2020 Vision: How To Make a 35mpg Car |
 One of the most significant cars at this year’s Geneva Show largely went unnoticed among the glittery concepts and new model launches. That’s because it looked just like a regular 2008 Mercedes-Benz C-class. But this particular C-class is worth a closer look, because it shows what it’s going to take for automakers to meet the 35mpg CAFE regulations coming in 2020.
Using a combination of engineering strategies Mercedes-Benz bundles under the name BlueEFFICIENCY, this C-class gets a claimed 36.2mpg (U.S) on the standard combined European fuel consumption test, on regular gasoline. By comparison, the entry-level C300 currently sold here in the U.S returns 18mpg to 25mpg according to official EPA numbers.
That’s some improvement. But how exactly did Mercedes-Benz engineers get a C-class from 2008 to 2020?
First, they put it on a diet, shaving off between 40 and 70lb. A newly developed laminated windshield uses a noise-reducing plastic membrane bonded between two planes of glass, which means its overall thickness can be reduced, saving 2.6lb. The weight of the noise insulating material on the firewall has been reduced 20 percent. And new 16in forged alloy wheels save a total of 15.4lb.
Next, they attacked rolling resistance. Mercedes says rolling resistance – caused primarily by the deformation of the tire as it contacts the road surface – has a greater effect on fuel consumption than aerodynamic drag up to 60mph. New tires developed with Michelin reduce rolling resistance 17 percent, and are almost a pound lighter each than regular tires thanks to a new steel belt design. 
Above 75mph aerodynamic drag accounts for about 50 percent of the total dynamic resistance a typical sedan must overcome. The regular C-class has a very competitive drag co-efficient of 0.27, but by adding smooth underbody cladding to reduce turbulence, partially blanking off the grille to reduce the airflow into the engine compartment, sealing the joins between the hood, headlights and bumpers, lowering the suspension half an inch, and ensuring the wheels and the mirrors were aerodynamically optimized, the engineers were able to improve the drag co-efficient seven percent, to 0.25.
To reduce friction losses the regular power steering assembly was fitted an additional valve that switches off the servo pump when it senses the car has been travelling in a straight line for a time. Mercedes says this small modification improves gas mileage by about two percent. A new taller final drive features improved bearings, forged gears and lightweight construction to reduce friction and cut engine revs while cruising. The biggest change is under the hood. In place of the 228hp 3.0-liter V-6 we’re used to is a 1.6-liter turbocharged four that develops 154hp at 5200rpm. Max torque is 169lb-ft at 3000-4500rpm, compared with 220lb-ft from the V-6 at 2700rpm. Oh, and you need to shift the gears yourself – standard transmission is a six speed manual with an overdrive top gear. An indicator on the dash signals the optimum moment to shift gears to save gas.
So, the 35mpg car – a reasonably sized, gasoline powered 35mpg car, not a sub-compact – is certainly doable. But we’re going to have to make compromises. Say goodbye to big engines and performance (the BlueEFFICIENCY C180 Kompressor is about two seconds slower than the C300 to 60mph, according to Mercedes). Say goodbye to big wheels and tires – they add weight and increase rolling resistance. And you might have to get used to shifting gears again. 
One thing is likely to stay the same, though – price. That’s right, by the time 2020 rolls around, don’t expect your 35mpg car to cost any less in comparative terms than the regular car you’re driving now. The additional cost of the lightweight materials and technologies, plus the engineering work required to achieve 35mpg, will be passed on to consumers. And in a market where every automaker will be selling cars with smaller engines and reduced performance do you really think they are going to charge you less for less?
Not a chance. |
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