Thermal flow meter

Abstract

Thermal flow meter, including: a secondary channel (307) that receives part of a fluid (30) flowing through a main channel (124); and a flow metering unit (451) located in the secondary channel, wherein the secondary channel comprises: a first passage (351) provided on a measuring surface side (451a) of the flow measuring unit; a second passage (352) provided on a rear side (451b) of the flow measuring unit; and an inclined passage (361) provided upstream of an inlet (351a) of the first passage in a forward flow direction (F) of the fluid in the first passage, wherein the secondary channel is further provided on a wall surface on the side of the second passage with a convex section (381) which projects in a thickness direction towards an opposite wall surface on the side of the first passage, and wherein the convex section in the region of the inclined passage has an inclined surface (371) which is inclined with respect to the forward flow direction from one side of the second passage to one side of the first passage in order to be closer to the side of the second passage than the flow measuring unit.

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 secondary channel arranged in a main channel through which a fluid flows and which receives a portion of the fluid; a flow measuring element arranged inside the secondary channel and having a heating resistance structure formed therein; and a support on which the flow measuring element is mounted (see claim 1 etc. of PTL 1 described below).

[0003] The conventional flow meter comprises a first fluid channel section and a second fluid channel section. The first fluid channel section consists of a surface on which a flow measuring element is mounted and a passage-forming surface of the secondary channel. The second fluid channel section consists of a surface on the opposite side of the surface on which a flow measuring element is mounted and the passage-forming surface of the secondary channel.

[0004] In a conventional flow meter, the passage-forming surface of the first fluid channel section, which is opposite the flow-sensing element on the upstream side of the fluid flow, has an inclined surface that causes the fluid flow to be aligned with the flow-sensing element. This inclined surface consists of two or more surfaces with different orientations.

[0005] With the above configuration, it is possible to suppress dust from rebounding from an inclined surface located on the opposite side of the upstream heating element of the fluid channel section to the side of the heating element and then flowing with the fluid flow to the heat-generating element. This makes it possible to suppress breakage or contamination of the flow-measuring element configured with the heating element and to provide a highly reliable flow meter that exhibits excellent dust resistance even in a highly variable flow field, such as a pulsating flow, and in which characteristic errors are hardly present (see paragraph 0009 etc. of the same literature). List of reference literature Patent literature

[0006] PTL 1: JP 2012-93203 A

[0007] A thermal flow meter with a configuration similar to the invention, but with a differently designed chamfer of the flow passages in front of the flow measuring surface, is described in DE 10 2012 224 049 A1. Another flow meter with similarities to the present invention is disclosed in DE 199 53 776 A1. Summary of the invention: Technical problem

[0008] With conventional thermal flow meters, there is a risk that the flow velocity measured by the flow measuring element is lower than the actual flow velocity, so the measurement error can increase if the flow velocity of the fluid flowing through the first fluid channel section becomes lower than the flow velocity of the fluid flowing through the second fluid channel section during the pulsation of the fluid.

[0009] The present invention was conceived in view of the above problem, and one object of the present invention is to provide a thermal flow meter that is able to reduce measurement error when a fluid is pulsating compared to the prior art. Solution to the problem

[0010] To solve the above problem, the present invention proposes the thermal flow meters defined in the independent claims. Further advantageous embodiments are described in the dependent claims. Advantageous effects of the invention

[0011] According to the thermal flow meter of the present invention, the first inclined surface of the inclined passage, which is provided upstream of the inlet of the first passage in the forward flow direction, deflects the fluid flowing through the secondary channel from the side of the second passage to the side of the first passage when the fluid pulsates. This increases the flow rate of the fluid flowing through the first passage in the forward flow direction, prevents the measured flow velocity from falling below the actual flow velocity, and reduces the measurement error compared to the prior art. Brief description of the drawings [ Fig. 1] Fig. Figure 1 is a schematic view showing an example of a system with a thermal flow meter according to a first embodiment, which is not an embodiment of the present invention. [ Fig. 2A] Fig. Figure 2A is a front view of the thermal flow meter according to the first embodiment. [ Fig. 2B] Fig. 2B is a left side view of the in Fig. 2A shown thermal flow meter. [ Fig. 2C] Fig. 2C is a rear view of the in Fig. 2A shown thermal flow meter. [ Fig. 2D] Fig. 2D is a right-side view of the in Fig. 2A shown thermal flow meter. [ Fig. 3A] Fig. 3A is a front view of the in Fig. 2A shows the thermal flow meter in a state in which a front cover has been removed. [ Fig. 3B] Fig. 3B is a rear view of the in Fig. 2C shows the thermal flow meter in a state in which a rear cover has been removed. [ Fig. 4A] Fig. 4A is a cross-sectional view along a line IVA-IVA of the in Fig. 2C shown thermal flow meter. [ Fig. 4B] Fig. 4B is a cross-sectional view along a line IVB-IVB of the in Fig. 2C shown thermal flow meter. [ Fig. 5] Fig. 5 is a schematic diagram of a secondary channel of the in Fig. 4A and Fig. 4B shown thermal flow meter. [ 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 front cover of the in Fig. Thermal flow meter shown in 6A. [ Fig. 7A] Fig. 7A is a front view of the rear cover of the [unclear text] Fig. 2C shown thermal flow meter. [ Fig. 7B] Fig. 7B is a rear view of the rear cover of the [unclear text] Fig. Thermal flow meter shown in 7A. [ Fig. 8A] Fig. 8A is a view showing the flow velocity of a fluid passing through the side channel of the in Fig. The flow is shown in section 5 of the thermal flow meter. [ Fig. 8B] Fig. 8B is a view showing the flow velocity of a fluid passing through a side channel without the first inclined surface, as in Fig. 5 shown, flows. [ Fig. 9] Fig. 9 is a graph showing flow measurement results of the in Fig. 8A and Fig. 8B represents the thermal flow meter shown. [ Fig. 10] Fig. Figure 10 is a graph that shows an example of a real flow velocity and a measured flow velocity during pulsation. [ Fig. 11A] Fig. Figure 11A is a graph showing an example of a measurement error of the thermal flow meter in Fig. 8A represents the first embodiment. [ Fig. 11B] Fig. 11B is a graph showing an example of a measurement error of the thermal flow meter of a [system / device]. Fig. 8B represents the comparative example shown. [ Fig. 12] Fig. Figure 12 is a schematic development of a secondary channel of a thermal flow meter according to a second embodiment, which is an embodiment of the present invention. [ Fig. 13] Fig. Figure 13 is a schematic development of a secondary channel of a thermal flow meter according to a third embodiment, which is an embodiment of the present invention. [ Fig. 14] Fig. Figure 14 is a schematic development of a secondary channel of a thermal flow meter according to a fourth embodiment, which is not an embodiment of the present invention. [ Fig. 15] Fig. 15 a schematic development of a secondary channel of a thermal flow meter according to a fifth embodiment, which is not an embodiment of the present invention. Description of embodiments

[0012] Embodiments of a thermal flow meter, which serve as examples or embodiments of the present invention for the purpose of understanding it, are described below with reference to the drawings. (First embodiment)

[0013] Fig. Figure 1 is a schematic representation showing an example of a control system for an internal combustion engine with electronic fuel injection, equipped with a thermal flow meter 300 according to the first embodiment, which is not an embodiment of the present invention. In this system, intake air, as the gas 30 to be measured, is drawn from an air filter 122 based on the operation of an internal combustion engine 110, which has a cylinder 112 and a piston 114, and is introduced, for example, via an intake manifold as the main channel 124, a throttle body 126, and an intake pipe 128 into a combustion chamber of the cylinder 112.

