GB2275745A - Torque overload limiter - Google Patents

Abstract

A torque overload limiter comprises an input hub 10 with an integral flange 11, an output ring 12, torque transfer elements such as balls 13, and a spring-loaded thrust plate which in the torque transfer mode its face to rotate and move axially, being spaced from the flange. On overload (Fig. 6), the balls enter a deeper recess in the thrust plate so that the thrust plate contacts the flange and the drive is disengaged. A bearing (27) (Fig. 7) may be used to facilitate resetting of the thrust plate, and a bearing (35) (Fig. 8) may facilitate contra-rotation between the thrust plate and the output ring on overload. <IMAGE>

Description

OVERLOAD TORQUE LIMITER This invention relates to overload torque limiters of the ball or roller detenting variety.

Detenting torque overload limiters are broadly divided in 2 categories, (a) the self resetting type which limits the transmitted torque without disconnecting the drive and (b) the disengaging type which not only limits the transmitted torque but disconnects the drive thus eliminating it altogether. A common feature is a sliding ring splined to the hub and a freely mounted ring rotatably locked to the former by a cluster of balls and detents. The distinguishing feature in the disengaging type is an elaborate system of wedges, balls and tapered rings to ensure that the torque transmitting detent rings are kept apart during the disengaging action.

The present-invention relates to both types of torque limiter and eliminates the mechanism mentioned above for keeping apart the detent rinqs after disengagement, thereby reducing the overall length of the clutch as well as the complexity and manufacturinq cost. Furthermore, it faCilitates its conversion to the self reset type thus enabling one basic clutch type to embrace both the self reset and disconnect typeS, The invention particularly relates to the type of torque overload limiter incorporating a freely mounted detent ring, a flange containing the ball-cluster integral with the hub and a floating pressure plate which applies thrust on the ball cluster without transmitting torque. It is the design of this plate which is the subject of the present invention. A key feature of this type of torque limiter is that when over load occurs and the drive ring rotates relatively to the hub flange in one direction, the rolling balls compel the pressure plate to turn in the opposite direction, a movement rendered possible by the interposition of a thrust bearing between the pressure plate and the loading spring.

According to the present invention there is provided a pressure plate carrying -on one face a circular groove: conforming to the ball radius. - On the same pitch circle a number of deeper cavities is provided so that each ball may drop in and travel a sufficient amount to clear its seat. In this condition, the drive ring may freely rotate without constraint from the balls, as required of a torque limiter of the disengaging type.

The resetting of the clutch is achieved by lining up the drive ring against the ball cluster and manually turning the pressure plate until the balls are transferred from the pockets to the plate groove, restoring the spring load.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings.

Fig. 1 shows the disengaging type of torque limiter described above, showing in particular the pressure plate which is the principal feature of the invention.

Fig. 2 shows the disposition of the disengagement cavities on the face of the pressure plate.

Fig. 3 is a cross section of the pressure plate showing the spring loaded balls in the driving mode.

Fig. 4 is a cross section of the pressure plate showing the disengagement cavities.

Fig. 5 is a part section of the clutch showing the drive ring, a ball and the pressure plate in the locked position.

Fig. 6 is a part section of the clutch showing the drive ring and the pressure plate with a ball in the disengagement cavity free of ,any constraint in the drive ring Fig. 7 shows the plate designpreferred in large clutches to eliminate the manual effort required to reset the unit after disengagement, Fig. 8 shows the self resetting version of the clutch.

Referring to Fig. 1, item 10 shows a hub with an integral flange 11 housinq a cluster of balls 13 pressed on to their seat in output ring 12. The thrust applied to the balls is obtained from spring 15 resting on the floating plate 14.

Loadinq is obtained from a nut 17 via a thrust bearing 16 which ensures rotation of 14, uninhibited by friction. Torque is transmitted from the hub 10 via the flange 11 to the output ring 12 and the essential feature is the axial and rotational freedom of plate 14. A consequence of this freedom is that on overload, the ring 12 rotates in one direction relatively to flange 11 and the plate 14 rotates in the opposite direction.

The operation of the clutch may now be described as follows: Fig. 5 shows a part section of the clutch in the driving condition i.e. with ball 18 pressed on to seat 19 by plate 20 under the thrust of spring 21 with clearance 22 between plate and adjoining flange.

On overload, relative rotation between 23 and 24 ejects the ball and compels it to turn about an axis normal to the clutch centre line. This results in rotation of plate 20 in the opposite direction to that of 23 until the deep cavity arrives opposite the ball.

Fig. 6 shows the same cavity 25 containing the ball clear of the rotating face 26 thus releasing 23 and disengaging the drive completely. In this condition the clearance 22 disappears and plate 20 and flange 24 are in contact at 27 with no relative rotation.

To re-engage the clutch to the driving condition, plate 20 is levered roiind until the plate is in contact wit the ball, restoring the clearance 22 and the spring thrust on the ball, in the condition of Fig. 5.

