GB2306201A - An adjustable and compact clutch slave cylinder having telescoping cylinder walls - Google Patents

Abstract

A clutch slave cylinder 10 comprises an axially fixed cylinder wall 14 and a telescoping axially movable wall 15 which contains an annular piston 11 having seal 16. Another seal 20 having a spring steel energising ring 20' acts between the fixed and movable walls 14, 15. The ring 20' due to frictional forces prevents the piston 11 moving wall 15 until it abuts against flange 15b. A wiper seal 30 is provided on the flange 15b to preclude contamination. The seals may be manufactured from EPMD or a silicone elastomer. Inner cylinder wall 13 and fixed wall 14 define a chamber 17 behind the piston 11. A sleeve 31 is carried by the piston 11 and has a metal retaining member 18 which holds a clutch release bearing captive by snapping over an internal flange 31b on sleeve 31. The piston 11 and sleeve 31 may be of metal or plastics material. In another embodiment the spring steel ring 20' may be complimented by a ratchet and pawl (114, fig 5). The slave cylinder 10 may be pre-filled before being associated with a vehicle.

Description

HYDRAULIC ACTUATORS This invention relates to hydraulic actuators and in particular to actuators of the so-called concentric slave cylinder type in which an annular actuating piston is axially displaceable between first and second cylinder walls to operate an associated clutch actuating mechanism.

Such concentric slave cylinders are well known and are conventionally installed with the piston operating on the clutch release bearing. It is therefore desirable for such slave cylinders to be compact and also to be able to accommodate the significant change in release bearing position which occurs when used with different clutches and also when the associated clutch wears.

It is an object of the present invention to provide an improved form of slave cylinder which meets the above criteria.

Thus according to the present invention there is provided a slave cylinder comprising: a piston axially displaceable relative to a cylinder wall to operate an associated device, the cylinder wall comprising an axially fixed portion and a telescoping axially moveable portion, the piston being in sealed sliding contact with the axially moveable portion via first sealing means, the axially moveable portion of the cylinder wall being in sealed sliding contact with the axially fixed portion via second sealing means, holding means to hold the axially moveable portion against axial displacement relative to the fixed portion, due to movement of the piston relative to the moveable portion and abutment means operatively connected with the piston contacting corresponding abutment means operatively connected with the moveable portion to move said moveable portion relative to the fixed portion to adjust the effective length of the cylinder wall.

The present invention is particularly applicable to concentric slave cylinders in which the piston is axially displaceable between first and second cylinder walls in which one of the cylinder walls comprises an axially fixed portion and a telesoping axially movable portion and the piston is in sealed sliding contact with both the movable portion of said one cylinder wall and with the other cylinder wall via the first sealing means.

A slave cylinder in accordance with the present invention is particularly suitable for operating a clutch.

The holding means may comprise of the seal friction generated by the second sealing means.

Alternatively the holding means may comprise of a ratchet mechanism, fixed to one of the moveable or fixed portions of the variable length cylinder wall, which acts on the other of the moveable or fixed portions of said variable length cylinder wall.

Furthermore the holding means may comprise of a combination of seal friction and a ratchet mechanism.

In a preferred concentric construction the other cylinder wall is of fixed axial length. Preferably the other cylinder wall is the radially inner wall.

In an alternative concentric construction both cylinder walls may be telescopic.

In concentric constructions the other wall may be tubular with an integral radial flange at one end which is secured to the fixed portion of said one wall to define a working chamber behind the piston.

In clutch applications the piston is operatively connected to a release bearing of the associated clutch.

Biasing means preferably acts on the release bearing to provide a clutch release mechanism pre-load.

The fixed and movable portions of the or each variable length cylinder wall preferably co-operate to prevent disengagement of their telescopic relationship.

The slave cylinder may be set up so that as the associated clutch wears the effective length of the or each variable length cylinder wall reduces. Alternatively the set up may be such that the effective length of the or each variable length cylinder wall increases.

In concentric slave constructions the first sealing means may comprise a common sealing member which acts on both the cylinder walls.

The first sealing means may comprise a seal having lips in contact with both cylinder walls and being attached to the piston by a dove tail and groove.

