Patent Publication Number: US-11661935-B2

Title: Blower

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 15/906,282 filed on Feb. 27, 2018, which is a continuation of International Application No. PCT/JP2016/074578 filed on Aug. 24, 2016 which claims priority from Japanese Patent Application No. JP 2015-170507 filed on Aug. 31, 2015. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to a blower that transports gas. 
     Description of the Related Art 
     Blowers that transport gas, such as air, are in widespread use. For example, Patent Document 1 discloses a piezoelectric micro-blower. 
       FIG.  20    is a sectional view of a piezoelectric micro-blower A according to Patent Document 1. The piezoelectric micro-blower A includes a vibrating plate  921 , a piezoelectric element  920 , a pump housing  910 , and an outer housing  950 . The vibrating plate  921  and the piezoelectric element  920  form an actuator  902 . 
     The piezoelectric element  920  expands and contracts when an alternating voltage is applied thereto, and thereby causes the vibrating plate  921  to vibrate. The pump housing  910  is connected to the vibrating plate  921  so as to form a pump chamber  903 . The outer housing  950  covers the pump housing  910  with a gap therebetween. 
     The pump housing  910  has a vent hole  911  through which the inside of the pump chamber  903  communicates with the outside of the pump chamber  903 . The vent hole  911  is symmetric about a central axis C of the pump chamber  903 . The outer housing  950  defines a vent passage  906 , which communicates with the vent hole  911 , between the outer housing  950  and the pump housing  910 . The outer housing  950  has an inlet  951  and an outlet  953  that communicate with the vent passage  906 . 
     The vent passage  906  is axisymmetric about the central axis C. Therefore, the distance from the central axis C to the left end of the vent passage  906  (the left inner wall surface of the outer housing  950 ) is equal to the distance from the central axis C to the right end of the vent passage  906  (the right inner wall surface of the outer housing  950 ). 
     In the piezoelectric micro-blower A having the above-described structure, the actuator  902  may be driven at a frequency higher than an audible frequency to prevent the generation of uncomfortable noise that is audible to the user.
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-50108   

     BRIEF SUMMARY OF THE DISCLOSURE 
     However, when the actuator  902  included in the piezoelectric micro-blower A according to Patent Document 1 is driven at a high frequency, a high-frequency pressure wave is outputted to the vent passage  906  through the vent hole  911 . The pressure wave outputted through the vent hole  911  propagates through the vent passage  906 , and is reflected by an inner wall surface of the outer housing  950 . When the frequency is high, the wave length of the pressure wave is short, and the pressure wave has antinodes in the vent passage  906 . As the frequency increases, the number of antinodes in the vent passage  906  increases. The vent passage  906  is axisymmetric about the central axis C. 
     Accordingly, the pressure wave reflected at the left end of the vent passage  906  and the pressure wave reflected at the right end of the vent passage  906  enhance each other at a plurality of locations in the vent passage  906 . Therefore, a large pressure amplitude occurs in the vent passage  906 . In other words, a large energy loss occurs in the vent passage  906 . 
     Thus, the piezoelectric micro-blower A according to Patent Document 1 has a problem that the pump characteristics (for example, discharge pressure and discharge flow rate) thereof are degraded. 
     Accordingly, an object of the present disclosure is to provide a blower capable of inhibiting the degradation of pump characteristics. 
     A blower according to the present disclosure includes a pump unit and an outer housing. The pump unit includes a vibrating body, a driving body that vibrates the vibrating body, and a pump housing that is connected to the vibrating body so as to form a pump chamber. The outer housing covers the pump unit with a gap therebetween. 
     The pump unit has a vent hole through which an inside of the pump chamber communicates with an outside of the pump chamber, the vent hole being symmetric about a central axis of the pump chamber. The outer housing defines a vent passage, which communicates with the vent hole, between the outer housing and the pump unit, and has an inlet and an outlet that communicate with the vent passage. At least one of the inlet and the outlet is displaced from the central axis of the pump chamber. 
     In this structure, when the driving body is driven at a predetermined frequency, a pressure wave is outputted to the vent passage through the vent hole. The pressure wave outputted through the vent hole propagates through the vent passage and is reflected at both ends of the vent passage (the inner wall surfaces of the outer housing). When the frequency is high, the pressure wave have a short wave length, and therefore have antinodes in the vent passage. The predetermined frequency is a frequency at which the pressure waves have antinodes in the vent passage (for example, 10 kHz or higher). 
     However, in this structure, most of the pressure wave reflected at one end of the vent passage is discharged to the outside of the outer housing through at least one of the inlet and the outlet. Accordingly, for example, the pressure wave reflected at the left end of the vent passage and the pressure wave reflected at the right end of the vent passage do not greatly enhance each other in the vent passage. As a result, a large pressure amplitude does not occur in the vent passage. In other words, a large energy loss does not occur in the vent passage. 
     Thus, in the blower having the above-described structure, the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited. 
     In the blower according to the present disclosure, preferably, the inlet and the outlet are both displaced from the central axis of the pump chamber. 
     In this structure, most of the pressure wave reflected at one end of the vent passage is discharged to the outside of the outer housing through the inlet and the outlet. Accordingly, for example, the pressure wave reflected at the left end of the vent passage and the pressure wave reflected at the right end of the vent passage do not greatly enhance each other in the vent passage. As a result, a large pressure amplitude does not occur in the vent passage. In other words, a large energy loss does not occur in the vent passage. 
     Thus, in the blower having the above-described structure, the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited. 
     A blower according to the present disclosure includes a pump unit and an outer housing. The pump unit includes a vibrating body, a driving body that vibrates the vibrating body, and a pump housing that is connected to the vibrating body so as to form a pump chamber. The outer housing covers the pump unit with a gap therebetween. 
     The pump unit has a vent hole through which an inside of the pump chamber communicates with an outside of the pump chamber. The outer housing defines a vent passage, which communicates with the vent hole, between the outer housing and the pump unit, and has an inlet and an outlet that communicate with the vent passage. A distance from the central axis to a first end of the vent passage differs from a distance from the central axis to a second end of the vent passage. 
