Hydraulic dual-circuit brake system

A hydraulic dual-circuit brake system with an anti-skid system and traction control for motor vehicles having first and second driven wheels and first and second non-driven wheels, having a master brake cylinder with first and second separate brake circuit outlets (16, 17) for controlling a brake pressure in first and second brake circuits by actuation of a brake pedal;

• a brake fluid tank that communicates with the master brake cylinder;
• a four-channel hydraulic unit (20) connected to said first and second brake circuit outlets of the master brake cylinder, said four-channel hydraulic unit has first and second outlet channels (21, 22) for connecting brake fluid to wheel brake cylinders (10) of said first non-driven vehicle wheel (13) and said first driven wheel (12), and third and fourth outlet channels (23, 24) for connecting brake fluid to wheel brake cylinders (10) of said second driven wheel (11) and said second non-driven wheel (14), first and second electromagnetic control valves (31 and 32) associated one each with said first and second outlet channels (21, 22) for controlling a brake pressure dependent on wheel slip or said first non-driven wheel and said first driven wheel, third and fourth electromagnetic control valves (33, 34) associated one each with said third and fourth outlet channels (23, 24) for controlling a brake pressure dependent on wheel slip of said second driven wheel and said second non-driven wheel, and a return pump (27) with first and second separate pumping elements (28, 29), said first pumping element (28) operative in said first brake circuit, for returning brake fluid from the wheel brake cylinders of said first non-driven wheel and said first driven wheel back to said first brake circuit upon brake pressure reduction, said second pumping element (29) operative in said second brake circuit for returning brake fluid from the wheel brake cylinders of said second driven wheel and said second non-driven wheel back to said second brake circuit upon brake pressure reduction, an inlet side of said first pumping element (28) is connected to an outlet side of said first and second electromagnetic control valves, an inlet side of said second pumping element (29) is connected to an outlet side of said third and fourth electromagnetic control valves, said four-channel hydraulic unit (20) has first, second, third, and fourth inlet channels (25, 25', 26, 26') which communicate via first, second, third, and fourth connecting lines (41, 41', 42, 42') with the first and second brake circuit outlets (16, 17) of the master brake cylinder (15);
• the first and second pump elements (28, 29) of the return pump (27) are connected on an output side to said first and third inlet channels (25, 26) to which the second and third control valves (32, 33) for the second and third outlet channels (22, 23) of the wheel brake cylinders (10) of the first and second driven wheels (12, 11) are connected;
• a second hydraulic unit (40) for generating a brake supply pressure in traction control, said second hydraulic unit has a hydraulically controlled charging valve (43), which at least in traction control connects said input side of said second pump element of the return pump with the brake fluid tank, and has a first electro-magnetic reversing valve (44), incorporated into a connection between an output side of said second pump element and said second brake circuit outlet of the master brake cylinder, said first electromagnetic reversing valve (44) is disposed in the third connecting line (2) leading from said second brake circuit outlet (17) of the master brake cylinder (15) to said second inlet channel (26), said second inlet channel communicates with said second pump element (29);
• a second reversing valve (44') is disposed in the first connecting line (41) leading from the said first brake circuit outlet (16) of the master brake cylinder (15) to said first inlet channel (25), which communicates with the outlet side of said first pump element (28);
• and that the second reversing valve (44')) is embodied such that in traction control, the first inlet channel (25) is disconnected from the master brake cylinder (15) and is connected to a third connecting line (46) between the first reversing valve (44) and the pressure limiting valve (47), in traction control the electromagnetic reversing valve disconnects said second pump element on the output side from the master brake cylinder and with an interpolation of a pressure limiting valve (47) connects the output side of said second pump element to the brake fluid tank, said second pump element (29) of the return pump (27) is embodied as a self-aspirating high-pressure pump, and that a check valve (45) having a flow direction toward the inlet of said second pump element is incorporated into a line connecting the inlet of said second pump element (29) to the third and fourth control valves (33, 34) of the second brake circuit associated with the second pump element (29).