GB2241298A

GB2241298A - A hydraulic cylinder

Info

Publication number: GB2241298A
Application number: GB9004369A
Authority: GB
Inventors: Boris Kopacin
Original assignee: Automotive Products France SA
Current assignee: Automotive Products France SA
Priority date: 1989-09-13
Filing date: 1990-02-27
Publication date: 1991-08-28
Also published as: GB9004369D0; FR2651841A1; FR2651841B1

Abstract

A hydraulic cylinder comprises a slave cylinder body 10 having an axial bore 14, a piston 16 slidable in the bore and an output member 17 through which movement of the piston is transmitted. The slave cylinder body 10 is connected to a master cylinder 11 by a conduit 11a and all three are prefilled with hydraulic fluid. A shipping and installation restraint 27 is provided for holding the output member 17 of the prefilled slave cylinder in a retracted position and the restraint ruptures upon first actuation of the slave cylinder of a clutch system. The output member 17 is formed integrally with the restraint 27 which is carried by the body 10. A gaiter 33 extends into the bore 14 of the body 10 and a pressure relief groove 26 relieves working pressure in the slave cylinder after the piston 16 has moved beyond a predetermined position in the bore 14. <IMAGE>

Description

A HYDRAULIC CYLINDER The invention relates to a hydraulic cylinder and is particularly, but not exclusively, concerned with a hydraulic slave cylinder for use with a motor vehicle clutch release system.

Hydraulic slave cylinders are known for operating a mechanism such as a vehicle clutch at a remote location under the influence of fluid supplied from a master cylinder. A conduit interconnects the master cylinder and slave cylinder and the system is filled with a hydraulic fluid such that when a piston of the master cylinder is actuated, a piston of the slave cylinder, and consequently an output member of the slave cylinder, is simultaneously actuated by displacement of the hydraulic fluid from the master cylinder to the slave cylinder through the conduit.

It has been proposed hitherto to pre-assemble such a system by filling the master cylinder, the slave cylinder and the conduit with hydraulic fluid, and bleeding the system before shipment of the assembly to a motor vehicle manufacturer for installation on a motor vehicle. With such an arrangement, it has been proposed to hold the output member of the slave cylinders in a retracted position by means of a shipping and installation strap, for example, as described in EP-A-86O6O. In EP-A-86060, the shipping and installation strap is a separate element which has to be fitted onto both the pushrod and a body of a cylinder and an object of the present invention is to provide a hydraulic cylinder having an improved installation and shipping restraint arrangement.

According to one aspect of the invention there is provided a hydraulic cylinder comprising a cylinder body having an axial bore, a piston slidable in the bore, an output member through which movement of the piston is transmitted and a shipping and installation restraint for holding the output member in a retracted position and which ruptures upon first actuation of the cylinder, one of the body and output member being formed integrally with the shipping and installation restraint which is carried by the other of the body and output member.

Such an arrangement is particularly useful in that the forming of the shipping and installation restraint integrally with one of the body and output member greatly simplifies the assembly of the cylinder.

Preferably, the output member is formed integrally with said shipping and installation restraint. That is particularly advantageous as the assembly of the pushrod into the cylinder automatically carries the shipping and installation restraint into a position where it can be easily attached to the body of the cylinder.

Preferably, the shipping and installation restraint is at an end of the output member remote from the piston. Such an arrangement enables the shipping and installation restraint to be formed at one end of the output member, which will normally be a pushrod, so that the shipping and installation restraint will be therefore easy to locate at one end of the cylinder body.

Conveniently, the shipping and installation restraint may include a plurality of radial straps which rupture upon first actuation of the cylinder. The straps are preferably of slender form and of sufficient strength to hold the output member in position during slipping and installation but relatively easily frangible on first operation of the slave cylinder.

It has been proposed hitherto to provide an axially flexible seal, bellows seal, boot, gaiter or the like (herein referred to as a "gaiter") arranged externally of the cylinder so as to extend axially from one end thereof onto the output member. The gaiter is axially expandable and contractable on movement of the output member to prevent the ingress of foreign matter into the bore of the cylinder.

Such a gaiter is shown in GB-A-2164494. As the gaiters of hitherto known slave cylinders have to grip the pushrod externally of the cylinder, the pushrod has to be made of a length sufficient to provide a surface area to be gripped by the gaiter.

This can be disadvantageous where space is at a premium and where any additional length of slave cylinder will be inconvenient. Another object of the present invention is to provide a hydraulic cylinder which will reduce such disadvantages.

According to another aspect of the invention there is provided a hydraulic cylinder comprising a cylinder body having an axial bore, a piston slidable in the bore, an output member through which movement of the piston is transmitted and a gaiter which co-operates with the output member and forms a seal to inhibit entry of foreign matter into the bore characterised in that the gaiter extends axially of the output member into the bore.

By ensuring that the gaiter extends axially into the bore, it is no longer necessary to provide an output member of extra length externally of the body and, therefore, the cylinder can be made very compact.

Preferably, the gaiter extends into a hollow interior of the piston. In that way, the cylinder can be made even more compact as it is possible to take full advantage of the internal length of the output member which extends into the piston to provide a surface for engagement with the gaiter.

