Basic Principles

Front oxygen sensor is in front of three-way catalytic converter,monitoring the content of oxygen in the exhaust gas.ECU will,according to the air-fuel raito reflected by the feedback signal of oxygen sensor,revise the fuel injection quantity by using the close-loop control to limit the air-fuel raito in a comparatively narrow range,which is the higher conversion efficiency obtained by the three-way catalytic converter,as shown in Fig.4.15.The rear oxygen sensor mainly monitors the conversion efficiency and performance of three-way catalytic converter.

Fig.4.15 The Close-loop Control Principle

The carbon canister in the fuel vapor emission system absorbs the gasoline vapor from the oil tank until the gasoline vapor is saturated and then the fresh air and the saturated fuel vapor in the carbon canister form the regenerated flow.When ECU opens the carbon canister purge solenoid,the fuel-air mixture is introduced into the intake manifold of the engine to take part in the combustion.Change the opening degree of purge solenoid by changing the Mark-Space Ratio of pulse signal provided by ECU to the coil of purge solenoid.At the same time,the pressure differential on the both sides of purge solenoid also affects the opening degree.The control of carbon canister purge solenoid opening by the ECU is mainly affected by such factors as the water temperature of the engine,rotation speed and saturation degree of carbon canister.(https://www.daowen.com)

Control Principle of Carbon Canister Purge Solenoid is shown as in Fig.4.16.

Fig.4.16 Control Principle of Carbon Canister Purge Solenoid