     In this structure, the phase of the pressure wave reflected at the first end of the vent passage is shifted from the phase of the pressure wave reflected at the second end of the vent passage. Therefore, the pressure wave reflected at the first end of the vent passage and the pressure wave reflected at the second end of the vent passage do not greatly enhance each other in the vent passage. As a result, a large pressure amplitude does not occur in the vent passage. In other words, a large energy loss does not occur in the vent passage. 
     Thus, in the blower having the above-described structure, the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited. 
     In the blower according to the present disclosure, the pump chamber and the valve chamber preferably have the same central axis. In addition, in the blower according to the present disclosure, the pump chamber is preferably axisymmetric about the central axis. 
     In this structure, when the driving body is driven at a high frequency, a pressure wave is generated in the pump chamber. The pressure wave generated in the pump chamber propagates through the pump chamber, and is reflected at both ends of the pump chamber (the inner side surfaces of the pump housing). In this structure, for example, the phase of the pressure wave reflected at the left end of the pump chamber matches the phase of the pressure wave reflected at the right end of the pump chamber. Therefore, the pressure wave reflected at the left end of the pump chamber and the pressure wave reflected at the right end of the pump chamber enhance each other. As a result, a large pressure wave is outputted from the vent hole. 
     Accordingly, the pump characteristics of the blower having the above-described structure can be improved. 
     In the blower according to the present disclosure, at least one of the inlet and the outlet is preferably provided in a side surface of the outer housing. 
     In this structure, only the phase of a pressure wave reflected at end portions of the vent passage at which the inlet and the outlet are provided is reversed, and becomes opposite to the phase of a pressure wave reflected at other end portions. Thus, the pressure waves cancel each other in the vent passage. As a result, a large pressure amplitude does not occur in the vent passage. In other words, a large energy loss does not occur in the vent passage. 
     Thus, in the blower having the above-described structure, the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited. 
     In this structure, when a tube is attached to at least one of the inlet and the outlet, the tube is attached to the side surface of the outer housing. Thus, the height of the blower having this structure can be reduced. 
     In the blower according to the present disclosure, preferably, the inlet and the outlet are both provided in the side surface of the outer housing. 
     In this structure, when tubes are attached to the inlet and the outlet, the tubes are attached to the side surface of the outer housing. Thus, the height of the blower having this structure can be reduced. 
     In the blower according to the present disclosure, preferably, the outer housing includes a first nozzle that surrounds the inlet and a second nozzle that surrounds the outlet, and one of the first nozzle and the second nozzle is disposed on a straight line that is orthogonal to the central axis of the pump chamber. 
     In this structure, no moment is generated when a tube is attached to one of the first nozzle and the second nozzle that is disposed on the straight line that is orthogonal to the central axis of the pump chamber, and therefore the outer housing does not rotate. Thus, the tube can be easily attached to and removed from the blower having the above-described structure. 
     In the blower according to the present disclosure, preferably, the outer housing includes a first nozzle that surrounds the inlet and a second nozzle that surrounds the outlet, and the first nozzle and the second nozzle are disposed at positions that oppose each other. 
     In this structure, forces generated when two tubes are simultaneously attached to or removed from the first nozzle and the second nozzle cancel each other, and therefore the outer housing is not displaced. Thus, the tubes can be more easily attached to and removed from the blower having the above-described structure. 
     In the blower according to the present disclosure, preferably, the outer housing includes a first nozzle that surrounds the inlet and a second nozzle that surrounds the outlet, and an angle between a central axis of the first nozzle and a central axis of the second nozzle is smaller than or equal to 90 degrees. 
     When two tubes are attached to the first nozzle and the second nozzle while the blower having the above-described structure is disposed at a corner between two wall portions, the outer housing is supported by the two wall portions. The wall portions are, for example, portions of a housing of an electronic device in which the blower having the above-described structure is mounted. Thus, the tubes can be more easily attached to the blower having the above-described structure. 
     According to the present disclosure, the reduction in pump characteristics can be inhibited. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG.  1    is an external perspective view of a piezoelectric blower  100  according to a first embodiment of the present disclosure. 
         FIG.  2    is a sectional view of the piezoelectric blower  100  illustrated in  FIG.  1    taken along line S-S. 
         FIG.  3    is an exploded perspective view of a valve unit  12  and a pump unit  13  illustrated in  FIG.  2   . 
         FIG.  4    is an exploded perspective view of an outer housing  17  illustrated in  FIG.  2   . 
         FIG.  5    is a sectional view of the piezoelectric blower  100  illustrated in  FIG.  1    taken along line S-S when the piezoelectric blower  100  is subjected to resonant driving at a frequency of a first-order vibration mode for a blower body. 
         FIG.  6    is also a sectional view of the piezoelectric blower  100  illustrated in  FIG.  1    taken along line S-S when the piezoelectric blower  100  is subjected to resonant driving at the frequency of the first-order vibration mode for the blower body. 
         FIG.  7    is a sectional view of a piezoelectric blower  200  according to a second embodiment of the present disclosure. 
         FIG.  8    is an external perspective view of a piezoelectric blower  300  according to a third embodiment of the present disclosure. 
         FIG.  9    is a sectional view of the piezoelectric blower  300  illustrated in  FIG.  8    taken along line T-T. 
         FIG.  10    is a plan view of a piezoelectric blower  400  according to a fourth embodiment of the present disclosure. 
         FIG.  11    is a plan view of a piezoelectric blower  500  according to a fifth embodiment of the present disclosure. 
         FIG.  12    is a plan view of a piezoelectric blower  600  according to a sixth embodiment of the present disclosure. 
         FIG.  13    is a sectional view of a piezoelectric blower  700  according to a seventh embodiment of the present disclosure. 
         FIG.  14    is an exploded perspective view of a pump unit  213  illustrated in  FIG.  13   . 
