectional view showing an alternative of an embodiment detail of the device according to the invention;

FIG. 4 is a top view of a tool provided with the second part of the assembly device according to the invention;

FIG. 4a is a partial front view showing a detail of the locking member of the second part of the device;

FIG. 5 is a top view of the device shown in FIG. 3;

FIG. 5a is a partial top view showing another alternative of the inclined stop for the guides of the assembly device;

FIG. 6 is a fragmentary, cross-sectional view taken along line 6-6 in FIG. 5;

FIG. 7 is a view on a larger scale showing a detail of the first part of the assembly device shown in FIG. 5;

FIG. 8 is a top view of a second embodiment of the quick-assembly device according to the invention in the mounted position; and

FIG. 9 is a fragmentary, cross-sectional view of the quick-assembly device taken along the line 9-9 in Figure 8. DETAILED DESCRIPTION

FIG. 1 is illustrative of the device of the present invention used in the quick assembly of a bucket on the arm of a hydraulic digger.

This device comprises a relatively elongated first part 1 forming a shoe comprising a base 2 having a generally parallelepipedal shape and ver¬ tical side members 3 extending therefrom. Side members 3 define orifices 4, 5 which enable the first part 1 to be articulated on the end of an arm (not shown) of a machine for public works, such as a hydraulic digger. The shoe is further provided at the ends of the base 2 with first and second bearing members in the form of first and second lateral studs 6 and 7, respectively. The studs 6, 7, as discussed below, are fastened in a relatively elongated second part 8 of the device secured to a tool 9. In the present example, the tool is comprised of a hydraulic digger bucket. Nevertheless, other tools and machines are also encompassed by the present invention. The base 2 further includes a bevel 2a at its forward end. The bevel 2a is intended to initially engage the second part 8 during the assembly of the device as will be more fully described below.

The first and second parts 1 and 8 of the assembly device according to the present invention are shown as being separated, before their assem¬ bly in FIG 1.

Still with reference to FIG. 1, but also to FIGS. 5, 6, 5a and 5b, it can be seen that the second part 8 is comprised of three elements 10, 11 and 12 — namely two lateral guides 10, 11 and a female locking member 12. The lateral guides 10, 11 are fastened to a plane wall 13 of the bucket 9 and positioned symmetrically with respect to the bucket's plane of symmetry. The female locking member 12 is fastened to the bucket in an axially sym¬ metrical position equdistant from the lateral guides 10 and 11.

Each of the guides 10 and 11 comprises a lateral slideway 14 having an outer wall 15. The outer walls 15 provide lateral guidance to the corre¬ sponding studs 6 of the base 2, when the shoe 1 is engaged in the second part 8. The guides 10, 11 each terminate at one of their ends in a hook 16 (FIG. 1), which serves as a first bearing element to retain the corresponding stud 6 received therein. The lateral guides 10, 11 have, at the ends opposite the hooks 16, inclined second bearing elements in the form of stops 17. Stops 17 interact by a wedging action with studs 7 arranged at the end of base 2 opposite to first studs 6. The inclined stops 17 are produced in the form of blocks made from a material of increased hardness, so as to enable them to withstand wear due to contact with the studs 7 during the various assembly operations. The hardened material is also important in withstanding wear generated during the operation of the machine. During operation of the machine, wear results from the forces sustained by the inclined stops during the digging operations carried out with the aid of the bucket 9.

The studs 6 and 7, the slideways 14 of the guides 10, 11, the stop blocks 17 and the contact surfaces of the female locking member 12 and the spindle 31 are likewise made from a hard material.

The stop blocks 17 are advantageously assembled by way of any appropriate means; such as by bolts which secure blocks 17 to heels 18 of the lateral guides 10, 11. The interposition of intermediate blocks 19 may also be used to take up any undue play in the assembly.

In the present embodiment, the stop blocks 17 are produced in the form of wedges so as to make it possible to compensate the wear of the studs 7 by engaging them gradually between the studs 7 and the correspond¬ ing heels 18. In FIGS. 4 and 5, the blocks 17 interact with cylindrical studs 7. In this construction the inclined stop surfaces 17a are parallel to the axes of the studs 7 with which they are in contact. The surfaces 17b in con¬ tact with the heels 18 are typically oblique relative to the direction of the guides 10, 11 primarily for general casting concerns. Of course, surfaces of the blocks 17 could have many shapes and orientations, so long as the engag¬ ing face 17a forms an inclined wedge face.

