Integrated control system for vehicle
An integrated control system for a vehicle is provided. The system includes a friction coefficient calculation unit that calculates friction coefficients of left side and right side road surfaces, respectively, based on vehicle wheel state information and a predetermined setting information collected during ABS operation. A feedforward braking pressure calculation unit calculates a feedforward braking pressure of each vehicle wheel using the friction coefficients. An ABS braking pressure calculation unit calculates an ABS braking pressure of the each vehicle wheel based on the feedforward braking pressure and slip rate information. A rear wheel steering control amount calculation unit calculates a rear wheel steering control amount for yaw compensation using the ABS braking pressure of each vehicle wheel and a rear wheel steering controller executes a rear wheel steering control according to the rear wheel steering control amount.
1. An integrated control system for a vehicle, comprising:
a friction coefficient calculation unit configured to calculate a friction coefficient of a left side road surface and a right side road surface, respectively, on which a left side wheel and a right side wheel are grounded in a road surface based on vehicle wheel state information and a predetermined setting information collected from the vehicle upon anti-lock brake system (ABS) operation;
a feedforward braking pressure calculation unit configured to calculate a feedforward braking pressure of each vehicle wheel using the calculated friction coefficients of the left side road surface and the right side road surface;
an ABS braking pressure calculation unit configured to calculate an ABS braking pressure of the each vehicle wheel based on the calculated feedforward braking pressure and information of the vehicle wheel;
a rear wheel steering control amount calculation unit configured to calculate a rear wheel steering control amount for yaw compensation using the calculated ABS braking pressure of each vehicle wheel; and
a rear wheel steering controller configured to perform a rear wheel steering control of the vehicle based on the calculated rear wheel steering control amount,
wherein the feed forward braking pressure calculation unit is configured to calculate a limit braking pressure using the calculated friction coefficient, and add or subtract the braking pressure for compensating a slip rate of each vehicle wheel within the calculated limit braking pressure to mitigate chattering,
wherein the friction coefficient calculation unit includes a friction coefficient convergence section configured to calculate the friction coefficient of the left side road surface and the right side road surface using the longitudinal force based left side road surface friction coefficient, the longitudinal force based right side road surface friction coefficient, and the lateral force based on the calculated road surface friction coefficient, and
wherein the friction coefficient convergence section is configured to:
calculate the current friction coefficient of the left side road surface and the current friction coefficient of the right side road surface using the longitudinal force based left side road surface friction coefficient, the longitudinal force based right side road surface friction coefficient, the lateral force based road surface friction coefficient, the weighting factors, and the friction coefficient determined in the previous control cycle using the following E1 and E2,
μ FL ( k )= w Lat_FL μ Lat +w Long_FL μ Long_FL +(1− w Lat_FL −w Long_FL )μ FL ( k− 1) E1
μ FR ( k )= w Lat_FR μ Lat +w Long_FR μ Long_FR +(1− w Lat_FR −w Long_FR )μ FR ( k− 1) E2
wherein, μ FL (k) refers to the current friction coefficient of the left side road surface, μ FR (k) to the current friction coefficient of the right side road surface, μ FL (k−1) to the friction coefficient of the left side road surface determined in the previous control cycle, μ FR (k−1) to the friction coefficient of the right side road surface determined in the previous control cycle, w Lat_FL to the left side wheel lateral weighting factor, μ Lat to the lateral force based road surface friction coefficient, w Long_FL to the left side wheel longitudinal weighting factor, μ Long_FL to the longitudinal force based left side road surface friction coefficient, w Lat_FR to the right side wheel lateral weighting factor, w Long_FR to the right side wheel longitudinal weighting factor, and μ Long_FR to the longitudinal force based right side road surface friction coefficient.
