GB2135412A

GB2135412A - Master cylinder for hydraulic brake systems of vehicles

Info

Publication number: GB2135412A
Application number: GB08402896A
Authority: GB
Inventors: Hans-Dieter Reinartz; Helmut Steffes
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1983-02-17
Filing date: 1984-02-03
Publication date: 1984-08-30
Also published as: FR2541209B1; FR2541209A1; DE3305442A1; GB2135412B; GB8402896D0

Abstract

A master cylinder comprises a piston (3) slidably accommodated in a bore (2) in the housing (1) and forming with the cylinder bore (2) a working chamber (4) which chamber is in communication with first and second passages (5, 6) for connection to a user circuit and to a fluid supply reservoir (7). A return spring (8) biases pistons (3) and (20) away from the bottom part (9) of the housing until piston (20) abuts a stop (10). A recuperation valve governs the flow through the second passage (6) and is formed by a radially spaced tubular member (11) with an outwardly extending portion (16) which is slidable in the cylinder bore (2) and formed at one end with an annular valve ring (12) to cooperate with an annular seat (13) which is situated in a plane which extends transversely relative to the master cylinder. A flange (17) on the piston (3) holds the valve open, when the master cylinder is not actuated to establish an open connection between the passages (5, 6) and a spring (15) moves the tubular member (11) in the closing direction, when the piston (3) is simultaneously displaced in the direction of the bottom part (9) of the master cylinder. <IMAGE>

Description

SPECIFICATION Master cylinder for hydraulic brake systems of vehicles The present invention relates to a master cylinder, in particular for hydraulic brake systems of vehicles.

Some master cylinders have a housing whose cylinder bore is open on one side, with a piston slidably accommodated in the housing and forming with the cylinder bore a working chamber which chamber is in communication with first and second channels for connection to a user circuit and to a supply reservoir for pressure fluid, with a return spring which biases the piston away from the bottom part of the housing against a stop, and with a valve for governing the flow of the pressure fluid through the second channel, the said valve being formed by a tubular member which is longitudinally slidably arranged with clearance in the cylinder bore that constitutes the working chamber, which tubular member carries at one end a valve ring to cooperate with an annular seat which is situated in a plane which extends transversely relative to the master cylinder, with means being provided which will move the tubular member, when the master cylinder is not actuated, to adopt a position in which the valve ring is spaced from its seat so that there is established an open connection between the channels, as well as with means to move the tubular member in the closing direction, while the piston is simultaneously displaced in the direction of the bottom part of the master cylinder.

There is known already a master cylinder for hydraulic brake systems of vehicles (German printed and published patent application 20 26 756), wherein an axially slidably supported tubular member which serves as a valve device comprises two sealing rings, one of which is provided at the end face of the tubular member and cooperates with a valve seat at a step of the master cylinder bore, while the other sealing ring acts in a radial direction and encompasses the tubular member. A supply bore, which establishes a connection between the supply reservoir and a working chamber, terminates in a radial direction into the working chamber in the area of a head part of the tubular member, a port of said supply bore being disposed between the two sealing rings.A working piston of this known master cylinder bears via a compression spring against the bottom part of the master cylinder, the said compression spring being accommodated within the working chamber itself. It is a disadvantage of this known master cylinder that the size of the working chamber has to be dimensioned such as to allow accommodation of the piston return spring, for which reason it is not possible to obtain a small and light-weight design of the known master cylinder.

The present invention seeks to provide a master cylinder which does not have the beforementioned disadvantages. The invention may include sealing assemblies of particularly long life and preferably wetted by fluid, the said master cylinder affording inexpensive manufacture and manufacturability of its cylinder bore without microfinish, in addition. Furthermore, the friction forces caused by seals are desired to be low so that, if the master cylinder is eventually of tandem-type design, the pressure differences between both hydraulic circuits occurring during operation will remain as smali as possible.

Finally, all requisite springs are to be held and guided in a buckling-resistant manner despite a shortest possible construction of the entire aggregate.

According to the present invention, the tubular member has an outwardly extending portion in sliding contact in the cylinder bore.