         FIG.  15    is a plan view of a vibrating plate  336 , which is a modification of a vibrating plate  36  illustrated in  FIG.  2   . 
         FIG.  16    is a plan view of a vibrating plate  436 , which is another modification of the vibrating plate  36  illustrated in  FIG.  2   . 
         FIG.  17    is a plan view of a vibrating plate  536 , which is another modification of the vibrating plate  36  illustrated in  FIG.  2   . 
         FIG.  18    is a plan view of a vibrating plate  636 , which is another modification of the vibrating plate  36  illustrated in  FIG.  2   . 
         FIG.  19    is a sectional view of a piezoelectric blower  800  according to an eighth embodiment of the present disclosure. 
         FIG.  20    is a sectional view of a piezoelectric micro-blower according to Patent Document 1. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     First Embodiment of Present Disclosure 
     A piezoelectric blower  100  according to a first embodiment of the present disclosure will now be described. 
       FIG.  1    is an external perspective view of a piezoelectric blower  100  according to a first embodiment of the present disclosure.  FIG.  2    is a sectional view of the piezoelectric blower  100  illustrated in  FIG.  1    taken along line S-S.  FIG.  3    is an exploded perspective view of a valve unit  12  and a pump unit  13  illustrated in  FIG.  2   .  FIG.  4    is an exploded perspective view of an outer housing  17  illustrated in  FIG.  2   . In  FIG.  4   , nozzles  18  and  118  are omitted. 
     As illustrated in  FIGS.  1  and  2   , the piezoelectric blower  100  includes a valve unit  12 , a pump unit  13 , a controller  14 , and an outer housing  17 . The piezoelectric blower  100  transports gas, such as air. 
     The valve unit  12  and the pump unit  13  are laminated together. As illustrated in  FIGS.  2  and  3   , the valve unit  12  is disposed in an upper section of the piezoelectric blower  100 . As illustrated in  FIGS.  2  and  3   , the pump unit  13  is disposed in a lower section of the piezoelectric blower  100 . 
     As illustrated in  FIGS.  2  and  4   , the outer housing  17  includes a top plate  80 , a side plate  81 , a bottom plate  82 , a nozzle  18 , an outlet  24 , a nozzle  118 , an inlet  124 , and a receiving portion  181 . The outer housing  17  has a hollow cylindrical shape. The outer housing  17  is made of, for example, a resin. Tubes (not shown) are attached to the nozzles  18  and  118 . 
     The top plate  80  is disc-shaped. The bottom plate  82  is also disc-shaped. The side plate  81  is annular-shaped. The side plate  81  has the receiving portion  181 , which projects toward a central axis C of a pump chamber  45  from the inner peripheral surface of the side plate  81 . The receiving portion  181  is annular-shaped. The valve unit  12  and the pump unit  13  are placed on the receiving portion  181 , and the periphery of the valve unit  12  is attached to the receiving portion  181 . The outlet  24 , through which gas is discharged, is formed in the nozzle  18 . The inlet  124 , through which gas is introduced, is formed in the nozzle  118 . 
     The outer housing  17  covers the valve unit  12  and the pump unit  13  with a gap between the outer housing  17  and each of the valve unit  12  and the pump unit  13 . Thus, vent passages  91  and  92  are formed between the outer housing  17  and the valve unit  12  and between the outer housing  17  and the pump unit  13 . The vent passage  91  is axisymmetric about the central axis C. Therefore, the distance from the central axis C to a left end  91 A of the vent passage  91  (the left inner wall surface of the outer housing  17 ) is equal to the distance from the central axis C to a right end  91 B of the vent passage  91  (the right inner wall surface of the outer housing  17 ). 
     The vent passage  92  is also axisymmetric about the central axis C. Therefore, the distance from the central axis C to a left end  92 A of the vent passage  92  (the left inner wall surface of the outer housing  17 ) is equal to the distance from the central axis C to a right end  92 B of the vent passage  92  (the right inner wall surface of the outer housing  17 ). The inlet  124  communicates with the vent passage  91 . The outlet  24  communicates with the vent passage  92 . The inlet  124  and the outlet  24  are both displaced from the central axis C of the pump chamber  45 . 
     The valve unit  12  and the pump unit  13  constitute an example of a “pump unit” according to the present disclosure. An upper plate  23  and a side wall plate  31  constitute an example of a “pump housing” according to the present disclosure. Each of the vent passages  91  and  92  corresponds to an example of a “vent passage” according to the present disclosure. 
     The pump unit  13  is a diaphragm pump including a vibrating plate  36  (diaphragm). As illustrated in  FIGS.  2  and  3   , the pump unit  13  has the shape of a hollow cylindrical container in which the pump chamber  45  is formed. The pump chamber  45  is axisymmetric about the central axis C. The pump chamber  45  is cylindrical. 
     The pump unit  13  includes the upper plate  23 , the side wall plate  31 , the vibrating plate  36 , and a piezoelectric element  33 . The upper plate  23 , the side wall plate  31 , the vibrating plate  36 , and the piezoelectric element  33  are laminated together. The upper plate  23 , the side wall plate  31 , and the vibrating plate  36  are connected together to form the pump chamber  45 . The upper plate  23 , the side wall plate  31 , and the vibrating plate  36  are made of a metal. For example, the upper plate  23 , the side wall plate  31 , and the vibrating plate  36  are made of stainless steel. 
     The upper plate  23  is disc-shaped. A plurality of communication holes  43  arranged in a predetermined pattern are formed in a central portion of the upper plate  23 . The top surface of the side wall plate  31  is attached to the bottom surface of the upper plate  23 . 
     The side wall plate  31  is annular-shaped. The pump chamber  45 , which has a predetermined opening diameter, is formed at the center of the side wall plate  31 . The side wall plate  31  and the vibrating plate  36  have the same outer diameter. The outer diameter of the side wall plate  31  and the vibrating plate  36  is smaller than the outer diameter of the valve unit  12  by a predetermined amount. The top surface of the vibrating plate  36  is attached to the bottom surface of the side wall plate  31 . The vibrating plate  36  is disc-shaped. The vibrating plate  36  has a suction hole  96  at the center thereof. 
