Abstract:
There is provided a piezoelectric pump including a piezoelectric vibrator formed by stacking a piezoelectric body on at least one of the front and rear surfaces of a shim made of a conductive metal thin plate, and a housing that makes the peripheral edge of the piezoelectric vibrator liquid-tight to form a pump chamber. An alternating current is applied to between the shim of the piezoelectric vibrator, and the piezoelectric body to vibrate the piezoelectric vibrator, thereby generating a pumping action. A cylindrical bent part is formed at a peripheral edge of the shim of the piezoelectric vibrator, and a liquid-tight seal member is interposed between the cylindrical bent part and the housing. As a result, the piezoelectric pump with a highly-reliable fluid-tight structure around the piezoelectric vibrator is obtained.

Description:
[0001]    This application claims benefit of priority under 35 U.S.C. §119 to Japanese Patent Application No. 2006-216772 filed on Aug. 9, 2006, which is hereby incorporated by reference. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    1. Field of the Disclosure 
         [0003]    The disclosure relates to a piezoelectric pump and a piezoelectric vibrator, using a piezoelectric vibrator. 
         [0004]    2. Description of the Related Art 
         [0005]    In a piezoelectric pump that vibrates a sheet-like piezoelectric vibrator to obtain a pumping action, a pump chamber is formed by the piezoelectric vibrator and a housing. A pair of flow passages are connected with the pump chamber. The pair of flow passages is provided with a pair of check valves which are different in the direction of flow (a check valve that allows the flow of fluid to the pump chamber, and a check valve that allows the flow of fluid from the pump chamber). When the piezoelectric vibrator is vibrated, since the volume of the pump chamber changes, and operation of opening one of the pair of check valves closes with this volume change, and closing the other check valve is repeated, the pumping action is obtained. Such a piezoelectric pump is made thin, and is used as, for example, a cooling-water circulating pump for a water-cooled notebook computer. 
         [0006]    The piezoelectric vibrator has a piezoelectric body stacked on at least one of the front and rear surfaces of a shim (thin conductive metal plate). The polarization characteristics are given in front and rear directions of the piezoelectric body. Thus, when positive and negative polarities are given in the same direction as or in a direction opposite to the polarization direction of the piezoelectric body, one surface expands and the area of the other surface reduces. For this reason, when the positive and negative polarities to be given to the front and rear surfaces of the piezoelectric body are reversed alternately, a cycle that one of the front and rear surfaces expands and the other surface shrinks is repeated, and thereby the shim will vibrate. 
         [0007]    See, for example: 1] JP-UM-B-2510590; 2] JP-UM-A-3-8679; and 3] JP-A-2004-257337. 
         [0008]    Conventionally, a piezoelectric vibrator used for such a piezoelectric pump has a flat-plate shape (disk shape), and has a fluid-tight structure in which an O ring (liquid-tight seal member) made to abut on a peripheral edge of the vibrator is compressed between the peripheral edge and the housing. The compressed O ring gives a force to between the piezoelectric vibrator and the housing in a direction in which they are separated from each other. Although this force does not affect the fluid-tight structure in a short term, it is possible to affect the fluid-tight structure over a long term. It is desirable to make a perfect fluid-tight structure for applications like the above-mentioned cooling-water circulating pump for a water-cooled notebook computer. 
       SUMMARY 
       [0009]    The disclosed structure aims at obtaining a piezoelectric pump with a highly-reliable fluid-tight structure around a piezoelectric vibrator on the basis of awareness of the above problems. 
         [0010]    The disclosed structure also aims at obtaining a piezoelectric vibrator capable of easily obtaining a highly-reliable fluid-tight structure. 
         [0011]    The disclosed structure has been made on the basis of a perception that the reliability of a piezoelectric vibrator improves when the axial direction of the vibrator is adopted as the compression direction of the vibrator, on the basis of a recognition that a liquid-tight seal member in a conventional flat-plate-shaped (disk-shaped) piezoelectric vibrator cannot be compressed in a direction orthogonal to a planar direction of the vibrator, and this compression structure is a destabilizing factor of a fluid-tight structure over a prolonged period of time. 
