Thermal flow meter

Abstract

Thermal flow meter (300), including a bypass passage (332, 334) for the flow of a measurement target gas taken up from a main channel, an airflow detection section (602) for measuring the throughput of the target gas by carrying out heat transfer with the target gas flowing through the bypass passage (332, 334), and a circuit assembly (400, 401, 402, 403, 404, 405, 406) with the airflow detection section (602), wherein the circuit assembly (400, 401, 402, 403, 404, 405, 406) is designed such that a measuring surface (430) and a rear surface are arranged on the back side of the measuring surface in the bypass passage (332, 334), the bypass passage (332, 334) is designed such that when the target gas is divided, it flows into a flow path on one side of the measuring surface of the circuit assembly (400, 401, 402, 403, 404, 405, 406) and a flow path on one side of the rear surface on the back of the measuring surface, and a reference line (700) which divides the circuit assembly (400, 401, 402, 403, 404, 405, 406) in a longitudinal direction of the circuit assembly (400, 401, 402, 403, 404, 405, 406), and delineates a measuring side with a measuring surface and a back side of the circuit assembly (400, 401, 402, 403, 404, 405, 406); and a flow-side end surface (704) of the circuit assembly (400, 401, 402, 403, 404, 405, 406) for dividing the target gas on the side of the measuring surface and on the side of the back of the measuring surface (430) has different shapes, characterized by the fact that a downstream end surface of the circuit assembly (400, 401, 402, 403, 404, 405, 406) for dividing the target gas on the side of the measuring surface and on the side of the back of the measuring surface (430) has different shapes, wherein the inflow-side end surface (704) is formed by an inclined surface (704a) on the side of the measuring surface (430) and a vertical surface (704b) on the side of the back of the measuring surface (430), and wherein a height (h5) of the inclined surface (704a) is such that it is greater than a height (h6) of the vertical surface (704b).

Description

Technical field

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

[0002] A thermal flow meter, which measures the flow rate of a gas, is designed to include an airflow sensing section for measuring the flow rate. The gas flow rate is measured by heat transfer between the airflow sensing section and the gas itself. The flow rate measured by the thermal flow meter is frequently used as an important control parameter for various devices. A key characteristic of the thermal flow meter is its ability to measure the flow rate of a gas, such as mass flow rate, with relatively high accuracy compared to other types of flow meters.

[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 regarding fuel economy and exhaust gas purification are high. To meet these requirements, it is desirable to measure the intake air volume, a key parameter of the internal combustion engine, with high accuracy.

[0004] In a conventional heat flow sensor, a sealing plastic covering a sensor chip is provided to cover the sensor chip in such a way that it is in contact with at least one side surface which extends perpendicular to a heat-generating surface of the sensor chip and which, with respect to an airflow detection section, is an upstream section with respect to the fluid flow, and that the heat-generating surface of the sensor chip and the covered side surface portion of the sealing plastic are flush with each other in the direction perpendicular to the heat-generating surface (see, for example, patent literature 1).

[0005] Patent literature 2 discloses a sensor arrangement for determining at least one parameter of a flowing fluid medium, in particular an intake air mass of an internal combustion engine.

[0006] Patent literature 3 describes a device for detecting at least one property of a fluid medium.

[0007] From patent literature 4, a device for measuring the mass of a flowing medium, in particular for measuring the intake air mass of internal combustion engines, is known, which has a control circuit that is housed in a housing of the device which is surrounded by the flowing medium, wherein a cooling channel extending in the direction of flow is provided in the housing, which extends transversely through the housing in such a way that heat generated in the control circuit is dissipated by the medium flowing through the cooling channel.

[0008] Patent literature 5 discloses a gas flow determination method and a corresponding gas flow determination device. List of references to patent literature Patent Literature 1: JP 2008-175780 A Patent literature 2: DE 10 2008 042 166 A1 Patent literature 3: DE 10 201 1 089 477 A1 Patent literature 4: DE 44 47 570 A1 Patent literature 5: DE 100 00 496 A1 Summary of the invention: Technical problem

[0009] To measure the flow rate of a gas with high accuracy using a thermal flow meter, it is necessary to position and secure an airflow sensing section of the thermal flow meter with high accuracy in the bypass passage. This section is provided within the thermal flow meter to capture gas flowing through the main passage. The thermal flow sensor described in patent literature 1 generates an airflow that passes through the airflow sensing section and measures the flow rate by detecting the temperature change caused by the airflow across the sensor chip. However, it is difficult to divide the air flowing through the airflow sensing section evenly between the sensor chip area and the area opposite it.Furthermore, a problem exists in that the same product can exhibit high or low throughput across the sensor chip area due to a very slight difference in the upstream end-surface shape of an element, such as an assembly or similar component that carries the sensor chip. Because of this issue, it has historically been difficult to further improve the measurement accuracy of thermal flow meters.

[0010] The present invention was made with regard to such problems, and one object of the present invention is to provide a thermal flow meter wherein the thermal flow meter has a high measuring accuracy. Solution to the problem

[0011] The problem is solved by a thermal flow meter with the features of claim 1. Advantageous embodiments are defined in the dependent claims. Advantageous effects of the invention

[0012] According to the present invention, it is possible to obtain a thermal flow meter with high measuring accuracy. Brief description of the drawings Fig. Figure 1 is a system diagram illustrating an internal combustion engine control system in which a thermal flow meter is used according to an embodiment of the invention. Fig. 2(A) and Fig. 2(B) are illustrations that depict an external appearance of the thermal flow meter, wherein Fig. 2(A) is a left side view and Fig. 2(B) is a front view. Fig. 3(A) and Fig. Figure 3(B) are illustrations depicting an external appearance of the thermal flow meter, wherein Fig. 3(A) is a right side view and Fig. 3(B) is a rear view. Fig. 4(A) and Fig. Figure 4(B) shows an external appearance of the thermal flow meter, wherein Fig. 4(A) is a top view and Fig. 4(B) is a bottom view. Fig. 5(A) and Fig. Figure 5(B) shows an illustration of the housing of the thermal flow meter, wherein Fig. 5(A) is a left side view of the case and Fig. 5(B) is a front view of the case. Fig. 6(A) and Fig. Figure 6(B) shows an illustration of the housing of the thermal flow meter, wherein Fig. 6(A) is a right side view of the housing and Fig. 6(B) is a rear view of the casing. Fig. Figure 7 is a partially enlarged view illustrating a state of a flow path surface arranged in the bypass passage. Fig. Figure 8 is an explanatory illustration to explain a diagram and a connecting opening that links a void provided inside the membrane and the opening. Fig. Figure 9 is an illustration that provides an overview of a manufacturing process for a thermal flow meter and illustrates a production process for the circuit assembly. Fig. Figure 10 is an illustration that provides an overview of a manufacturing process for the thermal flow meter and illustrates a production process for the thermal flow meter. Fig. Figure 11 is a circuit diagram illustrating a throughput detection circuit of the thermal flow meter. Fig. Figure 12 is an explanatory illustration that explains an airflow sensing section of the throughput sensing circuit. Fig. Figures 13(A) to 13(C) are schematic illustrations that demonstrate the relationship between an upstream end surface and a gas to be measured at an airflow detection section of a circuit assembly of the thermal flow meter according to the present invention, and Fig. 13(A) is a schematic illustration according to a first embodiment, Fig. 13(B) is a schematic illustration according to a second embodiment and Fig. Figure 13(C) is a schematic illustration according to a third embodiment. It should be noted that embodiments 1 to 3 shown in the description serve to illustrate the invention and facilitate understanding of the technical teaching. However, these embodiments are not covered by the scope of protection of amended claim 1. Fig. 14(A) is a schematic illustration according to a fourth embodiment and Fig. Figure 14(B) is a schematic representation of an essential section illustrating the operation of the fourth embodiment. Fig. Figure 15(A) is a schematic illustration depicting a fifth embodiment, and Fig. Figure 15(B) is a schematic illustration according to a sixth embodiment. It should also be noted that embodiments 5 and 6, as described in the text, serve to illustrate the invention and facilitate understanding of the technical teaching. However, these embodiments are not covered by the scope of protection of amended claim 1. Description of embodiments

[0013] The following examples of implementing the invention (hereinafter referred to as embodiments) solve various problems that are desirable in a practical product. In particular, the embodiments solve various problems relating to their use in a measuring device for measuring the intake air volume of a vehicle and exhibit various effects. One of the various problems addressed by the following embodiments is described in the section "Problems to be solved by the invention" above, and one of the various effects obtained by the following embodiments is described in the section "Effects of the invention." Further problems solved by the following embodiments and various effects obtained by the following embodiments are described in the section "Description of the embodiments."It is therefore assumed that the following embodiments also include effects or problems that are obtained or addressed by the embodiments and that differ from those described in “Problems to be solved by the invention” or “Effects of the invention”.

