WO2003019025A1

WO2003019025A1 - Motor vehicle clutch assembly

Info

Publication number: WO2003019025A1
Application number: PCT/IB2002/003327
Authority: WO
Inventors: Dean C. Paavola
Original assignee: Automotive Products (Usa), Inc.
Priority date: 2001-08-24
Filing date: 2002-08-16
Publication date: 2003-03-06

Abstract

A vehicular clutch mechanism in which a clutch release bearing assembly (36) centred on a transmission shaft (24) is moveable axially along the shaft to disengage the clutch (12) by an hydraulic pressure system including a master cylinder (60) operated by a clutch pedal (68) of the vehicle and a slave cylinder (62) receiving pressurised hydraulic fluid output from the master cylinder to move the release bearing assembly along the shaft to disengage the clutch and to provide coaction between a face (32a) on the release bearing assembly and a fixed surface (44a) of the housing (42) to operate a further function of the vehicle such as a clutch brake or clutch wear adjuster. Means (72) are provided which, in response to sensed increases in the hydraulic fluid pressure in the system beyond a predetermined limit, increase the volume of the hydraulic system thus minimising pressure spikes in the hydraulic pressure system initiated by the coaction between the release bearing assembly face and the housing fixed surface.

Description

MOTOR VEHICLE CLUTCH ASSEMBLY

BACKGROUND OF THE INVENTION This invention relates to motor vehicle clutch assemblies and, more particularly, to motor vehicle clutch assemblies of the hydraulically actuated type.

Manual transmission motor vehicles of necessity employ a clutch assembly to facilitate shifting of the transmission. Recently, hydraulically actuated clutch assemblies have enjoyed increasing usage. Although the hydraulically actuated clutch assemblies are generally satisfactory, problems have arisen when they are utilized in association with clutch assemblies in which the movement of the release bearing assembly to disengage the clutch is further utilized to perform a further function in the clutch assembly such, for example, as providing a clutch brake or providing self adjustment of the clutch friction material. Specifically, in these applications, pressure spikes have occurred in the hydraulic pressure system controlling the clutch assembly. Although these pressure spikes can be accommodated by increasing the strength of the components of the hydraulic control system, this solution adds significantly to the cost of the hydraulic control system.

SUMMARY OF THE INVENTION

This invention relates to an improved motor vehicle clutch assembly of the hydraulically actuated type.

More specifically, this invention relates to a hydraulically actuated motor vehicle clutch assembly in which pressure spikes in the hydraulic control system are eliminated in a cost effective manner. This invention relates to a vehicular clutch assembly of the type including a housing, a transmission input shaft journaled in the housing, a release bearing assembly centered on the clutch shaft and movable axially along the clutch shaft to disengage the clutch, and a hydraulic pressure system including a master cylinder actuated by a clutch pedal of the vehicle and a slave cylinder receiving pressurized hydraulic fluid output from the master cylinder and operative to move the release bearing assembly along the clutch shaft to disengage the clutch and to provide coaction between a face on the release bearing assembly and a fixed surface of the housing to operate a further function of the vehicle.

According to the invention, pressure spikes in the hydraulic pressure system initiated by the coaction between the release bearing assembly face and the housing fixed surface are minimized by increasing the volume of the hydraulic system in response to sensed increases in the hydraulic fluid pressure in the system. This methodology eliminates the problems associated with the pressure spikes without requiring the use of heavy duty components in the hydraulic pressure system.

The hydraulic pressure system preferably includes conduit means interconnecting the output of the master cylinder and the input of the slave cylinder and the volume of the system is increased by increasing the volume of the conduit means. This arrangement allows existing componentry of the hydraulic pressure system to be utilized to minimize the pressure spikes.

The conduit means preferably includes an accumulator interposed between the output of the master cylinder and the input of the slave cylinder and the volume of the conduit means is increased by increasing the volume within the accumulator. This arrangement allows the use of a simple inexpensive accumulator device to minimize the spikes in the system.