         [0012]    That is, according to one aspect, there is provided a piezoelectric pump including a piezoelectric vibrator formed by stacking a piezoelectric body on at least one of the front and rear surfaces of a shim made of a thin conductive metal. A housing makes the peripheral edge of the piezoelectric vibrator liquid-tight to form a pump chamber. An alternating current is applied to between the shim of the piezoelectric vibrator, and the piezoelectric body to vibrate the piezoelectric vibrator, thereby generating a pumping action. A cylindrical bent part is formed at a peripheral edge of the shim of the piezoelectric vibrator, and a liquid-tight seal member is interposed between the cylindrical bent part and the housing. 
         [0013]    As to the pump chamber, a type in which a pump chamber is formed on one of the front and rear surfaces of the piezoelectric vibrator, and a type in which pump chambers are respectively formed on both the front and rear surfaces can be adopted. In the type in which a pump chamber is formed on one of the front and rear surfaces of the piezoelectric vibrator, it is desirable that a liquid-tight seal member is located on either an inner peripheral surface or an outer peripheral surface of the cylindrical bent part of the shim of the piezoelectric vibrator. 
         [0014]    On the other hand, in the type in which pump chambers are formed on both the front and rear surfaces of the piezoelectric vibrator, it is desirable that liquid-tight seal members are respectively located on inner and outer peripheral surfaces of the cylindrical bent part of the shim of the piezoelectric vibrator. 
         [0015]    Further, it is preferable that the shim has an outwardly bent flange part formed at an end of the cylindrical bent part thereof. 
         [0016]    According to another aspect of the invention, there is provided a piezoelectric vibrator including a piezoelectric body stacked on at least one of the front and rear surfaces of a shim made of a conductive metal thin plate, and a cylindrical bent part formed at a peripheral edge of the shim. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic exploded view showing one embodiment of a piezoelectric vibrator according to the disclosure; 
           [0018]      FIG. 2  is a half-section perspective view of chief parts, showing one embodiment of a piezoelectric pump using the piezoelectric vibrator of  FIG. 1 ; 
           [0019]      FIG. 3  is a sectional view of  FIG. 2 ; 
           [0020]      FIG. 4  is a sectional view showing another embodiment of the piezoelectric pump using the piezoelectric vibrator of  FIG. 1 ; 
           [0021]      FIG. 5  is a schematic exploded view showing another embodiment of the disclosed piezoelectric vibrator; 
           [0022]      FIG. 6  is a sectional view showing one embodiment of the piezoelectric pump using the piezoelectric vibrator of  FIG. 5 ; 
           [0023]      FIGS. 7A and 7B  are schematic views showing an example of the conceptual configuration of a two-valve-type piezoelectric pump to which the invention is to be applied; and 
           [0024]      FIGS. 8A and 8B  are schematic views showing an example of the conceptual configuration of a four-valve-type piezoelectric pump to which the invention is to be applied. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]      FIG. 7  schematically shows an example of the conceptual configuration of a two-valve-type piezoelectric pump. The piezoelectric vibrator  10  is sandwiched and supported between an upper housing  20 U and a lower housing  20 L that constitute a housing  20 , and forms a pump chamber A with the upper housings  20 U. 
         [0026]    The housing  20  (upper housing  20 U) is formed with an inlet port  21  and an outlet port  22  for cooling water (or other liquid), and check valves  11  and  12  are respectively provided between the inlet port  21  and the pump chamber A and between the pump chamber A and the outlet port  22 . The check valve  11  is a suction-side check valve that allows flow of fluid from the inlet port  21  to the pump chamber A, and does not allow flow of the fluid reverse thereto, and the check valve  12  is a discharge-side check valve that allows flow of the fluid from the pump chamber A to the outlet port  22 , and does not allow flow of the fluid reverse thereto. 
         [0027]    In the above piezoelectric pump, if the piezoelectric vibrator  10  elastically deforms normally and reversely, the suction-side check valve  11  is opened and the discharge-side check valve  12  is closed, in a stroke where the volume of the pump chamber A is increased, so that liquid flows into the pump chamber A from the inlet port  21  ( FIG. 7B ). On the other hand, in a stroke where the volume of the pump chamber A is reduced, the discharge-side check valve  12  is opened and the suction-side check valve  11  is closed, so that the liquid flows out of the pump chamber A into the outlet port  22  ( FIG. 7A ). Accordingly, pumping action is obtained by causing the piezoelectric vibrator  10  to continuously elastically deform normally and reversely (causing the piezoelectric vibrator to vibrate). 
