Air-Fuel Ratio Control
The air-fuel ratio of the air-fuel mixture plays a crucial role in engine power, economy, and emissions performance. In carburetor engines, multiple systems and devices meet the air-fuel ratio requirements under various operating conditions. However, it is difficult to achieve timely and precise air-fuel ratio control using mechanical methods. Most modern engines employ electronic fuel injection technology. The engine controller determines the fuel injection quantity based on readings from a series of sensors:
The air flow sensor converts the intake air volume into an electrical signal and sends it to the engine controller, which is one of the important signals determining the injection quantity.
The manifold absolute pressure sensor measures the throttle opening when the driver depresses the accelerator pedal to determine the engine's output power.
The engine speed sensor measures the engine speed to determine the basic injection quantity and basic ignition advance angle.
The crankshaft position sensor determines the injection timing and ignition timing relative to the top dead center of each cylinder. In sequential injection engines, a cylinder identification signal is also required.
The oxygen sensor measures the oxygen content in the engine exhaust gas and is an important signal for closed-loop control of the air-fuel ratio.
Ignition Timing Control
Each ECU has a data table similar to SPM (spark advance map) recorded. When the sensors detect engine speed and intake manifold absolute pressure, they will obtain the corresponding amount of advance ignition, so that the fuel in the cylinder can be fully combusted by advance ignition.