JP6463245B2 - Thermal flow meter - Google Patents

Description

  The present invention relates to a thermal flow meter.

  The thermal flow meter that measures the flow rate of gas includes a flow rate detection unit for measuring the flow rate, and performs heat transfer between the flow rate detection unit and the gas that is a measurement target. Is configured to measure. In the thermal flow meter, a sub-passage structure such as centrifugal separation using a cyclone bypass or inertia separation using a branch passage is employed from the viewpoint of contamination prevention. For example, Patent Document 1 discloses a structure of a thermal flow rate measuring device in which a sub passage has a U-shape.

JP 2006-162631 A

  However, such a sub-passage structure has a bent portion, and due to this bent portion, a deviation occurs in the flow velocity of the gas to be measured in the sub-passage, which is the maximum when viewed in the cross section of the flow path. The flow velocity point deviates from the center of the sub-passage, and a region where the flow velocity is locally slow is formed.

  For example, the gas to be measured contains moisture, of which the moisture that could not be trapped by the air cleaner has a very small diameter, so even if it enters the sub-passage and reaches the flow rate detection unit as it is, there is a large error in measurement. Don't give.

  However, in the region where the flow rate of the gas to be measured is low, the moisture is liable to stay without flowing. Therefore, the staying water is combined and grows into large water droplets, and is easily blown away by the gas to be measured. There is a fear. And the magnitude | size of the water droplet which reaches | attains this flow volume detection part is larger than the water | moisture content of the fine diameter which passes an air cleaner, and has a big influence on the measurement precision of a flow volume detection part. Moreover, the large water droplets staying and growing in the sub-passage may block the sub-passage and reduce the flow path area, which may affect the measurement accuracy of the flow rate detection unit.

  It is an object of the present invention to provide a thermal flow meter that can efficiently drain moisture in the sub-passage.

  The thermal flow meter of the present invention that solves the above-described problems is a thermal flow meter according to the present invention, wherein heat transfer is performed between a sub passage that takes in a gas to be measured flowing through a main passage and the gas to be measured that flows through the sub passage. A flow rate detector that measures the flow rate, and the sub-passage has a passage-shaped passage part in which the maximum flow velocity point of the gas to be measured deviates from the center of the flow path, The passage portion is provided with a drain hole at a position opposite to the maximum flow velocity point of the gas to be measured through the flow path center.

  According to the present invention, moisture that has entered the sub-passage can be efficiently discharged. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is a system diagram showing an embodiment in which a thermal flow meter according to the present invention is used in an internal combustion engine control system. The front view which shows the external appearance of the thermal type flow meter which concerns on this invention. The left view which shows the external appearance of the thermal type flow meter which concerns on this invention. The rear view which shows the external appearance of the thermal type flow meter which concerns on this invention. The right view which shows the external appearance of the thermal type flow meter which concerns on this invention. The front view which shows the state of the housing which removed the front cover and the back cover from the thermal type flow meter which concerns on this invention. The rear view which shows the state of the housing which removed the front cover and the back cover from the thermal type flow meter which concerns on this invention. The rear view of a table cover. FIG. 4B is a sectional view taken along line BB in FIG. 4A. The rear view of a back cover. BB sectional drawing of FIG. 5A. It is explanatory drawing of the thermal type flow meter which shows Example 1 of this invention, and is a front view which shows the state inside a subchannel | path. FIG. 6B is a sectional view taken along line BB in FIG. 6A. The principal part enlarged view of FIG. 6A. Flow velocity distribution diagram of the second passage. FIG. 7 is an isovelocity diagram in the cross section of the second passage. It is explanatory drawing of the thermal type flow meter which shows Example 2 of this invention, and is a front view which shows the state inside a subchannel | path. FIG. 7B is a sectional view taken along line BB in FIG. 7A. It is explanatory drawing of the thermal type flow meter which shows Example 3 of this invention, and is a front view which shows the state inside a subchannel | path. FIG. 8B is a sectional view taken along line BB in FIG. 8A. It is explanatory drawing of the thermal type flow meter which shows Example 4 of this invention, and is a front view which shows the state inside a subchannel | path. BB sectional drawing of FIG. 9A.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment in which a thermal flow meter according to the present invention is used in an electronic fuel injection type internal combustion engine control system. Based on the operation of the internal combustion engine 110 including the engine cylinder 112 and the engine piston 114, intake air is sucked from the air cleaner 122 as the gas to be measured 30 and passes through the main passage 124 such as the intake pipe, the throttle body 126, and the intake manifold 128. Guided to the combustion chamber of the engine cylinder 112. The flow rate of the gas 30 to be measured, which is the intake air led to the combustion chamber, is measured by the thermal flow meter 300 according to the present invention, and fuel is supplied from the fuel injection valve 152 based on the measured flow rate. The gas to be measured is introduced into the combustion chamber together with a certain gas 30 to be measured. In this embodiment, the fuel injection valve 152 is provided at the intake port of the internal combustion engine, and the fuel injected into the intake port forms an air-fuel mixture together with the measured gas 30 that is the intake air, and passes through the intake valve 116. It is guided to the combustion chamber and burns to generate mechanical energy.

  The fuel and air guided to the combustion chamber are in a mixed state of fuel and air, and are burned explosively by spark ignition of the spark plug 154 to generate mechanical energy. The combusted gas is guided from the exhaust valve 118 to the exhaust pipe, and exhausted as exhaust 24 from the exhaust pipe to the outside of the vehicle. The flow rate of the gas 30 to be measured, which is the intake air led to the combustion chamber, is controlled by the throttle valve 132 whose opening degree changes based on the operation of the accelerator pedal. The fuel supply amount is controlled based on the flow rate of the intake air guided to the combustion chamber, and the driver controls the flow rate of the intake air guided to the combustion chamber by controlling the opening degree of the throttle valve 132, thereby The mechanical energy generated by the engine can be controlled.

