Apparatus for monitoring the auxiliary energy pressure of a slip-controlled brake system and switch failure indicating arrangement therefor

Apparatus for monitoring the pressure of the auxiliary energy source of a slip-controlled brake system for a motor vehicle having vehicle wheels including wheel brakes, comprising, in combination:

• a master cylinder having a cylinder housing forming at least one pressure fluid chamber;
• a pedal-operated hydraulic brake booster operatively coupled to said master cylinder;
• an auxiliary energy pressure source connected to said brake booster;
• a plurality of wheel sensors respectively coupled to each of said vehicle wheels;
• a plurality of pressure fluid lines respectively connecting one of said master cylinder and said brake booster with said wheel brakes;
• a plurality of electromagnetically operated control valves respectively provided in said fluid lines;
• means coupled to said sensors for providing at least one output signal indicative of wheel rotational behavior;
• means responsive to said output signal for controlling said control valves to provide slip control;
• a pressure-operated warning switch coupled to said auxiliary energy source and providing a warning output signal when the pressure of said auxiliary energy pressure source falls below a predetermined limit value;
• means coupled to said control valves and responsive to said warning output signal for varying said slip control;
• detecting means coupled to said pressure-operated warning switch for detecting a failure of said warning switch;
• means coupled to said detecting means and responsive thereto for providing an error signal indicative of said failure of said warning switch;
• and,
• wherein said pressure-operated warning switch comprises a normally open set of contacts coupled between a voltage source and a brake warning light and a normally closed set of contacts coupled between said voltage source and the means for varying said slip control.