Electrohydraulic brake system for motor vehicles

An electrohydraulic brake system for a motor vehicle which can be operated in a ‘brake-by-wire’ mode of operation both by an operator and independently of the operator, the brake system comprising:

• a master cylinder (1) connectable to wheel brake cylinders;
• a first piston (2) coupled to a brake pedal (3);
• a second piston (4) for actuating the master cylinder (1);
• a third piston (5) which can be operated by the first piston (2);
• at least one brake pedal characteristics simulation device (6, 7) provided between the first (2) and the third piston (5) for imparting a comfortable pedal feel to the operator in a ‘brake-by-wire’ mode of operation;
• a hydraulic chamber (21) cooperating with the brake pedal characteristics simulation device (6, 7) being limited between the first (2) and the third piston (5), wherein all three pistons (2, 4, 5) and the brake pedal characteristics simulation device (6, 7) are arranged in a housing (8);
• a hydraulic pressure source (9) operable by an electronic control and regulation unit;
• a valve device (10) operable by the third piston (5) for reducing the pressure of the pressure source (9) to a value used for application of the second piston (4), wherein the second (4) and the third piston (5) are isolated from each other by a space (11) so that the third piston (5) is acted upon by the pressure that acts on the second piston (4) in a direction opposite to a direction of application of the second piston (4);
• and
• a device (29-31, 45) which by way of a variation of the pressure fluid volume in the hydraulic chamber (21) controlled by electromagnetic valve, allows a pedal performance that differs from a brake pedal characteristics that is predefined by the brake pedal characteristics simulation device.