GB2156930A - Vacuum-operated brake power booster with master cylinder - Google Patents

Abstract

In a vacuum-operated brake booster and tandem master cylinder assembly, a jump (increase) of transmission ratio is achieved in the event of failure of the booster in that only a part of the push-rod piston (25) which has a smaller cross-sectional area is effective. For this purpose, the push-rod piston (25) is provided with a stem (26) which is coupled to the output force push-rod (12) of the booster and over which a sleeve (27) is slidable which controls the passage of hydraulic fluid through a duct (36, 36') provided in said stem (26) and which is, to this end, coupled to the control valve housing (7, 7') of the booster through a cap (21). In the event of failure of the booster, only the push-rod piston (25) with its stem (26) will shift, whereas the sleeve (27) will remain in its initial position, as a result whereof the passage of hydraulic fluid through the duct (36, 36') is opened up, which latter duct (36, 36') now links an annular chamber (28) positioned behind the shoulder (29) of the push-rod piston (25) to the pressure chamber (40) positioned before the push-rod piston (25), so that only a reduced cross-sectional area will be effective. Simultaneously the recuperation part (31) is closed by an annular valve member (32). <IMAGE>

Description

SPECIFICATION Vacuum-operated brake power booster with master cylinder This invention relates to a vacuum-operated brake power booster with a master cylinder, the booster including a movable wall sealed with respect to a booster housing and a control element housing co acting with the movable wall and containing a double valve, and including a valve piston slidable by a piston rod, the master cylinder-side end of the valve piston acting through a reaction device on a push-rod which actuates, on its part, a stepped piston-shaped push-rod piston of the master cylinder which is flanged to one housing shell of the booster housing.

Brake units of the kind under review are known in which on brake operation in the event of failure of the vacuum-operated brake power booster, the piston rod which is pivoted to the brake pedal pushes the valve piston of the double valve in the control element housing against the reaction device and then the latter, with entrainment of the control element housing and of the movable wall, against the push-rod co-acting with the push-rod piston so that a brake pressure can build up in the pressure chamber of the master cylinder.However, that generaily customary arrangement presents the disadvantage that in the event of failure of the vacuum-operated brake power booster, the brake pedal requires to be moved a comparatively large distance before a brake pressure is built up, the foot effort to be applied on overcoming the lost travel being, in addition, relatively sizeable since the effective cross-sectional area of the piston of the master cylinder remains unvaryingly large and must now be shifted by the foot effort alone, without any supporting power.

Beyond this, also a tandem master cylinder for a hydraulic braking system is known (German printed and examined patent application 2,460,529) whose primary piston is adjustable by means of an output element of a pedal-operable brake power booster with movable wall through which brake power booster a fluid pressure differential can be generated, with a device which reduces automatically the required pedal effort in the event of failure of the operating pressure of the brake power booster and which is furnished for that purpose with a valve which is preloaded toward the open position and urged into the closed position by the operating pressure of the brake power booster, which valve controls the linkage between a fluid reservoir and a pressure chamber.To this aim, the unit is equipped with an auxiliary piston having a diameter larger than that of the primary piston, the auxiliary piston being arranged between the output member of the brake power booster and the primary piston of the master cylinder and the pressure chamber being formed by a control pressure chamber located between the auxiliary piston and the primary piston, that is by a chamber which is separated from the primary pressure chamber and from a secondary pressure chamber of the master cylinder. This prior art tandem master cylinder presents, however, the disadvantage that in the event of failure of the vacuum, the pedal sags down a comparatively elevated distance over which the primary piston and the auxiliary piston rest on each other and allow to be shifted jointly as a common mechanical unit.

The present invention has the object to avoid the disadvantages of the known brake power booster with master cylinder and to create a brake unit which in case of availability of the operating pressure for the booster, renders possible a shorter pedal travel and which in the event of failure of the operating pressure switches the master cylinder over to a smaller effective piston area and thus enables a jump of transmission.

According to the invention there is provided a vacuum-operated brake power booster with a master cylinder, the booster including a movable wall sealed with respect to a booster housing and a control element housing co-acting with the said movable wall and containing a double valve, and including a valve piston slidable by a piston rod, the master cylinder-side end of the said valve piston acting through a reaction device on a push-rod which, on its part, actuates a stepped piston-shaped push-rod piston of the master cylinder which is flanged to one housing shell of the booster housing, characterised in that the said push rod is tied to the said control element housing through a cap fastened to said control element housing, an axial play being provided between the said cap and the said push-rod, by which play the said push-rod is shiftable relative to the said control element housing in the longitudinal direction of the housing, the said cap co-acting with a sleeve which on a shift of the said push-rod relative to the said control element housing actuates a first valve that links an annular chamber located behind a large step of the said push-rod piston to a pressure chamber of a primary circuit of the master cylinder through a duct provided in the said push-rod piston and through a second valve closes an intake port arranged between a socket pipe for a fluid reservoir and the said annular chamber.

