Southwest Research Institute^® (SwRI^®)  News

Transmission data used to improve drivetrain performance

San Antonio — November 20, 1995 — A world-recognized transmission testing and technology center has been established at Southwest Research Institute^® (SwRI^®) to assist the automotive industry in its continuing efforts to improve vehicle fuel economy. Over the last 20 years, more efficient engines and lighter-weight, aerodynamically designed vehicles helped improve average passenger car fuel consumption by 40 percent. To stretch the gains even further, transmissions are now being targeted for optimum performance and efficiency.

Program Manager Michael A. Kluger of the SwRI Fuels and Lubricants Research Division described the Institute’s state-of-the-art transmission research capabilities for SwRI trustees, assembled today for the Institute’s 48th annual meeting.

“The largest energy-consumer in the drivetrain (the engine) has and will continue to be made more efficient, but demands for increased fuel economy have not ceased,” Kluger explained. “As a result, manufacturers are pursuing efficiency gains in other components, such as transmissions. This is a difficult task, because transmissions are complex assemblies of more than 600 interrelated parts.”

The Institute has evaluated 60 different transmissions and transaxles produced by automotive manufacturers here and abroad. Test results are compiled in the largest database of its kind used to quantify upper and lower bounds for acceptable performance. This information is complemented by SwRI-established efficiency standards for automatic and manual transmissions, published by the Society of Automotive Engineers.

Institute-designed and fabricated transmission test stands reproduce a full range of engine and road conditions and incorporate such features as precision torque and speed transducers. This equipment allows engineers to make critical measurements of transmission and component efficiency, accurate to within ±1 ft-lb for transmissions, ±6 in-lbs for pumps, and ±1 in-lb for clutch packs. One ft-lb of torque loss in the drivetrain is equivalent to 0.1 mile per gallon of fuel economy.

“Vehicle manufacturers need efficiency data in order to make informed engineering decisions,” said Kluger. “SwRI conducts investigations of transmission and transaxle performance in more than 40 different areas for a broad range of vehicle applications, from the smallest compact cars to large, diesel-powered trucks.”

The Institute is in the process of expanding its transmission modeling activities and adding simulation capabilities. An internally funded project is under way to create a mathematical model of a clutch pack. Institute engineers have already developed a model of fixed and variable displacement pumps. “These models,” Kluger noted, “will eventually allow us to predict where power losses might occur in a new transmission design and to address problem areas before production begins.”

Kluger envisions that a comprehensive transmission simulation capability will be added to the Institute’s existing engine and vehicle modeling programs within a few years. In addition, Transmission Technology Section staff members are refining fiber optic diagnostic techniques to obtain, for the first time, real-time friction material temperatures during the clutch pack engagement process, as well as fluid flow measurements involving rotating components in transmissions. The results will help resolve issues such as whether today’s pump sizes are too large. Because these complex measurements were not possible in the past, manufacturers erred on the side of caution, incorporating larger pumps to ensure that enough fluid flow would take place for proper transmission lubrication. The new diagnostic capability will provide sound engineering data on which decisions can be based regarding the sizing of transmission components to achieve maximum life and performance.

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