Development of Traction Drive Motors for the Toyota Hybrid System

In terms of preventing global warming and conserving natural resources, automobiles are playing an increasingly critical role. To reduce the CO2 produced by automotive vehicles, fuel efficiency must be improved while cleaning exhaust gases as well as ensuring safety. At Toyota Motor Corporation, solving environmental issues has been being one of our most important tasks, and this focus enabled the company to be successful in making the Prius hybrid in December 1997. In accordance with starting the Prius exports in 2000, the propulsion and combustion characteristics of the THS system were reconsidered from a viewpoint of improving the product performances. Further improvements were continued thereafter, so that in April 2003 an increase in motor output by 50% was carried out by boosting up the electrical system voltage and renewing the control system. These innovations all contributed toward producing the next generation, Toyota Hybrid System “THS II”, which realized an unprecedented vehicle being coped with both low fuel consumption and a high degree of driving comfort. In that September, Toyota announced this achievement and started sales of the new model Prius featuring THS II. In 2005, in order to produce a new hybrid system suitable for a large sports utility vehicle (SUV) with a 3.3 liter engine, Toyota has developed a new class of high speed traction drive motor with more than twice the rotational speed of earlier models, resulting in a significant increase in power weight ratio as shown in Fig. 1. This paper presents the hybrid system developed in 2005 for SUV, and discusses the technical aspects of the traction drive motor such as the increase in power weight ratio and the reduction of losses.