Thermal flow meter

Abstract

A thermal flow meter (300) including a bypass passage for flowing a measurement target gas received from a main passage (124) and an air flow detection section (602) for measuring a flow rate of the measurement target gas based on heat transfer from a heat transfer surface to the measurement target gas flowing through the bypass passage, the thermal flow meter (300) comprising: a circuit assembly (400) in which the air flow detection section (602) and a lead wire (514) connected to the air flow detection section (602) have been sealed by a first resin molding process; and a housing (302) forming part of the bypass passage and fixing the circuit assembly (400) by a second resin molding process, wherein the connecting line (514) has an external connecting line (412) which is fixed to the housing (302) and protrudes from the circuit assembly (400), and a bent portion (416) having a bent shape is provided on the external connecting line (412), characterized in that that the bent portion (416) is bent in a curved shape that rises from the side of the circuit assembly (400) to an uppermost portion and falls from there in order to be able to deform upon temperature fluctuations and thus reduce mechanical stresses in the axial direction of the external lead (412) in the external lead (412).

Description

Technical area

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

[0002] A thermal flowmeter that measures a gas flow is configured to include an air flow detection section for measuring a flow, so that a gas flow is measured by performing heat transfer between the air flow detection section and the gas as a measurement target. The flow measured by the thermal flowmeter is widely used as an important control parameter for various devices. The thermal flowmeter is characterized in that a gas flow, such as a mass flow, can be measured with relatively high accuracy compared to other types of flowmeters.

[0003] However, it is desirable to further improve the measurement accuracy of the gas flow rate. For example, in a vehicle equipped with an internal combustion engine, the requirements for fuel economy or exhaust gas purification are high. To meet these requirements, it is desirable to measure the intake air amount, which is a key parameter of the internal combustion engine, with high accuracy. The thermal flow meter, which measures the intake air amount supplied to the internal combustion engine, includes a bypass passage that receives a portion of the intake air amount and an air flow detection section disposed in the bypass passage. The air flow detection section measures a state of the measurement target gas flowing through the bypass passage by performing heat transfer with the measurement target gas and outputs an electrical signal representing the supplied intake air amount to the internal combustion engine.This technique is discussed, for example, in JP 2011 252796 A (PTL 1).

[0004] JP 2009-85855 A (PTL 2) describes a flow measuring device including a housing having a proximal end portion fixed to an inlet channel and a front end portion projecting toward the center of the inlet channel. In this flow measuring device, a connector terminal is provided at the proximal end portion of the housing, and a flow detection device is provided at the front end portion of the housing. The flow detection device is provided on an electrical circuit fixed to the housing, and the electrical circuit and the connector terminal are connected by a bonding wire.

[0005] The temperature of the intake duct increases in accordance with the increase in temperature in the engine compartment, and heat is also transferred to the housing of the flow meter. Due to heat transfer from the intake duct, the temperature of the proximal end portion of the housing increases, while the front end portion of the housing is cooled by the intake air and its temperature decreases, causing a temperature difference in a direction perpendicular to the air flow direction of the intake duct.

[0006] Because of this temperature difference, the housing expands or contracts in the longitudinal direction, deforming the bonding wire, so that when there is a change in the distance between the electrical circuit and the connector terminal, the bonding wire is deformed in such a way as to accommodate the change in the distance therebetween.

[0007] PTL 3 discloses a flow sensor comprising a housing with a cylindrical portion disposed between an armature portion and a head portion. The diameter of the armature portion is typically larger than the diameter of the cylindrical portion, which in turn is typically larger than the diameter of the head portion.

[0008] PTL 4 describes a thermal-type air flow meter capable of suppressing deformation of a base element, thus reducing the influence of dimensional change on measurement accuracy. The meter includes a housing portion disposed in an intake port of an internal combustion engine and a base element attached to the housing portion. It includes a secondary air passage into which a portion of the air flowing into an intake duct enters.

[0009] PTL 5 discloses a flow sensor structure for sealing the surface of an electric control circuit and a part of a semiconductor device.

[0010] PTL 6 shows a measuring sensor of a thermal flow meter for determining the flow of a medium flowing through a measuring tube, wherein the measuring sensor has at least one thin-film resistance thermometer which is arranged in a sleeve. List of referencesPatent literature PTL 1: JP 2011-252796 A PTL 2: JP 2009-85855 A PTL 3: US 2010 / 0212433 A1 PTL 4: US 2012 / 0060599 A1 PTL 5: US 2011 / 0140211 A1 PTL 6: DE 10 2010 031 127 A1 Summary of the inventionTechnical problem

[0011] However, in the case of bonding wire connection, the wire must be separated, increasing the number of components. Furthermore, two locations—the connection point on the electrical circuit side and the connection point on the connector terminal side—need to be connected, increasing the number of steps and increasing costs.

[0012] On the other hand, when the lead wire, which is a wire rod whose rigidity is higher than that of the bonding wire, is directly connected to the connection point of the connector terminal, a stress is applied to the lead wire connecting the flow detection device and the connector terminal due to expansion due to the temperature difference between the proximal end portion side and the front end portion side of the housing, which may cause cracking and peeling at the connection point of the lead wire.

[0013] The present invention has been made in view of the above problem, and an object of the present invention is to provide a thermal flow meter having a terminal structure such that the stress can be absorbed when a stress is applied to the terminal line connecting the flow detection device and the connector terminal in accordance with the temperature difference. Solution to the problem

[0014] To solve the above problem, a thermal flow meter according to the present invention is a thermal flow meter including a bypass passage for flowing a measurement target gas received from a main passage and an air flow detection section for measuring a flow rate of the measurement target gas by performing heat transfer with the measurement target gas flowing through the bypass passage via a heat transfer surface, the thermal flow meter including a circuit assembly in which the air flow detection section and a lead wire connected to the air flow detection section have been sealed by a first resin molding process, and a housing forming a part of the bypass passage and fixing the circuit assembly by a second resin molding process, the lead wire including an external lead wire,which is attached to the housing and protrudes from the circuit assembly, and a bent portion with a bent shape is provided on the external lead. The bent portion is bent in a curved shape that rises from the side of the circuit assembly (400) to an uppermost portion and descends from there in order to be able to deform upon temperature fluctuations and thus reduce mechanical stresses in the axial direction of the external lead in the external lead (412). Advantageous effects of the invention

[0015] According to the present invention, the external lead attached to the housing has a bent portion protruding from the circuit board, so that when stress is applied to the lead in the axial direction due to a temperature difference between the housing and the circuit board, the bent portion deforms and can absorb the stress. Thus, this can prevent cracking and peeling due to the concentration of stress at the connection point between the lead and the connection point. Short description of the drawings Fig. 1 is a system diagram illustrating an internal combustion engine control system in which a thermal flow meter in accordance with an embodiment of the invention is used. 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(A) and Fig. 3(B) are diagrams showing an appearance of the thermal flow meter, in which Fig. 3(A) is a right side view and Fig. 3(B) is a rear view. Fig. 4(A) and Fig. 4(B) are diagrams showing an appearance of the thermal flow meter, in which Fig. 4(A) is a plan view and Fig. 4(B) is a bottom view. Fig. 5(A) and Fig. 5(B) are diagrams showing a casing of the thermal flow meter in which Fig. 5(A) is a left side view of the housing and Fig. 5(B) is a front view of the housing. Fig. 6(A) and Fig. 6(B) are diagrams showing a casing of the thermal flow meter in which Fig. 6(A) is a right side view of the housing and Fig. 6(B) is a rear view of the housing. Fig. 7 is a partially enlarged view illustrating a state of a flow path surface arranged in the bypass passage. Fig. 8 is a partially enlarged view showing a terminal connector. Fig. 9A is a cross-sectional view taken along line DD of Fig. 8, which is a cross-sectional view illustrating an embodiment of a terminal connection unit. Fig. 9B is a cross-sectional view taken along line DD of Fig. 8, which is a cross-sectional view illustrating another embodiment of a terminal connection unit. Fig. Figure 9C is a cross-sectional view along line DD of Fig. 8, which is a cross-sectional view illustrating another embodiment of a terminal connection unit. Fig. Figure 9D is a cross-sectional view along line DD of Fig. 8, which is a cross-sectional view illustrating another embodiment of a terminal connection unit. Fig. 10 is a partially enlarged view illustrating another embodiment of a terminal connecting unit. Fig. 11(A) to 11(C) are external views showing a circuit assembly in which Fig. 11(A) is a side view, Fig. 11(B) is a front view and Fig. 11(C) is a rear view. Fig. 12 is a view illustrating a state of a circuit assembly after a first resin molding process. Fig. 13A is a diagram illustrating an overview of a manufacturing process of a thermal flow meter and a manufacturing process of a circuit assembly. Fig. 13B is a diagram illustrating an overview of a manufacturing process of the thermal flow meter and a manufacturing process of the thermal flow meter. Fig. 14 is a circuit diagram showing a flow detection circuit of the thermal flow meter. Fig. 15 is an explanatory diagram showing an airflow detecting section of the airflow detecting circuit. Description of embodiments

[0016] Examples for embodying the invention described below (hereinafter referred to as embodiments) solve various problems, which is desired as a practical product. In particular, the embodiments solve various problems for use in a measuring device for measuring an intake air amount of a vehicle and exhibit various effects. One of the various problems addressed by the following embodiments is described in the above-described "Problems to be Solved by the Invention," and one of the various effects obtained by the following embodiments is described in the "Effects of the Invention." Various problems solved by the following embodiments and various effects obtained by the following embodiments are further described in the "Description of Embodiments."Thus, it will be appreciated that the following embodiments also include effects to be obtained by the embodiments or problems to be addressed other than those described in “problems to be solved by the invention” or “effects of the invention”.

[0017] In the following embodiments, even if introduced in different drawings, like reference numerals denote like elements and have the same functional effects. The components described in the preceding paragraphs need not be described in the drawings by designating them with reference numerals and symbols. 1. An internal combustion engine control system comprising a thermal flow meter in accordance with an embodiment of the invention

[0018] Fig. 1 is a system diagram illustrating a control system for an electronic fuel injection type internal combustion engine having a thermal flow meter in accordance with an embodiment of the invention. Based on the operation of an internal combustion engine 110 having an engine cylinder 112 and an engine piston 114, intake air as a measurement target gas 30 is drawn from an air cleaner 122 and guided to a combustion chamber of the engine cylinder 112 via a main passage 124 including, for example, an intake body, a throttle body 126, and an intake manifold 128. A flow rate of the measurement target gas 30 as intake air guided to the combustion chamber is measured by a thermal flow meter 300 in accordance with the invention.Fuel is supplied from a fuel injection valve 152 based on the measured flow rate and mixed with the measurement target gas 30 as intake air, so that the mixed gas is supplied to the combustion chamber. Note that in this embodiment, the fuel injection valve 152 is provided in an intake port of the internal combustion engine, and the fuel injected into the intake port is mixed with the measurement target gas 30 as intake air to form a mixed gas, so that the mixed gas is supplied to the combustion chamber via an intake valve 116 to generate mechanical energy through combustion.

[0019] In recent years, many vehicles have adopted a direct fuel injection method which has excellent effects in exhaust gas purification or fuel efficiency improvement, in which a fuel injection valve 152 is installed in a cylinder head of the internal combustion engine, and fuel is injected from the fuel injection valve 152 directly into each combustion chamber. The thermal flow meter 300 can be similarly used in a type in which fuel is directly injected into each combustion chamber, as well as in a type in which fuel is injected into the intake port of the internal combustion engine from Fig. 1 is injected. A method for measuring control parameters, including a method for using the thermal flow meter 300, and a method for controlling the internal combustion engine, including a fuel supply amount or ignition timing, are similar in terms of basic concept between both types. A representative example of both types, a type in which fuel is injected into the intake port, is shown in Fig. 1 shown.

[0020] The fuel and air supplied to the combustion chamber have a fuel / air mixture state and are explosively combusted by spark ignition of the spark plug 154 to generate mechanical energy. The gas after combustion is supplied from the exhaust valve 118 to an exhaust pipe and discharged from the exhaust pipe as exhaust gas 24 to the exterior of the vehicle. The flow rate of the measurement target gas 30 as intake air supplied to the combustion chamber is controlled by the throttle valve 132, the opening degree of which changes in response to the manipulation of an accelerator pedal. The fuel supply amount is controlled based on the flow rate of intake air supplied to the combustion chamber, and a driver controls the opening degree of the throttle valve 132 to control the flow rate of intake air supplied to the combustion chamber.As a result, it is possible to control the mechanical energy generated by the internal combustion engine. 1.1 Overview of the control of the internal combustion engine control system

[0021] The flow rate and temperature of the measurement target gas 30 as intake air received from the air cleaner 122 and flowing through the main passage 124 are measured by the thermal flow meter 300, and an electrical signal representing the flow rate and temperature of the intake air is input from the thermal flow meter 300 to the control device 200. Furthermore, an output of the throttle angle sensor 144, which measures an opening degree of the throttle valve 132, is input to the control device 200, and an output of a rotation angle sensor 146 is input to the control device 200 to measure a position or condition of the engine piston 114, the intake valve 116, or the exhaust valve 118 of the internal combustion engine, and a rotational speed of the internal combustion engine.In order to measure a mixture ratio state between the fuel amount and the air amount from the condition of the exhaust gas 24, an output of an oxygen sensor 148 is input to the control device 200.

