Patent Publication Number: US-2023151903-A1

Title: Solenoid valve

Description:
TECHNICAL FIELD 
     The present invention relates to a solenoid valve, particularly, to a solenoid valve suitable for hydraulic control of a hydraulic circuit. 
     BACKGROUND ART 
     A solenoid valve for hydraulic control in the related art includes a valve unit including a sleeve, a spool that is accommodated in the sleeve so as to be movable in an axial direction, a spring that biases the spool in the axial direction, and a retainer attached to an end portion of the sleeve to hold the spring; and a solenoid unit including a plunger that drives the spool in the axial direction, a stator, a solenoid molded body which is disposed on an outer periphery of the plunger and in which a coil and the like are covered with resin, and a solenoid casing that accommodates these components. The solenoid valve is disposed between a pressure source such a pump or an accumulator and a supply destination to be able to supply a fluid of which the pressure or the flow rate is adjusted by the movement of the spool, to the supply destination. 
      By the way, since the movement stroke of the spool inside the sleeve is relatively large, when the spool is driven in the axial direction, the fluid in an accommodation space where the plunger is accommodated in the solenoid unit becomes resistance to interfere with rapid movement of the plunger, which is a problem. 
     In a solenoid valve disclosed in Patent Citation 1, a breathing hole is formed in a sleeve to penetrate therethrough in a radial direction, and a fluid is moved between an accommodation space and the outside of the solenoid valve via the breathing hole, namely, so-called breathing is performed, so that resistance of the fluid involved by the movement of a plunger is reduced and responsiveness of the solenoid valve is improved. 
     Citation List 
     Patent Literature 
     Patent Citation 1: WO 2011/052371 A (PAGE 7 and  FIG.  1   ) 
     SUMMARY OF INVENTION 
     Technical Problem 
     In such a solenoid valve, the fluid is moved between the accommodation space and the outside of the solenoid valve through the breathing hole formed in the sleeve, by the movement of the plunger to drive a spool in an axial direction, so that resistance of the fluid involved by the movement of the plunger is reduced. However, in the solenoid valve of Patent Citation 1, since the breathing hole formed in the sleeve penetrates therethrough in the radial direction to communicate with an outer peripheral space of the spool, the spool is easily subjected to the flow, the pressure, or the like of the fluid when the fluid flows in, and the spool is inclined with respect to the sleeve, so that slidability is decreased and responsiveness of the solenoid valve is impaired, which is a problem. 
     The present invention is conceived in view of such problems, and an object of the present invention is to provide a solenoid valve in which responsiveness of the solenoid valve can be improved. 
     Solution to Problem 
     In order to solve the foregoing problems, according to the present invention, there is provided a solenoid valve including: a valve unit including a sleeve in which a spool is accommodated so as to be movable in an axial direction; and a solenoid unit including a plunger to be brought into contact with and separated from a stator by an electromagnetic force to drive the spool in the axial direction, a solenoid molded body disposed on an outer periphery of the plunger and of the stator, and a solenoid casing that accommodates the solenoid molded body. The plunger is disposed in an accommodation space of which at least a part is defined by the stator inside the solenoid unit. The solenoid valve further includes a first breathing flow passage extending at least in a circumferential direction on the outer periphery of the stator to communicate with an outside of the solenoid valve, a second breathing flow passage extending in the axial direction from part of the first breathing flow passage in the circumferential direction to communicate with a first space defined by the stator, the sleeve, and the spool, and a third breathing flow passage extending in the axial direction on an inner periphery of the stator to allow communication between the first space and the accommodation space. According to the aforesaid feature of the present invention, when a fluid is moved through a breathing passage from the outside of the solenoid valve to the inside by the movement of the plunger, the fluid flows out from the first breathing flow passage into the first space through the second breathing flow passage extending in the axial direction at a part in the circumferential direction, on the outer periphery of the stator, so that the fluid which has moved through the second breathing flow passage in the axial direction is dispersed in the first space and the flow of the fluid is weakened. Accordingly, the influence of the fluid in a radial direction is decreased, so that the spool can be held coaxially with the sleeve, smooth slidability of the spool with respect to the sleeve can be maintained, and responsiveness of the solenoid valve can be improved. In addition, since the breathing passage can be made long by the first breathing flow passage and the second breathing flow passage, it is difficult for a contamination existing outside the solenoid valve to infiltrate into the accommodation space. 
     It may be preferable that the first breathing flow passage is be formed in an annular shape, and communicates with the outside of the solenoid valve through an axial communication passage extending in the axial direction toward an opening formed in the solenoid casing or in the sleeve. According to this preferable configuration, since the breathing passage can be made long by the first breathing flow passage and the axial communication passage, it is difficult for the contamination existing outside the solenoid valve to infiltrate into the accommodation space. 
     It may be preferable that the second breathing flow passage communicates with the first space on a radially outer side with respect to the spool. According to this preferable configuration, the fluid that moves through the second breathing flow passage in the axial direction to flow out into the first space acts an axial force mainly on the sleeve, so that it is difficult for the fluid to affect the operation of the spool. 
     It may be preferable that the second breathing flow passage faces the axial communication passage in a radial direction. According to this preferable configuration, it is difficult for the contamination that has infiltrated into the first breathing flow passage from the outside of the solenoid valve through the axial communication passage to infiltrate into the second breathing flow passage. 
