Study On Transient Response Characteristics Of Vehicle Turbocharger

The lag phenomenon of the turbocharger during the change of operating conditions is the most prominent feature of the instantaneous operation of the turbocharged engine,which determines the overall operation status of the engine.The study of turbocharger response performance has been the top priority in the study of engine transients.The improved response properties of turbochargers can greatly enhance the efficiency of engine transient operation,decrease the emission of pollution during transient operation events,and enhance the handling performance of vehicles.In this paper,by investigating the transient response performance of turbocharged systems,seek its response mechanism,analyze the influencing factors of its transient process and the characteristics of its response,and evaluate its transient response time to promote its application in engineering.The transient performance test platform of the turbocharger was established,and the performance parameters of the compressor and turbine and the moment of inertia of the rotor were measured.On this basis,the transient simulation model of turbocharger is built,and the accuracy of the transient simulation model is verified by the turbocharger transient performance test platform.The essence of the transient response process is explored,and the response curve of the turbocharger under the unit step input signal is verified.It was shown that the response of the turbocharger when the external input changes is approximately that of a first-order system,and the turbocharger system can be modeled as a first-order system.The mechanism of each influencing factor of turbocharger transient process is investigated,and its impact regulations are sought and corresponding improving measures are recommended.The transient simulation model was simulated to find the influence of rotational inertia,pipe wall temperature and intake and exhaust pipe volume on the performance,and it was shown that the impact of pipe wall temperature on the transient response is relatively little compared to other factors,and its effect is relatively limited.The response processes caused by different airflow variation amplitudes at the turbine inlet,various compressor outlet back pressures,and the response process caused by the throttle opening variation at the compressor outlet end were simulated.It is found that the larger the amplitude of turbine inlet airflow variation,the more rapid the turbocharger response;the lower the back pressure at the compressor outlet,the faster the turbocharger response;the change of throttle opening at the compressor outlet is smaller than the response process caused by the change of valve opening at the turbine inlet,and its compressor operation trajectory is similar to a folding line.The time of the transient response process of the turbocharger is defined,and the time of the transient simulation process response is fitted with each influencing factor to discover the relative relationship between transient responding time of turbocharger and every major impact factor;the relationship between responding time and the end state flow q₀（q₀<q₁）,turbine inlet temperature T and rotational inertia J of the response process.The relationship can predict the transient response time of turbocharger,which is significant for the evaluation of transient response performance in the designing stage of turbocharger and the controlling of transient performance of turbocharged engine system.