WO2014008526A1

WO2014008526A1 - A clutch assembly

Info

Publication number: WO2014008526A1
Application number: PCT/AU2012/001049
Authority: WO
Inventors: Damian Michael BIBBY
Original assignee: Clutch Industries Pty Ltd
Priority date: 2012-07-13
Filing date: 2012-09-05
Publication date: 2014-01-16

Abstract

A clutch assembly (10) including a clutch plate (14), an annular pressure plate (13), and a diaphragm (12) and a thrust bearing (22) mounted about an input shaft (19). The diaphragm (12) has a radially outer ring in engagement with the pressure plate (13) and a plurality of radially inwardly extending fingers extending inwardly from the ring to a position proximate the outer surface of the input shaft (19). The diaphragm (12) is mounted to a fulcrum (24) so that movement of the fingers in one direction results in movement of the ring in the opposite direction, whereby movement of the thrust bearing (22) in engagement with the fingers in a first direction towards the clutch plate (4) causes the diaphragm (12) to rotate about the fulcrum (24) and permits the pressure plate (13) to move to disengage the clutch assembly, while movement of the thrust bearing (22) in engagement with the fingers in the second direction causes the diaphragm to move the pressure plate to engage the clutch assembly. The clutch assembly includes a sensor (39, 40) to sense the position of the thrust bearing (22) when the clutch assembly (10) is engaged.

Description

A CLUTCH ASSEMBLY

FIELD OF THE INVENTION

The present invention relates to a clutch assembly which includes an arrangement to monitor or measure wear in the friction material of an automotive clutch.

BACKGROUND OF THE INVENTION

The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement of what was part of the common general knowledge as at the priority date of the application.

Manual gearbox or transmission vehicles, as opposed to automatic transmission vehicles, employ a clutch assembly between the flywheel of the vehicle engine and the vehicle transmission. The clutch is operated by the vehicle driver through a foot pedal in the vehicle cabin, and allows the transmission to be disengaged from the flywheel, either for the purpose of changing gears in the transmission, or to allow the vehicle to come to a stop with the transmission in gear. A clutch assembly employs a clutch plate (otherwise known as a driven plate) which has a circumferential ring of friction material, and the friction material is sandwiched between the engine flywheel and a pressure plate when the clutch assembly is engaged. In this engaged condition, rotation from the flywheel can be transmitted through the clutch assembly to the transmission. To disengage the clutch assembly, the friction material is withdrawn from engagement with the flywheel, so that the flywheel can rotate freely without transmitting that rotation to the transmission.

The friction material can be withdrawn from engagement with the flywheel by withdrawing the pressure plate away from the flywheel, so that the pressure forcing the friction material into engagement with the flywheel is removed. The clutch plate will continue to rotate with the flywheel but flywheel rotation will not be transmitted to the pressure plate of the transmission. The arrangement for moving the pressure plate can comprise a plurality of fingers that extend radially inwardly from a radially outer ring, and which are in abutment at one end with the pressure plate and at the other end which bear against the thrust bearing of an actuator, such as a concentric slave cylinder or a slave cylinder that drives a pivoting arm. In the more common concentric slave cylinder form of actuator, the fingers are pivotable about a fulcrum located towards the abutment position of the fingers with the pressure plate by movement of the concentric slave cylinder. The pressure plate is naturally biased away from the flywheel but the fingers of the diaphragm engage the pressure plate and push it forward towards the flywheel against that bias when the concentric slave cylinder is in a withdrawn position. However, upon forward movement of the concentric slave cylinder the fingers pivot about the fulcrum and this allows the pressure plate to move rearwardly, or away from the flywheel. That movement releases the pressure on the friction material and allows it to withdraw from contact with the flywheel and thus disengage the clutch assembly.

