Abstract:
A pressure reducing valve comprises an open-close valve and a piston. The open-close valve makes switching between connecting and isolating a primary port and a secondary port. The piston makes sliding motion inside the cylinder according to a difference between force applied from the pressure regulating chamber and force applied from the pressure reducing chamber, thereby opening and closing the open-close valve. The open-close valve includes a valve stem and a valve seat fixing member. The valve seat fixing member restrains displacement of the piston toward a side upstream of the open-close valve by abutting on an end surface of the piston. The valve seat fixing member includes a channel hole communicatively connecting a housing part for the valve stem and the pressure reducing chamber.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a pressure reducing valve used to regulate the pressure of high-pressure gas such as hydrogen gas. 
         [0002]    A pressure reducing valve includes an open-close valve arranged between a primary port and a secondary port. Opening and closing the open-close valve causes inflow of high-pressure gas through the primary port, and the gas reduced in pressure is supplied to outside through the secondary port. 
         [0003]    As an example, Japanese Patent Application Publication No. 2011-108057 discloses a pressure reducing valve including a primary chamber communicating with a primary port, a secondary chamber communicating with a secondary port, and an open-close valve that makes switching between connecting and isolating the primary and secondary chambers. The open-close valve includes a valve stem, a valve seat fixing member, a valve seat member, a housing, a valve element, a valve spring, and a lid member. A valve seat placement part is provided in the housing. While the valve seat member is placed in the valve seat placement part, the valve seat fixing member is fitted to the housing by threads, thereby fixing the valve seat member to the valve seat placement part. 
         [0004]    An upper part of the valve seat fixing member is arranged in the secondary chamber. The secondary chamber houses a piston and a piston spring. The piston is always biased by the piston spring toward the primary chamber. The valve stem is housed inside the valve seat fixing member. An upper end of the valve stem always abuts on a lower end of the piston. The lid member is fixed to the primary chamber of the housing. The valve element is supported by a lower end of the valve seat member and an upper end of the lid member inside the housing. 
         [0005]    The valve element is always biased downstream by the biasing force of the valve spring arranged between the valve element and the lid member. An upper end of the valve element always abuts on a lower end of the valve stem. The valve element contacts or separates from the valve seat member in response to a difference between force acting from the secondary chamber toward the primary chamber and force acting from the primary chamber toward the secondary chamber, thereby switching between connecting and isolating the primary and secondary chambers. 
         [0006]    In the case of the pressure reducing valve of Japanese Patent Application Publication No. 2011-108057, the valve seat fixing member fixing the valve seat member has a channel groove formed in an end surface facing the piston. The channel groove extends along the radial direction of the housing. Even if the valve element is fully open, specifically even if the piston abuts on the end surface of the valve seat fixing member, this channel groove ensures a channel for high-pressure gas to flow from the primary port toward the secondary port. 
         [0007]    However, forming the channel groove in the valve seat fixing member reduces the strength of the end surface of the valve seat fixing member in an area where the channel groove is formed, compared to the case where the channel groove is not formed in the valve seat fixing member. Hence, when the piston contacts the valve seat fixing member to make the valve element open fully, the end surface of the valve seat fixing member in the area where the channel groove is formed might be worn easily. This might make wear debris mix in between the valve seat and the valve element, probably making it impossible to ensure hermeticity between the primary and secondary ports. This might be a cause for gas leakage to occur between the primary and secondary ports. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of this invention is to provide a pressure reducing valve capable of suppressing gas leakage that occurs between a primary port and a secondary port. 
         [0009]    In order to solve the aforementioned problem, a first aspect of this invention provides a pressure reducing valve. The pressure reducing valve comprises: an open-close valve that makes switching between connecting and isolating a primary port and a secondary port provided in a body member; a cylinder arranged downstream of the open-close valve, the cylinder communicating with the secondary port; and a piston dividing the cylinder into a pressure reducing chamber and a pressure regulating chamber, the piston making sliding motion inside the cylinder according to a difference between force applied from the pressure regulating chamber and force applied from the pressure reducing chamber, thereby opening and closing the open-close valve. The open-close valve includes a valve stem interposed between the open-close valve and the piston, and a plug that restrains displacement of the piston toward a side upstream of the open-close valve by abutting on an end surface of the piston. The plug has a function of housing the valve stem. The plug includes a channel hole communicatively connecting a housing part for the valve stem and the pressure reducing chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a sectional view of a pressure reducing valve of an embodiment of this invention; 
           [0011]      FIG. 2  is a top view taken along line  2 - 2  of  FIG. 1 ; and 
           [0012]      FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    An embodiment that embodies a pressure reducing valve of this invention is described below by referring to  FIGS. 1 to 3 . 