     The piezoelectric element  33  is disc-shaped. The diameter of the piezoelectric element  33  is smaller than the diameter of the vibrating plate  36 . The piezoelectric element  33  has a suction hole  93  at the center thereof. The top surface of the piezoelectric element  33  is attached to the bottom surface of the vibrating plate  36 . The piezoelectric element  33  is made of, for example, a lead zirconate titanate ceramic. 
     Electrodes (not shown) are formed on both principal surfaces of the piezoelectric element  33 , and the controller  14  applies a driving voltage across these electrodes. The piezoelectric element  33  has piezoelectric properties such that the piezoelectric element  33  expands and contracts in a planar direction in response to the applied driving voltage. 
     Therefore, when the piezoelectric element  33  receives the driving voltage, the piezoelectric element  33  expands and contracts in the planar direction. The expansion and contraction of the piezoelectric element  33  generates a concentric bending vibration of the vibrating plate  36 . Thus, the piezoelectric element  33  and the vibrating plate  36  constitute a piezoelectric actuator  37  and vibrate together. 
     The vibrating plate  36  corresponds to an example of a “vibrating body” according to the present disclosure. The piezoelectric element  33  corresponds to an example of a “driving body” according to the present disclosure. 
     The valve unit  12  has a function of regulating the flow of gas in one direction. The valve unit  12  has the shape of a hollow cylindrical container in which a valve chamber  40  is formed. The valve unit  12  is cylindrical. As illustrated in  FIGS.  2  and  3   , the valve unit  12  includes a cover plate  21 , a side wall plate  22 , and a film  20 . 
     The cover plate  21  and the side wall plate  22  are made of a metal. For example, the cover plate  21  and the side wall plate  22  are made of stainless steel (SUS). The film  20  is made of a resin. For example, the film  20  is made of a translucent polyimide. 
     The cover plate  21  is disposed at the top of the valve unit  12 . The side wall plate  22  is disposed between the cover plate  21  and the upper plate  23 . The upper plate  23  is disposed on the bottom surface of the valve unit  12 . The cover plate  21 , the side wall plate  22 , and the upper plate  23  are laminated together. The film  20  is disposed in the inner space of the valve unit  12 , that is, in the valve chamber  40 . 
     The cover plate  21  is disc-shaped. The side wall plate  22  is annular-shaped. The cover plate  21 , the side wall plate  22 , and the upper plate  23  have the same outer diameter. 
     The valve chamber  40  is formed at the center of the side wall plate  22  and has a predetermined opening diameter. The film  20  is substantially disc-shaped. The film  20  has a thickness smaller than the thickness of the side wall plate  22 . 
     In the present embodiment, for example, the thickness of the side wall plate  22  (the height of the valve chamber  40 ) is in the range from 40 μm to 50 μm, and the thickness of the film  20  is in the range from 5 μm to 10 μm. The film  20  is extremely light so that the film  20  can be moved in the valve chamber  40  in the up-down direction by air ejected from the pump unit  13 . 
     The outer diameter of the film  20  is substantially equal to the opening diameter of the valve chamber  40  in the side wall plate  22 . The outer diameter of the film  20  is slightly smaller than the opening diameter of the valve chamber  40  so that a small gap is provided. The film  20  has projections  25  at certain positions along the outer periphery thereof (see  FIG.  3   ). 
     The side wall plate  22  has cut portions  26 , which receive projections  25  with small gaps therebetween, at certain positions along the inner periphery thereof (see  FIG.  3   ). Thus, the film  20  is held in the valve chamber  40  so as to be non-rotatable but movable in the up-down direction. 
     A plurality of ejection holes  41  arranged in a predetermined pattern are formed in a central portion of the cover plate  21 . The communication holes  43  arranged in the predetermined pattern are formed in the central portion of the upper plate  23 . A plurality of film holes  42  arranged in a predetermined pattern are formed in a central portion of the film  20 . Thus, the valve chamber  40  communicates with the vent passage  92  through the ejection holes  41 , and with the pump chamber  45  through the communication holes  43 . 
     The ejection holes  41  and the communication holes  43  are arranged so as not to oppose each other. The film holes  42  and the ejection holes  41  are arranged so as to oppose each other. The film holes  42  and the communication holes  43  are arranged so as not to oppose each other. 
     The ejection holes  41 , the film holes  42 , the communication holes  43 , and the suction holes  93  and  96  are symmetric about the central axis C of the pump chamber  45 . 
     Each of the ejection holes  41 , the film holes  42 , the communication holes  43 , and the suction holes  93  and  96  corresponds to an example of a “vent hole” according to the present disclosure. 
     Referring to  FIG.  2   , the controller  14  is constituted by, for example, a microcomputer. The controller  14  adjusts, for example, the driving frequency of the piezoelectric element  33  to the resonant frequency of the pump chamber  45 . The resonant frequency of the pump chamber  45  is a frequency at which pressure vibration generated at the center of the pump chamber  45  resonates with pressure vibration that has been generated at the center of the pump chamber  45 , propagated toward and reflected by the outer peripheral portion, and returned to the central portion of the pump chamber  45 . 
     When the piezoelectric actuator  37  of the piezoelectric blower  100  is driven at a high frequency, a pressure wave is generated in the pump chamber  45 . The pressure wave generated in the pump chamber  45  propagates through the pump chamber  45 , and is reflected by the side surface of the pump chamber  45  (the inner surface of the side wall plate  31 ) at both sides. In the piezoelectric blower  100 , the phase of the pressure wave reflected by the left side surface of the pump chamber  45  matches the phase of the pressure wave reflected by the right side surface of the pump chamber  45 . 
