Patent Publication Number: US-2020284627-A1

Title: Flowmeter

Description:
TECHNICAL FIELD 
     The present invention relates to an impeller-type flowmeter that measures a flow rate of a fluid flowing through a flow path based on a rotation speed of an impeller. 
     BACKGROUND 
     For example, Patent Document 1 discloses a hot water supply apparatus that includes: a flow rate regulating valve that regulates a flow rate of water flowing through a water supply pipe; an impeller that is provided in a flow path communicatively connected to the flow rate regulating valve and has a magnet arranged on an outer periphery thereof and a flow rate sensor that is fixed to an outer wall of the flow path and measures a rotation speed of the impeller. In the hot water supply apparatus, the flow rate sensor converts a magnetic change associated with rotation of the impeller into a pulse signal, and a controller calculates the flow rate of the water based on the pulse signal (rotation speed signal) output from the flow rate sensor. 
     In general, for an impeller of a flow rate sensor, in order to ensure sufficient wear resistance, high hardness steel, ceramics, or the like is used as a material of a rotation shaft thereof. Further, since wing parts (blades) each have a complicated shape, an impeller is manufactured by insert-injection molding a plastic material mixed with a magnetic powder to mold the wing parts together with the rotation shaft, and further magnetizing the wing parts integrally molded with the rotation shaft. Then, a flowmeter equipped with such an impeller detects, for example, a change in magnetic flux density associated with rotation of the impeller by using a Hall element, and measures a rotation speed of the impeller based on a result of the detection. Further, a flow rate of a fluid flowing through the flow path is calculated from the rotation speed of the impeller by an arithmetic device. 
     RELATED ART 
     [Patent Doc. 1] JP Laid-Open Patent Application Publication 2007-46816 
     [Patent Doc. 2] JP Laid-Open Patent Application Publication 2009-229099 
     SUMMARY OF THE INVENTION 
     Subject(s) to be Solved by the Invention 
     In such a flowmeter, since the wing parts (blades) of the impeller are magnetized, for example, when the fluid flowing through the flow path contains an iron powder, the iron powder adheres to the wing parts. In this case, the iron powder accumulates on the wing parts, preventing smooth rotation of the impeller. As a result, there is a problem that an error in the measurement of the flow rate becomes large, and reliability of the device is decreased. Further, in order to improve accuracy of the wing parts, conventionally, an impeller is manufactured by cut-machining. However, there is a problem that a manufacturing cost is significantly increased. 
     On the other hand, Patent Document 2 discloses a technology for removing an iron powder and other undesired substances adsorbed on blades of a flowmeter. In this flowmeter, protruding parts opposing magnetic poles of a rotating body are provided on an inner circumferential surface of a pipe conduit, and undesired substances such as an iron powder adsorbed on the magnetic poles collide with the protruding parts and are removed from the magnetic poles. However, although this method can remove undesired substances such as an iron powder to some extent, the undesired substances accumulate on the magnetic poles until a thickness is reached at which collision with the protruding parts occurs. That is, the impeller is a permanent magnet, and front ends of the blades are magnetized to form magnetic poles, and thus, adsorption of an iron powder or the like cannot be completely eliminated, and a fundamental solution to the above problem has not been achieved. 
     Therefore, the present invention is accomplished in view of such a situation, and is intended to provide a flowmeter that achieves both high reliability and a low cost. 
     Means to Solve the Subject(s) 
     A flowmeter disclosed in the application includes an impeller that is rotatably supported in a flow path, a magnetic sensor that detects a magnetic change associated with a rotation of the impeller, and a magnet that applies a magnetic field to the magnetic sensor, wherein the impeller is formed of a magnetic material that is not magnetized, and the magnetic sensor and the magnet are arranged outside the flow path. 
     In the flowmeter of this invention, a rotation shaft and multiple wing parts that configure the impeller may be integrally molded. 
