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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.

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.

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 Mitsubishi GDI engine has adopted a pair of upright intake ports, to induce a rotating in-cylinder flow, reverse tumble, and control air fuel mixing with this flow. The port design of the GDI engine was optimized for achieving a high intensity of the reverse tumble while maintaining a high charge coefficient, by means of modeling of in-cylinder flow and experiment with a steady flow rig. First of all, the ideal design of the upright ports was discussed. It was found that for enhancing the reverse tumble, it is more effective to arrange a pair of the ports parallel, than to arrange them convergent. The parallel arrangement leads to the smoother flows passing through the intake sides of the intake valves, and then descending on the cylinder liner, that is turning toward the rotation direction of the reverse tumble, because of less impingement of the flows through a pair of the valves.

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.

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.

Mitsubishi Motors Corporation (MMC) has developed a new V configured 8 cylinder turbocharged and intercooled diesel engine (8M22T1) for the heavy-duty truck market. The engine is one of the first in its class to feature a common rail fuel injection system. This advanced engine management system was selected to meet the challenges of ever tightening emission regulation, specifically in the areas of smoke and noise. The 8M22T1 embodies a number of design innovations which have resulted in significant improvements in performance, fuel economy, durability and reliability.

In this study three EGR methods were applied to a 12 liter turbocharged and intercooled Dl diesel engine, and the exhaust emission and fuel consumption characteristics were compared. One method is the Low Pressure Route system, in which the EGR is taken from down stream of the turbine to the compressor entrance. The other two systems are variations of the High Pressure Route system, in which the EGR is taken from the exhaust manifold to the intake manifold. One of the two High Pressure Route EGR systems is with back pressure valve located at downstream of the turbine and the other uses a variable geometry(VG) turbocharger. It was found that the High Pressure Route EGR system using VG turbocharger was the most effective and practical. With this method the EGR area could be enlarged and NOx reduced by 22% without increase in smoke or fuel consumption while maintaining an adequate excess air ratio.

In this study a new water injection system was applied to an 11 liter naturally aspirated DI diesel engine in order to reduce exhaust emissions. In this system, the water and fuel were arranged in the injection nozzle during the time between injections as fuel, water and then fuel. The fuel and water were then injected into the cylinder in that order. The tests were conducted at several engine operating conditions from the Japanese 13 mode test cycle to clarify effects of water injection on exhaust emissions and fuel consumption. The results showed that NOx reduction was directly proportional to the relative amount of water injection, regardless of engine speed and load. By using the optimal relative amount of water injection at each engine operating condition, total NOx and particulate matter (PM) in the Japanese 13 mode test cycle were reduced by 50% and 25%, respectively, without a fuel consumption penalty.

When replacing a metal engine part with plastic, it is necessary to regard vibration damping as one of the important factors in terms of noise reduction as well as strength and heat resistance as being characteristics of the material. Plastics are far better for vibration damping than steel or aluminum, but this property is reduced by the addition of glassfiber-reinforced or high heat-resisting resins. We have taken notice of SMC (Sheet Molding Compound) which has the excellent strength and heat resistance properties and studied it in order to increase its vibration damping property. Since organic polymers show the peak value for vibration damping performance in the vicinity of the glass transition temperature (Tg), we studied a method to shift the Tg near the operating temperature region in order to improve the vibration damping property.

Since it is more difficult for truck door panels to realize curvature than passenger car door panels, internal stiffeners are mounted between the outer panel and inner panel through the use of an adhesive for ensuring stiffness. For this reason, a problem occurs as to the proper placement of the stiffeners so as to effectively improve stiffness. By FEM prediction and experimentation, the following have been clarified: (1) Arrangement of stiffeners for effectively improving stiffness (2) Stiffness share of stiffeners and outer panel against stiffness

We have developed a tappet with a cam lobe contacting tip made of a hard sintered material whose base material is cobalt, which adheres less to the steel of camshafts, and which also contains fine particles of tungsten carbide and chrome carbide. We have established a new evaluation method to access wear resistance performance of the tappet. It enables us to measure directly the friction force generated between the cam lobe and tappet and to evaluate anti-scuffing performance with high accuracy because we can clarify the time, load and cam angle at which scuffing occures.

Optimizing the design of automobile outer panels for weight reductions requires a consideration of stiffness and dent resistance. This paper presents a finite element analysis method for predicting the dent resistance of automobile body panels. The method is based on elastoplasticity analysis and nonlinear contact analysis. The analysis shows that dent resistance is greatly influenced not only by the stress-strain curve of the formed panel but also by the residual stress in the panel. An increase in yield stress improves dent resistance. The computed results obtained with this method compare favorably with experimental data, thereby validating this approach.

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.

Flow and flame structure visualization and modeling were performed to clarify the characteristics of bulk flow, turbulence and mixing in a four-valve engine to adopt the lean combustion concept named “Barrel-Stratification” to the larger displacement center-spark four-valve engine. It was found that the partitions provided in the intake port and the tumble-control piston with a curved-top configuration were effective to enhance the lean combustion of such an engine. By these methods, the fuel distribution in the intake port and the in-cylinder bulk flow structure are optimized, so that the relatively rich mixture zone is arranged around the spark plug. The tumble-control piston also contributes to optimize the flow field structure after the distortion of tumble and to enable stable lean combustion.

In recent year, higher strength for truck and bus transmission gear has become necessary. For the transmission gears, carburized gears have generally been used. We have examined the effects of shot peening and grinding using a CBN grindstone on the pitting strength and the bending fatigue strength of a carburized gear, and further evaluated a material which reduces the structual anomalies produced during carburization. As a result, it has been found that shot peening or CBN grinding is more effective for improving both pitting strength and bending fatigue strength than improving the material composition. Therefore, it is evident that residual compressive stress caused by shot peening or CBN grinding suppresses the propagation of cracks.

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.

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.

This paper describes an experimental analysis of frictional heat generated between the pads and rotors of disc brakes, to determine the paths and amounts of heat flow. The brakes were applied repeatedly at a constant initial speed, deceleration and interval until brake temperature became saturated. Under these conditions we measured an unsteady temperature distribution state during a single application of the brakes, and also a saturated (quasi-stationary) temperature distribution during repeated braking. Heat flow was studied in six paths: heat conduction to the pad; heat convection to the air from the friction areas of the inner and outer disc, from the ventilating parts and from the tube section of the rotor; and heat conduction to the rotor flange section.

At Mitsubishi Motors, a thin-walled exhaust manifold, made of stainless cast-steel, has been developed with the aim of achieving higher heat-resisting reliability as well as weight reduction. The new exhaust manifold is made of ferritic stainless cast-steel, employing an advanced vacuum casting (CLAS). Its geometry was designed using finite element analysis and its durability was confirmed by testing both on various test devices and on a vehicle. The exhaust manifolds has been adopted on a production engine model and has proven the following advantages over a conventional cast-iron ones; excellent heat resistance. weight reduction of over 20%. possible exhaust emission reduction as a result of lower heat-capacity of the exhaust manifold.