Method of controlling traveling stability of vehicle
Disclosed herein is a method of controlling traveling stability of a vehicle. In the present invention, a driver's desired yaw rate is estimated using a steering wheel angle and a reference speed of the vehicle while turning. The condition of a road surface the vehicle is traveling on is judged by comparing lateral acceleration of the vehicle, estimated using the estimated yaw rate and a reference vehicle speed, with lateral acceleration actually measured by a lateral acceleration sensor. A driver's desired reference yaw rate is determined according to the judged road surface condition. It is determined whether a vehicle is understeered or oversteered by comparing the determined reference yaw rate with an actual yaw rate measured by a yaw rate sensor. According to the determined result, braking force and driving force of the vehicle are controlled, thus obtaining excellent vehicle stability.
1. The method of controlling traveling stability of a vehicle, method comprising:
setting a driver's desired yaw rates on various road surface conditions using a steering wheel angle and a reference speed of the vehicle while turning;
judging a road surface condition on which the vehicle is traveling, by comparing lateral acceleration of the vehicle, which is estimated using the reference vehicle speed and a preset yaw rate on a preset reference road surface condition, with actual lateral acceleration measured by a lateral acceleration sensor;
determining one of the driver's desired yaw rates corresponding to the judged road surface condition as a reference yaw rate, and determining whether the vehicle is understeered or oversteered by comparing the determined reference yaw rate with an actual yaw rate measured by a yaw rate sensor;
controlling braking force and driving force according to the determination result;
wherein the reference vehicle speed is calculated to set the yaw rates, and if the vehicle is a four-wheel drive car, the reference vehicle speed is calculated using the following Equation by varying weighting factors according to reliability of a value detected by a vertical acceleration sensor and a wheel speed so as to calculate the reference vehicle speed in consideration of a perturbation factor due to an error of the vertical acceleration sensor and the gravity acceleration in traveling on a banked road:
V ref( n+ 1)=α[ a x0 ( n+ 1)+ a x ( n+ 1)]Δ t +(1−α)[ c 1 V ref( n )+(1 −c 1 ) V wheel ( n+ 1)]
where Vref is a reference vehicle speed, α is a weighting factor of the vertical acceleration, a x0 is a perturbation factor of the vertical acceleration, a x is a vehicle's vertical acceleration value, Δt is an integration time, c 1 is a weighting factor of a previous reference vehicle speed, and V wheel is a wheel speed.
2. The method of controlling traveling stability of a vehicle, method comprising:
setting a driver's desired yaw rates on various road surface conditions using a steering wheel angle and a reference speed of the vehicle while turning;
judging a road surface condition on which the vehicle is traveling, by comparing lateral acceleration of the vehicle, which is estimated using the reference vehicle speed and a preset yaw rate on a preset reference road surface condition, with actual lateral acceleration measured by a lateral acceleration sensor;
determining one of the driver's desired yaw rates corresponding to the judged road surface condition as a reference yaw rate, and determining whether the vehicle is understeered or oversteered by comparing the determined reference yaw rate with an actual yaw rate measured by a yaw rate sensor;
controlling braking force and driving force according to the determination result;
wherein at the braking force and driving force control step, braking pressure of a corresponding wheel and the amount of driving torque are controlled to satisfy the following Equation so as to prevent braking pressure from excessively increasing and locking the wheel, and facilitate the driver's will to travel by preventing an excessive decrease in engine torque:
J
=
∫
[
W
1
(
r
desired
-
r
measured
)
2
+
W
2
∑
1
4
P
i
+
W
3
(
T
desired
-
T
actual
)
2
]
ⅆ
t
where J is an objective function (performance index), W 1 , W 2 and W 3 are weighting factors, r desired is a driver's desired yaw rate, r measured is a measured yaw rate, P i is wheel control pressure, T desired is driver's desired engine torque and T actual is controlled engine torque.
3. The method of controlling traveling stability of a vehicle according to claim 2 , wherein the braking force and driving force control step is performed such that, if a slip value of the wheel is equal to or greater than a reference value, control pressure is not generated in the wheel, and the reference value is preset to correspond to a road surface friction coefficient and a vehicle speed.