In an alternative embodiment (FIG. 5a), each of the inclined stops consists of a block in the form of a wedge 17c. Its inclined surface 17d interacts with and is tangential to the lateral surface of a frustoconical stud 7 a. The surface 17e of block 17c, opposite to inclined surface 17d, and the surface of the heel 18 with which it is in contact are perpendicular to the direction of the guide. This construction makes it possible to minimize the forces tending to drive the blocks outwards when the machine is working.

It is also within the scope of this invention to use blocks having a constant section. Moreover, it is also possible to place intermediate blocks in between the blocks and the heels. In such an arrangement (FIG. 5b), an intermediate block 19 is arranged between a block 17c in the form of a wedge and the heel 18 of a guide. Intermediate blocks can, of course, also be associated with inclined blocks of constant thickness.

The locking member 12 fastened to the wall 13 of the bucket, equi¬ distant from the lateral guides 10 and 11, is in the general form of a cap piece. The locking member includes two flanges 20 which extend parallel to the axis of symmetry of the bucket 9 and a transverse core 21 connecting the flanges together. The core is perpendicular to the flanges 20 and com¬ prises a tapered orifice 22 which is oblong in shape (FIG. 4a) for reasons which will be explained below. The orifice 22 is adapted to receive a mov¬ able locking member carried by the shoe of the assembly device and which will be described with reference to FIGS. 5 and 6.

With reference now to FIG. 2, the studs 6 of the first part or shoe 1 of the assembly device are shown in abutment with the end hooks 16 of the lateral guides. As can be seen, the bevel 2a of the base 2 enables the studs 6 to be engaged in the hooks 16 when the shoe 1 is inclined relative to the lateral guides 10, 11 integrally connected to the bucket 9. As also shown in FIG. 2, the final positioning of the shoe 1 relative to the second part 8 of the device is then effected by an angular displacement of the shoe 1 in the direction of the arrow F.

The relative positions of the first and second parts when the angular displacement of the first relative to the second is complete are shown in FIG. 3. It can be seen in this figure that the studs 6 engaged in the end hooks 16 of the slideways 14, each engage its corresponding hook in two zones 24, 25 separated by a flattening 26. The flattenings 26 are each situ¬ ated to face the bottom of the hook, to prevent the studs from abutting the bottom of the hooks 16. The flattenings 26 thus allow the studs 6 to be in contact with the hooks 16 in two distinct zones of the latter.

In an alternative embodiment (FIG. 3a), the lateral surface of each of the studs 6 is cylindrical. In order to define the two contact zones 24, 25 between the stud 6 and the hook 16, the flattening 26 is replaced by a recess 26a hollowed out in the bottom of the hook.

The studs 7 arranged at the other end of the base 2 are in contact with the corresponding oblique stops 17 in zones such as 27. The application of a force, represented by the arrow 28, to the first part of the shoe 1 of the device causes the studs 7 to be wedged against the inclined stops 17. As they descend along the inclined stops 17, the studs 7 push, by operation of the wedging action, the studs 6 against the walls of the hooks 16 of the guides 10, 11. A space 29 is provided between the bottom of the slideways 14 and the side walls of the studs 7, so that wear of the plates 17 forming the oblique stops can be compensated when the machine is being used. When the first part l of the assembly device is situated in the engaged position with respect to the second part 8 formed by the lateral guides 10 and 11, the locking of this first part 1 relative to the second part 8 is ensured by a locking device. The locking device comprises a locking spin¬ dle 31 slidably mounted in a pierced hole 30 of the base 2 of the shoe 1. Locking spindle 31 has a frustoconical end 32 which is engaged in the oblong tapered orifice 22 provided in the core 21 of the locking member integrally connected to the bucket 9.

The locking spindle 31 is biased in the direction of its engagement in the orifice 22 by means of a spring 33 placed in the pierced hole 30 of the base 2 and surrounding that end of the spindle 31 opposite its frustoconical end 32. When locking spindle 31 is engaged in the oblong orifice 22 (FIG. 6), the frustoconical end 32 of the locking spindle 31 is in contact at 32a with the upper end of the oblong orifice 22. A gap 34 is left between the frustoconical end 32 and the lower end of the oblong hole 22. The presence of this gap 34 makes it possible, when the studs 7 descend gradually with respect to the oblique stops 17, to ensure permanently a locking free of play by virtue of a corresponding penetration of the frustoconical end 32 of the locking spindle 31 into the oblong hole 22. This permanent locking without play of the first part relative to the second is permitted by virtue of the presence of a clearance 35 between the face of the base 2 turned towards the bucket 9 and the surface 13 of the bucket carrying the guides 10, 11.

