This invention relates to clutch mechanisms in particular but not exclusively for automobile applications.

Clutch mechanisms are known having a clutch for selectively transmitting drive from a drive to a driven member. There is usually operating means for changing the state of the clutch between an operative and inoperative position. In addition there is actuating means for energising the operating means for operating the clutch. Mechanical linkages are provided between the actuating means and the operating means to transmit drive to the clutch. Automobile clutches usually have a short length of travel between the operative and inoperative positions which makes them sensitive to use. Proposals have been made for cushioning the clutch movement over the bite point, for example by the use of springs between the clutch plates. However these arrangements have tended to be somewhat costly to manufacture.

An object of the invention is to provide an improved clutch mechanism which is simple but effective.

According to the invention a clutch mechanism comprises a clutch for selectively transmitting drive member from a drive to a driven member, operating means for changing the state of the clutch between operative and inoperative positions, actuating means for energising the operating means for operating the clutch, and mechanically operated transmission means for transmitting drive between the actuating means and the operating means, wherein the transmission means includes cushioning means whereby during one phase of operation of the clutch, in particular during engagement and disengagement of the clutch, the transmission means transmits drive to the operating means at a different rate, whereby to extend the range of movement at the bite point of the clutch.

In a preferred arrangement the transmission means includes resilient means of predetermined resilience through which drive is transmitted to the clutch, the resilient means being arranged so that over an initial phase of clutch movement the resilient means acts to transmit drive without substantial deformation ; in a second phase of movement (which is over the bite point) the resilient means is deformed, and over a third phase, when full deformation has occurred, drive is directly transmitted to the clutch.

The resilient means may include spring means such as a helical spring, cone spring, or elastomeric material. The resilience of the resilient means may be variable over the extent of movement of the transmission means. The resilience is such that no movement occurs until the force exceeds a predetermined level.

In one arrangement the resilient means is incorporated into a housing in which is a movable member, and the resilient means is located between the housing and the movable member, whereby upon completion of the initial phase of movement, the resilient means is compressed, and in the third phase of movement the movable member acts directly on the housing so that the transmission means moves as one unit.

In an alternative arrangement the transmission means achieves its different rate of transmission of movement to the clutch by the use of a cam and follower arrangement, the cam being mounted on a rotary input and the follower being operatively connected to the clutch. By the arrangement of a suitable cam profile, the follower may be arranged to be divided into three phases of movement, an initial phase of movement followed by a slower rate of movement (over the bite point of the clutch), and a third quicker phase of movement after disengagement of the clutch.

In a further alternative arrangement the transmission means may include a different form of cam and follower which comprises a wedging surface engaged by a follower, the wedging surface being movable reciprocally in a generally straight line to be engaged by the follower which moves generally at a right angle to the direction of movement of the wedging surface, the wedging surfaces generally being divided into

three or more zones so that there is provided movement of the follower in an initial phase of movement, in a second slower phase of movement, and in a third phase of movement. The second slower phase of movement is selected to be over the bite point of the clutch.

Further features of the invention will appear from the following description of embodiments of the invention given by way of example only and with reference to the accompanying drawings, in which: Fig. 1 shows a conventional clutch mechanism; Fig. 2 shows a modified part of the mechanism of Fig. 1; Fig. 3 shows an alternative to the modification of Fig. 2 ; Fig. 4 shows a further modification of the arrangement of Fig. 1; Fig. 5 shows a further modification of the arrangement of Fig. 2; and Fig. 6 shows a graph illustrating the benefits of using the arrangements of Figs. 2, 3,4 or 5.

Referring to the drawings, Fig. 1 shows a conventional layout for a clutch mechanism in which there is provided clutch plates 10 located within a housing 12 and operated by clutch operating mechanism 13 by which the clutch plates 10 are moved between operative (engaged) and inoperative (disengaged) positions. For simplicity the operating means 13 is shown as a lever arm of which one end operatively engages the clutch plates 10, the other is attached to transmission means 14, in the form of a rod, and having a pivot 15.

The rod 14 is connected at its opposite end to an actuator 16 by which the rod 14 is moved reciprocally to operate the operating means 13. The actuator 16 includes a housing 17 in which is movable a piston 11, attached to the rod 14, by the introduction of fluid into the housing 17 upon receiving a signal at valve 19 to introduce or release fluid from the housing 17 which defines a cylinder.

In the arrangement shown in Fig. 1 operation of the clutch plates 10 is effected by direct movement of the piston 11 in the cylinder 17 causing the operating means 13 to engage or disengage the clutch. Referring to Fig. 6 the action of the clutch mechanism in this arrangement would result in a generally straight line displacement on the application of constantly increasing force. As can be seen from Fig. 6, if the bite point of the clutch occupies a displacement E this occurs over a short distance of displacement which may be only one or two millimetres in practice.

Although it has been proposed to increase the amount of displacement over the bite point this has involved the use of cushioning within the clutch plates which can be problematical in terms of cost and difficulty in assembly.

Referring now to Fig. 2 there is shown one arrangement whereby cushioning is introduced into the transmission between the actuating means 16 and the clutch operating means 13. In the Fig. 2 arrangement the rod 14 has interposed between its ends a cushioning arrangement 20 defined by a housing 21 in which is located a spring 23, a movable disc 24 acting as a piston and having a stop 25 extending from one side which, upon movement of the disc 24 along the housing 21 is engagable with the opposite end of the space within the housing 21.

The spring 23 has a resilience chosen to match the requirements of the clutch mechanism and may be a helical spring as shown, or can be another kind of resilient spring.

