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Mankind developed and enjoyed the automobile civilization, and has lauded the prosperity that it brought about. Commercial vehicle launched the heavy duty diesel engine have been contributing by main transportation system for development of society in the world. However both the local and global environment issues appear depend on the life of mankind, in the world. Especially, global warming is the most stringent issue for our life on the earth. We human beings must lay our existence on the line, and call upon expertise to create solutions for this situation. Diesel engine has great potential for the global warming compatibility by it's high thermal efficiency and diesel vehicle is expected to conserve the environment and to improve the fuel saving for keeping resources in the world. This paper introduces the surrounding of the automobile, such as exhaust emission regulation for heavy duty diesel vehicle, amount and contribution of CO2 emission and noise.

Sound Quality (SQ) improvement is recently one of the important issues in diesel engine development. Therefore a new method was developed by the authors about ten years ago to establish objective criteria for SQ assessment. Considering the sensitivity of human hearing to impulsive sounds such as diesel noise, the human auditory mechanism was simulated by introducing temporal masking in the time domain. Furthermore, each of the human auditory organs was simulated by computer codes, providing reasonable analytical explanations of typical human hearing responses to diesel noise. This method finally provides us a good index of sound quality, i.e. an SQ index, of diesel noise that includes high-frequency intermittent offensive sounds caused by impacting excitations of combustion, piston slap, etc. This paper describes human audibility of sound structures of diesel noise and also human hearing models, which are implemented in SQ evaluation tools by utilizing recent physiological knowledge.

Austempered ductile iron (ADI) is a material having excellent mechanical properties and damping capacity. However practical mass production of ADI gears has not been possible due to ADI's poor machinability and distortion during the austempering heat treatment. With a new process method of carrying out hobbing before austempering when the material is in its soft condition, then austempering it and lastly, conducting the shave finishing process, we have diminished the above defects and developed practical ADI gears. These new gears generate less noise than ordinary nitrocarburized steel gears and are superior in pitting resistance.

To reduce diesel engine noise that is induced mainly by main bearing impact forces, two types of low noise concepts of basic crankcase structures were studied. One is the “Isolated Skirt Type”, which has the feature to suppress vibrations of engine surface by separating the crankcase skirt from the main bearing caps. The other is the “Bed Plate Type”, which embodies the feature to suppress vibrations by stiffening the lower part of crankcase by adopting a bed plate design. Dynamic characteristics of both prototypes were investigated by means of experimental modal testings such as double pulse laser holography system and impulsive hydraulic excitation test rig which simulates the exciting force of combustion gas pressure in cylinder. As the result of many experimental tests, it was concluded that the “Bed Plate Type” was advantageous over the “Isolated Skirt Type” in terms of engine noise reduction.

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.