The withdrawal and insertion movements of the locking spindle 31 can be controlled by either a mechanical system or a hydraulic system.

Such a hydraulic system is shown in FIG. 5. In this construction, the locking spindle 31 is carried at one end of a rod 31a. At the rod's opposite end, a piston 31b is slidably mounted in a cylinder 31c. The cylinder 31c is sealed at one of its ends by a cover 31d provided with seals 31f and tra¬ versed by the rod 31a. The cylinder is supplied, on either side of the piston 31b, by ducts 31g and 31h for the admission and venting of hydraulic fluid.

The spring 33 is, in the present example, a prestressed helical spring surrounding the rod 31a and arranged between the cover 31d and a collar 31i pressed against the spindle 31. It can also consist of a stack of Belleville washers. The admission of a pressurized fluid in chamber 31c causes the piston 31b to withdrawal the locking spindle 31 by the displacement of the rod 31a assembly. The spring 33 arranged around the locking spindle 31 and at the rear part of the spindle 31 tends to constantly push the latter into the female abutment 12. The spring 33 thus compensates as mentioned above, the play which can occur under the action of digging forces.

The assembly device has been shown in the locking position in FIG. 5. It can be seen in this figure that the shoe 1 of the device is held in place relative to the bucket 9 by the engagement of its two front studs 6 in the slideways 14 of the lateral guides 10 and 11. In this engaged position, the base 2 of the shoe, via the studs 6 and 7 and the locking member 31, engages the bucket and device structure 9, 10, 11, 12 in seven zones. These zones include the two contact zones 24, 25 between each of the studs 6 and hooks 16, the contact zones 27 between each of the two studs 7 and the inclined stops 17, and the contact zone 32a between the locking spindle 31 and the oblong hole 22.

As can be seen more clearly in FIG. 7, each stud 6 has at its free end an inclined part 36. Inclined part 36 facilitates the introduction of the studs into the slideways 14 and prevents their wedging. The inclined parts 36 of the studs 6 each end in a corresponding flattening 26 as can be seen in FIG. 7.

The arrangement which has just been described with reference to the drawings makes it possible to make use of the stresses of the digging forces in order to ensure the holding of the two parts to be assembled in perma¬ nent contact. The digging forces in this inventive construction tend to reduce the play in the assembly.

Although, in the embodiments of the invention described with refer¬ ence to the drawings, the studs are carried by a piece integrally connected to the arm of the machine while the slideway guides are arranged on the tool, it is, of course, possible to design a device comprising wherein the studs are carried by the tool and the slideway guides are integrally con¬ nected to the arm of the machine. Furthermore, the number of studs can be other than four.

An alternative form of the quick-assembly device is illustrated in FIGS. 8 and 9 of the drawings. It comprises a first part or shoe 101 having a base 102 of general parallelepipedal shape and vertical side members 103 extending from the base. Side members 103 define orifices 104, 105 to enable the first part 101 to be articulated on the end of an arm (not shown) of a machine, such as a hydraulic shovel. The shoe further includes first bearing members in the form of lateral studs 106, at the first ends of the base 102. At the other end of the base, opposite the studs 106, the shoe 101 includes a second bearing member in the form of an axial projection 107 having inclined surfaces 108. The first part 101 of the device is fastened to the second part 109 carried by a tool 110 (such as, for example, a bucket of a hydraulic shovel) by virtue of the front studs 106 and rear inclined sur¬ faces 108 and locking member 123 (discussed more fully below).

The second part of the quick-fastening device according to the present invention is comprised of three elements 111, 112, 113 — namely two lateral guides 111 and 112 fastened to a plane wall 114 of the bucket 110 and a female locking member 113. The lateral guides 111, 112 are sym¬ metrically secured to wall 114 in relation to the plane of symmetry of the bucket. The female locking member 113 is fastened to the bucket in a posi¬ tion of axial symmetry at an equal distance between lateral guides 111 and 112.

Each of the guides 111 and 112 has a lateral slideway comprising a bottom wall 115 and an outer wall 116. Outer wall 116 provides lateral guid¬ ance to the corresponding first studs 106 of the base 102 during the engage¬ ment of the latter into the second part 109. The ends of guides 111, 112 each terminate in a first bearing element in the form of a hook 117 (FIG. 9). Hooks 117 are adapted to keep the corresponding stud 106 of the base 102 in place. The lateral guides 111 and 112 are open at their other ends, to allow the first studs 106 of the base to be easily and slidably received into the guides 111, 112 during the introduction of the first part 101 into the second part 109.

