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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.

Optimization of the clutch torsional characteristics is one of the effective methods to reduce the idling rattle noise. Many researches on th.s problem have been reported, but only few of them give sufficient consideration to the drag torque applied to the clutch disc during engine idling. This paper pays attention to the drag torque and discusses the mechanism of idling rattle noise by using vehicle testing, bench test with rotating torsional exciter and computer simulation. Reauction of Idling

During next decade, automotive engineers will take up unprecedented challenges to meet a variety of technical demands on passenger cars. While performance, refinement and reliability will continue to be major technical goals of passenger cars, reducing their impact on the environment not only in urban areas but also on the global basis will become an increasingly urgent issue. In addition, the need for energy and resources saving will necessitate development of more fuel efficient cars, exploitation of alternative energy and recycled materials. In this paper, the authors will review various alternative engines as candidates to satisfy the above demands. The authors will also discuss various alternative transportation energy sources such as alcoholic fuels, natural gas, hydrogen and electricity. Finally the trends of future passenger car engine design will be discussed.

Beta Ti alloy valve spring retainers are newly developed for use in mass produced automobiles for the first time. Ti alloy valve spring retainers vith a weight saving of 42%, compared to steel retainers, have reduced the inertial weight of the valve train components by 6%. And this weight reduction has the benefit of increasing the upper limit of the engine speed, which improves the engine performance. Ti alloy valve spring retainers are cold forged by the conventional fabrication facilities for steel retainers, using Ti-22V-4Al (the beta Ti alloy) which possesses excellent cold workability in a solution treated condition. Oxygen surface hardening is applied to protect Ti alloy valve spring retainers from wear damage. In addition, aging treatment and shot blasting are performed to improve strength and stiffness of valve retainers.

Spray motion visualization, mixture strength measurement, flame spectral analyses and flame behavior observation were performed in order to elucidate the mixture preparation and the combustion processes in Mitsubishi GDI engine. The effects of in-cylinder flow called reverse tumble on the charge stratification were clarified. It preserves the mixture inside the spherical piston cavity, and extends the optimum injection timing range. Mixture strength at the spark plug and at the spark timing can be controlled by changing the injection timing. It was concluded that reverse tumble plays a significant role for extending the freedom of mixing. The characteristics of the stratified charge combustion were clarified through the flame radiation analyses. A first flame front with UV luminescence propagates rapidly and covers all over the combustion chamber at the early stage of combustion.

Three zone mixture preparation model, assuming that fuel and air are distributed in three separate zones, fuel air and mixture zone, was proposed. Air Utilization Efficiency derived from the model was used to evaluate the mixing nonuniformity. Effect of the large scale nonisotropic turbulence downstream of the dimple or edge in the intake port of MPI engine on the convective mass transfer from fuel film was clarified by the proposed nondimensional index, Local Sherwood Number. It was found that when the fuel is injected toward the wall where large scale turbulence exists, almost all of the fuel is seeded in the air passing the region at the beginning of the intake process, resulting in the time-resolved nonuniformity of the mixture strength at the intake valve. Using the Air Utilization Efficiency, it was elucidated that time-resolved mixing nonuniformity at intake valves induces spatially nonuniform fuel/air distribution in the cylinder.

Protection of the Earth's environment by means of energy saving and cleaning up of air pollution on a global scale is one of the most important subjects in the world today. Because of this, the requirements for better fuel economy and cleaner exhaust emissions of internal combustion engines have been getting stronger, and, in particular, simultaneous reduction in nitrogen oxides (NOx) and particulate matter (PM) from heavy-duty diesel engines (HDDEs) without degrading fuel economy has become a major subject. Mitsubishi Motors Corporation (MM) has been selling diesel-powered heavy-duty trucks in the U.S. market since 1985 and has agressively carried out development work for meeting the 1991 model year exhaust emission standards.

The authors developed, for use in diesel engines, ceramic tappets cast in aluminum alloy that drastically improved wear resistance and valve train dynamics. The ceramic tappets consist of two parts: a ceramic head, which contacts the cam and push rod, and a tappet body made of aluminum alloy. Concerning the ceramic, silicon nitride was the best material of the three ceramics evaluated in the tests and the sliding surface, in contact with the cam and push rod, was left unground. As for the aluminum alloy, hyper-eutectic aluminum-silicon alloy with a controlled pro-eutectic silicon size was selected. A reliability analysis using the finite-element method (FEM) was also made on the structure of the ceramic tappet for enhanced durability and reliability. The combination of this tappet and a cam made of hardened ductile cast iron, hardened steel, or chilled cast iron, respectively exhibits excellent wear resistance.

Crankshaft torque fluctuation has been theoretically analyzed and possible sources of error have been reviewed in the cases of determining the indicated mean effective pressure (Pmi) from measurement of the flywheel angular-speed fluctuation. The specific objective of this study was to develop a new approach to determine Pmi from the crankshaft torque of a SI engine, and it has successfully proven that using an appropriate data processing for the angular-speed fluctuation, Pmi in low- to medium-speed ranges can be estimated with very high accuracy in terms of 99% or higher coefficient of correlation to the in-cylinder pressure sensor.

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.