         [0014]    As shown in  FIG. 1 , a pressure reducing valve  10  includes a body member  11  connecting a primary port  1 P and a secondary port  2 P. The body member  11  houses a valve element  12 , a valve seat  13 , a valve seat fixing member  14 , which serves as a plug, a valve stem  15 , and a piston  16 . 
         [0015]    A first cylindrical part  111 , a second cylindrical part  112 , a third cylindrical part  113 , and a cylinder  114  are formed coaxially inside the body member  11  in this order as viewed from the bottom. The inside diameters of the first to third cylindrical parts  111  to  113  and that of the cylinder  114  are determined so as to increase in the following order: the first cylindrical part  111 , the second cylindrical part  112 , the third cylindrical part  113 , and the cylinder  114 . The first cylindrical part  111  communicates with the primary port  1 P through a valve not shown in the drawings. The primary port  1 P is connected to a supply source for high-pressure gas such as a hydrogen tank. 
         [0016]    A screw groove  113   a  is formed as a first screw part in the inner wall of the third cylindrical part  113 . The first cylindrical part  111  houses the metallic valve element  12 . The outer diameter of the valve element  12  is slightly smaller than the inside diameter of the first cylindrical part  111 . The valve element  12  can move up and down inside the first cylindrical part  111 . The valve element  12  is always biased upward by a valve spring  71 . The valve element  12  includes a columnar valve element body part  21  and a valve element tip part  22  smaller in outer diameter than the valve element body part  21 . The valve element tip part  22  is provided above the valve element body part  21 . A valve element tapered part  23  is formed between the valve element body part  21  and the valve element tip part  22 . The outer diameter of the valve element tapered part  23  decreases gradually toward the valve element tip part  22 . The valve element tip part  22  passes through the second cylindrical part  112  into the third cylindrical part  113 . 
         [0017]    The second cylindrical part  112  houses the annular valve seat  13  made of synthetic resin. The valve seat  13  has a hole part  31  slightly larger than the outer diameter of the valve element tip part  22 . The valve seat  13  has a valve seat tapered part  33  positioned near a lower portion of the hole part  31 . The inside diameter of the valve seat tapered part  33  increases gradually toward the bottom. The thickness of the valve seat  13  is slightly greater than the depth of the second cylindrical part  112 . 
         [0018]    The cylindrical valve seat fixing member  14  is fitted to the third cylindrical part  113  by threads. A screw thread  14   a  is formed as a second screw part in the outer circumferential surface of the valve seat fixing member  14 . The valve seat fixing member  14  is made of a metallic material. The bottom surface of the valve seat fixing member  14  abuts on the upper surface of the valve seat  13 . Securing the valve seat fixing member  14  with threads  14   a  makes the valve seat fixing member  14  press the valve seat  13  axially (downward in  FIG. 1 ). As a result, the valve seat  13  is held between the valve seat fixing member  14  and the bottom of the second cylindrical part  112 . Further, hermeticity is ensured between the bottom of the second cylindrical part  112  and the valve seat  13 . 
         [0019]    As shown by alternate long and two short dashes lines of  FIG. 1 , the valve seat  13  may be held between the valve element  12 , which is biased by the valve spring  71 , and the valve seat fixing member  14 . In this case, the valve element tapered part  23  abuts on the valve seat tapered part  33 , so that hermeticity is ensured between the tapered part  33  and the valve element tapered part  23 . Further, a through hole  41  passing through the valve seat fixing member  14  in an axial direction is formed inside the valve seat fixing member  14 . The through hole  41  communicates with the hole part  31  of the valve seat  13 . This makes the valve element tip part  22  enter into the valve seat fixing member  14 . 
         [0020]    As shown in  FIG. 2 , the valve seat fixing member  14  has a hexagonal upper part  42 . The upper part  42  functions as a tool engagement part, and a hexagonal socket, or attachment tool, engages the upper part  42 . Rotating the hexagonal socket engaging the upper part  42  causes the threads  14   a  of the valve seat fixing member  14  to engage the corresponding threads  113   a  of the third cylindrical part  113 . 
