Hydraulic brake force amplifier

An hydraulic brake force booster for a vehicle braking system, wherein the system includes a brake pedal which exerts a brake-force;

• and wherein the hydraulic brake force booster includes:
• a control valve including a control slide,
• a travel-imparting spring connected between said control slide and said brake pedal plate such that movement of the brake pedal is limited in part by the travel-imparting spring;
• an end stop means for limiting movement of said control slide during normal pressure operation;
• at least one main piston;
• a pressure relief means;
• a pressure source;
• a main cylinder housing the at least one main piston and fluidly connected to the pressure source and the pressure relief means;
• said control valve being operative to regulate fluid flow, and is operatively connected to the brake pedal such that the control valve is actuated by a brake-force related to movement of said brake pedal and wherein the control valve regulates fluid flow between the at least one main cylinder and said pressure source;
• and between the at least one main cylinder and the pressure relief means;
• an end stop means for limiting movement of said control slide during normal pressure operation,
• a cutoff assembly including a barrier piston which is subject to an arresting pressure from said pressure source during normal operation, and wherein the cutoff assembly is operative to detect a failure in source pressure and to displace said end stop means for the travel-imparting spring in the event of such failure in source pressure;
• said cutoff assembly includes a valve to release the arrest pressure of the barrier piston and further wherein, due to the brake-force said travel imparting spring biases the barrier piston in a direction opposite to that of the arresting pressure.