The second sealing means may comprise a lip seal with a spring steel energising ring or an O-ring type seal.

Both seals are preferably mould in E.P.D.N. (Ethylene Propylene Diene Monomer) or silicone elastomer.

Also in accordance with the present invention there is also provided a concentric slave cylinder comprising: an annular piston in sealed axially sliding contact with a body having first and second cylinder walls, the body joining the cylinder walls at one end to define in combination with the piston a working chamber having an inlet which is sealable via a connecter, the working chamber being pre-filled with working fluid which in use is pressurised to create a thrust which acts on a bearing via the piston to operate an associated clutch, the cylinder being arranged so that prior to installation (eg. during transportation) a gap is present in the thrust path between the piston and bearing and during installation of the cylinder in its operating position the bearing is moved towards the piston against a preload device to reduce the gap in the thrust path without increasing the pressure in the working chamber.

Also in accordance with the present invention there is provided a method of assembly of a pre-filled concentric slave cylinder of the form described in the preceding paragraph into an associated vehicle transmission, the method consisting of: a) filling the working chamber with the working fluid; b) pre loading the bearing away from the piston to form a gap in the thrust path; c) abutting the bearing against a clutch release mechanism of the associated vehicle transmission; d) moving the body of the concentric slave cylinder to its fully installed position to reduce the gap in the thrust path, and e) coupling the inlet via the connecter to a clutch master cylinder pre-filled with working fluid.

In installations in which not all the thrust path gap has been closed by moving the body to its installed position in step d) above the method may comprise the further step of pressurising the working fluid to move the piston to fully close the gap in the thrust path.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a section through a concentric slave cylinder embodying the telescopic feature of the present invention showing the cylinder in its installed, clutch engaged position; Figure 2 shows the cylinder of Figure 1 in the clutch disengaged position; Figure 3 shows the cylinder of figures 1 and 2 about to adjust the effective length of the telescoping wall; Figure 4 shows the cylinder of figure 1 in its fully contracted maximum wear condition; Figure 4a shows the cylinder of figure 1 in a pre-filled shipping condition.

Figure 5 shows a section through a second embodiment of a concentric slave cylinder embodying the telescopic feature of the present invention showing the cylinder in its installed, clutch engaged position; Figure 5a shows the clip 143 of figure 5 in greater detail; Figure 6 shows a partial view of the cylinder of figure 5 in the clutch engaged position; and Figure 7 shows a partial view of the cylinder of figure 5 in its fully contracted maximum wear condition.

Referring to Figure 1, this shows a concentric slave cylinder 10 with a body lOA housing an outer cylinder wall 12 and an inner cylinder wall 13. The body 10A joins the cylinder walls 12 and 13 at one axial end. Outer cylinder wall 12 is in two parts, an axially fixed portion 14 and an axially moveable portion 15. The axially movable portion 15 is in sealed sliding contact with the fixed portion 14 in a telescoping manner. An annular piston 11 and sleeve 31 are axially displaceable between the cylinder walls 12 and 13.

Piston 11 and sleeve 31 maybe of metal or plastics material with portion lla of piston 11 abutting portion 31a of sleeve 31 in use. Piston 11 carries a first sealing means in the form of a seal 16 formed from EPDM or silicone elastomer which seals the piston to both the outer wall 12 and the inner wall 13 and which in combination with the body portion define a working chamber 17 behind the piston. Piston 11 is also fully guided at axially spaced locations on the inner wall 13. A clutch release bearing 18 is held captive on sleeve 31 by a metal retaining member 19 which snaps over an internal flange 31b on sleeve 31. Release bearing 18 operates on the radially inner ends of an associated clutch diaphragm spring (not shown) in the conventional manner to release the clutch by moving the release bearing in direction X of Figure 1.Piston 11 and sleeve 31 can move axially to a limited extent relative to each other.

The axially fixed portion 14 of outer cylinder wall 12 comprises a cast portion 14a which may be of metal or plastics construction and a sheet metal portion 14b. A second sealing means in the form of a seal 20 (also formed from EPDM or silicone elstomers) is held captive between wall portions 14a and 14b to seal the sliding contact with the axially movable portion 15 of the outer cylinder wall 12.

