Research On VNT Control Strategy Of High Pressure Common Rail Diesel Engine

The diesel engine with traditional turbocharger exists tons of issues such as insufficient output torque under low engine speed condition, easily overloading under high engine speed condition, turbocharger reaction sluggishly for engine torque requirement, and so forth. The fixed geometry turbocharger can’t give consideration to the performance of high and low engine condition, meanwhile, the turbocharger working out of the set point with low efficiency. These issues could be solved by using variable nozzle turbocharger (VNT).Firstly, the influence mechanism between VNT and diesel engine air system is studied, on the same time, the transfer relation of key factors and the solved model of VNT air system is found out, and the steady mathematics model of VNT air system is established, which offer the theory foundation for VNT matching and control with diesel engine.Secondly, the control system of diesel engine is analysed, the prototype of D19TCI is established and the turbocharger is matched by GT-POWER software, in the meantime, the VNT based boost pressure control MAP is simulated, which offer the theory foundation for experience research and control strategy study.Thirdly, the open-loop and adaptive PID closed-loop control means is put forward based on the air system analysis of sluggish and non-linear properties. The control model is established base on Simulink development platform and then downloaded into the system software architecture of K2 ECU to finish the bench test. For the D19TCI high pressure common-rail diesel engine, the impact of VNT vanes position on engine economy and discharge performance is researched. Simultaneously, the control constants, MAPs and curves are calibrated and optimized for precisely VNT control.The test demonstrated that the set point pressure could be traced within 3% control errors under the control of VNT model; the open-loop control means improve the response properties of VNT control system and the closed-loop means accelerate the convergence of control target; the power and economy performance of VNT diesel engine is obviously improved, the torque reserve is enhanced, especially in low engine speed condition; the fuel consumption rate is greatly decreased during the whole engine working range, especially decreased by 9% in low engine speed high load condition.