         [0021]    As shown in  FIGS. 1 to 3 , four radially extending channel holes  43  are formed in the upper part  42 . The four channel holes  43  communicatively connect the through hole  41  and the cylinder  114 . The four channel holes  43  are arranged at angular intervals of 90 degrees about the axis of the valve seat fixing member  14 . The four channel holes  43  are arranged in positions determined so that corners  42   a  of the upper part  42  do not intersect with the channel holes  43 . This ensures strength of engagement between the corners  42   a  of the upper part  42  and the hexagonal socket. An upper end surface  45  of the valve seat fixing member  14  is a flat surface without roughness. 
         [0022]    As shown in  FIG. 1 , the thickness of the valve seat fixing member  14  is greater than the depth of the third cylindrical part  113 . This makes the upper part  42  of the valve seat fixing member  14  enter the cylinder  114 . 
         [0023]    The metallic valve stem  15  is housed in the through hole  41 . The valve stem  15  includes a valve stem lower end part  51 , which has a truncated cone shape, a valve stem body part  52 , and a columnar valve stem upper end part  53 . The valve stem body part  52  is provided above the valve stem lower end part  51 , and the valve stem upper end part  53  is provided above the valve stem body part  52 . The valve stem lower end part  51  abuts on the valve element tip part  22  in the through hole  41 . 
         [0024]    As shown in  FIG. 2 , the valve stem body part  52  includes four radially extending lobes  52   a.  The four lobes  52   a  are arranged at intervals of 90 degrees about the axis of the valve stem  15 . Four channels  18  are provided in the valve seat fixing member  14 . Each of the channels  18  is a space defined by adjacent ones of the lobes  52   a  and the inner wall of the valve seat fixing member  14 . 
         [0025]    As shown by alternate long and two short dashed lines in  FIG. 1 , while the valve element tapered part  23  abuts on the valve seat tapered part  33 , the valve stem upper end part  53  protrudes from the upper part of the valve seat fixing member  14  to enter the cylinder  114 . The body member  11 , the valve element  12 , the valve seat  13 , the valve seat fixing member  14 , the valve stem  15 , and the valve spring  71  form an open-close valve  19 . 
         [0026]    The cylinder  114  houses the piston  16 , which moves axially (up and down in  FIG. 1 ). The piston  16  is made of a metallic material and is formed into a cylindrical shape. Various sealing members  80  are interposed between the inner wall of the cylinder  114  and the piston  16 . The various sealing elements  80  ensure hermeticity between the inner wall of the cylinder  114  and the piston  16 . The piston  16  divides the space inside the cylinder  114  into two parts. A pressure regulating chamber  91  and a pressure reducing chamber  92  are provided above and below the piston  16  respectively. 
         [0027]    The piston  16  houses a piston spring  72  inside. The piston  16  is always biased downward by the piston spring  72 . The biasing force of the piston spring  72  is determined to be greater than that of the valve spring  71 . This causes a lower end surface  61  of the piston  16  to always abut on valve stem upper end part  53 . The lower end surface  61  of the piston  16  is a flat surface without roughness. The diameter of the lower end surface  61  of the piston  16  is determined to be greater than the outer diameter of the upper end surface  45  of the valve seat fixing member  14 . This allows the lower end surface  61  of the piston  16  to abut on the upper end surface  45  of the valve seat fixing member  14 . Abutting contact between the lower end surface  61  of the piston  16  and the upper end surface  45  of the valve seat fixing member  14  restrains downward displacement of the piston  16 . 
         [0028]    The piston  16  moves up and down in response to atmospheric pressure inside the cylinder  114 . Specifically, if the atmospheric pressure inside the cylinder  114  increases, the piston  16  moves up against the biasing force of the piston spring  72 . If the atmospheric pressure inside the cylinder  114  drops, the piston  16  is moved down by the biasing force of the piston spring  72 . 
         [0029]    As shown by solid lines of  FIG. 1 , while the lower end surface  61  of the piston  16  abuts on the upper end surface  45  of the valve seat fixing member  14 , the valve element tapered part  23  distances itself from the valve seat tapered part  33 . This makes the open-close valve  19  open fully. 