BuKine this operation the plate is manually turned and slides over the balls against the frictional drag generated between balls and plate.

It can be shown that this friction torque is about 20;5 - 3 $ of the clutch torque setting and is likely to create difficulty in resetting large clutches. An extension of the invention overcoming this problem is shown in Fig.7, similar to Fig.1 but with following added features: Item 28 is a bearing transmitting the spring thrust of plate 30 to the hub flange 29 by bridging a small working clearance between ball 31 and plate 30. For as long as torque is not applied between hub 29 and output ring 32 (e.g. when the clutch is disengaged) ball 31 is free from plate 30 which may then be reset manually without effort. When torque is transmitted from 29 to 31, the ball is thrust against plate 30, reverting to the condition illustrated in Fig.1. The '0' ring 33 provides a light frictional restraint between plate 30 and hub 29 to avoid any random rotation of the plate during the resetting operation and provides a 'feel' to the operator.

Fig.6 shows a clutch with a plate 34 carrying a bearing 35 allowing friction free relative contra-rotation between plate 34 and the drive ring 38.

On overload the migration of the balls from seat to seat is achieved without the skidding friction associated with conventional systems.

Claims (4)

1. A torque overload limiting device comprising a flanged hub, an output ring1 a spring loaded thrust plate, ball or roller locking elements, arranged so that torque is transmitted from the hub to the output ring bypassing the thrust plate to ensure its freedom to contra rotate relatively to the output ring after the onset of overload.

2. A thrust plate containing holes sufficiently deep to contain the balls or rollers after torque release thereby disengaging the drive.

3. A thrust plate with a circular groove for radial location and for minimising contact stresses between balls and plate.

4. A torque overload clutch as described herein with reference to Figs. 1 to 8 of the accompanying drawings.

4. A torque overload clutch as in Claim 1 provided with a thrust plate as in Claims 2 or 3 and means for levering the said plate in order to transfer the balls or rollers from the deep holes to the circular groove; thereby restoring the clutch from the disengaged condition to the driving condition.

5. A torque overload clutch as in Claim 4 with means of reducing: or eliminating the manual effort of re-engaging the thrust plate comprising an additional thrust bearing locating the plate clear of the ball cluster thus ensuring that the ball thrust ag ainst the plate is applied only when torque is transmitted through the clutch and eliminated when the clutch is disengaged. Further means may be provided to introduce a light frictional restraint to the thrust plate during manual reset.

6. A torque overload limiter as in Claim 1 incorporating a plate with a thrust bearing eliminating sliding friction between the ball, its seat and the pressure plate.

7 A torque overload clutch as described herein with reference to Figs. 1 to 8 of the accompaning drawing.

Amendments to the claims have been filed as follows 1.A torque limiting clutch of the disengaging type comprising two co-axial driving and driven members relatively rotateable viz. a hub carrying a flange with a number bf angularly disposed and axially facing pockets and a drive ring with a plurality of detents matching the cylindrical pockets of the hub flange.

Keens including a bearing supporting the drive ring radially and axially with a thrust bearing interposed between the adjoining faces of the drive ring and the hub flange.

Respective rolling elements preferably balls housed in the hub flange pockets axially displaceable and of a diameter such that when seated on the drive ring detents a portion of their surface is exposed at the other side of the hub flange, A circular thrust plate located at its inner diameter by the hub member with a plain face in contact with the balls alternative3y a floating plate radially located by a circular groove in contact with the ball cluster and having a toroidal form or a conical V shape.

The thrust plate contains a number of open pockets facing the balls with the same angular pitching capable oS disangagement of housing the balls clear of the detents of the drive ring.

A thrust bearing at the interface between the thrust plate and the hub flange is located so tha with the balls seated on the pockets of the drive ring under zero torque and with the thrust plate resting on the bearing a small working clearance exists between the balls and the thrust plate. As a result under zero torque conditions the thrust plate is under a heavy spring thrust and located between.

two needle type thrust bearings. It can be manually turned in either direction without any effort.

Hoivsver,with the plate set in the drive position, as soon as torque is applied however small, the balls are thrust against the plate which is then held firmly and capable of turning when an overload torque is applied.

Means are provided in the form of a loading spring or springs to exert an adjustable force on the ball cluster via the thrust plate as well as an outboard thrust bearing to allow a friction free contra rotation of the thrust plate during the disengagement process.

2. An overload clutch according to Claim 1 in which a light frictional restraint is provided between the driving member and the thrust plate to eliminate any possibility of drift of the thrust plate during the re-engagement process. This restraint may take form of a rubber '0' ring in contact with the hub flange and the thrust plate and housed either in the former or the latter. Alternatively, spring loaded pressure pads may be used instead of an '0' ring.

3. An overload clutch according to Claims 1 and 2 in which a number of light springs are housed in axially directed holes in the hub flange and located between the two thrust bearings on either side of the said flange and ensuring that the thrust bearing housed in the thrust plate remains properly housed therein during the disengagement process.