Abstract:
A piezoelectric actuator includes a piezoelectric bending transducer, the first end of the bending transducer may be pivoted, while its second end, which is opposite to the first end, may be movably supported in a longitudinal transducer direction. Given a simultaneously large deflection path or bending lift, the actuator may attain a high restoring or working force. Thus, in the case of a valve piezoelectrically actuated by such an actuator, the sealing effect of a valve channel, which is closed or to be closed, may be significantly increased.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims the benefit of priority afforded by U.S. Provisional Patent Application Serial No. 60/265,753, entitled “Piezoelektrischer Aktor (Piezoelectric Actuator)”, filed on Jan. 31, 2001, to Schmauser et al., the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a piezoelectric actuator having a piezoelectric bending (or flexural) transducer. The present invention further relates to a valve that is actuatable by such an actuator.  
         BACKGROUND INFORMATION  
         [0003]    When using such actuators, the piezoelectric bending transducer is fixedly clamped either only at one end or at both ends. Thus, a valve that is able to be used as a pneumatic or hydraulic valve is known, for example, the reference German Patent Application No. DE 36 08 550 purportedly concerns a piezoelectric bending transducer fixed at its connection end, which is used for connecting to an electrical voltage source, inside a valve housing, in a narrow side of the housing, while the opposite, unattached end of the bending transducer, which bears a sealing element for closing a valve channel, is projected into the inside of the housing.  
           [0004]    In contrast, the reference U.S. Pat. No. 5,630,440 purportedly concerns a piezoelectrically actuated valve having a bending transducer that is clamped at both ends in the housing and consequently is fixed at both ends. By fixing both ends of the bending transducer, only a minimal and consequently insufficient deflection path, bending or flexural lift may be effected. In comparison to a configuration where only one end of the bending transducer is fixed, this may achieve a comparably high restoring or working force.  
         SUMMARY OF THE INVENTION  
         [0005]    Embodiments according to the present invention are directed to providing a piezoelectric actuator that functions as reliably and effectively as possible during normal operation. Further embodiments according to the present invention are directed to providing a valve, such as a pneumatic valve, that may be operable in an especially reliable manner using such an actuator.  
           [0006]    Another exemplary embodiment of the present invention is directed to providing that the first end of the bending transducer, which may be plate-like and/or rectangular, may be supported in a rotatable fashion, while the opposite, second end may be guided so as to be movable in the longitudinal transducer direction. The reversibility of the piezoelectric effect may allow this arrangement to be usable as a sensor as well.  
           [0007]    The transverse guidance of the one transducer side or of the one transducer end may render possible a longitudinal movement of the bending transducer when transitioning from the rest state to the energized state. At the same time, rotatably retaining the opposite transducer end (or the opposite transducer side) may prevent a counter-torque, which, otherwise, may inevitably occur as a result of the normal excitation of the bending transducer when this transducer end is securely clamped and consequently immovably fixed and which may cause the transducer material to break.  
           [0008]    In another exemplary embodiment of the present invention, the piezoelectric bending transducer may be guided, at least at the rotatably secured transducer end or may also be at both ends of the transducer, in a cylindrical holding element and securely joined thereto. In this context, the holding element provided at the rotationally fixed or retained fixing end of the bending transducer may be embedded in a suitably round or circular receiving groove that wraps around the cylindrical retaining (or holding) element, for example, around more than half of the cross-sectional area, i.e., more than 180°. This receiving groove, or a housing groove, may extend over the entire length of the cylindrical holding element. The appropriate receiving (or housing) groove may also wrap around the holding element only locally, for example, only in the center and/or outer region. The rotatably retained transducer end may be designed as a connection end that may be connected to an electrical voltage source for activating the actuator or transducer.  
           [0009]    Analogously, in another exemplary embodiment of the present invention, with respect to the deflection direction of the bending transducer, the holding element provided at the transversely displaceable end of the bending transducer may be inserted over its entire axial length or only partially in an appropriate, for example, approximately U-shaped receiving (or housing) groove.  