     It may be preferable that the axial communication passage is formed on a vertically lower side on the outer periphery of the stator in case the plunger is moved in a horizontal direction. According this preferable configuration, the fluid existing outside the solenoid valve easily flows into the first breathing flow passage through the axial communication passage, and the contamination that has infiltrated into the first breathing flow passage, together with the fluid, descend due to their own weight, so that the contamination can be easily discharged to the outside via the axial communication passage. 
     It may be preferable that a radial groove communicating with the second breathing flow passage and with the third breathing flow passage is formed in the stator or in the spool. According to this preferable configuration, regardless of the axial position of the spool, the second breathing flow passage and the third breathing flow passage always communicate with each other through the radial groove to prevent interference with the movement of the fluid in the breathing passage, so that resistance of the fluid involved by the movement of the plunger can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating a solenoid valve according to an embodiment of the present invention. 
         FIG.  2    is a cross-sectional view illustrating an off state of the solenoid valve of the embodiment taken along line A-A of  FIG.  1   . 
         FIG.  3    is a cross-sectional view illustrating an on state of the solenoid valve of the embodiment taken along line A-A of  FIG.  1   . 
         FIG.  4    is a perspective view illustrating a structure of a sleeve and a solenoid casing in the embodiment. 
         FIG.  5    is a perspective view illustrating a structure of a stator in the embodiment. 
         FIG.  6    is an enlarged cross-sectional view illustrating the flow of a fluid in a breathing passage when the solenoid valve is switched from an off state to an on state in the embodiment. Incidentally,  FIG.  6    illustrates a mode where the fluid moves from the inside of the solenoid valve to the outside. 
         FIG.  7    is an enlarged cross-sectional view illustrating the flow of the fluid in the breathing passage when the solenoid valve is switched from an on state to an off state in the embodiment. Incidentally,  FIG.  7    illustrates a mode where the fluid moves from the outside of the solenoid valve to the inside. 
         FIG.  8 A  is a cross-sectional view illustrating the flow of the fluid in the breathing passage when the solenoid valve is switched from an off state to an on state taken along line B-B of  FIG.  2   , and  FIG.  8 B  is a cross-sectional view illustrating the flow of the fluid in the breathing passage when the solenoid valve is switched from an on state to an off state taken along line B-B of  FIG.  3   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A mode for carrying out a solenoid valve according to the present invention will be described below based on an embodiment. 
     Embodiment 
     A solenoid valve according to an embodiment of the present invention will be described with reference to  FIGS.  1  to  8   . Hereinafter, a description will be given based on the assumption that left and right sides when seen from the front side of  FIGS.  2  and  3    are left and right sides of the solenoid valve. Incidentally, for convenience of description, a spool  22 , a plunger  34 , and a rod  35  illustrated in  FIGS.  2 ,  3 ,  6 , and  7    are illustrated not in cross-sectional views but in side views. 
     A solenoid valve  1  is a spool type solenoid valve, and is used in, for example, a hydraulically controlled apparatus such as an automatic transmission of a vehicle to control the pressure or the flow rate of a control fluid such as a hydraulic oil (hereinafter, simply referred to as a “fluid”) in a fluid circuit. 
     As illustrated in  FIG.  1   , the solenoid valve  1  is configured such that a valve unit  2  which adjusts the pressure or the flow rate of the fluid as a valve is integrally attached to a solenoid unit  3 . Incidentally, the attachment of the valve unit  2  to the solenoid unit  3  will be described in detail at a later stage. 
     As illustrated in  FIGS.  2  and  3   , the valve unit  2  includes a sleeve  21  having a substantially cylindrical shape; the spool  22  having a substantially columnar shape that is liquid-tightly accommodated in a through-hole  21   a  of the sleeve  21  to be movable in an axial direction; a spring  23  having a coil shape that is attached to an axially right end portion of the spool  22  to bias the spool  22  leftward in the axial direction; and a retainer  24  that is caulked and fixed to an axially right end portion of the sleeve  21  to hold the spring  23 . Incidentally, since this configuration is a well-known configuration of a spool valve, a detailed description thereof will be omitted. In addition, the sleeve  21 , the spool  22 , and the retainer  24  are made of a material such as aluminum, iron, stainless steel, or resin. 
     As illustrated in  FIGS.  2  and  3   , a pair of axial cut surfaces  21   f  and  21   f  formed along the axial direction and a pair of radial cut surfaces  21   g  and  21   g  formed along a radial direction are formed on both upper and lower sides at an axially left end portion of the sleeve  21 . Namely, as illustrated in  FIG.  4   , the axial cut surfaces  21   f  and  21   f  form a pair of linear portions when seen in the axial direction, and portions that extend radially outward between the pair of axial cut surfaces  21   f  and  21   f  and in which arc shapes remain form a pair of arc portions  21   b  and  21   b , so that the axially left end portion of the sleeve  21  is formed in a stadium shape. Incidentally, for convenience of description,  FIG.  4    illustrates a state where the axially left end portion of the sleeve  21  faces upward on the drawing sheet. 
     In addition, a slit  21   d  extending in a circumferential direction is formed at the axially left end portion of the sleeve  21  at a location distant from an end surface  21   m  having a stadium shape in the axial direction, so that a flange portion  21   c  is formed between the end surface  21   m  and the slit  21   d . Incidentally, since the slit  21   d  is formed, each of the axial cut surfaces  21   f  and  21   f  is formed in a substantially H shape. 
