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Autos: Electrifying Efficiency

Patrick C. Paternie

The 2006 Lexus RX 400h may be a greener version of the RX 330 SUV, but the carmaker recognizes that saving the planet is not the only concern of those who might drive the gas-electric hybrid. As Denny Clements, group vice president and general manager of the Lexus Division, noted—before letting us loose on the Big Island of Hawaii to test-drive the SUV—building the RX 400h was “not necessarily about being green or more fuel-efficient, or even about a higher level of performance. It was all about delivering a better total package to customers.”

Clements’ sentiments were echoed by Masaki Sanayama, the project manager and assistant chief engineer for the RX 400h, who previously was involved in the development of the Toyota Prius. Sanayama described how his engineering team had to shift its mind-set from building a vehicle whose buyers wanted to make the statement “I’m special, I’m green, and I’m into advanced technology” to designing one that would meet the expectations of Lexus customers. The challenge was not only to include the horsepower equivalent of a V-8 and the fuel economy of a compact sedan, but to do so in a luxury midsize SUV that represented more of an evolution of the popular RX 330 than a revolution. In this endeavor, Lexus has succeeded.

The RX 400h accelerates faster and handles better than the RX 330. Indeed, the handling is impressive compared to nearly any SUV. Responsive and precise steering comes from a new Electric Power Steering (EPS) system, which provides computer-controlled steering assist. The EPS belongs to a new proactive vehicle stability control system known as Vehicle Dynamics Integrated Management (VDIM). Besides the EPS, VDIM also includes traction control, stability control, ABS, and an Electronically Controlled Brake (ECB) system, all of which keep a vehicle on its proper course.

The RX 400h operates in an electric-only or gasoline-only mode, but the driver cannot tell which fuel is being consumed unless he views the dash-mounted display. A 3.3-liter V-6 works in concert with one of three electric motors to power the front wheels. A second electric motor powers the rear wheels, and the third serves as a starter and generator to power the other motors or charge the nickel-metal-hydride (NiMH) battery pack that sits under the rear seat. Instead of a traditional transmission, the RX 400h is equipped with planetary gears through which power is distributed to the wheels.
  
Lexus claims that the RX 400h can accelerate from zero to 60 mph in 7.3 seconds and that it will average about 28 miles per gallon of gasoline. It remains to be seen whether these numbers and the vehicle’s other attributes will have the world beating a path to its door for a luxury hybrid SUV, but Porsche already has come knocking, inquiring about using some of the technology for a hybrid Cayenne. For Lexus, however, the question is not whether the world is ready for a luxury hybrid SUV, but whether it wants a better RX 330.

Lexus, www.lexus.com

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