PARK BRAKE MODULE WITH RELAY VALVE AND SAFETY PISTON

The invention relates to a park brake module (1) comprising a relay valve unit (17) for providing a brake release pressure (pBR) to a working port (7) and a safety unit (19) for connecting the working port (7) to the exhaust (9). The relay valve unit (17) comprises a relay piston (25), wherein the working port (7) is in fluid communication with an exhaust (9) when the relay piston (25) is in an exhaust position (29). The relay piston (25) is slidable independently of a safety piston (54) of the safety unit (19) when the safety piston (54) is a neutral position (75), and the relay piston (25) is locked in the exhaust position (29) when the safety piston (54) is in a safety position (77). The invention further relates to a method (300) for controlling a park brake function, a brake system (100) and a commercial vehicle (202).