     Therefore, the pressure wave reflected by the left side surface of the pump chamber  45  and the pressure wave reflected by the right side surface of the pump chamber  45  enhance each other. As a result, a large pressure wave is outputted from the ejection holes  41  and the suction holes  93  and  96 . Accordingly, the pump characteristics of the piezoelectric blower  100  can be improved. 
     The flow of air while the pump unit  13  is in operation will now be described. 
       FIGS.  5  and  6    are sectional views of the piezoelectric blower  100  illustrated in  FIG.  1    taken along line S-S when the piezoelectric blower  100  is subjected to resonant driving at a frequency of a first-order vibration mode for the blower body.  FIG.  5    shows the state in which the volume of the pump chamber is increased.  FIG.  6    shows the state in which the volume of the pump chamber is reduced. The arrows in  FIGS.  5  and  6    indicate the flow of air. 
     When the controller  14  applies an alternating driving voltage across the electrodes on both principal surfaces of the piezoelectric element  33  in the state illustrated in  FIG.  2   , the piezoelectric element  33  expands and contracts, thereby generating a concentric bending vibration of the vibrating plate  36 . The vibration of the vibrating plate  36  is transmitted to the upper plate  23 , so that a concentric bending vibration of the upper plate  23  is generated in response to the bending vibration of the vibrating plate  36 . Accordingly, as illustrated in  FIGS.  5  and  6   , the piezoelectric actuator  37  is bent so as to periodically change the volume of the pump chamber  45 . 
     When the vibrating plate  36  is bent in a direction away from the pump chamber  45  as illustrated in  FIG.  5   , the pressure in the pump chamber  45  decreases, and the film  20  is pulled toward the upper plate  23  and comes into contact with the upper plate  23  in the valve chamber  40 . Accordingly, the communication holes  43  are blocked and the flow of air from the valve chamber  40  to the communication holes  43  is stopped. Also, outside air is sucked into the pump chamber  45  through the suction holes  93  and  96 . 
     When the vibrating plate  36  is bent in a direction toward the pump chamber  45  as illustrated in  FIG.  6   , the pressure in the pump chamber  45  increases, and air is ejected into the valve chamber  40  through the communication holes  43 . The ejected air pushes the film  20  toward the cover plate  21  so that the film  20  comes into contact with the cover plate  21 . 
     Accordingly, the communication holes  43  are uncovered, and air flows into the valve chamber  40  through the communication holes  43 . The air in the valve chamber  40  is ejected into the vent passage  92  through the ejection holes  41  in the valve unit  12 . The air ejected into the vent passage  92  is discharged to the outside of the outer housing  17  through the outlet  24 . The air in the pump chamber  45  is also ejected into the vent passage  91  through the suction holes  93  and  96 . 
     As described above, the bending vibration of the upper plate  23  is generated in response to the bending vibration of the vibrating plate  36 . Accordingly, when the film  20  is pulled toward the bottom surface of the valve chamber  40 , the moving distance and moving time of the film  20  are reduced. This enables the film  20  to follow the variation in air pressure, and increases the responsivity of the valve unit  12 . 
     In the above-described structure, when the piezoelectric actuator  37  is driven at a predetermined frequency, a pressure wave is outputted to the vent passage  92  through the ejection holes  41 . The pressure wave outputted through the ejection holes  41  propagates through the vent passage  92  and is reflected by the inner wall surface of the outer housing  17 . 
     Similarly, when the piezoelectric actuator  37  is driven at a predetermined frequency, a pressure wave is outputted to the vent passage  91  through the suction holes  93  and  96 . The pressure wave outputted through the suction holes  93  and  96  propagates through the vent passage  91  and is reflected by the inner wall surface of the outer housing  17 . The predetermined frequency is a frequency at which the pressure waves have antinodes in the vent passages  91  and  92  (for example, 10 kHz or higher). When the frequency is high, the pressure waves have a short wave length, and therefore have antinodes in the vent passages  91  and  92 . 
     In the piezoelectric blower  100 , the inlet  124  and the outlet  24  are both displaced from the central axis C of the pump chamber  45 . Therefore, most of the pressure wave reflected at the right end  92 B of the vent passage  92  is discharged to the outside of the outer housing  17  through the outlet  24 . Accordingly, the pressure wave reflected at the left end  92 A of the vent passage  92  and the pressure wave reflected at the right end  92 B of the vent passage  92  do not greatly enhance each other in the vent passage  92 . As a result, a large pressure amplitude does not occur in the vent passage  92 . In other words, a large energy loss does not occur in the vent passage  92 . 
     Similarly, in the piezoelectric blower  100 , most of the pressure wave reflected at the right end  91 B of the vent passage  91  is discharged to the outside of the outer housing  17  through the inlet  124 . Accordingly, the pressure wave reflected at the left end  91 A of the vent passage  91  and the pressure wave reflected at the right end  91 B of the vent passage  91  do not greatly enhance each other in the vent passage  91 . As a result, a large pressure amplitude does not occur in the vent passage  91 . In other words, a large energy loss does not occur in the vent passage  91 . 
     Therefore, in the piezoelectric blower  100 , the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited. 
     Although the inlet  124  and the outlet  24  are both displaced from the central axis C of the pump chamber  45  in the piezoelectric blower  100 , the arrangement thereof is not limited to this. For example, only one of the inlet  124  and the outlet  24  may be displaced from the central axis C of the pump chamber  45 . 
     A piezoelectric blower  200  according to a second embodiment of the present disclosure will now be described. 
       FIG.  7    is a sectional view of the piezoelectric blower  200  according to the second embodiment of the present disclosure. 
     The piezoelectric blower  200  differs from the piezoelectric blower  100  according to the first embodiment in the shape of an outer housing  217 . The outer housing  217  differs from the outer housing  17  of the piezoelectric blower  100  in the positions of the outlet  24  and the inlet  124  and in that projections  285  and  286  are provided. Other structures are the same as those of the piezoelectric blower  100  according to the first embodiment, and description thereof is thus omitted. 
