The function of the EGR is exhaust gas recirculation. By introducing exhaust gas into the combustion chamber, it reduces the peak combustion temperature of the engine, thereby achieving the goal of reducing NOx emissions. Diesel vehicles use an external system, where a pipe connects the exhaust pipe to the intake pipe, and a valve is installed in the pipe to control the amount of exhaust gas entering. It can be seen that the EGR valve is the core component of the entire system, and how to precisely control and monitor it is the development direction of the EGR system. EGR: The full name is Exhaust Gas Recirculation, a technique (or method) in which part of the exhaust gas from internal combustion engines is separated after combustion and reintroduced into the intake side for re-combustion. EGR valves are divided into mechanical and electronic control types. The EGR valve guides the exhaust gas from the engine combustion back to the intake manifold to participate in combustion, thereby reducing the combustion chamber temperature, improving engine efficiency, enhancing the combustion environment, reducing engine load, effectively reducing NOx emissions, minimizing knock, and extending the service life of various components. The working principle of the EGR solenoid valve is as follows: The EGR solenoid valve has three air ports. When the EGR solenoid valve coil is not energized, the spring of the EGR valve presses the valve body upward, cutting off the atmospheric port. At this time, the intake manifold of the EGR solenoid valve is connected to the vacuum chamber of the EGR valve. When the EGR solenoid valve coil is energized, the EGR valve body moves downward, connecting the atmospheric port, while the intake manifold of the EGR valve is disconnected from the vacuum chamber. One side of the EGR valve diaphragm (lower part) is exposed to the atmosphere, and the other side with a spring is the vacuum chamber, whose vacuum degree is controlled by the EGR solenoid valve. Increasing the vacuum degree in the vacuum chamber causes the diaphragm to overcome the spring force and arch upward, increasing the valve opening and thus the exhaust gas recirculation flow. When the upper part loses vacuum, the diaphragm arches downward under the spring force, closing the valve and blocking exhaust gas recirculation. In addition, increasing the exhaust gas recirculation rate will reduce the total exhaust gas mass flow, so the total pollutant output in the exhaust emissions will be relatively reduced. The task of the EGR system is to ensure that the exhaust gas recirculation volume reaches the optimal condition at every operating point, keeping the combustion process in the most ideal state and ultimately minimizing the pollutant components in the emissions. Since changes in exhaust gas recirculation volume may have completely opposite effects on different pollutant components, the so-called optimal condition is often a compromise to achieve the best overall emission reduction of related pollutants. For example, although increasing the exhaust gas recirculation rate has a positive impact on reducing nitrogen oxide (NOx) emissions, it may also negatively affect the increase in particulate matter and other pollutant components. Control principle: The engine's operating conditions vary, and so do the requirements for EGR volume. To make the EGR system more effective, the amount of exhaust gas participating in EGR must be limited. As the load increases, the EGR volume also increases accordingly and can reach the optimal value. At idle and low load, NOx emission concentration is low, so EGR is not performed to ensure normal combustion. During warm-up, the engine temperature is low, and NOx emission concentration is also low. To prevent EGR from worsening the combustion process, EGR is not performed. At high load, high speed, or full throttle, EGR is not performed to ensure the engine's power performance. During acceleration, to ensure the vehicle's acceleration performance and necessary purification effect, EGR functions during the transition process. Control method: According to the design principle of EGR, EGR must be controlled and adjusted to achieve the expected effect in engine applications.
