Abstract:
There is provided an air pump in which vibration noise generated in a drive unit of the pump is suppressed from being transmitted to the outside through a suction passage. A casing of the air pump has a suction port extending from an outer peripheral surface to inner peripheral surface of the casing, a noise reduction wall annularly formed on the outer peripheral surface of the casing such that the suction port opens in a region of the outer peripheral surface of the casing surrounded by the noise reduction wall, and a lid member closing the opening of the top of the noise reduction wall and cooperating with the noise reduction wall and the outer peripheral surface of the casing to define a noise reduction chamber communicating with the suction port. The noise reduction wall has an elongated noise reduction passage extending circumferentially in the noise reduction wall.

Description:
RELATED APPLICATIONS 
     This application is a continuation of PCT/JP2010/051233 filed on Jan. 29, 2010, which claims priority to Japanese Application No. 2009-019860 filed on Jan. 30, 2009. The entire contents of these applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to air pumps and, more particularly, to a noise reduction device for use in air pumps. 
     2. Description of the Related Art 
     An air pump sucks in air from the surroundings, compresses the air and discharges the compressed air. In this regard, vibration noise generated in a drive unit of the pump is transmitted to the outside through an air suction passage and so forth, thus emitting noise to the surroundings. Accordingly, various noise reduction devices have been developed. 
     For example, the following patent literature 1 discloses a noise reduction device having a circular cylindrical housing accommodating an air pump unit, wherein the housing is provided with noise reduction means. In the noise reduction device, an inner wall is provided inside a circular cylindrical wall (outer wall) of the housing to extend over about 300 degrees in parallel to the cylindrical wall to form a suction passage between the two walls. In one end of the passage, the inner wall is connected to the cylindrical wall to form a closed end. The other end of the passage is an open end. Air outside the housing is sucked into the suction passage from near the closed end and passed through the passage to the open end, from which the air enters the interior of the housing, in which the pump unit is accommodated. In the noise reduction device, the suction passage is lengthened in this way to suppress noise from being transmitted to the outside through the suction passage.
     Patent Literature 1: Japanese Examined Utility Model Application Publication No. 1994-00627   

     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an air pump in which a housing accommodating a pump unit is not used as a noise reduction device as stated above, but noise reduction means is provided in a suction section of the pump unit itself to further improve the noise reduction effect. 
     The present invention provides an air pump including a casing having a cylinder chamber. The casing accommodates a piston reciprocatable in the cylinder chamber and an electromagnetic drive unit for reciprocating the piston. The casing comprises a suction port extending from an outer peripheral surface to inner peripheral surface of the casing to suck air, which is to be supplied to the cylinder chamber, into the casing from the surroundings of the casing, an annular noise reduction wall annularly provided on the outer peripheral surface of the casing such that the suction port opens in a region of the outer peripheral surface of the casing surrounded by the noise reduction wall, and a lid member provided to close an opening defined by the top of the noise reduction wall. The lid member cooperates with the noise reduction wall and the outer peripheral surface of the casing to define a noise reduction chamber communicating with the suction port. The noise reduction wall has at least one elongated noise reduction passage extending circumferentially in the noise reduction wall. One end of the noise reduction passage opens on the outer surface of the noise reduction wall. The other end of the noise reduction passage opens on the inner surface of the noise reduction wall. 
     In this air pump, the casing is formed with a noise reduction wall as stated above, and air to be sucked into the casing is passed through a noise reduction passage formed in the noise reduction wall and introduced into the noise reduction chamber. From the noise reduction chamber, the air is introduced into the casing through a suction port provided to extend through the casing. Accordingly, the path extending from the casing to the outside through the suction port and the noise reduction chamber and further through the noise reduction passage is long so that it is possible to achieve a noise reduction effect to reduce noise leaking out of the casing through the path. The noise reduction chamber can be formed as a wide space, which makes it possible to further increase the noise reduction effect by a combination of the wide-space noise reduction chamber and the narrow noise reduction passage and suction port, which are upstream and downstream, respectively, of the noise reduction chamber. It should be noted that the lid member may be integrally formed with the noise reduction wall. 