  The flow rate and temperature of the gas 30 to be measured, which is intake air that is taken in from the air cleaner 122 and flows through the main passage 124, are measured by the thermal flow meter 300, and electrical signals representing the flow rate and temperature of the intake air are output from the thermal flow meter 300. Input to the control device 200. Further, the output of the throttle angle sensor 144 that measures the opening degree of the throttle valve 132 is input to the control device 200, and the positions and states of the engine piston 114, the intake valve 116, and the exhaust valve 118 of the internal combustion engine, and the rotation of the internal combustion engine. In order to measure the speed, the output of the rotation angle sensor 146 is input to the control device 200. The output of the oxygen sensor 148 is input to the control device 200 in order to measure the state of the mixture ratio between the fuel amount and the air amount from the state of the exhaust 24.

  The control device 200 calculates the fuel injection amount and the ignition timing based on the flow rate of intake air that is the output of the thermal flow meter 300 and the rotational speed of the internal combustion engine that is measured based on the output of the rotation angle sensor 146. Based on these calculation results, the amount of fuel supplied from the fuel injection valve 152 and the ignition timing ignited by the spark plug 154 are controlled. The fuel supply amount and ignition timing are actually based on the intake air temperature and throttle angle change state measured by the thermal flow meter 300, the engine rotational speed change state, and the air-fuel ratio state measured by the oxygen sensor 148. It is finely controlled. The control device 200 further controls the amount of air that bypasses the throttle valve 132 by the idle air control valve 156 in the idle operation state of the internal combustion engine, thereby controlling the rotational speed of the internal combustion engine in the idle operation state.

  FIG. 2 shows the appearance of the thermal flow meter 300. 2A is a front view of the thermal flow meter 300, FIG. 2B is a left side view, FIG. 2C is a rear view, and FIG. 2D is a right side view. The thermal flow meter 300 includes a housing 302. The housing 302 is inserted into the intake pipe and disposed in the main passage 124 (see FIG. 1). At the base end portion of the housing 302, a flange 305 for fixing to the intake pipe and an external connection portion 306 exposed outside the intake pipe are provided.

  The housing 302 is supported in a cantilever manner by fixing the flange 305 to the intake pipe, and is disposed so as to extend along a direction perpendicular to the main flow direction of the gas to be measured flowing through the main passage 124. The housing 302 is provided with a sub-passage for taking in the gas to be measured 30 flowing through the main passage 124, and a flow rate detector 602 for detecting the flow rate of the gas under measurement 30 is disposed in the sub-passage. Yes.

  An inlet 311 for taking a part of the measurement target gas 30 such as intake air into the sub-passage is provided at the upstream end disposed on the front end side of the housing 302 and on the upstream side in the main flow direction. A first outlet 312 and a second outlet 313 for returning the gas 30 to be measured from the auxiliary passage to the main passage 124 are provided at the downstream end disposed on the distal end side of the housing 302 and on the downstream side in the main flow direction. It has been. The first outlet 312 and the second outlet 313 are arranged side by side in the thickness direction of the housing 302 as shown in FIG. 2D.

  By providing the inlet 311 on the front end side of the housing 302, a gas in a portion close to the center portion away from the inner wall surface of the main passage can be taken into the sub-passage. Therefore, it becomes difficult to be influenced by the temperature of the inner wall surface of the main passage, and a decrease in measurement accuracy of the gas flow rate and temperature can be suppressed.

  In the vicinity of the inner wall surface of the main passage, the fluid resistance is large and the flow velocity is lower than the average flow velocity of the main passage. However, in the thermal flow meter 300 of the present embodiment, it extends from the flange 305 toward the center of the main passage. Since the inlet 311 is provided on the distal end side of the thin and long housing 302, a gas having a high flow velocity at the center of the main passage can be taken into the sub-passage. Further, since the first outlet 312 and the second outlet 313 of the auxiliary passage are also provided on the distal end side of the housing 302, the gas flowing in the auxiliary passage can be returned to the central portion of the main passage where the flow velocity is high.

  The housing 302 has a substantially rectangular wide surface on the front side, but has a narrow side surface (thin thickness). The housing 302 has a front surface and a back surface arranged along the main flow direction of the gas to be measured flowing through the main passage, and has a side surface opposed to the main flow direction. As a result, the thermal flow meter 300 can be provided with a sufficiently long sub-passage with a reduced fluid resistance with respect to the gas to be measured 30.

  That is, in the thermal flow meter of the present embodiment, the shape of the housing projected on the orthogonal plane orthogonal to the flow direction of the gas 30 to be measured flowing through the main passage 124 is in the first direction 50 on the orthogonal plane. A defined length dimension and a thickness dimension defined in a second direction 51 perpendicular to the first direction 50 (see FIG. 2B) on the orthogonal plane, the thickness dimension being a length The shape is smaller than the dimensions.

  The housing 302 is provided with a temperature detector 452 for measuring the temperature of the measurement target gas 30. The housing 302 has a shape that is recessed toward the downstream end at the center in the longitudinal direction and at the upstream end, and the temperature detector 452 is provided at the recessed position. The temperature detection unit 452 has a shape that protrudes from the recessed portion of the housing 302 along the main flow direction.

  FIG. 3 shows a state of the housing 302 with the front cover 303 and the back cover 304 removed from the thermal flow meter 300. 3A is a front view of the housing 302, and FIG. 3B is a rear view.

