Dual-function wheel drives using rotary-linear actuators in electric and hybrid vehicles

Electric and hybrid vehicles represent the future of ground transportation. In such vehicles, electric motor/s provide the propulsion thrust - eventually aiding the engine in case of parallel and mixed power trains. On the other hand, x-by-wire technologies are spreading, typically using electric drives to also perform actions such as steering, braking, active suspension etc. Any active wheel may then feature up to 4 related degrees of freedom, usually managed by separated drives. This paper proposes to use multi-degree-of-freedom drives, in particular rotary-linear, to integrate more of such basic movements inside a single motor, thus achieving potential benefits on size, weight, cost, complexity etc. Different combinations of functions are examined and the main types of rotary-linear machines found in the literature are briefly recalled and commented, finally focusing on a brushless isotropic rotary-linear machine.