GB2175357A

GB2175357A - Axial ratchet device

Info

Publication number: GB2175357A
Application number: GB08609574A
Authority: GB
Inventors: Michael John Neale; Thomas Alexander Polak; Stephen Payne
Original assignee: Cross Ltd T D
Current assignee: Cross Ltd T D
Priority date: 1985-04-18
Filing date: 1986-04-18
Publication date: 1986-11-26
Also published as: GB8609574D0; GB8509979D0; GB2175357B

Abstract

An axial ratchet device in which viscous drag surfaces 10, 11 between a driving member 1 and a ratchet member 3 which in addition to being engageable by means of axial ratchet teeth 5, 6 with the driving member 1 is connected to the driven member 2 by means permitting limited angular displacement resulting in limited axial displacement, operate to retain the ratchet and driving members out of engagement on over-run of the device. The ratchet member 3 may alternatively be engageable with the driven member 2 by means of ratchet teeth in which case the aforesaid connection will be between the ratchet member and the driving member 1. <IMAGE>

Description

SPECIFICATION Axial ratchet device This invention relates to axial ratchet devices in which ratchet teeth move in an axial direction to engage or disengage a drive and is concerned with certain improvements therein.

Axial ratchet devices comprise a driving member which may be a gear or chain wheel, a driven member which may be a hub, and a coupling member which is splined to either the driving or driven member and which is engageable with the other member by means of interengaging axial ratchet teeth on the coupling and driven (or driving) members. The driven member will normally be drivable by the driving member in a predetermined direction, the direction of drive of course depending upon the orientation of the ratchet teeth.

On over-run of the driven member relative to the driving member, the teeth on the driven member will over-run those of the coupling member (or the teeth on the coupling means member will over-run those on the driving member, as the case may be).

Whilst such ratchet devices represent a distinct improvement over the well known pawl type ratchet device in reducing loadings on the individual pawls since these are now replaced by ratchet teeth, difficulties are still encountered in applications where the device is required to over-run at speed for long periods of time when of course a high degree of ratchet teeth wear may be expected.

According to the present invention, an axial ratchet device for transmitting a rotary drive in a member comprises coupling means drivingly connected to a first of the members in a manner permitting limited angular displacement between the coupling means and the member which results in axial displacement between the coupling means and the member in a direction depending upon the sense of angular displacement and engageable with the second member to transmit a drive from the driving member to the driven member in said predetermined direction and means biasing the coupling means into engagement with the second member, adjacent surfaces of the coupling means and the second member defining a viscous drag area whereby on over-run of the driven member viscous drag on the coupling means assists in the disengagement of the coupling means from the second member permitted by the connection between the coupling means and the first member.

Preferably the coupling means comprises a single coupling member which is helically splined to the first member.

Preferably, the first member is the driven member and the second member surrounds the driven member with the coupling member located therebetween.

Advantageously, the biasing means is a disc spring.

One form of ratchet device is accordance with the invention will now be described by way of example with reference to the accompanying drawing which shows a sectional view of the device both in the disengaged and engaged states. The device comprises a driving member 1 which whilst shown as a collar may in practice have a series of sprocket teeth radically projecting therefrom to form a driving sprocket. Positioned inside of the sprocket 1 is a driven member 2, which may conveniently form a hub and be internally threaded for this purpose. Preferably both driving and driven members are of steel. Surrounding the driven member 2 is a coupling or ratchet member 3 which is helically splined as at 4 to the member 2 and which is preferably of reinforced plastics material.The ratchet member 3 is displaceable axially by being angularly displaced relative to the member 2, between a position of engagement with the driving member 1 in which position ratchet teeth 5 and 6 on the respective members 3 and 1 engage, and a position of disengagement from the driving member 1. The disengaged and engaged positions of the ratchet member are shown in the upper and lower parts of the drawing respectively.

In order to urge or bias the ratchet member 3 into engagement with the driving member 1, a spring washer 7 which may be a 'Wavywasher' spring, is constrained between the ratchet member and an end cap 8 of the device. At the other end a further end cap 9 is provided. The two end caps which are conveniently of plastics material may be held in position by circlips not shown. Adjacent surfaces 10 and 11 of the respective members 1 and 3 define a viscous drag area as will be described, the space formed by the inner and outer members 1 and 3 and the caps 8 and 9 being packed with a suitable lubricant. The cap 8 is shaped as at 12 to assist in retaining this lubricant within the space and futhermore a washer 13, preferably of steel, is interposed between the cap 8 and the driven member 2.

In operation of the device, the ratchet member 3 is normally urged by the spring 7 into engagement with the driving member 1. Assume that the splining 4 is left handed and that the orientation of the ratchet teeth 5 and 6 is such as to transmit torque between the member 1 and 2 when the member 1 is driven in a clockwise direction as viewed from the left in the drawing.

On over-run of the device, the increase speed of the driven member 2 relative to the member 1 will result in the teeth 5 over-riding the teeth 6 causing the coupling member 3 to be urged away from the member 1. The coupling member 3 will in fact rotate anticlockwise relative to the driven member 2, or 'unscrew' along the member 2 out of engagement with the member 1. This is assisted by the viscous drag on the coupling member which retains the member 3 out of engagement with the member 1. Reengagement of the coupling member with the driven member will only take place on removal of the overrunning force.

The device described is particularly suitable as a cycle free wheel device. Although on over-run the ratchet member still rotates, rotating at the speed of the driven member, disengagement of the ratchet member from the driving member avoids any "clicking" of the device whilst the cyclist is free wheeling.

The reinforced plastics material is particularly preferred for the ratchet member 3 as offering good wear characteristics when rubbing on steel at low velocities.

Various modifications are possible. Quite obviously, torque transmission by the device could be in the sense opposite to that described by changing the orientation of the teeth 5 and 6 and by forming the splining as right handed splining.

Furthermore, the roles of the inner and outer members could be reversed with the outer member serving as the driven member. With this arrangement, the ratchet member would not rotate on over-run. Instead of the spring 7 described a disc spring may be employed or alternatively a coil spring, preferably a tapered coil spring, may be used.

The device as described may be particularly suitable for automatic manufacture and assembly.

Claims

1. An axial ratchet device for transmitting a rotary drive in a predetermined direction from a driving member to a driven member comprising coupling means drivingly connected to a first of the members in a manner permitting limited angular displacement between the coupling means and the member which results in axial displacement between the coupling means and the member in a direction depending upon the sense of angular displacement and engageable with the second member to transmit a drive from the driving member in said predetermined direction and means biasing the coupling means into engagement with the second member, adjacent surfaces of the coupling means and the second member defining a viscous drag area whereby on over-run of the driven member, viscous drag on the coupling means assists in the disengagement of the coupling means from the second member permitted by the connection between the coupling means and the first member.

2. A device as claimed in claim 1, wherein the coupling means comprises a single coupling member which is helically splined to the first member.

3. A device as claimed in claim 2, wherein the first member is the driven member and the second member surrounds the driven member with coupling member located therebetween

4. A device as claimed in claims 2 or 3, wherein the driving and driven members are concentric annular members and the outer of these members has an inwardly projection annular flange one face of which carries a series of axial ratchet teeth engageable by a corresponding series of ratchet teeth on the coupling member.

5. A device as claimed in any one of claims 1 to 4, wherein the coupling member is of reinforced plastics material and the driving and driven members are of steel.

6. A device as claimed in any of claims 1 to 5, wherein the biasing means is a spring washer.

7. An axial ratchet device substantially as hereinbefore described with reference to the accompanying drawings.