  Inside the housing 302, a flow rate detection unit 602 for measuring the flow rate of the measurement target gas 30 flowing through the main passage 124 and a temperature detection unit 452 for measuring the temperature of the measurement target gas 30 flowing through the main passage 124 are provided. The circuit package 400 provided is molded integrally.

  The housing 302 is formed with a sub-passage groove for forming the sub-passage. In the present embodiment, the sub-passage grooves are recessed on both the front and back surfaces of the housing 302, and the front and rear covers 303 and 304 are placed on the front and back surfaces of the housing 302 to complete the sub-passage. . With such a structure, when the housing 302 is molded (resin molding process), molds provided on both surfaces of the housing 302 are used, so that both the front side sub-passage groove 321 and the back side sub-passage groove 331 are part of the housing 302. All can be molded as a part.

  The sub passage groove includes a back side sub passage groove 331 formed on the back surface of the housing 302 and a front side sub passage groove 321 formed on the surface of the housing 302. The back side auxiliary passage groove 331 has a first groove part 332 and a second groove part 333 that branches in the middle of the first groove part 332.

  The first groove 332 extends in a straight line from the upstream end 317 to the downstream end 318 along the main flow direction of the gas 30 to be measured at the front end of the housing 302, and enters the inlet 311 of the housing 302. One end communicates and the other end communicates with the outlet 312 of the housing 302. The first groove portion 332 includes a straight portion 332A that extends from the inlet 311 with a substantially constant cross-sectional shape, and a throttle portion 332B that gradually decreases in width as it moves from the straight portion 332A toward the outlet 312. .

  The second groove portion 333 branches from the straight portion 332A of the first groove portion 332 and proceeds toward the proximal end side of the housing 302 while curving, and enters the measurement flow path 341 provided in the longitudinal center portion of the housing 302. Communicate. Of the pair of side wall surfaces constituting the first groove portion 332, the second groove portion 333 communicates with the side wall surface 332 a positioned on the proximal end side of the housing 302, and the bottom wall surface 333 a is a straight line of the first groove portion 332. It is continuous with the bottom wall surface 332b of the portion 332A. A recess 333e is provided on the side wall surface 333b on the inner peripheral side of the second groove portion 333.

  When the gas 30 to be measured flowing through the main passage 124 collides with the thermal flow meter 300, the gas to be measured 30 receives the dynamic pressure by the outer wall surface facing the flow direction of the gas 30 to be measured, and the upstream side facing the outer wall surface. The pressure increases. On the other hand, the gas to be measured 30 on the wall surface parallel or substantially parallel to the main flow direction of the gas to be measured 30 is peeled off from the wall surface in the upstream portion of the wall surface, and the peeling portion (periphery) becomes negative pressure. The gas 30 to be measured gradually changes into a flow along the wall surface of the thermal flow meter 300 as it goes downstream from the part where the separation occurs. In the recess 333e, when a drain hole 376 is provided at a position where the water stagnates in the vicinity of the second groove 333 and closes the recess 333e in the back cover 304, a peeling portion (periphery) of the thermal flow meter 300 is provided. Due to the negative pressure generated in step S3, the sub-passage recess 333e can be discharged to the outside of the sub-passage, that is, the main passage 124 through the drain hole 376.

  The measurement flow path 341 is formed so as to penetrate the housing 302 in the thickness direction, and the flow path exposed portion 430 of the circuit package 400 is disposed so as to protrude. The second groove 333 communicates with the measurement channel 341 on the upstream side of the sub-passage with respect to the channel exposure part 430 of the circuit package 400.

  The second groove 333 has a shape in which the groove depth becomes deeper as it proceeds toward the measurement channel 341, and in particular, has a steeply inclined portion 333 d that becomes deeper in front of the measurement channel 341. Yes. The steeply inclined portion 333d is configured such that, in the measurement flow channel 341, of the surface 431 and the back surface 432 included in the flow channel exposed portion 430 of the circuit package 400, Gas is allowed to pass, and foreign matter such as dust contained in the measurement target gas 30 is allowed to pass through the back surface 432 side.

  The gas 30 to be measured gradually moves in the direction of the front side of the housing 302 (the back side in the drawing in FIG. 3B) as it flows through the back side sub-passage groove 331. Then, a part of the air having a small mass moves along the steeply inclined portion 333 d and flows in the measurement flow channel 341 toward the surface 431 of the flow channel exposed portion 430. On the other hand, a foreign substance having a large mass cannot easily flow along the steeply inclined portion 333d because it is difficult to change a course due to centrifugal force, and flows toward the back surface 432 of the flow channel exposed portion 430 in the measurement flow channel 341. .

  The flow rate detection unit 602 is provided on the surface 431 of the flow path exposure unit 430 of the circuit package 400. In the flow rate detection unit 602, heat transfer is performed with the measurement target gas 30 that has flowed toward the surface 431 of the flow path exposure unit 430, and the flow rate is measured.

  When the measurement target gas 30 passes through the front surface 431 side and the back surface 432 side of the flow path exposed portion 430 of the circuit package 400, the measurement target gas 30 flows into the front side sub passage groove 321 from the downstream side of the sub passage of the measurement flow path 341. It flows through the interior 321 and is discharged from the second outlet 313 to the main passage 124.

  As shown in FIG. 3A, one end of the front side sub-passage groove 321 communicates with the downstream side of the sub-passage of the measurement channel 341, and the other end of the outlet 313 formed in the downstream end 318 on the front end side of the housing 302. Communicate. The front side sub-passage groove 321 curves so as to gradually advance toward the downstream end 318 as it moves from the measurement flow path 341 to the front end side of the housing 302, and the main flow direction of the measurement target gas 30 at the front end portion of the housing 302 The groove extends in a straight line toward the downstream side, and the groove width gradually decreases toward the second outlet 313.