[0022] The control device 200 calculates a fuel injection amount or an ignition timing based on an intake air flow rate as an output of the thermal flow meter 300 and an engine speed measured by an output of the rotation angle sensor 146. Based on the calculation result, the fuel amount supplied from the fuel injection valve 152 and the ignition timing for igniting the spark plug 154 are controlled. In practice, the fuel supply amount or the ignition timing is more precisely controlled based on a change in the intake temperature or throttle angle measured by the thermal flow meter 300, a change in the engine speed, and an air-fuel ratio state measured by the oxygen sensor 148.In the idle drive state of the internal combustion engine, the control device 200 further controls the amount of air bypassing the throttle valve 132 using an idle air control valve 156 and controls a rotational speed of the internal combustion engine in the idle drive state. 1.2 Importance of improving the measurement accuracy of the thermal flow meter and the environment for mounting the thermal flow meter

[0023] Both the fuel supply amount and the ignition timing as a main control amount of the internal combustion engine are calculated using an output of the thermal flow meter 300 as a main parameter. Thus, improving the measurement accuracy, suppressing aging, and improving the reliability of the thermal flow meter 300 are important for improving the control accuracy of a vehicle or maintaining reliability. Particularly in recent years, there have been numerous demands for vehicle fuel economy and exhaust gas purification. To meet these demands, it is very important to improve the measurement accuracy of the flow rate of the measurement target gas 30 as intake air measured by the thermal flow meter 300. In addition, it is also important to maintain high reliability of the thermal flow meter 300.

[0024] A vehicle including the thermal flow meter 300 is used in an environment where temperature change is significant or in harsh weather such as storms or snow. When a vehicle travels on a snowy road, it travels on a road sprayed with antifreeze. Preferably, the thermal flow meter 300 is designed taking into account a countermeasure for the temperature change or a countermeasure for dust or contaminants in such a usage environment. Furthermore, the thermal flow meter 300 is installed in an environment where the internal combustion engine is subject to vibration. Furthermore, it is desirable to maintain high reliability against vibration.

[0025] The thermal flow meter 300 is installed in the intake pipe, which is affected by heat from the internal combustion engine. Therefore, the heat generated by the internal combustion engine is transferred to the thermal flow meter 300 through the intake pipe, which is a main passage 124. Since the thermal flow meter 300 measures the flow of the target gas by transferring heat with the target gas, it is important to suppress the influence of external heat as much as possible.

[0026] As described below, the thermal flow meter 300 mounted on a vehicle solves the problems described in "Problems to be Solved by the Invention" and provides the effects described in "Effects of the Invention." Furthermore, as described below, it solves various problems required as a product and provides various effects in light of various problems described above. Specific problems or effects solved or provided by the thermal flow meter 300 will be described in the following description of embodiments. 2. Configuration of the thermal flow meter 3002.1 External structure of the thermal flow meter 300

[0027] 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, in which Fig. 2(A) is a left side view of the thermal flow meter 300, Fig. 2(B) is a front view, Fig. 3(A) is a right side view, Fig. 3(B) is a rear view, Fig. 4(A) is a plan view and Fig. 4(B) is a bottom view. The thermal flow meter 300 includes a housing 302, a front cover 303, and a rear cover 304. The housing 302 includes a flange 312 for attaching the thermal flow meter 300 to an inlet pipe as a main passage 124, an external connector 305 having an external terminal (connector terminal) 306 for electrical connection with external devices, and a measuring section 310 for measuring a flow rate and the like. The measuring section 310 is internally provided with a bypass passage groove for establishing a bypass passage. In addition, the measuring section 310 is internally provided with a circuit assembly 400 including an air flow detection section 602 (see Fig. 14) for measuring a flow rate of the measurement target gas 30 flowing through the main passage 124 or a temperature detection section 452 for measuring a temperature of the measurement target gas 30 flowing through the main passage 124. 2.2 Effects based on the external structure of the thermal flow meter 300

[0028] Since the inlet port 350 of the thermal flow meter 300 is provided on the front end side of the measuring section 310 extending from the flange 312 toward the central direction of the main passage 124, the gas near the central section, which is distant from the inner wall surface, can be introduced into the ambient passage instead of from near the inner wall surface of the main passage 124. For this reason, the thermal flow meter 300 can measure a flow rate or temperature of the air distant from the inner wall surface of the main passage 124 of the thermal flow meter 300, so it is possible to suppress a reduction in measurement accuracy caused by the influence of heat and the like.Near the inner wall surface of the main passage 124, the thermal flow meter 300 is easily affected by the temperature of the main passage 124, so that the temperature of the measurement target gas 30 exhibits a condition different from an original temperature of the gas and a condition different from an average condition of the main gas within the main passage 124. In particular, when the main passage 124 serves as an intake pipe of the engine, it may be affected by heat from the engine and remains at a high temperature. For this reason, the gas near the inner wall surface of the main passage 124 often exhibits a higher temperature than the original temperature of the main passage 124, thus deteriorating the measurement accuracy.

[0029] Near the inner wall surface of the main passage 124, a fluid resistance increases and a flow velocity decreases compared to an average flow velocity in the main passage 124. For this reason, a reduction in the flow velocity compared to the average flow velocity in the main passage 124 may generate a measurement error if the gas near the inner wall surface of the main passage 124 is introduced into the bypass passage as the measurement target gas 30. Since in the Fig. 2(A), 2(B), 3(A), 3(B) and 4(A) to 4(C), the inlet port 350 is provided at the front end of the thin and long measuring section 310 extending from the flange 312 to the center of the main passage 124, it is possible to reduce a measurement error related to a reduction in the flow velocity near the inner wall surface. In the thermal flow meter 300 shown in 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 312 to the center of the main passage 124, an outlet port of the bypass passage is also provided in the rear end of the measuring section 310. Thus, it is possible to further reduce the measurement error.

[0030] The measuring section 310 of the thermal flow meter 300 has a shape extending from the flange 312 to the center direction of the main passage 124, and its front end is provided with an inlet port 350 for introducing a part of the measurement target gas 30, such as an inlet air, into the bypass passage and with an outlet port 352 for returning the measurement target gas 30 from the bypass passage to the main passage 124. While the measuring section 310 has a shape extending along an axis directed from the outer wall of the main passage 124 to the center, its width, as shown in Fig. 2(A) and Fig. 3(A), a narrow shape is shown. That is, the measuring section 310 of the thermal flow meter 300 has a front surface having an approximately rectangular shape and a side surface having a narrow width. As a result, the thermal flow meter 300 can have a bypass passage having a sufficient length, and it is possible to suppress fluid resistance to a small value for the measurement target gas 30. For this reason, by using the thermal flow meter 300, it is possible to suppress the fluid resistance to a small value and measure the flow rate of the measurement target gas 30 with high accuracy. 2.3 Structure of the temperature detection section 452

[0031] The inlet port 343 is positioned on the side of the flange 312 of the bypass passage provided on the side of the front end of the measuring section 310 and is, as shown in Fig. 2(A), Fig. 2(B), Fig. 3(A) and Fig. 3(B), the measuring section 310 is opened toward an inlet side of the flow of the measurement target gas 30. A temperature detection section 452 for measuring a temperature of the measurement target gas 30 is arranged inside the inlet opening 343. In the center of the measuring section 310 where the inlet opening 343 is provided, an inlet-side outer wall of the measuring section 310 contained in the housing 302 is recessed toward the outlet side, and the temperature detection section 452 is formed so as to protrude from the inlet-side outer wall with the recessed shape toward the inlet side. In addition, front and rear covers 303 and 304 are provided on both sides of the outer wall having a recessed shape, and the inlet-side ends of the front and rear covers 303 and 304 are formed to protrude from the outer wall having the recessed shape toward the inlet side.For this reason, the outer wall with the depressed shape and the front and rear covers 303 and 304 on both sides thereof form the inlet port 343 for receiving the measurement target gas 30. The measurement target gas 30 received from the inlet port 343 contacts the temperature detection portion 452 provided inside the inlet port 343 to measure the temperature of the temperature detection portion 452. Moreover, the measurement target gas 30 flows to the inlet side along a portion supporting the temperature detection portion 452 protruding from the outer wall of the case 302 with the depressed shape, and is discharged into the main passage 124 from the front-side outlet port 344 and the rear-side outlet port 345 provided in the front and rear covers 303 and 304. 2.4 Effects related to the temperature detection section 452

[0032] The temperature detection section 452 measures the temperature of the gas flowing from the inlet side in the direction along the flow of the measurement target gas 30 to the inlet port 343. Furthermore, the gas flows toward a neck portion of the temperature detection section 452 for supporting the temperature detection section 452, thus lowering the temperature of the portion for supporting the temperature detection section 452 to near the temperature of the measurement target gas 30. The temperature of the inlet pipe serving as a main passage 124 usually increases, and heat is transferred from the flange 312 or the heat insulation 315 to the portion for supporting the temperature detection section 452 via the inlet-side outer wall within the measurement section 310, which may affect the temperature measurement accuracy.As the measurement target gas 30 is measured by the temperature detection section 452 and then flows along the support portion of the temperature detection section 452, the aforementioned support portion is cooled. Thus, it is possible to suppress heat transfer from the flange 312 or the heat insulation 315 to the portion supporting the temperature detection section 452 via the inlet-side outer wall within the measurement section 310.

[0033] In particular, the inlet-side outer wall within the measuring section 310 in the support section of the temperature detection section 452 has a shape which (as will be described below with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B)) is concave to the outlet side. Thus, it is possible to increase a length between the inlet-side outer wall within the measuring section 310 and the temperature detection section 452. As the heat conduction length increases, a length of the cooling section using the measurement target gas 30 increases. Thus, it is also possible to reduce the influence of heat from the flange 312 or from the heat insulation 315. Accordingly, the measurement accuracy is improved. Since the inlet-side outer wall (as described below with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B)) has a shape that is concave to the outlet side, it is possible to use the circuit assembly 400 described below (see Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B)) easy to attach. 2.5 Structures and effects of the inlet side surface and the outlet side surface of the measuring section 310

[0034] An inlet-side protrusion 317 and an outlet-side protrusion 318 are provided on the inlet-side side surface and the outlet-side side surface of the measuring section 310 included in the thermal flow meter 300, respectively. The inlet-side protrusion 317 and the outlet-side protrusion 318 have a shape that narrows along the front end to the base point, so that it is possible to reduce fluid resistance of the measurement target gas 30 while intake air flows through the main passage 124. The inlet-side protrusion 317 is provided between the heat insulator 315 and the inlet port 343. The inlet-side protrusion 317 has a large cross-section and receives a large heat conduction from the flange 312 or the heat insulator 315.However, the inlet-side protrusion 317 is cut off near the inlet opening 343, and a length of the temperature detection portion 452 increases from the temperature detection portion 452 of the inlet-side protrusion 317 due to the recess of the inlet-side outer wall of the housing 302 as described below. For this reason, heat conduction from the heat insulator 315 to the support portion of the temperature detection portion 452 is suppressed.

[0035] A recess containing the terminal connector 320 is formed between the flange 312 or the heat insulator 315 and the temperature detection section 452, the terminal connector 320 being described below. For this reason, a distance between the flange 312 or the heat insulator 315 and the temperature detection section 452 increases, and the front cover 303 or the rear cover 304 is provided in this long section, so that this section serves as a cooling surface. Thus, it is possible to reduce the influence of the temperature of the wall surface of the main passage 124 on the temperature detection section 452. Furthermore, it is possible to guide a part of the measurement target gas 30 introduced into the bypass passage to near the center of the main passage 124 while increasing the distance between the flange 312 or the heat insulator 315 and the temperature detection section 452.It is possible to suppress a reduction in measurement accuracy caused by heat transfer from the wall surface of the main passage 124.

[0036] As in Fig. 2(B) or Fig. As shown in Fig. 3(B), both side surfaces of the measuring portion 310 inserted into the main passage 124 have a very narrow shape, and a front end of the outlet-side protrusion 318 or the inlet-side protrusion 317 has a narrow shape relative to the root point where the air resistance is reduced. For this reason, it is possible to suppress an increase in fluid resistance caused by inserting the thermal flow meter 300 into the main passage 124. Moreover, in the portion where the outlet-side protrusion 318 or the inlet-side protrusion 317 is provided, the inlet-side protrusion 317 or the outlet-side protrusion 318 protrudes toward both sides relative to both side portions of the front cover 303 or the rear cover 304.Since the inlet-side protrusion 317 or the outlet-side protrusion 318 is formed from a resin molding material, they are easily formed into a shape with low air resistance. Meanwhile, the front cover 303 or the rear cover 304 is shaped to have a wide cooling surface. For this reason, the thermal flow meter 300 has reduced air resistance and can be easily cooled by the measurement target gas flowing through the main passage 124. 2.6 Structure and effects of the flange 312

[0037] In order to reduce the heat transfer area with the main passage 124 and to make it difficult for the thermal flow meter 300 to receive an influence of heat, the flange 312 is provided with a plurality of recesses 314 on its lower surface, which is a portion opposite to the main passage 124. The screw hole 313 of the flange 312 is provided so that the thermal flow meter 300 is fixed to the main passage 124, and a space is formed between a surface opposite to the main passage 124 around each screw hole 313 and the main passage 124, so that the surface opposite to the main passage 124 around the screw hole 313 is spaced from the main passage 124.As a result, the flange 312 has a structure that can reduce heat transfer from the main passage 124 to the thermal flow meter 300 and prevent heat-induced deterioration in measurement accuracy. In addition to reducing heat conduction, the recess 314 can also reduce the influence of resin shrinkage of the flange 312 during the formation of the housing 302.

