RX400h: A New Driving Experience

“Conventional wisdom says that high driving performance and superior fuel efficiency cannot be achieved in the same vehicle. We have proven that wisdom wrong with the RX400h, and taken SUV driving to a new and different dimension” Mr. Osamu Sadakata, Chief Engineer, Lexus RX400h.

• The World’s first hybrid, petrol/electric car in the premium automotive segment.
• Second generation Hybrid Synergy Drive technology achieving power and performance levels appropriate to a luxury 4-wheel drive SUV.
• 3.3 litre, combined with electric motors to give a maximum power output of approximately 200kW/270DIN hp.
• 4-cylinder family sedan fuel consumption figures combined with an ultra low CO2 emissions level.
• Electric 4-wheel drive transmission and seamless, continuously variable automatic transmission.
• World-first application of Vehicle Dynamics Management (VDM), the most advanced vehicle stability control system.

With the unveiling of the revolutionary RX400h 4-wheel drive Sport Utility Vehicle at the 2004 Geneva Motorshow, Lexus today introduces the world’s first hybrid, petrol/electric powered car to the European premium automotive segment. RX400h will go on sale in Europe during the first quarter of 2005.

Boasting Lexus’ state-of-the-art Hybrid Synergy Drive technology, the RX400h is the ultimate technology expression of the Lexus marque. It offers performance normally associated with a larger engine, family car fuel consumption, ultra low CO2 emissions level, smoother, quieter operation and enhanced safety features.

Hybrid History

Though the world’s first volume production hybrid car, the Toyota Prius, has only been on sale since 1997, the launch of the new Lexus RX400h all but marks the centenary of the hybrid vehicle concept; the American H. Piper applied on 23rd November, 1905 to patent an electric motor augmented petrol engine powertrain capable of a heady, 0-40kph/25mph dash in just
10 seconds.

In fact, by the turn of the 20th century, numerous vehicle manufacturers were already assiduously pursuing the hybrid grail: Between 1897 and 1907 the Compagnie Parisienne des Voitures Electriques built a series of electric and hybrid vehicles, General Electric built a hybrid with a four cylinder petrol engine in 1900 and, in Austria, Jacob Lohner & Co. built cars featuring electric motors integrated into the wheel hubs – the brainchild of one Ferdinand Porsche. The company went on to produce a line of vehicles in which a petrol engine drove a generator, itself supplying power to the electric motors; the fundamental concept behind the classic, hybrid powerplant.

However, though the Walker Vehicle Company of Chicago did produce petrol/electric trucks until the early 1940s, most early hybrid designs were hampered by a combination of expensive, sporadically available electricity supplies, poor performance and excessive battery weight; one notable Briggs & Stratton hybrid requiring two rear axles to spread the load of 12, 66lb lead-acid batteries.

RX400h

Today, in recognition of the first successful dovetailing of a true performance dimension to the traditional hybrid advantages of fuel economy and low emissions, the newest, hybrid petrol/electric powered addition to the Lexus RX range is named “400” not to indicate the cubic capacity of the engine but, rather, in recognition of a power output comparable to that of a larger petrol unit, whilst the “h” suffix indicates the presence of Lexus’ sophisticated Hybrid Synergy Drive system.

Exterior and interior design

Sharing the svelte, muscular styling of the RX300, the new Lexus is hallmarked as the flagship of the RX range through bespoke, 18″ alloy wheels and a redesigned front grille, fog lamps and bumper. Astern, high visibility LED lamps are featured in both high level stop light and new, bright effect tail light clusters.

On board, the RX400h cabin displays all the trademark Lexus values of peerless comfort, outstanding quality and driving ergonomics, whilst exclusive, brushed aluminium trim reflects the state-of-the-art technology inherent in the unique powertrain. Within the driver’s instrument binnacle, a power meter replaces the traditional tachometer, and the driver will also be able to constantly monitor the Hybrid Synergy Drive system’s computer-controlled distribution of petrol/electric power via the 7″ touch panel display screen mounted in the centre console.

Hybrid Synergy Drive

The Lexus division engineers have created specifically for the RX400h a completely new hybrid system based on the Hybrid Synergy Drive concept, re-designing and refining the electrics, mechanical driving components and control elements to achieve the power and performance levels appropriate to a luxury 4-wheel drive SUV.

