GB2129889A

GB2129889A - Tandem master cylinder

Info

Publication number: GB2129889A
Application number: GB08323310A
Authority: GB
Inventors: Hajo Pickel; Ernst-Dieter Schaefer
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1982-11-11
Filing date: 1983-08-31
Publication date: 1984-05-23
Also published as: FR2536026B1; GB8323310D0; IT8323676A0; DE3241802C2; DE3241802A1; ES275605U; JPS59100044A; IT1169948B; ES275605Y; GB2129889B; FR2536026A1

Abstract

A tandem master cylinder for a vehicle hydraulic brake system has a stepped push-rod actuated piston (3) extending slidably into a second stepped piston (4) arranged in the stepped bore (2) of the housing (1) to provide a particularly short and compact design, wherein the working chamber (7), which is in communication via a connecting bore (22) with the first brake circuits provided in a blind bore (45) in the larger diameter portion of the second piston (4). The smaller portion of the second piston (4) plunges into and defines a working chamber (35) which is, via a connecting bore (23), in communication with the second brake circuit, the two pistons (3, 4) containing bores (42, 46) wherein are the piston springs (5, 12), the depths of the bores (42, 46) equalling the coil-bound lengths of the springs (5, 12). <IMAGE>

Description

SPECIFICATION Tandem master cylinder This invention relates to a tandem master cylinder for a vehicle hydraulic brake system, of the kind having a cylinder housing in whose bore a push-rod piston and an intermediate piston are axially slidably accommodated, a piston spring which is arranged in the cylinder chamber of the first brake circuit between the push-rod piston and the intermediate piston and which bears with its one end against the push-rod piston and bears with its other end against a stop sleeve, another piston spring which abuts, on the one hand, on the bottom of the master cylinder and abuts, on the other hand, in the intermediate piston, and a guide pin, secured to the stop sleeve, which is arranged in a longitudinal direction in the cylinder chamber and which carries a valve body at its end close to the piston, the said body co-operating with a bore in the push-rod piston, and another guide pin which is disposed in the cylinder chamber of the second brake circuit and whose valve body cooperates with a bore contained in the intermediate piston.

Known from German printed and published patent application 28 49 045 is a tandem master cylinder, wherein the cylinder housing contains a single piston bore, the diameter of which is the same for both pistons arranged in series, the housing of the tandem master cylinder confining laterally the two working cylinders. A disadvantage of this known tandem master cylinder is its large overall length and its relatively great operating stroke.

It is an object of the present invention to provide a tandem master cylinder which permits a comparatively short pedal travel while affording a particularly compact overall volume at the same time. In addition, all bores, in particular all supply bores, are to be so located that they are not overridden by the seals or sealing cups and sealing rings upon actuation of the master cylinder.

Finally, the tandem master cylinder is desired to afford particularly high reliability in operation.

According to the invention in its broadest aspect, a tandem master cylinder of the kind referred to is characterised in that the intermediate piston designed as a stepped piston contains at its end close to the bottom of the cylinder bore a recess or blind-end bore extending in the piston's longitudinal direction, into which the piston spring is immersed and whose depth corresponds to approximately the coil-bound length of the compression spring, and the pushrod piston containing a recess or blind-end bore at its end that is remote from the push rod and immersed into the cylinder bore of the large step of the intermediate piston, the piston spring engaging into the recess or blind-end bore whose depth corresponds to approximately the coilbound length of this spring.

Preferably, the large step of the intermediate piston, which step is designed as a piston sleeve and contains a cylinder bore, has at its peripheral surface an annular indentation or groove which forms an annular chamber together with the cylinder bore, the annular chamber communicating, on the one hand, via a channel or a bore in the piston sleeve with the cylinder chamber, while it is, on the other hand, connected via a channel or a bore to the first brake circuit.

In this arrangement, the length of the small step of the cylinder bore is less than that of the piston spring which is supported on the bottom of the cylinder bore when that spring is in its extended condition.

To make the overall length of the tandem master cylinder as short as possible, also the length of the cylinder bore in the large step of the intermediate piston designed as a stepped piston corresponds to at least the coil-bound length of the piston spring which is arranged between the intermediate piston and the push-rod piston.