     In addition, a cutout  21   h  as an opening extending from the end surface  21   m  in the axial direction is formed in the axial cut surface  21   f  that is disposed on a vertically lower side in a state where the valve unit  2  is attached to the solenoid unit  3  (refer to  FIGS.  2  and  3   ). Incidentally, the cutout  21   h  has a tapered surface  21   k  that is inclined leftward from a radially outer side toward a radially inner side in the axial direction (refer to  FIGS.  6  and  7   ). 
     In addition, a recessed portion  21   e  that is recessed rightward from a radially inner side of the end surface  21   m  in the axial direction is formed at the axially left end portion of the sleeve  21 . Incidentally, an inner diameter D1 of the recessed portion  21   e  is set to be larger than an inner diameter D2 of the through-hole  21   a  at a portion that is in sliding contact with a land portion  22   a  of the spool  22  (D1 &gt; D2, refer to  FIG.  2   ). 
     As illustrated in  FIGS.  2  and  3   , a protrusion portion  22   b  having a small diameter that protrudes leftward from a radially inner side of the land portion  22   a  in the axial direction to be inserted into a through-hole  33   a  of a stator  33  to be described later is formed at an axially left end portion of the spool  22 . An end surface of the protrusion portion  22   b , namely, an axially left end surface of the spool  22  is in contact with an axially right end surface of the rod  35  disposed in the through-hole  33   a  of the stator  33 . 
     In addition, an outer peripheral surface of the protrusion portion  22   b , an axially left end surface of the land portion  22   a , and an outer peripheral surface of the land portion  22   a  form a step portion  22   c  having an annular shape at the axially left end portion of the spool  22 . The step portion  22   c  is capable of coming into contact with and separating from an end surface of a protrusion portion  33   d  of the stator  33  to be described later. 
     As illustrated in  FIGS.  2  and  3   , the solenoid unit  3  mainly includes a solenoid casing  31  made of a metallic material such as iron having a magnetic property; a solenoid molded body  32  accommodated in the solenoid casing  31 ; the stator  33  disposed inside the solenoid molded body  32 ; and the plunger  34  disposed in an accommodation space  30  formed on an axially left side of the stator  33 , so as to be movable in the axial direction. 
     As illustrated in  FIG.  4   , the solenoid casing  31  has a cup shape including a plate portion  31   a  having a disk shape and a cylindrical portion  31   b , and an opening  31   d  having a stadium shape is formed at a center of the plate portion  31   a , the opening  31   d  having a slightly larger outer shape than the axially left end portion of the sleeve  21 , and including linear portions  31   e  and an arc portion  31   f . Incidentally, for convenience of description,  FIG.  4    illustrates a state where an axially right end portion of the solenoid casing  31  faces upward on the drawing sheet. 
     In addition, an end plate  39  is caulked and fixed to an axially left end portion of the cylindrical portion  31   b  of the solenoid casing  31  (refer to  FIGS.  2  and  3   ). In addition, a cutout  31   c  into which a connector portion  32   c  (refer to  FIGS.  2  and  3   ) of the solenoid molded body  32  is inserted is formed at the axially left end portion of the cylindrical portion  31   b . 
     Regarding the attachment of the valve unit  2  to the solenoid unit  3 , the sleeve  21  and the solenoid casing  31  are retained together in a state where the linear portions  31   e  and  31   e  of the opening  31   d  are interposed in the slit  21   d , by inserting the flange portion  21   c  of the sleeve  21  into the opening  31   d  of the solenoid casing  31  and by rotating the sleeve  21  around an axis by 90 degrees at a position where the slit  21   d  corresponds to the opening  31   d  (refer to  FIG.  1   ). 
     As illustrated in  FIGS.  2  and  3   , the solenoid molded body  32  is formed by molding a coil  32   a , a lower plate  32   b  having an annular shape, and the like with resin, and a control current is supplied to the coil  32   a  from a connector of the connector portion  32   c  extending from the cutout  31   c  of the solenoid casing  31  (refer to  FIG.  4   ) to the outside. 
     As illustrated in  FIGS.  2  and  3   , the plunger  34  is formed in a columnar shape from a metallic material such as iron having a magnetic property, and is disposed in the accommodation space  30  formed on the axially left side of the stator  33 , so as to be movable in the axial direction. 
     Incidentally, a first tubular body  36  made of a non-magnetic material is disposed on the axially left side of the stator  33 , a second tubular body  37  with a flange that is made of a magnetic material is disposed on an axially left side of the first tubular body  36 , and a third tubular body  38  made of a magnetic material is disposed over the first tubular body  36  and the second tubular body  37  inside the first tubular body  36  and the second tubular body  37 . Namely, the accommodation space  30  is defined by a recessed portion  33   b  of the stator  33  to be described later, inner peripheral surfaces of the first tubular body  36 , of the second tubular body  37 , and of the third tubular body  38 , and an axially right end surface of the end plate  39 . 
     In addition, the plunger  34  is disposed in the accommodation space  30  so as to be in slidable contact with the inner peripheral surface of the third tubular body  38  subjected to low friction processing. Incidentally, an outer peripheral surface of the plunger  34  and the inner peripheral surface of the third tubular body  38  are slightly separated from each other, but almost no fluid passes through this gap. 
     Namely, the plunger  34  is disposed to partition the accommodation space  30  into a second space S 2  and a third space S 3  in a substantially sealed state, the second space S 2  being formed on an axially right side of the plunger  34  and the third space S 3  being formed on the axially left side of the plunger  34 . Incidentally, the third space S 3  communicates with the outside of the solenoid valve  1  via a gap formed between an axially left end surface of the second tubular body  37  and the axially right end surface of the end plate  39  and via the cutout  31   c  of the solenoid casing  31  (refer to  FIG.  4   ) . 
