Thermal flow meter

Abstract

A thermal flow meter (300) with: a bypass channel (332, 334) for flowing through a part of a measurement target gas flowing through a main channel, and a flow sensor circuit (601) for measuring the flow rate of the measurement target gas flowing through the main channel by means of heat transfer from measurement target gas flowing through the bypass channel (332, 334), the bypass channel (332, 334) comprises an inlet opening for the inflow of the measurement target gas, an outlet opening for returning the measurement target gas to the main channel and an air flow measuring section (602) arranged between the inlet and outlet openings, which measures the flow by means of heat transfer between the flow sensor circuit and the measurement target gas, furthermore, a second channel (3528) is provided for connecting a bypass channel section at the inlet opening between the inlet opening of the bypass channel (332, 334) and the air flow measuring section (602) with a bypass channel section at the outlet opening between the air flow measuring section (602) in the bypass channel (332, 334) and the outlet opening, the second channel (3528) has an inlet opening (3542) which extends through a wall surface (4212) which forms the bypass channel section at the inlet opening of the bypass channel (332, 334) and which opens into the bypass channel section at the inlet opening, and an outlet opening (3544) which opens into the rear side (4213) of the wall surface (4212) which forms the bypass channel section at the inlet opening, characterized in that the bypass channel section in the inlet opening is formed such that a flow area of the bypass channel section in the inlet opening is increasingly narrowed starting from a through-bore (3512, 3522) of the second channel (3528) towards the air flow measuring section (602).

Description

Technical field

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

[0002] In some cases, a thermal flow meter is used in very harsh environmental conditions. For example, if a thermal flow meter is mounted on a vehicle to measure the intake air flow to an internal combustion engine, water can enter a bypass channel along with the intake air, through which the thermal flow meter's target gas flows. In some cases, the water can remain in the bypass channel.

[0003] The thermal flowmeter measures flow by heat transfer between the measured gas flowing through the bypass channel and a flowmeter circuit. Therefore, it is difficult to measure the flow accurately if water enters the bypass channel. Furthermore, the flowmeter circuit can be damaged by the water (e.g., erosion). For this reason, a known technique exists in which a through-hole in the bypass channel runs from the inside to the outside, ensuring that the water in the bypass channel is drained to the outside of the thermal flowmeter through the through-hole. One such technology can be found, for example, in JP 2006-162631 A. List of referencesReferences to the patent PTL 1: JP 2006-162631 A PTL 2: DE 101 35 142 A1 PTL 3: JP H07-113672 A PTL 4: JP H11-14421 A PTL 5: US 6 526 822 B1

[0004] PTL 2 describes a device for determining a parameter of a medium flowing in a line, having an inlet region from which, on the one hand, a flowing medium flows to a measuring channel and, on the other hand, liquid and solid particles flow past the measuring channel through at least one discharge opening.

[0005] PTL 3 describes a flow meter for use in an internal combustion engine.

[0006] PTL 4 describes a flow meter with a heat generator for measuring the amount of air drawn in by a vehicle engine.

[0007] PTL 5 describes a flow measuring device that prevents the accumulation of dirt on a detector. Summary of the inventionTechnical problem

[0008] A thermal flowmeter described in PTL 1 demonstrates a brilliant development, and the measurement accuracy has improved significantly in recent years. As shown in PTL 1, when a through hole is provided to directly connect the inside and outside of the bypass channel, not only the water but also the measurement target gas in the bypass channel will be discharged to the outside of the thermal flowmeter, which is undesirable in terms of measurement accuracy. In particular, the flow velocity of the measurement target gas on the outside of the thermal flowmeter is higher than that in the bypass channel, and the pressure will be slightly lower than that in the bypass channel. Such a state is suitable for discharge, but the measurement target gas will also be discharged, which is not beneficial for maintaining high measurement accuracy.

[0009] The present invention provides a thermal flow meter that can perform measurements with high accuracy and has a diverter function. The solution to the problem

[0010] To solve the above problem, the invention provides a thermal flowmeter. A thermal flowmeter includes a bypass channel for discharging a portion of the target gas flowing through a main channel, and a flow measurement circuit for measuring the flow of the target gas flowing through the main channel by heat transfer from the target gas flowing through the bypass channel. The bypass channel includes an inlet port for admitting the target gas, an outlet port for returning the target gas to the main channel, and an air flow measurement section disposed between the inlet and outlet ports, which measures the flow by heat transfer between the flow measurement circuit and the target gas.Furthermore, a second channel is provided for connecting a bypass channel at the inlet opening, between the inlet opening of the bypass channel and the airflow measuring section, to a bypass channel at the outlet opening, between the airflow measuring section in the bypass channel and the outlet opening. The second channel has an inlet opening that extends through a wall surface forming the bypass channel at the inlet opening of the bypass channel and that opens into the bypass channel at the inlet opening, and an outlet opening that opens into the rear side of the wall surface forming the bypass channel at the inlet opening.

[0011] Additionally, a thermal flow meter is provided with the following features: a bypass channel for passing a portion of the target gas flowing through a main channel, a flow measurement circuit for measuring the flow of the target gas flowing through the main channel by means of heat transfer by the target gas flowing through the bypass channel, and a housing containing a resin bypass channel for forming the bypass channel and protecting the airflow measurement section. The bypass channel includes an inlet port for the target gas flowing in and an outlet port for returning the target gas to the main channel. The airflow measurement section is arranged between the inlet port and the outlet port of the bypass channel and performs heat exchange with the target gas to measure the flow rate.In one surface of the bypass channel of the housing, a bypass channel is provided at the inlet port, connecting the inlet port of the bypass channel and the airflow measuring section. In the other surface of the bypass channel of the housing, a bypass channel is provided at the outlet port, connecting the airflow measuring section and the outlet port of the bypass channel. A drain channel is provided in a wall between the bypass channel at the inlet port and the bypass channel at the outlet port, penetrating the wall. Advantages of the invention

[0012] The present invention provides a thermal flow meter that can perform measurements with high accuracy and has a diverter function. Brief description of the drawings [ Fig. 1] Fig. 1 is a system diagram showing a control system for an internal combustion engine in which a thermal flow meter is used as a practical application of the invention. [ Fig. 2] Fig. 2(A) and Fig. 2(B) are diagrams showing an appearance of the thermal flow meter, where Fig. 2 (A) is a left side view and Fig. 2(B) is a front view. [ Fig. 3] Fig. 3(A) and Fig. 3(B) are diagrams showing an appearance of the thermal flow meter, where Fig. 3 (A) is a right side view and Fig. 3(B) is a rear view. [ Fig. 4] Fig. 4(A) and Fig. 4(B) are diagrams showing an appearance of the thermal flow meter, where Fig. 4 (A) is a plan view and Fig. 4(B) is a soffit. [ Fig. 5] Fig. 5(A) and Fig. 5(B) are diagrams showing a casing of the thermal flow meter, where Fig. 5(A) is a left side view of the housing and Fig. 5(B) is a front view of the housing. [ Fig. 6] Fig. 6(A) and Fig. 6(B) are diagrams showing a casing of the thermal flow meter, where Fig. 6(A) is a right side view of the housing and Fig. 6(B) is a rear view of the housing. [ Fig. 7] Fig. 7 is a partially enlarged view showing a state of a flow path surface located in the bypass channel trough. [ Fig. 8] Fig. 8(A) to 8(C) are diagrams showing an appearance of a front protective cover, wherein Fig. 8 (A) is a left side view, Fig. 8(B) is a front view and Fig. 8 (C) is a top view. [ Fig. 9] Fig. 9(A) to 9(C) are diagrams illustrating an appearance of a rear protective cover 304, wherein Fig. 9(A) is a left side view, Fig. 9 (B) is a front view and Fig. 9(C) is a top view. [ Fig. 10] Fig. 10 is a partially enlarged view showing an end cap. [ Fig. 11] Fig. 11 (A) to 11 (C) are external views of a circuit package, where Fig. 11(A) is a left side view, Fig. 11 (B) is a front view and Fig. 11(C) is a rear view. [ Fig. 12] Fig. 12 is a diagram illustrating a state in which switching components are mounted on a frame of the switching assembly. [ Fig. 13] Fig. Figure 13 is an explanatory diagram showing a diaphragm and a connecting channel connecting an opening and a slit inside the diaphragm. [ Fig. 14] Fig. 14 is a diagram illustrating a state of the circuit package after the first resin injection process. [ Fig. 15] Fig. 15(A) and Fig. 15(B) are diagrams showing another embodiment of the circuit package in Fig. 11, where Fig. 15 (A) is a front view of the circuit package and Fig. 15 (B) is a rear view. [ Fig. 16] Fig. Figure 16 is a diagram showing the manufacturing process of the circuit package. [ Fig. 17] Fig. Figure 17 is a diagram showing the manufacturing process of the thermal flow meter. [ Fig. 18] Fig. Figure 18 is a diagram showing another version of the manufacturing process of a thermal flow meter. [ Fig. 19] Fig. Figure 19 is a circuit diagram showing the flow meter measuring circuit for determining the flow rate. [ Fig. 20] Fig. Figure 20 is an explanatory diagram describing the sensor part of the flow rate detection circuit. [ Fig. 21] Fig. 21(A) to 21(C) are diagrams illustrating another embodiment of the thermal flow meter, wherein Fig. 21(A) is a front view, with Fig. 21(B) is a left side view and Fig. 21(B) is a rear view. [ Fig. 22] Fig. 22 (A) and Fig. 22 (B) are partially enlarged views showing still another embodiment, wherein Fig. 22 (A) is a left side view and Fig. 22(B) is a partially enlarged rear view. [ Fig. 23] Fig. 23(A) and Fig. 23(B) are partially enlarged views showing still another embodiment, wherein Fig. 23 (A) is a left side view and Fig. 23(B) is a partially enlarged rear view. Description of the embodiments

[0013] In the following description, the modes (referred to as "Em") for implementing the invention are intended to significantly improve the accuracy of flow measurement and solve a new problem caused by measurement accuracy. These issues will be described in detail below using the following embodiments; the overview is as follows.

[0014] In the thermal flowmeter according to the present invention, a portion of a measurement target gas is introduced into a bypass channel for flow measurement, and the flow measurement circuit performs heat transfer with the measurement target gas flowing through the bypass channel. To improve the accuracy of flow measurement, it is important to maintain the relationship between the bypass channel and the flow measurement circuit at a high precision and thus within a certain ratio. As follows: When a bypass channel groove is formed to form the bypass channel, the flow measurement circuit is attached to a housing containing the bypass channel groove. Specifically, a resin circuit package containing the flow measurement circuit is covered by a housing part with the bypass channel groove, so that the circuit package is fixed to the bypass channel in a precise positional relationship.In this way, it is possible to improve the measurement accuracy of the flow rate.

[0015] The embodiments described below eliminate various problems that are undesirable in a practical product. In particular, the embodiments solve various problems when applied to a measuring device for measuring the amount of intake air of a vehicle and exhibit various effects. One of these problems that one of the following embodiments solves is described in the section "Problems Solved by the Invention" above, and one of the various results achieved by the following embodiments is explained in "Effects of the Invention." Various problems and effects solved or achieved by the following embodiments are also explained in detail in "Description of Embodiments."Therefore, it would be desirable for the following statements to describe additional effects, problems or solutions to problems that are not described in the sections "Problems to be solved by the invention" and "Effects of the invention".

[0016] In the following explanations, identical reference numbers refer to identical elements with identical functions throughout the drawings. The components described in previous sections may not be identified by reference numbers or symbols in the drawings. 1. Internal control system of an internal combustion engine with a thermal flow meter according to an embodiment of the invention1.1 Configuration of the internal combustion engine control system

[0017] Fig. 1 is a system diagram showing a control system for an injection engine in which a thermal flow meter is used as a practical embodiment of the invention. Based on the operation of an internal combustion engine 110 having an engine cylinder 112 and an engine piston 114, incoming air as the target gas 30 is sucked through an air cleaner 122 and introduced into a combustion chamber of the engine cylinder 112 through a main passage 124, which also includes, for example, an intake manifold, a throttle valve 126, and an intake port 128. The flow rate of the target gas 30 as intake air supplied to the combustion chamber is measured by a thermal flow meter 300 according to the invention. Fuel is supplied from an injection valve 152 based on the measured flow rate and mixed with the target gas 30 as intake air, so that the mixed gas is introduced into the combustion chamber.It should be noted that in this embodiment, the fuel injection valve 152 is located in an intake port of the internal combustion engine, and the fuel injected into the intake port forms a gas mixture with the measurement target gas 30 as intake air, so that the gas mixture is passed through an intake valve 116 into the combustion chamber to generate mechanical energy by combustion.

[0018] In recent years, excellent effects in exhaust gas purification or fuel efficiency improvement have been achieved in many vehicles through direct fuel injection by installing a fuel injection valve 152 in a cylinder head of the internal combustion engine and injecting fuel from the fuel injection valve 152 directly into each combustion chamber. The thermal flow meter 300 can be used in engine types in which fuel is directly injected into each combustion chamber, as well as in types in which fuel is injected into the intake port of the combustion chamber, as in Fig. 1, can be used in the same way. Methods for measuring the control parameters, including those using the thermal flow meter 300, and methods for controlling the internal combustion engine, including the amount of fuel or the ignition timing, are similar for both basic types. An illustrative example of the two types, one in which fuel is injected into the intake port, is shown in Fig. 1 shown.

[0019] The fuel and the air fed into the combustion chamber form a fuel-air mixture and are explosively combusted by spark ignition of the spark plug 154, thus generating mechanical energy. The residual gas from the combustion is guided from the exhaust valve 118 to an exhaust pipe and discharged from the vehicle through the exhaust pipe as exhaust gas 24. The flow rate of the measurement target gas 30, which is fed to the combustion chamber as intake air, is controlled by the throttle valve 132, the opening degree of which is regulated by the operation of an accelerator pedal. The amount of fuel supplied is controlled by the flow rate of the intake air fed into the combustion chamber, and a follower controls the opening degree of the throttle valve 132 and thus the flow of air drawn into the combustion chamber. This makes it possible to control the amount of mechanical energy generated by the internal combustion engine. 1.2 Overview of the combustion engine control system configuration

[0020] The flow rate and temperature of the measurement target gas 30 as intake air taken in from the air cleaner 122 and flowing through the main passage 124 are measured by the thermal flow meter 300. The results are then input to the control element 200 of the thermal flow meter 300 as electrical signals representing the flow rate and temperature of the intake air. Additionally, an output of the throttle angle sensor 144 is installed, which measures the opening degree of the throttle valve 132 and transmits it to the control element 200. An output signal of a rotation angle sensor 146 is also output to the control element 200 to measure the position or state of the engine piston 114, the intake valve 116, or the exhaust valve 118 of the internal combustion engine, as well as the engine speed.The oxygen sensor 148 is provided to measure the mixture ratio between the amount of fuel and the amount of air in the exhaust gas 24 in the exhaust line of the internal combustion engine. The output signal of the oxygen sensor 148 is sent to the control element 200.

[0021] The thermal flow meter 300 for measuring the flow rate and temperature of the intake air (described as the measurement target gas 30 supplied to the internal combustion engine) is mounted on a real vehicle in various ways. An intake pipe serving as the main passage 124 is actually housed in an engine compartment in a curved rather than linear manner, as shown in Fig. 1. The thermal flow meter 300 is inserted from the side surface of the intake pipe (main channel 124) or can be inserted from above along a gravitational direction, or in a horizontal or oblique direction with respect to the gravitational direction. In a case where insertion occurs in a horizontal or inclined direction, an inlet port of the bypass channel of the thermal flow meter 300 described below is mounted above an outlet port of the bypass channel in the gravitational direction.

[0022] In a case where the bypass channel is curved rather than straight, and the inlet port of the bypass channel of the flowmeter 300 is located above the outlet port of the bypass channel, water will enter the bypass channel of the flowmeter 300 between the inlet port and the outlet port of the bypass channel. If water flows out from the inlet port, this water will remain in the bypass channel, causing various adverse effects. It is recommended to provide a drain channel described below to drain the water.

[0023] The control element 200 calculates an amount of fuel for injection or an ignition timing based on the intake air flow rate measured by the thermal flow meter 300 and an engine speed measured by the rotation angle sensor 146. Based on this calculation, the amount of fuel delivered from the fuel injection valve 152 and an ignition timing for the ignition of the spark plug 154 are controlled. In practice, the amount of fuel supplied or the ignition timing is determined even more precisely based on the change in the intake temperature or throttle angle detected by the thermal flow meter 300, or even on changes in the engine speed and a specific air-fuel ratio measured by the oxygen sensor 148.When the engine is idling, the control element 200 regulates the amount of air flowing through the throttle valve 132 by means of the idle air control valve 156 and controls the rotation speed of the engine at idle. 1.3 Improving the measuring accuracy of the thermal flow meter and requirements for the installation of the thermal flow meter

[0024] Both the amount of fuel supplied and the ignition timing, the most important control variables of the internal combustion engine, are calculated using the output of the thermal flow meter 300 as a main parameter. Furthermore, a control parameter is corrected as needed based on the intake air temperature, or the amount of fuel supplied and the ignition timing to be input to the internal combustion engine are corrected. Improving the measurement accuracy, slowing the aging process, and improving the reliability of the thermal flow meter 300 are extremely important for achieving and improving the reliability or control accuracy of a vehicle equipped with an ignition internal combustion engine. In particular, in recent years, demands for lower fuel consumption and better exhaust gas purification have increased.To meet such demands, it is extremely important to improve the measurement accuracy of the flow rates of the target gas 30 and the intake air measured by the thermal flow meter 300. Furthermore, it is also important to maintain the high reliability of the thermal flow meter 300.

[0025] A vehicle equipped with the thermal flow meter 300 is used in an environment with large temperature differences or harsh weather conditions such as storms or snow. If a vehicle is driving on a snow-covered road, it is traveling on a surface to which a de-icing agent has been applied. In this case, it is recommended to design the thermal flow meter 300 as a countermeasure for adverse environments with temperature fluctuations, dust, and pollutants. Furthermore, the thermal flow meter 300 can be installed in environments where the internal combustion engine is subject to vibration. It is also desirable that it operate extremely reliably even under severe vibration.

[0026] The vehicle may be exposed to adverse weather conditions or extremely harsh environmental conditions. For example, in an extreme case, the vehicle is likely to drive on wet roads during the rainy season. When the thermal flow meter 300 is used in adverse environmental conditions, water may enter through the inlet port of the bypass channel of the thermal flow meter 300 described below. The bypass channel forms an arc between the inlet port and the outlet port of the bypass channel. If the intake pipe (the main channel 124) is arranged vertically, the water entering through the inlet port of the bypass channel may remain in the arc section. The water is discharged through the drain channel described below.

[0027] The thermal flow meter 300 is installed in the main duct 124 as part of the intake pipe and is affected by the heat of the internal combustion engine. Therefore, the heat generated by the internal combustion engine is transferred to the thermal flow meter 300 via the intake pipe, which is the main duct 124. Because the thermal flow meter 300 measures the flow rate of the gas to be measured based on heat transfer across the same gas to be measured, it is important to suppress external heat influences as much as possible.

[0028] The vehicle-mounted thermal flow meter 300 solves the problems described in the "Problems to be Solved by the Invention" section and achieves what is documented under "Effects of the Invention." In addition, as described below, it solves various problems required of the product and offers various effects with respect to several of the problems described above. Specific problems or effects solved or achieved by the thermal flow meter 300 are documented in the following descriptions of the various embodiments. 2. Configuration of the thermal flow meter 3002.1 External structure of the thermal flow meter 300

[0029] Fig. 2 (A), Fig. 2 (B), Fig. 3 (A), Fig. 3 (B), Fig. 4 (A) and Fig. 4 (B) are diagrams showing the exterior of the thermal flow meter 300. Fig. 2 (A) shows the left side view of the thermal flow meter 300, Fig. 2(B) the front view, Fig. 3(A) the right side view, Fig. 3(B) is the back view, Fig. 4 (A) is a plan view and Fig. 4 (B) is the bottom view. The thermal flow meter 300 has a casing 301. The casing 301 includes a housing 302, a front cover 303, and a rear cover 304. Located within the housing 302 are a flange 312 for attaching the thermal flow meter to an intake housing as the main duct 124, an external connector 305 having external terminals 306 for electrical connections to external devices, and a measuring section 310 that measures, for example, the flow rate. The measuring section 310 is internally equipped with a bypass duct groove to form a bypass duct. In addition, the measuring section 310 has a built-in circuit package 400 with an air flow measurement component 602 (see Fig. 19) which measures the flow rate of the measurement target gas 30 flowing through the main channel 124, and a temperature measuring section 452 which measures the temperature of the measurement target gas 30 flowing through the main channel 124. 2.2 External structure of the thermal flow meter 300 and corresponding effects

[0030] Since the intake port 350 of the thermal flow meter 300 is located at the front end of the measuring section 310 and extends from the flange 312 toward the center of the main channel, and the gas 30 to be measured is located near the center, away from the inner wall surface, rather than near the inner wall surface of the main channel 124, the intake can be made into the bypass channel. Therefore, the thermal flow meter 300 can measure the flow rate or temperature of the measurement target gas 30 in a section separated from the inner wall surface of the main channel 124 of the thermal flow meter 300, making it possible to suppress measurement inaccuracies due to heat or other influences.In the vicinity of the inner wall surface of the main channel 124, the thermal flow meter 300 is easily affected by the temperature of the main channel 124, so that the measured temperature of the measurement target gas 30 may deviate from the actual temperature and output a measurement that deviates from the average state of the main gas in the main channel 124. In particular, when the main channel 124 serves as the intake casing of the engine, it may be affected by the heat of the engine and maintain a high temperature level. For this reason, the gas near the inner wall surface of the main channel 124 often has a higher temperature than the actual temperature of the main channel 124. This deteriorates the measurement accuracy.

