Coordinated Control Strategy Of Turbocharger And EGR For Vehicle Diesel Engine

As quality of our life is improving, vehicle ownership is growing fast recent years, which results in severe problems of energy shortage and environmental pollution, and it is very urgent to have those problems solved. As the most effective to reduce NOX emission, EGR has been used on the engine of vehicle, and it is very important to control EGR rate accurately. NOX emission can’t be reduced effectively if EGR rate is too low; fuel consumption will rise even smoke if EGR rate is too high.As ordinary turbochargers can’t meet demands, more and more engine manufacturers choose variable nozzle turbochargers in order to improve power capability of vehicle engine. Choosing smaller surface diameter ratio can enhance performance of engine when speed is low; Choosing bigger surface diameter ratio can reduce pumping loss and prevent turbocharger from overspeed when engine speed is high. But changes of both EGR valve and surface diameter ratio can affect the intake and exhaust system’s performance of engine, causing that boost pressure and EGR rate of engine can’t be controlled accurately when an engine has EGR system and variable geometry turbocharger and both of them connect intake pipes to exhaust pipe.First of all, this article study the influence that changes of EGR valve and surface diameter ratio have on the performance of engine intake and exhaust system. The results show that the bigger EGR valve opens, the lower pressure before turbo is; the higher temperature before turbo is; a constant or the lower boost pressure is; the higher inlet temperature is; the smaller inlet air mass and surplus coefficient of air are. The bigger VNT duty ratio is(the smaller surface diameter ratio is), the higher pressure before turbo is; a constant or the lower temperature before turbo is; the higher boost pressure is; a constant or the higher inlet temperature is; the bigger inlet air mass and surplus coefficient of air are.Then, a simulation model of test engine has been established based on the software GT-power in order to study the influence that changes of EGR valve and surface diameter ratio have on the wave of engine intake system. The results show that the bigger EGR valve and surface diameter ratio of VNT are, the smaller wave of engine intake process is.Finally, the EGR valve opening control model based on the correction of inlet flow mass and the VNT rack opening control model based on the correction of boost pressure are proposed on the basis of usual control strategy, and coordinated control strategy of turbocharger and EGR is formed by combination of them. A simulation model is also established based on software GT-power in order to verify the usability of this control strategy, and four different speed 1012r/min, 1597r/min, 2282r/min, 2738r/min are simulated by this model. The results show that coordinated control strategy of turbocharger and EGR has ideal control effect, and the maximum deviation rate is 1.4%.