Fail-safety valve unit for a parking brake function and parking brake valve arrangement

A parking brake valve arrangement for an electronically controllable pneumatic braking system for a vehicle, the parking brake valve arrangement comprising:

• a spring-type actuator port for connecting at least one spring brake cylinder thereto;
• a supply port for receiving supply pressure (pV);
• a main valve unit for receiving said supply pressure (pV) and being configured to output a spring brake pressure (pF) to said spring-type actuator port in dependence upon a parking brake control pressure (pS);
• a pilot control valve unit for providing said parking brake control pressure (pS);
• a fail-safety valve unit including a monostable release valve including a first release valve port;
• a parking brake function;
• a ventilating valve;
• said monostable release valve being configured, when energized, to provide a release pressure (pL) at said first release valve port for said parking brake function and, when deenergized, connecting said first release valve port to said ventilating valve for ventilating said first release valve port;
• said ventilating valve having a non-linear ventilating characteristic (E) and being configured to permit ventilating said first release valve port from said release pressure (pL) to a partial brake pressure (pLT) via a first gradient (G1) and ventilating said first release valve port from said partial brake pressure (pLT) to a full brake pressure (pLV) via a second gradient (G2);
• and,
• said first gradient (G1) being greater than said second gradient (G2);
• said fail-safety valve unit being configured to output said release pressure (pL) to said main valve unit;
• and,
• said main valve unit being further configured to output said spring brake pressure (pF) in dependence upon said release pressure (pL).