Patent Publication Number: US-10788027-B2

Title: Electric air pump

Description:
TECHNICAL FIELD 
     The present disclosure relates to an electric air pump. 
     BACKGROUND ART 
     Japanese Patent No. 5374524 discloses a compressor device including an electric air pump. This electric air pump is configured including a motor, a piston that is coupled to the motor through a crank, and a cylinder that houses the piston. In the electric air pump of Japanese Patent No. 5374524, driving the motor moves the piston back and forth within the cylinder, thereby supplying air in the cylinder to another device. 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the electric air pump according to Japanese Patent No. 5374524, since the axis line of the motor and the axis line of the cylinder cross in orthogonal directions, the size of the electric air pump is large. 
     The present disclosure provides an electric air pump that can be made more compact in size. 
     Solution to Problem 
     In a first aspect of the present disclosure, an electric air pump includes a motor, a crank, and a piston. The motor includes a rotary shaft provided with a worm. The crank includes a worm wheel which engages with the worm and a rod with one end rotatably coupled to the worm wheel. The piston is housed in a cylinder extending along an axial direction of the motor, is coupled to another end of the rod and moves back and forth along an extension direction of the cylinder due to actuation of the crank, and ejects air inside the cylinder from a valve provided at one end of the cylinder due to being moved toward the one end side of the cylinder. 
     In the electric air pump of the first aspect, the worm is provided to the rotary shaft of the motor. The worm wheel configuring the crank engages with the worm, and the one end of the rod configuring the crank is rotatably coupled to the worm wheel. The other end of the rod is coupled to the piston. 
     The piston is housed in the cylinder, and the piston moves back and forth along the extension direction of the cylinder due to actuation of the crank. The piston ejects air inside the cylinder from the valve provided at the one end of the cylinder due to being moved toward the one end side of the cylinder. 
     Note that the cylinder extends along the axial direction of the motor. The size of the electric air pump can therefore be made more compact along the radial direction of the motor, as compared to configurations in which the cylinder extends along the radial direction of the motor. 
     A second aspect of the present disclosure is an electric air pump, in the first aspect, at which the cylinder is disposed at a radial direction outer side of the motor so as to adjoin a motor housing portion which houses the motor. 
     In the second aspect, the cylinder is disposed at the radial direction outer side of the motor so as to adjoin the motor housing portion housing the motor. The cylinder can thus be disposed utilizing space at the radial direction outer side of the motor. The size of the electric air pump can therefore be made more compact along the axial direction of the motor. 
     A third aspect of the present disclosure is an electric air pump, in the first aspect or the second aspect, at which as viewed along an axial direction of the worm wheel, an axis line of the crank and an axis line of the cylinder are offset in a radial direction of the motor. 
     In the third aspect, the piston is able to be efficiently pushed out toward the one end side of the cylinder by the rod. Namely, during actuation of the crank, the rod is moved back and forth while swinging about its other end. Since the axis line of the crank and the axis line of the cylinder are offset, it is possible to reduce the swing angle of the rod when the piston is moved toward the one end side of the cylinder, as compared to a comparative example in which the axis line of the crank is, for example, aligned with the axis line of the cylinder. In other words, in contrast to the comparative example, the rod is able to be moved toward the one end side of the cylinder so as to run along the axis line of the cylinder. The piston is therefore able to be efficiently pushed out toward the one end side of the cylinder by the rod. 
     A fourth aspect of the present disclosure is an electric air pump, in the third aspect, at which as viewed along the axial direction of the worm wheel, the axis line of the crank is disposed between the axis line of the cylinder and an axis line of the motor. 
     In the fourth aspect, the axis line of the crank is disposed between the axis line of the cylinder and the axis line of the motor, enabling the size of the electric air pump to be made even more compact along the radial direction of the motor. 
     A fifth aspect of the present disclosure is an electric air pump, in any one of the first aspect to the fourth aspect, at which the rod is disposed on one axial direction side of the worm wheel, and a circuit board configuring a drive circuit that drives the motor is disposed on another axial direction side of the worm wheel. 
     In the fifth aspect, the crank and the circuit board are able to be disposed alongside each other along the axial direction of the worm wheel. This enables the size of the electric air pump to be made more compact along the axial direction of the worm wheel. 
     A sixth aspect of the present disclosure is an electric air pump, in any one of the first aspect to the fifth aspect, at which a portion of the rod facing the worm wheel along the direction of the rotary axis of the worm wheel extends linearly along a rotation radial direction of the worm wheel as viewed from a rotation radial direction outer side of the worm wheel. 
     In the sixth aspect, the space in which the rod is disposed can achieve greater space efficiency, as compared to cases in which a bent portion is formed to the rod to avoid the rotary shaft of the worm wheel. As a result, the electric air pump can be made more compact. 
     A seventh aspect of the present disclosure is an electric air pump, in any one of the first aspect to the sixth aspect, at which a space where the crank is disposed, and a space where a circuit board configuring a drive circuit that drives the motor is disposed, are disposed adjacent to each other along the direction of the rotary axis of the worm wheel, and the space where the crank is disposed, and the space where the circuit board is disposed, are disposed so as to overlap the piston along the direction of movement of the piston. 
