JP2017083319A - Thermal type flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal type flowmeter having a structure that secures smooth discharge of a measuring gas from an outlet without subjected to the vortex of the measuring gas generated at the downstream side of a housing and is capable of suppressing generation of pulsation error.SOLUTION: In a thermal type flowmeter 300 of the present invention, a housing 302 is disposed in a main passage 124 where a measuring gas 30 flows. The thermal type flowmeter takes in the measuring gas 30 from the main passage 124 into a sub passage 307 provided with the housing 302 to measure the flow rate of the measuring gas 30 by a flow rate detection section 602 disposed in the sub passage 307, and has a configuration such that the main flow direction of the measuring gas 30 flowing in the main passage 124 and the discharge direction of the measuring gas 30 discharged from the sub passage 307 define an angle of 0°<β<90°.SELECTED DRAWING: Figure 6B

Description

  The present invention relates to a thermal flow meter.

  Conventionally, a housing is arranged in the main passage through which the gas to be measured flows, the gas to be measured is taken from the main passage into the sub passage provided in the housing, and the flow rate of the gas to be measured is measured by the flow rate detection unit arranged in the sub passage. Various thermal flow meters for measuring have been proposed.

  In Patent Document 1, the sub-passage has a first passage along the flow direction of the main passage and a second passage that branches in the middle of the first passage, and a flow rate detector is disposed in the second passage, A structure is shown in which the gas to be measured that has passed through the flow rate detection unit joins the first passage again and is discharged from the outlet of the first passage.

US2013 / 0061684

  In the case of the structure in which the gas to be measured is discharged from the outlet of the first passage toward the downstream of the housing as in the structure shown in Patent Document 1, the gas to be measured discharged from the outlet of the first passage and the downstream of the housing The generated vortex may interfere and smooth discharge from the outlet of the gas to be measured may be hindered. In addition, the change in the vortex intensity increases the flow velocity distribution difference between the steady state and the pulsation, and a pulsation error occurs.

  The present invention has been made in view of the above points, and the object of the present invention is to make it possible to smoothly measure the gas to be measured from the outlet without being affected by the vortex of the gas to be measured generated on the downstream side of the housing. The object is to provide a thermal flow meter having a structure capable of ensuring discharge and suppressing the occurrence of pulsation errors.

  In the thermal flow meter of the present invention that solves the above-described problems, a housing is disposed in a main passage through which a gas to be measured flows, and the gas to be measured is taken from the main passage into the sub passage provided in the housing, and is disposed in the sub passage. A thermal flow meter that measures the flow rate of the gas to be measured by the flow rate detection unit, the main flow direction of the gas to be measured flowing through the main passage and the discharge direction of the gas to be measured discharged from the sub-passage The angle β has a configuration in which 0 ° <β <90 °.

  According to the present invention, avoiding interference between the gas to be measured discharged from the sub-passage and the airflow vortex generated downstream of the housing, ensuring smooth discharge from the outlet of the gas to be measured, during pulsation and during steady state It is possible to reduce the difference in flow velocity distribution at, and reduce pulsation error. 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. 1 is an external perspective view of a thermal flow meter in Embodiment 1. FIG. FIG. 6B is a sectional view taken along line BB in FIG. 6A. FIG. 4 is an external perspective view of a thermal flow meter in Embodiment 2. FIG. 7B is a sectional view taken along line BB in FIG. 7A.

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

<Example 1>
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, the intake air is sucked from the air cleaner 122 as the measurement target gas 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 from the side 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 vertical direction intersecting the main flow direction v1 of the gas to be measured flowing through the main passage 124. The The housing 302 is provided with a sub-passage 307 (see FIGS. 3A and 3B) for taking in the gas under measurement 30 flowing through the main passage 124, and the flow rate of the gas under measurement 30 is detected in the sub-passage 307. A flow rate detection unit 602 (see FIG. 3A) is arranged.

  An inlet 311 for taking a part of the measurement target gas 30 such as intake air into the sub-passage 307 is provided at the upstream end portion disposed on the distal end side of the housing 302 and on the upstream side in the main flow direction. The first end 312 (exhaust port) for returning the gas 30 to be measured from the sub-passage 307 to the main passage 124 is 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. Two outlets, two outlets (main outlet) 313, are provided. 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. That is, the first outlet 312 and the second outlet 313 are arranged side by side in a direction perpendicular to the main flow direction v1.

