GB2042655A

GB2042655A - Torque Limiting Clutch

Info

Publication number: GB2042655A
Application number: GB8004261A
Authority: GB
Original assignee: GKN Walterscheid GmbH
Current assignee: Walterscheid GmbH
Priority date: 1979-02-08
Filing date: 1980-02-08
Publication date: 1980-09-24
Also published as: DE2904683C2; GB2042655B; IT8006911V0; DE2904683A1; IT8005113A0; FR2448659A1

Abstract

A torque limiting clutch includes a driving member (9), a driven member (4), first biasing means (14) and second basing means (11), torque being transmitted from the driving member (9) to the driven member (4) through balls (10) located in slits in the driving member (9) and extending into recesses (24) in the driven member (4). When a predetermined torque is exceeded the balls (10) roll out of the recesses (24) causing momentary compression of the spring (14) and move to a non- torque transmitting position, (shown dotted), such movement causing an increase in the potential energy state of spring (11) which, once the speed of revolution of the driving member is reduced, causes the balls (10) to take up their torque transmitting position in recesses (24), the movement of the balls (10) into their torque transmitting position from their non- torque transmitting position not affecting the potential energy state even momentarily of the first biasing means (14). Thus the clutch can be automatically re-engaged merely by slowing down or stopping the drive shaft. A detent (18) may be provided to maintain the clutch in its disengaged condition. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Torque Limiting Clutches This invention relates generally to clutch assemblies and more particularly to a clutch assembly of the torque limiting type whereby when a predetermined level of torque transmission through the clutch is exceeded the clutch will automatically disengage thereby to limit the torque transmission therethrough.

More specifically, the invention relates to a type of clutch assembly comprising a driving member and a driven member and torque transmitting elements arranged therebetween and having a first position in which they engage with said driving and said driven members to enable torque to be transmitted therebetween, and a second position in which torque transmission is discontinued or limited.

Such a clutch is suitable for transmission of drive to machinery such as agricultural machinery and equipment from the power take-off shaft of an agricultural tractor.

A torque limiting clutch is described in West German GE-GM 1761856 which discloses a torque limiting clutch comprising a driving clutch member and a driven clutch member, the torque transmitting elements being in the form of balls retained in slits in one of the clutch members and engages in recesses in the other clutch member, the clutch members being urged together by an axial spring.

If the amount of torque to be transmitted by the clutch exceeds a predetermined value, the balls move out of the recesses and are guided into a concentric path of revolution by guide tracks formed in the driving clutch member. The clutch is re-engaged by reverse relative rotation of the two clutch members whereby the balls are restored to their torque transmitting position by virtue of the configuration of the slits.

A disadvantage of the clutch described in the above mentioned publication, in particular when applied to a drive shaft connecting an agricultural machine from a tractor, is that the clutch has to be manuaily re-engaged after an overload torque transmission has occurred. In practice, this means that the tractor driver has to dismount to reengage the clutch which can be very time wasting and tiring for the driver of the tractor, particularly when working in conditions where frequent disengagement is likely to occur.

It is an object of the present invention to provide a torque limiting clutch so constructed as to allow for automatic re-engagement after torque transmission has been discontinued by ceasing or reducing the revolutionary speed of the driving member.

According to the present invention we provide a torque limiting clutch comprising a driving member and a driven member, torque transmitting elements arranged therebetween, the torque transmitting elements having a first position in which they engage with both said driving and said driven members to enable torque to be transmitted therebetween, and a second position in which torque transmission is discontinued, first biasing means being provided for maintaining torque transmission until a predetermined torque level is reached, whereupon the torque transmitting elements move to their second position and wherein second biasing means are provided to bias the torque transmitting elements into their first position, the arrangement being such that during movement of the torque transmitting elements from their second to their first position there is no change in the amount of potential energy stored in the first biasing means.

The potential energy stored in the first biasing means will be changed, when, for example, the biasing means is compressed or reduced. Thus, while the torque transmitting elements move from their non-torque transmitting position to their torque transmitting position, there is no change in the potential energy stored by the first biasing means even for an instant of time.

One of the clutch members, i.e. the driving member or the driven member, may be provided with two paths along the first of which the torque transmitting elements move from a torque transmitting to a non-torque transmitting position, such movement causing energy to be initially stored and then released by the first biasing means, and a second path which is not the reverse of the first path along which the torque transmitting elements move from their non-toruqe transmitting position to their torque transmitting position, such movement causing no or negligible change in the energy state of the first biasing means.

