Winch brake mechanism

Abstract: A brake mechanism for a vehicle winch is automatically applied when the applied torque of the drive motor ceases and automatically released upon application of motor torque. Brake pads (22) move radially outward against the interior of a drum (12) to effect braking and retract radially inward to effect release of the brake. The pads have tapered ends that mate with opposed frusto-conical shoes (24,26). A cam (30) is rotatable with respect to a cam follower (40) in one direction to force one shoe toward the other to force the pads radially outward to engage the interior surface of the drum. Rotation of the cam with respect to the cam follower in the opposite direction releases the braking action. A wave spring (46) is incorporated to eliminate chatter as the brake is applied and released. The configuration of the brake components provides a conductive path for the dissipation of heat generated by the braking action.

Description: This invention relates to a brake mechanism for a winch, the mechanism having particular application to the control of the unwinding play out of the winch cable when the cable is under unwinding induced load tension. The type of winch particularly contemplated herein is a winch mounted to the front bumper of a vehicle, typically, a vehicle that has four-wheel drive and is driven on off road terrain. The winch includes a rotatable drum, a cable to be wound onto and off the drum, a motor, and a brake mechanism that controls the drum rotation. The winch may be used to pull the vehicle up steep hills through mud or snow and for lowering the vehicle down steep slopes. Lowering a vehicle down a steep slope, in particular, creates a braking problem for the winch with which the present invention is concerned. A heavy weight or force pulls against the cable and urges unwinding of the cable from the drum. The drum can be locked against rotation to prevent unwinding quite satisfactorily by a number of kinds of brake design. However, if the cable is to be controllably played off the winch, as when lowering the vehicle down a slope, the braking action is required to controllably resist or slow the drum rotation in order to maintain control over the play out. In known brake systems, the application of such controlled resistive, as differentiated from preventive, braking action generates excessive heat, creates rapid wear, and results in early brake failure. According to the present invention there is provided a brake mechanism for a winch having a drum rotatable to wind a cable onto the drum in one direction of rotation and off the drum in the other direction of rotation, and an interconnecting mechanism inter connecting a motor driven drive shaft and the drum for rotatably driving the drum, the interconnecting mechanism including a gear train reducing the rotational speed of the drum relative to the drive shaft the brake mechanism comprising at least one movable brake member located inside the drum and a brake surface of the drum, the brake member being movable towards and away from the brake surface between engagement so as to restrict rotative movement of the drum characterised by a cam mechanism for activating the brake mechanism, comprising a cam actuator and a cam follower having respective cooperating cam surfaces, the brake member being carried on one of the cam actuator or cam follower the cam surfaces being relatively movable to an axial nesting engagement position by relative rotational movement of the cam actuator and cam follower in a first rotative direction and to an axial separation position by relative rotational movement of the cam actuator and the cam follower in a second opposite rotative direction, and a biasing member connected to the cam actuator and the cam follower to bias relative rotative movement in the second, axial separation, direction, and coupling means coupling the drive shaft to the cam mechanism on rotation of the drive shaft to oppose the biasing member and urge the cam actuator and the cam follower in relative rotative movement in the first direction to disengage the brake mechanism. In the preferred embodiment, the brake mechanism is contained within the hollow cable drum with brake pads that radially expand against the inner wall of the drum. The drum itself absorbs the heat generated by the braking action which is conducted to the outer side of the drum and thus to the atmosphere. The prior problem of excessive heat is thereby alleviated. The brake pads are part-round segments that cooperatively form an open ended cylinder that is circumferentially expandable. The open ends form frusto-conical end surfaces. Frusto-conical