APPARATUS FOR SELECTIVELY TRANSMITTING OR BLOCKING THE TRANSMISSION OF TORQUE

Abstract: A torque transmitting and blocking device including a cylindrical drum (114), a pair of arcuate shoes (116 and 117) positioned within the drum, and a spanner bar (120) or ring extending between the shoes to one side of the axis of the drum. On the other side of the drum axis the shoes are displaceable toward each other, and may conveniently be lightly biased apart. The shoes have surfaces (130, 131, 134 and 135) (e.g.s holes, lateral or transverse projections, or the ends of the shoes) through which rotative forces can be transmitted from sources external of the drum and through which the shoes can retransmit such forces. Application of a rotational force through such a surface into a shoe in a direction tending to displace the shoes toward each other results in rotation of the shoes and bar within the drum. Application of a rotational force into a shoe in a direction tending to displace the shoes away from each other throws the shoes into a jamming relationship with the wall of the drum Applications of the device to winches, stepping clutches, and automatic load holders are disclosed.

Description: A.PPARSTUS FOR SELECTIVELY TRANSMITTING OR BLOCKING THE TRANSMISSION OF TORQUE This invention relates to apparatus for selectively transmitting torque from a torque input to a torque output, and for blocking transmission of torque from the output. The apparatus is applicable to stepping clutches, load holders, and winches, for example. There are many situations where it is desirable to control the transmission of torque through an apparatus, for example, to transmit it in one direction through a power train (from input to load), but block its transmission in the opposite direction (from load to input), in one or both directions of rotation. Apparatus for accomplishing such functions has in the past been complex in construction and limited in capabilities. In accordance with the present invention, apparatus is provided for transmitting torque, and for controlling its transmission both with respect to direction through a power train and with respect to direction of rotation. The apparatus may be a link in the power train itself, or in some applications, a side branch of the train which serves only to block torque transmission in a selected direction, without transmitting torque in the other direction. The apparatus of the invention is characterized by its simplicity, ruggedness in construction, and reliability in operation. In a given device, the geometry of the parts is fixed, and they respond to applied forces predictably without need for adjustment or tuning. In its preferred embodiments, the invention comprises a drum having a generally cylindrical inner surface. Depending upon the application, the drum may be mounted for rotation in either or both directions about its axis, or it may be fixed against rotation. A pair of shoes having arcuate surfaces generally conforming to the inner surface of the drum are mounted for selective relative or absolute rotation therein by sliding around the inner surface of the drum. The ends of the respective shoes approach each other but do not meet. A spanner bar or ring holds the shoes apart on one side of the axis of the drum. The spanner bar or ring bears against the inner surfaces of the shoes to hold them generally against the inner surfacce of the drum. At their ends lying across the drum axis from the spanner bar or ring the shoes are displaceable toward each other. In many cases it will be desirable to lightly bias these ends of the shoes apart. In accordance with the invention, the spanner bar or ring is so positioned with respect to the drum axis that a perpendicular struck from its centerline at the intersection of the centerline with the inner drum surface forms an angle with a drum inner surface tangent struck from the same point which is in the lock angle range for the materials employed to form the drum and shoe surface. Such an angle is generally in the neighborhood of seven (7) degrees. Such an angle is sometimes referred to herein as a jamming angle. In the case of a spanner ring, its "centerline" in the foregoing discussion is a line along a diameter of the ring struck perpendicular to the direction in which the ring is offset from the drum axis. Torques, and blocking torques, are transmitted into and out of the device through surfaces provided on the shoes, these surfaces being termed herein "force transmitting surfaces". The force transmitting surfaces of the shoes are oriented generally radially of the drum so that a force applied generally orthogonally therethrough produces a torque about the axis of the drum. The force transmitting sufaces may be variously formed, and may comprise holes or recesses in the shoes, lateral or transverse projections on the shoes, or the ends of the shoes. Cooperating with the force transmitting surfaces are force transmitting means which are engageable with the surfaces under various conditions to produce or block the transmission of torque. These force transmitting means are mounted for rotation about the drum axis, and may be positioned entirely within the confines of the drum, or partly externally of the drum. The force transmitting means may take various forms such as yokes with opposed working faces, collars with radial fingers, disks with pins, slotted disks, etc. In operation, torque is applied to a shoe of the device cf the invention through a force transmitting means acting against a force transmitting surface of the shoe. If the force is applied in a direction such that it tends to displace the shoes toward each other at their ends which lie across the drum axis from the spanner bar or ring, the shoes slidingly rotate with respect to the drum (assuming the input force is large enough to overcome internal and external forces opposing it). In many applications the drum will be fixed, so the rotation of the shoes is absolute, but in other applications the drum will be rotating, so the shoe rotation will be relative, with respect to the drum. In devices of the invention which form a direct link in a power train, as distinguished from a side branch, the shoes which are rotating in the manner just described have another force transmitting surface suitably located thereon which engages another force transmitting means mounted for rotation about the drum axis, thereby applying an output torque to it and causing iF to rotate, (again assuming the input forces are large enough to overcome internal and external forces opposing them). Torque consuming apparatus of many sorts may be connected to the second mentioned torque transmitting means. With the device operating in the manner just described, if torque input is discontinued, the torque consuming apparatus (the "load") will, in many cases, tend to apply an undesired back torque, either in the original direction of rotation, or in the opposite direction. This back torque, and/or the movement resulting therefrom is often undesirable in its effect on the load or the input power source, or both. In accordance with the invention, the second-mentioned force transmitting means applies a force through a force transmitting surface of a shoe in a direction tending to displace the shoes away from each other at their ends which lie across the drum axis from the spanner bar or ring. As a result, the shoes are thrown into a jamming relationship with the inner wall of the drum, because of the abovementioned jamming angle. Rotation (relative or absolute) of the shoes with respect to drum thus becomes impossible, and ceases. Transmission of torque is blocked by the jammed shoes. The fundamental apparatus as just described may be incorporated in many types of equipment performing a wide variety of functions. In the detailed description which follows, it is disclosed as embodied in a cable winch, two undirectional stepping clutches, two bi-directional stepping clutches, a