  In this embodiment, the flow path formed by the back side sub-passage groove 331 draws a curve from the front end side of the housing 302 toward the base end side which is the flange 305 side, and at the position closest to the flange 305, the sub-passage is formed. The flow of the gas 30 to be measured is in a direction opposite to the main flow direction of the main passage 124, and a back side sub-passage provided on the back side of the housing 302 in the reverse flow portion is provided on the front side. It leads to the front side auxiliary passage.

  The measurement channel 341 is divided into a space on the front surface 431 side and a space on the back surface 432 side by the channel exposure part 430 of the circuit package 400, and is not divided by the housing 302. That is, the measurement flow path 341 is formed so as to penetrate the front surface and the back surface of the housing 302, and the circuit package 400 projects in a cantilever manner in this one space. With such a configuration, the sub-passage grooves can be formed on both the front and back surfaces of the housing 302 in a single resin molding step, and the structure connecting the sub-passage grooves on both sides can be formed together. The circuit package 400 is fixed by being embedded in a fixing portion 351, 352, 353 of the housing 302 by a resin mold.

  Further, according to the configuration described above, the circuit package 400 can be inserted into the housing 302 and mounted at the same time as the resin molding of the housing 302. The back side sub-passage groove 331 and the front side sub-passage groove 321 are configured such that either the upstream side of the passage upstream of the circuit package 400 or the downstream side of the downstream side of the circuit package 400 is penetrated in the width direction of the housing 302. It is also possible to form the sub-passage shape connecting the two in a single resin molding step.

  The front side sub-passage of the housing 302 is formed when the upper end portions of the side walls on the upper side in the groove height direction of the pair of side wall surfaces constituting the front side sub-passage groove 321 and the back surface of the front cover 303 are in close contact with each other. The back side sub-passage of the housing 302 is formed by the close contact between the upper end of the side wall in the groove height direction of the pair of side wall surfaces constituting the back side sub-passage groove 331 and the back surface of the back cover 304.

  As shown in FIGS. 3A and 3B, the housing 302 has a cavity 342 formed between the flange 305 and the portion where the sub-passage groove is formed. The cavity 342 is formed by penetrating the housing 302 in the thickness direction. In the hollow portion 342, the terminal connection portion 320 that connects the connection terminal 412 of the circuit package 400 and the inner end 306a of the external terminal of the external connection portion 306 is disposed so as to be exposed. The connection terminal 412 and the inner end 306a are electrically connected by spot welding or laser welding. The cavity 342 is closed by attaching the front cover 303 and the back cover 304 to the housing 302, and the periphery of the cavity 342 is sealed by laser welding with the front cover 303 and the back cover 304.

  4A is a view showing the back surface of the front cover, and FIG. 4B is a cross-sectional view taken along the line BB of FIG. 4A. FIG. 5A is a diagram showing a back surface of the back cover, and FIG. 5B is a diagram showing a side surface of the back cover.

  The front cover 303 and the back cover 304 are thin plates and have a shape with a wide cooling surface. For this reason, the thermal flow meter 300 has an effect that air resistance is reduced, and further, the thermal flow meter 300 is easily cooled by the gas to be measured flowing through the main passage 124.

  The front cover 303 has a size that covers the surface of the housing 302. On the back surface of the front cover 303, a fifth region 361 that closes the front side sub-passage groove 321 of the housing 302, a sixth region 362 that closes the front side of the measurement flow path 341 of the housing 302, and the front side of the cavity 342 A seventh region 363 that closes is formed. And the recessed part 361a in which the side wall upper end part of the front side sub channel | path groove | channel 321 of the housing 302 enters is provided in the width direction both sides of the 5th area | region 361 and the 6th area | region 362. In addition, a recess 363 a into which the outer peripheral end of the cavity 342 enters is formed around the seventh region 363.

  On the back surface of the front cover 303, a convex portion 364 is provided that is inserted into a gap between the tip of the channel exposure portion 430 of the circuit package 400 and the measurement channel 341 of the housing 302. Further, a metal plate 501 is provided by insert molding at a position facing the surface 431 of the flow path exposed portion 430 of the circuit package 400.

  The back cover 304 has a size that covers the back surface of the housing 302. On the back surface of the back cover 304, a first region 371 A that closes the first groove 332 of the back side sub-passage groove 331 of the housing 302, a second region 371 B that closes the second groove 333, and a measurement flow path of the housing 302 A third region 372 that closes the back side of 341 and a fourth region 373 that closes the back side of the cavity 342 are formed. Further, on both sides in the width direction of the first region 371A, the second region 371B, and the third region 372, recessed portions 371a into which the upper end portions of the side walls of the rear side sub-passage grooves 331 of the housing 302 are recessed are provided. Further, around the fourth region 373, a recess 373a into which the rear outer peripheral end of the cavity 342 enters is provided.

  The back cover 304 has a drain hole 376 communicating with the sub passage. The drain hole 376 is formed so as to penetrate a position where the recess 333e of the housing 302 is closed with the back cover 304 attached to the housing 302, and the water taken into the recess 333e of the second groove 333 in the sub-passage. Can be discharged to the outside.

  On the back surface of the back cover 304, a convex portion 374 is provided that is inserted into a gap between the tip of the channel exposure portion 430 of the circuit package 400 and the measurement channel 341 of the housing 302. The convex portion 374 fills a gap between the tip of the flow channel exposed portion 430 of the circuit package 400 and the measurement flow channel 341 of the housing 302 in cooperation with the convex portion 364 of the front cover 303.