Vulcanized rubber hoses are difficult to recycle and have a complicated manufacturing process. Recently, we have developed the vacuum hose for engine control out of thermoplastic elastomers. As a result of this development, scrap material from the manufacturing process can be recycled and, in addition, about a 30 percent weight reduction and a 20 percent cost reduction are achievable by virtue of the lower specific gravity and by the more simplified manufacturing process. In order to assess the feasibility of using thermoplastic elastomers for vacuum hoses, we developed a heat aging simulation test method. This was achieved by first investigating the actual vehicle environmental conditions of currently used vacuum hoses by retrieving and examining these hoses from used vehicles. We then extrapolated what the condition of such hoses would be after being subjected to heat aging for 200,000 km of service in an actual vehicle, and applied this calculation to our newly developed hoses.

New systems or functionalities have been rapidly introduced for fuel economy improvement. Active vibration suppression has also been introduced. Control algorithm is required to be verified in real time environment to develop controller functionality in a short term. Required frequency domain property concept is proposed for representation of target phenomena with reduced models. It is shown how to select or reduce engine, transmission and vehicle model based on the concept. Engine torque profile which has harmonics of engine rotation is required for engine start, take-off from stand still, noise & vibration suppression and misfire detection for OBD simulation. An engine model which generates torque profile synchronous to crank angle was introduced and modified for real time simulation environment where load changes dynamically. Selected models and control algorithms were modified for real time environment and implemented into two linked universal controllers.

The gasoline direct injection engine starts significantly faster than a conventional engine. Fuel can be injected into the cylinder during the compression stroke at the same time of cranking start. When the spark plug ignites the mixture at the end of compression stroke, the engine has its first combustion, that is, the first combustion occurs within 0.2 sec after the start of cranking. This unique characteristic of quick startability has realized a idle stop system, which enables drivers to operate the vehicle in a natural manner.

The need of lightweight vehicle design is motivated by the recent global trend of less fuel consumption and lower emission in vehicle. However in NVH development of vehicle, it becomes more difficult for the lightweight vehicle to reach low vibro-acoustic sensitivity than, for the heavy weight one to do so. Inthis environment, this paper describes about the practical finite element (FE) modeling of vehicle structure and acoustics, in order to predict "boom" response to powertrain excitation. The FE modeling process through validation and updating with experimental mode makes, the accumulation of considerable expertise for improving prediction accuracy, possible. FE analysis based on this modeling process is so useful for predicting "boom" levels up to 200 Hz. Using the result of FE analysis, structural optimization is executed in order to improve "boom" level of 80 Hz.

Two-stage hybrid combustion for a 6-stroke gasoline direct injection SI engine is a new strategy to control the ignition of the HCCI combustion using hot-burned gas from the stratified lean SI combustion. This combustion is achieved by changing the camshafts, the cam-driven gear ratio and the engine control of a conventional 4-stroke gasoline direct injection engine without using a higher compression ratio, any fuel additives and induction air heating devices. The combustion processes are performed twice in one cycle. After the gas exchange process, the stratified ultra-lean SI combustion is performed. The hot-burned gas generated from this SI combustion is used as a trigger for the next HCCI combustion. After gasoline is injected in the burned gas, the hot and homogeneous lean mixture is recompressed without opening the exhaust valves. Thus the HCCI combustion occurs.

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.

A novel leanburn concept, ‘Barrel-Stratification’ is proposed. Fuel is introduced into the cylinder through one of the intake ports of a dual-intake-valve engine of which the tumbling air motion is intensified by the sophisticated intake port design. Because the velocity component in the direction parallel to the axis of tumble is small, charge stratification realized during the intake stroke is maintained until the end of the compression stroke. By the effects of charge stratification and the turbulence enhancement by tumble, stable combustion is realized even at extremely lean conditions. The concept was verified by flow field analysis applying a multi-color laser sheet technique and the flame structure analysis employing the blue-end image intensification realized by the interference mirror and the short delay phosphor.

In order to design a well-balanced truck frame, optimization of not only the stiffness of the entire body and stress of each member, but also the internal force of each member is necessary, including the effect of a rear body mounted on the frame. This paper proposes a new parameter, “torsional stiffness share rate,” that directly correlates the contribution of member torsional stiffness to frame torsional stiffness with the internal force of the members as to torsion of the truck frame. The merits of the torsional stiffness share rate are shown in comparison with the strain energy share rate and the stiffness contribution rate. The results of experimental and FEM analyses of the torsional stiffness share rate are also presented.

To improve vehicle startability and transient response of turbocharged diesel trucks, their phenomena have been investigated and analyzed in detail and various supercharging systems have been developed and installed on a truck for comparison of their characteristics. The systems considered were ceramic, variable geometry, variable entry,and air-assisted turbochargers and a combined supercharging system. The variable entry turbocharger has two turbine scrolls with different nozzle areas and two switching valves to get three different turbine flow capacities. The combined supercharging system consists of a mechanical supercharger and a turbocharger. These are linked in series. Both work in a low engine speed range, and the turbocharger only works in middle and high engine speed ranges. Among these systems, the combined supercharging system is the best for improving both vehicle startability and transient response of a truck.

To reduce friction is required to improve engine fuel economy. This study aimed to reduce piston skirt friction, which is a major factor in engine friction. ‘Soft skirt’ is a trendy item in recent gasoline engines, which can improve skirt sliding condition by larger deformation when the piston is pressed to the liner. The effect is confirmed by friction measurement and oil film observation, using prototype pistons. And also one major factor of the effect is clarified that not only side force but also cylinder pressure causes effective deformation of the skirt to create thick oil film at early combustion stroke.