Piezoelectric Injectors for Automotive Applications: Modeling and Experimental Validation of Hysteretic Behavior and Temperature Effects

Direct acting piezoelectric injectors seem to be a promising alternative to the electromagnetic ones because they permit a continuous control of the aperture. This characteristic can improve the performances and minimize the emissions of diesel engines. To exploit the potentialities of this kind of actuation, it is necessary to minimize the effects of the hysteretic behavior of piezoelectric materials. For this reason, the behavior of the actuator has to be modeled taking this effect into account. Additionally, the effects of the temperature must be considered, given the particularly critical position of the injectors near the engine. A modeling approach of piezoelectric injectors, including hysteresis and temperature effects as well as the electromechanical dynamic, is described in this paper. The model is based on a linear finite element (FE) discretization of the piezoelectric stack and the injector case. The hysteretic behavior is included in a second step by means of additional nonlinear state equations while the temperature effects are taken into account considering the temperature dependence of the material characteristics. A dedicated test bench has then been realized and experimental tests have been performed on piezoelectric injectors, with driving voltages and temperatures commonly used in automotive environment. The collected data allow to tune the model and to verify its validity even out of the tuning conditions.