[0014] The flow rate of the gas 30 to be measured, which is the intake air directed into the combustion chamber, is measured by the thermal flow meter 300. Fuel is supplied by a fuel injector 152 based on the measured flow rate and introduced into the combustion chamber as an air-fuel mixture together with the gas 30 to be measured, which is the intake air. In the present embodiment, the fuel injector 152 is arranged in an intake port of the internal combustion engine, and the fuel injected into the intake port is mixed with intake air, the gas 30 to be measured, to produce the air-fuel mixture. The air-fuel mixture is introduced into the combustion chamber via an intake valve 116 and combusted to generate mechanical energy.

[0015] The thermal flow meter 300 is not only used in the system for injecting fuel into the intake manifold of the Fig. The system can be used not only in the internal combustion engine shown in Figure 1, but also in a system for direct fuel injection into each combustion chamber. In both cases, the basic concepts of a control parameter measurement method using the thermal flow meter 300 and an internal combustion engine control method based on a fuel quantity and an ignition timing are essentially the same, and Fig. Figure 1 illustrates the system for fuel injection into the intake manifold as a representative example of both systems.

[0016] The fuel and air introduced into the combustion chamber are in the state of an air-fuel mixture, which is explosively ignited by a spark plug 154, generating mechanical energy. After combustion, the gas is directed through an exhaust valve 118 into an exhaust pipe and expelled from the vehicle as exhaust gas 24. The flow rate of the gas 30 to be measured, which is the intake air introduced into the combustion chamber, is regulated by a throttle valve 132, the opening of which is changed by actuating an accelerator pedal. A quantity of fuel is regulated based on the flow rate of the intake air directed to the combustion chamber, and a driver can control the mechanical energy generated by the internal combustion engine by regulating the opening of the throttle valve 132 and the flow rate of the intake air directed to the combustion chamber.

[0017] The flow rate and temperature of the gas 30 to be measured, which is the intake air taken from the air filter 122 and flowing through the main channel 124, are measured by the thermal flow meter 300, and electrical signals indicating the measured flow rate and temperature of the intake air are input from the thermal flow meter 300 to a control unit 200. Additionally, an output from a throttle angle sensor 144, which measures the opening degree of the throttle valve 132, is input to the control unit 200. Furthermore, an output from a rotary angle sensor 146 is input to the control unit 200 to measure the position or state of the piston 114, the intake valve 116, or the exhaust valve 118 of the internal combustion engine, as well as the rotational speed of the internal combustion engine.An output from an oxygen probe 148 is entered into the control unit 200 to measure a mixing ratio between the amount of fuel and the amount of air based on the condition of the exhaust gas 24.

[0018] The control unit 200 calculates the fuel injection quantity and ignition timing, for example, based on the flow rate, humidity, and temperature of the intake air (outputs from the thermal flow meter 300) and the engine speed (measured by the rotational angle sensor 146), etc. The fuel quantity supplied by the injector 152 and the ignition timing of the spark plug 154 are controlled based on these calculation results. In practice, the fuel quantity and ignition timing are controlled based on the intake air temperature (measured by the thermal flow meter 300), changes in the throttle angle, changes in the engine speed, and the air-fuel ratio (measured by the oxygen sensor 148).The control unit 200 also regulates the amount of air that bypasses the throttle valve 132 when the internal combustion engine is idling, using an idle air control valve 156, and regulates the speed of the internal combustion engine when idling.

[0019] Both the fuel quantity and the ignition timing, which are essential control variables of the internal combustion engine, are calculated as primary parameters based on the output of the thermal flow meter 300. Therefore, improving the measurement accuracy of the thermal flow meter 300, suppressing changes over time, and increasing its reliability are crucial for enhancing the control accuracy of a vehicle and ensuring its reliability. In recent years, the demands on fuel economy and exhaust gas purification have increased dramatically, particularly in vehicles. To meet these demands, it is essential to increase 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.

[0020] 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 images are each a left side view, a rear view, and a right side view of the object in Fig. 2A shown thermal flow meter.

[0021] The thermal flow meter 300 has a housing 310 consisting of a jacket 302, a front cover 303, and a rear cover 304. The front cover 303 and the rear cover 304 have a thin, flat shape with a large cooling surface. Thus, the thermal flow meter 300 has a structure in which air resistance is reduced and the housing 310 is slightly cooled by the gas to be measured, which flows through the main channel 124.

[0022] For example, the 310 housing has an essentially rectangular, parallelepiped flat shape and is, as in Fig. 1 shown inserted into the intake pipe and arranged inside the main channel 124. Although the details are described further below, the housing 310 defines a secondary channel that receives a portion of the gas 30 to be measured, which is a fluid flowing through the main channel 124.

[0023] In the following, each part of the thermal flow meter 300 is described using an orthogonal XYZ coordinate system, wherein a longitudinal direction of the housing 310, which is essentially parallel to the flow of the gas 30 to be measured in the main channel 124, is an X-axis direction, a vertical direction of the housing 310, which is perpendicular to the longitudinal direction and essentially parallel to a radial direction of the main channel 124, is a Y-axis direction, and a thickness direction of the housing 310, which is perpendicular to the longitudinal direction and to the vertical direction, is a Z-axis direction.

[0024] The housing 310 has a shape whose length extends along an axis from an outer wall of the main channel 124 to its center, and has a flat shape with a small thickness, as in Fig. 2B and Fig. The 2D representation shows that the housing 310 of the thermal flow meter 300 has a shape where the thickness along the side surface is thin and the front surface is essentially rectangular. This makes it possible to provide the thermal flow meter 300 with a secondary channel of sufficient length, thereby reducing the fluid resistance relative to the gas 30 being measured.

[0025] A flange 305, configured to attach the thermal flow meter 300 to the intake pipe, and a connector 306, which is an externally exposed connector outside the intake pipe for electrical connection to an external device, are provided on a proximal end section of the jacket 302. The jacket 302 is supported by the attachment of the flange 305 to the intake pipe.

[0026] Fig. 3A is a front view of the in Fig. 2A shows the thermal flow meter 300 in a state in which the front cover 303 has been removed. Fig. 3B is a rear view of the in Fig. 2C shows the thermal flow meter 300 in a state in which a rear cover 304 has been removed.

[0027] An inlet 311, configured to introduce a portion of the gas 30 to be measured, such as intake air (which is the fluid flowing through the main channel 124), into a secondary channel 307, is located at a position on a distal end face of the casing 302 and on an upstream side in a main flow direction. Accordingly, the inlet 311, configured to introduce the gas 30 to be measured flowing through the main channel 124 into the secondary channel 307, is located on the distal end face of the casing 310 and extends from the flange 305 in the radial direction of the main channel 124 towards its center.

[0028] This makes it possible to introduce a gas from a point located away from an inner wall surface of the main channel 124 into the secondary channel 307, thereby suppressing a decrease in the measurement accuracy of the flow rate and temperature of the gas, since it is hardly affected by the temperature of the inner wall surface of the main channel 124. Furthermore, the fluid resistance near the inner wall surface of the main channel 124 is high, and the flow velocity is lower than the average flow velocity of the main channel 124. Since the inlet 311 in the thermal flow meter 300 of the present embodiment is provided at the distal end section of the thin and long housing 310, which extends from the flange 305 to the center of the main channel 124, it is possible to introduce a gas with a high flow velocity into the secondary channel 307 at a central section of the main channel 124.