2. The integrated control system for the vehicle of claim 1 , wherein the friction coefficient calculation unit further includes:
a tire force calculation section configured to predict and calculate a tire force of the left side wheel and a tire force of the right side wheel for each road surface friction coefficient using a predetermined tire model for each road surface friction coefficient from the vehicle wheel state information, respectively; and
a friction coefficient estimation section configured to calculate a longitudinal force based left side road surface friction coefficient, a longitudinal force based right side road surface friction coefficient, and a lateral force based road surface friction coefficient from the tire force of the left side wheel and the right side wheel for each predicted road surface friction coefficient, and the estimated longitudinal and lateral tire force.
3. The integrated control system for the vehicle of claim 2 , wherein the tire force calculation section includes:
a left side tire force calculation section configured to calculate the tire force of the left side wheel in a front side wheel of the vehicle for each road surface friction coefficient using the predetermined tire model for the each road surface friction coefficient; and
a right side tire force calculation section configured to calculate the tire force of the right side wheel in the front side wheel of the vehicle for each road surface friction coefficient using the predetermined tire model for the each road surface friction coefficient.
4. The integrated control system for the vehicle of claim 2 , wherein the tire force calculation section is configured to calculate the longitudinal tire force and the lateral tire force for each road surface friction coefficient of the corresponding wheel, respectively, as the tire force of the left side wheel and the tire force of the right side wheel.
5. The integrated control system for the vehicle of claim 4 , wherein the estimated longitudinal tire force used in the friction coefficient estimation section includes the longitudinal tire force of the left side wheel and the right side wheel in the front side wheel of the vehicle.
6. The integrated control system for the vehicle of claim 5 , wherein the friction coefficient estimation section includes:
a first longitudinal force based friction coefficient estimation section configured to calculate the longitudinal force based left side road surface friction coefficient using the longitudinal tire force of the left side wheel for each road surface friction coefficient and the estimated longitudinal tire force of the left side wheel;
a second longitudinal force based friction coefficient estimation section configured to calculate the longitudinal force based right side road surface friction coefficient using the longitudinal tire force of the right side wheel for each road surface friction coefficient and the estimated longitudinal tire force of the right side wheel; and
a lateral force based friction coefficient estimation section configured to calculate the lateral force based road surface friction coefficient using the lateral tire force of the left side wheel for each road surface friction coefficient, the lateral tire force of the right side wheel for each road surface friction coefficient, and the estimated lateral tire force.
7. The integrated control system for the vehicle of claim 6 , wherein the first longitudinal force based friction coefficient estimation section is configured to:
determine a weighting factor for each road surface friction coefficient using a predetermined equation from the longitudinal tire force of the left side wheel for each road surface friction coefficient and the estimated longitudinal tire force of the left side wheel; and
calculate the longitudinal force based left side road surface friction coefficient by multiplying each road surface friction coefficient of the predetermined tire model by the determined weighting factor for each road surface friction coefficient and summing them.
8. The integrated control system for the vehicle of claim 6 , wherein the second longitudinal force based friction coefficient estimation section is configured to:
determine a weighting factor for each road surface friction coefficient using a predetermined equation from the longitudinal tire force of the right side wheel for each road surface friction coefficient and the estimated longitudinal tire force of the right side wheel; and
calculate the longitudinal force based right side road surface friction coefficient by multiplying each road surface friction coefficient of the predetermined tire model by the determined weighting factor for each road surface friction coefficient and summing them.
9. The integrated control system for the vehicle of claim 6 , wherein the lateral force based friction coefficient estimation section is configured to:
determine a weighting factor for each road surface friction coefficient using a predetermined equation from the lateral tire force of the left side wheel for each road surface friction coefficient, the lateral tire force of the right side wheel for each road surface friction coefficient, and the estimated lateral tire force; and
calculate the lateral force based road surface friction coefficient by multiplying each road surface friction coefficient of the predetermined tire model by the determined weighting factor for each road surface friction coefficient and summing them.
10. The integrated control system for the vehicle of claim 2 , wherein the vehicle wheel state information in the tire force calculation section includes a slip angle, a slip rate, and a normal force of the corresponding wheel.
