GB2267135A

GB2267135A - Master cylinders for hydraulic braking systems

Info

Publication number: GB2267135A
Application number: GB9310504A
Authority: GB
Inventors: Robert Alan Anderson; Philip William Sheriff
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1992-05-21
Filing date: 1993-05-21
Publication date: 1993-11-24
Anticipated expiration: 2013-05-21
Also published as: GB9310504D0; GB9210849D0; GB2267135B

Abstract

A recuperation valve (11) of the centre valve type comprises a valve head (13) at one end of a stem (12), and the stem (12) comprises two parts (12, 25) which are relatively rotatable to adjust the effective length of the stem and the spacing between two abutment members (17, 21) forming abutments for opposite ends of a helical spring (26). Adjusting the length of the stem enables the valve clearance to be set within close limits before the valve is assembled to a respective piston (3, 4). This is achieved by use of a non-circular formation (14) to hold the stem (12) against rotation whilst rotating the part (25) which comprises the head of a screw. <IMAGE>

Description

IMPROVEMENTS IN MASTER CYLINDERS FOR HYDRAULIC BRAKING SYSTEMS This invention relates to improvements in master cylinders for hydraulic braking systems for vehicles, the master cylinders being of the kind in which a piston working in a cylinder bore of a body is adapted to pressurise fluid in a pressure space defined in the bore in front of the piston.

When a recuperation valve for controlling communication between a reservoir for fluid and a pressure space defined in the bore in front of a piston comprises a centre valve, it is essential to be able to set the length of centre valve to achieve a suitable clearance between the valve head carried by a stem which is coupled to the piston, and a complementary seating surrounding a recuperation port when the piston is assembled in the bore.

According to our invention in a master cylinder for an hydraulic braking system, a recuperation valve for controlling in use communication between a reservoir for fluid and a pressure space comprises a stem of which the effective length is adjustable, a valve head carried by one end of the stem, an enlarged head at he opposite end of the stem, and a helical return spring surrounding the head and the stem and caged between first and second axially spaced abutment members, the first member comprises a guide for the head and a stop abutment defining a retracted position for the head, and the second abutment member comprises a guide for the stem and a stop abutment for the enlarged head to determine the effective length of the recuperation valve, in turn determined by adjustment of the effective length of the stem.

Setting the effective length of the valve stem enables the valve clearance to be set accurately during assembly of the piston assembly and before insertion of the piston assembly into the bore.

After setting the recuperation valve is coupled to its respective piston by a connection between the second stop abutment and the piston.

According to a second aspect of the invention, a tandem master cylinder for an hydraulic braking system is provided in which a pedal-operated main piston works in a first part of a cylinder bore of a body to define a first pressure space, a secondary piston works in a second part of the bore in front of the main piston to define a second pressure space, and first and second recuperation valves control in use communication between a reservoir or reservoirs and the first and second pressure spaces, each recuperation valve comprising a stem of which the effective length is adjustable, a valve head carried by one end of the stem, an enlarged head at the opposite end of the stem, and a helical return spring surrounding the head and the stem and caged between first and second axially spaced abutment members, the first member comprising a guide for the head and a stop abutment defining a retracted position for the head, and the second abutment member comprising a guide for the stem and a stop abutment for the enlarged head to determine the effective length of the recuperation valve, in turn determined by adjustment of the effective length of the stem, in which each valve head and its stem may be coupled to its respective piston by means of the second abutment member which may be in the form of a thimble of top hat configuration having an outwardly directed flange which defines the abutment or one end of the return spring, a body which acts as a guide for the stem, and an inwardly directed flange which acts as the abutment for the enlarged head.

The first abutment member is also in the form of a thimble of top hat configuration having an outwardly directed radial flange which defines the abutment for the return spring, a body which forms a guide for the primary recuperation valve head, and an inwardly directed flange forming the abutment for the valve head.

All the components of our piston assembly including the primary and secondary recuperation valves may be assembled together with the valve clearances set before the assembly is inserted into the cylinder bore of the master cylinder body. In such a construction the first abutment member of the primary recuperation valve is coupled to the secondary piston. The piston assembly, when assembled, can be contained within a tube from which it can be transferred into the bore simply by sliding the assembly from the tube and into the bore through its open outer end.