[0029] A first outlet 312 and a second outlet 313, configured to return the gas 30 to be measured from the secondary channel 307 to the main channel 124, are provided on the distal end of the jacket 302 and on an outflow side in the main flow direction. As shown in Fig. In the 2D representation, the first outlet 312 and the second outlet 313 are arranged side by side in the thickness direction (Z-axis direction) of the casing 302. Since the first outlet 312 and the second outlet 313, which are the outlet openings of the secondary channel 307, are thus provided at the distal end section of the casing 310, it is possible to redirect the gas flowing in the secondary channel 307 in the vicinity of the central section of the main channel 124, where the flow velocity is high.

[0030] A circuit package 400, comprising a flow meter 451 configured to measure the flow rate of the gas 30 flowing through the main channel 124, and a temperature meter 452 configured to measure the temperature of the gas 30 flowing through the main channel 124, and the like, is integrally cast into the jacket 302. Additionally, secondary channel grooves 330 and 331 are formed in the jacket 302, configured to define the secondary channel 307. In the present embodiment, the secondary channel grooves 330 and 331 are each recessed on a front and a back side of the jacket 302, respectively.

[0031] Therefore, it is possible to form the housing 310, which defines the secondary channel 307, by attaching the front cover 303 and the rear cover 304 to the front and rear of the jacket 302, respectively, to cover the secondary channel grooves 330 and 331 of the jacket 302 with the front cover 303 and the rear cover 304. For example, with a jacket 302 in such a configuration, it is possible to perform the molding of the jacket 302 and the formation of the secondary channel grooves 330 and 331 on the front and rear in a single resin molding step of the jacket 302 molding process, using molds arranged on both sides of the jacket 302.

[0032] As in Fig. As shown in 3B, the secondary channel grooves 331, which are provided on the rear side of the jacket 302, have a straight groove section 332 configured to define a straight passage 307A in a part of the secondary channel 307, and a branched groove section 333 configured to define a branched passage 307B in a part of the secondary channel 307.

[0033] The straight groove section 332 runs in a straight line along the main flow direction (positive X-axis direction) of the gas 30 to be measured at the distal end section of the jacket 302 such that one end of it is connected to the inlet 311 of the jacket 302 and the other end is connected to the first outlet 312 of the jacket 302. The straight groove section 332 has a straight section 332A, which extends from the inlet 311 such that it has a substantially constant cross-sectional shape, and a throttling section 332B, in which the groove width gradually narrows from the straight section 332A to the first outlet 312. The first outlet 312 serves as an outlet opening for releasing a fluid flowing through the straight passage 307A of the secondary channel 307, that is, a portion of the gas 30 to be measured. By providing the first outlet 312, foreign bodies such as, for example,Dust is released from the secondary channel 307, thereby making it possible to reduce the total amount of foreign matter introduced into the branched passage 307B of the secondary channel 307 and to prevent a decrease in the measuring performance of the flow measuring unit 451.

[0034] The branched groove section 333, which branches off from the straight section 332A of the straight groove section 332, extends towards the proximal end face of the shell 302, curving as it does so, and is connected to a measuring flow path 341, which is provided in a central section in a vertical direction (Y-axis direction), corresponding to the longitudinal direction of the shell 302. An upstream end of the branched groove section 333 is connected to a side wall surface 332a of a pair of side wall surfaces forming the straight groove section 332, located on the proximal end face of the shell 302, and a bottom wall surface 333a is continuously flush with a bottom wall surface of the straight section 332A of the straight section 332.

[0035] A receiving groove section 333A is provided on a side wall surface on an inside of the curve of the branched groove section 333. The receiving groove section 333A has a concave section 333B. The concave section 333B receives water that has entered the receiving groove section 333A, and the water is drained from a drainage hole 376 drilled at a location opposite the concave section 333B of the rear cover 304, as shown in Fig. 2C is shown, omitted from housing 310.

[0036] The measuring flow path 341 is formed by traversing the sheath 302 from the front to the back in the thickness direction. A section 430 of the circuit package 400, exposed in the flow path, is arranged such that it projects into the measuring flow path 341. The branched groove section 333 is connected to the measuring flow path 341 on the upstream side of the secondary channel 307 with respect to the section 430 of the circuit package 400 exposed in the flow path.

[0037] In the thermal flow meter 300 of the present embodiment, the secondary channel groove 331, which defines the secondary channel 307, has a steeply inclined section 333d on the upstream side of the gas 30 to be measured in the measuring flow path 341, which is described below. That is, the branched groove section 333 of the secondary channel groove 331, which defines the branched passage 307B of the secondary channel 307, extends in the vertical direction (Y-axis direction) of the casing 302 from the straight groove section 332 to the measuring flow path 341, curving in one direction (negative X-axis direction) opposite to the main flow direction of the gas 30 to be measured in the main channel 124.

[0038] The branched passage 307B of the secondary channel 307, defined by the branched groove section 333, is provided with the measuring flow path 341, which is oriented from the distal end of the jacket 302 to the proximal end, which is the flange 305 side, and traces a curve at a position closest to the flange 305. In the measuring flow path 341, the gas 30 to be measured, flowing through the secondary channel 307, flows in the opposite direction to the main flow direction of the main channel 124 (negative x-axis direction).

[0039] In the thermal flow meter 300 of the present embodiment, the branched groove section 333 has a three-dimensional shape, wherein a groove depth in the thickness direction (Z-axis direction) of the shell 302 gradually becomes deeper towards the measuring flow path 341 (see Fig. 4A). In the thermal flow meter 300 of the present embodiment, the branched groove section 333 has the strongly inclined section 333d, which is deeply recessed in front of the measuring flow path 341.

[0040] In the measuring flow path 341, the steeply inclined section 333d serves to allow a portion of the gas 30 to be measured to pass to a front face 431, on which the measuring surface 451a of the flow measuring unit 451 is located between the front face 431 and a rear face 432 of the exposed section 430 of the circuit assembly 400 in the flow path. Furthermore, the steeply inclined section 333d allows foreign matter, such as dust, contained in the gas 30 to be measured, to pass to the rear face 432 of the exposed section 430 of the circuit assembly 400, which corresponds to the rear face of the flow measuring unit 451, thereby improving the contamination resistance of the measuring surface 451a of the flow measuring unit 451.

[0041] This means that a portion of air, which has a small mass, moves along the steeply inclined section 333d and flows through a first passage 351 (see Fig. 4B) on the front side 431 of the exposed section 430 of the circuit assembly 400 in the flow path, that is, on the measuring surface 451a side of the flow measuring unit 451 in the measuring flow path 341. In contrast, due to centrifugal force, foreign bodies with large mass find it difficult to suddenly change course along the curve of the branched passage 307B of the secondary channel 307. Therefore, foreign bodies with large mass cannot follow the steeply inclined section 333d, but instead flow through a second passage 352 (see Fig. 4B) on the back side 432 of the exposed section 430 of the circuit package 400 in the flow path, that is, on the back side 451b of the flow measuring unit 451.

