First Drive: 2010 Mercedes-Benz S400 Hybrid

Six years ago, I attended the Electric Vehicle Symposium in Long Beach, California, and at the conclusion of a riveting presentation by a major advanced-tech battery manufacturer, a questioner asked about the prospects of lithium-ion batteries for automobiles. The presenter was stony-faced for a few seconds — and then responded with a cocked head. “What do you mean by lithium batteries in cars?” Nickel metal hydride was then considered the cutting-edge in battery tech for hybrids, and this question about lithium-ion — provoked by its chief advocate, the late Dr. Paul MacCready, who was elsewhere in the hall — seemed beyond the presenter’s grasp. The questioner might as well have asked when worm holes in the fabric of space and time were going to let cars blink from one place to another.
Well, I’ve just driven the world’s first mass-production automobile that employs a lithium-ion battery (the lithium-ion-using Tesla Roadster being a low-production affair). No, it isn’t a full electric vehicle as Dr. MacCready would have preferred. But there, tucked in the corner of the Mercedes-Benz S400 Hybrid‘s engine bay, was a 32-cell, 120 volt, 0.9 amp-hour, lithium-ion battery about the size of shoebox.

For lithium-ion’s first foray into mass production, the finicky battery type (dogged by YouTube videos of burning laptops) is getting kid-glove treatment. The most important kindness given it is cooling, performed by the AC system’s refrigerant which is circulated by an electric motor (this required to provide air conditioning while the engine is shut down.) To give you an idea how pampered this battery is, when we asked how long it’ll endure before replacement, Mercedes’ engineers responded, “It’ll last as long as the car itself” That’s become a common claim about nickel-metal-hydride batteries, but I suspect both Tesla’s and Chevy’s Volt engineers are blanching at that proclamation being applied to lithium.
The battery provides up to a 5-sec jolt of juice (limited by the system’s heat build-up) to a thin, 20-hp motor that’s slotted between the engine and seven-speed automatic transmission in much the same fashion as Honda’s familiar Integrated Motor Assist. However, unlike Honda’s system, Mercedes’ application is truly “mild” as it can’t propel the car in EV mode at all. Consider as well that the motor’s 20 hp is being applied to a 4575-lb sedan, a 9%-higher lb/hp ratio than the Honda Insight’s 13 hp in a 2735-lb vehicle. However, also notice that the motor’s whopping 118 lb-ft of torque is a disproportionate aid to the 255 lb-ft delivered by the 275-hp, 3.5L, four-valve/cylinder, Atkinson-cycle V-6 (the system’s combined horsepower is 295, combined torque is 283 lb-ft). Mercedes openly admits this is a first step in its sedan’s hybridization, and additionally it’s one that’s constrained by the transmission’s existing dimensions and the available room in the S-Class’s crowded engine bay (no batteries in the trunk, please). By the way, it was whispered that the next generation of electric motors is likely to produce 60 hp. At three times this motor’s output, this strongly suggests Mercedes will have to adopt a clutch between the motor and engine to allow pure EV mode. Unlike Honda, which gets away with powerlessly spinning its small-displacement engines, Mercedes’ 3.5L is a lot of engine to consider free-milling.
At a stop, the engine is typically off -though there are exceptions when the system’s software deems stop-start as non-profitable, such as in stop-and-go traffic and the like. However, the contrast in interior noise and vibration between idling and engine-off isn’t particularly striking-the S-Class’s chassis is already heavily sound-deadened (this matters more in lightly constructed cars such as Honda’s Insight and Civic). Lift off the brake when the light goes green, and the engine revives instantly-with silky smoothness-courtesy of the electric motor, which is thereafter available for melding its considerable torque with engine’s. Acceleration is liquidy-smooth, capable of hitting 60 mph in an estimated 7.1 sec and a top speed limited to 130 mph. While slowing, the engine usually switches off at 15 mph and, frankly, you have to watch the instrument display’s icon representation of the hybrid’s goings on to recognize any of this.
It’s interesting to compare the S400′s efficiency with Mercedes’ own highly advanced, diesel-powered S350 CDI Blue Efficiency drivetrain (not currently planned for U.S sale). Mercedes estimates the mileage of the long-wheelbase version of the Hybrid (the version we’ll be getting in the U.S) to be 23 mpg city/33 highway (27 mpg combined), or 8.1L/100 kilometers by the European method. The slower and smaller-displacement S350 CDI achieves better fuel consumption-7.7L/100 kilometers-but greater CO2 emissions due to diesel’s higher carbon-content per liter (the hybrid generates 190 grams per kilometer versus the oil-burner’s 200). So, depending on whether you’re a mileage or CO2 fan, you might say either wins. However, remember that this S400 represents a very light dose of hybridness. It’s reasonable to project that a full hybrid edition of it would put the diesel away. On the other hand, when queried, Mercedes’ execs wouldn’t discount a future diesel hybrid. Interesting.
The S400 includes a lengthy list of non-powertrain-related changes that will appear throughout the S-Class range, including a revised nose with a pointier grille, revised taillamps that include LED brake illumination which appears in a “Double C” pattern, and a revised steering wheel containing a smaller airbag.
Among the S-Class’s astonishing electronic dazzlements are Adaptive Highbeam Assist which enlists the radar to sense to the distance of oncoming traffic, and Pre-Safe Brake which similarly detects and an impending crunch and warns you 2.6 sec before impact, at 1.6 seconds applies 50% of its maximum braking, and at 0.6 sec frantically throws out the anchor. Another feature, Torque Vectoring Brake, aids turn-in crispness via a polite squeeze of an inboard rear brake to help rotate the car. Meanwhile, Night View Assist Plus highlights any murky nighttime shapes on its screen that could be human. Also available on the S400 is the now German-ubiquitous string of LEDs framing the lower portion of the headlights.
Three nifty ingredients that wouldn’t make the S400 cut (but find application elsewhere in the S-Class range) are Active Body Control (nixed because it needs the engine operating at all times), Crosswind Stabilization (which does exactly what it sounds like), and Attention Assist, which observes the driver’s steering wheel motions (among other things) to detect impending slumber (moreover, it does this by learning each driver’s individual behavior and then, as the motions become jerky, commences to alarm you). Ah, and a rare non-electronic enhancement is Direct Steer, which amounts to a simple mechanical-based solution for variable-ratio steering keying purely off steering angle. Mercedes claims it improves steering feedback; perhaps it does. I’d need to drive it against the pervious system to tell.
Unfortunately, not coming to the U.S. at all (at least initially) are Speed Limit Assist (yes, a forward camera spots speed postings, compares them with its GPS map for reasonableness, and then reproduces the sign on the dash)-and Split View. This is a center-dash display that, if viewed from the driver’s seat, displays typical driver information, but when observed from the passenger seat can offer, say, the latest blockbuster film. It borders on out-and-out magic and works dazzlingly well. And so who are the regulatory no-fun-niks keeping it from the U.S. market?
And finally, a kicker to how this whole story began: Just before we departed from the Mercedes parking lot for our day’s drive program through the Black Forest, a technician opened an S400′s hood so we get a better look at the hardware. “Can we see the battery?” we asked. The plastic molding covering it was popped off. “It’s made by Continental” the technician instructed. “Do they make the cells?” we asked.
“No” the technician replied. “They’re produced by Saft, in Europe.
And — yes, you guessed it — Saft is the same company whose representative couldn’t comprehend the question about lithium batteries in cars, six years earlier. This technology is moving really, really fast, friends.
[source:MotorTrend]