The Lexus GS 450h Hybrid System

12 February 2007


At last week’s SAE Hybrid Vehicle Technologies Symposium 2007, Akihiro Yamanaka from Toyota provided some details on the hybrid drivetrain for the Lexus GS 450h—the first FR (front-engine, rear-wheel drive) passenger car hybrid on the market.

As it has introduced more hybrid models, Toyota continues to develop enhancements to the original Hybrid Synergy Drive II, which is the core of the second-generation Prius, relevant to various vehicle applications.

The company’s first foray into hybrid systems for vehicles that require more power—such as SUVs—was the system applied in the Rx 400h and Highlander Hybrid SUV. This system adds a conventional planetary gearset as a motor speed reduction gear at the rear of the transmission to increase torque.

By increasing system torque with the reduction gear, Toyota was able to reduce the size of the transmission’s two electric motors, and properly match the hybrid system with a larger engine.


Schematic of the GS 450h transmission. Click to enlarge.
The hybrid system in the GS 450h takes a step further, and uses a two-stage motor speed reduction device. Specifically developed for rear-wheel drive systems, the Toyota Hybrid System II with Two-Stage Motor Speed Reduction Device utilizes the motor’s high-efficiency region over a wider range of gear ratios than before. The hybrid system in the GS 450h supports both high output and high vehicle speed.