| Since the beginning of the 21st century,with the rapid development of Chinses economy,the strength of scientific research and the process of industrialization have been rapidly improved.As a landmark product of industrialization,the internal combustion engine has made great progress.At present,the exhaust emission problem of internal combustion engine can not be ignored.The pollutants such as nitrogen oxides contained in the exhaust gas have caused serious harm to both humans and nature.With the continuous upgrading of domestic and international emission regulations,major internal combustion engine manufacturers are upgrading their exhaust after treatment systems.EGR technology occupies an important position in various post-processing systems because of its advantages of small space occupation and convenient replacement.As a key component of EGR technology,the development of EGR valves is of great significance.At present,domestic research and development of EGR valve is mainly used for small displacement diesel engine,but the EGR valve products fitting large displacement diesel engine are few.Different types of EGR valves at home and abroad are analyzed,and the butterfly valve form is adopted,and the scheme of separating the driving part and the valve body part is adopted.The flow diameter of the EGR butterfly valve is determined by calculation;due to the high temperature and corrosive characteristics of the exhaust gas,the packing seal is designed;the two-stage gear reducer and the torsion spring are designed and the aerodynamic force of the butterfly valve at different angles is calculated.For the designed EGR butterfly valve,it is necessary to reduce the flow diameter of the valve plate at different angles as much as possible,so it is of great significance to determine the flow coefficient and flow resistance coefficient of the EGR butterfly valve at different opening.The flow field simulation of the EGR butterfly valve is used to obtain the cloud image and streamline trajectory under different opening degrees.The pressure difference,flow coefficient and flow resistance coefficient of the butterfly valve at different rotation angles are calculated,and the simulated aerodynamic force and calculated values are compared and analyzed.The simulation results show that during the closing and opening of the EGR butterfly valve,the pressure difference between the front and rear of the valve plate decreases from 183457.19Pa to 482.62Pa,the flow coefficient increases from 0.56 to10.99,and the flow resistance coefficient decreases from 190.29 to 0.68.The high temperature exhaust gas at 600°C has a very serious influence on the driving part,so it is necessary to design and simulate the heat resistance and heat dissipation of the driving part.The temperature field simulation of the EGR butterfly valve under high temperature conditions,the average motor temperature is 258.3°C without any heat dissipation.A composite heat dissipation method is proposed:the heat dissipation rib is designed in the motor casing;and the aerogel felt of heat insulation material is placed in the motor casing bracket;at the same time,the cooling flow channel is designed in the motor casing,and the average motor temperature is 35.8°C,EGR valve can work normally.Set up the EGR valve leakage characteristic test bench to test the leakage of the butterfly valve under the specified pressure.The test leakage is 2.5±0.2m~3/h,which is lower than the specified flow rate(3m~3/h).The EGR valve angle sensor is tested to test the voltage values at full opening,full closing and different corners.The test values are within the normal range and meet the requirements for use. |