The inclined surfaces 108 provided in the axial projection 107 of the base 102 interact with corresponding inclined abutments 120 fastened to the female locking member 113. Inclined surfaces 108 each preferably has an outwardly curved shape, with a radius, for example, of about 75 mm. Of course, surfaces with different curvatures or planar surfaces could also be used. Inclined abutments 120 constitute the second bearing elements of the invention. As shown in FIG. 8, the inclined abutments 120 consist of reason¬ ably attached pieces arranged in corresponding recesses made in the female locking member 113 opposite the inclined surfaces 108 of the shoe 102. Abutments 120 are preferably bolted in place. The inclined surfaces 108 of the base 102 interact with the inclined abutments 120 by wedging. Further, although plural abutments and inclined surfaces are described in the pre¬ ferred embodiment, single elongated abutment and inclined surface may also be used. As in the device described in the embodiment of FIGS. 1-7, the female locking member 113 has a widened orifice 122 which is of oblong form. A moveable locking member is engaged in the orifice 122. The move- able locking member is carried by the first part or shoe 101 of the assembly device and consists of a pin 123 slidably mounted in a drillhole 124 defined in the base 102. Pin 123 has a frustoconical end 125 engaged in the oblong widened orifice 122 defined in the locking member 113.

The locking pin 123 is biased in the direction of its engagement in the orifice 122 by means of a stack of Belleville washers 126 arranged in a bore 127 of the pin 123. To facilitate this construction, the pin 123 is mounted to a hub 129 by a transverse axle 128, the ends of which are received in oblong holes 123a provided in the pin 123. Hub 129 forms a nut and is displaceable in translational movement in the drillhole 124 by means of a screw 130. The screw is mounted in the bore via a bearing 131 fixed to an outer flange 132. Flange 132 is secured in a recess 133 of the shoe 101 by means of screws 134. The hub 129 forming the nut has a tip 129a which compresses the Belleville washers 126 under the action of the screw 130. The axle 128 con¬ necting the pin 123 to the hub 128, passes through the tip portion 129a. The hub or nut 129 further includes a longitudinal groove 129b, in which is engaged a key 129c fixed to the base 102 and projecting into the drillhole 124, in order to immobilize the nut 129 in terms of rotation. The outer end of the screw 130 has a head 135 adapted to receive a spanner or other actu¬ ating device for ensuring the engagement of the locking pin 123 into the widened oblong hole 122.

As already described with reference to the device of FIGS. 1-7, the frustoconical end 125 of the locking pin 123 is in contact at 136 with the upper edge of the oblong orifice 122 during its engagement into the oblong orifice 122. A space 137 is left between the frustoconical end 125 and the lower end of the oblong hole 122. During the progressive descent caused by the insertion of pin 123 in hole 122, the inclined surfaces 108 abuttingly engage against the oblique abutments 120. The presence of space 137 makes it possible to permanently ensure a locking arrangement without play. This benefit is a result of the continued penetration of the frustoconical end 125 of the locking pin 123 into the oblong hole 122 and the wedging action of the inclined surfaces 108 and abutments 120 whenever play or looseness in the connection is experienced. In the embodiments of FIGS. 8-9, oblique contact surfaces 108 are formed on axial projection 107. Contact surfaces 108 can either be inte¬ grally formed with base 102 as separate pieces attached thereto. The inclined surfaces are preferably formed of a hardened material to reduce wear. The inclined abutments 120, which are adapted to interact with the contact surfaces 108, are fixed to the female locking member in an axial position between the two slideways 111 and 112. The result of this con¬ struction is that the contact surfaces 108 are displaced towards the middle of the device and are arranged on either side of and in proximity to the frustoconical end of the locking pin 123.

The inclined abutments 120 are comprised of either attached pieces placed in recesses provided for this purpose in the locking member 113 (FIG. 8) or are produced as one integral piece fastened to this same locking member.

Changing the location of the inclined surfaces 108 effecting the for¬ ward wedging action, according to the second embodiment (FIGS. 8 and 9) does not change the number of contact zones (i.e., seven) between the first and second parts of the fastening device. More specifically, as in the device of FIGS. 1-7, two contact zones are defined between each of the studs 106 and its associated guide 111, 112, a contact zone is defined between each engaged inclined surface 108 and abutment 120, and a contact zone is defined between pin 123 and opening 122. These contact zones are thus seven in number.

It is also preferable to have the first part provide the actuator (hydraulic or mechanical) for the locking member (31, 123) because this will always be present on the machine whereas the working tool (9, 110) may lie idle and have its actuator damaged.

