The Design Of Variable Nozzle Turbocharger(VNT) Electronic Control System Based On Test Bench

With the vigorous development of China's automobile industry and the popularity of Turbo technology,turbocharger is widely used in the automotive engine.Although there are strong advantages of low emission and high power,equipped with traditional fixed cross section turbocharger models also have low speed torque,instantaneous acceleration lag and other serious defects.One of the solutions is the variable geometry,the variable geometry turbocharger can achieve a good match between the turbocharger and the engine in the whole working condition,so as to improve the low speed torque reserve and the transient response.As the key technology of variable geometry turbocharger,the performance of electronic control system plays a decisive role in the realization of the matching between the turbocharger and the engine and the performance of the both.In the present study,a variable nozzle turbocharger(VNT)control system is designed,which is matched with the full operating condition of the combustor,and based on the current turbocharger performance test bench.The main research work is as follows:Firstly,make the programme of two-phase hybrid stepper motor as the actuator,close to the turbocharger,and gear group as the transmission device of the actuators,and overcome the previous shortcomings of long transmission distance,poor accuracy and slow response.Secondly,with Altium Designer as the circuit design platform,using the idea of modularization carrying out the design of electronic control system hardware circuit,and making signal acquisition and processing module and stepper motor driver module separation,so as to avoid the interference signal effectively,and at last completed the design of PCB.Thirdly,through the method of open loop system control,serial port software adjust making the compressor efficiency MAP,avoids the tedious process of making control MAP by replacing the pneumatic actuator,at the same time,it can ensure the accuracy of the control MAP.Fourthly,with Keil software as the development platform,using C language design of main program and subprograms.In order to improve the control precision of the system and the economy of the burner,formulate the closed loop feedback control strategy of making compressor efficiency as control target,and at the same time,in order to eliminate the system oscillation caused by the fluctuation of control target,adopt the integral separation PID control algorithm.Fifthly,five key performance parameters(boost ratio,compressor adiabatic efficiency,expansion ratio,turbine efficiency and turbocharger total efficiency)of VNT were studied in a turbocharger performance test bench,in order to analysis the performance of turbocharger and the electric control system which designed more intuitive,the open and closed loop curves of these parameters with the change of intake air flow under two different injection pressures are obtained,and use the average value of the experimental values of each parameter to measure the performance of the turbocharger compressor end,the turbine end and the whole machine.The test results show that the overall performance of VNT under high working condition is better than that of low working condition,and the designed electronic control system can achieve the expected goal.