1. Field of the Invention
The invention relates to a vehicle brake system and a vehicle control method, and more particularly, to a technology for suppressing the generation of heat by a motor that drives a pump to accumulate a fluid under pressure in an accumulator.
2. Description of the Related Art
Generally, an electronically controlled brake (ECB) system generates braking force by feeding brake oil to wheel cylinders in accordance with a brake operation. High-pressure brake oil is constantly accumulated in an accumulator to ensure a good response. However, the pressure within the accumulator decreases every time a driver operates a brake pedal, so in order to maintain sufficient pressure in the accumulator, it is necessary to operate a pump to feed the brake oil to the accumulator. A hydraulic pressure supply device that controls the pump operation to maintain the accumulated hydraulic pressure in the accumulator in a range between lower and upper limit values to prevent excessive increases in the pump load is described, for example, in Japanese Patent Application Publication No. JP-A-07-103201.
The pressure control system disclosed in JP-A-07-103201 cannot control the motor appropriately if an accumulator pressure sensor malfunctions, creating a risk that the accumulator pressure cannot be maintained within the appropriate range. In many hydraulic pressure supply systems, this problem is handled by setting the discharge volume of the oil pump to match the highest possible rate of brake oil consumption. When a malfunction occurs, the motor is operated such that the pump discharges the pre-set volume of oil. However, this means that when the brake oil consumption rate is lower than the maximum, the load on the motor that drives the oil pump is unnecessarily high, which increases the amount of heat generated by the motor.