[0014] In the following embodiments, identical elements are designated by the same reference numerals, even if they appear in different drawings, and they have the same functional effects. The components described in previous paragraphs may be described without specifying the reference numerals and symbols shown in the drawings. 1. Internal combustion engine control system with a thermal flow meter according to an embodiment of the invention

[0015] Fig. Figure 1 is a system diagram showing an internal combustion engine control system with electronic fuel injection, which includes a thermal flow meter according to an embodiment of the invention. Based on the operation of an internal combustion engine 110 with an engine cylinder 112 and an engine piston 114, intake air, as the target gas 30, is drawn in from an air filter 122 and supplied to a combustion chamber of the engine cylinder 112 via a main passage 124, which, for example, has an intake manifold, a throttle body 126, and an intake manifold 128. The flow rate of the target gas 30, as the intake air supplied to the combustion chamber, is measured by a thermal flow meter 300 according to the invention. Fuel is supplied by a fuel injector 152 based on the measured flow rate and mixed with the target gas 30 as intake air, so that a mixed gas is then supplied to the combustion chamber.It should be noted 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 target gas 30 as intake air to form the mixed gas, so that the mixed gas is supplied to the combustion chamber through an intake valve 116 to generate mechanical energy through combustion.

[0016] In recent years, many vehicles have used the direct fuel injection method, which has excellent effects in terms of exhaust gas purification and improved fuel efficiency. In this method, a fuel injector 152 is installed in a cylinder head of the internal combustion engine, and fuel is injected directly from the fuel injector 152 into the respective combustion chamber. The thermal flow meter 300 can be used in the same way in a design where the fuel is injected directly into each combustion chamber, as well as in a design where the fuel is injected into the intake manifold of the internal combustion engine. 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 quantity or ignition timing control, are similar in basic concept for both designs. As a representative example of both designs, in Fig. Figure 1 shows a design in which the fuel is injected directly into the intake manifold.

[0017] The fuel and air supplied to the combustion chamber are in a fuel / air mixture and are explosively combusted by spark ignition from the spark plug 154 to generate mechanical energy. After combustion, the gas is fed through the exhaust valve 118 to an exhaust pipe and released from the vehicle as exhaust gas 24. The flow rate of the target gas 30, the intake air supplied to the combustion chamber, is controlled by the throttle valve 132, the opening of which changes in response to the actuation of an accelerator pedal. The fuel supply quantity is controlled based on the flow rate of the intake air supplied to the combustion chamber, and a driver controls the opening of the throttle valve 132, thus controlling the amount of intake air supplied to the combustion chamber. As a result, the mechanical energy generated by the internal combustion engine can be controlled. 1.1 Overview of the control system of the internal combustion engine

[0018] The flow rate and temperature of the target gas 30, intake air drawn in from the air filter 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 sent from the thermal flow meter 300 to the control device 200. Furthermore, an output from a throttle angle sensor 144, which measures the opening degree of the throttle valve 132, is fed into the control device 200, and an output from a rotary angle sensor 146 is fed into the control device 200 to measure the position or state of the engine piston 114, the intake valve 116, or the exhaust valve 118 of the internal combustion engine, as well as the rotational speed of the internal combustion engine.In order to determine a mixture ratio state between the amount of fuel and the amount of air based on the state of the exhaust gas 24, an output of an oxygen sensor 148 is fed into the control device 200.

[0019] The control device 200 calculates a fuel injection quantity and an ignition timing based on the intake air flow rate, measured by the thermal flow meter 300, and the internal combustion engine speed, measured by the output of the rotary angle sensor 146. Based on the calculation of these values, the fuel quantity supplied by the fuel injector 152 and the ignition timing for firing the spark plug 154 are controlled. In practice, the fuel supply quantity and / or the ignition timing are further precisely controlled based on changes in the intake temperature or throttle angle, measured by the thermal flow meter 300, changes in engine speed, and the fuel / air ratio, measured by the oxygen sensor 148.In the idle drive state of the internal combustion engine, the control device 200 also controls the amount of air flowing past the throttle valve 132 by means of an idle air control valve 156 and regulates the speed of the internal combustion engine during the idle drive state. 1.2 Importance in relation to improving the measurement accuracy of the thermal flow meter and the environment for installing the thermal flow meter

[0020] Both the fuel delivery quantity and the ignition timing, as the main control variables of the internal combustion engine, are calculated using an output from the thermal flow meter 300 as the primary parameter. Therefore, improving the measurement accuracy, eliminating aging, and enhancing the reliability of the thermal flow meter 300 are crucial for improving the control accuracy of a vehicle and ensuring its reliability. Particularly in recent years, there have been many demands regarding fuel efficiency and exhaust gas purification. To meet these demands, it is essential to improve the measurement accuracy of the flow rate of the target gas 30 (intake air) measured by the thermal flow meter 300. Furthermore, maintaining high reliability of the thermal flow meter 300 is also vital.

[0021] A vehicle equipped with the 300 thermal flow meter operates in environments with significant temperature fluctuations or adverse weather conditions such as storms or snowfall. Driving on a snow-covered road, for example, involves driving on a road surface treated with antifreeze. In such an environment, the 300 thermal flow meter should ideally be designed to incorporate measures to counteract temperature fluctuations or to protect against dust or contaminants. Furthermore, the 300 thermal flow meter is installed in an environment where the internal combustion engine is subject to vibrations. Maintaining high reliability even under these conditions is essential.

[0022] The thermal flow meter 300 is installed in the intake manifold, which is affected by heat from the combustion engine. Therefore, the heat generated by the combustion engine is transferred to the thermal flow meter 300 via the intake manifold, which forms a main passage 124. Since the thermal flow meter 300 measures the flow rate of the target gas 30 by transferring heat with the target gas 30, it is important to minimize the influence of external heat as much as possible.

[0023] The thermal flow meter 300, mounted on the vehicle, solves the problems described in the section "Problems to be solved by the invention" and provides the effects described in the section "Effects of the invention," as described below. As further described below, it solves various problems, as required for a product, and provides various effects in light of the diverse problems described above. Specific problems or effects solved or provided by the thermal flow meter 300 are described in the following description of embodiments. 2. Design of the thermal flow meter 300 2.1 External structure of the thermal flow meter 300

[0024] Fig. 2(A), Fig. 2(B), Fig. 3(A), Fig. 3(B), Fig. 4(A) and Fig. Figures 4(B) are illustrations depicting the exterior of the thermal flow meter 300, wherein 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 top view and Fig. 4(B) is a bottom view. The thermal flow meter 300 has a housing 302, a front cover 303, and a rear cover 304. The housing 302 has a flange 312 for attaching the thermal flow meter 300 to an intake body as the main passage 124, an external connector 305 with an external port 306 for electrical connection to external devices, and a measuring section 310 for measuring flow rate and the like. The measuring section 310 is provided internally with a bypass channel to create a bypass passage. Additionally, the measuring section 310 is provided internally with a circuit assembly 400, which includes an airflow sensing section 602 (see Figure 4(B)). Fig. 11) for measuring the throughput of the target gas 30 flowing through the main passage 124 and a temperature detection unit 452 for measuring the temperature of the target gas 30 flowing through the main passage 124. 2.2 Effects due to the external design of the thermal flow meter 300

[0025] Since the inlet channel 350 of the thermal flow meter 300 is located at the front end of the measuring section 310, which extends from the flange 312 towards the center of the main passage 124, gas located near the inner wall surface of the main passage 124 can enter the bypass channel instead of gas located near the inner wall surface of the main passage 124. Therefore, the thermal flow meter 300 can measure the flow rate or temperature of air located away from the inner wall surface of the main passage 124 of the thermal flow meter 300, thus preventing a decrease in measurement accuracy caused by the influence of heat and the like.In the immediate vicinity of the inner wall surface of the main passage 124, the thermal flow meter 300 is slightly influenced by the temperature of the main passage 124, so that the temperature of the target gas 30 differs from the original temperature of the gas and from the average temperature of the main gas inside the main passage 124. Particularly when the main passage 124 serves as the intake body of the engine, it can be affected by heat from the engine and remain at a high temperature. For this reason, the gas in the immediate vicinity of the inner wall surface of the main passage 124 often has a temperature higher than the original temperature of the main passage 124, thus reducing the measurement accuracy.

[0026] In the immediate vicinity of the inner wall surface of the main passage 124, the fluid resistance increases and the flow velocity decreases compared to the mean flow velocity in the main passage 124. If the gas, as the target gas 30, enters the bypass passage in the immediate vicinity of the inner wall surface of the main passage 124, a measurement error can therefore occur due to a decrease in the flow velocity compared to the mean flow velocity in the main passage 124. In the case of the Fig. 2(A), Fig. 2(B), Fig. 3(A), Fig. 3(B), Fig. 4(A) and Fig. In the thermal flow meter 300 shown in Figure 4(B), since the inlet opening 350 is provided at the front end of the thin and long measuring section 310, which extends from the flange 312 to the center of the main channel 124, a measurement error associated with a decrease in flow velocity in the vicinity of the inner wall surface can be reduced. Fig. 2(A), Fig. 2(B), Fig. 3(A), Fig. 3(B), Fig. 4(A) and Fig. In addition to the inlet opening 350 provided at the front end of the measuring section 310, which extends from the flange 312 to the center of the main passage 124, the thermal flow meter 300 illustrated in Figure 4(B) also has an outlet opening of the bypass passage at the front end of the measuring section 310. Therefore, the measurement error can be reduced even further.