     In the seventh aspect, the space where the crank is disposed, and the space where the circuit board is disposed, are disposed so as to overlap the piston along the direction of movement of the piston. Such placement enables the electric air pump to be made more compact along the direction of the rotary axis of the worm wheel. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view cross-section illustrating an electric air pump according to an exemplary embodiment in a state in which a piston has reached the bottom dead center. 
         FIG. 2  is a plan view cross-section illustrating the electric air pump depicted in  FIG. 1  in a state in which the piston has reached the top dead center. 
         FIG. 3  is a lower face view illustrating the electric air pump depicted in  FIG. 1  in a state in which a second cover has been removed, as viewed from a lower side. 
         FIG. 4  is an enlarged side view cross-section (a cross-section along line  4 - 4  in  FIG. 2 ) illustrating the interior of the crank/circuit housing portion depicted in  FIG. 2 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Explanation follows regarding an electric air pump  10  according to an exemplary embodiment, with reference to the drawings. The electric air pump  10  is configured as an electric air pump installed in a vehicle (automobile). For example, the electric air pump  10  is configured as an electric air pump connected to an air blower that blows air on an onboard camera (lens) attached to the back door of a vehicle so as to supply air to the air blower. Detailed explanation thereof follows. Note that in the following explanation, arrow A and arrow B illustrated in  FIG. 4  indicate an vertical direction of the electric air pump  10 . Further, in  FIG. 1  to  FIG. 3 , a direction indicated by arrow C and arrow D that is orthogonal to the vertical direction is referred to as a first direction, and a direction indicated by arrow E and arrow F that is orthogonal to the first direction is referred to as a second direction. 
     As illustrated in  FIG. 1  to  FIG. 3 , the electric air pump  10  is configured including a housing  12 , a motor  30  (see  FIG. 1  and  FIG. 2 ), a crank  40  (see  FIG. 1  and  FIG. 2 ), a check valve  60 , and a drive circuit  80  (see  FIG. 3 ). The housing  12  configures an outer shell of the electric air pump  10 . The crank  40  is for transmitting drive force from the motor  30  to a piston  50 . The check valve  60  is a valve for discharging (ejecting) air from the electric air pump  10 . The drive circuit  80  is for controlling driving of the motor  30 . Explanation follows regarding the respective configurations thereof in the electric air pump  10 . 
     Housing  12   
     The housing  12  is formed in a substantially rectangular shape with its length direction in the first direction in plan view as seen from the upper side, and is configured as a hollow structural body. The housing  12  includes a motor housing portion  14 , a cylinder  16 , and a crank/circuit housing portion  18 . The motor housing portion  14  houses the motor  30 , described below. The cylinder  16  houses the piston  50 , described below. The crank/circuit housing portion  18  houses the crank  40  and the drive circuit  80  (circuit board  82 ), described below. 
     The motor housing portion  14  configures a portion at one first direction side (the arrow C direction side in  FIG. 1  to  FIG. 3 ) and one second direction side (the arrow E direction side in  FIG. 1  to  FIG. 3 ) of the housing  12 . The motor housing portion  14  is formed in substantially a circular tube shape with its axial direction along the first direction. 
     The cylinder  16  is disposed at the other second direction side (the arrow F direction side in  FIG. 1  to  FIG. 3 ) of the housing  12  so as to adjoin the motor housing portion  14 . The cylinder  16  is formed in substantially a circular tube shape with its axial direction along the first direction, and is integrally formed to the motor housing portion  14 . Namely, the cylinder  16  and the motor housing portion  14  are disposed side-by-side in the second direction (a radial direction of the motor housing portion  14 ) running parallel to each other. An axis line L 1  of the motor housing portion  14  (see  FIG. 1  and  FIG. 2 ) and an axis line L 2  of the cylinder  16  (see  FIG. 1  and  FIG. 2 ) are thereby disposed running parallel to each other. 
     The crank/circuit housing portion  18  is disposed at the other first direction side (the arrow D direction side in  FIG. 1  to  FIG. 3 ) of the housing  12  so as to adjoin the motor housing portion  14  and the cylinder  16 . As illustrated in  FIG. 3 , the crank/circuit housing portion  18  is formed in substantially a rectangular tube shape that opens in the vertical direction, and is integrally formed to the motor housing portion  14  and the cylinder  16 . As illustrated in  FIG. 4 , the crank/circuit housing portion  18  is provided with a dividing wall  20  that divides the inside of the crank/circuit housing portion  18  in the vertical direction. And end of the dividing wall  20  on the side of the motor housing portion  14  (not illustrated in  FIG. 4 ) and the cylinder  16  is bent toward the lower side in substantially a crank shape, and is integrally formed to the motor housing portion  14  and the cylinder  16 . A portion at the upper side (the arrow A direction side in  FIG. 4 ) of the division by the dividing wall  20  in the crank/circuit housing portion  18  configures a crank housing portion  18 A. The inside of the crank housing portion  18 A is in communication with the insides of the motor housing portion  14  and the cylinder  16 . An opening in the crank housing portion  18 A is closed off by a first cover  22 . A portion at the lower side (the arrow B direction side in  FIG. 4 ) of the division by the dividing wall  20  in the crank/circuit housing portion  18  configures a circuit housing portion  18 B. An opening in the circuit housing portion  18 B is closed off by a second cover  24 . Namely, in the present exemplary embodiment, the dividing wall  20  is disposed so as to serve as a boundary between the crank housing portion  18 A and the circuit housing portion  18 B, such that the crank housing portion  18 A and the circuit housing portion  18 B overlap in the vertical direction. 
