Relay Auto-tuning of PID Controllers for Calibration of EGR Controller Maps in Diesel Engines

This paper describes the application of the relay auto-tuning method for the automatic calibration of the conventional EGR closed-loop controller maps in a typical Diesel engine. The paper briefly presents the theoretical background on the relay auto-tuning procedure and describes the implementation of such a procedure for the PID tuning of the EGR closed-loop system on a 4-cylinder engine with common-rail injection and variable-geometry turbocharger, for passenger car application. The relay auto-tuning method involves the implementation of the relay action in closed-loop to estimate the critical gain and critical frequency of the system, which are in turn used to estimate plant parameters for a first-order system with delay. PID controller gains are then calculated based on well-established tuning rules. The effect of the relay amplitude on the critical parameters is examined and the modifications required in the presence of noise or asymmetries in the measurements are discussed. The agreement of the relay auto-tuning predictions with the manual tuning predictions is also investigated.

The results presented indicate that the relay auto-tuning process can successfully be applied to estimate the critical oscillation parameters for the EGR system and the resulting controllers can yield satisfactory closed-loop behaviour. The proposed methodology can be used to automate the population of the ECU PID gain maps effectively with a potential to increase robustness and reduce the calibration development time.