Patent Publication Number: US-2022214198-A1

Title: Flow Rate Measurement Device

Description:
TECHNICAL FIELD 
     The present invention relates to a flow rate measurement device that measures a flow rate of a gas to be measured. 
     BACKGROUND ART 
     The technique of PTL 1 is disclosed as an example of the flow rate measurement device. 
     CITATION LIST 
     Patent Literature 
     PTL 1: WO 2019/049513 
     SUMMARY OF INVENTION 
     Technical Problem 
     A flow rate measurement device has a structure in which the flow is divided into a flow path (hereinafter, referred to as D1) in which a measurement surface of a flow rate measurement element is disposed and a flow path (hereinafter, referred to as D2) in which the measurement surface is not disposed in a sub-passage. In PTL 1, reducing dimensional variations of D1 has studied, but reducing dimensional variations of D2 is not disclosed. As a result of intensive studies by the present inventors, it has been found that the measurement accuracy of the flow rate measurement device is affected by a flow dividing ratio between D1 and D2 in addition to the dimension of D1. In PTL 1, there is room for study on reducing the variation in the flow dividing ratio. 
     An object of the present invention is to provide an accurate flow rate measurement device. 
     Solution to Problem 
     In order to achieve the above object, a flow rate measurement device of the present invention includes: a circuit board which is mounted on a housing, and a part of which is disposed in a sub-passage; a support body which is mounted on the circuit board, and a part of which is disposed in the sub-passage; a flow rate measurement element which is mounted on the support body, and of which a measurement surface is disposed in the sub-passage; a first void which is formed of one surface of the support body and one surface of the circuit board in which the flow rate measuring element is disposed on the one surface side of the support body so as to face one surface side of a part on which the measurement surface of the flow rate measurement element is disposed in the sub-passage of the circuit board; a second void which is formed of a surface opposite to the one surface of the circuit board and the housing; and a third void which is formed of a surface opposite to the one surface of the support body and a cover. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide an accurate flow rate measurement device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of a flow rate measurement device according to a first embodiment of the present invention. 
         FIG. 2  is a plan view of the flow rate measurement device according to the first embodiment of the present invention before attachment of a cover. 
         FIG. 3  is a plan view of a circuit board and a sensor assembly according to the first embodiment of the present invention. 
         FIG. 4  is a plan view of the sensor assembly according to the first embodiment of the present invention. 
         FIG. 5  is a schematic cross-sectional view taken along line A-A of  FIG. 2  in the first embodiment according to the present invention. 
         FIG. 6  is a schematic cross-sectional view taken along line B-B of  FIG. 2  in the first embodiment according to the present invention. 
         FIG. 7  is a plan view of a circuit board and a sensor assembly according to a second embodiment of the present invention. 
         FIG. 8  is a schematic cross-sectional view taken along line B-B of  FIG. 2  in the second embodiment according to the present invention. 
         FIG. 9  is a schematic cross-sectional view taken along line B-B of  FIG. 2  in a third embodiment according to the present invention. 
         FIG. 10  is a schematic cross-sectional view taken along line B-B of  FIG. 2  in a fourth embodiment according to the present invention. 
         FIG. 11  is a schematic cross-sectional view taken along line B-B of  FIG. 2  in a fifth embodiment according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
     A first embodiment of a flow rate measurement device will be described with reference to  FIGS. 1 to 6 . 
     As illustrated in  FIGS. 1 and 2 , the flow rate measurement device  1  in the present embodiment includes a housing  11  constituting a part of a sub-passage  12 , a cover  31 , a circuit board  15  mounted on the housing  11 , and a sensor assembly  10  mounted on the circuit board  15 . The cover  31  and the housing  11  are fixed by, for example, an adhesive  17 . The housing  11  is formed with a sub-passage groove for forming the sub-passage  12 , and forms the sub-passage  12  for taking in a part of air  30  which is a medium to be measured in cooperation with the cover  31 . The sub-passage groove may be formed in the cover  31  and the sub-passage groove may not be formed in the housing  11 , or the sub-passage groove may be formed in both the cover  31  and the housing  11 . 
     As illustrated in  FIG. 3 , a circuit board assembly in which the sensor assembly  10  is mounted on the circuit board  15  is configured. The sensor assembly  10  having a flow rate detection element  4  for measuring a gas flow rate is mounted on the circuit board  15 . The sensor assembly  10  is electrically connected to the circuit board  15 , for example, by soldering. In addition to the sensor assembly  10 , a pressure sensor  6 , a humidity sensor  7 , and the like may be mounted on the circuit board  15 . By selecting whether or not to mount the pressure sensor  6  and the humidity sensor  7  according to needs, it is possible to provide a flow rate measurement device having various configurations. 
     In the sensor assembly  10 , at least a detection portion of the flow rate detection element  4  is located in the sub-passage  12 . The circuit board  15  is formed such that a part thereof is located in the sub-passage  12 . The sensor assembly  10  is mounted on the circuit board  15  such that a measurement portion of the flow rate detection element  4  faces a part located in the sub-passage  12  of the circuit board  15 . 
