Thermal flow meter

Abstract

Thermal flow meter, which includes the following: a secondary passage (307) configured to receive a portion of the fluid flowing in a main passage (124); and a flow rate measuring unit (451) arranged in the side passage (307), the side passage (307) comprising: a first passage (351) provided on a measuring surface side of the flow rate measuring unit (451); a second passage (352) provided on a rear surface side of the flow rate measuring unit (451); and a slope passage (361) which is provided on a downstream side in a forward direction of the fluid in the second passage (352) with respect to an outlet of the second passage (352), and the inclined passage (361) has a first inclined surface (371) on one side of the first passage (351) with respect to the flow rate measuring unit (451), wherein the first inclined surface (371) slopes from one side of the second passage (352) to the side of the first passage (351) with respect to the forward direction, wherein the inclined passage (361) has a second inclined surface (372) opposite the first inclined surface (371) in a direction perpendicular to a measuring surface (451a) of the flow rate measuring unit (451), and the second inclined surface (372) is inclined from the side of the second passage (352) to the side of the first passage (351) with respect to the forward direction, and wherein an inclination angle Θ2 of the second inclined surface (372) with respect to the forward direction is greater than an inclination angle Θ1 of the first inclined surface (371) with respect to the forward direction.

Description

Technical field

[0001] The present invention relates to a thermal flow meter. State of the art

[0002] A conventional thermal flow meter is known to be a flow meter comprising: a bypass arranged in a main passage through which fluid flows, wherein the bypass receives a portion of the fluid; a flow meter element arranged in the bypass, wherein the flow meter element is configured with a heating resistance pattern; and a support to which the flow meter element is attached (see, for example, claim 1 in patent literature 1).

[0003] The conventional flow meter comprises a first fluid passage section and a second fluid passage section. The first fluid passage section has a surface on which the flow meter is mounted and a passage forming a secondary passage area. The second fluid passage section has a surface on the side opposite the surface on which the flow meter is mounted and a passage forming a secondary passage area.

[0004] In the conventional flow meter, the passage forming a surface of the first fluid passage section, positioned on the upstream side of the fluid flow and opposite the flow meter, has an inclined surface that directs the fluid flow to the flow meter. The inclined surface has at least two sides facing in opposite directions.

[0005] The configuration allows dust to rebound on the inclined surface provided on the opposite surface on the upstream side with respect to the heating resistance pattern in the fluid passage section on the side of the heating resistance pattern, thus preventing the dust from flowing with the fluid flow to the heating resistance pattern. This allows the flow meter to be provided in a way that prevents damage or contamination of the flow meter element comprising the heating resistance pattern, and the flow meter itself exhibits excellent dust resistance in an unsteady flow field, such as a pulsating flow, and displays high reliability and virtually no characteristic error (see, for example, paragraph 0009 in patent reference 1).

[0006] Patent literature 2 discloses a sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel. The sensor arrangement comprises at least one sensor chip arranged in the channel for determining the parameter of the fluid medium. The sensor chip is mounted in a sensor carrier projecting into the channel. The sensor carrier has a leading edge arranged transversely to the flow of the fluid medium, which in turn has at least one turbulator configured to generate vortices in the flowing fluid medium in the region of the sensor carrier.

[0007] Patent literature 3 discloses a device for measuring a gas flow rate, comprising a tube body whose interior serves as a passage for a flowing gas to be measured. A housing, having a generally U-shaped bypass passage, is formed integrally with the tube body. A plate-shaped flow rate sensing element is arranged in a first passage of the bypass passage, wherein a passage restriction section is arranged in a second passage of the bypass passage downstream of the first passage in the flow direction.

[0008] Patent literature 4 discloses a protective device for a measuring element in a measuring device.

[0009] Patent literature 5 discloses an air mass meter for internal combustion engines with one measuring channel.

[0010] Patent literature 6 discloses a sensor device for detecting at least one flow property of a fluid medium, in particular for detecting the air flow in the intake tract or charge air tract of an internal combustion engine. List of known writings on patent literature Patent Literature 1: JP 2012-93203 A Patent literature 2: DE 10 2008 042 155 A1 Patent literature 3: DE 197 24 659 A1 Patent literature 4: DE 199 53 776 A1 Patent literature 5: DE 10 2011 051 196 A1 Patent literature 6: DE 10 2012 224 049 A1 Brief description of the invention: Technical problem

[0011] The conventional thermal flow meter has the disadvantage that the increase in the counterflow direction in the first fluid passage section due to the counterflow of the fluid during the pulsation of the fluid causes the flow rate to be measured by the flow meter element to fall below the actual flow rate, leading to an increase in the measurement error.

[0012] The present invention was made in consideration of the problem and an object of the present invention is to provide a thermal flow meter which makes it possible for the measurement error when fluid pulsates to fall below that of a conventional thermal flow meter. Solution to the problem

[0013] To solve this problem, the thermal flow meter of the present invention comprises: a secondary passage configured to receive a portion of the fluid flowing in a main passage; and a flow rate measuring unit arranged in the secondary passage. The secondary passage has: a first passage provided on a measuring surface side of the flow rate measuring unit; a second passage provided on a rear surface side of the flow rate measuring unit; and an inclined passage provided on a downstream side in a forward direction of the fluid in the second passage with respect to an outlet of the second passage.The inclined section has a first inclined surface on one side of the first section with respect to the flow rate measuring unit, the first inclined surface being inclined from one side of the second section to the side of the first section with respect to the forward direction. The second section has a second inclined surface relative to the first inclined surface in a direction perpendicular to a measuring surface of the flow rate measuring unit. The second inclined surface is inclined from the side of the second section to the side of the first section with respect to the forward direction. The angle of inclination of the second inclined surface with respect to the forward direction is greater than the angle of inclination of the first inclined surface with respect to the forward direction. Advantageous effects of the invention

[0014] According to the thermal flow meter of the present invention, even with counter-flowing fluid, a diversion from the first passage side to the side of the second passage can occur during fluid pulsation via the first inclined surface of the inclined passage, which is provided on the downstream side in the forward direction of the fluid in the second passage with respect to the outlet of the second passage. This arrangement allows the flow rate of the fluid flowing in the counter-flow direction in the first passage to fall below that of a conventional thermal flow meter, thus preventing the measured flow rate from falling below the actual flow rate and consequently reducing the measurement error to that of a conventional thermal flow meter. Brief description of the drawings [ Fig. 1] Fig. Figure 1 is a schematic view of an exemplary system with a thermal flow meter according to a first embodiment of the present invention. [ Fig. 2A] Fig. Figure 2A is a front view of the thermal flow meter according to the first embodiment of the present invention. [ Fig. 2B] Fig. 2B is a view of the in Fig. 2A shows the thermal flow meter from the left side. [ Fig. 2C] Fig. 2C is a rear view of the in Fig. 2A shown thermal flow meter. [ Fig. 2D] Fig. 2D is a view of the in Fig. 2A shows the thermal flow meter from the right side. [ Fig. 3A] Fig. 3A is a front view of the in Fig. 2A shows the thermal flow meter with a front cover removed. [ Fig. 3B] Fig. 3B is a rear view of the in Fig. 2C shown thermal flow meter, with a rear cover removed. [ Fig. 4] Fig. 4 is a sectional view along line IV-IV of the in Fig. 2C shown thermal flow meter. [ Fig. 5] Fig. 5 is a schematic diagram of a side passage of the in Fig. 4 thermal flow meters shown. [ Fig. 6A] Fig. 6A is a front view of the front cover of the in Fig. 2A shown thermal flow meter. [ Fig. 6B] Fig. 6B is a rear view of the in Fig. 6A shows the front cover of the thermal flow meter. [ Fig. 7A] Fig. 7A is a front view of the rear cover of the in Fig. 2C shown thermal flow meter. [ Fig. 7B] Fig. 7B is a rear view of the in Fig. 7A shows the rear cover of the thermal flow meter. [ Fig. 8] Fig. Figure 8 is a diagram showing an example measured value from a conventional thermal flow meter. [ Fig. 9] Fig. Figure 9 is a diagram showing an exemplary measured value of the thermal flow meter according to the first embodiment of the present invention. [ Fig. 10] Fig. Figure 10 is a schematic diagram of a secondary passage of a thermal flow meter according to a second embodiment of the present invention. [ Fig. 11] Fig. Figure 11 is a schematic diagram of a secondary passage of a thermal flow meter according to a third embodiment of the present invention. [ Fig. 12] Fig. Figure 12 is a schematic diagram of a bypass of a thermal flow meter according to a fourth embodiment of the present invention. Description of embodiments

