GB2227800A

GB2227800A - Torque overload release coupling

Info

Publication number: GB2227800A
Application number: GB8901220A
Authority: GB
Inventors: John Constantine Grey
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-01-20
Filing date: 1989-01-20
Publication date: 1990-08-08
Also published as: GB8901220D0

Abstract

A torque transmitting device of the overload release type comprises co-axial driving and driven members 13, 14 coupled with one or more sliding bolts 17 each loaded by at least one resilient detent ring so as to apply a predetermined axial force resisting a pre-determined peripheral force. The ring may apply outward pressure against a bush 19 fixed to the driving member 13 or inward pressure against the sliding bolt 17. A central screw 20 in each bolt provides positional and torque adjustment. Each bolt may cooperate directly with the member 14 or via a roller or a ball 21. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO TORQUE TRANSMITTING DEVICES.

This invention relates to torque transmitting devices such as torque overload release clutches in which torque is transmitted from the driving half member

the driven half through one or more locking devices designed to disconnect the drive when a preset limiting torque is reached.

Locking devices can be clearly classified as A & B thus: In system A the peripheral force is converted to an axial force by the use of rolling components without the intervention of friction. In system B this is achieved by a succession of sliding wedges operating with friction thereby introducing an element of unpredictability in the level of the release torque.

System A is described in my earlier patents (GB No.

2,037,908, USA No. 4,273,227). In all cases where system B is found to be acceptable it is the purpose of this invention to simplify the locking mechanism without affecting the frictional characteristics as well as reducing its-overall dimensions and its manufacturing cost.

The key component of the invention is a spring in the form shown in Fig. 1, having a toroidal circular form split to provide the necessary flexibility and similar to conventional locating wire rings. In Fig. 2 it is shown expanded over a shaft and applying an inward radial pressure on the locating circular groove. In Fig. 3 it is shown contracted into a bore and applying an outward radial pressure on the locating groove. It must be noted that both in Fig. 2 and Fig. 3, when the depth of the groove is equal to half the wire diameter, any axial shearing force applied to the ring cannot eject it from the groove because no radial force component is available to overcome the radial pressure.

Fig. 4 shows ring 10 mounted on the groove of shaft 11 having a diamater Ds smaller than D1. Fig. 5 shows ring 12 mounted on the groove of a

Db greater than D2. A force A applied against the ring at right angles to the toroidal plane in Fig. 4 produces a radial component R forcing the ring to slip out of the groove at point

When the ring reaches the plain part of the shaft its resistance to movement is confined to the frictional drag

An identical process prevails with the bore ring in Fig. 5. It must be noted that during this process the ring section cannot turn and in Figs. 4 and 5 friction forces are generated at points lOA-lOB-lOc-lOD.It can be shown that the ratio A/R depends on the pressure angle

and the friction coefficients P thus:

Fig. 6 shows this relationship with no friction and with two extreme friction coefficients of 0.15 and 0.25. It is typical of locking devices conforming with system B (see preamble of this application) and it must be noted that depending on the angle

selected, the ring can sustain axial forces up to 6 times the radial force R, a limit being set by uncertainties in the friction coefficient.

It can be shown that the radial force R may be predicted thus:

where h = wire diameter, d = mean diameter of ring, y = increase or reduCtion of the ring diameter when placed in the groove. It will be noted that small changes in the ratio h/d have a powerful effect on R, subject only to maximum design stresses. And when h/d is constant, R is proportional to the wire diameter h.

The invention will be described in more detail by way of example-with reference to the accompanying drawings in which: Fig. 1 shows the toroidal ring used in the locking bolt of the invention Fig. 2 shows the ring mounted on a shaft exerting inward pressure Fig. 3 shows the ring mounted in the bore of a bush exerting outward pressure Fig. 4 shows the forces involved in the ejection of a ring mounted on a bolt.

Fig. 5 shows the forces involved in the ejection of a ring mounted in the bore of a bush Fig. 6 shows the effect of friction on the ratio of the forces A/R in Figs. 4 and 5.

Fig. 7 is an axial half section of a torque transmitting device according to the invention in the form of an overload release coupling.

Fig. 8 shows alternative groove forms for a bore ring.

Fig. 9 shows a simplified version of an overload release coupling.

Fig. 10 shows the shaft ring groove of the bolt in Fig. 9 Fig. 11 shows a bolt with more than one ring.

Fig. 12 shows a comparison of properties between a friction free and friction containing ring Fig. 7 shows the driving and driven halves 13 and 14 of the coupling rotatably mounted on bearings 15 and 16 and locked together with one or more bolts each consisting of a ball or roller 21 slidably housed in bush 19 and detenting in a seat 18 of the driven member. The ring 22 is showncontractedinto the grooved bush 19 as in Fig. 5.

A cylindrical bolt 17 locates the ring in a rectangular groove permitting the inward movement of the ring during the sliding movement of the bolt. An adjusting screw

has a dual function: (a) it allows any "slack" arising from machining errors between the ball and the bolt face to be eliminated. (b) Further adjustment of this screw will expand the ring increasing the angle

thereby reducing the pre set axial force A of the bolt and the preset torque of the coupling. Fig. 8 shows alternative groove forms to the circular shape indicated in Fig. 7.

