Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1998-08-11
2000-06-27
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031161, 303 11, B60T 834, B60T 840
Patent
active
060797967
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention relates to a hydraulic brake system for a vehicle for anti-lock control.
U.S. Pat. No. 4,875,741 discloses a hydraulic brake system for a vehicle with an anti-lock control unit. The known vehicle brake system has a tandem master brake cylinder, to which two independent but analogously constructed brake circuits are connected, with each of which one driven vehicle wheel and one non-driven vehicle wheel can be braked. In each brake circuit, a branching brake line leads from the master brake cylinder to wheel brake cylinders of the vehicle driven vehicle wheel and the non-driven wheel. Each wheel brake cylinder is preceded by a wheel brake valve. Also associated with each wheel brake cylinder is a return feed pump, connected parallel to its wheel brake valve, whose suction side communicates with the wheel brake cylinder and whose compression side communicates with the master brake cylinder.
For the anti-lock control mode, the return feed pumps are turned on, and the wheel brake valve associated with the wheel brake cylinder of the vehicle wheel tending to lock is closed at least briefly, once. By variously long on and off times of the wheel brake valve (pulse width modulation), the average pressure of the brake fluid in the wheel brake cylinder can be reduced arbitrarily far compared with the brake fluid pressure in the master brake cylinder. The brake fluid pressure in the associated wheel brake cylinder thus has a sawtooth or triangular kind of course, as a result of which the pressure is modulated in such a way that the vehicle wheel does not lock.
ADVANTAGES OF THE INVENTION
The hydraulic brake system for a vehicle of the invention has a traction control device. It has the advantage that at minimal engineering expense, namely with a total of six magnet valves, a vehicle brake system with individual-wheel anti-lock control and with traction control can be realized. The two pumps of a brake circuit may for instance be embodied like the pumps is disclosed in the aforementioned U.S. Pat. No. 4,875,741, which is hereby incorporated by reference in this regard, or by a stepped piston pump, known per se. The return feed pump, to whose suction side the wheel brake cylinder of the non-driven vehicle wheel is connected, is according to the invention a self-aspirating pump, of the kind known per se.
For anti-lock control, the two return feed pumps are put into operation, and the brake fluid pressure in the wheel brake cylinder of a vehicle wheel that is tending to lock is reduced, for instance by pulse width modulation of the respective wheel brake valve. The switchover valve and wheel brake valves of wheel brake cylinders of the vehicle wheels not tending to lock remain in their open position.
For traction control, the return feed pumps are put into operation, the switchover valve is closed, and the wheel brake valve that precedes the wheel brake cylinder of the non-driven vehicle wheel remains open, so that the return feed pump, to whose suction side the wheel brake cylinder of the non-driven vehicle wheel is connected, pumps brake fluid to the wheel brake cylinder of the driven vehicle wheel, and builds up brake fluid pressure in it, thereby braking the driven vehicle wheel. The wheel brake valve of the wheel brake cylinder of the driven vehicle wheel remains open and the return feed pump to whose suction side the wheel brake cylinder of the driven vehicle wheel is connected pumps the quantity of brake fluid, which it draws from this wheel brake cylinder, back to the wheel brake cylinder through the wheel brake valve, so that it does not lower the brake fluid pressure in that wheel brake cylinder. If the brake fluid pressure is to be lowered, then the switchover valve is opened for a corresponding period of time.
The vehicle brake system of the invention has the further advantage that because of the individual-wheel pressure modulation, a distribution of braking force can be made, for instance between the front and rear axle, depending on the loading of the vehicle. A tendency to vehic
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Breitenbacher Jurgen
Heinsohn Rainer
Kaess Hermann
Klug Andreas
Schmidt Guenther
Greigg Edwin E.
Greigg Ronald E.
Oberleitner Robert J.
Robert & Bosch GmbH
Woller Jeffrey
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