[0015] Embodiments of a thermal flow meter of the present invention will now be described with reference to the drawings. (First embodiment)

[0016] Fig. Figure 1 is a schematic view of an exemplary control system for an internal combustion engine with electronic fuel injection, comprising a thermal flow meter 300 according to a first embodiment of the present invention. In the system, based on the operation of an internal combustion engine 110, comprising an engine cylinder 113 and an engine piston 114, intake air as the gas 30 to be measured is drawn in by an air filter 122 and is then directed to a combustion chamber of the engine cylinder 112 through an intake pipe, which is an example of a main passage 124, a throttle body 126 and an intake manifold 128.

[0017] The flow rate of the gas 30 to be measured, which is the intake air to be directed to the combustion chamber, is measured by the thermal flow meter 300. A fuel injector 152 supplies fuel based on the measured flow rate, and the fuel, together with the gas 30 to be measured (the intake air), is then directed to the combustion chamber in an air-fuel mixture. It should be noted that, in the present embodiment, the fuel injector 152 is located at an intake port of the internal combustion engine. The fuel injected into the intake port mixes with the gas 30 to be measured (the intake air) to form the air-fuel mixture. The air-fuel mixture is then directed through an intake valve 116 to the combustion chamber, where it combusts to generate mechanical energy.

[0018] The thermal flow meter 300 can be used not only for one model of fuel injection into the intake port of the internal combustion engine as shown in the illustration. Fig. 1, but also for a model of direct fuel injection into each combustion chamber. The underlying concept of a method for measuring a control parameter, including a method for using the thermal flow meter 300, and a method for controlling the internal combustion engine, including fuel supply and ignition timing, is essentially the same for both models. Fig. Figure 1 presents the model of fuel injection into the intake port as an illustrative example of both models.

[0019] The fuel and air, which are fed to the combustion chamber and are in a fuel-air mixture state, combust explosively due to the spark ignition of a spark plug 154 to generate mechanical energy. After combustion, the gas is directed by an exhaust valve 118 to an exhaust pipe and is then expelled from the vehicle as exhaust gas 24 through the exhaust pipe. The flow rate of the gas 30 to be measured, which is the intake air directed to the combustion chamber, is controlled by a throttle valve 132, the opening degree of which varies based on the operation of the accelerator pedal.Since the fuel supply is controlled on the basis of the flow rate of the intake air to be directed to the combustion chamber, an operator controls the opening degree of the throttle valve 132 in such a way as to control the flow rate of the intake air to be directed to the combustion chamber, so that the mechanical energy to be generated by the internal combustion engine can be controlled.

[0020] The flow rate and temperature of the gas 30 to be measured, which is the intake air flowing through the main passage 124 and drawn in by the air filter 122, are measured by the thermal flow meter 300. Electrical signals indicating the measured flow rate and temperature of the intake air are input from the thermal flow meter 300 to a control device 200. An output from a throttle position sensor 144, which measures the opening degree of the throttle valve 132, is input to the control device 200, as are outputs from a rotary angle sensor 146 to measure the positions and states of the engine piston 114, the intake valve 116, and the exhaust valve 118 in the internal combustion engine, and the rotational speed of the internal combustion engine.To measure the state of the mixing ratio between the amount of fuel and the amount of air from the state of the exhaust gas 24, an output from an oxygen sensor 148 is entered into the control device 200.

[0021] The control device 200 calculates the fuel injection quantity and the ignition timing based on the flow rate, humidity, and temperature of the intake air, which are exemplary outputs from the thermal flow meter 300, and, for example, the engine speed from the rotational angle sensor 146. Based on the calculation results, the amount of fuel to be supplied by the fuel injector 152 and the ignition timing for the spark plug 154 are controlled. In practice, the fuel supply and ignition timing are further controlled based on the intake temperature measured by the thermal flow meter 300, the degree of variation in the throttle valve angle, the degree of variation in engine speed, and the state of the air-fuel ratio measured by the oxygen sensor 148.The control device 200 further controls the amount of air bypassing the throttle valve 132 with an idle speed regulator 156 in the idle operating state of the internal combustion engine in order to control the speed of the internal combustion engine in the idle operating state.

[0022] Fuel supply and ignition timing, the main controlled variables in the internal combustion engine, are both calculated using the outputs of the thermal flow meter 300 as the primary parameters. Therefore, improving the measurement accuracy, reducing aging, and enhancing the reliability of the thermal flow meter 300 are crucial for improving control accuracy and ensuring vehicle reliability. In particular, the demands for low fuel consumption and exhaust gas purification have increased considerably in recent years. To meet these demands, it is essential to improve the measurement accuracy of the flow rate of the gas 30 being measured, which is the intake air measured by the thermal flow meter 300.

[0023] Fig. Figure 2A is a front view of the thermal flow meter 300 according to the present embodiment. Fig. 2B, Fig. 2C and Fig. 2D views are a left-side view, a rear view, and a right-side view of the object. Fig. 2A shown thermal flow meter.

[0024] The thermal flow meter 300 has a casing 310 comprising a housing 302, a front cover 303, and a rear cover 304. The front cover 303 and the rear cover 304, each designed as a thin plate, have a wider planar cooling surface. Thus, the thermal flow meter 300 features a configuration that reduces air resistance and allows the casing 310 to be readily cooled by the gas flowing in the main passage 124.

[0025] The casing 310, which, for example, has a substantially cuboid flat shape, is arranged in the main passage 134, with the casing 310 being inserted into the inlet pipe as shown in Fig. Figure 1 is shown. Although details will be described later, the casing 310 delineates a secondary passage that receives a portion of the gas 30 to be measured, which is fluid flowing in the main passage 124.

[0026] It is noted that in some cases each part of the thermal flow meter 300 is described by a Cartesian XYZ coordinate system which has the following: an X-axis direction in the longitudinal direction of the casing 310, which is substantially parallel to the flow of the gas 30 to be measured in the main passage 124; a Y-axis direction in the vertical direction of the casing 310, which is substantially parallel to the radial direction of the main passage 124, the vertical direction being perpendicular to the longitudinal direction; and a Z-axis direction in the thickness direction of the casing 310, which is perpendicular to the longitudinal and vertical directions.