Reverse movement of the concentric slave cylinder allows the fingers to pivot in the opposite direction, to push the pressure plate towards the flywheel and in that movement, the friction material of the clutch plate can again be sandwiched between the flywheel and the pressure plate. The arrangement of the clutch assembly is such that with the concentric slave cylinder in the withdrawn position, the pressure plate bears against the clutch plate under a load sufficient to sandwich the clutch plate against the flywheel. Thus, the natural position of the clutch assembly is with friction material of the clutch plate sandwiched between the flywheel and the pressure plate, while movement away from that sandwiched position is achieved by forward movement of the concentric slave cylinder against the fingers to cause them to pivot. In the arrangement comprising a slave cylinder and a pivoting arm, the clutch assembly can operate in the same manner, as well as in the reverse to the operation discussed above. The arrangements are known as "push" arrangement for the same manner of operation and a "pull" arrangement for the reverse operation. Thus, the pivoting arm has a fulcrum about which it rotates upon actuation by the slave cylinder and the slave cylinder pulls or pushes the arm to disengage the pressure plate from sandwiching the friction material against the flywheel. In a pull arrangement, movement of the slave cylinder forward or towards the flywheel allows the portion of the arm on the other side of the fulcrum to pivot to the rear or away from the flywheel and allows the pressure plate to move rearward or away from the flywheel, allowing the clutch plate to rotate freely. In a push arrangement, the opposite movement occurs.

The friction material of a clutch assembly wears over time. The speed of wear depends on numerous factors, including the amount of engaging and disengaging clutch activity that the clutch assembly is subject to, as well as the manner in which the vehicle driver engages and disengages the clutch. The friction material tends to wear only when there is slippage between the flywheel and the friction material and poor clutch use by the vehicle driver can increase the amount of slippage that occurs during engagement and disengagement. In addition, drivers can "ride" the clutch in order to maintain a vehicle stationary on an incline, or to reduce the speed of the vehicle, by depressing the clutch pedal partially rather than fully so that the friction material only engages the flywheel partially and so that the friction material slips relative to the flywheel. Riding the clutch in this manner can result in significant wear of the friction material, particularly if the clutch is frequently used in this manner.

It follows that the amount the friction lining of a clutch plate has worn is difficult to predict unless the clutch assembly is dismantled and the thickness of the friction material measured. Checking for wear in this manner is difficult and time consuming, and therefore rarely forms part of normal vehicle maintenance.

For most drivers, awareness of significant clutch plate wear only occurs when the performance of the clutch deteriorates. By that stage, the clutch has usually worn beyond a designed wear limit, potentially adversely affecting vehicle safety. In addition, there is a potential inconvenience to the driver by the relatively immediate need for clutch assembly repair or replacement.

It is an object of the invention to provide an arrangement which allows for more predictable assessment of friction lining wear in a clutch assembly.

SUMMARY OF THE INVENTION

The present invention provides a clutch assembly including

a clutch plate having an annular periphery to which an annular ring of friction material is applied to face in each of opposite directions, the clutch plate being mounted to an outer surface of a gearbox input shaft so that rotation of the clutch plate rotates the input shaft and the clutch plate being movable axially on the input shaft,

an annular pressure plate mounted concentrically about the input shaft and having an annular surface in facing relationship with the friction material,

a diaphragm mounted concentrically about the input shaft and having a radially outer ring in engagement with the pressure plate and a plurality of spaced apart radially inwardly extending fingers extending inwardly from the ring to a position proximate the outer surface of the input shaft, the diaphragm being mounted to a fulcrum so that movement of the fingers in one direction results in movement of the ring in the opposite direction,

a thrust bearing mounted about the input shaft, the thrust bearing being in engagement with the diaphragm fingers proximate to the input shaft and movable axially relative to the input shaft by an actuator,

whereby

movement of the thrust bearing in engagement with the fingers in a first direction towards the clutch plate causes the diaphragm to rotate about the fulcrum and permits the pressure plate to move in a second direction opposite the first direction to disengage the clutch assembly, and

movement of the thrust bearing in engagement with the fingers in the second direction causes the diaphragm to rotate about the fulcrum and to move the pressure plate in the first direction to engage the clutch assembly,

movement of the thrust bearing in the second direction terminating when the clutch assembly is engaged,

the clutch assembly further including a sensor to sense the position of the thrust bearing when the clutch assembly is engaged.

