Patent Publication Number: US-9429154-B2

Title: Electromagnetic pump device

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2011-183147 filed on Aug. 24, 2011 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an electromagnetic pump device in which a strainer is attached to a suction port. 
     DESCRIPTION OF THE RELATED ART 
     Hitherto, there has been proposed an electromagnetic pump device of this type, including an electromagnetic portion, a movable iron core capable of moving back and forth in the axial direction inside a pump chamber by turning on and off the electromagnetic portion, an inlet check valve mechanism that is built in the pump chamber and that allows working oil to flow in one direction from a suction port into the pump chamber, and an outlet check valve mechanism that is built in the pump chamber and that allows working oil to flow in one direction from the pump chamber to a discharge port (see Japanese Patent Application Publication No. 2006-291914 (JP 2006-291914 A), for example). In the electromagnetic pump device, the suction port extends in the axial direction from the inlet check valve mechanism, and opens in a direction orthogonal to the axial direction to be connected to an oil passage. A strainer is attached at the connection portion to remove foreign matter such as dust. In order to reduce the resistance against flow of the working oil through the strainer, a stepped portion is formed such that the portion of connection with the oil passage is slightly larger in diameter than the suction port. 
     SUMMARY OF THE INVENTION 
     In some of the thus configured electromagnetic pump devices, the inlet check valve mechanism is formed with a suction port that opens in the axial direction, and the strainer is disposed immediately before the inlet check valve mechanism. Also in such devices, it is conceivable to provide the stepped portion discussed above at the suction port in the inlet check valve mechanism. In order to provide the stepped portion, however, it is necessary to make the suction port of the inlet check valve mechanism slightly larger in inside diameter and then expand the inlet check valve mechanism in the axial direction, which may make the inlet check valve mechanism larger to lead to an increase in size of the electromagnetic pump device. 
     It is a main object of the electromagnetic pump device according to the present invention to smoothly suck a working fluid and have a compact configuration. 
     In order to achieve the foregoing main object, the electromagnetic pump device according to the present invention adopts the following means. 
     According to an aspect of the present invention, an electromagnetic pump device includes: 
     a suction check valve including a tubular portion and a flange portion that extends in a radial direction from an end edge of the tubular portion, the suction check valve being formed with a through hole that penetrates the tubular portion and the flange portion to form a suction port in an end surface of the flange portion; and 
     a strainer attached to the suction port and having a pore forming region which is larger than an inside diameter of the through hole at the tubular portion and in which a large number of pores are formed, in which 
     the suction check valve is formed with a diameter reducing portion formed such that the inside diameter of the through hole is reduced from the flange portion toward the tubular portion with a degree of diameter reduction varied from a large value to a small value. 
     The electromagnetic pump device according to the aspect of the present invention includes the suction check valve including the tubular portion and the flange portion which extends in the radial direction from an end edge of the tubular portion, the suction check valve being formed with the through hole which penetrates the tubular portion and the flange portion to form the suction port in an end surface of the flange portion, and the suction check valve is formed with the diameter reducing portion formed such that the inside diameter of the through hole is reduced from the flange portion toward the tubular portion with the degree of diameter reduction varied from a large value to a small value. Thus, the thickness at the boundary portion between the flange portion and the cylindrical portion can be suppressed while an increase in thickness of the flange portion is secured compared to a configuration in which the degree of diameter reduction is constant. In addition, a working fluid can be smoothly sucked through diameter reduction at the diameter reducing portion. As a result, it is possible to allow a working fluid to be smoothly sucked and to provide an electromagnetic pump device with a compact configuration. 
     In the electromagnetic pump device according to the above aspect of the present invention, the diameter reducing portion may be formed from two stages of tapered surfaces with different inclination angles. With this configuration, the diameter reducing portion can be formed though relatively easy processing. In the electromagnetic pump device according to this aspect of the present invention, in the diameter reducing portion, an inflection point at which the inclination angle of the two stages of tapered surfaces is varied may be determined at a position at which a thickness at a boundary portion between the tubular portion and the flange portion is equal to or more than a predetermined thickness. With this configuration, the thickness of the boundary portion between the flange portion and the cylindrical portion can be more reliably secured. 