The end of the gaiter which does not engage the piston rod is preferably mounted on an element carried by the body. That element may conveniently form part of the shipping and installation restraint which is preferably integral with the pushrod. With the latter arrangement it is possible to assemble the pushrod, gaiter and shipping and installation restraint already assembled into the cylinder whereas with previous arrangements it has been necessary to assemble the pushrod into the cylinder initially and then afterwards fit an external gaiter.

With a conventional slave cylinder, damage can result if the piston is over-stroked, i.e., if the piston reaches the end of the available travel distance before the piston of the master cylinder reaches the end of its working stroke. A further object of the present invention is to provide a hydraulic cylinder which reduces that disadvantage.

According to a further aspect of the invention there is provided a hydraulic cylinder comprising a body having an axial bore, a piston slidable in the bore and an output member through which movement of the piston is transmitted during a working stroke characterised in that the relief means is provided for relieving fluid pressure in the cylinder where the piston moves beyond a predetermined position in the bore.

Such an arrangement inhibits further axial movement of the slave cylinder piston once the relief means relieves fluid pressure thereby reducing the likelihood of damage to the slave cylinder in the event that further fluid is fed thereto by a master cylinder.

The relief means may comprise a groove extending axially of the bore or a port in a wall of the bore.

In either case, a. seal on the piston is preferably arranged to uncover the port or the entrance to the groove once the seal moves beyond the predetermined position to allow fluid pressure to be relieved.

Preferably, resilient means is provided which deforms if the piston moves beyond said predetermined position and which applies a bias to the piston in the opposite direction whereby following relief cf the pressure after cpening of the relief means by the piston the resilient means urges the piston in an opposite direction so as to close the relief means.

As will be described hereinafter, this particular feature is useful in that it can be used to assist in bleeding the hydraulic fluid of air when pre-filling the system.

The resilient means may be a wavy washer and may abut the stop for the piston.

A hydraulic cylinder in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Fig.l is a cross-section through a hydraulic slave cylinder in accordance with the invention showing an integral push rod and shipping and installation restraint, the latter being in an unruptured condition, Fig.2 is an end view of the cylinder of Fig.2 looking in the direction of arrow II in Fig.1, Fig.3 is a cross-section similar to Fig.l showing the installation and shipping restraint in a ruptured condition, Fig.4 is a cross-section through part of the slave cylinder shown in Figs.l and 2 showing a relief groove for the cylinder, Fig.5 is a view similar to Fig.4 showing a relief port for the cylinder.

Fig.6 is a cross section through a pre-assembled pushrod, shipping and installation restraint and gaiter, A slave cylinder 10 comprises a body 12 having an inlet 13 at its left hand end as viewed in the drawings, an axial bore 14 extending towards an open end 15, a piston 16 slidable in the bore and a pushrod 17 through which movement of the piston towards the right is transmitted to a clutch release arm 18 of a ven cle. The slave cylinder 10 and the clutch release arm 18 are suitably mounted on a bell housing indicated.generally at 19. Fluid is fed to the inlet by a master cylinder 11 (drawn to a smaller scale) via conduit 11a.

The piston 16 is hollow and has an open interior 20 into which the pushrod 17 extends so that a spherical convex end surface 22 of the piston rod engages a complementary concave spherical surface 23 of the piston 16. The piston is normally biased towards te pushrod 17 by means of a coil spring 24 in a working section 25 of the bore 14. The bore 14 is formed with an axial groove 26 which extends towards the open end 15 of the body.

The pushrod 17 is formed from plastics material and is moulded integrally with a shipping and installation restraint 27 comprising an annular element 28 having a cylindrical extension 29 and a plurality of circumferentially spaced straps 30 which extend between the annular element 28 and the push rod 17.

The master cylinder 11, slave cylinder 10 and interconnecting conduit 11a are pre-filled with hydraulic fluid and bled of air before shipment of the prefilled system to a motor vehicle manufacturer for installation on a motor vehicle. The use of the shipping and installation restraint 27 prevents movement of the piston 16 and pushrod towards the right during shipping and during installation of the hydraulic system into the vehicle. However, once the system has been installed and the pushrod aligned with a recess 32 on the clutch release arm 18, operation of the master cylinder 11 will urge the piston 16 to the right and thereby rupture the straps 30. The ruptured condition of the straps is shown in Fig.2.

The cylindrical extension 29 of the annular element 28, provides a convenient mounting groove 29a for one end of a gaiter 33 in the form of a bellows-seal having its opposite end sealingly engaged with the periphery of the pushrod 17. The arrangement is particularly compact as the gaiter 34 extends axially through the bore 14 and into the hollow open interior 20 of the piston 16. With such an arrangement, the length of the push rod can be kept to an absolute minimum as it is unnecessary to provide additional piston rod length externally of the cylinder for carrying the pushrod engaging end of the gaiter 33.

