GB2230575A

GB2230575A - Vacuum brake booster

Info

Publication number: GB2230575A
Application number: GB9001772A
Authority: GB
Inventors: Kazuhiko Suzuki; Akihiko Miwa; Yuzuru Sugiura; Satoshi Kawasumi
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1989-01-25
Filing date: 1990-01-25
Publication date: 1990-10-24
Anticipated expiration: 2010-01-25
Also published as: GB2230575B; GB9001772D0

Abstract

In a vacuum brake booster of the type in which the pressure differential across a diaphragm is controlled by selective seating of a valve seal portion 22a of a control valve element 22 on a valve seat 18b of the power piston and/or on a valve seat 21a of a plunger carried by a push rod 20, the control valve element 22 comprises a generally cylindrical axially flexible portion 22b1 with the valve seal portion 22a and an outwardly directed flange portion 22b2 for anchorage to a portion 18a of the power piston, the flange portion 22b2 being supported against flexure by being held in face-to-face abutment with a rigid disc member 31a carried by the power piston e.g. by sandwiching, adhesive or moulding to the disc member. The axial length of the control valve element 22 is thus not responsive to the pressure differential across the flange portion 22b2, which means that the control spring 29b can be downgraded, with a consequent decrease in the input load and an improved feel. <IMAGE>

Description

TITLE OF THE INVENTION: Vacuum Brake Booster Field of the Invention The invention relates to vacuum brake boosters for reducing the pedal force required to operate the hydraulic braking system of automotive vehicles. Such vacuum brake boosters are known, and draw their power source typically from the intake manifold of the internal combustion engine driving the automobile.

Description of the Prior Art A typical known vacuum brake booster is that described in Japanese Utility Model Laid Open Publication No.

57-92569 published on 1982 June 07. That brake booster comprises a vacuum housing divided by a diaphragm and a power piston into a constant pressure chamber and a variable pressure chamber, the power piston being axially movable in response to a pressure differential across the diaphragm. The pressure differential is controlled by selective seating of a valve seal portion of a control valve element on a valve seat of the power piston and/or on a valve seat of a plunger carried by a push rod, the two valve seats being arranged concentrically, the former around the latter. The control valve element of the above prior disclosure comprises a generally barrel-shaped portion carrying at one end the valve seal portion and at the other end an outwardly directed flange portion which at its outer periphery is anchored to the power piston.The outwardly directed flange portion is capable of flexure, which flexure is transmitted along the barrel-shaped portion and results in axial movement of the valve seal portion. The internal spring acting between the power piston and the push rod is always sized sufficient to overcome this tendency for elongation of the control valve element due to the pressure differential across the outwardly directed flange portion.

The present inventors have for the first time appreciated that substantial benefits can accrue from reinforcement of the outwardly directed flange portion of the valve seal portion to prevent flexure due to a pressure differential thereacross as long as the axial flexibility of the control valve element is provided by other means.

Summary of the Invention The invention provides a vacuum brake booster comprising a vacuum housing divided by a diaphragm and a power piston into a constant pressure chamber and a variable pressure chamber, the power piston being axially movable in response to a pressure differential across the diaphragm, which pressure differential is controlled by selective seating of a valve seal portion of a control valve element on a valve seat of the power piston and/or on a valve seat of a plunger carried by a push rod, wherein the control valve element comprises a generally cylindrical axially flexible portion with the valve seal portion at one end thereof and an outwardly directed flange portion at the other end thereof for anchorage to the power piston, the outwardly directed flange portion being supported against flexure by being held in face-to-face abutment with a rigid disc member carried by the power piston.

Because the axially extensible portion of the control valve element is a generally cylindrical portion, the pressure differential thereacross does not affect the axial length of the control valve element, and the designer is permitted to utilise a lower duty spring between the power piston and the push rod, for returning the push rod to its rest position. This also permits a reduction in the duty strength of the return spring provided to return the power piston itself to its rest position.

The reinforcement of the outwardly directed flange portion of the control valve element against flexure may be provided by holding that flange portion sandwiched between two rigid disc members both carried by the power piston; or by holding it sandwiched between one rigid disc member carried by the power piston and another carried by the first such rigid disc member; or by adhering it or otherwise making it fast in face-to-face contact With one such rigid disc member.

