Hybrid Modelling and Control of the Common Rail Injection System

We present an industrial case study in automotive control of significant complexity: the new common rail fuel injection system for Diesel engines, currently under production by Magneti Marelli Powertrain. In this system, a flow–rate valve, introduced before the High Pressure (HP) pump, regulates the fuel flow that supplies the common rail according to the engine operating point. The standard approach followed in automotive control is to use a mean–value model for the plant and to develop a controller based on this model. In this particular case, this approach does not provide a satisfactory solution as the discrete–continuous interactions in the fuel injection system, due to the slow time–varying frequency of the HP pump cycles and the fast sampling frequency of sensing and actuation, play a fundamental role. We present a design approach based on a hybrid model of the Magneti Marelli Powertrain common–rail fuel–injection system for four-cylinder multi–jet engines and a hybrid approach to the design of a rail pressure controller. The hybrid controller is compared with a classical mean–value based approach to automotive control design whereby the quality of the hybrid solution is demonstrated.