The outwardly extending portion may be cranked outwardly from the tubular member.

Preferably, the valve ring, which extends axially to the seat with the channel terminating into the working chamber, is arranged at the inside of the cranked portions abutting on the cylinder bore and is anchored in apertures or recesses of the tubular member by axially extending tongue-shaped portions.

To have available sufficient spacs for the tubular member, the piston which extends into tcie working chamber is designed as a plunger piston, the tubular member embracing the piston and being limited in its axial movement by a flange that is provided in the area of the end face of the piston.

Advantageously, the tubular member at its end nearest to the piston push rod is provided with a radially inwardly extending crank, which crank, in the piston's initial position, abuts the flange due to the spring acting upon the tubular member in the closing sense.

In a master cylinder design for two hydraulic circuits, a floating piston is provided downstream of the plunger piston which first piston is supported slidably in a second portion of the cylinder bore in a sealing relationship therewith, the said plunger piston comprises an anchor which extends towards the bottom part and by which it enters a blind-end bore of the floating piston, while the free end of the anchor grips behind a lug, a projection or a retaining ring on the floating piston and retracts the floating piston into its initial position during the return movement of the plunger piston.In a preferred embodiment of the dual-circuit master cylinder, the return spring embraces the end of the plunger piston, which is nearest to the pedal and projects from the cylinder housing, and is supported at one end on a collar or plate arranged on the piston, and on the cylinder housing or a lock ring coupled to the cylinder housing, at its other end. Preferably in this arrangement, the diameter of the end of the plunger piston nearest to the working chamber corresponds to the diameter of the floating piston, while the sealingly guided portion of the plunger piston has an external diameter slightly smaller than that of the lock ring which closes the cylinder bore on the pedal side.

In a particularly inexpensive design of a dual circuit master cylinder, the cylinder housing has a first housing portion which comprises the bottom part and which receives a working chamber for a floating piston designed as plunger piston, and a second housing portion which contains a longitudinal through-bore for the pedal-actuated plunger piston, with both housing portions being rigidly interconnected, for instance screwed or welded, and including a seal in the area of the connecting portion for the floating piston to extend through, the latter piston reaching up to the working chamber for the pedal-actuated plunger piston.To this effect, the floating piston comprises favourably a flange at its end facing the bottom part, behind which flange one end of a tubular member is gripping, the other end whereof carries at its end face a valve ring which is in abutment on the bottom part in the pressure phase and which closes a channel that is designed as a supply bore and terminates in an axial direction into a working chamber.

In order than the invention and its various other preferred features may be understood more easily, some embodiments thereof will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a longitudinal cross-section through a tandem master cylinder suitable for the generation of largely identical pressures in both operating circuits; Figure 2 is a perspective view of the tubular member of the tandem master cylinder in Figure 1, and Figure 3 is a longitudinal cross-section through a tandem master cylinder whose cylinder housing is of bipartite design and which serves to generate different volumes for both hydraulic circuits.