shaped shoes are axially positioned at the open ends of the brake pad segments, one being axially stationary and the other axially movable. For brake engagement, an axially directed force is applied to the movable shoe to force the conical surfaces of the open ends of the cylindrically arranged brake pads. The conical shape of the two shoes in concert acting against the conical surfaces of the brake pads forces radial expansion of the segments against the drum wall. For brake disengagement, the axial force on the movable shoe is removed to allow the brake pad segments to collapse inwardly away from the drum wall. The axial force applied to the movable shoe is cam actuated, i.e., a cam is biased by a torsion spring to rotate against a cam follower with the cam surfaces thereby urging axial movement of the shoe toward brake engagement. The biasing of the torsion spring is to supply the initial but low brake drag resistance. It is the load on the wire rope that causes the cam follower to ride up further on the cam, thus increasing brake resistance substantially and proportional to the load on the wire rope. The winch motor can be driven in both directions, one to wind and the other to permit unwinding of the cable onto and off of the drum. In the wind up direction, the cam follower is engaged by a motor shaft coupling to urge rotation counter to the spring biased rotation, thereby relaxing the brake and allowing the motor to drive the drum in the wind up direction. In the unwind direction, the cam (rather than the cam follower) is engaged which also is counter to the spring biased rotation, thereby relaxing the brake and allowing the load tension to controllably unwind the cable. The rotatable drum is directly coupled to the cam follower and rotation of the drum and cam follower as induced by the load pulling the cable and which becomes faster than the rotation of the motor driven cam allows re-engagement of the brake. This unwinding action results in a brake release/brake engagement repetition that is largely alleviated by a wave spring that permits restricted axial movement of the cam follower and avoids chatter. The invention is further described below, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a view of a motorised winch having a drum for winding and unwinding a length of cable and having a brake mechanism in accordance with the present invention; Fig. 2 is a cut away view on a larger scale of the drum of Fig. 1 showing the brake mechanism of the present invention; Fig. 3 is a view on view lines 3-3 of Fig. 2; Fig. 4 is an exploded view of the brake mechanism of Fig. 2; and Fig. 5 illustrates a gear train coupling incorporated in the winch of Fig. 1. The illustrated winch 10 is suited for mounting to a vehicle (not shown) such as a four-wheel drive pickup or the like. The winch 10 has a rotatable hollow cylindrical drum 12 for winding and unwinding a length of wire rope or cable 14 on its periphery. The drum 12 may be positively driven in either direction by a reversible motor 16. The motor 16 is typically electric, receiving its power input from the vehicle battery, but other types of motors, for example, hydraulic motors, may be utilised to provide the motive power to drive the winch 10. The motor 16 is coupled to the drum 12 by a speed reducing gear train 19 contained in an end housing 18 (Figure 5). The gear train reduces the rotational speed of the drum with respect to that of the motor, and thus provides torque amplification, in a manner such as disclosed in US-A-4 545 567. A shift lever 17 is provided to disengage the gear train so the drum may be rotated free of the gear train to allow the cable 14 to be played out off the drum, for example, manually. A brake 20 is provided in the interior cavity of the drum 12 between the drive motor 16 and the gear train in the end housing 18. The brake 20 is shown in detail in Figs. 2-4. It utilizes brake pads 22 that are segments of a cylinder having an outside dimension that closely approximates the interior dimension of the cylindrical drum 12. The pads 22 have internal tapers 23 at each of their ends and co-operatively form frusto conical surfaces that mate with frusto conical shoes 24,26. Axial movement of the shoes 24,26 inwardly against the internal tapers 23 of the pads 22 forces the pads, by way of a form of camming action, to move radially outward to frictionally engage the interior surface of the drum to thus cause a braking or locking of the drum, relative to the pads 22 and shoes 24,26. The shoe 24 is fixedly coupled to the shaft 29 which couples the rotation of shaft 28 to the gear train in the end housing 18. An end portion 32 