GB2175659A

GB2175659A - Vacuum-operated brake power booster

Info

Publication number: GB2175659A
Application number: GB08612027A
Authority: GB
Inventors: Rolf Fellinger
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1985-05-24
Filing date: 1986-05-16
Publication date: 1986-12-03
Also published as: GB8612027D0; FR2582274B1; DE3518660A1; GB2175659B; FR2582274A1

Abstract

In a vacuum-operated brake power booster, a rubber reaction disc (30) between a valve piston (16) mounted in a control housing (2) and a push rod (29) co-operating with a piston of a master cylinder (not shown) is shaped in the form of a truncated circular cone or part of a sphere with an edge of the rubber reaction disc (30), extending radially outwardly in the form of a flange, abutting a step (b) of a recess (24) of the control housing (2). The recess (24) of the control housing (2) also has a funnel-shaped portion (13) which is filled by means of the second (truncated-cone) portion (d) of the rubber reaction disc (30). The truncated cone shape of the rubber reaction disc (30) permits the use of a very soft elastic material, the volume increase of the rubber reaction disc (30) caused by differences in temperature being compensated in that the material flows into the gap between a disc (6) and the rubber reaction disc (30), since the large end face of the rubber reaction disc, firmly abuts on the push rod (29) of the master cylinder piston, which push rod is preloaded by means of a spring. A reduction of the gap between the disc (6) and/or the valve piston (16) and the rubber reaction disc (30) has the extremely favourable effect that the response or lost travel of the brake power booster is reduced. <IMAGE>

Description

SPECIFICATION Vacuum-operated brake power booster This invention relates to a vacuum-operated brake power booster with at least one booster piston sealed relative to a booster housing and a piston rod coupled with a brake pedal, for the actuation of a double valve, through the intermediary of which a working chamber of the brake power booster is connectible either with a vacuum or with a higher pressure differential, wherein a first valve is formed by a valve seat at the booster piston and a valve member preloaded in the direction of the valve seat, and a second valve is formed by the same valve member and a valve piston connected with the piston rod, the booster piston communicating effectively with a control housing, wherein the valve piston is displaceably arranged, and a rubber reaction disc being held in the control housing, said rubber reaction disc being acted upon, on the one hand, by the control piston and, on the other hand, by a push rod connected with a piston of the master cylinder.

In known vacuum-operated brake power boosters of the type in question, a rubber reaction disc is arranged between the valve piston moved by means of the brake pedal through the intermediary of a piston rod, and the pedal-side end of the push rod co-operating with the piston of the master cylinder.

The pressure built up in the master cylinder after a compensation port has been covered by a primary seal creates, via the master cylinder piston and the push rod, a reaction force corresponding to the ratio of transmission on the rubber reaction disc. The reaction pressure transmitted onto the valve piston causes the latter to be displaced and to bring its seat into sealing contact with the valve. Thus, the vacuum channel and the air passage are closed.

So far, most efforts regarding an improvment of the vacuum brake power booster have been directed towards a reduction of the hysteresis which denotes the different forceforce-path during actuation and release (outlet force at the push rod / inlet force at the piston rod).

From the brake power boosters in use today it is, however, further expected that the high temperatures generated in particular by modern high-performance engines (e.g. supercharged Otto engines) exercise no influence on the function of the rubber reaction disc of the brake power booster.

It is an object of the present invention to use a relatively soft material as reaction material and, at the same time, to so design the rubber reaction disc that even in the event of extreme changes in temperature, swelling or shrinking of the material will not have a considerable influence on the mode of operation of the brake power booster.

According to the present invention there is provided a vacuum-operated brake power booster with at least one booster piston sealed relative to a booster housing and a piston rod coupled with a brake pedal, for the actuation of a double valve, through the intermediary of which a working chamber of the brake power booster is connectible either with a vacuum or with a higher pressure differential, wherein a first valve is formed by a valve seat at the booster piston and a valve member preloaded in the direction of the valve seat, and a second valve is formed by the same valve member and a valve piston connected with the piston rod, the booster piston communicating effectively with a control housing, wherein the valve piston is displaceably arranged, and a rubber reaction disc being held in the control housing said rubber reaction disc being acted upon, on the one hand, by the control piston and, on the other hand, by a push rod connected with a piston of the master cylinder, characterised in that the rubber reaction disc comprises a first portion (a,a') having the shape of a circular disc and radially outwardly extending in the form of a flange, one end of said portion abutting on the push rod which displaces the piston of the master cylinder, and a second portion (d d) being adjacent to the first portion (a a') and being shaped in the form of a ball section or a truncated circular cone, the end face confining the second portion (d,d) on the side of the valve piston and having the shape of a circular disc which is smaller than the area of cross section adjacent to the first portion (a,a').