     In the electromagnetic pump device according to the aspect of the present invention, the suction check valve may include a straight portion provided between the end surface of the flange portion and the diameter reducing portion, the straight portion having a uniform diameter corresponding to an inside diameter of the suction port. With this configuration, a working fluid can be sucked more smoothly. In addition, the area of the end surface of the flange portion covered by the strainer can be made relatively large, and thus the pressure of a working fluid applied to the strainer can be received more appropriately. 
     In the electromagnetic pump device according to the aspect of the present invention, the suction check valve may be formed such that the inside diameter of the suction port is larger than an outside diameter of the tubular portion. Reducing the diameter of such an opening member with a constant degree from a second inside diameter toward a first inside diameter tends to result in a portion in which the thickness is locally significantly reduced. Therefore, the present invention can be applied highly significantly. 
     In the electromagnetic pump device according to the aspect of the present invention in which a piston moves back and forth within a cylinder to pump a working fluid, the suction check valve may be built in the cylinder. With this configuration, the electromagnetic pump device can be provided with a more compact configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a schematic configuration of an electromagnetic pump  20  according to an embodiment of the present invention; 
         FIG. 2  illustrates how a suction check valve  70  is assembled; 
         FIG. 3  shows the appearance of the suction check valve  70  after being assembled; 
         FIG. 4  is a perspective view of a plug  78 ; 
         FIG. 5  is an A-A sectional view showing an A-A section in the perspective view of the plug  78  of  FIG. 4 ; 
         FIGS. 6A to 6C  illustrate comparative examples for cases where a diameter reducing portion is formed differently from that in the embodiment; 
         FIG. 7  illustrates how a discharge check valve  80  is assembled to a piston  60 ; 
         FIG. 8  shows the appearance of the discharge check valve  80  and the piston  60  after being assembled; and 
         FIG. 9  illustrates how the piston  60 , the discharge check valve  80 , a spring  46 , the suction check valve  70 , and a strainer  90  are assembled to a cylinder  50 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the present invention will be described below. 
       FIG. 1  is a diagram showing a schematic configuration of an electromagnetic pump  20  according to an embodiment of the present invention. The electromagnetic pump  20  according to the embodiment includes a solenoid portion  30  that generates an electromagnetic force, and a pump portion  40  actuated by the electromagnetic force of the solenoid portion  30 . The electromagnetic pump  20  may be formed as a part of a hydraulic control device provided in a vehicle incorporating an engine and an automatic transmission to hydraulically drive friction engagement elements (clutches and brakes) included in the automatic transmission. 
     The solenoid portion  30  includes a solenoid case  31  that is a bottomed cylindrical member, an electromagnetic coil  32 , a plunger  34  that serves as a movable element, and a core  36  that serves as a stationary element. The electromagnetic coil  32 , the plunger  34 , and the core  36  are disposed in the solenoid case  31 . In the solenoid portion  30 , a current is applied to the electromagnetic coil  32  to form a magnetic circuit in which magnetic flux circulates through the solenoid case  31 , the plunger  34 , and the core  36 , and the plunger  34  is attracted to push out a shaft  38  provided in abutment with the distal end of the plunger  34 . 
     The pump portion  40  is formed as a piston pump that moves a piston  60  back and forth using the electromagnetic force from the solenoid portion  30  and the urging force of a spring  46  to pump working oil. The pump portion  40  includes: a cylinder  50  having a hollow cylindrical shape with its one end joined to the solenoid case  31  of the solenoid portion  30 ; the piston  60  slidably disposed within the cylinder  50  with its base end surface coaxially abutting against the distal end of the shaft  38  of the solenoid portion  30 ; the spring  46  that abuts against the distal-end surface of the piston  60  to urge the piston  60  in the direction opposite to the direction in which the electromagnetic force from the solenoid portion  30  is applied; a suction check valve  70  that supports the spring  46  from the side opposite to the distal-end surface of the piston  60 , that permits working oil to flow in the direction of being sucked into a pump chamber  56 , and that prohibits working oil to flow in the opposite direction; a strainer  90  disposed at the suction port of the suction check valve  70  to trap foreign matter such as dust contained in sucked working oil; a discharge check valve  80  that is built in the piston  60 , that permits working oil to flow in the direction of being discharged from the pump chamber  56 , and that prohibits working oil to flow in the opposite direction; and a cylinder cover  48  that covers the other end of the cylinder  50  with the piston  60 , the discharge check valve  80 , the spring  46 , and the suction check valve  70  disposed inside the cylinder  50 . In the pump portion  40 , a suction port  42  is formed at the axial center of the cylinder cover  48 , and a discharge port  44  is formed by cutting away a part of the side surface of the cylinder  50  in the circumferential direction. 
