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Dynamic characteristics of fuel supply system for multi-cylinder gasoline engine was studied analytically and experimentally. We investigaged. (1) The relation between the air flow rate upstream the throttle valve and the air flow rate into the cylinder, when the throttle valve is opened or closed rapidly. (2) The air fuel ratio in the cylinder affected by the above relation. (3) Pmax response affected by the residual fuel in the intake manifold.

Mixture formation and the ignition process in 4 cycle 4 cylinder spark ignition engines were investigated, using an optical combustion sensor that combines fiber optics with a conventional spark plug. The sensor consists of a 1-mm diameter quartz glass optical fiber cable inserted through the center of a spark plug. The tip of the fiber is machined into a convex shape to provide a 120-degree view of the combustion chamber interior. Light emitted by the spark discharge between spark electrodes and the combustion flames in the cylinder is transmitted by the optical cable to an opto-electric transducer. As a result, the ignition and combustion process which depends on the mixture formation can be easily monitored without installing transparent pistons and cylinders. This sensor can give more accurate information on mixture formation in the cylinders.

The control strategies of auto-ignition for homogeneous charge compression ignition and controlled auto ignition operations were investigated using a simple engine model. The fluctuations of auto-ignition characteristics during transients in variable timing of exhaust and intake valves were analyzed. When the valve timing changed stepwise, the characteristics fluctuated and differed slightly from these in steady state conditions because combustion in the prior cycle affected the gas exchange in the next cycle. To reduce such fluctuations, the control strategies of cylinder air mass, residual gas mass, fuel mass, air/fuel ratio were investigated for a simple engine dynamic model (a 4-cylinder, 4-stroke engine with total cylinder stroke volume of 2000 cm3), which could simulate the dynamics of gas exchange during transient valve timing in a wide dynamic range.

We have examined a new precise control method of the air fuel ratio during a transient state which provides improved exhaust characteristics of automobile engines. We investigated the measurement method for the mass of fresh air inducted by the cylinder, which is most important for controlling the air fuel ratio. The mass of fresh air must be measured in real time because it changes in each cycle during a transient state. With an conventional systems, it has been difficult to get accurate measurement of this rapidly changing mass of fresh air. The method we studied measures the mass of fresh air by using the intake manifold pressure and air flow sensors. During a transient state, the reverse flow of the residual gas from the cylinder into the intake manifold, which occurs at the first stage of the suction stroke, changes with each cycle. The mass of fresh air changes accordingly.

Mixture formation technology for gasoline engine multipoint fuel injection systems has been investigated. The fuel injector's spray, the volatility of droplets floating in the air flow, the movement of droplets around the intake valve's upper surface, the volatility of droplets on heated surfaces, and the process of atomizing droplets in the intake valve air flow was analyzed. Droplet diameters and spray patterns for good mixture formation without liquid film in cylinders have been clarified. When sequential injection is used for better responsiveness in fuel injection systems, engine performance may be reduced through increased HC emissions in some conditions. Reducing the diameter of spray droplets and preventing fuel from concentrating in the intake valve promotes vaporization, reduces fuel concentration on cylinder walls, and prevents reductions in engine performance.

The basic structure of a new engine control system for highly accurate air-fuel ratio control is introduced. Improved engine power and decreased fuel consumption are required for today's engines. Better air-fuel ratio control must be attained to set the air-fuel ratio to that of the maximum power and minimum fuel consumption. In order to enhance the accuracy of the air-fuel ratio control, the air flow meter, air-fuel ratio sensor, and fuel supply device are improved in the new system. Accuracy is lost in conventional system owing to the sensors' deterioration over long-term use. So prevention of air flow meter deterioration and compensation of air-fuel ratio sensor deterioration are taken into consideration. Fuel atomization of the fuel supply device is improved in order to reduce the air-fuel ratio fluctuation in the transient operating state. High power and decreased fuel consumption over long-term use are made possible with the new system.

Effects of mixture formation of fuel injection systems on gasoline engine performance have been studied. Several fuel injectors which produced various spray diameters and spray patterns were used in engine tests. Spray behavior in an air flow was investigated to clarify the spray distribution through the intake valve. The relationships between the spray distribution near the intake valve and the HC emission or engine response were considered. The amount of HC emissions increased if fuel was injected when the intake valve was open with a heavy load (e.g. an engine speed of 2000 rpm and a manifold pressure of 98 kPa), because fuel would flow into the cylinders one-sidedly, causing a liquid film to form. The amount of HC emissions also increased if fuel was injected when the intake valve was open with a light load (e.g. during idling), because the fuel injection pulse would be short and fuel would flow into the cylinders, but the air-fuel mixing would not be enough to cause a misfire.

An algorithm for a fuel efficient hybrid drivetrain control system that can attain fewer exhaust emissions and higher fuel economy was investigated. The system integrates a lean burn engine with high supercharging, an exhaust gas recycle system, an electric machine for power assist, and an electronically controlled gear transmission. Smooth switching of the power source, the air-fuel ratio,pressure ratio, exhaust gas ratio as a function of the target torque were analyzed. The estimation of air mass in cylinder by using an air flow meter was investegated to control the air-fuel ratio precisely during transients.

The combination of physical models including a combustion model of an advanced engine control system was proposed to obtain sophisticated air/fuel ratio and residual gas fraction control in lean mixture combustion and high boost engines, including homogeneous charge compression-ignition and activated radical combustion with a variable intake valve timing and a turbocharger or supercharger. Physical intake, engine thermodynamic, and combustion models predicted air mass and residual gas fraction at the beginning of compression in the cylinder, on the basis of signals from an air flow sensor and an in-pressure sensor. Then, these models determine control variables such as air mass, fuel mass, exhaust gas recycle valve opening, intake valve timing and combustion start crank angle, to attain an optimum air fuel ratio (A/F), optimum residual gas fraction, and high efficient low nitrogen oxides combustion without power degradation in the above conditions.

The combination of physical models, including a combustion model of an advanced engine control system, was proposed to obtain sophisticated air/fuel ratio and residual gas fraction control in lean mixture combustion and high boost engines, including homogeneous charge compression-ignition and activated radical combustion with variable intake valve timing and a turbocharger or supercharger. Physical intake, engine thermodynamic, and combustion models predict air mass and residual gas fraction at the beginning of compression in the cylinder, on the basis of signals from an air flow sensor and an in-pressure sensor. Then, these models determine control variables such as air mass, fuel mass, exhaust gas recycle valve opening, intake valve timing, exhaust valve timing and combustion start crank angle, to attain an optimum air fuel ratio (A/F), optimum residual gas fraction, and highly efficient low nitrogen oxides combustion without power degradation in the above conditions.

Generalized models of the air/fuel ratio control using estimated air mass in the cylinder were presented to obtain highly accurate control during transient conditions in high supercharged direct injection systems with a complex air induction system. The air mass change was estimated by using upstream models which estimated the pressure of the intake manifold by introducing the output of the air flow meter and the differential of the output into aerodynamic equations of the intake system. The air mass into the cylinders was estimated at the beginning of the intake stroke under a wide range of driving conditions, without compensating for changes in the downstream parameters of the intake system and engine. Therefore, the upstream models required relatively minor calibration changes for each engine modification to be able to estimate the air mass on a cylinder-by-cylinder basis.