Because automotive drivers demand quieter vehicles, automotive manufacturers are focusing their attention on drivetrain components other than the engine, and more specifically, to transmissions and transaxles.

Previously, noise testing and evaluation was conducted in anechoic chambers to obtain absolute noise measurements. These measurements were expensive and difficult to obtain for an operating transaxle. Southwest Research Institute (SwRI) performs an improved sound measuring technique known as sound intensity testing and evaluation. This technique lends itself easily to transmissions and transaxles because the transaxle can be operated with a background environment containing several noise sources, such as engine, drive motor, load dynamometer and cooling devices.

Sound intensity measurements quantify the sound power radiated from the transmission and transaxle, thus describing the time averaged rate of energy flow through a unit area. For transaxles and transmissions, measurements on a 5-sided grid enclosure are recorded to find the total source. The 6-sided grid consists of a sound radiating base for ease of measurements. Since sound intensity is a vector quantity, the background source noise entering one side of the enclosed area about the transmission and transaxle is canceled out when it leaves an opposing panel.

The net sound power produced by sources within the measurement volume is thus obtained. Sound intensity measurements can be made through a range of 125 to 500 Hz for noise levels of 95 dBA, with accuracies of ±1 dB. A typical test consists of sound intensity measurements as follows:

1,600, 3,200, and 4,800 rpm
Low, medium and high torques
All gears

During testing and evaluation, automatic transmission fluid (ATF) temperature is maintained at a constant level with external PID (proportional integral derivative) heating and cooling control circuits. Should areas and frequencies of high noise levels be detected, additional testing can be performed by narrowing the grid size to zero to locate the particular component causing the high noise.

For more information about drivetrain engineering capabilities and past project briefs at SwRI or how you can contract with SwRI, please contact Douglas Fussner at dfussner@swri.org or (210) 522-3972.

Contact Information

Douglas Fussner

Drivetrain Design and Development

(210) 522-3972

dfussner@swri.org

Related Terminology

transmission test
facility

transmission testing

automatic
transmissions

drivetrain database

drivetrain
engineering

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

September 30, 2008