Mercedes-Benz S400 HYBRID 2009 Review - International

Mercedes-Benz S 400 HYBRID

What we liked
>> Astounding fuel economy
>> Very few compromises in packaging or performance
>> Breakthrough tech, almost invisibly applied

About our ratings

OVERVIEW
-- low emissions to petrol party

Now, that's odd. From a rolling start, I've punched the throttle on the new Mercedes-Benz S-Class right down to the carpet to bring its bulk up to speed. It has accelerated firmly, though not quite aggressively. It has accelerated with a curious engine note, slightly rasping and nothing like as smooth as the V8-powered S500… But neither happenstance is especially odd.

No, all this time, I've been looking at the instant fuel-consumption readout.

By rights, taking a two-tonne limo up to 100km/h should be taking something like 30-40L/100km as it overcomes inertia and swings into the traffic flow. This S-Class is giving everything it's got, punching as hard as it can punch, but it's only using 13L/100km.

But this S-Class has a secret. It might arrive as part of the S-Class facelift, but it's not just an S-Class. It's Mercedes-Benz latest hybrid (Benz also builds the US-market ML450h and hybrid trucks and buses) and it works in a completely different way to hybrids from Toyota, Lexus and Honda.

Once upon a time, Benz built S-Classes with just one engine and waited for the captains of industry to come knocking. Those days have gone. Turbodiesels are the accepted norm for an S-Class throughout Europe, but the world is changing. China is now the biggest S-Class market in the world and the Chinese understanding of diesel engines in passenger cars ranks lower only than the USA.

So, while turbodiesels are pulling down CO2 emission rates in the old world, Benz felt it needed something more to make the same leap in the rest of the world.

"There are our traditional diesel models where people like the diesel strength and efficiency and won't take anything else, like Italy, France, the UK and Germany," S-Class product manager Frank Steinacher explained.

"But in Russia and China, they don't know diesels and they want petrol. In countries where NOx is the most important emission criteria, we offer both engines. In the US and Japan, hybrid is the better option."

So Benz has finally come to the emissions-reduction party with its biggest model and its flagship. It's breakthrough technology, too, with several world firsts and dozens of patents.

Where other hybrids run massive rechargeable battery packs to drive their electric motor systems, the S400 HYBRID (Benz specifies the capitals) has the world's first in-car Lithium-ion (Li-ion) battery pack -- not unlike the one in your mobile phone. Instead of the 200kg battery pack of conventional hybrids, this one weighs 27kg and you could fit it into an RM Williams boot box (see image).

New technology does not come cheap at Mercedes-Benz. In Germany, the S400 HYBRID sells for €71,700 -- €7,700 more than the S350 (with its direct-injection petrol V6 engine) and more than €10,000 upstream of the S350 CDI diesel.

Bearing in mind that the S350 is a tenth of a second slower to 100km/h (7.3 seconds) and emits 234g/km of CO2 and that the diesel does the same sprint in 7.8 seconds and emits just 199 grams, it's a sizeable investment that demands some serious thought.

Pricing in markets like Australia is not available. At this stage there are no firm plans to build right-hand drive versions of the S 400 HYBRID. The demands of important markets such as Japan and the United Kingdom could change that situation. Certainly Mercedes insiders Down Under say they would welcome the car.

Unlike other hybrids, whose 150-200kg nickel metal hydride (NiMH) battery packs take up so much space they demand attention right from the start of the chassis sketches, the S400 H's battery pack nestles neatly inside the engine bay, right back near the firewall. It's much cheaper to produce, because it basically bolts in to the same chassis engineering as the normal S-Class range.

Also, where other hybrids sit an electric motor alongside the petrol engine to drive the wheels, the big Benz does something completely different. It sits what it calls a "hybrid module" between the back of the engine and the gearbox.

Those are the big engineering differences, but for the driver, the one enormous philosophical difference between the S400 and other hybrids is that whenever the car is moving, the petrol engine is always running and always driving the wheels. The car never runs exclusively and silently on electric power alone.

That's because Benz has thought about it from another angle. Instead of using one engine (petrol) or the other (electric), it uses a clean-burning, smallish petrol engine with not-much torque and mates that to the torque-rich, disc-shaped electric motor. The idea is that the petrol engine can do the job all by itself when it's cruising along, the electric motor can pitch in to boost the torque when the car's accelerating and whenever you coast or brake you're regenerating the battery, so it's ready to go next time you need the electric motor.

It's actually a big magneto-electric motor full of induction coils that are, in theory at least, familiar to anybody who has pulled stuff apart.