In either of the"sandwiching" solutions one of the two rigid disc members utilised may be a spring seat for a return spring acting between the power piston and the push rod to return the push rod to its rest position on brake release.

Drawings Figure 1 is an axial section through a vacuum brake booster according to the invention in the brake releasing condition; Figure 2 is an enlarged detail of part of Figure 1; Figure 3 is a diagram showing the relationship between the input load and the output load of the vacuum brake booster in accordance with the invention , in comparison with one in which the outwardly directed flange portion of the control valve element is not reinforced against flexure; Figure 4 is an axial section through only one small portion of a vacuum brake booster according to a second embodiment of the invention, all other details of that vacuum brake booster being the same as in Figure 1; and Figure 5 is a detail similar to that of Figure 2, through a vacuum brake booster according to a third embodiment of the invention.

Referring first to Figures 1 and 2, a vacuum brake booster 10 comprises a vacuum housing 11 comprising a front shell 12 and a rear shell 13. The vacuum housing 11 is divided into a constant pressure chamber 16 and a variable pressure chamber 17 by a power piston 14 and a flexible diaphragm 15. The power piston 14 comprises a moulded body portion 18 made from a resin material, and a pressure plate 19 fast to the piston body 18.

The constant pressure chamber 16 communicates with a vacuum source such as the intake manifold of an automobile engine, and the variable pressure chamber 17 is placed in selective communication with either the constant pressure chamber 16 or the atmosphere by a control valve mechanism 23 provided in a cylindrical portion 18a of the piston body8. An output rod 25 is actuated by axial movement of the power piston 14, for actuation of a master cylinder piston which in use is mounted on the vacuum housing 11.

The control valve mechanism 23 comprises a valve plunger 21 which is mounted on the distal end of a push rod 20 which is connected to a brake pedal (not shown). An annular valve seat 21a is presented at the right-hand end of the valve plunger 21, in general alignment with an annular valve seat 18b of the power piston body 18.

Either one, or both, of the valve seats 18a and 21a can be seated against a valve seal surface 22a of. a control valve 22 which is shown more clearly in Figure 2. The control valve 22 comprises the valve seal surface 22a which is an annular surface at the extreme left end of the control valve 22 as illustrated, and a mounting portion 22b. The mounting portion comprises a generally cylindrical portion 22bl and a radially outwardly directed flange portion 22b2. The cylindrical portion 22bl is axially flexible, so that it is extensible in the axial direction to move the valve seal surface 22a against or away from the valve seat 18a of the power piston body 18 while the mounting portion 22b of the control valve element 22 is fast to the same power piston body portion 18.

The anchorage of the outwardly directed flange portion 22b2 of the control valve element 22 is as follows. A first retainer 31a is secured within the hollow central portion of the piston body 18, and comprises an elastomeric portion 31al, comprising a tubular portion contacting the internal recess in the power piston body 18 and a radially inwardly directed flange portion; and a reinforcing plate member 31a2 which is made of steel and which is secured to the elastomeric member 31al over the whole of its tubular and flanged portions.

Holding the flange portion 22b2 of the control valve element 22 firmly against the reinforcing plate member 31a2 is a 'second retainer 31b, with substantially the whole of the flange portion 22b2 of the control valve element 22 being firmly sandwiched between the two retainers. The retainer 31b also provides a seat for a spring 29b acting between the power piston 14, via the body portion 18 and the retainer 31b, and the push rod 20.

The pressure differential which in use is established across the control valve element 22 acts only on the generally cylindrical portion 22bl and does not affect the axial length of the control valve element 22. This is important because in the rest position of the brake, as shown in Figure 1, a small axial gap (not shown) is formed between the valve seat 18b and the seal surface 22a, this small gap being created by the action of the spring 29b on the push rod 20, acting to draw the valve plunger 21 carried at the left-hand end of the push rod 20 to the right to lift the seal surface 22a of the control valve element 22 away from the valve seat 18b.

Any pressure differential which were to act on the control valve element 22 in the axial direction would have the effect of opposing the force of the spring 29b, so that the vacuum booster of the invention has the advantage over the prior art as illustrated in Figure 3, representing a reduction in the prescribed duty of the spring 29b.