[0042] The secondary channel groove 330, which is located on the front of the in Fig. The jacket 302 shown in Figure 3A defines a section of the secondary channel 307 on the downstream side of the branched passage 307B. The section on the downstream side of the branched passage 307B, defined by the secondary channel groove 330, has one end that connects on the rear side of the jacket 302 via the measuring flow path 341 to a section on the upstream side of the branched passage 307B, and the other end connects to the second outlet 313 formed on the distal end side of the jacket 302.

[0043] The secondary channel groove 330, provided on the front of the jacket 302, is shaped such that it gradually curves towards the distal end of the jacket 302 in the direction of the main flow, so that it runs linearly towards the distal end of the jacket 302 in the direction of the main flow of the gas 30 to be measured, and has a groove width that gradually narrows towards the second outlet 313. The gas 30 to be measured and the foreign matter that has passed through the measuring flow path 341 flow through a downstream section of the branched passage 307B of the secondary channel 307, which is defined by the secondary channel groove 330 provided on the front of the jacket 302, and are discharged through the second outlet 313 and returned to the main channel 124.

[0044] The exposed section 430 of the circuit assembly 400 in the flow path projects from a wall surface of the branched groove section 333 of the secondary channel groove 331, which defines the flow path 341, in the vertical direction (Y-axis direction) of the casing 302 to the distal end of the casing 302. The exposed section 430 in the flow path has a thickness in the thickness direction (Z-axis direction) of the casing 302 and is formed in a rectangular plate shape along the flow direction of the gas 30 to be measured flowing through the flow path 341. The exposed section 430 in the flow path serves as a supporting element that carries the flow measuring unit 451 in order to position the flow measuring unit 451 in the secondary channel 307.

[0045] Fig. 4A is a cross-sectional view along a line IVA-IVA of the in Fig. 2C shown thermal flow meter 300. Fig. 4B is a cross-sectional view along a line IVB-IVB of the in Fig. 2C shown thermal flow meter 300.

[0046] The secondary channel 307 has the first passage 351, which is provided on the measuring surface 451a side of the flow measuring unit 451 in the measuring flow path 341, and the second passage 352, which is provided on the rear side 451b of the flow measuring unit 451. Additionally, the secondary channel 307 has the inclined passage 361, which is provided in the forward flow direction F of the fluid in the first passage 351, that is, in the forward flow direction F of the gas 30 to be measured in the first passage 351, upstream of the inlet 351a of the first passage 351.

[0047] The air, which is the gas 30 to be measured, flows along the forward flow direction F of the gas 30 in the first passage 351 of the measuring flow path 341. Heat is transferred to the gas 30 via the measuring surface 451a, which is a heat transfer surface provided in the flow measuring unit 451, thereby measuring the flow rate. A general measuring principle for thermal flow meters can be applied to measure the flow rate. The configuration of the flow measuring unit 451 is not particularly restricted, provided that it is possible to measure the flow rate of the gas 30 flowing through the main channel 124 based on a measurement taken by the flow measuring unit 451, as in the thermal flow meter 300 of the present embodiment.

[0048] The thermal flow meter 300 of the present embodiment is characterized by the inclined passage 361, which is provided in the forward flow direction F of the gas 30 to be measured in the first passage 351 upstream of the inlet 351a of the first passage 351, on the measuring surface 451a side of the flow measuring unit 451, in the measuring flow path 341 of the secondary channel 307. The inclined passage 361 comprises the first inclined surface 371, which is inclined with respect to the forward flow direction F of the gas 30 to be measured from the side of the second passage 352 to the side of the first passage 351, in order to be located closer to the side of the second passage 352 than the flow measuring unit 451.

[0049] The thermal flow meter 300 of the present embodiment also comprises the flat housing 310, which is arranged in the main channel 124 and defines the secondary channel 307, as described above. However, the measuring surface 451a of the flow measuring unit 451 arranged in the secondary channel 307 is essentially perpendicular to the thickness direction (Z-axis direction) of the housing 310.

[0050] In the thermal flow meter 300 of the present embodiment, the secondary channel 307 has the straight passage 307A, which receives a portion of the fluid flowing through the main channel 124, which is the gas 30 to be measured, as described above (see Fig. 3B). Additionally, the secondary channel 307 has the first outlet 312, which is the outlet opening for releasing a portion of the gas 30 to be measured, which is the fluid flowing through the straight passage 307A, and the branched passage 307B, which branches off from the straight passage 307A upstream of the first outlet 312 in the forward flow direction of the fluid flowing through the straight passage 307A. The first passage 351, the second passage 352, and the inclined passage 361, which were described above, are all provided in the branched passage 307B.

[0051] Fig. 5 is a schematic diagram of the secondary channel 307 of the in Fig. 4A and Fig. 4B shows the thermal flow meter 300. In Fig. Figure 5 shows a cross-section along the thickness direction (Z-axis direction) of the housing 310 in the front and rear sections of the measuring flow path 341 of the secondary channel 307 in a state in which it is developed as a cross-section parallel to a thickness direction (Z-axis direction) and a length direction (X-axis direction) of the housing 310.

[0052] As described above, the thermal flow meter 300 of the present embodiment comprises: the secondary channel 307, which receives a portion of the fluid flowing through the main channel 124, which is the gas 30 to be measured, and the flow measuring unit 451, which is arranged inside the secondary channel 307. The secondary channel 307 additionally comprises: the first passage 351, which is provided on the measuring surface 451a side of the flow measuring unit 451; the second passage 352, which is provided on the rear side of the flow measuring unit 451; and the inclined passage 361, which is provided upstream of the inlet 351a of the first passage 351 in a forward flow direction F of the gas 30 to be measured in the first passage 351.The inclined passage 361 comprises the first inclined surface 371, which is inclined with respect to the forward flow direction F of the gas 30 to be measured from the side of the second passage 352 to the side of the first passage 351, in order to be closer to the side of the second passage 352 than the flow measuring unit 451.

[0053] Furthermore, the inclined passage 361 in the Fig. In the example shown in Figure 5, a second inclined surface 372 is shown, which is opposite the first inclined surface 371 in the direction perpendicular to the measuring surface 451a of the flow measuring unit 451 (Z-axis direction). Corresponding to the first inclined surface 371, the second inclined surface 372 is inclined with respect to the forward flow direction F of the gas 30 to be measured, from the side of the second passage 352 to the side of the first passage 351. As shown in Fig. As shown in 3B, the second inclined surface 372 is provided on a bottom of the branched groove section 333 of the shell 302 and forms the strongly inclined section 333d in the branched groove section 333 of the shell 302.

[0054] Additionally, in the Fig. In the example shown in Figure 5, the inclination angle θ2 of the second inclined surface 372 with respect to the forward flow 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 flow direction F of the gas 30 to be measured. That is, the angle difference between the inclination angle θ1 of the first inclined surface 371 and the inclination angle θ2 of the second inclined surface 372 can, for example, be set between 3° and 15°.

[0055] Additionally, in the Fig. In the example shown in Figure 5, a section of the secondary channel 307 is provided in front of the inclined passage 361 in the forward flow direction F of the gas 30 to be measured on the second passage 352 side of the first passage 351 in the direction perpendicular to the measuring surface 451a of the flow measuring unit 451 (Z-axis direction).

