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Improvements of interior and exterior noise are important targets in vehicle engineering. There are many reports concerning the reduction of radiator cooling fan noise. But, most of those reports are associated with studies of air flow noise. A radiator cooling fan connected to a crankshaft occasionally radiates structure-borne noise in addition to air flow noise. This structure-borne noise is caused by fan blade vibration excited by torsional vibration of a crankshaft. In this paper, we surveyed the mechanism of the structure-borne noise and discussed some methods for the noise reduction. And, as a result, we developed one of the noise reduction technique aiming at isolation of crankshaft vibration by modifying viscosity of the oil in a fan clutch.

When truck tires have a deformation such as radial runout, flat spot, and abnormal wear as a result of panic braking, they affect vehicle vibration in the form of displacement input whose spectrum involves higher order terms of tire revolution. While a truck has vibration modes of frame bending as well as pitching and unsprung-mass viberation in the input frequency range, the tire displacement input induces vehicle vibration as a combination of these modes. Results of calculations and experiments of a 4x2 medium-duty truck are analyzed and an example of means for improving ride comfort is described in this paper.

The basic variables of fuel economy are compared among some truck types manufactured by Mitsubishi Motors Corporation, and their contribution on fuel consumption is discussed. As for heavy duty trucks, whose fuel economy is the prime concern of all fleet operators, the design improvements of engine fuel performance, driveline power losses, rolling resistance of Lires, vehicle air resistance and curve resistance are described, and their influences on fuel economy are discussed along with test data and calculations. In addition to these parameters, conditions of the vehicle operation such as vehicle speed and payload are recognized to have a great influence on fuel economy of trucks.

The equipment, methods and results of fuel consumption tests, and the parametric studies of in-service fuel economy simulation are described. The simulation is based on measurements by a unique laboratory test facility, and aims to get fuel saving measures at the development stages of vehicles. Although a human element is important especially on urban routes, this simulation in which the driver’s factor was simplified was found to give satisfactory predictions of in-service fuel economy for commercial vehicles over representative highways in Japan.