oneway load holder, and a two-way load holder. These examples are intended to illustrate the wide applicability of the invention. From the foregoing, it can be seen that a principal object of this invention is to provide a torque transmitting device which is simple and rugged in construction, reliable in operation, and versatile in operation. It is another obJect of the invention to provide a torque transmitting device in which torque throughput may be in either direction of rotation and blocking of back torque is effective in both directions of rotation. A further object of the invention is the provision of a torque transmitting stepping clutch operable in either direction of rotation. Still another object of the invention is the provision of a device which is an effective load-holder upon discontinuance of power input. The manner inwhich the foregoing objects and purposes are attained, together with other objects and purposes, may be best understood from a consideration of the detailed description which follows, together with the accompanying drawings. FIG. 1 is an isometric view of a cable winch embodying the torque transmission and blocking device of the invention; FIG. 2 is a longitudinal cross-sectional view of the winch of FIG. 1, the section being taken on the line 2-2 of FIG. 1; FIG. 3 is an isometric view of a shoe constructed in accordance with the invention, as used in the emobodiment of FIG. 1, as well as in other embodiments; FIG. 4 is an isometric view of a force transmitting means or yoke constructed in accordance with the invention, as used in the embodiment of FIG. li as well as in other embodiments; FIG. 5 is a transverse sectional elevational view of the winch of FIG. 1, the section being taken on the line 5-5 of FIG. 2; FIG. 6 is a fragmentary exploded isometric view of the manor torque transmitting and blocking parts of the winch of FIG. 1; ; FIG. 7, 8 and 9 are sequential diagrammatic sectional elevational views of the torque transmitting apparatus of the winch of FIG. 1, on a somewhat reduced scale, showing stages in the operation of the device; FIG. 10 is an isometric view of a unidirectional stepping clutch embodying the torque transmission and blocking device of the invention; FIG. 10A is an isometric view of a bi-directional stepping clutch embodying the torque transmission and blocking device of the invention; FIG. 11 is a longitudinal cross-sectional view of the clutch of FIG. 10, the section being taken on the line 11-11 of FIG. 10; ; FIG. 12 is a transverse sectional elevational view of the clutch of FIG. 10, the section being taken on the line 12-12 of FIG. 11, FIG. 13 is an isometric view of a force transmitting means or collar with projecting finger constructed in accordance with the invention as used in the embodiment of FIGS. 10 and lOA; FIG. 14, 15, 16 and 17 are diagrammatic sequential sectional elevational views of the clutch of FIG. 10, on a somewhat reduced scale, showing successive stages in a stepping operation; FIG. 18 is a fragmentary isometric view showing the -ac's- side of the clutch of FIG. 10; FIG. 19 is an isometric view, partly broken away of a oneway load holder emodying the torque transmitting and blocking device of the invention; ; FIG. 20 and 21 are sequential diagrammatic isometric views of the load holder of FIG. 20, on a somewhat reduced scale, showing the successive stages in its operation; FIG. 22 is an isometric view, partly broken away, of a two-way load holder embodying the torque transmitting and blocking device of the invention; FIG. 23 and 24 are somewhat diagrammatic elevational views, on a reduced scale of the load holder of FIG. 22 as applied in a conveyor system, illustrating different operating conditions to which the load holder may be exposed; FIG. 25 is an exploded isometric view of another embodiment of the invention in a bi-directional stepping clutch, the FIG. being laid out so that the axis of the unit recedes from the viewer in the direction of torque transmission; FIG. 26 is another exploded isometric view of the bidirectional stepping clutch of FIG. 25, the FIG. being laid out so that the axis of the unit approaches toward the viewer in the direction of torque transmission; FIG. 27 is an enlarged perspective view of the bidirectional stepping clutch of FIG. 25, with some parts broken away for clarity of illustration; FIG. 28 and 29 are perspective views of the clutch of FIG. 25 with FIG. 28 showing the clutch transmitting torque and FIG. 29 showing the clutch blocking torque; FIG. 30 is a transverse sectional view on an enlarged scale of the clutch of FIG. 25, the section being taken on the line 30-30 of FIG. 27, FIG. 31 is an exploded isometric view of still another embodiment of the invention in a uni-directional stepping clutch, the FIG. being laid out so that the axis of the unit approaches toward the viewer in the direction of torque transmission; FIG. 32 is an enlarged perspective view of the unidirectional stepping clutch of FIG. 31, with some parts broken away for clarity of illustration; and FIG. 33 is a transverse sectional view on an enlarged scale of the clutch of FIG. 31, the section being taken on the line 33-33 of FIG. 32. A. The Invention as Embodied in a Winch: FIGS. 1-9 illustrate the torque transmitting and blocking device of the invention embodied in a cable winch, such as may be employed in a flagpole winch. In these FIGS. the winch is designated generally as 100, while the torque transmission and blocking device is designated generally as 101. Winch 100 has a frame formed of front plate 102 and rear plate 103, held in spaced parallel relation by spacer bars 104. A hollow drive shaft i05 is journalled for rotation in the center of plates 102, 103. Part of shaft 105 is swaged down to square section, as at 106, for engagement with a removable crank 107 having a shank 108 of square cross section. A cable drum 109, formed of barrel 110 and end flanges or disks 111, 112, is mounted for rotation on drive shaft 105. Cable 113 is wound on the barrel, and leads to the load. Cable drum 109 is interconnected for rotation to drive shaft 105 through the torque transmission and blocking device 101, as is explained below. The torque transmission and blocking device 101 includes generally cylindrical drum 114, which is mounted on the back of front plate 102, and is coaxial with drive shaft 105 and barrel 110. Drum 114 has a generally cylindrical inner wall 115. The parts of the torque transmission and blocking device which are positioned within drum 115 can best be understood from a consideration of FIG. 2-6, and particularly FIGS. 5 and 6. A pair of shoes 116, 117 are positioned within drum 114. The shoes have arcuate outer surfaces 118 generally conforming to the curvature of wall 115. It is preferred that the two shoes subtend equal arcs and that the arc subtended by each shoe be a substantial portion of a semicircle. Each shoe is provided with a recess 119 on its inner or convex surface for receiving and engaging an end of spanner bar 120. Spanner bar 120 engages the shoes at points lying on the same side of the axis 121 of drum 114, as can best be seen from FIG. 5. Spanner bar 120 is offset somewhat from axis 121 to form a good jamming angle. This is illustrated in FIG. 5 where it can be seen that a tangent 125 struck from the inner wall 115 of the drum at the point where the wall is intercepted by the end-to-end centerline 123 of the spanner bar forms an angle 124 with a line 122 drawn perpendicular to the centerline 123 at the same point on the wall, which angle is about 7 degrees. At their ends on the opposite side of the drum axis from their points of engagement with the spanner bar, shoes 1-16 and 117 are displaceable toward each other. It is preferred, but not necessary, that they be lightly biased apart, as by spring 126, which fits into recesses 127 provided in the end faces of the shoes. Certain surfaces of shoes 116, 117 are termed herein "force transmitting