Vehicle dynamics control system

• US 20030218378A1
• Filed: 04/16/2003
• Published: 11/27/2003
• Est. Priority Date: 05/22/2002
• Status: Active Grant

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Tanaka, Nobuyuki, Itoh, Akihiro
• Granted Patent: US 7,125,086 B2
• Time in Patent Office: Days
• US Class Current: 303/146
• CPC Class Codes: B60T 2201/14 Electronic locking-differential
• CPC Class Codes: B60T 2270/302 for all-wheel drive vehicles
• 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 8/1766 Proportioning of brake forces according to vehicle axle loads, e.g. front to rear of vehicle
• CPC Class Codes: B60T 8/1769 specially adapted for vehicles having more than one driven axle, e.g. four-wheel drive vehicles
• CPC Class Codes: B60W 10/14 Central differentials for dividing torque between front and rear axles
• CPC Class Codes: B60W 10/184 with wheel brakes
• CPC Class Codes: B60W 2520/105 Longitudinal acceleration
• CPC Class Codes: B60W 2710/182 Brake pressure, e.g. of fluid or between pad and disc
• CPC Class Codes: B60W 30/02 Control of vehicle driving stability
• CPC Class Codes: B60W 40/13 Load or weight

Abstract

In a vehicle dynamics control (VDC) system for a four-wheel-drive vehicle employing a brake control system regulating braking forces applied to road wheels independently of each other and a differential mechanism controlling a differential motion between front and rear wheel axles, a VDC controller controls a braking force of each road wheel depending on whether the vehicle is in oversteering or understeering. The VDC controller includes a braking-force compensation section that compensates for a braking force of at least one of a first wheel, which is subjected to vehicle dynamics control, and a second wheel to which a transferred braking force is transferred from the first wheel through the differential mechanism, to reduce a braking force of the second wheel and to prevent the braking force of the second wheel from exceeding a lateral grip limit of the second wheel during the vehicle dynamics control.

Claims

1. A vehicle dynamics control system for a four-wheel-drive vehicle employing a brake control system regulating braking forces applied to road wheels independently of each other and a differential mechanism controlling a differential motion between front and rear wheel axles, comprising:

a braking-force compensation section that compensates for a braking force of at least one of a first wheel, which is subjected to vehicle dynamics control, and a second wheel to which a transferred braking force substantially corresponding to the braking force applied to the first wheel is transferred from the first wheel through the differential mechanism, to reduce a braking force of the second wheel exceeding a lateral grip limit of the second wheel during the vehicle dynamics control.

2. The vehicle dynamics control system as set forth in claim 1, wherein:

the braking-force compensation section compensates for the braking force of at least one of the first and second wheels to reduce the braking force of the second wheel by an excess of the braking force of the second wheel over the lateral grip limit of the second wheel during the vehicle dynamics control.

3. The vehicle dynamics control system as set forth in claim 1, wherein:

the braking-force compensation section compensates for the braking force of the first wheel, which is subjected to the vehicle dynamics control, based on a wheel load of each of the road wheels.

4. The vehicle dynamics control system as set forth in claim 1, which further comprises:

a turning-behavior state variable detection section that detects a state variable of turning behavior of the vehicle;

a control section that controls a braking force applied to each of the road wheels so that the state variable of turning behavior is brought closer to a desired value;

a lateral-grip state detection section that estimates a state of lateral grip of each of the road wheels on a road, from a wheel load of each of the road wheels; and

a braking-force compensation section compensates for the braking force of the first wheel, which is subjected to the vehicle dynamics control to bring the state variable of turning behavior closer to the desired value, to reduce the braking force of the second wheel, based on the state of lateral grip of each of the road wheels on the road, estimated from the wheel load of each of the road wheels.

5. The vehicle dynamics control system as set forth in claim 4, wherein:

in an oversteer suppression control mode that at least one of front wheels is subjected to the vehicle dynamics control and during vehicle deceleration with a driver'"'"'s brake-pedal depression, the braking-force compensation section compensates for the braking force of the front wheel, which is subjected to the vehicle dynamics control to bring the state variable of turning behavior closer to the desired value, so that the braking force of the front wheel, which is subjected to the vehicle dynamics control, decreases as a front wheel load increases.

