Method for regulating the driving stability of a vehicle

#The present invention relates to a method for regulating the driving stability, wherein pressures for individual brakes of the vehicle are determined in dependence on several input quantities so that the driving stability is enhanced by brake interventions at individual wheels.

#Abrupt steering and counter-steering maneuvers in e.g. obstacle avoidance maneuvers, when changing lanes, free style, and like maneuvers may cause instabilities of the vehicle at a high coefficient of friction. There is an increased risk of rollover for vehicles with a high center of gravity.

#A great number of driving stability control systems are known in the art in order to automatically counteract these vehicle instabilities. The term ‘driving stability control’ covers five principles for influencing the driving performance of a vehicle by means of predeterminable pressures or brake forces in or at individual wheel brakes and by means of intervention into the engine management of the driving engine. These systems concern brake slip control (ABS) preventing the locking of individual wheels during a braking operation, traction slip control (TCS) preventing the spinning of the driven wheels, electronic brake force proportioning (EBP) regulating the ratio of brake forces between front axle and rear axle of the vehicle, anti rollover braking (ARB) preventing rollover of the vehicle about its longitudinal axis, as well as yaw torque control (ESP—Electronic Stability Program) ensuring stable driving conditions during yawing of the vehicle about the vertical axis.

#In the drawings,

#FIG. 1 is an example of a double lane change.

#FIG. 2 shows signal sequences evaluated or produced according to the invention.

#FIG. 1 shows a double lane change that can e.g. be desired when an obstacle must be avoided suddenly. Reference numeral 10 relates to the desired course; the vehicle moves alongside the positions 11, 12, 13 and 14. The vehicle passes through various situations. To pass through the desired course, especially at high speeds, initially a highly dynamic steering maneuver with a comparatively large steering angle or abrupt steering movement of the front wheels 15, 16 is necessary (position 11). Subsequently, there is a return steering movement with steering wheel angle zero crossing (position 12) and thereafter a counter-steering action at the end of the first lane change (position 13) and further to the second lane change (position 14). When a like maneuver takes place at a high coefficient of friction without deceleration, typically, the vehicle becomes automatically unstable between position 13 and position 14 starting from a determined combination of vehicle speed, steering dynamics and steering amplitude, that means the vehicle develops greater sideslip angles (>2 degrees) which no longer can be mastered by the driver. Especially in vehicles having a high center of gravity the lateral dynamics developing may induce pitching motions and rolling motions that will lead to rollover of the vehicle about the longitudinal axis in the most unfavorable case. An ESP controller can detect the unstable driving performance and intervene in a correcting fashion, but it is unable to prevent the occurrence of the unstable condition. To avoid this danger situation, it is necessary to reduce the vehicle speed as well as the steering dynamics by an early intense brake intervention according to the invention.

#FIG. 2 shows the signal course during the first lane change (positions 11 to 13). When the vehicle assumes position 17, it exhibits a stable driving performance, that means the vehicle follows the driver's specifications without remarkable difference, the sideslip angle amounts to 0 degrees. The signals SWAP (steering wheel angle velocity), SWA (steering wheel angle), LA (lateral acceleration), YR (yaw rate) and (yaw velocity) provided by the control unit of the brake system in this stable driving condition are in a tolerance band 18 which is e.g. characterized by a steering wheel angle velocity less than 40 to 200 degrees/s. As is shown in FIG. 2 the situation described with respect to FIG. 1 (highly dynamic steering maneuver) can occur. The highly dynamic steering maneuver is determined from the variation of the steering wheel angle speed SWAP between leaving (time T1) and entering (time T3) the tolerance band 18. An unambiguous impulse of the steering wheel angle gradient SWAP characterizes a highly dynamic steering maneuver that is detected by way of the following conditions: a.) |SWAPMAX|/(T2−T1)>threshold value 1 b.) |SWAPMAX|/(T3−T2)>threshold value 2 c.) |SWAPMAX|>threshold value 3 wherein SWAP=steering wheel angle velocity, SWAPMAX=maximum of the steering wheel angle velocity, T1=point of time of the steering wheel angle velocity leaving the tolerance band 18, T2=point of time of the maximum of the steering wheel angle velocity, T3=point of time of entry of the steering wheel angle velocity into the tolerance band 18. Thus, the average steering wheel angle acceleration is determined until the maximum steering wheel angle velocity is reached, and the average steering wheel angle deceleration is determined until the entry into the tolerance band. When the steering wheel angle acceleration lies above a value in the range of 600 to 2000 degrees/s2 (threshold value S1), the steering wheel angle deceleration lies above a value in the range of 800 and 2500 degrees/s2 (threshold value S2) and the absolute value of the maximum SWAPMAX lies above a value in the range of 250 to 600 degrees/s2 (threshold value S3), a steering maneuver may be evaluated as highly dynamic. The steering amplitude above S3 is so great that a tendency towards a subsequent unstable driving performance (driving condition) can be predicted.

#When the conditions a.), b.), and c.) are satisfied and the absolute value of the yaw rate YR at the time T3 of the entry of the steering wheel angle velocity lies above a value in the range of e.g. 20 to 40 degrees/s (threshold value 7) and the lateral acceleration LA lies above a value in the range of e.g. 4.5 to 8 m/s2 (threshold value 8), the brake intervention is started at the curve-outward front wheel 16.