A service brake actuator with an electric motor as its energizing means is known. The rotating movement of the motor shaft is transformed into a linear, brake applying movement of brake linings or the like, cooperating with a brake disc or a brake drum of a vehicle, such as a road vehicle or a rail vehicle.
For such a service brake actuator it is of importance to attain a parking braking, when the vehicle is parked and the service brake actuator is electrically deenergized. It may also be important to have the brakes applied in the case of failure in the supply of electricity to the service brake actuator.
It is well known in the art to make use of a powerful spring in a spring brake actuator for the purpose of obtaining parking and emergency braking. In the case with a rotational operative shaft of the service brake actuator, it is obviously suitable to have a spring brake actuator shaft connected to or in rotative communication with the service brake shaft.