Injection Rate Estimation of a Piezo-Actuated Injector

Increasing demands on the emission reduction of high speed direct injection (HSDI) diesel engines require more accurate control of injection parameters such as the injection timing, injection rate, and injection quantity. In order to meet injection requirements, the piezo injector, which has a piezoelectric element as an actuator, has been recently developed. Compared with solenoid-actuated injectors, piezo-actuated injectors yield greater force and give faster response times, resulting in more accurate and faster injections.

In this study, a mathematical model of a piezo-actuated injector is developed. The injector model consists of three subsystems: the piezo-actuator subsystem, the mechanical subsystem, and the hydraulic subsystem. The constitutive relations of piezoelectricity are used for modeling the piezo-actuator subsystem. An estimation method of the injection timing and rate is introduced based on the proposed model. The sliding mode theory is applied to the estimator design in order to overcome uncertainties in the injector model. The injector model and the estimator are evaluated through injector experiments. The simulation results of the injector model are in good agreement with the experimental data. The sliding mode observer can effectively estimate the injection timing and the injection rate of the piezo-actuated injector.