[0027] The measuring section 310 of the thermal flow meter 300 has a shape extending from the flange 312 towards the center of the main passage 124, and its front end is provided with the inlet opening 350 for introducing a portion of the target gas, such as intake air, into the bypass passage and the outlet opening 352 for returning the 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 towards the center, its width is narrow, as shown in Fig. 2(A) and Fig. Figure 3(A) illustrates this. This means that the measuring section 310 of the thermal flow meter 300 has a front surface with an approximately rectangular shape and a side surface of narrow width. As a result, the thermal flow meter 300 can have a bypass passage of sufficient length, and the fluid resistance for the target gas 30 can be reduced to a low value. Therefore, using the thermal flow meter 300, it is possible to reduce the fluid resistance to a low value and measure the flow rate of the target gas 30 with high accuracy. 2.3 Structure of the temperature detection unit 452

[0028] The inlet opening 343 is arranged on the side of the flange 312, starting from the bypass passage provided at the front end of the measuring section 310, and is open towards an upstream side of the flow of the target gas 30, as shown in Fig. 2(A), Fig. 2(B), Fig. 3(A) and Fig. Figure 3(B) illustrates this. A temperature detection unit 452 for measuring the temperature of the target gas 30 is arranged within the inlet opening 343. In the middle of the measuring section 310, at the location of the inlet opening 343, an upstream-facing outer wall is recessed within the measuring section 310 contained in the housing 302 towards the downstream side, and the temperature detection unit 452 is configured such that it projects from the upstream outer wall with the recess towards the upstream side. Furthermore, a front and rear cover 303 and 304 are provided on both sides of the outer wall with the recess, and the upstream ends of the front and rear covers 303 and 304 are configured such that they project from the outer wall with the recess towards the upstream side.For this reason, the outer wall with its hollow shape and the front and rear covers 303 and 304 form the inlet opening 343 on both sides for receiving the target gas 30. The target gas 30 received by the inlet opening 343 comes into contact with the temperature detection unit 452, which is provided inside the inlet opening 343, in order to measure the temperature of the temperature detection unit 452. Furthermore, the target gas 30 flows along a section that holds the temperature detection unit 452, which projects upstream from the outer wall of the housing 302 with its hollow shape, and is discharged into the main passage 124 through a front outlet opening 344 and a rear outlet opening 345, which are provided in the front and rear covers 303 and 304. 2.4 Effects relating to the temperature detection unit 452

[0029] The temperature of the gas flowing into the inlet opening 343 from the upstream side, in the direction parallel to the flow of the target gas 30, is measured by the temperature detection unit 452. The gas then flows to a constricted section of the temperature detection unit 452, leading to its mounting bracket, thus reducing the temperature of this bracket to near the temperature of the target gas 30. The temperature of the intake pipe, which serves as the main passage 124, typically increases, and heat is transferred to the mounting bracket section of the temperature detection unit 452 through the upstream outer wall within the measuring section 310, starting from the flange 312 or the thermal insulation 315. This can affect the accuracy of the temperature measurement.The aforementioned mounting section is cooled when the target gas 30 is measured by the temperature detection unit 452 and then flows along the mounting section of the temperature detection unit 452. Therefore, the heat transfer to the mounting section of the temperature detection unit 452 through the upstream outer wall inside the measuring section 310, originating from the flange 312 or the thermal insulation 315, can be kept small. In particular, the mounting section of the

[0030] Temperature detection unit 452, the upstream outer wall inside the measuring section 310 has a shape that is concave towards the downstream side (as shown below with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) described). Therefore, the length between the upstream outer wall within the measuring section 310 and the temperature detection unit 452 can be increased. As the heat conduction length increases, so does the length of the cooling section, which uses the target gas 30. It is therefore possible to also reduce the influence of the heat emanating from the flange 312 or the thermal insulation 315. Accordingly, the measurement accuracy improves. Since the upstream outer wall has a shape that is concave towards the downstream side (as described below with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) described), the circuit assembly 400 described below (see Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B)) can be easily attached. 2.5 Structures and effects of the upstream and downstream side surfaces of measuring section 310

[0031] An upstream projection 317 and a downstream projection 318 are provided on the upstream and downstream side faces, respectively, of the measuring section 310 contained in the thermal flow meter 300. The upstream projection 317 and the downstream projection 318 have a shape that tapers towards the base along the leading edge, thus reducing the fluid resistance of the intake air 30 flowing through the main passage 124. The upstream projection 317 is located between the thermal insulation 315 and the inlet opening 343. The upstream projection 317 has a large cross-section and absorbs a significant amount of heat from the flange 312 or the thermal insulation 315 via thermal conduction.However, the upstream projection 317 is truncated near the inlet opening 343, and the length of the temperature detection unit 452 increases from the temperature detection unit 452 of the upstream projection 317 due to the recess in the upstream outer wall of the housing 302, as described below. For this reason, heat conduction from the thermal insulation 315 to the mounting section of the temperature detection unit 452 is prevented.

[0032] A void containing the connecting connector 320 and the connecting connector 320 described below are formed between the flange 312 or the thermal insulation 315 and the temperature detection unit 452. For this reason, the distance between the flange 312 or the thermal insulation 315 and the temperature detection unit 452 increases, and the front cover 303 or rear cover 304 is provided in this extended section, so that this section serves as a cooling surface. Therefore, the influence of the wall surface temperature of the main passage 124 on the temperature detection unit 452 can be reduced. Additionally, because the distance between the flange 312 or the thermal insulation 315 and the temperature detection unit 452 increases, a portion of the target gas 30 fed into the bypass passage can be directed so that it reaches the vicinity of the center of the main passage 124.It is possible to suppress a reduction in measurement accuracy caused by heat transfer from the wall surface of the main passage 124.

[0033] As in Fig. 2(B) or Fig. As shown in Figure 3(B), both side faces of the measuring section 310 inserted into the main passage 124 have a very narrow shape, and a leading end of the downstream projection 318 or the upstream projection 317 has a narrow shape relative to the base, where air resistance is reduced. For this reason, the increase in fluid resistance caused by inserting the thermal flow meter 300 into the main passage 124 can be kept small. Furthermore, in the section where the downstream projection 318 and the upstream projection 317 are provided, the upstream projection 317 and the downstream projection 318, respectively, project to both sides relative to both side sections of the front cover 303 or rear cover 304.Since the upstream projection 317 or the downstream projection 318 is formed from a molded plastic part, it can be easily produced in a mold with negligible air resistance. The front cover 303 or rear cover 304 is shaped to provide an extensive cooling surface. Therefore, the thermal flow meter 300 has reduced air resistance and can be easily cooled by the target gas flowing through the main passage 124. 2.6 Structure and effects of the flange 312

[0034] The flange 312 is provided with several recesses 314 on its underside, which form a section facing the main passage 124 in order to reduce the heat transfer surface area to the main passage 124 and to make it more difficult for heat to affect the thermal flow meter 300. The screw opening 313 of the flange 312 is provided for attaching the thermal flow meter 300 to the main passage 124, and a space is formed between a surface facing the main passage 124 around each screw opening 313 and the main passage 124, such that the surface facing the main passage 124 around each screw opening 313 is set back from the main passage 124. As a result, the flange 312 has a design that can reduce heat transfer from the main passage 124 to the thermal flow meter 300 and prevent a heat-related reduction in measurement accuracy.In addition to reducing heat conduction, the recess 314 is also able to reduce the influence of the contraction of the plastic of the flange 312 during the formation of the housing 302.

[0035] The thermal insulation 315 is provided on the side of the measuring section 310 of the flange 312. The measuring section 310 of the thermal flow meter 300 is inserted into the interior from an installation opening provided in the main passage 124 such that the thermal insulation 315 faces the inner surface of the installation opening of the main passage 124. The main passage 124 serves, for example, as an intake body and is often maintained at a high temperature. Conversely, it is conceivable that the main passage 124 is maintained at a rather low temperature if operation takes place in a cold region. If such a high or low temperature condition of the main passage 124 affects the temperature detection unit 452 or the flow rate measurement described below, the measurement accuracy is impaired.For this reason, several recesses 316 are provided side by side in the thermal insulation 315 adjacent to the inner surface of the main passage 124, and the thickness of the thermal insulation 315 adjacent to the inner surface of the hole between the adjacent recesses 316 is quite thin, for example, equal to or less than 1 / 3 of the width of the fluid flow direction of the recess 316. As a result, the influence of temperature can be reduced. In addition, a section of the thermal insulation 315 with a greater thickness is implemented. During the plastic molding of the housing 302, when the plastic cools from a high temperature to a low temperature and solidifies, volume shrinkage occurs, so that deformation is generated when stress is applied. By forming the recess 316 in the thermal insulation 315, the volume shrinkage can be distributed more evenly and stress concentration can be reduced.

