Limits of Noise Reduction of Trucks 785134

Interior and exterior noise reduction measures were tested in heavy vehicles. Major noise sources were identified as the engine, transmission, body, components, rolling of tires, and aerodynamic sources. Improvements were made on the intake and exhaust systems, the engine compartment, and the driver's compartment by incorporation of mineral wool. Engine performance was not sacrificed and engine covers were not used. However, significant results were achieved by emphasizing modifications of the engine and transmission and without exhausting other noise-reduction possibilities.

Tests on various, heavy vehicles indicated different relative influence of noise sources and correspondingly different levels of noise-reduction were achieved. Sometimes small modifications gave significant results, sometimes major alterations were required. Accordingly, no general noise-reduction levels can be cited. Even adaptation of vehicles to electrical drive systems did not show significant improvement without other simultaneous modifications. The costs of incorporating the tested improvements into series production were judged to be 2 to 4% of vehicle selling price. Areas of further potential improvement include the engine fan and the gas pedal linkage