[0031] In the vicinity of the inner wall surface of the main channel 124, there is an increased fluid resistance and a throttled flow rate compared to an average flow rate in the main channel 124. For this reason, a measurement error could occur if the gas near the inner wall of the main channel 124 is introduced into the bypass channel as the measurement target gas 30 and the flow rate is reduced compared to the average flow rate in the main channel 124. In the Fig. 2 (A), 2 (B), 3 (A), 3 (B) and 4 (A) to 4 (C), it is possible to minimize a measurement error with respect to a lower flow rate near the inner wall surface because the inlet opening 350 is located in the front end of the thin and long measuring section 310 and extends from the flange 312 to the center of the main channel 124. In the Fig. In the thermal flow meter 300 shown in FIGS. 2(A), 2(B), 3(A), 3(B), and 4(A) to 4(C), in addition to the inlet port 350 provided in the front end of the measuring section 310 extending from the flange 124 to the center of the main passage 124, an outlet port of the bypass passage is provided in the front end of the measuring section 310. Therefore, it is possible to reduce the measurement error in the future.

[0032] The measuring area 310 on the thermal flow meter 300 has a shape that extends from the flange 312 toward the center of the main channel 124. The front end is provided with an inlet opening 350, where a part of the measurement target gas 30 is introduced, such as intake air into the bypass channel, and with an outlet opening 352 for returning the measurement target gas 30 from the bypass to the main channel 124. While the measuring area 310 has a shape that is guided along an axis toward the center from the outer wall of the main channel 124, it is narrower in width, as shown in the Fig. 2 (A) and Fig. 3 (A). That is, the measuring area 310 of the thermal flow meter 300 has a nearly rectangular front and a narrow side surface. Consequently, the thermal flow meter 300 can provide a bypass channel of sufficient length, and it is possible to reduce the fluid resistance to a small value for the measurement target gas 30. For this reason, using the thermal flow meter 300, it is possible to reduce the fluid resistance to a small value and measure the flow rate of the measurement target gas 30 very accurately. 2.3 Structure and effect of the measuring range 310

[0033] In the flow direction of the target gas 30 through the main channel 124, an upstream protrusion 317 and a downstream protrusion 318 are provided in the corresponding side surface of the measuring section 310 included in the thermal flow meter 300. The upstream protrusion 317 and the downstream protrusion 318 taper from the front end to the base, thereby reducing the fluid resistance of the target gas 30 flowing through the main channel 124. The upstream protrusion 317 is positioned between the thermal insulation 315 and the inlet port 343. The upstream protrusion 317 has a large cross-section and receives strong heat conduction from the flange 312 or the thermal insulation 315.However, the upstream projection 317 is cut off near the inlet port 343, and the length of the temperature measuring portion 452 of the projection 317 is increased by the cavity of the upstream outer wall of the housing 302 as described below. For this reason, heat conduction from the heat insulation 315 to the support portion of the temperature measuring portion 452 is suppressed.

[0034] The temperature of the measurement target gas 30 entering through the inlet opening 343 is measured by the temperature measuring section 452, wherein the measurement target gas 30 is passed through the flow path of the outer wall hollow section 366 of the housing 302 described below (see Fig. 5). Then, it enters the main channel 124 from the front outlet port 344 or the rear outlet port 345. Since the measurement target gas 30 introduced from the inlet port 343 flows along the projection 424 of the temperature measuring section 452 (see Fig. 11) is guided using the cooling channel groove, the temperatures of the protrusion 424 and the temperature measuring portion 452 approach the temperature of the measurement target gas 30. Therefore, the influence of heat dissipated from other heat regions to the protrusion 424 can be reduced, and the temperature measurement accuracy of the measurement target gas 30 can be improved.

[0035] The end cap 320 described below and a gap 382 containing the end cap 320 are located between the flange 312 or the heat insulator 315 and the temperature measuring section 452. Therefore, the distance between the flange 312 or the heat insulator 315 and the temperature measuring section 452 increases, and the front cover 303 and the rear cover 304 located in this section serve as cooling surfaces due to their length. Therefore, it is possible to reduce the influence of the temperature of the wall surface in the main channel 124 on the temperature measuring section 452. In addition, since the distance between the flange 312 or the heat insulator 315 and the temperature measuring section 452 increases, it is possible to introduce part of the measurement target gas 30 into the bypass channel near the center of the main channel 124. Thus, a reduction in measurement accuracy caused by the wall surface of the main channel 124 can be avoided.

[0036] As in Fig. As shown in FIGS. 2(B) and 3(B), respectively, both side surfaces of the measuring portion 310 located in the main passage 124 have a very narrow shape, and the front end of the upstream protrusion 318 or the counterstream protrusion 317 has a narrow shape compared to the base. This reduces air resistance. Therefore, it is possible to prevent an increase in fluid resistance caused by installing a thermal flow meter 300 in the main passage 124. Furthermore, in the area where the downstream protrusion 318 or the upstream protrusion 317 is provided, the upstream protrusion 318 or the downstream protrusion 317 protrudes bilaterally relative to both side parts of the front cover 303 or the rear cover 304.Since the upstream protrusion 317 or the upstream protrusion 318 are made of cast resin, they can be easily molded so that air resistance is negligible. At the same time, the front cover 303 and the rear cover 304 have a large cooling effect due to their large-area shape. Therefore, the thermal flow meter 300 has lower fluid resistance and can be easily cooled by the gas 30 to be measured flowing through the main channel 124. 2.4 Structure and effect of the flange 312

[0037] The flange 312 is provided with a plurality of cavities 314 on its lower side. This is the part facing the main channel 124. This is intended to reduce the heat transfer surface with the main channel 124 and to make it more difficult for the thermal flow meter 300 to be affected by heat. The screw hole 313 on the flange 312 is intended for mounting the thermal flow meter to the main channel 124. This creates a gap between the surface opposite the main channel 124 around each screw hole 313 and the main channel 124, so that the surface facing the main channel 124 around each screw hole 313 protrudes from the main channel 124. The flange 312 is thus constructed to reduce heat transfer from the main channel 124 to the thermal flow meter 300 and prevent a reduction in measurement accuracy caused by heat.In addition to the effect of reducing heat conduction, the cavity 314 can reduce the influence of the contraction of the resin of flange 312 during the molding of the housing 302.

[0038] The thermal insulation 315 is located on the side of the measuring section 310 of the flange 312. The measuring section 310 of the thermal flow meter 300 is inserted into the device through the mounting hole in the main channel 124, so that the thermal insulation 315 is oriented toward the inner surface of the mounting hole in the main access 124. The main channel 124, which serves as an inlet body, for example, is often maintained at a high temperature. Conversely, the main channel 124 is designed to be maintained at an extremely low temperature when activated for operation in a cold environment. If such high or low temperatures of the main channel 124 affect the temperature measuring section 452 or the flow measurement described below, the measurement accuracy decreases.For this reason, a plurality of adjacent cavities 316 are provided in the thermal insulation 315 adjacent to the inner hole surface of the main channel 124, and an extremely small cross-section of the thermal insulation 315 adjacent to the inner hole surface between the adjacent cavities 316, which is equal to or less than 1 / 3 of the cross-section of the flow direction of the cavity 316. This makes it possible to reduce the influence of temperature. In addition, a portion of the thermal insulation 315 thickens. During resin molding of the housing 302, the resin cools from a high to a low temperature and hardens, resulting in volume shrinkage, which leads to deformation due to the shrinkage stress that occurs.By forming the cavity 316 in the thermal insulation 315, it is possible to achieve a more uniform volume shrinkage and reduce the concentration of shrinkage stress.

[0039] The measuring section 310 of the thermal flow meter 300 is inserted into the device through the mounting hole in the main channel 124 and screwed into the main channel 124 using the flange 312 of the thermal flow meter 300. The thermal flow meter 300 is preferably fastened in a predetermined position through the mounting hole provided in the main channel 124. The cavity 314 provided in the flange 312 can be used to determine the positioning between the main channel 124 and the thermal flow meter 300. By forming a convex section in the main channel 124, it is possible to specify a relationship between the convex section and the cavity 314 for positioning and to mount the thermal flow meter 300 at a precise position in the main channel 124. 2.5 Structure and function of the external connection 305 and the flange 312

[0040] Fig. 4 (A) is a plan view showing the thermal flow meter 300. Four external terminals 306 and one calibration terminal 307 are located inside the external terminal connection 305. The external terminals 306 include terminals for outputting the flow rate and temperature as a measurement result of the thermal flow meter 300, and a power terminal for supplying DC power to operate the thermal flow meter 300. The calibration terminal 307 uses the measured values supplied by the thermal flow meter 300 to obtain a calibration value for each thermal flow meter 300 and stores the calibration value in an internal memory of the thermal flow meter 300. In subsequent measurement operations of the thermal flow meter 300, the calibration data from the memory is used, not the calibration terminal 307.Therefore, the calibration port 307 has a different shape than the external port 306, which prevents the calibration port 307 from interfering with the connection between the external ports 306 and other external devices. Since the calibration port 307 is shorter than the external port 306 in this embodiment, the calibration port 307 does not interfere with the connection even when the connection port connected to the external port 306 is inserted into the external port 305 for connecting to external devices. Furthermore, numerous cavities 308 are provided along the external port 306 inside the external port 305 to reduce the concentration of shrinkage stress during cooling and curing of the resin used for the flange 312.

[0041] Since the calibration port 307 is provided in addition to the external port 306 used in the measurement operation of the thermal flow meter 300, it is possible to measure the characteristics of each thermal flow meter 300 before shipment, thereby detecting a deviation of the product, and storing a calibration value to reduce the deviation in the internal memory of the thermal flow meter 300. The calibration port 307 has a different shape than the external port 306, preventing the calibration port 307 from interfering with the connection between the external ports 306 and other external devices after calibration. In this way, when using the thermal flow meter 300, it is possible to reduce the deviations existing before shipment between each thermal flow meter 300 and improve the measurement accuracy. 3. Overall structure of housing 302 and effects 3.1 Structure and effect of the bypass channel and the air flow measuring section

[0042] Fig. 5(A) to 6(B) show the thermal flow meter housing 302 without front 303 and rear 304 covers. Fig. 5(A) shows the left side of the housing 302, Fig. 5(B) shows the front view of the housing 302, Fig. 6(A) shows the right side of the housing 302, and Fig. Figure 6(B) shows the rear view of the housing 302. In the housing 302, the measuring portion 310 protrudes from the flange 312 toward the center of the main channel 124, and a bypass channel groove is provided at the front end thereof to form a bypass channel. In this embodiment, the bypass channel groove is provided on both the front and rear sides of the housing 302. Fig. 5(B) shows a bypass channel groove at the front 332, and Fig. 6(B) shows a bypass channel groove at the rear side 334. Since an inlet groove 351 for forming the inlet port 350 of the bypass channel and an outlet groove 353 for forming the outlet port 352 are provided at the front of the housing 302, the gas removed from the inner wall surface of the main channel 124, that is, the gas flow through the center of the main channel 124 and its surroundings, can be taken in as the measurement target gas 30 through the inlet port 350. The gas flow near the inner wall surface of the main channel 124 is affected by the temperature of the wall surface of the main channel 124 and has a different temperature than the average temperature of the gas flowing through the main channel 124, such as the measurement target gas 30 in many cases.In addition, the gas flowing near the inner wall side of the main channel 124 often has a lower flow velocity than the average flow velocity of gas flowing through the main channel 124. Since the thermal flow meter 300 according to this embodiment is resistant to such an influence, it is possible to prevent deterioration of the measurement accuracy.

[0043] The above-described bypass channel, which consists of the front-side bypass channel groove 332 or the rear-side bypass channel groove 334, is connected to the thermal insulation 315 of the flange 312 via the outer wall hollow portion 366, the upstream outer wall 335, or the downstream outer wall 336. Furthermore, the upstream outer wall 335 is provided with the counterflow projection 317, and the downstream outer wall 336 is provided with the flow-direction projection 318. Since the thermal flow meter 300 is mounted on the main channel by means of the flange 312, the attachment of the measuring section 310, including the circuit package 400, to the main channel 124 is highly reliable.

[0044] In this embodiment, the housing 302 is provided with the bypass channel groove for forming the bypass channel, and the covers of the housing 302 are mounted on the front and rear surfaces, thereby forming the bypass channel from the bypass channel groove and the covers. With this configuration, it is possible to form the entirety of the bypass channel grooves as part of the housing 302 during the resin molding process for the same housing. Furthermore, since the dies are provided in both surfaces of the housing 302 during the manufacture of the housing 302, it is possible to form both the front-side bypass channel groove 332 and the rear-side bypass channel groove 334 using the dies for these two surfaces as part of the housing 302.Since the front cover 303 and the rear cover 304 are provided for both surfaces of the housing 302, it is possible to form the two bypass channels on the two surfaces of the housing 302. Since the bypass channel groove on the front 332 and the bypass channel groove on the rear 334 are formed on the two surfaces of the housing 302 using dies, it is possible to form the bypass channels with high accuracy and achieve high productivity.

[0045] As on Fig. 2 (A) , Fig. 2(B), Fig. 3(A), Fig. 3(B) and also Fig. 5(A), Fig. 5(B), Fig. 6(A), and Fig. 6(B), the upstream outer wall 335 and the downstream outer wall 336 projecting in the front and rear directions of the front and rear sides of the casing 302, a connecting portion along the thermal insulation 315 of the upstream outer wall 335 and the downstream outer wall 336, the inner wall of the bypass passage on the rear side 391 and the outer wall of the bypass passage on the rear side 392, and the upper portions of the inner wall of the bypass passage on the front side 393 and the outer wall of the bypass passage on the front side 394 are mounted on the front or rear cover 303 or 304 so as to contact the front or rear cover 303 or 304, respectively. A space enclosed by the housing 302 and the front or rear cover 303 or 304 and a bypass channel are formed.

[0046] The enclosed space contains the circuit package 400, described in more detail below, and the gap 382. The housing 302 and the front cover 303 or rear cover 304 are joined by laser welding. However, if the housing 302 and the front cover 303 or rear cover 304 are completely sealed, gas expansion caused by temperature changes can cause problems. Therefore, the enclosure is implemented, but a ventilation structure is provided. The ventilation structure reduces the pressure difference with respect to the outside due to temperature changes in the enclosed space.

[0047] According to Fig. 6(B), a portion of the measurement target gas 30 flowing through the main channel 124 is guided into the rear bypass channel groove 334 via the inlet groove 351, which forms the inlet opening 350. The rear bypass channel groove 334 becomes progressively deeper as the gas flow progresses, and the measurement target gas 30 slowly moves toward the front while flowing through the groove. Specifically, the rear bypass channel groove 334 is provided with a steep slope portion 347 that drops sharply near the opening 342, so that a portion of the air having a low mass moves along the steep slope portion 347 and then flows from the opening 342 to the measurement surface 430 side, as shown in Fig. 5(B). Since a foreign body with a larger mass has difficulty changing its path abruptly, it moves towards the back of the measuring surface 431, as shown in Fig. 6 (B). Then, the foreign matter flows through an opening 341 to the measuring surface 430, as shown in Fig. 5 (B).

[0048] In the bypass channel on the front 332, seen in Fig. 5 (B), the air as the measurement target gas 30 moves from the opening 342 to the bypass channel groove on the front side 332 and flows along the measurement surface 430, and heat transfer is performed with the air flow measurement section 602 to measure the flow rate by utilizing the exposure portion of the heat transfer surface 436 provided in the flow rate measurement surface 430. Both the measurement target gas 30 flowing through the measurement surface 430 and the air flowing through the opening 341 into the bypass channel groove on the front side 332 move through the bypass channel groove 332 on the front side and are discharged into the main channel 124 via the exhaust groove 353 to form the exhaust opening 352.

[0049] A substance with a larger mass, such as an impurity in the target gas 30, has a high moment of inertia and therefore has difficulty abruptly changing its trajectory in the channel towards the deep side of the channel along the surface of the steep slope section 347, where the channel drops steeply, as in Fig. 6 (B). Because the foreign matter with a larger mass moves along the back side of the measurement surface 431, it is possible to prevent it from passing near the exposure portion of the heat transfer surface 436. In this embodiment, since most foreign matters have a larger mass than the gas flowing through the back measurement surface 431, which is the back side of the measurement surface 430, it is possible to minimize the influence of contamination by foreign matters such as components of oils, carbon, or other impurities and prevent deterioration of the measurement accuracy. That is, since the path of the measurement target gas 30 steeply rises along the flow direction in the main channel 124, the influence of foreign matters contained in the measurement target gas 30 is reduced.

[0050] In this embodiment, the flow path including the bypass channel groove on the rear side 334 extends from the front end of the housing 302 to the flange along a curved line, and the gas flowing through the bypass channel closest to the flange moves opposite to the flow direction in the main channel 124. Thus, the bypass channel on the rear surface side (one side of the return flow) is connected to the bypass channel on the front surface side (the other side of the return flow). This allows for easy installation of the heat transfer surface exposure section 436 of the switching assembly 400 in the bypass channel and easy accommodation of the measurement target gas 30 in the position near the center of the main channel 124.

[0051] In this embodiment, the openings 342 and 341, which pass through the bypass channel grooves on the rear side 334 and the front side 332, are provided on the upstream and downstream sides of the flow direction on the flow rate measurement surface 430. Through the through openings 342 and 341, the bypass channel is shaped so that the measurement target gas 30 moves from the bypass channel groove on the rear side 334 formed in one surface of the housing 302 to the bypass channel groove on the front side 332 formed in the other surface of the housing 302. With this configuration, the bypass channel grooves on both surfaces of the housing 302 can be formed in a single resin molding process using a structure connecting the two surfaces.

[0052] By providing openings 342 and 341 on both sides of the sensing surface 430 formed in the circuit package 400, resin inflow into the heat transfer surface 436 exposure portion in the sensing surface 430 can be prevented by using dies to form openings 342 and 341 on both sides. Furthermore, openings 342 and 341 can be located on the upstream and downstream sides of the heat transfer surface 430 exposure portion. When the circuit package 400 is attached to the housing 302 using the resin molding process, the dies are aligned using these openings, allowing the circuit package 400 to be positioned and secured by the dies.

[0053] In the embodiment, there are two openings (opening 342 and opening 341). These are designed as through-openings through the bypass channel groove on the rear side 334 and the bypass channel groove on the front side 332. Even if the two openings 342 and 341 are not provided, if one of the openings is to be used, the bypass channel can be formed by connecting the bypass channel groove on the rear side 334 and the bypass channel groove on the front side 332 in a single resin molding process.

[0054] The inner wall of the rear bypass passage 391 and the outer wall of the rear bypass passage 392 are provided on both sides of the rear bypass passage groove 334. The inner side surface of the rear cover 304 abuts the front ends of the height alignment of each inner wall of the rear bypass passage 391 and the outer wall of the rear bypass passage 392, thus forming the rear bypass passage in the housing 302. Furthermore, the inner wall of the front bypass passage 393 and the outer wall of the front bypass passage 394 are provided on both sides of the front bypass passage groove 332. The inner side surface of the front cover 303 is located at the front ends of the height alignment of the inner wall of the bypass channel on the front side 393 and the outer wall of the bypass channel on the front side 394, so that the bypass channel on the front side is formed in the housing 302.

[0055] In this embodiment, the measurement target gas 30 flows dividedly across the measurement surface 430 and its rear side, and the heat transfer surface exposure portion 436 for measuring the flow rate is provided on one of these two surfaces. However, the measurement target gas 30 may also flow exclusively along the front surface of the measurement surface 430 instead of being divided into two channels. By curving the bypass channel along a second axis aligned with the first axis along the flow direction in the main channel 124, foreign matter in the measurement target gas 30 can be pushed to the side where the curvature of this second axis is insignificant. By placing the measurement surface 430 and the heat transfer surface exposure portion 436 at the location where the curvature of the second axis is significant, it is possible to reduce the influence of foreign matter.

[0056] In this embodiment, the measuring surface 430 and the heat transfer surface exposure portion 436 are provided in a connecting portion between the front-side bypass channel trough 332 and the rear-side bypass channel trough 334. However, the measuring surface 430 and the heat transfer surface exposure portion 436 may be provided in the front-side bypass channel trough 332 or the rear-side bypass channel trough 334 instead of the connecting portion between the front-side bypass channel trough 332 and the rear-side bypass channel trough 334.

[0057] A flow rate measurement aperture is formed in a portion of the heat transfer surface exposure section 436 in the measurement surface 430. This aperture increases the flow velocity and thereby improves measurement accuracy. Furthermore, even if eddies occur in the gas flow on the upstream side of the heat transfer surface exposure section 436, this aperture can cancel or attenuate such eddies, thus improving measurement accuracy.

[0058] Referring to Fig. 5 (A), Fig. 5 (B), Fig. 6 (A) and Fig. 6 (B), an outer wall hollow portion 366 is provided where the upstream outer wall 335 has a bulge toward the downstream side in a narrowed part of the temperature measuring portion 452. Due to this outer wall hollow portion 366, the distance between the temperature measuring portion 452 and the outer wall hollow portion 366 increases, so it is possible to reduce the influence of heat via the upstream outer wall 335.