[0036] The measuring section 310 of the thermal flow meter 300 is inserted into the interior from the installation opening provided in the main passage 124 and fastened to the main passage 124 by means of the flange 312 of the thermal flow meter 300 with screws. The thermal flow meter 300 is preferably attached to the installation opening provided in the main passage 124 with a predetermined positional relationship. The recess 314 provided in the flange 312 can be used to define a positional relationship between the main passage 124 and the thermal flow meter 300. By forming a convex section on the main passage 124, it is possible to provide an insertion relationship between the convex section and the recess 314 and to fasten the thermal flow meter 300 to the main passage 124 in the correct position. 2.7 Structure and effects of the external connector 305 and the flange 312

[0037] Fig. Figure 4(A) is a top view illustrating the thermal flow meter 300. Four external ports 306 and one calibration port 307 are provided inside the external connector 305. The external ports 306 include ports for outputting the flow rate and temperature as measurement results from the thermal flow meter 300 and a power port for supplying DC power to operate the thermal flow meter 300. The calibration port 307 is used to measure the manufactured thermal flow meter 300 in order to obtain a calibration value for 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 stored in the memory, representing the calibration value, is used, and the calibration port 307 is not used. To prevent the calibration port 307 from obstructing a connection between the external ports 306 and other external devices, the calibration port 307 has a different shape than the external port 306. Since the calibration port 307 is shorter than the external port 306, in this embodiment the calibration port 307 does not obstruct the connection, even when the connecting port, which is attached to the external port 306 for connecting to external devices, is inserted into the external connector 305.Additionally, since several recesses 308 are formed along the external connection 306 within the external connector 305, these recesses 308 reduce a stress concentration caused by shrinkage of the plastic when it cools and solidifies as the material of the flange 312.

[0038] Since the calibration port 307 is provided in addition to the external port 306, which is used during the measurement operation of the thermal flow meter 300, the characteristic curves of each thermal flow meter 300 can be determined metrologically before shipment. This allows for the determination of the product's variability and the storage of a calibration value in the thermal flow meter 300's internal memory to reduce this variability. The calibration port 307 has a different shape than the external port 306 to prevent it from obstructing the connection between the external port 306 and external devices after the calibration value setting process. In this way, when using the thermal flow meter 300, it is possible to reduce the variability of each thermal flow meter 300 before shipment 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 airflow capture section

[0039] In Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. Figure 6(B) illustrates a state of the housing 302 in which the front and rear covers 303 and 304 have been removed from the thermal flow meter 300. Fig. 5(A) is a left side view illustrating the housing 302, Fig. Figure 5(B) is a front view illustrating the housing 302, Fig. Figure 6(A) is a right side view illustrating the housing 302 and Fig. Figure 6(B) is a rear view illustrating the housing 302. In the housing 302, the measuring section 310 extends from the flange 312 towards the center of the main passage 124, and a bypass channel for forming the bypass passage is provided at its front end. In this embodiment, the bypass channel is provided at the front and rear of the housing 302. Fig. Figure 5(B) illustrates a front bypass passage channel 332, and Fig. Figure 6(B) illustrates a rear bypass passage 334. Since an inlet channel 351 is provided to form the inlet opening 350 of the bypass passage and an outlet channel 353 is provided to form the outlet opening 352 at the front end of the housing 302, the gas that is furthest from the inner wall surface of the main passage 124, i.e., the gas flow through the region near the center of the main passage 124, can be taken from the inlet opening 350 as the target gas 30. The gas flowing through the region near the inner wall surface of the main passage 124 is influenced by the temperature of the wall surface of the main passage 124 and in many cases has a temperature that differs from the mean temperature of the gas flowing through the main passage 124, such as the intake air.Furthermore, the gas flowing near 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 insensitive to such influences, a reduction in measurement accuracy can be prevented.

[0040] The bypass passage described above, formed by the front bypass channel 332 or the rear bypass channel 334, is connected to the thermal insulation 315 via the outer wall cavity 366, the upstream outer wall 335, or the downstream outer wall 336. Furthermore, the upstream outer wall 335 is provided with the upstream projection 317, and the downstream outer wall 336 is provided with the downstream projection 318. In this configuration, since the thermal flow meter 300 is attached to the main passage 124 by means of the flange 312, the measuring section 310 with the circuit assembly 400 is reliably attached to the main passage 124.

[0041] In this embodiment, the housing 302 is provided with the bypass channel for forming the bypass passage, and the covers are attached to the front and rear of the housing 302, so that the bypass passage is formed by the bypass channel and the covers. With this design, the entirety of the bypass channels can be formed as part of the housing 302 during the plastic molding process. Additionally, since the die-casting molds are provided on both surfaces of the housing 302 during its formation, it is possible to form both the front bypass channel 332 and the rear bypass channel 334 as part of the housing 302 using the die-casting molds for both surfaces. Since the front and rear covers 303 and 304 are provided on both surfaces of the housing 302, the bypass passages can be obtained on both surfaces of the housing 302.Since the front bypass channel 332 and the rear bypass channel 334 are formed on both surfaces of the housing 302 by means of the die-casting molds, the bypass can be formed with high accuracy and high productivity can be achieved.

[0042] With reference to Fig. 6(B) A portion of the target gas 30 flowing through the main passage 124 enters the interior of the back bypass channel 334 from the inlet channel 351, which forms the inlet opening 350, and flows through the interior of the back bypass channel 334. The back bypass channel 334 gradually deepens as the gas flow progresses, and the target gas 30 moves slowly forward as it flows along the channel. The back bypass channel 334 is provided, in particular, with a steep drop section 347 that drops steeply to the upstream section 342 of the circuit assembly 400, so that a portion of the air, which has a low mass, moves along the steep drop section 347 and then over the Fig. 5(B) illustrated side of the measuring surface 430 flows into the upstream section 342 of the circuit assembly 400. Since a foreign body with a large mass has difficulty abruptly changing its path due to inertial forces, it moves towards the side of the back of the in Fig. 6(B) illustrated measuring surface 431. Then the foreign body flows through the downstream section 341 of the circuit assembly 400 to the in Fig. 5(B) illustrated measuring area 430.

[0043] A flow of the target gas 30 in the immediate vicinity of the heat transfer surface exposure section 436 is described with reference to Fig. 7(A) and Fig. 7(B) described. In the front bypass passage 332 of Fig. 5(B) the air as measurement target gas 30, which moves from the upstream section 342 of the circuit assembly 400 to the side of the front bypass channel 332, flows along the measuring surface 430, and heat transfer to the airflow detection section 602 takes place for measuring the flow rate, using the heat transfer surface exposure section 436 provided in the measuring surface 430 for measuring the flow rate. Both the target gas 30, which flows past the measuring surface 430, and the air, which comes from the downstream section 341 of the circuit assembly 400 to the front bypass channel 332, flow along the front bypass channel 332 and are discharged from the outlet channel 353 to the main passage 124 to form the outlet opening 352.

[0044] A substance with a large mass, such as an impurity mixed into the target gas 30, possesses a high inertial force and has difficulty maintaining its path to the lower side of the channel along the surface of the steep drop section 347. Fig. 6(B), where the depth of the channel drops steeply, to change abruptly. Since a foreign body with a large mass moves along the side of the back of the measuring surface 431, it is therefore possible to prevent the foreign body from flowing through the immediate vicinity of the heat transfer surface exposure section 436. Since most foreign bodies, unlike the gas, have a large mass and flow past the back of the measuring surface 431, which is a rear surface of the measuring surface 430, it is possible in this embodiment to reduce the influence of contamination caused by a foreign body such as an oil component, carbon, or a contaminant, and to prevent a reduction in measurement accuracy. This means that, since the path of the target gas 30 changes steeply along an axis transverse to the flow axis of the main passage 124, the influence of a foreign body mixed into the target gas 30 can be reduced.

[0045] In this embodiment, the flow path containing the rear bypass channel 334 is directed from the front end of the housing 302 along a curved line towards the flange, and the gas flowing through the bypass on the side closest to the flange flows in the opposite direction to the flow of the main passage 124, so that the bypass on the rear surface is connected as one side of this reverse flow to the bypass formed on the front surface as the other side. As a result, it is possible to easily attach the heat transfer surface exposure section 436 of the circuit assembly 400 to the bypass and to easily receive the target gas 30 in a position near the center of the main passage 124.

[0046] In this embodiment, a design is provided in which the rear bypass channel 334 and the front bypass channel 332 penetrate the flow direction of the measuring surface 430 for measuring the flow rate. The front end of the circuit assembly 400 is not held by the housing 302, but has a recessed section 382, ​​so that the space of the upstream section 342 of the circuit assembly 400 is connected to the space of the downstream section 341 of the circuit assembly 400.By means of the design, which penetrates the upstream section 342 of the circuit assembly 400 and the downstream section 341 of the circuit assembly 400, the bypass passage is formed such that the target gas 30 moves from the rear bypass channel 334, formed on one face of the housing 302, to the front bypass channel 332, formed on the other face of the housing 302. With this design, the bypass channel on both faces of the housing 302 can be formed by a single plastic molding operation, and the molding can be performed with a single setup to align the bypass channels on both faces.