           [0010]    According to exemplary embodiments of the present invention, a valve having such a piezoelectric actuator may reliably close the valve channel to be blocked and, thus may be deactivated, even under extreme operating conditions, for example, under high pressure and high flow velocities of a medium flow to be controlled, by increasing the force, while at the same time, achieving a greatest possible deflection path or bending range. This increased pressure force or pressing force with which the sealing element may be pressed or pushed by the piezoelectric bending transducer of the actuator against the valve seat of the corresponding valve channel may be generated by the bending transducer itself, while accompanied by a simultaneously sufficient deflection path, since according to the present invention, the bending transducer is held at both ends inside of the valve housing, yet is only stationary at one transducer end, while the other transducer end is practically float-mounted and is, consequently, only supported in the manner of a counter support. As a result, on the whole, the operational performance of the actuator as such and in its use for actuating a valve may be improved, and the operational reliability of the valve may be enhanced.  
           [0011]    In this context, exemplary embodiments of the present invention may be based on the knowledge that in the case of a given supply voltage or operating voltage and, therefore, of a constant flexural torque of the piezoelectric transducer, the force generated by the transducer may increase with decreasing lever arm. Thus, if the bending transducer is fixed on both sides, the deflection force, which is exerted by the bending transducer as a result of a deflection of the bending transducer, and which acts as a pressing force exerted by the sealing element against the valve seat of the corresponding valve channel, may be significantly greater than that of a bending transducer clamped on one-side and having a free-moving unattached end. If in this context, a transducer end is guided in an axially movable manner, the deflection path may be at the same time greater than in the case of a bending transducer fixed on both sides. Moreover, in comparison with clamping this transducer end to immovably fix it, securing the fixed transducer end in a rotatable manner may prevent a corresponding counter-torque and, thus, may prevent the bending transducer from rupturing at this fixed end.  
           [0012]    In exemplary embodiments of the present invention, the bending transducer may be designed to be bent in the off-circuit state. For the valve control, this deflection or curvature may be concave in the direction of the valve channel. In other words, to control the valve, this deflection or curvature may be orientated toward the channel that is to be deactivated and closed in the rest state. As a result, the valve channel is able to be reliably closed in a particularly simple and effective manner already in the initial state or the rest state. Two such actuators having two appropriate bending transducers held in such a manner and arranged to run essentially in a parallel direction with respect to one another may also be provided inside of the valve housing.  
           [0013]    The bending characteristic of the bending transducer in the off-circuit or de-energized rest state may be achieved in that the bending transducer itself is prestressed or biased in the manner of a flat spring. Such prestressing may be achieved in turn using a suitable manufacturing method. In this context, a laminated bending transducer having a layer construction including at least one electrically conductive carrier layer and one piezoceramic layer is used as a baseline, heating and subsequent cooling of the layer construction resulting in layers prestressed to different extents due to different, material-dependent contraction properties. The prestressing of the layers to different extents then results in a deflection of the flat bending transducer about a neutral axis (or a bending axis) that runs perpendicularly to the bending transducer&#39;s longitudinal sides and parallelly to its narrow sides.  
           [0014]    According to exemplary embodiments of the present invention, an actuator, whose curved and prestressed piezoelectric bending transducer may be float-mounted at one transducer end and pivoted at the opposite transducer end, may be used to achieve a long deflection path or large bending lift and a particularly high restoring force or working force, while simultaneously having a long service life and reliable operational performance. Thus, in the case of a valve piezoelectrically actuated by such an actuator, the sealing effect of a valve channel that is closed or is to be closed may be more effective such that the operational reliability of the valve may be significantly increased. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 shows a perspective view of an exemplary embodiment of a piezoelectric actuator of the present invention having a bending transducer held on both sides in receiving grooves.  
         [0016]    [0016]FIG. 2 shows a representation according to FIG. 1 of a bending transducer locally supported at one pivoted transducer end according to an exemplary embodiment of the present invention.  
         [0017]    [0017]FIG. 3 shows a bending transducer according to FIG. 2 having a transducer end held via an axis of rotation according to an exemplary embodiment of the present invention.  
         [0018]    [0018]FIG. 4 shows a sectional view of a valve having an actuator according to an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]    [0019]FIG. 1 shows a piezoelectric actuator  1  having a plate-shaped, for example, rectangular, bending transducer  2  including a connection end  2   a  and a free end  2   b . Connection end  2   a  of bending transducer  2 , which is referred to as the first transducer end in the following, is pivoted in an approximately circular receiving groove  3  of a housing block  4 . For this purpose, bending transducer  2  bears at this transducer end  2   a  a (first) cylindrical retaining element  5 , whose circumference is not completely encompassed by receiving groove  3 , but preferably by more to 180°. Terminal contacts, which are connected by leads to a voltage source for activating bending transducer  2  and, as such, actuator  1 , may be supported at this transducer end  2   a  in a manner not more closely represented.  