     A shaft  20 A for axially supporting a worm wheel  42 , described below, is integrally formed to the dividing wall  20 . The shaft  20 A is formed in a circular column shape projecting toward the upper side from the dividing wall  20 . The shaft  20 A is disposed between the axis line L 1  of the motor housing portion  14  and the axis line L 2  of the cylinder  16  in plan view (see  FIG. 1 ). Plural bosses  20 B (three locations in the present exemplary embodiment) for fixing the circuit board  82 , described below, to the dividing wall  20  are integrally formed to the dividing wall  20 . The bosses  20 B are formed in circular column shapes projecting toward the lower side from the dividing wall  20 . A recess open toward the lower side is formed in a central portion of a lower face (leading end face) of each boss  20 B. 
     A dividing wall  21  is provided between the motor housing portion  14  and the crank housing portion  18 A. The dividing wall  21  partitions the motor housing portion  14  and the crank housing portion  18 A, and suppresses grease from the crank housing portion  18 A side from flying into the motor housing portion  14 . 
     Motor  30   
     As illustrated in  FIG. 1  and  FIG. 2 , the motor  30  is configured as what is known as a brushed DC motor. The motor  30  includes a substantially circular column shaped motor body  30 A. A magnet  30 C is fixed to an inner peripheral surface of the motor body  30 A. The motor body  30 A also includes a yoke housing  30 D, this being a magnetic body attached to (wrapped around) a portion of the outer peripheral surface of the motor body  30 A where the magnet  30 C is fixed. 
     The motor body  30 A is disposed in the housing  12  so as to be coaxial with the motor housing portion  14 , and is fitted inside the motor housing portion  14 . A rotary shaft  30 B of the motor  30  extends toward the other first direction side (the crank housing portion  18 A side) from the motor body  30 A. The axis line of the motor  30  is therefore aligned with the axis line L 1  of the motor housing portion  14 , and the cylinder  16  described above extends along the axial direction of the motor  30 . One length direction end of the motor housing portion  14  (arrow C direction side end in  FIG. 1  and  FIG. 2 ) is closed off by a substantially circular disc shaped cap  26 . 
     A worm shaft  32  is provided at the other first direction side (the crank/circuit housing portion  18  side) of the rotary shaft  30 B. The worm shaft  32  is disposed so as to be coaxial with the rotary shaft  30 B. One axial direction side (rotary shaft  30 B side) end of the worm shaft  32  is coupled to a leading end of the rotary shaft  30 B so as to be capable of rotating as a unit therewith. The worm shaft  32  is rotatably supported by a pair of bearings  36  at both length direction ends. The pair of bearings  36  are fixed to portions of the dividing wall  20  on the crank housing portion  18 A side. A worm  34  is integrally formed to a length direction intermediate portion of the worm shaft  32 , and a worm gear  34 A is formed around the outer circumference of the worm  34 . In the present disclosure, “a rotary shaft provided with a worm” thus encompasses cases in which the worm  34  is provided separately to the rotary shaft  30 B. Note that although the worm shaft  32  and the rotary shaft  30 B are configured by separate bodies in the present exemplary embodiment, the worm shaft  32  and the rotary shaft  30 B may be configured as a single unit. 
     Crank  40   
     The crank  40  is configured including the worm wheel  42  and a rod  46 . The worm wheel  42  is formed in a substantially circular disc shape with its axial direction in the vertical direction, and is rotatably supported by the shaft  20 A of the housing  12 . The worm wheel  42  is thus housed within the crank housing portion  18 A. An outer circumferential portion of the worm wheel  42  engages with the worm  34  on the worm shaft  32  of the motor  30 . Note that the worm wheel  42  and the worm  34  are coated with a lubricating grease. A crank pin  44  for coupling the rod  46 , described below, to the worm wheel  42  is also provided to the worm wheel  42 . The crank pin  44  is formed in a substantially circular column shape projecting toward the upper side from the worm wheel  42  (see  FIG. 4 ). In detail, as illustrated in  FIG. 4 , a recessed support hole  42 A that is open toward the upper side is formed in the worm wheel  42 . The crank pin  44  is fitted into the support hole  42 A through one end of the rod  46  and is supported by the support hole  42 A. An upper end of the crank pin  44  is integrally formed with a large-diameter portion  44 A that has a larger diameter than the diameter of the crank pin  44 . The rod  46  is thereby suppressed from coming off from the crank pin  44  toward the axial direction upper side of the crank pin  44  (arrow A direction side in  FIG. 4 ). 
