Generator

As with the electric motor, the generator is also of the AC synchronous type.


High-voltage Battery

The Lexus Hybrid Drive system features a high output, nickel-metal hydride (Ni-MH) 288 V battery. The battery is linked to a unit that monitors battery recharging conditions, detects problems and performs fail-safe system management.

Although possessing the same number of cells (240 cells of 1.2 volts), the GS 450h battery is 13% lighter than that of the RX 400h. Co-developed with Panasonic and virtually 100% recyclable, the battery is installed in the trunk, directly behind the rear seats. Being recharged by the operation of the hybrid drive system, it requires no external charging and was developed to last equal the lifespan of the other main powertrain components. Paramount to achieving such high durability is the nature of the battery's charge and discharge cycles. The hybrid system ECU, linked to the battery's monitoring unit, ensures that the SOC (state of charge) level never reaches high or low extremes, as well as controlling the recharge and discharge speed.


Power Control Unit (PCU)

The Power Control Unit consists of a voltage boost converter and a DC/AC inverter. The voltage boost converter within the Lexus Hybrid Drive's PCU converts the battery's voltage from 288 V to 650 V, to drive the motor and, occasionally, the generator. At the same time, the DC/AC inverter will convert this current from direct (DC) into alternating (AC).

Extensive efforts have been made to reduce the size and weight of this Lexus Hybrid Drive component through the adoption of smaller capacitors, and the combination of components to effect a more compact transistor module. The result is a unit of just 11.6 litres - 63% smaller and 43% lighter than that of the RX 400h - which is now comparable in size to a conventional 12-Volt battery.


Power Split Device

The Power Split Device is at the very heart of the GS 450h's Lexus Hybrid Drive system. It employs a planetary gear set (so called because planetary gears orbit a sun gear, as in the solar system) to divide the power output of the engine between the two routes. This comprises a central sun gear, an outer ring gear, and intermediary, planetary, pinion gears which engage both the former. The pinion gears are themselves attached to a carrier, enabling them to both rotate around their own axis and the central, sun gear.

The generator is connected to the sun gear. The engine is connected to the planetary pinion gear carrier. The electric motor is connected to the outer, ring gear, itself directly connected to the differential, which drives the wheels. Hence, with power transmitted to it either from the engine, the electric motor, or a combination of the two, the rotational speed of the ring gear being directly proportional to the speed of the vehicle.

The planetary gear set allows for the full range of power transmission options inherent in the Lexus Hybrid Drive system: during initial start up and at slow speeds, the engine is not running and the planetary pinion gear carrier is stationary. Powered by the electric motor, the ring gear revolves, driving the wheels and, via the pinion gears revolving on the stationary carrier, rotating the sun gear attached to the generator.

To start the engine as vehicle speed increases, momentarily stopping the rotation of the sun gear generates sufficient force (via the ring gear's rotation of the planetary gears) to set the planetary pinion gear carrier in motion, turning the engine crankshaft. Once the engine has started, it transmits power back through the pinion gears on the revolving carrier to both the outer ring gear, driving the wheels, and the inner sun gear. Rotated by the sun gear, the generator supplies electric power, via the Power Control Unit, to either recharge the battery or drive the motor.


Two-stage motor speed reduction gear

Unique to the GS 450h, the new hybrid transmission incorporates a two-stage motor speed reduction gear, coupled directly to the electric motor.

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