     As illustrated in  FIGS.  2  and  3   , the rod  35  is made of a non-magnetic material such as resin or rubber, and a flange portion  35   a  extending radially outward is formed at an axially left end portion of the rod  35 . Incidentally, the rod  35  is fixed in a state where an axially left end surface of the flange portion  35   a  is in contact with an axially right end surface of the plunger  34 . 
     In addition, when the coil  32   a  is energized to generate an electromagnetic force between the stator  33  and the plunger  34  and thus to move the plunger  34  and the rod  35  rightward toward the stator  33  in the axial direction, an axially right end surface of the flange portion  35   a  of the rod  35  made of a non-magnetic material is capable of coming into contact with a bottom surface of the recessed portion  33   b  of the stator  33 , so that the plunger  34  is prevented from being stuck to the stator  33 . 
     As illustrated in  FIGS.  2 ,  3 , and  5   , the stator  33  is a tubular body having the through-hole  33   a  at a center portion thereof, the through-hole  33   a  penetrating therethrough in the axial direction, and is made of a metallic material such as iron having a magnetic property. In addition, the recessed portion  33   b  (refer to  FIGS.  2  and  3   ) that is recessed rightward in the axial direction from a radially inner side of an axially left end surface of a base portion  33   c  is formed at an axially left end portion of the stator  33 , and the recessed portion  33   b  communicates with the through-hole  33   a . 
     In addition, the stator  33  includes the protrusion portion  33   d  having a small diameter that protrudes rightward in the axial direction from a radially inner side of an axially right end surface of the base portion  33   c . The protrusion portion  33   d  is fitted into the lower plate  32   b  having an annular shape and forming the solenoid molded body  32 , and into the recessed portion  21   e  of the sleeve  21 . Incidentally, a step portion  33   e  having an annular shape is formed at an axially right end portion of the stator  33  by an outer peripheral surface of the protrusion portion  33   d  and the axially right end surface and an outer peripheral surface of the base portion  33   c . 
     When the protrusion portion  33   d  is fitted into the lower plate  32   b  and into the recessed portion  21   e  of the sleeve  21 , the step portion  33   e  comes into contact with an axially left end surface of the lower plate  32   b  in the axial direction to define the degree of insertion of the protrusion portion  33   d  into the recessed portion  21   e  of the sleeve  21 . Accordingly, an end surface of the protrusion portion  33   d , namely, an axially right end surface of the stator  33  and a bottom surface of the recessed portion  21   e  of the sleeve  21  are separated from each other in the axial direction, and a first space S 1  having an annular shape is formed on an axial side opposite to the second space S 2  in the accommodation space  30  formed on the axially left side of the stator  33 , namely, on an axially right side of the stator  33 . Incidentally, the first space S 1  is defined by an axially right end surface of the protrusion portion  33   d , an inner peripheral surface and the bottom surface of the recessed portion  21   e  of the sleeve  21 , and an outer peripheral surface of the spool  22 . As described above, the axially left end portion of the spool  22  is housed in the first space Sl. 
     The first space S 1  is changed in volume according to the axial position of the spool  22 . In detail, the step portion  22   c  of the spool  22  is in contact with the end surface of the protrusion portion  33   d  of the stator  33  in an off state of the solenoid valve  1  (refer to  FIG.  2   ), so that the first space S 1  is formed only on a radially outer side of the land portion  22   a , has an annular shape, and has a minimum volume. In addition, when the coil  32   a  is energized to drive the spool  22  rightward in the axial direction, the step portion  22   c  is separated rightward from the end surface of the protrusion portion  33   d  of the stator  33  in the axial direction, so that in addition to being formed on the radially outer side of the land portion  22   a , the first space S 1  is also formed between the step portion  22   c  and the end surface of the protrusion portion  33   d  of the stator  33 , namely, on a radially outer side of the protrusion portion  22   b  of the spool  22  that has advanced rightward from the through-hole  33   a  of the stator  33  in the axial direction. Therefore, the volume of the first space S 1  increases (refer to  FIG.  3   ). Incidentally, in  FIG.  3   , the volume of the first space S 1  is maximized. 
     As illustrated in  FIG.  5   , an annular groove  33   f  that is recessed radially inward along the axially right end surface of the base portion  33   c  is formed in the outer peripheral surface of the protrusion portion  33   d  of the stator  33  over the circumferential direction. In addition, in the outer peripheral surface of the protrusion portion  33   d  of the stator  33 , an axial groove  33   g  extending from the annular groove  33   f  to a substantially center portion of the protrusion portion  33   d  in the axial direction is formed, and an axial groove  33   h  extending from the annular groove  33   f  to the end surface of the protrusion portion  33   d  in the axial direction is formed at a part in the circumferential direction, namely, at a portion having a predetermined width in the circumferential direction at a position where the axial groove  33   h  faces the axial groove  33   g  in the radial direction, namely, in a phase that is 180 degrees opposite to a radial center of the annular groove  33   f . Incidentally, the annular groove  33   f , the axial groove  33   g , and the axial groove  33   h  are formed to have substantially the same depth in the radial direction and to have substantially the same groove width. 
     In addition, in a state where the valve unit  2  is attached to the solenoid unit  3 , the axial groove  33   g  is disposed on a vertically lower side and the axial groove  33   h  is disposed on a vertically upper side (refer to  FIGS.  6  and  7   ). Incidentally, the axial groove  33   g  has a tapered surface  33   k  that is inclined leftward from the radially outer side toward the radially inner side in the axial direction, and is disposed to be continuous with the tapered surface  21   k  of the cutout  21   h  from the radially outer side to the radially inner side in a state where the valve unit  2  is attached to the solenoid unit  3 , the cutout  21   h  being formed in the sleeve  21 . 