  By providing the inlet 311 on the distal end side of the housing 302, a gas in a portion near the center portion away from the inner wall surface of the main passage 124 can be taken into the sub-passage 307. Therefore, it becomes difficult to be influenced by the temperature of the inner wall surface of the main passage 124, and a decrease in the measurement accuracy of the gas flow rate and temperature can be suppressed.

  In the vicinity of the inner wall surface of the main passage 124, the fluid resistance is large, and the flow velocity is lower than the average flow velocity of the main passage 124. However, in the thermal type flow meter 300 of this embodiment, the direction from the flange 305 toward the center of the main passage is increased. Since the inlet 311 is provided at the distal end side of the thin and long housing 302 that extends in a long way, the gas having a high flow velocity at the center of the main passage 124 can be taken into the sub-passage 307. In addition, since the first outlet 312 and the second outlet 313 of the sub-passage 307 are also provided on the distal end side of the housing 302, the gas flowing in the sub-passage 307 can be returned to the center of the main passage 124 having a high flow velocity. it can.

  The housing 302 has a substantially rectangular wide surface on the front side, but has a narrow side surface (thin thickness). The front surface and the rear surface of the housing 302 are disposed along the main flow direction v1 of the measurement target gas 30 flowing through the main passage 124, and the side surfaces are disposed so as to face the main flow direction v1. Thus, the thermal flow meter 300 can be provided with a sufficiently long sub-passage 307 with a reduced fluid resistance with respect to the gas to be measured 30.

  That is, in the thermal type 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 the first direction 50 ( 2B) and a thickness dimension defined in a second direction 51 perpendicular to the first direction 50 on the orthogonal plane, and the thickness dimension is The shape is smaller than the length dimension.

  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 detector 452 has a shape that protrudes from the recessed portion of the housing 302 along the main flow direction v1.

  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.

  The upstream end portion 315 of the housing 302 has a base end portion 315a, an intermediate portion 315b, and a distal end portion 315c. The base end portion 315a, the intermediate portion 315b, and the tip end portion 315c are configured by flat surfaces that are perpendicular to the main flow direction v1 of the measurement target gas 30, respectively. Between the base end portion 315a and the intermediate portion 315b, there is a tapered surface 322 that expands in a direction away from each other in the thickness width direction of the housing 302 as it moves from the upstream end portion 315 side toward the downstream end portion 316 side. Is provided. And between the taper surface 322 and the intermediate part 315b, the hollow part recessed in the downstream end part 316 side is provided, and the temperature detection part 452 is arrange | positioned. An inlet 311 is provided at the tip 315c.

  The downstream end portion 316 of the housing 302 has a base end portion 316a, an intermediate portion 316b, and a distal end portion 316c. The proximal end portion 316a, the intermediate portion 316b, and the distal end portion 316c are configured by flat surfaces perpendicular to the main flow direction v1 of the measurement target gas 30. Between the base end portion 316a and the intermediate portion 316b, a tapered surface 323 that becomes narrower in a direction approaching each other in the thickness width direction of the housing 302 as it moves from the upstream end portion 315 side toward the downstream end portion 316 side. Is provided. A first outlet 312 and a second outlet 313 are provided at the tip 316c. The first outlet 312 and the second outlet 313 are arranged side by side in the thickness width direction of the housing 302. In this embodiment, the first outlet 312 and the second outlet 313 are separated from the center in the thickness width direction to one side and the other side in the thickness direction of the housing 302. Further, they are arranged at positions separated from each other.

  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 307. In this 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, thereby completing the sub-passage 307. Yes. 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 330 and the back side sub-passage groove 331 are part of the housing 302. All can be molded as a part.

  The auxiliary passage groove includes a rear side auxiliary passage groove 331 formed on the back surface of the housing 302 and a front side auxiliary passage groove 330 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 portion 332 extends in a straight line from the upstream end portion 315 to the downstream end portion 316 along the main flow direction v <b> 1 of the measurement target gas 30 at the distal end portion of the housing 302, and the inlet 311 of the housing 302. One end communicates with the first outlet 312 of the housing 302 and the other end communicates with the first outlet 312 of the housing 302. The first groove portion 332 includes a straight portion 332A extending from the inlet 311 with a substantially constant cross-sectional shape, and a throttle portion 332B in which the groove width gradually decreases as it moves from the straight portion 332A toward the first outlet 312. ing.