surfaces" because of their function in the operation of the device. As will become apparent as this and other embodiments of the invention are discussed, these surfaces may be variously formed and positioned on the shoes. Despite such variations, the force transmitting surfaces share the characteristic that they are at least in part generally radially oriented with respect to the drum. This means that forces applied generally orthogonally through them (either into the shoe or out of the shoe) result in the generation of a torque about the axis of the drum. For example, one force transmitting surface of shoe 116 is end face .131, as is discussed below. As can be seen from FIG. 5, the plane of face 131 is approximately parallel to a vertical radius of the drum; hence it is "generally radially" oriented. A consideration of other force transmitting surfaces as they are discussed below will reveal that they have similar orientations. A force applied generally orthogonally into or out of the plane of face 131 will create a torque about drum axis 121. See FIG. 5. in the embodiment of FIGS. 1-6, each shoe has two force transmitting surfaces. Shoe 116 has a recess 128 formed in its convex wall, and a radially inwardly extending leg 129 formed adjacent the recess. These two constructions taken togther provide shoe 116 with its first force transmitting surface 130. The second force transmitting surface of shoe 116 is its end face 131. Similarly, shoe 117 is provided with a recess 132 and leg 133 to form its first force transmitting surface 134. (See FIG. 3) The second force transmitting surface of the shoe 117 is its end face 135. The device of FIGS. 1-6 is equipped with two force transmitting means, one of which cooperates with the input or drive shaft 105, and the other of which cooperates with the cable drum 109 which is the output mechanism of the winch. The input force transmitting means is yoke 136, which is secured on drive shaft 105 for rotation therewith. Yoke 136 has opposed faces 137 and 138, which cooperate with force transmitting surfaces 130 and 134 of shoes 116 and 117 respectively. As can best be seen in FIG. 5, opposed faces 137, 138 are located on legs 139, 140 of the yoke, which legs fitr into recesses 128, 132 of shoes 116, 117 respectively. Yoke 136 is apertured at 141 to fit on drive shaft 105. In the preferred embodiment yoke 136 is formed of sheet metal. Bosses 142 aid in maintaining it properly positioned. The output force transmitting means comprises pin 143 which projects laterally from cable drum disk 111 into the space betwen force transmitting surface 131 of shoe 116 and force transmitting surface 135 of shoe 117. Pin 143 is thus in a position to bear against, or to be borne against by, force transmitting surfaces of both shoes. With the foregoing description of the components of the torque transmitting and blocking device of the invention as embodied in a winch in hand, its mode of operation can be explained with reference to the diagrams of FIGS. 7-9. FIGS. 7 and 8 show how the device operates to transmit torque, and thus motion, from input shaft 105 to the output cable drum which carries pin 143. As shaft 105 is rotated clockwise (as is indicated by the arrow around the shaft), it rotates yoke 136 in the same direction. The face 137 of the yoke pushes against surface 129 of shoe 116 to rotate it clockwise also. The force exerted by yoke 136 on shoe 116 is in a direction tending to displace face 131 toward face 135, although such displacement does not occur because shoe 117 and spanner bar 120 rotate along with shoe 116. As shoe 116 is driven clockwise by yoke 136, its surface 131 pushes against pin 143 to rotate it and the cable drum on which it is carried. Torque, and rotary motion, are thus transmitted from input shaft to output drum. A consideration of the symmetry of the parts shown in FIGS. 7 and 8 will lead to the conclusion that the device will operate in the same manner if torque is input to drive shaft 105 to rotate it in a counterclockwise direction. Thus by turning crank 107 (FIG. 1) in one direction cable can be wound onto the cable drum, and by turning the crank in the other direction cable can be played off the drum in a controlled manner. FIG. 9 shows the torque-blocking condition of the device which occurs when an attempt is made, by application of force through the cable, or directly upon the cable drum, to rotate the cable drum other than by means of the crank. When a force (represented by the heavy straight arrow in FIG. 9) is applied to pin 143 in an attempt to rotate it counterclockwise, the pin pushes against surface 131 of shoe 116, that is, in a direction tending to displace surfaces 131 and 135 away from each other. This throws shoes 116 and 117 into a jamming relationship with the wall of drum 114, and prevents the transmission of torque to shaft 105. The counterclockwise movement thus attempted, and indicated by the phantom arrows in FIG. 9 cannot, and does not take place. Again, a consideration of the symmetry of the parts shown in FIG. 9 will lead to the conclusion that the device will operate in the same manner if force is applied through pin 143 in an attempt to rotate the cable drum in clockwise position. The cable drum is effectively frozen by the device against all move- ment except that caused by forces applied through shaft 105. B. The Invention as Embodied in a Unidirectional Stepping Clutch FIG. 10, and FIGS. 11-18 illustrate the torque transmission and torque blocking device of the invention as embodied in a unidirectional stepping clutch, that is, a clutch in which rotational motion in one direction of rotation is continuously supplied at the input, and a single revolution (or group of revolutions or even a fraction of a revolution) is obtained at chosen times at the output. Attention is first directed to FIGS. 10, 11-13 and 18. In these FIGS. the clutch is designated generally as 200. It has a hollow input shaft or bushing 201 on which belt driven sheave 202 is mounted. Rotation of the sheave thus results in rotation of shaft 201. Also mounted for rotation on and with shaft 201 is clutch drum 203. The output shaft of clutch 200 is formed in two pieces for convenience. One piece is a hollow shaft 204, having an internal keyway 205. Shaft 204 passes through hollow input shaft 201, and the fit between the two admits of relative rotation between them. A keeper ring 206 fixes the axial relationships of shafts 201 and 204. The other piece of the output shaft is solid shaft 207 which has an external spline 208 thereon. Shaft 207 fits into hollow shaft 204, with spline 208 interfitting in keyway 205 so that the two shafts are united for rotation. Shaft 207 is normally a part or component of the equipment driven by the stepping clutch. Within clutch drum 203 are positioned shoes 209 and 210, which are engaged by spanner bar 211. Spanner bar 211 is positioned on one side of the drum axis to form a jamming angle in the manner described above. Shoes 209, 210 are lightly biased apart by spring 212 working against shoe faces 213, 214. It should be noted that input shaft 201 has a flanged end 215 (FIG. 11) which serves as a spacer for force transmission means 216. Transmission means 216 is in the form of a collar fixed on output shaft piece 204 for rotation therewith, with a radially projecting finger 218 thereon. As can be seen in FIG. 12, finger 218 projects into the space between faces 213 and 214 of shoes 209, 210, and is in position to act on, and be acted upon by them. A spacer 219 separates force transmission mean 218 from control disk 220, which is journaled on output shaft piece 204, and is free to rotate with respect thereto. Control disk 220 comprises a force transmission means for the device. It is provided with a slot 221 into which projects pin 222 on shoe 209 and pin 223 on shoe 210. Pins 222 and 223 constitute force transmission surfaces of shoes 209, 210. Control disk 220 has a stop 224 on its periphery which