FRICTION CLUTCH

Abstract: A friction clutch comprises a clutch cover (21) attached to a flywheel with at least one spring acting on a pressure plate (13) to force a driven plate into frictional engagement with the flywheel. The clutch has at least one constant lift device (49, fig. 1) which limits lift of the pressure plate to a substantially constant value during each full disengagement of the clutch. The constant lift device is of the type which comprises a locking plate (60) pivotally mounted to one of either a wear sensing means, the pressure plate (13) or an axially fixed component of the clutch (132, fig. 7). The locking plate (60) has a hole (63) through which a pin (51) extends, and spring means (53) acting to tilt the locking plate relative to the pin to grip the pin to prevent axial movement of the pin relative to the locking plate in at least one direction. Resilient means (53C, fig. 6) is provided to eliminate or reduce free play in the pivotal mounting of the locking plate. The friction clutch may comprise an automatically adjusting clutch.

Description: FRICTION CLUTCH The present invention relates to friction clutches and in particular to self adjusting friction clutches. Friction clutches are known which comprise a clutch cover attached to a flywheel with at least one spring acting on a pressure plate to force a driven plate into frictional engagement with a counter pressure plate which may be a flywheel. Friction clutches are also known which comprise a constant lift device for maintaining the lift of the pressure plate during clutch disengagement substantially constant during the life of the driven plate. The applicant's co-pending patent application WO 98/41777, which disclosure is hereby incorporated by reference, discloses a number of constant lift devices for clutches (hereinafter referred to as being of the type described) which comprise a locking plate pivotally mounted to either a wear sensing means, the pressure plate or an axially fixed component of the clutch and having a hole through which a pin extends, and spring means acting to tilt the locking plate relative to the pin to grip the pin to prevent axial movement of the pin relative to the locking plate in at least one direction. Furthermore, it is known from the applicant's co-pending patent application GB 9818074.8, which disclosure is also hereby incorporated by reference, to provide a constant lift device of the type described in a self-adjusting clutch. It has now been found that in constant lift mechanisms of the type described, wear or manufacturing tolerances can result in excessive lateral movement or free play at the pivot of the locking plate which can be detrimental to the operation of the device. It is an object of the invention to provide a friction clutch having an improved form of constant lift device of the type described which overcomes or at least mitigates the problems identified Thus according to the present invention there is provided a friction clutch comprising a clutch cover attached to a flywheel with at least one spring acting on a pressure plate to force a driven plate into frictional engagement with the flywheel, and at least one constant lift device of the type described which limits lift of the pressure plate to a substantially constant value during each full disengagement of the clutch, resilient means being provided to eliminate or reduce free play in the pivotal mounting of the locking plate Where the pivotal mounting of the locking plate comprises a pivot member engaging in a slot, it is advantageous if the resilient means is provided between the pivot member and a first surface of the slot to bias the pivot member against a second surface of the slot opposite from the first The resilient means may advantageously comprise an elastomeric spring Alternatively, the resilient means may comprise a resiliently deformed portion of a plate-like member In a particularly preferred embodiment, the spring means of the constant lift device comprises a plate-like spring, in which case the plate-like member can be an integral part of the plate-like spring. In particular, the plate-like spring of the constant lift device may comprise a plate-like section having a hole through which the pin extends and a substantially U-shaped tab at one end of the plate-like section which tab biases the locking plate such that the locking plate tilts relative to the pin to grip the pin, in which a portion of the plate-like section remote from the U-shaped tab is resiliently deformed to provide the resilient means In an alternative embodiment, the spring means of the constant lift device may be a coil spring Preferably, the friction clutch further comprises an adjustment device for automatically compensating for wear of the friction surfaces of the clutch Several embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which Figure 1 is an axial partly cutaway view of a clutch assembly according to the present invention, Figure 2 is an enlarged view of part of Figure 1 , Figure 3 is a radial view taken from the direction of arrow W of Figure 1 including a flywheel, Figure 4 is a partial cross section view of the clutch cover assembly of Figure 