[0047] By clamping both sides of the measuring surface 430 formed in the circuit assembly 400 using a mold to form the housing 302, it is possible to form the structure that penetrates the upstream section 342 and the downstream section 341 of the circuit assembly 400, to carry out the plastic molding of the housing 302, and to embed the circuit assembly 400 in the housing 302. Since the housing 302 is formed by inserting the circuit assembly 400 into the die-casting mold in this way, the circuit assembly 400 and the heat transfer surface exposure section 436 can be embedded with high accuracy in the bypass.

[0048] In this embodiment, a design is provided that penetrates the upstream section 342 of the circuit assembly 400 and the downstream section 341 of the circuit assembly 400. However, a design can also be provided that penetrates either the upstream section 342 or the downstream section 341 of the circuit assembly 400, and the shape of the bypass passage connecting the rear bypass channel 334 to the front bypass channel 332 can be formed by a single plastic molding operation.

[0049] An inner wall of the rear bypass passage 391 and an outer wall of the rear bypass passage 392 are provided on both sides of the rear bypass passage channel 334, and the inner surface of the rear cover 304 abuts the front end sections of the vertical direction of 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 housing 302.Furthermore, an inner wall of the front bypass passage 393 and an outer wall of the front bypass passage 394 are provided on both sides of the front bypass passage channel 332, and the inner surface of the front cover 303 abuts the front end sections of the vertical direction of the inner wall of the front bypass passage 393 and the outer wall of the front bypass passage 394, so that the front bypass passage is formed in the housing 302.

[0050] In this embodiment, the target gas 30 flows in a split manner over the measuring surface 430 and its rear side, and the heat transfer surface exposure section 436 for measuring the flow rate is provided at one of these. However, it is also possible that the target gas 30 flows only past the front surface of the measuring surface 430, instead of splitting the target gas 30 into two passages. By curving the bypass passage such that it follows a second axis transverse to a first axis of the flow direction of the main passage 124, a foreign body that has mixed into the target gas 30 can be forced to the side where the curvature of the second axis is negligible. By providing the measuring surface 430 and the heat transfer surface exposure section 436 on the side where the curvature of the second axis is pronounced, the influence of a foreign body can be reduced.

[0051] In this embodiment, the measuring surface 430 and the heat transfer surface exposure section 436 are provided in a connecting section between the front bypass channel 332 and the rear bypass channel 334. However, the measuring surface 430 and the heat transfer surface exposure section 436 can also be provided in the front bypass channel 332 or the rear bypass channel 334, and not in the connecting section between the front bypass channel 332 and the rear bypass channel 334.

[0052] An opening shape is formed in part of the heat transfer surface exposure section 436 provided in the measuring surface 430 in order to measure a flow rate (as described below with reference to Fig. 7(A) and Fig. 7(B) is described), so that the flow velocity increases due to the orifice effect and the measurement accuracy is improved. In addition, even if a vortex forms in the gas flow on the upstream side of the heat transfer surface exposure section 436, this vortex can be eliminated or reduced by means of the orifice and the measurement accuracy is improved.

[0053] With reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) An outer wall cavity 366 is provided in which the upstream outer wall 335 has a hollow shape that is recessed towards the downstream side in a constriction section of the temperature detection unit 452. This outer wall cavity 366 increases the distance between the temperature detection unit 452 and the outer wall cavity 366, thus reducing the influence of heat transferred via the upstream outer wall 335.

[0054] Although the circuit assembly 400 is enclosed by the fixing section 372 for securing it, the fixing force can be increased by additionally fixing it using the outer wall cavity 366. The fixing section 372 encloses the circuit assembly 400 along a flow axis of the target gas 30. The outer wall cavity 366 encloses the circuit assembly 400 transversely to the flow axis of the target gas 30. This means that the circuit assembly 400 is enclosed in such a way that the enclosing direction is different with respect to the fixing section 372. Since the circuit assembly 400 is enclosed in two different directions, the fixing force is increased.Although the outer wall cavity 366 is part of the upstream outer wall 335, the circuit assembly 400 can be enclosed in a direction different from that of the fixing section 372, using the downstream outer wall 336 instead of the upstream outer wall 335, in order to increase the fixing force. For example, a plate section of the circuit assembly 400 can be enclosed by the downstream outer wall 336, or the circuit assembly 400 can be enclosed by using a recess hollowed out in the upstream direction or a projection extending upstream in the downstream outer wall 336.Since the outer wall cavity 366 in the upstream outer wall 335 is intended to enclose the circuit assembly 400, an effect can be provided to increase the thermal resistance between the temperature detection unit 452 and the upstream outer wall 335 in addition to fixing the circuit assembly 400.

[0055] Since the outer wall cavity 366 is located in a constricted section of the temperature detection unit 452, it is possible to reduce the influence of heat transferred from the flange 312 or the thermal insulation 315 through the upstream outer wall 335. Furthermore, a temperature measurement recess 368, formed by a groove, is provided between the upstream projection 317 and the temperature detection unit 452. This temperature measurement recess 368 reduces heat transfer to the temperature detection unit 452 through the upstream projection 317. As a result, the detection accuracy of the temperature detection unit 452 can be improved. In particular, the upstream projection 317, due to its large cross-section, can easily transfer heat, making the functionality of the temperature measurement recess 368, which minimizes heat transfer, crucial. 3.2 Structure and effects of the airflow capture section of the bypass passage

[0056] Fig. 7(A) and Fig. Figure 7(B) shows partially enlarged views of a state in which the measuring surface 430 of the circuit assembly 400 is arranged in the bypass channel, as a cross-sectional view along line AA of Fig. 6(A) and Fig. 6(B). It should be noted that this is Fig. 7(A) and Fig. 7(B) each concerns a conceptual scheme which, in comparison to the specific design of Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) are not presented in such detail and are simplified, and some details may be slightly modified. The left side of Fig. 7(A) and Fig. 7(B) is a closed end section of the rear bypass passage 334, and the right side represents a beginning end section of the front bypass passage 332. Although not unambiguously in Fig. 7(A) and Fig. As illustrated in Figure 7(B), penetrating sections are provided on both the left and right sides of the circuit assembly 400 having the measuring surface 430, and the rear bypass channel 334 and the front bypass channel 332 are connected to the left and right sides of the circuit assembly 400 having the measuring surface 430.

[0057] The target gas 30, which is taken in through the inlet opening 350 and flows through the rear bypass passage comprising the rear bypass channel 334, is drawn from the left side by Fig. 7(A) and Fig. 7(B) supplied here. Part of the target gas 30 flows to a flow path 386, which has the front of the measuring surface 430 of the circuit assembly 400 and the projections 356 provided on the front cover 303, through the penetration section of the upstream section 342 of the circuit assembly 400. The other target gas 30 flows to a flow path 387, which is formed by the rear of the measuring surface 431 and the rear cover 304. Then the target gas 30 flowing through the flow path 387 moves to the upstream flow passage 332 through a penetration section of the downstream section 341 of the circuit assembly 400 and is combined with the target gas 30 flowing through the flow path 386, so that it flows through the upstream flow passage 332 and is then discharged from the outlet opening 352 to the main passage 124.

[0058] Since the bypass channel is designed such that the flow path of the target gas 30, which is fed to the flow path 386 through the penetration section of the upstream section 342 of the circuit assembly 400 from the rear bypass channel 334, has a greater curvature than the flow path leading to the flow path 387, a substance with a large mass, such as an impurity contained in the target gas 30, accumulates in the flow path 387, which is less curved. For this reason, hardly any foreign matter finds its way into the flow path 386.

[0059] The flow path 386 is designed such that an opening is formed such that the front cover 303 leads continuously to the front end section of the front bypass channel 332, and the projection 356 extends uniformly towards the side of the measuring surface 430. The measuring surface 430 is located on one side of the opening section of the flow path 386 and is provided with the heat transfer surface exposure section 436 for conducting heat transfer between the airflow detection section 602 and the target gas 30. To perform the measurement of the airflow detection section 602 with high accuracy, the target gas 30 preferably has a laminar flow with low turbulence in the heat transfer surface exposure section 436. Furthermore, the measurement accuracy improves with increasing flow velocity.Therefore, the opening is designed such that the projection 356 on the front cover 303, which faces the measuring surface 430, protrudes uniformly towards the measuring surface 430. This opening reduces turbulence in the target gas 30, thus approximating the flow to a laminar flow. Furthermore, since the flow velocity increases in the opening section and the heat transfer surface exposure section 436 for measuring the flow rate is located in the opening section, the measurement accuracy of the flow rate is improved.