[0059] Since the outer wall hollow portion 366 is located in a narrowed part of the temperature measuring portion 452, it is possible to reduce the influence of heat from the flange 312 or from the heat insulation 315 through the upstream outer wall 335. Furthermore, the outer wall hollow portion 366 for temperature measurement is provided, formed by a notch between the upstream protrusion 317 and the temperature measuring portion 452. By using the outer wall hollow portion 366, it is possible to reduce heat transfer to the temperature measuring portion 452 through the upstream protrusion 317. As a result, it is possible to improve the detection accuracy of the temperature measuring portion 452. In particular, the upstream protrusion 317 can easily transfer heat due to its large cross-sectional area, thereby increasing the heat transfer blocking functionality of the outer wall hollow portion 366.

[0060] Furthermore, in the embodiment, a discharge channel 3528 is provided in the bypass channel for connecting a bypass channel 4232 at the inlet opening (between the inlet opening 350 and the measuring surface 430 functioning as an air flow measuring section) with a bypass channel 4234 at the outlet opening (between the measuring surface 430 functioning as an air flow measuring section in the bypass channel and the outlet opening 352). The discharge channel 3528 includes a through-bore 3522. The through-bore 3522 has an inlet opening 3542 that extends through a wall surface 4212 that forms the bypass channel 4232 at the inlet opening of the bypass channel, and that opens into the bypass channel 4232 at the inlet opening, and an outlet opening 3544 that opens into the rear side 4213 of the wall surface 4212 that forms the bypass channel 4232 at the inlet opening.

[0061] The thermal flow meter 300 is mounted at an angle crossing the direction of gravity. Water 3552 flows through the discharge channel 3528 from the inlet port 350 of the bypass channel along the bypass outer wall 3914 and is guided to the through-hole 3522 of the discharge channel 3528, which is provided in the wall surface of the bypass channel 4232 at the inlet port. The water is guided to the bypass channel 3544 at the outlet port through the discharge channel 3528 and discharged from the bypass channel 3544 at the outlet port to the main channel 124. On the other hand, the measurement target gas 30 flowing in through the inlet port 350 of the bypass channel is guided to the bypass channel 3544 at the outlet port through the discharge channel, but the discharge amount is smaller.This is because, in the conventional structure in which the discharge channel is connected to the outside of the thermal flow meter, the flow velocity of the measurement target gas 30 outside the thermal flow meter 300 increases rapidly compared to that in the bypass channel, and the pressure of the measurement target gas 30 outside the thermal flow meter 300 decreases rapidly compared to that in the bypass channel.

[0062] On the other hand, the difference in the flow velocity of the measurement target gas between the inside of the bypass channel 4232 at the inlet port and the inside of the bypass channel 3544 at the outlet port is small. This means that the pressure difference of the measurement target gas 30 between the inside of the bypass channel 4232 at the inlet port and the inside of the bypass channel 3544 at the outlet port is small. Therefore, in the structure in which the discharge channel 3528 connects the bypass channel 4232 at the inlet port and the bypass channel 4234 at the outlet port, less measurement target gas 30 escapes from the bypass channel 4232 at the inlet port into the bypass channel 3544 at the outlet port. For this reason, high measurement accuracy is achieved.

[0063] In Fig. 5(B), the outlet port 3544 of the discharge channel 3528 is provided downstream near the outlet groove 353 of the bypass channel. The proximity of the outlet groove 353 of the bypass channel results in a large cross-sectional area of the bypass channel, so that the flow velocity of the measurement target gas 30 flowing through it is low. Therefore, the center of the bypass channel has a high pressure of the measurement target gas 30 flowing through it. Since the outlet port 3544 of the through-hole 3522 connecting the inside of the bypass channel 4232 at the inlet port and the inside of the bypass channel 3544 at the outlet port is provided in a portion where the flow velocity of the measurement target gas 30 is low, the amount of the measurement target gas 30 escaping into the discharge channel 3528 is reduced. High measurement accuracy should be maintained.

[0064] As described above, the water flowing in from the inlet opening 350 of the bypass channel moves in the bypass channel 4232 at the inlet opening as shown by the arrow 3552. As with reference to Fig. 6(B) and Fig. 5(B), the water is guided to the bypass passage 3544 at the outlet port through the through-hole 3522 of the discharge passage 3528 provided on a side near the bypass passage 4232 at the inlet port, and the water is guided as shown by the arrow 3552 and discharged to the main passage 124. In this way, the water is prevented from flowing into the sensing surface 430 of the circuit package, which in turn protects the sensing surface from being penetrated by the water 3552.

[0065] Thus, the drain channel 3528 is configured such that the bypass channel 4232 at the inlet port, between the inlet port 350 in the bypass channel and the measuring surface 430 serving as the airflow measuring section, is connected to the bypass channel 4234 at the outlet port (between the measuring surface 430 in the bypass channel serving as the airflow measuring section and the outlet port 352). In this way, the water 3552 flowing in from the inlet port 350 of the bypass channel is prevented from flowing into the measuring surface 430 of the circuit package, which in turn protects the measuring surface from being penetrated by the water 3552. Accordingly, it is possible to prevent a flow measurement error, as well as damage to the flow measurement circuit such as corrosion, thus achieving high reliability of the thermal flow meter 300.As described above, by providing the discharge channel 3528, the measurement target gas 30 and the water 3552 flowing in from the inlet opening 350 are separated from each other before reaching the measuring surface 430. From there, the water 3552 is discharged through the discharge opening past the measuring surface 430 to the main channel 124.

[0066] In addition, in the embodiment as shown in Fig. 5, the inlet port 350 and the outlet port 352 of the bypass channel in the end portion of the thermal flow meter 300 are arranged in the opposite direction to the flange 312. The measuring surface 430 serving as the air flow measuring portion is arranged toward the flange 312 of the inlet port 350 and the outlet port 352. The bypass channel 4232 at the inlet port is formed to approach the measuring surface 430 serving as the air flow measuring portion of the inlet port 350 of the bypass channel while being bent toward the flange 312. The bypass channel 4232 at the inlet port is formed by the bypass channel groove 332 at the inlet port and the cover 304 covering it. The through hole 3522 of the discharge channel 3528 is provided in a wall surface 4213 in the opposite direction to the flange 312 of the bypass channel trough 332 at the inlet opening.With this arrangement, the flow of the measurement target gas 30 flowing in through the inlet port 350 of the bypass channel is regulated and directed to the measuring surface 430 serving as the air flow measuring section. At the same time, the water 3552 flowing in through the inlet port 350 is directed to the bypass channel 3544 at the outlet port without flowing to the measuring surface 430 serving as the air flow measuring section, through the drain line 3528, and discharged to channel 124. This allows the measurement to be performed with high accuracy.

[0067] In addition, the design, as in Fig. 2 (A) and Fig. 2 (B) and Fig. 3 (A) and Fig. 3(B), the bypass channel groove 332 at the inlet port for forming the bypass channel 4232 at the inlet port, and a first cover 304 for forming the bypass channel 4232 at the inlet port by covering the bypass channel groove 332 at the inlet port are provided in one surface of the thermal flow meter 300. Further, the bypass channel 334 at the outlet port groove for forming the bypass channel 4234 at the outlet port, and a second cover 303 for forming the bypass channel 4234 at the outlet port by covering the bypass channel 334 at the outlet port groove are provided in the other surface of the thermal flow meter 300.Even if the bypass channel groove 332 at the outlet port is configured such that the through-hole 3522 of the discharge channel 3528 is provided in a surface of the thermal flow meter 300, similar to the above embodiment, the water 3552 flowing in through the inlet port 350 of the bypass channel can be prevented from entering the measuring surface 430 of the circuit package 400. Furthermore, measurement errors and damage caused by water penetrating the measuring surface 430 can be avoided. The configuration and effects of another embodiment of the present invention will be described below.

[0068] In addition, in the embodiment as with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6 (B), the measuring surface 430 serving as the air flow measuring section is provided for measuring the flow rate of the gas flowing through the main channel. The housing 302 serving as the air flow measuring section, which has a resin bypass channel section for forming the bypass channel, contains the measuring section 430. The bypass channel includes the inlet port 350 for the inflow of the measurement target gas 30 and the outlet port 352 for returning the measurement target gas 30 to the main channel 124. The measuring surface 430 serving as the air flow measuring section is arranged between the inlet port 350 and the outlet port 352 of the bypass channel and performs heat exchange with the measurement target gas 30 to measure the flow rate. The bypass channel 4232 at the inlet opening for connecting the inlet opening 350 of the bypass channel with the measuring surface 430 serving as an air flow measuring section is provided in a surface of the bypass channel section of the housing 302.The inlet bypass channel 4232 for connecting the measuring surface 430 serving as the air flow measuring section to the outlet port 352 of the bypass channel is provided in the other surface of the bypass channel portion of the housing 302. The discharge channel 3528 penetrates the wall 4211 between the inlet bypass channel 4232 and the outlet bypass channel 4234. It is possible to achieve the effect achieved by the two-step resin molding process as described above, as well as that obtained by providing the discharge channel 3528. Furthermore, the thermal flow meter achieves high measurement accuracy.

[0069] In addition, in the embodiment as shown in Fig. 5 (A), Fig. 5 (B), Fig. 6(A) and Fig. As shown in Fig. 6(B), the through hole 3522 of the discharge passage 3528 is provided in the flow direction of the measurement target gas 30, that is, in the lateral direction across the bypass passage. The pressure added in the flow direction of the measurement target gas 30 is less exerted on the discharge passage 3528 provided in the side surface direction across the axial direction of the bypass passage, which is the flow direction of the measurement target gas 30. For this reason, the flow rate of the measurement target gas 30 flowing to the discharge passage 3528 can be reduced. Therefore, with the discharge passage 3528, the measurement error caused by the leakage of the measurement target gas 30 to the exhaust port can be reduced, and thus the measurement can be performed with high accuracy.

[0070] In addition, the design tapers as shown in Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B), the bypass passage 4232 at the inlet port is sized in cross-sectional area from the opening of the through-hole 3522 of the discharge passage 3528 to the measuring surface 430 serving as an air flow measuring section. With this configuration as described above, after the water and the measurement target gas 30 are separated by the discharge passage 3528, the flow velocity of the water and the separated measurement target gas 30 increases and flows to the measuring surface 430, so that high-accuracy measurement can be performed without impurities such as water.

[0071] In addition, in the embodiment as shown in Fig. 5 (A), Fig. 5 (B), Fig. 6(A) and Fig. 6(B), the measurement target gas 30 is made difficult to flow into the discharge channel 35298 because the inner diameter of the through hole 3522 of the discharge channel 3528 is smaller than that of the bypass channel. Therefore, the measurement error caused by the escape of the measurement target gas 30 to the outlet port can be reduced, and thus the measurement can be performed with high accuracy. Further, for example, the inner diameter of the through hole 3522 of the discharge channel 3528 can be set to fall within a range between 1 / 10 and 1 / 20 of the inner diameter of the bypass channel. In addition, the through hole, as shown in Fig. 5 (A), Fig. 5 (B), Fig. 6(A) and Fig. 6(B), it can be circular, rectangular, or elliptical. In addition, since the water flowing through the inlet opening 3552 flows along the bypass outer wall as described above, and the through-hole 3522 provided in the wall surface 4212 on the side near the bypass channel 4232 at the inlet opening is located near the outer wall 3914, the water 3552 flows easily through the opening 3522. 3.2 Structure and effect of the air flow measuring section of the bypass duct

[0072] Fig. 7 (A) and Fig. 7 (B) are partially enlarged cross-sectional views taken along the line AA in Fig. 6 (A) and Fig. 6 (B), showing the orientation of the measuring surface 430 of the switching assembly 400 inside the bypass channel groove. It should be noted that Fig. 7(A) and Fig. 7(B) are design diagrams that compare to the specific configurations of Fig. 5 (A), Fig. 5 (B), Fig. 6 (A) and Fig. 6 (B) provide simplified or incomplete representations, and that details may be slightly modified. The left side of Fig. 7(A) and Fig. 7(B) is the outlined end portion of the bypass channel trough on the rear side 334; the right side is the first portion of an end piece of the bypass channel trough on the front side 332. Although in Fig. 7 (A) and Fig. 7 (B), the openings 342 and 341 are provided on both the left and right sides of the circuit package 400 with the integrated measurement surface 430. The bypass channel grooves on the rear side 334 and on the front side 332 are connected to the left and right sides of the circuit package 400 and the measurement surface 430.

[0073] The measurement target gas 30 flowing in through the inlet port 350, which flows through the bypass channel on the back side, which includes the bypass channel groove on the back side 334, is supplied from the left side of Fig. 7 (A) and Fig. 7 (B). Part of the measurement target gas 30 flows through a flow path 386, which includes the front side of the measuring surface 430 of the switch assembly 400 and the protrusion 356 provided in the front cover 303, through the opening 342. The other part of the measurement target gas 30 flows through the flow path 387, which is formed by the back side of the measuring surface 431 and the back cover 304. Then, the measurement target gas 30 in the flow path 387 flows through the bypass channel groove on the front side 332 through the opening 341 and is mixed with the measurement target gas 30 from the flow path 386. From there, it flows through the bypass channel groove on the front side 332 and is discharged into the main channel 124 via the outlet port 352. It should be noted that the projection 358 located on the rear cover 304 projects into the flow path 387 toward the back of the measuring surface 431.

[0074] Because the bypass channel groove is shaped to direct the measurement target gas 30 from the bypass channel groove on the rear side 334 through the opening 342 into the flow path 386, it thus has a sharper curvature than the flow path for the flow path 387. Particles with a higher mass, such as impurities in the measurement target gas 30, are collected in the flow path 387 with its less sharp curvature. Therefore, there are almost no foreign bodies in the flow area of the flow path 386.

[0075] The flow path 386 is designed to form a mouth where the front cover 303 gradually connects to the front end of the bypass channel groove at the front face 332, and the protrusion 356 protrudes seamlessly toward the measuring surface 430. The measuring surface 430 is located in one side of the mouth area of the flow path 386. The measuring surface 430 is provided with the heat transfer surface exposure portion 436 for heat transfer between the air flow measurement portion 602 and the measurement target gas 30. In order to perform the measurement in the air flow measurement portion 602 with high accuracy, it is advantageous for the measurement target gas 30 to flow in the form of a laminar flow with a small vortex in the heat transfer surface exposure portion 436. In addition, as the flow velocity increases, the measurement accuracy also increases.Therefore, the orifice is shaped such that the protrusion 356 on the front cover 303 faces the measurement surface 430 and extends seamlessly toward it. This orifice reduces turbulence in the target gas 30 to such an extent that the flow approximates laminar flow. Since the flow rate increases in the orifice region and the exposure section of the heat transfer surface 436 for measuring the flow rate is located in the orifice region, the flow rate measurement accuracy also increases.

[0076] Since the opening is shaped such that the projection 356 protrudes toward the inside of the bypass channel groove and is located opposite the exposure section of the heat transfer surface 436 on the measuring surface 430, the measurement accuracy is increased. The projection 356 forming the opening is located on the cover opposite the exposure section of the heat transfer surface 436 provided on the measuring surface 430. Since, as shown in Fig. 7, in which the cover opposite the heat transfer surface exposure portion 436 provided at the measurement surface 430 is the front cover 303, the heat transfer surface exposure portion 436 is provided in the front cover 303. Alternatively, the protrusion 356 may also be located in the cover opposite the heat transfer surface exposure portion 436 provided in the measurement surface 430 of the front cover 303 or rear cover 304. Depending on which surface of the circuit package 400 the measurement surface 430 and the heat transfer surface exposure portion 436 are provided, the cover opposite the heat transfer surface exposure portion 436 changes.

[0077] The distribution of the measurement target gas 30 between the flow paths 386 and 387 also contributes to high measurement accuracy. The distribution of the measurement target gas 30 between the flow paths 386 and 387 can be adjusted by extending the protrusion 358 located in the rear cover 304 into the flow path 387. Furthermore, due to the location of the orifice portion in the flow path 387, it is possible to increase the flow velocity and direct foreign matter, such as contaminants, into the flow path 387. In the embodiment, the orifice formed by the protrusion 358 is used as one of the adjustment means between the flow paths 386 and 387. Alternatively, the above-mentioned flow rate distribution between the flow paths 386 and 387 can be adjusted by changing the distance between the back of the measuring surface 431 and the rear cover 304 and the like.In this case, the projection 358 in the rear cover 304 is not necessary.

[0078] Referring to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B), a pressed imprint 442, formed during the resin molding process by using the die for the circuit package 400, remains on the back side of the measurement surface 431 as the back side of the heat transfer surface exposure portion 436 on the measurement surface 430. This pressed imprint 442 does not pose a particular obstacle to flow rate measurement and does not cause problems even if it remains in place. As described below, it is also important to protect the semiconductor diaphragm in the air flow measurement portion 602 during the resin molding of the circuit package 400. For this reason, pressing the back side of the heat transfer surface exposure portion 436 is important. It is also extremely important to prevent the resin encasing the circuit package 400 from entering the heat transfer surface exposure portion 436.To this end, resin inflow is prevented when encasing the sensing surface 430 and the heat transfer surface exposure portion 436 by using a die, and another die is used to press the back surface of the heat transfer surface exposure portion 436. Since the circuit assembly 400 is formed by transfer molding, the resin pressure is high, and counter-pressing from the back surface of the heat transfer surface exposure portion 436 is important. Furthermore, since a semiconductor diaphragm is used in the airflow sensing portion 602, it is recommended to provide a vent portion at the gap for the semiconductor diaphragm during molding. For receiving and fixing a plate and for molding the vent portion, etc., it is important to apply counter-pressure from the back surface of the heat transfer surface exposure portion 436. 3.3 Shape of the cover of the thermal flow meter 300 and corresponding effects

[0079] Fig. 8(A) to 8(C) are diagrams illustrating an appearance of a front protective cover 303, wherein Fig. 8(A) is a left side view, Fig. 8 (B) is a front view and Fig. 8(C) is a top view. Fig. 9(A) to 9(C) are diagrams illustrating an appearance of a rear protective cover 304, wherein Fig. 9 (A) is a left side view, Fig. 9 (B) is a front view and Fig. 9(C) is a plan view. In Fig. 8 (A), Fig. 8 (B), Fig. 8 (C), Fig. 9 (A), Fig. 9 (B) and Fig. 9 (C), the front cover 303 and the rear cover 304 are attached to the front and rear sides of the housing 302. As shown in Fig. 5(A), Fig. 5 (B), Fig. 6(A) and Fig. As shown in Fig. 6(B), the front cover 303 and the rear cover 304 come into close contact with the upper portions (i.e., the height direction leading end portions closest to the outer side at the front and rear, respectively) of the upstream and downstream outer walls 335 and 336, which serve as outer walls of the casing 302. Further, the front cover 303 and the rear cover 304 come into close contact with the height direction leading end portions (at the outer front and rear sides of the fixing portion 3721) and further come into close contact with the flange 312, so that the closed gap 382 is formed therein. Furthermore, the front and rear covers 303 and 304 are used to form the bypass passage by covering the bypass passage groove of the casing 302. For this purpose, the front and rear covers 303 and 304, respectively, are designed to provide an opening in projection 356.For this reason, high manufacturing accuracy is desirable during the molding process. Since the front or back surface 303 or 304 is formed by injecting thermoplastic resin into a die in the resin molding process, it is possible to produce the front or back surface 303 or 304 with high dimensional accuracy.

[0080] The front protective portion 322 or the rear protective portion 325 is formed in the front cover 303 or the rear cover 304, respectively, as shown in Fig. 8 (A), Fig. 8 (B), Fig. 8 (C), Fig. 9 (A), Fig. 9 (B) or Fig. 9 (C). As shown in Fig. 2 (A), Fig. 2 (B), Fig. 3 (A) or Fig. As shown in Figure 3(B), the front protection portion 322 located in the front cover 303 is mounted on the front side of the inlet opening 343, and the rear protection portion 325 located in the rear cover 304 is mounted on the back side of the inlet opening 343. The temperature measuring portion 452 located in the inlet opening 343 is protected by the front and rear protection portions 322 and 325, so that the temperature measuring portion 452 is protected from mechanical damage that may be caused by a collision of the temperature measuring portion 452 with an object during production or when loading onto a vehicle.

[0081] The inner surface of the front cover 303 is provided with the projection 356. As shown in Fig. 7 (A) and Fig. As shown in Fig. 7(B), the protrusion 356 faces the measurement surface 430 and has a groove extending along the axis of the flow path in the bypass channel. An orifice is formed in the flow path 386 as described above so that, together with the measurement surface 430 and the protrusion 356, it reduces a vortex generated in the measurement target gas 30 and creates laminar flow. In this embodiment, the bypass channel with an orifice is divided into a groove part and a hood part that covers the groove and forms a flow path with an orifice. The groove part is created in a second resin molding process during the molding of the housing 302. After that, the front cover 303 with the protrusion 356 is formed in another resin molding process. The groove is covered by the front cover 303 as a hood to form the bypass channel.In the second resin molding process for forming the housing 302, the circuit package 400 having the measuring surface 430 is also attached to the housing 302. Since the structure of the groove has a complicated shape in the resin molding process and the projection 356 for the orifice must be located in the front cover 303, it is possible to form the flow path 386 in . Fig. 7 (A) and Fig. 7 (B) with high accuracy. In addition, since the arrangement provides a connection between the channel and the measuring surface 430 or the heat transfer surface exposure portion 436, high accuracy can be maintained, thus making it possible to avoid product deviations and achieve high dimensional accuracy. Therefore, productivity can be increased.

