ABS pump pressure controls pressure limiting valve and loading valve

An anti-lock controlled vehicle brake system including a wheel brake, comprising:

• an operator actuated braking pressure generator interconnected with said at least one wheel brake through a main pressure line;
• an auxiliary hydraulic pressure pump operable during anti-lock control to discharge pressurized fluid into an auxiliary pressure line, said auxiliary pressure line connected to said main pressure line;
• a low pressure fluid storage reservoir and a return line connecting said wheel brake to said low pressure fluid storage reservoir;
• an electromagnetically operable normally open inlet valve connected to said main and auxiliary pressure lines controlling communication of both said pressure generator and said auxiliary hydraulic pressure pump with said wheel brake;
• an electromagnetically operable normally closed outlet valve in said return line;
• a locking valve interposed in said main pressure line operable to isolate said pressure generator form said auxiliary pressure line upon operation of said auxiliary hydraulic pressure pump;
• and
• a pressure limiting valve having an inlet connected to said auxiliary hydraulic pressure pump, an outlet connected to and in fluid communication with said return line, and first and second control lines connected to said auxiliary pressure line upstream of said pressure limiting valve and to said wheel brake, respectively, said first and second control lines establishing controlled hydraulic communication of said auxiliary pressure line with said return line to effect control of auxiliary hydraulic pressure pump pressure supplied to said main pressure line in correspondence with said auxiliary hydraulic pressure pump pressure and said wheel brake pressure, said pressure limiting valve including means for establishing a predetermined pressure from said auxiliary hydraulic pressure pump to said main pressure line at a level equal to a fixed difference over said pressure at said wheel brake irrespective of the pressure generated by said braking pressure generator.