Vehicle motion control system involving priority oversteer and understeer restraining control

• US 5,762,406 A
• Filed: 11/14/1996
• Issued: 06/09/1998
• Est. Priority Date: 11/17/1995
• Status: Expired due to Term

• Current Assignee: Advics Company Limited (Aisin Corp.)
• Original Assignee: Aisin Seiki Co., Ltd. (Aisin Corp.)
• Inventors: Yamazaki, Norio, Yasui, Yoshiyuki, Itoh, Takayuki, Fukami, Masanobu, Tozu, Kenji
• Primary Examiner(s): Graham, Matthew C.
• Application Number:
  US08/748,660
• Time in Patent Office: 572 Days
• Field of Search: 303/146, 303/147, 303/148, 303/149
• US Class Current: 303/146
• CPC Class Codes: B60T 2230/02 Side slip angle, attitude angle, floating angle, drift angle
• CPC Class Codes: B60T 8/1755 Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve road vehicle drive control systems for control of driving stability otherwise than by controlling a particular sub-unit B60W30/02
• CPC Class Codes: B60T 8/246 Change of direction
• CPC Class Codes: B60T 8/445 replenishing the released brake fluid volume into the brake piping
• CPC Class Codes: B60T 8/4836 wherein a booster output pressure is used for normal or anti lock braking B60T8/4845, B60T8/4863, B60T8/489 take precedence

Abstract

The present invention is directed to a vehicle motion control system for maintaining vehicle stability by controlling the braking force applied to at least one of the front and rear wheels of a vehicle. Oversteer restraining control and/or understeer restraining control are performed by applying the braking force to at least one wheel, on the basis of a condition of the vehicle in motion and irrespective of depression of a brake pedal. In the oversteer restraining control, the braking force is applied to at least one wheel so as to cause an increase in turning radius, when an excessive oversteer occurs during vehicle motion. Whereas, in the understeer restraining control, the braking force is applied to at least one wheel so as to cause a decrease in turning radius, when an excessive understeer occurs during vehicle motion. When the excessive oversteer and excessive understeer occur simultaneously or sequentially during vehicle motion, priority is given to the oversteer restraining control over the understeer restraining control with respect to at least one of the front wheels, while priority is given to the understeer restraining control over the oversteer restraining control with respect to at least one of the rear wheels.

Claims

1. A vehicle motion control system for maintaining stability of an automotive vehicle when said vehicle is in motion, by controlling a braking force applied to front and rear wheels of said vehicle, comprising:

vehicle condition monitor means for monitoring a condition of said vehicle in motion to determine an excessive oversteer and excessive understeer;

braking means for applying a braking force to each wheel of said vehicle, said braking means being actuated in response to depression of a brake pedal, and said braking means being actuated on the basis of an output of said monitor means and irrespective of depression of said brake pedal;

oversteer restraining control means for actuating said braking means to apply the braking force to at least one of said wheels on the basis of the output of said monitor means and irrespective of depression of said brake pedal, said oversteer restraining control means actuating said braking means to apply the braking force to at least one of said wheels so as to cause an increase in turning radius, when an excessive oversteer occurs during vehicle motion;

understeer restraining control means for actuating said braking means to apply the braking force to at least one of said wheels on the basis of the output of said monitor means and irrespective of depression of said brake pedal, said understeer restraining control means actuating said braking means to apply the braking force to at least one of said wheels so as to cause a decrease in turning radius, when an excessive understeer occurs during vehicle motion; and

priority control means for giving priority to said oversteer restraining control means over said understeer restraining control means with respect to at least one of said front wheels, and giving priority to said understeer restraining control means over said oversteer restraining control means with respect to at least one of said rear wheels, when it is determined on the basis of the output of said monitor means that the excessive oversteer and excessive understeer occur simultaneously or sequentially during vehicle motion.

2. The vehicle motion control system as claimed in claim 1, wherein said oversteer restraining control means and said understeer restraining control means include desired slip rate setting means for setting a desired slip rate for at least one of said wheels, respectively, said priority control means providing the desired slip rate set by said oversteer restraining control means for at least one of said front wheels, and providing the desired slip rate set by said understeer restraining control means for at least one of said rear wheels, when it is determined on the basis of the output of said monitor means that the excessive oversteer and excessive understeer occur simultaneously or sequentially during vehicle motion, and further comprising:

actual slip rate measuring means for measuring an actual slip rate for at least one of said wheels; and

slip rate deviation calculating means for calculating a deviation between the desired slip rate and the actual slip rate, said braking means applying the braking force to at least one of said wheels on the basis of the deviation calculated by said slip rate deviation calculating means.

3. The vehicle motion control system as claimed in claim 2, wherein said priority control means provides the desired slip rate set by said oversteer restraining control means only for a front wheel located on the outside of a curve in said vehicle'"'"'s path, with respect to said front wheels.

4. The vehicle motion control system as claimed in claim 1, wherein said braking means comprises:

wheel brake cylinders operatively connected to said front and rear wheels for applying the braking force thereto, respectively;

a hydraulic pressure generator for supplying a hydraulic braking pressure to said wheel brake cylinders; and

actuating means disposed between said hydraulic pressure generator and said wheel brake cylinders for controlling the hydraulic braking pressure in said wheel brake cylinders.

5. The vehicle motion control system as claimed in claim 4, wherein said hydraulic pressure generator includes a master cylinder for generating the hydraulic braking pressure in response to depression of said brake pedal, and an auxiliary pressure source for generating the hydraulic braking pressure irrespective of depression of said brake pedal.

6. The vehicle motion control system as claimed in claim 1, wherein said vehicle condition monitor means includes wheel speed sensors for detecting wheel speeds of said front and rear wheels, a lateral acceleration sensor for detecting a vehicle lateral acceleration and a yaw rate sensor for detecting a yaw rate, said vehicle condition monitor means calculating an estimated vehicle speed and a vehicle slip angle on the basis of output signals of said wheel speed sensors, said lateral acceleration sensor and said yaw rate sensor, and said vehicle condition monitor means monitoring the condition of said vehicle in motion to determine if the excessive oversteer and/or the excessive understeer occur.