A clutch assembly of the above kind advantageously permits the wear condition of the friction material to be monitored over time and data from the sensor can be used to alert the vehicle driver, or maintenance personnel, to the requirement for friction material replacement. That alert can be made in advance of the friction material reaching a critical minimum thickness, and thus can prevent the clutch assembly reaching the stage where performance levels drop significantly, or where vehicle safety is compromised. Moreover, an alert can be generated which allows the vehicle owner to schedule clutch replacement at a time which is convenient, rather than when the clutch requires immediate replacement. Thus, the alert might be sent three or six months in advance of the date on which the clutch assembly is expected to require replacement, so that the owner can schedule replacement within that period at a convenient time. This is considered to be particularly advantageous for fleet operators, to minimise the number of cars which are out of use at any one time. For domestic vehicle owners, the alert could conveniently allow the owner to schedule the replacement during a period when use of the vehicle is known not to be required, such as when the owner might be on holidays.

The alert can appear as a dashboard display, or it can appear in the diagnostic testing equipment when the vehicle is serviced or both. The alert could alternatively be sent wirelessly to a vehicle service body that could then contact the vehicle owner to schedule a clutch service.

Still further, the present invention can provide the vehicle owner or user, information about the remaining life of the friction material so that the owner or user can see whether the clutch is expected to require replacement in a matter weeks, months, or years. This could, for example, a useful tool in the sale of a vehicle, whereby the vehicle owner can advertise the vehicle as having a certain amount of clutch life remaining.

The invention is applicable to clutch assemblies which utilise a concentric slave cylinder as the actuator to actuate the assembly during clutch engagement and disengagement or to clutch assemblies which utilise a slave cylinder and pivoting arm as the actuator and in which the slave cylinder acts in either direction as a push or pull arrangement for actuating and disengaging the clutch assembly. In either form, the actuator includes a thrust bearing which comprises both a carrier and a rotatable bearing. The rotatable bearing rotates with the pressure plate, while the carrier remains stationary relative to the bearing and carries the rotatable bearing during axial movement of the thrust bearing forward and away from the clutch plate.

Referring now to a typical form of concentric slave cylinder, such a cylinder will also include a base, and tube which extends from the base. In assembly, each of the base and the tube are mounted concentrically about the input shaft but are fixed against rotation. Thus, the input shaft can rotate within the base and tube. In the form of concentric slave cylinder which also includes a base and tube of the kind discussed above, the carrier and rotatable bearing are mounted on the tube and can move together axially relative to the base and tube. For this form of slave cylinder, the sensor can include a first sensor component fixed to the base or the tube and a second sensor component fixed to the carrier or the rotatable bearing. The first and second sensor components can be aligned, such as in facing alignment and wear in the friction material of the clutch assembly can measured as the function of the relative positions, such as the spacing, between the first and second sensor components when the clutch assembly is in an engaged position. Instead of spacing between the first and second sensor components, the components can be telescopically aligned for example, or otherwise aligned. Where a slave cylinder is employed which is not of the concentric kind, the sensor can include a first sensor component fixed to a part of the transmission which is stationary relative to the diaphragm and the pressure plate and a second sensor component which is fixed to the carrier or the rotatable bearing, or to the pivoting arm or to the portion of the slave cylinder itself which moves to actuate the clutch assembly. The first and second sensor components can thus move relative to each other and wear in the friction material of the clutch assembly can be measured as the function of the relative positions.

Sensors of the above kinds can be robust and accurate. The sensor includes minimal moving parts and can tolerate the environment within which it is situated without affecting is ability to transmit signals relating to the space between the first and second sensors. In some forms of the invention, the sensor is hardwired, with magnetically shielded properties, in order to transmit a signal, although wireless transmission is also possible. Typically, the hardwiring would extend through the transmission bell housing of the transmission with which the clutch assembly is associated and the hardwiring would extend to the vehicle computer within the engine bay, where after the signal is processed and relevant information stored, presented or transmitted as described above. While the relative positioning between the first and second sensors can be utilised in any appropriate manner to generate a suitable signal in relation to the thickness of the friction material, in some forms of the invention using a concentric slave cylinder, where spacing is employed, the spacing between the first and second sensor components increases upon disengagement of the clutch assembly and decreases on engagement of the clutch assembly. In these forms of the invention, the space between the first and second sensor components will decrease in the clutch engaged condition, as the friction material wears. That is, when the friction material is at maximum thickness and the clutch assembly is engaged, the space between the first and second sensor components will be greater than when the clutch assembly is engaged and the friction material has worn. The space between the first and second sensor components will continue to reduce when the clutch is in the engaged condition as the friction lining wears. The same will occur with a slave cylinder of the non-concentric form in a pull type clutch, while the reverse will occur with a slave cylinder of the non-concentric form in a push type clutch.

