<title>Piezoceramic multilayer actuators for fuel injection systems in automotive area</title>

Abstract

Cofired multilayer piezoceramic actuators as extremely fast valve driving elements will lead to a significant progress in the field of fuel injection systems. A careful adaptation of the component performance to the system demands, an extraordinary high reliability, and competitive low production costs are prerequisites for this large-scale industrial application.With proper material selection as basis, conventional multilayer technology has to he substantially extended in order to achieve large stack volumes, to avoid degradation effects during cofiring and nevertheless to meet the target costs. Under large-signal driving conditions, the static and dynamic behavior of the component is essentially influenced by driving pulse shape. clamping force, and stiffness of the load. Linear FE (Finite Element) methods arc employed to calculate the performance criteria of different actuator designs. Moreover, a FE-implementation using a micromechanical domain switching model was developed in order to describe the strongly nonlinear material behavior. Together with an quantitative estimation of crack initiation and propagation by means of fracture mechanics, these methods can give valuable hints for controlling the effects of fatigue and deterioration which may limit the operating life time.In order to optimize the interaction of the electrical and mechanical parts in the injection system, dynaniic models of pie7oelectric components must he provided. A nonlinear model of the stack actuator has been developed for the analysis software MATLAB/SIMULINK. Special attention has been paid to the hysteresis properties.

Fatigue responses of lead zirconate titanate stacks under semibipolar electric cycling with mechanical preload

“…However, their widespread use is hindered by a strong propensity for cracking due to the low fracture toughness ͑less than 1 MPa ͱ m͒ of the ceramic comprising the PZT stack. 7 This approach only partially succeeded in controlling the cause of tensile stress. [2][3][4][5] As a result of concern with the tensile strain limitation of a PZT stack, mechanical preload is usually introduced into a piezoelectric device to counteract any localized tensile stress.…”

Performance of PZT stacks under high-field electric cycling at various temperatures in heavy-duty diesel engine fuel injectors

“…Among them are engine fuel injectors, servo displacement positioners, and vibration suppressors. [1][2][3] Improvements in the design and fabrication of modern PZT stacks have enabled the use of high electric fields, but such fields also cause increased tensile stress related to mismatched strains, increased dynamic overshoot in unloading, enhanced field concentration near the active-inactive transitional zone, and increased piezoelectric and dielectric hysteresis. [4][5][6][7] These changes raise significant concerns about fatigue and failure in PZT stacks.…”

Numerical modelling of piezoelectric actuators exposed to hydrogen

“…Recently, advanced fuel injectors that utilize multilayer piezoelectric actuators ( Fig. 1) for injector needle opening have been introduced as an innovative alternative to conventional solenoid technology [4,5]. Piezo actuator-based fuel injectors represent a promising improvement in direct fuel injection technology with precise positioning and injection and rapid response time compared to conventional solenoid technology.…”