When it's needed at low engine speeds, it draws its juice from the Li-ion battery to directly drive the gearbox, which means the car only uses one drive system to turn the rear wheels and doesn’t need extremely complicated computing power to choose which engine to use and when to use it.

By itself, the electric motor has just 15kW of power, but it's got 160Nm of torque and it has it instantly. That's handy, because in its S400 guise, the V6 could hardly be described as dripping with midrange urge.

Benz has taken full advantage of this by using an Atkinson cycle engine, which fiddles around with the engine's compression ratio to produce an unusually clean burn and low emissions, but has very little torque compared to conventional engines.

It has 205kW of power, but down at the real-world end of the engine's performance, its 225Nm of torque is somewhere near normal four-cylinder outputs. But when the electric motor kicks in with its 160Nm, the S-Class's output suddenly jumps to 385Nm -- more than Benz's standard 3.5-litre V6 petrol engine.

Another 15kW to boot (220kW combined) plus this torque sees the S400 hit 100km/h in 7.2 seconds – a tenth quicker than the stock S350 V6. It runs to a limited 250km/h on the autobahn.

Even better, it uses just 7.9L/100km on the combined Euro test cycle, with 186 grams of carbon dioxide easing out every kilometre. By comparison, the S500 V8 uses 11.1L/100km and emits 258g/km of CO2.

With 90 litres of fuel capacity, the 400 should run beyond 1100km between fills, even on the highway cycles which have been the traditional handicaps of hybrid cars.

Li-ion batteries are nothing new. They're just new to cars and this is the first car in the world to use them. Everybody with a laptop computer, a mobile phone or an iPod has one. They are small, light and will take more charges without developing bad memories.

They're nothing new for Mercedes-Benz, either. Its boffins have been working to make Li-ion's advantages compatible with cars since 1992, but this is their first production version. Funny thing is that it's not even theirs. It's from heavy-hitting industry supplier Continental (which also does its breakthrough adaptive high beam system, designed to gradually creep back just in front of approaching cars to give maximum light all the time).

The battery's cells are actually from another company, called Zuft in Bordeaux in France, but the key to the whole thing is that it weighs 27kg. Add it together with the software and the electric motor and the entire system adds only 75kg to the S-Class.

And because of its compact size (and location), the Benz system doesn't rob anything from the luggage space. The battery has been tested at -35 degrees in the arctic and at 55 degrees in Death Valley and Benz has crashed "a lot" of vehicles with it. In the USA Benz will guarantee the battery for 10 years to overcome any initial suspicions.

PACKAGING
-- it’s all 100 per cent S-Class

This S-Class refuses to sacrifice any of its luxury just because some bits and pieces below decks are more eco-friendly than your average limo. It still gets everything you'd expect in an S-Class, which means an awful lot of fruit and the best seats in the business.

It's no lightweight and it's no midget. It tips the scales at 1955kg (or 2020kg in its long-wheelbase guise) and it's 5.1 metres long. Even the short wheelbase has 3035mm between its axles and, with a body width of 1871mm, luxury is still clearly an overriding factor.

Bi-xenon headlights have become standard, new bumpers and new tail lights have arrived and it's also adopted LED daytime running lights, but that's not the end of the light fantastic. The 400 buyer will have a choice of three interior 'ambient' mood light packages, ranging from a light amber, a white and an ice-blue. The amber feels warm and friendly, the blue cool and techie and the white just a bit bland.

Other hybrids tend to have their multi-media screens dominated by the power paths of their systems, but the S-Class has an even better trick. You can do that, for sure, but while you're at it, your passenger can be watching a movie on the same screen.

You can be paying attention to your satellite navigation while the passenger watches TV on the same screen. It's called Splitview and it actually works. The driver can't see anything at all on his passenger's screen and vice-versa, even though the images are being screened on the same screen at the same time.

SAFETY
-- top of its game

There is a dazzling array of software and hardware in here, including a drowsy-driver alert system, an adaptive high-beam which gradually lowers the light cone to stay just in front of the approaching car, lane assistance to warn when you're drifting out of your lane, a new crosswind stabilisation system and a development of PreSafe which now uses the cruise-control's radar to give full, emergency braking – with or without driver input – when it senses an inevitable crash.

S-Classes have long lead Benz's safety reputation and this one continues it, hybrid or otherwise.

The Adaptive High Beam and drowsy-driver-detecting Attention Assist will be dead handy in Australian conditions because they'll be coming on the [non-hybrid] S-Classes that will be coming here.

