Braking force control system
Motor-generators are arranged both at front and rear wheels so as to be capable of using all of four wheels for regeneration. The horizontal axis indicates deceleration of a vehicle, and the vertical axis indicates braking forces for the front and rear wheels, respectively above and below the horizontal axis. A setting value indicates a limit braking force for the rear wheels to be locked. A frictional braking force and a regenerative braking force at the rear wheels are controlled so that the total braking force for the rear wheels does not exceed the setting value.
1. A braking force control system comprising:
a regenerative braking force controller that controls a regenerative braking force for rear wheels of a vehicle, which is generated by a first motor-generator for driving the rear wheels;
a frictional braking force controller that controls a frictional braking force to be generated by the rear wheels of the vehicle; and
a braking force determiner that determines the frictional braking force and the regenerative braking force inclusive of a braking force equivalent to an engine brake, so that a total braking force to be applied to the rear wheels does not exceed a rear preset value
wherein the braking force determiner sets the rear preset value based on a target braking force distribution to the rear wheels, with which the rear wheels are not locked, and
wherein the target braking force distribution to the rear wheels is determined based at least on a road surface condition and a vehicle load.
2. The braking force control system according to claim 1 ,
wherein the braking force determiner sets a front preset value so as to be smaller than a limit value of a braking force for front wheels of the vehicle to be locked.
3. The braking force control system according to claim 1 ,
wherein the regenerative braking force controller also controls the regenerative braking force for front wheels to be generated by a second motor-generator for driving the front wheels of the vehicle; and
the frictional braking force controller also controls the frictional braking force to be generated by the front wheels of the vehicle, includes a slip state detector for detecting that the vehicle is slipping, and, on the condition that the slip state detector detects the vehicle for which the regenerative braking force is being generated is slipping, reduces at a predetermined ratio the regenerative braking force being applied to the front wheels and the regenerative braking force being applied to the rear wheels.
4. The braking force control system according to claim 3 , wherein the predetermined ratio is a target distribution ratio for distributing the frictional braking force to the front and rear wheels.
5. The braking force control system according to claim 3 , wherein the predetermined ratio is set so that a sum of the frictional braking force and regenerative braking force to be applied to the rear wheels does not exceed a limit braking force for the rear wheels to be locked.
6. The braking force control system according to claim 1 , further comprising:
an Antilock Braking System (ABS) controller that executes antilock brake control for reducing the frictional braking force upon detecting that the vehicle is slipping,
wherein the slip state detector detects that the vehicle is slipping, to reduce the regenerative braking forces to be applied to the front and rear wheels, with a variation in a vehicle condition which is smaller than that of the ABS controller detecting that the vehicle is slipping.
7. The braking force control system according to claim 1 , wherein if an accelerator pedal is stepped for operation at a time of a slip state detector detecting that the vehicle is slipping, a traveling mode is switched to one in which the front and rear wheels are driven by the first and second motor-generators, respectively.
8. A braking force control system comprising:
a regenerative braking force controller that controls a regenerative braking force for rear wheels of a vehicle, which is generated by a first motor-generator for driving the rear wheels;
a frictional braking force controller that controls a frictional braking force to be generated by the rear wheels of the vehicle; and
a braking force determiner that determines the frictional braking force and the regenerative braking force inclusive of a braking force equivalent to an engine brake, so that a total braking force to be applied to the rear wheels does not exceed a rear preset value;
wherein:
the braking force determiner sets a front preset value so as to be smaller than a limit value of the braking force for front wheels of the vehicle to be locked;
the regenerative braking force controller also controls the regenerative braking force for the front wheels to be generated by a second motor-generator for driving the front wheels of the vehicle;
the frictional braking force controller also controls the frictional braking force to be generated by the front wheels of the vehicle; and
the braking force determiner sets in advance distributions to the frictional braking force of the frictional braking force to be generated by the front wheels and the frictional braking force to be generated by the rear wheels, and, on a condition that a deceleration of the vehicle is within a predetermined range, makes the distribution of the frictional braking force to be generated by the rear wheels, in accordance with the preset distribution, smaller than the limit value for the rear wheels to be locked, and makes the distribution of the frictional braking force to be generated by the front wheels larger than a limit value for the front wheels to be locked.