VEHICLE CLUTCHES

Abstract: A vehicle clutch system in which a driven plate (13) is clamped between a pressure plate (15) and a flywheel (14) by a diaphragm spring (16). The clutch is released by depression of a clutch operating pedal (11) which is connected with the diaphragm spring (16) by an operating mechanism (24, 25, 26, 27, 30). The diaphragm spring (16) has a substantially flat spring clamp load characteristic such that the spring clamp load remains substantially constant throughout the operating life of the clutch. The clutch pedal (11) has an assistor spring means (30) which determines the resistance to depression of the pedal during release of the clutch, and the operating characteristics of the operating mechanism and /or the spring characteristics of the pedal assistor spring means ensure that the resistance to the depression of the pedal (11) increases up to a maximum resistance at or around the disengagement point of the clutch and thereafter reduces. A master cylinder (40, 50) is also disclosed which includes internal return and assistor spring means (46, 47; 56, 57) which act on a piston (42, 52) of the cylinder to provide assistance for the operation of an associated clutch pedal (11).

Description: VEHICLE- CLUTCHES This invention relates to vehicle clutches and in particular to vehicle clutch systems comprising a vehicle clutch in which a driven plate is clamped between a pressure plate and a reaction member (e.g. a flywheel) by a diaphragm spring, a clutch operating pedal, and an operating mechanism connecting the pedal with the diaphragm spring to release the clutch on depression of the pedal. Such clutch systems are hereinafter referred to as being "of the kind specified". One of the problems associated with a vehicle clutch system of the kind specified is that as the clutch driven plate wears the force which must be applied to the pedal to disengage the clutch can increase significantly to a level unacceptable to the vehicle driver. It is an object of the present invention to provide an improved form of vehicle clutch system of the kind specified which at least partially mitigates the above problem. Thus according to a first aspect of the present invention there is provided a vehicle clutch system of the kind specified characterised in that the diaphragm spring has a substantially flat spring clamp load characteristic such that the spring clamp load remains substantially constant throughout the operating life of the clutch; the clutch pedal has an assistor spring means which determines the resistance to depression of the pedal during release of the clutch, and the operating characteristics of the operating mechanism and/or the spring characteristics of the pedal assistor spring means ensure that the resistance to the depression of the pedal increases up to a maximum resistance at or around the disengagement point of the clutch and thereafter reduces. The operating characteristics of the operating mechanism (which could be mechanical, hydraulic or a combination of both) are preferably chosen to counteract the high load/low travel release characteristic of the diaphragm spring. Preferably the clutch is of the pull type. The geometry of a pull-type clutch provides a stiffer cover and ensures that the spring remains biased onto fulcrum during the entire clutch release. Where an axially cushioned driven plate is used it is desirable that a substantially constant cushioning force is provided throughout the operating life of the clutch. The driven plate may be cushioned by metal springs (e.g. leaf springs) or advantageously by elastomeric cushioning as described and claimed in, for example EP 0252583 and the other patents referred to later below. The assistor spring means may comprise one or more springs which operate directly on the pedal. Alternatively spring means may be built into the operating mechanism which operate indirectly on the pedal. For example, if an hydraulic operating mechanism is used with a master cylinder connected with the pedal and a slave cylinder connected with the diaphragm spring, the spring means may be built into the master cylinder. This spring means is preferably a diaphragm spring. According to a second aspect of the invention there is also provided a master cylinder for the actuation of a vehicle function, the master cylinder comprising a body having a bore in which an actuating piston is displaceable by a pedal operated push rod or other actuating means to displace fluid from the bore to actuate the function, the master cylinder being characterised in that one or more diaphragm springs act directly or indirectly on the piston, to reduce the load which needs to be applied by the pedal or other actuating means to operate the master cylinder. The invention also provides an assistor spring arrangement for the operation of a vehicle clutch in which a clutch driven plate is clamped between a pressure plate and a reaction member by a diaphragm spring, the assistor spring arrangement being characterised in that two diaphragm spring means are arranged to operate in opposite directions on a clutch actuator member, the diaphragm spring means being capable of operating on both sides of their flat condition to counteract the characteristics of the driven plate clamping diaphragm spring and assist movement of the clutch actuator. One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: - Figure 1 is a diagrammatic representation of a vehicle clutch system in accordance with a first aspect of the present invention; - Figure 2 shows- the clamp load/deflection characteristics for a clutch diaphragm spring having so-called flat characteristic; Figure 3 shows the clutch pedal 'feel' characteristic; Figures 4 and 5 show alternative forms of axial cushioning for use in the clutch driven plate; Figure 6 and 7 show diagrammatically details of a master cylinder in accordance with a second aspect of the present invention which includes an internal assistor spring means; Figures 8 and 9 show the general form of the load/deflection characteristics of a return spring and an assistor spring employed in the master cylinder of figures 6 and 7; Figures 10 shows the general form of the overall spring assistance provided by the internal springs of the master cylinder of figures 6 and 7, and Figure 11 shows a further alternative form of master cylinder including an internal assistor spring means. Referring to figure 1 this shows a clutch system in which a vehicle clutch 10 is controlled by a pedal 11 via an operating mechanism 12. Clutch 10 has a driven plate 13 which is clamped between a reaction member in the form of a flywheel 14 and a pressure plate 15 by a diaphragm spring 16 which reacts against a clutch cover 17 which is bolted to flywheel 14 at 18. Flywheel 14 is bolted at 19 to an engine crankshaft 20. The driven plate 13 is connected with a gearbox input shaft 21 via a central hub 22. The driven plate may include a sprung or compound centre 23 which employs circumferentially acting springs and friction members to absorb torsional vibrations within the vehicle driveline or may have a solid centre with no such ability to absorb torsional vibrations. In the system shown diagrammatically in figure 1 the operating mechanism 12 is hydraulic with a master cylinder 24 operated by pedal 11 and a slave cylinder 25 connected with diaphragm spring ! 6 via a release bearing 26 and a clutch operating lever 27 which is pivoted at 28 on a clutch housing (not shown). The pedal 11 is pivoted on a bulkhead of the vehicle at 29. In accordance with the present invention the diaphragm spring 16 has a substantially flat clamp load characteristic as shown in figure 2. Thus the clamp load applied by the diaphragm spring 11 (the vertical axis in figure 2) remains substantially constant over a significant proportion 'P' of the working deflection of the spring (the horizontal axis in figure 2). By arranging that over the intended operating life of the clutch the clamp load applied by the diaphragm spring always lies within portion 'P' of the spring characteristic, the clamp load applied by the diaphragm spring remains substantially constant (approximately 7000 Newton in the example shown) over the operating life of the clutch as the thickness of the driven plate decreases. By using a pull-type clutch the spacing 'F' between the spring fulcrum 31 and the cover bolts 18 is reduced so that deflection of the cover 17 is reduced and thus efficiency of the operating system is improved. Also by reducing the lever arm 'G' between the pressure plate fulcrum 32 and the line of action of the release bearing 26 deflection of the diaphragm spring is reduced, again helping to reduce losses in the system. The thickness of diaphragm spring 16 may also be increased to reduce losses due to deflection of the diaphragm spring. Optimisation of the efficiency of diaphragm spring 16 tends to produce a high load/low travel characteristic. This high load/low travel characteristic can be counteracted by adjusting the lever ratios of release lever 27 and pedal 11 and by adjusting the relative cross-sectional areas of the pistons 24a and 25a in the master and slave cylinders 24 and 25 respectively to give a pedal characteristic of the form shown in curve 'A' in figure 3. In accordance with the first aspect of the present invention the pedal 11 is acted on by an over- centre assistor compression spring 30 which applies a rotational spring bias to pedal 11 with a characteristic of the form shown in curve 'B' of figure 3. Spring 30 is mounted on the pedal bulkhead at 30a and is connected with pedal 11 at 30b. As the pedal is depressed the line of action of spring 30 (which joins 30a and 30b) crosses the line Z-Z which connects pedal pivot 29 and spring mount 30a at location 30b2 so that spring 30 goes over-centre. Thus when the pedal is fully released and connection 30b is in position 30bl spring 30 applies a counter clockwise movement about pivot 29. When pedal 11 has been depressed sufficiently to pass over line Z-Z (e.g. to position 30b3) the spring 30 applies a clockwise movement about pivot 29. This assistor spring modifies the resistance to the depression of pedal 11 about pivot 29 to the form shown in curve 'C of figure 3 where the resistance to the depression of the pedal increases to a maximum level at or around the clutch disengagement/engagement point after which the resistance decreases. Thus the Optimised Clutch System of the present invention provides a clutch system where the clutch clamp load remains substantially constant throughout the operating life of the clutch the variation in and the 'feel' of the clutch operating pedal (as represented by curve ς C of figure 3) is minimised and also remains substantially the same throughout the