CLUTCH ACTUATOR

The invention relates to an arrangement for connecting a clutch actuator to a clutch release lever within a clutch housing.

It is known to have a clutch housing which communicates through an opening with a clutch actuator push rod leading to a gear box. Such an arrangement is shown in Fig 1, in which the clutch actuator is mounted on the clutch housing. There is a bellows arrangement covering the opening in the clutch housing for the actuator for the push rod. This is to allow movement of the push rod without ingress of dirt. The bellows only protects the clutch actuator from external contamination.

The above mentioned arrangement can not be used when the clutch actuator is arranged within the gearbox, as suggested in French Patent 2,798,179. In such a case, the clutch actuator is fitted by movement in a direction transverse to the axial direction of movement of the clutch piston rod. As described in applicant's recently published PCT application NO2006/000292, the clutch actuator push rod may preferably be split into two parts. The clutch actuator may be an integral part of a shifting control unit, which is assembled to the gearbox as a single unit.

An object of the invention is to provide support for at least one of the first and second push rod parts. Without support means for the push rod, the first and second parts of the push rod would separate, and the push rod would not transfer an actuator force from the actuator cylinder to the release lever of the clutch.

Another object of the invention is to provide a clutch housing with sealing means to prevent dirt and oil passing from the clutch housing to the gear box and visa versa.

Without a seal between the clutch housing and the gear box, there is a risk of oil from the gearbox entering the clutch housing or dirt from the clutch housing entering the gear box. Oil entering the clutch housing would result in a reduction in friction between the clutch elements, and so reduced functionality of the clutch. Dirt entering the gear box would pollute the gear oil, and so result in increased wear on gear wheels within the gear box.

Advantageously, the invention may provide sealing means and support means allowing the clutch actuator to be inserted and removed in a direction transverse to the longitudinal axis of the push rod. The assembly and disassembly procedures for the clutch are facilitated by a bushing which surrounds at least a part of the push rod and permits longitudinal movement of the push rod. The bushing is itself arranged for limited movement in that direction within the housing to allow

for wear in the clutch. The bushing does not interfere with assembly and disassembly, but is long enough to surround the push rod to constrain it for longitudinal movement.

A further advantage which may accrue from the invention is that the seal against both dirt and oil is not destroyed by wear on the clutch. This is another reason for providing a sliding bushing arranged for limited longitudinal movement.

The invention provides an arrangement comprising part of a clutch housing incorporating a clutch release lever, the clutch release lever being capable of acting to bear on a push rod which acts through an opening in the clutch housing on a piston in a clutch actuator cylinder, in which the opening has a bushing or tube surrounding at least a part of the push rod and the bushing or tube has a seal for preventing leakage of fluid into the clutch housing and for preventing egress of particulate solids from the clutch housing.

In one particularly preferred form, the bushing is capable of sliding movement through the opening.

In this form it is preferred that the bushing is movable to a position in which it can be inserted or withdrawn in a direction transverse to its direction of sliding movement. It is further preferred that the bushing is biased to move to that position when a worn clutch is to be replaced or the actuator is to be removed or inserted. In the one particularly preferred form, it is preferred that, as the clutch becomes worn, the bushing moves towards the clutch actuator in a direction along the axis of movement of the piston rod.

It is also preferred that the bushing has at least one end stop disposed to cooperate with an associated surface on the piston rod to permit travel towards an initial position. It is further preferred that the end stop is formed as an inwardly directed circumferential rim at the end of the bushing nearer to the clutch release lever.

It is also preferred that the length of the bushing corresponds to the length of stroke of the clutch release lever. It is also preferred that the distance available for sliding of the bushing corresponds to the anticipated distance of travel due to wear of the clutch.

It is also preferred that the seal is fixed in relation to the clutch side of the actuator push rod, and is movable in relation to the bushing.

An example of the prior art and two specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure l is a sketch of a clutch operating system,

Figure 2 is a cross section through an assembly comprising part of a clutch housing and part of a clutch actuation mechanism, showing a new clutch in a disengaged position, and illustrating the provision for wear in the assembly, Figure 3 is a similar cross section, showing a worn clutch in an engaged position.

As shown in Figure 2, the left hand side of the figure comprises part of a clutch actuator 10 and the right hand side of the figure comprises part of a clutch housing 11. The clutch housing 11 has a clutch release lever 12, and the clutch actuator has a piston 14 within a cylinder 15. The piston 14 is biased towards the disengaged position shown in Figure 2 by a spring 16.

A piston rod 17 (forming part of a pneumatic external actuator) extends from the piston 14 into an opening 18 in the clutch housing 11, so to engage with the clutch release lever 12. Following the invention, the clutch housing has sealing means in the opening 18 in the clutch housing 11 , through which an actuator push rod 19 enters the clutch housing. The sealing means prevents oil from the gear box reaching the clutch housing, and dirt from the clutch housing reaching the gear box.

The sealing means is a telescopic bushing 21 surrounding the actuator push rod 19 and movable horizontally through the opening 18. A seal 22 lies between the internal bore of the telescopic bushing 21 and the external surface of the end 23 of the piston rod 17 nearer to the clutch release lever 12.

In applications where the clutch actuator is mounted in a direction transverse to the actuator push rod, the actuator push rod must be split into at least two parts. The piston part of the rod (17) must be of such a length that it can be retracted into the actuator cylinder (15). (This arrangement is illustrated in our co-pending PCT NO2006/000292 as piston rod 5.) An important advantage is that the clutch actuator can be dismantled. The opening 18 in the housing must be sealed off even when the clutch actuator is not in place.

For this reason the seal 22 must be on the clutch side of the clutch actuator push rod 17. To enable transverse insertion of the clutch actuator, the clutch side of the actuator push rod is so short that in the fully disengaged position it would lie outside the length of the opening 18 in the clutch housing 11. Hence the inner wall of the opening must be extended so that the clutch side of the actuator push rod is always within the opening 18 or an extension of the opening. The inner wall of the opening 18 is extended by the telescopic bushing 21 inserted in the opening through which the actuator push rod passes.

On one hand the bushing 21 must not interfere with the clutch release lever 12 when the clutch is worn (see Figure 3). On the other hand, when the clutch actuator is being inserted, the bushing must not be in a position where it interferes with the action of insertion. These requirements restrict the length of the bushing 21. The length of the bushing must be less than the total operative throw of the clutch release lever throughout the lifetime of the clutch, so that there is always sliding engagement between the bushing and the clutch side of the actuator push rod. For this reason it is important that the bushing 21 is slideably arranged in the opening 18 of the clutch housing. In its initial position, the bushing does not interfere with the insertion of the clutch actuator. As the clutch becomes worn, the release lever 12 will push the bushing 21 in a direction towards the clutch actuator. This could result in the bushing reaching a position in which it interferes with insertion of the clutch actuator. The bushing will therefore be urged to its initial position where it does not interfere with the insertion or removal of the actuator when the clutch actuator is to be mounted or dismounted. The bushing will also be biased to its initial position when a worn clutch is replaced by a new clutch. A circumferential rim or end stop 24 is formed at the right hand end of the bushing 21. This cooperates with the clutch release lever 12 so that the bushing 21 can be pushed to the left. The preferred length of the bushing 21 is the stroke length of the actuator push rod 19, and the sliding travel of the bushing is equivalent to the wear travel of the clutch.