Brake system for a towing vehicle

A braking system (1) for a towing vehicle (2), comprising:

• a pressure medium source (9) for supplying pressurized pressure medium;
• a parking brake module (5) having a control valve (6) and a redundancy valve (7);
• a trailer control valve system (16) for a trailer brake (3) of a trailer vehicle (4) which is towed by the towing vehicle (2);
• and
• an electronic control unit (25), wherein
• the control valve (6) and the redundancy valve (7) are mechanically preloaded in a closed state, and
• the electronic control unit (25) is configured to:
• control the control valve (6) and the redundancy valve (7) in such a way that (i) they can move into an open state counter to the mechanical preload, ii so that pressure medium is conducted from the pressure medium source (9) into a brake cylinder (23) of the towing vehicle (2) in order to build up a disengagement pressure in the brake cylinder (23), and (iii) so that a parking lock (24) of the towing vehicle (2) is disengaged, and
• control the trailer control valve system (16) in such a way that pressure medium can escape via the trailer control valve system (16) into a non-pressurized environment (U), whereby the pressure medium source (9) is emptied when (i) the control valve (6) or the redundancy valve (7) persists in the open state due to a mechanical defect and otherwise should be in the closed state, and (ii) when an ignition of the towing vehicle (2) and thus also a compressor (9.1) for filling the pressure medium source (9) are switched off.