operating life of the clutch. As will also be appreciated the operating mechanism which connects pedal 11 with diaphragm spring 16 could alternatively be, for example, a lever and cable system. The driven plate 13 of the clutch may have no axial cushion, as shown in figure 1, or more likely can include axial cushioning provided by a known means. For example, the clutch friction material annuli 13a and 13b of plate 13 maybe mounted on so-called spring segments 13c (shown diagrammatically in figure 4). Alternatively, and preferably, the driven plate may include an elastomeric axial cushion in which clutch -friction material annuli 13a and 13b are bonded to a backing plate 13c by beads of elastomeric adhesive 13d (figure 5) which are partially compressed when the clutch is engaged and the driven plate 13 is clamped between pressure plate 15 and flywheel 14. Examples of suitable elastomeric axial cushioning are shown, for example in EP 0252583, EP 0390797, EP 0323036, EP 0455694, EP 0510014, GB 2247725, EP 0442539, GB 2243419, GB 2272494 and EP 0638149. The use of elastomeric cushioning enables a greater degree of consistency to be achieved with regard to the cushioning force provided by the driven plate throughout the life of the clutch than can be provided by metal cushioning arrangement of the form shown in, for example, figure 3. This further aids the consistency of operation of the entire Optimised Clutch System to be further improved. Also, since elastomeric axial cushioning does not use rivets etc. to secure the friction annuli in position a greater thickness of useable friction material is available. Although in the example described above the pedal 11 is acted upon directly by the over-centre assistor spring 30 this over-centre spring action could be provided by one or more springs acting in the operating mechanism 12 between the pedal 11 and the diaphragm spring 16. For example, an assistor spring means could be provided within master cylinder 24 . Such a spring is preferably a diaphragm spring means arranged to counteract the previously described high load/low travel characteristic of spring 16. An example of such a master cylinder including an assistor spring means is shown diagrammatically in figure 6 where a master cylinder 40 having a reservoir 41 includes a piston 42 slideable in a bore 43 which pressurises a working chamber 44 which is in turn connected with a slave cylinder (not shown) via piping 45. A spring means in the form of first and second sets of diaphragm springs 46 and 47 acts on opposite sides of piston 42. The first set of diaphragm springs 46 acts as a return spring for the associated pedal 11 whereas the second set of diaphragm springs 47 acts as an assistor spring for pedal 11. The first set of diaphragm springs 46 comprises individual belleville springs 46a (see figure 7) which each have oppositely directed axially projecting peripheral flanges 46b and 46c respectively. This allows each belleville spring to act on both sides of its flat condition. Similarly the second set of diaphragm springs 47 comprises individual belleville springs 47a which again have oppositely directed axially projecting peripheral flanges to again allow each individual spring to act on both sides of its flat condition. The load deflection characteristic of return bellevilles 46a is generally of the flat form shown in figure 8 whereas the assisting bellevilles 47a have a steeper load/deflection characteristic of the general form shown in figure 9. These two spring characteristics combine to provide an overall master cylinder spring assistance characteristic for pedal 11 of the form shown in figure 10 which are generally of the form previously described above as curve B in figure 3. Figure 11 shows a further form of master cylinder 50 which includes an assistor spring means in the form of a single return diaphragm spring 56 and a single assistor diaphragm spring 57 which again acts on opposite sides of a piston 52 slideable in a bore 53. The bore is replenished from a reservoir 51 via a non-return valve 58 and piston 52 pressurises a working chamber 54 which is connected with a slave cylinder (not shown) via piping 55. The load/deflection characteristics of springs 56 and 57 are again generally of the form shown in figures 8 and 9 respectively and these springs thus combine to give an overall master cylinder spring assistance characteristic for pedal 11 generally of the form shown in figure 10. The master cylinder arrangements shown in figure 6 and 11 are not only useable with a main driven plate clamping diaphragm spring having a flat characteristic of the form shown in figure 2 but could be used in any actuation system requiring an assistance characteristic generally of the form shown in figure 10. Further, the master cylinder of figures 6 and 11 could be actuated by a means other than pedal 11. For example, the master cylinder could be electrically actuated when forming part of a pedalless automatically controlled clutch system of the type shown, for example, in GB Patent 2215791. Also, the spring arrangements 46/47 and 56/57 described above could be used outside the master cylinder provided they are appropriately connected with the pedal or other actuating means. These spring arrangements could also be used with mechanical operating mechanisms actuated by a pedal or other actuating means (e.g. an electric motor).