  The straight portion 332A of the first groove portion 332 has a substantially constant groove depth, and the bottom wall surface 332b of the straight portion 332A extends in parallel along the main flow direction v1 of the measurement target gas 30 flowing through the main passage 124. It is arranged to exist. The throttle part 332B of the first groove part 332 is formed so that the groove depth gradually decreases as it moves from the straight part 332A toward the first outlet 312, and the bottom wall surface 332c of the throttle part 332B (see FIG. 6B). Is inclined with respect to the main flow direction v1. The bottom wall surface 332c of the throttle portion 332B is the thickness of the housing 302 from the center in the width direction of the housing 302 as it moves downstream in the main flow direction of the measurement target gas 30 at the downstream end of the sub-passage 307. The 1st inclined surface which moves toward the back surface side which is a direction one side is formed.

  A plurality of ridges 335 are provided on the bottom wall surface 332c of the straight portion 332A of the first groove portion 332. On the bottom wall surface 332c of the straight portion 332A of the first groove portion 332, a plurality of protrusions 335 are provided so as to be arranged at predetermined intervals in the groove width direction of the first groove portion 332, and along the straight portion 332A. It extends from the inlet 311 to the boundary with the throttle 332B. The protruding portion 335 has a trapezoidal cross section, and the side surfaces on both sides are inclined obliquely. Therefore, when a water droplet adheres, the contact angle of the water droplet can be increased to reduce the height of the water droplet, the wettability can be increased, and the water can flow quickly from the upstream side toward the downstream side. Therefore, it is possible to effectively prevent water droplets from flowing into the second passage, and to quickly discharge the water droplets to the outside.

  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 332c 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 v1 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) has a 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 the above, it can be discharged from the recess 333e in the sub-passage 307 to the outside of the sub-passage 307, that is, the main passage 124 via 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 from the downstream side of the secondary passage of the measurement flow path 341 into the front side secondary passage groove 330. It flows through 330 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 330 communicates with the downstream side of the sub-passage of the measurement flow channel 341, and other than the second outlet 313 formed at the downstream end 316 on the front end side of the housing 302. The end communicates. The front side sub-passage groove 330 curves so as to gradually advance toward the downstream end portion 316 as it moves from the measurement flow path 341 toward 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.

  The front side sub-passage groove 330 has an upstream portion 330A, a midstream portion 330B, and a downstream portion 330C in order from the measurement flow path 341 toward the second outlet 313. The upstream portion 330 </ b> A and the middle flow portion 330 </ b> B of the front side sub-passage groove 330 have a substantially constant groove width, and the downstream portion 330 </ b> C has a throttle shape in which the groove width gradually decreases as it moves toward the second outlet 313. have. The upstream portion 330A of the front side sub-passage groove 330 gradually decreases in depth as it moves downstream, and the midstream portion 330B has a substantially constant groove depth that smoothly continues to the downstream end of the upstream portion 330A. The bottom wall surface 330a (see FIG. 6B) of the midstream portion 330B is disposed so as to extend in parallel along the main flow direction v1 of the measurement target gas 30 flowing through the main passage 124.

  The downstream portion 330C is formed such that the groove depth gradually decreases as it moves from the downstream end of the midstream portion 330B toward the second outlet 313, and the bottom wall surface 330b of the downstream portion 330C (see FIG. 6B). Are arranged so as to be inclined with respect to the main flow direction v1. The bottom wall surface 330b of the downstream portion 330C is located at the downstream end portion of the sub-passage 307 and moves from the central side in the width direction of the housing 302 toward the downstream side in the main flow direction of the gas 30 to be measured. The 2nd inclined surface which moves toward the front side which is the other side of a direction is formed.

  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 that is the flange 305 side, and at the position closest to the flange 305, the sub-passage 307 is located. The gas 30 to be measured flows in a direction opposite to the main flow direction v1 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. To the front side subway.

