An exhaust gas recirculation control strategy for passenger car diesel engines using an inverse valve model

Abstract

In diesel engines, accurate control of the exhaust gas recirculation (EGR) is important because of its effects on the nitrogen oxide and particulate matter emissions. The conventional EGR control system adopts a simple proportional-integral (PI) control algorithm with a lookup-table-based feedforward control and gain scheduling. However, this lookup-table-based control system has limited control performance in transient operations because the lookup tables are obtained from static engine data. The objective of this paper is to improve the control performance of the diesel engine EGR system by using a mathematical model of the EGR path. The proposed EGR control system is composed of PI controller gain scheduling and a feedforward control algorithm based on the mathematical model. The gain-scheduling algorithm provides a PI controller gain based on a sensitivity function that elucidates the relationship between the effective flow area of the EGR valve and the EGR mass flowrate. The feedforward algorithm calculates the EGR valve position based on the inverse model of the EGR valve. The driving cycle test result showed that, compared with the conventional EGR control system, the r.m.s. and maximum values of the target tracking error were reduced by 2.5 per cent and 8.0 per cent respectively.