     In the flowmeter of this invention, the rotation shaft and the multiple wing parts are integrally molded by metal injection molding in which a magnetic material, which is not magnetized, is used as a material. 
     Advantages of the Invention 
     According to the present invention, the impeller is formed of non-magnetized magnetic material, and the magnetic sensor and the magnet are arranged outside the flow path, and thereby, even when a fluid flowing through the flow path contains an iron powder, the iron powder does not adhere to and accumulate on the impeller, and smooth rotation of the impeller is not hindered. Therefore, sufficient measurement accuracy of the flowmeter is ensured. Further, the rotation shaft and the multiple wing parts of the impeller are integrally molded, and thereby, there is no need to join together the rotation shaft and the multiple wing parts, and thus, reliability of the impeller can be increased. Further, the rotation shaft and the multiple wing parts are integrally molded by metal injection molding in which a non-magnetized magnetic material is used as a material, and thereby, an impeller having a complicated shape can be molded with high precision. Therefore, a flowmeter that achieves both high reliability and a low cost can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  are respectively a top view, a front cross-sectional view and a bottom view of a flowmeter according to the present embodiment. 
         FIG. 2  illustrates a plan view and a side view of an impeller in the flowmeter illustrated in  FIGS. 1A-1C . 
         FIG. 3  is a cross-sectional view of a flow rate control device to which the flowmeter of  FIGS. 1A-1C  is applied, and, in particular, is a cross-sectional view in a plane including an axis line of a flow path and an axis line of a ball shaft. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     First, an embodiment of a flowmeter  1  of the present invention is described with reference to  FIGS. 1A-1C and 2 . For convenience, an up-down direction in  FIGS. 1A-1C  is defined as an up-down direction of the flowmeter  1 . 
     As illustrated in  FIGS. 1A-1C , the flowmeter  1  has a body  12  that is formed of plastic or a non-magnetic metal, and a flow path  13  that extends inside the body  12  in the up-down direction and through which a fluid (water) flows upward. The body  12  has an inlet  14  that opens at a lower end of the body  12  and to which an adapter  17  is connected (fitted), and an outlet  15  that opens at an upper end of the body  12  and to which an adapter  17  is connected (fitted). In each of the adapters  17 , a pipe tapered screw for connecting a pipe connector is formed. 
     The flowmeter  1  of the present embodiment is a so-called impeller-type (turbine-type) flowmeter that indirectly measures a flow rate of a fluid flowing through the flow path  13  based on a rotation speed of an impeller  42 , and has the impeller  42  and a supporting frame  45  that rotatably supports the impeller  42 . The impeller  42  is formed of a non-magnetized magnetic material, and, as illustrated in  FIG. 2 , has a rotation shaft  43  that is arranged on an axis line L (see  FIG. 1B ) of the flow path  13  and multiple (four in the present embodiment) wing parts  44  (turbine blades) that are provided at equal intervals around the rotation shaft  43 . In manufacturing the impeller  42  of the present embodiment, metal injection molding (MIM) in which a metal powder of a non-magnetized magnetic material is used as a material is applied, and the rotation shaft  43  and the multiple wing parts  44  are integrally (simultaneously) molded. As the material (magnetic material) of the metal injection molding, for example, a magnetic stainless steel (such as SUS630) is used. 
     As illustrated in  FIGS. 1A-1C , the supporting frame  45  is configured by being divided into a swirling flow plate  46  that generates a swirling flow in a flowing-in fluid, a sleeve  47  that surrounds the wing parts  44  of the impeller  42 , and a rectifier plate  49  that rectifies a flow of a flowing-out fluid. The swirling flow plate  46  is formed of plastic or a non-magnetic metal, and a bearing part  48 A supporting a lower end of the rotation shaft  43  of the impeller  42  is provided at a center of the swirling flow plate  46 . The sleeve  47  and the rectifier plate  49  are each formed of plastic or a non-magnetic metal; a bearing part  48 B supporting an upper end of the rotation shaft  43  of the impeller  42  is provided at a center of the rectifier plate  49 ; and multiple circular holes  49 A are formed on the same circumference. An upper end of the supporting frame  45  (sleeve  47 ) is abutted against a step part  50  formed in the flow path  13 , and thereby, the supporting frame  45  (sleeve  47 ) is positioned in the up-down direction, that is, a direction along the axis line L of the flow path  13 . Further, the supporting frame  45  (swirling flow plate  46 ) is prevented from moving downward (toward an upstream side) by a metallic C-shaped retaining ring  56  installed on an inner periphery of the flow path  13 . 
