Abstract:
An oil filter interposed in an oil passage and configured to perform filtering of oil by causing the oil to pass through a passage hole of a filter body formed by etching, wherein an oil passing section is etched to a half of plate thickness of the filter body on one surface of the filter body, and a plurality of the passage holes are formed by etching in a region where the oil passing section is formed on the other surface of the filter body.

Description:
FIELD 
       [0001]    The present invention relates to an oil filter and a valve device. 
       BACKGROUND 
       [0002]    In a valve device such as a pressure reducing valve applied to an oil hydraulic circuit, an oil filter is interposed in an oil passage for supplying oil to a spool. As the oil filter, an oil filter in which a wire gauge is used is present. However, recently, an oil filter in which passage holes are formed in a metal thin plate is also provided. With the oil filter of this type, it is unlikely that fluctuation in the passage holes due to loosening of the wire gauge is caused. It is possible to easily secure a certain level of quality (see, for example, Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Micro film disclosed in Japanese Utility Model Application No. S61-39036 
       SUMMARY 
     Technical Problem 
       [0004]    The oil filter of this type is generally formed by etching. When the oil filter is formed by etching, the shape and the positions of the passage holes can be arbitrarily set according to the shape of masking. Formation work can be simplified. However, in the oil filter, the inner diameter of the passage holes is extremely small. Therefore, there is a substantial limitation on plate thickness when the oil filter is formed by etching. Specifically, when the plate thickness is large, time for etching is long. When the plate thickness is large, because the shape of the passage holes formed by etching is conical and an area occupied by the passage holes is large, a distance among the passage holes has to be set large. It is difficult to increase the number of the passage holes. Therefore, sufficient rigidity cannot be secured for the oil filter. For example, when a jet stream occurs in the oil hydraulic circuit, it is likely that the oil filter is easily damaged. When the oil filter is damaged, unfiltered oil flows into a valve of a spool or the like. It is difficult to guarantee the function of the valve device. 
         [0005]    In view of the circumstances, it is an object of the present invention to provide an oil filter and a valve device that can secure sufficient rigidity and simplify formation work. 
       Solution to Problem 
       [0006]    To achieve the object mentioned above, according to the present invention, an oil filter interposed in an oil passage and configured to perform filtering of oil by causing the oil to pass through a passage hole of a filter body formed by etching, wherein an oil passing section is etched to a half of plate thickness of the filter body on one surface of the filter body, and a passage hole is formed by etching in a region where the oil passing section is formed on the other surface of the filter body. 
         [0007]    In the oil filter, passage holes are distributed such that a passage ratio of the oil in a portion located in a center of the filter body is smaller than a passage ratio of the oil in a portion located on a circumferential edge of the filter body. 
         [0008]    In the oil filter, a plurality of oil passing sections having a same size are uniformly arranged in a filter body, and the number of passage holes per unit area in an oil passing section arranged on a center side of a filter body is set smaller than the number of passage holes per unit area in an oil passing section arranged on an outer circumferential side of a filter body. 
         [0009]    In the oil filter, a plurality of oil passing sections having a same number of passage holes per unit area are arranged to be sparse in a center of a filter body compared with a circumferential edge of a filter body. 
         [0010]    In the oil filter, a shield section configured to prevent the passage of the oil is formed in a center of a filter body, and passage holes are provided around the shield section. 
         [0011]    In the oil filter, a shield plate is arranged in a center of a filter body. 
         [0012]    In a valve device according to the present invention, any one of the oil filters is interposed at least in an oil passage leading to a spool of a valve body. 
       Advantageous Effects of Invention 
       [0013]    According to the present invention, passage holes are formed in a state in which an oil passing section is formed. Therefore, as a filter body, a filter body having relatively large plate thickness can be applied. Consequently, it is possible to secure large rigidity of the filter body. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1A  is a diagram of an oil filter according to a first embodiment of the present invention. 
           [0015]      FIG. 1B  is an enlarged diagram of an oil passing section provided in the center of a filter body in the oil filter shown in  FIG. 1A . 