The annular element 28 is positioned behind a snap ring 34 located in a groove 35 in the body 12. The left hand side of the annular element 28 engages a resilient wavy washer 36. Normally, the working stroke of the piston 16 will cause the clutch release arm 18 to move clockwise as viewed in Figs.1 and 2 towards the broken line position 18a sufficiently to release the clutch before the right hand end of the piston engages the wavy washer 36. However, if circumstances dictate that the piston 16 is overstroked i.e., moved against the wavy washer 36 before the master cylinder 11 has reached its fully clutch released condition, additional application of pressure by the master cylinder will cause the piston 16 to compress the wavy washer 36 until a sea 21 carried by the piston uncovers the left hand end of the groove 26 as shown in Fig.5.Fluid can then escape from the working section 25 along the groove 26 into the remainder of the bore 14 to relieve pressure in the working section thereby avoiding possible damage to the slave cylinder. Once the pressure in working section 25 has fallen sufficiently, the wavy washer will urge the piston to the left to close the groove 26. The position at which the seal 21 opens the groove 26 or port 37 to the working section 25 constitutes substantially the aforesaid predetermined position of the piston.

Instead of using a groove 26, Fig.6 illustrates the use of a simple radial port 37 formed in the wall of the bore 14 which will be uncovered by the seal 21 if the piston is moved sufficiently far to the right to compress the wavy washer 36.

The use of the wavy washer 36 and groove 26 or port 37 may facilitate bleeding of the system during the pre-filling. By causing the piston 16 to move to the right so as to compress the wavy washer 36 when filling the system, the uncovering of the groove 25 or port 37 will permit release of fluid from the working section 25 until the system is completely bled whereupon release of fluid pressure will cause the wavy washer 36 to return the piston to the left to close the groove 26 or port 37.

The use of an integral piston rod and shipping and installation restraint 27 simplifies assembly considerably as there is no need to provide and fit a separate shipping and installation strap as in EP-A86060. Also, the annular element 28 makes a convenient stop for the piston and also forms a very convenient mounting for the internal gaiter 33.

Furthermore by positioning the gaiter between the inner section of the pushrod and the shipping and installation restraint 27, the gaiter and pushrod can be pre-assembled and the assembled pushrod, gaiter and shipping and installation restraint as shown in Fig.6 can be inserted in the cylinder bore. The assembly is then simply held in position by the snapring 34.

Claims

1. A hydraulic cylinder comprising a cylinder body having an axial bore, a piston slidable in the bore, an output member through which movement of the piston is transmitted and a shipping and installation restraint for holding the output member in a retracted position and which ruptures upon first actuation of the cylinder, one of the body and output member being formed integrally with the shipping and installation restraint which is carried by the other of the body and output member.

2. A hydraulic cylinder according to Claim 1 in which the output member is formed integrally with said shipping and installation restraint.

3. A hydraulic cylinder according to Claim 1 or 2 in which the shipping and installation restraint is at an end of the output member remote from the piston.

4. A hydraulic cylinder according to any of Claims 1 to 3 in which the shipping and installation restraint includes a plurality of radial straps which rupture upon first actuation of the cylinder.

5. A hydraulic cylinder according to any preceding Claim in which a gaiter co-operates with the output member and forms a seal to inhibit entry of foreign matter into the bore, the gaiter extending axially of the output member into the bore.

6. A hydraulic cylinder comprising a cylinder body having an axial bore, a piston slidable in the bore, an output member through which movement of the piston is transmitted and a gaiter which co-operates with the output member and forms a seal to inhibit entry of foreign matter into the bore in which the gaiter extends axially of the output member into the bore.

7. A hydraulic cylinder according to Claim 5 or 6 in which the gaiter extends into a hollow interior of the piston.

8. A hydraulic cylinder according to Claims 5 or 6 in which one end of the gaiter is mounted on an element carried by the body and the other end is mounted on the output member.

9. A hydraulic cylinder according to Claim 8 in which the element forms a stop for the piston.

10. A hydraulic cylinder according to any Claims 5 to 9 in which the element is part of a shipping and installation restraint for the output member.

11. A hydraulic cylinder according to any preceding Claim in which pressure relief means is provided for relieving fluid pressure in the cylinder where the piston moves beyond a predetermined position in the bore.

12. A hydraulic cylinder comprising a cylinder body having an axial bore, a piston slidably in the bore and an output member through which movement of the piston is transmitted during a working stroke in which the relief means is provided for relieving fluid pressure in the cylinder where the piston moves beyond a predetermined position in the bore.

13. A hydraulic cylinder according to Claim 11 or 12 in which the relief means comprises a groove extending axially of the bore.

14. A hydraulic cylinder according to Claim 11 or 12 in which the relief means comprises a port in a wall of the bore.

15. A hydraulic cylinder according to any of Claims 11 to 14 in which resilient means is provided which deforms if the piston moves beyond said predetermined position and which applies a bias to the piston in the opposite direction whereby following relief of the pressure after opening of the relief means by the piston the resilient means urges the piston in an opposite direction so as to close the relief means.

16. A hydraulic cylinder according to Claim 15 in which the resilient means is a wavy washer.

17. A hydraulic cylinder according to Claim 15 or 16 in which the resilient means abuts a stop for the piston.

18. A hydraulic cylinder constructed and arranged substantially as described herein with reference to the accompanying drawings.