Toyota Introduces New Hybrid System

Tokyo―TOYOTA MOTOR CORPORATION (TMC), riding on the success of its hot-selling hybrid Prius sedan, leaped two more steps ahead of the competition today when it unveiled its new minivan-minded Toyota Hybrid System-CVT (THS-C) and the world's first hybrid 4-wheel-drive powertrain, the "E-Four."

The front-wheel-drive THS-C consists of a high-efficiency gasoline engine, an electric motor and a continuously variable transmission. In the E-Four, this highly efficient combination is linked to a separate power-boosting rear motor. The result is strong performance, doubled fuel economy and reduced emissions―satisfying Japan's ultra-low-emission vehicle (J-ULEV) standards.

Toyota's engineers took a high-power, high-torque, 2.4-liter gasoline engine and gave it a high-expansion ratio cycle, which creates high thermal efficiency for the THS-C. In the E-Four, under normal driving conditions the engine's power is transferred to the front wheels through the CVT. During strong acceleration, the forward electric motor delivers added power to the front wheels; the rear motor kicks in to propel the rear wheels when even more boost is needed.

When engine efficiency is out of the optimum range, such as when the car first starts moving and during low-speed driving, the engine stops and the vehicle runs on the forward electric motor, transferring power to the front wheels alone.

Low-friction road surfaces bring out the most in the E-Four. When front-wheel slippage is detected, the power to the front axle is reduced by diverting power received from the engine. The front motor is then used as a generator to absorb engine power and produce electricity to drive the rear motor. The net effect is a transfer of power from the front to the rear wheels to combat the slippage.

Having two motors that can separately supply power to the front and rear wheels eliminates the need for the propeller shaft that connects the front and rear axles in conventional 4-wheel-drive vehicles. This makes the E-Four a lighter alternative and offers greater freedom in the vehicle package. Moreover, regenerative brakes on all four wheels collect a large amount of braking energy as electrical energy, raising the efficiency of the drive system.

Finally, the drive battery is a newly developed nickel-metal hydride battery that is compact and offers high performance. (See Attachment 3.)

THS-C Schematic