What does the GPR valve on the car refer to?

You're talking about EGR valve, the main component abandoned in the circulation system. The engine control computer ECU controls the solenoid valve to open in time according to the engine speed, load (throttle opening), temperature, intake flow and exhaust temperature. The vacuum degree of the intake pipe enters the EGR valve vacuum membrane chamber through the solenoid valve, and the diaphragm pull rod opens the EGR valve. A small amount of exhaust gas enters the intake system through EGR valve and is mixed with it.

After mixing, the gas enters the cylinder to participate in combustion. A small amount of exhaust gas enters the cylinder to participate in the combustion of mixed gas, which reduces the temperature in the cylinder during combustion. Because NOX is generated under the condition of high temperature and oxygen enrichment, the generation of NOX is suppressed, thus reducing the NOX content in exhaust gas. However, too much exhaust gas will affect the ignition and performance of the mixture, thus affecting the dynamic performance of the engine, especially when the engine is idling, low speed, light load and cold engine, the recycled exhaust gas will obviously affect the performance of the engine. Therefore, when the engine is at idle speed, low speed, low load and cold engine, ECU controls the exhaust gas not to participate in recirculation to avoid the engine performance being affected; When the engine exceeds a certain speed and load and reaches a certain temperature, ECU controls a small amount of exhaust gas to participate in recirculation, and the amount of exhaust gas involved in recirculation changes according to the engine speed, load, temperature and exhaust gas temperature, so as to achieve the lowest NOX in exhaust gas.