An electronically controlled brake system for a motor vehicle is known, which electrically controls the braking forces of braking devices for the respective wheels, namely, the hydraulic pressures supplied to wheels cylinders for driving the braking devices, in accordance with the amount of a braking operation, e.g., the amount of depression of a brake pedal. An example of a control apparatus for this type of brake system is disclosed in Japanese Laid-open Patent Publication No. 2004-243983.
In the vehicular brake control system as disclosed in the above-identified publication, when the vehicle operator or driver operates the brake pedal, a master cylinder generates a hydraulic pressure in accordance with the amount of operation of the brake pedal, and a part of the hydraulic oil flows into a stroke simulator so that the amount of operation of the brake pedal (represented by, e.g., pedal stroke) is controlled in accordance with the pedal pressure applied to the brake pedal (i.e., the force with which the brake pedal is depressed by the driver). In the meantime, the brake control system sets a target deceleration of the vehicle in accordance with the pedal stroke detected by brake ECU, and determines the distribution of the braking forces applied to the respective wheels, based on which certain hydraulic pressures are applied to the respective wheel cylinders.
In the known vehicular brake control system as described above, the master cylinder for generating a hydraulic pressure commensurate with the amount of operation of the brake pedal is equipped with the stroke simulator into which a part of the hydraulic oil is fed so as to control the amount of operation of the brake pedal. The master cylinder is also provided with pressurizing mechanisms for pressurizing the hydraulic oil to be supplied to the wheel cylinders of the four wheels via master cut valves. Since the pressurizing mechanisms are provided for the wheel cylinders of the respective wheels, the overall hydraulic system is complicated in construction, resulting in an increase in the manufacturing cost.