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Lexus LS600h Roadtest

A technical tour-de-force that sets definitive standards in the premium sector, the flagship Lexus nonetheless achieves the leaner side of luxury.

The 5.0-litre V8 engine is every bit as complex as the car it powers

"Oi! Wake up!" With a roll-up stuck to her lip, and her wig over one eye, my partner nudges me awake each morning with her walking stick. "Get up," she urges, "It's 'arf pass ten, and the goat wants feedin." I've asked her not to refer to my mother in that way but charm is not one of her strong points.

On the other hand, the Lexus 600h wakes you up with a polite buzz and a dab of the brakes. Well, not so much wakes you up, as alerts you: alerts you to an obstruction ahead of the car, which it knows you are unlikely to have seen as you were looking in the wing mirror at the time. It does so by monitoring your face through a camera mounted on the steering column, and if it detects that your head has turned by more than 15 degrees away from the road at the same time as stereo cameras pick up an obstruction ahead, the system alerts you in the manner described.

This so-called Driver Monitoring System (DMS) is just one of the many active safety devices that make the extraordinarily complex Lexus 600h even more extraordinary. The DMS proximity sensors employ near-infra-red wavelengths, which means that they also work at night, and are sensitive enough to detect pedestrians and animals.

Elements of this system also contribute to the Adaptive Cruise Control, which has been developed to the point where it now works in stop-start traffic. In those conditions, it can bring the vehicle to a complete standstill, and restart it when the car ahead moves off. Thankfully, the range is adjustable, so you can prevent its allowing a Transit to slip into the gap. Even so, I found the slight hesitation a little disconcerting.

The sensors are also linked to the Advanced Obstacle Detection System (AODS), which, in turn, forms part of the Pre-Crash Safety System (PCS). If AODS detects a hazard in front of the vehicle, PCS measures the position, speed and trajectory of the obstacle to determine the collision potential. If a crash seems likely, PCS pre-tensions the brakes, changes the steering ratio to exaggerate steering input, and stiffens the suspension.

All of this comes under the watchful eye of the Vehicle Dynamics Integrated Management (VDIM) system, which, says Lexus, is unique in that it can perform several interventions simultaneously, whereas other mechatronic systems can handle only one intervention at a time and therefore take longer to respond. In short, VDIM does everything in its considerable computing power to stop your having a crash.

And no matter how complex this all may seem, I can assure you that I have spared you the finer detail.

Yet fine detail underwrites the whole Lexus ethos. The 5.0-litre V8 engine is every bit as complex as the car it powers, and is assembled and tested in a manner that makes Volkswagen's fabled detailmeister seem comparatively slapdash. For example, an engineer listens to each and every engine with a stethoscope in order to ensure that there are no abnormal noises. And an accelerometer is used to measure the crankshaft speed at either end to check for torsional twist under heavy acceleration. And forget measuring tolerances to the nearest thou': a computer checks to the nearest micron - that's a millionth of a metre, or 0.000001m.

Unique Among Hybrids In That It Incorporates Four-Wheel Drive

But that's only the half of it. The Lexus 600h has not one engine, but two. Or rather, it has an engine and an electric motor, working in tandem to deliver improved fuel economy and reduced emissions. Unlike the Honda hybrid system, which uses an electric motor integrated with the engine block, the Lexus uses quite separate units, driving simultaneously through a planetary gearbox, which merges the combined outputs into a single drive to all four wheels via a CVT gearbox.

And here, the Lexus is unique among hybrids in that it incorporates four-wheel drive, which is biased slightly towards the rear to eliminate understeer.

Unless you accelerate hard when pulling away from standstill, the traction motor does all the work. That means zero emissions, and zero sound signature. As the car speeds up, so the engine begins to take over from the motor until it eventually is doing all the work and the motor is effectively disengaged.

On overrun, or during braking, the motor becomes a generator, when it both aids braking and charges the battery. This is known as regenerative braking. Any surplus power from the engine is also used to charge the battery, so there is generally sufficient charge for the traction motor alone to propel the car for short distances at modest speeds. To achieve this state of grace takes a little practice but with a light touch on the throttle, a few hundred yards or more are generally attainable at town speeds.

