Drive slip control system

Details Drive slip control system Drive slip control system

1990-06-20

1992-05-19

Rice, Kenneth R.

Motor vehicles

With means for detecting wheel slip during vehicle...

36442603, B60K 2816

Patent

active

051139634

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

Drive slip control systems vehicle are known, e.g. from U.S. Pat. No. 3,528,536, where at least one (usually two) driven wheels reduce the engine torque when a preset slippage threshold is exceeded. When the slippage value falls below this threshold, the engine torque is increased, for example, by changing the throttle position stepwise until at least one wheel is unstable again. This procedure is referred to as a control cycle which, in most cases, is repeated several times successively in a control procedure. In known systems, the height of the steps is continuously increased to obtain a progressive curve of increase of the engine torque curve.


SUMMARY OF THE INVENTION

The inventive control system maintains the height of the increasing steps constant but varies the maintenance times of constant torque between steps. This variation is then made to depend upon various conditions such as the slippage value, the vehicle acceleration and/or the number of cycles which already occurred in a control procedure. The maintenance time is calculated in each computation procedure, i.e. it is constantly adjusted to new road and vehicle conditions.
When the drive slip is high, close to the acceptable slippage limit, the maintenance times at the driven axle are extended since optimum slippage will soon be reached and a spinning (instability) of the driven wheels is about to occur. When the vehicle acceleration is high, the maintenance times are reduced (indication of high friction coefficient) since substantially more torque can be transmitted in this case.
A high vehicle acceleration is an indication of a high friction coefficient which permits a rapid increase without risking a spinning of the driven wheels. Low vehicle acceleration is caused either by a low friction coefficient or low engine torque.
When the engine torque is too low, the drive slippage is very small (close to 0 km/h) and, in this case, there is a rapid increase. A positive result thereof is improved traction when the friction coefficient has changed or when exiting a curve.
Allowing for the control cycles which already occurred in the control procedure permits a minute and careful approach to the optimum values of the engine torque so that the control vibrations decay faster and jolting is avoided. If a substantial slippage does not occur at the driven wheels (e.g. at .mu.-change) over a longer period of time in this condition, the number of control cycles which already occurred can be ignored for further calculation.
On the one hand, the vehicle acceleration can be analogously included in the calculation of the maintenance time, on the other hand, the maintenance time can be changed stepwise when discrete acceleration thresholds are exceeded. These discrete acceleration thresholds can be made to depend upon the vehicle speed (small acceleration at a high vehicle speed). It is also possible to change the maintenance time only after a prescribed threshold of the vehicle acceleration has been passed. This threshold too can be made to depend upon the speed of the vehicle.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a drive slip control in accordance with the invention,
FIG. 2 shows the possible curve of a controlled engine torque.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For reasons of simplicity FIG. 1 shows a drive slip control which acts only on the engine torque in case one of the wheels becomes instable. Only one sensor of a driven wheel is represented. The invention, however, can also be used with drive slip control systems when operating the brakes and acting upon the engine torque, the latter applies in particular when all driven wheels become unstable.
FIG. 1 shows a sensor 1 of a driven wheel and a sensor 2 of a non-driven wheel. The difference .DELTA.V of the two wheel speeds is formed in a block 3. If this difference (it corresponds to the wheel slippage) exceeds a positive threshold (drive slippage) preset in comparator 4, a motor-driven actuator 15 changes the position of the

REFERENCES:
patent: 4361871 (1982-11-01), Miller et al.
patent: 4682667 (1987-07-01), Hosaka
patent: 4804058 (1989-02-01), Leiber et al.
patent: 4866618 (1989-09-01), Tamura et al.

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