  The front cover 303 and the back cover 304 are attached to the front surface and the back surface of the housing 302, respectively, and form a sub passage by cooperation with the front side sub passage groove 321 and the back side sub passage groove 331.

  6 is a schematic diagram illustrating the structure of the sub-passage, FIG. 6A is a rear view showing a state inside the sub-passage, FIG. 6B is a cross-sectional view taken along the line BB of FIG. 6A, and FIG. FIG. 6D is a flow velocity distribution diagram of the second passage, and FIG. 6E is a constant flow velocity diagram in the flow path cross section of the second passage. In FIG. 6A and FIG. 6C, the back cover 304 is omitted.

  The back side sub-passage is configured by cooperation of the housing 302 and the back cover 304, and includes a first passage 701 and a second passage 702 branched from the first passage 701. The first passage 701 is formed by covering the first groove 332 (see FIG. 3A) of the housing 302 with the first region 371A (see FIG. 5A) of the back cover 304, and the second passage 702 is formed on the housing 302. The second groove portion 333 (see FIG. 3B) is covered with a second region 371B (see FIG. 5A) of the back cover 304.

  The first passage 701 takes in a part of the measured gas 30 flowing through the main passage 124 from the inlet 311 and discharges the taken measured gas 30 from the first outlet 312 to the main passage 124. The second passage 702 takes in part of the measurement gas 30 from the first passage 701 and guides the taken measurement gas 30 to the flow rate detection unit 602 provided in the measurement channel 340. The gas 30 to be measured that has passed through the flow rate detection unit 602 flows from the measurement channel 340 into the front side sub-passage, passes through the front side sub-passage, and is discharged to the outside through the second outlet 313.

  The first passage 701 is provided in a straight line between the upstream end 317 and the downstream end 318 of the housing 302 so as to extend along the main flow direction of the gas 30 to be measured flowing through the main passage 124. ing. The second passage 702 has a passage-shaped passage portion that curves in a direction away from the first passage 701 as it moves from the upstream side toward the downstream side in the main flow direction of the measurement target gas 30. The passage portion of the second passage 702 is curved so as to shift to the proximal end side of the housing 302 as it branches from the first passage 701 and moves toward the downstream end portion 318.

  In the passage portion of the second passage 702, the flow of the gas to be measured 30 is biased to the outside of the curve due to the shape of the passage, the flow velocity outside the curve becomes faster than the flow velocity inside the curve, and the gas to be measured in the passage portion of the second passage 702 The maximum flow velocity point Vmax of 30 is biased to the outside of the curve with respect to the flow path center CL as shown in FIGS. 6D and 6E. The flow rate is low at a position inside the curve of the passage portion of the second passage 702, that is, at a position opposite to the maximum flow velocity point Vmax of the gas to be measured via the flow path center CL of the passage portion of the second passage 702. A flow velocity region 704 is formed. In addition, the low-flow-velocity area | region 704 shown by hatching in FIG. 6A is shown notionally, and does not show an actual area | region strictly.

  The first passage 701 discharges foreign matter that has entered the sub-passage using the inertia effect, but it is difficult to discharge all foreign matter that has entered the sub-passage, and part of the foreign matter is also present in the second passage 702. invade. Among foreign matters that have entered the second passage 702, moisture in particular does not have a sufficient flow rate to move in the low flow rate region 704, and may stagnate in the second passage 702.

  When the surface area is increased by the waters stagnating in the second passage 702 being combined with each other, the gas to be measured 30 is swept downstream of the second passage 702 and moved as a lump. In this way, the size of the water that moves as a lump greatly affects the measurement accuracy when it adheres to the flow rate detector 602. Further, when the amount of moisture stagnating in the second passage 702 increases, the flow area of the second passage 702 is reduced by that amount, and the flow rate of the gas 30 to be measured passing through the second passage 702 is reduced. This may affect the detection accuracy of the flow rate detector 602.

  The present invention has been made in view of such a problem, and in order to efficiently discharge the water stagnated in the second passage 702, the flow path center CL of the second passage 702 in the passage portion of the second passage 702 is provided. A drainage hole 376 that communicates with the main passage 124 is provided in a low flow velocity region 704 that is located on the opposite side of the maximum flow velocity point Vmax of the gas to be measured. In the present embodiment, a recess 333e is formed on the side wall surface (passage wall surface) 333b inside the curve of the second groove 333 in the low flow velocity region 704, and the drain hole 376 of the back cover 304 communicates with the recess 333e.

  The concave portion 333e is recessed in a semicircular shape on the side wall surface 333b of the second groove portion 333, and has a depth extending from the upper end portion of the side wall of the second groove portion 333 to the bottom wall surface 333a in the groove depth direction. The concave portion 333e has a downstream wall 333f and an upstream wall 333g that face each other and are continuous with the side wall surface 333b. As shown in FIG. 6C, the downstream wall 333f and the upstream wall 333g form a predetermined angle θa and θb between the downstream wall 333f and the upstream wall 333g, as shown in FIG. Yes.

  The downstream wall 333f is disposed on the downstream side of the second passage 702, and θa is set to an angle larger than 90 ° so as to be opposed to the measurement target gas 30 flowing through the second passage 702. Yes. The upstream wall 333g is disposed on the upstream side of the second passage 702. For example, moisture flowing toward the first groove 332 side through the side wall surface 333b of the second passage 702 can be actively taken into the recess 333e. To make it possible, θb is set to an angle smaller than 90 °.

