Cycle-to-cycle estimation and control of multiple pulse profiles for a piezoelectric fuel injector

While common-rail diesel fuel injection systems utilizing solenoid-actuated injectors have drastically improved the ability to lower emissions, noise, and fuel consumption, their limited bandwidth does not allow for tightly spaced injections or rate shaping. Piezoelectric injectors have that capability, but introduce multiple control challenges that can compromise their improved functionality. This paper summarizes the use of estimation algorithms for cycle-to-cycle determination of an injection flow profile capable of being used as feedback for a closed-loop control algorithm. While the estimation equations are complex and require a small time step, the authors propose capturing important estimation feedback during the injection period and delaying the integration of state variables across the engine cycle to more efficiently utilize a real-time processor. Also, a simplified model is developed to represent the dynamics of simultaneously controlling the quantity of pulses as well as the realized dwell time in between pulses. The model accounts for the coupling between the two, and a control law is developed and refined to provide an overdamped response of both the pulse quantities and realized dwell time, in order to prevent pulse bleeding. Transient response of the controller is shown in simulation and validated with experimental data with good correlation.