GB2186648A

GB2186648A - A hydraulic cylinder

Info

Publication number: GB2186648A
Application number: GB08703614A
Authority: GB
Inventors: Keith Vernon Leigh Monstevens
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1986-02-18
Filing date: 1987-02-17
Publication date: 1987-08-19
Also published as: GB8703614D0; GB2186648B

Abstract

The hydraulic cylinder comprises a housing 12 comprising first and second tubular portions (14, 16) defining an elongate bore containing a reciprocable cylindrical piston 30. An internal groove 26 is formed in the bore of said housing and contains an annular seal member 28 in sliding engagement with said piston. A pressure chamber 13 is defined in said bore at one end of said piston. A load transmitting member 40 is co-operable with the other end of said piston and a valve 78,80 is provided for filling the pressure chamber with fluid. The housing has a passageway 74 in said first housing portion for connecting the pressure chamber to means for filling the pressure chamber. The passageway is adjacent one end of the housing and a mounting flange 56 is provided on the opposite end of the housing. <IMAGE>

Description

SPECIFICATION Hydraulic cylinder The present invention relates to a hydraulic cylinder structure and is particularly but not exclusively concerned with a hydraulic cylinder for operating the clutch, brakes or transmission of a motor vehicle.

Hydraulic cylinders, such as master cylinders and slave cylinders of hydraulic control systems for operating the clutch, the transmission or the brakes of a motor vehicle, for example, are conventionally made of a housing cast of metal or of a plastics material provided with a cylindrical bore in which is disposed a reciprocable piston. The piston is conventionally provided with at least one groove in which is placed an annular seal of elastomeric material which prevents leakage of hydraulic fluid from the high pressure side of the piston to the low pressure side.When the structure of the hydraulic cylinder is that of a master cylinder, an input member in the form of a rod is is attached to the free end of the piston for reciprocal displacement of the piston within the cylinder and for causing flow of hydraulic fluid from and into the pressure side of the cylinder on the other end of the piston. In structures adapted to operate as a slave cylinder, hydraulic fluid is introduced via an appropriate conduit from the outlet of the master cylinder to an inlet into the slave cylinder on one end of the piston and an output member is attached to the other end of the piston for operating a component such as the gear shift rail of a transmission, the throw-out bearing of a mechanical clutch, or the wheel brake mechanism of a motor vehicle, for example.

An object of the invention is to provide an improved hydraulic cylinder and, according to the invention, there is provided a hydraulic cylinder comprising a housing in the form of a tubular member having an elongate bore containing a reciprocable cylindrical piston, the housing comprising first and second portions attached end to end so as to define an internal groove therebetween, a sealing element in said groove in sliding engagement with the piston, a pressure chamber in said bore at one end of the piston, said first housing portion defining a passageway adjacent one end of the housing for connecting said pressure chamber to means for filling the pressure chamber with fluid, said housing including support means adjacent the opposite end by which the housing can be connected to a support, and a load transmitting member co-operable with the other end of the piston.

Such an arrangement provides a simple structure which is easy to manufacture and which provides a convenient location for the seal between the two housing portions. The housing may advantageously be formed from plastics material but, unlike prior proposals, it is unnecessary to provide a metallic tubular liner within the bore of the housing as the seal does not rub along the wall of the bore as in the case where the piston itself carries the seal. The two housing portions may be interconnected simply, eg by a bonding agent or by ultra-sonic welding.

In one embodiment, the support means is on the second housing portion and in another embodiment is on part of the first housing portion which, for example, contains a section of the second housing portion. Preferably, the first and second housing portions are tubular and the piston is slidable within both housing portions.

The internal groove may be defined against a juncture between the first and second housing portions.

In one embodiment one of the first and second housing portions has an enlarged bore end portion and the other housing portion is secured in said enlarged bore end portion.

That particular manner of forming the housing is simple and effective and facilitates simple location of the seal as the groove may be defined between surfaces of the first and second housing portions within said enlarged bore end portion. Preferably the groove is defined by first and second surfaces of said one housing portion and one surface of the other housing portion. Said one surface may be an annular end surface of said other housing portion with the first and second surfaces being an annular end surface and a cylindrical surface of said one housing portion. Said one housing portion may comprise either the aforesaid first housing portion which defines said passageway or the second housing portion.