Sensors which are suitable for use in the present invention include variable reluctance sensors, variable resistance sensors and magneto resistive sensors. Other sensing arrangements could also be employed.

The sensor can be arranged to provide a continuous output signal, or it can be arranged to provide a signal only when the transmission is in neutral gear and the clutch assembly is engaged. The present invention also extends to a transmission for a vehicle which has a bell housing attached to a front end thereof and within which a clutch assembly of the above kind is housed. The input shaft discussed above would extend from the clutch assembly into the transmission. In a transmission of this kind, the arrangement would include a thrust bearing mounted about the input shaft and actuated by a slave cylinder, which can include a concentric slave cylinder.

The present invention also provides a concentric slave cylinder comprising:

a base and a tube extending from the base, a thrust bearing comprising a carrier and a rotatable bearing mounted on the tube and which are movable axially together relative to the base and the tube,

a sensor to sense the position of the thrust bearing, the sensor including a first sensor component fixed to the base or the tube and a second sensor component fixed to the carrier or the rotatable bearing, the first and second sensor components being in alignment and the position of the thrust bearing being sensed as a function of the relative positioning between the first and second sensor components.

In a concentric slave cylinder of the above kind, the first and second sensor components can be in facing alignment and the position of the thrust bearing being sensed as a function of the spacing between the first and second sensor components.

In a concentric slave cylinder of the above kind, the sensor can be a variable reluctance sensor, a variable resistance sensor, or a magneto resistive sensor, as discussed above. Other sensors could also be employed.

The present invention further extends to a vehicle which includes a clutch assembly of the above described kind, and/or a concentric slave cylinder of the above kind. In such a vehicle, the vehicle includes a vehicle management computer, which is operable to receive a signal from the sensor of the clutch assembly or the concentric slave cylinder and to process the signal for determining the expected life of the clutch assembly friction material. In some forms of the invention, the computer can send an alert upon the sensor sensing that the friction material has reached a predetermined wear thickness. That thickness could be a critical thickness, indicating that the need for immediate clutch maintenance or replacement, or it could be sent in advance of that thickness being reached as a warning that the critical or minimum thickness is being approached. The alert could be displayed to the vehicle driver, or it could be displayed to service personnel servicing the vehicle, or it could be sent by wireless transmission to a third party, such as the diagnostic centre of an automotive repair business, who could inturn contact the vehicle owner or operator to alert them to the need for clutch repair or replacement. BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which: Figure 1 is a cross sectional view showing a clutch assembly according to the invention, installed between the flywheel of the vehicle engine and a gear transmission.

Figure 2 is a cross sectional view of the arrangement of Figure 1 , but showing the friction lining of the clutch assembly at maximum thickness.

Figure 3 is a cross sectional view of the arrangement of Figure 1 , but showing the friction lining of the clutch assembly at a reduced worn thickness. Figure 4 is a view of the concentric slave cylinder according to the invention.

Figure 5 shows the concentric slave cylinder of Figure 4 in more detail.

Figure 6 is a cross sectional view showing an alternative clutch assembly according to the invention, installed between the flywheel of the vehicle engine and a gear transmission.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to Figures 1 to 3, a cross sectional view of a clutch assembly 10 is shown comprising a cover assembly 1 1 , a diaphragm 12, a pressure plate 13 and a clutch plate 14.

The cover assembly 1 1 is bolted at radially outer ends 15 to a flywheel 16, which is itself bolted to a crank shaft 17. Rotation of the crank shaft 17 by the normal internal combustion engine of a vehicle results in rotation of the flywheel and thus of the cover assembly 1 1 .

The cover assembly 1 1 is connected to the pressure plate 13 via three relatively rigid metal straps (not shown) that are spaced apart equidistantly about the plate 13 and which allow the pressure plate to float relative to the cover assembly 1 1 . The straps are only short, but are arranged to bias the pressure plate away from the flywheel 16. As will be explained later herein, the diaphragm 12 tends to bias the pressure plate 13 towards the flywheel 16. The arrangement is such that the pressure plate 13 rotates with the cover assembly 1 1 .