[0082] This is also applied to the formation of the flow path 387 using the rear cover 304 and the back of the measuring surface 431. The flow path 387 is divided into the groove part and the hood part of the flow path 386. The groove part is formed by a second resin molding process for forming the housing 302 and covered by the rear cover 304 with the projection 358, thus forming the flow path 387. By forming the flow path 387 in this way, it is possible to form the flow path 386 with high accuracy, thereby increasing productivity. In addition, although the orifice is provided in the flow path 387 in this embodiment, the flow path 387 can also be used without using the projection 358 and without the orifice.

[0083] In Fig. 8(B), a notch 323 used for forming the outlet port 352 is provided on the leading end side of the front cover 303. As shown in Fig. As illustrated in Figure 2(B), the notch 323 extends the outlet port 352 not only on the right side of the housing 302 but also on the front of the housing 302. In this configuration, the fluid resistance of the entire bypass channel is reduced, and the measurement target gas 30 directed into the bypass channel through the inlet 350 is increased. Consequently, the flow rate measurement accuracy is improved. 3.4 Structure and effect of the connector 320

[0084] Fig. Figure 10 is an enlarged view showing the connector 320 of the housing 302 of the Fig. 5(A), Fig. 5(B), Fig. 6(A), and 6(B). However, the connector 320 differs in Fig. 10 of the Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6 (B) for the following reasons: In particular, Fig. 5(A), Fig. 5 (B), Fig. 6(A) and Fig. 6(B) the internal sockets are separated from the external terminals 361. However, in Fig. 10, the inner sockets of the external terminals 361 are not separated from each other, but are connected to each other by the connecting portion 365. While each of the inner sockets of the external terminals 361 projecting toward the circuit package 400 side of the external terminal 306 is superimposed on or located close to the corresponding connection terminals 412, each of the external terminals 306 is fixed to the housing 302 by resin molding in the second molding process. To prevent deformation or deviation of the arrangement of each external terminal 306, according to one embodiment, the external terminal 306 is fixed to the housing 302 by the resin molding process (the second resin molding process in a later description) to form the housing 302, while the inner sockets of the terminal 361 are connected to each other by the connecting portion 365.Alternatively, the external terminal 306 may be fixed to the housing 302 by the second molding process after the connecting terminals 412 and the inner sockets of the connector 361 are fixed. 3.5 Checking the finished product through the first resin molding process

[0085] In the embodiment of Fig. 10, the number of terminals provided in the circuit package 400 is greater than the number of inner sockets of the terminals 361. Of the terminals of the circuit assembly 400, each of the connecting terminals 412 is connected to each of the inner sockets of the external terminals 361, and the terminals 414 are not connected to the inner socket of the external terminals 361. That is, although the terminals 414 are provided in the circuit package 400, they are not connected to the inner socket of the external terminals 361.

[0086] In Fig. 10, in addition to the connection terminal 412 connected to the inner socket of the external terminal 361, the terminal 414 is provided that is not connected to the inner socket of the external terminal 361. After the circuit package 400 is manufactured through the first resin molding process, it is checked whether the circuit package 400 functions properly and whether an abnormality in the electrical connection was caused by the first resin molding process. As a result, it is possible to maintain high reliability for each circuit package 400. The terminal 414 that is not connected to the inner socket of the external terminal 361 is used in this check of the circuit package 400.Since the terminal 414 is not used after the inspection work, these free terminals 414 at the neck portion of the switch assembly 400 can be cut out or hidden in the resin after the inspection and serve as the terminal-side fixing portion 362, see FIG. By providing the terminal 414 that is not connected to the inner socket of the external terminal 361, it is possible to check whether an abnormality has been caused in the switch assembly 400 manufactured by the first resin molding process, and high reliability can be maintained. 3.6 Connection structure (air-permeable structure) between the gap 382 inside the housing 302 and outside and its effects

[0087] As shown in the partially enlarged view of Fig. 10, an opening 364 is provided in the housing 302. The opening 364 is connected to the opening 309 which is provided on the inside of the Fig. 4(A). According to the embodiment, both sides of the housing 302 are hermetically sealed with the front cover 303 and the rear cover 304. If the opening 364 is not provided, a pressure difference is generated between the air pressure inside the gap 382 and the atmospheric pressure due to a temperature change of the air inside the gap 382 that sandwiches the end termination 320. It is preferable to reduce such a pressure difference. For this reason, the opening 364, which communicates with the opening 309 on the inside of the external terminal 305, is provided inside the gap 382 of the housing 302. The external terminal 305 is constructed to be resistant to any deterioration by water or the like to achieve higher reliability of the electrical connection.By arranging the opening 309 within the external connection 305, it is possible to prevent the ingress of water or foreign matter, such as dirt or dust, from the opening 309. 4. Fastening structure for fastening the circuit package 400 using the housing 3024.1 Fastening structure for fastening the circuit package 400 to the housing 302

[0088] A mounting structure for mounting the circuit package 400 to the housing 302 will be described below with reference to Fig. 5 (A), Fig. 5 (B), Fig. 6 (A) and Fig. 6(B). The circuit package 400, which is used together with the flow rate sensor circuit 601 (see Fig. 19) for measuring the flow rate of the measurement target gas 30 flowing through the main channel 124 is fixed to the housing 302, which has a bypass channel groove. In this embodiment, the flange 312 and the bypass channel grooves 332 and 334 are connected by the upstream outer wall 335 and the downstream outer wall 336. A portion of the bypass channel grooves 332 and 334 is supported by the flange 312 by the upstream outer wall 335 and the downstream outer wall 336. Furthermore, the upstream outer wall 335 is located on the upstream side in the flow direction of the measurement target gas 30 flowing through the main channel 124, and the downstream outer wall 336 is located on the downstream side in the flow direction. The fixing portion 3721 is provided to connect the upstream outer wall 335 and the downstream outer wall 336.The fixing portion 3721 wraps the circuit package 400 over its entire circumference, thereby fixing the circuit package 400 to the casing 302. Furthermore, the gap 382, surrounded by the upstream outer wall 335, the downstream outer wall 336, and the flange 312, is formed on the flange side of the fixing portion 3721. The bypass channel grooves 332 and 334 are formed on a bypass channel side opposite the flange of the fixing portion 3721, and the bypass channel grooves 332 and 334 are configured to allow the measurement target gas 30 to flow through them. The fixing portion 3721 serves to maintain airtightness on the bypass channel side of the gap.

[0089] The outer wall hollow portion 366 located on the upstream outer wall 335 can further secure the circuit package 400 using the fixing portion 3723. In this embodiment, the above-described fixing portion 3721 wraps the circuit package 400 along the flow axis of the measurement target gas 30 (i.e., in a direction along the longitudinal axis of the measurement surface 430) to connect the upstream outer wall 335 and the downstream outer wall 336. Meanwhile, the outer wall hollow portion 366 of the upstream outer wall 335 wraps the circuit package 400 in a direction transverse to the flow axis of the measurement target gas 30. In other words, the fixing portion 3723 is formed differently from the fixing portion 3721 in the direction wrapping the circuit package 400, and wraps the circuit package 400.Because these fixing portions enclose and fix the circuit package 400 in different directions, it is possible to fix the circuit package 400 firmly to the housing 302.

[0090] Although the outer wall hollow portion 366 is part of the upstream outer wall 335, the circuit pack 400 may be wrapped in a different direction than the attachment portion 3721. For this purpose, the downstream outer wall 336 is used instead of the upstream outer wall 335 to increase strength. For example, one end of the circuit pack 400 may be wrapped by the downstream outer wall 336, or the circuit pack 400 may be wrapped by a bulge of the hollow space in the upstream direction of the downstream outer wall 336 or a protrusion extending in the upstream direction from the downstream outer wall 336.In this embodiment, since the outer wall hollow portion 366 is provided in the upstream outer wall 335 to enclose the circuit package 400, it is possible to enhance the effect of increasing the thermal resistance between the temperature sensing portion 452 and the upstream outer wall 335 in addition to securing the circuit package 400. In addition, since the outer wall hollow portion 366 forms the base of the protrusion 424 of the circuit package 400 with the temperature sensing portion 452 (see FIG. Fig. 11) wrapped and secured.

[0091] The fixing portions 3721 and 3723 each have a thick portion and a thin portion to reduce stress exerted on the circuit package 400. As shown in Fig. 5(A) and Fig. As illustrated in Figure 5(B), the fixing portion 3721 includes a thick portion 4714 and a thin portion 4710. The thin portion 4710 is provided to reduce the thickness of the resin surrounding the circuit package 400 by providing a cavity toward the circuit package 400. The thin portion 4710 is further formed on a side near the flange of the thin portion 4710. The thin portion, provided on a side near the flange of the thin portion 4710, is formed such that the thickness of the resin surrounding the circuit package 400 is thinner than the thickness of the thick portion 4714. However, the thin portion is formed such that the thickness of the resin surrounding the circuit package 400 is slightly thicker than the thickness of the thin portion 4710.Thus, since the thin portion 4714 and the thin portion are provided on one side near the flange for the thick portion 4714, the fixing portion 3721 secures an area of a predetermined size for wrapping the circuit package 400 and, at the same time, causes the stress exerted from the fixing portion 3721 on the circuit package 400 to be reduced to the area.

[0092] In Fig. 6(B), which shows the back of Fig. As illustrated in Figure 5(B), the fixing portion 3721 includes the thick portion 4714 and a thin portion formed by a cavity 373. With the thin portion provided as described above, the fixing portion 3721 secures a predetermined area for enclosing the circuit package 400 and, at the same time, has the effect of reducing the stress applied to the circuit package 400. Since the fixing portion 3721 is configured including a thick portion and a thin portion, the reliability of fixing the circuit package 400 is increased. That is, the airtightness between the circuit package 400 and the fixing portion 3721 is ensured.Furthermore, during the resin molding process, the stress exerted by the fixing portion 3721 on the circuit package 400, which occurs with the volume shrinkage that occurs when the fixing portion 3721 is cooled and hardened, can be reduced. Furthermore, since the thin portion is provided, the movement of the resin during the resin molding process is suppressed, and the temperature reduction of the resin is mitigated, thus increasing the time required for resin hardening. The resin of the fixing portion 3721 flows more easily into imbalances on the surface of the circuit package 400, and therefore, the airtightness between the circuit package 400 and the fixing portion 3721 is significantly increased.

[0093] Because the measurement target gas 30 flows on one side near the bypass channel of the fixing portion 3721, moisture and the like may penetrate into the gap 382 inside the housing 302 if the airtightness between the circuit package 400 and the fixing portion 3721 is lost. Due to the presence of the thin portion, the contact area between the fixing portion 3721 and the resin of the circuit package 400 can be increased, the airtightness can be improved, and the penetration of moisture into the gap 382 inside the housing 302 can be reliably prevented.

[0094] In Fig. 5 (B) and Fig. 6(B), the upstream outer wall 335 has the outer wall hollow portion 366. The outer wall hollow portion 366 serves as the fixing portion 3723 for fixing the circuit package 400 to the housing 302. The fixing portion 3723 has a thick portion 4715 and a thin portion 4716. Similar to the fixing portion 3721, the fixing portion 3723 can secure a large contact area with the circuit package 400. In addition, since the thin portion 4716 exerts only a small stress on the circuit package 400, the influence of the stress exerted by the fixing portion 3723 on the circuit package 400 can be reduced.Since the measurement target gas 30 flows on the upstream side of the fixing portion 3723, it is important to ensure the airtightness between the fixing portion 3723 and the circuit package 400, and the securing of the airtightness between the fixing portion 3723 and the circuit package 400 is made possible by the thin portion 4716 and the thick portion 4715. 4.2 Structure of the housing 302 formed by a resin molding process

[0095] Next, the attachment of the circuit package 400 to the housing 302 by a resin molding process will be described with reference to Fig. 5 (A), Fig. 5 (B) and Fig. 6(B). The circuit package 400 is arranged and fixed in the housing 302, so that the measuring surface 430 formed on the front surface of the circuit package 400 is arranged in a predetermined position of the bypass channel groove to form the bypass channel, such as a connecting portion between the bypass channel groove on the front side 332 and the bypass channel groove on the rear side 334 in the embodiment of the Fig. 5(A), Fig. 5 (B), Fig. 6 (A) and Fig. 6(B). The portion in which the circuit package 400 is embedded and fixed in the housing 302 by a resin molding process is provided on a side near the flange 312 of the bypass channel groove. The circuit package 400 is formed by the first resin molding process, as described below with reference to Fig. 16. The circuit package 400 formed by the first resin molding process is configured to hold and fix the circuit package 400 in such a manner that the fixing portion 3721 is formed when the housing 302 having the bypass passage is formed by a second resin molding process, and the fixing portion 3721 covers the outer diameter of the circuit package 400 formed by the first resin molding process.

[0096] As in Fig. 5(B), the cavity 376 and the thin portion 4710 having a hollow shape are provided on the front surface of the fixing portion 3721. As shown in Fig. As shown in Figure 6(B), the cavity 373 serves as a thin portion formed on the back side of the fixing portion 3721. Thanks to these cavities, the temperature of the resin during molding of the fixing portion 3721 can be cooled and volume shrinkage can be reduced. Therefore, it is possible to reduce the stress exerted on the circuit package 400. Since the use of the die for molding the above-mentioned cavity can slow down the flow of the resin, the rate at which the resin cools is also slowed, and the resin forming the fixing portion 3721 can smoothly flow into the unevenness on the surface of the circuit package 400.

[0097] Not the entire surface of the circuit package 400 is covered with the resin used to mold the housing 302, but a part of the surface where the outer wall of the circuit package 400 is exposed is provided in the flange (312) side of the fixing portion 3721. In the embodiment according to Fig. 5 (A), Fig. 5 (B), Fig. 6 (A) and Fig. 6(B), the area of a portion exposed by the resin of the housing 302 and not enclosed by the housing 302 is larger than the area of a portion enclosed by the resin of the housing 302 outside the outer peripheral surface of the circuit package 400. Furthermore, a portion of the measurement surface 430 of the circuit package 400 is also exposed by the resin of the housing 302.

[0098] In the second resin molding process for forming the housing 302, the periphery of the circuit package 400 is wrapped by forming the hollow space on the front and rear surfaces of the fixing portion 3721. The fixing portion 3721 covers the outer wall of the circuit package 400 over the entire periphery in a thin band shape. During the second resin molding process, it is possible to prevent excessive stress concentration by reducing the volume during the hardening of the fixing portion 3721. This excessive stress concentration can degrade the circuit package 400. 4.3 Improving the airtightness between housing 302 and circuit package 400

[0099] In order to more robustly fix the circuit package 400 to a small area by reducing the area of a portion enveloped by the resin of the case 302 of the outer peripheral surface of the circuit package 400, the adhesion of the circuit package 400 to the outer wall in the fixing portion 3721 should be increased. When a thermoplastic resin is used to form the case 302, it is preferable that the thermoplastic resin penetrates into fine imbalances on the surface of the circuit package 400 while having a low viscosity (i.e., at a high temperature), and the thermoplastic resin hardens while penetrating the fine imbalances on the front surface. In the resin molding process for forming the case 302, it is preferable that the inlet port of the thermoplastic resin be provided in or near the fixing portion 3721. The viscosity of the thermoplastic resin increases as the temperature decreases, so the resin solidifies.Thus, by allowing the thermoplastic to flow into or near the mounting portion 3721 at a high temperature, it is possible to harden the thermoplastic, which has a low viscosity, while adhering to the front surface of the circuit package 400. Furthermore, when forming the cavity 376, the thin portion 4710 as a cavity, and the cavity 373 of the mounting portion 3721, an obstruction portion is formed to restrict the flow of the thermoplastic using a die to form these cavities. This reduces the moving speed of the thermoplastic in the mounting portion 3721. As a result, a temperature decrease of the thermoplastic is suppressed and a low viscosity state is maintained, so that the adhesion between the circuit package 400 and the mounting portion 3721 can be improved.

[0100] By roughening the front surface of the circuit package 400, it is possible to increase the adhesion between the circuit package 400 and the fixing portion 3721. As a roughening method for the front surface of the circuit package 400, a roughening method that forms fine unevenness on the surface of the circuit package 400 after the circuit package 400 is formed by the first resin molding process is known, such as a frosting treatment. Further, as a roughening method for forming fine unevenness on the surface of the circuit package 400, roughening can be achieved using, for example, a sandblasting method. Furthermore, roughening can be achieved by laser processing.

[0101] As another roughening method, an uneven sheet is attached to an inner surface of the mold used in the first resin molding process, and the resin is pressed into the mold while the sheet is on this surface. Using this method, it is possible to form fine unevennesses on the surface of the circuit package 400 and roughen them. Alternatively, unevennesses may be directly attached to an inner surface of the mold to form the circuit package 400 and roughen the surface of the circuit package 400. The surface portion of the circuit package 400 for such roughening is at least a portion where the fixing portion 3721 is provided. In addition, adhesion can be further improved by roughening a surface portion of the circuit package 400 where the outer wall hollow portion 366 is provided.

[0102] When the surface treatment for forming bumps on the surface of the circuit package 400 is performed using the above-mentioned layer, the depth of the groove depends on the thickness of the layer. As the thickness of the layer increases, molding during the first resin molding process becomes difficult, so the layer thickness is limited. As the thickness of the layer decreases, the depth of the bump provided on the layer is limited. Therefore, when the above-mentioned layer is used, it is desirable that the depth of the bump between the bottom and top surfaces of the bump be set to 10 μm or greater and 20 μm or less. If the depth is less than 10 μm, the adhesion effect deteriorates. A depth greater than 20 μm is difficult to achieve from the above-mentioned layer thickness.

[0103] In roughening methods other than the above-mentioned method using the layer, it is desirable to set a thickness of the resin in the first resin molding process to form the circuit package 400 to 2 mm or less. Therefore, it is difficult to increase the depth of the unevenness between the bottom and top surfaces of the unevenness to 1 mm or more. Conceptually, it is anticipated that the adhesion strength between the resin covering the circuit package 400 and the resin used to form the housing 302 increases as the depth of the unevenness between the bottom and top surfaces of the unevenness on the surface of the circuit package 400 increases. For the reason described above, the depth of the unevenness between the bottom and top surfaces of the unevenness is preferably set to 1 mm or less.That is, when the unevenness having a thickness of 10 μm or greater and 1 mm or less is provided on the surface of the circuit package 400, it is desirable to increase the adhesive strength between the resin covering the circuit package 400 and the resin used to form the housing 302.

[0104] A thermal expansion coefficient differs between the thermosetting plastic used to form the circuit package 400 and the thermoplastic used to form the housing 302, which has the mounting portion 3721. It is desirable to prevent excessive stress exerted on the circuit package 400 caused by this difference in thermal expansion coefficient. With the cavity 373, the thin portion 4710 as a cavity, and the cavity 376, it is possible to reduce the stress exerted on the circuit package 400.

[0105] By forming the fastening portion 3721 that wraps the outer periphery of the circuit package 400 in a band shape and narrows the width of the band, it is possible to alleviate the stress caused by a difference in thermal expansion coefficient acting on the circuit package 400. The width of the band of the fastening portion 3721 is set to 10 mm or less, and preferably 8 mm or less. In this embodiment, since the outer wall hollow portion 366, as a constituent of the upstream outer wall 335 of the housing 302 and as the fastening portion 3721, surrounds the circuit package 400 to fix it, it is possible to further reduce the width of the band of the fastening portion 3721. For example, the circuit package 400 can be fixed if the width is set to 3 mm or more.

[0106] To reduce the stress caused by the difference in thermal expansion coefficient, a portion surrounded by resin used to form the housing 302 and an exposed portion not covered with resin are provided on the surface of the circuit package 400. A plurality of portions are provided where the surface of the circuit package 400 is exposed and not covered by the resin of the housing 302. One of these portions is for the measurement surface 430, which has the above-described heat transfer surface exposure portion 436. Furthermore, a portion exposed to a part of the flange 312 side with respect to the fixing portion 3721 is provided.Furthermore, the outer wall hollow portion 366 is formed to expose a portion of the upstream side with respect to the outer wall hollow portion 366, and this exposed portion serves as a support portion that supports the temperature measuring portion 452. A gap is formed such that a portion of the outer surface of the circuit package 400 in the flange (312) side with respect to the fixing portion 3721 encloses the circuit package 400 over its outer periphery, specifically, the side facing from the downstream side of the circuit package 400 toward the flange 312 and further extends over the upstream side of the portion near the terminal for the circuit package 400.Since this gap is formed around the portion where the surface of the circuit package 400 is exposed, the amount of heat transferred from the main channel 124 to the circuit package 400 via the flange 312 can be reduced, and deterioration of the measurement accuracy caused by the heat can be suppressed.