     Specifically, the arrangement may be as follows. The noise reduction wall has a first annular wall, the opposite ends of which are not connected to each other, and a second annular wall extending parallel to the first annular wall, the opposite ends of the second annular wall not being connected to each other. The noise reduction passage is defined between the first and second annular walls. 
     More specifically, the arrangement may be as follows. The first annular wall extends around the noise reduction chamber. One end of the first annular wall is positioned more outward than the other end thereof with respect to the noise reduction chamber. The second annular wall extends from an inner end thereof in parallel to the first annular wall in the same direction as the direction in which the first annular wall extends from the one end toward the other end. The inner end of the second annular wall is located in the middle in the longitudinal direction of the first annular wall and inward of the first annular wall. The second annular wall passes between the one end and the other end of the first annular wall and extends parallel to and outside the first annular wall to reach an outer end thereof located outward of the inner end. 
     In the above-described air pump, a portion of the casing that defines the suction port may be made greater in wall thickness than a portion of the casing surrounding the suction port-defining portion to lengthen the length of the suction port. This is for increasing the noise reduction effect. 
     The suction port may comprise a plurality of holes of a small diameter. The smaller the diameter of the holes, the higher the noise reduction effect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical sectional view of an air pump according to the present invention. 
         FIG. 2  is a sectional view taken along the line II-II in  FIG. 1 . 
         FIG. 3  is a sectional front view showing an assembly of a casing body constituting a casing of a pump unit and cylinder bodies and an assembly of pistons and an armature, in which only one of the pistons is not cut by the section line. 
         FIG. 4  is a side view of the assembly of the casing body and the cylinder bodies. 
         FIG. 5  is a bottom view of the assembly of the casing body and the cylinder bodies. 
         FIG. 6  is a plan view of an electromagnet pedestal member. 
         FIG. 7  is a sectional view taken along the line VII-VII in  FIG. 6 . 
         FIG. 8  is a sectional view taken along the line VIII-VIII in  FIG. 9 . 
         FIG. 9  is a plan view of the casing body. 
         FIG. 10  is a bottom view of a tank body. 
         FIG. 11  is a sectional view taken along the line XI-XI in  FIG. 10 . 
         FIG. 12  is a bottom view of the pump unit. 
         FIG. 13  is a plan view of an S-shaped pipe connecting between an air outlet of an air tank and an air discharge port of a housing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of an air pump according to the present invention will be explained below in detail with reference to the accompanying drawings. 
     As illustrated in the figures, an air pump  10  according to the present invention has a pump unit  12  for sucking in and compressing air from the surroundings and an air tank  20  for temporarily storing the compressed air from the pump unit  12  to suppress pulsation caused by reciprocating motion of pistons  16  of the pump unit  12  before discharging the compressed air. The air pump  10  further has a housing  24  accommodating the pump unit  12  and the air tank  20 . 
     First, these constituent elements and the overall structure will be outlined below. 
     First, the pump unit  12  has a casing  17  having a pair of cylinder chambers  14  disposed in bilateral symmetry as seen in  FIG. 1  to accommodate the pistons  16 , respectively. The pump unit  12  further has an electromagnetic drive unit  18  reciprocating the two pistons  16  in the state of the two pistons being connected to each other. Specifically, the casing  17  has, as shown in  FIGS. 2 to 5 , a casing body  26  having a box shape as a whole and defining a drive chamber accommodating the electromagnetic drive unit  18 , and a pair of cylinder members  28  fitted into through-holes  26 - 1  formed in left and right (as seen in  FIG. 1 ) side walls  26 - 13 , respectively, of the casing body  26 . Further, the casing  17  has head covers  30  installed so as to sandwich the casing body  26  from the left and right sides of the latter to define the cylinder chambers  14  together with the cylinder members  28 , and end wall members  33  abutted and secured to the respective end surfaces of the head covers  30  through seal members  31 . 
