Fluid-pressure and analogous brake systems – Speed-controlled – Wheel speed sensor and braking pressure sensor
Patent
1996-02-08
1998-02-24
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Wheel speed sensor and braking pressure sensor
36442601, G06F 770
Patent
active
057205345
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention pertains to a method and to an apparatus for determining the application pressure of a braking mechanism for vehicles by maesuring pressure in the mechanism and measuring the rotational speed in at least one of the wheels to be braked.
A process and a device of the type is question are known from DE 41 12 845 A1. In the compressed air brake system described in that document, the application pressure of the individual wheel brakes is determined by evaluation of the change in pressure over time during the actuation of the brake. The application pressure thus determined is used to correct the nominal pressure derived from the driver's command for the individual wheel brakes with the goal of producing the same braking force at all the wheels of the vehicle or at all the wheels of one axle. As a result, influences attributable to wear, variations in the coefficient of friction, mechanical losses, and tolerances at the individual wheel brakes are compensated. To determine the application pressure, the increase in pressure over time during a brake actuation is detected; and, upon recognition of an inflection, the brake pressure then prevailing is stored as the application pressure. As another way of determining the application pressure, a distance sensor can be used to determine the distance traveled by the piston rod of a brake cylinder. The pressure value which is present when an inflection occurs in the curve of the distance traveled by the piston rod versus time is then stored as the application pressure. The additional distance sensor for detecting the brake application pressure improves the accuracy of the determination of the application pressure, because the time-pressure curve depends strongly on the actuation of the nominal value transmitter by the driver. This distance sensor nevertheless represents another sensor for the brake system, a sensor which, furthermore, is actuated directly by the braking pressure.
The state of the art offers various methods and devices for determining the application pressure. These methods and devices determine the application pressure either on the basis of the pressure-time curve upon actuation and release of the brake or by the use of an additional distance sensor. Such methods and devices are described in DE 42 06 238 A1, DE 42 06 240 A1, and DE 42 30 911 A1.
SUMMARY OF THE INVENTION
The object of the invention is to improve the accuracy with which the application pressure of a braking mechanism in a vehicle is determined.
According to the invention, the change over time of the measured rotational speed is determined, and the application or release of a brake is determined based on the change over time. Based on the detected pressure when the brake is applied or released, an application pressure is determined, which is used to correct the nominal pressure derived from the driver's command.
The procedure according to the invention improves the way in which the application pressure is determined in electronically controlled brake systems, including electrical, electro-pneumatic, and electro-hydraulic brake systems, regardless of whether drum brakes or disk brakes are present. It is especially advantageous to use the braking pressure during the pressure release phase to determine the application pressure. Because the pressure medium is escaping during the pressure release phase, the conditions for evaluating the pressure curve are more stable than they are during the pressure buildup phase.
Determining the application pressure from pressure values which are obtained during both the pressure buildup and the pressure release phase is especially advantageous. In this case it is advantageous to determine the hysteresis which is present and to take this hysteresis into account in the determination of the application pressure.
Particular advantages are to be derived from implementing the process according to the invention in conjunction with the use of a proportional valve as a control valve for controlling the braking pressure. Because the si
REFERENCES:
patent: 3718374 (1973-02-01), Ochia
patent: 4414630 (1983-11-01), Harris
patent: 4811993 (1989-03-01), Matsumoto
Bartz C. T.
Oberleitner Robert J.
Robert & Bosch GmbH
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