of the shaft 28 is serrated and the shoe 24, which has a serrated bore 34, is pressed on the end 32 to fixedly secure the shoe 24 to the shaft 28. The shoe 24, as previously mentioned, is frusto conical and has a tapered surface 26. The shaft 29 is coupled to the shaft 28 in that the hexagonally-shaped shaft 29 is received in a hexagonal bore in the end of the shaft 28. Shaft 29 is coupled to the gear train 19 (see Fig. 5) to thereby rotatably couple the brake shaft 28 to the gear train. The gear train 19 is designed to substantially reduce the rate of rotation as between the shaft 28 and the drum. By locking the shoe 24 to the drum through the pads 22, the gear train 19 cannot generate the relative rotation as between the drum and shaft 29 and is thereby locked and the drum is prevented from rotating. Axial movement of the shoes 24,26 away from each other and thus away from the internal tapers 23 of the pads 22, permits the pads to move radially inward to thus relieve the braking action and allow the drum to rotate. Axial movement of the shoes 24,26 is effected by co-operative action of a cam (actuator, hereinafter designated also as a cam,) and cam follower which will now be explained with reference to Figs. 2-4. A cam 30 is mounted on the shaft 28 but is free to move rotatably and axially relative to the shaft. The shoe 26 is fixedly attached to the cam 30 (and not to shaft 28) and thus will have the same rotative and axial movement as the cam 30. The frusto-conical shoe 26 has a tapered surface 38. A cam follower 40 having a splined bore 42 is fitted to a splined end portion 44 of the shaft 28 adjacent to the cam 30. The cam follower 40 is non-rotative with respect to the shaft 28, but can move axially along the splines on the splined end 44 of the shaft 28. As best seen in Fig. 4, the cam follower 40 has two radially extending ears 68 positioned at 180 degrees from each other. The cam 30 also has two radially extending ears 70 positioned at 180 degrees from each other. A wave spring 46 is mounted adjacent the cam follower 40 as shown in Fig. 2. A clip 48 is fitted in a groove 49 on the end of the shaft 28 adjacent the wave spring 46 to secure the assembly of the components on the shaft 28. Accordingly, the cam follower 40 can move axially away from cam 30 through compression of the wave spring 46 but such movement is resisted. The cam 30 is biased to rotate on the shaft 28 by a torque spring 50. One end 52 of the torque spring 50 is fitted in a bore 54 in the cam 30 and the opposite end 56 engages a groove 58 in the shaft 28. With reference to Figs. 3 and 4, the cam 30 is biased by the spring 50 to rotate clockwise with respect to the shaft 28 and thus to the cam follower 40 (spline fit thereto) as indicated by the directional arrow 60. As seen from Fig. 1-3, the motor 16 is coupled to the cam 30 and follower 40 by a coupling 62 fitted to the shaft 66 of the motor 16. The coupling 62 is cup shaped and has tow drive dogs 64 extending radially inward within the cup portion of the coupling 62. The cup portion of the coupling 62 fits over the radially extending ears 68,70 of the cam follower 40 and the cam 30 in a manner that positions the drive dogs 64 of the coupling for rotative engagement with ears the 68,70 of the cam follower and the cam. Camming action is provided by two sloping cam surfaces 80 provided on the end of cam 30 (forming wave-like peaks and valleys) which slidingly engage two similar sloping cam surfaces 82 on the cam follower 40. When the peaks of cam surfaces 80 are nested in the valleys of cam surfaces 82, the shoe 26 is withdrawn axially, the pads 20 are withdrawn radially and the drum is free to rotate. Upon relative rotation of the cam 30 to cam follower 40, the cam surfaces 80,82 are ramped part which forces axial movement of shoe 26 toward the pads 22 to lock the drum. The action of the spring 50 is to induce rotation of cam 30 in direction 60 relative to follower 40 and thus urges separation of the cam and cam follower. The action of rotation in direction 60 of the coupling 62 is to engage the ears 68 of the follower 40 which opposes the spring 50 action thereby producing the nested position of the cam and follower to relax the brake. Rotation of the coupling 62 in the opposite direction engages the ear 70 of cam 30 which also opposes the spring 50 action to again relax the brake. Thus, in either direction of rotation of the cam and follower initiated by spring 50, results in brake engagement (the load effecting the full braking action). The effect of these relative braking actions is explained in the following "Operation" section. OPERATION The brake 20 is normally applied