         [0030]    With the open-close valve  19  is fully open, upward movement of the piston  16  makes the valve element tapered part  23  approach the valve seat tapered part  33 . Then, while the lower end surface  61  of the piston  16  distances itself from the upper end surface  45  of the valve seat fixing member  14 , the valve element tapered part  23  abuts on the valve seat tapered part  33 , as shown by the alternate long and two short dashes lines of  FIG. 1 . As a result, the open-close valve  19  is closed. The cylinder  114  communicates with the secondary port  2 P through an injector not shown in the drawings. 
         [0031]    The operation of the pressure reducing valve is described next. 
         [0032]    As shown in  FIG. 1 , the biasing force of the piston spring  72  acts on the piston  16  axially in a direction from the pressure regulating chamber  91  toward the pressure reducing chamber  92 . The biasing force of the valve spring  71  further acts on the piston  16  in an axial direction from the pressure reducing chamber  92  toward the pressure regulating chamber  91 . The biasing force of the valve spring  71  is smaller than that of the piston spring  72 . 
         [0033]    The description of the operation of the pressure reducing valve starts from a condition where the open-close valve  19  is fully open while the lower end surface  61  of the piston  16  abuts on the upper end surface  45  of the valve seat fixing member  14 . 
         [0034]    High-pressure gas supplied to the pressure reducing valve  10  is introduced into the pressure reducing chamber  92  after passing through the fully-open open-close valve  19 , the through hole  41  in the valve seat fixing member  14 , and the four channel holes  43 . The pressure of the high-pressure gas is reduced in the course of this process, and the gas reduced in pressure is supplied to the secondary port  2 P. The pressure of the gas introduced into the pressure reducing chamber  92  presses the piston  16  in an axial direction from the pressure reducing chamber  92  toward the pressure regulating chamber  91 . Specifically, the piston  16  is displaced based on the relative magnitudes of the force of the piston spring  72  and the sum of the forces of the gas pressure and the valve spring  71 . 
         [0035]    More specifically, if the biasing force of the piston spring  72  is smaller than the sum of the force of the gas pressure and the biasing force of the valve spring  71 , the piston  16  moves in the upward direction of  FIG. 1 . In response, the valve stem  15  and the valve element  12  move upward to close the open-close valve  19 . If the biasing force of the piston spring  72  is greater than the sum of the force of the gas pressure and the biasing force of the valve spring  71 , the piston  16  moves in the downward direction of  FIG. 1 . In response, the valve stem  15  and the valve element  12  move downward to open the open-close valve  19 . 
         [0036]    When the supply of the high-pressure gas to the pressure reducing valve  10  stops, the biasing force of the piston spring  72  becomes greater than the sum of the force of the gas pressure and the biasing force of the valve spring  71 . As a result, the piston  16  moves down. The lower end surface  61  of the piston  16  eventually abuts on the upper end surface  45  of the valve seat fixing member  14 . The lower end surface  61  of the piston  16  and the upper end surface  45  of the valve seat fixing member  14  are both flat surfaces, so that they come into surface-contact with each other. 
         [0037]    Thus, an impact caused by the contact between the piston  16  and the valve seat fixing member  14  is dispersed through the entire contact surface. This means that the impact caused by the contact between the piston  16  and the valve seat fixing member  14  is not applied intensively to a limited part of the valve seat fixing member  14 , thereby suppressing generation of wear debris. Thus, a mixture of wear debris in the first cylindrical part  111  is suppressed. Specifically, a mixture of wear debris in between the valve element tapered part  23  of the valve element  12  and the valve seat tapered part  33  of the valve seat  13  is suppressed. This makes it possible to ensure hermeticity between the valve element  12  and the valve seat  13 , allowing suppression of gas leakage from between the valve element  12  and the valve seat  13 . 
         [0038]    The number of the lobes  52   a  is the same as that of the channel holes  43 , so that there is one-to-one correspondence between the channels  18  and the channel holes  43 . Further, the four lobes  52   a  and the four channel holes  43  are arranged about the axis of the valve stem  15  and that of the valve seat fixing member  14 , respectively, both at angular intervals of 90 degrees. According to this structure, when gas is supplied to the through hole  41 , the valve stem  15  rotates in a way that makes the positions of the channels  18  correspond to those of the channel holes  43 , as shown in  FIG. 3 . In other words, the valve stem  15  rotates such that the lobes  52   a  do not block the channel holes  43 . This reduces pressure loss that might otherwise occur when gas flows from the channels  18  into the channel holes  43 . 
         [0039]    The aforementioned embodiment achieves the following effects. 
