Ever hear of the government's Corporate Average Fuel Economy (CAFE) regulations? First enacted by Congress in 1975 in response to the oil embargo of the era, it sets fuel economy standards for passenger cars and light trucks sold in the United States. CAFE regulations will climb rapidly by 2016, with requirements calling for 42 mpg for passenger cars and 26 mpg for light trucks, for an average of 35.5 mpg.
Now the Consumer Federation of America is urging President Obama to take it even further, looking for a mandated overall average of 45 mpg by 2020. While most manufacturers say this is an obtainable goal, it won't be easy. These improvements won't come from a focus on one system, but in little improvements in every area of vehicle design.
Weight Reduction
Reducing the weight of a vehicle reduces its rolling resistance, and that results in improved fuel economy. Lowering empty vehicle weight also allows engineers to use smaller engines, adding further to the overall efficiency. The problem with focusing purely on weight, however, is the consumer's desire for vehicles with plenty of room and loaded with a mixture of convenience features.
While many manufacturers are incorporating materials like magnesium, carbon fiber and ultra high strength steel (UHSS), aluminum has made the biggest inroad. According to the Aluminum Association, Inc., industry experts predict that aluminum ranks as a “top option” in meeting the federally mandated fuel efficiency requirements.
Currently, aluminum components make up an average of 8.6 percent of a 2009 model vehicle's curb weight in North America, up from just 2 percent in 1970 and 5.1 percent in 1990. More than 50 vehicles produced in North America contain more than 10 percent aluminum content.
Honda and BMW are the aluminum leaders, using an average of nearly 340 pounds of it per vehicle. General Motors, Toyota, Hyundai and Volkswagen aren’t far behind. The largest driver of aluminum use is the development of aluminum engine blocks, like the Chrysler Pentastar 3.6. Aluminum also is used for cylinder heads, transmission cases, steering components, even hoods, with more than 22 percent of the vehicles made in North America so equipped.
Body engineers surveyed by the association predict that 25 percent of the mandated fuel efficiency improvements will come from weight reduction, while powertrain engineers predict a 50 percent gain from weight reduction as more aluminum blocks are incorporated into their designs.
And it's good for the environment, with nearly 50 percent of the aluminum used in automotive applications originating from recycled stock.
Transmissions
New transmission technology is another factor in improved efficiency. Power from the engine has to pass through the tranny before it gets to the rear wheels, and power lost in the process is an area engineers seek to improve. In addition, every engine has its “sweet spot” where it is most efficient, and keeping the engine in that range under a variety of driving conditions will also lead to improved fuel usage.
Manual transmissions always have been considered more efficient than automatics, but many drivers shy away from them for obvious reasons. The new Dual Clutch manual transmissions could change their minds.
PAGE 2Essentially, DCT transmissions are like having two manual transmissions working in parallel, with each having its own clutch. Ford, for example, is equipping many of its 2010 models with its PowerShift 6-speed DTC. According to Ford, the PowerShift can improve overall fuel efficiency by nearly 9 percent, depending on application, and has stated a commitment to equipping nearly 100 percent of their model lineup with these transmissions by the 2013 model year.
The PowerShift has the odd gears on one shaft and the even on the other. Using electronic controls, shift feel is equivalent to an automatic as one clutch disengages and the other engages. Dry clutches are used on North American models, and the unit weighs 30 pounds less than the 4-speed automatic used in the Ford Focus.
Don’t count automatics out, though. New designs, like those offered by Mercedes-Benz, incorporate as many as eight speeds. Combined with improved electronics, shifting is seamless, almost imperceptible to the driver, with shift transitions occurring in less than 200 milliseconds. Further improvements also reduce power loss through the transmission, boosting fuel economy.
Engine Robbers
Take a look under the hood at all those components that are driven by the engine, by belt or otherwise. All of them take away horsepower that would otherwise be used to drive the wheels.
The Mobile Air Conditioning Society (MACS) says that some fixed displacement A/C compressors can require more power from the engine than the car does, cruising down the highway. If you’ve been keeping up, you've seen compressor size and system capacities going down and an increased use of variable displacement and electric drive compressors. All of these designs reduce the power drain from the engine.
Electronic steering assist is also becoming more common. Rather than run a hydraulic pump continuously, these systems only use power as needed. You’ve seen those systems with the motor attached to the column. But keep an eye out. New designs are moving the motor to the rack.
Improvements are being made in alternator design. One of many examples is Bosch’s recently introduced Efficiency Line of automotive alternators, which claim efficiencies of up to 77 percent. That means the same electrical power being generated using less mechanical energy from the engine.
According to a Bosch news release, fuel efficiency increases of up to 2 percent over previous designs can be achieved. Along with their improvements in the alternator design, Bosch is working on intelligent power management systems that would first determine the total electrical output capacity of the vehicle, and then determine the amount of energy demanded by the various electrical systems. Based on that information and using a priority matrix, the system would selectively shut power off to the users, reducing the load on the charging system. Reducing that load further reduces energy demand on the engine, and that means better fuel economy.
PAGE 3Rolling Resistance
Vehicle weight, road speed, caster and camber settings, tire pressure, even the tires themselves, all are variables that impact a vehicle’s rolling resistance. Lowering rolling resistance means it will take less energy to move the vehicle down the road.
Goodyear is one manufacturer that has designed a tire that offers lower rolling resistance than conventional tires. In fact, Popular Science just recognized the Goodyear Assurance Fuel Max tire as one of its “100 Most Innovative Products of the Year.”
The key is in the tread compound, using silica to replace, in whole or in part, the carbon black used in the past. Goodyear claims in its press release that the new tire design reduces rolling resistance by 27 percent and can improve fuel mileage by up to 4 percent over its standard Assurance tire.
Other tire manufacturers, like Michelin, also offer these “fuel saver” tires. Michelin claims better braking is possible as an additional benefit with the updated tread compound of its Energy Saver design.
Aerodynamics
Remember the old Triumph TR7? It was marketed with the slogan, “The Shape of Things to Come,” promoting its aerodynamic design. The truth is aerodynamics play an important role, especially at highway speeds. The dilemma is in the styling, though, as consumers want vehicles that look unique. If not, we’d all be driving cars that were shaped like the Toyota Prius (with a low coefficient of drag, or Cd, of 0.25) or its aerodynamic cousins, the Honda Insight and Chevrolet Volt.
Even with the limitations, reducing drag and increasing the Cd is an ongoing engineering focus. Beginning in 2008, the EPA fuel economy testing procedure incorporated a high-speed (approximately 80 mph) component and meeting fleet fuel economy mandates will include improvements in this area as well. All that undercar plastic you see when you’re doing that oil change is just one technique in reducing drag. Others are more subtle, like changing the sculpture of the side view mirrors or adding a spoiler to the rear roof.
According to engineers quoted in the SAE publication, Automotive Engineering International, an improvement of 50-60 points (0.36 to 0.30 Cd, for example) can improve fuel economy by up to 1 mpg.
Improving fuel economy is not a matter of large gains in one area, as you can see. Rather, the engineers designing tomorrow’s cars are looking hard at every aspect of vehicle design to garner small improvements — that is, a little here and a little there!