Advantageously, a back-up plate is envisaged for the purpose having a central opening and being furnished with radially extending studs or fingers which engage in openings arranged in the sleeve which surrounds a stem of the push-rod piston, said openings being sized such that the back-up plate is shiftable longitudinally a distance relative to the sleeve, and the pedal-side end of the sleeve being abutted against the cap of the control element housing.

Preferably, the sleeve being movable coaxially with the stem of the push-rod piston is furnished with a slidable friction ring at its end facing the master cylinder, said friction ring co-acting with a ring-shaped valve body which controls the passage of hydraulic fluid from the fluid reservoir through the intake port into an annular chamber located behind the push-rod piston, which annular chamber is connected, on its part, with the pressure chamber located before the push-rod piston via an intake duct arranged in the housing of the master cylinder, the passage of hydraulic fluid through the intake duct being controiled, on operation of the brakes, by means of a valve provided with a piston cup.

In a preferred embodiment, the stem of the pushrod piston isfurnishedwith a duct extending in the transverse direction and connected to the pressure chamber, the exit of the duct at the outer surface of the stem being provided in a plane which in the release position is covered by the master cylinderside end of the sleeve pushed over the stem and which in the braking position is freed by the sleeve in the event of failure of the booster.

Expediently, the back-up plate takes support at the pedal-side end, or at a head member, of the master cylinder through a spring, the latter spring urging the sleeve pushed overthestem of the push-rod piston via the back-up plate against the cap surrounding the reaction device.

According to the invention, the push-rod acting on the push-rod piston passes through an opening provided in the bottom section of the cap and is furnished at its pedal-side end with a push-plate which co-acts with the reaction device and which is retained by the cylindrical inner wall of the cap.

In orderto safeguard regular opening and closing of the slide valve, a play is envisaged in the release position between the master cylinder-side lateral face of the push-plate and the inner side of the bottom section of the cap, which play corresponds at least to the opening travel of the valve formed by the duct extending transversely through the stem and by the master cylinder-side end of the sleeve.

In a particularly favourable version under manufacturing technique aspects, the cap is formed with a radially outwardly bent rim serving to support the end of the apparatus spring on the side of the control element housing, with the back-up plate co-acting with the sleeve being configured roughly cup-shaped and with an apparatus spring being inserted between the bottom section of the back-up plate and a collar or stop ring which is arranged at the end of the sleeve on the side of the control element housing.Preferably, the back-up plate co-acting with the sleeve is furnished with a central opening in its bottom section through which the sleeve penetrates, the fingers of the back-up plate co-acting with a collar or a stop ring provided at the end of the stem of the push-rod piston on the side of the control element housing and the stop ring dragging the back-up plate when the push-rod piston shifts relative to the sleeve.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through an embodiment of a vacuum-operated brake power booster with a tandem master cylinderforthe braking system of an automotive vehicle; Figure 2 is a scaled up representation of an annular valve of Figure 1 controlling the passage of hydraulic fluid toward an annular chamber behind a large step of a push-rod piston; Figure 3 is a scaled up representation of a back-up plate with a sleeve forming a slide valve and of a push-rod according to Figure 1; and Figure 4 illustrates an alternative version of the tandem master cylinder.

The housing 1 of the brake power booster is composed of two housing shells 15,16 which are joined together at a connecting point 14. The inner space of the housing is subdivided by a diaphragm retainer 5 into a vacuum chamber 2 which is linked to a vacuum source through a connecting port, and into a power (working) chamber 3. The diaphragm retainer 5 is provided with a rolling diaphragm 4 snugly adhering to the diaphragm retainer 5 and with a control element housing 7 having a cylindrical configuration and being coupled to the diaphragm retainer 5 and to the rolling diaphragm 4.

The rolling diaphragm 4 is inserted at the connecting point 14 in a pressure-tight manner and with its inner section encircles the neck 17 of the diaphragm retainer 5 to seal it with respect to the control element housing 7. With its cylindrical portion 7', the control element housing 7 projects out of the booster housing 1 and by means of a sliding guide ring 18, seals off the power chamber 3 from the outside.

Within the housing 7, there is arranged in an axially slidable manner the control rod which is comprised of the piston rod 11 and the valve piston 9 and is connected to the brake pedal (not shown) of the automotive vehicle via a clevis (not shown). The control element housing 7,7' furthermore contains a valve arrangement 8, 13, 19 which is actuated by the valve piston 9 and which controls the pressure differential between the vacuum chamber 2 and the powerchamber3through ducts 19,20.