Advantageously, the sealing bodies which are each arranged at respective ends of the two guide pins are made from elastic material and are supported directly via springs which latter, in turn, abut on supporting discs provided between the ends of the piston springs and the bottoms of the blind-end bores.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing showing a longitudinal cross-section through the tandem master cylinder without the associated pressure fluid supply reservoir.

The tandem master cylinder illustrated comprises a cylinder housing 1 with a cylinder bore 2 in which there are slidably arranged in series a push-rod piston 3 actuable by a piston rod (not shown) and an intermediate piston 4. The intermediate piston 4 is supported on the cylinder bottom 6 via a compression spring 5. Extending coaxially into the cylinder chamber 7 between the push-rod piston 3 and the intermediate piston 4 is a guide pin 8 which is fixed to the push-rod piston 3. The guide pin projects with its free end through a central recess 9 of a stop sleeve 10 abutting on the intermediate piston 4, ease of motion of the stop sleeve 10 away from the push-rod piston 3 being limited by an enlarged portion at the free end of the guide pin 8 which forms a stop 11.

Arranged between the push-rod piston 3 and the stop sleeve 10 is a preloaded piston spring 1 2 which acts upon the stop sleeve 10 in the direction away from the push-rod piston 3.

The stop sleeve 10 is composed of a sheetmetal part shaped like a hat.

The guide pin 8, illustrated is a solid material bar, the one end whereof has a sealing body 17 by which the guide pin engages on axial bore 13 in the push-rod piston 3. The cylinder bore 2 of the cylinder housing 1 is designed as a stepped bore, with the intermediate piston 4 being slidably supported in the step A of smaller diameter, while the push-rod piston 3 is held and guided in the step B of larger diameter, the latter piston's end that is close to the push rod (not shown in detail) sliding via the shoulder 1 8 directly into the cylinder bore 2, while its front sleeve-shaped end 19 of smaller diameter is held in the tube-shaped piston sleeve 20 which latter is longitudinally slidably guided in the step B of the cylinder bore in a sealed manner.The piston sleeve 20 contains at its peripheral surface a circumferential groove which, together with the cylinder bore 2, forms an annular chamber 21 which communicates via a bore 22 in the wall of the cylinder housing 1 with the first brake circuit. A bore 23 at the left end of the cylinder housing 1 in the area of the cylinder bottom 6 connects the tandem master cylinder to the second brake circuit. The cylinder housing 1 is connected to a pressure fluid supply reservoir (not shown in detail) via the two sockets 24, 25, the sockets 24, 25 being each connected to the annular chambers 28 and 29, respectively, via supply bores 26 and 27, respectively.The annular chamber 28 of the first brake circuit is confined, on the one hand, by the annular end face 30 of the piston sleeve 20 guided in the step B and, on the other hand, by the shoulder 18 of the push-rod piston 3, the shoulder being sealed by the cup 31 in relation to the cylinder bore 2. The annular chamber 28 is connected to the cylinder chamber 7 via a channel 32 in the rear portion of the pushrod piston 3, the channel 32 being closable by the sealing body 17 at the end of the guide pin 8 close to the push rod. The annular chamber 29 which is confined endwise by the end face of the step 14 of the cylinder bore 2 and by the end face 33 of the piston sleeve 20 communicates via the channel 34 in the intermediate piston 4 with the cylinder chamber 35.The pressure fluid passage leading from the annular chamber 29 into the cylinder chamber 35 is closable through the sealing body 36 at the right end of the guide pin 37.

The operation of the tandem master cylinder is as follows: starting from the pressure fluid supply reservoir, the pressure fluid propagates via the supply bores 26, 27 and the gap 43, respectively, into the annular chambers 28, 29 and from here via the channels 32, 34 into the two cylinder chambers 7 and 35, respectively. Upon displacement of the push-rod piston 3 to the left, the sealing bodies 17 and 36, respectively, acted upon by the springs 39,40 will close the channels 32 and 34, respectively, thereby enabling braking pressure to develop in the cylinder chambers 7 and 35, respectively, which propagates from the cylinder chamber 7 via the radial bore 41, the annular chamber 21 and the bore 22 into the first brake circuit, on the one hand, and from the cylinder chamber 35 via the vore 23 into the second brake circuit, on the other hand.