  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 330 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 of the side wall on the upper side of the pair of side walls constituting the front side sub-passage groove 330 and the facing surface of the front cover 303 are in close contact with each other. The rear 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 opposing 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, a terminal connection portion that connects the connection terminal 412 of the circuit package 400 and the inner end 306 a of the external terminal of the external connection portion 306 is 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 to 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. 5A is a view showing the back surface of the back cover, and FIG. 5B is a cross-sectional view taken along the line BB of FIG. 5A.

  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 opposing surface of the front cover 303, a fifth region 361 that closes the front side sub-passage groove 330 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 the surface is formed. Further, on both sides in the width direction of the fifth region 361 and the sixth region 362, concave portions 361a into which the upper end portions of the side walls of the front side sub-passage grooves 330 of the housing 302 enter are provided. In addition, a recess 363 a into which the outer peripheral end of the cavity 342 enters is formed around the seventh region 363.

  A convex portion 364 that is inserted into a gap between the front end of the channel exposure portion 430 of the circuit package 400 and the measurement channel 341 of the housing 302 is provided on the facing surface of the front cover 303. 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 opposite surface of the back cover 304, a first region 371 A that closes the first groove portion 332 of the back side sub-passage groove 331 of the housing 302, a second region 371 B that closes the second groove portion 333, and the measurement flow of the housing 302 A third region 372 that closes the back side of the path 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.

  A convex strip portion 377 is provided in the first region 371A of the back cover 304. In the first region 371A of the back cover 304, the ridges 377 are provided so as to extend along the longitudinal direction and to be arranged at a predetermined interval in the lateral direction. The cross section of the protruding line portion 377 has a trapezoidal shape, and the side surfaces on both sides are inclined obliquely. Therefore, when water droplets adhere, the contact angle of the water droplets can be increased to reduce the height of the water droplets, the wettability can be increased, and the adhered water droplets can flow quickly from the upstream side toward the downstream side. Can do. Therefore, it is possible to effectively prevent water droplets from flowing into the second passage, and to quickly discharge the water droplets to the outside.

  A drainage hole 376 communicating with the sub passage 307 is formed in the back cover 304. 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 is taken into the recess 333e of the second groove 333 in the sub-passage 307. Water can be discharged to the outside.

  On the opposite surface of the back cover 304, a convex portion 374 is provided that is inserted into 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. 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 respectively attached to the front surface and the back surface of the housing 302, and form a secondary passage 307 in cooperation with the front side secondary passage groove 330 and the back side secondary passage groove 331.

  6A is an external perspective view of the thermal type flow meter in the first embodiment, and FIG. 6B is a cross-sectional view taken along line BB in FIG. 6A.

  A curved surface portion 317 is provided at the downstream end portion 316 of the housing 302. The curved surface portion 317 is provided in the vicinity of the first outlet 312 and the second outlet 313, and is arranged at a position between the intermediate portion 316b and the distal end portion 316c of the downstream end portion 316 in the present embodiment. The curved surface portion 317 has a curved surface shape whose axis is the longitudinal direction in which the housing 302 extends. Specifically, the curved surface portion 317 has a streamline shape whose cross section is a convex arc curve. The curved surface portion 317 is an inclined surface in which an angle formed between the normal vector and the main flow direction v1 of the measurement target gas 30 is in an angle range of 0 ° <α <90 °, and upstream of the measurement target gas 30 in the main flow direction. There are curved surfaces 317R and 317L in which the angle formed between the normal vector and the main flow direction v1 of the measurement target gas 30 gradually decreases as it moves from the side to the downstream side.

  The curved surfaces 317R and 317L of the curved surface portion 317 have a shape in which at least one curved surface having a radius of curvature smoothly continues, and a substantially constant cross-sectional shape between the intermediate portion 316b and the tip portion 316c. have. The downstream end is formed so as to be flush with the intermediate portion 316 b and the tip end portion 316 c of the downstream end portion 316 of the housing 302.