The portion of the control element housing 7 which is positioned in the vacuum chamber 2 is provided with a cap 21 in which a reaction device 10 with reaction levers or with a reaction disc of rubbery-elastic material is retained and which moreover guides a push-plate 22 of a push-rod 12 which actuates a brake master cylinder 23 fastened at the front face of the housing shell 16 forming part of the booster housing 1.

For the purpose of restoring the diaphragm retainer 5 with diaphragm 4 and control element housing 7, there is provided an apparatus spring 6 which is inserted between a radially outwardly bent rim 54 of the cap 21 of the control element housing 7 and the housing shell 16 of the booster housing 1.

A floating piston 24 and a push-rod piston 25, the latter configured in the shape of a stepped piston, are supported within the master cylinder 23, with a sleeve 27 serving as a control slide valve being positioned in longitudinally slidable manner on the stem 26 of the push-rod piston 25. Through an intake port 31 which is closable by means of a ringshaped valve body-32, an annular chamber 28 located behind a shoulder 29 (large step) of the push-rod piston 25 is linked to a fluid reservoir (not shown) which is connected to the socket pipe 30. On its side facing the control element housing 7, the aforesaid valve body 32 is subject to the force of a locking spring 33 whose one end takes support at a head member 34 which shuts off the master cylinder 23 on the side of the booster and is formed with a central opening for the passage of the sleeve 27. A slidable friction ring 35 (Figure 2) is applied on the sleeve 27 at its master cylinder-side end, which friction ring 35 takes care that the valve body 32 is maintained in the open position shown in Figures 1 and 2 when the push-rod piston 25 is in its initial position. The annular chamber 28 is linked to a filling chamber 37 through a duct 36. In addition, an intake duct 45,45' links the annular chamber 28 to the pressure chamber 40 located before the pushrod piston 25. In the illustrated release position of the (tandem) master cylinder 23, the two valves 38 and 32 as well as the valve arrangement 39 are open and a fluid connection is established from the socket pipe 30 to the pressure chamber 40 and to the filling chamber 37 and from the socket pipe 41 to a second pressure chamber 42.When a braking action is initiated (with the brake power booster in sound condition), the push-rod 12 and the sleeve 27 almost simultaneously move to the left, since immediately upon the shift of the piston rod 11, the double valve 8, 13, 19 causes the inflow of air into the power chamber 3 and the movable wall 46 comprised of the diaphragm retainer 5 and the diaphragm 4 shifts together with the control element housing 7 and the cap 21 in the direction of actuation. Owing to the foresaid simultaneous shift of the push-rod piston 25 and the sleeve 27, a brake pressure builds up in the pressure chambers 40 and 42 because the valves 38 and 39 shut off the intake ports 45,45', respectively 47 leading to the socket pipes 30 and 41, respectively.Since there is no appreciable relative motion between the push-rod piston 25 and the sleeve 27, the duct 36, 36' will also remain shut so that the full cross-sectional area a of the push-rod piston 25 is effective.

The push-rod 12 is tied to the control element housing 7 through the cap 21. There is an axial play x between the cap 21 and the push-rod 12, by which play x the push-rod 12 is shiftable relative to the control element housing 7 in the longitudinal direction of the housing. The cap 21 co-acts with the sleeve 27 which on a shift of the push-rod 12 relative to said control element housing 7 actuates a slide valve constituted by elements 26 and 27 that links the chamber 28 to the chamber 40.

There is a back-up plate 49 having a central opening and furnished with radially inwardly extending studs or fingers 56 (Figure 3) which engage in openings 51 (Figure 1) arranged in the sleeve 27. The openings 51 are sized such that the back-up plate is shiftable longitudinally a distance b relative to the sleeve 27, the pedal-side end of the sleeve 27 being abutted against the cap 21. The back-up plate 49 takes support on the head member 34 through a spring 52 which urges the sleeve 27 against the cap 21. The push-rod 12 passes through an opening in the bottom section 53 of the cap. The push-plate 22 which co-acts with the reaction device 10 is retained by the cylindrical inner wall of the cap 21.The playx is in the release position between the master cylinder side end face of the push plate 22 and the inner side of bottom section 53, which play x corresponds at least to the opening travel of the valve formed by the duct 36' extending transversely through the stem 26 and by the master cylinder-side end of the sleeve 27. The back-up plate 49 is configured roughly cup-shaped with a spring 58 inserted between the bottom section of the back-up plate and a collar or stop ring 55 which is arranged at the end of sleeve 27 on the side of the control element housing 7. The fingers 56 co-act with a collar or stop ring 57 provided at the end of the stem 26 on the side of the control element housing 7, the stop ring 57 dragging the back-up plate 49 when the push-rod piston 25 shifts relative to the sleeve 27 in the direction of arrow A.