[0027] Although the formwork 310 according to the illustration in Fig. 2B and Fig. Since the 2D form has an elongated shape along an axis from the outer wall of the main passage 124 to the center, the casing 310 has a flat shape with a small thickness. This means that the casing 310 of the thermal flow meter 300 has a thin thickness along the side surfaces and the front surface has a substantially rectangular shape. This arrangement allows the thermal flow meter 300 to reduce the fluid resistance for the gas 30 to be measured and to encompass the secondary passage with a sufficient length.

[0028] The base end section of the housing 302 is provided with a flange 305 for securing the thermal flow meter 300 to the inlet pipe and a connecting piece 306, which is an external connection section exposed outside the inlet pipe for electrical connection to external devices. The flange 305 is secured to the inlet pipe, thus securing the housing 302 in a projecting position.

[0029] Fig. 3A is a front view of the in Fig. 2A thermal flow meter 300 shown, with the front cover 303 removed. Fig. 3B is a rear view of the in Fig. 2C shown thermal flow meter 300, with the rear cover 304 removed.

[0030] At a position on the downstream side in a main flow direction on the front end of the housing 302, an inlet 311 is provided for receiving the gas 30 to be measured, such as the intake air, which is the fluid flowing in the main passage 124, into the secondary passage 307. In this way, the inlet 311 for receiving the gas 30 to be measured, which flows in the main passage 124, into the secondary passage 307 is provided on the front end of the casing 310, which extends from the flange 305 to the center in the radial direction of the main passage 124.

[0031] This arrangement allows the secondary passage 307 to draw air away from the inner wall surface of the main passage 124. Thus, the temperature of the inner wall surface of the main passage 124 has little effect, preventing a decrease in the measurement accuracy for the flow rate or the temperature of the gas. The fluid resistance is high near the inner wall surface of the main passage 124, and therefore the flow rate is lower than the average flow rate in the main passage 124. Since, in the thermal flow meter 300 of the present embodiment, the inlet 311 is provided at the front end section of the thin, elongated casing 310, which extends from the flange 305 to the center of the main passage 134, the secondary passage 307 can draw gas at a high flow rate in a central section of the main passage 124.

[0032] At positions on the downstream side in the main flow direction on the front end of the housing 302, a first outlet 312 and a second outlet 313 are provided for returning the gas 30 to be measured from the secondary passage 307 to the main passage 124. The first outlet 312 and the second outlet 313 are side by side in the thickness direction (Z-axis direction) of the housing 302 as shown in the illustration. Fig. 2D arranged. In this way, the first outlet 312 and the second outlet 313, which are the discharge outlets of the secondary passage 307, are provided on the front end section of the casing 310, so that the gas flowing in the secondary passage 307 can be returned to the vicinity of the central section of the main passage 127, where the flow rate is high.

[0033] A circuit package 400, comprising, for example, a flow rate measuring unit 451 for measuring the flow rate of the gas 30 to be measured flowing in the main passage 124, and a temperature measuring unit 452 for measuring the temperature of the gas 30 to be measured flowing in the main passage 124, is integrally formed and configured in the housing 302. The housing 302 is configured with secondary passage grooves 330 and 331 for limiting the secondary passage 307. In the present embodiment, the secondary passage grooves 330 and 331 are provided with recesses on the front surface and the rear surface of the housing 302, respectively.

[0034] Thus, the attachment of the front cover 303 and the rear cover 304 to the front and rear surfaces of the housing 302 allows the front cover 303 and the rear cover 304 to cover the secondary passage grooves 330 and 331 of the housing 302, so that the casing 310, which delimits the secondary passage 307, can be achieved. For the housing 302 with this configuration, the housing 302 and the front secondary passage groove 330 and the rear secondary passage groove 331 can be formed together with a molding tool arranged on both surfaces of the housing 302 in a resin molding process in which the housing 302 is formed.

[0035] The secondary passage groove 331, which is provided on the rear side of the housing 302, has a straight groove section 332 for limiting a straight passage 307A in a part of the secondary passage 307 and a branching groove section 333 for limiting a branching passage 307B in a part of the secondary passage 307 as shown in the illustration in Fig. 3B on.

[0036] The straight groove section 332 extends straight in the main flow direction (X-axis direction) of the gas 30 to be measured along the front end section of the housing 302. One end of the groove section is connected to the inlet 311 of the housing 302, and the other end is connected to the first outlet 312 of the housing 302. The straight groove section 332 comprises a straight section 332A extending from the inlet 311 and maintaining a substantially constant cross-sectional shape, and a tapered section 332B with a groove width that gradually tapers from the straight section 332A to the first outlet 312. The first outlet 312 is the discharge outlet, which discharges a part of the fluid flowing in the straight passage 307A of the secondary passage 307, namely a part of the gas 30 to be measured.The provision of the first outlet 312 allows foreign bodies, such as dust, to be expelled from the secondary passage 307, thus reducing the total volume of foreign bodies that are taken up into the branch passage 307B of the secondary passage 307 and preventing a deterioration of the measuring performance of the flow rate measuring unit 451.

[0037] The branching groove section 333, which branches off from the straight section 332A of the straight groove section 332, leads to the base end of the housing 302 in a curve and is connected to a flow channel for measurement 341, which is provided at a central section in the vertical direction (Y-axis direction), which is the longitudinal direction of the housing 302. The branching groove section 333 has an upstream end connected to a side wall surface 332a, which is positioned on the base end of the housing 302 of paired side wall surfaces contained in the straight groove section 332, and a lower wall surface 333a, which is flush with the lower wall surface of the straight section 332A of the straight groove section 332 without a height difference.

[0038] A housing groove section 333A is provided on the side wall surface on the inside of the curvature of the branching groove section 333. The housing groove section 333A has a recess section 333B. The recess section 333B receives water penetrating the housing groove section 333A and expels the water outside the housing 310 from a drain hole 376, which is located at a position of the rear cover 304 opposite the recess section 333B as shown in the illustration. Fig. 2C is drilled in, out.

[0039] The flow channel for measurement 341 is designed such that it extends from the front to the rear of the housing 302 in the thickness direction. A section 430 of the circuit package 400, exposed towards the flow channel, is arranged so that it projects into the flow channel for measurement 341. The branching groove section 333 is connected to the flow channel for measurement 341 on the upstream side of the bypass 307 with respect to the section 430 of the circuit package 400 exposed towards the flow channel. From the straight groove section 332 to the flow channel for measurement 341 in the vertical direction (Y-axis direction) of the housing 302, the branching groove section 333 extends in a curvature in the opposite direction (negative X-axis direction) to the main flow direction of the gas 30 to be measured in the main passage 124.

[0040] The branching passage 307B of the secondary passage 307, which is bounded by the branching groove section 333, leads from the front end of the housing 302 to the base end, which is the side of the flange 305, and forms a bend. The flow channel for measurement 341 is located at the position where the branching passage 307B is closest to the flange 305. In the flow channel for measurement 341, the gas 30 to be measured, which flows in the secondary passage 307, flows in the opposite direction (negative X-axis direction) to the main flow direction of the main passage 124.