Preferably, the rubber reaction disc's first portion has the configuration of a circular cylinder, adjacent to which portion is the second portion shaped in the form of a truncated circular cone, the smaller end face of the second section, which end face forms a circular disc, being directed towards the valve piston, and the first portion radially outwardly projecting over the peripheral surface of the second portion by means of a circumferential flangeshaped edge, said edge engaging in a circular groove in the control valve housing or abutting on a step of the longitudinal bore of the control valve housing.

In a preferential embodiment, the rubber reation disc's first portion has the shape of a circular cylinder, adjacent to which portion is the second portion which has the shape of a truncated cone, the second portion changing into a third portion having the shape of a smaller-diameter circular cylinder.

The second portion shaped in the form of a truncated cone and adjoining the first portion of the rubber reaction disc in the form of a circular cylinder is expediently provided with an end face shaped in the form of a circular disc, the diameter of said end face corre sponding to the diameter of the valve piston and/or that of a disc guided in the control housing.

A recess located in an end of the control housing, which end is situated on the side of the master cylinder, and designed to support and guide the rubber reaction disc, comprises, for that purpose, a surface extending at right angles to the longitudinal axis of the control valve housing and forming a bearing for the flange-shaped first portion, a funnel-shaped part being, towards the direction of the valve piston, adjacent to said surface designed to receive a conical second portion of the rubber reaction disc.

Advantageously, the third portion of the rubber reaction disc has a diameter which corresponds to that of the valve piston and/or that of the disc.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a longitudinal cross-section through a control unit of a brake power booster comprising two control housing parts which are displaceable relative to each other and a disc arranged between the valve piston and the rubber reaction disc; Figure 2 shows a design variant of a rubber reaction disc and Figure 3 shows the rubber reaction disc according to Figure 1.

As is shown in Figure 1, a brake power booster comprises substantially a booster housing 7, a rolling diaphragm 18 dividing the interior of the housing into chambers 20,23, a diaphragm plate 19, a spring 25, two control housing parts 2,4, a poppet valve 1, a valve piston 16, a rubber reaction disc 30, a piston rod 14 and a push rod 29.

The spring 25 urges the diaphragm plate 19 together with the first control housing part 2 through the intermediary of a sealing seat 12 against the poppet valve 1 and/or a sealing surface 11 and through the intermediary of the second control housing part 4 against the booster housing part 7, the spring 25 bearing for that purpose through the intermediary of the diaphragm plate 19 against the first control housing part 2.

The poppet valve 1 has, on its side directed away from the sealing surface 11, a stop 8 abutting on the control housing part 4 through the intermediary of a sleeve 36 in the inoperative position, the control housing part 4, on its part, preferably abuts on a sealing ring 5 and has thus a fixedly defined rear position. In this position, the sealing seat 9 at the valve piston 16 as well as the sealing seat 12 inside the control housing part 2 of the twopart control housing 2,4 is pressed against the sealing surface 11 of the poppet valve 1.

On actuating the piston rod 14, the sealing seat 9 of the valve piston can, therefore, lift off immediately, and the apparatus responds without a lost travel occurring.

When the piston rod 14 is actuated, the first control housing part 2 carries out a forward movement until a stop 3 entrains the second control housing part 4. The running surface for the sealing ring 5 is thus designed correspondingly short. The two control housing parts 2,4 are sealed relative to each other by means of the sealing edge 40 of the poppet valve 1.

The valve piston 16 is not tightly connected with a disc 6 which serves the purpose of setting the ratio of transmission of the apparatus since the stop 3 confines the opening travel of the valve piston 16. Due to the fact that the two control housings 2, 4 are compactly fitted within one another, a large guiding length is obtained, and a buckling or jamming of the control housing parts 2, 4 is thus prevented.

The two control housing parts 2, 4 perform a relative movement to each other, that is when the apparatus is responding and when the apparatus has returned to its rear position.

During all other functions, the two control housing parts 2, 4 are not moving relative to each other.

Due to the fact that in the inoperative position, the spring 25 and piston rod return spring 10 are bearing against the poppet valve 1 through the intermediary of the sealing surface 11, the sealing seats 9 and 12 are preferably designed such that after a deformation of the rubber of approx. 0.2 mm, a comparatively large surface will take effect in order to prevent the material from being damaged. A spring ring 17 mounted from the side confines the relative travel of the two control housing parts 2, 4 at the stop 3.

