Automated grille shutters for regulation of louver angle and thus air flow are increasingly important constituents of automotive engine thermal management systems. Regulation is conveniently accomplished by means of electromechanical actuators. The actuators turn the louvers of the grille shutter, generally through a gear train, to vary the size of the opening for air to flow to cool the radiator.
Open loop operation of stepper motor actuators is a reliable state of the art technique. In case of power failure or in any situation of incorrect louver positioning at shut down, however, a fail safe mechanism must be integrated in the grille shutter actuator. A return spring can for instance bring the louvers to an initial position (open or closed, whatever is required). In that case, when in operation, the actuator has to work permanently against the spring force plus any additional forces due to intense air flow when the vehicle is traveling at high speed. Normally that would require an over dimensioned or over powered electromagnetic motor to deliver the maximum torque at the extreme open (or closed) position. It also means high electric power consumption, which is not in accordance with an efficient environmentally-friendly or “green” system.
Hence there is a desire for an actuator for a vehicle grille shutter system, in which the output of the motor is more closely matched to the required output of the actuator. The present invention solves this problem by means of a progressive gear which compensates for the variable torque requirements.
Progressive or variable gears have been known for a long time. A comprehensive description of a progressive gear can be found in U.S. Pat. No. 2,061,322 or U.S. Pat. No. 8,196,487. In automotive applications progressive gears frequently appear in steering systems.