[0038] The thermal insulation 315 is provided on the measuring section 310 side of the flange 312. The measuring section 310 of the thermal flow meter 300 is inserted into the interior from an installation hole provided in the main passage 124 in such a manner that the thermal insulation 315 faces the inner surface of the installation hole of the main passage 124. The main passage 124 serves, for example, as an inlet pipe and is often kept at a high temperature. Conversely, it is conceivable that the main passage 124 is kept at a significantly low temperature when the operation is activated in a cold area. If such a high or low temperature condition of the main passage 124 affects the temperature detection section 452 or the flow measurement described below, the measurement accuracy will deteriorate.For this reason, a plurality of recesses 316 are provided adjacent to each other in the thermal insulation 315 adjacent to the hole inner surface of the main passage 124, and a width of the thermal insulation 315 adjacent to the hole inner surface between the adjacent recesses 316 is very thin, that is, equal to or smaller than 1 / 3 of the width of the fluid flow direction of the recess 316. As a result, it is possible to reduce the influence of temperature. In addition, a portion of the thermal insulation 315 becomes thick. When the resin is cooled from a high temperature to a low temperature and solidifies during resin molding of the housing 302, volume shrinkage occurs, so that deformation is generated because of stress. By forming the recess 316 in the thermal insulation 315, it is possible to make the volume shrinkage more uniform and reduce the concentration of stress.

[0039] The measuring portion 310 of the thermal flow meter 300 is inserted into the interior from the installation hole provided in the main passage 124 and is fixed to the main passage 124 with screws using the flange 312 of the thermal flow meter 300. Preferably, the thermal flow meter 300 is fixed in the installation hole provided in the main passage 124 with a predetermined positional relationship. The recess 314 provided in the flange 312 can be used to determine a positional relationship between the main passage 124 and the thermal flow meter 300. By forming the convex portion in the main passage 124, it is possible to ensure an insertion relationship between the convex portion and the recess 314 and to fix the thermal flow meter 300 in a precise position to the main passage 124. 2.7 Structures and effects of the external connector 305 and the flange 312

[0040] Fig. 4(A) is a plan view illustrating the thermal flow meter 300. Four external terminals 306 and one calibration terminal 307 are provided inside the external connector 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 drive the thermal flow meter 300. The calibration terminal 307 is used to measure the manufactured thermal flow meter 300, to obtain a calibration value of each thermal flow meter 300, and to store the calibration value in an internal memory of the thermal flow meter 300. In the subsequent measurement operation of the thermal flow meter 300, the calibration data representing the calibration value stored in the memory is used, and the calibration terminal 307 is not used.Thus, the calibration terminal 307 has a different shape from the external terminal 306 to prevent the calibration terminal 307 from interfering with the connection between the external terminals 306 and other external devices. Since the calibration terminal 307 is shorter than the external terminal 306 in this embodiment, the calibration terminal 307 does not interfere with the connection even when the connection terminal connected to the external terminal 306 for connection to external devices is inserted into the external connector 305. Furthermore, since a plurality of recesses 308 are provided along the external terminal 306 inside the external connector 305, the recesses 308 reduce the concentration of stress caused by resin shrinkage when the resin as a material of the flange 312 is cooled and solidified.

[0041] Since the calibration port 307 is provided in addition to the external port 306 used during the measurement operation of the thermal flow meter 300, it is possible to measure characteristics of each thermal flow meter 300 before shipping to obtain a deviation of the product and store a calibration value for reducing the deviation in the internal memory of the thermal flow meter 300. To prevent the calibration port 307 from interfering with the connection between the external port 306 and external devices after the calibration value setting process, the calibration port 307 is formed in a different shape than the external port 306. In this way, using the thermal flow meter 300, it is possible to reduce a deviation of each thermal flow meter 300 before shipping and improve measurement accuracy. 3. Overall structure of the housing 302 and its effects 3.1 Structures and effects of the bypass passage and the air flow detection section

[0042] Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) illustrates a state of the housing 302 when the front and rear covers 303 and 304 are removed from the thermal flow meter 300. Fig. 5(A) is a left side view showing the housing 302, Fig. 5(B) is a front view showing the housing 302, Fig. 6(A) is a right side view showing the housing 302, and Fig. 6(B) is a rear view illustrating the housing 302. In the housing 302, the measuring section 310 extends from the flange 312 toward the center of the main passage 124, and a bypass passage trench is provided on its front end side to form the bypass passage. In this embodiment, the bypass passage trench is provided on both the front and rear sides of the housing 302. Fig. 5(B) shows a bypass passage trench 332 on the front side and Fig. 6(B) illustrates a bypass passage trench 334 on the rear side. Since an inlet trench 351 for forming the inlet port 350 of the bypass passage and an outlet trench 353 for forming the outlet port 352 are provided at the front end of the housing 302, the gas distant from the inner wall surface of the main passage 124, that is, the gas flowing through the vicinity of the center of the main passage 124, can be received by the inlet port 350 as the measurement target gas 30. The gas flowing through the vicinity of the inlet wall surface of the main passage 124 is affected by the temperature of the wall surface of the main passage 124 and, in many cases, has a different temperature than the average temperature of the gas flowing through the main passage 124, such as the intake air.In addition, the gas flowing through the vicinity of the inner wall surface of the main passage 124 often has a lower flow velocity than the average flow velocity of the gas flowing through the main passage 124. Since the thermal flow meter 300 according to the embodiment is resistant to such an influence, it is possible to suppress a reduction in measurement accuracy.

[0043] The bypass passage formed by the front-side bypass passage trench 332 or the above-described rear-side bypass passage trench 334 is connected to the thermal insulation 315 via the outer wall recessed portion 366, the inlet-side outer wall 335, or the outlet-side outer wall 336. Furthermore, the inlet-side outer wall 335 is provided with the inlet-side protrusion 317, and the outlet-side outer wall 336 is provided with the outlet-side protrusion 318. In this structure, since the thermal flow meter 300 is fixed to the main passage 124 using the flange 312, the measuring section 310 including the circuit assembly 400 is fixed to the main passage 124 with high reliability.

[0044] In this embodiment, the housing 302 is provided with the bypass passage trench for forming the bypass passage, and the covers are installed on the front and rear sides of the housing 302 such that the bypass passage is formed by the bypass passage trench and the covers. In this structure, it is possible to form overall bypass passage trenches as part of the housing 302 in the resin molding process of the housing 302. In addition, since the molds are provided in both surfaces of the housing 302 during the formation of the housing 302, it is possible to form both the bypass passage trench 332 on the front side and the bypass passage trench 334 on the rear side using the molds for both surfaces as part of the housing 302.Since the front and rear covers 303 and 304 are provided in both surfaces of the housing 302, it is possible to obtain the bypass passages in both surfaces of the housing 302. Since the front and bypass passage trenches 332 on the front side and the bypass passage trenches 334 on the back side are formed using the molds on both surfaces of the housing 302, it is possible to form the bypass passage with high accuracy and maintain high productivity.

[0045] Based on Fig. 6(B), a portion of the measurement target gas 30 flowing through the main passage 124 is introduced from the inlet trench 351 forming the inlet port 350 into the interior of the rear bypass passage trench 334 and flows through the interior of the rear bypass passage trench 334. As the gas flows, the rear bypass passage trench 334 gradually becomes deeper, and the measurement target gas 30 slowly moves toward the forward direction while flowing along the trench. Specifically, the rear bypass passage trench 334 is provided with a steep slope portion 347 that steeply descends toward the inlet-side portion 342 of the circuit assembly 400, so that a portion of the air with a low mass moves along the steep slope portion 347 and then flows through the Fig. 5(B) side of the measuring surface 430 in the inlet-side section 342 of the circuit assembly 400. Since a foreign body having a large mass has difficulty in changing its path steeply due to an inertial force, it moves to the Fig. 6(B) shown side of the back of the measuring surface 431. The foreign matter then flows through the outlet-side section 341 of the circuit assembly 400 to the Fig. 5(B) shown measuring surface 430.

[0046] Based on Fig. 7, a flow of the measurement target gas 30 near the portion 436 of the exposed heat transfer surface is described. In the bypass passage trench 332 on the front side of Fig. 5(B), the air as a measurement target gas 30 moving from the inlet-side portion 342 of the circuit board 400 to the bypass passage trench 332 on the front side flows along the measurement surface 430, and heat transfer is performed with the air flow detecting portion 602 to measure a flow rate using the heat transfer surface exposed portion 436 provided in the measurement surface 430. Both the measurement target gas 30 passing over the measurement surface 430 and the air flowing from the outlet-side portion 341 of the circuit assembly 400 to the bypass passage trench 332 on the front side flow along the bypass passage trench 332 on the front side and are discharged from the outlet trench 353 to form the outlet port 352 to the main passage 124.

[0047] A substance with a large mass such as an impurity mixed into the measurement target gas 30 has a high inertial force and has difficulty making its way along the surface of the steep slope section 347 of Fig. 6(B), where a depth of the trench becomes steeply deeper, to change steeply toward the deep side of the trench. For this reason, since a foreign matter with a large mass moves over the side of the back of the measuring surface 431, it is possible to suppress the foreign matter from passing through the vicinity of the heat transfer surface exposed portion 436. In this embodiment, since most foreign matters other than gas with a large mass pass over the back of the measuring surface 431, which is a rear surface of the measuring surface 430, it is possible to reduce the influence of contamination caused by a foreign matter such as an oil component, carbon, or a pollutant, and suppress deterioration of the measurement accuracy.That is, since the path of the measurement target gas 30 changes steeply along an axis transverse to the flow axis of the main passage 124, it is possible to reduce the influence of a foreign matter mixed into the measurement target gas 30.

[0048] In this embodiment, the flow path including the bypass passage groove 334 on the rear side is directed from the front end of the housing 302 along a curved line toward the flange, and the gas flowing through the bypass passage on the side closest to the flange flows inversely to the flow of the main passage 124, so that the bypass passage on the rear surface side as one side of this reverse flow is connected to the bypass passage formed on the front surface side as the other side. As a result, it is possible to easily attach the heat transfer surface exposed portion 436 of the circuit board 400 to the bypass passage and easily receive the measurement target gas 30 at the location near the center of the main passage 124.

[0049] In this embodiment, a configuration is provided in which the bypass passage trench 334 on the rear side and the bypass passage trench 332 on the front side are penetrated on the front and back sides of the flow direction of the measuring surface 430 to measure the flow rate. Meanwhile, the front end side of the circuit assembly 400 is not supported by the housing 302, but has a cavity portion 382, ​​so that the space of the inlet-side portion 342 of the circuit assembly 400 is connected to the space of the outlet-side portion 341 of the circuit assembly 400.By using the configuration that penetrates the inlet-side portion 342 of the circuit assembly 400 and the outlet-side portion 341 of the circuit assembly 400, the bypass passage is formed such that the measurement target gas 30 moves from the bypass passage groove 334 formed on the back side in one surface of the case 302 to the bypass passage groove 394 formed on the other surface of the case 302. With this configuration, it is possible to form the bypass passage groove on both surfaces of the case 302 through a single resin molding process and to perform the molding with a structure for matching the bypass passage grooves on both surfaces.

[0050] By clamping both sides of the sensing surface 430 formed in the circuit assembly 400 using a mold to form the housing 302, it is possible to form the configuration penetrating the inlet-side portion 342 of the circuit assembly 400 and the outlet-side portion 341 of the circuit assembly 400, perform resin molding for the housing 302, and embed the circuit assembly 400 in the housing 302. Since the housing 302 is formed by inserting the circuit assembly 400 into the mold in this way, it is possible to embed the circuit assembly 400 and the heat transfer surface exposed portion 436 into the bypass passage with high accuracy.

[0051] In this embodiment, a configuration penetrating the inlet-side portion 342 of the circuit assembly 400 and the outlet-side portion 341 of the circuit assembly 400 is provided. However, a configuration penetrating the inlet-side portion 342 and / or the outlet-side portion 341 of the circuit assembly 400 may also be provided, and the bypass passage shape connecting the bypass passage trench 334 on the back side and the bypass passage trench 332 on the front side may be formed by a single resin molding process.

[0052] On both sides of the bypass passage trench, an inner wall of the rear bypass passage 391 and an outer wall of the rear bypass passage 392 are provided on the rear side 334, and the inner side surface of the rear cover 304 abuts against the front end portions in the height direction of both the inner wall of the rear bypass passage 391 and the outer wall of the rear bypass passage 392, so that the rear bypass passage is formed in the case 302.In addition, on both sides of the front side bypass passage trench 332, an inner wall of the front side bypass passage 393 and an outer wall of the front side bypass passage 394 are provided, and the inner side surface of the front cover abuts the front end portions in the height direction of the inner wall of the front side bypass passage 393 and the outer side wall of the front side bypass passage 334, so that the front side bypass passage is formed in the case 302.