or engaged whenever rotative torque from the motor is absent, by the cam action urged by the spring 50. An applied torque from the motor 16 in either direction is required to release the brake 20 to permit rotation of the drum 12. Consider first the condition in which it is desired to reel in the cable 14 onto the drum 12. This may be to pull a load, typically an object at a distance from the vehicle to which the cable is attached, or it may be desired to pull or assist in moving the vehicle by utilization of the winch with the end of the cable anchored. As previously stated, the brake 20 is normally applied to stop rotation of the drum and will remain applied until the drive motor 16 applies rotative torque to the brake 20. Referring to Fig. 3, the motor 16 is driven in the clockwise direction 60 to reel in the cable 14 on the drum 12. The drive dogs 64 of the coupling 62 will engage the ears 68 to rotate the cam follower 40. The cam 30 and the shoe 26 are in frictional engagement with the pads 22 and thus with the drum 12, and this rotation, as applied between the cam and cam follower, is opposite to the rotation urged by the spring 50. The effect of such motor driven rotation of cam follower 40 results in release of the braking action and because the cam follower 40 is splined to the shaft 28, through the gear train in housing 18 to the drum, the drum is rotated to reel in the cable. In the alternative condition in which a load is applied to the cable 14 and it is desired to play out cable 14 from the drum 12 under power, the motor 16 is driven counterclockwise, opposite to the direction of arrow 60. The drive dogs 64 of the coupling 62 will engage the ears 70 on the cam 30 to urge rotation of the cam in the counterclockwise direction. It will be recalled that the cam 30 is free to rotate on the shaft 28 independently of the cam follower 40. As the cam 30 is rotated by the motor 16, the cam 30 (and shoe 26) will move rotatably relative to follower 40, thus moving the cam surfaces 80,82 toward the nesting condition, resulting in movement of shoe 26 away from pads 22. The brake 20 is thereby relaxed just enough to permit the load on the cable 14 to force rotation of the drum 12 and play out of the cable. The motor torque in effect shifts the balance of forces from an overpowering brake force to an overpowering drum unwind force, that is, the motor 16 produces just enough torque to permit the force of the load to overcome the static action (converting it to a frictional steady braking action) and thereby effects controlled unwinding of the cable. The braking action as described to this point under the different operating conditions has dealt with the movement of the movable shoe 26 toward and away from the fixed shoe 24 to radially expand and retract the pads 22 to affect the application and the release of the brake. The rotative action of the motor 16 regardless of its direction of rotation always urges brake release, and the rotative action of spring 50 and the load on the cable always urge brake engagement. In the wind up rotative direction of motor 16, (direction 60) the load force (on the cable 14) is directly controlled by the action of the motor on the follower 40 (splined to shaft 28). Such rotation counters the rotation of the spring 50 but the spring continuously urged rotation of cam 30 away from cam follower 40. However, the slight frictional engagement between the shoe 26 and the pads 22 (possibly enhanced by friction between pads 22 and the drum interior) will ensure torsional compression of the spring 50 and maintain the shoe 26 in the retracted or released condition. In the opposite direction of motor drive, the rotative urging toward the engaged condition, induced by the load on the cable 14, can far exceed that of the spring 50. The countering forces applied to the cam 30 and follower 40 are, firstly, motor rotation of the cam 30 relative to follower 40 to release the brakes, then a load induced counter rotation of the follower relative to the cam to overtake the rotation of cam 30 thereby engaging the brake and stopping cable play out until the motor rotation again releases the brake, ad infinitum. This repetitive cycling of brake engagement end release set up a chatter that is undesirable. The function of the wave spring 46 serves to alleviate this chatter condition. Tests have shown that without the wave spring 46, the brake assembly is subject to abrupt impacts as the brake is applied and released resulting in severe vibrations or chattering which may rapidly damage or destroy the components of the brake 20. It is believed that the wave spring 46 provides a yieldable biasing