[0041] In the thermal flow meter 300 of the present embodiment, the branching groove section 333 has a three-dimensional shape in which the groove depth gradually deepens in the thickness direction (Z-axis direction) of the housing 302 with respect to the flow channel for measurement 341. In the thermal flow meter 300 of the present embodiment, the branching groove section 333 has a section 333d with a steep inclination that deepens rapidly on the side near the flow channel for measurement 341.

[0042] Section 333d, with its steep inclination, serves to guide the gas 30 to be measured, which is a gas, to the side of the front surface 431, on which a measuring surface 451a of the flow rate measuring unit 451 is provided, from a front surface 431 and a rear surface 432, which is the exposed section 430 of the circuit package 400 in the flow channel for measurement 341. Then, the foreign particles, such as dust, contained in the gas 30 to be measured, flow to the side of the rear surface 432 of the exposed section 430 of the circuit package 400, which is the rear surface of the flow rate measuring unit 451, thus improving the contamination resistance of the measuring surface 451a of the flow rate measuring unit 451.

[0043] More precisely, a portion of the low-mass air moves along section 333d at a steep incline and then flows into a first passage 351 (see Fig. 4) on the side of the front surface 431 of the section 430 of the circuit package 400 exposed towards the flow channel, namely on the side of the measuring surface 451a of the flow rate measuring unit 451 in the flow channel for measurement 341. At the same time, sharp path changes are difficult for the foreign bodies with large mass due to the centrifugal force along the curvature of the branching passage 307B of the secondary passage 307. Thus, since the foreign bodies with large mass cannot flow along the section 333d with a steep inclination, they flow on the side of the rear surface 432 of the section 430 of the circuit package 400 exposed towards the flow channel, namely in a second passage 352 (see Fig. 4) on the side of the rear surface 451b of the flow rate measuring unit 451.

[0044] The secondary through-hole 330 provided on the front of the housing 302 as shown in Fig. 3A limits the section on the downstream side of the branch passage 307B of the secondary passage 307. The section on the downstream side of the branch passage 307B, which is limited by the secondary passage groove 330, has one end connected to the section on the upstream side of the branch passage 307B on the rear of the housing 302 through the flow channel to the measuring 341 and the other end connected to the second outlet 313 formed at the front end of the housing 302.

[0045] In the thermal flow meter 300 of the present embodiment, the secondary passage groove 330, which limits the section on the downstream side of the branch passage 307B of the secondary passage 307, has a second inclined surface 372, which forms an inclined passage 361, which will be described later (see Fig. 5) limited, on the downstream side in the forward direction F of the gas to be measured 30 in the flow channel for measurement 341.

[0046] The secondary passage groove 330, provided on the front of the housing 302, gradually leads to the downstream side in the main flow direction, in a curvature corresponding to a transition to the front end of the housing 302, wherein the secondary passage groove 339 extends straight to the downstream side in the main flow direction of the gas 30 to be measured at the front end section of the housing 302, the secondary passage groove 330 having a shape in which a groove width gradually tapers towards the second outlet 313. The gas 30 to be measured and the foreign matter that has flowed through the flow channel to the measurement 341 flow through the section on the downstream side of the branch passage 307B of the secondary passage 307, which is bounded by the secondary passage groove 330 provided on the front of the housing 302.Then the gas 30 to be measured and the foreign bodies are expelled from the second outlet 313 and return to the main passage 12.

[0047] The exposed section 430 of the circuit package 400, facing the flow channel, projects from a wall surface of the branching groove section 333 of the secondary passage groove 331, which delimits the flow channel for measurement 341, into the flow channel for measurement 341 at the front end of the housing 302 in the vertical direction (Y-axis direction) of the housing 302. The exposed section 430, which has a thickness in the thickness direction (Z-axis direction) of the housing 302, is formed in the shape of a rectangular plate in the flow direction of the gas 30 to be measured, which flows in the flow channel for measurement 341. The exposed section 430 towards the flow channel acts as a support section, arranging the flow rate measuring unit 451 in the secondary passage 307 and supporting the flow rate measuring unit 451.

[0048] Fig. 4 is a sectional view along line IV-IV of the in Fig. 2C shown thermal flow meter 300.

[0049] The secondary passage 307 comprises the first passage 351, located on the side of the measuring surface 451a of the flow rate measuring unit 451, and the second passage 352, located on the side of the rear surface 451b of the flow rate measuring unit 451, in the flow channel for measurement 341. The secondary passage 307 includes the inclined passage 361, which is arranged on the downstream side in the forward direction F of the fluid in the second passage 352 with respect to an outlet 352b of the second passage 352, namely on the downstream side in the forward direction F of the gas 30 to be measured in the first channel 351.

[0050] The air, which is the gas 30 to be measured, flows in the forward direction F of the gas 30 to be measured in the first passage 351 of the flow channel to the measurement point 341. In this case, heat transfer with the gas 30 to be measured is carried out by the measuring surface 451a, which is a heat transfer surface provided on the flow rate measuring unit 451, and then the flow rate is measured. It should be noted that this flow rate measurement principle can be a general measurement principle for a thermal flow meter. As long as the flow rate of the gas 30 to be measured, which flows in the main passage 124, can be measured on the basis of a measured value that is measured by the flow rate measuring unit 451, such as the thermal flow meter 300 of the present embodiment, the configuration of the flow rate measuring unit 451 is not particularly limited.

[0051] The thermal flow meter 300 of the present embodiment has the described inclined passage 361, wherein the inclined passage 361 is provided on the downstream side in the forward direction F of the gas 30 to be measured in the second passage 352 with respect to the outlet 352b of the second passage 352, which is provided on the side of the rear surface 451b of the flow rate measuring unit 451 in the flow channel for measuring 341 of the secondary passage 307. The inclined passage 361 has a first inclined surface 371 (see Fig. 5) on the side of the first pass 351 with respect to the flow rate measuring unit 451, wherein the first inclined surface 371 is inclined from the side of the second pass 352 to the side of the first pass 351 with respect to the forward direction F of the gas 30 to be measured.

[0052] It is noted that, according to the above description, although the thermal flow meter 300 of the present embodiment comprises the flat casing 310 arranged in the main passage 124, the casing 310 which limits the secondary passage 307, the measuring surface 451a of the flow rate measuring unit 451 which is arranged in the secondary passage 307 is substantially perpendicular to the thickness direction (Z-axis direction) of the casing 310.

[0053] In the thermal flow meter 300 of the present embodiment, the secondary passage 307 has the straight passage 307A, which according to the above description (see Fig. 3B) receives the portion of the gas 30 to be measured, which is the fluid flowing in the main passage 124. The secondary passage 307 has the first outlet 312, which is the discharge outlet that discharges the portion of the gas 30 to be measured, which is the fluid flowing in the straight passage 307A, and the branching passage 307B, which branches off from the straight passage 307A, on the upstream side in the forward direction of the fluid flowing in the straight passage 307A with respect to the first outlet 312. The first passage 351, the second passage 352, and the inclined passage 361, which are described above, are all provided in the branching passage 307B.

[0054] Fig. 5 is a schematic diagram of the secondary passage 307 of the in Fig. 4 thermal flow meter 300 shown. Fig. Figure 5 shows a section in the thickness direction (Z-axis direction) of the formwork 310 at sections of the secondary passage 307 in front of and behind the flow channel for measurement 341, which was created parallel to the thickness direction (Z-axis direction) and the length direction (X-axis direction) of the formwork 310.