[0053] In this embodiment, the measurement target gas 30 flows in a dividing manner across the measurement surface 430 and its rear surface, and the exposed heat transfer surface portion 436 is provided for measuring the flow rate in one of them. However, the measurement target gas 30 can only pass across the front surface side of the measurement surface 430, instead of dividing the measurement target gas 30 into two passages. By curving the bypass passage along a second axis that is transverse to the first axis of the flow direction of the main passage 124, it is possible to collect a foreign matter mixed into the measurement target gas 30 on the side where the curve of the second axis is small. By providing the measurement surface 430 and the exposed heat transfer surface portion 436 on the side where the curve of the second axis is large, it is possible to reduce the influence of a foreign matter.

[0054] In this embodiment, the sensing surface 430 and the exposed heat transfer surface portion 436 are provided in a connecting portion between the front-side bypass passage trench 332 and the rear-side bypass passage trench 334. However, the sensing surface 430 and the exposed heat transfer surface portion 436 may be provided in the front-side bypass passage trench 332 or the rear-side bypass passage trench 334, rather than in the connecting portion between the front-side bypass passage trench 332 and the rear-side bypass passage trench 334.

[0055] In a part of the section 436 of the exposed heat transfer surface provided in the measuring surface 430 for measuring a flow (as will be described below with reference to Fig. 7), a constriction shape is formed, so that the flow velocity increases due to the constriction effect and the measurement accuracy is improved. Furthermore, even if a vortex is generated in a gas flow on the inlet side of the exposed heat transfer surface portion 436, it is possible to eliminate or reduce the vortex by utilizing the constriction and improve the measurement accuracy.

[0056] Based on Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B), where the inlet-side outer wall 335 has a recessed shape that is recessed toward the outlet side in a neck portion of the temperature detection portion 452, an outer wall recessed portion 366 is provided. Due to this outer wall recessed portion 366, a distance between the temperature detection portion 452 and the outer wall recessed portion 366 increases, so it is possible to reduce the influence of heat transmitted via the inlet-side outer wall 335.

[0057] Although the circuit assembly 400 is wrapped by the fastening portion 372 for fixing the circuit assembly 400, it is possible to increase a fixing force for the circuit assembly 400 by further fixing the circuit assembly 400 using the outer wall recess portion 366. The fastening portion 372 wraps the circuit assembly 400 along a flow axis of the measurement target gas 30. Meanwhile, the outer wall recess portion 366 wraps the circuit assembly 400 across the flow axis of the measurement target gas 30. That is, the circuit assembly 400 is wrapped in such a manner that the wrapping direction is different from the fastening portion 372. Since the circuit assembly 400 is wrapped along the two different directions, the fixing force is increased.Although the outer wall recessed portion 366 is part of the inlet-side outer wall 335, the circuit assembly 400 may be wrapped using the outlet-side outer wall 336 instead of the inlet-side outer wall 335 in a direction different from the fastening portion 372 to increase the fastening force. For example, a plate portion of the circuit assembly 400 may be wrapped by the outlet-side outer wall 336, or the circuit assembly 400 may be wrapped using a recess recessed in the inlet direction or a protrusion protruding in the inlet direction provided in the outlet-side outer wall 336.Since the outer wall recess portion 366 is provided in the inlet-side outer wall 335 to enclose the circuit assembly 400, it is possible to achieve an effect of increasing the thermal resistance between the temperature detection portion 452 and the inlet-side outer wall 335 in addition to fixing the circuit assembly 400.

[0058] Since the outer wall recessed portion 366 is provided in a neck portion of the temperature detecting portion 452, it is possible to reduce the influence of heat transmitted from the flange 312 or the heat insulator 315 via the inlet-side outer wall 335. Furthermore, a temperature measuring recess 368 formed by a cut between the inlet-side protrusion 317 and the temperature detecting portion 452 is provided. By using the temperature measuring recess 368, it is possible to reduce heat transmission via the inlet-side protrusion 317 to the temperature detecting portion 452. As a result, it is possible to improve the detection accuracy of the temperature detecting portion 452. In particular, the inlet-side protrusion 317, because it has a large cross-section, easily transmits heat, and a heat transmission suppressing functionality of the temperature measuring recess 368 becomes important. 3.2 Structure and effects of the air flow detection section of the bypass passage

[0059] Fig. Fig. 7 is a partially enlarged view showing a state in which the measurement surface 430 of the circuit package 400 is arranged within the bypass passage trench, as a cross-sectional view taken along the line AA of Fig. 6(A) and Fig. 6(B). It is noted that Fig. 7 is a conceptual representation that compares to the specific configuration of Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) has omissions and is simplified, and that details may be slightly changed. The left side of Fig. 7 is a terminal end portion of the bypass passage trench 334 on the rear side, and the right side is a starting end portion of the bypass passage trench 332 on the front side. Although this is Fig. 7, penetrating portions are provided on both the left and right sides of the circuit assembly 400 with the measuring surface 430, and the bypass passage trench 334 on the back side and the bypass passage trench 332 on the front side are connected to the left and right sides of the circuit assembly 400 with the measuring surface 430.

[0060] The measurement target gas 30 received from the inlet port 350 and flowing through the rear side bypass passage including the rear side bypass passage trench 334 is supplied from the left side Fig. 7. Part of the measurement target gas 30 flows through the penetrating portion of the inlet-side portion 342 of the circuit assembly 400 to a flow path 386 including the front side of the measurement surface 430 of the circuit assembly 400 and the protrusion 356 provided in the front cover 303. The other measurement target gas 30 flows to a flow path 387 formed by the rear side of the measurement surface 431 and the rear cover 304. Then, the measurement target gas 30 flowing through the flow path 387 moves to the bypass passage trench 332 on the front side via the penetrating portion of the outlet side portion 341 of the circuit assembly 400 and is combined with the measurement target gas 30 flowing through the flow path 386, so that it flows through the bypass passage trench 332 on the front side and is discharged from the outlet port 352 into the main passage 124.It is noted that the projection 358 provided in the rear cover 304, as shown in . Fig. 7, may protrude to the rear of the measuring surface 431 in the flow path 387.

[0061] Since the bypass passage groove is formed such that the flow path of the measurement target gas 30 guided through the penetrating portion of the inlet-side portion 342 of the circuit assembly 400 from the bypass passage groove 334 on the rear side to the flow path 386 is more curved than the flow path guided to the flow path 387, a substance with a large mass, such as an impurity contained in the measurement target gas 30, is collected in the flow path 387, which is less curved. For this reason, there is almost no flow of a foreign matter into the flow path 386.

[0062] The flow path 386 is structured to form a constriction such that the front cover 303 is provided following the front end portion of the bypass passage trench 332 on the front side, and the protrusion 356 protrudes seamlessly toward the measurement surface 430 side. The measurement surface 430 is arranged on one side of the constriction portion of the flow path 386 and is provided with the heat transfer surface exposed portion 436 to perform heat transfer between the air flow detection portion 602 and the measurement target gas 30. In order to perform the measurement of the air flow detection portion 602 with high accuracy, the measurement target gas 30 preferably forms a laminar flow with little turbulence in the heat transfer surface exposed portion 436. In addition, the measurement accuracy is further improved with the faster flow rate.For this reason, the constriction is formed such that the protrusion 356 provided in the front cover 303 opposite the measuring surface 430 protrudes seamlessly toward the measuring surface 430. This constriction reduces turbulence in the measurement target gas 30 to make the flow more laminar. Furthermore, the flow measurement accuracy is improved because the flow velocity increases in the constriction portion and because the exposed heat transfer surface portion 436 for measuring the flow is disposed in the constriction portion.

[0063] Since the constriction is formed such that the projection 356 protrudes into the interior of the bypass passage trench to oppose the exposed heat transfer surface portion 436 provided on the measurement surface 430, it is possible to improve the measurement accuracy. The projection 356 for forming the constriction is provided on the cover, which is opposite the exposed heat transfer surface portion 436 provided on the measurement surface 430. Since Fig. 7, the cover opposite the exposed heat transfer surface portion 436 provided on the measuring surface 430 is the front cover 303, the protrusion 356 is provided in the front cover 303. Alternatively, the protrusion 356 may also be provided in the cover opposite the exposed heat transfer surface portion 436 provided on the measuring surface 430 of the front or rear cover 303 or 304. Depending on which of the surfaces of the measuring surface 430 and the exposed heat transfer surface portion 436 are provided in the circuit assembly 400, the cover opposite the exposed heat transfer surface portion 436 is changed.

[0064] Based on Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B), a press mark 442 of the mold used in the resin molding process for the circuit assembly 400 remains on the back of the measuring surface 431 as a rear surface of the heat transfer surface exposed portion 436 provided at the measuring surface 430. The press mark 442 does not particularly hinder the flow measurement and does not cause a problem even if the press mark 442 remains. Furthermore, as described below, it is important to protect a semiconductor diaphragm of the air flow sensing portion 602 when the circuit assembly 400 is formed by resin molding. For this reason, pressing the rear surface of the heat transfer surface exposed portion 436 is important. Furthermore, it is important to prevent resin covering the circuit assembly 400 from flowing to the heat transfer surface exposed portion 436.From this point of view, the inflow of resin is suppressed by enclosing the sensing surface 430 including the exposed heat transfer surface portion 436 using a mold and pressing the rear surface of the exposed heat transfer surface portion 436 using another mold. Since the circuit assembly 400 is manufactured by transfer molding, resin pressure is high, and pressing from the rear surface of the exposed heat transfer surface portion 436 is important. Furthermore, since a semiconductor diaphragm is used in the airflow sensing portion 602, it is preferable to form a vent passage for a recess created by the semiconductor diaphragm. In order to hold and fix a plate and the like for forming the vent passage, pressing from the rear surface of the exposed heat transfer surface portion 436 is important. 3.3 Structure for fixing the circuit assembly 400 using the housing 302 and its effects

[0065] The following is again based on Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) describes the attachment of the circuit assembly 400 to the housing 302 by a resin molding process. The circuit assembly 400 is arranged and attached to the housing 302 in such a way that the measuring surface 430 formed on the front surface of the circuit assembly 400 is arranged in a predetermined position of the bypass passage groove to form the bypass passage, for example, in the embodiment of Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) to form a connecting portion between the front-side bypass passage trench 332 and the rear-side bypass passage trench 334. A portion for burying and fixing the circuit assembly 400 in the housing 302 by resin molding is provided as a fixing portion 372 for burying and fixing the circuit assembly 400 in the housing 302 on the side slightly closer to the flange 312 from the bypass passage trench. The fixing portion 372 is buried so as to cover the outer periphery of the circuit assembly 400 formed by the first resin molding process.

[0066] As in Fig. As shown in Fig. 5(B), the circuit assembly 400 is fixed by the fixing portion 372. The fixing portion 372 includes a circuit assembly 400 using a plane having a height at which the front cover 303 and a thin portion 376 are adjacent to each other. By making resin covering a portion corresponding to the portion 376 thin, it is possible to alleviate contraction caused when a temperature of the resin is cooled during formation of the fixing portion 372 and to reduce a concentration of stress applied to the circuit assembly 400. If the back side of the circuit assembly 400 is in the position shown in Fig. 6(B) shown above, it is possible to obtain better effects.

[0067] The entire surface of the circuit assembly 400 is not covered by a resin used to form the housing 302, but on the side of the flange 312 of the fixing portion 372, a portion is provided in which the outer wall of the circuit assembly 400 is exposed. In the embodiment of Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B), the area of ​​a portion exposed by the resin of the case 302 but not wrapped by the case 302 is larger than the area of ​​a portion wrapped by the resin of the case 302 of the outer peripheral surface of the circuit package 400. Moreover, a portion of the measurement surface 430 of the circuit package 400 is also exposed by the resin of the case 302.

[0068] Since the periphery of the circuit assembly 400 is wrapped in the second resin molding process for forming the housing 302 by forming a part of the fixing portion 372 covering the outer wall of the circuit assembly 400 in the shape of a thin strip over the entire periphery, it is possible to alleviate excessive stress concentration caused by volume contraction during solidification of the fixing portion 372. This excessive stress concentration may adversely affect the circuit assembly 400.

[0069] In order to more robustly fix the circuit assembly 400 with a small area by reducing the area of ​​a portion enveloped by the resin of the case 302 from the outer peripheral surface of the circuit assembly 400, it is preferable to increase the adhesion of the circuit assembly 400 to the outer wall in the fixing portion 372. When a thermoplastic resin is used to form the case 302, it is preferable that the thermoplastic resin penetrates into fine asperities on the outer wall of the circuit assembly 400 while having a low viscosity, and that the thermoplastic resin solidifies while having penetrated into the fine asperities of the outer wall. In the resin molding process for forming the case 302, it is preferable that the inlet port of the thermoplastic resin be provided in and near the fixing portion 372.The viscosity of the thermoplastic resin increases as the temperature decreases, causing it to solidify. Thus, by flowing the high-temperature thermoplastic resin into or near the mounting portion 372, the low-viscosity thermoplastic resin can solidify while adhering to the outer wall of the circuit assembly 400. As a result, a temperature decrease of the thermoplastic resin is suppressed and a low-viscosity state is maintained, thus improving the adhesion between the circuit assembly 400 and the mounting portion 372.