[0056] Additionally, the intersections in Fig. In the example shown in Figure 5, an extension line L1 of the first inclined surface 371 and an extension line L2 of the measuring surface 451a are located upstream of the measuring surface 451a in the forward flow direction F of the gas 30 to be measured in the cross-section of the secondary channel 307, perpendicular to the measuring surface 451a of the flow measuring unit 451 and parallel to the forward flow direction F of the gas 30 to be measured. Additionally, the extension line L1 of the first inclined surface 371 and the extension line L2 of the measuring surface 451a can intersect upstream of an upstream end section of the exposed section 430 of the circuit assembly 400, which serves as the support section for the flow meter 451, in the forward flow direction F of the gas 30 to be measured.

[0057] Fig. 6A and Fig. Figures 6B are each a front view and a rear view of the front cover 303 of the in Fig. 2A shown thermal flow meter. Fig. 7A and Fig. Figures 7B are each a front view and a rear view of the rear cover 304 of the in Fig. 2C shown thermal flow meter.

[0058] As described above, the front cover 303 and the rear cover 304 are components of the housing 310, which defines the secondary channel 307, and each has secondary channel grooves 335 and 336 configured to define the secondary channel 307 on the rear side opposite the jacket 302. The secondary channel groove 335 of the front cover 303, together with the one in Fig. 3A shows the secondary channel groove 330 of the jacket 302, the measuring flow path 341 of the secondary channel 307 and the downstream section thereof.

[0059] The secondary channel grooves 336 of the rear cover 304 have a straight groove section 337 configured to define the straight passage 307A in a portion of the secondary channel 307, and a branched groove section 338 configured to define the branched passage 307B in a portion of the secondary channel 307 located on the rear side of the cover 304. Fig. The secondary channel grooves 331 shown in 3B correspond to the mantle 302 shown. The first inclined surface 371 of the in Fig. 4A and Fig. The inclined passage 361 shown in Figure 5 is located on the bottom part of the branched groove section 338 of the in Fig. The rear cover 304 shown in Figure 7B is provided. The first inclined surface 371 is continuously connected to a wall surface 304a, which is provided on the bottom part of the branched groove section 338 of the rear cover 304.

[0060] As in Fig. 4A and Fig. As shown in Figure 5, the wall surface 304a is designed to define the measuring flow path 341 of the secondary channel 307 and to be opposite the second passage 352 on the rear side 451b of the flow measuring unit 451. Since the wall surface 304a, which regulates the width of the second passage 352 in the thickness direction (Z-axis direction) of the housing 310, is designed in this way, it is possible to improve the flow velocity of the gas 30 to be measured flowing through the measuring flow path 341.

[0061] The following describes the functions of the thermal flow meter 300 of the embodiment.

[0062] Fig. 8A is a view showing the flow velocity of the fluid passing through secondary channel 307 of the in Fig. The thermal flow meter 300 shown in diagram 5 is flowing. Fig. 8A shows the flow velocity of the gas 30 to be measured flowing through the secondary channel 307, represented by black and white shading, and the flow velocity of the gas 30 to be measured is higher the darker the color.

[0063] In the thermal flow meter 300 of the present embodiment, it is possible to deflect the flow of the gas 30 to be measured through the first inclined surface 371 of the inclined passage 361, which is provided upstream of the inlet 351a of the first passage 351 of the secondary channel 307 in the forward flow direction F, from the side of the second passage 352 to the side of the first passage 351. This makes it possible to increase the flow velocity of the fluid flowing through the first passage 351 in the forward flow direction F, even when the gas 30 to be measured is pulsating, compared to the prior art.

[0064] Fig. Figure 8B is a view representing the flow velocity of a fluid flowing through the secondary channel 307 of a thermal flow meter of a comparative example, in which the in Fig. The first inclined surface 371 shown in Figure 5 is not provided for. Fig. 8B is the flow velocity of the gas to be measured 30 as in Fig. 8A is represented by black and white shading.

[0065] In the thermal flowmeter of the comparative example, which does not have a first inclined surface 371, the deflection effect of the flow of the gas 30 to be measured from the side of the second passage 352 to the side of the first passage 351 in the forward flow direction F is small. Therefore, the flow velocity of the gas 30 to be measured flowing through the first passage 351 is lower than the flow velocity of the gas 30 to be measured flowing through the second passage 352, and the flow rate of the fluid flowing through the first passage 351 in the forward flow direction F even decreases when the gas 30 to be measured pulsates. This inclination becomes evident when the section of the secondary channel 307 upstream of the inclined passage 361 is positioned closer to the side of the second passage 352 than the first passage 351 in the direction perpendicular to the measuring surface 451a of the flowmeter 451.

[0066] Fig. Figure 9 is a graph representing a measurement result of the flow velocity, obtained with the thermal flow meter 300 of the in Fig. 8A shown in the present embodiment, and a measurement result of the flow velocity, which was obtained with the thermal flow meter of the in Fig. The comparative example shown in 8B was obtained. In the graph of Fig. Figure 9 represents the horizontal axis as an input flow velocity, that is, the actual flow velocity of the gas 30 to be measured, and the vertical axis represents an output flow velocity, that is, the flow velocity output by the thermal flow meter 300 of the present embodiment and by the thermal flow meter of the comparison example, respectively. When the input flow velocity changes during the pulsation of the gas 30 to be measured, the output flow velocity in the thermal flow meter of the comparison example decreases significantly compared to the input flow velocity, whereas in the thermal flow meter 300 of the present embodiment, the decrease in the output flow velocity is suppressed.

[0067] Fig. Figure 10 is a graph showing an example of a real flow velocity of a fluid during pulsation and the flow velocities of the fluid measured by the thermal flow meter 300 of the present embodiment and by the thermal flow meter of the comparison example. In the graph of Fig. 10 the horizontal axis represents time, the vertical axis represents the flow velocity, the solid line represents the actual flow velocity of the gas 30 to be measured, that is, the input flow velocity, the dashed line represents the flow velocity measured by the thermal flow meter 300 of the present embodiment, and the dash-dotted line represents the flow velocity measured by the thermal flow meter of the comparison example.

[0068] In the example of Fig. 10. The flow velocity of the gas 30 to be measured is measured by the thermal flow meter 300 of the present embodiment and by the thermal flow meter of the comparison example, while the inlet flow velocity changes from 3 m / s to 0 m / s or less, with a reference value of 1 m / s. In the thermal flow meter 300 of the present embodiment, the flow velocity of the first passage 351 in the forward flow direction F of the gas 30 to be measured takes on the following characteristics: Fig. 8A shown, so that a maximum value of the measured flow velocity as shown by the dashed line in Fig. The displayed value increases from 10, and as a result, a mean value V1 of the measured flow velocities corresponds approximately to a mean value V0 of the input flow velocities.

[0069] In the thermal flow meter of the comparison example, however, the flow velocity of the first passage 351 in the forward flow direction F of the gas 30 to be measured takes on the following characteristics: Fig. 8B shown, so that a maximum value of the measured flow velocity as shown by the dashed line in Fig. The displayed value of 10 does not increase sufficiently, and as a result, the mean V2 of the measured flow velocities falls below the mean V0 of the input flow velocities.

[0070] Since the mean value V1 of the flow velocities in the thermal flow meter 300 of the present embodiment is used, for example, as a measured value of the flow velocities, it is important to suppress the drop in the mean value V1 of the flow velocities below the mean value V0 of the actual flow velocities of the gas 30 to be measured. As described in Fig. As shown in Figure 10, in the thermal flow meter 300 of the present embodiment it is possible to shift the mean value V1 of the flow velocities more to a positive side than the mean value V2 of the flow velocities obtained by the thermal flow meter of the comparison example, in order to approach the mean value V0 of the actual flow velocities of the gas 30 to be measured.

