GB2157378A

GB2157378A - Vacuum-operated power brake booster

Info

Publication number: GB2157378A
Application number: GB08503270A
Authority: GB
Inventors: Hermann Seip
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1984-02-29
Filing date: 1985-02-08
Publication date: 1985-10-23
Also published as: GB8503270D0; ES284748U; IT1184347B; GB2157378B; IT8519690A0; ES284748Y; FR2560135B1; FR2560135A1; DE3407350A1

Abstract

In a vacuum-operated power brake booster comprising a booster piston sealed in relation to the booster housing and comprising a piston rod (14) coupled to the brake pedal for the actuation of a double valve (11, 9, 12'), which double valve serves to connect a working chamber of the power brake booster to either vacuum or a higher pressure, one or several of the valve seat surfaces of the double valve (11, 9, 12') is curved, for instance an annular-bead (17, 18) or a spherical zone (10). The functioning of the valve is comparatively unimpaired by manufacturing tolerances inherent in the parts of the double valve. In other embodiments, the seats (9, 12') are flat (Fig. 1, not shown) or the seat of the valve piston (16) is spherical (13, Fig. 3, not shown). <IMAGE>

Description

SPECIFICATION Vacuum-operated power brake booster The present invention relates to a vacuum operated power brake booster comprising a booster piston sealed in relation to a booster housing, and comprising a piston rod coupled to a brake pedal for the actuation of a double valve, which double valve permits connection of a working chamber of the power brake booster to either vacuum or to a higher pressure, wherein a first valve of the double valve is formed by a valve seat at a control housing connected to the booster piston and by a poppet valve preloaded in the direction of the valve seat, while a second valve of the double valve is formed by said poppet valve and by a valve piston connected with the piston rod.

It is known in power brake boosters of this type to design the surfaces of the valve seats at the poppet valve, at the control housing and at the valve piston as plane circular ring surfaces. Experience has shown however, that valve surfaces designed like this will cause leakage problems, if the mating sealing surfaces are not completely in parallel to one another due to manufacturing tolerances.

It is therefore an object of the present invention to design the double valve of a power brake booster such that, even if greater manufacturing tolerances are encountered, there will be accomplighed complete sealing between the poppet valve and the valve piston, on the one hand, and between the poppet valve and the control housing sealing seat, on the other hand, and that is to say even in the event of the mating components being in contact by only little force.

According to the present invention there is provided a vacuum-operated power brake booster comprising a booster piston sealed in relation to a booster housing, and comprising a piston rod coupled to a brake pedal for the actuation of a double valve, which double valve permits connection of a working chamber of the power brake booster to either vacuum or a higher pressure, wherein a first valve of the double valve is formed by a valve seat at a control housing connected to the booster piston and by a poppet valve preloaded in the direction of the valve seat, while a second valve of the double valve is formed by said poppet valve and by a valve piston connected with the piston rod, characterised in that one or more of the four valve seat surfaces of the double valve is of a curved design.

The poppet valve may have at least one annular-bead-like and outwardly extending projections on its circular ring-shaped, substantially plane end surface which faces the valve piston and which forms said one valve surface.

Preferably, the end surface of the poppet valve includes two concentrically arranged projections, each of said having the configuration of a torus cut transversely relative to its axis of rotation, the respective axis of rotation corresponding to the longitudinal axis of the poppet valve.

Alternatively, the valve piston may include a circular ring-shaped area at its end facing the piston rod and comprising said one valve seat surface, the surface of said circular ringshaped area close to the poppet valve being of curved design, for instance being a spherical zone. In this arrangement, the centre of curvature assigned to the spherical zone of the end surface of the valve piston can be located on the longitudinal axis of the valve piston.

Advantageously, the circular ring-shaped curved area at the frontal end of the valve piston is confined by a surface which corresponds to the one half of the surface of a torus, the axis of rotation of which corrresponds to the longitudinal axis of the valve piston.

In an alternative embodiment, the circular ring-shaped end surface of the control housing which mates with the poppet valve and forms a valve seat is of curved design, for instance a spherical zone.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal cross-section through a control housing of a power brake booster, wherein the poppet:valve includes annular-bead-type sealing surfaces; Figure 2 is a longitudinal cross-section through the poppet valve of Figure 2; Figure 3 is a longitudinal cross-section through a valve piston, the sealing surface of which is formed as spherical zone;; Figure 4 is a double valve in longitudinal cross-section, wherein a poppet valve according to Figure 2 is combined with a control housing, the sealing seat thereof being designed as spherical zone, and Figure 5 is a double valve in longitudinal cross-section, wherein an alternative embodiment of poppet valve is combined with a valve piston, the sealing seat thereof being designed as spherical zone The housing of a power brake booster shown partially in Figure 1 is composed of two housing shells interconnected at a junction by way of indentations, only the housing shell 7 close to a brake pedal (not shown) is illustrated (for the sake of clarity).The interior of the housing is subdivided by a control piston 1 9 into a pressure chamber 30 (vacuum chamber), which communicates via a connecting bore with a vacuum source (not illustrated), and into a working chamber 20. The booster piston 1 9 comprises a rolling diaphragm 21 that abuts in the working chamber 20 on the booster piston 19, as well as a cylindrically designed control housing 2 coupled to the booster piston 1 9 and the rolling diaphragm 21. Said rolling diaphragm 21 is clamped in pressuretightly at the junction 22 and embraces with its inner portion Inner rim 43 of the booster piston 1 9 and seals it relative to the control housing 2.With its cylindrical neck, said control housing 2 projects out of the booster housing 7 and is protected against contamination of its surface by a pleated bellows 23. By means of a slideway ring 24, the control housing 2 seals the working chamber 20 towards the outside.

