Brake control device for vehicle

1. A brake control device for controlling braking forces applied to wheels and thereby stabilizing behavior of a vehicle turning a corner, comprising:

a turning condition detection unit configured to detect a turning condition of the vehicle;

a braking amount setting unit configured to set braking amounts for the respective wheels of the vehicle based on the turning condition detected by the turning condition detection unit;

a brake control unit configured to apply braking forces to the wheels according to the braking amounts set by the braking amount setting unit; and

a road surface friction coefficient estimation unit configured to estimate a road surface friction coefficient of a road on which the vehicle is running;

wherein the braking amount setting unit is configured to change, when the vehicle is in a center differential lock mode or a direct four-wheel drive mode, upper limits of the braking amounts for the respective wheels according to the road surface friction coefficient estimated by the road surface friction coefficient estimation unit, to gradually increase target slip ratios for three of the wheels as the road surface friction coefficient increases, and

wherein if the road surface friction coefficient of the road is less than a predetermined value and the vehicle is in the center differential lock mode or the direct four-wheel drive mode, the braking amount setting unit is configured to set the upper limits of the braking amounts less than those that the braking setting unit is configured to set under an equivalent road surface friction coefficient condition when the vehicle is not in the center differential lock mode or the direct four-wheel drive mode.

2. The brake control device as claimed in claim 1 , wherein the predetermined value is approximately 0.3.

3. The brake control device as claimed in claim 1 , wherein if the road surface friction coefficient is less than a first threshold value, the braking amount setting unit is configured to set the upper limits of the braking amounts for rear wheels to zero and to set the braking amount only for an outer front wheel.

4. The brake control device as claimed in claim 3 , wherein if the road surface friction coefficient is not less than the first threshold value and not greater than a second threshold value, the braking amount setting unit is configured to set the upper limit of the braking amount for an inner rear wheel to zero and to set the braking amounts for the outer front wheel and an outer rear wheel.

5. The brake control device as claimed in claim 4 , wherein if the road surface friction coefficient is greater than the second threshold value, the braking amount setting unit is configured to set the braking amounts for three wheels other than an inner front wheel.

6. The brake control device as claimed in claim 2 , wherein if the road surface friction coefficient is less than a first threshold value, the braking amount setting unit is configured to set the upper limits of the braking amounts for rear wheels to zero and to set the braking amount only for an outer front wheel.

7. The brake control device as claimed in claim 6 , wherein if the road surface friction coefficient is not less than the first threshold value and not greater than a second threshold value, the braking amount setting unit is configured to set the upper limit of the braking amount for an inner rear wheel to zero and to set the braking amounts for the outer front wheel and an outer rear wheel.

8. The brake control device as claimed in claim 7 , wherein if the road surface friction coefficient is greater than the second threshold value, the braking amount setting unit is configured to set the braking amounts for three wheels other than an inner front wheel.

9. A brake control device for controlling braking forces applied to wheels and thereby stabilizing behavior of a vehicle turning a corner, comprising:

a turning condition detection unit configured to detect a turning condition of the vehicle;

a braking amount setting unit configured to set braking amounts for the respective wheels of the vehicle based on the turning condition detected by the turning condition detection unit;

a brake control unit configured to apply braking forces to the wheels according to the braking amounts set by the braking amount setting unit; and

a road surface friction coefficient estimation unit configured to estimate a road surface friction coefficient of a road on which the vehicle is running;

wherein the braking amount setting unit is configured to change upper limits of the braking amounts for the respective wheels according to the road surface friction coefficient estimated by the road surface friction coefficient estimation unit when the vehicle is in a center differential lock mode or a direct four-wheel drive mode,

wherein if the road surface friction coefficient is less than a first threshold value, the braking amount setting unit is configured to set the upper limits of the braking amounts for rear wheels to zero and to set the braking amount only for an outer front wheel, and

wherein if the road surface friction coefficient is not less than the first threshold value and not greater than a second threshold value, the braking amount setting unit is configured to set the upper limit of the braking amount for an inner rear wheel to zero and to set the braking amounts for the outer front wheel and an outer rear wheel.

10. The brake control device as claimed in claim 9 , wherein if the road surface friction coefficient is greater than the second threshold value, the braking amount setting unit is configured to set the braking amounts for three wheels other than an inner front wheel.

11. A brake control device for controlling braking forces applied to wheels and thereby stabilizing behavior of a vehicle turning a corner, comprising:

a turning condition detection unit configured to detect a turning condition of the vehicle;

a braking amount setting unit configured to set braking amounts for the respective wheels of the vehicle based on the turning condition detected by the turning condition detection unit;

a brake control unit configured to apply braking forces to the wheels according to the braking amounts set by the braking amount setting unit; and

a road surface friction coefficient estimation unit configured to estimate a road surface friction coefficient of a road on which the vehicle is running;

wherein the braking amount setting unit is configured to change upper limits of the braking amounts for the respective wheels according to the road surface friction coefficient estimated by the road surface friction coefficient estimation unit when the vehicle is in a center differential lock mode or a direct four-wheel drive mode,

wherein if the road surface friction coefficient of the road is less than approximately 0.3, the braking amount setting unit is configured to set the upper limits of the braking amounts less than those used when the vehicle is not in the center differential lock mode or the direct four-wheel drive mode,

wherein if the road surface friction coefficient is less than a first threshold value, the braking amount setting unit is configured to set the upper limits of the braking amounts for rear wheels to zero and to set the braking amount only for an outer front wheel, and

wherein if the road surface friction coefficient is not less than the first threshold value and not greater than a second threshold value, the braking amount setting unit is configured to set the upper limit of the braking amount for an inner rear wheel to zero and to set the braking amounts for the outer front wheel and an outer rear wheel.

12. The brake control device as claimed in claim 11 , wherein if the road surface friction coefficient is greater than the second threshold value, the braking amount setting unit is configured to set the braking amounts for three wheels other than an inner front wheel.