     The piston  60  is formed in a stepped shape with a piston main body  62  having a cylindrical shape, and a shaft portion  64  having a cylindrical shape with its end surface in abutment with the distal end of the shaft  38  of the solenoid portion  30  and being smaller in outside diameter than the piston main body  62 . The piston  60  moves back and forth within the cylinder  50  in conjunction with the shaft  38  of the solenoid portion  30 . A bottomed hollow portion  62   a  having a cylindrical shape is formed at the axial center of the piston  60 . The discharge check valve  80  is disposed in the hollow portion  62   a . The hollow portion  62   a  extends from the distal-end surface of the piston  60  through the inside of the piston main body  62  to a middle of a space inside the shaft portion  64 . The shaft portion  64  is formed with two through holes  64   a  and  64   b  that intersect each other at an angle of 90 degrees in the radial direction. The discharge port  44  is formed around the shaft portion  64 . The hollow portion  62   a  communicates with the discharge port  44  via the two through holes  64   a  and  64   b.    
     The suction check valve  70  includes a valve main body  72  fitted into the cylinder  50  and having a bottomed hollow portion  72   a  formed inside thereof and a center hole  72   b  formed at the axial center in the bottom of the hollow portion  72   a  to communicate between the hollow portion  72   a  and the pump chamber  56 , a ball  74 , a spring  76  that provides an urging force to the ball  74 , and a plug  78  that serves as a seat portion for the ball  74 .  FIG. 2  illustrates how the suction check valve  70  is assembled.  FIG. 3  shows the appearance of the suction check valve  70  after being assembled. As shown in the drawing, the suction check valve  70  is assembled by sequentially inserting the spring  76  and the ball  74  into the hollow portion  72   a  of the valve main body  72 , and press-fitting the plug  78  into the hollow portion  72   a . The plug  78  is formed as a flanged cylindrical member including a cylindrical portion  78   a  having an outside diameter that allows the plug  78  to be press-fitted into the hollow portion  72   a  of the valve main body  72 , and a flange portion  78   b  that extends in the radial direction from the end edge of the cylindrical portion  78   a . The strainer  90  is attached so as to cover the end surface of the flange portion  78   b . As shown in  FIG. 2 , the strainer  90  is composed of a disk portion  92 , in the center region of which a large number of pores are formed (pore forming region  92   a ) to form a strainer surface, and three leg portions  94  which extend from the outer peripheral edge of the disk portion  92  in the orthogonal direction and at the distal end of which clips that are bent inward are provided. Therefore, when the leg portions  94  of the strainer  90  are placed over the flange portion  78   b  of the plug  78  as shown in  FIG. 3 , the clips at the distal end of the leg portions  94  are engaged with a stepped portion between the flange portion  78   b  and the cylindrical portion  78   a , preventing the strainer  90  from slipping off. In the embodiment, the suction check valve  70  and the strainer  90  are assembled in this way to form a sub-assembly (see  FIG. 3 ). 
     Here, the shape of the plug  78  of the suction check valve  70  will be described in detail.  FIG. 4  is a perspective view of the plug  78 .  FIG. 5  shows an A-A section in the perspective view of the plug  78  of  FIG. 4 . As shown in the drawing, the plug  78  is formed with a through hole  78   c  that penetrates the cylindrical portion  78   a  and the flange portion  78   b . A center portion  79  with an inside diameter D 1  that is smaller than the outside diameter of the ball  74  and with a length L is formed on the cylindrical portion  78   a  side. The inside diameter D 1  is determined, for example, on the basis of the flow amount of working oil that passes through the center portion  79  and that is calculated from the discharge amount (suction amount) required for the electromagnetic pump  20 , the flow rate of working oil that passes through the center portion  79 , the resistance against flow of the working oil, and so forth. In addition, the plug  78  is formed with a tapered portion  79   a  that communicates with the center portion  79  and that becomes gradually larger in inside diameter from the left toward the right in  FIG. 5 . The ball  74  abuts against the tapered portion  79   a  to be positioned. Further, the plug  78  is formed with a straight portion  79   b  provided on an end surface  78   b   1  side of the flange portion  78   b  and extending over a predetermined length such that the straight portion  79   b  has an inside diameter D 2  that is equivalent to the diameter of the pore forming region  92   a  of the strainer  90 . The size and the number of the pores of the strainer  90  are determined as follows. For example, the size of the pores is calculated in consideration of the size of foreign matter desired to be trapped, the flow rate of working oil that passes through the pores, the resistance against flow of the working oil, and so