     The outer housing  217  covers the valve unit  12  and the pump unit  13  with a gap between the outer housing  217  and each of the valve unit  12  and the pump unit  13 . Thus, vent passages  291  and  292  are formed between the outer housing  217  and the valve unit  12  and between the outer housing  217  and the pump unit  13 . The distance from the central axis C to a left end  291 A of the vent passage  291  (the left inner wall surface of the outer housing  217 ) differs from the distance from the central axis C to a right end  291 B of the vent passage  291  (the right inner wall surface of the outer housing  217 ). The left end  291 A corresponds to an example of a “first end” according to the present disclosure. The right end  291 B corresponds to an example of a “second end” according to the present disclosure. 
     The distance from the central axis C to a left end  292 A of the vent passage  292  (the left inner wall surface of the outer housing  217 ) differs from the distance from the central axis C to a right end  292 B of the vent passage  292  (the right inner wall surface of the outer housing  217 ). The inlet  124  communicates with the vent passage  291 . The outlet  24  communicates with the vent passage  92 . The inlet  124  and the outlet  24  are both disposed on the central axis C of the pump chamber  45 . The left end  292 A corresponds to an example of a “first end” according to the present disclosure. The right end  292 B corresponds to an example of a “second end” according to the present disclosure. 
     In the piezoelectric blower  200 , the phase of the pressure wave reflected at the left end  292 A of the vent passage  292  is shifted from the phase of the pressure wave reflected at the right end  292 B of the vent passage  292 . Therefore, the pressure wave reflected at the left end  292 A of the vent passage  292  and the pressure wave reflected at the right end  292 B of the vent passage  292  do not greatly enhance each other in the vent passage  292 . As a result, a large pressure amplitude does not occur in the vent passage  292 . In other words, a large energy loss does not occur in the vent passage  292 . 
     Similarly, in the piezoelectric blower  200 , the phase of the pressure wave reflected at the left end  291 A of the vent passage  291  is shifted from the phase of the pressure wave reflected at the right end  291 B of the vent passage  291 . Therefore, the pressure wave reflected at the left end  291 A of the vent passage  291  and the pressure wave reflected at the right end  291 B of the vent passage  291  do not greatly enhance each other in the vent passage  292 . As a result, a large pressure amplitude does not occur in the vent passage  291 . In other words, a large energy loss does not occur in the vent passage  291 . 
     Therefore, in the piezoelectric blower  200 , the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited. 
     Although the piezoelectric blower  200  includes both the projection  285  and the projection  286 , the piezoelectric blower  200  is not limited to this. For example, the piezoelectric blower  200  may instead include only one of the projections  285  and  286 . 
     Although the inlet  124  and the outlet  24  are respectively formed in the bottom surface and the top surface of the outer housing  217  in the piezoelectric blower  200 , the arrangement thereof is not limited to this. As in a piezoelectric blower  300  illustrated in  FIGS.  8  and  9    described below, the arrangement may instead be such that at least one of the inlet  124  and the outlet  24  is formed in a side surface of the outer housing  217 . 
     A piezoelectric blower  300  according to a third embodiment of the present disclosure will now be described. 
       FIG.  8    is an external perspective view of the piezoelectric blower  300  according to the third embodiment of the present disclosure.  FIG.  9    is a sectional view of the piezoelectric blower  300  illustrated in  FIG.  8    taken along line T-T. 
     The piezoelectric blower  300  differs from the piezoelectric blower  100  according to the first embodiment in that the nozzles  18  and  118  (that is, the inlet  124  and the outlet  24 ) are both formed in a side surface of an outer housing  317 . Other structures are the same as those of the piezoelectric blower  100  according to the first embodiment, and the description thereof is thus omitted. 
     The outer housing  317  includes a side plate  381  having both the inlet  124  and the outlet  24 . A top plate  380  and a bottom plate  382  have neither the inlet  124  nor the outlet  24 . Therefore, when tubes are attached to the inlet  124  and the outlet  24  of the piezoelectric blower  300 , the tubes are attached to the side surface of the outer housing  317 . Thus, the height of the piezoelectric blower  300  can be reduced. 
     The nozzles  118  and  18  are disposed on line T-T, which is orthogonal to the central axis C of the pump chamber  45 . Accordingly, no moment is generated when a tube is attached to or removed from the nozzle  118  or the nozzle  18  of the piezoelectric blower  300 , and therefore the outer housing  317  does not rotate. Thus, the tube can be easily attached to and removed from the piezoelectric blower  300 . 
     In addition, in the piezoelectric blower  300 , the outlet  24  and the inlet  124  are both formed in the side surface of the outer housing  317 . Since the outlet  24  is provided at the left end  92 A of the vent passage  92 , the phase of the pressure wave reflected at the left end  92 A of the vent passage  92 , that is, at the outer end of the outlet  24 , is reversed. Accordingly, the pressure wave reflected at the right end  92 B of the vent passage  92  and the pressure wave reflected at the left end  92 A of the vent passage  92  have opposite phases, and therefore cancel each other. As a result, the pressure amplitude in the vent passage  92  is smaller than that in the piezoelectric blower  100 . In other words, the energy loss in the vent passage  92  is smaller than that in the piezoelectric blower  100 . 
     Similarly, since the inlet  124  is provided at the right end  91 B of the vent passage  91 , the phase of the pressure wave reflected at the right end  91 B of the vent passage  91 , that is, at the outer end of the inlet  124 , is reversed. Accordingly, the pressure wave reflected at the left end  91 A of the vent passage  91  and the pressure wave reflected at the right end  91 B of the vent passage  91  have opposite phases, and therefore cancel each other. As a result, the pressure amplitude in the vent passage  91  is smaller than that in the piezoelectric blower  100 . In other words, the energy loss in the vent passage  91  is smaller than that in the piezoelectric blower  100 . 
     Therefore, in the piezoelectric blower  300 , the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be further inhibited than in the piezoelectric blower  100 . 
