Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1991-09-04
1994-02-08
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 971, B60T 832
Patent
active
052843858
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In vehicles with an unfavourable ratio of the height of the centre of gravity to the wheelbase, extreme dynamic axle load transfers lead to a marked relief of the load on the rear axle, particularly in the case of high decelerations. If this state of affairs is not taken into account, a rear-axle pressure build-up decoupled from the vehicle deceleration and from the pressure level of the front axle leads inevitably to vehicle instability.
From DE-OS 2,215,608 (GB-A 1,376,581) it is known that, in vehicles equipped with an ABS and having a high centre of gravity and a short wheel base, overturning can be avoided by not permitting an excessively large difference of the brake pressures at the front and at the rear. If this difference exceeds a predetermined magnitude, the pressure at the front is not increased further.
SUMMARY OF THE INVENTION
The present invention takes account of the dynamic axle load transfer which occurs during ABS operation, in particular by a pressure build-up of reduced rate at the rear axle. The criterion for this is an excessively long continuation of the pressure build-up at the front axle. A high control frequency at the rear axle is thereby avoided and vehicle stability is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a first illustrative embodiment of an ABS designed in accordance with the invention,
FIGS. 2-5 show diagrams for the purpose of explaining various possibilities of intervention into the control of the rear axle,
FIG. 6 shows another illustrative embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, sensors allocated to the front wheels of a vehicle are denoted by 1 and 2 and sensors allocated to the rear wheels by 3 and 4. Their signals are fed to an evaluation circuit 5, which from these produces brake pressure control signals for the four wheel brakes. These signals are fed to solenoid valves 6 and 7 allocated to the front wheels and solenoid valves 8 and 9 allocated to the rear wheels. The solenoid valves 6 to 9 are 3/3-way valves which, in their normal position keep the brake line open, in an intermediate position interrupt it and, in a third position, effect a pressure reduction at the brakes.
It is assumed here that the pressure build-up following a pressure reduction is effected in pulsed fashion due to the control, the magnitude of the first pressure pulse depending on the prehistory (size of the preceding pressure reduction and/or length of the preceding pressure build-up phase(s), e.g. number of pulses which have occurred).
Counters 10 and 11 in each case count the pressure build-up pulses occurring after a pressure reduction at respective solenoid valves 6, 7 allocated to the front wheels. If this number of pulses counted exceeds a predetermined magnitude, the associated counter 10 or 11 emits a signal which can trigger one or more of the following effects:
a) The signal can be used to alter the pulse duty factor of a pulse generator 5' or 5" present in the evaluation circuit 5 and allocated to a rear wheel brake (lines 10' or 11'), e.g. to increase the holding phases of the pulses. It is in each case the pulse duty of the pulse generator 5' or 5" which belongs to that side of the vehicle at which pressure is built up for too long which is altered.
b) The signal can be fed to the evaluation circuit 5 in order to reduce there the first pressure pulse for the rear wheel brake to a predetermined extent e.g. to halve it (lines 10" and 11"), in the case of an excessively long pressure build-up at the front, and specifically for the associated vehicle side.
c) The signal fed in accordance with b) can in addition also lower the response thresholds for the pressure reduction (e.g. wheel deceleration threshold and/or slip threshold) for both rear wheels.
d) However, the signal can also be fed to a counter 12 or 13 respectively. This is activated thereby and subsequently counts the brake pressure build-up pulses occurring on the control line 8' or 9' respectively. After a predetermined number, the co
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Muller Elmar
Muller Werner
Oberleitner Robert J.
Robert & Bosch GmbH
Sallato Josie A.
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