     As illustrated in  FIG. 1  and  FIG. 2 , the rod  46  is formed in substantially an elongated plate shape with its plate thickness direction along the vertical direction. The rod  46  extends along the first direction (the extension direction of the cylinder  16 ). The portion of the rod  46 , facing the worm wheel  42  (the portion facing the worm wheel  42  along the direction of the rotary axis of the worm wheel  42 ), is bent into substantially a V shape that opens toward the motor housing portion  14  side in plan view, and is not bent in the vertical direction (plate thickness direction). A portion on one end side of the rod  46  is disposed at the upper side of the worm wheel  42 , and the one end of the rod  46  is supported by the crank pin  44 , which has its axial direction along the vertical direction, so as to be capable of rotating. In detail, as illustrated in  FIG. 4 , a first coupling hole  46 A is formed penetrating the one end of the rod  46 . The first coupling hole  46 A is disposed so as to be coaxial with the support hole  42 A of the worm wheel  42 . The dimensions of the outer diameter of the crank pin  44  and the inner diameter of the support hole  42 A are set so as to be substantially the same, with the inner diameter of the first coupling hole  46 A being set slightly larger than the outer diameter of the crank pin  44 . The crank pin  44  is inserted through the first coupling hole  46 A and fitted into the support hole  42 A. The one end of the rod  46  is thereby supported by the crank pin  44  so as to be capable of rotating. A length direction intermediate portion of the rod  46  is bent toward the lower side into substantially a crank shape at a position to the radial direction outer side of the worm wheel  42 . A portion on the other end side of the rod  46  is disposed in the cylinder  16 , and the other end of the rod  46  is coupled to the piston  50 , described below. A portion of the rod  46  facing the worm wheel  42  (a portion facing the worm wheel  42  along the direction of the rotary axis of the worm wheel  42 ), as viewed from a rotation radial direction outer side of the worm wheel  42 , extends linearly along a rotation radial direction of the worm wheel  42  and is parallel to the face of the worm wheel  42 . The rod  46  and the shaft  20 A are disposed with a predetermined clearance therebetween. 
     Piston  50   
     As illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 4 , the piston  50  is formed in substantially a bottomed circular tube shape that is open toward the other first direction side. The piston  50  is disposed so as to be coaxial with the cylinder  16 , and is housed within the cylinder  16  so as to be capable of movement. The axis line of the piston  50  is thus aligned with the axis line L 2  of the cylinder  16 . Note that the outer diameter of the piston  50  is set so as to be substantially the same dimension as the inner diameter of the cylinder  16 , with a non-illustrated sealing member being interposed between the piston  50  and the cylinder  16 . The piston  50  is disposed spanning from the crank housing portion  18 A to the circuit housing portion  18 B in the vertical direction. In other words, the crank housing portion  18 A and the circuit housing portion  18 B are disposed so as to overlap with the piston  50  along the direction of movement of the piston  50 . 
     A coupling shaft  52  with its axial direction along the vertical direction is fixed to the inside of the piston  50 . The coupling shaft  52  is disposed such that the axis line of the coupling shaft  52  passes through the axis line L 2  of the piston  50 . The other end of the rod  46  described above is disposed inside the piston  50  and is rotatably coupled to the coupling shaft  52 . The piston  50  is thereby coupled to the crank  40 . In detail, a fixing hole  50 B is formed penetrating an axial direction intermediate portion of the piston  50  in the vertical direction. A second coupling hole  46 B is formed penetrating the other end of the rod  46 . The second coupling hole  46 B is disposed so as to be coaxial with the fixing hole  50 B. The dimensions of the inner diameter fixing hole  50 B and the outer diameter of the coupling shaft  52  are set so as to be substantially the same, with the inner diameter of the second coupling hole  46 B being set slightly larger than the outer diameter of the coupling shaft  52 . The coupling shaft  52  is fitted into the fixing hole  50 B and inserted through the second coupling hole  46 B. The other end of the rod  46  is thereby pivotally coupled to the coupling shaft  52 . 
     When the motor  30  is driven to actuate the crank  40 , the piston  50  moves back and forth along the axis line L 2  of the cylinder  16 . Specifically, rotating the rotary shaft  30 B of the motor  30  in one rotary direction (forward rotation) rotates the worm wheel  42  in one rotary direction (the arrow G direction in  FIG. 1  and  FIG. 2 ) about the shaft  20 A such that the rod  46  moves the piston  50  back and forth along the axis line L 2  of the cylinder  16  (the first direction). The axis line L 3  of the crank  40  (specifically, a line passing through the center of rotation of the worm wheel  42  and extending along the direction of movement of the piston  50  (the first direction)) is set so as to extend parallel to the axis line L 2  of the piston  50  (cylinder  16 ) and the axis line L 1  of the motor  30  between the axis line L 2  of the piston  50  and the axis line L 1  of the motor  30 . Namely, the axis line L 3  of the crank  40  is disposed offset toward the one second direction side (the motor  30  side) with respect to the axis line L 2  of the piston  50  (cylinder  16 ). In the following explanation, a position where the piston  50  has been moved furthest toward the one first direction side (one end side of the cylinder  16 ) is referred to as the bottom dead center (the position illustrated in  FIG. 1 ), and a position where the piston  50  has been moved furthest toward the other first direction side (the other end side of the cylinder  16 ) is referred to as the top dead center (the position illustrated in  FIG. 2 ). The piston  50  moves toward the one first direction side (the piston  50  moves from the top dead center to the bottom dead center) in an outbound stroke, and the piston  50  moves toward the other first direction side (the piston  50  moves from the bottom dead center to the top dead center) in a return stroke. 
