Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1992-06-12
1994-03-15
Look, Edward K.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91376R, 92 99, 92101, F15B 910
Patent
active
052938085
DESCRIPTION:
BRIEF SUMMARY
The invention is related to a brake power booster with a booster housing which is divided into sealed vacuum power chambers by an axially movable wall subjected to a pneumatic pressure differential. A control valve positioned within a control housing, controls the pressure differential, and is actuatable by a valve piston. The valve piston is slidable by a piston rod which also acts on an output push rod by a connection comprised of a transmission ratio disc and an elastic reaction disc. A process must be employed during production for the precise adjustment of the axial distance between the transmission ratio disc and the reaction disc of the vacuum brake power booster.
It is necessary to adjust as exactly as possible the forementioned distance, the so-called "z" dimension, in order to reach the characteristic curves required.
In this context, the "z" dimension to be adjusted determines the behavior of the booster in the initial phase of its actuation, in particular, the level of the jumping rise of the output force during actuation with a pre-established input force (the so-called "jumper effect").
In the prior-art adjustment procedure, the booster housing of the ready-mounted vacuum brake power booster is evacuated, and the power chamber is vented simultaneously while measuring the output force. Venting takes place by sliding the valve piston under the effect of the pre-established input force of, for example, 300N. If and when the determined value of the output force falls within a pre-determined range, the adjustment procedure will be ended. If the above-mentioned force value falls outside the desired range, then both the push rod and the reaction disc with the transmission ratio disc being abutted against it must be removed in order to replace the transmission ratio disc with a new one which is correctly dimensioned. Upon reinstalling the reaction disc and the push rod, it is assumed that the desired "z" dimension has been reached, and the mounting operation can be finished.
The high costs of manufacture resulting from this complicated, time consuming adjustment procedure, is a significant disadvantage.
A further disadvantage arises in that all of the component parts (valve piston, reaction disc and transmission ratio disc) which are of importance for achieving the proper "z" dimension must meet very close tolerances.
Finally, there is a comparatively high reject rate caused by instances of incorrectly adjusted components.
It is, therefore, the object of the present invention to provide a vacuum brake power booster of the type described and a process for the adjustment of the "z" dimension which together with a considerable reduction of the mounting costs and of the reject rate results in a narrower range of output force levels.
SUMMARY OF THE INVENTION
According to the invention, this object is achieved in that the valve piston is provided with means which render possible a modification of its effective axial length from the point of engagement of the piston rod to the elastic reaction disc in the assembled brake power booster, the axial effective length of the valve piston adjusted to vary the "z" dimension to achieve the predetermined force output.
The valve piston may be constituted by two parts, axially movable in respect of each other to a limited extent. This may be accomplished by an adjustment bushing which is abutted against the transmission ratio disc in the axial direction and is axially guided within the control housing to be rotationally fixed, and by a front part which interacts with the piston rod, the adjustment bushing and front part interconnected by a threaded connection.
According to the process, the effective length of the valve piston is modified by rotating the front part in respect to the adjustment bushing, the front part and adjustment bushing being fixed in their adjusted position as soon as the desired range of the output force is reached.
In another embodiment of the inventive brake power booster, it is envisaged that the valve piston is constituted by a front part wh
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patent: 4487105 (1984-12-01), Harrison
patent: 4611526 (1986-09-01), Arino et al.
patent: 4892027 (1990-01-01), Wagner et al.
patent: 4970940 (1990-11-01), Boehm et al.
patent: 5136927 (1992-08-01), Rossigno et al.
patent: 5146837 (1992-09-01), Inoue
Bauer Jurgen
Jakobi Ralf
Kraft Peter
Rueffer Manfred
Alfred Teves GmbH
Lewis J. Gordon
Look Edward K.
Nguyen Hoang
Seitter Robert P.
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