  Since the recess 333 e is provided in the low flow velocity region 704, the flow rate of the measurement target gas 30 in the recess 333 e is very small compared to the flow rate in the second passage 702. Therefore, the droplet (water droplet) that has entered the bypass is the most likely area of stagnation. Therefore, by providing the drainage hole 376 in the vicinity where the water droplet is stagnating, the water taken into the recess 333e can be discharged to the main passage 124 through the drainage hole 376 (see FIG. 6B).

  Therefore, it is possible to prevent the stagnant water from becoming a large mass of water and passing through the second passage 702 and reaching the flow rate detection unit 602. In addition, it is possible to prevent the stagnant moisture from reducing the flow area of the second passage 702 and affecting the flow rate detection in the flow rate detection unit 602.

  In this embodiment, the recess 333e is provided in the low flow velocity region 704 of the passage portion of the second passage 702, and the drain hole 376 is provided in the recess 333e to communicate with the main passage 124. However, the recess 333e is not provided. Water can be discharged even if the drain hole 376 is directly connected to the sub-passage.

  When the drainage hole 376 is directly communicated with the vicinity of the large flow velocity point in the sub-passage, the flow in the sub-passage has a speed, so that the liquid droplet in the sub-passage is pushed downstream. Therefore, the stagnation of droplets (water droplets) becomes a rare frequency, and there is a possibility that the moisture that has entered the sub-passage cannot be sufficiently discharged.

  In the present embodiment, the recess 333e is provided in the low flow velocity region 704 of the passage portion of the second passage 702, and the drain hole 376 is provided in the recess 333e where the droplet is most likely to stagnate. Can be discharged. Further, it is possible to prevent the measured gas 30 in the sub passage from being excessively discharged to the main passage 124 and to reduce the influence on the measurement of the flow rate detection unit 602. Therefore, moisture that has entered the auxiliary passage can be efficiently discharged without reducing the flow velocity of the gas to be measured that passes through the flow rate detection unit 602.

  In the present embodiment, the configuration in which the drain hole 376 is provided in the back cover 304 has been described, but the present invention is not limited to this configuration, and may be provided in a place where liquid droplets are likely to stagnate. A drain hole 376 may be provided in the housing 302 so as to communicate with the front side sub-passage.

<Example 2>
Next, a second embodiment of the present invention will be described. FIG. 7 is an explanatory view of a thermal type flow meter showing Example 2 of the present invention, FIG. 7A is a front view showing a state inside the auxiliary passage, and FIG. 7B is a cross-sectional view taken along line BB of FIG. 7A. FIG. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The sub-passage is configured by cooperation of the housing 302 and the back cover 304, and includes a first passage 711 and a second passage 712 that branches from the first passage 711. As shown in FIG. 7A, the first passage 711 extends from the inlet 711a toward the outlet 711b, and the second passage 712 branches from the first passage 711 toward the flow rate detector 602, and the flow rate detector 602. After passing through, the first passage 711 joins again.

  The first passage 711 is provided in a straight line between the upstream end portion 317 and the downstream end portion 318 so as to extend along the main flow direction of the measurement target gas 30 in the main passage 124. The second passage 712 diverges from the first passage 711, is turned toward the upstream end 317 of the housing 302, and moves from the downstream side in the main flow direction of the measurement target gas 30 toward the upstream side. A passage-shaped passage portion that curves in a direction away from the passage. The passage portion of the second passage 712 is curved so as to move toward the proximal end side of the housing 302 as it moves toward the upstream end portion 317.

  In the passage portion of the second passage 712, the flow of the gas to be measured 30 is biased to the inside of the curve due to the shape of the passage, the flow velocity inside the curve becomes faster than the flow velocity outside the curve, and the gas to be measured in the passage portion of the second passage 712 The maximum flow velocity point Vmax of 30 is biased to the inside of the curve. The low flow rate is low at the position outside the curve of the passage portion of the second passage 712, that is, on the side opposite to the maximum flow velocity point Vmax of the gas to be measured via the flow path center CL of the passage portion of the second passage 712. A flow velocity region 714 is formed. In addition, the low flow velocity area | region 714 shown by hatching in FIG. 7A is shown notionally, and does not show an actual area | region strictly.

  The first passage 711 discharges foreign matter that has entered the sub-passage using the inertia effect, but it is difficult to discharge all foreign matter that has entered the sub-passage, and part of the foreign matter is also present in the second passage 712. invade. Among the foreign matters that have entered the second passage 712, moisture in particular does not have a sufficient flow rate to move in the low flow velocity region 714, and may stagnate in the second passage 712.

  Therefore, in order to efficiently drain the water stagnating in the second passage 702, the second passage 712 is positioned on the opposite side of the maximum flow velocity point Vmax of the gas to be measured via the flow path center CL of the second passage 712. A drainage hole 376 communicating with the main passage 124 is provided in the low flow velocity region 714. In the present embodiment, a recess 333e is provided on the side wall surface 333h outside the curve of the second passage 712 in the low flow velocity region 714, and the drain hole 376 of the back cover 304 communicates with the recess 333e.

  Since the recess 333 e is provided in the low flow velocity region 714, the flow rate of the measurement target gas 30 in the recess 333 e is very small compared to the flow rate in the second passage 712. Therefore, the droplet (water droplet) that has entered the bypass is the most likely area of stagnation. Therefore, by providing the drain hole 376 in the vicinity where the water droplets are stagnating, the water taken into the recess 333e can be discharged to the main passage 124 through the drain hole 376 (see FIG. 7B).

  Therefore, it is possible to prevent the water stagnating in the second passage 712 from passing through the second passage 712 and reaching the flow rate detection unit 602 as a large water mass. In addition, it is possible to prevent moisture stagnating in the second passage 712 from reducing the flow area of the second passage 712 and affecting the flow rate detection in the flow rate detection unit 602.