forth. The number of the pores is calculated on the basis of the calculated size of the pores and the flow amount at the center portion  79  discussed above so that a necessary flow amount of working oil can be sucked. The diameter of the pore forming region  92   a , that is, the inside diameter D 2 , is determined from the thus calculated size and number of the pores. In the embodiment, the inside diameter D 2  is determined to be larger than the outside diameter of the cylindrical portion  78   a . In addition, the plug  78  is formed with a diameter reducing portion  79   c , the inside diameter of which becomes gradually smaller from the flange portion  78   b  side toward the cylindrical portion  78   a  side (from the left toward the right in  FIG. 5 ). The diameter reducing portion  79   c  includes two stages of tapered surfaces  79   c   1  and  79   c   2  with different inclination angles of the surface with respect to the axial center of the center portion  79 . The diameter reducing portion  79   c  is formed such that the inclination angle (angle β in  FIG. 5 ) of the tapered surface  79   c   2  is smaller than the inclination angle (angle α in  FIG. 5 ) of the tapered surface  79   c   1 . Therefore, the tapered surfaces  79   c   1  and  79   c   2  are different from each other in degree of diameter reduction. The degree of diameter reduction in the tapered surface  79   c   2  is smaller than the degree of diameter reduction in the tapered surface  79   c   1 . That is, the diameter reducing portion  79   c  is formed such that the inside diameter of the through hole  78   c  is reduced from the inside diameter D 2  to the inside diameter D 1  with the degree of diameter reduction varied from a large value to a small value. The reason that the diameter reducing portion  79   c  is thus formed will be described below.  FIGS. 6A to 6C  show comparative examples for cases where the diameter reducing portion is formed differently from that in the embodiment. 
     First,  FIG. 6A  shows Comparative Example 1 in which a tapered surface at an inclination angle α (inclination angle of the tapered surface  79   c   1 ) is formed from the center portion  79  with the inside diameter D 1  to the straight portion  79   b  with the inside diameter D 2 . As shown in the drawing, the thickness T at the boundary portion between the cylindrical portion  78   a  and the flange portion  78   b  is significantly small compared to the embodiment, and therefore the rigidity of the plug  78  may be insufficient. In the embodiment, in particular, the inside diameter D 2  is larger than the outside diameter of the cylindrical portion  78   a , and thus the thickness T tends to be small. Next,  FIG. 6B  shows Comparative Example 2 in which a tapered surface at an inclination angle α is formed from the straight portion  79   b  with the inside diameter D 2  to the center portion  79  with the inside diameter D 1  such that the thickness T is maintained at the same value as in the embodiment. As shown in the drawing, the length L of the center portion  79  is larger than that in the embodiment, which may hinder working oil from flowing smoothly. Subsequently,  FIG. 6C  shows Comparative Example 3 in which a tapered surface at an inclination angle β (inclination angle of the tapered surface  79   c   2 ) is formed from the center portion  79  with the inside diameter D 1  to the straight portion  79   b  with the inside diameter D 2 . As shown in the drawing, the thickness of the flange portion  78   b  is increased compared to that in the embodiment, which makes the plug  78  larger. This also makes the suction check valve  70  larger, leading to an increase in size of the electromagnetic pump  20 . If the inside diameter D 1  and the inside diameter D 2  are thus connected by one stage of tapered surface with a constant inclination angle, the thickness T of the plug  78  may be insufficient to result in insufficient rigidity, the length L of the center portion  79  may be longer to hinder working oil from flowing smoothly, or the thickness of the flange portion  78   b  may be increased to lead to an increase in size of the suction check valve  70  (electromagnetic pump  20 ). In the embodiment, in contrast, the inside diameter of the through hole  78   c  is increased to the inside diameter D 2  while the thickness T at a sufficient value is ensured with the tapered surface  79   c   2  with a small degree of diameter reduction and an increase in thickness of the flange portion  78   b  is suppressed with the tapered surface  79   c   1  with a large degree of diameter reduction. In addition, the diameter reducing portion  79   c  is gradually reduced in diameter from the flange portion  78   b  side toward the cylindrical portion  78   a  side, which allows working oil to be smoothly sucked. This allows working oil to be smoothly sucked while securing the rigidity of the plug  78  and preventing an increase in size of the plug  78 . For this reason, the diameter reducing portion  79   c  is formed such that the inside diameter of the through hole  78   c  of the plug  78  is reduced from the inside diameter D 2  to the inside diameter D 1  with the degree of diameter reduction varied from a large value to a small value. 