         [0028]      FIGS. 1 to 3  show a first embodiment to which the disclosed structure is applied to, for example a piezoelectric pump having the basic configuration as described above. In the present embodiment, the piezoelectric vibrator  10  is a unimorph vibrator having a central shim  101 , and a piezoelectric body  102  stacked on one surface (lower surface of the figure) of the front and rear surfaces of the shim  101 . The shim  101  is integrally formed by a known method, such as press molding, from a conductive thin metal plate material, for example a stainless steel thin sheet having a thickness of about 0.2 mm, and has a cylindrical bent part  101   b  that is upward bent at the peripheral edge of a central circular part  101   a . A flange part  101   c  that is further bent outward is formed at the top end of the cylindrical bent part  101   b . The piezoelectric element  102  is made of, for example PZT (Pb(Zr, Ti)O 3 ) having a thickness of about 0.3 mm, and it is subjected to polarizing treatment in the front and rear directions thereof. The piezoelectric body  102  has a circular shape corresponding to the central circular part  101   a  of the shim  101 , is bonded to the rear surface of the central circular part  101   a  with conductive adhesive, and the upper and lower surfaces of the piezoelectric body  102  are covered with electrodes. 
         [0029]    The upper housing  20 U is formed with an annular groove  25  into which the cylindrical bent part  101   b  and the flange part  101   c  of the piezoelectric vibrator  10  (shim  101 ), and an O ring (liquid-tight seal member)  24  are inserted, and the lower housing  20 L is formed with a stepped recess  26  into which the flange part  101   c  of the shim  101  is inserted. The axial position of the piezoelectric vibrator  10  is determined by the stepped recess  26 . The O ring  24  is compressed in a direction parallel to the planar direction of the piezoelectric vibrator  10  and is liquid-tightly held between the inner peripheral surface of the cylindrical bent part  101   b , and the annular groove  25 . Although  FIGS. 2 and 3  show umbrellas as the check valves  11  and  12 , the basic configuration thereof is the same as that of  FIG. 1 . Although the flange part  101   c  of the shim  101  can be omitted, the existence thereof can enhance the positional accuracy of the piezoelectric vibrator  10 . Further, since the shim  101  includes the central circular part  101   a , the cylindrical bent part  101   b , and the flange part  101   c , which are integrally made of a thin stainless steel sheet, high liquid-tightness can be achieved. Moreover, since the compression direction of the O ring  24  is the planar direction, the upper housing  20 U and the lower housing  20 L can achieve rigidity even if they are thin. Therefore, it is possible to easily cope with making a piezoelectric pump thin. 
         [0030]    In the piezoelectric pump having the above configuration, as an alternating current is applied between the shim  101  and the piezoelectric body  102 , the piezoelectric vibrator  10  vibrates, and consequently the same pumping action as that described referring to  FIG. 7  is obtained. Also, the O ring  24  is compressed in a direction parallel to the planar direction of the piezoelectric vibrator  10 , and does not receive a force orthogonal to the planar direction. That is, since the O ring  24  does not exert a force on the upper housing  20 U and the lower housing  20 L in a direction which both of them are separated from each other, liquid-tightness over a prolonged period of time can be guaranteed. 
         [0031]      FIG. 4  shows another embodiment of the invention in which the O ring  24  is located at the outer periphery of the cylindrical bent part  101   b  of the shim  101 . In the present embodiment, the shim  101  (piezoelectric vibrator  10 ) is supported only by the annular groove  25  of the upper housing  20 U. In  FIG. 4 , only the upper housing  20 U is shown, and illustration of the lower housing  20 L is omitted. 
         [0032]    Although the unimorph piezoelectric vibrator  10  of the above embodiment has the piezoelectric body  102  stacked on a surface thereof opposite to the pump chamber A, the piezoelectric body  102  may be stacked on the side of the pump chamber A. However, since there is no possibility that liquid will touch the piezoelectric body  102  when the piezoelectric body  102  is stacked on the surface opposite to the pump chamber A, it is preferable to deliver, for example, liquid, such as a corrosive liquid or a water solution. Further, if the piezoelectric body  102  is stacked on the side of the pump chamber A, the piezoelectric body  102  is covered with a protective film, etc., ot prevent liquid from directly touching the piezoelectric body  102 . However, liquid may permeate the protective film due to prolonged use. Even from this viewpoint, it is preferable to stack the piezoelectric body  102  on the side opposite to the pump chamber A. 