  A first outlet 312 and a second outlet 313 are provided at the downstream end 316 of the housing 302. The first outlet 312 and the second outlet 313 are disposed at positions separated from one side and the other side in the thickness direction of the housing 302 at the distal end 316 c of the downstream end 316. The throttle portion 332B of the first groove portion 332 communicating with the first outlet 312 is shifted from the central side in the thickness width direction of the housing 302 to the one side in the thickness direction of the housing 302 as it moves downstream in the main flow direction of the measurement target gas 30. The bottom wall surface 332c (first inclined surface) is inclined so as to approach the back cover 304. The inclination angle of the bottom wall surface 332c is set to 0 ° <β <90 °. Therefore, the gas to be measured 30 passing through the throttle portion 332B of the first groove portion 332 is deflected in a direction approaching the back cover 304 from the center side in the thickness direction of the housing 302 as it flows downstream through the throttle portion 332B. The first outlet 312 is discharged. The gas 30 to be measured discharged from the first outlet 312 has an angle between the discharge direction v2 and the main flow direction v1 of the gas 30 to be measured flowing through the main passage 124 is 0 ° <β <90 °.

  The downstream portion 330C of the front side sub-passage groove 330 that communicates with the second outlet 313 moves from the central side in the thickness width direction of the housing 302 toward the other side in the thickness direction of the housing 302 as it moves downstream in the main flow direction of the gas 30 to be measured. It has a bottom wall surface 330b (second inclined surface) inclined so as to approach the front cover 303 which is the side. The inclination angle of the bottom wall surface 330b is set to 0 ° <β <90 °. Accordingly, the gas to be measured 30 passing through the downstream portion 330C of the front side sub-passage groove 330 is deflected in the direction approaching the front cover 303 from the thickness direction center side of the housing 302 as it flows downstream through the downstream portion 330C. And is discharged from the second outlet 313. The gas 30 to be measured discharged from the second outlet 313 has an angle between the discharge direction v2 and the main flow direction v1 of the gas 30 to be measured flowing through the main passage 124 is 0 ° <β <90 °.

  For example, in the case of a physical quantity measuring device having a structure in which a part of the sub-passage 307 is branched in order to discharge the pollutant as in the present embodiment, it is necessary to increase the flow velocity and discharge effect to ensure measurement accuracy. (A) If the discharge port is not opened toward the downstream side in the main flow direction, there is a possibility that dirt is collected at the corner. (B) If the branch passage is not as large as possible, the flow cannot bend completely, and the separation vortex expands to increase the difference in flow velocity distribution between the steady flow and the pulsating flow, so that the pulsation error increases. (C) If the main outlet is disposed upstream of the branching portion in the main flow direction, the flow around the flow rate detection unit 602 overshoots or undershoots during a transient flow rate change, and it is difficult to accurately measure the flow rate change. . For the reasons of (a), (b), and (c), the discharge port (corresponding to the first outlet 312) and the main outlet (corresponding to the second outlet 313) are located downstream of the branch portion in the main flow direction and It is desirable to arrange at the downstream end of the housing.

  However, by arranging the housing in the intake pipe (main passage), a vertical vortex having an axis parallel to the extending direction of the housing, called a Karman vortex, is generated around the downstream end of the housing, A lateral vortex having an axis perpendicular to the extending direction of the housing, called a tip vortex, is also generated. Therefore, these vortices interfere with the measurement target gas 30 discharged from the discharge port and the main outlet, and smooth discharge may be hindered. In addition, these vortices change the strength of the vortex due to a transient phenomenon such as a pulsating flow in the intake passage, so the degree to which the outlet and the main outlet arranged at the downstream end of the housing are shielded by the vortex changes. Depending on the degree of the change, the flow velocity distribution difference between the steady state and the pulsation increases, and a pulsation error occurs.

  On the other hand, in this embodiment, the angle formed between the main flow direction v1 of the measurement target gas 30 flowing through the main passage 124 and the discharge direction v2 of the measurement target gas 30 discharged from the first outlet 312 and the second outlet 313. Since the configuration is such that 0 ° <β <90 °, the vortex generated on the downstream side of the first outlet 312 and the second outlet 313 of the housing 302 by discharging the measurement target gas 30 obliquely from the housing 302. The axis of can be avoided. Accordingly, it is possible to prevent interference between the vortex generated on the downstream side of the housing 302 and the measurement target gas 30 discharged from the first outlet 312 and the second outlet 313. Therefore, the smooth discharge of the gas 30 to be measured from the first outlet 312 and the second outlet 313 is ensured without being influenced by the vortex, and the difference in flow velocity distribution between the pulsation and the steady state is reduced to generate the pulsation error. It can suppress and can improve measurement accuracy.