     In the embodiment, in addition, the thus configured diameter reducing portion  79   c  is implemented by providing the two stages of tapered surfaces  79   c   1  and  79   c   2 . Thus, the diameter reducing portion  79   c  can be formed relatively easily without requiring complicated processing. In the embodiment, further, an inflection point P (see  FIG. 5 ) at which the inclination angle of the two stages of tapered surfaces  79   c   1  and  79   c   2  is varied is determined in such a range that the thickness T at the boundary portion between the cylindrical portion  78   a  and the flange portion  78   b  is equal to or more than a predetermined thickness and at such a position that the thickness of the flange portion  78   b  can be made as small as possible. Therefore, the thickness of the flange portion  78   b  can be suppressed while the thickness T of the plug  78  is more reliably secured. The predetermined thickness may be determined as a thickness that can secure the rigidity, durability, etc. required for the plug  78  in consideration of the pressure, flow amount, etc. of working oil sucked via the strainer  90 , for example. In addition, the straight portion  79   b  is formed between the end surface  78   b   1  of the flange portion  78   b  and the diameter reducing portion  79   c . Thus, working oil can be caused to smoothly flow in, and the annular area of the end surface  78   b   1  can be increased to more appropriately receive the pressure of working oil applied to the cylinder cover  48  and the strainer  90 , compared to a configuration in which the tapered surface is extended to the end surface  78   b   1 . That is, the end surface  78   b   1  covered by the strainer  90  functions as a pressure receiving surface that receives the pressure of working oil applied to the cylinder cover  48  and the strainer  90 . Thus, an increase in area of the end surface  78   b   1  can prevent an excessive stress from acting on the strainer  90  and the flange portion  78   b  (plug  78 ). 
     The suction check valve  70  opens with the spring  76  compressed and the ball  74  moved away from the plug  78  when the pressure difference (P 1 −P 2 ) between the input-side pressure P 1  and the output-side pressure P 2  is equal to or more than a predetermined pressure to overcome the urging force of the spring  76 . The suction check valve  70  closes with the spring  76  expanded and the ball  74  pressed against the tapered portion  79   a  of the plug  78  to block the through hole  78   c  when the pressure difference (P 1 −P 2 ) discussed above is less than the predetermined pressure. 
     The discharge check valve  80  includes a ball  84 , a spring  86  that provides an urging force to the ball  84 , and a plug  88  formed as an, annular member with a center hole  89  having an inside diameter that is smaller than the outside diameter of the ball  84 .  FIG. 7  illustrates how the discharge check valve  80  is assembled.  FIG. 8  shows the appearance of the discharge check valve  80  and the piston  60  after being assembled. As shown in the drawing, the discharge check valve  80  is assembled by sequentially inserting the spring  86  and the ball  84  into the hollow portion  62   a  of the piston  60 , and press-fitting the plug  88  into the hollow portion  62   a . The plug  88  may be fixed to the piston  60  by a fixing member such as a snap ring. In the embodiment, the discharge check valve  80  is assembled to the piston  60  in this way to form a sub-assembly (see  FIG. 8 ). 
     The discharge check valve  80  opens with the spring  86  compressed and the ball  84  moved away from the center hole  89  of the plug  88  when the pressure difference (P 2 −P 3 ) between the input-side pressure (pressure on the output side of the suction check valve  70 ) P 2  and the output-side pressure P 3  is equal to or more than a predetermined pressure to overcome the urging force of the spring  86 . The discharge check valve  80  closes with the spring  86  expanded and the ball  84  pressed against the center hole  89  of the plug  88  to block the center hole  89  when the pressure difference (P 2 −P 3 ) discussed above is less than the predetermined pressure. 
     In the cylinder  50 , the pump chamber  56  is formed as a space surrounded by an inner wall  51 , the distal-end surface of the piston  60 , and a surface of the suction check valve  70  on the spring  46  side. When the piston  60  is moved by the urging force of the spring  46 , the volume inside the pump chamber  56  is expanded to open the suction check valve  70  and close the discharge check valve  80  to suck working oil via the suction port  42 . When the piston  60  is moved by the electromagnetic force of the solenoid portion  30 , the volume inside the pump chamber  56  is reduced to close the suction check valve  70  and to open the discharge check valve  80  to discharge the sucked working oil via the discharge port  44 . 