     The electromagnetic drive unit  18  has an armature  34  connecting the pair of pistons  16  to each other and having plate-shaped permanent magnets  32  disposed in bilateral symmetry as seen in  FIG. 1 , and electromagnets  36  provided at the opposite sides, respectively, of the armature  34  as seen in  FIG. 2 . The electromagnets  36  act on the permanent magnets  32 , thereby causing the armature  34  to reciprocate in the lateral direction as seen in  FIG. 1 . Coil springs  35  are provided at the left and right sides, respectively, of the armature  34  as seen in  FIG. 1  to hold the armature  34  in the center of the pump unit  12 . When an alternating electric current is applied to the electromagnets  36 , an alternating magnetic field is generated to reciprocate the armature  34  equipped with the permanent magnets  32 , together with the pistons  16  at the opposite ends of the armature  34 . Consequently, the surrounding air is sucked into the pump unit  12  through a filter  38  installed in the top of the housing  24 . The sucked air is compressed in the cylinder chambers  14  and supplied into the air tank  20 . The flow of air is, although the details of the air flow path are not shown, as follows. As shown by the arrows A, first, the air enters the drive chamber in the casing  17 . Then, the air passes through check valves (not shown) provided in the pistons  16  to reach the cylinder chambers  14 . The electromagnetic drive unit  18  is a technique known to those skilled in the art as disclosed, for example, in Japanese Patent Application Publication No. 2007-16761. Therefore, a detailed explanation of the structure of the electromagnetic drive unit  18  is omitted herein. 
     The air tank  20  has a resinous tank body  44  having a rectangular top wall  40  on which the pump unit  12  is placed. The tank body  44  further has a peripheral wall  42  extending downward from the top wall  40 . Thus, the tank body  44  has a downward facing opening. The air tank  20  further has a metallic bottom wall member  46  installed to close the opening of the tank body  44 . The bottom wall member  46  has a plurality of bolts  47  passed through a peripheral edge portion thereof. The bolts  47  are thread-engaged with the metallic casing  17  of the pump unit and tightened to clamp the resinous tank body  44  between the metallic bottom wall member  46  and the casing  17 . 
     Specifically, the housing  24 , which accommodates the pump unit  12  and the air tank  20 , has a flat-bottomed pan-shaped bottom part  50 , a housing body  52  installed on the bottom part  50 , and a cover  54  attached to the top of the housing body  52 . An air intake passage  58  with a rainwater trap portion  56  is provided between the cover  54  and the housing body  52 . Air introduced into the housing  24  through the rainwater trap portion  56  passes into the inside of the housing body  52  through the filter  38  provided in the top of the housing body  52 . The bottom part  50  of the housing  24  supports the air tank  20  through support studs  66  made of a damper rubber. 
     The above is the outline of the air pump according to the present invention. The following is an explanation of the details of the air pump. 
       FIG. 3  shows an assembly of the casing body  26  and a pair of cylinder members  28  fitted into the left and right (as seen in the figure) through-holes  26 - 1 , respectively, of the casing body  26  to constitute the casing  17 , and also shows an assembly of the pistons  16  and the armature  34 , which is to be loaded into the first-mentioned assembly. The casing body  26  has an electromagnet-loading opening  26 - 2  in the center of the bottom wall thereof. As shown in  FIG. 5 , the opening  26 - 2  is rectangular in shape as seen from below. Regarding the pair of cylinder members  28 , one cylinder member  28  is inserted into one through-hole  26 - 1  and bolted, and the other cylinder member  28  is inserted into the other through-hole  26 - 1  and bolted in a state where a circular cylindrical inner peripheral surface  28 - 1  of the other cylinder member  28 , which receives the associated piston  16 , is axially aligned with the inner peripheral surface  28 - 1  of the one cylinder member  28  (see  FIGS. 4 and 5 ). The assembly of the armature  34  and the pistons  16  can be set in the casing body  26  by inserting, as shown in  FIG. 3 , the assembly into the casing body  26  from the outside thereof through one cylinder member  28  in the axial direction thereof. 
