Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1985-08-16
1987-07-14
Caldwell, Sr., John W.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303109, 364724, B60T 860
Patent
active
046798668
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for ascertaining the set-point braking moment for various wheels of a vehicle.
It is known that a motor vehicle tire attains the maximum braking force while locking only in the rarest cases. As a rule, the maximum braking force is transmitted if the rotational speed of the wheel is slightly below that of an unbraked wheel. Anti-locking or anti-skid braking systems (ABS) are designed such that the rotational speed of the wheel is kept in the vicinity of this optimum.
In order to keep the wheel speed in the vicinity of the optimum, the wheel speed is continuously measured and the wheel acceleration is calculated. From these two status parameters, an algorithm for determining the optimum is derived. The two status parameters, wheel speed and wheel acceleration, describe the wheel behavior. In ABS braking, the wheel behavior thus determines the course of regulation.
For good ABS function, the wheel behavior should be known as accurately as at all possible. If the wheel speed could be measured without error, then it would be possible to determine the wheel behavior exactly. However, such measuring methods are at the least very expensive. Distortion in force transmission between the tire and the road or in the brake system can interfere with regulation. Such distortion can be attenuated by using threshold values, based on a study of the physics of the situation.
When a Kalman filter is used in accordance with the invention, the deviations in the measured and regulated variables are estimated. Also, with a mathematical description of the regulated path (for instance of the wheel), the status is pre-calculated and the result is compared with the (noisy) measurement signal. Since the mathematical description of the regulated path includes the laws of physics, further studies of the physics of the situation are no longer needed.
It is presumed here that the signals for the wheel speeds and the vehicle speed are in fact available. It does not matter how they are obtained or whether they have already undergone filtering.
In the present invention, the Kalman filter is used not only to filter out measurement errors but also to estimate unknown variables such as the individual braking forces. The tire slip is derived from the vehicle speed and the wheel speed. This slip is compared with a predetermined slip, and the difference is furnished to the brake pressure regulator. The brake pressure regulator is designed such that the tire slip is as close as possible the set-point tire slip value.
The set-point slip can be either fixed or variable and can then be calculated using the vehicle speed and the characteristics of the road. The object of fixing the set-point slip could be to shift the mean tire slip value to where the braking force is maximal. Since the maximum of the slip curve varies with the vehicle speed, adapting the set-point slip to the vehicle speed results in shorter braking distances. The situation with road characteristics is similar. It is known, however, that lateral guidance force decreases as the tire slip increases. To improve lateral guidance of the vehicle, the set-point slip should be selected to be a smaller value than that at which the braking force is maximal. If the road is unsymmetrical, the influence of this reduction of the set-point slip is twofold. First, the yawing moment can be reduced thereby, and second, the guide forces are increased.
The braking moment is regulated according to the invention by regulating slip. Various regulators will be proposed hereinafter for controlling the braking moment. One of the regulators, a multi-step regulator, also takes the dynamic principles of the wheel into account. The multi-step regulator controls the braking moment in such a way that the tire slip approximately reaches the set-point slip value in one or more steps.
Exemplary embodiment of the invention will now be explained, referring to the drawings. Shown are:
FIG. 1, a block circuit diagram of an anti-skid regulating system embodied in accordance with the inventi
REFERENCES:
patent: 3520575 (1970-07-01), Steigerwald
patent: 3614173 (1971-10-01), Branson
patent: 3702714 (1972-11-01), Branson
patent: 4080007 (1978-03-01), Acker et al.
patent: 4320287 (1982-03-01), Rawicz
patent: 4472812 (1984-09-01), Sakaki et al.
IEEE Transactions on Communication Technology, vol. COM-19, No. 6, Dec. 1971, New York (US), R. E. Lawrence et al., "The Kalman Filter for the Equalization of a Digital Communications Channel"; pp. 1137-1141.
Geering Hans P.
Heess Gerhard
van Zanten Anton
Caldwell Sr. John W.
Greigg Edwin E.
Oberley Alvin
Robert & Bosch GmbH
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