     In addition, a radial groove  33   m  extending radially inward from the axial groove  33   h  is formed in the end surface of the protrusion portion  33   d  of the stator  33 . 
     Next, a breathing passage that allows communication between the second space S 2  in the accommodation space  30  and the outside of the solenoid valve  1  will be described. Incidentally, since breathing between the third space S 3  in the accommodation space  30  and the outside of the solenoid valve  1  is independently performed via a gap formed between the second tubular body  37  and the end plate  39  and via the cutout  31   c  of the solenoid casing  31 , a detailed description will be omitted. 
     As illustrated in  FIGS.  6  and  7   , on an outer periphery of the protrusion portion  33   d  of the stator  33 , an axial communication passage  102  extending in the axial direction is formed by the axial groove  33   g  and an inner peripheral surface of the lower plate  32   b , a first breathing flow passage  103  having an annular shape and extending in the circumferential direction is formed by the annular groove  33   f  and the inner peripheral surface of the lower plate  32   b , and a second breathing flow passage  104  extending in the axial direction is formed by the axial groove  33   h  and the inner peripheral surfaces of the lower plate  32   b  and of the recessed portion  21   e  of the sleeve  21 . 
     An axially left end of the axial communication passage  102  communicates with the first breathing flow passage  103  in the axial direction, and an axially right end portion of the axial communication passage  102  communicates with a breathing hole  101  in the radial direction, the breathing hole  101  being formed by the cutout  21   h  of the sleeve  21  and an axially right end surface of the lower plate  32   b . Incidentally, the breathing hole  101  communicates with the outside of the solenoid valve  1  via the opening  31   d  of the solenoid casing  31 . In addition, a flow passage that is inclined radially outward toward the opening  31   d  of the solenoid casing  31  is formed in the breathing hole  101  by the tapered surface  21   k  of the cutout  21   h  of the sleeve  21  and chamfering of an opening  32   d  of the solenoid molded body  32  that faces the tapered surface  21   k  in the radial direction, and the fluid easily flows in and out between the breathing hole  101  and the opening  32   d  of the solenoid molded body  32 . 
     An axially left end of the second breathing flow passage  104  communicates with the first breathing flow passage  103  in the axial direction, and an axially right end of the second breathing flow passage  104  communicates with the first space S 1  in the axial direction. In addition, an axially right end portion of the second breathing flow passage  104  communicates with a third breathing flow passage  105  formed by an inner peripheral surface of the through-hole  33   a  of the stator  33  and outer peripheral surfaces of the protrusion portion  22   b  of the spool  22  and of the rod  35 , in the radial direction through the radial groove  33   m  extending radially inward in the end surface of the protrusion portion  33   d  of the stator  33 . 
     An axially left end of the third breathing flow passage  105  communicates with the second space S 2  (refer to  FIGS.  2  and  3   ), and an axially right end of the third breathing flow passage  105  is capable of directly communicating with the first space S 1  according to the axial position of the spool  22 . 
     As described above, in the present embodiment, the breathing passage that allows communication between the second space S 2  in the accommodation space  30  and the outside of the solenoid valve  1  includes the opening  31   d  of the solenoid casing  31 , the breathing hole  101 , the axial communication passage  102 , the first breathing flow passage  103 , the second breathing flow passage  104 , the first space S 1 , the radial groove  33   m , and the third breathing flow passage  105  in order from the outside of the solenoid valve  1 . 
     Next, the flow of the fluid in the breathing passage involved by operation of the solenoid valve  1  will be described. As illustrated in  FIG.  6   , when the coil  32   a  is energized to switch the solenoid valve  1  from an off state to an on state and thus to move the plunger  34  rightward toward the stator  33  in the axial direction, the fluid existing in the second space S 2  passes through the third breathing flow passage  105 , through the radial groove  33   m , through the second breathing flow passage  104 , through the first breathing flow passage  103 , through the axial communication passage  102 , and through the breathing hole  101  in order from the inside of the solenoid valve  1 , and is discharged to the outside of the solenoid valve  1  (refer to solid line arrows in  FIG.  6   ). 
     Incidentally,  FIG.  6    illustrates a state immediately after the energization of the coil  32   a , namely, an initial movement state of the plunger  34 , and the fluid that has moved rightward in the axial direction to be pushed out from the second space S 2  through the third breathing flow passage  105  collides with the axially left end surface of the land portion  22   a  of the spool  22 , flows into the second breathing flow passage  104  via the radial groove  33   m , and moves through the second breathing flow passage  104  leftward in the axial direction, to generate a force to push out the fluid in the first breathing flow passage  103  to the outside from the axial communication passage  102  and from the breathing hole  101  that are disposed on a vertically lower side. 
     In addition, as illustrated in  FIG.  8 A , since the first breathing flow passage  103  is formed in an annular shape, in an off state of the solenoid valve  1 , a contamination having heavy specific gravities in the fluid inside the first breathing flow passage  103  is easily collected in the vicinity of the axial communication passage  102  that is formed on the vertically lower side, and is easily discharged to the outside through the axial communication passage  102  and through the breathing hole  101 , together with the fluid. 
     In addition, as illustrated in  FIG.  6   , on an axially right side of the axial communication passage  102  and of the breathing hole  101 , the tapered surface  33   k  of the axial groove  33   g  and the tapered surface  21   k  of the cutout  21   h  are continuous with each other, and the flow of the fluid is guided from the radially inner side toward the radially outer side, so that it is difficult for a vortex to be generated in the axial communication passage  102  and in the breathing hole  101 , and the contamination is easily discharged to the outside, together with the fluid. 