     The cylinder  50  is formed with a step between an inner wall  52 , over which the piston main body  62  slides, and an inner wall  54 , over which the shaft portion  64  slides. The discharge port  44  is formed at the stepped portion. The stepped portion forms a space surrounded by an annular surface of the stepped portion between the piston main body  62  and the shaft portion  64 , and the outer peripheral surface of the shaft portion  64 . The space is formed on the opposite side of the piston main body  62  from the pump chamber  56 . Thus, the volume of the space is reduced when the volume of the pump chamber  56  is expanded, and expanded when the volume of the pump chamber  56  is reduced. In this event, variations in volume of the space are smaller than variations in volume of the pump chamber  56  because the area (pressure receiving area) over which the piston  60  receives a pressure from the pump chamber  56  side is larger than the area (pressure receiving area) over which the piston  60  receives a pressure from the discharge port  44  side. Therefore, the space serves as a second pump chamber  58 . That is, when the piston  60  is moved by the urging force of the spring  46 , an amount of working oil corresponding to the amount of expansion in volume of the pump chamber  56  is sucked from the suction port  42  into the pump chamber  56  via the suction check valve  70 , and an amount of working oil corresponding to the amount of reduction in volume of the second pump chamber  58  is discharged from the second pump chamber  58  via the discharge port  44 . When the piston  60  is moved by the electromagnetic force of the solenoid portion  30 , an amount of working oil corresponding to the amount of reduction in volume of the pump chamber  56  is fed from the pump chamber  56  into the second pump chamber  58  via the discharge check valve  80 , and an amount of working oil corresponding to the difference between the amount of reduction in volume of the pump chamber  56  and the amount of expansion in volume of the second pump chamber  58  is discharged via the discharge port  44 . Thus, working oil is discharged from the discharge port  44  twice while the piston  60  moves back and forth once, which makes it possible to reduce discharge non-uniformities and improve the discharge performance. 
       FIG. 9  illustrates how the electromagnetic pump  20  according to the embodiment is assembled. The electromagnetic pump  20  according to the embodiment is assembled by sequentially inserting the sub-assembly of the piston  60  and the discharge check valve  80 , the spring  46 , and the sub-assembly of the suction check valve  70  and the strainer  90  into the cylinder  50 , and thereafter attaching the cylinder cover  48 . The outer peripheral surface of the cylinder  50  and the inner peripheral surface of the cylinder cover  48  are engraved with spiral threads (not shown), and the cylinder cover  48  is attached by placing the cylinder cover  48  over the cylinder  50  and screwing the cylinder cover  48 . When the cylinder cover  48  is attached, the outer peripheral edge of the strainer  90  is pressed by an annular pressing surface  48   a  of the cylinder cover  48  to fix the strainer  90 . 
     In the electromagnetic pump  20  according to the embodiment described above, the suction check valve  70  is formed with the diameter reducing portion  79   c  formed such that the inside diameter of the through hole  78   c  is reduced from the flange portion  78   b  of the plug  78  toward the cylindrical portion  78   a  with the degree of diameter reduction varied from a large value to a small value. Thus, the thickness T at the boundary portion between the flange portion  78   b  and the cylindrical portion  78   a  can be secured while an increase in thickness of the flange portion  78   b  is suppressed compared to a configuration in which the degree of diameter reduction is constant. In addition, working oil can be smoothly sucked due to diameter reduction at the diameter reducing portion  79   c . As a result, working oil can be smoothly sucked and an increase in size of the suction check valve  70  can be prevented, providing the electromagnetic pump  20  with a compact configuration. 
     In addition, the diameter reducing portion  79   c  is formed from the two stages of tapered surfaces  79   c   1  and  79   c   2 , and therefore can be formed through relatively easy processing. Further, the inflection point P that serves as the boundary between the respective inclination angles of the two stages of tapered surfaces  79   c   1  and  79   c   2  is determined in such a range that the thickness T at the boundary portion between the cylindrical portion  78   a  and the flange portion  78   b  is equal to or more than a predetermined thickness. Thus, the thickness T can be more reliably secured. The straight portion  79   b  is formed between the end surface  78   b   1  of the flange portion  78   b  and the diameter reducing portion  79   c . Thus, working oil can be more smoothly sucked, and the pressure of working oil applied to the strainer  90  can be received by the end surface  78   b   1  more appropriately. In addition, the suction check valve  70  is built in the cylinder  50 , providing the electromagnetic pump  20  with a compact configuration. 