1 and associated driven plate and flywheel taken along the line XX of Figure 1, Figure 5 is a view taken along line Y-Y of Figure 1 with components 60, 53 and 59 shown rotated through 90 degrees for clarity Figure 6 is an isometric view of the spring 53 of Figure 5, Figure 7 is a partial cross sectional view taken along line Y-Y of Figure 1 but showing a modified form of constant lift device according to the invention; Figure 8 is an isometric view of plate 190 in Figure 7, and Figure 9 is a view of a further form of a constant lift mechanism according to the invention. With reference to Figures 1 to 6 there is illustrated a clutch 10 which includes a flywheel 1 1, a clutch cover assembly 20 and a driven plate 15. The flywheel 11 is fixed to the end of a crankshaft (not shown) of an associated internal combustion engine. In this embodiment the clutch is an automatically adjusting clutch but it will be understood that the invention is not limited to application on friction clutches having automatic adjusting devices to compensate for wear. The clutch cover assembly 20 comprises a clutch cover 21, a diaphragm spring 12, a pressure plate 13, lift straps 14, one adjuster means 44 and three constant lift devices 49 each comprising a constant lift mechanism 50, a lever 80 and a sensing device 46, 86. The clutch cover 21 is fixed rotationally and axially fast to the flywheel 11 by bolts (not shown) and supports the diaphragm spring 12 via two support rings 22 situated one on each axial side of the diaphragm spring 12 in a manner well known in the art. The diaphragm spring biases the pressure plate 13 towards the flywheel 11. The clutch driven plate 15 is situated between the pressure plate 13 and flywheel 11 and is connected to the input shaft of a gear box (not shown). When the clutch is engaged i.e. when the diaphragm spring 12 biases the pressure plate 13 towards the flywheel, clamping the driven plate 15, power can be transmitted between the associated engine and gearbox. By applying an axial force to the fingers 12A of the diaphragm spring 12 in a direction towards the flywheel 11 the clutch can be disengaged in a manner well known in the art The pressure plate 13 comprises a first part 30 coaxial with a second part in the form of a pivot ring 40 First part 30 is generally annular in shape and has significant thermal mass and is thus capable of absorbing heat generated by frictional contact with the adjacent friction facing 16 of the driven plate 15 during engagement and disengagement of the clutch 10 On the radially outer periphery of the first part 30 there are three circumferentially equi-spaced lugs 31 Each lug is fixed to one end 14A of a tangentially orientated lift strap 14 by a rivet 17 The other end 14B of the strap 14 is fixed to the clutch cover 21 by a rivet 19 The straps 14 ensure the first part 30 remains concentric with and rotationally fast with the clutch cover 21 but allow axial movement of the first part 30 relative to the clutch cover 21 When the clutch is engaged the straps 14 are stressed and bias the first part 30 away from the flywheel This biasing assists in separating the first part 30 from the driven plate 15 when the clutch is disengaged Adjuster means 44 comprises a pawl means having pawl teeth 41 which engage an array of helical adjuster teeth 42 carried on the pivot ring 40 of the pressure plate 13 The pawl means is mounted to the clutch cover 21 by a spring 43 and a rivet 19 For a full explanation of the operation of the adjuster means 44 see the Applicant's co-pending International application WO 97/10448 However in summary the operation is as follows Following a sufficient amount of wear of the clutch driven plate friction facings 16 one of the pawl teeth 41 will move over the top of the helical tooth 42 it is resting on and will be biased into the valley between adjacent helical teeth Upon subsequent disengagement of the clutch, the axial movement of the second part 40 of the pressure plate, and hence the helical tooth 42, causes the pawl tooth 41 to also move away from the flywheel However the pawl tooth is constrained to move in an arc by spring 43 which deforms about an axis 43 A located on a curved portion 43B of the spring adjacent a flat portion 43 C which is fixed to the cover 21 rivet 19 When the clutch has disengaged sufficiently, so that the clamp load between spring 12 and pivot ring 40 is sufficiently low, the energy stored in the spring 43 is sufficient to cause the pawl tooth 41 acting on the helical teeth 42 to rotate in a reverse direction about axis 43 A and hence cause the second part 40 of the pressure plate 13 to rotate relative to the first part 30 about axis A The first and second parts of the pressure plate have facing ramps 45 and as relative rotation occurs the effective thickness of the pressure plate 13 increases to compensate for the reduction in thickness of the driven plate fπction facings 16 Each constant lift device 49 is attached to an associated lug 31 of first part 30 of the pressure plate 13 Since all the constant lift mechanisms 49 identical only one will be described in detail The constant lift device 49 comprises a constant lift mechanism (see Figure 