In the event of failure of the second brake circuit connected to the bore 23, the intermediate piston 4 will move to the left so far, until the left end face of the intermediate piston 4 has moved into abutment on the cylinder bottom 6 and the annular surface 33 of the large step of the intermediate piston 4 abuts on the step 14 of the cylinder bore 2, respectively. Since a further displacement of the intermediate piston 4 in a longitudinal direction is no more possible, working pressure can develop in the cylinder chamber 7. In the event of failure of the first brake circuit, connected to the bore 22, the push-rod piston rushes to the left, until its sleeve-shaped end 19 is in abutment on the right end face 44 of the intermediate piston 4, displacing the latter in the direction of effect.

It is a special advantage of the tandem master cylinder described that both the push-rod piston 3 and the intermediate piston 4 have particularly long guidances preventing them from canting or tilting despite the particuarly short overall length of the tandem master cylinder. In addition, the springs 5, 12 for retraction of the pistons 3,4 can be of particularly long design, whereby spring fracture is reliably precluded. The particularly short overall length will be achieved among other ways by arranging the piston springs 5, 12 partially within the pistons 3, 4.

Claims

1. A tandem master cylinder for a vehicle hydraulic brake system, of the kind having a cylinder housing (1) in whose bore (2) a push-rod piston (3) and an intermediate piston (4) are axially slidably accommodated, a piston spring (12) which is arranged in the cylinder chamber (7) of the first brake circuit between the push-rod piston (3) and the intermediate piston (4) and which bears with its one end against the push-rod piston (3) and bears with its other end against a stop sleeve (10), another piston spring (5) which abuts, on the one hand, on the bottom (6) of the master cylinder (1) and abuts, on the other hand, on the intermediate piston (4), and a guide pin (8), secured to the stop sleeve (10), which is arranged in a longitudinal direction in the cylinder chamber (7) and which carries a valve body (17) at its end close to the piston, the said valve body cooperating with a bore (32) in the push-rod piston (3), and another guide pin (37) which is disposed in the cylinder chamber (35) of the second brake circuit and whose valve body (36) co-operates with a bore (34) contained in the intermediate piston (4), characterised in that the intermediate piston (4) designed as a stepped piston contains at its end close to the bottom (6) of the cylinder bore (2) a recess or blind-end bore (42) extending in the piston's longitudinal direction, into which the piston spring (5) is immersed and whose depth corresponds to approximately the coil-bound length of the compression spring (5), and the push-rod piston (3) containing a recess or blind-end bore (46) at its end that is remote from the push rod and immersed into the cylinder bore (45) of the large step of the intermediate piston (4), the piston spring (12) engaging into the recess or blind-end bore whose depth corresponds to approximately the coil.bound length of this spring (12).

2. A tandem master cylinder as claimed in claim 1 , characterised in that the large step of the intermediate piston (4), which step is designed as a piston sleeve (20) and contains a cylinder bore (45), has at its peripheral surface an annular indentation or groove which forms an annular chamber (21) together with the cylinder bore (2), the annular chamber (21) communicating, on the one hand, via a channel or bore (41) in the piston sleeve (20) with the cylinder chamber (7), while it is, on the other hand, connected via a channel or a bore (22) to the first brake circuit.

3. A tandem master cylinder as claimed in claim 1 or 2, characterised in that the length (A) of the small step of the cylinder bore (2) is less than that of the piston spring (5) which is supported on the bottom (6) of the cylinder bore (2) when that spring is in its extended condition.

4. A tandem master cylinder as claimed in claim 1 or 2, characterised in that the length of the cylinder bore (45) in the large step of the intermediate piston (4) designed as a stepped piston corresponds to at least the coil-bound length of the piston spring (12) which is arranged between the intermediate piston (4) and the pushrod piston (3).

5. A tandem master cylinder as claimed in any one of the preceding claims, characterised in that the sealing bodies (1 7, 36) which are arranged at respective ends of the two guide pins (8, 37) are made from elastic material and are supported directly via springs (40 and 39, respectively) which latter, in turn, abut on supporting discs (47, 48) provided between the ends of the piston springs (S 12) and the bottoms of the blind-end bores (42, 46).

6. A tandem master cylinder substantially as described with reference to the accompanying drawings.