     On the other hand, the flowmeter  1  has a sensor unit  51  that measures a rotation speed of the impeller  42 . The sensor unit  51  includes a sensor substrate  52 , a GMR (giant magnetoresistance) sensor  53  mounted on the sensor substrate  52 , and a bias magnet  57  (for example, a ferrite bulk magnet) that applies a bias magnetic field to the GMR sensor  53 , and is arranged outside the supporting frame  45  that forms the flow path  13 . That is, the sensor unit  51  is accommodated inside a waterproof connector  66  attached to a recess part  16  of the body  12 , and thereby, is completely isolated from the flow path  13  through which a fluid flows. Then, the sensor unit  51  measures a rotation speed of the impeller  42  based on a change in magnetic field strength associated with the rotation of the impeller  42  detected by the GMR sensor  53 , and outputs to the outside via the waterproof connector  66  a pulse signal (for convenience, referred to as a “rotation speed signal”) corresponding to a result of the measurement. 
     In the present embodiment, the GMR sensor  53  is configured such that two GMR elements are arranged on the sensor substrate  52  at an interval in a rotation direction of the impeller  42  (sight directions in  FIGS. 1A and 1B ) to form a Wheatstone bridge, and a change in magnetic field strength is detected based on changes in resistance values of the two GMR elements. Further, a reference numeral “ 55 ” in  FIG. 1B  denotes a signal cable that connects the sensor substrate  52  to a connector terminal of the waterproof connector  66 . 
     Next, with reference to  FIG. 3 , a flow rate control device  11  incorporating therein the flowmeter  1  having the above-described configuration is described. For convenience, an up-down direction in  FIG. 3  is defined as an up-down direction of the flow rate control device  11 . 
     As illustrated in  FIG. 3 , the flow rate control device  11  has a body  12  that is formed of plastic or a non-magnetic metal, and a flow path  13  that extends inside the body  12  in the up-down direction and in which a fluid (water) flows upward. The body  12  has an inlet  14  that opens at a lower end of the body  12  and to which a joint adapter  71  is connected, and an outlet  15  that opens at an upper end of the body  12  and to which an adapter  17  is connected (fitted). Here, for convenience, a flow path from the inlet  14  to the outlet  15  of the body  12  is referred to as the flow path  13 . In the adapter  17 , a pipe tapered screw for connecting a pipe connector is formed. 
     (Flow Rate Regulating Valve) 
     The flow rate control device  11  has a flow rate regulating valve  21  formed by a ball valve mechanism. The flow rate regulating valve  21  has a valve body  22  that includes a shaft part  25  and a ball part  23 , the ball part  23  being provided on a front end (right end in  FIG. 3 ) of the shaft part  25  and capable of blocking the flow path  13 . A base end (left end in  FIG. 3 ) of the shaft part  25  is connected to a rotation shaft  24 A of a motor actuator  24 . In the body  12 , a shaft hole  26  is formed that penetrates the body  12  in a horizontal direction (left-right direction in  FIG. 3 ) and communicatively connects to the flow path  13 . The shaft part  25  of the valve body  22  is slidably fitted in the shaft hole  26 . An O-ring  27  seals between the shaft part  25  of the valve body  22  and the shaft hole  26  of the body  12 . Further, the motor actuator  24  includes a stepping motor, a speed reduction mechanism, and a position detecting sensor. 