Transmission of crank shaft rotation to the actual gear transmission 18 occurs when the clutch plate 14 is sandwiched into firm engagement with the pressure plate 13 and the flywheel 16. In that condition, each of the flywheel 16, the cover assembly 1 1 , the diaphragm 12, the pressure plate 13, and the clutch plate 14 rotate. The clutch plate 14 is mounted on a gearbox input shaft 19 by a splined connection, so that the clutch plate 14 can move axially on the shaft 19, but is fixed in rotation with the shaft 19.

The clutch assembly 10 can be disengaged by withdrawing the pressure plate 13 in a direction away from the flywheel 16, to disengage the firm frictional connection between the pressure plate 13, the clutch plate 14 and the flywheel 16. Upon that disengagement, the cover assembly 1 1 and the pressure plate 13 will continue to rotate with the flywheel 16, but no rotational movement will be imparted to the clutch plate 14.

The clutch assembly 10 is biased towards a clutch engaged condition whereby the clutch plate 14 is firmly sandwiched between the pressure plate 13 and the flywheel 16. That biasing arrangement includes the diaphragm 12, which abuts the pressure plate 13 at its radially outer end to, and which bears against a facing end of a thrust bearing 22 of a concentric slave cylinder 23 at its radially inner end. The diaphragm 12 includes a plurality of radially extending fingers that extend inwardly from a radially outer ring and is mounted for pivoting rotation about an annular fulcrum 24. The fingers and ring of the diaphragm 12 are not shown clearly in the cross-sectional figures, but effectively, radially outward of the fulcrum 24 is the ring and radially inward of the fulcrum 24 is the fingers.

The biasing load of the diaphragm 12 on the pressure plate 13 exceeds the strap bias described earlier between the cover assembly 1 1 and the pressure plate 13, so that the load biasing the pressure plate towards the flywheel 16 exceeds that acting in the opposite direction.

The thrust bearing 22 of the concentric slave cylinder 23 is moveable axially of and along the tube 25 of the cylinder 23, and is rotatable about the axis of the input shaft 19 through engagement with the diaphragm 12. The thrust bearing 22 is biased towards an extended condition relative to the base 26 of the cylinder 23 by a coil spring 27. The coil spring 27 thus urges the thrust bearing 22 to maintain engagement with the radially inner ends 28 of the diaphragm 12.

In addition, the diaphragm 12 is mounted so that it applies a permanent biasing load to the pressure plate 13, tending to push the pressure plate 13 towards the flywheel 16, so that in absence of an opposite force, the clutch plate 14 is sandwiched into firm engagement between the pressure plate and the flywheel 16. Thus, the home condition of the clutch assembly is with the clutch plate 14 sandwiched between the pressure plate 13 and the flywheel 16.

The clutch plate 14 includes an annular periphery to which an annular ring of friction material 30 is applied to face in each of opposite directions. That friction material 30 wears over time and upon sufficient wear past a critical or minimum thickness, operation of the clutch assembly 10 can be compromised. Figures 1 and 2 show the friction material 30 in an unworn state, i.e. a newly installed state, while Figure 3 shows the material 30 significantly worn. From Figure 3, it can be seen that as the friction material 30 wears, the diaphragm 12 pivots anti-clockwise about the fulcrum 24, to maintain pressure against the pressure plate 13 to sandwich the clutch plate 14 between the pressure plate 13 and the flywheel 16. It can be seen that as the diaphragm 12 pivots in an anti-clockwise direction, the radially inner ends 28 of the diaphragm 12 push the thrust bearing 22 axially away from the flywheel 16. Disengagement of the clutch assembly 10 from the home condition discussed above is by movement of the thrust bearing 22 axially of the input shaft 19 towards the flywheel 16 and against the radially inner ends 28 of the diaphragm 12, to pivot the diaphragm 12 clockwise. By that clockwise movement, the radially outer ends of the diaphragm 12 shift away from the flywheel 16 and that relieves the biasing load on the pressure plate 13, so that the straps connecting the pressure plate 13 to the cover assembly 1 1 can bias the pressure plate 13 to shift away from the flywheel 16 and thus relieve the sandwiching pressure previously exerted on the clutch plate 14. Effectively, clockwise movement of the diaphragm 12 allows the pressure plate 13 to shift away from the flywheel 16. The thrust bearing 22 is moved in this manner via hydraulic fluid, which is driven by depression of the clutch pedal in the vehicle cabin through the hydraulic fluid lines 32. This hydraulic operation is well-known and thus requires no further explanation herein. By forward movement of the thrust bearing 22 against the radially inner ends 28 of the diaphragm 12, the pressure plate 13 shifts away from the flywheel 16 as discussed above, so that the flywheel 16 can rotate with the cover assembly 1 1 , the diaphragm 12 and the pressure plate 13, but not transmit that rotation to the clutch plate 14. Thus, the clutch plate 14 can discontinue rotating and thus discontinue driving the input shaft 19. The result is that with the engine running and the crank shaft rotating, no transmissive force is delivered to the gear transmission 18.