The accumulator preferably comprises a casing and a spring biased piston slidably mounted in the casing and exposed to hydraulic fluid system pressure, and the volume of the accumulator is increased by sliding spring resisted movement of the piston in the casing in response to sensed increases in the system pressure. This arrangement facilitates the use of the accumulator device to minimize the pressure spikes. The accumulator preferably includes a casing having a main body portion defining a bore and left and right end walls each having a central aperture for communication with opposite ends of the bore; means defining a fixed annular shoulder surface in the bore; a piston slidably mounted in the casing bore and defining a central piston bore extending axially through the piston; a spring device of annular configuration positioned in the casing bore, bearing at a left end thereof against the left wall of the casing, and bearing at a right end thereof against the left end of the piston to urge an annular surface of the piston against the annular shoulder surface of the casing to position the right end of the piston in axially spaced relation to the right casing wall and define a predetermined voided fluid volume therebetween; a left conduit means extending through the aperture in the left wall of the casing and through the annular spring device for connection to the left end of the piston in communication with the piston bore; and right conduit means connected to the aperture in the right wall of the casing in communication with the predetermined voided fluid volume. This arrangement allows the piston to readily yield in response to spikes in system pressure to increase the volume of the accumulator and thereby the volume of the system whereby to minimize the pressure spikes.

The casing bore may have a stepped configuration including a relatively large diameter left bore section, a relatively small diameter right bore section, and an annular shoulder, constituting the fixed annular shoulder surface in the bore, interconnecting the left and right bore sections; the spring being positioned in the large diameter left bore section; and the piston includes a main body portion slidably mounted in the right bore section and an annular external flange, defining the annular shoulder surface of the piston, coacting with the annular casing shoulder to position the piston relative to the right wall of the casing under the urging of the spring. This arrangement provides a simple means of defining the initial voided volume of the accumulator while readily allowing the piston to move in response to pressure spikes in the system to increase the fluid volume of the system and minimize the spikes.

The coaction between the face on the release bearing assembly and the fixed surface of the housing is preferably arranged to operate a clutch brake. The invention also provides a method of minimising pressure spikes in a clutch mechanism as described above by increasing the volume of the hydraulic system in response to sensed increases in the hydraulic fluid pressure in the system beyond a predetermined limit.

Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:

Fig. 1 is a somewhat schematic view of a motor vehicle clutch assembly according to the invention;

Fig. 2 is a cross sectional view of an accumulator utilized in the clutch assembly;

Fig. 3 is a cross sectional perspective view of the accumulator; and

Fig. 4 is a plot of pedal travel versus system pressure comparing the behavior of a prior art system to the system of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The motor vehicle clutch assembly 10 seen somewhat schematically in Fig. 1 includes a clutch 12 and a clutch actuating system 13.

Clutch 12 includes a clutch housing 14; a fly wheel 16 driven by the crank shaft 18 of the associated engine; a clutch cover 20 fixedly secured to and rotating with the fly wheel; a transmission input or clutch shaft 24; a pressure plate 26; a diaphragm spring 28; a hub 30 carried by and rotating with the clutch cover 20; a hollow quill shaft 32 positioned in surrounding relation to transmission input shaft 24 and fixedly secured to hub 30 whereby to rotate as a unit with the hub 30, the clutch cover 20 and the fly wheel 16; a release bearing housing 34; a bearing 36 including a non-rotating outer race 38 carried by the release bearing housing 34 and a rotating inner race 40 carried by quill shaft 32; a transmission housing 42 housing the transmission gearing in known manner and secured to the rear end 14a of the clutch housing; a bearing cap 44 carried by the front end of the transmission housing and mounting a transmission input bearing 46; a clutch brake disk 48 slidably splined on transmission input shaft 24 between the front face 44a of bearing cap 44 and the rear face 32a of a flange 32b at the rear end of quill shaft 32; and a release lever 50 mounted on a cross shaft 52 carried by the clutch housing and including a release finger portion 50a coacting with a lug portion 34b of release bearing housing 34. Transmission input shaft 24 is journaled at its front end 24a in a pilot bearing 52 carried by the front end 18a of crank shaft 18 and is further journaled as it enters the transmission by transmission input bearing 46. The inner ends 28a of the fingers of diaphragm spring 28 are received in a groove 30a in hub 30 so that, in response to counterclockwise movement of release lever 50 and by virtue of the coaction between release lever finger portion 50a and release bearing housing lug portion 34b, as the release bearing and quill shaft move to the right the fingers 28 pivot about posts 54 carried by clutch cover 20 to allow pressure plate 26 to move away from disk 22 and disengage the clutch. The rightward movement of the quill shaft 32 to affect disengagement of the clutch also has the effect of braking the transmission input shaft 24. Specifically, as the quill shaft 32 moves to the right, the flange 32b of the quill shaft moves into engagement with clutch brake disk 48 and squeezes the brake disk between the rear face 32a of flange 32 and the front face 44a of bearing cap 44 whereby, by virtue of the splined connection between the clutch brake disk 48 and shaft 24, the shaft is braked to facilitate the shifting operation occurring within the transmission following disengagement of the clutch.