cooperates with liftable dog 225 to prevent rotation of the disk except when such rotation is desired. The operation of stepping clutch 200 may be understood from a consideration of FIGS. 14-17. In FIG. 17, the unit is shown with torque being continuously input through shaft 201 (not visible as FIG. 17 is drawn), which causes drum 203 to continuously rotate. Disk 220, which is in front of the plane of the drawing in FIGS. 14-17, is indicated in FIG. 17 as restrained against rotation by dog 225 working against stop 224. Under these conditions disk 220 exerts a virtual force by means of slot 221 against pin 223 in a direction tending to displace shoe end faces 213, 214 toward each other. This force holds shoes 209 and 210 out of jamming relationship with drum 203, and at a standstill. The standstill condition of the shoes is in fact relative rotation with respect to the drum, since the drum is rotating. The start of an output shaft revolution is shown in FIG. 15, where dog 225 is shown as lifted, freeing disk 220 to rotate. Shoes 209, 210 wil start to decelerate with respect to the drum, i.e., start to move with it because of friction between the drum and shoes, upon the removal of the above described force exerted by the disk 220 on pin 223. This will quickly bring shoe face 213 into contact with finger 218, and throw the shoes into jamming relationship with the rotating drum. In FIG. 16, the jammed shoes are shown pushing finger 218 clockwise, which imparts clockwise rotation to output shaft 207. The jammed shoes also rotate disk 220 clockwise, because pin 223 pushes on the edge of slot 221. Such rotation continues until dog 225 engages stop 224 to halt the rotation of disk 220, as is shown in FIG. 17. The halted disk again applies a virtual force through pin 223 to unjam the shoes. This removes the torque applied to the output shaft through finger 218, and rotation of the output shaft ceases until dog 225 is again lifted. If more than one output shaft rotation is desired, dog 225 may be held in lifted position to allow more than one shaft revolution. On the other hand, if fractional revolutions of the output shaft are desired, the number of stops on the periphery of disk 220 may be increased or a plurality of dogs may be placed around disk 220. If power input through sheave 202 is discontinued, and an attempt is made to rotate output shaft 207, it will be found that shaft 207 is restrained from such'rotation because finger 218 throws the shoes into jamming relationship with the now stopped drum 203. C. The Invention as Embodied in a Bi-directional Stepping Clutch FIG. 10A illustrates a bi-directional stepping clutch 300 constructed in accordance with the invention. In structure it is the same as unidirectional clutch 200 of FIGS. 10 and 11-18, except that disk 301 is provided with two oppositely facing stops 302, 303, and each stop is provided with an appropriately oriented dog 304, 305. The belt of sheave 306 is powered to drive in either direction. A consideration of the symmetry of the parts of the clutch, as explained in connection with FIGS. 10 and 11-18, will reveal that the mode of operation illustrated in FIGS. 14-17 will be the same if the rotation is in the counterclockwise direction instead of the clockwise direction. D. The Invention as Embodied in a One-Way Load-Holder FIGS. 19-21 illustrate the invention as embodied in a one-way load-holder, that is, an apparatus which permits the transmission of torque in one direction of rotation from a power source to a load, but blocks the transmission of torque from the load back toward the power source in the other direction of rotation. The embodiment of FIGS. 19-21 differs from all of the other embodiments disclosed herein in that the jamming shoes of the invention are not a direct link in the power train between the power source and the load, but are rather in a "side branch" of the power train and are drawn into jamming operation only upon the occurrence of back torque such as would often occur upon a failure or stoppage at the power source. In FIG. 19, the load holder is designated generally as 400. It is associated with a power train which includes a belt drive 401; drive shaft 402; cable drum 403, mounted on the shaft; and cable 404, connected to load 405. This power train is illustrative of a wide variety of possible power train arrangements to which the load holder 400 can be applied. The load holder 400 includes a generally cylindrical drum 406 mounted coaxially of shaft 402 by integral bracket 407. Within the drum are positioned two arcuate shoes 408, 409, configured much like those shown and described in connection with earlier embodiments. The shoes are engaged by a spanner bar 413, positioned to one side of the drum axis to form a jamming angle. Shoe 409 has a hole 411 formed therein. As FIG. 19 is drawn, the left side of hole 411 constitutes a first force transmitting surface through which an externally applied force in the counterclockwise direction will tend to displace the ends of the shoes remote from the spanner bar toward each other. The right hand side of hole 411, as FIG. 19 15 drawn, constitutes a second force transmitting surface through which an externally applied force in the clockwise direction ill tend to displace the ends of the shoes remote from the spanner bar away from each other. A disk 412 is mounted on Shaft 402 for rotation to herewith adjacent drum 406. Pin 413 is mounted on#disk 412 and extends into hole 411 of shoe 409. In the terms in which the invention has been discussed herein, pin 413 and disk 412 constitute a force transmitting means coc,perating with the force transmitting surfaces formed by the left and right sides of hole 411. The operation of load holtier 400 is as follows: As power is supplied to shaft 402 by belt drive 401, the shaft turns counter-clockwise to rotate cable drum 403, thus winding up the cable and lifting load 405. The dlsk 412 rotates counterclock# wise with shaft 402, and the pin 413 pushes on the left hand side of hole 411 to rotate the shoes and spanner bar within the drum. The force applied by pin 413 to shoe 409 is in a direction such that it does not jam the shoes. The situation just described is illustrated in FIG. 19, where the various arrows indicate the direction of movement of the parts. This situation is alsO illustrated in the diagram¯ matic view of FIG. 20, where a series of small arrows diagram matically indicate application force through the shaft 402 both to the load (through the celt) and to shoe 409 (through disk 412). The arrows illustrate the comment made above that the load holder is not a direct link in the power train, but is rather a side branch thereof. In FIG. 19, a power failure is illustrated symbolically by the belt break shown in phantom lines at 414. Other types of power stoppages may occur, but the operation of load holder 400 is the same regardless of the kind of power stoppage. When application of power to the power train ceases, the dominant force on the system is the load 405, which tends to unwind cable off the cable drum and rotate shaft 402 clockwise. Attempted rotation of shaft 402 clockwise causes pin 413 to push on shoe 409 in a direction which throws the shoes into a jamming relationship with the inner wall of drum 406. This situation is illustrated in FIG. 19, where the series of small arrows indicate application of force by the load to shoe 409 through the cable, shaft, disk and pin. E. The Invention as Embodied in a Two-Way Load-Holder FIGS. 22-24 illustrate the application of the invention to a two-way load-holder useful in power trains in which torque may be applied to the load in either direction of rotation, and in which the load is liable to apply a back torque to the power train in either direction. Such a situation is shown very diagrammatically in FIGS. 23 and 24. There, load-holder 500 forms part of a power train between power source 501 and conveyor system 502. The conveycr system is one which