Fig. 9 shows a simplified construction which may be used when manufacturing cost and size are a compelling consideration and a prolonged working life of secondary importance. This construction is similar to that of Fig. 7 except for a simpler bearing layout 22 and one or more bolts 23 loaded by rings of the type shown in Fig. 4. The bush 19 shown in Fig. 7 is omitted and it will be noted that once the ring has been inserted in the rectangular groove 24 of Fig. 9, it cannot be readily taken out for replacement.

In both cases of Fig. 7 and Fig. 9 the the bolts 17 and 23 are retained after disconnection of the drive by the frictional force applied by the rinF on the cylindrical portion of the bolt or the plain bo 5 of The bush in Fig. 7. Alternatively, positive retention can be obtained by a second light groove adjacent to the ring groove in the bolt or the bore of the bush.

A simple method for increasing the axial force capacity of a bolt of given diameter is shown in Fig. 11. In Fig. 7 the bolt 17 is shown fitted with one ring 22.

Fig. 11 shows a similar bolt 24 fitted with more than one ring e.g. four rings 26, 27, 28 and 29 engaged in corresponding grooves in bush 25. This construction may be used with bolts in the style of Figs. 2 and 4 and in either case the aggregate axial force capacity is proportional to the number of rings used. The pitching of the grooves is preferably calculated to prevent, on disconnection, ring 26 falling into groove 27, ring 27 into groove 28 and so on.

A further advantage of the construction emerges when a given axial force A is shared by a number of rings each carrying a proportionate fraction of the ratio (A/R). Fig. 12 shows the effect of a given friction coefficient

on the ratio (A/R) as a multiple of the same ratio when

indicating an optimum angle

between 350 and 700.

Claims

1. A torque transmitting device comprising rotary input and output members on a common axis drivingly coupled by at least one bolt parallel to the centreline of the coupling held in position by a toroidal ring of circular section engaged partly in the bolt and partly in the bore containing the bolt and pressing either directly or via a ball or roller into a recess in the driven coupling member thereby creating a fixed peripheral force opposing the peripheral force generated by torque. When the latter force exceeds the former the bolt is axially ejected forcing a contraction or expansion of the ring depending on whether the ring is assembled compressed into the housing bore f4, of the bolt or expanded on toAbolt.At the end of the bolt travel the ring embraces the cylindrical portion of the bolt thus maintaining it in the retracted position or the ring may be allowed to drop into a retaining groove for positive retention.

2. A device according to claim 1 comprising at least one bolt directed radially either at right angles to the coupling centre line or at any other angle less than 900.

3. A device according to claim 1 or claim 2 comprising detent locking members of spherical, cylindrical or conical shape.

4. A device according to claim 2 comprising resilient rings and bolts of a mass calculated to retract and disconnect the drive on reaching a pre-determined speed at which the centrifugal force acting on the bolts exceeds the restraining force created by the rings.

5. A device according to claim 1 and claim 2 comprising a bush surrounding the locating ball at the thrust line or both the ball and the bolt.

6. A device according to claim 1 comprising bolts with adjusting screws on their centre line to compensate machining errors and for final adjustment of the release torque.

7. A device according to claim 1 comprising a bolt of a diameter smaller than the mean diameter of the torus when assembled together. The outer part of the ring is located in the surrounding bore in a groove of rectangular section with plane flanks containing the ring in both axial directions.

8. A device according to claim 1 comprising a bush of a bore greater than the mean diameter of the torus when assembled together. The inner surface of the ring is located in the bolt in a groove of rectangular section with plane flanks containing the ring in both directions.

9. A device according to claim 1 comprising bolts with more than one ring either in the external style of Fig. 2 or the internal style of Fig. 3.

10. A torque disconnecting device constructed and arranged for use and operation substantially as described herein with reference to any of the examples shown in the -accompanying drawings.

Amendments to the claims have been filed as follows 1. A torque transmitting device comprising rotary input and output members on a common axfs drivingly coupled by at least one bolt parallel to the centreline of the coupling held in position by a toroidal ring of circular section engaged partly in the bolt and partly in the bore containing the bolt and pressing either directly or via a ball or roller into a recess in the driven coupling member thereby creating a fixed peripheral force opposing the peripheral force generated by torque. When the latter force exceeds the former the bolt is axially ejected forcing a contraction or expansion of the ring depending on whether the ring is assembled compressed into the housing bore tZe of the bolt or expanded on toAbolt.At the end of the bolt travel the ring embraces the cylindrical portion of the bolt thus maintaining it in the retracted position.

2. A device according to claim 1 comprising at least one bolt directed radially either at right angles to the coupling centre line or at any other angle less than 900 3. A device according to claim 1 or claim 2 comprising detent locking members of spherical or cylindrical shapes.

5. A device according to claim 1 Id claim 2 comprising a bush surrounding the locating ball at the thrust line or both the ball andthe-bolt.