In the inoperative position, the second control housing part 4 abuts with its collar 28 on the sealing ring 5 with a stop 27, which sealing ring is pressed into the booster housing part 7, the poppet valve 1 abutting with the stop 8 in the control housing part 4 through the intermediary of the sleeve 36. The sealing seat 9 of the valve piston 16 is urged by means of the spring 10 against the sealing surface 11 of the poppet valve, the sealing seat 12 of the control housing part 2 being urged by the spring 25 via the diaphragm plate 19 against the sealing surface 11 of the poppet valve 1. In the position of the two control housing parts 2,4 illustrated in the drawing, a pressure balance exists in the chambers 20,23.

When a brake actuation commences, a movement in the direction of arrow A is generated at the piston rod 14 so that the sealing seat 9 of the valve piston will lift off the sealing surface 11 of the poppet valve and atmospheric pressure will flow into the chamber 20. Due to the pressure differential which is being built up between the chambers 20,23, a force will be generated which urges the first control housing part 2 in the direction of the master cylinder (not shown). The reaction force for proportioning the apparatus will be transmitted to the piston rod 14 through the intermediary of the rubber reaction disc 30.

During the first stage of movement, the sealing seat 12 of the control housing will be sealedly held by the sealing surface 11 of the poppet valve 1 running along with the control housing part 2 in that spring 15 takes support through the intermediary of the sealing seat 12 of the control housing until the sealing seats 12 and 9 have assumed the so-called breathing position.

When the brake actuation commences, the control housing 4 will remain, at first, unmoved until it is entrained by the spring ring 17 via the stop 3. After this relative movement, spring 41, assisted by the spring 15, will now hold the two control housing parts 2, 4 in this position.

During a brake release operation, the force at the piston rod 14 will be relieved, thus allowing the spring 10 to force the valve piston 16 with the sealing seat 9 back until the sealing seat 12 of the control housing is opened. The opening travel will be confined by the stop 3 of the two control housing parts 2,4. The atmospheric pressure can now be sucked out of the chamber 20 via the channels 31, 32. The sealing seat of the control housing will remain open until the apparatus has performed a total return movement and the control housing part 4 abuts with its collar 28 on the stop 27, and the sealing seat 12 of the control housing is forced back by means of the spring 25. Both control housing parts 2,4 will then move into each other, and the stop 3 will be released so that the apparatus will now be in the inoperative position.

On its end directed away from the piston rod 14, the valve piston 16 is provided with an end face 42 shaped in the form of a ball section, which end face abuts on the disc 6, thereby preventing a jamming of the disc 6 in its guide in the control housing part 2.

During assembly, the piston rod 14 is inserted into the control housing part 2 together with the sleeve 36, the poppet valve 1, the valve piston 16 and the springs 41 and 15, the shoulder 43 bearing against noses 44 extending radially inwardiy from the sleeve 36, so that the sleeve 36 can be forcedly inserted together with the poppet valve 1 and the springs 41 and 15 through the intermediary of the piston rod 14. During the last stage of the assembly, the control housing part 4 is slid onto the control housing part 2, the noses 45 then abutting on the control housing part 4 at the sleeve 36 and holding the springs 41 and 15 in a preloaded position. Finally, the two control housing parts 2,4 are locked relative to each other by means of the spring ring 17.

The poppet valve 1 is particularly advantageous in that it is, on the one hand, held and guided at the first control housing part 2 and in that it is with its circular lip or sealing edge 40 in sealing contact with the cylindrical interior wall of the second control housing part 4, thus rendering superfluous an additional sealing ring which seals the two control housing parts 2,4 relative to each other.

In order to maintain the force acting upon the rear part of the control housing part 4 due to the atmospheric pressure as small as possible, the sealing of the poppet valve 1 relative to the control housing part 4 is radially outwardly arranged and is there effected by means of the sealing edge 40. The poppet valve 1, on its part, is in sealing contact with the first control housing part 2. Due to this arrangement, the atmopsheric force becomes very small and can be fully compensated for by the spring 41.

In order to be able to install a push rod 29 with a large diameter in the installation space available in the control unit, a recess 24 is provided which narrows at one end in the form of a funnel (conical) and which comprises a cylindrical part permitting a movement of the pressure disc 33 into the control housing 2.

As is shown in Figure 1, the rubber reaction disc'30 is provided with a first portion a which has a cylindrical shape and whose part protruding radially outwardly abuts on a step (b) of the control housing 2.

The rubber reaction disc 30 fills the funnelshaped recess of the control housing 2 by means of a second portion d having the shape of a truncated circular cone. For that purpose, this substantially conically shaped rubber reaction disc 30 is exactly adapted to the funnelshaped portion 13 of the recess 24. In the embodiment according to Figure 2, the rubber reaction disc 30' comprises a first cylindrical portion a', a second portion Cf, shaped in the form of a truncated cone, and a third cylindrical portion e, the third portion e having a diameter which corresponds to that of the disc 6 arranged between the valve piston 16 and the rubber reaction disc 30', thus allowing the third portion e to enter the bore for the disc 6.