[0107] A gap is formed between the circuit package 400 and the flange 312, which serves as a terminal joint 320. The terminal joint 412 of the circuit package 400 and the inner socket of the outer terminal 361, which is arranged in the housing (302) side of the outer terminal 306, are electrically connected to each other using the terminal joint 320 by spot welding, laser welding, or a similar connection. As described above, the gap of the terminal joint 320 can suppress heat transfer from the housing 302 to the circuit package 400 and can be used as a space for performing connection work between the terminal joint 412 of the circuit package 400 and the inner socket of the outer terminal 361 of the outer terminal 306. 4.4 Formation of the housing 302 by a second resin molding process and increase of the measurement accuracy

[0108] In the housing 302, which is in the Fig. 5 (A), Fig. 5 (B), Fig. 6(A) and Fig. As shown in Figure 6(B) and described above, the circuit package 400 including the airflow measurement section 602 or the processing unit 604 is manufactured through the first resin molding process. The casing 302, which has, for example, the front-side bypass channel groove 332 or the rear-side bypass channel groove 334 for forming the bypass channel where the measurement target gas 30 flows through it, is then manufactured through the second resin molding process. Through this second resin molding process, the circuit package 400 is embedded in the resin of the casing 302 and fixed to the inside of the casing 302 by resin molding.As a result, heat transfer to the measurement target gas 30 occurs in the air flow measurement section 602, so that a configuration dependency, such as a positional or directional dependency, between the exposure section of the heat transfer surface 436 for flow measurement and the bypass channel, including, for example, the front-side bypass channel groove 332 or the rear-side bypass channel groove 334, can be maintained with remarkably high accuracy. In addition, an error or deviation caused during each production of the circuit package 400 can be suppressed or reduced to a very small value. If the dependency relationship between the circuit package 400 and the bypass channel through which the gas 30 to be measured flows is established during the second resin molding process, this dependency relationship will not change thereafter.When the attachment is made with an adhesive, the dependency relationship may vary slightly even after production. As described in the embodiment, if the dependency relationship between the circuit package 400 and the bypass passage through which the measurement target gas 30 flows does not change, very high accuracy can be achieved by correcting the deviation after production. This can achieve a remarkable improvement in the measurement accuracy for the circuit package 400. For example, compared to a conventional method in which the attachment is performed using an adhesive, a twofold or even greater increase in the measurement accuracy can be achieved.Since the thermal flow meter 300 is usually manufactured in large quantities, it is difficult to use an adhesive while performing strict measurement in all manufacturing processes, and there are limitations on improving measurement accuracy. However, if the circuit package 400 is manufactured during the first resin molding process as described in the present embodiment, and the bypass channel is subsequently formed in a second resin molding process to form the bypass channel through which the measurement target gas 30 flows while fixing the circuit package 400 and the bypass channel, a remarkable reduction in measurement accuracy fluctuations and a remarkable improvement in measurement accuracy can be achieved for each thermal flow meter 300. This is similarly true for the embodiment of FIG. Fig. 7 and the following embodiments of Fig. 5 (A), Fig. 5(B), Fig. 6(A) and Fig. 6(B).

[0109] With further reference to the embodiment of, for example, Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. 6(B), it is possible to fix the circuit package 400 to the housing 302 in such a way that a relationship between the bypass channel groove on the front side 332, the bypass channel groove on the rear side 334, and the heat transfer surface exposure portion 436 is set to a definite relationship. Accordingly, for each of the thermal flow meters 300 that are mass-produced, a positional relationship or a configuration relationship between the heat transfer surface exposure portion 436 of each circuit package 400 and the bypass channel can be maintained with remarkably high accuracy. Since the bypass channel groove is fixed where the heat transfer surface exposure portion 436 of the circuit package 400 is fixed, for example, the bypass channel groove on the front side 332 and the bypass channel groove on the rear side 334 can be formed with remarkably high accuracy.To form the bypass channel in this bypass channel groove, it is necessary to cover both sides of the housing 302 using the front cover (303) or rear cover (304). This process is very simple and has few factors that can affect measurement accuracy. In addition, the front cover (303) or rear cover (304) is formed by a resin molding process, which has high molding accuracy. Therefore, the bypass channel can be manufactured with high precision in a specific relationship to the exposure portion of the heat transfer surface 436 of the circuit package 400. In this way, it is possible to achieve high productivity in addition to improving measurement accuracy.

[0110] In comparison, the prior art thermal flowmeter was manufactured by first manufacturing the bypass channel and then bonding the flow measurement section to the bypass channel using an adhesive. This adhesive-based method has disadvantages because the thickness of the adhesive is inconsistent and the position or angle of the adhesive varies in each product. Therefore, there have been limitations in improving measurement accuracy. When this work is performed in mass production, it is still difficult to improve measurement accuracy.

[0111] In the embodiment of the invention, first, the circuit package 400 including the airflow measuring section 602 is manufactured by a first resin molding process, and then the circuit package 400 is fixed by resin molding, while the bypass channel groove for forming the bypass channel is formed by resin molding during a second resin molding process. Therefore, the shape of the bypass channel groove can be formed with very high accuracy, and the airflow measuring section 602 of the flow sensor circuit 601 (see Fig. 19) to the bypass channel.

[0112] A portion related to flow measurement, such as the heat transfer surface exposure portion 436 of the air flow measurement portion 602 or the measurement surface 430 mounted in the heat transfer surface exposure portion 436, is formed on the surface of the circuit package 400. Subsequently, the measurement surface 430 and the heat transfer surface exposure portion 436 are exposed from the resin used to form the housing 302. That is, the heat transfer surface exposure portion 436 and the measurement surface 430 are no longer covered by the resin used to form the housing 302. The measurement surface 430 formed by resin molding the circuit package 400 or the heat transfer surface exposure portion 436 is used to measure the flow of the thermal flow meter 300 or a temperature immediately after the resin molding of the housing 302.This increases the measurement accuracy.

[0113] In the embodiment of the present invention, the circuit package 400 is integrally formed with the housing 302 to fix the circuit package 400 to the housing 302 having the bypass passage. Therefore, it is possible to fix the circuit package 400 to the housing 302 with a small fixing area. That is, the surface area of the circuit package 400 that does not contact the housing 302 can be increased. The surface area of the circuit package 400 that does not contact the housing 302 is exposed, for example, in a gap. The heat from the intake pipe is transferred to the housing 302 and then transferred from the housing 302 to the circuit package 400.Even if the contact area between the housing 302 and the circuit package 400 is reduced, instead of surrounding the entire surface or a large part of the entire surface of the circuit package 400 with the housing 302, it is possible to maintain high reliability and high accuracy and fix the circuit package 400 to the housing 302. For this reason, heat transfer from the housing 302 to the circuit package 400 can be suppressed, as well as the reduction in measurement accuracy caused by the above-mentioned heat transfer.

[0114] In the Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. In the embodiment shown in Fig. 6(B), the area A of the exposed surface of the circuit package 400 can be set to a value equal to or larger than the area B covered by a molding compound used to form the housing 302. In this embodiment, the area A is larger than the area B. This makes it possible to suppress heat transfer from the housing 302 to the circuit package 400. Furthermore, a stress caused by the difference between the thermal expansion coefficient of the thermosetting resin used to form the circuit package 400 and the thermal expansion coefficient of the thermoplastic resin used to form the housing 302 can be reduced. 4.5 Fixing of the circuit package 400 by a second resin molding process and the corresponding effects

[0115] In the Fig. 11(A) to 11(C), the hatched portion shows a mounting surface 432 and a mounting surface 434 for covering the circuit package 400 using the thermoplastic used in the second resin molding process for mounting the circuit package 400 to the housing 302. As already described above with reference to the Fig. 5 (A), Fig. 5 (B), Fig. 6 (A) and Fig. As described in Figure 6(B), it is important to maintain high accuracy to maintain a specific relationship between the measurement surface 430, the exposure portion of the heat transfer surface 436 within the measurement surface 430, and the shape of the bypass channel. In the second resin molding process, the bypass channel is formed, and the circuit package 400 is fixed to the housing 302 that forms the bypass channel. Consequently, a relationship between the bypass channel, the measurement surface 430, and the exposure portion of the heat transfer surface 436 can be maintained with remarkably high accuracy. That is, since the circuit package 400 is fixed to the housing 302 in the second resin molding process, it is possible to position and fix the circuit package 400 within the mold used to form the housing 302 having the bypass channel with high accuracy.By injecting a thermoplastic having a high temperature into this mold, the bypass channel is formed with high accuracy and the circuit package 400 is fixed with high accuracy by the fixing portion 3721 and the fixing portion 3723.

[0116] In this embodiment, not the entire surface of the circuit package 400 constitutes the mounting surface 432 covered with the resin used to form the housing 302, but the front surface is exposed to the connection terminal 412 side of the circuit package 400. That is, a part of the surface is provided so that it is not covered by the resin used to form the housing 302. In the Fig. 11(A) to 11(C), from the front surface of the circuit package 400, the area that is not surrounded by the resin used to form the housing 302 but is exposed from the resin used to form the housing 302 is larger than the area of the mounting surfaces 432 and 434 that are surrounded by the resin used to form the housing 302.

[0117] The thermal expansion coefficient of the thermosetting resin used to form the circuit package 400 differs from that of the thermosetting resin used to form the housing 302, which has the mounting portion 3721. Stress on the circuit package 400 caused by this difference in thermal expansion coefficient should be prevented as much as possible. By reducing the front surface area of the circuit package 400 and the mounting surface 432, it is possible to reduce the influence based on the difference in thermal expansion coefficient. For example, it is possible to reduce the mounting surface 432 on the front surface of the circuit package 400 by providing a band shape having a width L.Furthermore, by providing a thick and a thin portion in the fixing portions 3721 and 3723 covering the fixing surface 432 as described above, the stress applied to the surface of the circuit package 400 based on the thin portion can be suppressed. Furthermore, the circuit package 400 can be prevented from being subjected to high stress. Although the airtightness between the fixing portion 3723 and the fixing surface 432 of the circuit package 400 is improved because the fixing surface 432 is relatively wide, the influence of the stress on the circuit package 400 can be suppressed by using the thin portion.Because the flow sensor circuit 601 is embedded in the circuit package 400, the flow sensor circuit 601 may be adversely affected if a heavy load is applied to the circuit package 400, thus affecting the flow measurement accuracy or, in some cases, even causing malfunction. However, these effects can be mitigated.

[0118] It is possible to increase the mechanical strength of the protrusion 424 by providing the fastening surface 432 in the neck portion of the protrusion 424. It is possible to more robustly fasten the circuit package 400 and the housing 302 to each other by providing a band-shaped fastening surface along the flow axis of the measurement target gas 30 on the front surface of the circuit package 400 and a fastening surface across the flow axis of the measurement target gas 30. On the fastening surface 432, a band-shaped portion around the circuit package 400 with a length L along the measurement surface 430, as described above, serves as a fastening surface along the flow axis of the measurement target gas 30, and a portion covering the base of the protrusion 424 serves as a fastening surface across the flow axis of the measurement target gas 30.Both mounting surfaces are enclosed by the mounting section 3721 or 3723, each having a thin and a thick section and attached to the housing 302.

[0119] In the Fig. 11 (A), Fig. 11 (B) and Fig. 11(C), as described above, the circuit package 400 is formed by the first resin molding process. Note that the hatched portion in the external appearance of the circuit package 400 shows the mounting surface 432 and the mounting surface 434 where the circuit package 400 is covered by the resin used in the second resin molding process when the housing 302 is formed by the second resin molding process after the circuit package 400 is manufactured by the first resin molding process. Fig. 11 (A) is a left side view showing the circuit package 400, while Fig. 11 (B) a front view and Fig. 11 (C) shows a rear view of the circuit package 400. The circuit package 400 is embedded together with the air flow measuring section 602 or with the processing unit 604, which will be described below, and all of these units are manufactured in an integrated molding process using a thermosetting resin. On the surface of the circuit package 400 in Fig. 11 (B), the measuring surface 430, which serves as a plane for the flow of the measurement target gas 30, is formed in a shape extending in the flow direction of the measurement target gas 30. In this embodiment, the measuring surface 430 has a rectangular shape extending in the flow direction of the measurement target gas 30. The measuring surface 430 is formed to be thinner than other portions, as shown in Fig. 11 (A), and a part of it is provided with the heat transfer surface exposure portion 436. The embedded air flow measuring portion 602 performs heat transfer to the measurement target gas 30 through the heat transfer surface exposure portion 436 to measure a state of the measurement target gas 30, such as a flow rate of the measurement target gas 30, and outputs an electrical signal representing the flow rate of the main channel 124.

[0120] In order to measure a state of the measurement target gas 30 with high accuracy using the embedded air flow measuring section 602 (see Fig. 19 and Fig. 20), the gas flowing through the vicinity of the heat transfer surface exposure section 436 should preferably flow in a laminar flow with a small vortex. For this reason, there should be no height difference between the surface on the flow side of the heat transfer surface exposure section 436 and the plane of the measuring surface 430 that guides the gas flow. In this configuration, it is possible to suppress irregular stress or deformation that would be exerted on the air flow measuring section 602 while maintaining high flow measurement accuracy. Note that the aforementioned height difference can be provided if it has no effect on the flow measurement accuracy.

[0121] On the back side of the measuring surface 430 of the exposure section of the heat transfer surface 436 remains a press impression 442 of the mold that holds an inner substrate or plate during the resin molding process for the circuit package 400, as shown in Fig. 11(C). The heat transfer surface exposure portion 436 is used to perform heat exchange with the measurement target gas 30. In order to accurately measure the state of the measurement target gas 30, heat exchange between the air flow measurement portion 602 and the measurement target gas 30 should be properly performed. For this reason, it is necessary to prevent a part of the heat transfer surface exposure portion 436 from being covered by the resin in the first resin molding process. Molds are mounted both in the heat transfer surface exposure portion 436 and on the back surface of the measurement surface 431, which is its back surface. Using this mold, the resin is prevented from flowing into the heat transfer surface exposure portion 436. A press mark 442 having a concave shape is formed on the back surface of the heat transfer surface exposure portion 436.In this section, a device serving as the airflow measuring section 602 or a similar device should be placed nearby to dissipate the heat generated by the device to the outside environment as effectively as possible. The concave section formed is less affected by the resin and allows for easy heat dissipation.

[0122] The heat transfer surface exposure portion 436 is internally equipped with a semiconductor diaphragm belonging to the air flow measurement portion 602. A gap is formed on the back side of this semiconductor diaphragm. The semiconductor diaphragm is obtained by forming a gap on the back side of the flow measurement portion 602. If the gap is covered, the semiconductor diaphragm deforms, and measurement accuracy is affected due to a pressure change inside the gap caused by a temperature change. For this reason, in this embodiment, an opening 438 communicating with the gap on the back side of the semiconductor diaphragm is provided on the front surface of the circuit package 400, and a communication channel for connecting the gap on the back side of the semiconductor diaphragm to the opening 438 inside the circuit package 400 is provided.It should be noted that the opening 438 in the unshaded area is in the . Fig. 11 (A) to 11 (C) is provided to prevent the opening 438 from being covered by the resin by the second resin molding process.

[0123] The opening 438 is formed by the first resin molding process. Resin inflow into the opening 438 portion is suppressed by fitting the molds to both a portion of the opening 438 and the back of the opening 438, and by applying pressure to the molds. This forms the opening 438. The formation of the opening 438 and the connecting channel connecting the gap on the back of the semiconductor diaphragm to the opening 438 will be described below.

[0124] In the circuit package 400, the press mark 442 is retained on the back of the circuit package 400 where the heat transfer surface exposure portion 436 is formed. In the first resin molding process, to prevent resin from flowing into the heat transfer surface exposure portion 436, a mold, such as an immersion mold, is placed in a portion of the heat transfer surface exposure portion 436, and a mold is placed in a portion of the press mark 442 directly opposite the mold to suppress resin from flowing into the heat transfer surface exposure portion 436. By forming a portion of the heat transfer surface exposure portion 436 in this manner, it is possible to measure the flow rate of the measurement target gas 30 with significantly higher accuracy.Furthermore, since little or no resin remains in the area of the press imprint 442 from the second resin molding process, there is a greater effect of heat radiation. As a result, if the second plate 536 is used as a lead wire, the adjacent circuits can be effectively heated and irradiated by the lead wire. 5. Assembly of the circuit components in the circuit package5.1 Assembly of the frame and the circuit components of the circuit package

[0125] Fig. 12 illustrates the frame 512 of the circuit package 400 and the mounting state of a chip as a circuit component 516 that is mounted on the frame 512. Note that the dotted line 508 indicates a portion covered by the mold used to form the circuit package 400. A lead wire 514 is mechanically connected to the frame 512, and a board 532 is mounted in the center of the frame 512. A chip-like airflow sensing section 602 and a processing unit 604 as a large-scale integrated circuit (LSI) are mounted on the board 532. A diaphragm 672 is provided in the airflow sensing section 602. Each terminal of the airflow sensing section 602, which will be described below, and the processing unit 604 is connected using a wire 542.Furthermore, each terminal of the processing unit 604 and a corresponding lead wire 514 are connected using a wire 543. Furthermore, the lead wire 514, which is arranged between a portion corresponding to the connection terminal of the circuit package 400 and the board 532, is connected with the chip-like circuit component 516 therebetween.

[0126] The air flow sensing section 602, which includes the diaphragm 672, is arranged at the leading end when the circuit package 400 is formed in this way. The processing unit 604 is arranged on the side corresponding to the connection terminal for the air flow sensing section 602 in an LSI form. Furthermore, a connecting wire 543 is arranged on the connection side of the processing unit 604. By sequentially arranging the air flow sensing section 602, the processing unit 604, the wire 543, the circuit component 516, and the connecting line 514 in the order mentioned from the leading end of the circuit package 400 to the connection terminal, the entire circuit package 400 becomes simple and compact.

[0127] A thick wire is provided to support the plate 532. This wire is fixed to the frame 512 using wire 556 or 558. Note that a wire surface having the same area as that of the plate 532 connected to the thick wire is provided on the lower surface of the plate 532, and the plate 532 is mounted on the wire surface. This wire surface is connected to ground. Therefore, noise can be suppressed by commonly grounding the circuit of the airflow measuring section 602 or the processing unit 604 using the wire surface, thereby increasing the measurement accuracy of the measurement target gas 30.Additionally, a conduit 544 is provided in the upstream side of the flow path of plate 532, that is, in such a way that it protrudes along an axis directed transversely to the axis of the airflow measuring section 602, the processing unit 604, or the above-described circuit component 516. A temperature measuring element 518, for example, a chip-like thermistor, is connected to this conduit 544. Furthermore, a conduit 548 is provided in the vicinity of the processing unit 604, which forms a base of the protruding part and electrically connects the conduits 544 and 548 using a thin connecting conduit 546. Since the conduits 548 and 544 are directly connected, heat is transferred through the conduits 548 and 544 to the temperature measuring element 518, so it may be difficult to accurately measure the temperature of the measurement target gas 30.Therefore, by connecting a wire having a small cross-sectional area and high thermal resistance, the thermal resistance between the leads 548 and 544 can be increased. As a result, the accuracy of the temperature measurement of the measurement target gas 30 can be increased by preventing the influence of heat from reaching the temperature measuring element 518.

[0128] Lead 548 is fixed to the frame 512 through lead 552 or 554. A connecting portion between lead 552 or 554 and the frame 512 is fixed to the frame 512 while being inclined against the protrusion direction of the protruding temperature sensing element 518, and the mold is also inclined in this area. When the molding resin flows along this inclination in the first resin molding process, it flows smoothly to the leading end portion where the temperature sensing element 518 is provided, thus increasing reliability.

[0129] In Fig. In Figure 12, arrow 592 indicates a resin injection direction. The lead frame on which a circuit component is mounted is covered by the mold, and a pressed fitting hole 590 for resin injection into the mold is provided at the circled location, so that a thermosetting resin is injected into the mold along the arrow direction 592. The circuit component 516 or the temperature measuring element 518 and the conduit 544 for holding the temperature measuring element 518 are provided along the arrow direction 592 from the pressed fitting hole 590. Furthermore, the plate 532, the processing unit 604, and the air flow measuring section 602 are provided in a direction approximately corresponding to the arrow direction 592. With this arrangement, the resin flows smoothly during the first resin molding process.In the initial resin molding process, a thermosetting resin is used; therefore, it is important that the resin fully expands before hardening occurs. For this reason, the arrangement of the circuit component, the lead 514 or a wire, and the relationship between the pressed fitting hole 590 and the injection direction are important. 5.2 Structure of the connecting gap on the back of the membrane and opening and the corresponding effects

[0130] At Fig. 13 is a representation of a part of the cross-sectional area taken along a line CC in Fig. 12, which is used to describe a communication port 676 connecting a gap 674 provided inside the diaphragm 672 and the air flow measuring section (flow sensor element) 602, and the opening 520. As described above, the air flow measuring section 602 for measuring the flow rate of the measurement target gas 30 is provided with a diaphragm 672, and a gap 674 is provided on the back of the diaphragm 672. Although not shown here, the diaphragm 672 is provided with an element for heat exchange with the measurement target gas 30, and the flow rate is measured thereby. When heat is transferred to the elements formed in the diaphragm 672 through the diaphragm 672 separately for heat exchange with the measurement target gas 30, it is difficult to accurately measure the flow rate. Therefore, the thermal resistance of the diaphragm 672 should be increased, and the diaphragm 672 should be made as thin as possible.

[0131] The air flow measurement section (flow sensor element) 602 is embedded and fixed in the thermosetting resin of the circuit package 400 formed by the first resin molding process in such a way that the heat transfer surface 437 of the diaphragm 672 is exposed. The surface of the diaphragm 672 is provided with the above-described elements (not shown). These elements perform heat exchange with the measurement target gas 30 (not shown) using the heat exchange surface 437 on the surface of the elements in the heat transfer surface exposure section 436 associated with the diaphragm 672. The heat transfer surface 437 can be provided on the surface of each element or can be provided with a thin protective film thereon. The heat transfer between the elements and the measurement target gas 30 should be uniform, and direct heat transfer between the elements should be reduced as much as possible.

