Research on a Closed-Loop Control Strategy of Boost Pressure in Diesel Engines with Regulated Two-Stage Turbocharging System

摘要

The level of boost pressure has a significant effect on optimizing the steady-state and transient performance of turbocharged diesel engines. However the problem of matching the wide speed range diesel engine and the high pressure turbocharging system has to be resolved. The regulated two-stage (RTS) system is an effective method to improve the fuel economy, transient response and smoke emissions. Compared with the difficult matching problem of the RTS system, the problem of boost pressure control is more complex due to the frequently changing operating conditions. To overcome the limitations of an open-loop control strategy, a closed-loop boost pressure control strategy was studied numerically using a mean value model of a diesel engine with RTS system. The system identification was conducted for the transient response from the turbine bypass opening command to the boost pressure. A gain-scheduling proportion integration (PI) feedback controller was designed, and a feed-forward module was built. Therefore, a closed-loop control system was constructed and the numerical simulation of transient loading was carried out. The results of transient loading process at 1400r/min revealed that the closed-loop dynamic control strategy achieved the fastest response characteristic. A feed-forward boost pressure command designed to optimize fuel economy combined with the closed-loop control strategy produced a better response than the open-loop dynamic control strategy, demonstrating that the closed-loop control strategy could optimize economy and dynamic performance simultaneously. According to the closed-loop control strategy, a PI controller with the variable parameters produced better transient characteristic than that with the constant parameters, due to its ability for adjusting the PI controller parameters according to the actual changing operating conditions.