has a crest or high point in it, and as FIGS. 23 and 24 are drawn, is transporting bulk material from right to left. In FIG. 23, the heavier load is to the right of the power source. If a power failure occurs while this situation obtains, the conveyor will run away to the right, i.e. in the backward direction, in the absence of means for holding it in stopped position. In FIG. 24, the heavier load is to the left of the power source. If a power failure occurs while this situation obtains, the conveyor will run away to the left, i.e. in the forward direction, in the absence of means for holding it in stopped position. FIG. 22 illustrates the structure of load-holder 500. It comprises drum 503, mounted by bracket 505 so it will not rotate; belt driven input shaft 506; output shaft 507, driving belt 508; and pillow blocks 509, 510. The parts mounted internally of drum 503 are the same in structure and arrangement as those in the winch embodiment of FIG. 1, and they operate in the same way. Thus, they include yoke 511, mounted on input shaft 506; disk 512 carrying pin 513, shoes 514 and 515; and spanner bar 516. In operation, load holder will transmit torques in either direction of rotation from the input shaft to the output shaft, but will block transmission of back torques in either direction applied by the output shaft, and thus effectively hold the load against movement in the event of a failure in the power train. F. The Invention as Embodied in Another Bi-Directional Stepping Clutch FIGS. 25-30 illustrate the torque transmitting and blocking device of the invention in another bi-directional stepping clutcn differing somewhat in arrangement from the bi-directional stepping clutch shown in FIG. 10A and discussed above. In FIGS. 25-30 the bi-directional stepping clutch is designated generally as 600. It includes an input means 601, in the form of a short hollow collar-like shaft, which may be connected to a source of torque in various ways. Mounted for rotation with input shaft 601, and preferably formed integrally with it is cylindrical drum 602. Output means 603 are provided in the form of a solid output shaft, on which is mounted output collar 604. Collar 604 is fixed for rotation with the output shaft by a set screw 605 (See FIG. 27) threaded into a hole 606 in the output collar, and seated in longitudinal groove or flat 607 in shaft 603. The output collar is provided with a hollow cylindrical axial extension 608 which is of such a length that when the parts are assembled, it fits through hollow input shaft 601. A circumferential groove 609 on the extension accepts keeper 610 to fix the axial relationship of the parts. Input shaft 601 is provided with an internal anti friction bushing 611 to reduce friction between it and the extension 608 when they are in relative rotation. A pair of shoes 612, 613, are provided. The outer surfaces 614, 615 of the shoes conform to the cylindrical inner surface 616 of drum 602, and the shoes fit within the drum in much the same manner as the shoes of the embodiments discussed above. Each of the shoes 612, 613, is provided with a laterally extending shoe shoulder 617, 618, the generally radially oriented faces of which comprise the force transmitting surfaces of the shoes. These are numbered 619, 620 on shoe shoulder 617, and are numbered 621, 622 on shoes shoulder 618. A stop collar 623 is provided to serve as the control element of the clutch. It is generally cylindrical, and has a cylindrical bore sized to match the outside diameter of the main portion of output collar 604, as well as the curvature of the outer surfaces of shoe shoulders 617, 618. In the bore of stop collar 623 is mounted tang 624, which comprises a force transmitting means. Tang 624 fits between shoe shoulder faces 619 and 621, it being remembered that these comprise force transmitting means. On the outside surface of stop collar 623, a stop 625 is provided, preferably at a position diametrically opposite tang 624. Output collar 604 has mounted thereon a tang 629 which fits between shoe shoulder faces 620 and 622, and which comprises a force transmitting means cooperating with those force transmitting surfaces. The embodiment of the invention shown in FIGS. 25-30 employs a spanner ring instead of a spanner bar to perform the function of positioning the shoes in the drum so that the shoes bear against it, are displaceable toward one another at their ends across the drum axis from the spanner, and will jam against the drum upon application of forces tending to spread them at those same ends. Spanner ring 626 is sized to fit within the curved inner surfaces of shoes 612, 613 and to bear against those surfaces to achieve the above enumerated functions. The axis 627 of the spanner ring is offset from the axis 628 of the unit as a whole, which is also the drum axis. Attention is now directed to FIG. 30, from which it can be seen that the axis 627 of the spanner ring is offset from the drum axis 628, which is also the axis of the unit taken as a whole. For the spanner ring 626 to function as the spanner bar of the earlier discussed embodiments does, its effective centerline is taken as an extension of a spanner ring diameter struck perpendicular to the direction in which the ring is offset from the drum axis. In FIG. 30, this direction is indicated by arrow 630, and the effective centerline of the ring is indicated by dashed line 631. Also shown on FIG. 30 is a radial dashed line 632 between the drum axis 627 and the point at which effective centerline 631 intercepts the inner surface of the drum, this point being designated 633. Constructed line 634 is struck perpendicular to effective centerline 631, and constructed line 635 is struck from radial line 632. The angle between lines 634 and 635 is designated 636 and is in the lock angle range for the materials from which the shoes and drum are constructed. So long as the drum, shoes, and spanner ring are proportioned and constructed so that angle 636 is in the lock angle range, the device will function in accordance with the invention. As can be seen in FIGS. 27-29, means are provided for cooperation with stop 625 on control collar 623. These are in the form of spring biased dogs 637 and 638. The dogs may be constructed in various ways and be actuated in various manners, both powered and manual. It is only necessary that each dog be selectively positionable with respect to stop 625 to block rotation of control collar 623 in one direction, while permitting rotation of collar 623 in the other direction. As can be seen from FIGS. 28 and 29, when dog 637 is in the withdrawn position (FIG. 28) collar 623 is free to rotate in the clockwise direction, since dog 637 is out of the path of rotation of stop 625, and the stop can ride over dog 638 against its spring bias. As will be explained more fully below, torque and rotary motion are transmitted from the input shaft to the output shaft when stop collar 623 is free to rotate in the direction of rotation applied at the input shaft. This condition is illustrated in FIG. 28, and in FIG. 27. On the other hand, when stop collar 623 is blocked by a dog from rotation in the direction of applied torque, as is shown in FIG. 29, torque transmission from the input shaft to the output shaft is blocked. With the foregoing description of the bi-directional stepping clutch of FIGS. 25-30 in hand, its mode of operation may now be described with particular reference to FIG. 30, but with the other FIGS. held in view. As a starting condition, assume that torque is being applied to the input shaft to rotate integral drum 602 in the clockwise direction, as indicated by arrow 639 and that a dog is blocking clockwise rotation of stop collar 623 by working against stop 625, as indicated by arrow 540 in FIG. 30. Under this condition, shoes 612 and 613 will attempt to rotate clockwise with the drum. But such rotation will be blocked when face 619 of shoe 612 encounters tang 624 on stationary stop collar 