Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1992-04-02
1994-07-12
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031132, 180197, 36442603, B60T 824
Patent
active
053282558
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a wheel slip control system. It is known that there are, for example, anti-locking systems, drive slip control systems or engine drag moment control systems which avoid the excessive wheel slippage caused, under certain road surfaces,. by braking too hard, or excessive or insufficient driving torque. In the case of these systems, in addition to the other control criteria, the wheel slip may be determined and compared with a limit value. If the limit value is exceeded, then the brake pressure is reduced or increased, and if necessary the engine torque is reduced or increased.
Some vehicles have a tendency when cornering to understeer or to oversteer. This feature is intensified by greater wheel slip, i.e. on cornering, and with the control system running, the feature occurs in an intensified manner.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a wheel slip control system which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a wheel slip control system which has a bend recognition device detecting a bend and sending a signal to an evaluation circuit, and through this signal the control system is switched over to different permitted slippage values on two sides of the vehicle so that the yawing moment is created to counteract the yawing moment created by the tendency of the vehicle to oversteer or understeer.
When the wheel slip control system is designed in accordance with the present invention, a yawing moment is artificially created which is dependent on the vehicle type and which works to counteract the specific tendency (oversteering or understeering) of the vehicle. By this means, the driving stability is increased.
The invention is based on the characteristic of the .mu.-slip curve, i.e. on the relationship of the friction force between the tires and the road surface as a function of the wheel slip
Through wheel slip control systems such as ABS, drive slip control or engine drag moment control, the operating point on the .mu.-slip curve can be determined individually for each wheel via the setting of limit values for the wheel slip (slip thresholds). In the case of the drive slip control and engine drag moment control function, a system with active brake engagement on the driving wheels would be necessary for this, i.e. it requires the application of pressure. The respective control system now tries to adjust each wheel to the specified limit value. Since in the case of the aforementioned slip control systems, usually relatively low slip values are set in order to maintain driving stability (lateral guidance), it can be assumed that the operating point is to be found in the steeply rising range (almost linear rise) of the .mu.-slip curve. Thus the driving or braking force transferred in this range is approximately proportional to the set slip.
Through the slip being set differently on the right and left sides of the vehicle, and the differing braking or driving forces resulting from this, a yawing moment can be created. Used purposefully, this yawing moment can counteract or completely cancel out any tendency to oversteer or to understeer on. cornering (motion of rotation around the vertical axis of the vehicle).
Here, the increase in driving stability is not associated with a loss of capacity for acceleration or deceleration if a reduction in slip on one side of the vehicle is opposed by an increase on the other side. However, an increase in slip means an increase in the transmitted power, so long as the operating point is in the rising range of the .mu.-slip curve. For the total of both wheels, the lateral guiding force remains approximately constant.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method
REFERENCES:
patent: 4511014 (1985-04-01), Makita
patent: 4779202 (1988-10-01), Leiber
patent: 4809808 (1989-03-01), Sommer
patent: 4917208 (1990-04-01), Komoda
patent: 4933856 (1990-06-01), Leiber
patent: 4998593 (1991-03-01), Karnopp et al.
patent: 5051908 (1991-09-01), Shiraishi
Butler Douglas C.
Muratori Alfred
Robert & Bosch GmbH
Striker Michael J.
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