The means for filling the pressure chamber with fluid may be a reservoir, eg in the case of the cylinder being a master cylinder. The reservoir may be integral with the first portion of the housing. Such an arrangement is particularly applicable where the housing is made of plastics material.

Valve means may be operable by movement of the piston for controlling flow of fluid between the pressure chamber and passageway.

The valve means may include a member carried by a piston. Preferably the member carried by the piston, is a plunger reciprocably mounted on the piston, the plunger having a valve head mounted on one end thereof engageable with a valve seat of the valve means formed at one end of said passageway. Biasing may be provided for urging the valve head towards the valve seat, means for limiting the movement of the valve head being provided so as to hold the valve head clear of the valve seat when the piston is in one extreme position whereby said valve head engages the valve seat when the piston is displaced away from said extreme position. The piston may be formed with a longitudinal bore in alignment with the plunger for allowing the plunger to retract in said longitudinal bore.

Said means for filling the pressure chamber with fluid may be a master cylinder having a piston for displacing said fluid from said master cylinder to the pressure chamber. Such an arrangement lends itself to, eg a clutch actuating master and slave cylinder arrangement for a motor vehicle.

Hydraulic cylinders in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic longitudinal section of a hydraulic cylinder of the master cylinder type according to the present invention; Figure 2 is a view similar to Fig. 1 but showing the hydraulic cylinder in operation.

Figure 3 is a partial view of a modification thereof; Figure 4 is a schematic longitudinal section through a hydraulic cylinder of the slave type according to the present invention; Figure 5 is a view similar to Fig. 1 but showing the modified structure for a master cylinder; and Figure 6 illustrates a slave cylinder version of a modification of the invention shown at Fig. 5.

Referring to the drawings, and to Fig. 1 more particularly, a hydraulic cyinder 10, of the master cylinder type and according to the invention, comprises a housing 12 made preferably of two separate tubular plastic moldings, forming respectively, a pressure chamber cylinder portion 14 surrounding the cylinder pressure chamber 13, and a rear cylinder, or piston guiding, portion 16. The pressure chamber cylinder portion 14 has a closed end 17 and an open end provided with a flange 18 having a peripheral cylindrical surface 20.

The flange peripheral cylindrical surface 20 is fitted within an annular collar 22 formed internally in a corresponding flange 24 at an end of the cylinder rear portion 16. The peripheral flange cylindrical surface 20 and the internal surface of the annular collar 22 are attached to each other by an appropriate bonding agent, or by ultra-sonic welding. Alternatively, a bayonet mount or a screw-thread joint may be provided for attaching the rear cylinder portion 16 to the pressure chamber cylinder portion 14.

The end flange 18 of the pressure chamber cylinder portion 14 has an annular end face 23 and the end flange 24 has an annular end face 25, spaced apart from the annular end face 23, defining the sidewalls of an annular recess or groove 26 in which is installed a static annular seal member 28 made of elastomeric material, the portion of the internal surface of the collar 22 between the annular end faces 23 and 25 defining the bottom of the groove 26. A piston 30 is slidably disposed in the bore 32 of the cylinder housing 12, and is normally urged by a coil spring 34, installed between the closed end 17 of the bore 32 in the pressure chamber 13 and the corresponding end of the piston 30, against a split spring ring retainer 36 installed in an internal groove 38 proximate the open end of the cylinder rear portion 16.Although it could also be made of plastic, the piston 30 is preferably metallic.

An input rod 40 has a partially spherical end 42 disposed in a hemispherical cavity 44 formed in the end face of the piston 30, appropriate means being provided for maintaining the partially spherical end 42 of the rod 40 in the hemispherical cavity 44 such as, for example, a cylindrical collar 46, formed integrally at the end of the piston 30, surrounding a reduced diameter portion 48 of the rod 40 and crimped as shown at 50, so as to at least partly engage into the reduced diameter portion 48 of the rod 40. The end of the rod 40 is provided with a crimped on, or otherwise fastened, clevis head 52 for attachment to an input member such as a lever or pedal, not shown. Introduction of dirt into the cylinder bore 12 from the open end of the rear cylinder portion 14 is prevented by an appropriate elastomeric boot 54.The cylinder portion 16 also has an integral mounting flange 56 for installing the cylinder 10 at an appropriate location, with the input rod 40 projecting through an opening in a bulkhead or the floorboard, not shown, of a motor vehicle, for example.