     As described above, the rod  46  is bent into substantially a V shape that is open toward the motor housing portion  14  side in plan view. Accordingly, due to the bent portion of the rod  46 , the rod  46  thus does not interfere with the motor housing portion  14  when the crank  40  is being actuated. 
     As illustrated in  FIG. 4 , plural intake ports  50 A are formed penetrating a central portion of one end (a bottom wall) of the piston  50 . The inside of the piston  50  (the inside of the crank housing portion  18 A) and the inside of the cylinder  16  are placed in communication through the intake ports  50 A. An intake valve  54  with substantially an umbrella shape is provided at the one first direction side of the piston  50 . Specifically, the intake valve  54  is formed in substantially a circular plate shape with its plate thickness direction along the axial direction of the piston  50 . An outer circumferential portion of the intake valve  54  is inclined toward the piston  50  side on progression toward the radial direction outer side thereof. The intake valve  54  is attached to the one end (the bottom wall) of the piston  50  by a screw  56 . The head of the screw  56  is disposed on the one first direction side of the intake valve  54 . A washer  58  is interposed between the head of the screw  56  and the intake valve  54 . The intake valve  54  is configured as a check valve. Namely, during the outbound stroke of the piston  50 , the outer circumferential portion of the intake valve  54  abuts the one end of the piston  50  and the intake valve  54  adopts a closed state. During the return stroke of the piston  50 , the outer circumferential portion of the intake valve  54  opens (comes away from the one end of the piston  50 ), drawing air is into the cylinder  16  through the intake ports  50 A, due to the pressure within the cylinder  16  dropping such that air drawn from outside the electric pump  10  flows into the cylinder  16 . 
     Check Valve  60   
     As illustrated in  FIG. 1  and  FIG. 2 , the check valve  60  is configured including a valve body  62 , a cap  64 , a stopper  66 , a stopper spring  68 , and a valve  70 . The valve body  62  is formed in substantially a bottomed circular tube shape that is open toward the other first direction side. An opening end of the valve body  62  is fitted into the one end of the cylinder  16 . The one end of the cylinder  16  is thereby closed off by the valve body  62 . A stopper housing portion  62 A for housing the stopper  66 , described below, is formed inside the valve body  62 . The stopper housing portion  62 A is formed with a recessed shape that is open toward the cylinder  16  side, and the stopper housing portion  62 A is formed with a substantially circular cross-section profile as taken in the second direction. 
     A substantially circular tube shaped connection portion  62 B is integrally formed to a bottom wall of the valve body  62 . The connection portion  62 B is disposed so as to be coaxial with the axis line L 2  of the cylinder  16 , and projects toward the one first direction side (one axial direction side of the cylinder  16 ) from the bottom wall of the valve body  62 . A non-illustrated hose is connected to the connection portion  62 B. Air is supplied to the hose from the electric air pump  10  such that air is supplied to the air blower. 
     A substantially circular tube shaped attachment tube  62 C for attaching the stopper spring  68 , described below, is integrally formed to the bottom wall of the valve body  62 . The attachment tube  62 C is disposed so as to be coaxial with the connection portion  62 B, and projects toward the stopper housing portion  62 A side. The insides of the connection portion  62 B and the attachment tube  62 C are in communication with one another, and this communicated portion configures an exhaust path  62 D. The outside of the electric air pump  10  (inside the hose) is placed in communication with the stopper housing portion  62 A through the exhaust path  62 D. Further, an opening end on the connection portion  62 B side of the exhaust path  62 D configures an exhaust port  62 E. 
     The cap  64  is formed in a comparatively shallow-bottomed, circular tube shape that is open toward the other first direction side. The cap  64  is disposed inside the one end of the cylinder  16 , and is fitted into the opening end of the valve body  62 . A bottom wall of the cap  64  is formed with a projection  64 A that projects toward the one first direction side. The projection  64 A is fitted into the opening end of the stopper housing portion  62 A. A substantially circular exhaust hole  64 B is formed penetrating the projection  64 A. The exhaust hole  64 B is disposed so as to be coaxial with the axis line L 2  of the cylinder  16 . 
