Fluid-pressure and analogous brake systems – Speed-controlled – Regenerative brakes
Patent
1995-11-01
1998-06-23
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Regenerative brakes
303 3, B60T 800, B60L 726
Patent
active
057695091
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention pertains to a brake unit for motor vehicles with electric drive and with a driven axle and a nondriven axle, comprising: pedal and to which both the friction brakes acting on the driven axle and the friction brakes acting on the nondriven axle are connected; the friction brakes acting on the driven axle can be connected via pressure control units which can be switched over electrically; motor of the motor vehicle for braking and energy recovery; and actuation of the brake pressure actuator, the brake pressure brought about by the actuation and the velocity of the vehicle, and evaluates it for controlling both the drive motor and the friction brakes acting on the driven axle.
Such a brake unit is known from, e.g., DE-OS 41 24 496. A single-circuit, pedal-actuated main cylinder, to which the friction brakes associated with the nondriven axle are connected directly and the friction brakes associated with the driven axle are connected via a hydraulic 2/2-way valve, which is closed in the currentless state (CC), as well as a pressure control unit each, is provided in the prior-art brake unit. In addition, the friction brakes associated with the driven axle are in connection with an auxiliary hydraulic pressure source, wherein pressure sensors, which detect the pressures generated in the friction brakes, are provide. In addition, a pedal position transducer is provided for recognizing the driver's wish to brake.
The fact that no hydraulic pressure can be built up in the friction brakes associated with the driven axle in the case of a failure of the electronic controller or of the electrical system of the vehicle is felt to be a disadvantage of the prior-art brake unit. Another disadvantage is the fact that the driver's wish to brake cannot be recognized with the pressure sensor in the case of a failure of the brake circuit of the nondriven axle. The risk of an irregular braking of the two driven wheels, which can be attributed to an inequality of the pressures caused by, e.g., a permanent deviation during the individual wheel pressure regulation or by a drift of the electronic system or of the pressure sensors, e.g., because of temperature effects, cannot be considered to be particularly advantageous, either.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to increase the reliability of operation of the brake unit of the class described above by making possible the buildup of a hydraulic pressure in the friction brakes associated with the driven axle in the case of failure of the electronic controller or of the entire electric system of the vehicle.
This task is accomplished according to the present invention by the brake pressure actuator being designed as a two-circuit main brake cylinder, to the first pressure space of which the friction brakes acting on the nondriven axle, and to the second pressure space of which the friction brakes acting on the driven axle are connected, wherein the connection between the second pressure space and the friction brakes acting on the driven axle is via at least one shut-off valve, which can be switched over electrically and is open in the currentless state. Due to these measures, in case of a failure of the electric or electronic system of the vehicle, both of the friction brakes associated with the driven axle, which can no longer be actuated electrohydraulically (break-by-wire), can be directly actuated by the driver. Preferably, the brake pressure actuator is designed as a tandem main brake cylinder. The entire unit (brake pedal, tandem main cylinder and wheel brakes) are designed correspondingly.
An advantageous variation of the present invention is the inclusion of a hydraulic connection, which can be shut off by means of a second shut-off valve, which can be switched over electrically, between the friction brakes acting on the driven axle. The second shut-off valve is preferably designed as a valve which is open in the currentless state (CO). Individual wheel pressure control, which is neces
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Berthold Thomas
Feigel Hans-Jorg
Graber Johannes
Kircher Dieter
Graham Matthew C.
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
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