A reservoir 58 of hydraulic fluid is molded integrally with the cylinder portion 14. The reservoir 58 is separated into two chambers by a cup-shaped flexible diaphragm 60. The chamber within the cup-shaped flexible diaphragm 60 defines an air chamber 62 vented to the atmosphere through a vent port 64 in a cover cap 66 screwed or otherwise fastened, over the open end of the reservoir 58, the cup-shaped diaphragm 60 having an integral annular flange 68 squeezed between the lower surface of the cap 66 and the edge 70 of the reservoir open end. A hydraulic fluid chamber 72 is formed below the cup-shaped diaphragm 60. The hydraulic fluid chamber 72 is placed in fluid communication with the cylinder pressure chamber 13 via a passageway 74, transverse to the axis of the cylinder bore 32, and a longitudinal passageway 76. The longitudinal passageway 76 terminates in the cylinder pressure chamber 13 as a port 77 presenting an annular valve seat 78 engageable by the face 79 of a valve head 80 in the form of an elastomeric disk 81 attached to a face of a metallic flanged washer 82 mounted on the end of a rod or plunger 84, the valve head 80 being attached on the end of the rod or plunger 84 by way of a screw or rivet 85.

The other end of the rod or plunger 84 has an enlarged head 86 which is disposed behind a cup-shaped clip 88 press-fitted in a cylindri cal cavity 90 formed at the free end of the piston 30. The clip 88 has a central aperture 92 for passage therethrough of the rod 84, and a coil spring 94, which is disposed surrounding the rod 84 and held slightly in compression between the clip 88 and the metallic washer 82 backing the valve disk 81, tends to urge the face 79 of the valve disk 81 in engagement with the valve seat 78.

Prior to operation of the hydraulic apparatus of which the master cylinder 10 is a component, the reservoir hydraulic fluid chamber 72, the passageways 74 and 76, and the cylinder pressure chamber 13, and other components of the apparatus, are appropriately filled with hydraulic fluid and purged of air. In the position indicated at Fig. 1, in view of the length of the plunger or rod 84, the face 79 of the valve head 80 is held away from the port valve seat 78 by the rod 84, due to the enlarged head 86 of the plunger or rod 84 abutting against the rear surface of the clip 88.The cylinder pressure chamber 13 is thus in fluid communication with the hydraulic fluid chamber 72 in the reservoir 58, hydraulic fluid filling the cylinder pressure chamber 13 and being drawn from or returned to the reservoir hydraulic fluid chamber 72 at the end of the return stroke of the piston 30 to keep the apparatus constantly filled with hydraulic fluid and compensate for losses in fluid and contraction and expansion of the fluid due to temperature changes. As soon as the piston 30 is displaced forwardly by the piston input rod 40, the valve head face 79 is caused to engage the valve seat 78, and to remain engaged therewith under the action of the coil spring 94.The piston 30 has a longitudinal bore 96 enabling the rod enlarged head 86 and a portion of the plunger or rod 84 to retract within the piston 30 in the course of the stroke of the piston 30, Fig. 2, with the result that the hydraulic fluid in the cylinder pressure chamber 13 between the piston end and the cylinder end 1 7 is caused to flow through an outlet passageway 98 placed in communication with an operative component, such as a slave cylinder, by an appropriate conduit 100. In the course of a pressure stroke of the piston 30, the annular seal 28 in the cylinder internal groove 26 effectively prevents flow of hydraulic fluid around the periphery of the piston 30 from the pressure chamber 13 to the ambient.

Instead of forming an integral part of the cylinder portion 14, the fluid reservoir 58 may be remotely installed, as shown at Fig. 3. In such a structure, the reservoir 58 of hydraulic fluid is provided with an integral bottom wall 102 through which is formed a passageway 74' leading into a fitting 104 connected to the passageway 76 of the master cylinder via an appropriate fitting 106 and a flexible conduit 108.