Adaptive High Beam combines cameras in the windscreen with steering sensors and software to give drivers maximum vision all the time without blinding oncoming drivers. It gradually steps the light cone back so it stays just in front of the oncoming car, reducing the traditional blind spot when the 400 metre high-beam spread drops quickly to 60 metres or so for low beam.

Attention Assist uses an ultra-sensitive steering input sensor as one of 70 parameters to warn drivers before their fatigue levels become dangerous.

Both systems were launched earlier this year in the new generation E-Class.

A new technology for the S-Class is a modification of its Active Body Control system to stabilise the car in crosswinds. While it will be optional (in Europe) on all but the V12s, it uses the ESP's sensors to detect, then negate, the disturbing effects of crosswinds and, in our experience, it's quite effective.

It also extends the range of its Brake Assist Plus system by tying it in to the short-range parking sensors. It now uses three different sensing systems – a long, narrow radar beam, a wider, shorter beam and the even-shorter range of the parking sensors -- to do wash off speed if the drivers aren't up to the job.

If it detects an object that could probably cause a crash ahead, it will warn the driver. If the warning is ignored, it will partially brake the car and, if it decides a crash is inevitable, it will automatically jump to maximum emergency braking and, at the same time, it will move the seats back, close the sunroof and tighten the seat belts.

COMPETITORS
-- sparking a civil war

"With our first hybrid model," S-Class product manager Frank Steinacher explained, "we wanted to disprove the theory that sustainable mobility is only conceivable with small cars.

"Compact cars are also important, but just not necessarily for all of our customers. Our approach is to reduce fuel consumption and emissions on all models, because many of our customers want a large, luxurious and prestige vehicle. We don't believe anybody is asking purely for an S-Class Hybrid. Customers are getting more knowledgeable about hybrid technology. They buy it because of the emissions effects and figures.

"People do not accept to not have load space in the trunk and they don't accept to carry around 200kg of technology that they don't feel a benefit from," he explained.

What Steinacher doesn't explain is that the S-Class is not the first luxury hybrid. Lexus has been at this game for years, with varying successes in different markets. In Europe, Lexus is an almost invisible brand, as it is in, ironically, Japan. So, if it's lining up exclusively against other hybrids, it's got a tiny market almost to itself.

But Benz admits its prime competition will come from within its own stable.

The barrier to right-hand drive production is simple -- the new battery sits exactly where the steering column would need to go. Benz insiders say, once the company proves the commercial viability of the concept consideration will be given to RHD solutions.

The S400's engine note is a little coarse and never feels like it brings enormous strength to the party, so the ultra-quiet electric motor can feel a bit like the wingman who gets his louder, more-obnoxious mate out of trouble at parties. That's not to say the combination doesn't work almost seamlessly, because it does. It's just that, when the engine's doing the job by itself, it never feels like a 3.5-litre V6 should feel.

It's at its smoothest whenever you stop at traffic lights because it is the first S-Class to use Stop-Start technology -- this switches the engine off when you're coasting down to a halt or are already stopped. When the air-conditioning needs help or you need to move in a hurry, it fires up again smoothly and almost instantly.

The seven-speed transmission is utterly conventional, because all of the hybrid system's work to add speed or to regenerate energy happens upstream of it, so it doesn't have to do anything in the HYBRID that it isn't already doing in every other S-Class. It's smooth and efficient and you barely ever notice it's even there.

So, apart from the ability to switch the car's display screen over to an 'energy path' screen showing when the battery is charging and when it's being drained, don't go looking around the cabin for signs that the S400 is different.

Instead, the best place to spot the differences between the S400 Hybrid and the rest of the Benz range is in the brakes.

Benz's research shows that most people brush their brake pedals a lot, usually when they want just a bit of confidence coming into a corner or when they're slowly washing off speed up to the traffic lights. What they've done, then, is they've stopped these soft brushes on the brake pedal from actually activating the brakes. Instead, a soft brush will activate the electric motor, which then generates enough resistance to make the car slow down at about the same rate.

Instead of wearing out brake pads, the S400 will recharge its battery.

It does work, and it works well, but it leaves you with a brake pedal that feels like it's got a tennis ball stuck under it. It's soft when you initially brush it, then it gets squishy before, finally, it starts to feel conventional once you're through the electric motor bit and into the actual braking stuff.

But having this as the biggest driving negative and the biggest intrusion into conventional driving techniques is some achievement. Besides this, the S400 HYBRID drives, turns, rides and handles just as you'd expect an S-Class limo to drive, turn, ride and handle.

And, what's more, it doesn't ask the driver to do anything he or she doesn't do already.

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