[0055] As described above, the thermal flow meter 300 of the present embodiment has a secondary passage 307, which receives the portion of the gas 30 to be measured, which is the fluid flowing in the main passage 124, and a flow rate measuring unit 451 arranged in the secondary passage 307. The secondary passage 307 has a first passage 351 provided on the side of the measuring surface 451a of the flow rate measuring unit 451, a second passage 352 provided on the side of the rear surface 451b of the flow rate measuring unit 451, and an inclined passage 361 provided on the downstream side in the forward direction F of the gas 30 to be measured in the second passage 352 with respect to the outlet 352b of the second passage 352.The inclined passage 361 has the first inclined surface 371 on the side of the first passage 351 with respect to the flow rate measuring unit 451, wherein the first inclined surface 371 slopes from the side of the second passage 352 to the side of the first passage 351 with respect to the forward direction F of the gas 30 to be measured. The first inclined surface 371 is provided on the side of the rear surface of the front cover 303, as for example in . Fig. 6B is shown.

[0056] Furthermore, the incline section 361 in the Fig. In the example shown in Figure 5, the second inclined surface 372 is inclined relative to the first inclined surface 371 in a direction perpendicular to the measuring surface 451a of the flow rate measuring unit 451 (Z-axis direction). Similar to the first inclined surface 371, the second inclined surface 372 is inclined from the side of the second passage 352 to the side of the first passage 351 with respect to the forward direction F of the gas 30 to be measured. The second inclined surface 372 is located on the lower section of the secondary passage groove 330 of the housing 302 as shown in Figure 5. Fig. 3A is planned.

[0057] At the in Fig. In the example shown in Figure 5, the angle of inclination θ2 of the second inclined surface 372 with respect to the forward direction F of the gas 30 to be measured is greater than the angle of inclination θ1 of the first inclined surface 371 with respect to the forward direction F of the gas 30 to be measured. In particular, the angle difference between the angle of inclination θ1 of the first inclined surface 371 and the angle of inclination θ2 of the second inclined surface 372 can, for example, be in the range of 3° to 15°.

[0058] In the Fig. In the example shown in Figure 5, the secondary passage 307 has a section on the downstream side in the forward direction F of the gas 30 to be measured with respect to the inclined passage 361, wherein the section on the side of the first passage 351 with respect to the second passage 352 is provided in the direction perpendicular to the measuring surface 451a of the flow rate measuring unit 451 (Z-axis direction).

[0059] In the Fig. In the example shown in Figure 5, the secondary passage 307 has the extended line L1 of the first inclined surface 371 and the extended line L2 of the measuring surface 451a, which intersect on the downstream side in the forward direction F of the gas 30 to be measured with respect to the measuring surface 451a in the section that runs perpendicular to the measuring surface 451a of the flow rate measuring unit 451 parallel to the forward direction F of the gas 30 to be measured. In the forward direction F of the gas 30 to be measured, the extended line L1 of the first inclined surface 371 and the extended line L2 of the measuring surface 451a can intersect on the downstream side with respect to the end section on the downstream side of the section 430 of the circuit package 400 exposed towards the flow channel, wherein the section 430 exposed towards the flow channel acts as the support section for the flow rate measuring unit 451.

[0060] Fig. 6A and Fig. Figures 6B are a front view and a rear view of the front cover 303 of the [unclear text]. Fig. 2A thermal flow meter 300 shown. Fig. 7A and Fig. Figures 7B are a front view and a rear view of the rear cover 304 of the in Fig. 2C shown thermal flow meter 300.

[0061] As described above, the front cover 303 and the rear cover 304 are components of the casing 310, which delimits the bypass 307, and have bypass grooves 335 and 336, respectively, for delimiting the bypass 307 on their rear surfaces opposite the housing 302. The bypass groove 335 of the front cover 303 delimits the flow channel for measuring 341 of the branching passage 307B of the bypass 307 and the section on its downstream side, together with the bypass groove 330 of the housing 302, as shown in the illustration. Fig. 3A. The lower section of the secondary passage groove 335 of the front cover 303 is provided with the first inclined surface, which in Fig. The inclination passage 361 shown in section 5 is limited.

[0062] The secondary passage groove 336 of the rear cover 304 has a straight groove section 337 for limiting the straight passage 307A in a part of the secondary passage 307 and a branching groove section 338 for limiting the branching section 307B in a part of the secondary passage 307, similar to the secondary passage groove 331 provided on the rear of the housing 302, which is located in Fig. 3B is shown.

[0063] The function of the thermal flow meter 300 of the present embodiment is described below.

[0064] At the in Fig. In the control system for an internal combustion engine shown in Figure 1, it is likely, depending on the conditions, that the intake air, which is the gas 30 to be measured and which flows in the main passage 124, pulsates and that the gas 30 to be measured flows from the downstream side to the upstream side in the opposite direction to the main flow direction.

[0065] Here, the thermal flow meter 300 of the present embodiment includes the secondary passage 307, which receives a portion of the fluid flowing in the main passage 124, as described above. Thus, if the gas 30 to be measured flows against the main passage 124, as described above, Fig. As shown in Figure 5, it is likely that the gas 30 to be measured in the flow channel for measurement 341 of the secondary passage 307 flows in the counterflow direction R opposite to the forward direction F from the downstream side to the upstream side in the forward direction F of the flow channel for measurement 341.

[0066] The thermal flow meter 300 of the present embodiment comprises the flow rate measuring unit 451, which is arranged in the flow channel for measuring 341 of the secondary channel 307, as described above. The secondary channel 307 has the first passage 351, which is provided on the measuring surface 451a of the flow rate measuring unit 451, and the second passage 352, which is provided on the rear surface of the flow rate measuring unit 451. Thus, if the gas 30 to be measured, which flows in the opposite direction in the flow channel for measuring 341, flows in large quantities into the first passage 351, the average value of the flow rate to be measured by the flow rate measuring unit 451 falls below the actual flow rate, resulting in the disadvantage that a measurement error increases.

[0067] Fig. Figure 8 is a diagram showing an example measured value from a conventional thermal flow meter without a tilt path 361. Fig. Figure 8 shows that the horizontal axis represents time and the vertical axis represents the throughput rate. Fig. 8 The variation of the measured value of the flow rate from the conventional thermal flow meter is indicated by a solid line, and the variation of the actual flow rate of the gas to be measured 30 is indicated by a dashed line.

[0068] The increase in straightness due to the inertial effect of the fluid while the gas 30 to be measured is pulsating is greater than in a steady state where no pulsation occurs. Thus, the gas 30 to be measured flows in the forward direction from the inlet 311 to the side passage 307 as shown in the diagram. Fig. The gas 30, which is taken in through the straight passage 307A, does not branch off into the branching passage 307B, so that the flow rate to be expelled from the first outlet 312 increases. As a result, the flow rate of the gas 30 to be measured, which branches off from the straight passage 307A to the branching passage 307B of the secondary passage 307, decreases, and then the flow rate of the gas 30 to be measured decreases in the forward direction F, which flows into the flow channel for measurement 341. Thus, according to the illustration in Fig. 8 the maximum value umax of the measured value of the flow rate from the thermal flow meter below the maximum value of the actual flow rate of the gas to be measured 30.

