GB2220239A

GB2220239A - Brake actuating unit for automotive vehicles

Info

Publication number: GB2220239A
Application number: GB8914884A
Authority: GB
Inventors: Lothar Schiel; Vladimir Dusil
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1988-07-01
Filing date: 1989-06-29
Publication date: 1990-01-04
Anticipated expiration: 2009-06-29
Also published as: GB8914884D0; GB2220239B; DE3822261A1; FR2633574A1; FR2633574B1

Description

LI. 3 k-A 1 -L = -L 1:7 - 1 1 222n -29 BRAKE ACTUATING UNIT FOR-AUTOMOTIVE

VEHICLES The present invention is concerned with a brake actuating unit for automotive vehicles, comprising a vacuum brake force booster and a tandem master cylinder including a primary piston and a secondary piston, with the vacuum brake force booster having a booster housing subdivided by an axially movable wall into a vacuum chamber and a working chamber, further comprising a control valve disposed in a control housing and mechanically operable by an input member for connecting the working chamber to the vacuum chamber and the atmosphere, respectively, which is formed by a vacuum sealing seat provided on the control housing and by a seat sealing against the atmosphere and provided on the valve piston, that are closed in the releasing position by a poppet valve, and comprising a reaction mechanism for transferring a force reaction occurring in the decelerating process.

A vacuum brake force booster suitable for use with a brake actuating unit of this type has been taught by DE-OS 3318744. The special feature of the vaccum, brake force booster of this type resides in that the control housing is formed by two control housing portions telescopically movable relative to one another by a limited extent, that the second control housing portion, in the initial position, is in abutment with a point stationary on the housing, and that a stop is provided on the control housing 2 confining the movement of the poppet valve.

Although one afore-mentined power brake unit solves the problem encountered, viz. reducing the so-called lost travel to a minimum, in a satisfactory manner, the design thereof is complex and, therefore, costintensive.

The present invention seeks to provide a brake actuating unit of the afore-described type, in which a particularly simple and low-cost design of individual components results without a reduction in the operational safety of the unit.

According to the invention there is provided a brake actuating unit for automotive vehicles, consisting of a vacuum brake force booster and a tandem master brake cylinder having a primary piston and a secondary piston, with the vacuum brake force booster having a booster housing subdivided by an axially movable wall into a vacuum chamber and a working chamber, comprising a control valve disposed in a control housing and mechanically actuable by an input member for connecting the working chamber to the vacuum chamber and the atmosphere, respectively, which is formed by a vacuum sealing seat formed on the control housing and by a seat sealing against the atmosphere and formed on a valve' piston, which seats are closed in the releasing position by a poppet valve, and comprising a reaction mechanism for transferring a reaction force occurring in a decelerating process, characterised in that the movable wall of the vacuum brake force booster is movable independently of the input member and is in communication with a first portion of the primary piston of two-piece configuration of the tandem master brake cylinder, the second portion of which is in operating communication with the valve piston 3 and cooperates with a stationary stop.

The problem with prior art units may be overcome by the invention by making the movable wall of the vacuum brake force booster movable independently of the input member and connecting it to a first part (external piston) of the primary piston of two-piece configuration of the tandem master cylinder the second part (internal piston) of which is in operating communication with the valve piston and in cooperation with a stationary stop. This measure permits an integral simple design of the control housing in which vacuum and atmospheric passageways of major cross-sections can be formed, thereby enabling substantial reductions in response and releasing times to be attained.

In a refinement of the invention, the internal piston is formed as a plunger on the end of an extension of the valve piston facing the master brake cylinder, and the internal piston is sealingly guided in axially displaceable manner within the external piston, thereby attaining a particularly compact and reliably operating brake actuating unit.

To enable a particularly simple assembly of the stop in the tandem master brake cylinder, according to another refinement of the invention, it is suggested that the external piston is connected to the movable wall by means of two axial extensions of circular-segment-type configuration supported on the bottom of an axial recess in the control housing.

The force transmission between the outer piston and the movable wall is effected by means of a metallic sleeve placed into the recess, thereby attains a uniform distribution of the force acting upon' the control housing and substantial strength advantages 4 result in the support area of the extensions.

The reaction mechanism may be formed by the front faces of the two parts of the primary piston to which the pressure fluid volume enclosed in the primary pressure chamber is applied. This measure, in a particularly space-saving manner, permits the transfer of the reaction force to the brake pedal, insuring a substantial improvement in the hysterisis of the functional characteristic of the power brake unit.

In order to convey to the driver the brake feeling in the case of a failure of the primary brake circuit, there may be disposed, in the primary pressure chamber, a second reaction means enabling, in case of failure thereof, in the secondary pressure chamber, a pressure build-up in proportion to the input force according to a predetermined characteristic.

