Caterpillar Inc.

M Kathryn Christensen

Everett Gene Brandt

W Charles Sahm

Robert A Herold

Minjiang Ji

Sen M Kuo

The system employing and the processing of, an indirectly sensed signal representative of a periodic noise acoustic wave into an input signal for a noise cancelling system where the indirectly sensed signal is converted into a pulse signal per period that carries fundamental and harmonic frequency information of the periodic noise. A tachometer type RPM signal is processed in a counter circuit controlled by a logic circuit to produce a signal of one pulse per revolution with a controlled duration, the pulse amplitude is adjusted, the pulses are low pass filtered and any D.C. is blocked from the noise cancelling system input.

Indirectly sensed signal processing in active periodic acoustic noise

Most existing noise reduction enclosures used with engines and engine driven equipment have failed to meet the reduced noise emission requirements of today and of the future. A few of the present enclosures meet the reduced noise emission requirements of today and of the future but are extremely expensive to purchase and are large bulky structures. The subject enclosure (10) is reasonably priced and provides an enclosure which is effective in reducing the noise emitted therefrom. The enclosure (10) includes a housing (32) having a generally rectangular configuration and being divided into an engine portion (56) defining an engine compartment (57) and a duct portion (54). The outlet ducts (88) having a length greater than the inlet ducts (84). To further enhance the noise reduction of the enclosure (10) a plurality of dynastic hardware is attached to the housing (32).

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Metamora, IL, United States of America

M Kathryn Christensen