One embodiment of our invention is disclosed in the accompanying drawings in which: Figure 1 is a longitudinal section through a tandem master cylinder of the two-centre valve (CV) type showing the components in a rest position; Figure 2 is a view similar to Figure 1 with both recuperation valves closed; and Figure 3 is a view similar to Figures 1 and 2 but showing the relative positions assumed by the components in a "stroked" or fully actuated position.

The tandem master cylinder illustrated in the drawings comprises a body 1 having a bore 2 which extends longitudinally from an open end to a closed end and is of a constant diameter throughout its axial length. A pedal-operative main piston 3 works in a part of the bore, and a secondary piston 4 works in a part of the bore between the main piston 3 and a wall 5 forming the inner end of the wall The pistons respectively apply pressure to fluid in pressure spaces 7 and 8 which, in the retracted positions of the pistons as shown in Figure 1 of the drawings, are in open communication with a reservoir or reservoirs for fluid through ports 9 and 10 in the wall of the body 1 under the control of respective recuperation valves 11 and lla which are similar in construction and of which each is of the centre valve (CV) type.

The primary CV valve 11 comprises a stem 12 which projects axially from the main piston 3 and at its outer end carries a valve head 13. The stem comprises a non-circular formation 14 projecting from the head 13, and a self-locking screw having an enlarged head 25 and which is screwed into the stem. A sealing member 15 cf a elastomeric material surrounds the threaded member 14 and is trapped between it and a flange 16 at the inner end of the stem 12.

The head 13 is retained within a first abutment member constituted by retainer 17 in the form of a thimble of top hat outline having oppositely directed inner and outer radial flanges 18 and 19 of which the external flange 19 at the inner end of the thimble 17 is a force-fit in a blind bore 20 at the adjacent end of the secondary piston 4, and the inwardly directed flange 18 forms a guide for the stem 12.

In a modification the flange 19 on the thimble 17 may be a slide-fit in the bore 20.

A second abutment member 21 comprising a thimble of top hat outline has an outwardly directed radial flange 22 retained in a recess 23 in the main piston 3 by means of angularly spaced sprag fingers 28 co-operating with a stop shoulder 29 and an inwardly directed inner flange 24 which forms a stop abutment for the enlarged head 25 at the inner end of the stem 12 and which is guided for axial sliding movement in the body of the thimble 21. The head 25 comprises the head of a self-locking screw adapted to be screwed into a bore in the adjacent end of the stem 12 to adjust the effective length of the recuperation valve itself.

A helical return spring 26 surrounding the stem 27 and the head 13 abuts at opposite ends between the outwardly directed flange 19 of the thimble 17 and the outwardly directed flange 22 of the thimble 21.

In the rest position illustrated in Figure 1 of the drawing the head 13 is spaced from a seating 30 at the inner end of a short axial passage 31 in the secondary piston 4 and which is disposed at the innermost end of a radial passage 32 of which the outer end communicates with the port 9 through an annular recess 33 in the wall of the secondary piston 4.

The secondary recuperation valve 11a is of similar construction to the recuperation valve 11 and corresponding components qualified by the suffix 'a' have been applied to corresponding parts. In this construction, however, the outwardly directed flange 19a on the thimble 17a is slidably received in a recess 40 in the wall 5.

The piston assembly, comprising the main piston 3, the secondary piston 4 and the two recuperation valves 11 and lla are assembled together as shown in the drawings. Initially each recuperation valve 11, Ila is assembled on its own in and by the use of a jig or other setting and measuring equipment by holding the stem 12, 12a against rotation, by means of the non-circular formation 14, 14a, and rotating the screw by means of the head 25, 25a. The effective length of the stem, and in consequence, the valve clearance, can be set within close limits.

After assembly each recuperation valve 11, lla is assembled to its respective primary and secondary piston 3, 4. This is achieved by inserting the outer flange 22, 22a of the thimble 21, 21a into the recess 23, 23a until the sprag fingers 28, 28a co-operate with the stop shoulder 29, 29a.

Each valve 11, lla thus forms a dedicated unit with its respective piston 3, 4.

The thimble 17 is inserted into the blind bore 20 in the adjacent end of the secondary piston 4. When this is a force fit the two pistons 3, 4 will be coupled together into a single assembly.

After the components have been assembled to form the piston assembly they may be stored within an open-ended tube from which they can simply be removed by a continuous sliding operation and transferred into the bore 2 as illustrated in Figure 1.

