Fluid-pressure and analogous brake systems – Electric control
Reexamination Certificate
1999-02-16
2001-02-20
Graham, Matthew (Department: 3613)
Fluid-pressure and analogous brake systems
Electric control
C303S152000, C303SDIG009, C303S122040
Reexamination Certificate
active
06189981
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a brake system for a motor vehicle having electromechanical brake actuators assigned to wheels.
Nowadays, passenger cars are almost always provided with hydraulic brake systems. The increasing demands which are made of additional brake functions, such as anti-lock brake functions, driving stability systems and traction control systems, as well as requirements for reduction in the installation and maintenance costs and a decrease in the hydraulic devices, have led to the development of electromechanical brake systems.
In such brake systems, the driver is disconnected from the brake in terms of force, that is to say the braking torque request which emanates from the driver is not transferred directly as a force through a hydraulic system but rather only as a signal through an electrical lead. That signal is used to control an electric brake actuator which generates a force at a brake with an electric power supply and that force brings about the desired braking torque through the use of a friction element. In the case of a disk brake, the force which generates the braking torque is referred to as a brake engagement force.
In an electromechanical brake system, such as is described, for example, in German Patent DE 196 15 186 C1, corresponding to U.S. application Ser. No. 08/843,887, filed Apr. 17, 1997, the brake actuator is mounted directly on the respective wheel of the motor vehicle so that a brake engagement force is expediently not transmitted over large distances in the vehicle. The braking torque request and the brake controller are disposed at a central point, for example in the vicinity of the brake pedal. The brake system is thus distributed over the entire vehicle, and since it forms a central safety function of the vehicle, increased safety demands are made of the electrical transmission of the braking torque requests.
The braking torque request is usually tapped from the brake pedal through the use of force sensors and displacement sensors. However, such sensors have non-detectable fault states so that a number of them, for example three, are disposed in a redundant way. Therefore, even when a sensor fails, the braking torque request can still be reliably detected, for example through the use of a 2 out of 3 majority decision.
Brake systems which distribute all of the sensor signals to the brake actuators have been known to date. The majority decision is then taken in a decentralized manner in the control unit of the respective brake actuator, as in German Patent DE 195 21 175 C1. That provides a high degree of safety, but the expenditure involved, especially on the cabling in the vehicle, is considerable.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a brake system for a motor vehicle, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which is fault-tolerant, in particular with regard to the transmission of the braking torque requests.
With the foregoing and other objects in view there is provided, in accordance with the invention, a brake system in a motor vehicle, comprising a brake pedal; a pedal unit having at least two sensors for sensing activations of the brake pedal and supplying sensor signals; at least two parallel central units for calculating setpoint values for a brake activation force from the sensor signals and for converting the setpoint values together with unprocessed sensor signals, into a serially encoded signal; a multi-channel signal line connecting the pedal unit and the central units to one another for transmitting the sensor signals; electromechanical brake actuators assigned to the wheels; decentralized control units associated with the brake actuators for comparing the setpoint values during fault-free operation, for comparing the sensor signals in the event of a fault and for generating control signals on the basis of the setpoint values and sensor signals; and two data buses each respectively connecting one of the central units and two of the brake actuators to one another for serially transmitting the encoded signals.
In accordance with another feature of the invention, the central units generate control signals for supplementary braking functions.
In accordance with a further feature of the invention, the two central units exchange and compare signals permitting mutual monitoring.
In accordance with an added feature of the invention, the central units expand the encoded signal with redundant supplementary information permitting the control units associated with the brake actuators to detect transmission faults.
In accordance with an additional feature of the invention, the sensor signals and existing information paths are used to activate the system during a pause in operation.
In accordance with a concomitant feature of the invention, the pedal unit has at least three of the sensors for sensing the activations of the brake pedal; and the decentralized control units compare the setpoint values in the case of fault-free operation and the sensor signals in the event of a fault, and generate control signals on the basis of the most frequently occurring corresponding values.
The advantages of the invention lie especially in the fact that the safety of the brake system is increased with little expenditure and simple measures. In addition, the sensor signals can be used to activate the system during a pause in operation, that is to say when the engine is at a standstill.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a brake system for a motor vehicle, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 4345796 (1982-08-01), Reineckt
patent: 5335979 (1994-08-01), Natou et al.
patent: 5372410 (1994-12-01), Miller et al.
patent: 6030054 (2000-02-01), Doericht
patent: 3504096A1 (1986-08-01), None
patent: 19521175C1 (1996-07-01), None
patent: 19615186C1 (1997-08-01), None
Graham Matthew
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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