The planetary gear housing features external gear teeth and can be rotated by a motor and worm gear. Alteration of the housing position allows rotation of the output sun gear independently of the input sun gear position. I.e. if the driver were to hold the steering wheel (and therefore the input sun gear) stationary, driving the planetary gear housing will result in the rotation of the steering pinion (and therefore a steering action at the front wheels). By manipulating the position of the planetary gear housing, the active steering ECU can synthesize a variable steering ratio or generate steering actions independently of the driver.