Toyota has finally officially launched the several times-delayed 2006 Lexus RX 400h, the world's first petrol/electric hybrid-powered luxury SUV, which will go on sale in the United States in April.

Based on the petrol RX 330, the best-selling SUV in its US market category, the RX 400h is claimed to deliver greater performance, improved fuel efficiency and significantly reduced emissions at no sacrifice of luxury or utility.

The latest Lexus has a new, advanced Hybrid Synergy Drive system that combines the 3.3-litre V6 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 said to be better than many V8-powered competitors. The RX 400h's estimated EPA combined fuel economy rating of 28 mpg (US gallons, remember) matches the average for new compact sedans and is a 33% improvement over the petrol RX 330 AWD. The hybrid also gains a 67% edge over RX 330 in city fuel economy - its estimated EPA city fuel economy rating of 30 mpg also exceeds most V8 and many V6-powered luxury SUVs by over 100%.

"The RX 400h… [is] 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," said Denny Clements, Lexus group vice president and general manager.

The new RX 400h will become the premium model in the US-market RX series, with numerous standard features that are optional on the RX 330. Lexus claims 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.

Subtle new look

Externally, the RX 400h differs in a few subtle ways from the RX 330 with its revised grille, a new front fascia with additional air intake, round fog lamps, unique 18-inch alloy wheels and LED tail lamps. Inside, brushed aluminium accents replace wood trim, and a power meter replaces the tachometer.

The RX 400h also has struts with internal rebound springs and linear control valves and specific suspension tuning for sportier handling.

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

The RX 400h uses a 3.3-litre V6 that is based on the engine in the RX 330 (European versions still have a three-litre V6) 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 petrol 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 petrol 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 petrol 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.

Friction reduction

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, claims its maker. The innovative electric AWD system employs a separate 50kW 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 manoeuvres.

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.

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 stabilising corrections while allowing higher dynamic capability

New electronic braking

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 optimised 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 optimise 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 is claimed to dramatically enhance the RX 400h's dynamic qualities and maximise its performance capability, driving pleasure and safety.

Enhanced DVD navigation

The available DVD navigation system features Lexus' latest technology that expands the system's capability and improves performance. The system provides multi-language selection and very fast route calculation (about five seconds).

Voice activation makes operation easier and more intuitive than ever. Map modes with easy-to-understand graphics show freeway exit information, an intersection guide, upcoming exits (a benefit if the driver passes an intended exit), points of interest at the exits and a compass.

System functions include multi-route calculation, route preview, simplified highway junction graphics, and a dual-map screen mode. The DVD map database contains more than five million points of interest (POI).

The database for Chicago, Detroit, Los Angeles and New York features "building footprint" graphics, which shows 3D renderings of buildings in their locations. This feature can be useful for identifying buildings and their surroundings.

The Lexus Navigation System integrates Bluetooth wireless technology. When combined with a Bluetooth equipped phone, this global wireless technology allows the driver to transfer personal phone books to the navigation system and make hands-free phone calls through the navigation system's touch-screen control panel.

Like other Lexus vehicles, the RX 400h comes with a 48-month/50,000-mile basic limited warranty with roadside assistance for 48-months/unlimited miles. Powertrain and restraint system coverage is provided for 72 months/70,000 miles. Corrosion perforation protection is covered for 72 months, regardless of mileage. The hybrid-related components, including the HV battery, battery control module, hybrid control module and inverter with converter, are covered for eight years/100,000 miles.