This ground-breaking development features the world’s first series parallel hybrid system to employ two powerful electric motors and a highly efficient petrol engine working in tandem to both provide an “intelligent” electric
4-wheel drive capability and significantly improve low to mid-speed acceleration, braking and fuel efficiency, whilst minimising CO2 emissions.

In addition to a petrol engine and two electric motors, the system further comprises a generator, a high performance battery, a power split device which combines and re-allocates power from the engine, electric motors and generator according to operational requirements, and a power control unit to govern the high speed interaction of the system components.

Electrical power enhancements to the new Hybrid Synergy Drive include the use of booster devices, an increase in the system’s electrical capability, a new, high-speed front motor operating at twice the speed and delivering more than double the power than that of the Toyota Prius, the addition of a rear motor to facilitate four-wheel drive, and the use of a newly developed, nickel-metalhydride battery with a metal case, providing nearly double the power of that found in the Prius.

In comparison, then, whilst the Prius powertrain combines a 1.5 litre petrol engine with an electric motor to generate a maximum power output of 82kW/110DIN hp, the new Lexus RX400h employs a 3.3 litre petrol engine and a front and a rear electric motor (to drive the rear wheels when necessary) all combining to produce a maximum power output of approximately 200kW/270DIN hp.

This imbues the RX400h with a comparable top speed to that of the existing RX300, but overall performance superiority thanks to class leading acceleration figures of 0-100kph/62mph in less than 8 seconds. Furthermore, its fuel consumption figures are more usually associated with a 4-cylinder family sedan than a luxury SUV.

Already compliant with EURO IV emissions standards, the new Lexus will produce much less CO2 emissions compared to a Premium SUV with a similar engine power.

A single, dashboard mounted gearshift lever engages the drive system, which acts as a seamless, continuously variable transmission.

Over the course of any journey, the new Hybrid Synergy Drive system operates in several different modes to maximise the RX400h’s overall efficiency: At rest, the engine stops automatically to conserve fuel. Under operating conditions of low engine efficiency such as start up and low to mid-range speeds, the vehicle runs on the electric motors alone, thus eradicating CO2 emissions. Under normal driving conditions, engine power is divided by the power split device to both drive the wheels directly and power the generator which, in turn, drives the electric motors. In these circumstances, power allocation is constantly monitored and adjusted between engine and motors to maximise efficiency. When sudden acceleration is required, engine and electric motors again operate in tandem, with extra power supplied from the battery to boost motor response.

Unique to the RX400h’s Hybrid Synergy Drive, the vehicle’s rear wheels are driven by a second electric motor to provide Electric 4-Wheel Drive system under various driving conditions: Controlled by the Vehicle Dynamics Management installation, 4-wheel drive is automatically engaged via continuously adjusted front and rear electric motor torque under hard acceleration (both from a standstill and through the gears), when driving through corners and whenever the front wheels lose traction.

Moreover, during deceleration and under braking, the engine switches off and both high-output electric motors act as high-output generators driven by all four wheels. This regenerative braking system optimises energy management in the new RX400h’s Hybrid Synergy Drive system by recovering kinetic energy (normally wasted as heat under braking and deceleration) as electrical energy for storage in the high performance battery. Furthermore, battery power level is constantly managed via the engine driven generator to obviate any requirement to recharge the system from an external source.

Vehicle Dynamics Management

In conjunction with the new RX400h’s Hybrid Synergy Drive system, handling and driving stability have been further enhanced through re-tuned suspension, specially designed EPS (Electronic Power Steering) and the installation of the most advanced vehicle stability control system, the Vehicle Dynamics Management (VDM).

The new VDM system is less obtrusive than conventional VSC systems, but ultimately more effective. Via high-speed “by-wire” throttle, brake and transmission technology, VDM co-ordinates control of the Hybrid Synergy Drive system, new Electric 4-Wheel Drive and ECB (Electronically Controlled Braking), adjusting both front and rear electric motor torque according to driving conditions, as well as stabilising vehicle behaviour when low traction surfaces such as snow are encountered.

A full hybrid capable of operating in both petrol or electric modes alone as well as a combination of both, the RX400h’s Hybrid Synergy Drive offers a unique combination of high performance, quiet, seamless progress, frugal fuel consumption and ultra-low CO2 emissions, re-defining the premium SUV segment and establishing Lexus as the pre-eminent marque in the production of luxury hybrid vehicles.

Preliminary technical specifications RX400h

ENDS