The HEV power train of the Prius
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The latest model of the Prius released in December 2015
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Toyota Motor Corp delivered a lecture on the driving motor of the latest Prius' HEV system at "Latest Technologies of Power Transmission Systems 2016," a symposium that the Society of Automotive Engineers of Japan Inc had Nov 10, 2016, in Tokyo.

For the HEV system, Toyota reduced the size of its transaxle, which consists of a motor, generator and power dividing mechanism. Especially, the volume and diameter of the motor were reduced by 35% and about 20%, respectively, compared with the motor of the previous model of the Prius.

As the size of the motor was reduced, the maximum torque of the motor decreased from 207N·m to 163N·m. However, with the speed reduction mechanism, the reduction ratio of the motor was increased from 2.636 to 3.118. As a result, the maximum torque transmitted to tire axes was kept at the same level as the previous model, Toyota said.

Toyota reduced the number of components of the speed reduction mechanism and its loss by replacing the planetary gear mechanism of the previous model with a parallel shaft gear mechanism. The mechanical loss of the entire transaxle was reduced by 19% by reducing the sizes of the speed reduction mechanism and shaft bearings.