[0070] By roughening the outer wall surface of the circuit assembly 400, it is possible to improve the adhesion between the circuit assembly 400 and the mounting portion 372. As a method for roughening the outer wall surface of the circuit assembly 400, a roughening method for forming fine asperities on the surface of the circuit assembly 400, such as a satin finishing treatment after the circuit assembly 400 is formed by the first resin molding process, is known. As the roughening method for forming fine asperities on the surface of the circuit assembly 400, the roughening can be achieved using, for example, shot blasting. Furthermore, the roughening can be achieved by laser machining.

[0071] 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 onto the mold with the sheet on the surface. Also using this method, it is possible to form fine unevenness on a surface of the circuit assembly 400 and roughen it. Alternatively, an unevenness may be applied to the inner side of the mold for forming the circuit assembly 400 to roughen the surface of the circuit assembly 400. The surface portion of the circuit assembly 400 for this roughening is at least a portion where the fixing portion 372 is provided. In addition, adhesion is further enhanced by roughening a surface portion of the circuit assembly 400 where the outer wall recessed portion 366 is provided.

[0072] When machining the unevenness for the surface of the circuit board 400 using the above-mentioned sheet, the depth of the trench depends on the thickness of the sheet. If the thickness of the sheet increases, the molding process becomes difficult during the first resin molding process, so the thickness of the sheet has a limitation. If the thickness of the sheet decreases, the depth of the unevenness provided on the sheet has a limitation in advance. For this reason, it is preferable that the depth of the unevenness between the bottom and top of the unevenness be set to 10 μm or greater and 20 μm or less when using the above-mentioned sheet. At a depth less than 10 μm, the adhesion effect is deteriorated. At a depth greater than 20 μm, it is difficult to obtain from the above-mentioned thickness of the sheet.

[0073] In roughening methods other than the above-mentioned methods of using the sheet, it is preferable to set a thickness of the resin in the first resin molding process for forming the circuit board 400 to 2 mm or less. For this reason, it is difficult to increase the depth of the unevenness between the bottom and top of the unevenness to 1 mm or more. Conceptually, it is expected that the adhesion between the resin covering the circuit board 400 and the resin used to form the housing 302 increases as the depth of the unevenness between the bottom and top of the unevenness on the surface of the circuit board 400 increases. However, the depth of the unevenness between the bottom and top of the unevenness is preferably set to 1 mm or less for the reason described above.That is, if 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 preferable to increase the adhesion between the resin covering the circuit package 400 and the resin used to form the case 302.

[0074] A thermal expansion coefficient differs between the thermosetting resin used to form the circuit assembly 400 and the thermoplastic resin used to form the housing 302 with the mounting portion 372. It is preferable to prevent excessive stress generated from this difference in thermal expansion coefficient from being exerted on the circuit assembly 400.

[0075] By forming the fixing portion 372 that wraps the outer periphery of the circuit assembly 400 in a strip shape and narrowing the width of the strip, it is possible to mitigate stress caused by a difference in thermal expansion coefficient being applied to the circuit assembly 400. A width of the strip of the fixing portion 372 is set to 10 mm or less, and preferably to 8 mm or less. In this embodiment, since the outer wall recessed portion 366 as a part of the inlet-side outer wall 335 of the housing 302 and the fixing portion 372 wrap the circuit assembly 400 to fix the circuit assembly 400, it is possible to further reduce the width of the strip of the fixing portion 372. For example, the circuit assembly 400 can be fixed if the width is set to 3 mm or more.

[0076] To reduce stress caused by the difference in thermal expansion coefficient, a portion covered by the resin used to form the housing 302 and an exposed portion without covering are provided on the surface of the circuit assembly 400. A plurality of portions are provided where the surface of the circuit assembly 400 is exposed from the resin of the housing 302, and one of them is the measurement surface 430 having the above-described heat transfer surface exposed portion 436. Furthermore, a portion exposed to a part of the flange 312 side with respect to the fixing portion 372 is provided. Furthermore, the outer wall recessed portion 366 is formed to expose a portion of the inlet side with respect to the outer wall recessed portion 366, and this exposed portion serves as a support portion that supports the temperature detection portion 452.A recess is formed such that a portion of the outer surface of the circuit assembly 400 on the flange 312 side relative to the fixing portion 372 surrounds the circuit assembly 400 around its outer periphery, specifically, the side opposite the flange 312 from the outlet side of the circuit assembly 400, and further, the outlet side of the portion near the terminal of the circuit assembly 400. Since the recess is formed around the portion where the surface of the circuit assembly 400 is exposed, it is possible to reduce the amount of heat transferred from the main passage 124 to the circuit assembly 400 via the flange 312 and suppress deterioration of measurement accuracy caused by the heat.

[0077] A recess is formed between the circuit assembly 400 and the flange 312, and this recess serves as a terminal connector 320. The connection terminal 412 of the circuit assembly 400 and the external terminal inner coupling 361 positioned on the housing 302 side of the external terminal 306 are electrically connected to each other using this terminal connector 320 by spot welding, laser welding, and the like. The recess of the terminal connector 320 can suppress heat transfer from the housing 302 to the circuit assembly 400 described above and is provided as a space that can be used for performing connection work between the connection terminal 412 of the circuit assembly 400 and the external terminal inner coupling 361 of the external terminal 306. 3.4 Structure of the terminal connector 320 and its effects

[0078] Fig. Figure 8 is an enlarged view showing the terminal connector 320 of the housing 302 of Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B). However, the terminal connector 320 differs from Fig. 8 from that of 5(A), 5(B), 6(A) and 6(B) for the following reasons. More specifically, the inner couplings 361 of the outer connections in Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) are separated from each other. In contrast, the inner couplings 361 of the outer connections are Fig. 8, they are not separated from each other, but are connected to each other by the connecting portion 365. Although each inner coupling 361 of the outer terminals, which protrudes toward the circuit assembly 400 side of the outer terminal 306, overlaps or is close to the corresponding connection terminals 412, each outer terminal 306 is fixed to the housing 302 by resin molding in the second molding process. In order to prevent deformation or deviation of the arrangement of each outer terminal 306, according to an embodiment, the outer terminal 306 is fixed to the housing 302 by the resin molding process (second resin molding process) for forming the housing 302, while the inner couplings 361 of the outer terminals are connected to each other by the connecting portion 365.Alternatively, the outer terminal 306 may be fixed to the housing 302 by the second resin molding process after the connecting terminals 412 and the inner coupling 361 of the outer terminals have been fixed. 3.5 Control of the finished product through the first resin molding process

[0079] In the embodiment from Fig. 8, the number of terminals provided in the circuit assembly 400 is greater than the number of inner couplings 361 of the outer terminals. Of the terminals of the circuit assembly 400, each of the connecting terminals 412 is connected to each of the inner couplings 361 of the outer terminal, and the terminals 414 are not connected to the inner coupling 361 of the outer terminals. That is, although the terminals 414 are provided in the circuit assembly 400, they are not connected to the inner coupling 361 of the outer terminals.

[0080] In addition to the connection port 412, which is connected to the inner coupling 361 of the outer port, Fig. 8, the terminal 414 is provided that is not connected to the inner coupling 361 of the outer terminal. After the circuit assembly 400 has been manufactured through the first resin molding process, it is checked whether the circuit assembly 400 is operating properly and whether an anomaly in the electrical connection was generated in the first resin molding process. As a result, it is possible to maintain high reliability for each circuit assembly 400. During such an inspection of the circuit assembly 400, the terminal 414 that is not connected to the inner coupling 361 of the outer terminal is used. Since the terminal 414 is not used after the inspection work, this unused terminal 414 can be cut out at the base of the circuit assembly 400 after the inspection, or it can be, as shown in Fig. 8, buried in the resin serving as the terminal-side fixing portion 362. By providing the terminal 414 not connected to the inner coupling 361 of the outer terminal in this manner, it is possible to control whether an abnormality is generated in the circuit assembly 400 manufactured by the first resin molding process and to maintain high reliability. 3.6 Connection structure between the recess inside the housing 302 and outside the thermal flow meter 300

[0081] As shown in the partially enlarged view from Fig. 8, a hole 364 is provided in the housing 302. The hole 364 is connected to the opening 309 which is provided in the interior of the Fig. 4(A). According to the embodiment, both sides of the housing 302 are sealed with the front and rear covers 303 and 304. If the hole 364 is not provided, a difference between the air pressure within the recess and the atmospheric pressure is generated due to a temperature change of the air within the recess including the terminal connector 320. It is preferable to reduce such a pressure difference. For this reason, the hole 364 connected to the opening 309 is provided inside the external connector 305 within the recess of the housing 302. In order to improve the reliability of the electrical connection, the external connector 305 has a structure resistant to the adverse effects of water and the like.By providing the opening 309 inside the external connector 305, it is possible to prevent the intrusion of water and a foreign matter such as a contaminant or dust from the opening 309. 3.7 Formation of the housing 302 by the second resin molding process and effects thereof

[0082] In the case described above Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. In the case 302 shown in FIG. 6(B), the circuit assembly 400 including the airflow detection section 602 or the processing unit 604 is manufactured through the first resin molding process. Subsequently, the case 302, which has, for example, the front-side bypass passage trench 322 or the rear-side bypass passage trench 334 for forming the bypass passage through which the measurement target gas 30 flows, is manufactured through the second resin molding process. Through this second resin molding process, the circuit assembly 400 is embedded in the resin of the case 302 and fixed to the interior of the case 302 by resin molding. As a result, the air flow detecting portion 602 performs heat transfer with the measurement target gas 30, so that a configuration relationship such as a positional relationship or a directional relationship is established between the flow rate measuring heat transfer exposed surface portion 436 and the bypass passage including, for example,of the bypass passage trench 332 on the front side or the bypass passage trench 334 on the back side can be maintained with significantly high accuracy. Furthermore, it is possible to suppress an error or deviation generated in each circuit assembly 400 to a very small value. As a result, it is possible to significantly improve the measurement accuracy of the circuit assembly 400. For example, compared with a conventional method in which attachment is performed using an adhesive, it is possible to improve the measurement accuracy by two or more. Since the thermal flow meter 300 is usually manufactured in large quantities, the method of using an adhesive together with accurate measurement has a limitation on improving the measurement accuracy.On the other hand, if the circuit assembly 400 is manufactured through the first resin molding process as in this embodiment, and then the bypass passage is formed in the second resin molding process to form the bypass passage in which the measurement target gas 30 flows while fixing the circuit assembly 400 and the bypass passage, it is possible to significantly reduce deviation in measurement accuracy and significantly improve the measurement accuracy of each thermal flow meter 300. This is similar to the embodiment of FIG. Fig. 7 and to the embodiments of Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. 6(B).

[0083] Further on the basis of the embodiment, for example from Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. 6(B), it is possible to fix the circuit assembly 400 to the housing 302 in such a manner that a relationship between the bypass passage groove 332 on the front side, the bypass passage groove 334 on the back side, and the heat transfer surface exposed portion 436 is set to a specific relationship. As a result, in each of the thermal flow meters 300 that is mass-produced, a positional relationship or a configuration relationship between the heat transfer surface exposed portion 436 of each circuit assembly 400 and the bypass passage can be uniformly obtained with significantly high accuracy. Since the bypass passage groove in which the heat transfer surface exposed portion 436 of the circuit assembly 400 is formed, for example,Since the bypass passage trench 332 on the front side and the bypass passage trench 334 on the back side can be formed with significantly high accuracy, a work for forming the bypass passage in this bypass passage trench is a work of covering both sides of the case 302 using the front or rear cover 303 or 304. This work is very simple and is a work process that has few factors of deteriorating measurement accuracy. In addition, the front or rear cover 303 or 304 is manufactured by a resin molding process with high formation accuracy. Thus, it is possible to form the bypass passage provided in a specific relationship with the heat transfer surface exposed portion 436 of the circuit board 400 with high accuracy. In this way, it is possible to achieve high productivity in addition to improving measurement accuracy.

[0084] In comparison, the thermal flowmeter in the related field was manufactured by fabricating the bypass passage and then bonding the measuring section to the bypass passage using an adhesive. This method of using an adhesive is disadvantageous because the thickness of the adhesive is uneven and the position or angle of the adhesive is different in each product. Therefore, there was a limitation on improving measurement accuracy. If this work is performed in mass production, it is even more difficult to improve measurement accuracy.

[0085] In the embodiment according to the invention, the circuit assembly 400 with the airflow sensing portion 602 is first manufactured through a first resin molding process, and then the circuit assembly 400 is fixed by resin molding, while the bypass passage trench for forming the bypass passage is formed by resin molding through a second resin molding process. As a result, it is possible to form the shape of the bypass passage trench and fix the airflow sensing portion 602 to the bypass passage trench with significantly high accuracy.

[0086] On the surface of the circuit board 400, a portion related to flow measurement is formed, such as the exposed heat transfer surface portion 436 of the air flow sensing portion 602 or the sensing surface 430 incorporated into the exposed heat transfer surface portion 436. Subsequently, the sensing surface 430 and the exposed heat transfer surface portion 436 are exposed from the resin used to form the housing 302. That is, the exposed heat transfer surface portion 436 and the sensing surface 430 around the exposed heat transfer surface portion 436 are not covered by the resin used to form the housing 302.The measuring surface 430 formed by resin molding the circuit assembly 400, the exposed heat transfer surface portion 436, or the temperature detection portion 452 is directly used to measure a flow rate of the thermal flow meter 300 or a temperature even after the resin molding of the housing 302. As a result, the measurement accuracy is improved.

