GB2122282A

GB2122282A - Overload release coupling

Info

Publication number: GB2122282A
Application number: GB08314067A
Authority: GB
Inventors: Derek Francis Brindley
Original assignee: SAVILLE BRINDLEY PRECISION ENG
Current assignee: SAVILLE BRINDLEY PRECISION ENG
Priority date: 1982-06-22
Filing date: 1983-05-20
Publication date: 1984-01-11
Also published as: GB8314067D0

Abstract

An overload release coupling including driving and driven members (10, 12) and means whereby they can be made to rotate freely one relative to the other when subjected to a predetermined maximum torque. So that the drive can very easily be re-established after the coupling has failed, and so that the torque at which it is arranged to fail can be adjusted, the driving member (10) and driven member (12) are frictionally connected together and a pre-loading of resilient means (24) holding the driving and driven members together is reduced by any slipping which takes place due to a screw-threaded connection (28) between the driving member and a spring abutment (26) rotatable with the driven member. <IMAGE>

Description

SPECIFICATION Overload release coupling The invention relates to overload release couplings, that is to say a torque transmitting device which is adapted to become inoperative when subjected to a pre-determined degree of torque.

Overload release couplings are used in a great many situations where excessive torque would result in failure of mechanical drive transmission mechanism or damage to a drive motor for example.

Perhaps the simplest kind of overload release coupling is that comprising a pair of discs drivably connected together by means of at least one shear pin. However, the main disadvantage of this kind of overload release coupling is that when the at least one shear pin has failed it requires the services of an engineer to fit new shear pins before the drive can be re-established. In addition, an overload release coupling of this kind is generally designed to fall at a particular torque and cannot be re-adjusted to fail at a variable overload unless there is provision for the fitment of a selected number of shear pins.

The invention has for its object to provide an overload release coupling of very simple construction with means whereby the torque at which it is arranged to fail can be adjusted to fine limits.

According to the invention, there is provided an overload release coupling including driving and driven members frictionally connected together, resilient means being provided for loading said driving and driven members together, and adjustable means being provided for pre-loading said resilient means to adjust the torque at which the coupling can be arranged to fail, said adjustable means including a sleeve or nut element engaging a screwthreaded portion of the driving member but being rotationally fixed, at least throughout the range of normal adjustment of the resilient means, relative to the driven member, the arrangement being such that any slipping which takes place at the frictional driving surfaces ofthe driving and driven members causes the pre-loading of the resilient means to be reduced so that further slipping is brought about and the sleeve or nut element is very soon completely slackened off and the frictional driving surfaces relieved of all load. A disc of friction material may be located between the driving and driven members for transmitting drive from the one to the other. Indeed, so that a relatively high torque can be transmitted and at the same time so that the coupling can be of relatively small diameter, a plurality of friction discs may be provided between driving and driven plates slidably splined with respect to the driving and driven members.On the other hand, in order to increase the torque transmitting capacity of the coupling, the frictional driving surfaces of the driving and driven members may be of conical form and in this case especially, depending on the angle of taper of the friction surfaces, it may be found that metal to metal contact is sufficient to transmit a required load. The arrangement will preferably be such that as the resilient means become relieved of all pre-load, the sleeve or nut element becomes free to turn relative to the driven member. The resilient means will preferably be constituted by a coil compression spring.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawing which is a longitudinal section through an overload release coupling embodying the invention.

Referring now to the drawing, the overload release coupling there illustrated includes driving and driven members 10 and 12 frictionally connected together by a disc 14 of friction material between them. The driving member includes a drive shaft 16 which is adapted to be drivably connected to an electric motor. The driven member has a central boss portion 18 mounted rotatably on the driving member and is provided with a radially outer portion in the form of an open ended cylindrical driving element 20 which can be connected to one end of a drive shaft (not shown) by means of driving pins (not shown) which engage a plurality of holes 22 in said cylindrical driving element.