  In this embodiment, the drain hole 376 is provided in the back cover 304 and communicated with the main passage 124. However, the present invention is not limited to such a configuration, and the liquid droplet is likely to stagnate. For example, the drain hole 376 may be configured to communicate with the downstream portion of the second passage 712.

<Example 3>
Next, Embodiment 3 of the present invention will be described. FIG. 8 is an explanatory view of a thermal type flow meter showing Example 3 of the present invention, FIG. 8A is a front view showing the state inside the sub-passage, and FIG. 8B is a cross-sectional view taken along line BB of FIG. FIG. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The sub-passage has a back-side sub-passage 721 and a front-side sub-passage (not shown). The sub-passage passes through the back-side sub-passage 721 and the front-side sub-passage from the inlet 721 a that opens at the upstream end 317 of the housing 302. It has a shape that continues in a loop until the outlet 721b that opens to the end 318. As shown in FIG. 8A, the back side sub-passage 721 moves from the upstream side to the downstream side along the main flow direction of the measurement target gas 30 flowing through the main passage 124 with respect to the main flow direction of the measurement target gas 30. It has a passage-shaped passage portion that curves in a direction in which the intersection angle gradually increases. The passage portion of the back side sub-passage 721 is curved so as to move toward the base end side of the housing 302 as it moves from the upstream end portion 317 of the housing 302 toward the downstream end portion 318.

  In the back side sub-passage 721, the flow of the gas 30 to be measured is biased to the outside of the curve due to the shape of the passage, the flow velocity outside the curve becomes faster than the flow velocity inside the curve, and the maximum flow velocity point Vmax of the gas 30 to be measured in the back side sub-passage 721. Is biased to the outside of the curve. A low flow velocity region 724 with a low flow velocity is formed inside the curve of the back side sub-passage 721, that is, on the opposite side of the maximum flow velocity point Vmax of the gas to be measured through the flow path center CL of the backside sub-passage 721. The In addition, the low flow velocity area | region 724 shown by hatching in FIG. 8A is shown notionally, and does not show an actual area | region strictly.

  The back side sub-passage 721 discharges foreign matter that has entered the sub-passage using centrifugation, but it is difficult to completely discharge all foreign matter that has entered the sub-passage. Among them, in particular, moisture does not have a sufficient flow rate to move in the low flow rate region 724 and may stagnate in the back side sub-passage 721.

  In the back side sub-passage 721, a drain hole 376 communicating with the main passage 124 is provided in the low flow rate region 724 located on the opposite side of the maximum flow rate point Vmax of the gas to be measured via the flow path center CL of the back side subpassage 721. . In the present embodiment, a recess 333e is provided on the side wall surface 333b inside the curve of the back side sub-passage 721 in the low flow velocity region 724, and the drain hole 376 of the back cover 304 communicates with the recess 333e.

  Since the recess 333e is provided in the low flow velocity region 724, the flow rate of the measurement target gas 30 in the recess 333e is very small compared to the flow rate in the back side sub-passage 721. Therefore, the droplet (water droplet) that has entered the bypass is the most likely area of stagnation. Therefore, by providing the drain hole 376 in the vicinity where the water droplets are stagnating, the water taken into the recess 333e can be discharged to the main passage 124 through the drain hole 376 (see FIG. 8B).

  Therefore, it is possible to prevent the water remaining in the back side sub-passage 721 from passing through the back side subpassage 721 and reaching the flow rate detection unit 602 as a large water mass. In addition, it is possible to prevent the water stagnating in the back side sub-passage 721 from affecting the flow rate detection in the flow rate detection unit 602 by narrowing the flow area of the back side sub-passage 721.

  In this embodiment, the drain hole 376 is provided in the back cover 304 and communicated with the main passage 124. However, the present invention is not limited to such a configuration, and the liquid droplet is likely to stagnate. What is necessary is just to provide, for example, it is good also as a structure which connects the drain hole 376 to a front side subway not shown.

<Example 4>
Next, a fourth embodiment of the present invention will be described. FIG. 9 is an explanatory view of a thermal type flow meter showing Example 4 of the present invention, FIG. 9A is a front view showing a state inside the sub-passage, and FIG. 9B is a cross-sectional view taken along line BB in FIG. 9A. FIG. The same components as those in the second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The sub-passage 731 is configured by the cooperation of the housing 302 and the back cover 304, and has an Ω shape from an inlet 731 a that opens to the upstream end 317 of the housing 302 to an outlet 731 b that opens to the downstream end 318 of the housing 302. It has a shape that curves and detours.

  As shown in FIG. 9A, the secondary passage 731 has an upstream portion 732 and a downstream portion 733, and the upstream portion 732 is a straight line extending linearly from the inlet 731 a toward the downstream end 318 of the housing 302. And a passage in the shape of a passage that is folded back toward the upstream end 317 of the housing 302 at the downstream end of the straight portion and curves away from the straight portion as it moves from the downstream in the main flow direction toward the upstream. Has a part. The passage portion of the upstream portion 732 curves so as to shift to the proximal end side of the housing 302 as it moves from the straight portion to the upstream end portion 317 side. The passage portion of the upstream portion 732 has a shape that curves in a direction in which the intersecting angle of the measurement target gas 30 with respect to the main flow direction gradually increases as it moves from the downstream side to the upstream side in the main flow direction.

  The downstream portion 733 advances from the upstream end portion 317 side toward the downstream end portion 318 side on the proximal end side of the housing 302, and a flow rate detection unit 602 is disposed in the middle thereof, and the downstream end of the housing 302 is located further than the flow rate detection unit 602. It bends toward the front end of the housing 302 at a position near the portion 318, bends toward the downstream side in the main flow direction at the front end of the housing 302, and communicates with the outlet 731b.

