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This paper describes a study of drag reduction devices for production pick-up trucks with a body-on-frame structure using full-scale wind tunnel testing and Computational Fluid Dynamics (CFD) simulations. First, the flow structure around a pick-up truck was investigated and studied, focusing in particular on the flow structure between the cabin and tailgate. It was found that the flow structure around the tailgate was closely related to aerodynamic drag. A low drag flow structure was found by flow analysis, and the separation angle at the roof end was identified as being important to achieve the flow structure. While proceeding with the development of a new production model, a technical issue of the flow structure involving sensitivity to the vehicle velocity was identified in connection with optimization of the roof end shape. (1)A tailgate spoiler was examined for solving this issue.

ONE ISSUE IN NEW VEHICLE DEVELOPMENT that has become increasingly more important is the need to put attractive vehicles on the market at the right time. In recent years vehicle design has become a very crucial factor in this effort. Automakers are required to create vehicles having a higher quality design in a shorter period of time and supply them to the market in a timely fashion. As part of the effort to meet these requirements the automakers have developed a variety of CAD/CAM systems, which counterparts in Industry in general. Although most CAD/CAM systems are currently being used primarily at the design and manufacturing stages, the full potential of CAD systems has yet to be realized at the design stage. At Nissan, we have developed a CAD styling system called the Digitized Image Modeling System (DIMS), which serves as a support tool for the creation of new vehicle designs.

It has been reported by several researchers that the L-jetronic fuel injection system offers better idle speed stability than the D-jetronic one in port fuel injection engines. However, the volume between the throttle valve and the intake valves in the L-jetronic system acts as a first order lag element in the system and causes air-fuel ratio fluctuation which, in turn, induces idle speed hunting under certain conditions. This study employs computer simulation to determine the influence of three parameters on idle speed stability: (1) flywheel inertia, (2) intake manifold volume, and (3) air-fuel ratio calibration. It also explores means of improving idle speed stability by controlling the air-fuel ratio and ignition timing. The use of actual engine torque data to estimate the generated torque from the amount of air and fuel in each combustion cycle was the unique feature of this study.

The purpose of this paper is to clarify the mechanisms of unburnt hydrocarbon (HC) emissions from a small direct - injection (DI) diesel engine. HC emission levels of small DI diesel engines are considerably higher than those of corresponding indirect - injection (IDI) diesel engines, even when sacless injection nozzles that are effective in reducing HC emissions are installed on them. In this study, analytical engine tests were performed to evaluate the relative significance of various potential sources of HC emissions from a small DI diesel engine equipped with sacless type injectors.