[0087] In the embodiment according to the invention, the circuit assembly 400 is formed integrally with the housing 302 to fix the circuit assembly 400 to the housing 302 having the bypass passage. Thus, it is possible to fix the circuit assembly 400 to the housing 302 with a small fixing area. That is, it is possible to increase the surface area of ​​the circuit assembly 400 that is not in contact with the housing 302. The surface of the circuit assembly 400 that is not in contact with the housing 302 is exposed, for example, to form a recess. The heat of the intake pipe is transferred to the housing 302 and is then transferred from the housing 302 to the circuit assembly 400.Even if the contact area between the housing 302 and the circuit board 400 is reduced, instead of enclosing the entire surface or most of the surface of the circuit board 400 with the housing 302, it is possible to maintain high reliability with high accuracy and fix the circuit board 400 to the housing 302. For this reason, it is possible to suppress heat transfer from the housing 302 to the circuit board 400 and suppress a reduction in measurement accuracy.

[0088] In the Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. In the embodiment illustrated in Fig. 6(B), the area A of the exposed surface of the circuit package 400 can be set equal to or larger than the area B covered by a molding material used to form the housing 302. In the embodiment, the area A is larger than the area B. As a result, it is possible to suppress heat transfer from the housing 302 to the circuit package 400. In addition, it is possible to reduce stress generated by a difference between a thermal expansion coefficient of the thermosetting resin used to form the circuit package 400 and a thermal expansion coefficient of the thermoplastic resin used to form the housing 302. 4. Appearance of the circuit assembly 4004.1 Formation of the measuring surface 430 with the section 436 of the exposed heat transfer surface

[0089] Fig. 11(A) to 11(C) illustrate an appearance of the circuit assembly 400 formed by the first resin molding process. Note that the hatched portion in the appearance of the circuit assembly 400 indicates a mounting surface 432 where the circuit assembly 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 assembly 400 is manufactured by the first resin molding process. Fig. 11(A) is a left side view showing the circuit assembly 400, Fig. 11(B) is a front view illustrating the circuit assembly 400, and Fig. 11(C) is a rear view illustrating the circuit assembly 400. The circuit assembly 400 is embedded with the airflow sensing section 602 or the processing unit 604 described below, and they are integrally molded using a thermosetting resin.

[0090] On the surface of the circuit assembly 400 made of Fig. 11(B), the measurement surface 430, which serves as a plane for flowing the measurement target gas 30, is formed in a shape that runs in a flow direction of the measurement target gas 30. In this embodiment, the measurement surface 430 has a rectangular shape that runs in the flow direction of the measurement target gas 30. As shown in Fig. As shown in Figure 11(A), the measurement surface 430 is formed thinner than other portions, and a part of it is provided with the exposed heat transfer surface portion 436. The embedded air flow detection portion 602 performs heat transfer to the measurement target gas 30 via the exposed heat transfer surface portion 436 to measure a condition 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 passage 124.

[0091] To detect a condition of the measurement target gas 30 using the embedded air flow detecting section 602 (see Fig. 14) with high accuracy, the gas flowing past the vicinity of the exposed heat transfer surface portion 436 preferably forms a laminar flow with little turbulence. For this reason, it is preferable that there be no height difference between the side surface of the flow path of the exposed heat transfer surface portion 436 and the plane of the measuring surface 430 that guides the gas. With this configuration, it is possible to suppress uneven stress or deformation from being applied to the air flow sensing portion 602 while maintaining high flow measurement accuracy. Note that the above-mentioned height difference may be provided if it does not affect the flow measurement accuracy.

[0092] As in Fig. As shown in Fig. 11(C), a press mark 442 of the mold supporting an inner substrate or plate during resin molding of the circuit assembly 400 remains on the rear surface of the measurement surface 430 of the heat transfer exposed surface portion 436. The heat transfer exposed surface portion 436 is used to perform heat exchange with the measurement target gas 30. In order to accurately measure a condition of the measurement target gas 30, it is preferable to properly perform heat transfer between the air flow detection portion 602 and the measurement target gas 30. For this reason, it is necessary to prevent a part of the heat transfer exposed surface portion 436 from being covered by the resin in the first resin molding process.Molds are installed in both the exposed heat transfer surface portion 436 and the back of the measurement surface 431 as a rear surface thereof, and inflow of the resin to the exposed heat transfer surface portion 436 is prevented using this mold. A press mark 442 having a concave shape is formed on the rear surface of the exposed heat transfer surface portion 436. Preferably, a device serving as the airflow detection portion 602 or the like is disposed nearby in this portion to discharge the heat generated by the device to the outside as much as possible. The formed concave portion is less affected by the resin and easily discharges heat.

[0093] In an airflow detection section (flow detection element) 602, a semiconductor diaphragm corresponding to the exposed heat transfer surface portion 436 containing a semiconductor device is formed. The semiconductor diaphragm can be obtained by forming a recess on the rear surface of the airflow detection element 602. If the recess is covered, the semiconductor diaphragm will be deformed, and measurement accuracy will deteriorate due to a change in pressure within the recess caused by a change in temperature. For this reason, in this embodiment, an opening 438 is provided on the front surface of the circuit package 400, communicating with the recess of the rear surface of the semiconductor diaphragm, and a communication channel for connecting the recess of the rear surface of the semiconductor diaphragm and the opening 438 is provided within the circuit package 400.It is noted that the opening 438 in the in . 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.

[0094] It is necessary to form the opening 438 through the first resin molding process while suppressing resin inflow to the portion of the opening 438 by fitting molds to both a portion of the opening 438 and a rear surface thereof and pressing the molds. The following describes the formation of the opening 438 and the communication channel connecting the recess on the rear surface of the semiconductor diaphragm and the opening 438.

[0095] 4.2 Formation of the Temperature Detection Section 452 and the Protrusion 424 and Effects Thereof The temperature detection section 452 provided in the circuit package 400 is also provided in the front end of the protrusion 424 extending in the inlet direction of the measurement target gas 30 to support the temperature detection section 452, and also has a function of detecting a temperature of the measurement target gas 30. In order to detect a temperature of the measurement target gas 30 with high accuracy, it is preferable to reduce heat transfer to portions other than the measurement target gas 30 as much as possible. The protrusion 424 supporting the temperature detection section 452 has a shape having a front end thinner than its base and is provided with the temperature detection section 452 in its front end portion.Because of such a shape, it is possible to reduce the influence of heat from the neck portion of the projection 424 on the temperature detecting portion 452.

[0096] After the temperature of the measurement target gas 30 is detected using the temperature detection section 452, the measurement target gas 30 flows along the protrusion 424 to bring the temperature of the protrusion 424 closer to the temperature of the measurement target gas 30. As a result, it is possible to suppress the influence of the temperature of the neck portion of the protrusion 424 on the temperature detection section 452. Specifically, in this embodiment, the temperature detection section 452 is thinner near the protrusion 424 having the temperature detection section 452 and thickens toward the neck of the protrusion. For this reason, the measurement target gas 30 flows along the shape of the protrusion 424 to effectively cool the protrusion 424.

[0097] The hatched portion of the neck portion of the protrusion 424 is a mounting surface 432 covered by the resin used to form the housing 302 in the second resin molding process. A recess is provided in the hatched portion of the neck portion of the protrusion 424. This indicates that a recessed portion not covered by the resin of the housing 302 is provided. In this way, if such a recessed portion not covered by the resin of the housing 302 is provided in the neck portion of the protrusion 424, it is possible to further facilitate cooling of the protrusion 424 using the measurement target gas 30. 4.3 Connection of the circuit module 400

[0098] The circuit assembly 400 is provided with the connection terminal 412 for supplying electrical power for operating the embedded airflow sensing section 602 or the processing unit 604 and for outputting the flow measurement value or the temperature measurement value. Furthermore, a terminal 414 is provided for monitoring whether the circuit assembly 400 is operating properly or whether an abnormality is generated in a circuit component or a connection thereof. In this embodiment, the circuit assembly 400 is formed by performing transfer molding for the airflow sensing section 602 or the processing unit 604 using a thermosetting resin through the first resin molding process. By performing transfer molding, it is possible to improve the dimensional accuracy of the circuit assembly 400.However, since a high-pressure resin is forced into the interior of the sealed mold where the airflow sensing section 602 or the processing unit 604 is embedded in the transfer molding process, it is preferable to check whether there is a disturbance in the airflow sensing section 602 or the processing unit 604 and in such a wiring relationship for the resulting circuit assembly 400. In this embodiment, a control terminal 414 is provided, and the control is performed for each of the manufactured circuit assemblies 400. Since the control terminal 414 is not used for measurement, the terminal 414 is not connected to the inner coupling 361 of the outer terminal as described above. In addition, each connection terminal 412 is provided with a bent portion 416 to increase a mechanical elastic force.If a mechanical elastic force is provided in each connection terminal 412, it is possible to absorb mechanical stress caused by a difference in the thermal expansion coefficient between the resin of the first resin molding process and the resin of the second resin molding process. That is, each connection terminal 412 is affected by the thermal expansion caused by the first resin molding process, and the inner coupling 361 of the outer terminal connected to each connection terminal 412 is affected by the resin of the second resin molding process. Thus, it is possible to absorb the generation of mechanical stress caused by the difference in the resin.

[0099] Fig. 9A to 9D are figures showing sections of cross sections along DD of Fig. 8, which are explanatory diagrams showing specific examples of connection structures between the lead wire of the circuit assembly and the external terminal of the package.

[0100] The circuit assembly 400 has a connection terminal (an external lead wire) 412 protruding from the sealed portion sealed with the first molding resin by the first resin molding process. As shown in Fig. 8, the connection terminal 412 has a strip plate shape extending in a line having a certain width, with a plurality of connection terminals 412 arranged in parallel on the same plane.

[0101] As in Fig. 9A to Fig. As shown in Fig. 9C, the outer terminal 306, which is a connector terminal, is fixed to the housing 302, and the inner coupling 361 of the outer terminal, which projects into the circuit assembly 400, is configured so that each overlaps with the corresponding connection terminal 412. The inner coupling 361 of the outer terminal is made of a plate-shaped member having a slightly wider and slightly thicker plate thickness than each connection terminal 412, and extends in the same direction as the connection terminal 412 projecting from the flange 312 side to the circuit assembly 400 side. In other words, the plate thickness of the connection terminal 412 is configured to be smaller than the plate thickness of the inner coupling 361 of the outer terminal.

[0102] The connecting terminal 412 and the female coupling 361 of the male terminal are electrically connected to each other by spot welding, laser welding, and the like using the terminal connector 320, which is the recess formed between the circuit assembly 400 and the flange 312. The connection unit between the connecting terminal 412 and the female coupling 361 of the male terminal is arranged on the main passage side with respect to the intake pipe.

[0103] The bent portion 416 is provided in the connection terminal 412 in such a way that it is arranged in the terminal connector 320, which is the location on the side of the circuit assembly 400 with respect to the flange 316. The bent portion 416 is formed so that it is bent in the direction of the thickness of the lead wire, which is the direction transverse to the lead wire surface of the connection terminal 412. As shown in Fig. 9A, the bent portion 416 has a shape such that the bent portion 416 is bent in a curved shape that gently rises and gently descends from the uppermost portion above the transition from the circuit assembly 400 side to the flange 312 side. As shown in Fig. 9B, the shape of the bent portion 416 may be such a shape that it is bent to form a sine curve wherein a projection and a recession are continuous, or as shown in Fig. 9C, the shape of the bent portion 416 may be such that it is bent in a step-like manner with a difference in height therebetween. When the bent portion 416, as shown in Fig. 9A and Fig. 9B, this can prevent stress from being concentrated at a single point such as a bending point, allowing the stress to be distributed over the entire curved portion. In the above specific example, an example was explained in which the bent portion 416 is formed in the connection terminal 412, but the curved portion may be formed in the inner coupling 361 of the outer terminal instead of in the connection terminal 412.

[0104] In the thermal flow meter 300, the proximal end portion of the measuring section 310 is heated by the radiant heat of the internal combustion engine, and the front end portion is cooled by the cooling of the intake air, causing a temperature difference in a direction perpendicular to the flow direction of the intake air. Specifically, the circuit assembly 400 is molded by a thermosetting resin, which is a first molding resin, and the housing 302 is molded by a thermoplastic resin, which is a second molding resin. When the thermal expansion coefficients are different from each other, stress is likely to be applied to the connection terminal 412 due to the temperature difference.

[0105] For example, components such as the housing 302, the circuit assembly 400, the connection terminal 412, and the connector terminal 306 have different thermal expansion coefficients from each other. In the entire thermal flow meter 300, not only expansion / contraction but also deformation such as bending and twisting occur in the axial direction. Thus, the maximum mechanical stress may be applied to a low-rigidity portion such as a thin line (thin wire) and a thin plate (thin lead wire) in the circuit assembly 400, which may cause the portion to crack.