force allowing the cam follower 40 to have a slightly rearward flexing action as the cam surfaces 80,82 are urged back and forth due to the rapid relative rotative changes of the cam 30 and the cam follower. The brake 20 is thus not abruptly applied to stop the drum 12, but is applied relatively gradually to thus decelerate the brake 20 and the drum 12 from a rotating condition to a stopped condition. This same flexing action is believed to provide for the gradual release of the brake. The brake 20 is of course driven by the motor at a much higher rate than the drum 12, the ratio being on the order of 200 to 1, so that the deceleration of the drum is not visually discernable. In a situation where the load on cable 14 is not sufficient to generate play out rotation of the drum, the coupling 62 driven by the motor will initially contact the ears 70 of the cam 30 and as rotation continues, the brake will be released as previously described. Since the load is not adequate to cause rotation of the drum, the cam 30 rotates relative to the cam follower 40 until the ears 68,70 are in alignment and the drive dogs 64 of the coupling 62 engage both sets of ears 68,70. The drive dogs 64 of the rotating coupling 62, by engaging the ears 68 of the cam follower 40, which is fixedly coupled to the drum 12, will rotate the drum. Alternatively, the operator can manually play out the cable without the use of the motor by disengaging the gear train, that is, by disengaging the shaft 28 from the drum 12 by operation of the lever 17. Additional observations are believed to be of some importance to optimum operation of the illustrated. First, the angle of the frusto conical surfaces 23 and mated surfaces 36 and 38 provided on the pads and shoes 24,26, is selected to force unassisted axial movement of movable pad 26 when the cam 30 and follower 40 are in the nested position. Using typical friction brake lining braking materials for the frusto conical faces, e.g., FMC NA104, manufactured by Friction Material Corp., South Bend, IN., the angle alpha (Fig. 2) is preferably about 25 degrees, with an acceptable range of about 15 degrees to about 35 degrees. Whereas the pads 22 are designed to slide rotatably relative to the cable drum 12 during cable wind up and unwinding, the initial release of the brake requires a rotative sliding of one of the shoes 24,26 relative to the pads 22. Shoe 26, of course, has to rotate relative to shoe 24 (which is locked to shaft 28) in order to collapse the spring 50 and release the brake. Whereas a drive train that includes gear reduction is common for winches of the type contemplated herein, such gear reduction is important to achieve braking of the drum rotation in the brake mechanism of the invention, because locking the drum 12 to the drive shaft 28 would not prevent rotation if the shaft and the drum were coupled for rotation at the same rate. Because the gear reduction imposes different rotative speeds for the drum and the drive shaft, the gear train 19 provides an important element in braking operation. The train 19 illustrated in Fig. 5 can suitably correspond to the mechanism illustrated in US-A-4 545 567 and is therefore not described herein in detail. The invention is not limited by the description and drawings but is to be determined by the appended claims.

Claims: A brake mechanism for a winch having a drum (12) rotatable to wind a cable (14) onto the drum in one direction of rotation and off the drum in the other direction of rotation, and an interconnecting mechanism inter connecting a motor driven drive shaft and the drum for rotatably driving the drum, the interconnecting mechanism including a gear train (19) reducing the rotational speed of the drum relative to the drive shaft the brake mechanism comprising at least one movable brake member (22) located inside the drum and a brake surface of the drum (12), the brake member being movable towards and away from the brake surface between engagement so as to restrict rotative movement of the drum characterised by a cam mechanism (30,40) for activating the brake mechanism, comprising a cam actuator (30) and a cam follower (40) having respective cooperating cam surfaces (80,82), the brake member being carried on one of the cam actuator (30) or cam follower (40). the cam surfaces (80,82) being relatively movable to an axial nesting engagement position by relative rotational movement of the cam actuator (30) and cam follower in a first rotative direction and to an axial separation position by relative rotational movement of the cam actuator (30) and the cam follower (40) in a second opposite rotative direction, and a biasing member (50) connected