6. The vehicle dynamics control system as set forth in claim 4, wherein:

in an oversteer suppression control mode that at least one of front wheels is subjected to the vehicle dynamics control and during vehicle acceleration with a driver'"'"'s accelerator-pedal depression, the braking-force compensation section compensates for the braking force of the front wheel, which is subjected to the vehicle dynamics control to bring the state variable of turning behavior closer to the desired value, so that the braking force of the front wheel, which is subjected to the vehicle dynamics control, increases as a rear wheel load increases.

7. The vehicle dynamics control system as set forth in claim 4, wherein:

in an understeer suppression control mode that at least one of rear wheels is subjected to the vehicle dynamics control and during vehicle acceleration with a driver'"'"'s accelerator-pedal depression, the braking-force compensation section compensates for the braking force of the rear wheel, which is subjected to the vehicle dynamics control to bring the state variable of turning behavior closer to the desired value, so that the braking force of the rear wheel, which is subjected to the vehicle dynamics control, decreases as a rear wheel load increases.

8. The vehicle dynamics control system as set forth in claim 4, wherein:

in an understeer suppression control mode that at least one of rear wheels is subjected to the vehicle dynamics control and during vehicle deceleration with a driver'"'"'s brake-pedal depression, the braking-force compensation section compensates for the braking force of the rear wheel, which is subjected to the vehicle dynamics control to bring the state variable of turning behavior closer to the desired value, so that the braking force of the rear wheel, which is subjected to the vehicle dynamics control, increases as a front wheel load increases.

9. The vehicle dynamics control system as set forth in claim 1, wherein:

the braking-force compensation section decreasingly compensates for the braking force of the second wheel, on which the transferred braking force acts, in presence of a driver'"'"'s brake-pedal depression during the vehicle dynamics control.

10. The vehicle dynamics control system as set forth in claim 1, which further comprises:

a turning-behavior state variable detection section that detects a state variable of turning behavior of the vehicle;

a control section that controls a braking force applied to each of the road wheels so that the state variable of turning behavior is brought closer to a desired value;

a braking-force application device that applies a braking force to each of the road wheels, which is produced by a driver'"'"'s brake-pedal depression; and

a braking-force compensation section decreasingly compensates for the braking force of the second wheel, on which the transferred braking force acts, to prevent a sum of the braking force applied to the second wheel, produced by the driver'"'"'s brake-pedal depression, and the transferred braking force, transferred from the first wheel via the differential mechanism to the second wheel from exceeding a lateral grip limit of the second wheel, in presence of the driver'"'"'s brake-pedal depression during the vehicle dynamics control.

11. The vehicle dynamics control system as set forth in claim 10, wherein:

the braking-force compensation section comprises;

(a) a slip state detection section that detects a state of slip of the second wheel on which the transferred braking force acts;

(b) a lateral-grip margin calculation section that estimates a margin for the lateral grip of the second wheel; and

(c) a braking-force decrement calculation section that sets a braking force decrement of the second wheel based on the margin for the lateral grip of the second wheel.

12. The vehicle dynamics control system as set forth in claim 10, wherein:

the braking-force compensation section cancels decreasingly compensating for the braking force of the second wheel when the state variable of turning behavior has been converged closer to the desired value.

13. The vehicle dynamics control system as set forth in claim 12, wherein:

the braking-force compensation section cancels decreasingly compensating for the braking force of the second wheel when a first condition that a deviation between the state variable of turning behavior and the desired value is less than a predetermined threshold value is satisfied, and simultaneously a second condition that the deviation begins to reduce is satisfied.

14. The vehicle dynamics control system as set forth in claim 10, wherein:

in an oversteer suppression control mode that at least one of front wheels is subjected to the vehicle dynamics control and during vehicle deceleration with the driver'"'"'s brake-pedal depression, the braking-force compensation section decreasingly compensates for the braking force of each of rear wheels.

15. The vehicle dynamics control system as set forth in claim 10, wherein:

in an understeer suppression control mode that at least one of rear wheels is subjected to the vehicle dynamics control and during vehicle deceleration with the driver'"'"'s brake-pedal depression, the braking-force compensation section decreasingly compensates for the braking force of each of front wheels.