[0060] Since the opening is designed such that the projection 356 extends towards the interior of the bypass channel to face the heat transfer surface exposure section 436 provided at the measuring surface 430, it is possible to improve the measurement accuracy. The projection 356 for forming the opening is provided on the cover facing the heat transfer surface exposure section 436 provided at the measuring surface 430. Fig. 7(A) and Fig. 7(B) The cover facing the heat transfer surface exposure section 436, which is provided on the measuring surface 430, is the front cover 303, and the projection 356 is provided on the front cover 303. Alternatively, the projection 356 can also be provided on the cover facing the heat transfer surface exposure section 436, which is provided on the measuring surface 430 of the front or rear cover 303 or 304, respectively. Depending on which of the surfaces the measuring surface 430 and the heat transfer surface exposure section 436 are provided on in the circuit assembly 400, the cover facing the heat transfer surface exposure section 436 changes.

[0061] The distribution of the target gas 30 between the flow paths 386 and 387 also relates to the high-precision measurement. This distribution can be adjusted by providing a projection in the rear cover 304, causing it to protrude towards the flow path 387. Furthermore, since the opening section is provided in the flow path 387, it is expected that this will create an effect in which a foreign body, such as a contaminant, is drawn into the flow path 387. The opening formed by the projection serves as one of the means for adjusting the distribution between the flow paths 386 and 387. Alternatively, the aforementioned distribution of the flow between the flow paths 386 and 387 can be adjusted by adjusting the width between the rear of the measuring surface 431 and the rear cover 304, and so on. As described in Fig. As illustrated in Figure 7, the projection provided in the front cover 303 is not necessary in this case.

[0062] With reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) A mold imprint 442 from the die-casting mold used in the plastic molding process of the circuit assembly 400 remains on the back of the measuring surface 431 as the back surface of the heat transfer surface exposure section 436 provided on the measuring surface 430. The mold imprint 442 does not significantly impede the measurement of the throughput and does not cause any problems even if the mold imprint 442 is permanent. As described above, it is also important to protect a semiconductor membrane of the airflow detection section 602 when the circuit assembly 400 is formed by plastic molding. For this reason, pressurizing the back surface of the heat transfer surface exposure section 436 is important. Furthermore, it is important to prevent plastic covering the circuit assembly 400 from flowing to the heat transfer surface exposure section 436.With regard to this aspect, the inflow of the plastic is prevented by encasing the measuring surface 430, including the heat transfer surface exposure section 436, using a mold and applying pressure to the rear surface of the heat transfer surface exposure section 436 using another mold. Since the circuit assembly 400 is manufactured by injection molding, the pressure of the plastic is high, and applying pressure from the rear surface of the heat transfer surface exposure section 436 is important. Additionally, since a semiconductor membrane is used in the airflow detection section 602, a ventilation passage is preferably formed for a void created by the semiconductor membrane. Applying pressure from the rear surface of the heat transfer surface exposure section 436 is important for holding and fixing a plate or similar component to form the ventilation passage. 3.3 Shapes and effects of the front and rear covers 303 and 304

[0063] The front or rear cover 303 or 304 is used to form the bypass passage by covering the bypass channel of the housing 302. Furthermore, the front or rear cover 303 or 304 has the projection 356 and is used to provide an opening in the flow path. For this reason, it is preferred to increase the imaging accuracy. Since the front or rear cover 303 or 304 is formed by a plastic molding process by injecting a thermoplastic material into a die-casting mold, it is possible to form the front or rear cover 303 or 304 with high imaging accuracy. In addition, the front and rear covers 303 and 304 are provided with the projection (the projection 356 of the front cover of Fig. 7) and are designed such that a void of the hollow section 382 of the front end face of the in Fig. 5(B) and Fig. 6(B) is embedded in the circuit assembly 400 illustrated, and cover the front end section of the circuit assembly 400 when the protrusions are fitted to the housing 302.

[0064] The front protective section 322 or the rear protective section 325 is formed in the front or rear cover 303 or 304. As shown in Fig. 2(A), Fig. 2(B), Fig. 3(A) or Fig. As illustrated in Figure 3(B), the front protective section 322, provided in the front cover 303, is arranged on the front side surface of the inlet opening 343, and the rear protective section 325, provided in the rear cover 304, is arranged in the rear side surface of the inlet opening 343. The temperature detection unit 452, which is located inside the inlet opening 343, is protected by the front protective section 322 and the rear protective section 325, thus preventing mechanical damage to the temperature detection unit 452 caused by collisions during the manufacture or loading of a vehicle.

[0065] The inner side surface of the front cover 303 is provided with the projection 356. As shown in Fig. 7(A) and Fig. As illustrated in Figure 7(B), the projection 356 is arranged such that it faces the measuring surface 430 and has a shape extending along an axis of the bypass flow path. The cross-sectional shape of the projection 356 may be inclined towards the downstream side with respect to a top surface of the projection, as shown in Fig. Figure 7 illustrates this. An orifice is formed in the previously described flow path 386 by means of the measuring surface 430 and the projection 356, thus reducing the vortex generated in the target gas 30 and producing a laminar flow. In this embodiment, the bypass passage with the orifice section is divided into a channel section and a cover section that covers the channel to form a flow path with an orifice. The channel section is formed by a second plastic molding operation to create the housing 302. Then, the front cover 303 with the projection 356 is formed by another plastic molding operation, and the channel is covered by using the front cover 303 as the cover of the channel to form the bypass passage. In the second plastic molding operation to form the housing 302, the circuit assembly 400 with the measuring surface 430 is also attached to the housing 302.Since the formation of the channel, which has such a complicated shape, is carried out by a plastic molding process and a projection 356 for the opening is provided in the front cover 303, it is possible to define the flow path 386 of . Fig. 7(A) and Fig. 7(B) can be formed with high accuracy. Furthermore, since a highly accurate arrangement relationship between the channel and the measuring surface 430 or the heat transfer surface exposure section 436 can be maintained, it is possible to reduce product modification and, as a result, obtain a good measurement result. Therefore, productivity can be improved.

[0066] This is similarly applied to the formation of the flow path 387 by means of the rear cover 304 and the back of the measuring surface 431. The flow path 387 is divided into a channel section and a cover section. The channel section is formed by a second plastic molding operation, which forms the housing 302, and the rear cover 304 covers the channel to form the flow path 387. When the flow path 387 is formed in this way, it is possible to form the flow path 387 with high accuracy and improve productivity. Although in this embodiment the opening in the flow path 386 is provided on the side of the front cover 303, the flow path 387 with the opening can also be used by providing the projection on the side of the rear cover 304 (not shown). 3.4 Setup for mounting the circuit assembly 400 using the housing 302 and related effects

[0067] Next, the fastening of the circuit assembly 400 to the housing 302 via a plastic molding process is again described with reference to Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B) described. The circuit assembly 400 is arranged in and attached to the housing 302 such that the measuring surface 430, which is formed on the front surface of the circuit assembly 400, is arranged in a predetermined position of the bypass channel for forming the bypass, for example in a connecting section between the front bypass channel 332 and the rear bypass channel 334 in the embodiment of Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. 6(B). A section for embedding and fixing the circuit assembly 400 in or on the housing 302 by plastic molding is provided as a fixing section 372 for embedding the circuit assembly 400 in the housing 302 or for attaching it to the housing 302 on the side that is slightly closer to the flange 312, starting from the bypass channel. The fixing section 372 is embedded such that the outer circumference of the circuit assembly 400, which is formed by the first plastic molding operation, is covered.

[0068] As in Fig. As illustrated in Figure 5(B), the circuit assembly 400 is fixed via the fixing section 372. The fixing section 372 comprises a circuit assembly 400 utilizing a plane with a height adjacent to the front cover 303 and a thin section 376. By designing a thin plastic covering a section corresponding to the section 376, it is possible to mitigate the contraction caused when the temperature of the plastic decreases during the formation of the fixing section 372, and to reduce the stress concentration applied to the circuit assembly 400. Even better effects can be achieved if the rear side of the circuit assembly 400 is formed in the shape described above, as shown in Figure 5(B). Fig. 6(B) is shown.

[0069] Not the entire surface of the circuit assembly 400 is covered with the plastic used to form the housing 302; rather, a section is provided on the side of the flange 312 of the fixing section 372 where 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 section that is excluded from the plastic of the housing 302 and is not enclosed by the housing 302 is larger than the area section that is enclosed by the plastic of the housing 302 outside the outer circumferential surface of the circuit assembly 400. Furthermore, a section of the measuring surface 430 of the circuit assembly 400 also remains uncovered by the plastic of the housing 302.

[0070] Since the circumference of the circuit assembly 400 is encased in the second plastic molding process to form the housing 302 by creating a portion of the fixing section 372, which covers the outer wall of the circuit assembly 400 across its entire circumference in a thin strip form, an excessively high stress concentration caused by volume contraction during the solidification of the fixing section 372 can be mitigated. This excessively high stress concentration could negatively affect the circuit assembly 400.

