Image Number 4 for United States Patent #6994191.
A vehicle 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 air cylinder includes an extendable shaft that supports a lock member. When a parking demand request is initiated by moving a hand control, an air chamber is pressurized with air from a parking reservoir via a valve assembly to apply the wheel brake. Air pressure is released from the air cylinder and the lock member is moved into engagement with a brake component to lock the wheel brake in the applied condition. The wheel brake remains locked even if pressure is released from the air chamber. When a release command is initiated, the air cylinder is pressurized and the lock member is moved out of engagement with the brake component.