623. Tang 624 exerts a counter clockwise force on the shoes, tending to displace the shoe faces 620 and 622, which are across the drum axis from the axis 627 of spanner ring 626, toward each other. The shoes thus move out of jamming or heavy frictional engagement with the rotating drum, and remain stationary. Remaining stationary, they can exert no rotative force on tang 629 of the output collar 604r and hence transmission of torque from the input shaft to the output shaft is effectively blocked. A consideration of the symmetry of the parts will lead to the conclusion that the device of FIG. 30 will operate in the manner just described if the direction of rotation of drum 602 is reversed to become counterclockwise, and a dog is positioned to prevent rotation of stop collar 623 in the counterclockwise direction. The clutch is thus bi-directional in its torque blocking capacity. Assume now that the restraining force on stop 625 represented by arrow 640 is removed while drum 602 is being driven clockwise, as shown in FIG. 30. Face 619 of shoe 612 remains in contact with tang 624 of the stop collar, but it now rotates the stop collar clockwise as it attempts to rotate with the rotating drum, inasmuchas the tang 624 is no longer restrained against rotation. The shoes (and tang 624) thus rotate clockwise slightly in frictional association with the rotating drum. After only a very slight rotation in this mode, face 622 of shoe 613 encounters tang 629 of the output collar, which until this point has remained stationary. Tang 629 transmits to shoe 613 a reactive force derived from the inertia of the load. This reactive force throws the shoes into jamming relationship with the inner surface of the rotating drum, and the shoes commence locked clockwise rotation with the drum. In doing so they transmit torque to tang 629 of the output collar, and hence to output shaft 603. Again, a consideration of the symmetry of the parts will reveal that the same mode of operation will obtain if the drum is rotated counterclockwise. The clutch is thus bi-directional in its ability to transmit torque. If stop collar 623 is again restrained from rotation, as by stop 625 encountering a dog newly positioned to intercept its clockwise rotation, arrested tang 624 throws the jammed shoes out of jamming relation with the rotating drum. The shoes halt rotation and cease transmission of torque to tang 629 of the output collar. The conditions with which this example began obtain once more. G. The Invention as Embodied. in Another Uni-Directional Stepping Clutch FIGS. 31-33 illustrate a uni-directional stepping clutch of the invention which differs somewhat from the uni-directional clutch of FIGS. 10-18. The structure of the clutch of FIGS. 31-33 is very similar to that of the bi-directional clutch of FIGS. 25-30, discussed immediately above, and reference is made to that discussion for a primary understanding of the FIG. 31-33 clutch also. Only the differences between these two clutches will be discussed here. In some applications there is only need to selectively block and permit torque transmission in a single direction. In such situations the clutch of FIGS. 25-30 is modified as shown in FIGS. 31-33 by providing the recesses 710, 711, in the shoe shoulders to establish additional force transmitting surfaces for the shoes. The stop collar tang 712 is relocated to cooperate with one or the other of these recesses, depending upon whether a clockwise or counterclockwise capability is desired. In all other respects the structure of the clutch is the same as discussed above, and its mode of operation is the same, except that its torque blocking and transmitting capabilities are limited to a single direction of rotation. The invention also provides a stepping clutch, characterised in that it comprises an input shaft, a generally cylindrical drum mounted for rotation with said input shaft, an output shaft axially aligned with said input shaft, a collar mounted for rotation on said output shaft within said drum, said collar having a radially extending tang, a pair of arcuate shoes positioned in said drum on opposite sides of said collar tang, a spanner ring extending between said shoes and engaging them at least at points on the same side of the drum axis as said tang, a control collar mounted for rotation on said output shaft having means thereon engagable with a shoe, and means for selectively restraining rotation of said control collar in at least one direction. Alternatively the stepping clutch is characterised in that it comprises an input shaft, a generally cylindrical drum mounted for rotation with said input shaft, an output shaft axially aligned with said input shaft, a collar mounted for rotation on said output shaft within said drum, said collar having a radially extending finger, a pair of arcuate shoes positioned in said drum on opposite sides of said collar finger, a spanner bar extending between said shoes and engaging them at points on the opposite side of the drum axis from said finger, a disc mounted for rotation on said output shaft having means thereon engagable with a shoe, and means for selectively -restraining rotation of said disc in at least one direction. The restraining means may be constructed and arranged to selectively restrain rotation in either direction. A load holder in accordance with the invention is characterised in that it comprises a rotatable shaft, a generally cylindrical drum fixedly mounted axially of said shaft, a pair of arcuate shoes positioned for sliding rotation within said fixed drum, a spanner bar extending between said shoes and engaging them at points on the same side of said drum axis, a disc mounted for rotation on said shaft, a transverse hole in one of said shoes, and a pin on said disc extending into said hole. A two-way load holder, is characterised in that it comprises a rotatable output shaft, a power input shaft axially aligned with said output shaft, a generally cylindrical drum fixedly mounted against rotation aligned axially with said output shaft, a pair of arcuate shoes positioned for sliding rotation within said fixed drum, the ends of said shoes being spaced apart, a spanner bar extending between said shoes and engaging them at points to one side of the axis of said fixed drum, a yoke mounted for rotation with said input shaft and engagable with said shoes at points on the other side of the axis of said fixed drum from said spanner bar, a disc mounted on said output shaft for rotation therewith, and a pin mounted on said disc and extending between said shoe ends on the other side of said fixed drum axis from said spanner bar in position to transmit forces to and from the ends of said shoes. A winch in accordance with the invention is characterised in that it comprises a rotatable cable drum having end flanges, a power input shaft passing axially through said cable drum, a generally cylindrical drum fixedly mounted against rotation at one end of said cable drum and aligned axially therewith, a pair of arcuate shoes positioned for sliding rotation within said fixed drum, the ends of said shoes being spaced apart, a spanner bar extending between said shoes and engaging them at points to one side of the axis of said fixed drum, a yoke mounted for rotation with said input shaft and engagable with said shoes at points on the other side of the axis of said fixed drum from said spanner bar, and a pin mounted on an end flange of said cable drum and extending between said shoe ends on the other side of said fixed drum axis from said spanner bar in position to transmit forces to and from the ends of said shoes. In an alternative aspect of the invention, apparatus for selectively transmitting torque from a torque input means to a torque output means, and for blocking transmission of torque from said output means is characterised in that it comprises a drum having a cylindrical inner surface, a wedging or spanner bar or ring, surfaces adjacent the outer surface