     As illustrated in  FIG. 4 , the sensor assembly  10  is a resin package sealed with a resin such that at least a measurement portion of the flow rate detection element  4  is exposed. The flow rate detection element  4  is a semiconductor element formed by a MEMS process, and includes a thin portion (detection unit) in which a heating element is formed. The sensor assembly  10  is a resin package that seals the flow rate detection element  4 , an LSI  3 , and a lead frame  5  with a resin, and has a structure in which a flow rate detection unit of the flow rate detection element  4  is partially exposed. The sensor assembly  10  has a shape including a recess  14 , and the measurement surface of the flow rate detection element  4  is located at a bottom of the recess. The recess has a throttle shape that gradually narrows in a measurement surface direction from end portions toward the flow rate measurement element. By forming the throttle shape with the resin for sealing the flow rate measurement element, a positional relationship between the throttle and the measurement portion can be configured with high accuracy, which is preferable because the measurement accuracy is improved. In addition, as compared with a case of where the air is throttled in a direction perpendicular to the measurement surface, the amount of air containing contaminants guided by the measurement surface is reduced by throttling in a direction parallel to the measurement surface, so that the air is excellent in contamination resistance. Note that the LSI and the flow rate detection element  4  may be integrated with each other, or the LSI may be fixed to the circuit board  15 . In addition, the sensor assembly  10  may have a structure in which the flow rate measurement element  4  is mounted on a resin molding (sensor support body) in which a metal terminal is sealed with a resin. The sensor assembly  10  is a support body including at least the flow rate detection element  4  and a member that supports the flow rate detection element. 
     As illustrated in  FIGS. 5 and 6 , a first void  32  is formed of one surface of a part of the circuit board  15  located in the sub-passage  12  and one surface of the sensor assembly  10  on the measurement portion side of the flow rate measurement element  4 , a second void  33  is formed of the other surface of the part of the circuit board  15  located in the sub-passage  12  and the housing  11 , and a third void  34  is formed of the other surface of the sensor assembly  10  and the cover  31 . 
     The first void  32  is first formed by mounting the sensor assembly  10  on the circuit board  15 . Thereafter, the circuit board  15  on which the sensor assembly  10  is mounted is mounted on the housing  11  to form the second void  33 . Finally, the cover  31  is mounted on the housing  11  to form the third void  34 . After the circuit board  15  is mounted on the housing  11  to form the second void  33 , the sensor assembly  10  may be mounted on the circuit board  15  to form the first void  32 . That is, in the present embodiment, the third void  34  is formed after both the first void  32  and the second void  33  are formed. 
     A fluid flowing through the sub-passage  12  is divided into a flow path D1 having a measurement surface and a flow path D2 having no measurement surface by the circuit board  15 . The first void corresponds to D1 and the second void corresponds to D2. 
     The dimensional variation of the first void  32  in the thickness direction is affected by the thickness variation of the sensor assembly  10  and a fixing member such as a solder for fixing the sensor assembly  10  to the circuit board. 
     The dimensional variation of the second void  33  in the thickness direction is affected by the housing  11  and the thickness variation of the adhesive  17  for fixing the circuit board to the housing. 
     The dimensional variation of the third void  34  in the thickness direction is affected by the thickness variation of the housing  11 , the adhesive  17  for fixing the circuit board to the housing, the circuit board  15 , the sensor assembly  10 , the fixing member such as a solder for fixing the sensor assembly  10  to the circuit board, and the adhesive  17  for bonding the cover  31  and the housing  11  to each other. 
     By mounting the sensor assembly  10  on the circuit board such that the flow rate measurement element  4  faces the circuit board  15 , the variation in the thickness of the circuit board  15  does not affect the variation in the thickness direction of the first void  32 . By bonding the housing  11  and the other surface of the circuit board to each other, the variation in the thickness of the circuit board  15  and the variation in the thickness of the sensor assembly  10  do not affect the variation in the thickness direction of the second void  33 . 
     Then, both the first void  32  and the second void  33  are formed, and then the third void  34  is formed (in other words, the third void  33  is located on the upper side than the first void  32  and the second void  33  in a stacking direction. That is, the first void  32  is located between the second void  33  and the third void  34 ), so that the stacking tolerance variation can be aggregated in the third void  34 . The third void  34  formed between the sensor assembly  10  and the cover  31  may be filled with an adhesive or the like. By filling the third void  34 , it is possible to suppress the air from flowing into the third void, and thus, it is possible to suppress the influence on the fluid by providing the third void. 
     In the present embodiment, the third void is formed in addition to the first void and the second void, and the dimensional variation of each member is aggregated in the third void, whereby the dimensional variation of D1 and D2 can be reduced, and the D1 dimension and the flow dividing ratio of D1 and D2 can be configured with high accuracy. Therefore, it is possible to provide an accurate flow rate measurement device. 
