Lexus RX 400h front-wheel-drive model's hybrid powertrain employs two motor-generators. Known as MG1 and MG2, each one performs specific functions and each does double duty as motors and generators (although MG1 is a starter and provides no motive force). The engine-driven generator (MG1) can charge the battery pack or power other electric motors as needed. The all-wheel-drive Lexus RX 400h adds a third motor-generator, MGR, to drive the rear wheels.


Powerful Partnership

Power from the gas engine and front electric drive motor (MG2) is distributed to the drive wheels via a planetary gear-type continuously variable transmission, which eliminates specific gear ratios. Two planetary gear units are used in the system. The Power-Split unit divides the engine's drive force two ways: one to drive the wheels and the other to drive MG1 so it may function as a generator. The Motor Speed Reduction unit reduces the speed of MG2 and increases its drive torque, significantly boosting acceleration performance. MG2 produces peak torque from zero-to-1,500 rpm, giving the RX 400h powerful and instantaneous response that will be felt in low- and mid-speed performance, especially in 30-50 mph merging and passing maneuvers.

In addition to its motor-generator duties, MG1 adds two functions: one, as a starter motor for the gas engine; and two, as a regulator for the amount of electrical power it generates (which varies its rpm). MG1 controls the output speed of the transaxle through the planetary gearset - without clutches or a viscous coupling. This is one of the key elements of the hybrid powertrain and is how it eliminates the "shift shock" that is typically felt as even the most refined modern automatic transmissions change gears.

The all-wheel-drive model uniquely generates rear-wheel power with a separate 50-kW electric motor (MGR) that provides up to 650 lb.-ft. of additional drive torque on demand. Thus, Lexus RX 400h does not require power-transfer gearing or a driveshaft from the front. The system electronically varies front and rear torque distribution depending on traction conditions.

The power-steering pump, water pump and air-conditioning compressor are driven electrically rather than by the engine. This is necessary because the gas engine often shuts down - a fuel-saving benefit of the hybrid system - especially when the vehicle is stopped or driven slowly through traffic. Driving these components electrically notably reduces parasitic losses to the engine and improves fuel consumption.

A regenerative-braking system further boosts system efficiency. When Lexus RX 400h is coasting or its brakes are applied, the electric motors function as generators, capturing kinetic energy that would normally be lost as heat through the brakes and transforming it into useable electricity to recharge the batteries.


Proactive Vehicle Stability Control

The RX 400h was the first Lexus model to feature Vehicle Dynamics Integrated Management (VDIM). This new vehicle stability control system goes well beyond conventional controls that simply react to challenging conditions. Instead, VDIM anticipates loss of vehicle control in virtually any direction and can make corrections while allowing higher dynamic capability.

Electronically Controlled Brakes (ECB) are a vital element of VDIM. This advanced braking system translates brake pedal stroke speed and pressure and generates the precise amount of combined electric regeneration and hydraulic pressure needed for virtually any driving condition.

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