Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1992-04-13
1994-01-04
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031134, 36442602, B60T 824
Patent
active
052754758
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
As is known, vehicle dynamics are influenced by the forces exerted on the tires of the vehicle by the roadway. It is known that, when the vehicle is braking, the skew running stiffness of the tires depends on the brake slips of the tires. In general, the skew running stiffness of the tires decreases with increasing brake slip.
For guiding the vehicle, cornering forces on the tires are necessary. For the yawing dynamics of the vehicle, yawing moments on the vehicle are necessary. These yawing moments can be caused both by the braking forces and by the cornering forces. For the yawing movement of the vehicle, the braking forces are thus important for two reasons. Firstly because the braking forces can exert a yawing moment on the vehicle and secondly because the braking forces can influence the yawing moment of the cornering forces (indirectly via the brake slip) by changing the skew running stiffness.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of controlling vehicle dynamics.
The driving dynamics are thus influenced by means of brake intervention. The driving dynamics are optimized during a braking operation yet the braking distance is also minimised.
For this purpose, it is necessary to seek a compromise in which the brake slip values at the tires are set in such a way that, on the one hand, the yawing dynamics are improved without, on the other hand, wasting too much braking retardation. For this purpose, it is determined at each tire how, on the one hand, the yawing moment on the vehicle changes and how, on the other hand, the braking retardation of the vehicle changes when there is a small change in the brake slip. The ratio of the change in the yawing moment to the change in the braking retardation is calculated for each wheel. For control of the yawing moment, the wheel with the largest ratio is used most and the wheel with the smallest ratio is used least. This settles the central question of how the distribution of the braking forces or the distribution of the brake slips is to be configured.
The change in the braking and cornering forces due to changes in the brake slips can either be measured directly or estimated by suitable estimating algorithms.
For the determination of the necessary brake slip changes at the wheels, a control deviation is required. A model-based follow-up control is chosen for this purpose. Since, however, the position of the vehicle cannot immediately be measured, only the transitional behavior of the vehicle transverse acceleration and vehicle yawing speed is simulated. The damping of the systems is to be critical since this is considered the best dynamic behavior by most drivers.
For the following description, the notation given in FIG. 1 and on page 9 applies.
The model is described as follows: .multidot..DELTA..delta. (I) .multidot..DELTA..delta. (II) .delta.=1/R).
They are obtained from the following calculation ##EQU1## If the Ackermann condition .delta.=1/R is made less severe, i.e. .delta.=k.sub.a .multidot.1/R, k.sub.a >1,) the following applies: ##EQU2## The model is therewith established. The handling can be influenced via the parameters k.sub.1, . . . , k.sub.4, k.sub.a.
In the Ackermann diagram, the line ##EQU3## intersects the curves at their maximum when k.sub.a .apprxeq.2.
In order to effect the changes in .phi. and y, changes must be introduced into the horizontal tire forces:
The following equations apply: ##EQU4##
As a possible variation, there are the wheel brake-slip values of the four wheels. However, to ensure that as little braking retardation as possible is wasted, the slip values must be chosen so that .DELTA.B.sub.1 +.DELTA.B.sub.2 +.DELTA.B.sub.3 +.DELTA.B4 is approximately at its maximum, i.e. that the sum of the braking force reductions is at its minimum.
The values for .DELTA.B.sub.1. . . .DELTA.B.sub.4 can be calculated from the stability reserve, while .DELTA.S.sub.1. . . .DELTA.S.sub.4 can be calculated from the transverse stability reserve, it being possible to var
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Ehret Thomas
Hartmann Uwe
Kost Friedrich
van Zanten Anton
Muratori Alfred
Oberleitner Robert J.
Robert & Bosch GmbH
Striker Michael J.
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