           [0016]      FIG. 1C  is an enlarged diagram of an oil passing section provided on the inner circumferential side of the circumferential edge of the filter body in the oil filter shown in  FIG. 1A . 
           [0017]      FIG. 1D  is an enlarged diagram of an oil passing section provided on the outer circumferential side of the circumferential edge of the filter body in the oil filter shown in  FIG. 1A . 
           [0018]      FIG. 2  is an enlarged sectional view of a main part of the oil filter shown in  FIG. 1A . 
           [0019]      FIG. 3  is a sectional view of a valve device to which the oil filter shown in  FIG. 1A  is applied. 
           [0020]      FIG. 4A  is a diagram of an oil filter according to a second embodiment of the present invention. 
           [0021]      FIG. 4B  is an enlarged diagram of oil passing sections provided in the center of a filter body in the oil filter shown in  FIG. 4A , on the inner circumferential side of the circumferential edge of the filter body, and on the outer circumferential side of the circumferential edge of the filter body. 
           [0022]      FIG. 5A  is a diagram of an oil filter according to a third embodiment of the present invention. 
           [0023]      FIG. 5B  is an enlarged diagram of an oil passing section provided on the outer circumferential side of the circumferential edge of a filter body in the oil filter shown in  FIG. 5A  and on the inner circumferential side of the circumferential edge of the filter body. 
           [0024]      FIG. 6A  is a diagram of an oil filter according to a fourth embodiment of the present invention. 
           [0025]      FIG. 6B  is an enlarged diagram of an oil passing section provided on the outer circumferential side of the circumferential edge of a filter body in the oil filter shown in  FIG. 6A  and on the inner circumferential side of the circumferential edge of the filter body. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Preferred embodiments of an oil filter and a valve device according to the present invention are explained in detail below with reference to the accompanying drawings. 
       First Embodiment 
       [0027]      FIGS. 1A to 2  are diagrams of an oil filter according to a first embodiment of the present invention. As shown in  FIG. 3 , oil filters  10  illustrated herein are interposed in a supply oil passage  113   a  leading from an oil supply source  111  to a spool  112  and a discharge oil passage  113   b  for discharging oil passed through the spool  112  in a valve body  110  of a valve device  100  to filter the oil passing through the respective oil passages  113 . The valve device  100  moves the spool  112  in the axis direction using an electromagnetic solenoid  114  as a driving source and performs passage control for the oil from the supply oil passage  113   a  to the discharge oil passage  113   b.  In the supply oil passage  113   a  and the discharge oil passage  113   b,  filter housing sections  113   c  are formed in regions where the oil filters  10  are set. The filter housing sections  113   c  have a transverse section formed in a circular shape having a diameter larger than the diameter of the oil passages  113 . Steps  113   d  are formed between the filter housing sections  113   c  and the oil passages  113 . 
         [0028]    In the oil filter  10  attached to the filter housing section  113   c,  as shown in  FIGS. 1A to 3 , a filter body  11  is formed in a disk shape having a diameter slightly smaller than the diameter of the filter housing section  113   c  of the valve body  110 . A spacer ring  115  is fit in the filter housing section  113   c,  whereby the filter body  11  is fixed and set in the filter housing section  113   c  in a state in which the circular circumferential edge of the filter body  11  is held between the step  113   d  and the spacer ring  115 . 
         [0029]    In the filter body  11 , a plurality of oil passing sections  12   a,    12   b,  and  12   c  are provided. The oil passing sections  12   a,    12   b,  and  12   c  are recesses formed on one surface of the filter body  11 . The oil passing sections  12   a,    12   b,  and  12   c,  openings of which are formed in circular shapes having the same size, are disposed in a region (hereinafter referred to as “effective region  11 A”) opposed to openings of the supply oil passage  113   a  and the discharge oil passage  113   b  in the filter body  11 . The oil passing sections  12   a,    12   b,  and  12   c  are uniformly arranged in the effective region  11 A of the filter body  11 . The number per unit area of the oil passing sections  12   a,    12   b,  and  12   c  is substantially the same in any place of the effective region  11 A. 
