Vehicle brake-pressure control device for electrohydraulic multi-circuit brake system

A brake-pressure control device for a vehicle with electrohydraulic multi-circuit brake system having an electronic control unit, comprising

• (a) hydraulic servo-cylinders individually assigned to vehicle wheel brakes and arranged to be driven by an electric motor to permit, in one stroke of a respective piston thereof, a maximum brake pressure in a connected wheel brake for which the wheel brake is configured to be increased and decreased and, under control of output signals of the electronic control unit implements at least:
• (i) spot braking in accordance with desired-value signals triggerable by a vehicle driver by a desired-value setting unit and characteristic of anticipated value of deceleration of the vehicle, including control of the front-axle/rear-axle braking force distribution;
• (ii) anti-lock braking control by automatic brake pressure modulation;
• (iii) traction control by automatic activation of the wheel brake of a vehicle wheel tending to slip;
• and
• (iv) vehicle movement control by automatically controlled increase in brake slip at at least one of the vehicle wheels,
• (b) the desired-value setting unit comprising a single-circuit master cylinder having an output pressure space connected to front-wheel brakes by a change-over valve configured as a two-position solenoid valve with a blocking functional position to which it is moved when its switching magnets are excited, to block off the front-wheel brakes from the single-circuit master cylinder and with a flow position to which it is moved as normal position, to displace brake fluid directly into the front-wheel brakes by activating the master cylinder, wherein:
• (c) the single-circuit master cylinder is configured such that the volume of brake fluid displaceable from an output pressure space thereof as a result of displacement of a piston thereof by a maximum stroke s.sub.max is substantially greater than a capacity of the wheel brakes of the front-axle brake circuit which has to be displaced into the brake to achieve a defined pressure necessary for minimum deceleration;
• (d) the front-wheel brakes are configured to be also blocked off from the single-circuit master cylinder in the event of electrically controlled spot braking, and a maximum capacity of output pressure spaces of the brake-pressure servo-cylinders of the front-wheel brakes is limited to a volume capable of being displaced into the respectively connected front-wheel brake to achieve a maximum brake pressure;
• (e) a storage element into which brake fluid can be displaced from the single-circuit master cylinder counter to an increasing reaction force is connected to a pressure outlet of the single-circuit master cylinder of the desired-value setting unit, the maximum capacity of the storage element corresponding at maximum to an additional amount by which the volume of brake fluid which is displaceable from the master cylinder is greater than the volume of brake fluid which can be displaceable into the front-wheel brakes in emergency operating mode to achieve the defined minimum deceleration.