Preferably, the path along which a respective torque transmitting element moves in said one of the driving or driven members in a direction from a torque transmitting to a non-torque transmitting position, includes a generally circumferentially directed component and a radial component; the path from a non-torque transmitting to a torque transmitting position may include only a radial component. The torque transmitting elements will only re-engage when they are aligned with the part leading to their respective torque transmitting positions.

Said one clutch member may include a first annular zone which has a substantially planar surface, against which the torque transmitting elements, which may be balls or rollers, may bear or come into contact when in the non-torque transmitting position, and a second annular zone in which there are provided a plurality of recesses, one for each torque transmitting element, which recesses are connected to the first annular zone by grooves formed in said one clutch member.

Preferably, said grooves are of constant depth or are of a depth which increases in a direction towards said recesses.

The second biasing means which may be a spring will provide a force which is considerably weaker than the first biasing means which may also be a spring, the strength of the first biasing means determining the torque value at which the clutch will disengage. The second biasing means will determine the speed at which the clutch will re-engage after disengagement.

The second annular zone of said one of the clutch members, which is preferably the driven member, may include an extension part extending along the rotational axis of the clutch, and the first and second annular zones may be connected by a transitional zone which may be of frusto-conical configuration or be step-like for example.

The grooves connecting the planar part to the recesses will be formed in the annular extension and will extend in a generally radial direction.

The ends of the grooves may provide the recesses, the distance of the recess or end of the groove from the transitional zone, being such that when the clutch is transmitting torque and the predetermined torque limit is reached, there will be a tendency for relative rotation to occur between the driving clutch member and the driven clutch member which will tend to cause rolling movement of the ball. The rolling movement, because of the relationship between the position of recess and said transitional zone and the diameter of the ball, tending to cause the ball to move along an initial circumferential path and then in a general direction towards the first zone which provides the planar surface with which the torque transmitting balls make contact in their second non-torque transmitting position.

Such a provision ensures that when the torque limit is reached, the clutch disengages correctly and the provision of having the grooves of equal depth along their length or of increasing depth towards the recesses ensures that the balls will be turned in a satisfactory manner to that torque transmitting position on a reduction of the speed differential between the driving and driven clutch members.

According to another aspect of the invention, the torque transmitting clutch is so arranged that the first biasing means provides little or no force to the torque transmitting elements when either in their torque transmitting position or their nontorque transmitting position. The only time that the potential energy state of the first biasing means is affected is during disengagement of the clutch from its torque transmitting position to its non-torque transmitting position.

The second biasing means may be provided by an annular member having slots through which the torque transmitting elements extend and being so arranged that it may rotate at least by a limited amount about the clutch axis relative to the driving member, the relative rotational position of the driving clutch member and the annular member may be biased by spring means, the arrangement being that longitudinal axes of the recesses or slots in the driving clutch member and the slots in the annular member are nonaligned with each other so that displacement of a torque transmitting element from its torque transmitting position will cause relative rotation between the driven clutch member and the annular member causing the spring to stretch and hence providing a biasing force tending to force the torque transmitting element back to its torque transmitting position.

The substantially planar first zone provides a non-torque transmitting contacting face with one of the clutch members and may be located either radially inwardly or radially outwardly relative to the clutch rotational axis of the second annular zone which provides the recesses with torque transmission. The second annular zone is preferably situated radially outwardly of the first annular zone in order that, in view of the larger size, the torque transmitting balls may receive support over their maximum possible effective diameter which enables a relatively small clutch to transmit as much torque as possible.

The second annular zone may alternatively be situated radially inwardly of the first annular zone, particularly in applications where the clutch is to be used at high revolutionary speeds, and the centrifugal force acting on the torque transmitting balls becomes significant. By placing the balls as near as possible to the axis when in their torque transmitting positions the centrifugal force is reduced to a minimum.

Means may be provided to maintain the torque transmitting elements in their non-torque transmitting position in order to permanently or temporarily disconnect a drive line.

The invention will now be described in more detail by way of example only with reference to the accompanying drawings wherein.

Figure 1 is a part sectional view of one embodiment of torque limiting clutch of the present invention; Figure 2 is a detailed illustration of the second biasing means; Figure 3 is a part sectional view of a second embodiment of torque limiting clutch of the present invention; Figure 4 illustrates means for maintaining the torque limiting clutch is a non-torque transmitting position; Figure 5 is another illustration of the means for maintaining the clutch in a non-torque transmitting position, illustrating the position of the torque transmitting elements; Figure 6 is a third embodiment of torque limiting clutch of the present invention.

