Brake fluid pressure control apparatus for vehicle

1. A brake fluid pressure control apparatus for executing rollover prevention control, in which a brake is applied to at least one wheel of a vehicle at a timing when a rollover tendency of the vehicle is detected through a rollover detection parameter while the vehicle is turning, the brake fluid pressure control apparatus comprising:

a parameter calculation unit that calculates the rollover detection parameter; and

a steering maneuver determination unit that determines whether or not an abrupt steering maneuver is made,

wherein the parameter calculation unit calculates a first composition roll angle as the rollover detection parameter by combining, at a predetermined first composition roll angle weight assignment ratio, a first roll angle with a second roll angle, the first roll angle being equivalent to an actual roll angle and the second roll angle being obtained using a parameter which changes with a phase earlier than the first roll angle, and

wherein the parameter calculation unit calculates the first composition roll angle by changing the first composition roll angle weight assignment ratio such that a weight of the second roll angle is higher when the steering maneuver determination unit determines that the abrupt steering maneuver is made than when the steering maneuver determination unit determines that the abrupt steering maneuver is not made.

2. The brake fluid pressure control apparatus according to claim 1 , further comprising a steering-back maneuver determination unit that determines whether or not an abrupt steering-back maneuver is made, and

wherein the parameter calculation unit calculates a second composition roll angle as the rollover detection parameter by combining, at a predetermined second composition roll angle weight assignment ratio, a third roll angle with the first composition roll angle, the third roll angle being obtained from a parameter which changes with a phase earlier than the first roll angle and the second roll angle, and

wherein the parameter calculation unit calculates the second composition roll angle by changing the second composition roll angle weight assignment ratio such that a weight of the third roll angle is higher when the steering-back maneuver determination unit determines that the abrupt steering-back maneuver is made than when the steering-back maneuver determination unit determines that the abrupt steering-back maneuver is not made.

3. The brake fluid pressure control apparatus according to claim 1 , wherein the steering maneuver determination unit determines that the abrupt steering maneuver is made, if at least one of the following conditions is satisfied:

(a) an absolute value of a steering wheel turning speed is equal to or greater than a predetermined steering wheel turning speed value, and an absolute value of a lateral acceleration is equal to or greater than a predetermined lateral acceleration value; and

(b) the absolute value of the steering wheel turning speed is equal to or greater than the predetermined steering wheel turning speed value, and a filtered absolute value of the lateral acceleration resulting from a filtering process by which a decrease of the absolute value of the lateral acceleration is retarded is equal to or greater than the predetermined lateral acceleration value.

4. The brake fluid pressure control apparatus according to claim 1 , wherein the parameter calculation unit comprises a first counter that increases a first count value if the steering maneuver determination unit determines that the abrupt steering maneuver is made, and to decrease the first count value if the steering maneuver determination unit determines that the abrupt steering maneuver is not made, and a first weight coefficient setting unit configured to set a first weight coefficient, which is equivalent to the weight of the second roll angle, in accordance with the first count value and in a range equal to or smaller than a predetermined upper limit value, and

wherein the first counter increases the first count value even after the first weight coefficient reaches the predetermined upper limit value.

5. The brake fluid pressure control apparatus according to claim 2 , wherein signs of values are defined by assigning first signs respectively to a value of a steering angle when the steering wheel is turned left, values of a lateral acceleration acting on the vehicle and a roll angle exhibited while the vehicle is stably turning left, and a value of a roll rate exhibited when the roll angle takes a greater value due to a left turn of the vehicle, and by assigning second signs respectively to a value of a steering angle when the steering wheel is turned right, values of the lateral acceleration acting on the vehicle and the roll angle exhibited while the vehicle is stably turning right, and the value of the roll rate exhibited when the roll angle takes a greater value due to a right turn of the vehicle, and the steering-back maneuver determination unit determines that the abrupt steering-back maneuver is made if all of the following conditions are satisfied:

(1) one of the values of the steering angle and the lateral acceleration has the first sign, while the other one of the values has the second sign;

(2) one of the values of the first roll angle and a first roll rate calculated from the first roll angle has the first sign, while the other one of the values has the second sign, or/and one of values of the second roll angle and a second roll rate calculated from the second roll angle has the first sign, while the other one of the values has the second sign; and

(3) an absolute value of the first roll rate that satisfies the above condition (2) is equal to or greater than a predetermined first roll rate value or/and an absolute value of the second roll rate that satisfies the above condition (2) is equal to or greater than a predetermined second roll rate value.

6. The brake fluid pressure control apparatus according to claim 5 , wherein the parameter calculation unit comprises a second counter that increases a second count value if the steering-back maneuver determination unit determines that the abrupt steering-back maneuver is made, and to decrease the second count value if the steering-back maneuver determination unit determines that the abrupt steering-back maneuver is not made, and a second weight coefficient setting unit configured to set a second weight coefficient, which is equivalent to the weight of the third roll angle, in accordance with the second count value and in a range equal to or smaller than a predetermined upper limit value, and

wherein the second counter increases the second count value even after the second weight coefficient reaches the predetermined upper limit value.

7. The brake fluid pressure control apparatus according to claim 1 , wherein the first roll angle is calculated from a lateral acceleration, and the second roll angle is calculated from a yaw rate.

8. The brake fluid pressure control apparatus according to claim 2 , wherein the third roll angle is calculated from a steering angle.