Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication
Reexamination Certificate
1999-07-23
2001-05-15
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
C707S793000, C707S793000, C707S793000, C303S144000, C303S149000, C303S154000, C180S197000
Reexamination Certificate
active
06233505
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of determining the nominal driving behavior of a vehicle.
A method of the afore-described type is disclosed by DE 40 30 653 A1 describing a method for determining the slip angles and/or the lateral guiding forces of a decelerated vehicle. Based on a simplified vehicle model wherein the speed of the individual wheel, the steering angle, the yawing angle speed and the braking pressure are used as measurable variables, the slip angles and/or the lateral guiding forces are determined as estimated values. When plotting, in a diagram, the lateral guiding forces exerted on a wheel versus the momentary slip angles, a linear relationship will arise at least in respect of small slip angles. The slope of the straight line extending through the zero point is called “slip rigidity” of the respective wheel. However, a growing slip angle will render the relationship between lateral guiding force and slip angle non-linear. With a growing slip angle, the lateral guiding force approaches a peak value from which it negligibly departs again in the course of the curve. If the slip angles are in the non-linear range of the characteristic of lateral force/slip-angle, substantial differences occur between factual and simulated speeds of the yawing angle. As according to the prior known method the yawing angle speed is measured, the difference between measured and simulated yawing angle speeds are indicative of the transition from the linear to the non-linear range of the characteristic of lateral-force/slip-angle. Once it has been detected that the linear range of the lateral-force/slip-angle characteristic has been abandoned, the interconnection between lateral guiding force and slip angle is approximately defined by a straight line of a lower slope. For precisely adapting the vehicle model to the real conditions, in the prior art process, the slip rigidity of the front wheels and of the rear wheels is correspondingly modified so that the lateral-force/slip-angle characteristics of both axes conform to the real course of the curve.
Generally, a neutral driving conduct is striven for through a yawing moment control in a curve, which means that the self-steering gradient should, if possible, be zero. To that effect, it is easier for the driver to tackle a slight understeering by an additional steering lock than oversteering the vehicle. A neutral driving behavior exists if the slip rigidity values of the rear axle multiplied by the distance of the rear axle from the vehicle center correspond to the slip rigidity values of the front axle multiplied by the distance of the front axle from the vehicle center. If this product is smaller for the rear axle than the one for the front axle, thee is an oversteering behavior. The basic lay-out of modern vehicles, as a rule is slightly understeering. Assuming that the slip rigidities are identical at the front and rear, the vehicle model, in the linear range, always exhibits an understeering behavior if the distance of the rear axle from the vehicle center exceeds the distance from the front axle because the slip rigidities take constant values. However, if the slip rigidity values with a growing slip angle decrease, it might happen that the slip angles of the rear axle are already within a range in which the slip rigidity values are reduced while the front axle is still in the linear range of the characteristic of lateral-force/slip-angle. At that moment, the vehicle model would exhibit an oversteering behavior. This will involve danger, especially so if the vehicle model serves for computing a nominal value of, for example, the nominal speed of the yawing angle. In that case, the vehicle control would receive a nominal value corresponding to an oversteering behavior thus requiring a control manipulation causing the vehicle to oversteer. This involves great danger as it is substantially more difficult for the driver to tackle an oversteering than an understeering behavior. Even if the real vehicle with no manipulated control is caused to exhibit an oversteering behavior, the vehicle control, initially, does not interfere because such a behavior would then correspond to the nominal value.
The object of the present invention resides in providing a method for determining the nominal behavior of a vehicle which also takes into account the non-linear range of the lateral-force/slip-angle characteristic but preventing a nominal value corresponding to an oversteering behavior from occurring.
SUMMARY OF THE INVENTION
This problem, in the practice of the invention, is solved by reducing the slip rigidities (C
L
) only of the wheels of the front axle. The principle underlying the invention resides in that the slip rigidities on the rear axle are kept constant so that the size of the slip angles on the rear axle is irrelevant. The slip rigidities of the vehicle model on the rear axle, in no driving situation, can become smaller than the ones on the front axle as they always correspond to the peak value of the front axle. Accordingly, the nominal value, in any event, corresponds to a neutral or slightly understeering behavior, i.e. driving situations that can be easily tackled by the driver.
In the event of further increasing slip angles then also the lateral-force/slip-angle characteristic of the front axle can be adjusted to the course of the real curve in that the lateral guiding force as of a predetermined slip angle remains constant at a peak value.
As the strongest lateral guiding force when driving through a curve is generated by the front wheel at the outer side of the curve, the adaptation of the lateral-force/slip-angle characteristic of the front axle to the real course involves a higher control quality. No instability can occur in the calculation of the vehicle state even with a zero slope, as on the rear axle, a slip angle can respectively be clearly associated to a predetermined lateral guiding force.
The reduction of the slip rigidity values of the front axle can commence when a predetermined slip angle or a threshold of a value clearly correlated to the slip angle is exceeded; thus applies both to the reduction of a slope of the lateral-force/slip-angle characteristic to a lower value, and to zero. The slip angles respectively releasing the reduction of the slope or the correlating values can be determined in response to the frictional coefficient so that the threshold for beginning and boosting the reduction of the slip rigidities is a slip angle the more so smaller slip angle, the smaller the friction coefficient between the road and the tire is.
Preferred relationships between the threshold slip angles and the friction coefficient of the road as well as other details of the invention will now be described with reference to the accompanying drawing.
REFERENCES:
patent: 4849891 (1989-07-01), Krohn et al.
patent: 5188434 (1993-02-01), Ruf et al.
Search Report of the German Patent Office Relating to Parent German Patent Application No. 19617590.9 filed Nov. 25, 1996.
Duis Holger
Endress Ralf
Kranz Thomas
Wanke Peter
Beaulieu Yonel
Continental Teves AG & Co. oHG
Cuchlinski Jr. William A.
Rader & Fishman & Grauer, PLLC
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