Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1994-08-19
1996-01-02
Look, Edward K.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
913693, 91376R, F15B 910
Patent
active
054798442
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a pneumatic booster with electromagnetic servo control, especially for motor vehicle brake systems as recited in the preamble of claim 1.
In a known brake pressure booster of this kind (EP 0 478 396) the abutment member is secured to the valve housing and the piston has a broad annular groove engaged, with axial clearance, by the abutment member. Behind the groove, in axial direction, the piston has a second, narrower annular groove followed axially by a cylindrical section on which the valve closing member is guided for axial displacement. The valve closing member has a rear end which is bent radially inwardly like a hook and engages with axial clearance in the second annular groove of the piston, whereby the axial relative movability of the valve closing member with respect to the piston is limited. The electromagnet is disposed at an axial distance behind the sealing member, it comprises a coil which is fastened on the actuator member as well as a sleeve-like armature which is guided for axial displacement on the actuator member. In the area of its rear end, the valve closing member has a flange which projects radially inwardly at an axial distance behind the rear end of the piston. The valve spring is located between this flange and the piston. Between the flange and the armature, a sleeve is guided on the actuator member to be pushed forwardly by the armature upon excitation of the electromagnet. Hereby it displaces the valve closing member, too, in forward direction away from the sealing member. In this manner, forward movement of the valve closing member can be effected electromagnetically, independently of or in addition to forward movement of the piston caused by way of the actuator member, so as to separate the two chambers in the valve housing from each other and let ambient air flow into the rear chamber.
With this known booster, the normal position of the valve closing member is defined exclusively by the position of the sealing member which is engaged by the second valve seat formed at the valve closing member, while the sealing member itself engages the first valve seat which is formed at the valve housing. The full force of the valve spring acts through the valve closing member on the sealing member so that the latter must be loaded in opposite direction by a corresponding stronger spring to make sure it can engage the first valve seat. The positioning of the valve closing member depends on the location of the valve housing, on certain tolerances of length of the same, and on elastic deformations of the sealing member and, as a consequence, it is inaccurate. Due to this inaccurate positioning of the valve closing member the relative motions between the two valve seats and the sealing member which are needed to initiate and terminate a normal braking operation can be achieved only by relatively great axial movements of the actuator member. This means that corresponding distances of loss occur at a brake pedal, or the like, which is connected to the actuator member.
It is the object of the invention to improve a brake pressure booster of the kind specified initially in such manner that it can be controlled especially sensitively by small movements of the actuator member.
The object is met, according to the invention, by the features of claim 1.
True, a pneumatic brake pressure booster is known (EP 0 405 603 A2) with which a piston or tappet disposed between an actuator member and an output member is adapted to find support on a stop of the booster casing through a radial abutment member which is fixed to the piston or tappet. In this way a normal position is defined for the piston and for a valve seat formed directly on the piston. However, there is no possibility of exerting any electromagnetic influence on the position of this valve seat.
The arrangement according to the invention of an abutment member which is fixed to a piston disposed between the actuator member and the output member and which passes with axial clearance through a recess formed in a valve closing
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Heibel Helmut
Pickenhahn Josef
Look Edward K.
Lucas Industries Public Limited Company
Nguyen Hoang
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