Vehicle brake fluid pressure control apparatus

1. A vehicle brake fluid pressure control apparatus for controlling a fluid pressure generated in a fluid pressure source based on at least a wheel speed for transmission to a wheel brake, comprising:

a normally open electromagnetic valve which is disposed on a fluid pressure line extending from the fluid pressure source to the wheel brake;

a normally closed electromagnetic valve which is disposed on a fluid pressure line extending from the wheel brake to the fluid pressure source; and

a controller configured to control a fluid pressure in the wheel brake to increase or reduce by controlling the normally open electromagnetic valve and the normally closed electromagnetic valve, wherein

the controller performs:

a pressure reducing in a pressure reducing cycle in which a basic pressure reducing control and a gradual pressure control are performed continuously in a case that the controller determines to execute a pressure reducing control with wheel speed decreasing;

a pressure reducing control in a basic pressure reducing amount in the basic pressure reducing control; and

a temporary holding control for holding the fluid pressure and a fine pressure reducing control for executing a pressure reducing in an amount smaller than the basic pressure reducing amount in a case that the wheel speed tend to decrease after the temporary holding control in the gradual pressure reducing control.

2. The vehicle brake fluid pressure control apparatus according to claim 1 , wherein

the controller repeats the temporary holding control and the fine pressure reducing control while the wheel speed tend to decrease in the gradual pressure reducing control.

3. The vehicle brake fluid pressure control apparatus according to claim 1 , wherein

a pressure reducing amount in the fine pressure reducing control is made small in a case that an estimated road surface friction coefficient is larger than a predetermined threshold and a vehicle body speed is smaller than a predetermined threshold.

4. The vehicle brake fluid pressure control apparatus according to claim 3 , wherein

when making small the pressure reducing amount in the fine pressure reducing control, an application time of a pulse signal for a single pressure reducing is shortened.

5. The vehicle brake fluid pressure control apparatus according to claim 1 , wherein

a predetermined time to hold the fluid pressure in the temporary holding control is lengthened in a case that the estimated road surface friction coefficient is larger than the predetermined threshold and the vehicle body speed is smaller than the predetermined threshold.

6. The vehicle brake fluid pressure control apparatus according to claim 1 , wherein

the basic pressure reducing amount is compensated based on a total pressure reducing amount of pressure reducing amounts used in the basic pressure reducing control and the gradual pressure reducing control in the previous pressure reducing control.

7. The vehicle brake fluid pressure control apparatus according to claim 1 , wherein

in a case that the fine pressure reducing control is not executed in the gradual pressure reducing control in the previous pressure reducing cycle, the basic pressure reducing amount is set so as to be smaller by a predetermined amount than that in the previous pressure reducing cycle.

8. The vehicle brake fluid pressure control apparatus according to claim 1 , wherein

in a case that the fine pressure reducing control is executed in the gradual pressure reducing control in the previous pressure reducing cycle, the basic pressure reducing amount is set so as to be larger by a predetermined amount than that in the previous pressure reducing cycle.