     Although the inlet  124  and the outlet  24  are both formed in the side surface of the outer housing  317  in the piezoelectric blower  300 , the arrangement thereof is not limited to this. The arrangement may instead be such that at least one of the inlet  124  and the outlet  24  is formed in the side surface of the outer housing  317 . 
     A piezoelectric blower  400  according to a fourth embodiment of the present disclosure will now be described. 
       FIG.  10    is a plan view of the piezoelectric blower  400  according to the fourth embodiment of the present disclosure. 
     The piezoelectric blower  400  differs from the piezoelectric blower  100  according to the first embodiment in the positions of the nozzles  18  and  118  (that is, the positions of the inlet  124  and the outlet  24 ) and the shape of an outer housing  417 . The outer housing  417  is rectangular parallelepiped-shaped. Other structures are the same as those of the piezoelectric blower  100  according to the first embodiment, and the description thereof is thus omitted. 
     In the piezoelectric blower  400 , the nozzles  118  and  18  are arranged so as to oppose each other. Therefore, forces generated when two tubes are simultaneously attached to or removed from the nozzles  118  and  18  of the piezoelectric blower  400  cancel each other, and therefore the outer housing  417  is not displaced. Thus, the tubes can be more easily attached to and removed from the piezoelectric blower  400 . 
     A piezoelectric blower  500  according to a fifth embodiment of the present disclosure will now be described. 
       FIG.  11    is a plan view of the piezoelectric blower  500  according to the fifth embodiment of the present disclosure. 
     The piezoelectric blower  500  differs from the piezoelectric blower  100  according to the first embodiment in the positions of the nozzles  18  and  118  (that is, the positions of the inlet  124  and the outlet  24 ). Two wall portions  527  are, for example, portions of a housing of an electronic device in which the piezoelectric blower  500  is mounted. Other structures are the same as those of the piezoelectric blower  100  according to the first embodiment, and the description thereof is thus omitted. 
     In the piezoelectric blower  500 , the angle between a central axis P 1  of the nozzle  118  and a central axis P 2  of the nozzle  18  is 90 degrees. Therefore, when a tube is attached to the nozzle  118  or the nozzle  18  while the piezoelectric blower  500  is disposed at the corner between the two wall portions  527 , the outer housing  517  is supported by the two wall portions  527 . Thus, the tube can be more easily attached to the piezoelectric blower  500 . 
     A piezoelectric blower  600  according to a sixth embodiment of the present disclosure will now be described. 
       FIG.  12    is a plan view of the piezoelectric blower  600  according to the sixth embodiment of the present disclosure. 
     The piezoelectric blower  600  differs from the piezoelectric blower  100  according to the first embodiment in the positions of the nozzles  18  and  118  (that is, the positions of the inlet  124  and the outlet  24 ). Other structures are the same as those of the piezoelectric blower  100  according to the first embodiment, and the description thereof is thus omitted. 
     In the piezoelectric blower  600 , the angle between the central axis P 1  of the nozzle  118  and the central axis P 2  of the nozzle  18  is less than or equal to 90 degrees. Therefore, when a tube is attached to the nozzle  118  or the nozzle  18  while the piezoelectric blower  600  is disposed at the corner between the two wall portions  527 , the outer housing  617  is supported by the two wall portions  527 . Thus, in the piezoelectric blower  600 , the tube can be more easily attached. 
     A piezoelectric blower  700  according to a seventh embodiment of the present disclosure will now be described. 
       FIG.  13    is a sectional view of the piezoelectric blower  700  according to the seventh embodiment of the present disclosure.  FIG.  14    is an exploded perspective view of a pump unit  213  illustrated in  FIG.  13   . 
     The piezoelectric blower  700  differs from the piezoelectric blower  100  according to the first embodiment in that a vibrating plate  236  and a piezoelectric element  233  are provided. Other structures are the same as those of the piezoelectric blower  100  according to the first embodiment, and the description thereof is thus omitted. 
     The vibrating plate  236  includes a frame portion  234 , a plurality of connecting portions  235 , and a vibrating portion  238 . The frame portion  234  is annular-shaped. The vibrating portion  238  is disc-shaped, and is arranged so that gaps are provided between the vibrating portion  238  and the frame portion  234 . The connecting portions  235  are disposed between the frame portion  234  and the vibrating portion  238  so as to connect the vibrating portion  238  to the frame portion  234 . 
     Thus, the vibrating portion  238  is supported in midair by the connecting portions  235 , and is movable in the thickness direction, that is, in the up-down direction. The gaps between the frame portion  234  and the vibrating portion  238  serve as eight suction holes  296 . The eight suction holes  296  are symmetrical about the central axis C of the pump chamber  45 . 
     The piezoelectric element  233  differs from the piezoelectric element  33  in that it does not have the suction hole  93 . The piezoelectric element  233  is disc-shaped. The top surface of the piezoelectric element  233  is attached to the bottom surface of the vibrating portion  238 . 
     In the above-described structure, when the piezoelectric element  233  receives a driving voltage, the piezoelectric element  233  expands and contracts in the planar direction, and a concentric bending vibration of the vibrating portion  238  is generated. The piezoelectric element  233  and the vibrating portion  238  constitute a piezoelectric actuator  37  and vibrate together. 
     Also in the piezoelectric blower  700 , the inlet  124  and the outlet  24  are both displaced from the central axis C of the pump chamber  45 . Therefore, also in the piezoelectric blower  700 , the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited as in the piezoelectric blower  100 . 
     A piezoelectric blower  800  according to an eighth embodiment of the present disclosure will now be described.  FIG.  19    is a sectional view of the piezoelectric blower  800  according to the eighth embodiment of the present disclosure. 
     The piezoelectric blower  800  is a modification of the piezoelectric blower  200  according to the second embodiment illustrated in  FIG.  7   . The piezoelectric blower  800  differs from the piezoelectric blower  200  in the length of a receiving portion  881  and the arrangement of the valve unit  12  and the pump unit  13 . Other structures are the same as those of the piezoelectric blower  200  according to the second embodiment, and the description thereof is thus omitted. 