Claims: CLA S 1) A vehicle clutch system of the kind specified characterised in that the diaphragm spring has a substantially flat spring clamp load characteristic such that the spring clamp load remains substantially constant throughout the operating life of the clutch; the clutch pedal has an assistor spring means which determines the resistance to depression of the pedal during release of the clutch, and the operating characteristics of the operating mechanism and/or the spring characteristics of the pedal assistor spring means ensure that the resistance to the depression of the pedal increases up to a maximum resistance at or around the disengagement point of the clutch and thereafter reduces. 2) A clutch system according to claim 1 characterised in that the operating characteristics of the operating mechanism are chosen to counteract the high load/low travel characteristic of the diaphragm spring. 3) A clutch system according to claim 1 or 2 characterised in that the clutch is of the pull type. 4) A clutch system according to any one of claims 1 to 3 characterised in that the thickness of the diaphragm spring is increased to reduce losses due to the deflection of the spring. 5) A clutch system according to any one of claims 1 to 4 in which the diaphragm spring has radially extending spring fingers whose length is kept to a minimum in order to reduce losses due to deflection of the fingers. 6) A clutch system according to any one of claims 1 to 5 characterised in that the assistor spring means comprises one or more springs which operate directly on the pedal. 7) A clutch system according to any one of claims 1 to 5 characterised in that the assistor spring means is built into the operating mechanism and operates indirectly on the pedal.- 8) A clutch system according to claim 7 having an hydraulic operating mechanism with a master cylinder connected with the pedal and a slave cylinder connected with the diaphragm spring, the clutch being characterised in that the assistor spring means is built into the master cylinder. 9) A clutch system according to any one of claims 6 to 8 characterised in that the assistor spring means is itself a diaphragm spring or springs. 10) A clutch system according to claim 9 characterised in that the assistor spring means comprises a plurality of axially spaced diaphragm springs arranged in series, the springs being capable of operating on both sides of their flat condition to counteract the characteristic of the driven plate clamping diaphragm spring. 11) A clutch system according to claim 10 having a piston displaceable in a bore to pressurise a working chamber, the clutch being characterised in that two series of diaphragm springs act respectively in opposite directions on the piston to return and assist the piston respectively. 12) A clutch according to any one of claims 1 to 11 characterised in that the driven plate is of the axially cushioned type. 13) A clutch system according to claim 12 characterised in that the axial cushioning is provided by elastomeric material which bonds friction material of the driven plate to a backing plate. 14) A master cylinder for the actuation of a vehicle function, the master cylinder comprising a body having a bore in which an actuating piston is displaceable by a pedal operated push rod or other actuating means to displace fluid from the bore to actuate the function, the master cylinder being characterised in that one or more diaphragm springs act directly or indirectly on the piston, to reduce the load which, needs to be applied by the pedal or other actuating means to operate the master cylinder. 15) An assistor spring arrangement for the operation of a veliicle clutch in which a clutch driven plate is clamped between a pressure plate and a reaction member by a diaphragm spring, the assistor spring arrangement being characterised in that two diaphragm spring means are arranged to operate in opposite directions on a clutch actuator member, the diaphragm spring means being capable of operating on both sides of their flat condition to counteract the characteristics of the driven plate clamping diaphragm spring and assist movement of the clutch actuator. 16) An arrangement according to claim 15 characterised in that the actuator member is moved by an associated pedal. 17) An arrangement according to claim 15 characterised in that the actuator member is moved by an electric motor. 18) A clutch system of the kind specified constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings. 19) A master cylinder constructed and arranged substantially as hereinbefore described with reference to and as shown in figure 6 to 10 or 11 of the accompanying drawings.

Inventors: STRUVE BENJAMIN CHETWOOD, YOUNG ALASTAIR JOHN, STRUVE, BENJAMIN, CHETWOOD, YOUNG, ALASTAIR, JOHN
Applicants: AP TMF LTD, AUTOMOTIVE PRODUCTS UK LTD, STRUVE BENJAMIN CHETWOOD, YOUNG ALASTAIR JOHN, AP TMF LIMITED, AUTOMOTIVE PRODUCTS UK LIMITED, STRUVE, BENJAMIN, CHETWOOD, YOUNG, ALASTAIR, JOHN
Application year: 2001
Main classification: B60T11
IPC codes: F16D25