In the event of failure of the booster, the control element housing 7 initially remains in the release position when the brake pedal is depressed, that is when the piston rod 11 is shifted, whereas the pushrod 12 shifts to the left, in the direction of actuation.

Already in the initial phase of pressure build-up in the pressure chambers 40 and 42, the passage of hydraulic fluid from the annular chamber 28 through the ducts 36,36' to the filling chamber 37 (which is in linkage with the pressure chamber 40 via a groove 48) will be opened up since the sleeve 27 acts as a control slide valve. A further shift of the piston rod 11 in the direction of the arrow A (to the left) will then (upon overcoming the playx between the push-piate 22 and the cap 21) cause the control element housing 7 with the movable wall 46 to move against the force of the apparatus spring 6.

When the play b between the back-up plate 49 and the sleeve 27 has been overcome, also the sleeve 27 together with the push-rod piston 25 will be moved in the direction indicated by the arrow A. In this motional phase, the ring-shaped valve body 32 will shut off the intake port 31, since due to the motion of the sleeve 27, the locking spring 33 is freed by the friction ring 35 coupled to the sleeve 27 and is allowed to move the valve body 32 to the left. A further shift of the elements 11, 13, 12,25, and 27 in the direction of the arrow A will then cause the push-rod piston 25 to act as a plunger piston, with the effective cross-sectional area now being c and a comparatively elevated hydraulic pressure being allowed to build up in the brake circuit (assuming a given pedal effort).The pressure before and behind the shoulder 29 of the push-rod piston 25 is identical in this phase of brake operation. During this while, the primary cup 50 of the valve 38 is out of function.

When the pedal returns, that is when the piston rod 11 moves contrary to the direction indicated by the arrow A, the hydraulic fluid will flow from the annular chamber 28 located behind the shoulder 29 through the primary cup 50 into the pressure chamber 40 and through the ducts 45, 45' and the socket pipe 30 back into the fluid reservoir. In the release position, the ring-shaped valve body 32 will then be open again and the slide valve (which is constituted by the elements 27, 26, respectively by the duct 36') be closed.

In conventional boosters, the diameter of the tandem master cylinder is dimensioned to account for the failure of the brake power booster. In the subject matter of the present invention, the diameter of the sleeve 27 is sized in such a manner that its cross-sectional area is dimensioned for the mere foot pressure, the increase of the diameter of the piston 25 relative to the sleeve 27 rendering possible the reduction of the pedal travel when the system is sound. In the booster according to the invention, both a reduction of the pedal travel and an increase of the braking effect are attainable owing to the feature that the effective crosssectional area of the piston is switched down from a to the cross-section of the sleeve 27 when the boosting fails. Moreover, it is a particuiar advantage offered by the inventive booster that it can be fitted in lieu of a conventional booster, without the need of any further modifications either in the braking system or in the automotive vehicle.

As is shown in Figure 4, a floating piston 24' which is centered by means of a screw 59 and a spring pot 60 with spring 61 may be provided as an alternative taking the place of the master cylinder 23 shown in Figure 1 and furnished with a floating piston 24 which is tied to the plunger 44 of the pushrod piston 25. This version bears the advantage that the hydraulic fluid existing in the annular chamber 28 may smoothly flow back during the return stroke, any potential pressure differentials in the pressure chambers 40', 42' as well as in the filling chamber 37' allowing to be easily balanced at the same time.

Claims (11)

1. A vacuum-operated brake power booster with a master cylinder (23), the booster including a movable wall (46) sealed with respect to a booster housing (1) and a control element housing (7) coacting with the said movable wall (46) and containing a double valve (8, 13, 19), and including a valve piston (9) slidable by a piston rod (11), the master cylinder-side end of the said valve piston (9) acting through a reaction device (10) on a push-rod (12) which, on its part, actuates a stepped pistonshaped push-rod (25) of the master cylinder (23) which is flanged to one housing shell (16) of the booster housing, characterised in that the said pushrod (12) is tied to the said control element housing (7) through a cap (21) fastened to said control element housing (7), an axial play (x) being provided between the said cap (21) and the said push-rod (12), by which play (x) the said push-rod (12) is shiftable relative to the said control element housing (7) in the longitudinal direction of the housing, the said cap (21) co-acting with a sleeve (27) which on a shift of the said push-rod (12) relative to the said control element housing (7) actuates a first valve (26,27) that links an annular chamber (28) located behind a large step (a, 29) of the said push-rod piston (25) to a pressure chamber (40) of a primary circuit of the master cylinder through a duct (36, 36') provided in the said pushrod piston (25) and through a second valve (32) closes an intake port (31) arranged between a socket pipe (30) for a fluid reservoir and the said annular chamber (28).