         [0020]    Opposite (second) transducer end  2   b  is held in an approximately U-shaped receiving groove  6  of an additional housing block  7  and is supported there so as to be displaceable in longitudinal transducer direction  8 . This second transducer end  2   b  is, thus, supported so as to be displaceable in a direction transverse to deflection direction  9 , which runs in the direction of working force F of bending transducer  2 . At this transducer end  2   b , bending transducer  2  also bears a (second) cylindrical retaining element  10 , which is, in practice, float-mounted, with respect to longitudinal transducer direction  8 , in receiving groove  6 , which forms an upper and lower stop. Instead of a cylindrical retaining element  5 ,  10 , an impression or indentation of a middle sheet or plate of bending transducer  2  in the manner of a crimp may be provide as the retaining element. In this context, a torque-free, longitudinally displaceable retaining action is useful.  
         [0021]    During normal operation of actuator  1  and, as such, in an energized state of bending transducer  2 , the transducer may move in deflection direction  9 , left (second) transducer end  2   b  in FIG. 1 being able to move along arrow direction  11  in longitudinal transducer direction  8 , inside receiving groove  6 . At the same time, right (first) transducer end  2   a , which is pivoted in receiving groove  3 , may rotate in arrow direction  12 . Activating bending transducer  2  causes its curvature or convexity to increase or decrease. The rotatable mounting of transducer end  2   a  and the transversely displaceable mounting of transducer end  2   b  enable transducer  2  to adapt to the new curvature without internal stresses being formed in the supports or cutouts or receiving grooves.  3 ,  6  or counter-torque being produced in cutout  3 . Even given the working force F, internal stresses or counter-torques may not be produced or at least are minimized in exemplary embodiment(s) of the present invention using the cutouts or receiving grooves  3 ,  6 . Working force F may be tapped off in the middle region of bending transducer  2 , since it is greatest in the center of the bending transducer as a result of bending transducer  2  being held on both sides.  
         [0022]    As shown by a dotted line, both housing blocks  4 ,  7  may also be designed as a housing unit. For this purpose, both housing blocks  4  and  7  may be connected to one another via a bar-like housing segment  13  on the underside of the housing in relation to which bending transducer  2  is convexly bent or curved. The represented bending or curvature characteristic of bending transducer  2  may be achieved by a special manufacturing method in which a layer construction having an electrically conductive carrier layer, for example, in the form of a flat sheet-metal strip, and having a piezoceramic layer adhered thereto is prestressed along longitudinal transducer direction  8  by heating and subsequent cooling.  
         [0023]    In the exemplary embodiment of the present invention according to FIG. 2, receiving groove  3  extends only over a portion of the axial length of cylindrical retaining element  5  at pivoted transducer end  2   a . For this purpose, housing block  4  has an accordingly smaller design than the exemplary embodiment of the present invention according to FIG. 1. Instead of an individual housing block  4  having a receiving groove  3  surrounding cylindrical retaining element  5  at rotatable transducer end  2   a  approximately in the middle region, two such housing blocks  4  may also be provided whose receiving grooves  3  then encompass retaining element  5  in the region of its two ends. As in the exemplary embodiment of the present invention according to FIG. 1, the, or every, locally active housing block  4  may have a circular or round receiving groove  3 , which is circumferentially not completely closed, bending transducer  2  emerging from the receiving groove&#39;s opening side.  
         [0024]    According to the exemplary embodiment of the present invention according to FIG. 3, a rotational mount of cylindrical retaining element  5  provided at rotatable transducer end  2   a  is provided in the form of a shaft. For this purpose, two rotating shafts or shaft extensions  14 ,  15  engage on the end faces with corresponding bore holes  16  and  17 , respectively, of cylindrical retaining element  5 . The two shaft extensions  14 ,  15  then support, in a manner not shown in greater detail, the plus and minus poles, respectively, of a control electronics for controlling piezoelectric actuator  1 .  
         [0025]    [0025]FIG. 4 shows a valve  20 , which is actuated by such a piezoelectric actuator  1  and, for example, has a plastic and rectangular valve housing  21  having a likewise rectangular or even circular-cylindrical interior  22 . Two diametrically opposed valve channels  23  and  24  lead into interior space  22 . In an exemplary embodiment of the present invention, an additional valve channel or input channel  25 , which empties into interior space  22  of valve housing  21 , runs perpendicularly (or transversely) with respect to both valve channels  23  and  24 .  