     Further, since the flow passage that is inclined toward the radially outer side on which the opening  31   d  of the solenoid casing  31  is formed is formed in the breathing hole  101  by the tapered surface  21   k  of the cutout  21   h  of the sleeve  21  and chamfering of the opening  32   d  of the solenoid molded body  32 , the contamination is easily discharged to the outside, together with the fluid. 
     Incidentally, when the spool  22  is driven rightward in the axial direction by the movement of the plunger  34  and the rod  35 , the axially left end surface of the land portion  22   a  of the spool  22  is separated rightward from the end surface of the protrusion portion  33   d  of the stator  33  in the axial direction, so that the fluid which has moved through the third breathing flow passage  105  rightward in the axial direction directly flows out into the first space S 1 . At this time, the radial groove  33   m  is opened toward the first space S 1 , and the fluid that has moved rightward in the axial direction to be pushed out from the second space S 2  through the third breathing flow passage  105  flows out to the first space S 1  which is increased in volume. For this reason, the force from the fluid to push the spool  22  rightward is not large more than necessary. 
     In addition, since the breathing passage can be made long by the first breathing flow passage  103  having an annular shape and the second breathing flow passage  104  extending in the axial direction, the fluid existing in the breathing passage is prevented from being discharged to the outside of the solenoid valve  1  more than necessary. 
     On the other hand, as illustrated in  FIG.  7   , for example, when the energization of the coil  32   a  is cut off to switch the solenoid valve  1  from an on state to an off state and thus to move the plunger  34  leftward in the axial direction, the fluid existing outside the solenoid valve  1  passes through the breathing hole  101 , through the axial communication passage  102 , through the first breathing flow passage  103 , through the second breathing flow passage  104 , through the radial groove  33   m , through the first space S 1 , and through the third breathing flow passage  105  in order from the outside of the solenoid valve  1 , and is supplied to the second space S 2  (refer to solid line arrows in  FIG.  7   ). 
     Incidentally,  FIG.  7    illustrates a state immediately after the energization of the coil  32   a  is cut off, namely, an initial movement state of the plunger  34 , and the fluid that has flowed into the first breathing flow passage  103  from the outside of the solenoid valve  1  through the breathing hole  101   and through the axial communication passage  102  and has moved rightward in the axial direction to be pushed out from the first breathing flow passage  103  through the second breathing flow passage  104  mainly flows out to the first space S 1  which is increased in volume, from a position on a radially outer side of the spool  22 . For this reason, the flow of the fluid is weakened by the dispersion of the fluid in the first space S 1  without directly collision with the spool  22 , so that the influence of the fluid in the radial direction is decreased. Therefore, the spool  22  can be held coaxially with the sleeve  21  without being inclined, smooth slidability of the spool  22  with respect to the sleeve  21  can be maintained, and responsiveness of the solenoid valve  1  can be improved. 
     In addition, as illustrated in  FIG.  8 B , the first breathing flow passage  103  is formed in an annular shape, and even when the contamination existing in the fluid outside the solenoid valve  1  infiltrate into the first breathing flow passage  103  through the breathing hole  101  and through the axial communication passage  102  that are formed on the vertically lower side, in order to flow into the second breathing flow passage  104  that is disposed on a vertically upper side to face the axial communication passage  102  in the radial direction, the contamination needs to move through the first breathing flow passage  103  approximately 180 degrees in the circumferential direction, together with the fluid. Accordingly, the contamination having heavy specific gravities in the fluid easily descend to a lower side of the first breathing flow passage  103 , and it is difficult for the contamination to infiltrate into the second breathing flow passage  104 . Incidentally, since the fluid existing in the first space S 1  is mainly supplied to the second space S 2  through the third breathing flow passage  105 , it is also difficult for the contamination to infiltrate into the second space S 2 . 
     In addition, since the breathing hole  101  and the axial communication passage  102  are disposed on the vertically lower side, for example, even when the solenoid valve  1  is installed to be half immersed in oil, the fluid existing outside the solenoid valve  1  is easily taken in. 
     In addition, since the breathing passage can be made long by the first breathing flow passage  103  having an annular shape and the second breathing flow passage  104  extending in the axial direction, it is difficult for the contamination existing outside the solenoid valve  1  to infiltrate into the second space S 2 . 
     In addition, as illustrated in  FIG.  7   , since the second breathing flow passage  104  communicates with the first space S 1  on the radially outer side of the spool  22 , particularly, immediately after the energization of the coil  32   a  is cut off, namely, in an initial movement state of the plunger  34 , the fluid that moves through the second breathing flow passage  104  rightward in the axial direction to flow out into the first space S 1  acts mainly on the sleeve  21  on the radially outer side of the spool  22 , so that it is difficult for the fluid to affect the operation of the spool  22 . 
     In addition, since the radial groove  33   m  that is opened to the first space S 1  to allow communication between the second breathing flow passage  104  and the third breathing flow passage  105  is formed in the end surface of the protrusion portion  33   d  of the stator  33 , and regardless of the axial position of the spool  22 , the second breathing flow passage  104  and the third breathing flow passage  105  always communicate with each other, the movement of the fluid in the breathing passage is not interfered with, so that resistance of the fluid involved by the movement of the plunger  34  can be reliably reduced. 
