GB2277566A

GB2277566A - Locking device for rotatable sprocket

Info

Publication number: GB2277566A
Application number: GB9309074A
Authority: GB
Inventors: Ronald Smith
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1993-05-01
Filing date: 1993-05-01
Publication date: 1994-11-02
Also published as: GB9309074D0

Abstract

A locking device 9 for temporary insertion between the toothed periphery 12 of a first sprocket 1 of an assembly, such as a motor vehicle combustion engine, and a surface 13 e.g. a second sprocket, has oppositely directed faces 10 and 11 adapted to engage respectively with the toothed periphery 12 and the surface 13 to releasably lock the first sprocket 1 against rotation relative to the assembly and to permit the insertion of the device in a direction having at least a component substantially parallel to the axis of the first sprocket 1. The sprockets 1 and 2 are preferably combustion engine cam-shaft sprockets. The locking device preferably has a cross-section when cut transversely to the axis of the first sprocket, which is of diabolo shape. Further, the faces 10 and 11 preferably have toothed profiles to engage each of the toothed peripheries 12 and 13 over an arc of from 30 DEG to 90 DEG . <IMAGE>

Description

Locking Device for Rotatable Sprocket This invention relates to a locking device for a rotatable sprocket and particularly but not exclusively for a sprocket component of a combustion engine such as that of a motor vehicle.

Sprockets incorporated in mechanical apparatus often require to be precisely rotationally positioned in relation to other components of the apparatus so that their rotation effects correctly timed operations. This is particularly so in the case of sprockets employed in a combustion engine such as that of a motor vehicle for example, wherein the correctly timed operation of inlet and exhaust valves through sprocket-driven cam-shafts is fundamental to the engine functioning properly.

The servicing of mechanical apparatus often requires the drive to such a sprocket to be temporarily removed whereby, during the servicing operation, the sprocket may be inadvertently moved from its correct position in relation to other components. In the case of sprocket-driven cam-shafts for example, where it is particularly important to have correct positioning of the sprocket, re-timing of the camshaft operation is then necessary. This is time consuming and renders the servicing expensive.

Published British patent specification 2217807A discloses a sprocket retention and chain guide assembly for a timing chain on an internal combustion engine in which a chain and two sprockets are assembled and retained in a pre-timed relationship with one another for ease of assembly onto the engine. In the arrangement described, the sprockets are retained in this relationship by the chain. Thus, any servicing requiring the removal of the chain would permit the sprockets to rotate relative to one another whereby retiming would become necessary.

According to the present invention there is provided a locking device for temporary insertion between the toothed periphery of a first sprocket of an assembly and a surface of the assembly adjacent to the first sprocket, which locking device has oppositely directed first and second faces adapted to engage respectively with said toothed periphery of the first sprocket and with said surface to releasably lock the first sprocket against rotation about its own axis relative to the assembly and to permit the insertion of the locking device in a direction having at least a component substantially parallel to the axis of rotation of the first sprocket.

By means of the locking device of this invention, the position of a sprocket of a combustion engine of a motor vehicle for example may be temporarily fixed relative to an adjacent surface while maintenance procedures are carried out whereby a precision sprocket setting can be preserved and the need for resetting avoided.

It is preferred that the first sprocket is mounted in the assembly for rotation about a fixed axis, relative to the assembly.

The assembly is preferably a mechanical apparatus and is more preferably a combustion engine of a motor vehicle.

However, the assembly may comprise a packaging or other assembly in which releasable locking of the first sprocket against rotation relative to the assembly is required.

While the surface of the assembly adjacent to the first sprocket may be a fixed surface for example, it is preferably a surface non-concentric with the periphery of the first sprocket. Accordingly, it may be a concave, flat or convex surface. However, the surface preferably comprises the toothed periphery of a second sprocket lying in a common plane with the first sprocket and having an axis of rotation. This second axis, which is preferably a fixed axis, is preferably parallel to the axis of the first sprocket. Such second sprocket may be in meshing relationship with the first sprocket but a non-meshing relationship is preferred.

The first sprocket, and the second sprocket when providing the adjacent surface, are each preferably cam-shaft sprockets mounted in an assembly comprising a motor vehicle combustion engine.

