Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1996-03-01
1997-11-25
Nguyen, Hoang
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91376R, F15B 910
Patent
active
056900155
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pneumatic brake booster comprising a housing which is divided into a vacuum chamber and a working chamber, in which a dual valve arrangement having a first valve means between the vacuum chamber and the working chamber and a second valve means between the ambient atmosphere and the working chamber is arranged at the housing, in which the valve arrangement, in an inoperative position, allows having pressure levels in the vacuum chamber and in the working chamber which are different from the ambient atmospheric pressure, and in an operative position, keeps the vacuum chamber sealed off and allows communication between the ambient atmosphere and the working chamber, and in normal operation is actuatable by an actuating rod.
A pneumatic brake booster of this type has been known from EP 0 478 396 A1. But it is a drawback of said arrangement that the construction of the valve necessitates different, relatively small cross-sections of the valve passages which may cause undesired whistling or sizzling upon actuation of the brake booster. Besides, the speed of pressure build-up or pressure decay, respectively, is relatively low because of the small cross-sections. Another disadvantage of the arrangement of the electromagnetic actuator is that the coil is immovable with respect to the valve housing of the brake booster and an armature slidingly displaceable on the actuating rod is disposed in the interior of the electromagnetic coil; said armature must be able to move with little delay and low friction both with respect to the inner wall of the coil and with respect to the actuating rod. Since the actuating rod performs also a slight tilting movement during its movement in longitudinal direction, it is possible that problems are encountered (jamming, canting or the like of the armature relative to the actuating rod or the coil). Another problem in said arrangement is constituted by the number of movable parts or parts to be moved which have to be provided with the respective tolerances and made wear resistant.
Another drawback of said arrangement is that, when the pedal is not actuated, an automatic braking by activation of the magnetic coil is not possible, for an effective sealing of the working chamber vis-a-vis the vacuum chamber along the entire stroke of the valve housing cannot be attained because of the high axial movability of the valve housing relative to the actuating rod, and the comparatively small, possible opening stroke of the valve between the working chamber and the ambient atmosphere.
From DE 39 20 766 A1 it has been known to provide a vacuum pressure brake booster in which the valve body can be pulled in opposite directions by two electromagnets disposed in the control valve housing, for building up pressure in the brake system independently of the pedal actuation.
It has been known from EP 0 140 187 B1 to provide a brake booster in which, for pressure compensation, the vacuum chamber and the working chamber may be connected by an electromagnetically controlled valve. It is furthermore described that an actuation of the brake system is achieved by a controlled additional ventilation of the working chamber. The arrangement described in said patent is relatively large in size and complex, however, due to the externally arranged separate solenoid valve.
From DE 38 20 657 A1 it has been known to provide a pneumatic brake booster comprising a housing which is divided into a vacuum chamber and a working chamber. A dual valve arrangement is disposed with a first valve means between the vacuum chamber and the working chamber, and with a second valve means between the ambient atmosphere and the working chamber. In an inoperative position, the valve arrangement allows a pressure level in the vacuum chamber and in the working chamber that is different from the ambient atmosphere. In an operative position, the valve arrangement keeps the vacuum chamber sealed off and allows a communication between the ambient atmosphere and the working chamber. An electromagnetic actuator w
REFERENCES:
patent: 5263399 (1993-11-01), Flory et al.
patent: 5460074 (1995-10-01), Balz et al.
patent: 5479844 (1996-01-01), Heilbel et al.
Michels Erwin
Schluter Peter
Lucas Industries Public Limited Company
Nguyen Hoang
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