Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1990-08-09
1992-03-24
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303DIG2, 303DIG6, B60T 840
Patent
active
050981730
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an anti-locking hydraulic brake system comprising at least one wheel brake and an auxiliary pressure source, with an inlet valve being inserted into the conduit between the auxiliary pressure source and the wheel brake and an outlet valve connected to the return conduit.
A brake system of this type is disclosed, for example, in German patent document DE-OS 36 27 000 which discloses a dual-circuit brake system comprising a tandem master cylinder and a pump for each brake circuit. The wheel brake cylinders, through respective inlet valves, are each in communication with the pressure conduit leading to the pump, and with the brake circuit leading to the master brake cylinder, respectively, and, through an outlet valve, to the return conduit leading to the reservoir. The inlet valve is normally opened, while the outlet valve is normally closed.
During a deceleration process, the rotation of the wheels is permanently monitored. If one of the wheels tends to lock, the pump drive is actuated, and the inlet and outlet valves of the wheel tending to lock are excited such that a pressure is adjusted in the wheel brakes correlating with the optimum slip value of the wheel. For lowering the pressure, the outlet valve is opened and the inlet valve closed, while, for maintaining the pressure, both valves are closed, and, for increasing the pressure, the inlet valve is opened and the outlet valve closed.
The inlet and outlet valves are electromagnetically excited valves comprising a closure member seated on a valve seat. During an anti-locking-controlled deceleration operation, on the valves, a pressure gradient occurs in the brake fluid resulting in control noises causing annoying the driver of the automotive vehicle. It is, therefore, an object of the present invention to substantially decrease the control noises on the valve.
SUMMARY OF THE INVENTION
The underlying problem is solved in accordance with the present invention in that a differential pressure limiter is inserted between the auxiliary pressure source and the inlet valve, whereby a brake fluid pressure exceeding the pressure corresponding to the force of a valve spring is relieved, to cause a defined constant pressure gradient on the inlet valve determined by the valve spring. Such a pressure gradient may be adjusted to, for example, 25 bar which is thus substantially lower than the pressure gradient usually occurring with a panic anti-locking-controlled deceleration in the brake system according to the afore-mentioned German patent document. It has been found that the control noises increases with an increasing pressure gradient, being particularly noisy once the driver, in a panic deceleration, applies full force to the brake pedal. If this occurs at a lower locking level (frozen roads) maximum pressure gradients exist that cause maximum control noises which will particularly affect the inlet valve. Lowering the pressure gradient on the inlet valve, substantially reduces control noises.
Another recognized advantage that is provided by the present invention resides in that the algorithm for controlling the valves can be substantially simplified. Due to the firmly adjusted pressure gradient on the inlet valve, the flow volume flowing through gradient on the inlet valve, the flow volume flowing through the valve per unit of time is precisely fixed. The pressure increase on the wheel brakes to be expected is, therefore, known. Complex calculations for fixing the opening time of the valve can be eliminated in the control algorithm. The pressure gradients on the inlet valve thus maintained constant during the control, in addition to the lower control noise, involve three other notable advantages as follows: (a) reduced stopping distance; (b) improved quality control by increasing the control frequency, and, (c) reduced brake fluid consumption with the consequence of an enhanced brake reserve n deceleration processes on surfaces exhibiting suddenly changing frictional values.
A space-saving arrangem
REFERENCES:
patent: 4685749 (1987-08-01), Otsuki et al.
patent: 4708407 (1987-10-01), Maehara
patent: 4750789 (1988-06-01), Belart et al.
patent: 4790608 (1988-12-01), Burgdorf et al.
patent: 4865348 (1989-04-01), Takeuchi et al.
patent: 4957330 (1990-09-01), Morikawa et al.
Beck Erhard
Luetteke Harald
Alfred Teves GmbH
Lewis J. Gordon
Oberleitner Robert J.
Seitter Robert P.
Young Lee W.
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