Fluid-pressure and analogous brake systems – Multiple systems – Fluid pressure and electric
Reexamination Certificate
1999-08-31
2001-04-03
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Multiple systems
Fluid pressure and electric
C303S009630, C303S015000
Reexamination Certificate
active
06209966
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention takes as its starting point an electrically controlled braking system which is intended for a wheeled vehicle.
A braking system of this kind is known from U.S. Pat. No. 4,802,562, FIG.
9
. As is customary, the input means are there formed by a brake pedal, which is pressed down by a driver of a vehicle in accordance with the retardation of the vehicle he requires. The brake pedal is assigned two sensors, which can, for example, be designed as rotary potentiometers. Each sensor records the extent of actuation of the brake pedal and outputs an electrical output signal corresponding to this extent. In the case of the known braking system, two electronic control units which operate independently of each other are furthermore provided, one control unit being supplied with the output signal of one sensor and the other control unit being supplied with the output signal of the other sensor at the brake pedal as an input signal. Each wheel of the vehicle is assigned a brake cylinder and a braking pressure modulator valve which is fluid-connected to the brake cylinder and has an electric actuating element, namely a piezoelectric actuator. The two electric actuating elements of two braking pressure modulator valves can only be activated by one control unit and the two actuating elements of two other braking pressure modulator valves can only be activated by the other control unit. If one control unit fails, therefore, only two braking pressure modulator valves continue to operate.
DE 31 44 961 A1 has disclosed a braking system for a wheeled vehicle in which actuating a brake pedal adjusts a pneumatic or hydraulic pilot control valve and an angle transmitter. A braking pressure modulator valve can be adjusted, on the one hand, pneumatically, or hydraulically by means of a pressure fed in by the pilot control valve or by an electromagnet which is activated in accordance with the position of the angle transmitter. In this braking system, if one control circuit fails the braking pressure modulator valve can still be actuated with the aid of the other control circuit.
SUMMARY OF THE INVENTION
The object on which the invention is based is to develop an electrically controlled braking system of the above mentioned type in such a way that safety is enhanced.
According to the invention in an electronically controlled braking system of this type, this object is achieved wherein the braking system pressure modulator valve has a second electric actuating element which acts in the same direction, when activated, as the first electric actuating element, and by the fact that the second electric actuating element can be activated by the second electronic control unit at the same time as the first electric actuating element is being activated by the first electronic control unit.
Whereas, therefore, in the braking system of U.S. Pat. No. 4,802,562, each braking pressure modulator valve can be activated only by one of the two control units, this is performed by each of the two control units in a braking system according to the invention. If the braking pressure modulator valve is constructed as a proportionally adjustable pressure-regulating valve, both electric actuating elements normally act against a force, produced by the braking pressure, acting on the regulating piston of the braking pressure modulator valve. If a control unit or an electric actuating element fails, there is therefore only half the force and hence also only half the braking pressure available in a particular position of the input means. However, braking is still possible at each wheel or each axle, it being possible to at least partially compensate for the failure of an actuating element by increased actuation of the input means. If the braking pressure modulator valve is an on-off valve, this can be constructed in such a way that its moving valve member can also be switched by each electric actuating element alone. If an actuating element fails, the same braking pressure can then be produced in a particular position of the input means as when the system is operating correctly.
According to the particularly preferred configuration, the two electronic control units are supplied separately with an electric voltage. This ensures that, if a voltage supply fails, one of the two control units still functions.
It is very advantageous, particularly in the case of heavy trucks wherein, the two control units can be supplied with electrical signals from sensors by means of which the axle loads are recorded. The braking effects at a front axle and at a rear axle of the vehicle can then be matched to one another approximately in accordance with the optimum braking force distribution, and allowance is also made for the fact that, if at all, the wheels at the front axle of the vehicle should be allowed to lock up before those on the rear axle.
It is advantageous wherein the axle loads and other vehicle parameters are recorded by two sensors. The electrical output signal of each sensor is supplied to both control units, with the result that, if one sensor fails, both control units still function correctly. Here, the control units can, for example, control the braking pressure modulator valves in accordance with the output signal of one of the two sensors which entails the lower braking pressure at one wheel.
A particularly preferred configuration is wherein there is an electronic monitoring unit which can be supplied with the electrical output signal of a sensor and which triggers an alarm signal if the sensor detects a defect in a component of the braking system or a defect in the sensor itself is detected.
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Farber Martin A.
Mannesmann Rexroth AG
Rodriguez Pamela J.
Schwartz Christopher P.
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