Fig. 4 illustrates an example of slave cylinder 110 having a structure utilizing the same principle of seal-less piston as the master cylinder 10 of Fig. 1. The slave cylinder 110, Fig. 4, has a housing 112 made of two plastic moldings forming a pressure chamber cylinder 114 and a cylinder rear portion 16, the latter being identical to the cylinder rear portion 16 of the master cylinder 10. The slave cylinder 110, Fig. 4, is provided with a modified cylindrical metallic piston 130 which, for the sake of simplifying production, may generally be shaped as the piston 30 of the master cylinder 10 but, preferably, without any longitudinal bore.

The piston 130 engages at one end a pushrod 140 having a generally hemispherical end 142 engaged in a corresponding hemispherical cavity 144 formed in the end of the piston, the other end of the pushrod 140 having, for example, a hemispherical portion 140 in engagement with, for example, a clutch release mechanism 148 such as the fork lever engaged with a clutch release bearing carrier, as is well known in the art.The piston 130 is shown at Fig. 4 in the position generally occupied by the piston of the slave cylinder 110 which corresponds to full release of a motor vehicle clutch, for example, as a result of hydraulic fluid having been transferred from the pressure chamber 13 of the master cylinder 10, Figs. 1-2 by the displacement of the master cylinder piston 30 causing hydraulic fluid to be transferred from the pressure chamber 13 of the master cylinder 10 to the pressure chamber 113 of the slave cylinder 110, via the conduit 100 and the passageway or port 198. A coil spring 134 disposed in the pressure chamber 113 between the piston 130 and the cylinder end wall 117 constantly biases the piston 130 and the pushrod 140 towards the clutch release mechanism 148.

Referring now to Figs. 5 and 6 which represent modifications of the invention, still utilizing the same principle of a seal-less piston structure for a hydraulic cylinder, there is more specifically illustrated at Fig. 5 a master cylinder structure 210 and at Fig. 6 a slave cylinder structure 310. The housing 212, Fig. 5, of the master cylinder 210 comprises a generally tubular plastic molding 214 having an enlarged diameter portion 216 such as to define an annular shoulder 218 between the bore 32 of the housing 212 and an enlarged bore 220 formed within the enlarged diameter portion 216 of the tubular member 214. A plastic sleeve 222 is installed within the enlarged bore 220.An annular abutment 224 formed in the surface of the bore 220 engages with a corresponding annular abutment 226 on the periphery of the sleeve 222, and acts as a spacing means limiting the introduction of the sleeve 222 within the enlarged diameter portion 216. The annular groove 26 in which is installed the static annular seal member 28, is thus formed between the annular shoulder 218 of the tubular member 214 and the end face 228 of the sleeve 222. The peripheral surface of the sleeve 222 in engagement with the surface of the enlarged diameter bore 220 is appropriately bonded thereto by means of an appropriate bonding agent, or by ultrasonic welding.

A similar arrangement is used for forming the annular recess or groove 26 in which is disposed the annular seal 28 in the structure of the slave cylinder 310 of Fig. 6. The slave cylinder 310 has a housing 312 provided with an enlarged diameter portion 316 in which is fitted a sleeve 322, a pair of abutment shoulders 324 and 326, one disposed in the bore 320 of the housing enlarged diameter portion 316 and the other on the peripheral surface of the sleeve 322, limiting the engagement of the sleeve 322 within the bore 320. The groove 26 is thus formed between the shoulder annular surface 318, at the junction between the bore 32 of the housing 312 and the bore 320 of the enlarged portion 316, and the annular end face 328 of the sleeve 322. The annular elastomeric seal member 28 is disposed in the groove 26 in engagement with the peripheral surface of the reciprocable piston 330.The piston 330 has one end, beyond which is disposed the pressure chamber 313, provided with a cavity or blind bore 332 in which is disposed the end of a weak biasing spring 334 having its other end disposed around a boss 336 formed on the end wall 317 of the cylinder housing 312. The other end of the piston 330 has a recess 344 of generally concave hemispherical shape in which is engaged the hemispherical end 342 of the pushrod 340, the other end 346 of which is also preferably hemispherically shaped in engagement with, for example, the clutch release member 148. The biasing spring constantly urges the piston 330 and the pushrod 340 towards the clutch release mechanism 148.The position of the piston 330, as illustrated at Fig. 6, corresponds substantially to the position occupied by the piston in the clutch full release position with the slave cylinder pressure chamber 312 filled with hydraulic fluid transferred through the passageway or port 398, via the conduit 100, from the pressure chamber 13 of a master cylinder such, for example, as the master cylinder 10 of Figs. 1-2 or 210 of Fig. 5.

