2006 Lexus RX400h Road Test

A preview of the Lexus hybrid SUV

PONTE VEDRA, Fla. Hybrid vehicles may still be a bit of a novelty, but the Lexus RX400h shows that hybrids are going to play an increasingly important role in the future.

Toyota was one of the first companies to adopt hybrid technology, primarily because the company decided in the early 1990s to develop all phases of its hybrid program in house without relying on outside contractors or suppliers. That decision is now paying huge dividends in terms of a knowledge base. The second-generation Prius is light years ahead of the first model, and the company is branching out with V-6 hybrids for Lexus, the American luxury division of Toyota.

The all-wheel-drive RX400h combines a 3.3-liter V-6 engine with three electric motors, one of which drives the rear wheels. Getting this complex powertrain to work seamlessly is no easy task, but Toyota has done it. This vehicle has so much computer technology that it may be more accurate to think of it as a computer on wheels.

The RX400h is based on the RX330, Lexus highest volume vehicle. It is 1 inch longer and 300 pounds heavier, and it can tow 3,500 pounds. Everything underneath is radically different, however. The 3.3-liter V-6 engine produces about 208 horsepower, and the electric motors add the equivalent of 60 more horsepower, for a total of approximately 268. That yields acceleration to 60 miles per hour in 7.3 seconds, which is fractionally quicker than the standard RX330.

Prices start at $48,535, and the vehicle should arrive in showrooms by April 15. Lexus expects to receive about 27,000 units the first year.

A Toyota Highlander SUV with the same powertrain will go on sale in early summer.

The RX400h is a full hybrid, which means it can operate in electric-only or gasoline-only modes, as well as simultaneously. The air conditioner, water pump, alternator and power-steering pump are driven electrically instead of by belts from the gasoline engine. That means the vehicle has power steering and cool air even when the gasoline engine shuts down.

In addition to the gasoline engine, the hybrid powertrain has three electric motor-generators. Each does double duty as a drive motor and a generator. One is a starter for the engine and also charges the battery pack, which is mounted under the rear seat. The second electric motor distributes drive to the front wheels through a planetary-gear-type continuously variable transmission. The third motor drives the rear wheels when needed.

Lexus is quick to emphasize that this is not an off-road four-wheel-drive system, but one suitable for dirt, wet or slick roads.

Dave Hermance, executive engineer of environmental engineering at Toyotas Technical Center, said performance, not fuel economy, was the goal with the RX400h system. Consequently, the V-6 engine uses the regular Otto combustion cycle and not the Atkinson cycle used in the Prius.

Nevertheless, the fuel mileage rating of 31 miles per gallon in the city and 27 on the highway is quite good. The city rating is a 72 percent increase over the 18 mpg of the RX330. Hybrids get better city mileage because they are able to rely solely on electric power for moving away from a stop. The gasoline engine kicks in as more power is needed.

In terms of emissions, the RX400h meets Californias Super Ultra Low Emission Vehicle standard, one of the most stringent in the industry. The RX400h uses a closed fuel system to avoid evaporation of gasoline fumes. An electric fuel door keeps the system closed until it is time to refuel. The electric door wont open until fuel vapors have been directed into the evaporation canister.

When the vehicle is coasting or braking, the electric motors function as generators. They capture the kinetic energy that would normally be lost as heat and transform it into electricity that recharges the batteries.

Lexus developed a Vehicle Integrated Dynamic Management system for the RX400h that goes well beyond the traditional traction and stability controls. VDIM, according to Hermance, anticipates vehicle instability in any direction and makes corrections so subtly that the driver can hardly feel them happening. Electronically controlled braking of each individual wheel is a key part of VDIM, as is the electronic throttle and electronic power steering.

I’ll offer drive impressions after production vehicles are available.

Specifications

Standard Equipment
(partial list)

• Adaptive Front lighting System
• HID headlamps with auto-leveling
• Privacy glass
• Water-repellant front door glass
• Rain-sensing wipers (includes headlamp washers)
• Regency leather interior trim
• 10-way power drivers seat
• 8-way power front passengers seat
• Touch-screen DVD navigation system includes Bluetooth and voice activation
• Rear back-up camera
• Power tilt/telescoping steering wheel
• Memory seat for driver
• Power one-touch tilt/slide moonroof
• Automatic dual-zone climate control
• Auto on/off headlights
• Programmable Homelink garage door opener
• Lexus Premium Audio with AM/FM cassette with RDS, Six-disc, single-feed in-dash CD auto-changer and 8 speakers
• Standard Vehicle Dynamics Integrated Management system (VDIM)
• Large front seat-mounted side airbags
• Front and rear side-curtain shield airbags with roll-over sensor
• Drivers side knee airbag

Major Available Options

• Mark Levinson premium audio with 11 speakers
• Adjustable front seat heaters
• DVD rear seat entertainment system