     The flow rate regulating valve  21  has a pair of ball packings  28  and  29  that are respectively arranged on an upstream side and a downstream side of the flow path  13  sandwiching the ball part  23  of the valve body  22 . The ball packing  28  on the upstream side is pressed toward a downstream side (upward in  FIG. 3 ) by a fixing nut  30 , and thereby, a valve seat part  28 A is slidably in close contact with the ball part  23 . Further, the ball packing  29  on the downstream side is pressed toward an upstream side (downward in  FIG. 3 ) by a fixing nut  31 , and thereby, a valve seat part  29 A is slidably in close contact with the ball part  23 . Here,  FIG. 3  illustrates a state in which the flow rate regulating valve  21  is fully opened. In this state, an axis line of a flow path  23 A of the ball part  23  of the valve body  22  coincides with an axis line of a flow path  32  extending through the ball packing  28  and the fixing nut  30  and coincides with an axis line of a flow path  33  extending through the ball packing  29  and the fixing nut  31 , and, by extension, coincides with an axis line L of the flow path  13 . 
     The flow path  32  has a diameter-reducing part  32 A at an end part thereof on an opposite side (lower side in  FIG. 3 ) with respect to the ball part  23  side (valve seat part  28 A side) where a flow path area of the diameter-reducing part  32 A gradually decreases. Further, the flow path  33  has a diameter-increasing part  33 A at an end part thereof on an opposite side (upper side in  FIG. 3 ) with respect to the ball part  23  side (valve seat part  29 A side) where a flow path area of the diameter-increasing part  33 A gradually increases. Further, an O-ring  34  seals between the fixing nut  30  and the flow path  13 . Further, an O-ring  35  seals between the fixing nut  31  and the flow path  13 . Further, a reference numeral “ 36 ” in  FIG. 3  denotes a retaining plate that prevents movement of the valve body  22  in an axis line direction (left-right direction in  FIG. 1 ) with respect to the shaft hole  26 . Further, a reference numeral “ 59 ” in  FIG. 3  denotes an O-ring that seals between the swirling flow plate  46  and the sleeve  47 . 
     The flow rate control device  11  includes a control part  61  that feedback-controls opening of the flow rate regulating valve  21  based on a measurement result (rotation speed of the impeller  42 ) of a flow rate measurement part  41  formed of the flowmeter  1 . The control part  61  is a so-called microcomputer that includes an arithmetic part, a storage part, and the like, and feedback-controls (PID-controls) the opening of the flow rate regulating valve  21  based on a rotation speed signal output from the flow rate measurement part  41  (a flow rate measured by the flow rate measurement part  41 ). That is, the control part  61  converts a rotation speed signal into a flow rate measurement value. In other words, the control part  61  converts a rotation speed into a flow rate based on a data table, and arithmetically processes the measured value (flow rate measurement value) and a set value (flow rate target value). Then, based on a result of the arithmetic processing, the control part  61  controls the motor actuator  24  to rotate the valve body  22 , and hence the ball part  23 , and adjusts the flow rate of the fluid flowing through the flow path  13 . 
     The control part  61  has a control substrate  62  accommodated in a recess part  16  formed on one side (left side in  FIG. 3 ) of the body  12 . A housing  63  that is formed of an aluminum alloy and accommodates the motor actuator  24  is provided on the one side of the body  12 , and a space between the housing  63  and the recess part  16  is sealed by a packing  64 . The packing  64  is fitted in a packing groove  65  formed on a peripheral edge of the recess part  16  of the body  12 . Further, a waterproof connector  66  used for communication with the outside (“RS485” in the present embodiment) is attached to a lower portion of the housing  63 . Further, the waterproof connector  66  and the control substrate  62  are connected to each other by a signal cable  67  (a five-core cable in the present embodiment). Further, a reference numeral “ 68 ” in  FIG. 3  denotes an LED (full color) mounted on the control substrate  62 . Further, a reference numeral “ 69 ” in  FIG. 3  denotes a light transmission window formed of a transparent resin for visually confirming the LED  68  from the outside. 