With reference to Figure 4, the concentric slave cylinder 23 includes a base 26 and a tube 25 integral with the base 26 and extending from the base 26 substantially perpendicular to it. This is shown in more detail in Figure 5. The tube 25 includes internal passageways to accept the hydraulic fluid for clutch operation and includes a cylindrical outer surface on which is mounted the thrust bearing 22. The thrust bearing 22 comprises a carrier 37 and a rotatable bearing 38. The carrier 37 cooperates with the coil spring 27 (Figure 4) and includes a mount on which the rotatable bearing 38 is mounted to rotate. As shown in each of Figure 4 and 5, the carrier 37 includes a first sensor component 39, while, upstanding from the base 26, is a second sensor component 40. The respective first and second sensor components 39 and 40 are in facing alignment. It could equally be the case that the first and second sensor components 39 and 40 are telescopically aligned, or otherwise aligned.

With reference now to Figures 2 and 3, the spacing Si of Figure 2 shows the spacing between the first and second sensor components 39 and 40 on a newly installed clutch, where the friction material 30 is at maximum thickness Ti . In contrast, Figure 3 shows a reduced spacing S₂ compared to the spacing Si , when the friction material 30 has worn and is of reduced thickness T₂. That reduction in spacing between Si and S₂ occurs principally as a function of the thickness of the friction material 30. In the figures, it can be seen that the diaphragm 12 has rotated anti-clockwise to drive the thrust bearing 22 rearwardly or away from the flywheel 16, so that the distance D₂ as shown in Figure 3, is greater than the distance Di of Figure 2. The dimensions Di and D₂ measure the distance between the very front end of the rotatable bearing 38 facing the clutch plate 14, and a datum surface of the flywheel 16, being that surface to which the cover assembly 1 1 is bolted.

It has been established through testing, that the position of the thrust bearing 22 relative to the base 26 and the tube 25 has a direct relationship with the thickness of the friction material 30. Thus, as the friction material wears, the spacing between the first and second sensor components 39 and 40 can accurately measure that thickness reduction and that measurement can be transmitted in a useful way to alert a vehicle owner to the state of the friction material. As indicated above, suitable alerts can be provided either at a critical thickness of friction material, or in advance of that critical thickness. It can be seen from the figures, that the base 26 of the concentric slave cylinder 23 is bolted to the base 41 of the bell housing 42, which houses the clutch assembly 10. The bell housing 42 is likewise connected to the transmission housing 43 of the transmission 18 and the bell housing 42 can be an integral part of the housing 43 or can be otherwise connected thereto. The base 26 is thus firmly connected to a stationary datum point and movement of the thrust bearing 22 is relatively easy to measure. As discussed earlier, suitable sensing arrangements include variable reluctance sensors, variable resistance sensors or magneto resistive sensors.

Figure 6 illustrates a clutch assembly 50 which has a different form of actuator to the concentric slave cylinder 23 of the earlier figures. The assembly 50 of Figure 6 includes various clutch components which are the same as the assembly 10, and those like components have been given the same reference numeral in Figure 6 plus 100. The operation of the clutch assembly 50, as it applies to the diaphragm 1 12, the pressure plate 1 13, the clutch plate 1 14 and the friction material 130, is as described in relation to the clutch assembly 10 earlier herein. Where the clutch assembly 50 differs from the clutch assembly 10, is in relation to the actuator for driving engagement and disengagement of the pressure plate 1 13 from sandwiching the friction material 130 to the flywheel 1 16.