The axial lengths of the short axial passages 31 and 31a are sufficient to accommodate the full length of the non-circular formations 14 and 14a so that, when the master cylinder is actuated and both recuperation valves 11 and 12 are closed as shown in Figure 2 of the drawings, there is a clearance between each formation and the adjacent wall of the respective passage 31, ~31a.

Similarly the lengths of the stems 12 and 12a and the thimbles 21 and 21a are chosen to accommodate the full axial movements of the pistons 3 and 4 into fully advanced positions as shown in Figure 3 of the drawings.

Claims

1. A master cylinder for an hydraulic braking system, in which a recuperation valve for controlling in use communication between a reservoir for fluid and a pressure space comprises a stem of which the effective length is adjustable, a valve head carried by one end of the stem, an enlarged head at the opposite end of the stem, and a helical return spring surrounding the head and the stem and caged between first and second axially spaced abutment members, the first member comprising a guide for the head and a stop abutment defining a retracted position for the head, and a stop abutment for the enlarged head to determine the effective length of the recuperation valve, in turn determined by adjustment of the effective length of the stem.

2. A master cylinder according to claim 1, in which the stem comprises a threaded member and self-locking screw screwed thereto.

3. A master cylinder according to claim 1 or claim 2, in which the first abutment member is in the form of a thimble of top hat configuration having an outwardly directed radial flange which defines the abutment Los the return spring, a body which forms a guide for the recuperation valve head, and an inwardly directed flange forming the abutment for the valve head.

4 A master cylinder according to any of claims 1 to 3, in which the recuperation valve is coupled to a piston by a connection between the second stop abutment and the piston.

5. A method of assembly of a master cylinder according to any of claims 1 to 4, in which the recuperation valve is assembled prior to insertion into a cylinder bore of a master cylinder body.

6. A tandem master cylinder for an hydraulic braking system in which a pedal-operated main piston works in a first part of a cylinder bore of a body to define a first pressure space, a secondary piston works in a second part of the bore in front of the main piston to define a second pressure space, and first and second recuperation valves control in use communication between a reservoir or reservoirs and the first and second pressure spaces, each recuperation valve comprising a stem of which the effective length is adjustable, a valve head carried by one end of the stem, an enlarged head at the opposite end of the stem, and a helical return spring surrounding the head and the stem and caged between first and second axially spaced abutment members, the first member comprising a guide for the head and a stop abutment defining a retracted position for the head, and a stop abutment for the enlarged head to determine the effective length of the recuperation valve, in turn determined by adjustment of the effective length of the stem, in which each valve head and its stem may be coupled to its respeste VQ piston by means of the second abutment member which may be in the form of a thimble of top hat configuration having an outwardly directed flange which defines the abutment or one end of the return spring, a body which acts as a guide for the stem, and an inwardly directed flange which acts as the abutment for the enlarged head.

7. A master cylinder according to claim 6, in which one or both of the stems are screw threaded and have a self-locking screw screwed thereto.

8. A master cylinder according to claim 6 or claim 7, in which one or both of the first abutment members are in the form of a thimble of top hat configuration having an outwardly directed radial flange which defines the abutment for the return spring, a body which forms a guide for the primary recuperation valve head, and an inwardly directed flange forming the abutment for the valve head.

9. A master cylinder according to any of claims 6 to 8, in which the first abutment member of the primary recuperation valve is coupled to the second piston.

10. A master cylinder according to claim 9, in which the first abutment member forms a force fit in a blind bore in the second piston.

11. A master cylinder according to claim 9, in which the first abutment member forms a slide fit in a blind bore in the secondary piston.

12. A master cylinder according to any of claims 6 to 11, in which the recuperation valve is coupled to its respective piston by a connection between the second stop abutment and the piston.

13. A master cylinder according to claim 12, in which the second stop abutment has an outwardly directed radial flange retained in a recess in the main piston.

14. A master cylinder according to claim 12, in which the flange is retained by means of angularly spaced sprag fingers co-operating with a stop shoulder.

15. A method of assembly of a master cylinder according to any of claims 6 to 14, in which the master cylinder is assembled prior to insertion of the master cylinder into the cylinder bore of the body.

16. A master cylinder substantially as described herein with reference to and as illustrated in the accompanying drawings.

17. A method of assembly of a master cylinder substantially as described herein with reference to and as illustrated in the accompanying drawings.