to the cam actuator (30) and the cam follower (40) to bias relative rotative movement in the second, axial separation, direction, and coupling means (62,64) coupling the drive shaft (66) to the cam mechanism (30,40) on rotation of the drive shaft to oppose the biasing member (50) and urge the cam actuator (30) and the cam follower (40) in relative rotative movement in the first direction to disengage the brake mechanism. A brake mechanism according to claim 1 wherein the drum (12) has an inner surface which is cylindrical, and the brake member comprises a plurality of brake pads (22) arranged to form a cylinder located inside the drum (12), the brake pads being radially movable toward and away from the brake surface of the drum (12) under the action of relatively axially displaceable tapered brake shoes mounted on the interconnecting mechanism and engaging opposite ends of the brake pads (22). A brake mechanism according to claim 1 or claim 2 wherein the biasing member (50) comprises a spring. A brake mechanism as claimed in claim 2 or 3 wherein one of the cam actuator (30) and the cam follower (40) is coupled to the movable brake shoe (26) for axial movement therewith in one direction, and wherein a second biasing member (46) permits restricted axial movement of the other of the cam actuator and cam follower in the opposite direction to cushion the effect of repetitive braking in the drum (12) during cable unwinding. A brake mechanism as claimed in any one of claims 2 to 4 and wherein the one of the cam actuator (30) and the cam follower (40) is engaged by the second biasing member (46) and the other of the cam and cam follower urges the movable shoe (26) toward the brake pads (22). A brake mechanism as claimed in claim 4 or 5 wherein the second biasing member is a wave spring (46) interposed between the shaft end and the one of the cam actuator (30) and cam follower (40). A brake mechanism as claimed in any one of claims 2 to 6 wherein the brake pads (22) have frusto conical end surfaces (23), and the fixed brake shoe (24) has a frusto conical surface (36) for co-operating with the end surfaces at one end of the brake pads, the movable brake show (26) has a frusto conical surface (38) for co-operating with the end surfaces at the other end of the brake pads, and the separating movement of the cam actuator (30) and the cam follower (40) moves the movable shoe against the adjacent end surfaces of the brake pads, the end surfaces at the opposite end being thereby forced against the frusto-conical surface of the fixed shoe to effect the radial movement of the brake pads. A brake mechanism as claimed in any one of claims 2-7 wherein the interconnecting mechanism includes a shaft (28) extending from one of the cam actuator and the cam follower having a spline fit to the shaft whereby rotation of the one of the cam actuator and cam follower forces rotation of the gear train and thereby rotation of the drum, and wherein the coupling means includes a drive dog (64) and the cam actuator and cam follower include ears (70,68) rotatively engageable by the drive dog, the rotative positions of the drive dog and ears being so arranged that in one rotative direction of the motor shaft the ear of the one of the cam actuator and cam follower is engaged by the drive dog and urged counter to the urging of the first-mentioned biasing member (50), and in the other rotative direction of the motor shaft the ear of the other of the cam actuator and cam follower is engaged by the drive dog and urged counter to the urging of the biasing member. A brake mechanism as claimed in claim 8 wherein engagement by the drive dog (64) with the ear of the one of the cam actuator (30) and the cam follower (40) urges cable wind-up rotation of the drum. A brake mechanism as claimed in claim 8 or 9 wherein the biasing member is a torsional spring (50), the spring having one end anchored to the shaft (28) to be thereby rotatively fixed to the one of the cam actuator (30) and cam follower (40), and the other end fixed under tension to the other of the cam actuator and cam follower to urge relative rotation there between. A winch comprising a housing, a cable drum assembly having opposed ends and a cylindrical exterior surface, said drum assembly rotatably mounted to the housing and a cable mounted to the drum to be wound onto and off of the drum upon altenate rotation of the drum, and a brake mechanism according to any one of the preceding claims.

Inventors: TELFORD THOMAS M, TELFORD, THOMAS M.
Applicants: WARN IND INC, WARN INDUSTRIES, INC.
Application year: 1992
Main classification: B66D5
IPC codes: B66D1, F16D59, B66D5, F16D65, F16D51