The Drive for Better Fuel Economy

Fuel, lubricant and component testing helps industry meet Corporate Average Fuel Economy standards

By Lee Grant     image of PDF button

After the oil embargo of 1973-74 and the ensuing energy crisis, Congress passed the Energy Policy and Conservation Act, which established the Corporate Average Fuel Economy (CAFE) standards for new passenger cars and light trucks. The initial standards were set at 18 miles per gallon (mpg) for passenger cars and 17.2 and 15.8 mpg for two-wheel and four-wheel drive light trucks, respectively. Both standards have been increased gradually to the current standards of 27.5 mpg for cars and 20.7 mpg for light trucks.

To ensure compliance with CAFE, the U.S. Environmental Protection Agency (EPA) computes an overall average fuel economy for each manufacturer each model year. Manufacturers take fuel economy measurements for each vehicle type at the same time EPA is determining emissions compliance for that vehicle. The numbers of each vehicle type sold weights the overall CAFE fuel economy compliance figures. If a manufacturer does not meet the standard, it is liable for a civil penalty of $5 for each 0.1 mpg its fleet falls below the standard, multiplied by the number of vehicles it produces.

From left, Michael A. Kluger of the Engine and Vehicle Research Division and Steven D. Marty, Lee J. Grant and Larry A. Eckhardt of the Automotive Products and Emissions Research Division, are among the Institute's experts on procedures designed to evaluate fuel economy and the design of equipment and procedures to do so. Their specialties include fuel effects on emissions, fuel evaluation and performance, engine research, engine test development, automotive fluids analysis and fleet analysis.

On March 13, 2002, the U.S. Senate defeated an effort to increase fuel economy standards by 50 percent over the next 13 years for cars, light trucks, minivans and sport utility vehicles. Had it passed, the measure would have provided the first increase in the standards for passenger cars since 1986, and since 1996 for light trucks. Since the inception of CAFE standards in 1978, the fuel economy of the nation's new car and truck fleet has increased by more than 20 percent. However, improvements in fuel economy peaked during the model years of 1987-88. With the rise in popularity of minivans and SUVs the fuel economy of the nation's fleet has since decreased some 7 percent. This decrease in fuel economy prompted the most recent congressional review of the standard.

The model year 1987 fleet, including both domestic and imported passenger cars and light trucks, had a CAFE of 26.2 mpg, a whopping 30 percent increase over 1979 averages. In the late 1980s, in a move Congress didn't anticipate in 1975, automakers began to phase out most full-size cars and station wagons as consumers began the switch to light trucks, a category that includes pickups, minivans and sport utility vehicles. When Congress enacted the original standards, light trucks comprised less than 10 percent of the new-vehicle market.

Today, after a decade of low fuel prices and the public's continued love affair with size and horsepower, half of all new vehicles sold are pickups (20.5 mpg average); minivans (22.5 mpg average); and SUVs (20 mpg average).

American consumers have traded fuel economy for acceleration and weight, and consequently the average fuel economy has slipped to 24 mpg.

Participating in automotive research for more than 50 years, the Institute's Automotive Products and Emissions Research Division and Engine and Vehicle Research Division have long been involved with clients seeking an independent site to evaluate technologies for incremental fuel economy improvements.

Beginning in the 1970s, automotive manufacturers made huge gains just by tackling the aerodynamics of design and the weight of their vehicles. Since then, gains in fuel economy have been smaller and tougher to come by. For many years, SwRI has offered industry-standard and proprietary test procedures with which to validate these minute improvements.

The axle efficiency test stand is used to evaluate different types of axles or oils for their fuel efficiency benefits.

Vehicle and oil testing procedures

The Institute follows the same EPA test procedure to measure fuel economy that it uses to measure light-vehicle emissions. SwRI engineers test vehicles by driving them on a chassis dynamometer under laboratory conditions. One cycle simulates the slower speeds, stops, idling, and accelerations of stop-and-go driving. The other cycle simulates a 10-mile highway trip with little idling and one stop before the end of test. Fuel consumption numbers are combined to compute fuel economy.

Though CAFE does not extend to heavy- duty vehicles, fuel economy is nevertheless a high priority for manufacturers and fleet operators. SwRI engineers often use a Society of Automotive Engineers fuel consumption test to evaluate fuel economy benefits associated with fuel additives, engine oil and driveline lubricant formulations, as well as tires and other fuel-saving devices. Technicians drive trucks and buses on a prescribed minimum 40-mile "course" to simulate a long-haul route. During this procedure, engineers compare the in-service fuel consumption of a control truck to one to three test trucks. SAE introduced this test method in 1986, and experience shows that it has an overall accuracy of plus or minus 1 percent.

