Antilocking system

Antilocking system for a road vehicle with a hydraulic two-circuit brake installation in which rear wheel brakes are combined in a static brake circuit, which is connected to an output pressure space of a main brake unit means which can be actuated by means of a brake pedal;

• wherein said main brake unit means is capable of generating an output pressure proportional to the actuating force of the pedal;
• wherein said output pressure is connected to the wheel brakes of said static brake circuit by means of brake pressure control valve means provided for controlling brake pressure reduction, brake pressure retention and brake pressure restoration phases;
• wherein the antilocking system operates on the pump-back principle according to which, in a brake pressure reduction phase, brake fluid is drained from wheel brakes subject to the control system and is pumped back by a return pump means into the output pressure space of the main brake unit means associated with the static brake circuit;
• wherein said return pump means is a piston pump which is driven hydraulically by a drive pressure space being subjected to and relieved from pressure by control of solenoid valve means;
• wherein an output pump chamber of the piston pump is connected to wheel brakes currently subjected to the control system via an inlet non-return valve and via an outlet non-return valve to the output pressure space of the main brake unit associated with the static brake circuit;
• wherein an antilocking control takes place on the select-low principle according to which, independent of whether a locking tendency occurs on one or both rear wheels of the vehicle, brake pressure applied to both rear wheel brakes by the main brake unit means is always kept at the same value;
• wherein control signals generating means for switching of the brake pressure control valve means and the solenoid valve means controlling the pump operation are provided by an electronic control unit means, which generates these signals by a process of comparing and differentiating--with respect to time--electrical output signals from wheel rotational speed sensors whose output signals, in level and/or frequency, are a measure of the wheel peripheral speeds of the vehicle wheels;
• wherein the brake pressure control valve means is a 2/2-way solenoid valve which is located hydraulically in parallel with the output pump chamber and the inlet and outlet non-return valves connected to it, between an output of the main brake unit means associated with the static brake circuit and a section of a main brake pipe of the rear axle brake circuit branching to the wheel brakes of the static brake circuit;
• said 2/2-way solenoid valve associated with normal braking operation not subject to control, is in a through-flow position wherein it connects the pressure space of the main brake unit means to the rear wheel brakes;
• wherein a change of volume of the outpump chamber between a minimum and maximum value is at least 1/4 of a volume of that quantity of brake fluid which must be forced into the rear axle brake circuit in order to generate a maximum possible brake installation design pressure in the wheel brakes of said brake circuit;
• wherein the electronic control unit means for controlling brake pressure reduction phases of the antilocking control generates a combination of output signals by means of which the brake pressure control valve means is switched into its shut-off position and the drive pressure space of the return pump means is initially connected to a sump tank of an auxiliary pressure source and is subsequently reconnected to a pressure output, of the auxiliary pressure space for controlling the brake pressure retention phases by connecting the drive pressure space of the return pump means to the pressure output of the auxiliary pressure source while the brake pressure control valve means is held in its shut-off position;
• and
• wherein for controlling brake pressure restoration phases, the electronic control means generates signal combination by means of which the drive pressure space of the return pump is connected to the high pressure output of the auxiliary pressure source and the brake pressure control valve is switched back into its through-flow position.