The shaping of the rubber reaction disc 30,30', substantially in the form of a truncated circular cone, permits the use of a very soft and elastic material, the volume increase of the rubber reaction disc 30,30' caused by differences in temperature being compensated in that the material flows into the gap between the disc 6 and the rubber reaction disc 30, 30', since the large end face of the rubber reation disc 30, 30', which end face is situated on the side of the master cylinder, firmly abuts on the push rod 29 of the master cylinder piston, which push rod is preloaded by means of a spring. A reduction of the gap between the disc 6 and/or the valve piston 16 and the rubber reaction disc 30, 30' has the extremely favourable effect that the response or lost travel of the brake power booster is reduced.

Alternatively the second portion may be shaped in the form of a ball section and the recess 24 correspondingly shaped.

Claims

1. A vacuum-operated brake power booster with at least one booster piston (18,19) sealed relative to a booster housing (7) and a piston rod (14) coupled with a brake pedal, for the actuation of a double valve (11,9 and/or 11,12), through the intermediary of which a working chamber (20) of the brake power booster is connectible either with a vacuum or with a higher pressure differential, wherein a first valve (11,12) is formed by a valve seat (12) at the booster piston (18,19) and a valve member (1) preloaded in the direction of the valve seat (12), and a second valve (9,11) is formed by the same valve member (1) and a valve piston (16,9) connected with the piston rod (14), the booster piston (18,19) communicating effectively with a control housing (2,4), wherein the valve piston (16) is displaceably arranged, and a rubber reaction disc (30,30') being held in the control housing (2,4), said rubber reaction disc being acted upon, on the one hand, by the control piston (16) and, on the other hand, by a push rod (29) connected with a piston of the master cylinder, characterised in that the rubber reaction disc (30,30') comprises a first portion (a,a') having the shape of a circular disc and radially outwardly extending in the form of a flange, one end of said portion abutting on the push rod (29) which displaces the piston of the master cylinder, and a second portion (d d) being adjacent to the first portion (a a') and being shaped in the form of a ball section or a truncated circular cone, the end face (21,21') confining the second portion (do^) on the side of the valve piston and having the shape of a circular disc which is smaller than the area of cross section adjacent to the first portion (a,a').

2. A vacuum-operated brake power booster according to claim 1, characterised in that the first portion (a,a') has the configuration of a circular cylinder, adjacent to which portion is the second portion (d,) shaped in the form of a truncated cone, the smaller end face (21,21') of the second section (d,d), which end face forms a circular disc, being directed towards the valve piston (16), and the first portion (a,a') radially outwardly projecting over the peripheral surface of the second portion by means of a circumferential flange-shaped edge, said edge engaging in a circular groove in the control valve housing (2) or abutting on a step of the longitudinal bore of the control valve housing (2).

3. A vacuum-operated brake power booster according to claim 1, characterised in that the first portion (a') has the shape of a circular cylinder, adjacent to which portion is the second portion (d) which has the shape of a truncated cone, the second portion (d) changing into a third portion (e) having the shape of a smaller-diameter circular cylinder.

4. A vacuum-operated brake power booster according to claim 1, characterised in that the second portion (d) is shaped in the form of a truncated cone and adjoins the first portion (a') of the rubber reaction disc (30') which in the form of a circular cylinder, which second portion (d') is provided with an end face (21') shaped in the form of a circular disc, the diameter of said end face corresponding to the diameter of the valve piston (16) and/or that of a disc (6) guided in the control housing (2).

5. A vacuum-operated brake power booster according to any one of the preceding claims, characterised in that a recess (24) located in an end of the control housing (2,4), which end is situated on the side of the master cylinder, and designed to support and guide the rubber reaction disc (30,30'), comprises a surface extending at right angles to the longitudinal axis of the control valve housing (2) and forming a bearing for the flange-shaped first portion (a,a'), a funnel-shaped part (13,13') being, towards the direction of the valve piston (16), adjacent to said surface designed to receive a conical second portion (d,) of the rubber reaction disc (30,30').

6. A vacuum-operated brake power booster according to claim 3, characterised in that the third portion (e) of the rubber reaction disc (30') has a diameter which corresponds to that of the valve piston (16) and/or that of a disc (6) guided in the control housing.

7. A vacuum-operated brake power booster substantially as herein described with reference to and as illustrated in Figures 1 and 3 or Figure 2 of the accompanying drawings.