Resilient means, constituted by a coil compression spring 24, are provided for loading the driving and driven members together against opposite sides of the friction disc 14. adjustable means which are provided for preloading said spring to adjust the torque at which the coupling can be arranged to fail are constituted by a sleeve element 26 engaging a screwthreaded portion 28 of the drive shaft. It will be seen that the spring acts at one end against the driven member 12 and reacts at its other end against the sleeve element 26, the latter being located at a pre-determined position along the drive shaft.The sleeve element is held in its adjusted position, during normal operation of the coupling, by a screw 30 which projects radially outwards from the driven member 12 and which engages a slot 32 extending longitudinally of the sleeve element 26 from an open end thereof which encircles the driven member.

The drive shaft is adapted to be driven in clockwise direction (as viewed from the left hand end of the illustrated coupling) and the thread of the screwthreaded portion 28 of the dive shaft is a right hand thread. Consequently, the arrangement is such that any slipping which takes place at the frictional driving surfaces of the driving and driven members causes the sleeve element 26 to be turned relative to the drive shaft and this causes the preloading of the spring 24 to be reduced. This in turn causes further slipping to be brought about and the sleeve element is very soon completely slackened off so that the frictional driving surfaces are relieved of all load.It will be understood that as the spring becomes relieved of all pre-load, the sleeve element is displaced axially relative to both the driving and driven members so that the screw 30 becomes disengaged from the slot 32 in said sleeve element. When this happens, the sleeve element becomes free to turn relative to the driven member; it is then able to rotate with the drive shaft so that it will not necessarily become disengaged from the screwthreaded portion of said shaft.

It will be understood that the coupling is capable of adjustments to fine limits in order to vary the torque at which twill fail. Such adjustments can be made by removing the screw 30 and turning the sleeve element relative to the driving and driven members to increase or decrease the degree of preload on the spring. The screw is then replaced in engagement with the slot 32. A finer degree of adjustment would of course be possible if a number of slots 32 were provided at intervals around the open end portion of the sleeve; in this case the screw could be engaged with a selected one of said slots.

Various other modifications could be made. For example, the resilient means provided for loading the driving and driven members together could be constituted by means other than a coil compression spring; a stack of"Belville" type spring washers could be used. Furthermore, it will be understood that in order to increase the torque transmitting capacity of the coupling, whilst retaining its relatively small outside diameter, it could be provided with a plurality of friction discs connecting the driving and driven members. In this case, such discs could be provided, as in multi-plate friction clutches, between driving and driven plates slidably splined with respect to the driving and driven members. Alternatively, the frictional driving surfaces of the driving and driven members could be of conical form and it will be understood that this would have the same effect of greatly increasing the torque transmitting capacity of the coupling. In this case, especially, depending on the angle of taper of the frictionally engaging surfaces, it may be found that metal to metal contact is sufficient to transmit a required load.

In a coupling adapted to be driven in an anticlockwise instead of clockwise direction the screwthreaded portion 28 of the drive shaft would need to have a left hand thread.

Claims

1. An overload release coupling including driving and driven members frictionally connected together, resilient means being provided for loading said driving and driven members together, and adjustable means being provided for preloading said resilient means to adjust the torque at which the coupling can be arranged to fail, said adjustable means including a sleeve or nut element engaging screwthreaded portion of the driving member but being rotationally fixed, at least throughout the range of normal adjustment of the resilient means, relative to the driven member, the arrangement being such that any slipping which takes place at the frictional driving surfaces of the driving and driven members causes the pre-loading of the resilient means to be reduced so that further slipping is brought about and the sleeve or nut element is very soon completely slackened off and the frictional driving surfaces relieved of all load.

2. An overload release coupling according to claim 1, in which a disc of friction material is located between the driving and driven membersfortrans- mitting drive from the one to the other.

3. An overload release coupling according to either one of the preceding claims, in which, so that a relatively high torque can be transmitted and at the same time the coupling can be of relatively small diameter, a plurality of friction discs are provided between driving and driven plates slidably splined with respect to the driving and driven members.

4. An overload release coupling according to either one of claims 1 and 2, in which the frictional driving surfaces of the driving and driven members are of conical form.

5. An overload release coupling according to any one of the preceding claims, in which the arrangement is such that as the resilient means become relieved of all pre-load, the sleeve or nut element becomes free to turn relative to the driven member.

6. An overload release coupling according to any one of the preceding claims, in which the resilient means are constituted by a coil compression spring.

7. An overload release coupling constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.