When the second sprocket provides the adjacent surface it is preferred that the insertion of the locking device in accordance with this invention, locks both the first sprocket and the second sprocket against rotation in either direction about their respective axes and relative to the assembly.

The first face of the locking device preferably has a toothed profiled to interlock with at least one tooth on the first sprocket, more preferably at least two and most preferably a multiplicity of teeth on the first sprocket.

The first face of the locking device is preferably profiled to engage the toothed periphery of the first sprocket over an arc of from 30 to 90 preferably 40 to 80 and preferably has a toothed profile to interlock with all the teeth of the first sprocket over such arc.

The second face of the locking device preferably has a profile corresponding to the surface adjacent to the first sprocket. Accordingly, it is preferably non-concentric with the first face and may be convex, flat or concave for example. However, the second face preferably has a toothed profile to interlock with at least one tooth on a second sprocket providing the adjacent surface, more preferably at least two and most preferably a multiplicity of teeth on a second sprocket. The second face is preferably profiled to engage the toothed periphery of such a second sprocket over an arc of from 30 to 90 preferably 40 to 80- and preferably has a toothed profile to interlock with all the teeth of such a second sprocket over such arc.

In a preferred embodiment of this invention wherein the locking device has first and second faces adapted to engage respectively with the toothed periphery of the first sprocket and with the toothed periphery of a second sprocket providing the adjacent surface, the cross-section of the locking device when cut transversely to the direction of the axis of rotation of the first sprocket is preferably of diabolo shape.

It will be appreciated that the locking device may comprise two spaced ends with a connecting bridge between them. By employing this expedient intermeshed teeth of the first sprocket and of a second sprocket providing the surface adjacent thereto, when in intermeshing relationship with one another, can be bridged. When such a connecting bridge is employed, the ends of the locking device may be connected by the bridge before the insertion of the locking device or after.

Further, it will be appreciated that if the first face and/or the second face of the locking device has a toothed profile to interlock respectively with teeth on the first sprocket and/or a second sprocket providing the adjacent surface, the teeth of the toothed profile should be such that they can be aligned with the respective sprocket teeth and such that each extend in a direction having at least a component parallel to the sprocket axes. It is preferred that the teeth of the locking device each extends in a direction such that they can be aligned with sprocket teeth with which they interlock and which each extends in a direction parallel with its respective sprocket axis.

The locking device of this invention may be made of plastic by for example cold casting or injection moulding but is preferably made of metal by a casting and machining process.

The locking device of this invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sketch of an exploded view of the cam-shaft drive of a motor vehicle combustion engine.

Figure 2 is a sketch of part of the cam-shaft sprockets within the area indicated by X in Figure 1 but between which a locking device according to this invention has been inserted.

Figure 3 is a sketch of a locking device similar to that illustrated in Figure 2.

In the drawings, in which like numbers correspond, 1 and 2 are cam-shaft sprockets for driving the cam-shafts 3 and 4 to which they are respectively fixed and forming part of an assembly comprising a motor vehicle combustion engine. The cam-shafts 3 and 4 rotate with the cam-shaft sprockets 1 and 2 about their respective common axes. The rotational positions of the cam-shaft sprockets relative to one another and to that of the driving sprocket 5 is such as to cause cams (not shown) on the cam-shafts 3 and 4 to operate, in correctly timed fashion, the inlet and exhaust valves (not shown) of the engine for its proper functioning. Drive from the driving sprocket 5 to the cam-shaft sprockets 1 and 2 is transmitted by toothed timing belt 6 which passes over the sprockets 1, 2 and 5 and also over the tensioner wheel 7 and the idler wheel 8. When the timing belt 6 is fitted for driving the cam-shaft sprockets 1 and 2 it can be seen that the rotational positions of sprockets 1 and 2 relative to one another and to that of the driving sprocket 5 are maintained by the timing belt 6. However, in the absence of the timing belt 6 it will be seen that without taking avoiding steps, the cam-shaft sprockets 1 and 2 will each be free to rotate about its respective axis whereby their timed rotational relationships would be upset. Owing to the manner in which the driving sprocket 5 is driven, its rotational position is not so vulnerable to inadvertent disturbance as the sprockets 1 and 2.