Referring first to Figure 1, there is illustrated a torque limiting clutch comprising a hub-like member 9 which is adapted to be fitted in a drive shaft, for example the power take-off shaft of an agricultural tractor and which comprises a driving clutch member of the assembly.

The driven clutch member comprises a flangelike part 3 to which a joint fork 1 is secured or formed integrally therewith, the flange-like part 3 being rotationally rigidly connected to a plate member 4.

The plate member 4 and the flange-like part 3 are secured axially to the hub 9 by axial securing means 2.

The clutch hub 9 also has a flange-like extension in which radially directed recesses in the form of passageways or slits 21 are formed therein. Torque transmitting elements which are in the form of balls 10 are provided one to each slit 21.

Between the flange like extension of the clutch hub 9 and the driven plate member 4 there is provided an annular guide member 7 which is provided with slits 20, also through which the balls 10 extend. The longitudinal axis of the slits 20 are not parallel to the longitudinal axes of the slits 21 in the flange-like extension of the clutch hub 9 but include an angle therewith as illustrated in Figure 2.

Second biasing means in the form of a helical spring 11 is provided between the flange-like extension of the clutch hub 9 and the annular guide member 7, one end of the spring being hooked into a recess 19 on the annular member 7 andthe other end being connected to a spring support part 1 3 provided on the flange-like extension of the clutch hub 9.

As shown in Figure 2, the spring 11 holds the annular member 7 in such a position relative to the clutch hub 9 that the balls 10 are urged towards a radially outermost position.

In the embodiment shown in Figure 1, a first annular zone is provided in the form of a planar rolling surface 26 on the plate member 4 indicated at 26. The plate member 4 is provided with an extension 6 which projects axially relative to the rotational axis of the clutch, which axial extension provides a second annular zone and is connected to the first annular zone via a transitional region 24 between the surface 26 and extension 6, the transitional region 24 in this case is of frusto-conical configuration.

The extension 6 on the plate member 4 is provided with a plurality of recesses for accommodating the balls 10 when they are in their torque transmitting position. The recesses may comprise radially orientated slots, the recess terminating at the radially outermost point of the slot, the slot communicating with the substantially planar first zone 26.

When the torque limiting clutch is in a torque transmitting position, the balls 10 are retained in the recesses 24 due to the co-action between the annular guide member 7 and the flange-like extension of the hub 9 due to the force applied by the spring 11.

The torque limiting clutch is provided with first biasing means in the form of a spring 14 which bears on the axis of the clutch on the flange-like extension of the cluth hub 9. However, when no torque load is applied to the clutch, any axial force exerted by the spring 14 is not imparted to the torque transmitting elements 10 since the depth of the recesses 24 is such that the balls 10 are accommodated in their torque transmitting position, in a no-load situation, the end of the spring bearing only on the flange-like extension 9 and not imparting any resilient force to the balls 10.

When a torque load is applied to the clutch, there will be a tendency if the driven member meets with resistance, for the balls 10 to climb out of the recesses 24 i.e. there will be a tendency towards relative rotation between the plate member 4 and the flange-like extension of the hub 9 which immediately causes the spring member 14 adjacent the balls 10 to come into contact therewith and provide a resilient bias to oppose any tendency for the balls 10 to escape from the recesses 24.

When a predetermined nominal torque load of the clutch is exceeded, the balls 10 will climb in a circumferential direction out of their recesses 24 in the plate 4 since the tendency to roll out due to the torque load will overcome the force applied by the spring 14.

When an overload situation occurs and the balls 10 start to move out of their respective recesses 24, since the recesses are of such a configuration and the balls such a diameter that their centre lies radially inwardly of the innermost point of contact between the recess 24 and each ball 10, then their rolling movement will direct them both circumferentially and radially inwardly in the direction towards the substantially planar first zone 26.

When the balls 10 have reached the substantially planar first zone 26, the axial spring 1 4 will have reverted to its initial energy state before torque overload occurred and provide no force on the balls 10. The clutch will then be fully disengaged. Such movement of the balls 10 from their torque transmitting position to a non-torque transmitting position will have caused rotation of the annular guide member 7 relative to the flange-like extension of hub 9 in view of their intersecting obliquely aligned slots. Such relative rotation will have stretched the spring 11 which will have the effect of tending to cause the balls 10 to return to their torque transmitting position.

The force provided by the spring 11 may be very small compared to the force provided by spring 14 and hence the "ratchet" action will be minimal while the driving member 9 continues to rotate at its normal speed while the driven member 1 is stopped.