     As a further good example, the third void  34  is smaller than the first void  32  and the second void  33 . By reducing the amount of air flowing into the third void, it is possible to suppress the influence of the third void on the fluid flow. The first void  32  is more preferably smaller than the second void  33 . Since a large amount of contaminants contained in the fluid flows into the second void  33  side, the amount of contaminants flying to the flow rate measurement element  4  can be reduced, so that the contamination resistance is improved. 
     Second Embodiment 
     A second embodiment of the present embodiment will be described with reference to  FIGS. 7 and 8 . Description of configurations similar to those of the first embodiment will be omitted. In  FIG. 7 , a part of the end portion of the circuit board  15  that is hidden by the sensor assembly  10  and is not visible is indicated by a broken line. 
     In the present embodiment, a width (distance in the flow direction of the fluid flowing through the sub-passage  12 ) of the part of the circuit board  15  located in the sub-passage  12  is formed to be smaller than a width (distance in the flow direction of the fluid flowing through the sub-passage  12 ) of the part of the sensor assembly  10  located in the sub-passage  12 . An upstream end portion  19  of the part of the sensor assembly  10  located in the sub-passage  12  is located on the upstream side from an upstream end portion  18  of the part of the circuit board  15  located in the sub-passage  12 . 
     In the present embodiment, by forming an opening to the third void before the fluid is divided into D1 (the first void  32 ) and D2 (the second void  33 ), the flow path having a cross-sectional area larger than D1 and the third void  34  have a dividing relationship, and the dividing resistance of the third void is increased, so that the air flow flowing into the third void can be further suppressed. Therefore, the influence on the fluid by forming the third void can be further suppressed. 
     As a further preferable example, a downstream end portion  21  of the part located in the sub-passage of the sensor assembly is located on the downstream side from a downstream end portion  20  of the part of the circuit board  15  located in the sub-passage  12 , so that the same effect can be obtained on the reverse flow. 
     Third Embodiment 
     A third embodiment of the present invention will be described with reference to  FIG. 9 . The description of the same configuration as that of the previous embodiment will be omitted. 
     In the present embodiment, a recess  35  is formed in the cover  31 , and the flow rate measurement element  4  is formed in the recess  35 . In other words, the upstream end portion  19  of the sensor assembly  10  is housed in the recess  35 . 
     According to the present embodiment, since an opening of the third void  34  to the sub-passage  12  is provided to be offset, it is possible to further suppress the fluid flowing through the sub-passage from flowing into the third void  34 , and it is possible to further suppress the influence on the fluid by forming the third void. 
     As a further preferable example, the downstream end portion  21  of the sensor assembly  10  is housed in the recess  35 , so that the same effect can be obtained for the reverse flow. 
     Fourth Embodiment 
     A fourth embodiment of the present invention will be described with reference to  FIG. 10 . The description of the same configuration as that of the previous embodiment will be omitted. 
     In the present embodiment, a protrusion  36  is formed on the cover  31  on the upstream side from the upstream end portion  19  of the sensor assembly  10 . The protrusion  36  is a shape having an inclination on the upstream side. The upstream end portion  19  of the sensor assembly  10  is located at a position offset toward the cover  31  side from the apex of the protrusion  36 . According to the present embodiment, since the fluid is guided to the side opposite to the opening of the third void  34  to the sub-passage  12  by the inclined shape, it is possible to further suppress the fluid from flowing into the third void  34 , and it is possible to further suppress the influence on the fluid by forming the third void. 
     As a further preferable example, the protrusion  36  having an inclination on the downstream side from the downstream end portion  21  of the sensor assembly  10  is formed in the cover  10 , and the downstream end portion  21  of the sensor assembly  10  is disposed to be offset toward the cover  31  side from the apex of the protrusion  36 , so that a similar effect can be obtained for the reverse flow. 
     Fifth Embodiment 
     A fifth embodiment of the present invention will be described with reference to  FIG. 11 . The description of the same configuration as that of the previous embodiment will be omitted. 
     In the present embodiment, the second void  33  is larger than the first void  32 , and the third void  34  is larger than the first void  32 . With the configuration in which the flow is actively taken into the third void  34 , it is possible to positively flow contaminants into the third void  34  and to improve the contamination resistance. 
     REFERENCE SIGNS LIST 
     
         
           1  flow rate measurement device 
           3  LSI 
           4  flow rate detection element 
           5  lead frame 
           6  pressure sensor 
           7  humidity sensor 
           10  sensor assembly 
           11  housing 
           12  sub-passage 
           13  throttle shape 
           14  recess 
           15  circuit board 
           17  adhesive 
           18  upstream end portion 
           19  upstream end portion 
           20  downstream end portion 
           21  downstream end portion 
           30  fluid 
           31  cover 
           32  first void 
           33  second void 
           34  third void 
           35  recess 
           36  protruding portion