Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1996-11-26
1999-08-24
Poon, Peter M.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031134, 3031153, B60T 844
Patent
active
059416092
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for controlling the braking pressure in an automotive vehicle brake system equipped with an ABS system and including a brake power booster operable by an electric control element, wherein the rotational speed of the individual vehicle wheels is determined.
A control method of this type is disclosed in German patent application No. 42 17 409, for example. In the implementation of the method described in the application, the braking pressure introduced into the wheel brake is compared with a memorized braking pressure nominal value, and the brake power booster is operated in order to vary the boosting force as a function of the comparison result. A disadvantage of this known method is the high costs incurred by the pressure measurement.
German patent application No. 42 38 333 discloses a vacuum brake power booster including a control valve which is electrically operable by an electromagnet. The electromagnet interacting with the valve member of the control valve is rigidly connected to a valve piston which operates the control valve mechanically. The valve member defines a pneumatic chamber in a control housing accommodating the control valve. The pneumatic chamber is connected to the ventilatable working chamber of the brake power booster by way of passages. Thus, the valve member is permanently pressure-balanced.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a method of braking pressure control of the type previously referred to which permits achieving an accurate analog control of the pressure introduced into the wheel brakes of the vehicle by making use of data which are already provided in up-to-date anti-lock brake systems.
According to the present invention, this object is achieved by a comparison of the actual rotational speed value measured on the wheel during braking with a memorized, desired rotational speed nominal value and by operation of the electric control element as a function of the comparison result. In specifying the present invention, the brake power booster is configured as a vacuum brake power booster which is operable by an electromagnet independently of the driver's wish, and the current which is to be supplied to the electromagnet is controlled directly proportionally as a function of the comparison result. Preferably, a value of the hydraulic pressure introduced in the master brake cylinder is assigned to each value of the independent actuating force generated by the electromagnet, to such effect that an increase in the hydraulic pressure corresponds to an increase in the independent actuating force.
In another preferred aspect of the present invention, the quality of the proposed control operation is enhanced because the current to be supplied to the electromagnet is controlled proportionally to the pneumatic differential pressure acting on the valve member. It is particularly favorable that a pneumatic effective surface is provided which interacts with the valve member of the control valve and, when acted upon by the pneumatic differential pressure, generates a force that counteracts the actuating force generated by the electromagnet.
The force counteracting the actuating force generated by the electromagnet includes the force of a valve spring, which biases the valve member in the closing direction of the control valve, and two pneumatic force components which act in opposition to each other. The first force component, which counteracts the force of the valve spring, is produced by the pneumatic pressure difference between the atmospheric pressure and the pressure prevailing in the working chamber, and by a first effective surface provided on the valve member. The second force component supporting the force of the valve spring is produced by the pneumatic pressure difference between the pressure prevailing in the working chamber and the vacuum prevailing in the vacuum chamber, and by a second effective surface provided on the valve member.
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REFERENCES:
patent: 4484281 (1984-11-01), Skarvada
patent: 5173859 (1992-12-01), Deering
patent: 5224410 (1993-07-01), Graichen et al.
patent: 5460074 (1995-10-01), Balz et al.
U.S. application No. 07/423,315 (Labeled "A") for Automotive Vehicle Brake System.
German Search Report.
European Search Report.
Bauer Jurgen
Dusil Vladimir
Wagner Wilfried
ITT Automotive Europe GmbH
Poon Peter M.
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