     As illustrated in  FIG.  19   , also in the piezoelectric blower  800 , the inlet  124  and the outlet  24  are both displaced from the central axis C of the pump chamber  45 . Therefore, also in the piezoelectric blower  800 , the degradation of the pump characteristics (for example, discharge pressure and discharge flow rate) can be inhibited as in the piezoelectric blower  100 . 
     Other Embodiments 
     Although air is used as the gas in the above-described embodiments, the gas is not limited to this. The gas may instead be gas other than air. 
     In addition, although the piezoelectric element  33  is used as the drive source for the blower in the above-described embodiments, the drive source is not limited to this. For example, the blower may instead be electromagnetically driven. 
     In addition, although the piezoelectric element  33  is made of a lead zirconate titanate ceramic in the above-described embodiments, the material thereof is not limited to this. For example, a lead-free piezoelectric ceramic material, such as a potassium sodium niobate ceramic or an alkali niobate ceramic, may instead be used. 
     In addition, although a unimorph piezoelectric vibrator is used in the above-described embodiment, the piezoelectric vibrator is not limited to this. For example, a bimorph piezoelectric vibrator in which the piezoelectric element  33  is provided on each surface of the vibrating plate  36  may instead be used. 
     In addition, although the piezoelectric elements  33  and  233  are disc-shaped in the above-described embodiments, the shape thereof is not limited to this. For example, the piezoelectric elements may instead be elliptical or polygonal ring-shaped. Alternatively, the piezoelectric elements may be polygonal plate-shaped or elliptical plate-shaped. 
     In addition, although the vibrating plate  36  and the upper plate  23  are disc-shaped in the above-described embodiments, the shape thereof is not limited to this. For example, the vibrating plate  36  and the upper plate  23  may instead be rectangular plate-shaped, polygonal plate-shaped, or elliptical plate-shaped. 
     In the piezoelectric blower  100 , as illustrated in  FIG.  3   , a single suction hole  96  that is point-symmetric about the central axis C of the pump chamber  45  is formed in the vibrating plate  36 . In the piezoelectric blower  700 , as illustrated in  FIG.  14   , eight suction holes  296  that are arranged point-symmetric about the central axis C of the pump chamber  45  in an octagonal pattern are formed in the vibrating plate  236 . However, the arrangement of the suction holes is not limited to this. In practice, a plurality of suction holes may be arranged symmetric about the central axis C of the pump chamber  45  in the following manner. 
     For example, as illustrated in  FIG.  15   , a plurality of suction holes  396  may be formed in a vibrating plate  336  so as to have 4-fold rotation symmetry about the central axis C of the pump chamber  45 . As illustrated in  FIG.  16   , a plurality of suction holes  496  may be formed in a vibrating plate  436  so as to have 6-fold rotation symmetry about the central axis C of the pump chamber  45 . As illustrated in  FIG.  17   , a plurality of suction holes  596  may be formed in a vibrating plate  536  so as to have 3-fold rotation symmetry about the central axis C of the pump chamber  45 . As illustrated in  FIG.  18   , a plurality of suction holes  696  may be formed in a vibrating plate  636  so as to have 3-fold rotation symmetry about the central axis C of the pump chamber  45 . Similar to the suction holes, a plurality of ejection holes, a plurality of film holes, and a plurality of communication holes may also be arranged point-symmetric about the central axis C of the pump chamber  45  as illustrated in  FIGS.  15  to  18   . 
     Although the vent passages  91  and  92  are substantially cylindrical in the above-described embodiments, the shape thereof is not limited to this. For example, the vent passages may instead be prism shaped. In addition, as in the vent passages  291  and  292  illustrated in  FIG.  7   , the projections  285  and  286  may be formed. 
     In addition, although the piezoelectric blowers  100  to  700  are subjected to resonant driving at a frequency of the first-order vibration mode in the above-described embodiments, the frequency is not limited to this. In practice, the piezoelectric blowers  100  to  700  may instead be subjected to resonant driving at a frequency of a vibration mode in which a plurality of vibration antinodes are provided, such as a third-order vibration mode. 
     In addition, although a concentric bending vibration of the upper plate  23  is generated in response to the bending vibration of the vibrating plate  36  in the above-described embodiment, the upper plate  23  is not limited to this. In practice, for example, only the bending vibration of the vibrating plate  36  may be generated, and it is not necessary that the bending vibration of the upper plate  23  be generated in response to the bending vibration of the vibrating plate  36 . 
     Finally, it should be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present disclosure is defined not by the above-described embodiments but by the scope of the claims. Furthermore, the scope of the present disclosure includes the scope equivalent to the scope of the claims.
         A piezoelectric micro-blower     12  valve unit     13  pump unit     14  controller     17  outer housing     18  nozzle     20  film     21  cover plate     22  side wall plate     23  upper plate     24  outlet     25  projection     26  cut portion     31  side wall plate     33  piezoelectric element     36  vibrating plate     37  piezoelectric actuator     38  side plate     40  valve chamber     41  ejection hole     42  film hole     43  communication hole     45  pump chamber     80  top plate     81  side plate     82  bottom plate     91 ,  92  vent passage     93 ,  96  suction hole     100 ,  200 ,  300 ,  400 ,  500 ,  600 ,  700  piezoelectric blower     118  nozzle     124  inlet     181  receiving portion     213  pump unit     217  outer housing     233  piezoelectric element     234  frame portion     235  connecting portion     236  vibrating plate     238  vibrating portion     285  projection     291 ,  292  vent passage     296  suction hole     317 ,  417 ,  517 ,  617  outer housing     336 ,  436 ,  536 ,  636  vibrating plate     380  top plate     381  side plate     382  bottom plate     396 ,  496 ,  596 ,  696  suction hole     527  wall portion     902  actuator     903  pump chamber     906  vent passage     910  pump housing     920  piezoelectric element     921  vibrating plate     950  outer housing     951  inlet     953  outlet