The clutch assembly 50 also includes a diaphragm 1 12, which comprises a plurality of elongate fingers, a pair of which are shown in Figure 6. Radially inner ends 128 of the diaphragm 1 12 are engaged by a thrust bearing 51 which comprises a rotatable bearing 52 and a carrier 53. The bearing 52 is rotatable relative to the carrier 53.

The actuator further includes a pivotable arm 54 which has a carrier engaging end 55 and an actuated end 56.

The actuated end 56 is engaged by a slave cylinder 57 and movement of the arm 54 under actuation by the slave cylinder 57 is about a fulcrum 58. The clutch assembly 50 operates as a "pull" assembly, in which disengagement of the assembly 50 is by a pushing movement of the slave cylinder 57 on the arm 54. That pushing movement causes the arm 54 to rotate clockwise and to pull the thrust bearing 51 towards the transmission 1 18. That movement causes the diaphragm 1 12 to pivot about the fulcrum 124 and to shift the pressure plate 1 13 away from the flywheel 1 16 against the bias of the diaphragm 1 12. Note that the position of engagement of the pressure plate 1 13 on the diaphragm 1 12 in radially inboard of the fulcrum 124, which is different to the earlier figures, and which allows the away movement of the pressure plate 1 13 from the flywheel 1 16 upon clockwise rotation of the arm 54.

Opposite movement of the slave cylinder 57 is such as to allow the arm 54 to pivot in an anti-clockwise direction, and that allows the thrust bearing 51 to move toward the flywheel 1 16 and to allow the diaphragm 1 12 to return the pressure plate 1 13 to a position in which it sandwiches the friction material 130 to the flywheel 1 16. The slave cylinder 57 is operated by delivery of hydraulic fluid through the hydraulic line 59.

A slave cylinder 57 includes a manifold 60 and a piston 61 . A sensor 62 is connected to the piston 61 . The piston 61 is connected to the arm 54 by a rotatable connector 63.

A sensor 64 is connected to an end section of the transmission 1 18 and similar to the sensors 39 and 40 described in the earlier figures, the first sensor 62 shifts toward and away from the sensor 63 during actuation of the slave cylinder 57. The spacing between the respective sensors 62 and 64 can be used to calculate wear of the friction material 1 13 and in the arrangement of the clutch assembly 50, measurement of the spacing between the sensors 62 and 64 is made when the pressure plate 1 13 is in a position sandwiching the friction material 130 to the flywheel 1 16. As the material 130 wears, the spacing between the sensors 62 and 64 will decrease. This is similar to the arrangement of the clutch assembly 10, in which the spacing inbetween the sensors 39 and 40 also decreases with friction material wear.

In the push type arrangement, the spacing between the sensors 62 and 64 will increase as the material 130 wears.

The data collected from the sensors 62 and 64 can be used in the same manner as with the sensors 39 and 40 described earlier to calculate the life of friction material remaining, and to provide alerts when appropriate. The arrangement of the clutch assembly 50 illustrates that the invention has application to both "pull" and "push" clutch assemblies and concentric and non- concentric slave cylinder assemblies, although the expectation is that the "push" type assembly as illustrated in Figures 1 to 5 will more commonly be employed with the present invention.

Throughout the description and claims of this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps. The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the present disclosure.

Claims

1 . A clutch assembly including:

a clutch plate having an annular periphery to which an annular ring of friction material is applied to face in each of opposite directions,

the clutch plate being mounted to an outer surface of a gearbox input shaft so that rotation of the clutch plate rotates the input shaft and the clutch plate being movable axially on the input shaft,

a diaphragm mounted concentrically about the input shaft and having a radially outer ring in engagement with the pressure plate a plurality of spaced apart radially inwardly extending fingers extending inwardly from the ring to a position proximate the outer surface of the input shaft, the diaphragm being mounted to a fulcrum so that movement of the fingers in one direction results in movement of the ring in the opposite direction,

whereby

movement of the thrust bearing in engagement with the fingers in a first direction towards the clutch plate causes the diaphragm to rotate about the fulcrum and permits the pressure plate to move in a second direction opposite the first direction to disengage the clutch assembly and

2. A clutch assembly according to claim 1 , the thrust bearing comprising a carrier and a rotatable bearing which are movable axially together and the sensor being operable to sense the position of the carrier or the rotatable bearing.