Inside the control housing 2, a control rod composed of piston rod 14 and valve piston 1 6 is axially slidably accommodated, the said control rod being connectible to a brake pedal of an automotive vehicle through a forkhead (not shown). Further,the control housing 2 contains a valve assembly 9, 11, 1 2 which is actuated by the valve piston 16 and which controls the pressure difference between the vacuum chamber 30 and the working chamber 20 via channels 28, 29.

The part of the control housing 2 located in the vacuum chamber 30 contains furthermore a stepped bore 31 in which a reaction disc 32 and a lock washer 34 are axially held through a clamping sleeve 35. A push rod 33 actuates a master brake cylinder (not shown), which is secured to the end surface of the bottom of the booster housing.

For resetting of the booster piston 19, there is provision of a resetting spring (not shown) which is disposed between the clamping sleeve 35 of the booster piston 1 9 and the bottom of the booster housing.

A cross member 41 is sideways slid into an aperture 40 which is arranged crosswise and opens radially outwardly towards the working chamber 20. It is the purpose of said cross member 41 to limit axial displacement of the valve piston 1 6 relative to the control housing 2. Moreover, said cross member 41 ensures that, in the release position, the control housing will move back in relation to the booster housing until it assumes a specific position (the illustrated one), i.e. it will move so far in direction of the brake pedal until the control housing 2, via the cross member 41, is in abutment on the stationary stop at the booster housing 7 designed as bead 8 of ring 24.

The cross member 41 is of U-shaped configuration and comprises a fork portion 39 and two legs 38, by which the cross member 41 moves to bear against the bead 8 of the slideway ring 24. The power brake booster illustrated in Figure 1 operates as follows: In the release position, valve piston 1 6 and piston rod 14 are retained by a compression spring 37 in the right-hand end position in the control housing 2, as a result whereof the passage to atmosphere is closed and the vacuum channel 28 in control housing 2 is opened, there being a very small gap between valve elements 11 and 1 2 in the release position.When the engine is running, the air existing on the left side of the booster piston 1 9 will be sucked out through a vacuum check valve; as the right-hand side of the booster piston 1 9 is communicating through the vacuum channel in control housing 2 with the left-hand booster piston side when the vacuum passage is opened, balance of vacuum will prevail on both sides of the booster piston 1 9. The booster piston 19 will be held in its right end position by the piston return spring. Though atmospheric air is allowed to enter into the space around the piston rod 14, its access to the working cylinder will be prevented due to the passage to atmosphere being closed by valve 9,. 11.In the release position of the brake unit, likewise the piston in the hydraulic master cylinder will be retained in its initial position by the compression spring.

When the brake pedal is applied, the piston rod 14 together with the valve piston 16 will be displaced to the left in opposition to the force of the valve compression spring 37.

During this action, the compression spring 36 of the poppet valve 1 will urge said to the left onto the seat 1 2 in the control housing 2, and the vacuum channel 28 will be closed. In the further course of motion, the valve piston 1 6 moves away from the poppet valvel, the passage to atmosphere between 9 and 11 will be opened. Now there is free passage for atmospheric air to propagate through the control bore in control housing 2 to the right-hand side of the booster piston 19, the vacuum being discharged as a consequence.The force which is generated by the pressure difference prevailing now on the right and left sides of the booster piston 1 9 displaces the latter to the left in opposition to the force of the piston return spring, and displaces likewise the push rod 33 and the piston in the master cylinder.

The pressure developing in the master cylinder after the supply bore has been overridden by the primary sleeve will exert via the piston and the push rod a reaction force on the valve disc 32 corresponding to the transmission ratio. The reaction pressure will likewise be transmitted onto the valve piston 16, as a result whereof said displaces to the right and moves with its seat 9 into sealing abutment on the valve 11. Thus, vacuum channel 28 and passage to atmosphere are closed. The valve piston 1 6 thereby has adopted its sotermed alert position.

In the brake's fully applied position, there will be constant opening of the passage to atmosphere, the maximum attainable pressure difference at the booster piston 1 9 and thus the maximum boosting pressure being accomplished thereby. The operating pressure limit of the unit is hereby achieved. Still higher pressure in the master cylinder now can only be attained by exerting additional force on the piston rod 14 due to the driver applying pedal force. When the brake pedal is released com pletely, the valve piston 1 6 will return to its initial position, the passage to atmosphere being closed and the vacuum channel being constantly opened.In consequence of the balance ofvacuum compulsorily resulting therefrom at the booster piston 19, no more force will be exerted on said piston, and the resett ing force of the piston return spring suffices to return said piston to its release position. Thus, likewise the piston of the master cylinder will return to its release position.