As the piston 11 of the actuating means 16 moves to the left as seen in Fig. 1, this causes the rod 14 to move, and compressive force is applied to the spring 23. Until the compressive force on the spring is sufficient to overcome the resilience of the spring no compression occurs and the unit 20 moves as one towards the left with the piston 11 and causes the clutch operating means 13 to move the clutch towards the disengaged position. Such movement continues until the clutch approaches its bite position and, when this occurs, the cushioning device 20 comes into play with the spring 23 beginning to compress according to the predetermined resilience of the spring chosen.

Thus the disc 24 moves along the housing towards the opposite end thereof until the projection 25 engages with the opposite end of the housing 21 which is when the clutch has moved through the bite point. Thereafter the unit 20 moves as one with the rod 14 through a further phase of movement of the clutch.

To explain the phases of movement more clearly and referring to Fig. 6, displacement of the clutch is initially by movement of the piston 11 causing movement of the operating means 13 with the cushioning means 20 and rod 14 moving as one. Such movement is over the distance A in Fig. 6, and constitutes a first phase of movement.

A second phase of movement is over the distance E in Fig. 6 which is through the bite point of the clutch. When the clutch is in the form having the cushioning means 20 of Fig. 2 the extent of the bite point changes to that of B in Fig. 6 which, it can be seen, gives rise to a bigger displacement over this movement.

After passing through the bite point the clutch then moves a further distance, shown as C in Fig. 6 which can be termed a third phase of movement. This is the same with the Fig. 1 arrangement as with the arrangement as modified according to Fig. 2.

It will be appreciated that the spring 23 may be of a different kind to that shown and may be arranged to give a variable resilience over its extent of movement, according to the requirements of the mechanism. It will also be appreciated that the cushioning means of Fig. 2 can be used in other arrangements to that shown in Fig. 1, for example in arrangements in which the transmission to the clutch operating means 13 is in tension instead of compression.

Referring now to Fig. 3 there is shown an alternative to the cushioning of Fig. 2. In this case the cushioning effect is achieved by providing a cam 31 carried on a rotary shaft 32 and having a cam surface 33 engaged by a follower 34. As can be seen from Fig. 3 there are three parts of the cam surface 33 that covered by the arc A, which gives a gradual increase in the displacement of the follower 34 ; that covered by the arc B which has a greater displacement about the axis of shaft 32 for the equivalent movement of the

follower 34 ; and that about the arc C which decreases the extent of displacement for a given amount of rotation of the shaft 32. The arcs A, B and C of Fig. 3 correspond with the displacements A, B and C shown in Fig. 6 and the arrangement of Fig. 3 is intended to give rise to similar benefits of cushioning the transmission to the clutch over the bite point.

Referring to Fig. 4 there is shown an alternative way of cushioning the transmission of movement from the clutch actuating means to the clutch operating means and this time a wedging mechanism 40 is employed which includes a reciprocally movable member 41 guided for movement between a fixed member 42 and a movable follower member 43 and which is operatively connected to the operating means 13.

The member 41 has three wedging surfaces 44,45 and 46 of different inclinations to the direction of travel which are engagable with the follower 43 upon said reciprocal movement to cause the follower 43 to move to the left, as shown, at a differential rate of displacement depending upon whether the surface 44,45 or 46 is in engagement with the follower 43. The movement resulting from the surface 44 engaging the follower 43, causes the follower to move a distance A which corresponds the distance A in Fig. 6.

Further movement of the member 41 in the downwards direction as seen with the follower 43 in contact with the surface 45 causes the follower to move a distance B which corresponds with distance B in Fig. 6 and such movement is intended to be over the extent of the bite point of the clutch 10.

In the further phase of movement the surface 46 engages the follower 43 to bring about the movement C which completes the movement of the clutch during operation.

The embodiment of Fig. 4 is another means for providing cushioned movement of the transmission between the actuating means 16 and the operating means 13 of the clutch which, in effect, provides for greater displacement of the actuating means during engagement and disengagement over the bite point. Since movement through the bite point is small an increase in the displacement of only small amounts significantly

affects the operation. For example the effect of the cushioning means may be to extend the displacement by between 1-3 mm.

Referring now to Fig. 5, there is shown a spring based cushioning arrangement 20 which is similar in principle to the arrangement of Fig. 2 and similar parts are given the same reference numbers. The Fig. 5 arrangement is a tension arrangement in which tension is applied between one end and the other of this arrangement 20. A housing 21 admits a headed end 50 of the rod 14 which end defines a shoulder 52.

The rod 14 enters the housing through an opening 54 in an annular member 56 secured within the housing 21 by a ring 58. The rod 14 carries a ring 60 engagable with the annular member 56 to restrict the movement of the rod 14 to the right, as seen. This member 56 also defines a further shoulder 62 and between the shoulders 52 and 62 is located a cone spring 64. Thus when tension is applied across the housing 21 the headed end 50 is urged towards the opposite end of the housing against the action of the spring 64. Upon a predetermined tension being reached, which is intended to be at the bite point of the clutch, the cone spring 64 permits relative movement between the rod 14 and the outer part of the housing 21 for the same purpose as previously explained.

After a small amount of relative movement the unit or assembly again moves as one to complete the clutch operation.

It will be appreciated that the clutch 10 may take different forms and may be a multi-plate clutch or a single plate clutch.

Although the arrangement of Fig. 2 shows a fixed rate spring a variable rate spring can be introduced and/or the spring may be pre-loaded.

The illustrated arrangements are intended to assist in the movement of clutch mechanisms between the beginning and end of the clutch engaging and disengaging positions. This has application to manual and automatic transmission systems and is a simple and effective answer to overcoming restricted travel of clutch mechanisms.