Seal 20 includes a spring steel energising ring 20' to provide a high frictional force between seal 20 and cylinder wall portion 15.

The end 15a of axially moveable portion 15 is flared outwardly for the majority of its circumference to prevent movable portion 15 sliding out of the end of fixed portion 14 beyond the position shown in Figure 1. Similarly piston 11 has a radially outwardly turned flange llc which co-operates with a flange 15b on movable portion 15 to prevent the piston 11 exiting the end of portion 15. Flange 15b also carries a wiper seal 30 which is always in contact with the outer surface of sleeve 31 to prevent the entry of contamination.

A flange 14c formed on one end of the sheet metal portion 14b is rolled-over a flange 21, which is integral with inner cylinder wall 13, to axially locate inner cylinder wall 13 relative to the axially fixed portion 14. A retaining ring 33 on inner cylinder wall 13 prevents the disassembly of the bearing 18 and sleeve 31 under the influence of spring 24 during shipping from manufacturer to the vehicle assembly line where the sleeve is to be fitted. (see figure 4A).

Fluid for pressurising working chamber 17 to displace piston 11 in direction X and thus release the associated clutch is admitted into working chamber 17 via an inlet 23. A compression spring 24 acts between the fixed portion 14 of the outer wall and the release bearing 18 to apply a predetermined preload in direction X on the clutch release mechanism.

The installed clutch engaged position of the concentric slave cylinder is shown in Figure 1. Portion 14a is bolted to an appropriate support within a clutch bell housing (not shown).

The release bearing 18 is pressed against the clutch release mechanism (not shown) by the spring 24. It will be noted that piston 11 occupies a position substantially midway along the axial extent of the movable wall portion 15.

To disengage the clutch, pressurised fluid is admitted via inlet 23 into working chamber 17 to create a thrust which moves bearing 18. This thrust acts in turn along a thrust path within the seal 16, the sleeve 31 and the bearing 18.

To engage the clutch the pressure in working chamber 17 is reduced and the release bearing 18 is returned in direction Y by the clamping springs provided in the associated clutch.

The piston will then return substantially to the position shown in Figure 1.

During the return stroke of piston 11 the movable outer wall portion 15 is held fixed relative to the fixed portion 14 by the friction applied to the outer surface of movable portion 15 by the seal 20 acting as a holding means.

As the associated clutch (not shown) wears the position occupied by the release bearing 18 when the clutch is in the engaged condition moves progressively to the left as viewed in Figure 1 until the position shown in Figure 3 is eventually obtained in which the flange 15b abuts the inside surface 18a of the release bearing. Any further wear of the components of the associated clutch will result in the engaged position of the release bearing 18 moving still further to the left which will result in the axially movable portion 15 of the outer cylinder wall 12 being moved to the left relative to the fixed portion 14 as shown in dotted detail 15a' in Figure 3.

As will be appreciated, when working chamber 17 is pressurised to displace piston 11, the frictional force generated by seal 20 with its energising ring 20' which tends to prevent movement of wall portion 15 relative to wall portion 14, must be greater than the frictional drag generated by seal 16 plus the force generated by the working chamber pressure acting on the annular end area of end 15a of movable wall 15.

Figure 4 shows the concentric slave cylinder in its fully telescoped condition which is occupied when the associated clutch is fully worn. In this condition the seal 16 and end portion 15a of movable wall portion 15 are not in contact with flange 21 of inner wall portion 13 to ensure a small fluid passage 32 between the seal and flange 21. The fully telescoped height of the slave cylinder is achieved when the bearing surface 18a contacts the end of wall portion 14b.

It will therefore be appreciated that using Figure 1 as the initial starting position of the concentric slave cylinder, the cylinder is capable of accommodating clutch wear equivalent to a release bearing displacement of A before the movable wall portion 15 is moved relative to the fixed portion 14 and still further wear of the clutch equivalent to a release bearing displacement B by moving the movable portion 15 relative to the fixed portion 14. Thus the total wear which can be accommodated is equal to A + B.