[0071] To further secure the circuit assembly 400 with a small surface area, while simultaneously reducing the area covered by the plastic of the housing 302 of the circuit assembly 400's outer circumferential surface, it is preferred to increase the adhesive strength of the circuit assembly 400 to the outer wall in the fixing section 372. If a thermoplastic material is used to form the housing 302, the thermoplastic material should preferably penetrate the fine irregularities on the outer wall of the circuit assembly 400 while exhibiting low viscosity, and the thermoplastic material should solidify as it penetrates these fine irregularities. During the plastic molding process for forming the housing 302, it is preferred that the inlet opening for the thermoplastic material be provided in and around the fixing section 372.The viscosity of the thermoplastic increases with rising temperature, causing it to solidify. Therefore, by allowing a high-temperature thermoplastic to flow into or from the immediate vicinity of the fixing section 372, the low-viscosity thermoplastic can be solidified while in contact with the outer wall of the circuit assembly 400. As a result, a temperature drop in the thermoplastic is prevented, and a low viscosity state is maintained, thus improving the adhesion between the circuit assembly 400 and the fixing section 372.

[0072] Roughening the outer surface of the circuit assembly 400 improves the adhesion between the circuit assembly 400 and the fixing section 372. One known method for roughening the outer surface of the circuit assembly 400 is a roughening process for creating fine irregularities on the surface of the circuit assembly 400, such as a matting treatment, after the circuit assembly 400 has been formed by the first plastic molding process. Another roughening method for creating fine irregularities on the surface of the circuit assembly 400 is, for example, sandblasting. Furthermore, roughening can be achieved by laser processing.

[0073] As another roughening method, a rough insert is attached to an inner surface of the die-casting mold used in the first plastic forming process, and the plastic is pressed against the die-casting mold, which has the insert on its surface. Using this method, it is also possible to create or roughen fine irregularities on a surface of the circuit assembly 400. Alternatively, irregularities can be applied to an inner surface of the die-casting mold used to form the circuit assembly 400 in order to roughen its surface. The surface area of ​​the circuit assembly 400 for such roughening corresponds at least to the area where the fixing section 372 is provided. Furthermore, the adhesion is further enhanced by roughening the surface area of ​​the circuit assembly 400 where the outer wall cavity 366 is provided.

[0074] When the surface irregularity of circuit assembly 400 is created using the aforementioned insert, the channel depth depends on the insert's thickness. Increasing the insert's thickness makes the initial plastic molding process more difficult, thus limiting the insert's thickness. Conversely, decreasing the insert's thickness inherently limits the depth of the irregularities. Therefore, when using the aforementioned insert, the depth of the irregularity between its base and tip should be set at 10 µm or more and 20 µm or less. A depth of less than 10 µm reduces adhesion. Achieving a depth greater than 20 µm is difficult, given the aforementioned insert thickness.

[0075] In roughening processes other than the one mentioned above, which uses the insert, it is preferred to set the thickness of the plastic in the first plastic forming operation for forming the circuit assembly 400 to 2 mm or less. For this reason, it is difficult to increase the depth of the unevenness between the base and the tip of the bump to 1 mm or more. Conceptually, it is expected that the adhesion between the plastic covering the circuit assembly 400 and the plastic used to form the housing 302 will increase with increasing depth of the unevenness between the base and the tip of the bump on the surface of the circuit assembly 400. However, for the reason described above, the depth of the unevenness between the base and the tip of the bump is preferably set to 1 mm or less.This means that if an unevenness with a thickness of 10 µm or more and 1 mm or less is provided on the surface of the circuit assembly 400, it is preferred to increase the adhesion between the plastic covering the circuit assembly 400 and the plastic used to form the housing 302.

[0076] The coefficients of thermal expansion of the thermosetting plastic used to form the circuit assembly 400 and the thermosetting plastic used to form the housing 302 with the fixing section 372 are different. Preferably, the circuit assembly 400 should not be subjected to excessive stress resulting from this difference in coefficients of thermal expansion.

[0077] By forming the fixing section 372, which encloses the outer circumference of the circuit assembly 400, in a band shape and narrowing the width of the band, it is possible to mitigate stress caused by a difference in the coefficient of thermal expansion, which is exerted on the circuit assembly 400. The width of the band of the fixing section 372 is set to 10 mm or less, and preferably to 8 mm or less. Since the outer wall cavity 366, as part of the upstream outer wall 335 of the housing 302, and the fixing section 372 enclose the circuit assembly 400 for its fixation, it is possible in this embodiment to further reduce the width of the band of the fixing section 372. The circuit assembly 400 can, for example, be fixed when the width is set to 3 mm or more.

[0078] To reduce stress caused by a difference in the coefficient of thermal expansion, the surface of the circuit assembly 400 is provided with a section covered by the plastic used to form the housing 302 and an exposed, uncovered section. Several sections are provided where the surface of the circuit assembly 400 is not covered by the plastic of the housing 302, and one of these is associated with the measuring surface 430 with the heat transfer surface exposure section 436 described above. Furthermore, a section is provided that is exposed to a portion of the side of the flange 312 with respect to the fixing section 372. Additionally, the outer wall cavity 366 is configured such that a section of the upstream side is exposed relative to the outer wall cavity 366, and this exposed section serves as a mounting section that holds the temperature detection unit 452.A void is formed such that a section of the outer surface of the circuit assembly 400 on the side of the flange 312, with respect to the mounting section 372, surrounds the circuit assembly 400 over its entire outer circumference, in particular the side facing the flange 312 from the downstream side of the circuit assembly 400, and furthermore over the upstream side of the section near the termination of the circuit assembly 400. Since the void is formed around the section where the surface of the circuit assembly 400 is exposed, the amount of heat transferred to the circuit assembly 400 through the flange 312 from the main passage 124 can be reduced, and a reduction in measurement accuracy caused by heat can be prevented.

[0079] A void is formed between the circuit assembly 400 and the flange 312, and this void serves as a connector 320. The connection terminal 412 of the circuit assembly 400 and the inner socket of the external port 361, which is positioned on the side of the housing 302 of the external port 306, are electrically connected to each other by means of this connector 320 via spot welding, laser welding, or the like. The void of the connector 320 prevents heat transfer from the housing 302 to the circuit assembly 400 as described above, and provides a space that can be used to perform a connection between the connection terminal 412 of the circuit assembly 400 and the inner socket of the external port 361 of the external port 306. 3.5 Structure and effects of the connection between the empty space in the housing 302 and outside the thermal flow meter 300

[0080] As in Fig. As shown in Figure 4(A), the opening 309, which is provided inside the external connector 305, is connected to a bore (not shown) provided in the housing 302. In this embodiment, both surfaces of the housing 302 are sealed by the front cover 303 and the rear cover 304. If the bore connected to the opening 309 were not provided, a pressure difference would arise between the air pressure in the void and atmospheric pressure due to temperature changes in the air in the void, including the connecting connector 320. It is preferred to reduce such a pressure difference. For this reason, the bore connected to the opening 309, which is provided on the inside of the external connector 305, is provided in the void of the housing 302.The external connector 305 has a design that resists the adverse effects of water and the like, in order to improve the reliability of the electrical connection. The provision of the opening 309 inside the external connector 305 prevents the ingress of water and foreign matter, such as contaminants or dust, through the opening 309. 3.6 Formation of the housing 302 by the second plastic molding process and its effects

[0081] In the above-described, in Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. In the housing 302 illustrated in Figure 6(B), the circuit assembly 400, which includes the airflow detection section 602 or the processing unit 604, is produced by the first plastic molding operation. Then, the housing 302 is produced, for example, with the front bypass channel 332 or rear bypass channel 334 to form the bypass through which the target gas 30 flows, by means of the second plastic molding operation. In this second plastic molding operation, the circuit assembly 400 is embedded in the plastic of the housing 302 and fixed to the inside of the housing 302 by plastic molding.As a result, the airflow detection section 602 performs heat transfer to the target gas 30, so that a design relationship, such as a positional or directional relationship, between the heat transfer surface exposure section 436 for measuring the flow rate and the bypass passage, which includes, for example, the front bypass channel 332 or the rear bypass channel 334, can be maintained with remarkably high accuracy. Furthermore, it is possible to reduce any error or deviation that arises at each circuit assembly 400 to a very small value. Consequently, the measurement accuracy of the circuit assembly 400 can be significantly improved. For example, compared to a conventional method where the assembly is attached using an adhesive, the measurement accuracy can be improved by a factor of two or more.Since the thermal flow meter 300 is typically manufactured in large quantities, the method of using an adhesive in conjunction with precise measurement has limitations regarding the improvement of measurement accuracy. However, if the circuit assembly 400 is manufactured by the first plastic molding process as in this embodiment, and then the bypass passage is formed in the second plastic molding process to create the bypass through which the target gas 30 flows while the circuit assembly 400 and the bypass passage are fixed, the change in measurement accuracy can be significantly reduced, and the measurement accuracy of each thermal flow meter 300 can be considerably improved. This applies similarly to the embodiment of [reference missing]. Fig. 7 and the embodiment of Fig. 5 or Fig. 6.

