Fluid-pressure and analogous brake systems – Electric control
Reexamination Certificate
1999-08-19
2001-04-10
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Electric control
C303S122040, C188S158000, C701S070000
Reexamination Certificate
active
06213567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention belongs to the automotive arts. Specifically, the invention concerns a brake system for a motor vehicle and a method for transmitting data in an electrically controlled brake system for a motor vehicle.
The brake systems of modern motor vehicles are subject to a variety of new requirements—such as anti-locking systems ABS, drive stability systems, traction control systems, so-called intelligent cruise controllers, brake assistants, etc.—and they are subject to a demand for reduced assembly and maintenance costs, which are very considerable for present-day brake systems. These new requirements and demands, have led to the development of purely electric brake systems, which are also known as “brake-by-wire” systems. (See, for example, German published patent application DE 195 11 287 A1; and journal mot 20 (1995), p. 46).
With such electric brake systems the driver is separated from the brake in respect of the force exerted, i.e. the braking moment demanded by the driver is no longer transmitted directly as force through a hydraulic system but only as a signal over an electrical connection. The signal is used to control an electric brake actuator which by means of a source of electric power generates force at a brake which in turn produces the required braking moment through a friction element. In the case of a disk brake the force generating the braking moment through friction is designated as the brake application force.
A completely electric brake system is described, for example, in the commonly assigned, copending application No. 08/843,887, filed Apr. 17, 1997. There, the brake actuator is attached directly at the wheel of the motor vehicle in order to avoid transmitting a brake application force over long distances in the motor vehicle, while the brake controller and the detection of the braking moment demanded by the driver are arranged at a central position, for example in the vicinity of the brake pedal. Thus the brake system is distributed over the entire motor vehicle and, since the brake system forms a central safety function of the motor vehicle, stricter safety requirements must be met in respect of the electrical transmission of the braking moment demand. The transmission must be fail-safe and fault-tolerant, i.e. errors occurring during the communication must be detected reliably by the brake system and suitable strategies must be available for handling errors. In addition, all subscribers in the electrical communication process must be able to recognize faulty behavior on the part of another subscriber. In particular, a minimum braking capability must be guaranteed even if communication is interrupted.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an automotive brake system and a method for transmitting data in an electrically controlled automotive brake system, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which offers a fail-safe and fault-tolerant brake system, in particular in respect of the communication over electrical lines.
With the foregoing and other objects in view there is provided, in accordance with the invention, a brake system for a motor vehicle, comprising:
a pedal unit with a sensor detecting an actuation of a brake pedal of the motor vehicle and generating a sensor signal with a desired value corresponding to a driver demand for a brake application force;
electrically actuated brake actuators disposed at each of a plurality of wheels of the motor vehicle;
an electronic central controller(
13
) evaluating the sensor signals and generating control signals for additional braking functions;
a data bus interconnecting the pedal unit, the brake actuators, and the central controller, the data bus being adapted to exchange data blocks in a predefined, cyclically repeated time pattern; and
an additional signal line interconnecting the pedal unit, the brake actuators, and the central controller, the additional signal line carrying a transmission of the desired value for the brake application force from the pedal unit to the brake actuators and the central controller(
13
) and a data exchange concerning a status of the brake actuators.
In accordance with an added feature of the invention, the data bus is a twin-wire bus for a symmetrical transmission of digital signals and the brake actuators, the pedal unit, and the central controller forming respective nodes each having a fixed time slot with exclusive token-holding within a transmission cycle assigned thereto by a respective subscriber defined as a bus master.
In accordance with an additional feature of the invention, the sensor is one of a plurality of redundant sensors detecting a brake pedal movement and issuing sensor signals, and the pedal unit further comprises a safety circuit connected to the plurality of sensors, the safety circuit determining the driver demand as a majority decision from the sensor signals.
In accordance with another feature of the invention, the brake actuators are controllers regulating a brake application force to the desired value for the brake application force received through the bus system.
With the above and other objects in view there is also provided, in accordance with the invention, a method of transmitting data in an electrically controlled brake system for a motor vehicle, which comprises the following steps:
cyclically exchanging data over a data bus among a plurality of subscribers including a plurality of brake actuators, a pedal unit, and an electronic central controller;
defining one of the subscribers as a bus master and synchronizing all subscribers with the bus master in a global time pattern and defining within a communications cycle a fixed time slot for each subscriber to have exclusive token holding within the time slot;
dispatching with the individual subscribers data blocks containing information about a current communications cycle and the respective sender, the respective data and a checksum; and
including in the data sent by the subscribers a braking moment demand of the driver and the electronic controller, measured values delivered by the sensors, and status parameters of the subscribers.
In accordance with again an added feature of the invention, a subscriber is detected as having failed if the respective subscriber fails to transmit a data block in the time slot assigned to the respective subscriber.
In accordance with again an additional feature of the invention, it is determined that a subscriber is sending in an incorrect time slot if fault symptoms appear in the “incorrect” time slot.
In accordance with again another feature of the invention, an additional signal line interconnects the pedal unit, the brake actuators, and the central controller, and a desired value for the brake application force is transmitted from the pedal unit to the brake actuators and the central controller and data are exchanged via the additional signal line concerning a status of the subscribers.
In accordance with again a further feature of the invention, the data transmission and exchange on the additional signal line is effected with pulse-width modulation.
In accordance with yet an added feature of the invention, system errors can be detected by comparing the desired values transmitted over the data bus with the desired values transmitted over the additional signal line in the case of non-active auxiliary braking functions.
In accordance with a concomitant feature of the invention, the additional signal line is an optical waveguide and signal transmission and exchange is effected through optical transmission.
The primary advantages of the invention consist particularly therein that the fail-safety and fault correction measures of the brake system are achieved with little outlay.
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
Deml Ulrich
Zittlau Dirk
Greenberg Laurence A.
Lerner Herbert L.
Oberleitner Robert J.
Siconolfi Robert A.
Siemens Aktiengesellschaft
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