     In the electromagnetic pump  20  according to the embodiment, the diameter reducing portion  79   c  of the plug  78  of the suction check valve  70  is formed from the two stages of tapered surfaces  79   c   1  and  79   c   2 . However, the diameter reducing portion  79   c  may be formed from a plurality of stages, namely three or more stages, of tapered surfaces, or may be formed from a plurality of staircase-like stepped surfaces or rounded curved surfaces in section, rather than tapered surfaces. 
     In the electromagnetic pump  20  according to the embodiment, the inside diameter D 2  is equivalent to the diameter of the pore forming region  92   a  and larger than the outside diameter of the cylindrical portion  78   a . However, the inside diameter D 2  may be equivalent to or smaller than the outside diameter of the cylindrical portion  78   a.    
     In the electromagnetic pump  20  according to the embodiment, the straight portion  79   b  is formed on the plug  78  of the suction check valve  70 . However, the straight portion  79   b  may not be formed. 
     In the electromagnetic pump  20  according to the embodiment, the suction check valve  70  is built in the cylinder  50 . However, a suction check valve may be incorporated in a valve body outside the cylinder  50 , rather than being built in the cylinder  50 . In this case, the suction check valve may be formed by closing the opening of the cylinder  50  in which the suction check valve  70  is disposed and forming a suction port that leads to the pump chamber, attaching the strainer  90  to the flange portion  78   b  such that the strainer  90  covers the end surface  78   b   1  of the plug  78  of the suction check valve  70 , and connecting between the suction port of the pump chamber of the cylinder  50  and the output port (corresponding to the center hole  72   b  in the embodiment) of the suction check valve  70  through an oil passage. 
     The electromagnetic pump  20  according to the embodiment is configured such that working oil is discharged from the discharge port  44  twice while the piston  60  moves back and forth once. However, the present invention is not limited thereto, and the electromagnetic pump  20  according to the embodiment may be any type of electromagnetic pump, such as a type in which working oil is sucked from the suction port into the pump chamber when the piston is moved forward by the electromagnetic force from the solenoid portion and the working oil in the pump chamber is discharged from the discharge port when the piston is moved backward by the urging force of the spring, and a type in which working oil is sucked from the suction port into the pump chamber when the piston is moved backward by the urging force of the spring and the working oil in the pump chamber is discharged from the discharge port when the piston is moved forward by the electromagnetic force from the solenoid portion. 
     The electromagnetic pump  20  according to the embodiment is used for a hydraulic control device that hydraulically drives clutches and brakes of an automatic transmission mounted on an automobile. However, the present invention is not limited thereto, and the electromagnetic pump  20  according to the embodiment may be applied to any system that transports fuel, transports a liquid for lubrication, or the like. 
     Here, the correspondence between the main elements of the embodiment and the main elements of the invention described in the “SUMMARY OF THE INVENTION” section will be described. In the embodiment, the strainer  90  corresponds to the “strainer”. The cylindrical portion  78   a  of the plug  78  corresponds to the “tubular portion”. The flange portion  78   b  corresponds to the “flange portion”. The through hole  78   c  corresponds to the “through hole”. The suction check valve  70  corresponds to the “suction check valve”. The diameter reducing portion  79   c  corresponds to the “diameter reducing portion”. The correspondence between the main elements of the embodiment and the main elements of the invention described in the “SUMMARY OF THE INVENTION” section does not limit the elements of the invention described in the “SUMMARY OF THE INVENTION” section, because the embodiment is an example given for the purpose of specifically describing the best mode for carrying out the invention described in the “SUMMARY OF THE INVENTION” section. That is, the invention described in the “SUMMARY OF THE INVENTION” section should be construed on the basis of the description in that section, and the embodiment is merely a specific example of the invention described in the “SUMMARY OF THE INVENTION” section. 
     While a mode for carrying out the present invention has been described above by way of an embodiment, it is a matter of course that the present invention is not limited to the embodiment in any way, and that the present invention may be implemented in various forms without departing from the scope and sprit of the present invention. 
     The present invention is applicable to the electromagnetic pump device manufacturing industry and so forth.