         [0040]    (1) The channel holes  43  connecting the through hole  41  and the pressure reducing chamber  92  are formed in the valve seat fixing member  14 . This structure makes it unnecessary to provide a groove serving as a channel for gas in the upper end surface  45  of the valve seat fixing member  14  abutting on the piston  16 . In this case, the lower end surface  61  of the piston  16  and the upper end surface  45  of the valve seat fixing member  14  come into surface-contact with each other. Thus, an impact caused by the contact between the piston  16  and the valve seat fixing member  14  is dispersed through the entire contact surface. This suppresses wear caused by the contact between the piston  16  and the valve seat fixing member  14 . Thus, a mixture of wear debris in the first cylindrical part  111  is suppressed. Specifically, accumulation of a mixture of wear debris between the valve element tapered part  23  of the valve element  12  and the valve seat tapered part  33  of the valve seat  13  is reduced. This makes it possible to ensure hermeticity between the valve element  12  and the valve seat  13 , so that the pressure of gas to be supplied to the outside is prevented from increasing more than expected. 
         [0041]    (2) The valve seat fixing member  14  has the hexagonal upper part  42 . This ensures strength of engagement between the corners  42   a  of the upper part  42  and the hexagonal socket. Further, the four channel holes  43  are arranged in positions that are determined such that the corners  42   a  of the upper part  42  do not coincide with the channel holes  43 . Thus, the channel holes  43  are not blocked when the valve seat fixing member  14  is attached to the third cylindrical part  113 . Additionally, there is no probability of removal of the corners  42   a,  so that the valve seat fixing member  14  can be attached to the third cylindrical part  113  smoothly. 
         [0042]    (3) The number of the lobes  52   a  is the same as that of the channel holes  43 , so that the number of the channels  18  becomes the same as that of the channel holes  43 . Further, the four lobes  52   a  and the four channel holes  43  are arranged about the axis of the valve stem  15  and that of the valve seat fixing member  14 , respectively, both at intervals of 90 degrees. According to this structure, when gas is supplied to the through hole  41 , the valve stem  15  rotates in a way that makes the positions of the channels  18  correspond to those of the channel holes  43 , as shown in  FIG. 3 . In other words, the valve stem  15  rotates such that the lobes  52   a  do not block the channel holes  43 . This avoids a pressure loss that otherwise may occur when gas flows from the channels  18  into the channel holes  43 . 
         [0043]    The aforementioned embodiment can be changed as follows. 
         [0044]    While the number of the channel holes  43  is four in the aforementioned embodiment, it can be any number. 
         [0045]    In the aforementioned embodiment, the four channel holes  43  are not necessarily required to be spaced at equal angular intervals. 
         [0046]    While the number of the lobes  52   a  is four in the aforementioned embodiment, the number of lobes is not so limited. The lobes  52   a  can be removed from the valve stem  15  as long as a channel is ensured between the valve stem  15  and the valve seat fixing member  14 . 
         [0047]    In the aforementioned embodiment, the four lobes  52   a  are not necessarily required to be spaced apart at equal angular intervals. 
         [0048]    In the aforementioned embodiment, the number of the lobes  52   a  and that of the channel holes  43  are not necessarily required to be the same. 
         [0049]    In the aforementioned embodiment, the channel holes  43  may be provided at the corners  42   a  of the upper part  42 . 
         [0050]    In the aforementioned embodiment, the upper part  42  is not necessarily required to be hexagonal in outer shape. The upper part  42  can be of any shape that allows engagement of the upper part  42  with an attachment tool not shown in the drawings. While a socket is shown as the attachment tool, the attachment tool may also be a wrench and a recessed part to engage the wrench may be formed in the upper part of the valve seat fixing member  14 . In this case, the upper part  42  can be circular in outer shape and the valve seat fixing member  14  is fixed to the body member  11  by threads with the attachment tool. 
         [0051]    In the aforementioned embodiment, the piston  16  and the valve stem  15  can be integrated. 
         [0052]    In the aforementioned embodiment, the valve element  12  and the valve stem  15  can be integrated. 
         [0053]    In the aforementioned embodiment, the gas to be reduced in pressure by the pressure reducing valve is hydrogen gas. However, the gas to be reduced in pressure may be gas other than hydrogen gas such as oxygen or nitrogen gas. The gas to be reduced in pressure can be gas composed of multiple elements as well as gas composed of a single element.