     As described above, the solenoid valve  1  of the present embodiment is capable of not only having damping performance that is stable due to the breathing passage, but also exhibiting high responsiveness and contamination resistance. 
     In addition, since the axial communication passage  102 , the first breathing flow passage  103 , and the second breathing flow passage  104  that form the breathing passage are formed by the annular groove  33   f , the axial groove  33   g , and the axial groove  33   h  that are provided in an outer peripheral surface of the stator  33 , a part of the breathing passage can be easily formed on an outer periphery of the stator  33  by processing each groove in the outer peripheral surface of the stator  33 . 
     The embodiment of the present invention has been described above with reference to the drawings; however, the specific configuration is not limited to the embodiment, and changes or additions that are made without departing from the scope of the present invention are included in the present invention. 
     For example, in the embodiment, a case has been described in which the first space S 1  forming the breathing passage is defined by the axially right end surface of the protrusion portion  33   d  of the stator  33 , the inner peripheral surface of and the bottom surface of the recessed portion  21   e  of the sleeve  21 , and the outer peripheral surface of the spool  22 ; however, the present invention is not limited to the case, and the first space S 1  may be defined by other members such as the rod as long as the first space S 1  is formed on an axial side opposite to the accommodation space formed on the axially left side of the stator, namely, on the axially right side of the stator. 
     In addition, in the embodiment, a case has been described in which the axial communication passage  102 , the first breathing flow passage  103 , and the second breathing flow passage  104  that form the breathing passage are formed by the annular groove  33   f , the axial groove  33   g , and the axial groove  33   h  that are formed in the outer peripheral surface of the stator  33 ; however, the present invention is not limited to the case, and for example, grooves may be formed in the inner peripheral surface of the lower plate and in the inner peripheral surface of the recessed portion of the sleeve to form the outer peripheral surface of the protrusion portion of the stator and the breathing passage. 
     In addition, in the embodiment, a case has been described in which the first breathing flow passage  103  is formed in an annular shape; however, the present invention is not limited to the case, and the first breathing flow passage may be formed in a shape with an end as long as the first breathing flow passage extends on the outer periphery of the stator in the circumferential direction. 
     In addition, in the embodiment, a case has been described in which the first breathing flow passage  103  communicates with the outside of the solenoid valve  1  via the axial communication passage  102  extending toward the opening  31   d  of the solenoid casing  31  in the axial direction; however, the present invention is not limited to the case, and without the axial communication passage being provided, the first breathing flow passage may communicate with the outside via the breathing hole and via the opening of the solenoid casing. 
     In addition, in the embodiment, a case has been described in which the breathing hole  101  is formed by the cutout  21   h  of the sleeve  21  and the axially right end surface of the lower plate  32   b ; however, the present invention is not limited to the case, and for example, the breathing hole may be formed by a through-hole penetrating through the sleeve in the radial direction. 
     In addition, in the embodiment, a case has been described in which the second breathing flow passage  104  communicates with the first space S 1  on a radially outer side of the land portion  22   a  of the spool  22 ; however, the present invention is not limited to the case, and the axially right end of the second breathing flow passage may be formed to face the axially left end surface of the land portion of the spool in the axial direction. 
     In addition, in the embodiment, a case has been described in which the second breathing flow passage  104  faces the axial communication passage  102  in the radial direction; however, the present invention is not limited to the case, and for example, the second breathing flow passage and the axial communication passage may be formed with a phase shift of 90 degree in the circumferential direction. Incidentally, from the viewpoint of contamination resistance, it is preferable that the second breathing flow passage and the axial communication passage are shifted in phase by 90 degrees or more in the circumferential direction. 
     In addition, the axial communication passage  102  may not be formed on the vertically lower side on the outer periphery of the stator  33 . Incidentally, from the viewpoint of contamination resistance, fluid intake, or the like, it is preferable that the axial communication passage is formed to communicate with the lower side of the first breathing flow passage. 
     In addition, in the embodiment, a case has been described in which the radial groove  33   m  is formed in the end surface of the protrusion portion  33   d  of the stator  33 ; however, the present invention is not limited to the case, and the radial groove may be formed in an end surface of the land portion of the spool that faces the end surface of the protrusion portion  33   d  of the stator  33  in the axial direction. In addition, the radial groove may not be formed in the stator or in the spool. 
     In addition, in the embodiment, a case has been described in which the breathing hole  101  forming the breathing passage is formed on an axially left side of the opening  31   d  of the solenoid casing  31 , namely, inside the solenoid casing  31 ; however, the present invention is not limited to the case, and the breathing hole may be formed in an outer portion of the solenoid casing, or the fluid may directly flow into and out from the breathing passage via a breathing hole that is an opening formed in the sleeve. 
     In addition, in the embodiment, a case has been described in which the rod  35  is formed separately from the spool  22 ; however, the present invention is not limited to the case, and the rod and the spool may be integrally formed. 
     
