New Honda Motor

Left:Structure of original TF motor. Right: new TF motor. -32% is the relative reduction in axial length compared to a conventional motor. Takizawa et al. Click to enlarge.

Honda has proposed and is developing a Transverse Flux motor (TF motor) in order to shorten the axial length of the motor for hybrid electric vehicles (HEVs). At the 2013 SAE World Congress, Honda engineers described their progress in improving the new type of three-dimensional magnetic circuit motor.

In contrast to conventional stators composed of a stator core (made from magnetic steel sheet) and winding wires, the TF motor’s stator is composed of a soft magnetic composite (SMC) core and a coil. While reducing axial length and achieving a simple stator architecture comprising only five parts, the new motor raises issues including the need further to improve motor efficiency (currently at 83.7%) and the development of techniques for the manufacture of rectangular wave-shaped coils.

Background. Honda’s front-wheel drive IMA hybrid powertrain system features a motor located between the internal combustion engine and a continuously variable transmission (CVT); as a result, the width of the powertrain increases according to the axial length of the motor. To use the hybrid vehicle system on various vehicle types with different width requirements, the axial length of the motor needs to be shortened.

In an effort to shorten the axial length of the motor, Honda engineers focused on eliminating the coil end, which does not contribute to the generation of torque, by proposing a transverse flux motor, reported in a paper in 2011 (Aoki and Takahashi). The original TF motor featured internal ring-shaped coils and new type of flux pat. The design was later improved to counter magnetic saturation and magnetic “short circuits”.

While the stator of a salient-pole concentrated winding motor, in which each tooth is a separate part, is composed of 110 parts, the TF motor uses a simple stator made by stacking the three 3-dimensional stator cores and two rectangular wave-shaped coils.

However, efficiency in the original design was relatively low (79.1%) due to iron loss characteristics of the soft magnetic composites (SMC) used to make the stator). Too, manufacturing methods for producing rectangular wave-shaped coils from ring-shaped coils was also an issue.

In the new SAE paper, Honda engineers describe methods for reducing iron loss, the development of a method for manufacturing rectangular wave-shaped coils, and the creation and testing of a prototype TF motor that incorporates these elements.

Efficiency. To improve efficiency, the Honda engineers conducted a parametric study on the constituents of the SMC core and manufacturing conditions, and developed SMC specification conditions that reduce iron loss.

Specifically, they needed to reduce the hysteresis loss and the eddy current loss to bring the TF motor iron loss close to their target.