  Further, in the present embodiment, a curved surface portion 317 having a curved surface whose axial center extends along the extending direction of the housing 302 is provided in the vicinity of the first outlet 312 and the second outlet 313. The size of the vortex generated on the downstream side of the 312 and the second outlet 313 can be reduced, and in particular, the size of the vertical vortex (Kalman vortex) can be reduced. Therefore, the influence exerted by the vortex on the measurement target gas 30 discharged from the first outlet 312 and the second outlet 313 can be reduced. Therefore, the generation of pulsation errors can be further suppressed, and the measurement accuracy can be improved.

  In the present embodiment, the configuration example in which the curved surface portion 317 is provided in the downstream end portion 316 of the housing 302 has been described in the present embodiment, but the configuration without the curved surface portion 317 may be used. In the present embodiment, the case where the sub-passage 307 has two outlets, that is, the first outlet 312 and the second outlet 313 has been described as an example. Any gas can be used as long as the gas 30 to be measured can be discharged obliquely so as to avoid the axis of the generated vortex. For example, one outlet may be provided.

<Example 2>
Next, Embodiment 2 of the present invention will be described below with reference to FIGS. 7A and 7B.
FIG. 7A is an external perspective view of the thermal type flow meter in the second embodiment, and FIG.

  What is characteristic in the present embodiment is that the first outlet 312 and the second outlet 313 are provided on the curved surface portion 317 of the downstream end 316 of the housing 302.

  In the present embodiment, the downstream end 316 of the housing 302 has a curved surface portion 317 extending from the intermediate portion 316 b to the tip of the housing 302, and the first outlet is formed on the curved surface on one side in the thickness direction of the housing 302. 312 is arranged, and the second outlet 313 is arranged on the curved surface on the other side in the thickness direction. Then, the measurement target gas 30 is discharged obliquely from the first outlet 312 toward one side in the thickness direction, and the measurement target gas 30 is discharged obliquely from the second outlet 313 toward the other side in the thickness direction. It has become.

  According to such a configuration, the curved surface portion 317 can further reduce the size of the vortex generated on the downstream side of the first outlet 312 and the second outlet 313 as compared with the first embodiment. Therefore, compared with Example 1, the influence of the vortex can be further reduced, the occurrence of pulsation error can be effectively suppressed, and the measurement accuracy can be greatly improved.

  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 307 Sub-pass 312 First outlet 313 Second outlet 317 Curved surface portion 330b Bottom wall surface (second inclined surface)
332c Bottom wall surface (first inclined surface)
602 Flow rate detector

Claims (5)

Heat that measures the flow rate of the gas to be measured by the flow rate detector installed in the sub-passage, the housing being placed in the main passage through which the gas to be measured flows, Type flow meter,
A thermal type characterized in that an angle formed by a main flow direction of the gas to be measured flowing through the main passage and a discharge direction of the gas to be measured discharged from the sub-passage satisfies 0 ° <β <90 °. Flowmeter. The housing has a predetermined thickness in a direction intersecting a main flow direction of the measurement target gas,
The sub-passage has an inclined surface that shifts from the central side in the thickness direction of the housing toward the outside as it moves downstream in the main flow direction of the measurement target gas at the downstream end of the sub-passage. The thermal flow meter according to claim 1, wherein: The sub-passage has a first outlet and a second outlet at the downstream end of the housing and at positions separated from one side and the other side in the thickness direction of the housing,
The first outlet has a first inclined surface that moves from the thickness direction center side of the housing toward the thickness direction one side as it moves to the downstream side in the main flow direction of the measurement target gas,
The second outlet has a second inclined surface that shifts from the central side in the thickness direction of the housing toward the other side in the thickness direction as it moves downstream in the main flow direction of the gas to be measured. The thermal flow meter according to claim 2.   The thermal flow meter according to claim 3, wherein the housing has a curved surface in the vicinity of the first outlet and the second outlet.   The curved surface has a shape in which an angle formed by a normal vector of the curved surface and a main flow direction of the measurement target gas gradually decreases as the measurement target gas moves from an upstream side to a downstream side in the main flow direction. The thermal flow meter according to claim 4, wherein

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