[0106] Unlike other components that are constantly exposed to high temperatures, the thermal flow meter 300 in particular alternately repeats a state in which the entire thermal flow meter 300 is either at a high temperature or at a low temperature, and a state in which the entire thermal flow meter 300 is partially cooled by the cooling action of the intake air, with a temperature difference depending on the sections, and this repetition occurs extremely frequently. As described above, since the thermal flow meter 300 is used in a harsh environment where there is a lot of expansion and contraction due to the heat of each component, it is necessary to mitigate the mechanical stress caused by the heat.

[0107] In the present embodiment, the bent portion 416 is provided in the connecting terminal 412, so that when the connecting terminal 412 receives stress in the axial direction, the bending direction, the deformation direction, and the like due to the temperature difference, the bent portion 416 deforms to absorb the stress thereof. Thus, this can prevent cracking and peeling from occurring at the connection point between the connecting terminal 412 and the inner coupling 361 of the outer terminal.

[0108] In the explanation based on Fig. 9A to Fig. 9C, the connecting terminal 412 and the inner coupling 361 of the outer terminal are connected, for example, by welding and the like. As shown in Fig. However, as shown in Fig. 9D, the connection terminal 412 may be formed integrally with the external terminal 306, and the bent portion 416 may be provided at the connection terminal 412. The connection terminal 412, which is the external lead, is configured to penetrate and be fixed to the housing 302, with the outer end thereof disposed on the outside of the housing 302 to form the external terminal 306. In this case, when there is stress in the axial direction of the connection terminal 412 due to the temperature difference, the bent portion 416 deforms and can absorb the stress, so that this can prevent excessive stress from being applied to the circuit board 400 from the connection terminal 412.When the external terminal 306 is integrally formed with the connecting terminal 412, the step of connecting the external terminal 412 and the external terminal 306 can be omitted, thus increasing the yield by reducing the manufacturing time. Furthermore, it is not necessary to prepare the external terminal 306 as a separate component, thus reducing the number of components.

[0109] Fig. 10 is an explanatory view showing another specific example of a connection structure between a lead wire of a circuit assembly and an external terminal of a housing. In the embodiment shown in Fig. In the example shown in Figures 9A to 9D, the bent portion 416 has been explained which is bent in the direction of the thickness of the connecting line, but instead of the bent portion 416, for example, the bent portion 417 which, as shown in Fig. 10, along the lead surface of the connection terminal 412 is bent in the direction of the lead width.

[0110] The bent portion 417 has a shape that is bent in the direction of the width of the connecting line along the connecting line surface at an intermediate point of the connecting line terminal 412 in a crank-like manner. When a mechanical stress is applied in the axial direction of the connecting terminal 412, the bent portion 417 deforms and can absorb the mechanical stress, which can prevent cracking and peeling from occurring at the connection point between the connecting terminal 412 and the inner coupling 361 of the outer terminal. Compared to the one shown in Fig. 9A to 9D, the size of the lead wire can be reduced in the thickness direction and the terminal connector 320 can be made in a compact size.

[0111] In explanation of the as in Fig. 9A to 9D and Fig. For example, in the embodiment shown in Figure 10, the circuit assembly 400 is molded with the thermosetting resin, which is the first molding resin, and the housing 302 is molded with the thermoplastic resin, which is the second molding resin. However, the present embodiment can also be applied to a case where the first molding resin and the second molding resin are the same resin, and the housing 302 and the circuit assembly 400 can be made of the same resin material. 4.4 Fixing of the circuit assembly 400 by the second resin molding process and effects thereof

[0112] The hatching section in Fig. 11(A) to 11(C) indicate a mounting surface 432 for covering the circuit assembly 400 using the thermoplastic resin used in the second resin molding process to fix the circuit assembly 400 to the housing 302 in the second resin molding process. As described above with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. 6(B), it is important to maintain high accuracy to ensure a specific relationship between the measurement surface 430, the exposed heat transfer surface portion 436 provided in the measurement surface 430, and the shape of the bypass passage. In the second resin molding process, the bypass passage is formed, and the circuit assembly 400 is fixed to the housing 302 forming the bypass passage. Thus, it is possible to maintain a relationship between the bypass passage, the measurement surface 430, and the exposed heat transfer surface portion 436 with significantly high accuracy. That is, since the circuit assembly 400 is fixed to the housing 302 in the second resin molding process, it is possible to position and fix the circuit assembly 400 with high accuracy in the mold used to form the housing 302 with the bypass passage.By injecting a thermoplastic resin having a high temperature into this mold, the bypass passage is formed with high accuracy and the circuit assembly 400 is fixed with high accuracy.

[0113] In this embodiment, the entire surface of the circuit assembly 400 is not a mounting surface 432 covered by the resin used to form the housing 302, but the front surface is exposed to the side of the connection terminal 412 of the circuit assembly 400. That is, a portion is provided that is not covered by the resin used to form the housing 302. In the embodiment shown in Fig. 11(A) to 11(C), of the front surface of the circuit package 400, the area which is not covered by the resin used to form the housing 302 but is exposed to the resin used to form the housing 302 is larger than the area of ​​the mounting surface 432 covered by the resin used to form the housing 302.

[0114] A thermal expansion coefficient differs between the thermosetting resin used to form the circuit assembly 400 and the thermoplastic resin used to form the housing 302 with the fixing portion 372. It is preferable to prevent stress caused by this difference in thermal expansion coefficient from being applied to the circuit assembly 400 as long as possible. By reducing the front surface of the circuit assembly 400 and the fixing surface 432, it is possible to reduce the influence due to the difference in thermal expansion coefficient. For example, it is possible to reduce the fixing surface 432 on the front surface of the circuit assembly 400 by providing a strip shape with a width L.

[0115] It is possible to increase the mechanical strength of the protrusion 424 by providing the fixing surface 432 at the base of the protrusion 424. It is possible to fix the circuit assembly 400 and the housing 302 more robustly by providing, on the front surface of the circuit assembly 400, a strip-shaped fixing surface along a flow axis of the measurement target gas 30 and a fixing surface across the flow axis of the measurement target gas 30. On the fixing surface 432, a portion surrounding the circuit assembly 400 in a strip shape with a width L along the measurement surface 430 is the above-described fixing surface along the flow axis of the measurement target gas 30, and a portion covering the base of the protrusion 424 is the fixing surface across the flow axis of the measurement target gas 30.

[0116] Fig. 12 illustrates a state in which the frame has been molded with a thermosetting resin through the first resin molding process and is covered with the thermosetting resin. Through this molding, the measurement surface 430 is formed on the front surface of the circuit package 400, and the heat transfer surface exposed portion 436 is provided on the measurement surface 430. The temperature detection portion 452 for measuring a temperature of the measurement target gas 30 is provided in the front end of the protrusion 424, and the temperature detection element 518 is embedded inside.

[0117] A sloped portion 594 or 596 is formed at the base of the protrusion 424. The flow of the resin in the first resin molding process becomes smooth. Furthermore, the target gas 30 measured by the temperature detection portion 452 flows smoothly from the protrusion 424 to its base using the sloped portion 594 or 596 to cool the base of the protrusion 424 while the temperature detection portion 452 is installed and operated in a vehicle. Thus, it is possible to reduce the influence of heat on the temperature detection portion 452. According to the state of Fig. 12, the connecting line 514 is separated from each terminal so that it becomes the connecting terminal 412 or the terminal 414.

[0118] In the first resin molding process, it is necessary to prevent resin inflow to the exposed heat transfer surface portion 436 or to the opening 438. For this reason, in the first resin molding process, resin inflow is suppressed at a location of the exposed heat transfer surface portion 436 or the opening 438. For example, a press die larger than the diaphragm 672 is installed, and a press is installed in the rear surface thereof in such a way that it is pressed from both surfaces. As shown in Fig. 11(C), the press imprint 442 or 441 corresponding to the portion 436 of the exposed heat transfer surface or the opening 438 of Fig. 12 or the portion 436 of the exposed heat transfer surface or the opening 438 of Fig. 11(B). 5. Process for manufacturing the thermal flow meter 3005.1 Process for manufacturing the circuit assembly 400

[0119] The Fig. 13A and Fig. 13B illustrate a process for manufacturing the thermal flow meter 300, wherein Fig. 13A illustrates a process for manufacturing the circuit assembly 400 and Fig. 13B illustrates a process for manufacturing a thermal flow meter. In Fig. In Figure 13A, step 1 shows a process for manufacturing a frame. This frame is formed, for example, by machining.

[0120] In step 2, the board 532 is first mounted on the frame obtained in step 1, and then the airflow sensing section 602 or the processing unit 604 is further mounted on the board 532. Then, the temperature detection element 518 and the circuit component such as a chip capacitor are mounted. In step 2, the electrical wiring is performed between the circuit components, between the circuit component and the lead, and between the lead. In step 2, the lead wires 544 and 548 are connected using a connecting wire 546 to increase thermal resistance. In step 2, the circuit component is mounted on the frame 512, and the electrical wiring is further performed to form an electrical circuit.

[0121] Then, in step 3, the first resin molding process is used to mold using a thermosetting resin. This state is Fig. 12. Furthermore, in step 3, each of the connected leads is separated from the frame 512 and the leads are separated from each other, so that the circuit assembly 400 is made of Fig. 11(A) to 11(C). In this as in Fig. The circuit assembly 400 shown in Figures 11(A) to 11(C) forms the sensing surface 430 or the portion 436 of the exposed heat transfer surface.

[0122] In step 4, a visual inspection or an operational inspection is carried out for the obtained circuit assembly 400. In the first resin molding process of Fig. 3, the electrical circuit obtained in step 2 is mounted on the inside of the mold, and a high-temperature resin is injected into the mold at high pressure. Thus, it is preferably checked whether there is an abnormality in the electrical component or the electrical wiring. For this check, in addition to the connection terminal 412, Fig. 11(A) to 11(C) or 18, terminal 414 is used. Since terminal 414 is not used thereafter, it is noted that it can be cut out of the base point after this inspection. 5.2 Process for manufacturing the thermal flow meter 300 and for calibrating the properties

[0123] In the process of Fig. 13B are as in Fig. 13A and the external connector 306 are used. In step 5, the housing 302 is formed by the second resin molding process. In this housing 302, a resin-formed bypass passage trench, the flange 312, or the external connector 305 are formed, wherein the Fig. 11(A) to 11(C) is covered with the resin in the second resin molding process, so that the circuit assembly 400 is fixed to the housing 302. By combining the manufacturing (step 3) of the circuit assembly 400 by the first resin molding process and the formation of the housing 302 of the thermal flow meter 300 by the second resin molding process, the flow detection accuracy is significantly improved. In step 6, each inner coupling 361 of the outer terminal is Fig. 8. In step 7, the connecting port 412 and the inner coupling 361 of the outer port are connected.

[0124] In step 7, the housing 302 is obtained. Then, in step 8, the front and rear covers 303 and 304 are installed in the housing 302 in such a way that the interior of the housing 302 is sealed with the front and rear covers 303 and 304 and the bypass passage for flowing the measurement target gas 30 is obtained. In addition, a projection 356 provided in the front or rear cover 303 or 304 with respect to Fig. 7 is formed. Note that the front cover 303 is formed by the molding of step 10, and the rear cover 304 is formed by the molding of step 11. Furthermore, the front and rear covers 303 and 304 are formed by separate processes using different molds.

[0125] In step 9, a characteristic curve test is performed by actually supplying air to the bypass passage. Since the relationship between the bypass passage and the airflow detection section is maintained with high accuracy as described above, significantly high measurement accuracy is obtained by performing characteristic curve calibration through a characteristic curve test. Furthermore, since molding is performed with positioning, or since the configuration relationship between the bypass passage and the airflow detection section is determined by the first resin molding process and the second resin molding process, the characteristic curve does not change significantly even in long-term use, and high reliability is maintained in addition to high accuracy. 6. Circuit configuration of the thermal flow meter 3006.1 Overall circuit configuration of the thermal flow meter 300

[0126] Fig. Fig. 14 is a circuit diagram illustrating the flow detection circuit 601 of the thermal flow meter 300. It is noted that the measuring circuit described in the above-mentioned embodiment with respect to the temperature detection section 452 is also present in the thermal flow meter 300, in Fig. 14 but intentionally omitted. The flow detection circuit 601 of the thermal flow meter 300 includes the air flow detection 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 of the air flow detection section 602 and outputs a signal representing the flow rate via the terminal 662 based on the output of the air flow detection section 602. For this processing, 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 for storing data representing a relationship between the calibration value or the measured value and the flow rate, and a power circuit 622 for supplying a specific voltage to each necessary circuit.The power circuit 622 is supplied with DC power from an external power supply, such as a vehicle-mounted battery, via a terminal 664 and a ground terminal (not shown).

[0127] The air flow detection section 602 is provided with a heat generator 608 for heating the measurement target gas 30. A voltage V1 is supplied from the power circuit 622 to a collector of a transistor 606 included in a power supply circuit of the heat generator 608, and a control signal from the CPU 612 is applied to a base of the transistor 606 via the output circuit 616. Based on this control signal, current is supplied to the heat generator 608 from the transistor 606 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 such that a temperature of the measurement target gas 30 increases by heating using the heat generator 608 from an initial temperature by a predetermined temperature, e.g., 100°C.

