The invention relates to a piezoelectric actuator device with at least one piezoelectric transducer which has at least one piezoelectric body and an electrode unit assigned to this piezoelectric body with overall capacitance and comprised of two electrodes mounted on opposite sides of the piezoelectric body.
The invention also relates to a valve for controlling a fluid, equipped with such a piezoelectric actuator device and in which the piezoelectric transducer forms a valve member or a drive element for a valve member.
A piezoelectric actuator device of this type known from DE 20 2005 006 126 U1 contains a piezoelectric transducer designed as bending actuator with a piezoelectric body composed of piezoelectrically active material and two electrodes flanking the piezoelectric body on opposite long sides and together forming an electrode unit which has an overall capacitance determined by the base area of the electrodes. In operation of the piezoelectric actuator device, a drive voltage is applied to the electrode unit, resulting in a charge inflow to the two electrodes which leads among other things to a change in length of the piezoelectric body. Since the piezoelectric body is placed on a piezoelectrically inactive substrate, the change in length of the piezoelectric body results in a bending of the bending actuator, which may be used for example to actuate a valve.
The piezoelectric transducer of the type according to the invention may also be designed as a stack actuator which has several piezoelectric bodies mounted one above the other and each flanked by an electrode unit. Here in particular a change in thickness of the piezoelectric bodies resulting from the inverse piezoelectric effect may be used for actuation purposes.
WO 02/089160 A2 describes a piezoelectric transducer with a so-called multi-layer structure, in which thin piezoelectric body layers alternating with electrodes are mounted on top of one another in layers, which has the advantage that acceptable elongations of the piezoelectric material and accordingly appreciable deformations of the piezoelectric transducer may be obtained with relative low drive voltages.
Known from US 2011/0057543 A1 is a vibration drive which has an actuator body comprised of a stack arrangement of piezoelectric layers and internal positive and negative electrode layers. Each electrode layer consists of several divided electrodes, so that positive and negative electrodes lie opposite in pairs which may be driven electrically in a variable manner in order to deform the actuator body at high frequency and to generate vibrations which may be used to shift a movably mounted element to and fro. Each electrode pair is connected to a separate voltage source with an interposed coil.
In principle, the obtainable elongation of a piezoelectric body and the resulting mechanical lifting work of the assigned piezoelectric transducer is dependent on the applied drive voltage. In particular for applications which require a certain degree of explosion protection and the observance of associated standards, however, there are limits to the use of high drive voltages. High drive voltages lead to high currents during the inflow and outflow of the charges to and from the electrodes which, in an applicable environment, may lead to dangerous explosions caused by spark-over. To avoid this, a piezoelectric transducer in an applicable environment may be operated only in so-called intrinsically safe mode and moreover only with limited drive voltage. This has an adverse effect on the mechanical lifting work achievable in operation. If a piezoelectric transducer is used for example as an actuator for valve operation, it generally leads to a limit to the controllable rates of flow.