In order that the invention and its various other preferred features may be understood more easily, an embodiment thereof will now be described, by way of example only, with reference to the drawing the single figure of which is an axial sectional view of a brake actuating unit constructed in accordance with the invention.

The vacuum brake force booster as shown in the drawing comprises a vacuum housing 1 subdivided by an axially movable wall 2 into a working chamber 3 and a vacuum chamber 4. The axially movable wall 2 consists of a diaphragm plate 5 deep-drawn from sheet metal, and a flexible diaphragm 6 in abutment therewith (not shown in any detail) which forms, between the outer circumference of the diaphragm plate 5 and the vacuum housing 1, a rolling diaphragm serving as a seal.

A control valve 7 actuable by an input member 8 (piston rod) is coupled with a valve piston 10 having a first valve seat 18 which valve piston is axially guided in a control housing 11 provided with a second valve seat 19.

The two valve seats 18,19 are disposed in a plane in a direction vertical to the actuating direction of the vacuum brake force booster, and cooperate with a poppet valve 23 which, through a pre-stress sleeve 21, by means of a compression spring 24 supported on a flange formed on the piston rod 8, is forced against the valve seats 18.19. The working chamber 3 is in communication with the vacuum chamber 4 through an external air passageway 34 formed in the control housing 11, the control valve 7 and a vacuum passageway 17.

A reset spring 16 schematically shown in the drawing, which is supported on the vacuum-sided front wall of the booster housing 1, maintains the movable wall 2 in the initial position as shown. Moreover, a second compression spring 20 is provided which is supported on the control housing 11 and on the piston rod 8, with the force of such spring providing pre-stress of the valve piston 10 and the first valve seat 18 thereof, respectively, visa-vis the poppet valve 23.

Secured to the front wall of the vacuum housing 1 as shown to the left of the drawing, is a tandem master brake cylinder 40 a housing 41 part of which extends into the vacuum pressure chamber 4 of the vacuum brake force booster. The housing 41 has a longitudinal bore 51 in which a primary piston 42 and a seconary piston 43 confine a primary pressure chamber 44 and a secondary pressure chamber 45 which, through central valves 47,48 and intake 6 chambers 52,53, are in communication with a pressure fluid reservoir (not shown) connected to which are individual brake circuits (not shown either). The primary piston 42, preferably of a two-piece configuration, comprises an external piston 15 guided within the longitudinal bore 51 and provided with a sealing sleeve 27, which external piston, by means of two extensions 22 of segmented cylindrical form is in commupication with the control housing 11, and an internal piston 14 sealingly guided therein in displaceable manner. The front wall of the control housing 11 is provided with an axial recess 31 in which a metallic sleeve 32 is located on which are axially supported the ends of the extensions 22. A safety ring 54 provides locking connection of the extensions 22 to the control housing 11, which safety ring is inserted into a radial groove in the control housing 11, cooperating while radially passing through the metallic sleeve 32 with a groove formed in the surface of the extensions 22. The internal piston 14 pre - ferably formed as a plunger and sealed from the axial port of the external piston 15 by means of an 0-ring 26, is formed by an axial extension 13 of the valve piston 10 which is guided in an axial bore 55 within the control housing 11 and which bore is sealed by a gasket 25. The axial movement of the internal piston 14 to the right is confined by a stationary stop 33 which, in the example as shown, is formed by a disc disposed in the housing 41 of the tandem master brake cylinder 40.

The brake force is transferred to the pressure fluid volume enclosed in the primary pressure chamber 44 by means of a first reaction mechanism 9 formed by two front faces 50 and 49.respectively.

7 provided on the external piston 15 and the internal piston 14, to which front faces the hydraulic pressure prevailing in the primary chamber 44 is applied.

In order to enable the reaction force to be transferred to the brake pedal also in the case of a failure of the primary brake circuit, a second reaction mechanism 12 is provided 'in the primary pressure chamber 44. which reaction mechanism 12 is formed by a resilient reaction disc 29 located in a body 28 in abutment with the external piston 15, which reaction disc 29. on the one hand, is in direct contact with the internal piston 14 and, on the other hand, by means-of a pressure plate 30, cooperates with the opening mechanism 46 of the first central valve 47.

The operation of the brake actuating unit shown in the drawing will now be described.