         [0033]      FIG. 8  shows the principle of operation of a four-valve-type piezoelectric pump to which the disclosed structure is to be applied. In this four-valve piezoelectric pump, pump chambers A and B are respectively formed between a piezoelectric vibrator  10  and an upper housing  20 U and between the piezoelectric vibrator  10  and a lower housing  20 L. A housing  20  is provided with a single inlet port  21  and a single outlet port  22 , first and second suction-side check valves  11 U and  11 L that allow flow of fluid to the pump chambers A and B from the inlet port  21  and do not allow flow of the fluid in a direction reverse thereto are respectively provided between the pair of pump chambers A and B and the inlet port  21 . First and second discharge-side check valves  12 U and  12 L that allow flow of the fluid to the outlet port  22  from the pair of pump chambers A and B and do not allow flow of the fluid in a direction reverse thereto are respectively provided between the pair of pump chambers A and B and the outlet port  22 . 
         [0034]    In this four-valve-type piezoelectric pump, if the piezoelectric vibrator  10  is elastically deformed (vibrated) normally and reversely, a stroke in which the volume of one of the pump chambers A and B increases, and the volume of the other chamber decreases is repeated. In a stroke in which the volume of the pump chamber A increases (the volume of the pump chamber B decreases), the check valve  11 U is opened and thereby fluid flow into the pump chamber A from the inlet port  21 , and the fluid within the pump chamber B opens the check valve  12 U, and flows into the outlet port  22  ( FIG. 8B ). Conversely, in a stroke in which the volume of the pump chamber A decreases (the volume of the pump chamber B increases), the suction-side check valve  11 L is opened, and thereby the fluid flow into the pump chamber B from the inlet port  21 , and the fluid within the pump chamber A opens the discharge-side check valve  12 U, and flows into the outlet port  22  ( FIG. 8A ). Accordingly, the cycle of the pulsation in the discharge port  22  can be shortened (reduced to half as compared with a case where a pump chamber is formed only in one of upper and lower parts of the piezoelectric vibrator  10 ). 
         [0035]      FIGS. 5 and 6  show an embodiment to which the disclosed structure is applied to the four-valve-type piezoelectric pump according to the above principle of operation. In the present embodiment, the piezoelectric vibrator  10  is a bimorph piezoelectric vibrator in which the piezoelectric bodies  102  are stacked on both surfaces of the central circular part  101   a , respectively, and an annular groove  27  into which the cylindrical bent part  101   b  of the shim  101  and the O ring  24  are inserted is formed between the upper housing  20 U and the lower housing  20 . That is, the annular groove  27  is formed by a cylindrical protrusion  27   a  of the upper housing  20 U, and a cylindrical recess  27   b  of the lower housing  20 L. The O rings  24  that are respectively located at the inner peripheral surface and outer peripheral surface of the cylindrical bent part  101   b  are inserted into the annular groove  27 , and they are compressed in a direction parallel to the planar direction of the piezoelectric vibrator  10  and are liquid-tightly held. Although  FIGS. 5 and 6  show umbrellas as the check valves  11 U,  11 L,  12 U, and  12 L, the basic configuration of the piezoelectric pump is the same as that of  FIG. 8 . 
         [0036]    Even in this four-valve-type embodiment, an alternating current is applied to between the shim  101  and the piezoelectric bodies  102  on the front and rear surfaces thereof, which are made to have the same potential, to vibrate the piezoelectric vibrator  10 , so that the pumping action can be obtained. According to the bimorph piezoelectric vibrator  10 , as compared with a unimorph vibrator, the amplitude of vibration can be made large, and the pump efficiency can be enhanced. Also, the O rings  24  that are respectively located at the inner peripheral surface and outer peripheral surface of the cylindrical bent part  101   b  of the shim  101  are compressed in a direction parallel to the planar direction of the piezoelectric vibrator  10 , and are not compressed in a direction orthogonal to the planar direction. Consequently, a liquid-tight structure over a prolonged period of time can be guaranteed without applying a force to the upper housing  20 U and the lower housing  20 L in direction in which they are separated from each other.