Braking system for a road vehicle equipped with a drive-slip control (ASR) and an anti-lock system (ABS)

Claim 1

A hydraulic dual-circuit vehicle brake system comprising: a plurality of wheel brakes; a first brake circuit assigned to driven wheels of a vehicle; a second brake circuit assigned to non-driven wheels of the vehicle; a brake unit that actuates vehicle brakes and having first and second outlet-pressure spaces, said first brake circuit being coupled to said first outlet-pressure space and said second brake circuit being coupled to the second outlet-pressure space; a buffer accumulator that accumulates brake fluid; a return line connected between a wheel brake and the buffer accumulator during anti-lock control; a return pump having an inlet side connected to the buffer accumulator and an outlet side connected to the brake unit; an anti-lock system ABS that operates on the first brake circuit in a return-flow manner such that, during pressure-reduction phases of anti-lock control by the anti-lock system ABS, a quantity of brake fluid corresponding to a quantity of brake fluid that flows off from a wheel brake into the return line connected to the buffer accumulator during anti-lock control, is pumped into the brake unit by the return; a drive-slip control device ASR having an auxiliary-pressure source that decelerates a vehicle wheel that is tending to spin by subjecting the wheel brake of the vehicle wheel to brake pressure from the auxiliary-pressure source in such a way that a drive slip of the vehicle wheel remains within a value range compatible with a sufficient dynamic stability of the vehicle; a precharging pump connected to the inlet side of the return pump via an outlet non-return valve for supplying the auxiliary pressure source brake pressure to driven wheel brakes of the vehicle wheels to be decelerated by the drive-slip control ASR such that brake fluid is conveyed from a reservoir of the brake unit to an inlet side of the return pump of the first brake circuit, said precharging pump having an outlet; an ASR control valve that has a basic position for normal braking in which brake fluid is positively displaced into the brakes of the driven vehicle wheels as a result of the actuation of the brake unit, and an alternative functional ASR position in which brake fluid is prevented from flowing off from a main brake line of the first brake circuit towards the first outlet-pressure space of the brake unit; an ASR outlet valve connected between the reservoir of the brake unit and a pressure medium line; valve means activatable by outlet pressure of the precharging pump through a control line coupled between the precharging pump and the valve means; wherein during normal braking the valve means connects the outlet non-return valve of the precharging pump and the ASR outlet valve to the pressure medium line subjected to brake pressure, and during drive-slip control ASR connects the pressure medium line to the return line and the outlet of the precharging pump to the inlet of the return pump of the first brake circuit.