[0132] A portion of the air flow measuring section (flow sensor element) 602, in which the elements are provided, is arranged in the exposure portion of the heat transfer surface 436 of the measuring surface 430, and the heat transfer surface 437 is exposed from the resin used to mold the measuring surface 430. The outer periphery of the air flow measuring section (flow sensor element) 602 is covered by the thermosetting resin used in the first resin molding process to form the measuring surface 430.If only the side surface of the air flow measuring section (flow sensor element) 602 is covered with the thermosetting resin, and the outer peripheral surface side of the air flow measuring section (flow sensor element) 602 is not covered with the thermosetting resin, stress in the resin used to form the measuring surface 430 will be absorbed only by the side surface of the air flow measuring section (flow sensor element) 602, thus causing deformation in the diaphragm 672 and resulting in deterioration of its properties. The deformation of the diaphragm 672 is reduced by covering the outer peripheral portion of the air flow measuring section (flow sensor element) 602 with the thermosetting resin, as shown in FIG. Fig. 13. Meanwhile, if there is a large height difference between the heat transfer surface 437 and the measurement surface 430 where the measurement target gas 30 flows, the flow of the measurement target gas 30 will be disturbed, thus affecting the measurement accuracy. Therefore, the height difference W between the heat transfer surface 437 and the measurement surface 430 where the measurement target gas 30 flows should be small.

[0133] The diaphragm 672 is made thin to suppress heat transfer between the respective elements and a gap 674 formed on the back side of the air flow measuring section (flow sensor section) 602. When this gap 674 is sealed, the pressure of the gap 674 formed on the back side of the diaphragm 672 changes depending on a temperature change. When the pressure difference between the gap 674 and the surface of the diaphragm 672 increases, the diaphragm 672 absorbs this pressure and deforms. This makes accurate measurement difficult. Therefore, an opening 520 connected to the opening 438 (see Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 15(A) and Fig. 15(B)) that is open to the outside is provided in the plate 532, and a communication hole 676 that connects this hole 520 and the gap 674 is provided. This communication hole 676 is formed, for example, from a pair of plates including the first and second plates 534 and 536. The first plate 534 is provided with holes 520 and 521 and a groove for forming the communication hole 676. The communication hole 676 is formed by covering the groove and the holes 520 and 521 with the second plate 536. By using the communication hole 676 and the hole 520, the pressures applied to the front and rear surfaces of the diaphragm 672 approximately equalize to each other, so that the measurement accuracy is improved.

[0134] As described above, the connection opening 676 can be formed by covering the groove and the openings 520 and 521 with the second plate 536. Alternatively, the lead frame can be used as the second plate 536. As described with respect to the Fig. 12, the diaphragm 672 and the LSI circuit serving as the processing unit 604 are provided on the plate 532. A lead frame for supporting the plate 532, to which the diaphragm 672 and the processing unit 604 are attached, is provided below. Therefore, by using the lead frame, the structure becomes simpler. In addition, the lead frame can be used as a ground electrode. When the lead frame serves as the second plate 536 and the connection opening 676 is formed by covering the openings 520 and 521 formed in the first plate 534 using the lead frame and covering the groove formed in the first plate 534 using the lead frame, the entire structure can be simplified. In addition, since the lead frame serves as a ground electrode, it is possible to reduce the influence of noise from outside the diaphragm 672 and the processing unit 604.

[0135] In the circuit package 400, which is in the Fig. As illustrated in FIG. 11, the press mark 442 is retained on the back of the circuit package 400 where the heat transfer surface exposure portion 436 is formed. In the first resin molding process, in order to prevent resin from flowing into the heat transfer surface exposure portion 436, a mold, such as an immersion mold, is placed in a portion of the heat transfer surface exposure portion 436, and a mold is placed in a portion of the press mark 442 directly opposite the mold to suppress resin from flowing into the heat transfer surface exposure portion 436. By forming a portion of the heat transfer surface exposure portion 436 in this manner, it is possible to measure the flow rate of the measurement target gas 30 with significantly higher accuracy.

[0136] Fig. 14 shows a state where the frame of Fig. 12 is molded with a thermosetting resin through the first resin molding process and covered by the thermosetting resin. Through this molding, the measuring surface 430 is formed on the front surface of the circuit package 400, and the heat transfer surface exposure portion 436 is provided on the measuring surface 430. In addition, the gap 674 on the back of the diaphragm 672, which is located in the heat transfer surface exposure portion 436, is connected to the opening 438. The temperature measuring portion 452 for measuring a temperature of the measurement target gas 30 is provided at the front end of the projection 424, and the temperature measuring element 518 (see Fig. 12) is embedded inside. As in Fig. As illustrated in Figure 12, to suppress heat transfer, a line for discharging the electrical signal from the temperature measuring element 518 is segmented inside the protrusion 424, and a connecting line 546 having a high thermal resistance is arranged. As a result, it is possible to suppress heat transfer from the base of the protrusion 424 to the temperature measuring section 452 and thus also suppress the influence of heat.

[0137] A slope section 594 or 596 is formed in the lower part of the projection 424 in Fig. 14 is formed. The resin is evenly distributed in the first resin molding process. In addition, the measurement target gas 30 measured by the temperature measuring section 452 flows evenly from the protrusion 424 to its lower part using the inclination section 594 or 596 while the temperature measuring section 452 is mounted and operated in a vehicle, so that the lower part of the protrusion 424 is cooled. Therefore, it is possible to reduce the influence of heat on the temperature detecting section 452. According to the state according to Fig. 14, the line 514 is separated from each terminal to form the connecting terminal 412 or terminal 414.

[0138] In the first resin molding process, it is necessary to prevent resin inflow to the exposure portion of the heat transfer surface 436 or the opening 438. Therefore, in the first resin molding process, resin inflow is suppressed at a location of the exposure portion of the heat transfer surface 436 or the opening 438. For example, a submerged mold larger than the membrane 672 is installed, and a press is installed on the back of the mold to apply pressure from both surfaces. Fig. 11(C), the press imprint 442 or 441 remains on the back side, which leads to the exposure section of the heat transfer surface 436, to the opening 438 in Fig. 14, to the exposure section of the heat transfer surface 436 or to the opening 438 in Fig. 11(B).

[0139] In Fig. In FIG. 14, a cutout surface of the conduit separated from the frame 512 is exposed from the resin surface, so that moisture or the like may penetrate into the cutout surface of the conduit during use. It is important to prevent such a problem from the standpoint of durability or reliability. For example, a part of the mounting surface 434 in FIG. 14 is covered by the resin from the second resin molding process, and the surface cutout is exposed. In addition, the cutout portion for the conduit at the slope portion 594 or 596 is covered by the resin by the second resin molding process, and the surface cutout between the conduits 552 or 554 and the frame 512, as shown in FIG. Fig. 12 is covered by resin. This makes it possible to prevent erosion of the lead 552 or 554 or the ingress of water from the cutout portion. The cutout portion of the lead 552 or 554 is adjacent to an important lead portion that transmits the electrical signal of the temperature measuring portion 452. Therefore, covering the cutout portion in the second resin molding process is desirable. 5.3 Another embodiment of the circuit package 400 and corresponding effects

[0140] Fig. 15(A) and Fig. 15(B) illustrate another embodiment of the circuit package 400, in Fig. 15(A) the front view of the circuit package 400 and Fig. 15(B) shows its rear view. Similarity reference numbers indicate similar elements to those in other drawings, and a description will be given, for the sake of simplicity, only for a part thereof. In the embodiment described with reference to Fig. 11(A) to 11(C) above, the connection terminal 412 and the terminal 414 of the circuit package 400 are provided on the same side of the circuit package 400. In comparison, the connection terminal 412 and the terminal 414 in the embodiment of Fig. 15(A) and Fig. 15(B) on different sides. The port 414 is a port that is not connected to the connection port that is connected to the outside in the thermal flow meter 300. When the connection port 412 that is connected to the outside in the thermal flow meter 300 and the port 414 that is not connected to the outside are provided in different directions in this way, a distance between the connection port 412 and the port can be widened and workability can be improved. Furthermore, when the port 414 extends in a direction different from that of the connection port 412, it is possible to prevent the piping inside the frame 512 from Fig. 12 is concentrated on one part, and the arrangement of the line within the frame 512 is facilitated. In particular, a chip capacitor as circuit component 516 is connected to a portion of the line corresponding to the connection terminal 412. A somewhat larger space is required to provide such a circuit component 516. In the embodiment according to Fig. 15(A) and Fig. 15(B), it is possible to easily obtain a space for the wire corresponding to the connection terminal 412.

[0141] Similar to the switching assembly 400 in Fig. 11, also has the switching assembly 400, which is Fig. 15, has sloped portions 462 and 464 with a smoothly varying thickness. The sloped portion is formed in the narrowed portion of the projection 424 and protrudes from the switch assembly 422. The effects of these configurations are consistent with those described with reference to Fig. 11. That is, in Fig. 15, the protrusion 424 protrudes from the side surface of the switching assembly 422 in a shape that extends in the flow direction of the measurement target gas. The temperature measuring portion 452 is provided in the region of the front end of the protrusion 424, and the temperature measuring element 518 is embedded inside the temperature measuring portion 452. The sloped portions 462 and 464 are provided in a portion connecting the protrusion 424 and the switching assembly 422. The protrusion 424 is shaped such that its base is thickened by the sloped portions 462 or 464. The neck portion of the protrusion 424 gradually narrows toward the front end. That is, when the protrusion direction is an axis, the protrusion 424 has a shape in its neck portion in which a cross-sectional area across the axis in the protrusion direction gradually decreases toward the front end of the protrusion 424.

[0142] With this mold, a layer (sheet) can be formed inside the die to protect the element during the resin molding process when creating the circuit package 400. In this case, the layer and the inner surface of the die can be securely bonded, thus improving the reliability of the circuit package 400. Furthermore, the mechanical strength of the protrusion 424 is weak, so it is prone to bending. The protrusion 424 is thickened at its base and tapers toward its front end. This alleviates the stress at the base, giving it excellent mechanical strength. In addition, the protrusion is prone to bending due to a volume change caused by resin curing when the protrusion 424 is formed in the resin molding process. This effect can be reduced.To measure the temperature of the target gas 30 as accurately as possible, the protrusion 424 should be long. The heat transfer from the switching assembly 422 to the temperature measuring element 518 located in the temperature measuring section 452 can be easily reduced by making the protrusion 424 long.

[0143] As in Fig. 11(B) and Fig. 11(C), in another embodiment in Fig. 15 (A) and Fig. 15 (B), the base of the protrusion 424 is formed thick and surrounded by the housing 302. This fixes the circuit package 400 to the housing 302. Since the base of the protrusion 424 is covered with the resin of the housing 302 in this way, damage to the protrusion 424 due to mechanical impacts is prevented. In addition, various effects related to Fig. 11 described.

[0144] The descriptions for opening 438, exposure section of the heat transfer surface 436, measuring surface 430, press impression 441 and press impression 442 in Fig. 15(A) and Fig. 15(B) are similar to the above descriptions and have the same functional effects. For simplicity, the detailed descriptions are not repeated here. 6. Process of manufacturing the thermal flow meter 3006.1 Process of manufacturing the circuit package 400

[0145] Fig. 16 illustrates a process of manufacturing the circuit package 400 within a process of manufacturing the thermal flow meter 300. Fig. 17 illustrates a process of manufacturing the thermal flow meter 300 and Fig. 18 illustrates a process of manufacturing the thermal flow meter 300 in another embodiment. Fig. 16 shows in step 1 the manufacturing process of a frame of the Fig. 12. This frame is formed, for example, by a press forming process. In step 2, the plate 532 is first mounted on the frame produced by step 1, and the air flow measuring section 602 or the processing unit 604 is further mounted on the plate 532. Subsequently, the temperature measuring element 518 and the circuit component, for example, a chip capacitor, are mounted. In step 2, the electrical wiring between the circuit components, between the circuit component and the lead, and between the leads is performed. In step 2, the leads 544 and 548 are connected using a connecting lead 546 to increase a thermal resistance. In step 2, the Fig. 12 is mounted on the frame 512 and the electrical wiring is continued to form an electrical circuit.

[0146] Then, in step 3, the first resin molding process, which is Fig. 12, in which the circuit elements are mounted and electrically connected, is molded using a thermosetting resin, and the circuit package 400 is manufactured. The circuit package 400 in a molded state is shown in Fig. 14. In addition, in step 3, all connected lines are separated from the frame 512 and the lines are separated from each other, so that the circuit package 400 of the Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 15(A) or Fig. 15(B). In this circuit package 400, as shown in Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 15(A) or Fig. 15(B), the measuring surface 430 or the exposure section of the heat transfer surface 436 is formed. Another embodiment of the device shown in Fig. 15(A) and Fig. 15(B) corresponds to the basic production process.

[0147] In step 4, the resulting circuit assembly 400 is visually inspected or checked for functionality. In the first resin molding process in step 3, a resin injection method is used. The electrical circuit created in step 2 is fixed to the inside of the die. Resin is then injected into the die at high temperature and high pressure. Therefore, checking the electrical component or electrical wiring for deviations is advantageous. For this inspection, the terminal 414 is inserted in addition to the connecting terminal 412 in Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 15(A) or Fig. 15(B). It should be noted that the connector 414 can be detached from the base after testing, as it is no longer required. For example, the connector 414, as shown in Fig. 15(A) and Fig. 15(B), separated from the base after use. 6.2 Manufacturing process of a thermal flow meter 300 and calibration of the measurement parameters

[0148] In Fig. 17, the switching assembly 400 according to Fig. 16 and the external terminal 306 are manufactured according to a method used (not shown). In step 5, the housing 302 is formed in the second resin molding process. In this housing 302, a bypass channel groove made of resin, the flange 312 and the external terminal 305 are formed, and the shaded portion of the circuit package 400, which is shown in Fig. 11 (A) to 11 (C) is covered by the resin in the second resin molding process, so that the circuit package 400 is fixed to the housing 302. By combining the manufacture (step 3) of the circuit package 400 in the first resin molding process and the formation of the housing 302 of the thermal flow meter 300 in the second resin molding process, the accuracy of detecting the flow rate is noticeably improved. In step 6, each inner socket of the external terminal 361 is Fig. 10. In step 7, the connection terminal 412 and the inner socket of the external connector 361 are connected.

[0149] As with reference to Fig. 5(B) and Fig. 6(B), the fixing portions 3721 and 3723 for fixing the circuit package 400 to the housing 302 include the thin portions 4710 and 4716 in addition to the thick portions 4714 and 4715. When the two fixing portions 3721 and 3723 enclosing the circuit package 400 are formed from the thick portion, high pressure is exerted on the surface of the circuit package 400 because the resin is heated due to a temperature drop in the discharged resin in the second resin molding process in step 5 of Fig. 17 shrinks. When high pressure is applied to the surface of the circuit package 400, because the shrinkage of the resin forms the fixing portion 3721 or 3723, the electrical circuit in the circuit package 400 (shown in Fig. 12) may be damaged. Since the fixing portion 3721 or 3723 is partially formed by the thin portion and not only the thick portion, the thickness of the resin molded in the second resin molding process for covering the surface of the circuit package 400 is made from the thin portion in this embodiment. Therefore, the force exerted on the surface of the circuit package 400 is reduced. Alternatively, the force exerted on a unit area of the circuit package 400 also becomes small. For this reason, the electrical circuit in the circuit package 400 (shown in Fig. 12) less damaged.

[0150] If the attachment portion 3721 or 3723 of the housing 302 significantly decreases, the housing 302 may be bent or distorted. Specifically, the attachment portion 3721 or 3723 is connected to the upstream outer wall 335 or the downstream outer wall 336 connecting the bypass passage and the flange 312. Pressure caused by the reduction of the attachment portion 3721 or 3723 is applied to the upstream outer wall 335 or the downstream outer wall 336. Since the upstream outer wall 335 and the downstream outer wall 336 are formed in an elongated shape, warping or bending may occur. Since the thin portion is provided, the force applied to the upstream outer wall 335 or the downstream outer wall 336 can be reduced or dispersed, so that the bending or warping of the upstream outer wall 335 or the downstream outer wall 336 can be prevented.

[0151] The housing is obtained in step 13. In step 8, the front and rear covers 303 and 304 are attached to the housing 302 so that the inside of the housing 302 is sealed by the front and rear covers 303 and 304. In addition, the bypass channel through which the measurement target gas 30 flows is created, and the thermal flow meter 300 is obtained. In addition, an orifice structure, as in connection with Fig. 7, formed by the protrusion 356 or 358 provided in the front cover 303 or the rear cover 304. Note that the front cover 303 is formed by the molding in step 10, and the rear cover 304 is formed by the molding in step 11. Furthermore, the front and rear covers 303 and 304 are formed in separate processes using two different dies.

[0152] In step 9, a flow rate characteristic test of the measurement target gas 30 is performed by introducing a predetermined amount of gas into the bypass channel of the thermal flow meter 300. Since, as described above, the relationship between the bypass channel and the airflow measurement section must be very precise, very high measurement accuracy is ensured by performing calibration to obtain accurate measurement characteristics based on the flow rate characteristic test. Furthermore, since the molding of the bypass channel and the airflow measurement section is performed to maintain a certain positional or configuration relationship during the first and second resin molding processes, this characteristic does not change even with long-term use, and high reliability is achieved in addition to high measurement accuracy. 6.3 Another embodiment for manufacturing the thermal flow meter 300

[0153] Fig. 18 is another embodiment for the manufacture of the thermal flow meter 300. In Fig. 18, the already manufactured circuit package 400, as in Fig. 16, and the external terminal 306 manufactured according to a method (not illustrated) is used. In step 12, the connection terminal 412 of the circuit package 400 and the inner socket of the external terminal 361 are connected before the second resin molding process. In this case, or in the process before step 12, each inner socket of the external terminal 361 is formed as shown in Fig. 10. In step 13, the housing 302 is formed in the second resin molding process. In the housing 302, the resin bypass channel groove, the flange 312 and the external terminal 305 are formed, and the shaded portion of the circuit package 400, which is inserted into the Fig. 11(A) to 11(C) is covered by the resin in the second resin molding process, so that the circuit package 400 is fixed to the housing 302. By combining the manufacturing (step 3) of the circuit package 400 in the first resin molding process and the formation of the housing 302 of the thermal flow meter 300 in the second resin molding process, the accuracy of detecting the flow rate is remarkably improved as described above.

[0154] While the housing is obtained in step 13, in step 8, the front and rear covers 303 and 304 are attached to the housing 302 so that the inside of the housing 302 is sealed by the front and rear covers 303 and 304. Furthermore, the bypass channel through which the measurement target gas 30 will flow is created. In addition, the orifice structure is formed as described in connection with Fig. 7, formed by the protrusion 356 or 358 provided in the front cover 303 or the rear cover 304. As described above, the front cover 303 is formed by the molding in step 10, and the rear cover 304 is formed by the molding in step 11. Furthermore, the front and rear covers 303 and 304 are formed in separate processes using two different dies.

[0155] In step 9, a special practical test is demonstrated by passing a predetermined amount of air through the bypass duct. Because the relationship between the bypass duct and the airflow measuring section is maintained with high accuracy as described above, remarkably high measurement accuracy is achieved by calibrating the measurement properties using a measurement property test. In addition, since the molding of the bypass duct and the airflow measuring section is performed to maintain a certain relationship of position or configuration in the first and second resin molding processes, this property does not change even with long-term use, and in addition to high measurement accuracy, high reliability is achieved. The above-mentioned effects are achieved by using Fig. 17 scored. 7. Circuit configuration of the thermal flow meter 3007.1 Overview of the circuit configuration of the thermal flow meter 300

[0156] Fig. Fig. 19 is a circuit diagram showing the flow rate sensor circuit 601 of the thermal flow meter 300. It is noted that the measuring circuit described with respect to the temperature measuring section 452 in the above-mentioned embodiment is also provided in the thermal flow meter 300, but not explicitly in Fig. 19. The flow rate sensor circuit 601 of the thermal flow meter 300 includes the air flow measuring section 602 with the heat generator 608 and the processing unit 604. The processing unit 604 controls a heat amount of the heat generator 608 as part of the air flow measuring section 602 and outputs a signal representing the flow rate based on the output of the air flow measuring section 602 via the terminal 662. For this operation, the processing unit 604 includes a central processing unit (hereinafter referred to as "CPU") 612, an input circuit 614, an output circuit 616, a memory 618 that can store data from the relationship between the calibration value or the measured value and the flow rate, and a main circuit 622 for supplying a specific voltage for each required circuit. The main circuit 622 is powered by DC power from an external power source.This can be a car battery connected via terminal 664 and a ground connection (not shown).

[0157] The air flow measuring section 602 is equipped with a heat generator 608 for heating the measurement target gas 30. A voltage V1 is supplied from the main circuit 622 to the collector of a transistor 606 included in a power supply circuit of the heat generator 608. Furthermore, a control signal from the CPU 612 is applied to the base terminal of a transistor 606 via the output circuit 616. Based on this control signal, a current is supplied from the transistor 606 to the heat generator 608 via the terminal 624. The amount of current supplied to the heat generator 608 is controlled by a control signal applied from the CPU 612 to the transistor 606 of the power supply circuit of the heat generator 608 via the output circuit 616.The processing unit 604 controls the heat amount of the heat generator 608 so that the temperature of the measurement target gas 30 increases by a predetermined temperature difference, for example, by heating with the heat generator 608 by 100°C, measured from the initial temperature.

[0158] The air flow measuring section 602 includes a heat control bridge 640 for controlling a heat amount of the heat generator 608 and a bridge circuit of the air flow sensor 650 for measuring the flow rate. A predetermined voltage V3 is supplied to one end of the heat control bridge 640 from the main circuit 622 via terminal 626. The other end of the heat control bridge 640 is connected to the ground terminal 630. In addition, a predetermined voltage V2 is applied to one end of the heat control bridge of the air flow sensor 650 from the main circuit 622 via terminal 625. The other end of the heat control bridge 640 of the air flow sensor 650 is connected to the ground terminal 630.

