A hydraulic dual-circuit brake system with an anti-skid system and traction control for motor vehicles including driven and nondriven wheels, having a master brake cylinder with first and second brake circuit outlets for controlling a brake pressure by brake pedal actuation;
- a four-channel hydraulic unit with first, second, third and fourth outlets channels distributed to first and second brake circuits connected to said first and second brake circuit outlets for connection with first, second, third, and fourth wheel brake cylinders of the driven and nondriven wheels, first, second, third, and fourth electromagnetic input control valves connected respectively with said first, second, third and fourth outlet channel for controlling a brake pressure dependent on wheel slip in the wheel brake cylinders, each of aid first, second, third, and fourth electromagnetic input control valves include an output connected respectively with said first, second, third and fourth outlet channels and each of said first and second electromagnetic input control valves include an inlet connected to a first connecting line connecting to said first brake circuit outlet and each of said third and fourth electromagnetic input control valves include an inlet connected to a second connecting line connected with said second brake circuit outlet of the master brake cylinder, first, second, third and fourth electromagnetic output control valves each including an input connected respectively to said first, second, third and fourth outlet channels, a return pump including first and second pump elements, said first pump element includes an inlet connected with an outlet of each of said first and second electromagnetic output control valves and said second pump element includes an inlet connected with an outlet of each of said third and fourth electromagnetic output control valves for returning brake fluid in the first, second, third and fourth wheel brake cylinders upon brake pressure reduction, said first pumping element includes an outlet connected to said first connecting line which is connected to said first brake circuit output and said second pump element includes an outlet connected to said second connecting line which is connected to the second brake circuit outlet of the master brake cylinder, a reversing valve disposed in said first connecting line between said first brake circuit outlet of the master brake cylinder and the outlet of said first pump element assigned to said first brake circuit which is assigned to at least one driven wheel, said reversing valve is triggered during a traction control operation, a first low pressure reservoir connected to the input of said second pump element, a second low pressure reservoir connected to said input of said first pump element, said second low pressure reservoir including a first reservoir cylinder, a first reservoir piston and a first reservoir spring, a brake fluid reservoir including a second reservoir cylinder, a second reservoir piston axially displaceable in said second reservoir cylinder by a force of a second restoring spring due to a force of a hydraulic pressure from a hydraulic drive connected thereto, said first reservoir cylinder, said second reservoir cylinder, said first reservoir piston, said second reservoir piston, said first reservoir spring, and said second restoring spring are integrated with one another to form a combined reservoir, including a single reservoir cylinder, a single reservoir piston, said first and second low pressure reservoirs function to temporarily hold brake fluid upon brake pressure reduction, said brake fluid reservoir communicates with said first pump element in said first brake circuit including at least one driven wheel and charges the pump element with brake fluid in traction control operation, said brake fluid reservoir is embodied as an active reservoir that is controllable with respect to the charge pressure generated by it;
- that the brake pressure in the wheel brake cylinder of at least one driven wheel required in traction control operation is established by the first pump element by controlling the charge pressure generated by the brake fluid reservoir, said brake fluid reservoir in traction control operation, is activated during a brake pressure buildup and is deactivated during a brake pressure holding and reduction.