A thin DC brushless motor was developed as auxiliary power for the Civic Hybrid, which is positioned to take the world lead in fuel consumption for five-passenger automobiles. The concept was to create a hybrid car using an existing mass-produced engine in an existing mass-produced car body. This raised more issues than the Insight, which was made with an engine and body specifically designed for that purpose. The Civic has a heavier body than the Insight. In order to assure its power performance and increase the energy regenerated during deceleration the engine displacement had to be increased and the regenerative performance of the motor had to be improved. However, the Civic body has the same width as the Insight, so it was not possible to increase the motor width in correspondence with the regenerative performance. The objective in development of the motor, therefore, was to improve performance while keeping the motor the same width. The methods used to achieve this objective were to increase the torque constant and to reduce the losses in all parts involved. Specifically, the space gained in the axial direction by functional integration of parts made it possible to increase the cumulative stator thickness, and the adoption of new coil winding methods made it possible to enlarge the coil diameter and the width of the teeth. As a result, the motor regenerative torque was improved approximately 30% while maintaining the same motor width, and the average efficiency of the motor in the practical use area was improved approximately 3%.
Article of Honda R&D Technical Review Vol.14 No.2 (25 - 30)