[0159] The heat control bridge 640 has a resistor 642, which is a resistance thermometer with a resistance value dependent on the temperature of the heated measurement target gas 30. The resistors 642, 644, 646, and 648 form a bridge circuit. A potential difference between a node A between the resistors 642 and 646 and a node B between the resistors 644 and 648 is fed into the input circuit 614 via the terminals 627 and 628. The CPU 612 controls the current supplied by the transistor 606 to control the amount of heat generated by the heat generator 608 in such a way that the potential difference between the nodes A and B is set to a predetermined value, for example, to a zero voltage in this embodiment. The flow rate sensor circuit 601 in Fig. 19, heats the measurement target gas 30 with the heat generator 608 so that the temperature rises by a predetermined temperature. For example, 100°C always starting from an initial temperature of the measurement target gas 30. In order to perform this heating control with high accuracy, the resistance values of the individual resistors of the heat control bridge 640 are set so that the potential difference between nodes A and B is zero when the temperature of the measurement target gas 30 is increased by the heat generator 608 by a predetermined temperature, for example, always by 100°C starting from an initial temperature. Therefore, in the flow rate sensor circuit 601 in Fig. 19 the CPU 612 controls the electric current fed into the heat generator 608 so that the potential difference between nodes A and B becomes zero.

[0160] The bridge circuit of the air flow sensor 650 includes four resistance temperature sensors, resistors 652, 654, 656, and 658. The four resistance temperature sensors are arranged along the flow direction of the measurement target gas 30 in such a way that resistors 652 and 654 are located upstream of the flow path of the measurement target gas 30 with respect to the heat generator 608, while resistors 656 and 658 are arranged downstream of the flow path of the measurement target gas 30 with respect to the heat generator 608. In addition, to increase measurement accuracy, resistors 652 and 654 are arranged so that their distances from the heat generator 608 are approximately equal, and resistors 656 and 658 are arranged so that their distances from the heat generator 608 are also approximately equal.

[0161] A potential difference between a node C between resistors 652 and 656 and a node D between resistors 654 and 658 is applied to the input circuit 614 via terminals 631 and 632. To increase measurement accuracy, each resistor of the bridge circuit of the air flow sensor 650 is set to a target value, for example, such that a potential difference between nodes C and D is set to zero while the flow rate of the measurement target gas 30 is also set to zero. Therefore, while the potential difference between nodes C and D is set to zero, for example, the CPU 612 outputs an electrical signal at terminal 662 indicating a flow rate in the main channel 124 of zero. This result is output based on the measurement result obtained by measuring at a flow rate of the measurement target gas 30 of zero.

[0162] When the measurement target gas 30 is along the arrow direction in Fig. 19, the resistor 652 or 654 located on the upstream side is cooled by the measurement target gas 30. The resistors 656 and 658 located downstream of the measurement target gas 30 are heated by the measurement target gas 30 heated by the heat generator 608, so that the temperature of the resistors 656 and 658 rises. For this reason, a potential difference is generated between nodes C and D of the bridge circuit of the air flow sensor 650, and this potential difference is applied to the input circuit 614 via terminals 631 and 632. The CPU 612 searches for data indicating a relationship between the flow rate of the main channel 124 and the aforementioned potential difference, which is stored in the memory 618 based on the potential difference between nodes C and D of the bridge circuit in the air flow sensor 650, to obtain the flow rate of the main channel 124.An electrical signal indicative of the flow rate thus obtained in the main channel 124 is output via terminal 662. It should be noted that although terminals 664 and 662 shown in . Fig. 19 are designated with new reference numerals, these in the connection terminal 412 of Fig. 5 (A), Fig. 5(B), Fig. 6(A), Fig. 6(B) or Fig. 10, as described above.

[0163] As with reference to Fig. 1, the thermal flow meter 300 is mounted on the intake pipe of the internal combustion engine and used to measure the intake air quantity. In a certain operating state of the internal combustion engine, the intake air flowing through the intake pipe pulsates. The intake air flows to an intake valve of the internal combustion engine and back. In the above-mentioned reverse flow state, the intake air flows in the opposite direction to an arrow of the measurement target gas (see Fig. 19). That is, a reverse flow occurs. In the reverse flow state, the resistors 652 and 654 are heated by the measurement target gas 30, which in turn is heated by the heat generator 608. On the other hand, the resistors 656 and 658 are cooled by the backward flowing measurement target gas 30. In this way, the process is reversed, so that the flow of the measurement target gas 30 in the forward direction and a potential difference in the flow rate in the forward direction is generated between nodes C and D. The flow direction of the measurement target gas 30 can be determined from the polarity of the voltage across terminals 631 and 632. It is possible to calculate the flow rate of the intake air flowing into the internal combustion engine by reducing the flow rate in the reverse direction of the determined flow rate in the forward direction.

[0164] In the memory 618, the data indicating a relationship between the potential difference between nodes C and D and the flow rate of the main section 124 in addition to the backflow state are stored. Furthermore, calibration data is stored to reduce measurement errors, such as a deviation, based on the actual measured value of the gas after the thermal flow meter 300 is manufactured. It is noted that the actual measured value of the gas after the production of the thermal flow meter 300 and the calibration value based thereon are stored in the memory 618 using the external terminal 306 or the calibration terminal 307 provided in Fig. 4(A) and Fig. 4(B). In this embodiment, when manufacturing the thermal flow meter 300, it is important to ensure that the alignment of the bypass channel through which the measurement target gas 30 flows and the measurement surface 430, or the arrangement between the bypass channel through which the measurement target gas 30 flows and the heat transfer surface exposure portion 436, are mutually consistent and manufactured with high accuracy and as little deviation as possible. Therefore, it is possible to obtain a measurement result with extremely high accuracy by calibrating according to the calibration values. 7.2 Configuration of the flow rate sensor circuit 601

[0165] Fig. 20 shows a diagram of the circuit configuration of the flow rate measuring section 602 as shown in Fig. 19. The air flow measuring section 602 is made of a semiconductor chip having a rectangular shape. Fig. Figure 20 shows how the measurement target gas 30 flows in the direction of the arrow from the left to the right side of the air flow measuring section 602. However, in a reverse flow state, the measurement target gas 30 flows in the opposite direction to the arrow. This means that a reverse flow occurs. Fig. The flow rate measuring section 602 shown in Figure 20 performs heat transfer with the measurement target gas 30 so that not only the forward flow rate but also the reverse flow rate can be determined. A diaphragm 672 has a rectangular shape and is formed in the air flow measuring section 602. The diaphragm 672 has a narrow region 603 (indicated by the dashed line) with a thin semiconductor chip. The gap is formed on the rear surface of the narrow region 603 and is aligned with the opening 438. Fig. 11(A) to 11(C) or Fig. 5(A) and Fig. 5(B) so that the gas pressure in the gap depends on the pressure of the gas flowing through the opening 438.

[0166] When the thickness of the narrow region 603 of the membrane 672 is reduced, the thermal conductivity decreases. This suppresses heat transfer to the resistors 652, 654, 658, and 656 in the narrow region 603 via the membrane 672. Due to the heat transfer, the temperature of the resistors rises to approximately the temperature of the measurement target gas 30.

[0167] The heat generator 608 is arranged in the center of the narrow region 603 of the diaphragm 672, and the resistor 642 of the heat control bridge 640 is applied around the heat generator 608. Furthermore, the resistors 644, 646, and 648 of the heat control bridge 640 are provided on the outside of the narrow region 603. The resistors 642, 644, 646, and 648 thus formed constitute the heat control bridge 640.

[0168] In addition, resistors 652 and 654 are arranged as upstream resistance thermometers, and resistors 656 and 658 are arranged as downstream resistance thermometers to interpose the heat generator 608. Resistors 652 and 654 as upstream resistance thermometers are arranged in the direction of the arrow with the flow of the measurement target gas 30 relative to the heat generator 608. Resistors 656 and 658 as downstream resistance thermometers are arranged in the direction of the arrow against the flow of the measurement target gas 30 relative to the heat generator 608. In this way, the bridge circuit 650 of the air flow sensor 650 is formed by the resistors 652, 654, 656, and 658 in the narrow region. The above description assumes that the measurement target gas 30 flows in the forward direction. However, when backflow occurs, the measurement target gas 30 flows from the downstream side to the upstream side.

[0169] Both ends of the heat generator 608 are connected to each of the terminals 624 and 629 located in the lower half of Fig. 20. Here, as in Fig. 19, the current supplied by transistor 606 to heat generator 608 is applied to terminal 624, and terminal 629 is connected to ground.

[0170] The resistors 642, 644, 646 and 648 of the thermal control bridge 640 are connected to the terminals 626 and 630. In Fig. 19, it can be seen that terminal 626 is supplied with a predetermined voltage V3 from the main circuit 622, and terminal 630 is connected to ground. Furthermore, the nodes between resistors 642 and 646 and the nodes between resistors 646 and 648 are connected to terminals 627 and 628, respectively. As shown in Fig. 20, terminal 627 outputs an electrical potential of node A between resistors 642 and 646, and terminal 627 outputs an electrical potential of node B between resistors 644 and 648. Fig. 19 shows that terminal 625 is supplied with a predetermined voltage V2 from the main circuit 622, and that terminal 630 is connected to ground as a ground terminal. Furthermore, the node between resistors 654 and 658 is connected to terminal 631. Terminal 631 provides an electrical potential of node B in Fig. 19. The node between resistors 652 and 656 is connected to terminal 632 and terminal 632 outputs an electrical potential of node C, which is Fig. 19 is illustrated.

[0171] Since the resistance 642 of the heat control bridge 640 is formed in that of the heat generator 608, it is possible to measure the temperature of the gas heated by the heat of the heat generator 608 with great accuracy (see Fig. 20). Meanwhile, because the resistors 644, 646, and 648 of the heat control bridge 640 are arranged away from the heat generator 608, they are not easily affected by the heat from the heat generator 608. The resistor 642 is configured to be sensitive to the temperature of the gas heated by the heat generator 608, and the resistors 644, 646, and 648 are configured not to be affected by the heat generator 608. For this reason, the measurement accuracy for the measurement target gas 30 is high using the heat control bridge 640, and the control for heating the measurement target gas 30 by only a predefined temperature, starting from its initial temperature, can be performed with high accuracy.

[0172] In this embodiment, a gap is formed on the back of the membrane 672 which communicates with the opening 438 as shown in Fig. 11(A) to 11(C) or 5(A) and 5(B), so that a difference between the pressure of the gap at the back of the diaphragm 672 and the pressure at the front of the diaphragm 672 does not increase. It is possible to suppress deformation of the diaphragm 672 caused by this pressure difference. This contributes to increased flow rate measurement accuracy.

[0173] As described above, by forming the narrow region 603 and reducing the thickness of the narrow region 603 in the diaphragm 672, the heat conduction of the diaphragm 672 is suppressed as little as possible. Since the influence of heat conduction through the diaphragm 672 is suppressed, the bridge circuit of the air flow sensor 650 or the heat control bridge 640 is more likely to respond to the temperature of the measurement target gas 30, thus improving the measurement process. Therefore, high measurement accuracy is achieved. 8. Temperature detection of the target gas 308.1 Structure of the temperature measuring section 452 and corresponding effects

[0174] As in Fig. 2(A), Fig. 2(B), Fig. 3(A), Fig. 3(B), Fig. 4(A), Fig. 4(B), Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. As shown in Figure 6(B), the temperature of the measurement target gas 30 is measured by the temperature measuring section 452 in the thermal flow meter 300. The temperature measuring section 452 protrudes from the upstream side of the housing 302 and comes into direct contact with the measurement target gas 30. With this structure, the measurement accuracy of the temperature sensor of the measurement target gas 30 is improved. In addition, the temperature of the gas flowing along the upstream side of the measurement target gas 30 to the inlet port is measured by the temperature measuring section 452. The gas flows to the throat section supporting the temperature measuring section 452. Therefore, the section supporting the temperature measuring section 452 is cooled and approaches the temperature of the measurement target gas 30. With this structure, the measurement accuracy is improved.

[0175] The temperature of the intake pipe serving as the main passage 124 increases significantly compared to the typical measurement target gas 30. Heat is transferred to the region supporting the temperature measuring section 452 through an upstream outer wall in the measuring section 310 from the flange 312 or the heat insulation 315, so that the accuracy of the measured temperature may be affected. As described above, when the measurement target gas 30 is measured by the temperature measuring section 452, the support section is cooled and flows along the support section of the temperature measuring section 452. Therefore, it is possible to prevent heat from being transferred to the region supporting the temperature measuring section 452 through the upstream outer wall within the measuring section 310 from the flange 312 or the heat insulation 315.

[0176] Specifically, in the support portion of the temperature measuring portion 452, the upstream outer wall within the measurement area 310 has a concave shape toward the downstream side. Therefore, it is possible to increase the distance between the upstream outer wall within the measurement area 310 and the temperature measuring portion 452. As the heat transfer length increases, the distance of the cooling portion with the measurement target gas 30 also increases. Therefore, it is possible to reduce the influence of the heat from the flange 312 or the heat insulation 315. Accordingly, the measurement accuracy is improved.

[0177] Since the upstream outer wall is concave to the downstream outer wall (the inside of the housing 302), it can be secured by the downstream outer wall 335 of the housing 302. This simplifies the attachment of the circuit package 400. It also affects the strength of the projection 424 (see Fig. 11(A), Fig. 11(B) and Fig. 11(C)) with the temperature measuring section 452.

[0178] As above with reference to Fig. 2(A), Fig. 2(B), Fig. 3(A) and Fig. As shown in Figure 3(B), the inlet port 343 is provided upstream of the measurement target gas 30 in the housing 301. The measurement target gas 30, which is guided through the inlet port 343, flows near the temperature measuring section 452 and is guided from the front side of the outlet port 344 and the rear side of the outlet port 345 to the main channel 124. The temperature measuring section 452 measures the temperature of the measurement target gas 30. The electrical signal indicating the measured temperature is output from the external terminal 306 of the external terminal 305. The housing 301 of the thermal flow meter 300 includes the front cover 303, the rear cover 304, and the housing 302. The housing 302 includes the recess for forming the inlet port 343. The recess is formed by the outer wall hollow portion 366 (see Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B)). The front exhaust port 344 or the rear exhaust port 345 is formed by the opening on the front cover 303 or the rear cover 304. As described above, the temperature sensing portion 452 is provided with the leading end portion of the protrusion 424 and has weak mechanical strength. The front cover 303 or the rear cover 304 protects the protrusion 424 from mechanical impact.

[0179] The front protective portion 322 or the rear protective portion 325 is formed in the front cover 303 or the rear cover 304, respectively, as shown in Fig. 8(A), Fig. 8(B), Fig. 8(C) , Fig. 9(A), Fig. 9(B) or Fig. 9(C). As shown in Fig. 2(A), Fig. 2(B), Fig. 3(A) or Fig. As shown in Figure 3(B), the front protection portion 322, located in the front cover 303, is mounted on the front side of the inlet opening 343, and the rear protection portion 325, located in the rear cover 304, is mounted on the back side of the inlet opening 343. The temperature measuring portion 452, located in the inlet opening 343, is protected by the front and rear protection portions 322 and 325, so that the temperature measuring portion 452 is protected from mechanical damage that may be caused by a collision of the temperature measuring portion 452 with an object during production or when loading onto a vehicle.

[0180] As in Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 15(A) or Fig. As shown in Figure 15(B), the neck portion of the protrusion 424 supporting the temperature measuring section 452 gradually increases in thickness toward the neck. Since the measurement target gas 30, when entering through the inlet port 343, flows along the gradually thickening neck portion, the cooling effect increases. The neck portion of the protrusion 424 is located close to the flow measuring circuit and can be affected by the heat output of the flow measuring circuit. The piping 548, through which the temperature measuring element 518 in the temperature measuring section 452 is connected, is embedded in the neck portion of the protrusion 424. Therefore, it is possible to transfer heat through the piping 548. Since the contact area with respect to the measurement target gas 30 becomes larger when the neck portion of the protrusion 424 is thick, the cooling effect can be increased. 8.2 Structure of the temperature measuring section 452 and the projection 424 and corresponding effects

[0181] The circuit package 400 includes the circuit package body 422 and the protrusion 424 for embedding the air flow measuring section 602 and the flow rate measuring processing unit 604. As shown in Fig. 2(A) and Fig. As shown in Fig. 2(B), the projection 424 protrudes from the side surface of the circuit package body 422 in a shape extending in the flow direction of the measurement target gas 30. The temperature measuring portion 452 is formed in the region of the front end of the projection 424, and the temperature measuring element 518 is embedded inside the temperature measuring portion 452 (see Fig. 12). The chamfers 462 and 464 are located in the connecting portion between the projection 424 and the circuit package body 422, as shown in Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 15(A) or Fig. 15(B). The protrusion 424 is formed such that its base is thickened by the sloped portions 462 or 464. The neck portion of the protrusion 424 gradually narrows toward the front end. The cross-sectional area crossing an axis in the protrusion direction is reduced in the neck portion of the protrusion 424 toward the front end.

[0182] Since the contact area between the surface of the circuit package 400 and the surface of the protrusion 424 gradually changes, when the circuit package 400 is molded through the resin molding process, the resin can be directed to the sheet in the mold to protect the element, so that the sheet contacts the inside of the mold, and reliability is improved. When the front surface changes, excessive force is applied to the sheet, causing a deviation in the contact area between the sheet and the inner wall surface of the mold, so that resin molding is not performed satisfactorily. In addition, the mechanical strength of the protrusion 424 is weak, so it is easy to buckle. If the base of the protrusion 424 is thickened and tapered toward its front end, the stress at the base is alleviated, giving it excellent mechanical strength.In addition, the protrusion 424 is easily bent due to a volume change caused by resin curing when it is formed during the resin molding process. This effect can be reduced. To measure the temperature of the measurement target gas 30 as accurately as possible, the protrusion length should be quite large. Heat transfer from the circuit package body 422 to the temperature measuring element 518 in the temperature detection section 452 can be easily reduced by increasing the protrusion length of the protrusion 424.

[0183] As in Fig. 11(B) and Fig. As shown in Figure 11(C), the base of the protrusion 424 is thickened and surrounded by the housing 302. This secures the circuit package 400 to the housing 302. Since the base of the protrusion 424 is covered with the resin of the housing 302, damage to the protrusion 424 due to mechanical impact is prevented.

[0184] To measure the temperature of the target gas 30 with high accuracy, heat transfer to portions other than the target gas 30 must be limited as much as possible. The outer end of the protrusion 424, which supports the temperature measuring portion 452, has a narrow shape at the base, and the measuring portion 452 is located at its outer end. This shape reduces the influence of heat from the neck portion of the protrusion 424 on the temperature measuring portion 452.

[0185] After the temperature of the measurement target gas 30 is measured by the temperature measuring section 452, the measurement target gas 30 flows along the protrusion 424, and the temperature of the protrusion 424 approaches the temperature of the measurement target gas 30. Therefore, the effects of the temperature of the neck portion of the protrusion 424 in the temperature measuring section 452 are suppressed. Specifically, in the embodiment, the vicinity of the protrusion 424 provided with the temperature measuring section 452 becomes thicker as it approaches the base of the protrusion 424. For this reason, the measurement target gas 30 flows along the structure of the protrusion 424, and the protrusion 424 is efficiently cooled.

[0186] In Fig. 11(A), Fig. 11(B) and Fig. In Figure 11(C), the hatched area of the neck portion of protrusion 424 represents the mounting surface 432 covered by the resin that forms the housing 302 in the second resin molding process. A cavity is provided in the hatched area of the neck portion of protrusion 424. It is clear that a portion of the cavity is provided that is not covered by the resin of the housing 302. By providing such a portion not covered by the resin of the housing 302 with a cavity in the neck portion of protrusion 424 in this way, it is possible to easily further cool the protrusion 424 using the measurement target gas 30. Fig. 15(A) and Fig. 15(B), the hatched area is the same as in Fig. 11(A), Fig. 11(B) and Fig. 11(C), although this is not shown.

[0187] The circuit package 400 is equipped with the connection port 412 for supplying power to the embedded airflow measuring section 602 or the processing unit 604 and for outputting the measured values for flow or temperature. Additionally, there is a port 414 for checking the correct operation of the circuit package 400 or for detecting faults in circuit components or connections. In this embodiment, the circuit package 400 is formed by resin injection for the airflow measuring section 602 or the processing unit 604 using a thermosetting resin in the first resin injection process. The transfer molding process can increase the dimensional accuracy of the circuit package 400.However, during the transfer molding process, it is necessary to check whether there is a defect in the air flow sensing section 602 or the processing unit 604 and the corresponding wiring for the circuit package 400, because the resin is forced at high pressure into the closed mold in which the air flow sensing section 602 or the processing unit 604 is embedded. In this embodiment, an inspection port 414 is provided, and inspection is performed for each of the manufactured circuit packages 400. Since the inspection port 414 is not used for measurement, the port 414 is not connected to the inner socket of the external terminal 361 as described above. In addition, each connection port 412 is provided with a curved portion 416 to increase mechanical elasticity.By providing mechanical elasticity in each connection terminal 412, stress caused by a difference in the expansion coefficient between the resin of the first resin molding process and the resin of the second resin molding process can be neutralized. Each connection terminal 412 is affected by thermal expansion caused by the first resin molding process. The inner socket of the external terminal 361, which is connected to the connection terminal 412, is affected by the second resin molding process. Therefore, it is possible to absorb the stress caused by the different resins. 8.3 Function of the bevels 462 and 464 in the neck section of projection 424 and corresponding effects

[0188] As already mentioned with reference to Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 14, Fig. 15(A) or Fig. As described in Figure 15(B), the neck portion of the protrusion 424 has slopes 462 and 464. With the slope portion 462 or 464, the neck portion of the protrusion 424 is formed such that the base of the protrusion 424 is thick and gradually narrows toward the front end. That is, when the protrusion direction is an axis, the protrusion 424 has a shape in its neck portion in which a cross-sectional area gradually decreases across the axis in the protrusion direction.