The master cylinder of Figure 1 has a housing portion 1 containing a cylinder bore 2, 44, the said cylinder bore being designed as a stepped bore, a plunger piston 3 which is held and guided in a lock ring 27, on the one hand, and which, on the other hand, enters via an anchor 22 with its free end 24 into a biind-end bore 23 which latter is contained in a floating piston 20 that is longitudinally slidably arranged in the smaller-diameter cylinder bore 44. and is finally composed of a tubular member 11 having a crank 19 close to the pedal which abuts a ring 14 in the initial position of the plunger piston 3.The ring 14 bears in turn against a flange 17 formed adjacent the end face 18 on the plunger piston 3, while a tubular member 11 is provided at its end close to the floating piston 20 with radial cranks 1 6 encompassing a sealing ring 1 2 which controls the pressure fluid flow through a channel 6. The channel 6 provides a connection from a supply reservoir 7 to a working chamber 4.The working chamber 4 in front of the plunger piston 3 communicates via a channel 5 with a user circuit, whilst a working chamber 76 in front of the floating piston 20 is connected via a channel 77 to a supply reservoir 65, on the one hand, and via a channel 78 to a second user circuit, on the other hand. Siidability of the floating piston 20 in a longitudinal direction is limited by a stop 10 which is designed as a screw bolt and is screwed into the housing portion 1 , with its end that extends into the cylinder bore 21 projecting into a corresponding recess 79 in the periphery of the floating piston.The largest diameter a of the plunger piston 3 corresponds to diameter b of the cylinder bore 44 for the floating piston 20, so that the plunger piston 3 is able to plunge into the cylinder bore 44 when it is displaced in the direction of the bottom part 9 of the housing portion 1. The diameter c of the plunger piston 3 is dimensioned such that the stop ring 1 4 is slidable on the periphery of the plunger piston 3, on the one hand, while, in its end position illustrated in Figure 1, it strikes against the flange 1 7 of the plunger piston 3, on the other hand. The end of the plunger piston 3 nearest to the pedal is provided with a plate 26, bearing against which is a return spring 8 whose end nearest to the master cylinder abuts on a step of the lock ring 27.

Upon actuation of the master cylinder according to Figure 1, first the plunger piston 3 will be moved in the direction of the working chamber against the force of the spring 1 5, until the valve ring 12 of the tubular member 11 covers the channel 6 so that pressure can develop in the working chamber 4 which propagates via the channel 5 to a user circuit. In response to pressure build-up in the working chamber 4, the floating piston 20 is moved in the actuating direction so that the seal 64 overrides the channel 77 and pressure is allowed to develop in the working chamber 76 which propagates via the channel 78 to a user circuit. Upon failure of the user circuit connected to the channel 78, the floating piston 20 moves so far in the direction of the bottom part 9 until its end face 21 abuts on the bottom part 9 and pressure can develop in the user circuit connected to the channel 5.It is evident that in this case the plunger piston 3 performs a stroke movement in the direction of the bottom part 9 which is large enough to permit insertion of the plunger piston 3 into the cylinder bore 44. When performing a return movement in the direction of the pedal (not illustrated), the plunger piston 3 is driven by the return spring 8, and, via its anchor 22 and its free end 24, respectively, the plunger piston 3 will retract the floating piston 20 into its initial position illustrated in Figure 1, since the enlarged free end 24 of the anchor 22 abut on a retaining ring 25, in consequence whereof it cannot be drawn out of the blind-end bore 23 of the floating piston 20.

In the stepped tandem master cylinder illustrated in Figure 3, a plunger piston 32 is sealingly held and guided in a lock ring 67 which, in turn, is screwed to a housing portion 33 which, in turn, is welded to a housing portion 31: In the area of its end face 71, the plunger piston 32 is embraced by a tubular member 52 whose radially inwardly bent edge or crank 72 abuts a stop ring which, in turn, bears against a flange 53.The plunger piston 32 is coupled, via a compression spring 80, to a floating piston 30 which is held and guided by a spacer 81 that is arranged in a connecting portion 36 between the two housing portions 31 and 33 in a cylinder bore 34, 43. The intermediate floating piston 30 comprises a flange 39 abutting on which is a radially inwardly extending crank of a tubular member 40, the tubular member securing in the area of its cranks 68 a valve ring which controls the passage of the pressure fluid at a channel 42. A tubular member 52 of similar design grips with its radial crank 72 behind a stop ring which is slidably supported on the plunger piston 32 and which bears against a flange 53 in the initial position of the plunger piston.The tubular member 52 is provided with cranks 55 and further comprises a valve ring 51 which controls the passage of the pressure fluid in the area of a channel 45. Seals 37, 38 provided in the area of the spacer 81 isolate working chambers 29,35 hermetically from one another, with a radially extending channel 82 in the spacer 81 ensuring that these seals 38, 37 remain permanently wetted by the pressure fluid.

