Pneumatically actuated parking brake for electronic braking system

A parking brake system pneumatically actuates an air cylinder to mechanically lock a wheel brake in an applied position in response to a parking demand request. The parking brake system includes a dual hand control that has an electronic control element and a pneumatic control element. The electronic control element communicates with an electronic braking system control unit and the pneumatic control element communicates with a parking brake air reservoir. When the dual hand control is moved to a park position, the electronic control element generates an electronic control signal that applies a parking brake force to the wheel brake. The pneumatic control element generates an air signal that is sent to the air cylinder. The air cylinder includes an extendable shaft that supports a lock member. The air signal moves the lock member into engagement with a brake operating member to lock the wheel brake in the applied condition. The wheel brake remains locked even if pressure is released or leaks from the air chamber. When a release command is initiated, the electronic control unit actuates the wheel brake to unload the lock member and return the air cylinder to an unlocked position.