       
         
           
               
               
             
               
                 REFERENCE SIGNS LIST 
               
             
            
               
                 
                   1 
                 
                 Solenoid valve 
               
               
                 
                   2 
                 
                 Valve unit 
               
               
                 
                   3 
                 
                 Solenoid unit 
               
               
                 
                   21 
                 
                 Sleeve 
               
               
                 
                   21 
                   a 
                 
                 Through-hole 
               
               
                 
                   21 
                   e 
                 
                 Recessed portion 
               
               
                 
                   21 
                   h 
                 
                 Cutout (opening) 
               
               
                 
                   21 
                   k 
                 
                 Tapered surface 
               
               
                 
                   22 
                 
                 Spool 
               
               
                 
                   22 
                   a 
                 
                 Land portion 
               
               
                 
                   22 
                   b 
                 
                 Protrusion portion 
               
               
                 
                   30 
                 
                 Accommodation space 
               
               
                 
                   31 
                 
                 Solenoid casing 
               
               
                 
                   31 
                   d 
                 
                 Opening 
               
               
                 
                   32 
                 
                 Solenoid molded body 
               
               
                 
                   32 
                   b 
                 
                 Lower plate 
               
               
                 
                   33 
                 
                 Stator 
               
               
                 
                   33 
                   a 
                 
                 Through-hole 
               
               
                 
                   33 
                   b 
                 
                 Recessed portion 
               
               
                 
                   33 
                   c 
                 
                 Base portion 
               
               
                 
                   33 
                   d 
                 
                 Protrusion portion 
               
               
                 
                   33 
                   e 
                 
                 Step portion 
               
               
                 
                   33 
                   f 
                 
                 Annular groove 
               
               
                 
                   33 
                   g 
                 
                 Axial groove 
               
               
                 
                   33 
                   h 
                 
                 Axial groove 
               
               
                 
                   33 
                   k 
                 
                 Tapered surface 
               
               
                 
                   33 
                   m 
                 
                 Radial groove 
               
               
                 
                   34 
                 
                 Plunger 
               
               
                 
                   35 
                 
                 Rod 
               
               
                 
                   35 
                   a 
                 
                 Flange portion 
               
               
                 
                   36 
                 
                 First tubular body 
               
               
                 
                   37 
                 
                 Second tubular body 
               
               
                 
                   38 
                 
                 Third tubular body 
               
               
                 
                   39 
                 
                 End plate 
               
               
                 
                   101 
                 
                 Breathing hole 
               
               
                 
                   102 
                 
                 Axial communication passage 
               
               
                 
                   103 
                 
                 First breathing flow passage 
               
               
                 
                   104 
                 
                 Second breathing flow passage 
               
               
                 
                   105 
                 
                 Third breathing flow passage 
               
               
                 S 1 
 
                 First space 
               
               
                 S 2 
 
                 Second space (accommodation space) 
               
               
                 S 3 
 
                 Third space (accommodation space)