Anti-lock braking system

Details Anti-lock braking system Anti-lock braking system

1991-06-14

1993-11-16

Chin, Gary

Boots, shoes, and leggings

303 95, 303103, B60T 858

Patent

active

052629511

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

From WO 88/06544 (U.S. Ser. No. 392,932, incorporated herein by reference) FIG. 7 with associated description it is known, in an anti-lock control system which uses the slip of the wheels as controlled variable, to generate a reference speed signal and an auxiliary reference speed signal for the purpose of slip formation. In the case of the auxiliary reference speed signal, the fastest wheel determines its curve. The gradient of this auxiliary reference speed signal serves only for the determination of the gradient of the reference speed signal during the instability of a wheel, the magnitude of the reference otherwise being determined by the second-fastest wheel.


SUMMARY OF THE INVENTION

The invention provides a closer approximation of the reference speed to the actual vehicle speed and hence an improvement of closed-loop control overall, in particular in extreme conditions such as .mu. jumps and in the case of initial braking.


BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative embodiment of the invention will be described in greater detail with reference to the
FIG. 1 shows a block diagram of the illustrative embodiment
FIG. 1A illustrates the formation of the gradient of the auxiliary reference signal,
FIG. 1B is a graphic illustration of the gradient of the auxiliary reference signal.
FIG. 2 shows the behaviour of the signals in the case of a negative .mu. jump


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, wheel sensors 1-4 associated with the vehicle wheels, generate and transmit their signals to an evaluation circuit 5. On the basis of the signals from the sensors 1-4, the circuit 5 controls 3/3 solenoid valves 6 associated with the wheels and varies the brake pressure at the wheels so as to avoid too large a brake slip.
For this purpose, the brake slip can be formed and compared with a setpoint brake slip or the slip can be used or involved in closed-loop pressure control in some other way. Slip should here be taken to mean both the difference between the reference speed and the wheel speed and the difference relative to the reference speed.
As shown above, for the purpose of slip formation a reference speed is required. This can be formed in the manner described in WO 88/06544 with reference to FIG. 7. The important point here is that the gradient of an auxiliary reference speed signal is used for its formation. The formation of the reference speed signal, which does not form a subject-matter of this invention, is performed in the evaluation circuit 5 while the formation, according to the invention, of the auxiliary reference speed signal is performed in the lower part 5a of the evaluation circuit.
The evaluation circuit 5 supplies a shift register 51 with the values of the speed of the fastest wheel, determined in the evaluation circuit 5 at a predetermined clock rate. The shift register has a.sub.1 places, of which only the last a.sub.2, e.g. a.sub.2 =.sup.a 1/4 are evaluated outside ABS control.
Referring to FIG. 1A, each new measured value input brings the longest-stored of the a.sub.2 measured values out of block 51 evaluation. In each clock cycle, those a.sub.2 measured values which have just been stored are added up in a block 521 and divided by a.sub.2 in block 522. This value a.sub.2 ' is likewise stored in block 523. The filtered measured value newly obtained is now subtracted from the longest-stored filtered measured value in block 524 and the difference is divided in block 525 by the expression (a.sub.2 -1). T, T being the clock time. The result is a measure of the gradient of the auxiliary reference signal (FIG. 1B).
The number of places which can be evaluated in block 52 can be changed over and is changed over to a.sub.1 (e.g. 4a.sub.2) at the beginning of closed-loop control (line 53). The possibility of changing over has the advantage that a more rapid and better adaptation is obtained during initial braking. The gradient signal at the output of the block 52 is now fed to an adder/subtracter 54. The evaluation circuit 5 contains a

REFERENCES:
patent: 4675819 (1987-06-01), Fennel
patent: 4693522 (1987-09-01), Wupper et al.
patent: 4736994 (1988-04-01), Fennel et al.
patent: 4818037 (1989-04-01), McEnnan
patent: 4969100 (1990-11-01), Takata et al.
patent: 4970649 (1990-11-01), Matsuda
patent: 4991910 (1991-02-01), Shimanuki et al.
Bosch Technische Berichte, English special edition (Feb. 1982).

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