Figure 2 shows part of the cam-shaft sprockets 1 and 2 within the area indicated by X in Figure 1 but between which a locking device 9 according to the invention has been inserted.

The locking device 9 is an aluminium casting which has been machined to provide oppositely directed precision profiled faces 10 and 11 permitting the device 9 to be inserted between the sprockets 1 and 2 in a direction substantially parallel with the axes of the sprockets 1 and 2 and with the direction in which each sprocket tooth extends. The locking device 9 could alternatively be a methacrylate polymer cold casting similarly machined. Such a cold casting may be produced using a mixture of Acrulite Microtech - type A powder and liquid products supplied by Rubert & Co Ltd into which Omniplus aluminium filler, supplied by Henkel Industrial Adhesives is incorporated. The respective profiles of the faces 10 and 11 are toothed to correspond with the teeth of the toothed peripheries 12 and 13 of the sprockets 1 and 2 to interlock therewith. The arc of each of the sprockets 1 and 2 over which the locking device 9 engages their toothed peripheries is approximately 75-.

It can be seen that the locking device 9 has a cross-section transverse to the axes of the sprockets which is substantially diabolo shaped.

A locking device similar to that shown in Figure 2 is shown in Figure 3 wherein locking device 91 has oppositely directed faces 101 and 111.

Insertion of the locking device 9 between the sprockets 1 and 2 locks the sprockets 1 and 2 against rotation about their respective axes relative to one another and relative to the engine assembly. This locking of the sprockets 1 and 2 by locking device 9 is independent of the timing belt 6 which, with the locking device 9 in position, can be removed for replacement or to permit other parts of the engine to be serviced, replaced or repaired. On completion of servicing for example, the timing belt 6 can be replaced and tension adjusted and the locking device 9 then removed by withdrawing in a direction parallel with the axes of the sprockets 1 and 2 thereby allow the timing belt 6 to rotate the sprockets 1 and 2 from their undisturbed positions.

It will be appreciated that the locking device 9 may be employed to lock the sprockets 1 and 2 against relative rotation following their positions being initially set in engine assembly prior to a timing belt 6 being installed.

Further, the relative positions of sprockets such as the sprockets 1 and 2 could be pre-set and locked by a locking device such as the locking device 9 in an assembly comprising a mounting block or packaging prior to the sprockets being incorporated in an engine assembly for example.

Claims

1. A locking device for temporary insertion between the toothed periphery of a first sprocket of an assembly and a surface of the assembly adjacent to the first sprocket, which locking device has oppositely directed first and second faces adapted to engage respectively with said toothed periphery of the first sprocket and with said surface to releasably lock the first sprocket against rotation about its own axis relative to the assembly and to permit the insertion of the locking device in a direction having at least a component substantially parallel to the axis of rotation of the first sprocket.

2. A locking device as claimed in Claim 1 wherein the first sprocket is mounted in the assembly for rotation about a fixed axis relative to the assembly.

3. A locking device as claimed in either Claim 1 or Claim 2 wherein the assembly comprises a combustion engine of a motor vehicle.

4. A locking device as claimed in any one of the preceding claims wherein the surface of the assembly adjacent to the first sprocket comprises the toothed periphery of a second sprocket, the second sprocket lying in a common plane with the first sprocket and having an axis of rotation parallel to the axis of the first sprocket.

5. A locking device as claimed in Claim 4 wherein the cross-section of the locking device when cut transversely to the direction of the axis of the first sprocket is of diabolo shape.

6. A locking device as claimed in either Claim 4 or Claim 5 wherein the axis of rotation of the second sprocket is fixed.

7. A locking device as claimed in any one of Claim 4, Claim 5 or Claim 6 wherein the first and second sprockets are each cam-shaft sprockets mounted in an assembly comprising a motor vehicle combustion engine.

8. A locking device as claimed in any one of claims 4 to 7 wherein the second face of the locking device has a toothed profile to engage the toothed periphery of the second sprocket over an arc of from 30 to 90g.

9. A locking device as claimed in any one of the proceeding claims wherein the first face of the locking device has a toothed profile to engage the toothed periphery of the first sprocket over an arc of from 300 to 90 .

10. A locking device substantially as described herein with reference to the accompanying drawings.