Fluid-pressure and analogous brake systems – Speed-controlled – Variable target slip values
Patent
1994-12-30
1996-08-13
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Variable target slip values
303DIG7, B60T 832, B60K 2816
Patent
active
055449506
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
Traction (drive slip) control systems which, when the driven wheels spin or are expected to spin, brake the wheels or reduce the driving torque of the engine in order to avoid spinning are known. It is also known that the control system in anti-lock systems and traction control systems can be triggered erroneously if the diameters of the tires differ, e.g. due to differences in pressure, thus simulating a slip between a wheel speed and the vehicle speed.
In the prior art, the diameters of the wheels are matched to one another computationally in order to avoid incorrect triggering.
SUMMARY OF THE INVENTION
The invention takes a different approach to the solution of the problem from the prior art in that it raises the slip thresholds when an impermissible difference between the diameters of tires on the driven wheels is detected. This solution is easier to implement. If the solution adopted in the traction control system is one where the slip threshold is reduced continuously from a high initial value to a low threshold, as described in DE-A 42 16 514, the invention can be implemented in such a way here that, when a difference is detected, the slip threshold is set to the high threshold value or held there.
The specification will describe the conditions under which the monitoring of the tire tolerances is performed and how it can be performed.
BRIEF DESCRIPTION OF THE DRAWING
The sole FIGURE is a schematic of the drive slip control system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Wheel speed sensors 1 and 2 are associated with the non-driven wheels (front wheels) and sensors 3 and 4 are associated with the driven wheels. A traction control unit 5 receives the sensor signals and, when there is a risk of spinning, outputs control signals for brake-pressure control valves 6 and 7 assigned to the driven wheels and/or for an element 8 designed, for example, to influence the throttle valve.
In the control unit 5, the speed signals from the non-driven wheels are used to produce a reference signal to which the speed signals from the driven wheels are compared. If the wheel-speed signal of a driven wheel exceeds the reference signal by a predetermined slip value .lambda..sub.s, then the driven wheels, for example, are braked. The slip value .lambda..sub.s (slip threshold) can be varied between an upper and a lower limiting value .lambda..sub.o and .lambda..sub.u respectively, the upper limiting value .lambda..sub.o being taken as the starting point at the beginning of control and the slip value being reduced continuously to .lambda..sub.u if and for as long as at least one wheel is unstable. Starting from the slip value .lambda..sub.x that has been reached, the slip value is then raised continuously to .lambda..sub.o as long as none of the wheels is unstable. Starting from the particular slip value .lambda..sub.x reached, the slip value is then raised or lowered again, depending on whether at least one wheel is unstable or both are stable.
According to the invention, the slip threshold .lambda..sub.s is to be set to the high slip value or held there if the system detects that the diameters of the tires differ and that there is thus a danger that control will be triggered erroneously.
The check for an impermissible difference is only carried out if it is ascertained in a block 9 that the engine torque is in progress of the non-driven wheels)
In addition, account can also be taken of the condition
If these conditions are fulfilled, block 9 outputs a signal to AND gates 10 and 11.
In a block 12, the system ascertains, by checking the following conditions, whether there is a difference which could have the effect of triggering control erroneously.
An impermissible difference is taken to be present if either by a predetermined percentage x of the mean speed of the non-driven wheels (VMAN-VMNA)>x VMNA or greater than a percentage x of the mean speed of the non-driven wheels .vertline.VHL-VHR.vertline.>x VMNA and, in addition, either (VHL-VHR)>0 and (VNAR-VHR)<x VMNA or (VHL-VHR)<0
REFERENCES:
patent: 4530059 (1985-07-01), Brearley et al.
patent: 4545623 (1985-10-01), Sato et al.
patent: 4566737 (1986-01-01), Masaki et al.
patent: 4763960 (1988-08-01), Uchida et al.
patent: 4783126 (1988-11-01), Arikawa et al.
patent: 4843552 (1989-06-01), Inagaki
patent: 4844557 (1989-07-01), Giers
patent: 5015042 (1991-05-01), Yoshino
patent: 5060747 (1991-10-01), Eto
patent: 5117934 (1992-06-01), Tsuyama et al.
patent: 5292184 (1994-03-01), Takata
patent: 5299131 (1994-03-01), Haas et al.
patent: 5415468 (1995-05-01), Latarnik et al.
patent: 5429428 (1995-07-01), Yasuda
Burg Andreas
Schmitt Johannes
Butler Douglas C.
Robert & Bosch GmbH
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