Upon actuation of the tandem master cylinder illustrated in Figure 3, the plunger piston 32 will be moved in the direction of the bottom part 28, while a spring 54 which is clamped in between the lock ring 67 and the crank 55 of the tubular member 52 ensures that the tubular member abuts with its valve ring 51 on a seat 50 and covers the channel 45 so that pressure may develop in the working chamber 35 which propagates via the channel 46 to a user circuit.

The pressure build-up in the working chamber 35 causes the floating piston 30 to move in the direction of the bottom part 28, while the compression spring 83 ensures that the tubular member 40 covers the channel 42 with its valve ring 41 , thereby enabling pressure to develop in the working chamber 29, too, which pressure propagates via a channel 56 to a second user circuit. The compression spring 80 makes provisions that both valves close simultaneously, prior to the development of pressure in the working chamber 35.

In the master cylinders shown in Figure 1 and 3, all seals 63, 64, 66 and 37, 38, 62, respectively, serving to seal the piston 3, 20 and 30, 32, respectively, are wetted by the pressure fluid so that premature wear is avoided and no appreciable differential pressures are allowed to develop in the working chambers 4, 76 and 35, 29, respectively, on account of high friction forces in the area of the seals. To guide the piston 3 and 32, in their regions near to the pedal, merely the bottom part 27 and 67, respectively, is provided with a particularly short, precisely machined bore; the working chamber 4 and 35, respectively, in front of the piston 3 and 36, respectively, designed as a plunger, is provided with an unfinished cylinder bore 2 or 34, respectively.As is shown in the illustrations, the tandem master cylinder can be designed in a stepped fashion particularly easily, i.e. it can be designed such that the floating piston is of smaller diameter than is the push-rod piston (the piston close to the pedal) respectively. The valve devices 6, 1 2, 1 3 and 45, 50, 51 and 42, 41, 74, respectively, are designed such as to allow the tandem master cylinders described to be employed in brake systems with an anti-skid device. Finally, an advantage of the valve devices as shown in Figures 1 and 3 is that these valve devices are capable of sucking fluid upon the occurrence of pressure below atmospheric pressure in the hydraulic circuit so that, in the event of lack in volume, pressure fluid will be topped up during the backstroke of the piston. The return spring 8, 48 for the plunger piston 3, 32 respectively, which spring is located outside the housing, enahles a flanged connection of the tandem master cylinder to a vacuum booster in a space-saving manner, the special ratio of length:diameter of the return springs, 8, 48 being determined such as to reliabily preclude buckling of the return springs during the working stroke.

Claims

1. A master cylinder, in particular for hydraulic brake systems of vehicles, with a housing (1 or 31, 33) whose cylinder bore (2, 44 or 34, 43) is open on one side, with a piston (3 or 32) slidably accommodated in the housing (1 or 31, 33) and forming with the cylinder bore (2 or 34) a working chamber (4 or 35) which chamber is in communication with first and second channels (5, 6 or 45, 46) for connection to a user circuit and to a supply reservoir (7 or 47) respectively for pressure fluid, with a return spring (8 or 48) which biases the piston (3 or 32) away from the bottom part (9 or 28) of the housing against a stop (10 or 49), and with a valve 6,12,13 or 45,50,51) for governing the flow of the pressure fluid through the second channel (6 or 45), the valve being formed by a tubular member (11 or 52) which is longitudinally slidably arranged with clearance in the cylinder bore (2 or 34) that constitutes the working chamber (4 or 35), which tubular member (11 or 52) carries at one end a valve ring (12 or 51) to cooperate with an annular seat (13 or 50) which is situated in a plane which extends transversely relative to the master cylinder, with means (17 or 53) being provided which will move the tubular member (11 or 52), when the master cylinder is not actuated, to adopt a position in which the valve ring (12 or 51) is spaced from its seat (13 or 50) so that there is established an open connection between the channels (5, 6 or 45, 46), as well as with means (15 or 54) to move the tubular member (11 or 52) in the closing direction, while the piston (3 or 32) is similtaneously displaced in the direction of the bottom part (9 or 28) of the master cylinder characterised in that the tubular member (11 or 40, 52) has an outwardly extending portion (16 or 55, 68) in sliding contact in the cylinder bore (2 or 34, 43).