     The stopper  66  includes a bottomed, circular tube shaped stopper body  66 A that is open toward the one first direction side. The stopper body  66 A is housed within the stopper housing portion  62 A of the valve body  62  so as to be capable of movement in the first direction (the axial direction of the cylinder  16 ). The stopper  66  is thus configured so as to be capable of moving between an open position illustrated in  FIG. 1  and a closed position illustrated in  FIG. 2 . Plural communication holes  66 A 1  are formed in a bottom wall of the stopper body  66 A. The communication holes  66 A 1  are disposed side-by-side around the circumferential direction of the stopper body  66 A, and are disposed at the radial direction outer side of the exhaust hole  64 B of the cap  64  described above. 
     The stopper spring  68  is provided between the bottom wall of the stopper body  66 A and the bottom wall of the valve body  62  in a state deformed by compression. The stopper spring  68  is configured by a compression coil spring. The attachment tube  62 C is inserted into one end of the stopper spring  68 . The other end of the stopper spring  68  is disposed inside the stopper body  66 A so as to abut the bottom wall of the stopper body  66 A. The stopper  66  is thereby biased toward the other axial direction side (cap  64  side) of the cylinder  16  by the stopper spring  68  so as to be disposed in the closed position. 
     A substantially circular column shaped stopper shaft  66 B is integrally formed to a central portion of the bottom wall of the stopper body  66 A. The stopper shaft  66 B projects toward the cap  64  side from the bottom wall of the stopper body  66 A. The outer diameter of the stopper shaft  66 B is set so as to be smaller than the inner diameter of the exhaust hole  64 B, and the stopper shaft  66 B is inserted through the exhaust hole  64 B. When the piston  50  has reached the bottom dead center, the head of the screw  56  of the piston  50  presses a leading end of the stopper shaft  66 B toward the one first direction side such that the stopper  66  moves to the open position. 
     The valve  70  is formed in substantially an annular plate shape. The stopper shaft  66 B is fitted into the valve  70 , and the valve  70  is disposed at the radial direction outer side of a base end of the stopper shaft  66 B. The outer diameter of the valve  70  is set so as to be larger than the inner diameter of the exhaust hole  64 B. Thus, in a state in which the stopper  66  is disposed at the closed position, the exhaust hole  64 B is closed off by the valve  70 . The valve  70  is disposed at the radial direction inner side of the communication holes  66 A 1  of the stopper body  66 A. In other words, the outer diameter of the valve  70  is set so as to be disposed at the radial direction inner side of the communication holes  66 A 1 . Thus, moving the stopper  66  toward the open position side opens the exhaust hole  64 B such that the inside of the cylinder  16  and the outside of the electric air pump  10  are in communication with each other through the exhaust hole  64 B, the communication holes  66 A 1 , and the exhaust path  62 D. 
     Drive Circuit  80   
     As illustrated in  FIG. 3  and  FIG. 4 , the drive circuit  80  is configured as a circuit that controls driving of the motor  30  described above. The drive circuit  80  includes the substantially rectangular plate shaped circuit board  82 . The circuit board  82  is housed within the circuit housing portion  18 B with its plate thickness direction in the vertical direction (the axial direction of the worm wheel  42 ). Specifically, the circuit board  82  is placed on leading ends of the bosses  20 B of the dividing wall  20  in the housing  12 . Screws  84  are screwed into the recesses in the bosses  20 B. The circuit board  82  is thereby fixed to the housing  12  by the screws  84 . A connector  86  that supplies electric power to the drive circuit  80  is mounted on the circuit board  82 . The connector  86  projects toward the other first direction side from the housing  12 . The circuit board  82  is electrically connected to the motor  30 . Non-illustrated electronic components that control driving of the motor  30  are mounted on the circuit board  82 . Driving of the motor  30  is thus controlled by the drive circuit  80 . 
     Explanation follows regarding operation of the present exemplary embodiment. 
     In the electric air pump  10  configured as described above, when the motor  30  is driven by the drive circuit  80 , the rotary shaft  30 B of the motor  30  is rotated in one rotary direction (rotated forward). The worm shaft  32  provided to the rotary shaft  30 B so as to be capable of rotating as a unit therewith thus rotates in the one rotary direction, actuating the crank  40 . Specifically, the worm wheel  42  rotates in one rotary direction about the shaft  20 A, and the piston  50  coupled thereto by the rod  46  moves back and forth between the bottom dead center and the top dead center along the axial direction of the cylinder  16 . 
     Movement of Piston  50  from Top Dead Center to Bottom Dead Center 
     As illustrated in  FIG. 2 , in a state in which the piston  50  is disposed at the top dead center, the piston  50  is disposed away from the check valve  60 , on the other first direction side thereof. Thus, in the check valve  60 , the stopper  66  is disposed at the closed position due to biasing force from the stopper spring  68 , and the exhaust hole  64 B is closed off by the valve  70 . On the outbound stroke of the piston  50  from the top dead center to the bottom dead center, air in the cylinder  16  is compressed as a result of the outbound movement of the piston  50 . During this time, the state in which the exhaust hole  64 B is closed off by the valve  70  is maintained due to the biasing force of the stopper spring  68 . 
