Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1996-10-30
1998-06-02
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031142, 3031152, 303DIG4, 303162, 188358, B60T 832, B60T 836, B60T 860, B60T 1366
Patent
active
057589305
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an electronically controllable anti-lock brake actuation system for automotive vehicles, including a dual-circuit master brake cylinder operable by an actuating pedal, braking pressure generators actuatable by an electronic control unit, each of the braking pressure generators having a piston slidable in a cylinder bore from an initial position, each piston separating a first working chamber, which is confined by the large piston surface and to which each one wheel brake of the vehicle is connected directly and the master cylinder is connected by way of a closable hydraulic connection, from a second working chamber which is confined by the small piston surface and is connected to the master cylinder, wherein the stepped piston is operable to achieve a braking pressure generation or boosting.
BACKGROUND OF THE INVENTION
DE-OS 34 24 912 discloses a brake actuation system of this type. In this known brake actuation system, the hydraulic connections between the braking pressure generators and the master brake cylinder are closed by way of bores (breathering bores) provided in the hydraulic cylinders of the braking pressure generators. During operation of the braking pressure generators, the bores are overridden by sealing elements arranged on the pistons.
Apart from the fact that pedal resetting without attenuation against the driver's foot occurs in this arrangement, the closable hydraulic connections do not permit reduction of the hydraulic pressure prevailing in the wheel brakes to almost zero bar in an ABS control operation because the necessary entire resetting movement of the braking pressure generator piston would cause opening of the above-mentioned bore, where the comparatively high pressure generated by the driver prevails.
Further, the valve assembly, formed of the combination of the bore (breathering bore) and the sealing element, is directly operated with a time delay by the electric drive due to the not negligible mass inertias. The time delay, in turn, causes the introduction of a considerable pressure fluid volume, thereby rendering impossible a pressure reduction to values proximate zero bar also for this reason. In particular control operations at low .mu.-values are thereby impaired.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is the improvement of an electronically controllable brake actuation system of the previously mentioned type so that the shortcomings involved especially in ABS control operations are prevented. More particularly, the pedal feel shall be improved, and the quality of ABS control shall be enhanced in addition.
According to the present invention, a first object is achieved because a first and a second electromagnetically operable separating valve is inserted in the connection between the first working chamber and the master brake cylinder, and in that the connection between the master brake cylinder and the second working chamber is effected exclusively by way of the second separating valve, and in that the initial position of the stepped piston permits a return stroke in opposition to its actuating direction.
A second object of the present invention, wherein no connection exists between the first working chamber and the master brake cylinder and the second working chamber is connected to the master brake cylinder by way of a closable hydraulic connection, and the stepped piston is operable only so as to achieve a braking pressure generation, is achieved in that an electromagnetically operable valve is interposed between the second working chamber and the master brake cylinder, and the connection is open in the valve's first switch position and, in the valve's second switch position, the master brake cylinder is isolated from the second working chamber and a connection is established between the first and the second working chamber, and in that the initial position of the stepped piston permits a return stroke in opposition to its actuating direction.
These measures render possible a
REFERENCES:
patent: 4756391 (1988-07-01), Agarwal et al.
patent: 5163744 (1992-11-01), Tierney et al.
patent: 5246283 (1993-09-01), Shaw et al.
Feigel Hans-Jorg
Klen Andreas
Neumann Ulrich
Schiel Lothar
Butler Douglas C.
ITT Automotive Europe GmbH
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