     (Operation) 
     Referring to  FIG. 3 , a fluid (“water” in the present embodiment) to be controlled passes through a filter  7  in the joint adapter  71  and is introduced into the flow path  13  from the inlet  14 . The fluid flowing through the flow path  13  becomes a swirling flow that swirls in a certain direction by passing through the swirling flow plate  46 . The swirling flow rotates the impeller  42  arranged in the flow path  13 . The sensor unit  51  detects with the GMR sensor  53  a change in magnetic field strength associated with the rotation of the impeller  42 , and measures the rotation speed of the impeller  42  based on the change in magnetic field strength. Then, the sensor unit  51  outputs a rotation speed signal (pulse signal) as a flow rate measurement result of the flow rate measurement part  41  to the control part  61 . 
     The control part  61  converts the received rotation speed signal into a flow rate measurement value, and arithmetically processes the measured value (flow rate measurement value) and a set value (flow rate target value). Such a arithmetically processing is termed as PID processing. The control part  61  outputs a control signal corresponding to a result of the arithmetic processing to the motor actuator  24 . As a result, the motor actuator  24  receives the control signal from the control part  61  and operates, and the opening of the flow rate regulating valve  21  (ball valve), that is, the flow path area of the flow path  13  is adjusted, and hence, the flow rate of the fluid flowing through the flow path  13  is adjusted. 
     Effects 
     According to the present embodiment, the impeller  42  of the flow rate measurement part  41  was manufactured by metal injection molding in which an unmagnetized magnetic material is used as a material. Therefore, the impeller  42  having a complicated shape can be molded with high precision. Further, a manufacturing cost thereof can be significantly reduced as compared to a cut-machined impeller. As a result, the rotation shaft  43  and the multiple wing parts  44  of the impeller  42  can be integrally molded, and the number of parts can be reduced as compared to an impeller of which a rotation shaft  43  and multiple wing parts  44  are separately manufactured. Further, for an impeller manufactured by joining (press-fitting, bonding or the like) a rotation shaft  43  and multiple wing parts  44  instead of cut-machining in order to reduce a manufacturing cost, there is a problem that stricter quality control is required due to a decrease in reliability of joining parts. However, for the impeller  42  according to the present embodiment, by applying metal injection molding, such a problem can be solved. 
     Further, in the present embodiment, a magnetic stainless steel (magnetic material) as a non-magnetized magnetic material is used as the material of the impeller  42 , and a change in magnetic field strength associated with the rotation of the impeller  42  is detected by the bias magnet  57  and the GMR sensor  53  arranged outside the flow path  13 , and thereby, the flow rate of the fluid flowing through the flow path  13  is detected. Therefore, for example, even when an iron powder is contained in the fluid, the impeller  42  in the flow path  13  is not magnetized, and thus, unlike a magnetic impeller in which wing parts  44  (blades) are magnetized, the iron powder does not adhere to and accumulate on the impeller  42 , and smooth rotation of the impeller  42  is not hindered. As a result, sufficient measurement accuracy of the flow rate measurement part  41  can be ensured, and hence, reliability of the flow rate control device  11  can be improved. 
     Further, in the present embodiment, the control substrate (control substrate  62 ) is accommodated in the closed housing  63 . Therefore, the flow rate control device  11  can be reduced in size. Further, an aluminum alloy having excellent heat dissipation performance is used as the material of the housing  63 . Therefore, for example, a flow rate of a fluid of a relatively high temperature can be controlled. Further, the light transmission window  69  for visually confirming the LED  68  (full color) is provided on a surface of the housing  63 . Therefore, filter clogging, a sensor abnormality or the like can be visually confirmed from the outside. 
     LEGENDS 
     
         
           1 : flowmeter 
           13 : flow path 
           41 : flow rate measurement part 
           42 : impeller 
           43 : rotation shaft 
           44 : wing part 
           53 : GMR sensor 
           57 : bias magnet