     As illustrated in  FIG. 1 , when the piston  50  has reached the bottom dead center, the head of the screw  56  provided at the one end side of the piston  50  presses the leading end of the stopper shaft  66 B toward the one first direction side against the biasing force of the stopper spring  68 . The stopper  66  is thereby moved from the closed position to the open position, ending the state in which the exhaust hole  64 B is closed off by the valve  70 , and opening the exhaust hole  64 B. The inside of the cylinder  16  and the outside of the electric air pump  10  are thus placed in communication with each other through the exhaust hole  64 B, the communication holes  66 A 1 , and the exhaust path  62 D. As a result, compressed air inside the cylinder  16  is discharged (ejected) through the exhaust port  62 E into the hose and supplied to the air blower via the hose. 
     Movement of Piston  50  from Bottom Dead Center to Top Dead Center 
     On the return stroke of the piston  50  from the bottom dead center, the head of the screw  56  provided at the one end side of the piston  50  moves away from the leading end of the stopper shaft  66 B, toward the other first direction side thereof. The stopper  66  is thus moved from the open position to the closed position by biasing force from the stopper spring  68 , and the exhaust hole  64 B is closed off by the valve  70 . During the return stroke of the piston  50 , the outer circumferential portion of the intake valve  54  to opens, drawing air is drawn into the cylinder  16 , due to the pressure within the cylinder  16  dropping such that air drawn in from outside the electric pump  10  flows into the cylinder  16 . When the piston  50  has reached the top dead center, a state is adopted in which air has been drawn into the cylinder  16 . 
     In the electric air pump  10 , when the motor  30  is driven, the piston  50  moves back and forth between the top dead center and the bottom dead center such that compressed air inside the cylinder  16  is supplied to the air blower via the hose. 
     Note that in the electric air pump  10 , the housing  12  configuring an outer shell of the electric air pump  10  is configured including the motor housing portion  14  housing the motor  30  and the cylinder  16  housing the piston  50 . The cylinder  16  extends along the axial direction of the motor  30 . This enables the size of the electric air pump  10  to be made more compact along the radial direction of the motor  30 , as compared to configurations in which the cylinder  16  extends along the radial direction of the motor  30  (a direction orthogonal to the axis line L 1  of the motor  30 ) such as described in Background Art. 
     Further, the cylinder  16  is disposed at the radial direction outer side of the motor housing portion  14  so as to adjoin the motor housing portion  14 . Specifically, the cylinder  16  and the motor housing portion  14  are disposed side-by-side in the radial direction of the motor  30  (in the second direction) in the housing  12 . The cylinder  16  can thus be disposed utilizing space at the radial direction outer side of the motor  30 . This enables the size of the electric air pump  10  to be made more compact along the axial direction of the motor  30 , as compared to cases in which the cylinder  16  is, for example, disposed at the other first direction side of the crank/circuit housing portion  18 . 
     Further, in the electric air pump  10 , as viewed along the axial direction (vertical direction) of the worm wheel  42 , the axis line L 3  of the crank  40  and the axis line L 2  of the cylinder  16  are offset in the second direction. This enables the piston  50  to be efficiently pushed out by the rod  46  when the rod  46  moves the piston  50  from the top dead center to the bottom dead center. Namely, when the piston  50  moves from the top dead center to the bottom dead center, the one end of the rod  46  rotates about the shaft  20 A such that the rod  46  moves while swinging about its other end (the portion coupled to the piston  50 ) (see arrow H 1  and arrow H 2  in  FIG. 2 ). Since the axis line L 3  of the crank  40  and the axis line L 2  of the cylinder  16  are offset, it is possible to reduce the swing angle of the rod  46  when the piston  50  is on the outbound stroke, as compared to a comparative example in which the axis line L 3  of the crank  40  is, for example, aligned with the axis line L 2  of the cylinder  16 . In other words, in contrast to the comparative example, the rod  46  is able to be moved along the axis line L 2  of the cylinder  16  when the rod  46  moves the piston  50  from the top dead center to the bottom dead center. This enables the piston  50  to be efficiently pushed out by the rod  46  when the rod  46  moves the piston  50  from the top dead center to the bottom dead center. 
     Further, in the electric air pump  10 , as viewed along the axial direction (vertical direction) of the worm wheel  42 , the axis line L 3  of the crank  40  is disposed between the axis line L 2  of the cylinder  16  and the axis line L 1  of the motor  30 . This enables the size of the electric air pump  10  to be made even more compact along the radial direction of the motor  30 , as compared to cases in which the axis line L 3  of the crank  40  is disposed on the opposite side of the axis line L 2  of the cylinder  16  to the axis line L 1  of the motor  30  (the other second direction side). 
     Further, in the electric air pump  10 , the one end side of the rod  46  is disposed on the upper side of the worm wheel  42 , and the circuit board  82  is disposed on the other axial direction side of the worm wheel  42 . The crank  40  and the circuit board  82  are thus able to be disposed alongside each other along the axial direction of the worm wheel  42 . This enables the size of the electric air pump  10  to be made more compact along the axial direction of the worm wheel  42 . 