         [0030]    A plurality of passage holes  13  are formed in each of the oil passing sections  12   a,    12   b,  and  12   c.  The passage holes  13  are through-holes having the same inner diameter. The inner diameter of the passage holes  13  is set to a dimension necessary for exhibiting a desired filter function. As it is evident from  FIGS. 1B to 1D , the passage holes  13  formed in the oil passing sections  12   a,    12   b,  and  12   c  are formed such that the number per unit area of the oil passing sections  12   b  and  12   c  arranged on the circumferential edge of the filter body  11  is large compared with the oil passing sections  12   a  arranged in the center of the filter body  11 . On the circumferential edge of the filter body  11 , the passage holes  13  of the oil passing sections  12   c  located further on the outer circumferential side are set to be larger in the number per unit area than the oil passing sections  12   b  located on the inner circumferential side. 
         [0031]    As shown in  FIG. 2 , all of the oil passing sections  12   a,    12   b,  and  12   c  and the passage holes  13  are formed by applying etching to the filter body  11 . More specifically, a filter body made of metal is applied as the filter body  11 . First, in a state in which one surface of the filter body  11  is masked, the oil passing sections  12   a,    12   b,  and  12   c  are formed to a half of the plate thickness of the filter body  11  by applying etching to the other surface (so-called half etching). Thereafter, in a state in which the surface on which the oil passing sections  12   a,    12   b,  and  12   c  are formed is masked, the passage holes  13  are formed by etching from the surface on the opposite side of the filter body  11 . 
         [0032]    In the oil filter  10  configured as explained above, the passage holes  13  are formed in a state in which the oil passing sections  12   a,    12   b,  and  12   c  are formed. Therefore, a filter body having relatively large plate thickness can be applied as the filter body  11 . The passage holes  13  of the oil filter  10  have an extremely small inner diameter. Therefore, when the passage holes  13  are formed by etching, there is a substantial limitation on the plate thickness of the filter body  11 . However, if the oil passing sections  12   a,    12   b,  and  12   c  are formed as explained above, the plate thickness of a portion where the passage holes  13  are formed can be set small irrespective of the plate thickness of the filter body  11 . Consequently, it is possible to secure large rigidity of the filter body  11 . Above all, in the center of the filter body  11 , because the number of the passage holes  13  is small compared with the circumferential edge of the filter body  11 , the rigidity is large compared with the circumferential edge. The flow velocity distribution of the oil in the oil passage  113  is large in the center compared with the circumferential edge. Therefore, the oil filter  10  configured to have the large rigidity in the center is extremely advantageous in terms of durability. 
         [0033]    Further, in the oil filter  10 , the aperture ratio of the passage holes  13  in the center of the filter body  11 , i.e., the passage ratio of the oil is small compared with the circumferential edge. Therefore, when the oil filter  10  is attached to the oil passage  113 , passage resistance is large in the center where the flow velocity of the oil is large. On the other hand, passage resistance on the circumferential edge is small. As a result, the flow of the oil is dispersed to substantially the entire area on the transverse section of the oil passage  113 . Therefore, even when a jet stream occurs in the oil passage  113 , the jet stream does not directly collide with the center of the filter body  11 . A load due to the jet stream is also dispersed to the entire filter body  11 . As a result, it is possible to prevent damage to the filter body  11  due to the jet stream and improve reliability and durability of the valve device  100  to which the oil filter  10  is applied. 
         [0034]    In the oil filter  10 , a large difference does not occur in a caused pressure loss and pressure resistance irrespective of whether the oil passing sections  12   a,    12   b,  and  12   c  are faced to the upstream side or the downstream side. Therefore, when the oil filter  10  is inserted, it is unnecessary to particularly pay attention to the direction of the oil filter  10 . 
         [0035]    In the valve device  100  according to the first embodiment explained above, the oil filters  10  are interposed in both of the supply oil passage  113   a  and the discharge oil passage  113   b.  However, the oil filter  10  can be interposed only in one of the supply oil passage  113   a  and the discharge oil passage  113   b,  more preferably, in the supply oil passage  113   a.    
