System Description

Fig. 1 Open-loop control chart.:

The air/fuel ratio is controlled by either closed-loop or open-loop control, depending on coolant temperature, engine RPM, battery voltage, exhaust gas sensor signal, manifold vacuum and various other parameters depending on application.
During open-loop control, the air/fuel ratio is determined by the ECC control unit. The air/fuel ratio solenoid is controlled by open-loop control Fig. 1.
Closed-loop control operation is designed to maintain the air/fuel ratio precisely to the stoichiometric point so that the three-way catalyst can minimize all exhaust emissions simultaneously. The system used the exhaust gas sensor, located in the exhaust manifold, to give an indication of whether air/fuel mixture is leaner or richer than the stoichiometric point. The sensor transmits a nonlinear voltage to the ECC control unit. The control unit adjusts the feedback pulse width according to sensor voltage so that mixture ratio will be within the narrow window of the three-way catalyst. This system becomes open during engine warm-up until the sensor reaches operating temperature.
Air/Fuel Ratio Control Solenoid Valve
The air/fuel ratio control solenoid valve opens or closes every 65 milliseconds. During open-loop control, opening and closing time of the valve is maintained at the specified level according to condition of engine. During closed-loop control, opening and closing time is feedback controlled in the ECC control unit by the exhaust gas sensor signal.