3. A clutch assembly according to claim 1 or 2, the actuator being a concentric slave cylinder which includes the thrust bearing.

4. A clutch assembly according to claim 3, the concentric slave cylinder comprising a base and a tube extending from the base, each of the base and the tube being mounted concentrically about the shaft and being fixed relative to rotation of the shaft, the thrust bearing comprising a carrier and a rotatable bearing mounted on the tube and which are movable axially together relative to the base and the tube, the sensor including a first sensor component fixed to the base or the tube and a second sensor component fixed to the carrier or the rotatable bearing, the first and second sensor components being aligned and wear in the friction material being measured as a function of the relative position between the first and second sensor components when the clutch assembly is engaged.

5. A clutch assembly according to claim 4, the first and second sensor components being in facing alignment and wear in the friction material being measured as a function of the spacing between the first and second sensor components when the clutch assembly is engaged.

6. A clutch assembly according to claim 5, the spacing between the first and second sensor components increasing upon disengagement of the clutch assembly and decreasing on engagement of the clutch assembly, the spacing between the first and second sensor components decreasing in the clutch engaged condition as the friction material wears.

7. A clutch assembly according to claim 1 or 2, the actuator including a slave cylinder and a pivotable arm pivotable about a fulcrum, the arm having one end for engaging the slave cylinder and the other end for engaging the thrust bearing, whereby actuation of the slave cylinder facilitates rotation of the arm to shift the thrust bearing in the first direction to disengage the clutch assembly.

8. A clutch assembly according to any one of claims 1 to 7, the sensor being a variable reluctance sensor.

9. A clutch assembly according to any one of claims 1 to 7, the sensor being a variable resistance sensor.

10. A clutch assembly according to any one of claims 1 to 7, the sensor being a magneto resistive sensor.

1 1 . A clutch assembly according to any one of claims 1 to 10, the sensor being arranged to provide a continuous output signal.

12. A clutch assembly according to any one of claims 1 to 10, the sensor being arranged to provide an output signal when the the transmission is in neutral gear and the clutch assembly is engaged.

13. A transmission for a vehicle, the transmission having front and rear ends and having a bell housing attached to the front end within which a clutch assembly according to any one of claims 1 to 12 is housed, the gearbox input shaft of the clutch assembly extending into the transmission, the clutch assembly including a thrust bearing mounted about the input shaft and fixed to the bell housing and being shiftable on the input shaft by an actuator.

14. A concentric slave cylinder comprising:

a base and a tube extending from the base,

a thrust bearing comprising a carrier and a rotatable bearing mounted on the tube and which are movable axially together relative to the base and the tube,

a sensor to sense the position of the thrust bearing, the sensor including a first sensor component fixed to the base or the tube and a second sensor component fixed to the carrier or the rotatable bearing, the first and second sensor components being in alignment and the position of the thrust bearing being sensed as a function of the relative position between the first and second sensor components.

15. A concentric slave cylinder according to claim 14, the first and second sensor components being in facing alignment and the position of the thrust bearing being sensed as a function of the spacing between the first and second sensor components.

16. A concentric slave cylinder according to claim 14, the sensor being a variable reluctance sensor.

17. A concentric slave cylinder according to claim 14, the sensor being a variable resistance sensor.

18. A concentric slave cylinder according to claim 14, the sensor being a magneto resistive sensor.

19. A concentric slave cylinder according to any one of claims 14 to 18, the sensor being arranged to provide a continuous output signal.

20. A vehicle including a clutch assembly according to any one of claims 1 to 12, and a vehicle management computer, the computer being operable to receive a signal from the clutch assembly sensor and to process the signal for determining the expected life of the clutch assembly friction material.

21 . A vehicle according to claim 20, the computer sending an alert upon the sensor sensing that the friction material has reached a predetermined wear thickness.

22. A vehicle according to claim 21 , the predetermined wear thickness being a greater thickness than the minimum operable thickness.

23. A vehicle according to claim 21 or 22, the alert being displayed to the vehicle driver.

24. A vehicle according to claim 21 , the alert being sent by wireless transmission to a third party.