[0069] Simultaneously, all the gas 30 to be measured flows in the counter-current direction, from the second outlet 313 into the secondary passage 307 as shown in the illustration. Fig. 3A is taken in and flows into the flow channel for measurement 341 without being expelled in between. Therefore, while the gas 30 to be measured flows against it, the flow rate of the gas 30 to be measured in the counterflow direction R, which flows into the flow channel for measurement 341, does not decrease. According to the illustration in Fig. 8 corresponds to the minimum value umin of the measured value of the flow rate from the thermal flow meter essentially to the actual flow rate of the gas 30 to be measured. In this case, the average value uave of the measured value of the conventional thermal flow meter without inclination 361 falls below the average value u0 of the actual flow rate of the gas 30 to be measured, and thus a negative measurement error occurs.

[0070] In contrast, the thermal flow meter 300 of the present embodiment, as shown in the illustration in Fig. 5 the inclined passage 361, which is provided on the downstream side in the forward direction F of the gas 30 to be measured, which is the fluid in the second passage 352, with respect to the outlet 352b of the second passage 352, which is provided on the rear surface side of the flow rate measuring unit 451. The inclined passage 361 has the first inclined surface 371 on the side of the first passage 351 with respect to the flow rate measuring unit 451, wherein the first inclined surface 371 inclines from the side of the second passage 352 to the side of the first passage 351 with respect to the forward direction F of the gas 30 to be measured.

[0071] Thus, the gas 30 to be measured, which flows in the counterflow direction R from the downstream side to the upstream side in the forward direction F of the gas 30 to be measured with respect to the inclined passage 361, flows along the first inclined surface 371 of the inclined passage 361 and is diverted from the side of the first passage 351 to the side of the second passage 352. This arrangement can increase the flow rate of the gas 30 to be measured, which flows in the counterflow direction R in the second passage 352, compared to the conventional thermal flow meter without an inclined passage 361, while decreasing the flow rate of the gas 30 to be measured, which flows in the counterflow direction R in the first passage 351.

[0072] Fig. Figure 9 is a diagram showing an exemplary measured value of the thermal flow meter 300 according to the present embodiment. Fig. In figure 9, the horizontal axis represents time and the vertical axis represents the throughput rate. Fig. 9 The variation of the measured value of the flow rate from the thermal flow meter 300 of the present embodiment is indicated by a solid line, and the variation of the actual flow rate of the gas 30 to be measured is indicated by a dashed line.

[0073] According to the above description, the thermal flow meter 300 of the present embodiment can increase the flow rate of the gas 30 to be measured, which flows in the counterflow direction R in the second passage 352, compared to the conventional thermal flow meter without an inclined passage 361, in such a way as to decrease the flow rate of the gas 30 to be measured, which flows in the counterflow direction R in the first passage 351. Thus, according to the illustration in Fig. 9. The absolute value of the minimum value umin of the measured value of the flow rate from the thermal flow meter 300 is lower than the absolute value of the actual flow rate of the gas 30 to be measured. This arrangement increases the average value uave of the measured value and reduces the negative measurement error between the average value uave of the measured value and the average value u0 of the actual flow rate of the gas 30 to be measured in the thermal flow meter 300 of the present embodiment. As a result, the time-averaged value uave of the flow rate to be measured by the thermal flow meter 300 while the gas 30 to be measured is pulsating can essentially correspond to the average value u0 of the actual flow rate of the gas 30 to be measured, so that the measurement error of the thermal flow meter 300 can fall below that of the conventional thermal flow meter.

[0074] In the thermal flow meter 300 of the present embodiment, the inclined passage 361 has a second inclined surface 372 relative to the first inclined surface 371 in the direction perpendicular to the measuring surface 451a of the flow rate measuring unit 451 (Z-axis direction). The second inclined surface 372 slopes from the side of the second passage 352 to the side of the first passage 351 with respect to the forward direction F of the gas 30 to be measured. This arrangement prevents the formation of a vortex in the counterflow direction R of the gas 30 to be measured, which is diverted due to the first inclined surface 371 of the inclined passage 361, so that the flow rate of the gas 30 to be measured, which flows in the counterflow direction R in the second passage 352, can increase.

[0075] In the thermal flow meter 300 of the present embodiment, the inclination angle θ2 of the second inclined surface 372 with respect to the forward direction F of the gas 30 to be measured is greater than the inclination angle θ1 of the first inclined surface 371 with respect to the forward direction F. This arrangement effectively prevents the occurrence of a vortex in the flow of the gas 30 to be measured, which is diverted due to the first inclined surface 371 of the inclined passage 361, so that the flow rate of the gas 30 to be measured, which flows in the counterflow direction R in the second passage 352, can increase.

[0076] The angular difference between the inclination angle θ1 of the first inclined surface 371 and the inclination angle θ2 of the second inclined surface 372, which is, for example, in the range of 3° to 15°, can prevent a vortex that can easily occur in the radially expanding tube. This means that by ensuring that the angle at which the inclined passage 361 expands radially is shallow, the counterflow direction R of the gas 30 to be measured in the flow channel for measurement 341 is corrected, so that the counterflow direction R of the gas 30 to be measured can be stabilized in the first passage 351 and the second passage 352.

[0077] In the thermal flow meter 300 of the present embodiment, the secondary passage 307 has, as shown in the illustration in Fig. 5 the section on the downstream side in the forward direction F of the gas 30 to be measured with respect to the inclination passage 361, wherein the section on the side of the first passage 351 with respect to the second passage 352 is provided in the direction perpendicular to the measuring surface 451a of the flow rate measuring unit 451 (Z-axis direction). Thus, in a case where the inclined passage 361 does not have a first inclined surface 371, the counter-current flow R of the gas 30 to be measured easily flows into the first passage 351. However, the inclined passage 361 with the first inclined surface 371 allows the counter-current flow R of the gas 30 to be measured to be diverted from the side of the first passage 351 to the side of the second passage 352, so that the flow rate of the fluid flowing in the counter-current direction R in the first passage 351 can be reduced.

[0078] In the thermal flow meter 300 of the present embodiment, the secondary passage 307 has, as shown in the illustration in Fig. 5 the extended line L1 of the first inclined surface 371 and the extended line L2 of the measuring surface 451a, which intersect on the downstream side in the forward direction F of the gas 30 to be measured with respect to the measuring surface 451a in the section that runs perpendicular to the measuring surface 451a of the flow rate measuring unit 451 and parallel to the forward direction F of the gas 30 to be measured. This arrangement allows the flow along the first inclined surface 371 to allow the introduction of the flow in the counterflow direction R of the gas 30 to be measured, which is diverted from the side of the second passage 352 to the side of the first passage 351, into the second passage 352.In a case where the extended line L1 of the first inclined surface 371 and the extended line L2 of the measuring surface 451a intersect on the downstream side with respect to the end section on the downstream side of the section 430 of the circuit package 400 exposed to the flow channel, the diverted current in the countercurrent direction R of the gas 30 to be measured is easily introduced into the second passage 352.

