Thorsten Steinkopff

Piezoceramic multilayer actuators for fuel injection systems in automotive area

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 be 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 methods are 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 a quantitative estimation of crack initiation and propagation by means of fracture mechanics, these methods can give valuable hits 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, dynamic models of piezoelectric components must be 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.

Energy considerations of PZT multilayer actuators under dynamic driving conditions

By means of fast optical two channel elongation measurement, with a resolution of 0.05 /spl mu/m, the dynamic behavior of PZT multilayer stack actuators, consisting of some layers and with typical dimensions of 10/spl times/10/spl times/20 mm/sup 3/, driven under different clamping conditions is investigated. In addition to the deflection measurement, the electrical power consumption and the dynamic and static forces are measured simultaneously. Starting from the measurement of the working characteristics, including the determination of dynamic stiffness and blocking force, the mechanical output for different mechanical preloads and for different mechanical stiffnesses of load is evaluated. Choosing the optimum preload and stiffness of load, maximum mechanical output can be achieved. It can be shown that the mechanical load also influences the electrical power consumption of the clamped actuator. Depending on the composition of the PZT ceramic, the clamping conditions may cause depolarization. Under driving conditions additional repolarization effects induce increased deflection. This can be used to find optimum material compositions for given mechanical preloads of clamped actuators.

Limitation of the degradation effect in piezoelectric multilayer actuators with ceramic layer thickness below 50 /spl mu/m

During the cofiring of PZT actuators, interactions between electrodes and ceramics occur that induce a degradation in the large signal piezoelectric properties for ceramic layer thicknesses below 50 /spl mu/m. It has been shown that the clamping forces applied to the ceramics due to thermal mismatch between the electrode and the ceramics are responsible for the reduction in the large signal piezocoefficient d/sub 33/ A shift in the ratio of electrode/ceramic layer thickness proved to be the best method to reduce the clamping forces applied to the ceramics. Consequently, an increase in d/sub 33/ of 50% could be achieved for samples with a 17 /spl mu/m ceramic layer thickness.