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Thesis (M.S.)—University of Nebraska—Lincoln, 1970. Department of Agricultural Engineering.


Copyright 1970, the author. Used by permission.


Studying the problems of measuring tractor noises at the operator’s station using the drawbar test equipment at the Tractor Testing Laboratory was separated into two phases.The first of these two phases was concerned with the effect of noise being reflected from the front section of the test car and background interference due to noise generated by the test equipment.After it was determined that the noise generated by the test equipment did affect measurement of tractor noise, individual noise sources were isolated and studied which created the second phase.These sources included exhausting of compressed air, mechanical engine noise, transmission noise, and radiator cooling fan noise.

Results from the test conducted to evaluate noise reflection from the front section of the test car indicated that this would not cause problems in measuring tractor noise.

Studying the preliminary results indicated that noise generated by the drawbar test equipment did create excessive background interference in the octave bands above 4000 Hz.To correct this difficulty the exhaust air outlet used for small load adjustments was relocated from beneath the instrument cab to the rear of the test car.Relocating of this outlet solved the problem of high frequency background interference due to the fact that compressed air was muffled while traveling through flexible exhaust pipe and also the outlet was positioned a considerable distance from the operator’s station.

The other sources of test equipment noise investigated were the compressed air outlet in the load unit exhaust system, radiator cooling fan, mechanical engine noise, and the load unit transmission.None of these sources caused excessive interference which would contribute to error in accurately determining tractor noise.

An important fact that resulted from the studying of individual components was that a large reduction of noise at its source can be achieved but may result in little or no reduction of interference at the tractor operator’s station.

Determination of the most efficient method of absorbing power with respect to generation of test equipment noise was also studied.The major cause of drawbar test equipment noise was the exhausting of compressed air from beneath the instrument cab.It was also concluded that consistent noise measurements could be obtained without regard to the background interference of campus traffic.

Advisor:G. W. Steinbruegge