The clutch will be unable to re-engage since as soon as the balls 10 are moved radially outwardly they will be knocked back radially inwardly by the transitional portion 5 connecting the planar zone 26 to the recesses 24.

In order for the clutch to be automatically reengaged, the speed of the driving member 9 is reduced or completely stopped depending on the design of clutch, and in particular the force provided by spring 11, so that the interaction between the flange-like extension 9 and the annular guide member 7 causes the balls 10 to be moved radially outwardly back into the recesses 24.

The path of travel of the torque transmitting balls 10 from their non-torque transmitting position to their torque transmitting position does not cause a change in the energy state of spring 14 since even if contact occurs, the balls 10 are not pressed against the spring 14 thus reengagement of the balls 10 to their torque transmitting position can be governed solely by the force due to spring 11 and some centrifugal force if the driving member 9 is still being rotated.

The clutch can therefore be re-engaged solely by slowing down or stopping the drive shaft revolving.

In order to facilitate the disengagement of the clutch, in particular the movement of the balls 10 out of their recesses 24 when overload occurs, it is desirable at least that part of the spring 14, which is directly effective on the balls 10 during such movement, be supported by a bearing such as that shown at 1 5, the other end of the spring 14 bearing on an axial abutment 1 6 fitted to the clutch hub 9.

Referring now to Figure 3, a slightly modified form of torque limiting clutch is illustrated which in principle operates in the manner the same as the clutch shown in Figure 1 but the transitional region 5' between the axially extending part 6 in which the recesses 24 are formed, and the substantially planar second zone 26 is of step-like configuration.

Figure 4 illustrates an example of means for maintaining the torque limiting clutch in a nontorque transmitting or freewheeling position if so desired.

A ball catch 18 is biased in a radially outward direction by a spring 1 7 into the flange-like extension of clutch hub 9. The annular guide member 7 has an opening so positioned that it corresponds to the position of the ball catch when the clutch is in a freewheeling of non-transmitting state, so enabling the ball 18 to pass therethrough and engage in a recess provided in a cover cap 8 which is associated with the annular guide member 7.

Thus the torque limiting clutch may be locked in its freewheeling position following an overload situation. The recess 22 and the cap 8 is preferably provided with an inclined face 22 which enables the lock to be cancelled simply by sliding the cover cap 8 forward against the force of its remaining spring 12 preparatory to reengagement of the clutch.

Referring now to Figure 6, a different arrangement of second biasing means is illustrated.

In the embodiment shown, the force is exerted by an axial spring 14, during movement of the balls 10 from a torque transmitting position to a non-torque transmitting position, on the balls 10 through a thrust ring 25. An axially projecting extension 6 which has a frusto-conical part is arranged on the thrust ring 25. The second biasing means which is in the form of a coil spring 27, which urges the balls 10 back into their torque transmitting position is also arranged along the clutch axis.

When an overload situation occurs, the relative rotation between the driving and driven members momentarily compressing the spring 14 and allowing it to return to its normal potential energy statue, the spring 27 will also be compressed and the ball 10 will take up a position radially inwardly from that shown.

If the speed of the driving member is then reduced, the spring 27 through its connecting plate will urge the balls 10 back into their torque transmitting position.

It is important to ensure that movement of the balls 10, from their non-torque transmitting position to their torque transmitting position, does not involve any compression of the spring 14 so that free passage of the balls 10 to their torque transmitting position is possible. Thus the relative angle, and the distance, between the frustoconical surface 5 and a line drawn along the entry path to the recess 24 along which each ball 10 will travel from its non-torque transmitting to its torque transmitting position, will be such that movement of the ball along that path will not cause it to bear with any force against the thrust ring 25, and no change in the potential energy stored by the spring 14 will occur. The force returning each ball 10 to its torque transmitting position being due to spring 27.

The entry path to the recess 24 may be substantially parallel to the frusto-conical surface 5 and the distance therebetween will be at least as great as the diameter of the ball 10.

In practice, as shown in Figure 6, the recess may have a configuration so that during travel of the ball 10 towards its torque transmitting position it is brought into contact or substantially irito contact with the thrust ring 25 at the end of its travel. Thus, when the ball 10 is in its torque transmitting position, even though the spring 14 is not providing any force on the ball, the ball 10 is correctly located. Only when the clutch transmits torque and the balls 10 tend to climb out of the recess 24, will there be any change in the potential energy state of spring 14.