2. A master cylinder as claimed in claim 1, characterised in that the outwardly extending portion (16 or 55, 68) is cranked radially outwardly from the tubular member (11).

3. A master cylinder as claimed in claim 1 or 2, characterised in that the valve ring (12 or 41,51) which extends axially to the seat (13 or 50, 74) is arranged at the inside of the portions (16 or 55, 68) of the tubular member (11 or 40, 52) that abut on the cylinder bore (2 or 34, 43), and is anchored in apertures or recesses (70) of the tubular member (11 or 40, 52) by means of axially extending tongue-shaped portions (69), the second channel (6 or 42, 45) terminating in the working chamber (4 or 29, 35) in the area of the seat (13 or 50,74).

4. A master cylinder as claimed in claim 1,2 or 3, characterised in that the piston (3 or 32) which extends into the working chamber (4 or 35) is actuated by the push rod and is designed as a plunger piston, and in that the tubular member (11 or 52) partially embraces the piston (3 or 32), while it is limited in its axial movement by a flange (17 or 53) provided in the area of the end face (18 or 71) of the piston (3 or 32).

5. A master cylinder as claimed in any one of claims 1 to 4, characterised in that the tubular member (11 or 52) at its end nearest to the push rod is provided with a radially inwardly extending crank (1 9 or 72) which crank abuts the flange (1 7 or 53) in the piston's initial position due to the spring (15 or 54) acting upon the tubular member (11 or 52) in the closing sense.

6. A master cylinder as claimed in any one of the preceding claims, characterised in that connected downstream of the plunger piston (3 or 32) is a floating piston (20 or 30) which is slidably supported in a second portion of the cylinder bore, which plunger piston (3 or 30) comprises an anchor (22 or 58) which extends towards the bottom part (9 or 28) and by which it enters a blind-end bore (23 or 60) of the floating piston (20 or 30), the free end (24 or 59) of the anchor (22 or 58) gripping behind a lug, a projection or a retaining ring (25 or 73) on the floating piston (20 or 30) and retracting the floating piston into its initial position during the return movement of the plunger piston (3 or 32).

7. A master cylinder as claimed in any one of the preceding claims, characterised in that the return spring (8 or 48) embraces the end of the plunger piston (3 or 32) which is nearest to the pedal and projects from the cylinder housing (1 or 33), and is supported at one end on a collar or plate (26 or 57) arranged on the piston (3 or 32), and on the cylinder housing (1 or 33) ora bottom part (27 or 67) coupled to the cylinder housing at its other end.

8. A master cylinder as claimed in any one of the preceding claims, characterised in that the diameter (a) of the end of the plunger piston (3) nearest to the working chamber corresponds to the diameter (b) of the floating piston (20), while the sealingly guided portion of the plunger piston (3) has an external diameter (c) slightly smaller than that of the lock ring (27) which closes the cylinder bore (2) on the pedal side.

9. A master cylinder as claimed in any one of the preceding claims, characterised in that the cylinder housing has a first housing portion (31) which comprises the bottom part (28) and which receives a working chamber (29) for a floating piston (30) designed as a plunger piston, and a second housing portion (33) which contains a longitudinal through-bore (34) for the plunger piston (32) actuated by the push rod, with both housing portions (31,33) being rigidly interconnected, for instance screwed or welded, and including a seal (37, 38) in the area of the connecting portion (36) for the floating piston (30) to extend through, the latter piston reaching up to the working chamber (35) for the pedal-actuated plunger piston (32).

10. A master cylinder as claimed in any one of the preceding claims, characterised in that a floating piston (30) comprises a flange (39) at its end facing the bottom part (28), behind which flange one end of a tubular member (40) is gripping, the other end whereof carries at its end face a valve ring (41) which is in abutment on the bottom part (28) in the pressure phase and which closes a channel (42) that is designed as a supply bore and that terminates in an axial direction via an annular channel into a working chamber (29).

11. A master cylinder for a hydraulic brake system of a vehicle, substantially as described herein with reference to the drawings.