World's First Luxury Hybrid-Electric SUV Rolls Out

Lexus RX400h offers 7.3 seconds zero-to-sixty acceleration, better than many V-8 competitors, while delivering EPA-estimated combined fuel economy of 28 mpg.

Published: 02-Feb-2005

Lexus RX400h TORRANCE, Calif., Feb. 1  -- Lexus announced the launch of the all-new 2006 RX 400h, the world's first gas/electric hybrid-powered luxury vehicle, which will go on sale in April 2005. Based on the RX 330, the best-selling SUV in the luxury category, the RX 400h delivers greater performance, improved fuel efficiency and significantly reduces emissions while sacrificing none of its luxury or utility.

The first luxury vehicle to feature hybrid technology, the RX 400h incorporates a new, advanced Hybrid Synergy Drive system that combines the 3.3-liter V6 engine with a high-torque electric drive motor-generator, plus a rear electric drive motor-generator to provide on-road all-wheel drive capability.

With a combined system output of approximately 268 horsepower, and more significantly, 3,500 lb.-ft. of axle torque at launch, the RX 400h delivers rapid acceleration with unexpected fuel efficiency. At 7.3 seconds, acceleration from zero to 60 mph is about 0.5 seconds quicker than the RX 330 and better than many V8-powered competitors. The RX 400h's estimated EPA combined fuel economy rating of 28 mpg matches the average for new compact sedans and marks a 33 percent improvement over RX 330 AWD. It also gains a 67 percent edge over RX 330 in city fuel economy. And its estimated EPA city fuel economy rating of 30 mpg exceeds most V8 and many V6-equipped luxury SUVs by over 100 percent.

"The RX 400h will open a new era in luxury vehicles, setting a new benchmark for luxury SUV performance and environmental compatibility," said Denny Clements, Lexus group vice president and general manager. "It's truly a breakthrough in terms of hybrid technology because, for the first time, it adds an enhanced performance dimension to the widely known hybrid advantages of excellent fuel mileage and low emissions."

The new RX 400h will become the premium model in the RX series, adding numerous standard features that are offered as options on the RX 330. The seamless power delivery of the hybrid powertrain will be another plus for the RX 400h, because it will feel even smoother than conventionally-powered vehicles. The RX 400h will be rated as a Super Ultra Low Emission Vehicle (SULEV) in California (Tier 2 -- Bin 3 in other states), one of the most stringent emissions ratings in the industry.

Externally, the RX 400h differs in subtle ways from the RX 330. The RX 400h features a revised grille, a new front fascia with additional air intake, sporty round fog lamps, unique 18-inch alloy wheels and LED tail lamps. Inside, brushed aluminum accents replace wood trim, and a power meter replaces the tachometer. The RX 400h will also include struts with internal rebound springs and linear control valves and feature specific suspension tuning for sportier handling.

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.

In conventional AWD vehicles, the weight and friction of the additional drive components reduce the vehicle's acceleration performance compared to the same model with 2WD. Not so with the RX 400h. The innovative electric AWD system employs a separate 50-kW electric motor (MGR) at the rear that provides up to 650 lb.-ft. of additional drive torque on demand. The system electronically varies front and rear torque distribution depending on traction conditions.

The Lexus hybrid technology also allows extended electric-mode operation during low speed or stop-and-go driving conditions. The permanent-magnet front electric drive motor (MG2) produces peak torque from zero-to-1,500 RPM, giving the RX 400h powerful and instantaneous response that will be especially felt and appreciated in low- and mid-speed performance and in merging and passing maneuvers.

A regenerative braking system further boosts system efficiency. When the RX 400h is coasting or the 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.

Vehicle Dynamic Integrated Management (VDIM)

With the RX 400h, Lexus also introduces a new generation of vehicle stability control systems known as Vehicle Dynamics Integrated Management (VDIM). This new system goes well beyond conventional traction and stability controls that simply react to challenging conditions. Instead, VDIM anticipates vehicle instability in virtually any direction and makes stabilizing corrections while allowing higher dynamic capability.

A vital component of VDIM is a new Electronically Controlled Braking system (ECB). The ECB 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.

Under guidance from VDIM, such precise brake control at individual wheels allows more optimized operation of the vehicle's dynamic handling systems that employ the brakes: ABS, Brake Assist, Vehicle Stability Control (VSC) and traction control (TRAC). VDIM also interfaces with the Electronic Throttle Control system, allowing it to modify vehicle power when needed, and a new Electronic Power Steering system (EPS) to optimize steering assist for each situation.

The EPS uses a DC motor and gear reduction system built into the steering gear housing to provide steering assist. This compact unit contributes to fuel economy by eliminating the traditional power steering pump and by providing its computer-controlled assist only when called for by the driver. EPS also allows a more precise and timely control of steering assist than conventional engine-driven hydraulic systems.

VDIM constantly calculates vehicle motion based on signals from a yaw rate and deceleration sensor, speed sensor and steering sensor. Using these inputs, VDIM controls all of the vehicle's dynamic handling systems and can employ them collectively and seamlessly, allowing it to quickly detect the onset of instability and correct it. The ability to operate 'proactively' means that corrections to vehicle attitude are typically faster, more accurate and more subtle than traditional systems, making VDIM feel smooth and essentially transparent to the driver.

Coupled with the natural security of all-wheel traction, VDIM dramatically enhances the RX 400h's dynamic qualities and maximizes its performance capability, driving pleasure and safety.

Driving the RX 400h

All of the comfort and luxury found inside the RX 330 is present in the RX 400h, with a few notable additions. The brushed-aluminum accents lend a contemporary look and the view of the instruments has evolved: In place of a traditional tachometer, the RX 400h has an illuminated power meter that displays the level of power generated by the hybrid powertrain. The driver can also monitor the gas-electric power distribution on the multi-information display or on the optional navigation system's seven-inch touch panel display screen.

One of the most remarkable attributes of the RX 400h is how similar this SUV is to its cousin, the RX 330. The computer-controlled powertrain seamlessly blends power from the V6 gasoline engine and the electric drive motors.

The generous combined torque of the engine and electric motors makes city and highway driving effortless. The result is less need to rev the engine for power, which translates to a relaxed and quiet, yet responsive and powerful driving experience.

With the confident blend of all-wheel traction and VDIM, the RX 400h makes short work of challenging roads and conditions, yet provides an unexpectedly sporty driving experience with a quiet and comfortable ride.

A Super Ultra Low Emission Vehicle

The RX 400h has been certified by the California Air Resources Board (CARB) as a Super Ultra Low Emission Vehicle (SULEV), California's most stringent gasoline vehicle emission standard. It's one of the first luxury vehicles to achieve this strict standard, producing about 90 percent fewer smog-forming emissions than typical new vehicles. The RX 400h is also certified as a zero evaporative emission vehicle in California and those states adopting California standards. In states not adopting California rules, it's certified to Tier 2 -- Bin 3 emission levels.

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