Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-03-25
2001-07-03
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S003000
Reexamination Certificate
active
06254198
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the automotive arts. Specifically, the invention pertains to a method and a corresponding circuit for controlling the braking process in a motor vehicle.
State of the art braking systems with the anti-lock brake feature (e.g. European patent EP 0 644 836 B1) control the brake pressure of the individual wheels of a motor vehicle in such a way that the wheels are prevented from locking during braking. The steerability of the motor vehicle is thus maintained in that the wheel brake pressure is adapted to the respective frictional adhesion of the tire to the road surface. That adaptation is carried out by virtue of the fact that when unacceptably high slip occurs the brake pressure which acts on the individual wheels is reduced and increased again intermittently, and thus discontinuously, using brake pressure control valves.
New requirements that are being made of braking functions and which improve the safety and comfort of the operation of motor vehicles, for example anti-lock brake systems, driving stability systems, traction controllers, “intelligent” driving speed controllers, have led, together with the requirement for a reduction in the assembly and maintenance costs, to the development of new, electrically controlled and actuated brake systems. See, for instance, German published patent application DE 195 29 664. Those systems greatly reduce, or entirely remove, the need for the considerable expenditure on master brake cylinders, brake pressure lines etc. in conventional brake systems.
In such an electric brake system, which is referred to as a brake by wire system, the driver is disconnected from the brake in terms of force, i.e. the braking torque request which the driver makes is no longer transferred directly as force on a hydraulic system but rather now merely an electrical signal is transmitted on an electrical line. The signal thus controls an electric brake actuator. The brake actuator is supplied with electrical energy and generates a frictional force at the individual wheel brakes, by means of which force a braking torque is built up at the respective wheel.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a circuit configuration which permit the braking process in motor vehicles with electric brake systems, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allows controlling the system in an analogous way and, particularly, to prevent a braked wheel from locking in a sensitive and effective way.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of controlling a braking process in a motor vehicle with a plurality of wheels, which comprises:
measuring wheel speeds of at least some wheels of a motor vehicle and transmitting corresponding signals to a control unit;
calculating with the control unit a wheel slip from the signals representing the wheel speeds;
determining a correction value for a setpoint value of a wheel brake pressure the wheel slip; and
continuously changing the setpoint value of the wheel brake pressure in dependence on the wheel slip with the correction value.
In accordance with an added feature of the invention, the determining step comprises obtaining the correction value from a characteristic curve defining the correction value in dependence on the wheel slip.
In accordance with an additional feature of the invention, the correction value is multiplied, as a factor, by the setpoint value of the wheel brake pressure.
In accordance with another feature of the invention, the correction value assumes a value between zero (in case of no activation of the brakes) and one (in case the brake pressure is unchanged).
In accordance with a further feature of the invention, a rate of change of the correction value which increases as the wheel slip decreases is limited.
With the above and other objects in view there is also provided, in accordance with the invention, a brake system with control of the braking process in a motor vehicle having a plurality of wheels, comprising:
wheel speed sensors disposed to measure wheel speeds of at least some wheels of a motor vehicle;
a control unit connected to receive signals from the wheel speed sensors representing the wheel speeds, the control unit calculating a wheel slip from the wheel speeds measured by the wheel speed sensors, and changing a setpoint value of a wheel brake pressure in dependence on the wheel slip, the control unit including an arithmetic circuit for determining a continuous correction value for the setpoint value of the brake pressure from the wheel slip;
a plurality of electrically actuated wheel brake actuators each assigned to a respective wheel of the motor vehicle and each connected to the control unit, the wheel brake actuators continuously adjusting a brake pressure at the wheels and individually setting the brake pressure for each wheel group formed from at least one wheel; and
the control unit generating control signals for the wheel brake actuators for changing the brake pressure by means of a logic operation on the correction value.
In accordance with a concomitant feature of the invention, the correction value is stored as a characteristic curve in the control unit as a function of the wheel slip.
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 method and circuit configuration for controlling the braking process in 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: 5072393 (1991-12-01), Mori et al.
patent: 5669679 (1997-09-01), Hammoud et al.
patent: 5941608 (1999-08-01), Campau
patent: 6079801 (2000-06-01), Zittlau
patent: 38 06 213 c2 (1992-03-01), None
patent: 195 30 735 A1 (1997-02-01), None
patent: 195 29 664 A1 (1997-02-01), None
patent: 0 644 836 B1 (1996-10-01), None
patent: 1 346 678 (1974-02-01), None
Bartz C. T.
Greenberg Laurence A.
Lerner Herbert L.
Schwartz Christopher P.
Siemens Aktiengesellschaft
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