As can be appreciated from Figure 4 the fully telescoped length of the concentric slave cylinder is extremely short thus facilitating an axially compact transmission. The concentric slave can also accommodate a considerable amount of axial displacement of the release bearing 18. This enables the slave cylinder to accommodate not only the release travel and wear travel of the associated clutch, but also the large variation in clutch finger height which can occur when using different sizes of clutches within the same clutch housing or clutches from different clutch suppliers.

Figure 4A shows the concentric slave cylinder in a pre-filled condition in a shipping position i.e. not installed in a vehicle. One end of a tube 25 (shown schematically) is fixed to inlet 23 and a quick connect coupling 26 (shown schematically) is fixed on the other end of the tube. Once the concentric slave cylinder 10 is installed in the clutch bell housing of a transmission the quick connect coupling 26 is situated at a relatively easily accessible position external to the bell housing.

Prior to shipping the working chamber 17, inlet 23 and tube 25 are filled with a predetermined volume of hydraulic fluid in a manner which ensures no air remains in the chamber 17, inlet 23, or tube 25 and the components of the concentric slave cylinder 10 adopt the relative positions shown in fig 4A. The quick connect coupling 26 prevents subsequent egress of the hydraulic fluid and ingress of air.

By comparing figures 4A and 1 it will be noted that the shipping position of piston 11 is axially towards flange 21 when compared with the installed clutch engaged position.

This shipping postion of piston 11 is maintained due to the volume of hydraulic fluid in chamber 17 remaining constant.

It will further be noted that the shipping position of the bearing 18 is axially to the right when compared with the installed clutch engaged position when viewing figures 4A and 1. This shipping position of bearing 18 is maintained by the action of the compression spring 24 and the retaining ring 33.

It is apparent that in the shipping position there is a gap G in the thrust path between piston 11 and sleeve 31 more particularly the gap G is between portion lla and portion 31a.

The sequence of events to install the pre-filled concentric slave cylinder is as follows: a) concentric slave cylinder 10 is pre-filled with hydraulic fluid and all components assume the relative positions as shown in figure 4A.

b) the concentric slave cylinder is shipped to the vehicle assembly site c) the concentric slave cylinder is installed in an associated clutch bell housing with portion 14a bolted to an appropriate support and with quick connect coupling 26 external to the bell housing.

d) The bell housing is attached onto an engine upon which is already mounted a clutch and a clutch release mechanism. This causes the bearing 18 to compress spring 24 and reduce the thrust path gap G until these two components adopt a position as shown in figure 1. Note at this stage the piston 11 remains in a position as shown in figure 4A and there remains a relatively smaller thrust path gap G.

e) the quick connect coupling 26 is joined to a corresponding quick connect coupling which in turn is joined via a tube to a clutch master cylinder.

This clutch master-cylinder and tube are pre filled with hydraulic fluid. The quick connect couplings are arranged such that no egress of hydraulic fluid occurs and no ingress of air occurs when they are joined together.

f) the clutch pedal which operates the master cylinder is depressed a number of times. This moves the piston 11 from the position shown in figure 4A to the position shown in figure 1 and closes the thrust path gap G.

The above sequence of events ensures that immediately prior to joining the quick connect couplings the hydraulic fluid in the concentric slave cylinder is substantially not pressurised, thus making the joining of the couplings relatively easy. Also at no time is the hydraulic fluid in the concentric slave cylinder substantially below ambient atmospheric pressure which ensures no ingress of air (especially past seal 16) during shipping or joining of the quick connect couplings. Furthermore, no shipping straps are necessary to retain particular components in fixed relationship during shipping. This is possible because the bearing 18 can move axially to a limited extent relative to the seal 16 during installation of the concentric slave cylinder.

It will be appreciated that in an alternative embodiment a bearing 18 could be designed to move relative to a seal 16, in a concentric slave cylinder with both cylinder walls being telescopic or neither cylinder wall being telescopic, and such embodiments could be designed for the so called "push" or "pull" type clutch.

