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Structural attenuation of a running diesel engine measured by a new technique showed a constant value regardless of engine speeds. It was verified by this result that structural attenuation is a physical quantity unique to the structure of each engine and, therefore, a good indicator for evaluation of low noise engine structure. In addition, a hydraulic excitation test rig was devised to measure structural attenuation directly and to make effective use of it for noise reduction. Based on the accurate measurements by the excitation test rig, modal analysis and system simulation were conducted for implementation of countermeasures against noise.

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 4M5 series of four-cylinder, in-line, direct-injection diesel engines has been released by Mitsubishi Motors Corporation for light and medium-duty trucks and buses. Featuring an updated structure and reflecting the employment of state-of-the-art technology in the design of every component, the new engine series offers high reliability and compact dimensions. Moreover, the new series well meets contemporary demands for high performance, low noise, and clean combustion.

This paper presents the results of acoustic analyses of light duty truck cabs by actual vehicle testing and by numerical analysis utilizing the boundary element method (BEM). In the resonance mode analysis using BEM, by taking into account the vibration characteristics of cab panels, the presence of the modes other than the purely acoustic cavity resonance modes were confirmed. The contribution of the panel vibrations to booming noise that occurs in actual light duty trucks was analyzed. BEM analysis showed that some of the panel vibration had a negative contribution to booming noise. In other words, decreasing vibration in such a section was shown to increase sound pressure. The results of the BEM analysis match well with actual test results. It has thus been demonstrated that BEM is an effective method for analyzing truck interior noise reduction.

To meet the increasingly strong demand for high-speed transportation, better fuel economy, higher reliability and the social requirements for more strict Japanese regulations against exhaust and noise emissions, Mitsubishi Motors Corporation has recently developed the 6D40T1 in-line 6-cylinder, 12.0-liter turbocharged and intercooled diesel engine for heavy-duty trucks. This engine meets the 1989 Japanese exhaust emission regulations and has an output of 258 kW. To achieve both fuel economy and good drivability, Mitsubishi's original, electronically-controlled fuel injection system was adopted. The so-called prestroke-controlled fuel injection pump is capable of flexible and precise control of both fuel injection rate and timing. The basic structure of the 6D40T1 was designed with high rigidity to permit high cylinder pressures. In addition, to reduce friction and heat losses, a 4-valve design, roller cam followers with needle roller bearings, and shortened exhaust ports were adopted.

Torsional vibration of a truck's powertrain system is due to the exciting force generated by the angular velocity fluctuation originating from the setting angle of the universal joint of the propeller shaft, which can cause such problems as rattling noise, booming noise, etc.. This paper will clarify the difference between a 6x4 truck and a 6x2 truck in the torsional vibration characteristics from the experimental results. This is accomplished by computation with a simple torsional vibration model of the powertrain system and investigating the contribution of torsional rigidities of the powertrain system's various components by a parameter study. As a result it has been clarified that the torsional rigidity of the through shaft for transmitting power to the two rear axles has a great influence on Noise, Vibration and Harshness of 6x4 trucks.

Recent global environmental problems which have come to light must be solved for ensuring the survival of the human race. And it is of the utmost importance that we give to our descendants a world full of nature and beauty. In the past years Mitsubishi Motors Corporation (MMC) has long been positive in research and the development activities so as to satisfy the demands for low emission and good fuel economy vehicles. (1) As one example of our research efforts, the technology that will meet the US '94 HDDE exhaust emission regulations, which is one of the most stringent regulations in the world, is described in this paper. The exhaust emissions were reduced by improvement of combustion, using the pre-stroke control type fuel injection pump and optimizing the combustion chamber shape. Efforts were also made to improve the oil consumption, in order to reduce PM (Particulate Matter) emission.

In the diesel engine industry, the growing trends are toward wider use of electronically controlled high pressure fuel injection equipment to provide better engine performance, while conforming to the stringent exhaust emission standards. Although there have been some recent announcements of a diesel engine that applies an electronically controlled common rail type fuel injection system, there is little literature published about any attempt to reduce both exhaust emissions and noise and to improve engine performance by varying injection pressure and injection timing independently and introducing pilot injection in combination. This paper describes the details of a study made on the parameters associated with injection timing, injection pressure and pilot injection and the procedures for their optimization, with an electronically controlled common rail type fuel injection system installed in an in-line 6-cylinder 6.9 liter turbocharged and intercooled DI diesel engine.

In order to investigate the effects of high injection pressure on engine performance and exhaust emissions, some experimental high injection pressure in-line pumps were made and tested. Increasing fuel spray momentum by high injection pressure could reduce smoke emission, but excessive increase in injection pressure was found not so effective in further reducing smoke emission. Accordingly, a high injection pressure should be accomplished within the low engine speed range a feature that has been very difficult to achieve for a conventional in-line pump. An electronic controlled injection-rate-control pump with a variable prestroke mechanism can provide higher injection pressure in low engine speed range and advances injection timing in high engine speed range. This pump can improve fuel economy in low engine speed range and emissions (smoke and particulate) over transient FTP for HDE's.