Model based rail pressure control for variable displacement pumps

A method of controlling a hydraulic system is preferably applied to common rail fuel injection systems. The problem in these systems is to control pressure in the common rail while at the same time maintaining the fluid supply to the rail in a way that precisely meets the dynamically changing consumption demands on the hydraulic system. In order to control the hydraulic system, the present invention contemplates the combination of a standard feedback controller with observer models of the various hardware items that make up the hydraulic system. Using this strategy, the system can generally be thought of as controlling fluid supply in an open loop type fashion based upon the consumption rates estimated by the various observer models, and utilizing a conventional feedback controller to make the slight pump adjustments needed to control pressure and to correct for any errors between the actual hardware performance and that predicted by the observer models.