SwRI also uses several other SAE test procedures to establish relative fuel economies of components and systems. For example, the fuel economy measurement road test procedure provides fuel economy measurement techniques for light-duty vehicle components. This test can be performed on the road or on a chassis dynamometer and, like the EPA procedure, it simulates a mix of city, suburban and highway driving conditions.

A clutch pack drag test stand is used to measure the parasitic losses associated with different transmission clutch pack variables such as friction material groove design, oil flow, relative component speeds and axial clearance.

In another effort to improve fuel economy, automakers and oil and additive suppliers have demonstrated the benefits of energy-conserving, low-viscosity, multigrade engine oils. To qualify such oils for the marketplace, SwRI engineers use the Sequence VIB test, which measures the effects of engine oils on the fuel economy of light-duty vehicles and the ability of the oil to retain its fuel economy benefits over an entire oil change interval. SwRI performs a similar procedure, the Mercedes-Benz M-111 Fuel Economy Test, on an engine dynamometer test stand that simulates the European emissions test procedure. SwRI still uses a 1982 forerunner of the Sequence VI test for research purposes in evaluating fuels, engine oils, gear oils and automatic transmission fluids.

In this procedure, engineers drive five cars through varied driving cycles on the chassis dynamometer to demonstrate differences in fuel economy.

Additional research

According to a 2001 EPA study, only about 15 percent of the energy content of the gasoline in a vehicle's tank actually moves the car down the road. About two-thirds of the available energy in the fuel is rejected as heat in the exhaust and coolant or frictional losses. Energy is lost to engine friction, pumping losses, drivetrain friction and slippage, the operation of accessories such as air-conditioning, aerodynamic drag, tire rolling resistance and idling in traffic. Each of these losses is an opportunity for advanced technology to improve fuel economy.

Researchers often measure motoring friction to determine the effects of any device on engine friction and to map engines and calculate fuel consumption while looking at the effects of different components, front-end accessory devices, fuel-enhancement devices and fuel additives. Because air filters can affect fuel economy, SwRI has a procedure to measure the dust capacity of a filter to determine its load before there is a drop in air pressure. With the goal of finding an additional fraction of a mile per gallon, SwRI has developed benchmarking programs for auto manufacturers in which engines, transmissions, pumps and accessories of clients are evaluated.

SwRI design engineers play a major role in helping their clients reduce engine friction through component design and the use of advanced materials. Combustion modeling has been used to develop intake systems with improved combustion, and advanced engine controls have contributed to improved cold-start fuel consumption.

Two drivetrain components that auto and component manufacturers often ask SwRI staff to evaluate are the drive axle and the transmission. Axle efficiency improvements smaller than 1 percent can be significant for fuel economy.

SwRI uses several published and proprietary procedures to evaluate axle hardware and shaft speeds and to log data as the load is increased linearly to some elevated load. SwRI technicians repeat this procedure at many different speeds and temperatures.

Similar to the trend in engine oils, automatic transmission fluids are evaluated for viscometrics and friction properties. Maintenance of friction properties is necessary for the proper operation of the slipping torque converter, itself a major contributor to overall transmission efficiency improvement. Lower viscosity transmission fluids reduce the drag within the transmission to improve performance, particularly at lower temperatures.

The Institute has become a world-class transmission test facility for studying transmission performance, transmission fluid performance and component efficiencies. Transmissions operate over such a wide range of power conditions that their efficiencies can vary from 65 to 95 percent. Components are isolated outside the transmission to study their singular contribution to efficiency losses.


Despite the Senate's March 13 vote to block an increase in CAFE standards for cars and light-duty trucks, greater fuel economy will remain a high priority in the automotive industry. Crude oil is still a finite resource, and light vehicles account for about 40 percent of all U.S. oil consumption. Other nations, as well as environmental groups, will continue to pressure the President and Congress to address global warming. Major automakers have started to compete on environmental issues. For example, Ford has announced plans to increase the fuel economy of its SUVs by 25 percent by 2005, and General Motors has pledged to remain the fuel economy leader in light trucks. Through continuous development of industry and proprietary procedures, SwRI will retain its leadership role in assisting manufacturers and fleet operators with lower emissions and improvements in fuel economy.

Published in the Fall 2002 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.

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