         [0026]    In the case of valve  20 , which is represented without voltage connections, bending transducer  2  is in turn supported on both sides in valve housing  21 . In this context, retaining element  5  of transducer end  2 a, which has a circular cross-section and is fixed to the transducer end, is pivoted in a corresponding receiving or housing groove  3 , while opposite transducer end  2   b  is in turn supported in a corresponding receiving or housing groove  6  so as to be longitudinally displaceable, i.e., displaceable in longitudinal transducer direction  8  or transversely displaceable and, therefore, float-mounted. In an exemplary embodiment of the present invention, this transducer end  2   b  may be inserted directly, i.e., without an additional retaining element, into housing groove  6 . In this instance, transducer end  2   b  is minimally bent up in such a manner that it runs at least approximately parallel to the groove walls of housing groove  6 , which in turn is almost U-shaped.  
         [0027]    In a further exemplary embodiment of the present invention, the center region of bending transducer  2  is curved or bent in the rest state, in the direction of valve channel  23 . In this center region, a sealing element  26 , which may be designed to be curved on both sides and be effective on the convex as well as the concave side of bending transducer  2 , may be placed or slid onto bending transducer  2 . In this context, mutually opposing sealing convexities or bulges  26   a ,  26   b  may have a hemispherical shape. As a result, a particularly reliable sealing effect can be achieved, in particular, even in the case of a comparatively narrow internal width or a comparably small inner diameter of valve channels  23 ,  24 . Valve channel  24 , which is opposite valve channel  23 , may be extended in housing interior  22  in the direction of sealing element  26  and, thus, may extend into the effective vicinity of bending transducer  2 .  
         [0028]    When pneumatic valve  20 , which is designed as a three-way valve in a further exemplary embodiment of the present invention, is in operation, sealing element  26  is pressed against valve seat  27  by off-circuit and, consequently, de-energized bending transducer  2 , thereby closing valve channel  23  while valve channel  24  is open. Working or pressing force F needed for this purpose may be exerted by bending transducer  2  itself in that it is concavely curved in the direction of valve seat  27  in the rest state and is also prestressed in the manner of a flat spring as a result of an appropriate installation position. By reversing the polarity of the voltage, for example, of a d.c. voltage of 200V, valve channel  24  may be closed and valve channel  23  may be simultaneously opened as a result of bending transducer  2  bending in a direction opposite to represented bending direction  9  and pressing sealing element  26  onto valve seat  28 .  
         [0029]    Air L, which flows via the inlet or intake channel  25  into  30  valve housing  21  at a predefined pressure p and a predefined flow velocity v, may be discharged from valve housing  21  via valve channel  24 , which is open in this off-circuit rest state. Intake channel  25  empties into interior space  22  via housing side or narrow side  29  of valve housing  21 , which may  35  be provided with oblong housing groove  6  for transducer end  2   b , which is supported in a transversely movable manner. Intake channel  25  may also be guided into interior  22  of the valve housing via opposite housing side or narrow side  30  of valve housing  21 , which may be provided with round housing groove  3  for pivoted transducer end  2   a . Air L, which flows via intake channel  25  into valve housing  21 , may be discharged via valve channel  24  or, using appropriate polarity of the voltage source, via valve channel  23 .  
         [0030]    In comparison with a piezoelement or bending transducer clamped on one end, the configuration of bending transducer  2  of the present invention supported at both ends inside of a consequently piezoelectrically operated valve  20  may significantly increase force F for closing valve channels  23  and  24 , respectively. While the prestressing of bent bending transducer  2  in the rest state already causes sealing element  26 , which is supported by bending transducer  2 , to be pressed against valve seat  27  with a sufficiently high pressing force F, the pressing force F necessary to close valve channel  24 , which is open in the rest state, is achieved by bending transducer  2  being supported on both sides in combination with sealing element  26  being arranged in a middle position. The reason for this may be an increase in force due to a particularly favorable lever arm effect with a constant flexural torque. Such a rupture joint due to a counter-torque in the region of fixedly held transducer end  2   a  may be prevented also in this instance as a result of this transducer end  2   a  being rotatably attached.