Analysis And Research On Control Strategy Of Electronic-controlled Gasoline Engine

A lot of experiments and researches have been done in the gasoline engine of 4 cylinder and some favorable control logics have been provided to improve the performances of electronic-controlled gasoline engine, which include emissions, economy and drivability.The components and functions of Gasoline Engine Management System is introduced in the paper and more detail control logics and experiments are given in the key subsystems, which are Fuel control, Spark control and Idle Air control.The Sequential Fuel Injection strategy is applied for the system, which allows better fuel control, especially under transient condition. It is the assignment of the fuel control subsystem to calculate a precise fuel pulse width for each cylinder, based on current engine operation conditions. The calculation of fuel is base on the Speed Density. If the volume, pressure, and intake air temperature are known, the basic fuel mass will be calculated. The air fuel ratio control should be correct especially in cold start, catalytic converter over-temperature protection and power enrichment. When the engine has warmed-up, the air furl ratio will be set 14.7. In fuel close loop, Integral term and Proportional term are all active on the fuel calculation correction.Spark control include three parts, Dwell control, Spark advance control and Knock control. Dwell calculation provide adequate time for coil current to flow. Dwell calculation must assure that the dwell time does not exceed certain thresholds which would damage the coils or coil drivers. On the other hand, a too short dwell time would lead to misfire. Spark advance calculation must be accurate and it is so important that will directly influence the engine's performance. The value is summation of main spark and many correction terms derived from different engine run conditions. Knock control will reduce spark advance to protect engine when the knock is detected.The purpose of the idle speed control logic is to control engine speed at closed throttle. The control logic should prevent engine stall, maintain a stable engine speed during changing engine loads at idle, and provides for a smooth transition while changing from or to closed throttle. In this system, the ECU controls a step-control-motor with pintle valve mounted in the throttle body, which regulates bypass air around throttle plate. By extending or retracting the LAC (Idle Air Control) valvemotor, a controlled amount of air is diverted around the throttle to increase or decrease the engine speed depending on engine operating conditions such as throttle position, vehicle speed, coolant temperature, manifold pressure, engine speed...etc. In close loop IAC mode, the ECU uses the actual engine speed information as a feedback to automatically adjust the IAC motor position if the idle speed is sensed to be too low or too high.The results of the tests show that the advanced control logic will help to improve the engine's integrative performances.