It is to be noted that in the fully engaged position of the clutch mechanism, a spring force is exerted on the end 146, Fig. 4, or 346, Fig. 6, of the slave cylinder 110 or 310, which maintains the rod 140 or 340 with its respective ends 142 or 342 fully engaged in the piston end cavity 144 or 344, the majority of the hydraulic fluid in the pressure chamber 113 or 313 having been returned to the master cylinder 10 or 210 via the conduit 100, as a result of the master cylinder piston 30 having been returned to its home position, as illustrated at Fig. 1 and Fig. 5.

The portions 14 and 16 of the housing 12 constitute the aforesaid first and second housing portions.

Claims

1. A hydraulic cylinder comprising a housing in the form of a tubular member having an elongate bore containing a reciprocable cylindrical piston, the housing comprising first and second portions attached end to end so as to define an internal groove therebetween, a sealing element in said groove in sliding engagement with the piston, a pressure chamber in said bore at one end of the piston, said first housing portion defining a passageway adjacent one end of the housing, for connecting said pressure chamber to means for filling the pressure chamber with fluid, said housing including support means adjacent its opposite end by which the housing can be connected to a support, and a load transmitting member cooperable with the other end of the piston.

2. A hydraulic cylinder according to Claim 1 in which the support means is on the second housing portion.

3. A hydraulic cylinder according to Claim 1 in which the support means is on a part of the first housing portion which contains a section of the second housing portion.

4. A hydraulic cylinder according to any preceding claim in which the first and second housing portions are tubular and the piston is slidable within both housing portions.

5. A hydraulic cylinder according to any preceding claim in which the internal groove is defined adjacent a juncture between the first and second housing portions.

6. A hydraulic cylinder according to any preceding claim in which one of the first and second housing portions has an enlarged bore end portion and the other housing portion is secured in said enlarged bore end portion.

7. A hydraulic cylinder according to Claim 6 in which the groove is defined between surface of the first and second housing portions within said enlarged bore end portion.

8. A hydraulic cylinder according to Claim 7 in which the groove is defined by first and second surfaces of said one housing portion and one surface of the other housing portion.

9. A hydraulic cylinder according to Claim 8 in which the said one surface is an annular end surface of said other housing portion and the first and second surfaces comprise an annular end surface and a cylindrical surface of said one housing portion.

10. A hydraulic cylinder according to any of Claims 6 to 9 in which said one housing portion comprises the first housing portion which defines said passageway.

11. A hydraulic cylinder according to any preceding claim in which said means for filling the pressure chamber with fluid is a reservoir.

12. A hydraulic cylinder according to Claim 11 in which the reservoir is integral with said first portion of the housing.

13. A hydraulic cylinder according to Claim 11 or 12 in which valve means is operable by movement of the piston for controlling flow of fluid between the pressure chamber and passageway.

14. A hydraulic cylinder according to Claim 13 in which the valve means include a member carried by the piston.

15. A hydraulic cylinder according to Claim 14 in which the member carried by the piston is a plunger reciprocably mounted on the piston, the plunger having a valve head mounted on one end thereof engageable with a valve seat of the valve means formed at one end of said passageway.

16. A hydraulic cylinder according to Claim 15 including biasing means for urging said valve head towards valve seat and means for limiting the movement of the valve head so as to hold the valve clear of the valve seat when the piston is in one extreme position whereby said valve head engages the valve seat when the piston is displaced away from said extreme position.

17. A hydraulic cylinder according to Claim 15 or 16 in which the piston is formed with a longitudinal bore in alignment with the plunger for allowing the plunger to retract in said longitudinal bore.

18. A hydraulic cylinder according to any preceding claim in which said first housing portion defines an outlet port for fluid adjacent said one end.

19. A hydraulic cylinder according to any of Claims 1 to 10 in which said means for filling said pressure chamber with fluid is a master cylinder having a piston for displacing said fluid from said master cylinder to said pressure chamber.

20. A hydraulic cylinder constructed and arranged substantially as described herein with reference to Figs. 1 and 2, Fig. 3, Fig. 4, Fig.

5 or Fig. 6 of the accompanying drawings.