2. A vacuum-operated brake power booster as claimed in claim 1, characterised by a back-up plate (49) having a central opening and being furnished with radially extending studs or fingers (56) which engage in openings (51) arranged in the said sleeve (27) which surrounds a stem (26) of the said pushrod piston (25), said openings (51) being sized such that the said back-up plate (49) is shiftable longitudinally a distance (b) relative to the said sleeve (27), and the pedal-side end of the said sleeve (27) being abutted against the said cap (21) of the said control element housing (7).

3. A vacuum-operated brake power booster as claimed in claim 2, characterised in that the said sleeve (27) being movable coaxially with the said stem (26) of said push-rod piston (25) is furnished with a slidable friction ring (35) at its end facing the master cylinder (23), said friction ring (35) coacting with a ring-shaped valve body (32) which controls the passage of hydraulic fluid from the fluid reservoir through the said intake port (31) into said annular chamber (28) located behind the said pushrod piston (25), which said annular chamber (28) is connected, on its part, with the pressure chamber (40) located before the said push-rod piston (25) via an intake duct (45,45') arranged in the housing of the said master cylinder (23), the passage of hydraulic fluid being controlled, on operation of the brakes, by means of a valve (38) provided with a piston cup (50).

4. A vacuum-operated brake power booster as claimed in claim 2 or claim 3, characterised in that the said stem (26) of the said push-rod piston (25) is furnished with a duct (36,36') extending in the transverse direction and connected to the said pressure chamber (40), the exit of the said duct (36, 36') at the outer surface of the said stem (26) being provided in a plane which in the release position is covered by the master cylinder-side end of the said sleeve (27) pushed over the said stem (26) and which in the braking position is freed by the said sleeve (27) in the event of failure of the booster.

5. A vacuum-operated brake power booster as claimed in any one of claims 2 to 4, characterised in that the said back-up plate (49) takes support at the pedal-side end, or at a head member (34), of the said master cylinder (23) through a spring (52), the latter said spring (52) urging the said sleeve (27) pushed over the said stem (26) of the said push-rod piston (25) via the said back-up plate (49) against the said cap (21) surrounding the said reaction device (10).

6. A vacuum-operated brake power booster as claimed in any of the preceding claims, characterised in that the said push-rod (12) acting on the said push-rod piston (25) passes through an opening provided in the bottom section (53) of said cap (21) and is furnished at its pedal-side end with a push-plate (22) which co-acts with the said reaction device (10) and which is retained by the cylindrical inner wall of the said cap (21).

7. A vacuum-operated brake power booster as claimed in any one of the preceding claims, characterised in that the play (x) is envisaged in the release position between the master cylinder-side lateral face of the said push-plate (22) and the inner side of the said bottom section (53) of said cap (21), which said play (x) corresponds at least to the opening travel of the valve formed by the said duct (36') which extends transversely through the said stem (26), and by the master cylinder-side end of the said sleeve (27).

8. A vacuum-operated brake power booster as claimed in any one of the preceding claims, characterised in that the said cap (21) is formed with a radially outwardly bent rim (54) serving to support the end of an apparatus spring (6) on the side of the said control element housing (7).

9. Avacuum-operated brake power booster as claimed in claim 2, characterised in that the said back-up plate (49) coacting with said sleeve (27) is configured roughly, cup-shaped with a spring (58) being inserted between the bottom section of said back-up plate (49) and a collar or a stop ring (55) which is arranged at the end of said sleeve (27) on the side of said control element housing (7).

10. A vacuum-operated brake power booster as claimed in claim 1, characterised in that a back-up plate (49) coacting with the said sleeve (27) is furnished with a central opening in its said bottom section through which the said sleeve (27) penetrates, radially-inwardly extending studs or fingers (56) of said back-up plate (49) co-acting with a collar or a stop ring (57) provided at the end of said stem (26) of said push-rod piston (25) on the side of said control element housing (7) and the said stop ring (57) dragging the said back-up plate (49) when the said push-rod piston (25) shifts relative to said sleeve (27) in the direction of actuation (direction indicated by the arrow A).

11. A vacuum-operated brake power booster with a master cylinder substantially as herein described with reference to and as illustrated in Figures 1 to 3 with or without reference to Figure 4 of the accompanying drawings.