5) having an adjustment pin 51, a locking plate 60, a locking spring 53, an adjusting spring 54 and a washer 55 (in Figure 5 components 53, 59 and 60 have been rotated through 90 degrees for ease of explanation) Adjustment pin 51 comprises a shank portion 51 A and a head portion 5 IB with a domed abutment surface 51C. Spring 53 has a central hole 53 A which is a clearance fit on the adjustment pin 51 and also has a tab 66 bent through approximately 180 degrees in the shape of a "U" It is the resilience of the mateπal that causes the U-shaped portion of the spring 53 to act as a spring and bias the locking plate 60 away from the head 5 IB of the adjustment pin 51 Locking plate 60 is mounted via a central hole 63 on adjustment pin 51 and is of generally rectangular shape with a tab 61 which is biased away from the head 5 IB by spring 53 The locking plate 60 is restrained from moving away from the head 5 IB because a second tab or pivot member pivot member 62 remote from tab 61, is situated in a slot 59 of first part 30 of the pressure plate 13 This causes the locking plate 60 to tip sufficiently such that the edges 64 of the locking plate 60 contact the pin 51 The adjustment pin 51 is mounted in a hole 70 of a tab 32 with head 5 IB positioned on the side of tab 32 remote from the flywheel Tab 32 is secured to a first part 30 of the pressure plate 13 by a rivet 17 Situated between the head 51 B and the hole 70 is a spring 54 which is retained on the adjustment pin 51 by a washer 55 Spring 54 is tensioned such that it biases the adjustment pin to the right when viewing Figure 5 However, when the lever 80 applies a force to the head 5 IB to the left, when viewing Figure 5, the edges 64 of the locking plate 60 firmly engage shank portion 51 A and no movement of the adjustment pin 51 is possible towards the flywheel (i.e. movement to the left when viewing Figure 5) Thus, in use the adjustment pin 51 can only move relative to first part 30 in a direction away from the flywheel and is blocked from moving relative to the first part 30 in a direction towards the flywheel A full description of the operation of the constant lift device shown in Figures 1 to 5 including details of the operation of the lever 80 can be found in the Applicant's co-pending patent application GB 9818074. However, in summary the operation is as follows. Following wear of the friction facings 16, with the clutch engaged the wear results in one of the pawl teeth 41 of the adjuster 44 moving over a coπesponding helical tooth 42 as described above. Disengagement of the clutch causes the pressure plate 13 and constant lift device to move away from the flywheel with a first abutment 82 of the lever 80 ultimately contacting a second abutment 23 on the clutch cover limiting the lift of the first part 30 of the pressure plate 13 away from the flywheel. Further movement of the diaphragm fingers 12A of the diaphragm spring 12 towards the flywheel results in the clamp load on the pivot ring 40 being reduced. At this stage the spring load in the spring 43 causes the pivot ring 40 to rotate slightly relative to the clutch 10 resulting in an increase in the effective thickness of the pressure plate as a result of relative movement of the ramps 45 thus adjusting for the wear of the friction facings. The resulting axial movement of the pivot ring 40 creates a gap between a third abutment 86 on lever 80 and a fourth abutment 46 on the pivot ring 40. During re- engagement of the clutch, the pivot ring 40, first part 30 and tab 32 move towards the flywheel in unison. However, the first abutment 82 of the lever 80 is biased against the second abutment 23 by the spring 54 acting through the adjustment pin 51 which causes the lever 80 to pivot about pivot 84 until the gap created between the third abutment 86 of lever 80 and the fourth abutment 46 of pivot ring 40 is closed. Further engagement of the clutch causes the pressure plate and, constant lift device to all move in unison towards the flywheel until full engagement is achieved. During re-engagement of the clutch whilst the gap between the third abutment 86 and fourth abutment 46 is being closed, the pin 51 moves under the bias of spring 54 in a direction away from the flywheel. As the pin 51 moves, friction between the pin 51 and the edges 64 of the locking plate 60 tends to rotate the locking plate 60 in a clockwise direction, as viewed in Figure 5, against the bias of the spring 53 until the edges 64 of the locking plate no longer engage the surface of the shank 51 A of pin 51. At this point the pin 51 can move axially relative to the locking plate 60 away from the flywheel. Following movement of the pin 51 sufficient to close the gap, the spring 53 will again tilt the locking plate 60 so that the edges 64 engage with the shank 51 A of the pin 51. However, if the tab or pivot member 62 of the locking plate 60 is able to move axially within the slot 59 of the first part 30 due to free play, the frictional contact between the pin 51 and the edges 64 of the locking plate 60 will tend to move the locking plate 60 axially to take up the free play before pivoting it against the spring 53. If this happens then the pin 51 will not move