[0071] Fig. 11A and Fig. Figures 11B are graphs, each showing examples of measurement errors of the in Fig. 8A thermal flow meter of the first embodiment and of the one shown in Fig. Figure 8B shows the thermal flow meter of the comparison example. As in Fig. As shown in Figure 11A, it is possible to suppress an error in the measured flow velocity in the thermal flow meter 300 of the first embodiment, even if a pulsation amplitude of the flow velocity of the gas 30 to be measured increases, since the flow velocity of the first passage 351 increases in the flow direction F of the gas 30 to be measured, as shown in Fig. 8A shown. In contrast, in the thermal flow meter of the comparison example, an error in the flow velocity to be measured increases when a pulsation amplitude of the flow velocity of the gas 30 to be measured increases, since the flow velocity of the first passage 351 decreases in the forward flow direction F of the gas 30 to be measured, as shown in Fig. 8B shown.

[0072] Accordingly, the thermal flow meter 300 of the present embodiment is provided with the inclined passage 361, which is located upstream of the inlet 351a of the first passage 351 in the forward flow direction F of the gas 30 to be measured in the first passage 351 in the measuring flow path 341 of the secondary channel 307 on the measuring surface 451a side of the flow measuring unit 451. Furthermore, the inclined passage 361 comprises the first inclined surface 371, which is inclined with respect to the forward flow direction F of the gas 30 to be measured from the side of the second passage 352 to the side of the first passage 351, in order to be located closer to the side of the second passage 352 than the flow measuring unit 451.

[0073] With such a configuration, the thermal flow meter 300 of the present embodiment is able to deflect the flow of the gas 30 to be measured in the forward flow direction F through the first inclined surface 371 of the first inclined passage 361 from the side of the second passage 352 to the side of the first passage 351. This makes it possible to increase the flow rate of the gas 30 to be measured flowing through the first passage 351 in the forward flow direction F, even when the gas 30 to be measured is pulsating, compared to the prior art. Therefore, according to the present embodiment, the thermal flow meter 300 is able to suppress a drop in the flow velocity measured by the flow measuring unit 451 below the actual flow velocity, even when the gas 30 to be measured is pulsating, and to reduce the measurement error compared to the prior art.

[0074] Furthermore, the inclined passage 361 in the thermal flow meter 300 of the present embodiment has a second inclined surface 372, which is opposite the first inclined surface 371 in the direction perpendicular to the measuring surface 451a of the flow measuring unit 451 (Z-axis direction), as shown in Fig. Figure 5 shows the diagram. Furthermore, the second inclined surface 372 is inclined with respect to the forward flow direction F of the gas 30 to be measured, from the side of the second passage 352 to the side of the first passage 351, which corresponds to the first inclined surface 371. This makes it possible to suppress the formation of vortices in the flow of the gas 30 to be measured, which was deflected by the first inclined surface 371 of the first inclined passage 361, and to increase the flow rate of the gas 30 to be measured through the first passage 351 in the forward flow direction F.

[0075] Additionally, 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 flow 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 flow direction F of the gas 30 to be measured. This makes it possible to more effectively suppress the formation of turbulence in the flow of the gas 30 to be measured, which has been deflected by the first inclined surface 371 of the first inclined passage 361, and to increase the flow rate of the gas 30 to be measured through the first passage 351 in the forward flow direction F. Furthermore, it is possible to reconcile the contamination resistance of the flow measuring unit 451 with the reduction of the measured flow velocity of the thermal flow meter 300 compared to the actual flow velocity of the gas 30 to be measured.

[0076] Furthermore, it is possible to suppress the vortex that is highly likely to occur in a pipe with an expanded diameter by adjusting the angle difference between the inclination angle θ1 of the first inclined surface 371 and the inclination angle θ2 of the second inclined surface 372 to, for example, between 3° and 15°. That is, the angle at which the inclined passage 361 expands in diameter is gently adjusted to correct the flow of the gas 30 to be measured in the measuring flow path 341 in such a way that it is possible to stabilize the flow of the gas 30 to be measured in the first passage 351 and in the second passage 352.

[0077] Additionally, in the thermal flow meter 300 of the present embodiment, the section of the secondary channel 307 is provided upstream of the inclined passage 361 in the forward flow direction F of the gas 30 to be measured on the second passage 352 side of the first passage 351 in the direction perpendicular to the measuring surface 451a of the flow measuring unit 451 (Z-axis direction).

[0078] If the inclined passage 361 does not have a first inclined surface 371, as in Fig. As shown in Figure 8B, the flow velocity of the gas 30 to be measured flowing through the second passage 352 is higher than the flow velocity of the gas 30 to be measured flowing through the first passage 351, and the flow velocity of the gas 30 to be measured flowing through the first passage 351 therefore decreases. However, if the inclined passage 361 has the first inclined surface 371, it is possible to deflect the flow of the gas 30 to be measured in the forward flow direction F from the side of the second passage 352 to the side of the first passage 351 and to increase the flow velocity in the forward flow direction F of the fluid flowing through the first passage 351.

[0079] Additionally, in the thermal flow meter 300 of the present embodiment, the extension line L1 of the first inclined surface 371 and the extension line L2 of the measuring surface 451a intersect in front of the measuring surface 451a in the forward flow direction F of the gas 30 to be measured, as shown in Fig. Figure 5 shows this. This increases the probability that the gas 30 to be measured, which has been deflected from the side of the second passage 352 towards the side of the first passage 351 by flowing along the first inclined surface 371, will be introduced into the first passage 351. Furthermore, if the extension line L1 of the first inclined surface 371 and the extension line L2 of the measuring surface 451a intersect upstream of the upstream end section of the exposed section 430 of the circuit assembly 400 in the flow path, the deflected gas 30 to be measured will be more easily introduced into the first passage 351.

[0080] As described above, the thermal flow meter 300 according to the present embodiment is able to suppress a drop in the flow velocity measured by the flow measuring unit 451 below the actual flow velocity and to reduce the measurement error even when the gas 30 to be measured is pulsating compared to the prior art. (Second embodiment)

[0081] Next, a second embodiment, which is an exemplary embodiment of the thermal flow meter of the present invention, will be described using the following examples: Fig. 12 Referring to Fig. 1 to 4B and Fig. Described in sections 6A to 7B. Fig. Figure 12 is a schematic diagram of the secondary channel 307 of a thermal flow meter of the present embodiment, which Fig. 5 of the thermal flow meter 300 of the first embodiment corresponds.

[0082] The thermal flow meter of the present embodiment is described below in terms of its differences from the thermal flow meter 300 described above. Fig. The first embodiment is described in Figure 5. The thermal flow meter of the present embodiment has the same configuration as the thermal flow meter of the first embodiment, except for the configuration described below. Therefore, identical parts to those of the thermal flow meter 300 of the first embodiment are identified by the same reference numerals, and their description is omitted.

[0083] As in Fig. As shown in Figure 12, the thermal flow meter of the present embodiment is provided with a convex section 381 on a wall surface on the side of the second passage 352 between wall surfaces of the secondary channel 307 that are opposite each other in the thickness direction (Z-axis direction) of the housing 310. The convex section 381 projects in the thickness direction (Z-axis direction) of the housing 310. The convex section 381 has the first inclined surface 371. One area in which the first inclined surface 371 is provided is the inclined passage 361 in the secondary channel 307 of the thermal flow meter of the present embodiment.