With reference to Figures 5 to 7 there is shown a second embodiment of a concentric slave cylinder 110, wherein all parts which are clearly analagous to corresponding parts of the concentric slave cylinder shown in figures 1 to 4 are denoted by similar reference characters plus 100. Note bearing 118 is held on by a series of circumferentially arranged rubber teeth 150.

Also clutch diaphragm spring 140 is shown and a rubber boot 141 fulfils a similar function to wiper seal 30, that is to prevent the entry of contamination.

On a first axial end of movable portion 115 remote from the diaphragm spring 140 there is attached a clip 143 which consists of a cylindrical portion 143a joined to a disc like portion 143b. The cylindrical portion 143a has a plurality of circumferentially spaced radially inwardly bent tabs 143c.

Tabs 143c engage in a circumferential groove 115a in movable portion 115 to ensure clip 143 remains axially fast with movable portion 115. Cylindrical portion 143a also has a plurality of circumferentially spaced radially outwardly bent tabs 143d which are interspersed between tabs 143c. Tabs l43d engage in a series of circumferential grooves 144 formed on the radially inner surface of fixed portion 114. Tabs 143d are resilient and arranged so that the movable portion 115 can slide in the direction P of Figure 5 but is restrained from moving in the direction Q of Figure 5.

A clutch is disengaged by pressurised hydraulic fluid entering the working chamber 117 via port 123 and forcing the piston 111 in direction Q (See Figure 6) subsequent release of the pressurised hydraulic fluid allows the piston 111 to substantially return to the position shown in Figure 5.

Wear of the associated clutch causes the axial position of bearing 118 to move in the direction P when the clutch is in the fully engaged position this causes the piston 111 to abut the second axial end 115b of movable portion 115 and cause movable portion 115 to move in a direction P. After sufficient wear has taken place the tab 143d will engage in the next axial groove 144. This ratcheting type mechanism will continue until the clutch is fully worn and the concentric slave cylinder is in a position as shown in Figure 7.

It will be appreciated that when working chamber 117 is pressurised there is a force acting on movable portion 115 in the direction Q which is resisted by the clip 143 acting as a holding means.

When the pressurised hydraulic fluid is released and the piston 111 returns to its engaged position. The total friction force generated by seal 120 and clip 143 is greater than the friction force generated between the radially inner wall of movable portion 115 and its contact with seal 116 and piston 111. This ensures that upon engagement of the clutch, the seal 116 initially slides on the inner wall of moveable portion 115 in preference to moveable portion 115 moving relative to fixed portion 114, until the second axial end 115b of moveable portion 115 abuts the piston 111.

The embodiments of the invention shown have been designed for use in a 'push' type clutch i.e. a clutch in which the force required to disengage a pressure plate acts in the opposite direction to the movement of the pressure plate. Further embodiments of the invention could be designed for use in a 'pull' type clutch i.e. in a clutch in which the force required to disengage a pressure plate acts in the same direction as the movement of the pressure plate.

Claims (21)

1. A slave cylinder (10) comprising a piston (11) axially displaceable relative to a cylinder wall (14,15) to operate an associated device, the cylinder being characterised in that the cylinder wall comprises an axially fixed portion (14) and a telescoping axially moveable portion (15), the piston being in sealed sliding contact with the axially moveable portion via a first sealing means (16), the axially moveable portion of the cylinder wall being in sealed sliding contact with the axially fixed portion via second sealing means (20), holding means (20,20') to hold the axially moveable portion (15) against axial displacement relative to the fixed portion (14), due to movement of the piston relative to the moveable portion, and abutment means (18a) operatively connected with the piston contacting corresponding abutment means (15b) operatively connected with the moveable portion (15) to move said moveable portion relative to the fixed portion to adjust the effective length of the cylinder wall.

2. A slave cylinder according to Claim 1 characterised in that an annular piston (11) is axially displaceable between first (14,15) and second (13) cylinder walls in which one of the cylinder walls comprises said axially fixed portion (14) and said telescoping axially moveable portion (15) and the piston (11) is in sealed sliding contact with both the moveable portion (15) of said one cylinder wall and with the other cylinder wall (13) via the first sealing means (16).

3. A slave cylinder according to claims 1 or 2 characterised in that the holding means is provided by the seal friction generated by the second sealing means (20,20').

