GB2272734A - Disengaging torque overload module - Google Patents

Abstract

A torque overload limiting module for incorporation in the driving and driven members of a clutch comprises a pair of contacting balls or rollers 1 located in a pin 2 and loaded by a split cylindrical spring 4 designed to apply balanced forces on the balls to oppose the axial force arising from torque. Excessive torque disengages the clutch by moving the balls etc. into recesses within the cylindrical spring (FIG 7). <IMAGE>

Description

DISENGAGING TORQUE OVERLOAD MODULES This invention relates to torque transmitting devices such as torque limiting clutches and torque sensors.

In my earlier UK Patent No. 2 037 908 a torque limiting device is described comprising a driving and a driven member locked together by a number of contacting balls or rollers arranged in pairs so that their centre to centre line coincides with the tangential torque thrust of one member, balanced by an opposite thrust of the other member, this thrust being offset from the ball centre to centre line. The torque thrust generates a smaller force at right angles to the centre to centre line and parallel to the centre line of the drive members. It is independent of friction due to the rolling action at all contact points. In the earlier invention this force is contained by a pin with a spring loaded ball da.tent set to give way when overload occurs.The disadvantage of the system was the introduction of sliding friction at the ball detent and at the contact of the ball pair 'with8ace of the pin. It is the object of the present invention to eliminate all sliding friction by replacing the foresaid assembly by a simpler, more compact assembly referred to below as a 'Module', According to the present invention there is provided a pin containing a floating ball pair surrounded by a spring in the form of a split annulus.

This is housed in one of the drive members so that on assembly the ball pair r forms a bistable unit i.e. it locks one drive member when it thrusts against the ball seat in the other member or releases the two members when the ball pair is withdrawn into the spring cavity.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig.1 is a cross section of the module in a plane parallel to the centre line of the clutch, showing the ball pair, the pin, the ball retaining circlip and the circular spring.

Fig.2 is a view of the module in direction 'A' showing the circular spring split at 5.

Fig.3 is a side view of the module showing the jaws of the pin retaining the ball pair.

Fig.4A and 4B show detail 7 (Fig.1) of the ball track at the active face of the spring.

Fig.5 is a view of the circular spring through which the module reaches from one drive member to the other.

Fig.6 shows diagramatically the ball pair in the locked position with the spring thrusting the balls against their seat.

Fig.7 shows diagramatically the ball pair in the disengaged position retained by the spring in the sloping scollops shown in Fig.4A.

tig.8 shows a typical overload clutch embodying the features of the invention Referring to Figs 1 and 3 a pin 2 holds the ball pair 1 by jaws 6 retained loosely by a circlip 3. A circular spring 4 is shown in Fig.2 split at 5 to provide flexibility. The spring inner diameter in its free state is smaller than 2 ball diameters by an amount which, when assembled as in Fig.6, ensures that the clamping points are offset from the ball centre and providing sufficient axial thrust to balance the opposing axial force arising from torque.

Referring to Fig. 4A, a sloping cylindrical track 8 at an angle g is influenced by the conical deformation of the spring (angle Ci ) when the ball pair travels beyond point 9 towards position 10. Thus if < oC the ball pair will be ejected out of the spring but if & it will be propelled into the spring as required after clutch disengagement. This property is used to minimise tEle axial force required for the manual resetting of the module after disengagement.

The invention thus provides for the angular location between module-pin and spring as well as angular location between module and clutch drive member without external means such as pins and slots. Fig.5 shows the circular opening 11 through which the nose 6 of the module pin (Fig.3) reaches out from one clutch member to the other. Two scallops 12 are shown cut into the diameter of this opening, the purpose of which is to reduce the stresses on the flange as well as to provide angular location to the module.

Fig.6 shows diagramatically the relationship between the ball pair 13, the ball seat 14, the thrust flange 15 and the spring 16 in the torque transmitting condition. On overload the ball pair migrates into the spring with rolling at all five pressure points 17, 18, 15, 19 and 20.

Fig.7 shows the balls engaged in the sloping tracks 21 and 22 of the spring providing a reversal of axial thrust on the ball pair and ensuring their retraction to the position shown, clear of the rotating drive member 23.

It is important to note that during this cycle of events, the module pin (item 2 Fig.1) is not subjected to any thrust thereby elimiting any sliding frictional losses.

Fig.8 shows a typical application of the invention. The drive members on 24 and 25 are mountedsbearings 26 and 27 with a number of modules disposed on the periphery. In the construction shown the securing flange 28 and the drive hub 29 in one piece. If necessary, they may be separate.

Claims (5)

CLAMS

1. A torque overload limiting device in a modular form comprising two contacting balls or rollers, a pin containing the ball pair and a spring in the form of a split cylindrical ring applying two balanced clamping forces resulting in a friction free axial force which accurately dictates the limiting torque.

2. A spring in the form of a split cylindrical ring of constant orvariable section used to apply equal and opposite forces on the ball pair, at points offset from their centres.

3. A spring as in Claim 2 carrying at one or both ends diametrically opposed cylindrical tracks inclined to the centre line of the spring and intended to retract the module after disconnection. At the same time the tracks are designed to compensate the conical distortion of the spring during disconnection and to reduce to a minimum the manual effort required to reset the module to the driving position. Also to ensure the correct angular relationship between the pin and the spring.

I

4. A torque overload clutch as in Claim 1 comprising a drive member with circular apertures carrying two scollops in the peripheral direction to reduce contact stresses and for the angular location of the module in relation to the drive member.

5. A torque overload module as described herein with reference to figures 1 to 8 of the accompanying drawing.

5. A torque overload module as described herein with reference to figures 1 to 8 of the accompanying drawing.

Amendments to the claims have been filed as follows 1. A torque overload limiting device comprising the known twin ball or roller system, combined with an annular loading spring applying two balanced forces on the ball pair. A rolling action at all the loaded contact points ensures friction free and consistently accurate disconnecting side forces. The ball tracks at the inner surface of the spring are desigried to retain the ball pair after disconnection as well as to ensure that the axial force required to restore the module to its driving position is conveniently small.

2. A spring in the form of a split cylindrical ring of constant orvariable section used to apply equal and opposite forces on the ball pair, at points offset from their centres.

3. A spring as in Claim 2 carrying at one or both ends diametrically opposed cylindrical tracks inclined to the centre line of the spring and intended to retract the module after disconnection. At the same time the tracks are designed to compensate the conical distortion of the spring during disconnection and to reduce to a minimum the manual effort required to reset the module to the driving position. Also to ensure the correct angular relationship between the pin and the spring.

I 4. A torque overload clutch as in Claim 1 comprising a drive member with circular apertures carrying two scollops in the peripheral direction to reduce contact stresses and for the angular location of the module in relation to the drive member.