[0189] When the circuit package 400 is formed through the resin molding process and the resin flows to the layer in the mold to protect the element, the layer comes into contact with the inside of the mold, and reliability is improved. Furthermore, the mechanical strength of the protrusion 424 is weak, so it is prone to bending. The protrusion 424 is thickened at its base and tapers toward its front end. This alleviates the stress at the base, giving it excellent mechanical strength. Furthermore, when the protrusion 424 is formed in the resin molding process, the protrusion is prone to bending due to a volume change caused by the curing of the resin. This effect can be reduced. To measure the temperature of the measurement target gas 30 as accurately as possible, the protrusion 424 should be long.The heat transfer from the switching assembly 422 to the temperature measuring element 518 located in the temperature measuring section 452 can be easily reduced by making the projection 424 long.

[0190] As in Fig. 11(B) and Fig. As shown in Figure 11(C), the base of the protrusion 424 is thick and surrounded by the housing 302. This secures the circuit package 400 to the housing 302. Since the base of the protrusion 424 is covered with the resin of the housing 302, damage to the protrusion 424 due to mechanical impact is prevented.

[0191] Since the sloped portion 462 or 464 is provided in the base of the protrusion 424, the neck portion can be provided such that the base of the protrusion 424 is thick and gradually narrows toward the front end. With this shape, a sheet can be formed inside the die to protect the element during the resin molding process when creating the circuit package 400. In this case, the sheet and the inner surface of the die can be securely bonded, thus improving reliability. In addition, the mechanical strength of the protrusion 424 is weak, so it is prone to buckling. The protrusion 424 is thickened at its base and tapers toward its front end. This alleviates the stress at the base, giving it excellent mechanical strength.In addition, the protrusion can be easily bent due to a volume change caused by resin curing when the protrusion 424 is formed during the resin molding process. This effect can be reduced. To measure the temperature of the measurement target gas 30 as accurately as possible, the protrusion 424 should be long. Heat transfer from the switching assembly 422 to the temperature measuring element 518 located in the temperature measuring section 452 can be easily reduced by making the protrusion 424 long.

[0192] In Fig. 11(A), Fig. 11(B), Fig. 11(C), Fig. 21(A), Fig. 21(B) or Fig. 21(C), the base of the protrusion 424 is thick. The base of the protrusion 424 is covered by the resin of the housing 302, which forms the bypass channel by enclosing the base with the fixing portion 3723 of the housing 302. For this reason, the base is protected from mechanical impacts, and damage to the protrusion 424 can be prevented. Fig. 11(A), Fig. 11(B), Fig. 11(C), the hatched portion in the diagram of the circuit package 400 indicates the mounting surface 432, the mounting portion 3723, and the mounting surface 434 where the circuit package 400 is covered by the resin used in the second resin molding process when the housing 302 is molded by the second resin molding process after the circuit package 400 is manufactured by the first resin molding process. That is, the mechanical strength of the circuit package 400 is increased by these mounting surfaces, and in particular, the mechanical strength of the base of the protrusion 424 can be improved by the mounting surface 432. In addition, various effects related to Fig. 11(A), Fig. 11(B), Fig. 11(C). 9. Form of cover for temperature measurement of target gas 309.1 Overview of temperature measurement of target gas 30 and corresponding effects

[0193] As in Fig. 2(A), Fig. 2(B), Fig. 3(A) and Fig. As shown in Figure 3(B), the measurement target gas 30 is supplied from the inlet port 343 open to the upstream side, and the temperature of the measurement target gas 30 supplied to the temperature measuring section 452 in the front end of the protrusion 424 is measured. The temperature measuring section 452 is provided in the circuit package 400 for measuring the flow rate, and the thermal flow meter 300 is attached to the measurement target, such as the intake pipe, to measure the temperature of the measurement target gas 30 and the flow rate, ensuring excellent processability. The protrusion 424 with the temperature measuring section 452 is located on the inside of the intake pipe 343, which is enclosed by the front cover 303, the rear cover 304, and the housing 302 to improve stability.

[0194] In order to measure the temperature of the target gas 30 with high accuracy, the target gas should be brought into contact with the temperature measuring section 452 as closely as possible. Furthermore, heat transfer from another heat source to the temperature measuring section 452 should be made difficult. As described above with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. As described in Fig. 6(B), the temperature measuring portion 452 is provided at the front end of the protrusion 424. Therefore, the measurement target gas 30 introduced from the inlet port 343 opened to the upstream side easily comes into contact with the temperature measuring portion 452, and the protrusion 424 is formed long, so that heat is hardly transferred from the base to the front end. Since the measurement target gas 30 introduced from the inlet port 343 flows along the protrusion 424, the heat transferred from the base of the protrusion 424 to the front end of the measurement target gas 30 is reduced. With this structure, the influence of another heat source is unlikely. Thus, the temperature of the measurement target gas 30 can be measured with high accuracy.

[0195] As above with reference to Fig. As described in Figure 12, the line 548 that transmits the electrical signal from the temperature measuring element 518 (provided in the temperature measuring section 452 and measuring the temperature) to the processing unit 604 used as a temperature measurement control circuit is separated from the line 544 to which the temperature measuring element 518 is connected, so that the electrical signal from the temperature measuring element 518 is transmitted via the connecting line 546 to the line 548 with a high thermal resistance. With this configuration, it is possible to reduce the effects of heat transmitted via the line 548, thereby increasing the measurement accuracy.

[0196] Since the temperature measuring element 518 is connected to the line 544, the temperature measuring element 518 is held by the line 544 to ensure high reliability. Subsequently, the Fig. 12 is subjected to a transfer molding process to form the protrusion 424. Since the temperature sensing element 518 is attached to the lead 544, it is less likely to be damaged by the transfer molding process. This also allows for excellent productivity.

[0197] As in Fig. 2(A), Fig. 2(B), Fig. 3(A) or Fig. 3(B), the front protecting portion 322 or the rear protecting portion 325 is provided in the front cover 303 or the rear cover 304 to protect the front end of the protrusion 424. The protrusion 424 is thereby mechanically protected. In addition, the outlet port of the front side 344 or the rear side 345 is provided in the neck portion of the protrusion 424. The outer surface of the front cover 303 and the rear cover 304 is flat, and the flow velocity of the measurement target gas 30 to the outside of the front outlet port 344 or the rear outlet port 345 is high. Therefore, the pressure is lower than that on the inside of the front outlet port 344 or the rear outlet port 345. Therefore, the measurement target gas 30 introduced through the inlet port 343 is discharged via the front outlet port 344 or the rear outlet port 345.Since the inlet port 343 is opened upstream, a dynamic pressure of the measurement target gas 30 is applied to the inlet port 343. With this configuration, the measurement target gas 30 is sufficiently guided from the inlet port 343, the protrusion 424 is cooled while the temperature is measured, and the measurement target gas 30 is then discharged into the main channel 124 via the front outlet port 344 or the rear outlet port 345. In this way, the temperature of the measurement target gas 30 can be measured with high accuracy. 10 Shape of the drainage channel for draining the water flowing into the bypass channel10.1 Another embodiment of the drainage channel

[0198] Fig. 21(A) to 21(C) show another embodiment of the thermal flow meter in Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. 6(B). The same configuration is indicated with the same symbols, where Fig. 21(A) is a front view, with Fig. 21(B) is a left side view and Fig. 21(C) is a rear view. The bypass passage includes a wall 4211, an inner wall 3912, and an outer wall 3914. Furthermore, in this embodiment, a discharge passage 3528 is provided for connecting the outer wall 3914 of the bypass passage 4232 in the inlet port. The discharge passage 3528 includes a through hole 3512. The through hole 3512 includes an inlet opening 3542 open to the inner surface of the bypass outer wall 3914 of the bypass passage 4232 in the inlet port, and an outlet opening 3544 open to the outer wall 3914.

[0199] As in the embodiment with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. 6(B), the water flowing into the inlet port 350 of the bypass channel is likely to remain in the bypass channel when the longitudinal direction of the thermal flow meter 300 is mounted at an angle that crosses the direction of gravity. As shown in Fig. As shown in Fig. 21(C), since the through-hole 3512 is provided in the bypass outer wall 3914, the water flows from the inlet groove 351 along the inner surface of the bypass outer wall 3914 and is guided through the opening 3512 of the discharge channel 3528 in the bypass outer wall 3914 of the bypass channel 4232 in the inlet port. The water is guided to the bypass channel 3544 in the outlet port through the discharge channel 3528 and discharged from the bypass channel 3544 in the outlet port to the main channel 124. Similar to the description of the embodiment above, when the discharge channel is connected to the outside of the thermal flow meter 300, the flow velocity of the measurement target gas 30 increases, and the pressure of the measurement target gas 30 in the bypass channel is likely to decrease.Therefore, the measurement target gas 30 for measuring the flow rate of the water in the bypass channel may escape to the outside of the thermal flow meter 300 via the discharge channel 3528 and reduce the measurement accuracy of the flow rate.

[0200] In this embodiment, since the discharge channel 3528 is connected to the bypass channel 4232 in the inlet port and the bypass channel 4234 in the outlet port, the leakage of the measurement target gas 30 via the discharge channel 3528 can be reduced for the following reasons. One of the reasons for reducing the leakage is that there is only a small difference in the flow velocity of the measurement target gas between the inside of the bypass channel 4232 in the inlet port and the inside of the bypass channel 3544 in the outlet port. That is, the pressure difference between the inside of the bypass channel 4232 in the inlet port and the inside of the bypass channel 3544 in the outlet port is small. Another reason is that the outlet opening of the through hole 3512 of the discharge channel 3528 is located in the side area of the bypass channel 3544 in the outlet opening or next to the bypass channel.Since the flow in the side area of the bypass channel 3544 in the outlet port or adjacent to the bypass channel is low, the outlet port pressure in the outlet port or adjacent to the bypass channel 3512 is high, and the leakage through the through hole 3512 can be reduced. This maintains measurement accuracy.

[0201] The water flowing from the inlet opening 350 of the bypass channel and located in the bypass channel 4232 in the inlet opening flows along the inner surface of the bypass outer wall 3914 (as shown by arrow 3552) through the through-hole 3512 of the discharge channel 3528 in the bypass outer wall 3914 of the bypass channel 4232 in the inlet opening, and is guided to the bypass channel 3544 in the outlet opening via the discharge channel 3528 with the through-hole 3512. The water guided through the bypass channel 3544 in the outlet opening is discharged from the outlet opening 353 to the main channel 124. Therefore, there is no inflow to the measuring surface 430 of the circuit package 400. In this way, the water flowing from the inlet opening 350 of the bypass channel does not affect the measuring surface 430 of the circuit package 400 because the discharge channel 3528 connects the outer wall 3914 of the bypass channel 4232 in the inlet opening.It is possible to prevent flow rate measurement errors and damage, such as erosion of the flow rate sensor circuit. Similar to the above-mentioned embodiment, it is possible to perform the measurement with high accuracy.

[0202] In Fig. 21(C), the outlet port of the through-hole 3512 is located in a section between the bypass outer wall 3914 and the bypass outer wall 3916. Since the flow velocity in the section between the bypass outer wall 3914 and the bypass outer wall 3916 is low and the pressure is high compared to other sections, the leakage of the measurement target gas 30 in the bypass channel can be reduced and high measurement accuracy can be maintained. Since the section is covered and the upper portions of the bypass outer wall 3914 and the bypass outer wall 3916 come into contact with the cover upwards, the pressure is further increased and the leakage is suppressed. 10.2 Another embodiment for the temperature measurement of the target gas 30

[0203] Fig. 22(A) and Fig. 22(B) are partially enlarged views showing still another embodiment, wherein Fig. 22(A) is a left side view and Fig. 22(B) is a partially enlarged rear view. The bypass channel includes a wall 4211, an inner wall 3912, and an outer wall 3914. In the embodiment corresponding to the Fig. 21(A) to 21(C), the discharge passage 3528 is provided for connecting the outer wall 3914 of the bypass passage 4232 in the inlet port. The discharge passage 3528 includes a through hole 3512. The through hole 3512 includes an inlet port 3542 opened to the inner surface of the bypass outer wall 3914 of the bypass passage 4232 in the inlet port, and an outlet port 3544 opened to the outer wall 3914 (rear wall). In this embodiment, a protrusion 3515 is provided to suppress the flow of gas on the downstream side of the through hole 3512 in the discharge passage 3528. The discharge passage 3528 is formed by bypassing the front end 3514 of the protrusion 3515. Since the protrusion 3515 is provided, the discharge channel 3528 is extended. Furthermore, the fluid resistance becomes high, and the leakage of the measurement target gas 30 through the through hole 3512 can be reduced.

[0204] Through the discharge channel 3528 (similar to the above-mentioned embodiment), the water flows from the inlet opening 350 of the bypass channel along the bypass outer wall 3914 to the through-hole 3512 of the discharge channel 3528 provided in the bypass outer wall 4232 at the inlet opening. The water is guided to the bypass channel 3544 in the outlet opening through the discharge channel 3528 and discharged from the bypass channel 3544 in the outlet opening to the main channel 124. Fig. 22(A) and Fig. 22(B) represent a similar structure to Fig. 21(A) to 21(C), so that the leakage of the measurement target gas 30 through the discharge channel 3528 can be suppressed and the high measurement accuracy can be maintained.

[0205] In this embodiment, a protrusion 3515 is provided to suppress the gas flow on the downstream side of the through-hole 3512 in the discharge channel 3528. The discharge channel 3528 is formed by bypassing the front end 3514 of the protrusion 3515. Therefore, it is possible to lengthen the narrow discharge channel 3528. The water 3552 flowing through the through-hole 3512 in the discharge channel 3528 flows along the wall surface. The water flowing along the wall surface suppresses the leakage of the measurement target gas 30.

[0206] Since the protrusion 3515 is provided in the discharge channel 3528, the air pressure at the inlet port of the through-hole 3512 becomes high, and the leakage through the through-hole 3512 can be reduced. With this structure, it is possible to prevent measurement errors and maintain high measurement accuracy. Furthermore, the fluid resistance at the side of the outlet port of the through-hole 3512 of the discharge channel 3528 is high because a wall 3518 is provided between the protrusion 3515 and the outlet port 3544. Thus, the leakage of the measurement target gas 30 through the through-hole 3512 can be reduced.

[0207] Fig. 23(A) and Fig. 23(B) are partially enlarged views showing still another embodiment, wherein Fig. 23(A) is a left side view and Fig. 23(B) is a partially enlarged rear view. The bypass channel includes a wall 4211, an inner wall 3912 and an outer wall 3914. In the embodiment similar to those in Fig. 21(A) to 21(C) and in Fig. 22(A) and Fig. 22(B), the discharge passage 3528 is provided with the through-hole 3512 for connecting the outer wall 3914 of the bypass passage 4232 in the inlet port. In this embodiment, the projections 3532 and 3534 include the projections 3536 and 3538 on the downstream side of the through-hole 3512 in the discharge passage 3528 to suppress gas flow. The discharge passage 3528 is provided by bypassing the front ends 3524, 3525, and 3526 of the projections 3534, 3536, and 3538. The included discharge passage 3528 is formed by the projections 3534, 3536, and 3538, and the fluid resistance is increased. This configuration reduces the leakage of the target gas 30 in the bypass channel.

[0208] With this shape of the bypass channel 3528 (similar to the above-mentioned embodiment), the flow velocity of the downstream side of the through-hole 3512 is reduced, the pressure of the through-hole 3512 remains high, and the leakage of the measurement target gas 30 is prevented. Water flows along the front side of the protrusion. Even though the protrusion 3532 is formed, the water is sufficiently drained. On the other hand, the leakage of the measurement target gas 30 in the bypass channel is suppressed by fluid resistance. With this structure, the leakage of the measurement target gas 30 in the bypass channel can be suppressed and the high measurement accuracy of the flow rate can be maintained. Industrial availability

[0209] The present invention relates to a measuring apparatus for measuring a gas flow rate as described above. Reference list designations 300 Thermal Flow Meter 302 housing 303 Front cover 304 Rear cover 305 External connection 306 External connection 307 Calibration port 310 measuring section 320 connection terminals 332 Bypass channel on the front 334 Bypass channel at the rear 356, 358 lead 359 Harz section 361 Internal socket of the external connection 365 connecting section 400 circuit package 412 connection port 414 connection 422 circuit base body 424 lead 430 measuring surface 432, 434 mounting surface 436 Exposure section of the heat transfer surface 438 Opening 452 Temperature measuring section 590 press-in opening 594, 596 bevels 601 Flow rate sensor circuit 602 Air flow measuring section 604 processing unit 608 Heat generator 640 heat control bridge 650 Bridge circuit of the air flow measurement 672 Membran 3512, 3522 through hole 3528 drainage channel 4232 Bypass channel in the inlet opening 4234 Bypass channel in the outlet opening

Claims

A thermal flow meter (300) comprising: a bypass channel (332, 334) for flowing through a part of a measurement target gas flowing through a main channel, and a flow sensor circuit (601) for measuring the flow rate of the measurement target gas flowing through the main channel by means of heat transfer from the measurement target gas flowing through the bypass channel (332, 334). The bypass channel (332, 334) comprises an inlet opening for the inflow of the measurement target gas, an outlet opening for returning the measurement target gas to the main channel, and an air flow measuring section (602) arranged between the inlet and outlet openings, which air flow measuring section measures the flow by means of heat transfer between the flow sensor circuit and the measurement target gas. Furthermore, a second channel (3528) for connecting a bypass channel section at the inlet opening between the inlet opening of the bypass channel (332,334) and the air flow measuring section (602) with a bypass channel section at the outlet opening between the air flow measuring section (602) in the bypass channel (332, 334) and the outlet opening, the second channel (3528) has an inlet opening (3542) which runs through a wall surface (4212) which forms the bypass channel section at the inlet opening of the bypass channel (332, 334), and which opens into the bypass channel section at the inlet opening, and an outlet opening (3544) which opens into the rear side (4213) of the wall surface (4212) which forms the bypass channel section at the inlet opening, characterized in that the bypass channel section is formed in the inlet opening such that a flow area of the bypass channel section in the inlet opening, starting from a through-bore (3512, 3522) of the second channel (3528) is increasingly narrowed towards the air flow measuring section (602). The thermal flow meter (300) according to claim 1, wherein a flange (312) is provided for supporting the thermal flow meter (300), the inlet opening of the bypass channel (332, 334) and the outlet opening of the bypass channel (332, 334) are arranged in an end portion of the thermal flow meter (300) in the opposite direction to the flange (312), the air flow measuring portion is arranged towards the flange (312) from the inlet opening of the bypass channel (332, 334) and the outlet opening of the bypass channel (332, 334), the bypass channel portion in the inlet opening is configured to approach the air flow measuring portion in a curved shape, the bypass channel portion in the inlet opening is configured to provide a bypass channel groove in the inlet opening, and the through-hole (3512, 3522) of the second channel (3528) is provided in a wall surface in the opposite direction to the flange (312) of the bypass channel groove in the inlet opening. The thermal flow meter (300) according to claim 1 or 2, wherein a projection (3515) for suppressing a gas flow is provided on a downstream side of the through hole (3512) in the second channel (3528), and the second channel (3528) is formed by bypassing the front end (3514) of the projection (3515). The thermal flow meter (300) according to one of claims 1 to 3, wherein a bypass channel groove is provided in the inlet opening for forming the bypass channel portion in the inlet opening, and a first cover is provided for forming the bypass channel portion in the inlet opening by covering the bypass channel groove in one surface of the thermal flow meter (300); a bypass channel portion is provided in an outlet opening groove for forming the bypass channel portion in the outlet opening, and a second cover is provided for forming the bypass channel portion in the outlet opening by covering the bypass channel portion in the outlet opening by covering the bypass channel portion in the outlet opening groove of the other surface of the thermal flow meter (300); and the through-hole (3512) of the second channel (3528) is opened in the bypass channel groove in the inlet opening on one surface of the thermal flow meter (300). A thermal flow meter (300) comprising: a bypass channel (332, 334) in which a portion of a measurement target gas flows, which is guided through a main channel; an air flow measuring section (602) for measuring the flow rate of the measurement target gas flowing through the main channel to the bypass channel (332, 334) by means of heat transfer; and a housing (302) containing a resin bypass channel for forming the bypass channel (332, 334) and protecting the air flow measuring section (602); wherein the bypass channel (332, 334) comprises an inlet opening for the inflow of the measurement target gas and an outlet opening for returning the measurement target gas to the main channel; the air flow measuring section (602) is arranged between the inlet opening and the outlet opening of the bypass channel (332, 334) and has a heat exchange with the measurement target gas for measuring the flow rate, a bypass channel section is provided at the inlet opening in a surface of the bypass channel (332, 334) of the housing (302),which connects the inlet opening of the bypass channel (332, 334) and the air flow measuring section (602), in the other surface of the bypass channel (332, 334) of the housing (302), a bypass channel section is provided at the outlet opening, which connects the air flow measuring section (602) and the outlet opening of the bypass channel (332, 334), and in a wall (4212) between the bypass channel section at the inlet opening and the bypass channel section at the outlet opening, a second channel (3528) is provided, which penetrates the wall, characterized in that the bypass channel section is formed in the inlet opening such that a flow area of the bypass channel section in the inlet opening increases from a through-bore (3512, 3522) of the second channel (3528) towards the air flow measuring section (602) is narrowed.,

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