Brake-slip-controlled automotive vehicle brake system

A brake-slip-controlled automotive vehicle brake system having a pedal operated master cylinder for applying fluid to a wheel brake circuit by way of hydraulic brake lines, a braking pressure modulator, a pneumatic control line for said pressure modulator and an electromagnetically operated closing valve associated with the wheel of the automotive vehicle, said pressure modulator comprising a volume receiver, having a separating valve and a plunger forming a chamber therebetween, and a pneumatic piston-and-cylinder apparatus responsive to said pneumatic control line and which, acts on said volume receiver, and is connected to a vacuum source and a pressure source via an electromagnetically operated change-over valve actuated by a brake slip control circuit, said connection being such as to ensure that in the normal position of the change-over valve, said pneumatic piston is biased by a return spring into a position in which said volume receiver takes up the smallest volume and said separating valve is open thereby establishing a communication between said master cylinder and said wheel brake circuit, and that in the change-over position of the change-over valve, said separating valve is closed and said pneumatic piston is moved against the force of said return spring into a position in which the volume of said volume receiver increases wherein an improvement comprises:

• an electromechanically operated pilot valve, inserted into said pneumatic control line between said master cylinder and said pressure modulator, said valve having a normal position allowing free passage in either direction and a suction position allowing free passage only in the direction from said master cylinder to said pressure modulator;
• a connectable by-pass connected to said brake line and extending around said separating valve;
• a wheel speed sensor attached to each of said wheel brake circuits;
• a traction slip control circuit, for receiving signals from said wheel speed sensors, which actuates said pilot valve, said change-over valve, said by-pass, and said closing valve of the driven wheel, in dependence on the signals from said wheel speed sensor at the driven wheel, so that as traction slip is detected, said pilot valve is first switched to the suction position, the change-over valve is switched to the change-over position, and said by-pass, being normally closed, is opened, whereupon said pressure modulator displaces said volume receiver into an increased volume position to take in hydraulic fluid through said pilot valve and by-pass, and subsequently, said change-over valve is switched to a position wherein the control pressure applied to said modulator ceases, and the closing valve associated with the driving wheel is actuated by the traction slip control circuit to pass the increased pressure, generated by said return spring, to the wheel brake cylinders of the driven wheel to the extent required to prevent traction slip.