Concept study of a double rotor induction machine used as continuously variable transmission

In a drive train a continuously variable transmission (CVT) has the advantage that the combustion engine can be driven in its optimal point along the requested power curve, which enhances overall efficiency. Moreover there is no power loss during shifting of gears which is often demanded in off highway applications. Several mechanical and hydraulic CVT's exist that have already proven their functionality, each having their pros and cons. This paper introduces the concept of an electromagnetic CVT which has some inherent advantages compared to mechanical systems being the absence of friction and the need for lubrication, only two moving parts and inherent overload protection. The machine can be seen as a conventional induction motor with two rotors. The rotors are arranged in a concentric way and are electromagnetically coupled. The working principle is explained, and an efficiency map is calculated for a scaled test case. It is concluded that with a smart choice of the interrotor flux a good efficiency can be achieved in a broad range of torque and flux of the interrotor.