GoAuto 22/12/2006

IT would take approximately 3.3 million years – give or take a few million - to recoup in fuel savings the extra $19,300 you’d pay for a Lexus RX400h over a conventionally engined Lexus RX350. But you’d at least have a lot of fun watching the multi-coloured electronic digital displays on the instrument panel in the meantime.

The boldness with which the Japanese luxury car-maker has embraced hybrid technology is highly applaudable – and if anybody was to engender confidence in their ability to produce reliable cutting-edge technology, Lexus is undoubtedly first on a short list – but the benefits to the consumer are difficult to measure in purely pragmatic ways.

Lexus says the RX400h will return an average 8.1L/100km, which is a lot better than the RX350’s 11.2L/100km and certainly also to be applauded, even if in reality the figure we achieved on test was always hovering around 9L/100km or so according to the trip computer.

Perhaps more importantly, less fuel consumed means fewer exhaust pipe pollutants – Lexus says C02 emissions are about 58 per cent of a regular petrol engine doing the same job - although once again the reduced exhaust emissions come at some cost, such as the manufacture of the monster battery sitting under the back seat and its eventual need for disposal some ten years or so down the track.

Justifying the RX400h in normal terms is a little difficult, although Lexus expects the same factors that are driving the incredible growth of diesel in Australia could come into play here – to the tune of maybe 60 per cent of demand for the new hybrid coming from the diesel luxury SUV segment where BMW, Mercedes-Benz and Audi are all significant players.

Perhaps that’s the best way to get a handle on the RX400h. According to the figures it’s as economical as a good turbo-diesel (in fact Lexus says better, by as much as 14 per cent, than competing luxury SUV autos) yet if offers a silent experience on the road and a clean one at the fuel pump.

The principles behind the RX400h are pretty familiar and well proven within the Toyota family now, beginning with the front-drive Toyota Prius and more recently showcased in the impressively powerful rear-drive Lexus GS450h.

But the RX400h goes a few steps further than either Prius or GS450h by adding all-wheel drive into the mix in a system that does away with a driveshaft to the rear wheels because they can be powered by their own electric motor.

So where the Prius and GS450h employ one electric motor to kick in and help the regular petrol engine, the RX400h has two – one for the front wheels as part of the planetary gearbox system also involving the petrol engine, and one for the back wheels exclusively (there are actually three electric motors in RX400h – and two in Prius and GS450h – because there’s also one used to power-up the engine).

Like the other hybrids in the family, the RX400h apportions its various power flows – out of the petrol engine, out of the electric motor and back into the battery via power generation from the petrol engine, deceleration and regenerative braking – via a planetary gearbox that has also been cleverly configured to operate as a constantly-variable (CVT) transmission.

Thank goodness the rear wheels are looked after independently because it would have been a mechanical nightmare working all-wheel drive into it as well.

So there’s always something going on within this complex system, as the driver can see by actuating the colourful display panel that also houses the standard satellite navigation.

But, like the Prius and GS450h, the driver can also choose to be blissfully unaware of all this and simply drive the RX400h like a regular SUV, unaware that the back wheels are occasionally being brought into action to assist traction, and that at times the petrol engine is switched off altogether as the Lexus glides through the side streets purely on electric power.

About the only thing that takes getting used to is the fact that, most of the time provided the battery is sufficiently charged, switching on the ignition will produce nothing more than silence from under the bonnet unless the A/C compressor is working.

This can be a bit unnerving at first as you select drive and there’s nothing prompting you say the car will start to move as soon as the accelerator is depressed. But start it does, often with the V6 remaining static when moving forwards and nearly always when being backed out of a parking spot.

With all three engines contributing their bit, the RX400h is able to unleash a healthily dose of torque, and therefore acceleration, when asked. It will reach 100km/h., according to Lexus, in a pretty rapid 7.6 seconds but, because it’s a fair bit weightier than the GS450h and because total power and torque are trimmed back to better suit SUV requirements, the RX400h doesn’t have the same massive surge as the sedan. But it’s impressive nonetheless and we’d challenge any driver to pick when the rear electric motor (MGR) comes into play.

The hybrid RX gets a different – electric – steering system to that used in regular petrol models, chiefly because it was the only practical way to maintain power assistance without the engine running.

A side benefit is that the RX400h therefore gets the Lexus Vehicle Dynamics Integrated Management (VDiM) system where the steering is written into the stability control system and intervenes to apply minute corrections that help keep the vehicle on line if it errs towards over or understeer.

Speaking dynamically, the RX400h, like the RX350, is a comfy SUV first and a sporting SUV second. There’s not too much wrong with the way it handles but you’re never encouraged to have a go on that tight and winding mountain road.

And the seemingly long-travel, all-corner MacPherson strut ride feels less cushy and absorbent than we recall in earlier RXs.

But the seats are comfy, there’s ample room for five in a well-lit and airy cabin, as well as a spacious load area behind the three-piece 40/20/40 split-fold rear seat.

When we mentioned earlier that the RX400h is nearly $20,000 more expensive than the regular petrol model, much of that is explained by the longer list of standard equipment.

The close to $100,000 Lexus SUV ($10,000 above the similarly-equipped Sports Luxury version) gets a comprehensive list of safety equipment including front and front side airbags, full-length curtain airbags and another to protect the driver’s knees.

There’s nothing to add in terms of cabin comfort where full-leather trim (very light-coloured and easily marked), power (and heated) front seats with driver’s side memory, climate-control air-conditioning, rearview camera, power tailgate, active Xenon headlights, glass sunroof and a potent 11-speaker Mark Levinson sound system with an MP3/WMA-compatible six-disc CD stacker are all standard.

As we said earlier, the RX400h is decidedly a beneficiary of the Lexus badge. Put the same technology into just about anything else and buyers would be more than shy in taking the near-$100,000 plunge, especially with the availability elsewhere of proven turbo-diesel technology.

As it is, the whole thing s comes down to: a how environmentally responsible SUV buyers are inclined to be and, b how much does a measurable saving in fuel consumption mean to those spending so much on a new vehicle mean anyway?

Lexus should have the answers to those questions in the next few years.