       Second Embodiment 
       [0036]    In the first embodiment explained above, the passage ratio of the oil is changed by changing the number of the passage holes  13  per unit area in the center and on the circumferential edge of the oil passing sections  12   a,    12   b,  and  12   c  uniformly arranged in the effective region  11 A of the filter body  11 . On the other hand, in a second embodiment shown in  FIGS. 4A and 4B , the passage ratio of oil is changed by changing the arrangement of oil passing sections in a filter body is changed in the center and on the circumferential edge of the filter body. 
         [0037]    Specifically, in an oil filter  20  according to the second embodiment, oil passing sections  22  are arranged to be denser on the circumferential edge than in the center of a filter body  21 . The number per unit area of passage holes  23  formed in the oil passing sections  22  is the same in the center and on the circumferential edge. When the oil filter  20  is formed, as in the first embodiment, etching only has to be applied to the filter body  21  made of metal to form the oil passing sections  22  and thereafter form the passage holes  23 . 
         [0038]    In the oil filter  20  configured as explained above, as in the oil filter  10 , the passage holes  23  are formed in a state in which the oil passing sections  22  are formed. Therefore, a filter body having relatively large plate thickness can be applied as the filter body  21 . Consequently, it is possible to secure large rigidity of the filter body  21 . Above all, in the center of the filter body  21 , because the number of the passage holes  23  is small compared with the circumferential edge of the filter body  21 , the rigidity is large compared with the circumferential edge. The flow velocity distribution of the oil in the oil passage  113  is large in the center compared with the circumferential edge. Therefore, the oil filter  20  configured to have the large rigidity in the center is extremely advantageous in terms of durability. 
         [0039]    Further, in the oil filter  20 , the passage ratio of the oil in the center of the filter body  21  is small compared with the circumferential edge. Therefore, when the oil filter  20  is inserted into the oil passage  113  ( FIG. 3 ), passage resistance is large in the center where the flow velocity distribution of the oil is large. On the other hand, passage resistance on the circumferential edge is small. As a result, the flow of the oil is dispersed to substantially the entire area on the transverse section of the oil passage  113  ( FIG. 3 ). Therefore, even when a jet stream occurs in the oil passage  113  ( FIG. 3 ), the jet stream does not directly collide with the center of the filter body  21 . A load due to the jet stream is also dispersed to the entire filter body  21 . As a result, it is possible to prevent damage to the filter body  21  due to the jet stream and improve reliability and durability of the valve device  100 . 
         [0040]    In the second embodiment, the number of the passage holes  23  per unit area is set the same in the center and on the circumferential edge of the oil passing section  22 . However, the present invention is not limited to this. The number of the passage holes  23  per unit area can be set large on the circumferential edge compared with the center. 
       Third Embodiment 
       [0041]    In the first embodiment explained above, the passage ratio of the oil is changed by changing the number of the passage holes  23  per unit area in the center and on the circumferential edge of the oil passing sections  22  uniformly arranged in the effective region  11 A of the filter body  21 . On the other hand, in an oil filter  30  according to a third embodiment shown in  FIGS. 5A and 5B , oil passing sections  32  are formed only on the circumferential edge of a filter body  31  and are not provided at all in the center of the filter body  31 . The number of passage holes  33  per unit area is set the same among the oil passing sections  32  arranged on the circumferential edge. A method of forming the oil filter  30  is the same as those in the first embodiment and the second embodiment. 
         [0042]    In the oil filter  30  configured as explained above, as in the oil filters  10  and  20 , the passage holes  33  are formed in a state in which the oil passing sections  32  are formed. Therefore, a filter body having relatively large plate thickness can be applied as the filter body  31 . Consequently, it is possible to secure large rigidity of the filter body  31 . Above all, in the center of the filter body  31 , because the oil passing sections  32  and the passage holes  33  are not present at all, the rigidity is large compared with the circumferential edge. The flow velocity distribution of the oil in the oil passage  113  ( FIG. 3 ) is large in the center compared with the circumferential edge. Therefore, the oil filter  30  configured to have the large rigidity in the center is extremely advantageous in terms of durability. 
