Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1994-09-30
1995-10-24
Look, Edward K.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91376R, F15B 910
Patent
active
054600740
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a vacuum brake power booster for automotive vehicles and more particularly to a vacuum brake power booster for automotive vehicles having a booster housing whose interior is subdivided into a vacuum chamber and a working chamber and wherein the booster housing includes a control housing carrying the movable wall and accommodating a control valve which controls the pressure differential acting upon the movable wall.
BACKGROUND OF THE INVENTION
A vacuum brake power booster of this general type is disclosed in European patent application 0 478 396 A1. The electromagnet in this prior-art vacuum brake power booster which actuates the third sealing seat guided in the control housing is associated with the control housing or, rather, is immovably arranged in a recess thereof facing the vacuum chamber. On independent actuation of the vacuum brake power booster by the electromagnet, relative movement occurs between the control housing or, respectively, a third sealing seat and the valve piston. This means lost travel must be additionally overcome by the electromagnet which already must generate a high amount of actuating force at the beginning of the independent actuation in order to open the control valve in opposition to the forces caused at its valve member.
Also, the problems arising with the assembly of a master brake cylinder which projects into the booster housing, are considered unfavourable and can only be overcome by modifying the assembly dimensions of the brake power booster.
Therefore, the object of the present invention is to propose arrangements which considerable reduce the independent actuating force to be generated by the electromagnet.
This object is achieved by the present invention in that the electromagnet, rigidly coupled to the valve piston, is arranged so as to be slidable in the control housing so that the third sealing seat is synchronously movable with the valve piston.
To realize the inventive idea, in an advantageous improvement upon the present invention, wherein a push rod transmitting the output force of the vacuum brake power booster takes support on the control housing by the intermediary of a rubber-elastic reaction disc, the electromagnet is arranged in a preferably bowl-shaped axial extension of the valve piston, the extension being closed by a closure member which, additionally, permits transmitting the input force introduced at the actuating rod to the reaction disc. This design is compact and does not require an increased axial overall length and which permits to expediently integrate a master brake cylinder connected downstream of the vacuum brake power booster in the booster housing.
In order to obtain a favourable course of the lines of flux generated by the electromagnet, according to another favourable improvement upon the subject matter of this invention, the armature of the electromagnet is partly guided in the closure member, the force transmission between the third sealing seat and the armature taking place by means of a cylindrical pin to which a force-transmitting plate carrying the third sealing seat is secured. These provisions permit to reduce magnetic losses which are caused by stray fluxes or radial forces, respectively.
In a weight-optimized design variant of the subject matter of the present invention, the third sealing seat is provided on a ring which is sealedly guided in the control housing and is connected to the force-transmitting plate by means of at least two retaining arms, preferably opposed in radial direction. Preferably, the force-transmitting plate has a rectangular configuration and can be arranged in a radial groove in the valve piston.
Further, it is preferable that the third sealing seat is interposed radially between the two sealing seats.
Proper functioning of the brake power booster according to the present invention, in particular upon return movement of the movable wall, is ensured in another favourable embodiment in that the third sealing seat is arranged in an axially offset manner
REFERENCES:
patent: 4608825 (1986-09-01), Fontaine
patent: 5096267 (1992-03-01), Volz
patent: 5172964 (1992-12-01), Levrai et al.
patent: 5233904 (1993-08-01), Gautier et al.
Balz Jurgen
Bauer Jurgen
Bill Karlheinz
Drott Peter
Harth Ralf
ITT Automotive Europe GmbH
Look Edward K.
Nguyen Hoang
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