[0079] According to the above description, the thermal flow meter 300 of the present embodiment prevents a flow rate to be measured by the flow rate measuring unit 451 from falling below the actual flow rate, even while the gas 30 to be measured is pulsating, so that the measurement error can fall below that of the conventional thermal flow meter. (Second embodiment)

[0080] Next, a second embodiment of the thermal flow meter of the present invention will be described. Fig. 10 using Fig. 1-4 and Fig. Described in sections 6A to 7B. Fig. Figure 10 is a schematic diagram of a secondary passage 307 of a thermal flow meter according to the present embodiment, wherein Fig. 10 Fig. 5 of the thermal flow meter 300 is equivalent to the first embodiment described above.

[0081] The main differences between the thermal flow meter of the present embodiment and the thermal flow meter 300 of the first embodiment described above are outlined below. Fig. Figure 5 is described. With the exception of a configuration described below, the configuration of the thermal flow meter of the present embodiment is similar to that of the thermal flow meter 300 of the first embodiment described above. Thus, parts that are identical to those of the thermal flow meter 300 of the first embodiment are provided with the same reference numerals, and therefore descriptions thereof are appropriately omitted.

[0082] Similar to the thermal flow meter 300 of the first embodiment described above, the thermal flow meter of the present embodiment comprises the secondary passage 307, which receives a portion of the gas 30 to be measured, which is a fluid flowing in a main channel 134, and a flow rate measuring unit 451 arranged in the secondary passage 307. It is noted that in the thermal flow meter of the present embodiment, the flow rate measuring unit 451 and the section 430 of a circuit package 400 exposed towards the flow channel are embedded in a wall surface of a flow channel for measurement 341, which delimits the flow channel for measurement 341, of the secondary passage 307.

[0083] In the thermal flow meter of the present embodiment, the secondary passage 307 has the flow channel for measurement 341, which points to a measuring surface 451a of the flow rate measuring unit 451, and an inclined passage 361, which is provided on the downstream side in the forward direction F of the gas 30 to be measured, which is the fluid flowing in the flow channel for measurement 341, with respect to the flow channel for measurement 341. In the thermal flow meter of the present embodiment, the inclined passage 361 has a first inclined surface 371, which inclines from the side of the measuring surface 451a to the side of the rear surface 451b of the flow rate measuring unit 451 in the forward direction F of the gas 30 to be measured.

[0084] It is noted that the first inclined surface 371 is provided on a wall surface on the side of the flow rate measuring unit 451 of the side passage 307 in a direction perpendicular to the measuring surface 451a of the flow rate measuring unit 451 (Z-axis direction). A projecting section 381 is provided on a wall surface opposite the flow rate measuring unit 451 of the side passage 307 in a direction perpendicular to the measuring surface 451a of the flow rate measuring unit 451. The projecting section 381 extends from the wall surface opposite the flow rate measuring unit 451 of the side passage 307 to the measuring surface 451a of the flow rate measuring unit 451.

[0085] In the thermal flow meter of the present embodiment with the configuration, the gas 30 to be measured flows in the counterflow direction R from the downstream side to the upstream side in the forward direction F of the gas 30 to be measured in the flow channel for measurement 341, while the gas 30 to be measured pulsates, along the first inclined surface 371 of the inclined passage 361 and is then diverted in a direction that leads away from the measuring surface 451a of the flow rate measuring unit 451. This arrangement allows the flow rate of the gas 30 to be measured, which flows in the opposite direction R between the projection section 381 and the measuring surface 451a of the flow rate measuring unit 451, to increase at a position away from the measuring surface 451a of the flow rate measuring unit 451 and to decrease near the measuring surface 451a of the flow rate measuring unit 451.

[0086] This allows the thermal flow meter of the present embodiment to compensate for the time-averaged flow rate measured by the thermal flow meter while the gas 30 to be measured is pulsating, essentially to the actual flow rate of the gas to be measured, similar to the thermal flow meter 300 of the first embodiment. Thus, according to the thermal flow meter of the present embodiment, the measurement error can fall below that of a conventional thermal flow meter, similar to the thermal flow meter 300 of the first embodiment. (Third embodiment)

[0087] Next, a third embodiment of the thermal flow meter of the present invention is described with Fig. 11 using Fig. 1-4 and Fig. Described in sections 6A to 7B. Fig. Figure 11 is a schematic diagram of a secondary passage 307 of a thermal flow meter of the present embodiment, wherein Fig. 11 Fig. 5 of the thermal flow meter 300 is equivalent to the first embodiment described above.

[0088] The main differences between the thermal flow meter of the present embodiment and the thermal flow meter of the second embodiment, which are described below, are outlined below. Fig. Figure 10 is shown and described. With the exception of a configuration described below, the configuration of the thermal flow meter of the present embodiment is similar to that of the thermal flow meter of the second embodiment described above. Thus, parts that are identical to those of the thermal flow meter of the second embodiment and the thermal flow meter 300 of the first embodiment are designated with the same reference numerals, and therefore descriptions thereof are appropriately omitted.

[0089] According to the representation in Fig. 11. The thermal flow meter of the present embodiment comprises a projecting section 382 on a wall surface on the side of the first passage 351 opposite the wall surfaces of the secondary passage 307 in the thickness direction (Z-axis direction) of a casing 310, wherein the projecting section 382 projects in the thickness direction (Z-axis direction) of a casing 310. The projecting section 382 has a first inclined surface 371. An inclined passage 361 in the secondary passage 307 of the thermal flow meter of the present embodiment includes the area in which the first inclined surface 371 is provided.

[0090] The in Fig. The first inclined surface 371 shown in Figure 11, which is provided on the side of the first passage 351 with respect to a flow rate measuring unit 451, inclines from the side of the second passage 352 to the side of the first passage 351 with respect to a forward direction F similar to the first inclined surface 371, which is located in Fig. 5 is shown. The first inclined surface 371, which is in Fig. Figure 11 shows the extended line L1 of the first inclined surface 371 and the extended line L2 of a measuring surface 451a, which intersect on the downstream side in the forward direction F with respect to the measuring surface 451a and on the downstream side in the forward direction F with respect to a section 430 of a circuit package 400 exposed towards the flow channel, wherein the section 430 exposed towards the flow channel acts as a support section for the flow rate measuring unit 451.

[0091] Thus, the first inclined surface 371 of the inclined passage 361 according to the thermal flow meter of the present embodiment can redirect the flow in the counter-current direction R of gas 30 to be measured from the side of the first passage 351 to the side of the second passage 352, so that an effect similar to that of the thermal flow meter of the second embodiment and the thermal flow meter 300 of the first embodiment, which is described above, can be achieved. (Fourth embodiment)

[0092] Next, a fourth embodiment of the thermal flow meter of the present invention is described with Fig. 12 using Fig. 1-4 and Fig. Described in sections 6A to 7B. Fig. Figure 12 is a schematic diagram of a secondary passage 307 of a thermal flow meter according to the present embodiment, wherein Fig. 12 Fig. 5 of the thermal flow meter 300 is equivalent to the first embodiment described above.

[0093] The main differences between the thermal flow meter of the present embodiment and the thermal flow meter 300 of the first embodiment described above are outlined below. Fig. Figure 5 is shown and described. With the exception of a configuration described below, the configuration of the thermal flow meter of the present embodiment is similar to that of the thermal flow meter 300 of the first embodiment described above. Thus, parts that are identical to those of the thermal flow meter 300 of the first embodiment are designated with the same reference numerals, and therefore descriptions thereof are appropriately omitted.