         [0043]    Further, in the oil filter  30 , the passage ratio of the oil in the center of the filter body  31  is zero. Therefore, when the oil filter  30  is inserted into the oil passage  113  ( FIG. 3 ), passage resistance is large in the center where the flow velocity distribution of the oil is large. On the other hand, passage resistance on the circumferential edge is small. As a result, the flow of the oil is dispersed to the circumferential edge on the transverse section of the oil passage  113  ( FIG. 3 ). Therefore, even when a jet stream occurs in the oil passage  113  ( FIG. 3 ), the jet stream does not directly collide with the center of the filter body  31 . A load due to the jet stream is also dispersed to the entire filter body  31 . As a result, it is possible to prevent damage to the filter body  31  due to the jet stream and improve reliability and durability of the valve device  100 . 
       Fourth Embodiment 
       [0044]    In the third embodiment explained above, the oil passing sections  32  are formed only on the circumferential edge of the filter body  31 . On the other hand, in an oil filter  40  according to the fourth embodiment shown in  FIGS. 6A and 6B , oil passing sections  42  are uniformly provided in an effective region  41 A of a filter body  41 . The number per unit area of passage holes  43  formed in the oil passing sections  42  is uniform in all the oil passing sections  42 . In other words, the filter body  41  of the oil filter  40  used in the past can be applied. However, in the oil filter  40  according to the fourth embodiment, the passage ratio of oil is changed in the center and on the circumferential edge of the filter body  41  by disposing a disk-like shield plate  45  in the center of the filter body  41 . As the shield plate  45 , an independent plate can be fixed to the center of the filter body  41 . However, it is also possible to provide the shield plate  45  in the spacer ring  115  ( FIG. 3 ) used when the oil filter  40  is inserted into the valve body  110 . In particular, when the shield plate  45  is provided in the spacer ring  115  ( FIG. 3 ), it is unnecessary to apply, to the oil filter  40 , machining other than etching, for example, machining for fixing the shield plate  45  to the filter body  41 . Therefore, it is unlikely that complication of a manufacturing process is caused. 
         [0045]    In the oil filter  40  configured as explained above, the center of the filter body  41  is covered with the shield plate  45 . Therefore, the rigidity of the center covered with the shield plate  45  in the oil passage  113  ( FIG. 3 ) is large compared with the circumferential edge. This is extremely advantageous in terms of durability. 
         [0046]    Further, in the oil filter  40 , the passage ratio of the oil in the center of the filter body  41  is zero. Therefore, when the oil filter  40  is inserted into the oil passage  113  ( FIG. 3 ), passage resistance is large in the center where the flow velocity distribution of the oil is large. On the other hand, passage resistance on the circumferential edge is small. As a result, the flow of the oil is dispersed to the circumferential edge on the transverse section of the oil passage  113  ( FIG. 3 ). Therefore, even when a jet stream occurs in the oil passage  113  ( FIG. 3 ), the jet stream does not directly collide with the center of the filter body  41 . The shield plate  45  that covers the center receives a load due to the jet stream. As a result, it is possible to prevent damage to the filter body  41  due to the jet stream and improve reliability and durability of the valve device  100 . 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  OIL FILTER 
           11  FILTER BODY 
           12   a,    12   b,    12   c  OIL PASSING SECTIONS 
           13  PASSAGE HOLES 
           20  OIL FILTER 
           21  FILTER BODY 
           22  OIL PASSING SECTIONS 
           23  PASSAGE HOLES 
           30  OIL FILTER 
           31  FILTER BODY 
           32  OIL PASSING SECTIONS 
           33  PASSAGE HOLES 
           40  OIL FILTER 
           41  FILTER BODY 
           42  OIL PASSING SECTIONS 
           43  PASSAGE HOLES 
           45  SHIELD PLATE 
           100  VALVE DEVICE 
           113  OIL PASSAGE 
           115  SPACER RING