Tenneco moving toward noise-cancellation system

By 1998 Tenneco Automotive's noise-cancellation exhaust system could be added to the list of successful products -- like Kellogg's Corn Flakes and Post-It Notes -- that were the result of R&D mistakes or surprise benefits of other products.

Originally designed to merely make cars more quiet, the Tenneco system allows automakers to take out a significant amount of back pressure, boosting engine fuel economy and power, says Richard A. Snell, Tenneco's president. The system uses speakers mounted in the exhaust piping to cancel out noise by producing opposite frequency sound waves.

Mr. Snell adds that Chrysler Corp. is taking a look at the system for some '98 model cars, and that Ford Motor Co. also is keenly interested.

The system is being used in some large vehicle applications, such as buses, Mr. Snell says, and is likely to next be put in use in medium- and heavy-duty trucks. Speaker size is one of the major hurdles to passenger-car applications, but most speaker makers are scrambling to develop the technology because of the huge market potential. "We've got every speaker company drooling over this one," says Mr. Snell.

Another issue is aesthetics. In order to make the muffler-less exhaust system look good, Tenneco, which makes Walker mufflers and Monroe shocks, has designed piping to resemble a dual exhaust system, with one tube emitting the exhaust and the other housing the speaker used to cancel noise.

The company also is developing an exhaust system that uses "air-gap" piping to transfer heat quickly to the catalytic converter for faster light-off, which should improve emissions. Reducing cold-start emissions is one area the industry must tackle to comply with '98 clean-air regulations. The Tenneco system uses thin steel tubing housed in a thicker, more durable steel tube, to quickly get heat from the manifold to the catalytic converter. The two tubes do not touch, and the air between them acts as an insulator to keep the inner tube hot and the outer tube cooler. The system cuts catalytic converter light-off time from a couple of minutes to about 20 seconds, Mr. Snell says. Some air-gap piping already is in use on certain Ford, Chrysler, Honda and Toyota vehicles, he says.