In the initial position (with the engine in the stand-still position). the two working chambers 3 and 4 may be under atmospheric pressure so that the movable wall 2 is in pressure-equilibrium and is held through the reset spring 16 on the stop in the rearward vacuum housing wall. As the valve piston 10, through the internal piston 14, by the stop 33. is positioned within the tandem master brake cylinder 40, the control valve 7 is in a condition in which the seat 18 sealing against the atmosphere and formed on the valve piston 10. is open and the vacuum seat 19 on the control housing 11 is closed so that the two working chambers 3 and 4 are separate from one another. If the vacuum chamber 4 is now evacuated (during starting of the engine), the pressure difference acting on the movable wall 2 causes movement thereof toward the master brake 8 cylinder 40 so that first the seat 18 sealing against the atmosphere is closed and, immediately thereafter, the vacuum seat 19 is opened. This will permit evacuation of the working chamber 3 in the meanwhile separated from the atmosphere so that, on the movable wall 2, a state of equilibrium re-occurs in which both sealing seats 18,19 of the control valve 7 are closed and the vacuum brake force booster is in a ready-for- use position.

If, during deceleration, the brake pedal (not shown) is actuated, the input member 8 along with the valve piston 10, by the application of force, are displaced to the left, thereby actuating the control valve 7 and causing a pressure difference in proportion to the pedal force to be created on the movable wall 2. This pressure difference generates a boostering force added to the pedal force and transferred to the primary piston 42 of the tandem master brake cylinder 40 to develop a hydraulic pressure in the two pressure chambers 44 and 45 which, through the brake circuits (not shown) is passed to the individual wheel brakes of the automotive vehicle.

If the actuating force acting on the input member 8 is taken away from a partial or fullapplied position, the second compression spring 20 will force the valve piston 10 against the poppet valve 23 so that the first seat (sealing against the atmosphere) is closed and the second (vacuum) sealing seat 19 is opened. Through the second sealing seat 19 now open, a pressure equilibrium between the vacuum chamber 4 and the working chamber 3 is effected so that a subsequent reset of the movable wall 2 will be possible under the action of the reset spring 16 until the internal piston 14 9 abutments the stop 33. At that moment, the aforementioned ready-for-use position is reached.

is 1 3,

Claims

CLAIMS:

A brake actuating unit for automotive vehicles, consisting of a vacuum brake force booster and a tandem master brake cylinder having a primary piston and a secondary piston, with the vacuum brake force booster having a booster housing subdivided by an axially movable wall into a vacuum chamber and a working chambert comprising a control valve disposed in a control housing and mechanically actuable by an input member for connecting the working chamber to the vacuum chamber and the atmosphere, respectively, which is formed by a vacuum sealing seat formed on the control housing and by a seat sealing against the atmosphere and formed on a valve pistonk which seats are closed in the releasing position by a poppet valve, and comprising a reaction mechanism for transferring a reaction force occurring in a decelerating process, characterised in that the movable wall of the vacuum brake force booster is movable independently of the input member and is in communication with a first portion of the primary piston of two-piece configuration of the tandem master brake cylinder, the second portion of which is in operating communicazion with the valve piston and cooperates with a stationary stop.
2. A brake actuating unit as claimed in claim 1, characterised in that the stationary stop is disposed in the tandem master brake cylinder.
3. A brake actuating unit as claimed in claim 1, char&cterised in that the internal piston is formed as a plunger on the end of an extension of the valve piston, facing the tandem master brake cylinder.
4. A brake actuating unit as claimed in claim characterised in that the internal piston is 11 sealingly guided in axially displaceable manner within the external piston.
5. A brake actuating unit as claimed in claim 1, characterised in that the external piston is in communication with the movable wall by means of two axiai extensions of cylindrical segment configuration which are supported on the bottom of an axial recess in the control housing.
6. A brake actuating unit as claimed in claim 5, characterised in that the force transmission between the external piston and the movable wall is effected by means of a metallic sleeve which is mounted in the recess.
7. A brake actuating unit as claimed in any one of the preceding claims, characterised in that the reaction mechanism is formed by front faces of the two pistons to which the pressure fluid volume enclosed within the primary pressure chamber is applied.
8. A brake actuating unit as claimed in any one of claims 1 to 7, characterised in that disposed in the primary pressure chamber is a second reaction mechanism which, in case of a failure thereof, in the secondary pressure chamber, enables a pressure build-up to develop in proportion to the input force in accordance with a predetermined characteristic.
9. A brake actuating unit as claimed in any one of the preceding claims, characterised in that the second reaction mechanism is formed by a resilient reaction disc disposed in a cylindrical body and in operating communication with the external piston through the cylindrical body and, with the internal piston, in direct operating communication, with a pressure plate in abutment with the side thereof facing away from the primary piston, on which 12 pressure plate is supported a part of an opening mechanism of a first central valve.
10. A brake actuating unit substantially as described herein with reference to the drawing.

Published1989 at The PatentOffice, StateHOuse, 66PIl HighHolbornLondonWClR4TF.Furtner c 3piesmaybe obtainedfromThe PauntOfnee.

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