[0094] In the thermal flow meter of the present embodiment, the secondary passage 307 has a second inclined passage 362 on the upstream side in a forward direction F with respect to an inlet 351a of a first passage 351. The second inclined passage 362 has a third inclined surface 373 on the side of the first passage 351 with respect to a flow rate measuring unit 451, wherein the third inclined surface 373 slopes from the side of the second passage 352 to the side of the first passage 351 with respect to the forward direction F.

[0095] In the thermal flow meter of the present embodiment, the second inclined passage 362 has a fourth inclined surface 374 relative to the third inclined surface 373 in a direction perpendicular to a measuring surface 451a (Z-axis direction). The fourth inclined surface 374 is inclined from the side of the second passage 352 to the side of the first passage 351 with respect to the forward direction F.

[0096] Furthermore, the secondary passage 307 of the thermal flow meter of the present embodiment has a section on the upstream side in the forward direction F with respect to the second inclined passage 362, wherein the section on the side of the second passage 352 with respect to the first passage 351 is provided in the direction perpendicular to the measuring surface 451a (Z-axis direction). In other words, the secondary passage 307 has an inclined passage 61 and the second inclined passage 362 on the upstream and downstream sides in the forward direction F of a flow channel for measurement 341, wherein the inclined passage 361 and the second inclined passage 362 have point symmetry with respect to a point on the flow rate measuring unit 451.

[0097] The thermal flow meter of the present embodiment, with a configuration similar to that of the thermal flow meter 300 of the first embodiment described above, achieves an effect similar to that of the thermal flow meter 300 of the first embodiment described above. Furthermore, the third inclined surface 373 of the thermal flow meter of the present embodiment, with the second inclined passage 362, can divert the gas 30 to be measured, which flows in the forward direction F from the upstream side in the forward direction F of the gas 30 to be measured in the channel to measurement 341, from the side of the second passage 352 to the side of the first passage 351.

[0098] This arrangement allows the flow rate of the gas 30 to be measured, which flows in the forward direction F (negative X-axis direction) in the first pass 351 while the gas 30 is pulsating, to exceed that of a conventional thermal flow meter. This arrangement can bring the average value uave of the flow rate measured by the thermal flow meter closer to the average value u0 of the actual flow rate of the gas 30 to be measured, resulting in a positive shift of the maximum value umax of the measured value of the thermal flow meter as shown in Fig. 9 is coming.

[0099] Furthermore, in the thermal flow meter of the present embodiment, the second inclined passage 362 has a fourth inclined surface 374 relative to the third inclined surface 373, wherein the fourth inclined surface 374 slopes from the side of the second passage 352 to the side of the first passage 351 with respect to the forward direction F. This arrangement can prevent the formation of a vortex in the flow in the forward direction F of the gas 30 to be measured, which is diverted due to the third inclined surface 373 of the second inclined passage 362, so that the flow rate of the gas 30 to be measured, which flows in the forward direction F in the first passage 351, can increase.

[0100] Thus, the thermal flow meter of the present embodiment effectively prevents the flow rate to be measured by the flow rate measuring unit 451 from falling below the actual flow rate, even while the gas 30 to be measured is pulsating, so that a measurement error can fall below that of the conventional thermal flow meter.

[0101] The embodiments of the present invention have been described in detail above with reference to the drawings; however, the specific configurations are not limited to these embodiments. Therefore, any modifications to the design that do not deviate from the scope of protection of the concept of the present invention are also covered by the present invention. Reference symbol list 30 Gas (fluid) to be measured 124 Main Passage 300 thermal flow meters 307 Side passage 307A straight passage 307B Branch passage 310 Formwork 312 First outlet (exhaust outlet) 341 Flow channel for measurement 351 first round 351a First entry 352 second round 352b Second passage outlet 361 Incline passage 362 second incline pass 371 first inclined surface 372 second inclined surface 373 third inclined surface 374 fourth inclined surface 451 Flow rate measuring unit 451a Measuring surface 451b Back surface F Forward direction L1 extended line of the first inclined surface L2 extended line of the measuring surface θ2 Inclination angle of the second inclined surface θ1 Inclination angle of the first inclined surface

Claims

A thermal flow meter comprising: a secondary passage (307) configured to receive a portion of the fluid flowing in a main passage (124); and a flow rate measuring unit (451) arranged in the secondary passage (307), the secondary passage (307) comprising: a first passage (351) provided on a measuring surface side of the flow rate measuring unit (451); a second passage (352) provided on a rear surface side of the flow rate measuring unit (451); and a slope passage (361) which is provided on a downstream side in a forward direction of the fluid in the second passage (352) with respect to an outlet of the second passage (352), and the slope passage (361) has a first slope surface (371) on one side of the first passage (351) with respect to the flow rate measuring unit (451),wherein the first inclined surface (371) is inclined from one side of the second passage (352) to the side of the first passage (351) with respect to the forward direction, wherein the inclined passage (361) has a second inclined surface (372) relative to the first inclined surface (371) in a direction perpendicular to a measuring surface (451a) of the flow rate measuring unit (451), and wherein the second inclined surface (372) is inclined from the side of the second passage (352) to the side of the first passage (351) with respect to the forward direction, and wherein an inclination angle Θ2 of the second inclined surface (372) with respect to the forward direction is greater than an inclination angle Θ1 of the first inclined surface (371) with respect to the forward direction. Thermal flow meter according to claim 1, wherein the secondary passage (307) has a section on the downstream side in the forward direction with respect to the inclined passage (361), wherein the section on the side of the first passage (351) with respect to the second passage (352) is provided in a direction perpendicular to the measuring surface (451a) of the flow rate measuring unit (451). Thermal flow meter according to claim 1, wherein the secondary passage (307) has in a section perpendicular to the measuring surface (451a) of the flow rate measuring unit (451) parallel to the forward direction an extended line of the first inclined surface (371) and an extended line of the measuring surface (451a) which intersect on the downstream side in the forward direction with respect to the measuring surface (451a). Thermal flow meter according to claim 1, wherein the secondary passage (307) comprises: a straight passage configured to receive the portion of the fluid flowing in the main passage (124); a discharge outlet configured to discharge the portion of the fluid flowing in the straight passage; and a branching passage branching off from the straight passage on an upstream side in the forward direction of the fluid flowing in the straight passage with respect to the discharge outlet, and the first passage (351), the second passage (352) and the inclined passage (361) being provided in the branching passage. Thermal flow meter according to claim 1, comprising: a flat casing (310) arranged in the main passage (124), wherein the casing limits the secondary passage (307), wherein the measuring surface (451a) of the flow rate measuring unit (451) is perpendicular to a thickness direction of the casing (310). Thermal flow meter according to claim 1, wherein the secondary passage (307) has a second inclined passage (362) on an upstream side in the forward direction with respect to an inlet of the first passage (351), and the second inclined passage (362) has a third inclined surface (373) on the side of the second passage (352) with respect to the flow rate measuring unit (451), wherein the third inclined surface (373) inclines from the side of the second passage (352) to the side of the first passage (351) with respect to the forward direction. Thermal flow meter according to claim 6, wherein the second inclined passage (362) has a fourth inclined surface (374) relative to the third inclined surface (373) in a direction perpendicular to the measuring surface (451a) of the flow rate measuring unit (451), and the fourth inclined surface (374) is inclined from the side of the second passage (352) to the side of the first passage (351) with respect to the forward direction.

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