The World’s First Hybrid Power SUV: The Lexus RX400h

Key points

• The world’s first hybrid petrol-electric car in the premium segment
• Second generation Hybrid Synergy Drive technology delivers power and performance appropriate for a luxury 4×4
• 3.3-litre V6 petrol engine combines with electric motors to produce approximately 270bhp
• Fuel consumption to match a standard four-cylinder saloon and ultra-low carbon dioxide emissions
• Continuously variable automatic transmission
• World-first application of Vehicle Dynamics Management (VDM) advanced vehicle stability control system
• UK debut of production model, due for UK sale in 2005

The Lexus RX400h makes its UK debut at the Sunday Times Motor Show Live, a vehicle that is set to make history as the first hybrid petrol-electric production model in the premium car market when sales begin in early 2005.

Equipped with the latest development of Hybrid Synergy Drive technology, the RX400h offers performance worthy of a conventional 4.0-litre V8 engine, yet achieves substantial improvements in fuel economy, exhaust emissions along with smoother and quieter operation.

At the same time as the RX400h makes important advances in technology, it makes no compromises in the high levels of quality and refinement that are characteristic of all Lexus models, which have helped make the RX series a great success since the all-new model range was launched in 2003.

NEW HYBRID POWER SYSTEM

Fuel economy and low emissions have been traditional advantages of hybrid power systems. Where the RX400h is concerned, these qualities are now matched by impressive power output, too. The 400 in the vehicle’s name refers not to engine capacity, but to the fact the output can compare to that of a 4.0-litre petrol engine.

Lexus engineers have developed a hybrid system specifically for the RX400h, based on the Hybrid Synergy Drive concept used to great effect in the new Toyota Prius. They redesigned and refined the electrics, mechanical components and control elements to achieve performance levels appropriate for a luxury 4×4.

The powertrain uses a conventional 3.3-litre V6 petrol engine working in tandem with two powerful electric motors to provide an intelligent four-wheel drive system, improved low to mid-range acceleration, braking and fuel efficiency and minimised carbon dioxide emissions.

In addition to the petrol engine and the electric motors, the system also features a generator, high-performance battery and a power split device that enables power from the different sources to be combined or re-allocated according to driving conditions. The high-speed interaction of the different components in the system is governed by a power control unit.

In order to achieve higher output from the Hybrid Synergy Drive system, electrical capability was increased. Booster devices were added and a new high-speed front motor that operates at twice the speed, producing more than twice the power of that used in the Prius. Adding a rear motor enables four-wheel drive, and a newly developed nickel-metalhydride battery again produces almost double the power of that in the Prius.

The strength of the RX400h’s powertrain is expressed in a maximum output of around 270bhp, compared to 110bhp for the Prius. This gives the RX400h a top speed to match the existing RX300, but with a nought to 62mph acceleration time of less than eight seconds. More than that, fuel consumption is improved to a level usually associated with a four-cylinder family saloon.

The powertrain complies with Euro IV emissions standards and produces much less carbon dioxide compared to rival premium 4x4s with a similar power output.

Maximum efficiency, minimum fuss

Although the RX400h makes extensive use of advanced technologies, it is not complex to drive. The drive system is engaged by means of a gearlever mounted on the dashboard, operating a seamless, continuously variable transmission.

In the course of any journey, the Hybrid Synergy Drive system will operate in several different modes in order to maximise efficiency. At rest, the engine will automatically stop to conserve fuel. At times when engine efficiency is low, such as on start-up and at low to mid-range speeds, the vehicle will run on its electric motors alone, reducing exhaust emissions to zero.

In normal driving, power from the engine will be divided by the power split device both to drive the wheels directly and to power the generator, which, in turn, drives the electric motors. In these circumstances, power allocation is constantly monitored and adjusted between the engine and motors to maximise efficiency. When sudden acceleration is required, engine and electric motors operate in tandem, with extra power supplied by the battery to boost motor response.

Intelligent four-wheel drive

The RX400h’s Hybrid Synergy Drive system uniquely features a second electric motor to drive the rear wheels and provide electric four-wheel drive for certain driving conditions.

Controlled by the Vehicle Dynamics Management system, the four-wheel drive is automatically engaged via continuously adjusted front and rear electric motor torque, as when accelerating hard from standstill or through the gears, when cornering, or whenever a loss of traction from the front wheels is detected.

Moreover, during deceleration and under braking, the engine switches off and the electric motors act as high-output generators, driven by all four wheels. This regenerative braking system optimises energy management by recovering kinetic energy that would usually be lost as heat and storing it as electrical energy in the battery. In addition, battery power level is constantly managed by the engine-driven generator, which means there is no need to recharge the system from an external source.

VEHICLE DYNAMICS MANAGEMENT

In conjunction with the new Hybrid Synergy Drive system, the RX400h has enhanced handling and driving stability thanks to its re-tuned suspension, specially designed Electronic Power Steering (EPS) and the installation of Vehicle Dynamics Management, one of the most advanced vehicle stability control systems currently available.

The VDM is less obtrusive that conventional VSC systems, but is ultimately more effective. By means of high-speed “by-wire” throttle, brake and transmission technology, VDM co-ordinates control of the Hybrid Synergy Drive, the electric four-wheel drive and Electronically Controlled Braking (ECB), adjusting front and rear electric motor torque according to driving conditions and stabilising vehicle behaviour on low grip surfaces, such as snow or mud.

FLAGSHIP OF THE RX SERIES

The RX400h shares the sleek and muscular styling of the RX300, but will be the flagship of the range riding on bespoke 18-inch alloy wheels and featuring a redesigned front grille, fog lamps and bumper.

The cabin displays all the trademark Lexus values of peerless comfort, outstanding quality and driving ergonomics. Exclusive brushed aluminium trim reflects the state-of-the-art technology used in the powertrain.

On the instrument panel in front of the driver, the tachometer is replaced by a power meter. The driver can also monitor the operation of the different elements in the Hybrid Synergy Drive system by means of a continuous read out on the seven-inch touch display screen on the centre console.

LEXUS RX400h PRELIMINARY TECHNICAL SPECIFICATION

ENDS