of said spanner ring or opposite ends of the spanner bar bearing against the inner surface of said drum at pairs of opposed points on said inner surface, each of said pairs of opposed points being located so that a first line joining them is parallel to but offset from a diameter of said drum and so that a second line struck perpendicular to said first line at either of said points forms a jamming angle with a drum inner surface tangent struck from either of said points,first force transmitting means to apply a first force to said spanner ring or bar such that said first force results in application of force through said spanner ring or bar to urge said spanner ring or both ends of said spanner bar substantially radially of said cylindrical inner surface to frictionally engage said opposed portions of the cylindrical inner surface, and second force transmitting means to apply a second force to said spanner ring or bar to move said spanner ring or bar relative to the central axis of the cylindrical inner surface to prevent simultaneous engagement of opposite sides of said spanner ring or bar with the cylindrical inner surface. The jamming angle is preferably approximately 70. Second force transmitting means may be adapted to move said surfaces into jamming relationship with the cylindrical inner surface of said drum. The first force transmitting means may be adapted to remove said surfaces from jamming relationship with the cylindrical surfaces of said drum. According to another aspect of the invention, apparatus for selectively transmitting torque from a torque-input means to a torque output means, and for blocking transmission of torque from said output means to said input means is characterised in that is comprises a drum having a generally cylindrical inner surface and a central axis, a spanner bar or ring having a length which is slightly less than the distance between pairs of opposed points on said generally cylindrical inner surface each of said pairs of opposed points being located so that a first line joining them is parallel to but offset from a diameter of said drum, said spanner bar or ring having surfaces adjacent opposite ends thereof engagable with said pairs of opposed points on said inner surface, a diametrically extending second line through one of said contact points and the drum axis and said first line intersecting at an angle which is sufficiently small to permit rotation of said spanner bar or ring relative to said cylindrical inner surface when a force is applied in a first direction to the spanner bar or ring tending to rotate the spanner bar or ring in a direction to move said opposite sides of said spanner ring or opposite ends of said spanner bar out of jamming relationship with said inner cylindrical surface and to jam said opposite sides of said spanner ring or opposite ends of said spanner bar into engagement with said inner surface to prevent rotation of said spanner bar or ring relative to said inner cylindrical surface when force is applied in a second direction to said spanner bar or ring tending to rotate said bar or ring in a direction opposite to said first direction, and force transmitting means adapted to apply force in said first or second direction to said spanner bar or ring. The force transmitting means preferably comprises a pin or a tang, and means supporting said pin or tang for rotation about the axis of said cylindrical inner surface such that movement of the pin or tang relative to said spanner bar or ring results in application of force to said spanner bar or ring. The apparatus may be further characterised by the addition of means to prevent movement of the line extending through each of said contact points when a force is applied tending to move said line past the central axis. Alternatively, the force transmitting means may be adapted to apply a first force in a direction to urge said spanner ring or a central portion of said spanner bar toward the central axis or a second force in a direction to urge said spanner ring or a central portion of said spanner bar away from the central axis.

Claims: CLAIMS 1. Apparatus for selectively transmitting torque from a torque input means to a torque output means, and for blocking transmission of torque from said output means to said input means, characterised in that it comprises: a drum having a cylindrical inner surface; a pair of shoes positioned within said drum, each of said shoes having an arcuate surface bearing against the inner surface of said drum; a spanner means extending between said shoes and engaging their inner surfaces at least at points lying on the same side of the axis of said drum; said shoes being displaceable toward each other at their ends lying on the side of the drum axis opposite their points of engagement with said spanner means; said shoes having among them at least two force transmitting surfaces oriented generally radially of said drum; force transmitting means engagable with each of said surfaces; ; one of said force transmitting surfaces being oriented such that a force applied generally orthogonally therethrough by said force transmitting means sets a shoe in jamming relationship with the inner surface of said drum; and the other of said force transmitting surfaces being oriented such that a force applied generally orthogonally therethrough by said force transmitting means slidingly rotates said shoes within said drum without jamming thereagainst. 2. Apparatus according to Claim 1, characterised in that the spanner means is a spanner bar. 3. Apparatus according to Claim 2, characterised in that it comprises means biasing the ends of said shoes lying on the side of the drum axis opposite their points of engagement with said spanner bar away from each other. 4. Apparatus according to Claim 2 or 3 characterised in that at least one of said force transmitting surfaces comprises an end of a shoe. 5. Apparatus according to Claim 2, 3 or 4 characterised in that at least one of said force transmitting surfaces comprises a wall of a cavity formed on the radially inward surface of a shoe. 6. Apparatus according to Claim 2, 3 or 4, characterised in that at least one of said force transmitting surfaces comprises a wall of a cavity formed on a surface of a shoe which lies transverse to the axis of said drum. 7. Apparatus according to Claim 2, 3 or 4, characterised in that at least one of said force transmitting surfaces comprises an extension of said shoe projecting axially of said drum. 8. Apparatus according to any of Claims 2 to 7, characterised in that said force transmitting means comprises a shaft axially aligned with the axis of said drum and a yoke mounted for rotation with said shaft, said yoke being engagable with at least one of said force transmitting surfaces. 9. Apparatus according to Claim 8, characterised in that said shaft is rotatable in both directions and said yoke is engagable with two oppositely facing force transmitting surfaces. 10. Apparatus according to any of Claims 2 to 7, characterised in that said force transmitting means comprises a shaft axially aligned with the axis of said drum and a disc mounted for rotation with said shaft, said disc having a pin thereon or slot therein, the pin or slot being engagable with at least one of said force transmitting surfaces. 11. Apparatus according to any of Claims 2 to 7, characterised in that said force transmitting means comprises a shaft axially aligned with the axis of said drum and a collar mounted for rotation with said shaft, said collar having radially extending finger thereon engagable with at least one of said force transmitting surfaces. 12. Apparatus according to Claim 2, characterised in that said torque input means and said torque output means comprise a shaft mounted axially of said drum, and being rotable with respect thereto, said force transmitting surfaces comprises two surfaces on a single shoe, and, said force transmitting means comprises a single element mounted for rotation with said shaft and engagable with each of said force transmitting surfaces. 