Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1991-06-14
1993-02-09
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 96, 303103, 303109, B60T 866
Patent
active
051848767
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
From WO 88/06544 FIG. 7 with associated description, a method is known for the generation of a reference speed signal and an auxiliary reference speed signal in an antilocking control system, in which the wheel slip is used as a control variable to develop slippage value. With the auxiliary reference speed signal, the filtered speed signal of the fastest wheel determines its course. The slope of this auxiliary reference speed signal is used only to determine the slope of the reference speed signal during a sudden drop in wheel speed. Otherwise the size of the reference speed signal is as a rule determined by the second fastest wheel.
SUMMARY OF THE INVENTION
The generation of the reference signal in accordance with the invention, with switch-over to another control variable has the advantage, as a rule, that in the absence of ABS control, the reference signal is generated by the mean value of the speeds of the non-driven wheels. A driven wheel influences the size of the reference signal only when the wheel speed signal exceeds the reference signal.
In addition, the design in accordance with the invention has the effect that the controller can distinguish between light `touch` braking and a braking on low .mu.. With the development of the sum S of the amounts of slip, this does not exceed the threshold, and there is no switch-over before the commencement of control.
Contrary to this, the wheel speeds diverge during braking at low .mu., so that compared to the mean value of the speeds of non-driven wheels, i.e. the reference, slippages develop, the sum S of which exceeds the threshold a. There then occurs a switch-over to the reference being developed by the second fastest wheel, even before control commences. The presence of slip is thus recognized much sooner than without switch-over, i.e. the control commences earlier at low .mu..
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram of an embodiment.
FIGS. 2 and 3 show explanatory diagrams.
FIGS. 4-5 disclose prior art block diagram and explanatory diagram.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, the speed sensors 1-4 allocated to the wheels of the vehicle supply their signals to an evaluation circuit 5. Sensors 1 and 2 are the transmitters of speed signals for the non-driven front wheels. On the basis of the transmitter signals, the evaluation circuit 5 for its part controls the 3/3 solenoids 6 which are allocated to the wheels, and varies the braking pressure on the wheels such that it prevents excessive brake slip.
The brake slip can be generated and compared with a target brake slip, or the slip can be used or utilised in another way for pressure control. Slip is here to be understood both as the difference between the reference speed and the wheel speed, and this difference related to the reference speed.
As shown above, a reference speed is needed in order to generate a slip value. This can be generated as shown in WO88/06544 FIG. 7.
FIGS. 7 and 8 of WO 88/06544 are included herein as respective FIGS. 4 and 5.
The prior art embodiment of FIG. 4 operates with an auxiliary reference speed. In a unit 70 the maximum V.sub.max of two wheel speeds V.sub.R1 and V.sub.R2 is supplied to a unit 71 which outputs the slope of V.sub.max to a unit 73 as the calculated vehicle deceleration a.sub.F. Meanwhile, a unit 72 selects the minimum V.sub.min of the two wheel speeds V.sub.R1 and V.sub.R2 to determine the second fastest wheel speed, and supplies this to unit 73. Unit 73 determines an actual vehicle reference speed V.sub.Ref from the speed V.sub.min from unit 72, the deceleration a.sub.F from unit 71, and a percentage from unit 75.
FIG. 8 shows the corresponding diagram for the emergency wheel R1, which is smaller diameter than normal wheels and therefore turns faster. V.sub.R1 is the characteristic curve for this wheel and is used to generate an auxiliary reference value V'.sub.Ref. V.sub.R2 is the characteristic curve for the second fastest wheel R2, and is used to generate the actual refere
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Beyer Claus
Dominke Peter
Sonntag Eberhard
Butler Douglas C.
Robert & Bosch GmbH
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