     As shown in  FIGS. 5 and 3 , the casing body  26  has a top wall  26 - 3  with an inner surface  26 - 4  corresponding to the electromagnet-loading opening  26 - 2  of the bottom wall thereof. The inner surface  26 - 4  of the top wall  26 - 3  is provided with mutually spaced internal thread portions  26 - 6  having threaded holes  26 - 5  vertically extending through the top wall  26 - 3 . The internal thread portions  26 - 6  are positioned corresponding to the peripheral edge of the bottom opening  26 - 2 . The internal thread portions  26 - 6  are provided symmetrically about a horizontal line as seen in  FIG. 5 . As shown in  FIGS. 6 and 7 , a U-shaped electromagnet pedestal member  26 - 7  has holes  26 - 8  provided corresponding to the threaded holes  26 - 5 . The electromagnet pedestal member  26 - 7  is provided for each of the upper and lower groups of internal thread portions  26 - 6  and abutted against the associated internal thread portions  26 - 6 . As shown in  FIG. 2 , bolts  36 - 1  are inserted through the electromagnets  36  from below and further through the holes  26 - 8  and thread-engaged with the threaded holes  26 - 5  of the internal thread portions  26 - 6 , thereby setting the electromagnets  36  at respective proper height positions with respect to the permanent magnets  32  of the armature  34 . 
     The casing body  26  has a noise reduction wall  26 - 9  standing on the upper surface of the top wall  26 - 3 . Specifically, the noise reduction wall  26 - 9  comprises, as shown in  FIG. 9 , a pair of parallel extending loop-shaped or annular walls  26 - 10  and  26 - 10 ′. One wall  26 - 10  extends counterclockwise from the upper left of the figure through about 360° such that the terminating end of the wall  26 - 10  is inward of the starting end thereof. The other wall  26 - 10 ′ extends clockwise from a lower right position in parallel to and inward of the one wall  26 - 10 , passes between the starting and terminating ends of the one wall  26 - 10 , and further extends parallel to and outward of the one wall  26 - 10 . The other wall  26 - 10 ′ extends through about 360° in total. Between the walls  26 - 10  and  26 - 10 ′ is formed an air intake passage  26 - 11  also functioning as a noise reduction passage. A plate-shaped lid member  29  is placed on and bolted to the top of the noise reduction wall  26 - 9 . Thus, a noise reduction chamber  26 - 14  is defined by the outer peripheral surface of the housing, the noise reduction wall  26 - 9  and the lid member  29 . Air introduced into the housing body  52  through the filter  38  provided in the top of the housing body  52  enters the noise reduction chamber  26 - 14  through the noise reduction passage  26 - 11  and is introduced into the casing body  26  through holes  26 - 12  ( FIGS. 2 and 5 ) provided to extend through the top wall  26 - 3 . The inner surface defining the holes  26 - 12  of the top wall  26 - 3  extends downward to lengthen the holes  26 - 12 . The noise reduction wall  26 - 9 , the noise reduction chamber  26 - 14 , the holes  26 - 12  and so forth are configured so that noise generated by the reciprocating motion of the armature  34  is reduced and suppressed from being transmitted to the outside through air-introducing passages such as the holes  26 - 12 , the noise reduction chamber  26 - 14  and the noise reduction passage  26 - 11 . 