4. A slave cylinder according to claim 1 or 2 characterised in that the holding means comprises a pawl means (143) fixed to one of the moveable (115) or fixed (114) portions of the variable length cylinder wall which acts on a ratchet means (144) fixed on the other of the moveable or fixed portions of said variable length cylinder wall.

5. A slave cylinder characterised in that the holding means comprises a combination of the seal friction of Claim 3 and the pawl and ratchet means of Claim 4.

6. A slave cylinder according to claim 2 or 3 to 5 when dependent on claim 2 characterised in that the other cylinder wall (13) is of fixed axial length.

7. A slave cylinder according to Claim 6 characterised in that the other cylinder wall (11) is the radially inner wall.

8. A slave cylinder according to claim 2 or 3 to 5 when dependent on claim 2 characterised in that both cylinder walls have an axially fixed portion and an axially moveable portion and are of variable effective length.

9. A slave cylinder according to claim 2 or 3 to 8 when dependent on claim 2 characterised in that the other wall (13) is tubular with an integral radial flange (21) at one end which is secured to the fixed portion (14a) of said one wall (14,15) to define a working chamber (17) behind the piston (11).

10. A slave cylinder according to any one of claims 1 to 9 characterised in that the fixed and moveable portions (14,15) of the or each variable length cylinder wall (14a,15a) co-operate to prevent disengagement of their telescopic relationship.

11. A slave cylinder according to claim 2 or 3 to 10 when dependent on claim 2 characterised in that the first sealing means (16) comprises a common sealing member which acts on both cylinder walls (13,15).

12. A slave cylinder according to Claim 11 characterised in that the common sealing member (16) has seperate lips each of which contacts a respective one of said cylinder walls.

13. A slave cylinder according to any one of claims 1 to 12 characterised in that the second sealing means comprises a lip seal (20) with an internal energising ring (20').

14. A slave cylinder according to any one of claims 1 to 12 characterised in that the second sealing means comprises an O-ring.

15. A slave cylinder according to any one of claims 1 to 14 characterised in that the piston (11) is operatively connected to a clutch release bearing (18).

16. A slave cylinder according to claim 15 characterised in that as an associated clutch wears the effective length of the or each variable length cylinder wall (14,15) reduces.

17. A slave cylinder according to Claim 15 characterised in that as an associated clutch wears the effective length of the or each variable length cylinder wall (14,15) increases.

18. A slave cylinder according to any one of claims 15 to 17 characterised in that a biasing means (24) acts on the release bearing (18) to provide a clutch release mechanism pre-load.

19. A concentric slave cylinder comprising an annular piston (11) in sealed axially sliding contact with a body (10A) having first (14,15) and second (13) cylinder walls, the body joining the cylinder walls at one end to define in combination with the piston a working chamber (17) having an inlet (23) which is sealable via a connector, the working chamber being pre-filled with working fluid which in use is pressurised to create a thrust which acts on a release bearing (18) via the piston (11) to operate an associated clutch, the cylinder being characterised in that prior to installation (eg. during transportation) a gap (G) is present in the thrust path between the piston (11) and bearing (18) and during installation of the cylinder in its operating postion the bearing is moved towards the piston against a preload device (24) to reduce the gap in the thrust path without increasing the pressure in the working chamber (17).

20. A method of assembly of a pre-filled concentric slave cylinder according to Claim 19 into an associated vehicle transmission, the method consisting of: a) filling the working chamber with the working fluid; b) pre-loading the bearing away from the piston to form a gap in the thrust path; c) abutting the release bearing against a clutch release mechanism of the associated vehicle transmission; d) moving the body of the concentric slave cylinder to its fully installed position to reduce the gap in the thrust path; e) coupling the inlet via the connector to a clutch master cylinder pre-filled with working fluid, and f) (in installations in which not all the thrust path gap has been closed by moving the body to its installed postion) the further step of pressurising the working fluid to move the piston to fully close the gap in the thrust path.

21. A slave cylinder constructed and arranged substantially as hereinbefore described with reference to and as shown in Figures 1 to 4A or Figures 5 to 7 of the accompaying drawings.