Lexus Introduces RX 400h, the World's First Luxury Hybrid SUV

Lexus Hybrid Technology with New Electric AWD System

The Lexus RX 400h is defined as a "full hybrid," which means that it is capable of operating in electric-only or gas engine-only mode as well as a mode that combines the power of the gas engine and electric motor. In contrast, other hybrid technologies are not capable of running only on electrical power, but instead require constant gas engine operation.

The RX 400h uses a 3.3-liter V6 that is based on the engine in the RX 330 but with revisions to promote smooth integration with the hybrid system. These include revised calibrations to the Variable Valve Timing with intelligence (VVT-i) and Electronic Throttle Control (ETC) systems.

In making the transition to a hybrid powertrain, the alternator, power steering pump, water pump and AC compressor are no longer engine belt-driven. This is 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. With the exception of the alternator, which is replaced by motor-generators, all components are now electrically powered which means notably lower parasitic losses to the engine and improved fuel consumption.

The hybrid system uses a 288-volt DC Nickel metal hydride (Ni-MH) battery pack that fits neatly under the rear seat. The battery's power is directed through a "boost converter" that efficiently raises voltage to 650V DC. An inverter changes this to 650V AC, providing its elevated power to a front-mounted 123-kW electric motor that turns as high as 12,400 RPM.

Three motor-generators are employed in the hybrid powertrain. Known as MG1, MG2 and MGR, each have specific functions and each do double duty as both drive 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.

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.

In addition to its motor-generator duties, the crucial MG1 adds two functions: One as a starter motor for the gas engine; and two, by regulating the amount of electrical power it generates (which varies its RPM), MG1 controls the output speed of the transaxle through the planetary gear set—without clutches or viscous couplings. This is one of the keys elements of the hybrid powertrain and is why RX 400h eliminates the "shift shock" that can typically be felt as even the most refined modern automatic transmissions change gears.

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