[0084] The first inclined surface 371, which is in Fig. As shown in Figure 12, it is provided on the second passage 352 side of the flow measuring unit 451 and is inclined with respect to the forward flow direction F from the side of the second passage 352 to the side of the first passage 351, which is shown in Fig. The first inclined surface shown in Figure 5 corresponds to this. Additionally, the extension line L1 of the first inclined surface 371 and the extension line L2 intersect in the forward flow direction F in front of the measuring surface 451a and in the forward flow direction F in front of the exposed section 430 of the circuit assembly 400, which is the support section of the flow meter 451 in the forward flow direction F, in the first inclined surface 371, as shown in Figure 5. Fig. 12 shown.

[0085] In addition, the inclined passage 361 of the secondary channel 307 in the thermal flow meter of the present embodiment does not have a second inclined surface 372, and a section of the secondary channel 307 upstream of the inclined passage 361 in the forward flow direction F is not provided on the side of the second passage 352 in relation to the first passage 351 in the direction perpendicular to the measuring surface 451a.

[0086] However, the thermal flow meter of the present embodiment has in the secondary channel 307 the first passage 351, the second passage 352 and the inclined passage 361, and the inclined passage 361 has the first inclined surface 371 which is inclined with respect to the forward flow direction F from the side of the second passage 352 to the side of the first passage 351 in order to be closer to the side of the second passage 352 than the flow measuring unit 451, which corresponds to the thermal flow meter 300 of the first embodiment.

[0087] Therefore, according to the present embodiment, the thermal flow meter is able to deflect the flow of the gas 30 to be measured in the forward flow direction F through the first inclined surface 371 of the inclined passage 361 from the side of the second passage 352 to the side of the first passage 351 and to obtain the same effects as those of the thermal flow meter 300 of the first embodiment. (Third embodiment)

[0088] Next, a third embodiment, which is an exemplary embodiment of the thermal flow meter of the present invention, will be described using the following examples: Fig. 13 Referring to Fig. 1 to 4B and Fig. Described in sections 6A to 7B. Fig. Figure 13 is a schematic diagram of the secondary channel 307 of a thermal flow meter of the present embodiment, which Fig. 5 of the thermal flow meter 300 of the first embodiment corresponds.

[0089] The thermal flow meter of the present embodiment is described below in terms of its differences from the thermal flow meter 300 described above. Fig. The second embodiment is described in Figure 12. The thermal flow meter of the present embodiment has the same configuration as the thermal flow meter of the second embodiment, except for the configuration described below. Therefore, identical parts of the thermal flow meter of the second embodiment and of the thermal flow meter 300 of the first embodiment are identified by the same reference numerals, and their description has been omitted.

[0090] As in Fig. As shown in Figure 13, in the thermal flow meter of the present embodiment, the wall surface 304a projects on the side of the second passage 352 between wall surfaces of the secondary channel 307, which are opposite each other in the thickness direction (Z-axis direction) of the housing 310. The wall surface 304a is provided, for example, by a projecting rear side of the rear cover 304. The first inclined surface 371 is provided at an end section of the wall surface 304a on the upstream side in the flow direction F of the gas 30 to be measured in the secondary channel 307. One area in which the first inclined surface 371 is provided is the inclined passage 361 in the secondary channel 307 of the thermal flow meter of the present embodiment.

[0091] The thermal flow meter of the present embodiment has in the secondary channel 307 the first passage 351, the second passage 352 and the inclined passage 361, and the inclined passage 361 has the first inclined surface 371 which is inclined with respect to the forward flow direction F from the side of the second passage 352 to the side of the first passage 351 in order to be closer to the side of the second passage 352 than the flow measuring unit 451, which corresponds to the Fig. 5 thermal flow meter 300 of the first embodiment and the one shown in Fig. 12 corresponds to the thermal flow meter of the second embodiment shown.

[0092] Therefore, according to the present embodiment, it is possible for the thermal flow meter to deflect the flow of the gas 30 to be measured in the forward flow direction F through the first inclined surface 371 of the inclined passage 361 from the side of the second passage 352 to the side of the first passage 351 and to obtain the same effects as those of the thermal flow meter 300 of the first embodiment and the thermal flow meter of the second embodiment. (Fourth embodiment)

[0093] Next, a fourth embodiment, which is not an embodiment of the thermal flow meter of the present invention, will be described using the following examples: Fig. 14 Referring to Fig. 1 to 4B and Fig. Described in sections 6A to 7B. Fig. Figure 14 is a schematic diagram of the secondary channel 307 of a thermal flow meter of the present embodiment, which Fig. 5 of the thermal flow meter 300 of the first embodiment corresponds.

[0094] The thermal flow meter of the present embodiment is described below in terms of its differences from the thermal flow meter described above. Fig. The second embodiment is described in Figure 12. The thermal flow meter of the present embodiment has the same configuration as the thermal flow meter of the second embodiment, except for the configuration described below. Therefore, identical parts of the thermal flow meter of the second embodiment and of the thermal flow meter 300 of the first embodiment are identified by the same reference numerals, and their description is omitted.

[0095] As in Fig. As shown in Figure 14, the exposed section 430 of the circuit assembly 400 in the thermal flow meter of the present embodiment, acting as a support section for the flow meter 451, is inclined with respect to the forward flow direction F (negative X-axis direction) of the gas 30 to be measured in the first passage 351. That is, the front face 431 of the exposed section 430 on the side of the first passage 351 is inclined with respect to the forward flow direction F from the side of the second passage 352 to the side of the first passage 351.

[0096] In the thermal flow meter of the present embodiment, the first passage 351 is a section of a passage which overlaps in the thickness direction (Z-axis direction) of the housing 310 with the measuring surface 451a and which is provided on the measuring surface 451a side of the flow measuring unit 451 by the section 430 of the circuit package 400 exposed in the flow path inside the secondary channel 307.

[0097] In the thermal flow meter of the present embodiment, a section upstream of an inlet of the first passage 351 in the forward flow direction F of the front face 431 of the exposed section 430, which is inclined with respect to the forward flow direction F, forms the first flow path 371. Furthermore, the section upstream of the inlet 351a of the first passage 351 in the forward flow direction F of the passage provided on the measuring surface 451a side of the flow measuring unit 451 by the exposed section 430 forms the inclined passage 361.

[0098] That is, the thermal flow meter of the present embodiment has in the secondary channel 307 the first passage 351, the second passage 352 and the inclined passage 361, and the inclined passage 361 has the first inclined surface 371 which is inclined with respect to the forward flow direction F from the side of the second passage 352 to the side of the first passage 351 in order to be closer to the side of the second passage 352 than the flow measuring unit 451, which corresponds to the thermal flow meters of the second and third embodiments.

[0099] Therefore, according to the present embodiment, it is possible for the thermal flow meter to deflect the flow of the gas 30 to be measured in the forward flow direction F through the first inclined surface 371 of the inclined passage 361 from the side of the second passage 352 to the side of the first passage 351 and to obtain the same effects as those of the thermal flow meter of the second and third embodiments. (Fifth embodiment)

[0100] Next, a fifth embodiment, which is not an embodiment of the thermal flow meter of the present invention, will be described using the following examples: Fig. 15 Referring to Fig. 1 to 4B and Fig. Described in sections 6A to 7B. Fig. Figure 15 is a schematic diagram of the secondary channel 307 of a thermal flow meter of the present embodiment, which Fig. 5 of the thermal flow meter 300 of the first embodiment corresponds.