11. The integrated control system for the vehicle of claim 2 , wherein the estimated longitudinal tire force used in the friction coefficient estimation section includes the longitudinal tire force of the left side wheel and the longitudinal tire force of the right side wheel in the front side wheel of the vehicle.
12. The integrated control system for the vehicle of claim 2 , wherein the friction coefficient calculation unit further includes:
a left side wheel weighting factor calculation section configured to determine a left side wheel longitudinal weighting factor and a left side wheel lateral weighting factor from the slip rate and slip angle information of the left side wheel as the vehicle wheel state information collected from the vehicle; and
a right side wheel weighting factor calculation section configured to determine a right side wheel longitudinal weighting factor and a right side wheel lateral weighting factor from the slip rate and slip angle information of the right side wheel as the vehicle wheel state information,
wherein the friction coefficient convergence section is configured to:
calculate a current friction coefficient of the left side road surface and a current friction coefficient of the right side road surface using the longitudinal force based left side road surface friction coefficient, the longitudinal force based right side road surface friction coefficient, and the lateral force based road surface friction coefficient calculated by the friction coefficient estimation section, the weighting factors determined by the left side wheel weighting factor calculation section and the right side wheel weighting factor calculation section, and the friction coefficient determined in a previous control cycle.
13. The integrated control system for the vehicle of claim 1 , wherein the feedforward braking pressure calculation unit includes:
a limit braking pressure calculation section configured to calculate a limit braking pressure using the calculated friction coefficient of the left side road surface and the right side road surface, and a tire normal force of the vehicle wheel,
wherein the feedforward braking pressure calculation unit is configured to calculate the feedforward braking pressure of each vehicle wheel based on a driver braking pressure according to a brake pedal operation of a driver and the calculated limit braking pressure calculated.
14. The integrated control system for the vehicle of claim 13 , wherein the feedforward braking pressure calculation unit includes:
a left side wheel feedforward braking pressure calculation unit including the limit braking pressure calculation section configured to calculate the limit braking pressure of the left side wheel from the friction coefficient of the left side road surface and the tire normal force of the left side wheel, and calculate the feedforward braking pressure of the left side wheel from the calculated limit braking pressure of the left side wheel and the driver braking pressure; and
a right side wheel feedforward braking pressure calculation unit including the limit braking pressure calculation section configured to calculate the limit braking pressure of the right side wheel from the friction coefficient of the right side road surface and the tire normal force of the right side wheel, and calculate the feedforward braking pressure of the right side wheel from the calculated limit braking pressure of the right side wheel and the driver braking pressure.
15. The integrated control system for the vehicle of claim 14 , wherein the ABS braking pressure calculation unit includes:
a left side wheel ABS braking pressure calculation unit configured to calculate an ABS braking pressure of the left side wheel from the calculated feedforward braking pressure of the left side wheel, a target slip rate, and a current slip rate of the left side wheel; and
a right side wheel ABS braking pressure calculation unit configured to calculate an ABS braking pressure of the right side wheel from the calculated feedforward braking pressure of the right side wheel, a target slip rate, and a current slip rate of the right side wheel.
16. The integrated control system for the vehicle of claim 13 , wherein the feedforward braking pressure of the corresponding wheel is determined as the driver braking pressure when the limit braking pressure for each wheel is greater than the driver braking pressure, and the feedforward braking pressure of the corresponding wheel is determined as the limit braking pressure when the limit braking pressure for each wheel is equal to or less than the driver braking pressure.
17. The integrated control system for the vehicle of claim 1 , wherein the rear wheel steering control amount calculation unit is configured to:
calculate a yaw moment (ΔM z ) caused by an asymmetric braking pressure in a braking situation where the friction coefficient of the left side road surface and the right side road surface are different from each other; and
calculate a rear wheel steering control amount from the calculated yaw moment (ΔM z ), using the ABS braking pressure of each vehicle wheel calculated by the ABS braking pressure calculation unit.