In stop-start motoring, the engine usually cuts out when the vehicle comes to a halt, and remains idle until it automatically re-starts when the car reaches around 15-20 mph, or when the battery output drops below a pre-determined level. The extent to which the motor intervenes can be controlled by a toggle switch on the centre console. The self-explanatory settings are Hybrid, Power and Snow.

The battery and its associated control elements are tucked behind the rear seats, where they impinge on the boot space, and earn the Lexus its only black mark. And because it's not possible to tilt the rear seats, what you see is what you get - less than 12 cubic feet.

The petrol engine has a rating of 389 bhp, and the motor, 221 bhp. These are not cumulative and so the maximum output is a combination of both, namely 439 bhp. Like all such devices, the electric motor exerts maximum torque at zero revolutions (which is why washing machines don't need a clutch), and therefore makes its greatest contribution at low revs - some 300 Newton metres being on tap to aid acceleration and mid-range response. The engine delivers 500 Nm and the combined (not cumulative) effect results in a 0-62 time of 6.3 seconds, en-route to a limited maximum speed of 155 mph.

Needless to say, hybrid drive has a noticeable effect on fuel consumption, and this 5.0-litre, 5-metre, two-and-a-half-tonne car achieves a combined fuel consumption of 30.4 mpg - a consumption way beyond the reach of an equivalent petrol-only premium saloon. A CO2 rating of 219 g/km means that the 600h avoids the Band G VED rating, and instead it falls into Band F, which means a more modest annual bill of £205. And its hybrid status means that the Lexus is exempt from the London congestion charge. Even though it takes up the road space of about four smarts - that's a total charge of £32 in Kengeld - the Lexus is charged not a single penny.

Extraordinary Technology

That might help offset the £81,400 sticker price for which you get every imaginable extra. The 600h is a technophile's dream car, and the standard specification reads like a what's what of gadgets. It puts ticks in boxes for which most cars don't have boxes.

For example, roof-mounted sensors measure the ambient temperature of each occupant, and adjust the four-zone air-conditioning accordingly.

And then there is the self-park. Just like the Prius, the Lexus is capable of parking itself. Sensors measure the space, then take charge of the steering to ensure that it slots into the space in text-book fashion. All the driver has to do is ensure that the car is not reversing at more than 2.5 mph. That's the theory, at least. In practice, it takes practice, and I would give it five out of ten for effort. And it takes time, so its use is not recommended on a busy road. But you can choose between parallel and series parking, so it is meant to work in supermarket car parks, too. A colour reversing camera helps you keep an eye on things, and an array of sensors bleep their various warnings if someone happens to step into the target zone. And you could always use the mirrors and do it yourself, of course.

If the kids get bored with the to-ing and fro-ing they could always lower the roof-mounted monitor and watch a DVD. And in the centre rear armrest, along with comfort controls, is a radio, which is independent of the driver's radio. Headphones for the rear entertainment module are located in recesses behind the powered rear headrests.

Given the performance of the hybrid power source, the Lexus can be considered a sports saloon. And the adaptive suspension - with three settings - and the variable ratio steering, are intended to provide handling levels concomitant with performance driving.

But luxury tends to have a calming effect, and I was generally disinclined to put the big Lexus through its paces. Unless you are in the mood for seeing off lesser mortals, it is very tempting to switch to hybrid mode and comfort suspension and let the lazy engine and seamless transmission waft you about in the manner of Ali Baba and his magic carpet. But, if you do feel like pressing on, the CVT transmission can be switched to sports mode and used like a sequential 'tiptronic' shifter.

I preferred to throttle back, and from time to time glance at the power monitor, which shows the status of the hybrid system. Get it right, and the dotted lines join the battery and wheel symbols, which means a few moments of silent motoring and zero fuel consumption. Every litre helps.

Such is the extraordinary technology of the Lexus that I could write another 1600 words and still not do it justice: there are features I have not mentioned, and technology I have not touched upon. Indeed, other luxury car-makers should look closely at the 600h and consider it a wake-up call.

Posted on 25.01.2008 by Graham Whyte
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