As is shown in Figure 2, the poppet valve 1 is provided at its end facing the valve piston with two concentrically arranged, annular bead-type and outwardly extending projections 17, 1 8. These projections 17, 1 8 cooperate with the valve seat surface 1 2 (Figure 1) or 12' (Figure 4) at the control housing 2, 2' or, respectively, with the valve seat surface 9 (Figure 1) 9' (Figure 3) at the end surface of the valve piston 1 6, 16'. Tolerances which may be caused in the manufacture of the power brake booster, for instance cantings of two parts in relation to one another, will be compensated for by the curved valve seat surfaces 17, 1 8 at the poppet valve 1.

Instead of the annular-bead-type sealing surfaces at the one annular end surface of the poppet valve 1, illustrated in Figures 1 and 2, a curved sealing surface having e.g. the shape of a spherical zone 1 3 may likewise be designed at the end surface of the valve piston 16', as is displayed in Figure 3. Finally, Figure 4 shows a double valve 12', 11, 9, wherein the valve piston 1 6 includes a plane sealing seat surface which coacts with an annular-bead-type projection 1 7 at the poppet valve 1, while the sealing seat 12' at the control housing 2' is shaped as spherical zone 10 and is matable with the annular-bead-type valve surface 1 8 of the poppet valve 1.

Figure 5 shows a double valve 12, 11', 9', wherein the valve piston 16' disposes of a curvedsealing seat surface which cooperates with the sharp edge 25 of the valve seat 11' of the poppet valve 1, while the annular-beadtype projection 18' at the poppet valve 1 mates with the valve seat 1 2 designed as a plane circular ring-shaped surface.

Claims

1. A vacuum-operated power brake booster comprising a booster piston (1 9) sealed in relation to a booster housing (7), and comprising a piston rod (14) coupled to a brake pedal for the actuation of a double valve (11, 9, 9' and 11, 12, 12' respectively), which double valve permits connection of a working chamber (20) of the power brake booster to either vacuum or a higher pressure, wherein a first valve (11, 12, 12') of the double valve is formed by a valve seat (12, 12') at a control housing (2, 2') connected to a booster piston (19) and by a poppet valve (1) preloaded in the direction of the valve seat (1 1), while a second valve (9, 9', 11) of the double valve is formed by said poppet valve (1) and by a valve piston (1 6, 1 6', 9) connected with the piston rod (14), characterised in that one or more of the four valve seat surfaces of the double valve is of a curved design.

2. A vacuum-operated power brake booster as claimed in claim 1, characterised in that the poppet valve (1) comprises at least one annular-bead-type and outwardly extending pojection (17, 18, 18') on a circular ringshaped, substantially plane end surface thereof which faces the valve piston (16, 16') and which forms said one valve surface.

3. A vacuum-operated power brake booster as claimed in claim 2, characterised in that the end surface (b) of the poppet valve (1) comprises two concentrically arranged projections (17, 18), each thereof having the configuration of a torus cross-sectionally cut transversely relative to its axis of rotation, the respective axis of rotation corresponding to the longitudinal axis of the poppet valve (1)

4. A vacuum-operated power brake booster as claimed in claim 1, characterised in that the valve piston (16') includes a circular ringshaped area at its end facing the piston rod (14) and comprising said one valve seat surface, the said circular ring-shaped area's surface close to the poppet valve (1) being of curved design, for instance a spherical zone (13).

5. A vacuum-operated power brake booster as claimed in claim 4, characterised in that the centre of curvature allocated to the spheri cal zone (13) of the end surface of the valve piston (16') is arranged on the longitudinal axis of the valve piston (16').

6. A vacuum-operated power brake booster as claimed in claim 4, characteriseed in that the circular ring-shaped, curved area (a) at the frontal end of the valve piston (16') is confined by a surface which corresponds to the one half of the surface of a torus, the axis of rotation of which latter corresponding to the longitudinal axis of the valve piston (16').

7. A vacuum-operated power brake booster as claimed in claim 1, characterised in that a circular ring-shaped end surface of the control housing (2') mating with the poppet valve (1) and forming the corresponding valve seat (12') is of curved design, for instance a spherical zone (10).

8. A vacuum-operated power brake booster as claimed in claim 1, characterised in that the poppet valve (1) comprises an annularbead-type, outwardly extending projection (18') on its circular ring-shaped, substantially plane end surface which faces the valve piston (16') and which forms the corresponding valve surface, the said projection (18') coacting with a circular plane valve seat (12) of the control housing (2), while a radially inwardly disposed annular edge (25) of the valve seat (11 ') mates with the valve seat (9') at the control piston (16'), the said valve seat being designed as a curved surface.

9. A vacuum-operated power brake booster substantially as herein described with refer ence to Figures 1 and 2, Figure 4 or Figures 3 and 5 of the accompanying drawings.