The torque limiting clutch of the present invention, when provided with means for maintaining it in a non-torque transmitting position is of particular use in the case of a machine driven from a central source but having a plurality of moving parts driven by subsidiary drive shafts. By employing the clutch of the present invention with the means for maintaining it in its freewheeling position, various subsidiary drive lines may be isolated as required.

In order to isolate such a drive line it is necessary to turn the cap 8 which is connected with the annular guide member 7 until the ball catch 1 8 can locate in the recess 22. To reengage the clutch, the cover cap 8 is pushed forward as has hereinbefore been described, so that the ball catch can run out of the recess along the inclined face 23 and the guide member 7 may rotate once more into the angular position thereof which cause movement of the torque transmitting balls 10 into their torque transmitting position.

Claims

1. A torque limiting clutch comprising a driving member and a driven member, torque transmitting elements arranged therebetween, the torque transmitting elements having a first position in which they engage with both said driving and said driven members to enable torque to be transmitted therebetween and a second position in which torque transmission is discontinued, first biasing means being provided for maintaining torque transmission until a predetermined torque level is reached, whereupon the torque transmitting elements move to their second position and wherein second biasing means are provided to bias the torque transmitting elements to their first position, the arrangement being such that during movement of the torque transmitting elements from their second to their first position, there is no change in the amount of potential energy stored in the first biasing means.

2. A torque limiting clutch as claimed in Claim 1 wherein two paths are provided along the first of which the torque transmitting elements move from a torque transmitting to a non-torque transmitting position and a second path which is not the reverse of the first path along which the torque transmitting elements move from their non-torque transmitting position to their torque transmitting position.

3. A torque limiting clutch as claimed in Claim 2 wherein said first path includes a generally circumferential and a radial component relative to the clutch axis and wherein said second path includes only a generally radial component.

4. A torque limiting clutch as claimed in any one of the preceding claims wherein one of said driving or driven members includes a first annular zone having a substantially planar surface and a second annular zone in which is formed recesses and in which the torque transmitting elements engage when in their torque transmitting position.

5. A torque limiting clutch as claimed in Claim 4 wherein said recesses comprise slots extending generally radially from the clutch axis.

6. A torque limiting clutch as claimed in Claim 4 or Claim 5 wherein a generally frusto-conical transitional zone interconnects two said annular zones.

7. A torque limiting clutch as claimed in Claim 4 or Claim 5 wherein a generally step-like transitional zone interconnects the two zones.

8. A torque limiting clutch as claimed in any one of Claims 4 to 7 wherein said second annular zone is positioned radially outwardly relative to the clutch axis from said first annular zone.

9. A torque limiting clutch as claimed in any one of claims 4 to 8 wherein said one clutch member comprises the driven clutch member.

10. A torque limiting clutch as claimed in Claim 5 wherein the torque transmitting elements are balls and the relationship between the depth of the slot and the diameter of the ball is such that movement of the ball out of sit torque transmitting position to its non-torque transmitting position will include movement of the ball relative to said one clutch member in which said slot is formed in both a circumferential and radial direction relative to the clutch axis.

11. A torque limiting clutch as claimed in any one of the preceding claims wherein said first biasing means comprises a spring element adapted to provide a resilient bias to said torque transmitting elements only during torque transmission.

12. A clutch as claimed in Claim 4 wherein said second resilient means comprises a spring element interconnecting said other of the clutch members to an annular guide member, said other of the clutch members having slits in which the respective torque transmitting elements are located, the annular guide member having similar slits relatively inclined to the slits in said other of the clutch members, the arrangement being such that movement of the torque transmitting elements from their torque transmitting position to their non-torque transmitting position causes limited relative rotation between said other of the clutch members and said annular guide member causing an increase in the potential energy state of said spring.

13. A torque limiting clutch as claimed in Claims 1, 2 or 3 wherein the force exerted by said first biasing means during torque transmission if thc torque transmitting elements are transmitted through a thrust ring.

14. A torque limiting clutch as claimed in any one of the preceding claims wherein means are provided for maintaining the torque transmitting elements in a non-torque transmitting position.

1 5. A torque limiting clutch substantially as hereinbefore described with reference to and as illustrated in Figures 1, 2, 4 and 5 of the accompanying drawings.

1 6. A torque limiting clutch substantially as hereinbefore described with reference to and as illustrated in Figure 3 of the accompanying drawings.

17. A torque limiting clutch substantially as herein before described with reference to and as illustrated in Figure 6 of the accompanying drawings.

1 8. A torque limiting clutch including any novel feature or combination of features as described herein and/or illustrated in the accompanying drawings.