Claims

1. A device for effecting a quick fastening of a tool to a machine, said device comprising a pair of separable parts including a first part secured to one of said tool and machine and a second part secured to the other of said tool and machine, said first part defining a plurality of bearing members and a first locking member, said second part defining at least one hook releasably receiving therein one of said bearing members, at least one wedge member having a wedge face in opposed relation to said hook, said wedge face selectively engaging another of said bearing members, and a second locking member, said locking members having corresponding inclined surfaces selec¬ tively engaged against one another, one of said parts further including an actuator for applying a force to relatively move said locking members such that said movement causes said engaged inclined surfaces to pull said tool toward said machine and move said bearing member along said wedge face such that said one bearing mem¬ ber is driven tightly into said hook, said force being a constant biasing force to continually urge each of said engaged inclined surfaces of said locking member, said engaged bearing member and wedge face, and said engaged bearing member and hook to be continually urged into further and tighter engagement to thereby eliminate the development of play in the device during operation of the tool and machine.

2. A device in accordance with claim 1, in which said second part includes a pair of spaced apart hooks, and in which said actuator and said locking members are positioned in axial alignment with each other sub¬ stantially equidistant between said hooks.

3. A device in accordance with claim 2, in which said second part includes a pair of spaced apart wedge members positioned such that one of said wedge members are axially aligned with each of said hooks.

4. A device in accordance with claim 3, in which said wedge members are releasably secured in place to facilitate replacement thereof when said wedge members become unduly worn, without requiring the replacement of any other element of said second part.

5. A device in accordance with claim 2, in which said second part includes a pair of spaced apart wedge members positioned such that said wedge members are in close proximity with said locking members in between said hooks.

6. A device in accordance with claim 5, in which said wedge members are releasably secured in place to facilitate replacement thereof when said wedge members become unduly worn, without requiring the replacement of any other element of said second part.

7. A device in accordance with claim 1, in which said wedge members are releasably secured in place to facilitate replacement thereof when said wedge members become unduly worn, without requiring the replacement of any other element of said second part.

8. A device for fastening a tool to a machine, said device comprising: a first part secured to one of said tool and machine including: a base; a plurality of first and second bearing members each project¬ ing from said base; and a reciprocal locking member centrally positioned on said base, said locking member defining a distal end having an inclined bearing sur¬ face; and a second part secured to the other of said tool and machine including: a plurality of hooks adapted to receive therein said first bear¬ ing members; a plurality of wedge members adapted to engage said second bearing members; and a locking element positioned centrally between said hooks and wedge members, said locking member defining an enlarged opening having an inclined upper end, said upper end being adapted to engage said bearing surface of said locking member so that as said locking member is inserted into said opening said second bearing members are driven across the wedge members to force the first bearing members into tight engagement with said hooks.

9. A device according to claim 8, in which said wedge members are removably attached to one of said tool and machine so that they can each be replaced when worn to thereby compensate for the development of play in the device.

10. A device according to claim 8, in which said wedge members are axially aligned with said hooks.

11. A device according to claim 8, in which said wedge members are positioned in close proximity to said locking element in between said hooks.

12. A device according to claim 8, further including an actuator for reciprocating said locking member into and out of engagement with said opening, said actuator being centrally mounted to said base and in axial alignment with said locking member.

13. A device for fastening a tool to a machine, said device comprising: a shoe secured to an arm of a machine, said shoe including: a base having a first end and a second end; a pair of first studs extending laterally in opposite directions from said first end of said base; a pair of second studs extending laterally in opposite direc¬ tions from said second end of said base; a single locking spindle centrally mounted to said base between said studs, said locking spindle defining a distal end having an inclined bearing surface; and a single actuator axially aligned with said locking spindle and connected therewith to cause the linear reciprocation of said locking spin¬ dle to lock and release the tool from the machine; and an assembly secured to the machine, said assembly including: a pair of spaced apart hooks adapted to receive said first studs when the shoe is locked to said assembly; a pair of wedge members having an inclined wedge face adapted to engage said second pair of studs when the shoe is locked to said assembly; and a single locking element centrally positioned between said hooks, said locking element defining an enlarged opening having a tapered upper end adapted to receive said locking spindle therein when said shoe is locked to said assembly, said locking spindle being received within said opening such that said inclined bearing surface engages said tapered upper end to force said second studs across said wedge members and in turn said first studs into tight engagement with said hooks.

14. A device in accordance with claim 1, in which said wedge members are releasably secured to the tool so that they can each be replaced when unduly worn without requiring the replacement of any other element of said assembly.