[0101] The thermal flow meter of the present embodiment is described below in terms of its differences from the thermal flow meter described above. Fig. The first embodiment is described in Figure 5. The thermal flow meter of the present embodiment has the same configuration as the thermal flow meter 300 of the first embodiment, except for the configuration described below. Therefore, identical parts to those of the thermal flow meter 300 of the first embodiment are identified by the same reference numerals, and their description has been omitted.

[0102] In the thermal flow meter of the present embodiment, the secondary channel 307 has a second inclined passage 362 on the downstream side of an outlet 351b of the first passage 351 in the forward flow direction F. The second inclined passage 362 has a third inclined surface 373 which, with respect to the forward flow direction F, is inclined from the side of the first passage 351 to the side of the second passage 352 in order to be closer to the side of the first passage 351 than the flow measuring unit 451.

[0103] Additionally, the second inclined passage 362 in the thermal flow meter of the present embodiment has a fourth inclined surface 374, which is opposite the third inclined surface 373 in the direction perpendicular to the measuring surface 451a (Z-axis direction). The fourth inclined surface 374 is inclined with respect to the forward flow direction F from the side of the second passage 352 to the side of the first passage 351.

[0104] Furthermore, in the thermal flow meter of the present embodiment, a section of the secondary channel 307 is provided on the downstream side of the second inclined passage 362 in the forward flow direction F and on the first passage 351 side of the second passage 352 in the direction perpendicular to the measuring surface 451a (Z-axis direction). In other words, the secondary channel 307 has the inclined passage 361 and the second inclined passage 362 on the upstream and downstream sides of the measuring flow path 341 in the forward flow direction F, which have a point-symmetric configuration with respect to a point on the flow measuring unit 451.

[0105] The thermal flow meter of the present embodiment has the same configuration as the thermal flow meter 300 of the first embodiment described above and can therefore achieve the same effects as the thermal flow meter 300 of the first embodiment described above. In addition, the thermal flow meter of the present embodiment has the second inclined passage 362, and therefore it is possible to deflect the gas 30 to be measured, which flows in a reverse flow direction R opposite to the forward flow direction F, from the downstream side in the forward flow direction F of the gas 30 to be measured in the measuring flow path 341 by the third inclined surface 373 from the side of the first passage 351 to the side of the second passage 352.

[0106] This makes it possible, when pulsing the gas 30 to be measured, to increase the flow velocity of the gas 30 flowing in the reverse flow direction R (positive X-axis direction) through the second passage 352 compared to the prior art, and to decrease the flow velocity of the gas 30 flowing in the reverse flow direction R through the first passage 351 compared to the prior art. This makes it possible to avoid a negative peak in a flow velocity waveform represented by the dashed line in Fig. 10 is shown, to shift to a positive side and to approximate the mean value V1 of the flow velocity measured by the thermal flow meter to the mean value V0 of the actual flow velocity of the gas 30 to be measured.

[0107] Furthermore, in the thermal flow meter of the present embodiment, the second inclined passage 362 has the fourth inclined surface 374, which is opposite the third inclined surface 373, and is inclined with respect to the forward flow direction F from the side of the second passage 352 to the side of the first passage 351. This makes it possible to suppress the formation of turbulence in the flow of the gas 30 to be measured, which has been deflected by the third inclined surface 373 of the second inclined passage 362, and to increase the flow rate of the gas 30 to be measured through the second passage 352 in the reverse flow direction R.

[0108] Therefore, according to the present embodiment, the thermal flow meter is able to suppress a drop in the flow velocity measured by the flow measuring unit 451 below the actual flow velocity more effectively, even when the gas 30 to be measured is pulsating, and to reduce the measurement error compared to the prior art.

[0109] Although embodiments of the present invention have been described in detail above with reference to the drawings, a specific configuration is not limited to the embodiments, and design changes and the like are within the scope of the present invention, provided they are within the scope of the claims. List of reference symbols 30 Gas (fluid) to be measured 124 Main Channel 300 thermal flow meters 307 Secondary channel 307A straight passage 307B branch passage 310 cases 312 first outlet (outlet opening) 351 first round 351a Entrance 351b First passage outlet 352 second round 361 inclined passage 362 second inclined passage 371 first inclined surface 372 second inclined surface 373 third inclined surface 374 fourth inclined surface 451 Flow measuring unit 451a Measuring surface 451b reverse F Forward flow direction L1 Extension line of the first inclined surface L2 Extension line of the measuring surface θ1 Inclination angle of the first inclined surface θ2 Inclination angle of the second inclined surface

Claims

[1] Thermal flow meter comprising: a secondary channel (307) that receives part of a fluid (30) flowing through a main channel (124); and a flow metering unit (451) located in the secondary channel, wherein the secondary channel comprises: a first passage (351) provided on a measuring surface side (451a) of the flow measuring unit; a second passage (352) provided on a rear side (451b) of the flow measuring unit; and an inclined passage (361) provided upstream of an inlet (351a) of the first passage in a forward flow direction (F) of the fluid in the first passage, wherein the secondary channel is further provided on a wall surface on the side of the second passage with a convex section (381) which projects in a thickness direction towards an opposite wall surface on the side of the first passage, and wherein the convex section in the region of the inclined passage has an inclined surface (371) which is inclined with respect to the forward flow direction from one side of the second passage to one side of the first passage in order to be closer to the side of the second passage than the flow measuring unit. [2] Thermal flow meter, comprising: a secondary channel (307) that receives part of a fluid (30) flowing through a main channel (124); and a flow metering unit (451) located in the secondary channel, wherein the secondary channel comprises: a first passage (351) provided on a measuring surface side (451a) of the flow measuring unit; a second passage (352) provided on a rear side (451b) of the flow measuring unit; and an inclined passage (361) provided upstream of an inlet (351a) of the first passage in a forward flow direction (F) of the fluid in the first passage, wherein a wall surface (304a) of the secondary channel on the side of the second passage projects in a thickness direction towards an opposite wall surface on the side of the first passage, and wherein an inclined surface (371) is provided at an end section of the wall surface on an upstream side of the fluid in the forward flow direction in the region of the inclined passage, which is inclined with respect to the forward flow direction from one side of the second passage to one side of the first passage in order to be closer to the side of the second passage than the flow measuring unit. [3] Thermal flow meter according to claim 1 or 2, wherein in a cross-section of the secondary channel (307) parallel to the forward flow direction (F) and perpendicular to the measuring surface (451a) of the flow measuring unit (451) an extension line (L1) of the inclined surface (371) and an extension line (L2) of the measuring surface intersect in the forward flow direction in front of a flow measuring surface. [4] Thermal flow meter according to claim 1 or 2, wherein The secondary channel (307) comprises: a straight passage (307A) that receives a portion of the fluid (30) flowing through the main channel (124); an outlet opening (312) that discharges a portion of the fluid flowing through the straight passage; and a branched passage (307B) upstream of the outlet opening in the forward flow direction (F) of the fluid flowing through the straight passage, and the first passage (351), the second passage (352) and the inclined passage (361) are provided in the branched passage. [5] Thermal flow meter according to claim 1 or 2, further comprising a flat housing (310) that is arranged inside the main channel (124) and defines the secondary channel (307), wherein the measuring surface (451a) of the flow measuring unit (451) is perpendicular to a thickness direction of the housing.

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