Brake pressure setting device for automatic control of brake pressure change and brake pressure retention phases of an antilocking control system and a drive slip control system for stabilizing the dynamic behavior of the vehicle by acting on the wheel brakes of a road vehicle, comprising:
- wheel brakes means for two driven vehicle wheels which are combined into a static brake circuit;
- each of said wheel brakes means being operable to be shut off individually or jointly from a main brake pipe by means of a solenoid brake pressure control valve means;
- a solenoid connection control valve means switchable to shut off the main brake pipe from an outlet pressure space, associated with a static brake circuit of a main brake unit provided for brake pressure supply and operable by the driver;
- a pressure modulator unit designed as a stepped cylinder which has two housing steps of different diameters, within which, movable boundaries of a control pressure space and a modulation chamber are formed by diameter flanges of a modulator piston means corresponding to the two housing steps of different diameters;
- wherein the modulation chamber is a smaller diameter chamber than the control pressure space and is connected to the main brake pipe of the static brake circuit between the connection control valve means and the brake pressure control valves means;
- wherein there is a return spring urging the modulator piston means into an end position associated with a maximum volume of the modulation chamber;
- wherein function control valve means are provided to alternatively connect the control pressure space of the pressure modulator to a pressure outlet of an auxiliary pressure source or to a non-pressurized sump container for displacing the modulator piston for controlling brake pressure changes;
- a position indicator means for generating an electrical output signal, characteristic of the position of the modulator piston means;
- an electronic control means generating the output signals necessary for correct triggering of the connection control valve means, the function control valve means and the brake pressure control valve means by processing the output signals of the position indicator and output signals of wheel rotational speed sensors, which generate electrical output signals characteristic of the dynamic behavior of the vehicle wheels;
- wherein there is a mechanical controlled valve means connected between the outlet pressure space associated with the brake circuit of the driven vehicle wheels and the connection control valve means;
- a valve chamber connected to the modulation chamber of the pressure modulator via an outlet non-return valve which can be driven into its open position by higher pressure in the modulation chamber relative to a pressure in the valve chamber;
- said mechanically controlled valve is a displacement-controlled valve means having a valve body that is displaced in direction of a shut-off position for causing the outlet pressure space of the brake unit to be shut off relative to the valve chamber in response to displacement of the modulator piston means for reducing a volume of the modulation chamber from an intermediate position of the piston means corresponding to a volume of the modulation chamber of between 75% and 50% of its maximum volume;
- said mechanically controlled valve being designed as a pressure-controlled valve which, at least when the modulator piston means is located in the intermediate position or in a position corresponding to a larger volume of the modulation chamber, can be driven into an open position by pressure in the outlet pressure space of the main brake unit, which pressure is higher than pressure in the valve chamber;
- wherein upon an appearance of a locking tendency of the rear wheel brakes of the static brake circuit, the electronic control means generates output signals operating the antilocking control by displacing the modulator piston means into its intermediate position, subsequently switches the connection control valve means into its shut-off position, drives the brake pressure control valve means of a rear vehicle wheel brake not tending to lock into its shut-off position, and switches the function control valve means into a functional position causing pressure relief of the control pressure space;
- wherein, upon the appearance of a spin tendency on one of the driven vehicle wheels, the electronic control means generates an output signals by which drive slip control operation is controlled, so that:
- the function control valve means is driven into a functional position causing connection of the control pressure space to the pressure outlet of the auxiliary pressure source, the connection control valve means is driven into a shut-off position, and the brake pressure control valve means of a vehicle wheel not tending to spin is also driven into its shut-off position;
- and wherein
- in normal braking not subject to a control system, the connection control valve means and the brake pressure control valves means are held in a through-flow position and the modulator piston means, monitored by means of the position indicator means, is held in a position which at least corresponds to the volume of the modulation chamber associated with its intermediate position.