     Further, the motor  30  configuring part of the electric air pump  10  includes the yoke housing  30 D, this being a magnetic body wrapped around locations corresponding to the magnet  30 C. The thickness of portions of the yoke housing  30 D that contribute little to the magnetic field (for example, a portion where a brush holder is housed) are thus able to be made thinner. This enables the motor  30  to be made more compact, and enables the electric air pump  10  configured including the motor  30  to be made more compact. 
     Further, in the electric air pump  10 , the length direction intermediate portion of the rod  46  is bent toward the lower side (namely, the circuit housing portion  18 B side) so as to form substantially a crank shape at a position to the radial direction outer side of the worm wheel  42 . In addition, the portion of the rod  46  facing the worm wheel  42  (the portion facing the worm wheel  42  along the direction of the rotary axis of the worm wheel  42 ), as viewed from a rotation radial direction outer side of the worm wheel  42 , extends linearly along a rotation radial direction of the worm wheel  42  and is parallel to the face of the worm wheel  42 . This enables the crank housing portion  18 A in which the rod  46  is disposed to be achieve greater space efficiency in the vertical direction. As a result, the electric air pump  10  can be made more compact in the vertical direction. 
     Further, in the electric air pump  10 , the piston  50  is disposed spanning from the crank housing portion  18 A to the circuit housing portion  18 B in the vertical direction. Such configuration enables the electric air pump  10  to be made more compact in the vertical direction. 
     Note that although the axis line L 2  of the cylinder  16  and the axis line L 1  of the motor  30  are set so as so run parallel to each other in the present exemplary embodiment, the axis line L 2  of the cylinder  16  may be disposed angled slightly with respect to the axis line L 1  of the motor  30  as viewed along the vertical direction. Namely, “a cylinder extending along an axial direction of a motor” in the present disclosure encompasses cases in which a cylinder extends along a direction that is angled with respect to an axial direction of a motor. The size of the electric air pump  10  is able to be made more compact along the radial direction of the motor  30  in these cases as well, as compared to configurations in which the cylinder  16  extends along the radial direction of the motor  30  (a direction orthogonal to the axial direction). 
     Further, although the motor housing portion  14  and the cylinder  16  are set so as to be adjoining in the present exemplary embodiment, configuration may be such that the crank  40  is disposed between the motor housing portion  14  and the cylinder  16  along the length directions thereof as viewed along the vertical direction. The size of the electric air pump  10  is able to be made more compact along the radial direction of the motor in these cases as well, as compared to configurations in which the cylinder  16  extends along the radial direction of the motor  30  (a direction orthogonal to the axial direction). 
     Further, in the present exemplary embodiment, configuration is such that the rotary shaft  30 B of the motor  30  is rotated in one rotary direction to move the piston  50  back and forth between the top dead center and the bottom dead center. Alternatively, configuration may be such that the rotary shaft  30 B of the motor  30  is rotated forward and in reverse by the drive circuit  80  to move the piston  50  back and forth between the top dead center and the bottom dead center. 
     Further, in the present exemplary embodiment, configuration is such that the head of the screw  56  provided to the one first direction side of the piston  50  pushes the stopper shaft  66 B to open the check valve  60 . Alternatively, configuration may be such that the check valve  60  is opened when the pressure within the cylinder  16  (in the space formed between the cylinder  16  and the piston  50 ) on the outbound stroke of the piston  50  becomes greater than or equal to a given pressure. In such cases, the biasing force of the stopper spring  68  is set such that the check valve  60  opens when the pressure within the cylinder  16  becomes greater than or equal to the given pressure. 
     Further, in the configuration of the check valve  60  that opens when the pressure within the cylinder  16  becomes greater than or equal to the given pressure, it is not necessary for the connection portion  62 B (the exhaust hole  64 B) to be coaxial with the axis line L 2  of the cylinder  16 . For example, the connection portion  62 B (exhaust hole  64 B) may be to the radial direction outer side (in a direction orthogonal to the axis line L 2  of the cylinder  16 ) of the cylinder  16 . 
     Further, in the present exemplary embodiment, as illustrated in  FIG. 4 , configuration is such that the circuit board  82  (circuit housing portion  18 B) is disposed overlapping with the cylinder  16  in the vertical direction (the axial direction of the worm wheel  42 ). Alternatively, configuration may be such that the circuit board  82  is not disposed overlapping with the cylinder  16  in the vertical direction. The size of the electric air pump  10  is able to be made more compact along the vertical direction in these cases as well, as compared to configurations in which the circuit board  82  overlaps with the cylinder  16  in the vertical direction. 
     The disclosure of Japanese Patent Application No. 2015-226909, filed on Nov. 19, 2015, and the disclosure of Japanese Patent Application No. 2016-146537, filed on Jul. 26, 2016, are incorporated in their entirety in the present specification by reference herein. 
     All cited documents, patent applications, and technical standards mentioned in the present specification are incorporated by reference in the present specification to the same extent as if each individual cited document, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.