Brake hydraulic pressure control device for vehicle

1. A brake hydraulic pressure control device for a vehicle, configured to control hydraulic pressure generated in a hydraulic pressure source to transmit the hydraulic pressure to a wheel brake, the brake hydraulic pressure control device comprising:

a normally open linear solenoid valve arranged in a hydraulic pressure passage from the hydraulic pressure source to the wheel brake, the normally open linear solenoid valve being configured to adjust a valve closing force depending on an power supply amount;

a normally closed solenoid valve arranged in a hydraulic pressure passage from the wheel brake to the hydraulic pressure source; and

a controller configured to control the power supply amount to the normally open linear solenoid valve and the normally closed solenoid valve, thereby controlling switching of the hydraulic pressure within the wheel brake between a pressure increasing state, a pressure holding state, or a pressure reducing state, wherein:

when shifting to the pressure increasing state from the pressure reducing state or the pressure holding state is made, the controller controls the power supply amount so that increasing is made at a first gradient up to a turning point target hydraulic pressure, and increasing is made at a second gradient gentler than the first gradient from the turning point target hydraulic pressure up to the end of the increasing;

the controller subtracts an offset pressure from the hydraulic pressure at the time of previous pressure reduction start, thereby determining the turning point target hydraulic pressure;

the offset pressure is obtained from a preset data table which sets a relationship between the offset pressure and the hydraulic pressure at the time of the previous pressure reduction start or a fixed value depending on a type of vehicle; and

the relationship is set such that the offset pressure decreases as the hydraulic pressure at the time of the pressure reduction start is lower.

2. The brake hydraulic pressure control device according to claim 1 , wherein the offset pressure is corrected based on an estimated road surface friction coefficient.

3. The brake hydraulic pressure control device according to claim 1 , wherein the turning point target hydraulic pressure is determined as a hydraulic pressure which is lower than a hydraulic pressure at the time of the previous pressure reduction start by a predetermined offset pressure irrespective of a previous pressure reduction amount.

4. The brake hydraulic pressure control device according to claim 3 , wherein the hydraulic pressure at the time of the previous pressure reduction start is closer to a brake hydraulic pressure corresponding to a highest braking force which can be exhibited on a road surface at that time, and the hydraulic pressure which is lower than the hydraulic pressure by the predetermined offset pressure is set as the turning point target hydraulic pressure.

5. The brake hydraulic pressure control device according to claim 4 , wherein the time taken for performing braking with the highest braking force is secured while the hydraulic pressure is gradually increased from the turning point target hydraulic pressure up to the end of increasing.

6. The brake hydraulic pressure control device according to claim 1 , wherein the turning point target hydraulic pressure does not significantly change even if there is a change in a pressure reduction amount.

7. The brake hydraulic pressure control device according to claim 1 , wherein the offset pressure is obtained from the pressure reduction start pressure, on the basis of the data table of the pressure reduction start pressure and the offset pressure, set in advance.

8. The brake hydraulic pressure control device according to claim 1 , wherein the first gradient is obtained by:

P G1 =( P B <P I ) TC/B,

wherein:

P G1 is the first gradient,

P B is the turning point target hydraulic pressure,

B is defined as a first regulation time at a time of start of increasing, and

TC is defined as a cycle during which power is supplied to inlet valves and outlet valves.

9. The brake hydraulic pressure control device according to claim 8 , wherein the second gradient is set so as to be smaller than the first gradient.

10. The brake hydraulic pressure control device according to claim 8 , wherein when a subsequent target hydraulic pressure after a caliper pressure has reached the turning point target hydraulic pressure is used as the pressure reduction start pressure, the second gradient is obtained by P G2 =(P R −P B )TC/C, wherein C is a second regulation time until the pressure reduction start pressure (P R ) is reached from the turning point target hydraulic pressure.

11. A brake hydraulic pressure control device for a vehicle, configured to control hydraulic pressure generated in a hydraulic pressure source to transmit the hydraulic pressure to a wheel brake, the brake hydraulic pressure control device comprising:

a controller configured to control the power supply amount to solenoid valves to control switching of the hydraulic pressure within the wheel brake between a pressure increasing state, a pressure holding state, or a pressure reducing state, wherein:

when shifting to the pressure increasing state from the pressure reducing state or the pressure holding state is made, the controller controls the power supply amount so that increasing is made at a first gradient up to a turning point target hydraulic pressure, and increasing is made at a second gradient gentler than the first gradient from the turning point target hydraulic pressure up to the end of the increasing; and

the controller subtracts a fixed offset pressure from the hydraulic pressure at the time of previous pressure reduction start, thereby determining the turning point target hydraulic pressure.

12. The brake hydraulic pressure control device according to claim 11 , wherein the fixed offset pressure is a fixed value depending on a type of vehicle.

13. The brake hydraulic pressure control device according to claim 11 , wherein the fixed offset pressure is obtained from a preset data table set based on the hydraulic pressure at the time of the previous pressure reduction start.

14. The brake hydraulic pressure control device according to claim 13 , wherein the data table is set so that the offset pressure decreases as the hydraulic pressure at the time of pressure reduction start is lower.