Braking control device

1. A braking control device of a vehicle in which a braking force generator that generates a braking force that acts in a direction to reduce a rotation of a plurality of wheels is connected to a differential mechanism to which the plurality of wheels is connected, and a friction brake that generates a braking force that acts in a direction to stop the rotation of the wheels through friction is provided for each of the wheels, the braking control device comprising

a controller configured to control the braking force that is generated by the braking force generator and the braking force that is generated by the friction brake, wherein

the controller is configured to:

detect the wheel having a tendency of locking in which a slip ratio is larger than a predetermined determination value in a state where the braking force is transmitted to each of the wheels from the braking force generator via the differential mechanism;

reduce the tendency of locking by changing the braking force of the friction brake that is provided for the other wheel connected to the differential mechanism to which the wheel having the tendency of locking is connected; and

wherein the braking force generator is an energy regenerator that generates negative torque by regenerating an energy as the braking force.

2. The braking control device according to claim 1 , wherein the controller is configured to:

obtain a target wheel rotational speed of the other wheel; and

control the braking force applied to the other wheel by the friction brake that is provided for the other wheel such that a rotational speed of the other wheel matches the target wheel rotational speed.

3. The braking control device according to claim 2 , wherein when the vehicle is making a turn, the target wheel rotational speed is a rotational speed including a value that is a half of a right and left wheel speed difference obtained based on a steering angle and a vehicle speed of the vehicle.

4. The braking control device according to claim 2 , wherein the target wheel rotational speed of the other wheel is a rotational speed at which the slip ratio of the other wheel takes a value within a predetermined range.

5. The braking control device according to claim 1 , wherein the controller is configured to:

obtain, when a deceleration request is made, a base friction braking force that is required to be generated by the friction brake by subtracting a predetermined base braking force to be generated by the braking force generator from a required deceleration of the deceleration request;

obtain a target rotational speed of the braking force generator that corresponds to a target wheel speed during braking based on the deceleration request; and

correct the base braking force such that a rotational speed of the braking force generator matches the target rotational speed.

6. The braking control device according to claim 5 , wherein the controller is configured to control, when a wheel speed of one of the wheels connected to the differential mechanism increases in excess by a predetermined value or more from a wheel speed that corresponds to a target wheel rotational speed in accordance with the correction of the base braking force, the braking force of the friction brake that is provided for the one of the wheels such that the wheel speed of the one of the wheels matches a wheel speed that corresponds to the target wheel rotational speed.

7. The braking control device according to claim 1 , wherein the controller calculates a vehicle body speed based on a wheel speed of each of the wheels;

calculates the slip ratios of each of the wheels based on a deviation between the vehicle body speed and the wheel speed of each of the wheels;

determines the tendency of locking of the wheels increases when the slip ratio increases; and

reduces the braking force to eliminate the tendency of locking of the wheels, which causes a rotational speed of the wheel to become a target wheel rotational speed obtained based on the vehicle body speed.

8. A braking control device of a vehicle in which a braking force generator that generates a braking force that acts in a direction to reduce a rotation of a plurality of wheels is connected to a differential mechanism to which the plurality of wheels is connected, and a friction brake that generates a braking force that acts in a direction to stop the rotation of the wheels through friction is provided for each of the wheels, the braking control device comprising

a controller configured to control the braking force that is generated by the braking force generator and the braking force that is generated by the friction brake, wherein

the controller is configured to:

detect the wheel having a tendency of locking in which a slip ratio is larger than a predetermined determination value in a state where the braking force is transmitted to each of the wheels from the braking force generator via the differential mechanism;

reduce the tendency of locking by changing the braking force of the friction brake that is provided for the other wheel connected to the differential mechanism to which the wheel having the tendency of locking is connected;

obtain a target wheel rotational speed of the other wheel;

control the braking force applied to the other wheel by the friction brake that is provided for the other wheel such that a rotational speed of the other wheel matches the target wheel rotational; and

wherein when the vehicle is making a turn, the target wheel rotational speed is a rotational speed including a value that is a half of a right and left wheel speed difference obtained based on a steering angle and a vehicle speed of the vehicle.

9. The braking control device according to claim 8 , wherein the target wheel rotational speed of the other wheel is a rotational speed at which the slip ratio of the other wheel takes a value within a predetermined range.

10. The braking control device according to claim 8 , wherein the braking force generator is an energy regenerator that generates negative torque by regenerating an energy as the braking force.

11. The braking control device according to claim 8 , wherein the controller is configured to:

obtain, when a deceleration request is made, a base friction braking force that is required to be generated by the friction brake by subtracting a predetermined base braking force to be generated by the braking force generator from a required deceleration of the deceleration request;

obtain a target rotational speed of the braking force generator that corresponds to a target wheel speed during braking based on the deceleration request; and

correct the base braking force such that a rotational speed of the braking force generator matches the target rotational speed.

12. The braking control device according to claim 11 , wherein the controller is configured to control, when a wheel speed of one of the wheels connected to the differential mechanism increases in excess by a predetermined value or more from a wheel speed that corresponds to a target wheel rotational speed in accordance with the correction of the base braking force, the braking force of the friction brake that is provided for the one of the wheels such that the wheel speed of the one of the wheels matches a wheel speed that corresponds to the target wheel rotational speed.

13. The braking control device according to claim 8 , wherein the controller calculates a vehicle body speed based on a wheel speed of each of the wheels;

calculates the slip ratios of each of the wheels based on a deviation between the vehicle body speed and the wheel speed of each of the wheels;

determines the tendency of locking of the wheels increases when the slip ratio increases; and

reduces the braking force to eliminate the tendency of locking of the wheels, which causes a rotational speed of the wheel to become a target wheel rotational speed obtained based on the vehicle body speed.