Clutch actuating system 13 includes a master cylinder 60, a slave cylinder 62 and a conduit assembly 64.

Master cylinder 60 is of known form and may be mounted for example in the engine wall 66 of the vehicle for coaction with the push rod 68a of a clutch pedal 68. Slave cylinder 62 is of known form, receives pressurized fluid via conduit assembly 64 from master cylinder 60, and includes a push rod 62a pivotally connected at 70 to the upper end 50b of release lever 50.

Conduit assembly 64 includes an accumulator 72, a first conduit section 74 interconnecting the output of master cylinder 60 and the input of accumulator 72, and a second conduit section 76 interconnecting the output of differential accumulator 72 and the input of slave cylinder 62.

Accumulator 72 (Figs. 2 and 3) includes a housing or casing 80, an end cap 82, a piston 84, a spring device 86, an input fitting 88, an output fitting 90, and a piston seal 92.

Casing 80 is formed of a suitable rigid material such as aluminum and has a stepped configuration including a relatively large diameter left end portion 80a defining a relatively large diameter bore 80b and a relatively small diameter right end portion 80c defining a relatively small diameter bore 80d. Portions 80a and 80c are interconnected by an annular shoulder 80e defining an annular shoulder surface 80f interconnecting bore portions 80b and 80d. The right hand end of casing 80 is closed by a right end wall 80g defining a central aperture 80h.

End cap 82 is fixedly positioned in the left end of the casing via a snap ring 94 whereby to constitute a left end wall of the casing defining a central aperture 82a.

Piston 84 may be formed of a suitable rigid material such as aluminum and includes a right hand main body portion 84a receiving seal 92 and sized to be slidably and sealingly received in bore 80d, a left hand external flange portion 84b slidably received in piston bore 80b, and a left hand fitting portion 84c. A central bore 84d extends through the main body portion 84a and communicates with a central bore 84e in fitting portion 84c.

Spring 86 may be formed of any suitable spring material and has an angular or coiled configuration and a rectangular cross sectional configuration. The left coil 86a of the spring is positioned against end cap 82 and the right coil 86b of the spring is positioned against piston annular flange 84b whereby to urge the flange into engagement with casing shoulder 80f. Input fitting 88 has a barbed configuration and is fitted into the aperture 80h of casing end wall 80g.

Output fitting 90 has a similar barbed configuration and is fitted into aperture 84e in piston fitting portion 84c and extends leftwardly within coil spring 86.

First conduit section 74 is formed of a suitable flexible hose material, is fitted at one end 74a thereof to the output of master cylinder 60, and is fitted at another end 74b thereof over barbed input fitting 88 of the accumulator.

Second conduit section 76 is formed of a suitable flexible hose material, extends at a first end 76a thereof through accumulator aperture 82a and through coil spring 86 for connection to barbed output fitting 90, and is fitted at another end 76b thereof to the input of slave cylinder 62.

OPERATION

In the normal operation of the clutch assembly seen in Fig. 1, as the clutch pedal is depressed by the vehicle operator to disengage the clutch, pressurized fluid is discharged from the master cylinder and moves through conduit section 74 to the accumulator 72, moves through the accumulator without disturbing the position of the piston 84 or the disposition of the spring 86, and is delivered to the input of the slave cylinder which thereupon extends to pivot release lever 50 in a counterclockwise direction as viewed in Fig. 1 to move the release bearing 34 to the right. As the release bearing moves to the right, the quill shaft 32 and hub 30 move to the right which has the effect via the groove 30a of pulling on the ends of the spring fingers 28 and pivoting the spring fingers about the pivot axes defined by the pivot posts 28 whereby to release the pressure plate 26 and allow the pressure plate to move to the right to relieve the pressure on friction plate 22 and disengage the clutch.

