Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1991-06-03
1993-02-23
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031134, B60T 824
Patent
active
051884348
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In conventional ABS designs, the longitudinal dynamics of the vehicle are of primary importance, if only for reasons of sensory analysis (revolution sensor). Suitable matching is necessary in order to obtain a good, invariable compromise between the braking distance and controllability for widely differing roads and driving maneuvers.
Whereas, during braking in a straight line, the driver's need for maximum deceleration in the longitudinal direction of the vehicle can be understood clearly, a conflict of aims arises during simultaneous steering movements, since the brake force and lateral guiding force cannot be at their maximum at the same time. If it is assumed that a driver wants instantaneously to change the state of movement of his vehicle as much as possible, it seems plausible to maximize the resultant force arising from the brake force and lateral guiding force. If there are no possibilities of varying the angles of inclination by an active steering intervention, there remains as a "possibility of rapid intervention" the tire slip (in the longitudinal direction) which can be set by means of ABS valves to a new desired value after 100-200 ms at the latest.
An anti-lock control system is known from DE-Al-3,611,822, to which U.S. Pat. No. 4,758,053 corresponds. In this the desired slip values on the individual axles are varied as a function of the steering angle and of the yawing movement.
SUMMARY OF THE INVENTION
The control concept differs from the pure wheel controllers working on the optimizer principle and set at the maximum brake force, if only in that, during running at an inclination, the working point of the controller does not shift to higher slip values, but is first maintained at the optimum value for braking in a straight line, and furthermore on specific wheels the slip is reduced. The driving behaviour was assumed to have understeering tendencies virtually neutral at low speeds and increasing slightly at an increasing speed:
The angle of inclination on the rear axle is set to a value which, dependent on the instantaneous vehicle speed, is somewhat lower than the angle of inclination of the front axle.
However, this concept is maintained only as long as the angles of inclination on the front wheels do not exceed the maximum permissible angle of inclination as a result of too high a steering lock (for example, the driver's panic reaction). Since there is no possibility of reducing the "overdone" steering angle to a suitable value, in this case the angles of inclination of the rear axle are regulated to the maximum permissible angle of inclination reduced by the amount of the desired "understeering coefficient".
This overriding controller intervenes in the subordinate wheel controller by means of desired slip values .lambda.*.sub.1 to .lambda.*.sub.4 dependent on the angles of inclination .alpha..sub.1 to .alpha..sub.4. Before these desired slip values are calculated a distinction is drawn between the following three driving situations. For these, the subordinate controller can have the structure of the slip controllers which are described, for instance, in German Offenlegungsschriften 3,624,007, 3,731,075 and 3,734,878 (to which U.S. Pat. No. 5,070,459 corresponds). In addition, possibilities of direct intervention (via valve opening times or differential pressures when there is a measured wheel-brake cylinder pressure) are possible.
In contrast to the state of the art, in the invention different desired slip values can be preset for all the wheels.
I Driving behaviour with too much understeer:
The angles of inclination on the front and rear axles have the same sign, but the amount of the angle of inclination on the front axle is clearly greater than that on the rear axle. Reducing the desired slip value on the front wheel on the outside of the bend both increases the lateral guiding force at the front and, as a result of the simultaneous reduction of the brake force, generates a slight yawing moment. The two effects improve the steerability. In contrast, t
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Hartmann Uwe
Kost Friedrich
Ruf Wolf-Dieter
van Zanten Anton
Muratori Alfred
Oberleitner Robert J.
Robert & Bosch GmbH
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