Canadian and U.S. government legislation requires light passenger vehicles to achieve a sales weighted corporate average fuel economy (CAFE) fleet average of 35.5 mpg (U.S) or 6.6 L/100 by 2016, a 25% increase over current levels.
It’s a major challenge, and with conventional combustion engine cars dominating North American sales, engineers will have to use every trick they can devise to make them more efficient.
Hybrids and battery electrics will contribute, but unless they gain more than their current 2% market share their impact will be small. Here are some refinements being pursued and their approximate fuel economy contributions.
Stop-start function: Shutting off the engine to eliminate idling when the car is stationary, e.g. at stoplights, is a significant contributor to fuel economy and one of the reasons hybrids do so well in the city. It does the same for regular vehicles. There are challenges such as maintaining engine-off cabin heating and cooling, and battery/starter durability, but these are being overcome. Start-stop is appearing on such cars as Porsche and Ford Fusion and is expected to proliferate. Economic gain is in the neighbourhood of 5%.
Cylinder de-activation: Called different names by manufacturers, disabling some engine cylinders either electronically or mechanically during low-load conditions such as in highway cruising mode reduces fuel use. It is used by Chrysler, Honda and others and is expected to increase – saves 7% or more.
Direct fuel injection: injecting gasoline directly into combustion chambers rather than by upstream port injection is rapidly increasing. It provides more precise timing, direction and pattern of fuel spray for more efficient combustion, although it requires much higher pressure. It also cools the combustion process, allowing higher compression ratios and sharper ignition timing. Combining it with forced induction (turbo or supercharging) such as Ford’s Ecoboost and some GM Ecotec engines can yield 10% economy gain or more.
More transmission ratios: Slower turning engines, achieved with more transmission ratios, use less fuel. As engineers anticipate highway engine speeds falling to 1000 rpm or lower during cruising mode, maintaining traditional performance with the ultra-high gear ratios required will mean more than the typical 6-speeds now used.
Porsche just released 7-speed manual (a first) and automatic transmissions, and Audi, Chrysler, Lexus, Mercedes-Benz and others have 8-seed automatics. Germany’s ZF has just developed a light and compact 9-speed that will appear in some Chrysler products and others. Savings: 10 to 16%.
Dual-clutch automatic transmissions with two clutches, one for even gears and one for odd, usually with manual selection available, are replacing the traditional hydraulic torque converter and its inherent slippage. They provide extremely quick shifts and fuel savings up to 10%.
Reduced vehicle weight is an old favourite being more vigorously pursued than ever. Audi has been a leader here (trying to compensate for that extra 4wd Quattro mass?) with an aluminum space frame in such models as the A6 and A8.
The 2012 A6 body, for example, is 32 kg lighter than its predecessor thanks to extensive aluminum. Other materials such as high-strength steel and carbon fibre are also being used.
And reduced body mass spreads through the vehicle to lighter brakes, suspensions, steering, etc. Audi estimates fuel economy improves 0.3 to 0.5 L/100km for each 100 kg of mass reduction.
Diesel engines: The easiest route to better fuel economy, modern automobile diesels offer strong low-speed torque, smooth, clean, quiet operation, exemplary durability and a 25 to 30% economy improvement. Look for more manufacturers to offer a diesel option in North America.
Smaller engines: The progression continues. First it was V8s replacing sixes, and now it’s from sixes to four or even three cylinders. More “power dense” engines can be smaller, and these smaller, harder working engines will power heavier vehicles.
Ford’s economical 3.5 litre Ecoboost V6, traditionally tiny for a full size pickup, is a popular option in the F-150. The 2012 Buick Regal GS’s 2 litre four with turbocharging and direct injection produces a hefty 270 hp and 295 lb ft of torque, the most power dense engine GM has ever produced.
The 2016 fuel economy target is daunting, and alas these gains aren’t linearly cumulative. But with smart engineering the old reciprocator will meet the requirements.
Bill Vance is a founding member of the Automotive Journalists Association of Canada and author ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).
Hybrids and battery electrics will contribute, but unless they gain more than their current 2% market share their impact will be small. Here are some refinements being pursued and their approximate fuel economy contributions.
Stop-start function: Shutting off the engine to eliminate idling when the car is stationary, e.g. at stoplights, is a significant contributor to fuel economy and one of the reasons hybrids do so well in the city. It does the same for regular vehicles. There are challenges such as maintaining engine-off cabin heating and cooling, and battery/starter durability, but these are being overcome. Start-stop is appearing on such cars as Porsche and Ford Fusion and is expected to proliferate. Economic gain is in the neighbourhood of 5%.
Cylinder de-activation: Called different names by manufacturers, disabling some engine cylinders either electronically or mechanically during low-load conditions such as in highway cruising mode reduces fuel use. It is used by Chrysler, Honda and others and is expected to increase – saves 7% or more.
Direct fuel injection: injecting gasoline directly into combustion chambers rather than by upstream port injection is rapidly increasing. It provides more precise timing, direction and pattern of fuel spray for more efficient combustion, although it requires much higher pressure. It also cools the combustion process, allowing higher compression ratios and sharper ignition timing. Combining it with forced induction (turbo or supercharging) such as Ford’s Ecoboost and some GM Ecotec engines can yield 10% economy gain or more.
More transmission ratios: Slower turning engines, achieved with more transmission ratios, use less fuel. As engineers anticipate highway engine speeds falling to 1000 rpm or lower during cruising mode, maintaining traditional performance with the ultra-high gear ratios required will mean more than the typical 6-speeds now used.
Porsche just released 7-speed manual (a first) and automatic transmissions, and Audi, Chrysler, Lexus, Mercedes-Benz and others have 8-seed automatics. Germany’s ZF has just developed a light and compact 9-speed that will appear in some Chrysler products and others. Savings: 10 to 16%.
Dual-clutch automatic transmissions with two clutches, one for even gears and one for odd, usually with manual selection available, are replacing the traditional hydraulic torque converter and its inherent slippage. They provide extremely quick shifts and fuel savings up to 10%.
Reduced vehicle weight is an old favourite being more vigorously pursued than ever. Audi has been a leader here (trying to compensate for that extra 4wd Quattro mass?) with an aluminum space frame in such models as the A6 and A8.
The 2012 A6 body, for example, is 32 kg lighter than its predecessor thanks to extensive aluminum. Other materials such as high-strength steel and carbon fibre are also being used.
And reduced body mass spreads through the vehicle to lighter brakes, suspensions, steering, etc. Audi estimates fuel economy improves 0.3 to 0.5 L/100km for each 100 kg of mass reduction.
Diesel engines: The easiest route to better fuel economy, modern automobile diesels offer strong low-speed torque, smooth, clean, quiet operation, exemplary durability and a 25 to 30% economy improvement. Look for more manufacturers to offer a diesel option in North America.
Smaller engines: The progression continues. First it was V8s replacing sixes, and now it’s from sixes to four or even three cylinders. More “power dense” engines can be smaller, and these smaller, harder working engines will power heavier vehicles.
Ford’s economical 3.5 litre Ecoboost V6, traditionally tiny for a full size pickup, is a popular option in the F-150. The 2012 Buick Regal GS’s 2 litre four with turbocharging and direct injection produces a hefty 270 hp and 295 lb ft of torque, the most power dense engine GM has ever produced.
The 2016 fuel economy target is daunting, and alas these gains aren’t linearly cumulative. But with smart engineering the old reciprocator will meet the requirements.
Bill Vance is a founding member of the Automotive Journalists Association of Canada and author ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).
Bill Vance
Automotive Scene Columnist: Automotive history author and member, Automotive Journalists Association of Canada.
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