As the release bearing continues to move to the right in response to further depression of the clutch, the system pressure, (as seen by the solid line plot of Fig. 4 representing system behavior without benefit of the accumulator 72) by this point has increased to, for example, approximately 750 psi. As the release bearing continues to move to the right in response to further depression of the clutch pedal 68, quill shaft annular flange 32b moves into engagement with clutch brake disk 48 and squeezes the clutch brake disk between the quill shaft flange and bearing end cap 44 whereby to slow the transmission input shaft 24 and facilitate shifting of the transmission. However, as seen by further reference to the solid line plot of Fig. 4, the system in effect bottoms out as the clutch disk is squeezed between the quill shaft flange and the bearing end cap with the result that the system pressure spikes up and approximately doubles to, for example, a value of 1500 psi. This pressure spike requires that the entire pressure system be beefed up utilizing heavier more expensive materials such for example as ferrous materials to withstand the pressure spikes without generating bursting failures in the system. By contrast, when the accumulator 72 is included in the system (and as seen by the dash line plot of Fig. 4) the accumulator has the effect of totally removing the spike in the pressure plot occurring in response to bottoming out of the system and limits the increase in pressure in response to bottoming out to a minimal amount so that the maximum pressure experienced by the system may, for example, not exceed 800 psi thereby allowing the use of relatively lightweight, inexpensive materials in the system without risking bursting.

The removal of the spike in the system is achieved by increasing the volume of the hydraulic system in response to sensed increases in the hydraulic fluid pressure in the system and, specifically, by allowing spring 86 to yield and compress to the left to allow piston 84 to move to the left to in effect increase the volume defined within the accumulator. The parameters are chosen such that the increase in accumulator volume is sufficient to maintain the system pressure at a substantially constant value and thereby totally eliminate the spike in the system. In this regard, it is critical that spring 86 have a relatively low spring rate, for example, 88 pounds per inch. From a packaging standpoint, the use of a coil spring having a rectangular cross section minimizes the size of the spring and thereby the size of the accumulator package required to provide a desired spring rate, and the use of a working face 84F of the accumulator piston 84 having a diameter that is greater than the diameter of the master cylinder piston 90, yet sufficiently small to minimize the required spring load to provide the desired system performance, further minimizes the accumulator package size. In overview, it will be understood that the accumulator functions to generate extra system volume once a predetermined pressure limit has been achieved so that the system pressure increase is governed by the rate of the compression spring whereby the compression spring can be designed with a low spring rate to maintain the overall system pressure at or below a given maximum. By incorporating the accumulator, the system pressures can be contained thereby eliminating the need for costly metal cylinders and hydraulic lines.

Whereas the invention has been described in association with a clutch system of the type employing a clutch brake, it will be understood that the accumulator of the invention may be utilized in any clutch system wherein the release bearing coacts with a fixed surface of the transmission housing to generate a force or signal that is utilized to facilitate the operation of the clutch system. For example, the accumulator of the invention maybe utilized in a self adjusting clutch system wherein the release bearing contacts the transmission bearing cap in order to generate a force signal that is utilized to adjust the clutch to compensate for wear in the friction material of the clutch.

The invention will be seen to provide an arrangement whereby pressure spikes can be readily eliminated in a clutch system whereby to allow the use of relatively lightweight and inexpensive components in the system without risking bursting failures in the system.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Claims

1. A vehicular clutch mechanism comprising:- a housing;

a transmission input shaft journaled in the housing;

a release bearing assembly centred on the shaft and moveable axially along the shaft

to disengage the clutch; a hydraulic pressure system including a master cylinder actuated by a clutch pedal of the vehicle and a slave cylinder receiving pressurised hydraulic fluid output from the master cylinder and operative to move the release bearing assembly along the shaft to disengage the clutch and to provide coaction between a face on the release bearing assembly and a fixed surface of the housing to operate a further function of the vehicle; and means operative in response to sensed increases in the hydraulic fluid pressure in the system beyond a predetermined limit to increase the volume of the hydraulic system whereby to minimise pressure spikes in the hydraulic pressure system initiated by the coaction between the release bearing assembly face and the housing fixed surface.

2. A clutch mechanism according to claim 1 wherein: the hydraulic pressure system includes conduit means interconnecting the output of the master cylinder and the input of the slave cylinder; and the means operative to increase the volume of the hydraulic system comprises means operative to increase the fluid volume of the conduit means.

3. A clutch mechanism according to claim 2 wherein: the conduit means includes an accumulator between the output of the master cylinder and the input of the slave cylinder; and the volume of the conduit means is increased by increasing the volume of the accumulator

4. A clutch mechanism according to claim 3 wherein: the accumulator comprises a casing, a spring positioned in the casing, and a piston slideably mounted in the casing, biased by the spring, and exposed to hydraulic fluid system pressure; and the volume of the accumulator is increased by sliding, spring resisted movement of the piston in the casing in response to sensed increases in the system pressure.