relative to the locking plate 60 or at least will not move sufficiently to fully compensate for the wear of the friction surfaces 16 and correct adjustment of the device 49 will not occur. To reduce or eliminate free play of the tab or pivot member 62 within slot 59, a section 53B of the spring 53 remote from the U-shaped tab 66 has been deformed to produce a resilient portion 53 C, as can best be seen in Figure 6. The resilient portion 53 C is located between the tab 62 of the locking plate 60 and the tab 32 and acts to bias the tab 62 towards a surface 59A of the slot 59 opposite from the tab 32. The resilient biasing of the tab 62 need not be provided by means of a resilient portion on the spring 53, and any other suitable means for biasing the tab 62 in the slot 59 could be used. For example, the resilient biasing could be provided by a spring means which is separate from the spring 53 such as an elastomeric spring. Also, it is not essential to the invention that the tab 62 be biased towards the surface 59 A of the slot 59. As an alternative, means could be provided between the tab 62 and the surface 59A to bias the tab 62 towards the tab 32. Figures 7 and 8 show a modified version 149 of the constant lift device 49 with features that fulfil the same function as those in constant lift mechanism 49 being labelled one hundred greater, significant differences are as follows: a) spring 153 is a coil spring which extends between the tab 161 of the locking plate 160 and a tongue 181 of the lever 180. A tang 181 A is provided on the tongue 181 which extends into the coil spring 153 to help maintain the spring 153 in position; b) tab or pivot member 162 of locking plate 160 is pivotally received in a slot 132A of a plate 132 which is connected to the fist part 130 of the pressure plate; c) a plate 190 (see Figure 8) is provided between the plate 132 and the tab 162. The plate 190 is deformed to provide a resilient portion 191 which biases the tag 162 towards the surface 132B of the slot 132 A; d) the head portion 15 IB of the pin 151 is of diameter substantially equal to the external diameter of the spring 154, thus no additional washer equivalent to washer 55 is required. Figure 9 shows a further embodiment of a constant lift device the operation of which is described in detail in the applicant's co-pending application WO 98/41777 to which the reader is refeπed. According to the invention, the constant lift device 249 has been modified in a manner similar to that of device 49 in that the spring 253 has been deformed at an end portion 253B remote from the U-shaped portion to provide a resilient portion 253C which biases the tab 262 towards the surface 259A of the slot 259 in the pressure plate 230.

Claims: Claims 1. A friction clutch comprising a clutch cover attached to a flywheel with at least one spring acting on a pressure plate to force a driven plate into frictional engagement with the flywheel, and at least one constant lift device of the type described which limits lift of the pressure plate to a substantially constant value during each full disengagement of the clutch, resilient means being provided to eliminate or reduce free play in the pivotal mounting of the locking plate. 2. A friction clutch as claimed in claim 1 in which the pivotal mounting of the locking plate comprises a pivot member engaging in a slot, the resilient means being provided between the pivot member and a first surface of the slot to bias the pivot member against a second surface of the slot opposite from the first. 3. A friction clutch as claimed in claim 1 or claim 2 in which the resilient member is an elastomeric spring. 4. A friction clutch as claimed in claim 1 or claim 2 in which the resilient means comprises a resiliently deformed portion of a plate-like member. 5. A friction clutch as claimed in any previous claim in which the spring means of the constant lift device comprises a plate-like spring . 6. A friction clutch as claimed in claim 5 when dependent on claim 4 in which the plate¬ like member is an integral part of the plate-like spring. A friction clutch as claimed in claim 6 in which the plate-like spring comprises a plate¬ like section having a hole through which the pin extends and a substantially U-shaped tab at one end of the plate-like section which tab biases the locking plate such that the locking plate tilts relative to the pin to grip the pin, in which a portion of the plate-like section remote from the U-shaped tab is resiliently deformed to provide the resilient means A fπction clutch as claimed in anyone of claims 1 to 4 in which the spring means of the constant lift device is a coil spring A friction clutch according to any one of claims 1 to 8 in which the clutch further comprises an adjustment device for automatically compensating for wear of the friction surfaces of the clutch A friction clutch substantially as hereinbefore described with reference to the Figures 1 to 6, or Figures 7 & 8, or Figure 9 of the accompanying drawings

Inventors: YOUNG ALASTAIR JOHN, YOUNG, ALASTAIR, JOHN
Applicants: WHITNASH PLC, YOUNG ALASTAIR JOHN, YOUNG, ALASTAIR, JOHN
Application year: 1999
Main classification: F16D13
IPC codes: F16D13