FIRST DRIVE: Mercedes-Benz S400 Hybrid

Mercedes-Benz S400 Hybrid

The lithium limosine hits the road at last

What's this?
Mercedes-Benz's first gasoline-electric hybrid model, the S400 Hybrid. It's planned to go on sale in North America in September just prior to the arrival of Mercedes-Benz's second hybrid model, the ML450 Hybrid, in US showrooms.
Pricing hasn't been announced just yet but Mercedes-Benz is already hinting at a sticker close to the S550's $90,225. Ouch! Still, the S400 Hybrid looks likely to end up being a good deal cheaper than the more comprehensively equipped Lexus LS600h, which retails for $105,885.
The S400 Hybrid is a mild hybrid. That means it can run on gasoline or a combination of gasoline and electric power depending on the driving conditions and charge of the battery. What it doesn't possess is an ability to run exclusively on electricity. So don't expect any zero emission hype from this latest Mercedes-Benz model.
It is based around the S350, and like all new S-class models benefits from a mid-life facelift that provides it with a smarter appearance thanks to some detailed changes up front and new tail light graphics. It also gets some slight revisions to the trim inside, but they are all rather minor compared to the tinkering that has gone on with the drivetrain.
Sitting up front is a reworked version of Mercedes-Benz's 24-valve 3.5 litre V6 gasoline engine. Strangely, it's not the new direct injection engine that goes into the E350 CGI and is claimed to deliver even better fuel consumption. Rather, it's the older multi point fuel injected unit running a slightly higher 11.7:1 compression ratio than it did previously. Peak power is 279bhp, while torque extends to 350Nm between 2400 and 5000rpm.
The efforts of the gasoline engine are backed up by a disc shaped AC electric motor that's mounted between the gasoline engine and the S400 Hybrid's standard seven-speed automatic gearbox. It delivers 20bhp and muscular 160Nm the moment the magneto is engaged. Owing the specific characteristics of Mercedes-Benz's hybrid system, however, you can't just take the numbers and add them together to get an overall output. That's because the torque produced by the electric motor begins to trail off following an initial burst of thrust. As such, the S400 Hybrid possesses an overall 299bhp and 385Nm of torque.
Supplying energy in the form of electricity to the electric motor is a lithium ion battery that uses the very latest nickel-cobalt-aluminum charging process. It's mounted up front underneath the hood in a position that is usually reserved for the S-class’s standard lead acid battery which leaves the packaging of the rear wheel drive S400 Hybrid unchanged over other S-class models. All up, the battery weighs 60 lbs. But with all its various cables and other ancillaries the weigh gain over the S350 is put at 165lbs at 4310lbs in short wheelbase form. The long wheelbase model gains a further 55lbs at 4363lbs.

How does it drive?
Superbly. For a start, there's no need to learn how to operate the S400 Hybrid. You just get in, crank the key as usual, disengage the electronic hand brake, brush the throttle with your right foot and move off as you would in any of the new S-class models. The added low end torque serves to provide it with a relaxed feel in an urban driving environment, mainly because the gearbox isn’t continually forced to find a new ratio in the stop and go of urban traffic.
The gasoline engine cuts out completely as you coast to rest at speeds below 9mph as part of a range of fuel saving measures incorporated on the S400. It then springs back to life when, ready to move away, you lift your foot from the brake pedal. It’s an odd feeling, sitting in silence waiting for the lights to change to green. However, any anxiety quickly subsides because the gasoline engine is fired by the electric motor rather than the usual starter motor. Being more powerful, it leads to a start up process that’s noticeably smoother and a lot more rapid than in the S350.
Accelerating away from the traffic lights it feels a touch more powerful than the S350 – up to around 30mph, say. However, there's not much between the two in overall performance terms: Mercedes-Benz claims a 0-to-62mph time of 7.2sec for the S400 Hybrid and 7.3sec for the S350, while top speed for both is 155mph.
At kick down, the electric motor doesn’t help that much; it’s real purpose is to complement the gasoline engine rather than replace it. So, while the 3.5 litre V6 lacks for outright go under 2000rpm, it is here where the electric motor has been conceived to deliver its best. It’s all about providing an optimal balance in power delivery. Keep your foot planted and the contribution of the electric motor fades and the efforts of the gasoline engine are extended.
At cruise, there are few tell tales signs to signal that you’re behind the wheel of a hybrid. As with all S-class models, the S400 Hybrid possesses extraordinary straight line stability. We got the chance to run it all the way up to its limited 155mph top speed at one point on the autobahn heading south out of Stuttgart. At which point it felt superbly planted and eager for more. Progress is also hushed in the best of S-class traditions. It’s only the appearance of a charge indicator in the centre of the instrument binnacle that really gives the game away.
With this kind of driving the lithium ion battery is quickly drained of energy. It gets its charge from regenerative braking rather than the engine, which makes for a much simpler and cost effective system than with a full hybrid like that found in the LS600h. Mercedes-Benz’s claims that it has developed a battery with extra fast recharging capabilities. And indeed, after a few stabs of the brakes it quickly recovered its charge.
The brakes operate via a new mechanism, which has robbed them of feel compared to other S-class models. The modulation seems to vary depending on the charge of the battery. When it is low, the first degrees of pedal travel are aimed at providing regenerative braking, and only when you apply more pressure do they operate to pull the car up. When the battery charge is high, you get full braking performance from the get go. If there’s one areas where the S400 Hybrid needs improving it is here.

Bottom Line
Mercedes-Benz has taken a typically cautious approach to the introduction of hybrid technology to its production car line-up. The S400 Hybrid is fairly straightforward – much simpler than the LS600h, for example. But that doesn’t mean it is found lacking in any way.
For, just like the rest of the facelifted S-class line-up, if feels tremendously well engineered. Performance is acceptable, if not dazzling. Refinement is truly outstanding. But while its claimed consumption of 29.8mpg is a worthwhile 6.3mpg up on the S350, it still fails to get the better of the S350 CDI, whose excellent 235bhp 3.0-litre V6 common rail diesel engine endows it with an even more impressive 30.9mpg.
For cashed up early adopters - presuming there are still a few about in a world left reeling from the effects of the credit crunch, the S400 Hybrid is going to be hard to resist. If only for purpose of image alone.

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