Motors: expansible chamber type – Working member position feedback to motive fluid control – Plural input signal means for single motor valve
Reexamination Certificate
2003-04-30
2004-01-06
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Plural input signal means for single motor valve
C091S369200
Reexamination Certificate
active
06672198
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a vacuum brake booster having a vacuum chamber and a working chamber separated from one another by a movable wall, a control valve, which comprises a housing coupled workingly to the movable wall and which to achieve a pressure difference at the movable wall is capable of controlling the supply of atmospheric pressure or above-atmospheric pressure to the working chamber in dependence upon the displacement of an actuating piston, and having an emergency braking aid comprising a permanent magnet and an armature, which cooperates with the permanent magnet and is resiliently biased counter to actuating direction and during an emergency braking operation is drawn into abutment with the permanent magnet, with the result that the control valve is held open for the supply of atmospheric pressure to the working chamber.
Vacuum brake boosters have been known for some time and millions are in use for boosting the actuating forces of a vehicle hydraulic brake system and therefore keeping the actuating forces at a level which is comfortable for the driver of a vehicle. Likewise known are so-called emergency braking aids, which are frequently also referred to as “brake assists”. These are devices which, given substantially the same actuating force, in an emergency braking situation provide a driver with increased braking power.
Emergency braking aids may be divided into electro-magnetically actuated and mechanically actuated systems. For reasons of cost, the use of a mechanical system is frequently desirable.
A vacuum brake booster having such a mechanical emergency braking aid is known, for example, from WO 00/07862, and corresponding U.S. Pat. No. 6,505,539 B2 which is incorporated by reference herein. Said vacuum brake booster has a vacuum chamber and a working chamber separated from one another in a pressure-tight manner by a movable wall. A control valve, which has a housing coupled workingly to the movable wall, comprises an atmospheric valve seat, which to achieve a pressure difference at the movable wall is capable of controlling the supply of atmospheric pressure to the working chamber in dependence upon the displacement of an actuating piston, coupled to an input element of the brake booster.
For improved boosting of the braking force during emergency braking operations, a mechanical emergency braking aid is disposed in the housing of the control valve. The emergency braking aid comprises an armature, which cooperates with a permanent magnet and is rigidly connectable in actuating direction to the actuating piston by means of a stop formed on the actuating piston. The armature is resiliently biased counter to the actuating direction of the brake booster towards the stop formed on the actuating piston and, in the initial position of the control valve, is held at a first distance from the permanent magnet. In the course of an approach towards the permanent magnet the armature, when it is less than a previously defined second distance, which is smaller than the first distance, from the permanent magnet is drawn by the permanent magnet counter to the resilient bias force acting upon the armature and with simultaneous cancellation of its, in actuating direction, rigid coupling to the actuating piston into abutment with the permanent magnet. Consequently, the atmospheric valve, whose valve seat is formed integrally with a sleeve-shaped extension coupled rigidly to the armature, is held open to the maximum extent. The maximum possible pressure difference then builds up, with the result that the maximum possible boosting force of the brake booster is achieved.
After an emergency braking operation the armature has again to be detached from the permanent magnet. This is effected by means of a bar, which is rigidly connected to the actuating piston, extends at right angles to a longitudinal axis of the actuating piston and projects through a recess of the sleeve-shaped extension of the armature, which extension extends counter to actuating direction. During a return stroke of the input element of the brake booster, the actuating piston as well is displaced counter to actuating direction. The bar coupled to the actuating piston in said case comes into abutment with an end of the recess of the sleeve-shaped extension facing the vacuum chamber, so that the forces displacing the actuating piston counter to actuating direction are introduced into the sleeve-shaped extension coupled to the armature. As said forces exceed the force required to detach the armature from the permanent magnet, the displacement of the actuating piston counter to actuating direction, which is associated with a reduction of the actuating force summoned up by the driver, leads finally to a detaching of the armature from the permanent magnet.
Because of the displacement of the actuating piston counter to actuating direction which is necessary to detach the armature from the permanent magnet, the stop formed for the armature on the actuating piston has also moved away from the armature by the displacement distance of the actuating piston. After the detachment of the armature from the permanent magnet, the armature is consequently accelerated along the displacement path of the actuating piston by the bias force acting counter to the actuating direction of the brake booster upon the armature. The armature therefore impacts at high speed against the stop formed on the actuating piston. Said impact of the armature on the stop provided for the armature produces a clearly perceptible, obtrusive cutout noise.
Operating positions of the brake booster are additionally possible, in which, prior to the impact of the armature on the stop formed on the actuating piston, the valve seat formed on the free end of the sleeve-shaped extension of the armature impacts on the associated valve sealing element of the control valve and pulls the latter abruptly open. As a result, the connection between the working chamber and the vacuum chamber is opened and the braking force boost summoned up by the brake booster is abruptly reduced, which manifests itself to the driver in the form of an unpleasant force impact on the brake pedal.
SUMMARY OF THE INVENTION
The object of the invention is to provide a vacuum brake booster with mechanical emergency braking aid, which presents improved operating behaviour.
Proceeding from a vacuum brake booster of the type initially described, said object is achieved according to the invention by provision of a coupling device, which allows detachable coupling of the armature to the actuating piston.
By means of the coupling device according to the invention the movement of the armature counter to actuating direction relative to the actuating piston may be influenced in order to prevent an uncontrolled relative movement between armature and actuating piston as a result of detaching of the armature from the permanent magnet. The coupling device makes it possible, after the detachment of the armature from the permanent magnet, to prevent an acceleration of the armature counter to actuating direction or at least reduce such an acceleration in such a way that the cutout problems observed in prior art vacuum brake boosters no longer arise in vacuum brake boosters according to the invention.
Coupling is preferably effected as a consequence of a return stroke movement of the actuating piston, i.e. the coupling device may be activated by a return stroke movement. Coupling may be effected before or after the armature was pulled off the permanent magnet.
The coupling of armature and permanent magnet may be effected e.g. by means of frictional, non-positive or positive engagement. Preferably, the coupling device is designed in such a way that a coupling is effected only after a specific return stroke of the input element of the vacuum brake booster but still before detachment of the armature from the permanent magnet. Armature and actuating piston may be coupled both directly and indirectly to one another. An indirect coupling of actuating piston and armature is possible, for
Friedsam Ludwig
Plewnia Heinrich
Puscher Gerd
Schlüter Peter
Lazo Thomas E.
Look Edward K.
Lucas Automotive GmbH
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