How does the exhaust gas recirculation valve work?

Exhaust gas recirculation is a technology (technology or method) that discharges a part of the burned exhaust gas and introduces it into the intake side to re-inhale it. The main purpose is to reduce nitrogen oxides (NO x) in exhaust gas and improve fuel economy at part load. Take the prefix "EGR" of each English word as a generic term.

Working principle of exhaust gas recirculation valve:

EGR system has many forms and control modes. According to the action control form of the system actuator (EGR valve), it can be divided into mechanical control EGR system and electronic control EGR system; According to the control object of EGR valve, that is, the way of system control, it can be divided into direct control EGR system and indirect control EGR system; According to the number of valves in EGR system, it can be divided into single valve control type and multi-valve control type; According to the control structure of EGR system, it can be divided into open-loop control EGR system and closed-loop control EGR system.

1) mechanically controlled EGR system

Mechanically controlled EGR system is the earliest EGR device designed and used. Its working principle is to control the opening and closing of EGR valve through vacuum degree and exhaust back pressure.

The main component of mechanically controlled EGR system is a diaphragm exhaust gas recirculation valve. According to the different valve control methods, there are positive back pressure control EGR and negative back pressure control EGR. However, for the mechanically controlled EGR system, the control range of EGR rate is limited (generally 5%- 15%), and the control accuracy is far from meeting the actual needs of the engine, so all new automobile engines tend to choose the computer-controlled EGR system, that is, the electronically controlled EGR system.

2) electronically controlled EGR system

The electronically controlled EGR system not only has a large EGR rate control range (smart%-20%), but also has a large degree of control freedom. Its main function is to select engine operating conditions with large NOX emission and carry out appropriate EGR control. When the engine is working, the microprocessor Ecu determines the current working state of the engine according to the signals of various sensors, such as speed sensor, water temperature sensor, throttle position sensor and ignition switch. So as to output an instruction to control the opening or closing of the EGR solenoid valve to start or stop EGR.