Automotive engineers have been trying to substantially improve internal combustion engines and transmissions for years, but no break-throughs yet.
A practical and cost comparative alternative for the gasoline-fueled, internal combustion engine seems to perpetually elude us. The IC engine has been around for more than 100 years, but nothing better has been invented so far that can replace it for ordinary automobiles. Although we have an encouraging line-up of somewhat more efficient vehicles for the 2009 model year, achieving 50 to 100 mpg every day probably will never be realized. Even the hybrids are reported to achieve only about 75% of the EPA ratings. So what is the answer? In spite of this, some hope that hybrid and flex-fuel vehicles will, at least, be among the latest configurations to take us a few giant steps forward. For 2009, Volkswagen and Mercedes-Benz are offering several clean diesel options, while Honda Civic CNG has a compressed natural gas-fueled engine. But these technologies offer little more fuel efficiency than other incremental advances that automobile manufacturers have been making since the 1960’s.
For example, automotive engineers have achieved modest but meaningful fuel efficiency improvements through better designs for both IC engines and transmissions. The greatest improvement in many years came from Bendix Corporation’s Electronic Fuel Injection systems in the early 1970’s. The first EFI Systems replaced one or more carburetors at the intake manifold with fuel injectors for each cylinder. New microprocessor chips then afforded engineers an opportunity to design compact control computers to reduce emissions and improve fuel economy at reasonable prices. Most vehicles today use a version of this type of fuel management.
The Automated Manual Transmission (AMT) also called a semi-automatic transmission, clutchless manual transmission, and e-gear, among various names. They combine the efficiency of a manual transmission with the convenience of an automatic gearbox, and they can improve fuel efficiency by an average of 7%. These systems shift gears electronically by following the manual gear-shift lever’s motion. No clutch pedal is needed since this computer-controlled system manages both the clutch and shifting functions electronically.
The Continuously Variable Transmission (CVT) improves fuel economy by approximately 6%. It replaces a conventional transmission with a system that gradually increases and decreases the gear ratio. Efficiency increases by running the engine at its optimal speed without the surges that typically accompany conventional shifts. Car makers have made various CVT systems based on chains, belts, steel-belts, rollers, and pulley drives.
Cylinder Deactivation System-equipped vehicles can increase fuel efficiency more than 7% by temporarily deactivating some cylinders under low-load conditions such as cruising along a level freeway. They hold valves in a position that prevents fuel induction and allows low-resistance movement of so-called idle pistons. This kind of system is also known as Active Fuel Management (AFM), Multi-Displacement System (MDS), and Displacement-on-Demand (DoD).
Turbochargers and Superchargers have been around for a long time. They increase engine power by pumping additional air under positive pressure into the cylinders during intake. A greater mass of air triggers additional fuel, which in turn, increases engine power and torque. Superchargers are driven by a belt, gear, or chain coupled to the crankshaft while the vehicle’s exhaust system drives turbochargers. Both methods can increase fuel efficiency by approximately 7% with a smaller, lighter engine that can maintain the same power rating as a larger engine without chargers.
Variable Valve Timing (VVT) systems automatically adjust the lift, duration, and timing of intake and exhaust valves in an order which depends upon engine speed to achieve optimum air and fuel flow. The valves accept more air and fuel at higher engine speeds and improve fuel efficiency by 5% on average. The most basic VVT systems advance or retard intake or exhaust valve timing. More complex systems switch from one set of cam lobes to another as engine speed increases. Some high-end vehicles use Continuous Variable Valve Timing (CVVT) systems that modify timing and lift continuously.
Then what fundamental technology should we pursue? After all, what is a reasonable or realistic goal? The Energy Independence and Security Act of 2007 may encourage us to at least allocate resources in a more organized manner for new discoveries, but until we are blessed with another Edison, Ford, Einstein, or someone else who can actually invent something new, we may be in for another 100 years of reliance on rationed petroleum and corn juice.
The average efficiency improvement numbers given for each example were developed by the United States Department of Energy.
For more information go to:www.fueleconomy.gov
Filed Under: Automotive, Green engineering