[0128] The airflow detection section 602 includes a heating control bridge 640 for controlling a heat amount of the heat generator 608 and an airflow detection bridge circuit 650 for measuring a flow rate. A predetermined voltage V3 is applied to one end of the heating control bridge 640 from the power circuit 622 via terminal 626, and the other end of the heating control bridge 640 is connected to the ground terminal 630. Furthermore, a predetermined voltage V2 is applied from the power circuit 622 to one end of the airflow detection bridge circuit 650 via terminal 625, and the other end of the flow detection bridge circuit 650 is connected to the ground terminal 630.

[0129] The heating control bridge 640 includes a resistor 642, which is a resistance temperature detector having a resistance value that changes depending 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 input to the input circuit 614 via the terminals 627 and 628. The CPU 612 controls the current supplied by the transistor 606 to control the heat quantity of the heat generator 608 such that the potential difference between the nodes A and B is set to a predetermined value, for example, zero voltage in this embodiment. Fig. The flow detection circuit 601 shown in Figure 14 heats the measurement target gas 30 using the heat generator 608 in such a way that a temperature increases from an initial temperature of the measurement target gas 30 by a predetermined temperature, for example, 100°C, at all times. In order to perform this heating control with high accuracy, the resistance values ​​of each resistor of the heating control bridge 640 are set such that the potential difference between nodes A and B becomes zero at all times when the temperature of the measurement target gas 30 heated by the heat generator 608 increases from an initial temperature by a predetermined temperature, for example, 100°C. Thus, the CPU 612 in the flow detection circuit 601 controls Fig. 14 the electric current supplied to the heat generator 608 in such a way that the potential difference between nodes A and B becomes zero.

[0130] The bridge circuit of the air flow detection 650 includes four resistance temperature detectors of resistors 652, 654, 656, and 658. The four resistance temperature detectors are arranged along the flow of the measurement target gas 30 in such a manner that the resistors 652 and 654 are arranged on the inlet side with respect to the heat generator 608 in the flow path of the measurement target gas 30, and that the resistors 656 and 658 are arranged on the outlet side with respect to the heat generator 608 in the flow path of the measurement target gas 30. In order to increase the measurement accuracy, the resistors 652 and 654 are also arranged such that the distances to the heat generator 608 are approximately equal, and the resistors 656 and 658 are arranged such that the distances to the heat generator 608 are approximately equal.

[0131] A potential difference between a node C between resistors 652 and 656 and a node D between resistors 654 and 658 is input to the input circuit 614 via terminals 631 and 632. To increase measurement accuracy, each resistor of the bridge circuit of the air flow detector 650 is adjusted, for example, such that a positional difference between nodes C and D is set to zero while the flow of the measurement target gas 30 is set to zero. Thus, while the potential difference between nodes C and D is set to zero, for example, the CPU 612 outputs an electrical signal indicating that the flow of the main passage 124 is zero from terminal 662 based on the measurement result that the flow of the measurement target gas 30 is zero.

[0132] When the measurement target gas 30 is along the arrow direction in Fig. 14, the resistor 652 or 654 arranged on the inlet side is cooled by the measurement target gas 30, and the resistors 656 and 658 arranged on the outlet side 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 increases. For this reason, a potential difference is generated between the nodes C and D of the bridge circuit of the air flow detection 650, and this potential difference is input to the input circuit 614 via the terminals 631 and 632. The CPU 612 searches, based on the potential difference between the nodes C and D of the bridge circuit of the air flow detection 650, data indicating a relationship between the flow rate of the main passage 124 and the above-mentioned potential difference stored in the memory 618 to obtain the flow rate of the main passage 124.An electrical signal is output via terminal 662 indicating the flow rate of the main passage 124 thus obtained. Although the flow rate shown in . Fig. 14 are designated by new reference numerals, it is noted that they are included in the above-described connection terminal 412 of Fig. 5(A), Fig. 5(B), Fig. 6(A), Fig. 6(B) or Fig. 8 are included.

[0133] The memory 618 stores the data indicating a relationship between the potential difference between the nodes C and D and the flow rate of the main passage 124, and calibration data for reducing a measurement error such as a deviation obtained based on the actual measured value of the gas after the manufacture of the circuit assembly 400. It is noted that the actual measured value of the gas after the manufacture of the circuit assembly 400 and the calibration value based thereon are stored in the memory 618 using the external terminal 306 or the calibration terminal 307 shown in Fig. 4(A) and Fig. 4(B). In this embodiment, the circuit assembly 400 is manufactured while maintaining a high-accuracy, low-deviation arrangement relationship between the bypass passage for flowing the measurement target gas 30 and the measurement surface 430, or a high-accuracy, low-deviation arrangement relationship between the bypass passage for flowing the measurement target gas 30 and the heat transfer exposed surface portion 436. Thus, it is possible to obtain a measurement result with significantly high accuracy by calibrating using the calibration value. 6.2 Configuration of the flow detection circuit 601

[0134] Fig. 15 is a circuit configuration diagram showing a circuit arrangement of the above-described flow detection circuit 601 of Fig. 14. The flow detection circuit 601 is made of a semiconductor chip with a rectangular shape. The measurement target gas 30 flows along the arrow direction from the left side to the right side of the Fig. 15 shown flow detection circuit 601.

[0135] In the airflow detection section (flow detection element) 602 made of a semiconductor chip, a diaphragm 672 having a rectangular shape is formed with a thin semiconductor chip. The diaphragm 672 is provided with a thin surface (i.e., the above-mentioned heat transfer surface) 603, which is indicated by the dotted line. On the rear surface side of the thin surface 603, the above-mentioned recess is formed, and this is in contact with the Fig. 11(A) to 11(C) or 5 in such a way that the gas pressure within the recess depends on the pressure of the gas guided by the opening 438.

[0136] By reducing the thickness of the diaphragm 672, the thermal conductivity is reduced and the heat transfer to the resistors 652, 654, 658 and 656 provided in the thin surface (heat transfer surface) 603 of the diaphragm 672 through the diaphragm 672 is suppressed, so that the temperatures of the resistors are approximately adjusted by the heat transfer with the measurement target gas 30.

[0137] The heat generator 608 is provided in the center of the thin surface 603 of the diaphragm 672, and the resistor 642 of the heating control bridge 640 is provided around the heat generator 608. Furthermore, the resistors 644, 646, and 648 of the heating control bridge 640 are provided on the outside of the thin surface 603. The resistors 642, 644, 646, and 648 thus formed constitute the heating control bridge 640.

[0138] In addition, resistors 652 and 654 as inlet-side resistance temperature detectors and resistors 656 and 658 as outlet-side resistance temperature detectors are arranged in such a manner that the heat generator 608 is interposed. Resistors 652 and 654 as inlet-side resistance temperature detectors are arranged on the inlet side in the direction of the arrow where the measurement target gas 30 flows with respect to the heat generator 608. Resistors 656 and 658 as outlet-side resistance temperature detectors are arranged on the outlet side in the direction of the arrow where the measurement target gas 30 flows with respect to the heat generator 608. In this way, the bridge circuit of the air flow detection 650 is formed by the resistors 652, 654, 656, and 658 arranged in the thin surface 603.

[0139] Both ends of the heat generator 608 are connected to each of the lower half of Fig. 15 shown terminals 624 and 629. As shown in Fig. 14, the current supplied from the transistor 606 to the heat generator 608 is applied to the terminal 624, with the terminal 629 being grounded.

[0140] The resistors 642, 644, 646 and 648 of the heating control bridge 640 are connected together and are connected to the terminals 626 and 630. As in Fig. As shown in Figure 14, a predetermined voltage V3 is supplied to terminal 626 from power circuit 622, and terminal 630 is grounded. Furthermore, the node between resistors 642 and 646 and the node between resistors 646 and 648 are connected to terminals 627 and 628, respectively. As shown in Fig. 15, 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. As shown in Fig. As shown in Figure 14, a predetermined voltage V2 is supplied to terminal 625 from power circuit 622, and terminal 630 is grounded as a ground terminal. Furthermore, a node between resistors 654 and 658 is connected to terminal 631, and terminal 631 outputs an electric potential of node B. Fig. 14. The node between resistors 652 and 656 is connected to terminal 632 and terminal 632 outputs an electrical potential of the Fig. 14 shown node C.

[0141] Since the resistor 642 of the heating control bridge 640, as in Fig. 15, is formed near the heat generator 608, it is possible to measure the temperature of the gas heated by the heat from the heat generator 608 with high accuracy. Meanwhile, since the resistors 644, 646, and 648 of the heating control bridge 640 are arranged away from the heat generator 608, they are not easily affected by the heat generated by 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 to be unaffected by the heat generator 608. For this reason, the detection accuracy of the measurement target gas 30 is high using the heating control bridge 640, and the control for heating the measurement target gas 30 only by a predetermined temperature from its initial temperature can be carried out with high accuracy.

[0142] In this embodiment, a recess is formed on the side of the rear surface of the membrane 672 and is in contact with the Fig. 11(A) to 11(C) or 5(A) and 5(B), so that a difference between the pressure of the recess on the back side of the diaphragm 672 and the pressure on the front side 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 improving flow measurement accuracy.

[0143] As described above, heat conduction through the diaphragm 672 is suppressed to be as small as possible by forming the thin surface 603 and reducing the thickness of a portion including the thin surface 603 in the diaphragm 672. Thus, while the influence of heat conduction through the diaphragm 672 is suppressed, the bridge circuit of the air flow detection 650 or the heating control bridge 640 tends to operate more depending on the temperature of the measurement target gas 30, so that the measurement operation is improved. For this reason, high measurement accuracy is obtained.

[0144] As described above, the embodiments of the present invention have been explained in detail, but the present invention is not limited to the embodiments. Various design changes can be applied to the embodiments, and they can be changed without departing from the gist of the present invention described in the claims. For example, the embodiments explained above have been explained in detail to enable the present invention to be easily understood, and the embodiments are not necessarily limited to those having all of the constituent elements explained above. A part of a configuration of a certain embodiment may be replaced by a configuration of another embodiment. In a part of the configuration of each embodiment, another configuration may be added, deleted, or replaced. Industrial availability

[0145] The present invention is applicable to a measuring device for measuring a gas flow as described above. List of reference symbols 300 thermal flow meter 302 housing 303 front cover 304 rear cover 305 external connection unit 306 external connection 307 Calibration port 310 measuring section 320 connection connectors 332 Bypass ditch on the front 334 Bypass ditch on the back 356 lead 359 Harz section 361 Internal coupling of the external connection 365 connecting section 372 fastening section 400 circuit assembly 412 Connection connection (external connection line) 414 connection 424 lead 430 measuring area 432 mounting surface 436 Section of exposed heat transfer surface 438 Opening 452 Temperature detection section 514 connecting cable 594 Incline section 596 incline section 601 Flow detection circuit 602 Air flow detection section 604 processing unit 608 heat generators 640 Heating control bridge 650 Bridge circuit of air flow detection 672 Membran

Claims

[1] A thermal flow meter (300) including a bypass passage for flowing a measurement target gas received from a main passage (124) and an air flow detection section (602) for measuring a flow rate of the measurement target gas based on heat transfer from a heat transfer surface to the measurement target gas flowing through the bypass passage, the thermal flow meter (300) comprising: a circuit assembly (400) in which the air flow detection section (602) and a lead wire (514) connected to the air flow detection section (602) have been sealed by a first resin molding process; and a housing (302) forming part of the bypass passage and fixing the circuit assembly (400) by a second resin molding process, wherein the connecting line (514) has an external connecting line (412) which is fixed to the housing (302) and protrudes from the circuit assembly (400), and a bent portion (416) having a bent shape is provided on the external connecting line (412), characterized by , that the bent portion (416) is bent in a curved shape that rises from the side of the circuit assembly (400) to an uppermost portion and falls from there in order to be able to deform upon temperature fluctuations and thus reduce mechanical stresses in the axial direction of the external lead (412) in the external lead (412). [2] Thermal flow meter (300) according to claim 1, comprising a connector terminal (306) penetrating the housing (302), wherein an inner end thereof is opposite the external connection line (412) and an outer end thereof is arranged outside the housing (302), the outer connection line (412) and the inner end of the connector terminal (306) are connected. [3] The thermal flow meter (300) according to claim 2, wherein the housing (302) has a measuring section (310) whose proximal end portion is fixed to an inlet pipe forming the main passage (124) and whose front end portion protrudes into the main passage (124), wherein the connector terminal (306) is provided at the proximal end portion of the measuring section (310), and wherein the circuit assembly (400) is arranged at the front end portion of the measuring section (310). [4] The thermal flow meter (300) according to claim 3, wherein the connection unit is provided between the outer connection line (412) and the inner end of the connector port (306) on an inner side of the inlet pipe. [5] The thermal flow meter (300) according to claim 1, wherein the external lead wire (412) has a connector terminal (306) penetrating the housing (302), an outer end of which is disposed outside the housing (302). [6] The thermal flow meter (300) according to any one of claims 1 to 5, wherein the bent portion (416) is formed to be bent in a direction of a thickness of the lead wire (514) transverse to the lead wire surface of the lead wire (514). [7] The thermal flow meter (300) according to any one of claims 1 to 5, wherein the bent portion (416) has a shape such that it is bent in a width direction of the lead wire (514) along the lead wire surface of the lead wire (514). [8] The thermal flow meter (300) according to any one of claims 2 to 4, wherein the outer lead wire (412) has a smaller thickness than a thickness of the inner end of the connector terminal (306).

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