5. A clutch mechanism according to claim 3 or 4 wherein the accumulator comprises; a casing having a main body portion defining a bore and left and right end walls each having a central aperture for communication with opposite ends of the bore; means defining a fixed annular shoulder surface in the bore; a piston slideably mounted in the casing bore and defining a central piston bore extending axially through the piston; a spring device of annular configuration positioned in the casing bore, bearing at a left end thereof against the left wall of the casing, and bearing at a right end thereof against a left end of the piston to urge an annular surface of the piston against the annular shoulder surface of the casing to position a right end of the piston in axially spaced relation to the right casing end wall and define a predetermined voided fluid volume therebetween; a left conduit means extending through the aperture in the left wall of the casing and through the annular spring device for connection to the left end of the piston in communication with the piston bore; and a right conduit means connected to the aperture in the right wall of the casing in communication with the predetermined voided fluid volume.

6. A clutch mechanism according to claim 5 wherein; the casing bore has a stepped configuration including a relatively large diameter left bore section, a relatively small diameter right bore section, and an annular shoulder, constituting the fixed annular shoulder surface in the bore, interconnecting the left and right bore sections; the spring is positioned in the large diameter left bore section; and the piston includes a main body portion slideably mounted in the right bore section and an annular external flange, defining the annular shoulder surface of the piston, coacting with the annular casing shoulder to position the right end of the piston relative to the right wall of the casing under the urging of the spring.

7. A clutch mechanism according to claim 6 wherein the spring has a coil configuration and a rectangular cross sectional configuration.

8. A clutch mechanism according to claim 7 wherein the diameter of the piston main body portion is less than the diameter of the spring.

9. A clutch mechanism according to any one of claims 1 to 8 wherein the coaction between the face on the release bearing assembly and the fixed surface of the housing operates a clutch brake.

10. A clutch mechanism according to claim 9 wherein a clutch brake disc rotatable with and in coaxial surrounding relationship with the transmission input shaft is clamped between the release bearing assembly and the fixed surface of the housing to operate the brake.

11. A clutch mechanism according to any one of claims 1 to 10 wherein the coaction between the face on the release bearing assembly and the fixed surface on the housing generates a force signal that is utilised to adjust the clutch to compensate for wear of friction material of the clutch.

12. In a vehicular clutch mechanism of the type including a housing, a transmission input shaft journaled in the housing, a release bearing assembly centred on the shaft and moveable axially along the shaft to disengage the clutch, and a hydraulic pressure system including a master cylinder actuated by a clutch pedal of the vehicle and a slave cylinder receiving pressurised hydraulic fluid output from the master cylinder and operative to move the release bearing assembly along the shaft to disengage the clutch and to provide coaction between a face on the release bearing assembly and a fixed surface of the housing to operate a further function of the vehicle; a method of minimising pressure spikes in the clutch mechanism initiated by the coaction between the release bearing assembly face and the housing fixed surface is provided by increasing the volume of the hydraulic system in response to sensed increases in the hydraulic fluid pressure in the system beyond a predetermined limit.

13. A method according to claim 12 wherein the coaction between the face on the release bearing assembly and the fixed surface of the housing operates a clutch brake.

14. An accumulator for use in an hydraulic pressure system of the type including a master cylinder, a slave cylinder and a conduit assembly connecting the output of the master cylinder to the input of the slave cylinder, the accumulator comprising: a casing having a main body portion defining a bore and left and right end walls each having a central aperture for communication with opposite ends of the bore; means defining a fixed annular shoulder surface in the bore; a piston slideably mounted in the casing bore and defining a central piston bore extending axially through the piston; a spring device of annular configuration positioned in the casing bore, bearing at a left end thereof against the left wall of the casing, and bearing at a right end thereof against a left end of the piston to urge an annular surface of the piston against the annular shoulder surface of the casing to position a right end of the piston in axially spaced relation to the right casing end wall and define a predetermined voided fluid volume therebetween; a left conduit means extending through the aperture in the left wall of the casing and through the annular spring device for connection to the left end of the piston in communication with the piston bore; and a right conduit means connected to the aperture in the right wall of the casing in communication with the predetermined voided fluid volume.