Because the duty or preset load of the spring 29b can be reduced according to the invention, so it is easier to design a spring to fit into the limited space available in the cylindrical portion of the distal body 18. Furthermore, it is possible to downgrade the material of the spring 29b, with a consequent reduction in the manufacturing cost of the vacuum brake booster 10. In addition, a return spring 30 acting on the power piston 14 has to be designed to a preset magnitude such as to move the power piston 14 when the brake pedal is released from its depressed position.

Reduction of the preset force of the spring 29b facilitates a corresponding reduction in the preset force of the return spring 30, making further cost reductions possible.

Figure 4 shows a small detail of construction of a second embodiment of the invention, being similar to the first except for the anchorage and reinforcement of the outwardly directed flange portion 22b2 of the control valve element 22. In Figure 4, a retainer 131a is inserted into the piston body portion 18a, with an O-ring 40 providing a pneumatic seal thereacross. The retainer 131a is rigid, and is a force fit in the piston body portion 18a. The outwardly directed flange portion 22b2 of the control valve element 22 is sandwiched between an inwardly directed flange portion of that retainer 131a and a pressed metal spring retainer 131b which receives the left-hand end of the spring 29b.

The combination of the retainers 131a and 131b provide the flange portion 22b2 with reinforcement and support over a substantial part of its radial extent, although it will be appreciated that even greater advantages are possible according to the invention by extending the inwardly directed flange portion of the retainer 131a even further to provide the flange portion 22b2 with reinforcement and support over the whole of its radial extent.

Figure 5 illustrates a further embodiment of the invention, in which the details are as discussed and illustrated for the earlier embodiments except for the anchorage of the outwardly directed flange portion 22b2 of the control valve element 22. In this third embodiment a retainer 231 is firmly secured to the whole of the outwardly facing face of the flange portion 22b2 by adhesive or as part of the moulding process, and provides rigid support and resistance to axial flexure of the whole of that flange portion.

Claims

CLAIMS:

1. A vacuum brake booster comprising a vacuum housing divided by a diaphragm and a power piston into a constant pressure chamber and a variable pressure chamber, the power piston being axially movable in response to a pressure differential across the diaphragm, which pressure differential is controlled by selective seating of a valve seal portion of a control valve element on a valve seat of the power piston and/or on a valve seat of a plunger carried by a push rod, wherein the control valve element comprises a generally cylindrical axially flexible portion with the valve seal portion at one end thereof and an outwardly directed flange portion at the other end thereof for anchorage to the power piston, the outwardly directed flange portion being supported against flexure by being held in face-to-face abutment with a rigid disc member carried by the power piston.

2. A vacuum brake booster according to claim 1, wherein the outwardly directed flange portion of the control valve element is supported against flexure by being held in face-to-face abutment with the rigid disc member carried by the power piston, over the whole of its radial extent.

3. A vacuum brake booster according to claim 1 or claim 2, wherein the outwardly directed flange portion of the control valve element is supported against flexure by being sandwiched between the rigid disc member carried by the power piston and a further rigid disc member carried by the power piston or by the first such rigid disc member.

4. a vacuum brake booster according to claim 3, wherein the further rigid disc member is a spring retainer for a spring which acts to release the seating of the valve seal portion of the control valve element from the valve seat of the power piston in the brake-releasing rest condition of the power booster.

5. A vacuum brake booster according to claim 1 or claim 2, wherein the outwardly directed flange portion of the control valve element is supported against flexure by being bonded to the adjacent face of the rigid disc member.

6. A vacuum brake booster according to claim 5, wherein the rigid disc member is a spring retainer for a spring which acts to release the seating of the valve seal portion of the control valve element from the valve seat of the power piston in the brake-releasing rest condition of the power booster.

7. A vacuum brake booster substantially as described herewith with reference to Figures 1 to 3 of the drawings.

8. A vacuum brake booster substantially as described herein with reference to Figures 1 to 3 as modified by Figure 4 of the drawings.

9. A vacuum brake booster substantially as described herein with reference to Figures 1 to 3 as modified by Figure 5 of the drawings.