Torque density improvement of transverse-flux dual rotor machine for power-split hybrid electric vehicle application

A new brushless compound-structure transverse-flux permanent magnet synchronous machine (CS-TFPMSM) is proposed in this paper. It can help the hybrid electric vehicles (HEVs) to fulfill power split and adjust the torque and speed from the internal combustion engine (ICE). As the key component of the CS-TFPMSM, the transverse-flux dual rotor machine (TFDRM) originates from the transverse-flux machine (TFM). The TFDRM can keep the principle of TFM unchanged, and fulfill the elimination of brushes. The operation principle is described; and the expression for the torque density is deduced. Based on that, the characteristics of the TFDRM are investigated. Because of the three-dimensional (3D) complicated magnetic circuit, the 3D finite element method (FEM) is used to simulate the performances of the TFDRM. The influences of main geometry parameters, such as the pole-pair number, the length of the outer/inner air gap, the sizes of the permanent magnets, and so on, on the torque density are simulated with the 3D FEM. The methods to enhance the torque density are discussed.