  In the upstream portion 732, the flow of the gas to be measured 30 is biased to the inside of the curve due to the shape of the passage, the flow velocity inside the curve becomes faster than the flow velocity outside the curve, and the maximum flow velocity point Vmax of the gas to be measured 30 in the upstream portion 732 is Deviations inside the curve. A low flow velocity region 734 having a low flow velocity is formed outside the curve of the upstream portion 732, that is, on the opposite side of the maximum flow velocity point Vmax of the gas to be measured via the flow path center CL of the upstream portion 732. In addition, the low flow velocity area | region 734 shown by hatching in FIG. 9A is shown notionally, and does not show an actual area | region strictly.

  The upstream portion 732 discharges foreign matter that has entered the sub-passage 731 using centrifugation, but it is difficult to completely discharge all foreign matter that has entered the sub-passage 731, and the foreign matter that has entered the upstream portion 732 is difficult to remove. In particular, moisture does not have a sufficient flow rate to move in the low flow rate region 734 and may stagnate in the upstream portion 732.

  In the upstream portion 732, a drain hole 376 that communicates with the main passage 124 is provided in the low flow velocity region 734 that is located on the opposite side of the maximum flow velocity point Vmax of the measured gas 30 via the flow path center CL of the upstream portion 732. In the present embodiment, a recess 333e is provided on the side wall surface 333h outside the curve of the upstream portion 732 in the low flow velocity region 734, and the drain hole 376 of the back cover 304 communicates with the recess 333e.

  Since the recess 333 e is provided in the low flow velocity region 734, the flow rate of the measurement target gas 30 in the recess 333 e is very small compared to the flow rate in the upstream portion 732. Therefore, the droplet (water droplet) that has entered the bypass is the most likely area of stagnation. Therefore, by providing the drain hole 376 in the vicinity where the water droplets are stagnating, the moisture taken into the recess 333e can be discharged to the main passage 124 through the drain hole 376 (see FIG. 9B).

  Therefore, it is possible to prevent the water stagnating in the upstream portion 732 from passing through the upstream portion 732 and reaching the flow rate detection portion 602 as a large water mass. In addition, it is possible to prevent moisture stagnating in the upstream portion 732 from reducing the flow area of the upstream portion 732 and affecting the flow rate detection in the flow rate detection unit 602.

  In this embodiment, the drain hole 376 is provided in the back cover 304 and communicated with the main passage 124. However, the present invention is not limited to such a configuration, and the liquid droplet is likely to stagnate. For example, the drain hole 376 may be configured to communicate with the downstream portion 733.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

300 Thermal flow meter 302 Housing 303 Front cover 304 Back cover 333b, 333h Side wall surface (passage wall surface)
333e Concave portion 376 Drain hole 602 Flow rate detecting portion 731 Sub passage 701, 711 First passage 702, 712 Second passage 704, 714, 724, 734 Low flow velocity region CL Center of flow passage

Claims (7)

A thermal flow rate comprising: a sub-passage that takes in the gas to be measured flowing through the main passage; and a flow rate detection unit that measures the flow rate of the gas under measurement by transferring heat between the gas to be measured flowing through the sub-passage. It is a total,
The sub-passage has a passage-shaped passage portion in which the maximum flow velocity point of the measured gas deviates from the center of the flow path, and the maximum flow velocity of the measured gas passes through the flow path center in the passage portion. A recess is provided at a position opposite to the point ,
A thermal flowmeter, wherein a drainage hole is provided in the recess . The sub-passage has a first passage extending along a main flow direction of the gas to be measured flowing through the main passage, and a second passage branched from the first passage toward the flow rate detection unit. ,
The second passage has the passage portion, and the passage portion curves in a direction away from the first passage as the measurement target gas moves from the upstream side toward the downstream side in the main flow direction. Has a shape,
The thermal flow meter according to claim 1 , wherein the recess is formed in a passage wall surface inside the curve of the passage portion. The sub-passage has a first passage extending along a main flow direction of the gas to be measured flowing through the main passage, and a second passage branched from the first passage toward the flow rate detection unit. ,
The second passage has the passage portion, and the passage portion curves in a direction away from the first passage as it moves from the downstream side in the main flow direction of the measurement target gas toward the upstream side. Has a shape,
The thermal flow meter according to claim 1 , wherein the concave portion is formed on a passage wall surface outside the curve of the passage portion. The passage portion has a passage shape that curves in a direction in which an intersection angle with respect to the main flow direction gradually increases as the gas to be measured flowing through the main passage moves from the upstream side to the downstream side along the main flow direction. Have
The thermal flow meter according to claim 1 , wherein the recess is formed in a passage wall surface inside the curve of the passage portion. The sub-passage has a linear portion which moves along the flow direction of the measurement gas flowing through said main passage, is folded back toward the upstream side from the main flow direction downstream side of the object to be measured gas at the downstream end of the straight portion , Having a passage shape that curves in a direction away from the linear portion as it moves toward the upstream side in the main flow direction of the gas to be measured,
The thermal flow meter according to claim 1 , wherein the recess is formed on a passage wall surface outside the curve of the passage portion. A housing disposed inside the main passage, and a cover attached to the housing;
The drainage holes, the thermal type flow meter according to claims 1, characterized in that in communication between the main passage and the recess is formed in the cover to one of the claims 5 . The drainage holes, said auxiliary passage thermal flow meter as claimed in any one of claims 5, characterized in that said communicates with the downstream position than the flow rate detecting part of.

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