In this paper, the reasons causing the noise level of the homemade but exceeded the national standard are analyzed and the main noise source and their frequency spectrum are found by the method of noise separation process and frequency spectrum. The maximum acceleration noise outside vehicle declines from 91.5dB(A) to below 86dB(A) and meets the national standards, after following measures have been implemented: (1) On condition that refrigeration is efficient, the speed of the refrigeration-fan has been slowed down moderately and the vanes have been lengthened, (2) The muffler's ability of noise reduction is increase and its effective lower limit frequency band of noise reduction is extended, (3) Flexible-connection is applied between ventpipe and muffler and the directionof muffler's outlet is changed from right-side to rear, (4) The shape of colling air's intake is modified for reduction of noise reflection, (5) The sound absorber is stuck to the inner wall of the engine cabin and the cooling-air intake.
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