     The air tank body  44  has a peripheral wall  42  having a double-wall structure comprising, as shown in  FIGS. 1 ,  10  and  11 , an outer wall  42 - 1 , an inner wall  42 - 2 , and an air gap  42 - 3  provided between the outer and inner walls  42 - 1  and  42 - 2 , thereby making it difficult for the vibration noise of air in the tank to be transmitted to the outside. In the illustrated example, a plurality of air gaps  42 - 3  are formed being spaced from each other in the circumferential direction of the peripheral wall  42 . An intermediate wall  42 - 9  is formed between each pair of mutually adjacent air gaps  42 - 3  to connect together the outer and inner walls  42 - 1  and  42 - 2 . In the air tank body  44 , partition walls  42 - 4  are formed being suspended from the top wall  40  of the air tank body  44  to partition the interior space of the air tank body  44  into a plurality of spaces. Each partition wall  42 - 4  is provided with an air passage  42 - 5  extending upward from the bottom of the partition wall  42 - 4 . Air introduced from air inlets  42 - 6  provided in the top wall  40  flows to an air outlet  42 - 10  through the air passages  42 - 5 , thereby suppressing the pulsation of air discharged from the air outlet  42 - 10 . The partition walls  42 - 4  and the inner wall  42 - 2  are shorter in length than the outer wall  42 - 1 . The air outlet  42 - 10  is connected to an air discharge port  50 - 1  of the housing bottom part  50  through an S-shaped pipe  74  as shown in  FIG. 13 . The purpose of using the S-shaped pipe  74  is to absorb vibrations between the housing bottom part  50  and the air tank  20 . 
     The peripheral wall  42  is provided with a plurality of screw-receiving holes  42 - 7  vertically extending therethrough. The bolts  47  inserted through the peripheral portion of the metallic bottom wall member  46  are passed through the screw-receiving holes  42 - 7  and thread-engaged with the bottom portion of the metallic casing  17 , thereby clamping the air tank body  44  between the bottom wall member  46  and the bottom portion of the casing  17 . The partition wall  42 - 4  in the center of the air tank body  44  is also provided with a screw-receiving hole  42 - 8 . A bolt  49  inserted through the center of the bottom wall member  46  is passed through the screw-receiving hole  42 - 8 , and the distal end of the bolt  49  is thread-engaged with a nut  49 - 1  fitted into the upper end of the screw-receiving hole  42 - 8 , thereby securing the bottom wall member  46  to the tank body  44 . The bottom wall member  46  has a sheet-shaped seal member  43  stacked on the upper surface thereof inside the outer wall  42 - 1  of the air tank body  44 . The seal member  43  is made of a material more flexible than the resin used to form the air tank body  44 . Thus, the inner wall  42 - 2  and partition walls  42 - 4  of the air tank body  44  sealingly clamp the seal member  43  between themselves and the bottom wall member  46 . As shown in  FIG. 11 , ridges  42 - 2 ′ and  42 - 4 ′ capable of being forced into the seal member  43  are provided on the bottoms of the inner wall  42 - 2  and partition walls  42 - 4  of the air tank body  44  to extend along the respective walls. 
       FIG. 12  is a bottom view of the pump unit  12 . Through the electromagnet-loading opening  26 - 2  of the casing body  26  are seen the armature  34  and the electromagnets  36  provided at the opposite sides of the armature  34 , together with wiring  36 - 2  to the electromagnets  36 . Threaded holes  47 - 1  are formed in the respective bottoms of the casing body  26  and the head covers  30 . The distal (upper) ends of the bolts  47  are thread-engaged with the threaded holes  47 - 1 , respectively, to secure the air tank body  44  as stated above The bottoms of the head covers  30  are further formed with air discharge openings  30 - 1 , respectively, from which air discharged from the cylinder chambers  14  is discharged toward the air tank  20 . The air discharge openings  30 - 1  are positioned to align with the air inlets  42 - 6  formed in the top wall  40  of the air tank body  44 , which are shown in  FIG. 10 . Around the air discharge openings  30 - 1 , annular ridges  70  are formed along the peripheral edges of the air discharge openings  30 - 1 , respectively, so as to being forced into a sheet-shaped seal member  76  that is clamped between the air tank  20  and the bottom of the pump unit  12  when the former is secured to the latter, thereby sealingly engaging with the seal member  76 . Around the electromagnet-loading opening  26 - 2 , an annular ridge  76  is formed along the peripheral edge of the opening  26 - 2  so as to engage with the peripheral edge portion of an opening formed in the seal member  76  to correspond to the electromagnet-loading opening  26 - 2 .