13. Apparatus according to Claim 12, characterised in that said force transmitting surfaces comprise opposite sides of a axially extending hole in said single shoe and in that said force transmitting means comprises a pin on said single element extending into said hole. 14. Apparatus according to Claim 2, characterised in that said torque input means comprises a first shaft mounted axially of said drum and rotatable with respect thereto, said torque output means comprises a second shaft mounted axially of said drum and rotatable with respect thereto, said force transmitting surfaces comprise four surfaces, each of said shoes having a surface of the one kind and a surface of the other kind, and said force transmitting means comprises a first force transmitter mounted for rotation with said first shaft and engagable with both surfaces of said other kind a second force transmitter mounted for rotation with said second shaft and engagable with both surfaces of said one kind. 15. Apparatus according to Claim 14, characterised in that said force transmitting surfaces of said other kind comprise walls of cavities formed on the radially inward surface of each shoe, and said first force transmitter comprises a yoke having two legs, one of which extends into each of said cavities. 16. Apparatus according to Claim 14, characterised in that said force transmitting surfaces of said one kind comprise opposed end faces of said shoes, and said second force transmitter comprises an element extending radially of said drum axis and having a part interposed between said opposed end faces. 17. Apparatus according to Claim 2, characterised in that said torque input means comprises a first shaft rota tably mounted axially of said drum and adapted to rotate said drum therewith, said torque output means comprises a second shaft rotatably mounted axially of said drum, said force transmitting means comprises a first force transmitter mounted for rotation axially of said drum and engagable with said other surface of said shoes and a second force transmitter mounted for rotation with said second shaft and engagable with said one surface of said shoes, and means are provided for selectively admitting and restraining rotation of said first force transmitting means in the same direction as the direction of rotation of said drum. 18. Apparatus according to Claim 17, characterised in that said first shaft is adapted for rotation in both directions, said force transmitting surfaces comprise four surfaces, each of said shoes having a surface of the one kind and a surface of the other kind, said first force transmitter is engagable with both of the surfaces of the other kind, said second force transmitter is engagable with both of the surfaces of the one kind, and said means for selectively admitting and restraining rotation of said first force transmitting means include means for selectively admitting and restraining rotation in both directions. 19. Apparatus according to Claim 2, characterised in that said spanner bar is so positioned with respect to the drum axis that a perpendicular struck from its centerline at the intersection of the centerline with the inner drum surface forms an angle with a drum inner surface tangent struck from the same point which is in the lock angle range for the materials employed to form the drum and shoe surfaces. 20. Apparatus according to Claim 1, characterised in that the spanner means is a spanner ring. 21. Apparatus according to Claim 20, characterised in that said spanner ring is so positioned with respect to the drum axis that a perpendicular struck from its effective centerline at the intersection of the centerline with the inner drum surface forms an angle with a drum inner surface tangent struck from the same point which is in the lock angle range for the materials employed to form the drum and shoe surfaces. 22. Apparatus according to Claim 20 or 21, characterised in that at least one of said force transmitting surfaces comprises an end of a shoe. 23. Apparatus according to Claim 20 or 21, characterised in that at least one of said force transmitting surfaces comprises a wall of a cavity formed on a surface of a shoe which lies transverse to the axis of said drum. 24. Apparatus according to Claim 20 or 21, characterised in that at least one of said force transmitting surface comprises an extension of said shoe projecting axially of said drum. 25. Apparatus according to any of Claims 20 to 24, characterised in that said force transmitting means comprises a shaft axially aligned with the axis of said drum and a collar mounted rotatably on said shaft, said collar having a tang thereon engagable with at least one of said force transmitting surfaces. 26. Apparatus according to Claim 20 or 21, characterised in that said torque output means comprises a shaft mounted axially of said drum and rotatable with respect thereto, said force transmitting surfaces comprise two surfaces on a single shoe, and said force transmitting means comprises a single element mounted rotatably on said shaft and engagable with each of said force transmitting surfaces. 27. Apparatus according to Claim 20 or 21, characterised in that said force transmitting surfaces comprise opposite sides of a axially extending recess in said single shoe and said force transmitting means comprise a tang on said single element extending into said hole. 28. Apparatus according to Claim 20 or 21, characterised in that said torque input means comprises a first shaft mounted axially of said drum and rotatable therewith, said torque output means comprises a second shaft mounted axially of said drum and rotatable with respect thereto, said force transmitting surfaces comprise four surfaces, each of said shoes having a surface of the one kind and a surface of the other kind, and said force transmitting means comprise a first force transmitter mounted rotatably on said first shaft and engagable with both surfaces of said other kind and a second force transmitter mounted for rotation with said second shaft and engagable with both surfaces of said one kind. 29. Apparatus according to Claim 28, characterised in that said force transmitting surfaces of said one kind comprise opposed end faces of said shoes, and said second force transmitter comprises an element extending radially of said drum axis and having a part interposed between said opposed end faces. 30. Apparatus according to Claim 20 or 21, characterised in that said torque input means comprises a first shaft rotatably mounted axially of said drum and adapted to rotate said drum therewith, said torque output means comprises a second shaft rotatably mounted axially of said drum, said force transmitting means comprises a first force transmitter mounted for rotation axially of said drum and engagable with said other surface of said shoes and a second force transmitter mounted for rotation with said second shaft and engagable with said one surface of said shoes, in that means are provided for selectively admitting and restraining rotation of said first force transmitting means in the same direction as the direction of rotation of said drum. 31. Apparatus according to Claim 30, characterised in that said first shaft is adapted for rotations in both directions, said force transmitting surfaces comprise four surfaces, each of said shoes having a surface of the one kind and a surface of the other kind, said first force transmitter is engagable with both of the surfaces of the other kind, said second force transmitter is engagable with both of the surfaces of the one kind, and said means for selectively admitting and restraining rotation of said first force transmitting means include means for selectively admitting and restraining rotation in both directions.

Inventors: WEST, JOE EDWARD
Applicants: WEST, JOE EDWARD
Application year: 1980
Main classification: F16D41
IPC codes: F16D41, B66D1