A buffet of canny tweaks to improve your car's mileage

Under the shapely sheet metal and ultraglossy finishes of the vehicles introduced at the auto show here were technical details just as captivating as the visual attractions.

The advances ranged from minor interior convenience features to entirely new approaches in structural design.

Given tightening fuel-economy standards and shifting buyer preferences, it was no surprise that automakers brought more electrics and hybrids to the show, and this year there seems to be a growing recognition that plug-in hybrids are a logical transition to wider acceptance of battery-powered vehicles.

Still, the move is gradual, and the industry displayed a philosophy that might be best described as less of this and more of that: less displacement in conventional engines and more power per liter; more miles per gallon and less power-robbing friction; less weight and more transmission ratios to keep engines running in their sweet spot.
Here is a look at some emerging engineering trends at the show:

Lightweight luxury

Like Mercedes-Benz SL sports cars of the past, the 2013 SL550 showcases the automaker’s technical prowess. Among its innovations is a body that is almost entirely aluminum – and 308 pounds lighter than that of the previous model.

Numerous forming techniques and welding technologies are employed in creating the structure. Gunter Fischer, programme manager for the SL-Class, said the body, which was seven years in development, sets a benchmark for torsional rigidity among roadsters.

Trans-Atlantic sharing

With Fiat in control of Chrysler, the two companies are increasingly functioning as one. The partnership has yielded dividends in the form of the Dodge Dart compact, which is built on a longer, wider version of Fiat’s Alfa Romeo Giulietta platform – underpinnings that will be used as a starting point for various compact Chrysler products.

Existing platforms are used to make a wide variety of vehicle types: According to a Buick spokesman, Phil Colley, GM’s global small-car platform was used as the basis for the Chevrolet Sonic subcompact and the Buick Encore crossover introduced here.

Plugging in

Ford’s 2013 Fusion Hybrid upgrades to a lithium-ion battery pack – the current model is equipped with nickel-metal-hydride batteries – and a 2-liter 4-cylinder engine will replace today’s 2.5-liter 4-cylinder. The smaller engine produces less power, but fuel economy improves, to 47 mpg in town and 44 on the highway, compared with the previous model’s 41/36. The Fusion Energi plug-in hybrid, using the same 2-liter engine, is expected to deliver 100 mpge (the electric equivalent of fuel economy).

According to Ford, this is 8 mpge better than the Chevrolet Volt. Ford also introduced a plug-in hybrid version of its C-Max compact crossover; Honda, Volvo and other automakers will follow the path of the Toyota Prius plug-in to showrooms.

Unlikely pairing

The E300 BlueTec Hybrid sedan from Mercedes-Benz upends standard practice by combining a diesel engine (a 201-horsepower 4-cylinder) with a 27-horsepower electric motor. Fuel economy is estimated at 56 mpg on the European test cycle. For now, the car will be available only in Europe.

With diesels being more efficient than gasoline engines, one might think such a pairing optimises the hybrid powertrain. But the traditional match-up of a gas engine and an electric motor is a happy one in that an electric motor provides maximum torque from zero rpm. Torque from the gas engine peaks at a relatively high speed, while diesel engines generate maximum torque at low rpm, so there could be a personality clash when diesels and electric motors meet. Even so, the Stuttgart engineers are not alone in thinking this marriage can work; Volvo will introduce a diesel-electric hybrid in Europe combined fuel economy at 45 mpg and 0-to-60 mph acceleration times at less than nine seconds.

Because turbocharged engines can be tuned to deliver power over a broad range of speeds – this one generates 184 pound-feet of torque from 1,400 to 3,500 rpm – and electric motors produce maximum torque at startup, this should prove a happy union. A 7-speed dual-clutch automatic transmission keeps the engine in its power band.

The Jetta Hybrid has a clutch between its electric motor and gas engine, so the vehicle can be driven from a stop using just electric power – up to 31 mph. The clutching mechanism allows the engine to shut down when not needed, as when slowing for a stoplight or cruising. An example of what is rapidly becoming the de facto configuration for small gasoline engines could be found in the engine bay of the Cadillac ATS sedan: a 2-liter 4-cylinder engine that incorporates twin-scroll turbocharging, direct fuel injection, a relatively high compression ratio and low-friction internal parts.

The engine is Cadillac’s first 4-cylinder in more than 20 years. Here, the leading-edge technology translates to 270 horsepower and highway fuel economy estimates of more than 30 mpg. The engine layout is similar to those arriving from many automakers, including Mazda, Ford and, most recently, Honda.

Divide and conquer

Typical of the latest turbocharged engines, the 201-horsepower 4-cylinder of the Hyundai Veloster Turbo is equipped with a twin-scroll turbocharger. By splitting the flow of exhaust gases between two passageways, twin-scroll turbos isolate cylinders whose exhaust pulses interfere, reducing the delay in building pressure to make the engine more responsive.

Direct delivery

Hyundai says that the use of direct fuel injection, variable valve timing and variable intake tuning in the Genesis Coupe’s 3.8-liter V-6 produce net gains of 42 horsepower and 29 pound-feet of torque. Peak horsepower is now 348; torque tops out at 295 pound-feet.

Direct fuel injection sprays fuel into the engine’s cylinders, rather than the passageways farther upstream, improving the precision of its delivery and providing some cooling effect. The cooling enables higher compression ratios and more turbocharger pressure, both of which increase power output. Direct injection is key to the power and efficiency of many modern engines, including Mazda’s Skyactiv-G 4-cylinder and Ford’s EcoBoost engines. The technology is not new, but it was not practical until on-board computers made exact control possible.

Doing without a throttle

The new Dodge Dart uses Fiat’s MultiAir 2 valve-throttling system in two of its available 4-cylinder engines (one of which is from Fiat). Like the Valvetronic system that BMW pioneered 10 years ago, MultiAir 2 uses the engine’s valves rather than a throttle plate to control air coming into the cylinder under certain conditions. Power losses resulting from the engine having to pull air past the throttle are reduced, and engine efficiency is enhanced.

Double-clutching

Another benefit of Fiat’s ownership comes to Chrysler in the form of Fiat Powertrain Technologies’ dual-clutch 6-speed transmission. Volkswagen pioneered dual-clutch transmissions in production cars nearly a decade ago, but they have only recently become common. This technology offers automatic shifting but provides better efficiency than conventional automatics because it assures a no-slip mechanical coupling of the engine to the gearbox rather than a fluid coupling.