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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.

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.

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 effect of the use of the EGR system on the lubrication of a passenger car diesel engine was investigated. The higher the EGR rate, the more soot in the oil. And the most detrimental effect was found in valve train wear. Some engine tests, including motoring tests, were carried out to investigate the contribution of soot to valve train wear. The mechanism of cam and rocker arm wear in used oils was studied by analyzing for elements on the lubricated metal surface and subsequently the mechanism was more thoroughly studied using the four-ball test. Soot seems to act as an abrasive on the anti-wear solid film formed by the oil on the metal surface and this film contains Ca, O, P and S. Some hardware modifications and oil formulations to reduce valve train wear are also discussed.

Mitsubishi Motors Corporation uses spiral bevel gears in the transfer system for 4-wheel drive passenger cars modified from the front wheel drive configuration. This transfer gear ratio is near 1:1, and gears have uniform depth teeth cutting by the continuous generating method of OERLIKON cutting machine. In this method, the cutter and the work rotations are timed together to accomplish continuous indexing and cutting in order to enable high productivity. In general, it is difficult to reduce the meshing noise of spiral bevel gears and control its quality. The authors established the tooth surface coordinates, to reduce the meshing noise, by studying the influence of tooth surface coordinates on the meshing transmission error (MTE).

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.

A two-stage combustion is one of the Mitsubishi GDI™ technologies for a quick catalyst warm-up on a cold-start. However, when the combustion is continued for a long time, an increase in the fuel consumption is a considerable problem. To solve the problem, a stratified slight-lean combustion is newly introduced for utilization of catalysis. The stratified mixture with slightly lean overall air-fuel ratio is prepared by the late stage injection during the compression stroke. By optimizing an interval between the injection and the spark timing, the combustion simultaneously supplies substantial CO and surplus O2 to a catalyst while avoiding the soot generation and the fouling of a spark plug. The CO oxidation on the catalyst is utilized to reduce the cold-start emissions. Immediately after the cold-start, the catalyst is preheated for the minimum time to start the CO oxidation by using the two-stage combustion. Following that, the stratified slight-lean combustion is performed.

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.

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.

This paper presents several methods for reducing engine weight primarily through substitution with light-weight materials. The efficiency and performance of the engine were reviewed using a light-weight experimental engine (hereinafter called “weight-reduced engine”) constructed by the authors in order to investigate the possibility of practical use of the proposed weight reduction measures. The weight-reduced engine is based on an in-line 4-cylinder, 2.0 liter, gasoline engine with the base engine weight of 162 kg excluding engine oil and coolant and was reduced by 37 kg by applying alternative light-weight materiaLs and new manufacturing techniques. This corresponds to 23 % weight reduction. The materials used in the weight-reduced engine are 53 % steel, 33 % aluminum, 7 % plastics and 7 % other light-weight materials. It was found that by application of light-weight materials, the engine performance of the weight-reduced engine could be improved.

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.

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.

In response to stringent particulate matter (PM) emission regulations worldwide, developments of diesel particulate filter (DPF) continue apace in addition to engine modification for PM reduction. Particularly with buses used in urban areas, reduction methods in black smoke emissions are being researched in addition to the efforts to satisfy the aforementioned PM regulations. The system described in this paper was developed for use mainly with buses in large urban concentrations. The system described in this paper mainly consists of both wall-flow monolith filters for filtration of PM emissions and electric heaters for regeneration. A key feature of this system is that exhaust gas is used for effective combustion of PM during regeneration. With conventional systems, airpumps have been used to feed air for PM combustion during regeneration. With the new system, however, the use of an air pump was discontinued due to durability and cost considerations.

In this study, the oxidation stability, soot dispersancy, antiwear performance, and friction-reducing capability of friction modifiers (FMs) were evaluated, and an SAE 5W-30 fully synthetic oil with MoDTC type FMs was developed for heavy-duty diesel engines. In several engine tests, it was confirmed that the developed oil can double the oil drain interval in comparison with API CD SAE 30, even when EGR is applied, and improves the fuel efficiency.

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.

A particulate trap oxidizer system to reduce diesel particulate emissions has been developed. This system consists of a ceramic foam filter with an optimum volume, shape, and mesh number in terms of collection efficiency, pressure loss and particulate blow-off; a catalyst with a low activated-temperature for particulate incineration and with no sulfate formation during highway driving; and a regeneration system which prevents particulate overcollection during long-term continuous low-load/low-speed driving where it is difficult to achieve self-burning of particulates with a catalytic reaction. This paper describes the development of the particulate trap oxidizer system with these technologies and presents the results of practicability evaluations and 50,000-mile vehicle durability tests.

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.

An investigation of anti-corrosion steel sheets (non-galvanized) which contain copper for automobile body parts has been conducted. Copper additives accelerate the formation of amorphous substrates. These substrates decrease the rate of corrosion. In order to retain the steel's formability and weldability, the contents of the alloying elements have been optimized. As a result, this newly developed steel sheet can be used for many different applications such as door sashes and door panels of mass produced cars. This paper describes the key properties of the newly developed steel sheet and additionally the mechanism of corrosion prevention, weldability, formability, and so on.

Auto-regeneration of diesel particulate traps, particularly combustion mode of soot in a wall flow filter with fuel additives, was investigated using a diesel engine of a light duty truck and truck itself. Soot burning in the trap and regeneration were observed under any engine operating condition including prolonged idling and stop-and-go driving at 0.18g metal/1 dosage of a mixture of copper and lead in the fuels. However, trap life was limited by ash clogging due to the metallic compounds. Although the influence of metallic additives on the environment was debatable, test results of the trap durability and calculations of soot burning based on the thermal ignition theory indicated that dosage and kind of fuel additives should be optimized in view of both trap life and reliability of soot burning.

For meeting more stringent regulations to be imposed for reducing particulate matter (PM) in exhaust gas from diesel engines, it is required to improve performance of a trap system or other post-processing devices as well as fuel combustion efficiency of the engine itself. In the trap system, a trap filter is equipped to collect PM from exhaust gas. For continuous use of the trap filter, a regenerative processing must be carried out to remove PM by means of forced burning when a certain amount of PM has been trapped. The combustibility or burning characteristics of collected PM have a significant effect on the regenerative processing with an electric heater/burner. To clarify the combustibility of PM collected in the trap filter, we have examined the relationships between engine drive conditions (exhaust gas temperature), PM characteristics, and combustibility.