Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1994-08-25
1996-01-23
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031154, 3031161, 3031191, 303901, 303 841, B60T 834, B60T 848, B60T 842
Patent
active
054860407
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is concerned with a brake pressure controller for a hydraulic vehicle brake system. The brake system includes a master cylinder, at least one wheel brake cylinder for actuating a brake and a brake conduit for providing pressure fluid communication between the wheel brake cylinder and the master brake cylinder. A brake pressure control circuit is provided in the brake conduit between the master brake cylinder and the wheel brake cylinder.
The brake system also includes a pump and control valves, controllable through a controller, which connect the wheel brake cylinder to the brake conduit or a return conduit leading to the inlet of the pump. The control valves include at least one valve provided in the brake conduit between the master brake cylinder and the brake pressure control circuit, which at least one valve, in a first operating mode, connects the outlet of the pump, through the brake conduit, to the master brake cylinder, and, in a second operating mode, discontinues the connection between the outlet of the pump and the master brake cylinder and permits a connection between the inlet of the pump and the master brake cylinder or a reservoir.
A brake pressure controller of the above-described type is known from German Patent No. DE-OS 38 31 426. The automatic control system of the brake pressure acting on the wheel brake cylinders responds to the rotating movement of one or several wheels of an automotive vehicle monitored by a monitoring system. The control system prevents the wheels from locking during a braking operation through brake slip control, and prevents the driven wheels from racing, during start-up, through traction slip control.
The first mode of operation is provided for brake slip control while the second mode of operation is provided for traction slip control. In known brake pressure control systems, the brake pressure cylinder, in the first mode of operation during a pressure reducing step for lowering the brake pressure, is connected only to a low-pressure accumulator and to the inlet of the pump. If the low pressure accumulator is empty, there is a danger that the pressure in the wheel brake cylinder may be lowered, through the intake force of the pump, to such an extent that a retraction of the brake piston and an ingress of air are likely to occur, which might affect the braking operation and the brake pressure control.
SUMMARY OF THE INVENTION
It is an object of the invention to improve a brake pressure controller of the above-mentioned type that, during operation, the pressure of a wheel brake cylinder cannot fall below atmospheric.
This problem, in the practice of the invention, is solved in that the inlet of the pump includes a pressure holding valve which is closed in the resting position. In the first mode of operation, the pressure holding valve requires, for opening, an excess pressure in the return conduit which is above atmospheric pressure. In the second mode of operation, the pressure holding valve requires only a slight opening pressure in the return conduit to enable an automatic intake of the pump.
The configuration according to the present invention prevents the brake pressure in the wheel brake cylinder from dropping below the opening pressure of the pressure holding valve which is above atmospheric pressure, during those instances of first mode of operation when the wheel brake cylinder is separated from the master brake cylinder. Even with a complete pressure decrease through corresponding control commands of the controller, a residual pressure of above 1 bar will be maintained in the return conduit so that an ingress of air or a withdrawal of the brake piston is effectively avoided.
In the second mode of operation, the wheel brakes of the driving wheels of the vehicle are controlled by the controller without actuating the master brake cylinder and, in this way, are automatically actuated. The required brake pressure is generated by the pump. The higher opening pressure of the pressure holding valve, which is
REFERENCES:
patent: 5000525 (1991-03-01), Reinartz et al.
patent: 5152586 (1992-10-01), Burgdorf
patent: 5297862 (1994-03-01), Reinartz et al.
patent: 5383718 (1995-01-01), Burgdorf et al.
Beck Erhard
Dinkel Dieter
Butler Douglas C.
ITT Automotive Europe GmbH
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