[0082] With further reference to the embodiment of, for example, Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. 6(B) It is possible to attach the circuit assembly 400 to the housing 302 such that a specific relationship is established between the front bypass channel 332, the rear bypass channel 334, and the heat transfer surface exposure section 436. As a result, a positional or design relationship between the heat transfer surface exposure section 436 of each circuit assembly 400 and the bypass can be consistently obtained with remarkably high accuracy in each of the mass-produced thermal flow meters 300.Since the bypass channel, where the heat transfer surface exposure section 436 of the circuit assembly 400 is attached, for example the front bypass channel 332 and rear bypass channel 334, can be formed with remarkably high accuracy, one task of forming the bypass channel consists of covering both sides of the housing 302 with the front and rear covers 303 and 304, respectively. This task is very simple and involves only a few factors that degrade measurement accuracy. Furthermore, the front and rear covers 303 and 304 are manufactured by a plastic molding process with high precision. Therefore, the bypass, which is provided in a specific ratio to the heat transfer surface exposure section 436 of the circuit assembly 400, can be formed with high accuracy.In this way, high productivity can be achieved in addition to improving measurement accuracy.

[0083] In comparison, the prior art involves manufacturing thermal flow meters by creating a bypass passage and then connecting the measuring section to the bypass passage using adhesive. This method of using adhesive is disadvantageous because the adhesive thickness is inconsistent, and the position or angle of the adhesive varies for each product. Consequently, there were limitations on improving measurement accuracy. Furthermore, when this process is carried out in mass production, improving measurement accuracy becomes even more challenging.

[0084] In the embodiment according to the invention, the circuit assembly 400 with the airflow detection section 602 is first produced by the first plastic molding process, and then the circuit assembly 400 is fixed in place by plastic molding, while the bypass channel is formed by plastic molding in a second plastic molding process. As a result, it is possible to form the shape of the bypass channel with remarkably high accuracy and to fix the airflow detection section 602 to the bypass channel with remarkably high accuracy.

[0085] A section relating to the measurement of the throughput, such as the heat transfer surface exposure section 436 of the airflow detection section 602 or the measuring surface 430 used in the heat transfer surface exposure section 436, is formed on the surface of the circuit assembly 400. The measuring surface 430 and the heat transfer surface exposure section 436 are then recessed by the plastic used to form the housing 302. This means that the heat transfer surface exposure section 436 and the measuring surface 430 around the heat transfer surface exposure section 436 are not covered by the plastic used to form the housing 302.The measuring surface 430 formed by the plastic molding of the circuit assembly 400, the heat transfer surface exposure section 436, or the temperature detection unit 452 are used directly, even after the plastic molding of the housing 302, to measure the flow rate of the thermal flow meter 300 or a temperature. As a result, the measurement accuracy is improved.

[0086] In the embodiment according to the invention, the circuit assembly 400 is formed in one piece with the housing 302, which includes a bypass passage for fixing the circuit assembly 400 to the housing 302. Therefore, the circuit assembly 400 can be fixed to the housing 302 with a small mounting surface. This means that 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 does not contact the housing 302 is, for example, open to a void. The heat from the intake pipe is transferred to the housing 302 and then from the housing 302 to the circuit assembly 400.Even if the contact area between the housing 302 and the circuit assembly 400 is reduced, instead of covering the entire surface or a large part of the surface of the circuit assembly 400 with the housing 302, high reliability and high accuracy can be maintained, and the circuit assembly 400 can be attached to the housing 302. For this reason, the heat transfer from the housing 302 to the circuit assembly 400 can be kept low, and a decrease in measurement accuracy can be prevented.

[0087] In the Fig. 5(A), Fig. 5(B), Fig. 6(A) or Fig. In the embodiment illustrated in Figure 6(B), the area A of the exposed surface of the circuit assembly 400 can be positioned such that it is equal to or larger than an area B covered by a molding material used to form the housing 302. In this embodiment, area A is larger than area B. As a result, the heat transfer from the housing 302 to the circuit assembly 400 can be minimized. Furthermore, it is possible to reduce the stress caused by the difference between the coefficient of thermal expansion of the thermosetting polymer used to form the circuit assembly 400 and the coefficient of thermal expansion of the thermoplastic used to form the housing 302. 4. External appearance of the circuit assembly 4004.1 Formation of the measuring surface 430 with the heat transfer surface exposure section 436

[0088] To determine the state of the target gas 30 using the airflow detection section 602 embedded in the circuit assembly 400 (see Fig. 11) To determine the flow rate with high accuracy, the gas flowing through the immediate vicinity of the heat transfer surface exposure section 436 preferably has a laminar flow with low turbulence. For this reason, it is preferred that there is no height difference between the flow path-side surface of the heat transfer surface exposure section 436 and the plane of the measuring surface 430 that guides the gas. This design prevents the airflow detection section 602 from being subjected to irregular stress or distortion, while simultaneously ensuring high measurement accuracy with respect to the flow rate. It should be noted that the aforementioned height difference can be provided if it does not impair the measurement accuracy of the flow rate.

[0089] On the back side of the measuring surface 430 of the heat transfer surface exposure section 436, as shown in Fig. Figure 8 shows a press impression 442 of the die-casting mold, which supports an inner substrate or plate during the plastic molding of the circuit assembly 400. The heat transfer surface exposure section 436 is used to facilitate heat exchange with the target gas 30. To accurately determine the state of the target gas 30, it is preferred to ensure that the heat transfer between the airflow detection section 602 and the target gas 30 occurs in a suitable manner. For this reason, it is necessary to prevent any part of the heat transfer surface exposure section 436 from being covered by the plastic during the first plastic molding process.Molding tools are used both at the heat transfer surface exposure section 436 and on the back side of the measuring surface 431, preventing the plastic from flowing into the heat transfer surface exposure section 436. A concave impression 442 is formed on the back side of the heat transfer surface exposure section 436. A component, preferably serving as the airflow detection section 602 or the like, is preferably positioned in close proximity to this section to dissipate the heat generated by the component as much as possible to the outside. The resulting concave section is less affected by the plastic and dissipates heat effortlessly.

[0090] A semiconductor membrane corresponding to the heat transfer surface exposure section 436 is formed in an airflow sensing section (flow rate sensing element) 602, which includes a semiconductor device. The semiconductor membrane can be obtained by forming a void on the back surface of the flow rate sensing element 602. If the void is covered, the semiconductor membrane will deform, and the measurement accuracy will be reduced, due to a pressure change in the void caused by a temperature change. For this reason, in this embodiment, an opening 438, which communicates with the void on the back surface of the semiconductor membrane, is provided on the front surface of the circuit assembly 400, and a connecting channel for connecting the void on the back surface of the semiconductor membrane to the opening 438 is provided in the circuit assembly 400.It should be noted that opening 438 is provided in the section which is in . Fig. 14(A) to 14(C) is not hatched to prevent the opening 438 from being covered with plastic by the second plastic forming process.

[0091] It is necessary to form the opening 438 by the first plastic molding operation, while preventing the plastic from flowing into the section of the opening 438, both to a section of the opening 438 and to its rear surface, by adjusting the molding tools and pressing the molding tools into place. The formation of the opening 438 and the connecting channel that links the void on the rear surface of the semiconductor membrane to the opening 438 is described below. 4.2 Formation of the temperature detection unit 452 and the projection 424 and their effects

[0092] The temperature detection unit 452 provided in the circuit assembly 400 is also located at the front end of the projection 424, which extends upstream of the target gas 30 to hold the temperature detection unit 452 and also serves to detect the temperature of the target gas 30. To detect the temperature of the target gas 30 with high accuracy, it is preferred that the heat transfer to sections other than the target gas 30 be reduced as much as possible. The projection 424, which holds the temperature detection unit 452, has a shape with a front end that is thinner than its base and is provided with the temperature detection unit 452 at its front end section. This shape makes it possible to reduce the influence of heat from the neck section of the projection 424 on the temperature detection unit 452.

[0093] After the temperature of the target gas 30 has been detected by the temperature detection unit 452, the target gas 30 flows along the projection 424, and the temperature of the projection 424 approaches the temperature of the target gas 30. As a result, the influence of the temperature of the neck section of the projection 424 on the temperature detection unit 452 is minimized. In particular, in this embodiment, the temperature detection unit 452 is thinner in the immediate vicinity of the projection 424 and thicker towards the neck of the projection 424. This allows the target gas 30 to flow along the shape of the projection 424, effectively cooling it. 4.3 Connection of the circuit assembly 400

[0094] The circuit assembly 400 is provided with the connection terminal 412 to supply electrical energy for operating the embedded airflow sensing section 602 or the processing unit 604 and to output the throughput measurement or the temperature measurement. A terminal 414 is also provided in parallel to the connection terminal 412 to check whether the circuit assembly 400 is functioning correctly or not, or whether a fault exists in a circuit component or its connection. In this embodiment, the circuit assembly 400 is formed by an injection molding process for the airflow sensing section 602 or the processing unit 604 using a thermosetting plastic in the first plastic molding operation. The dimensional accuracy of the circuit assembly 400 can be improved by performing the injection molding process.Since the plastic is injected into the interior of the tightly sealed die-casting mold under high pressure and temperature, where the airflow detection section 602 or the processing unit 604 is embedded, it is preferable to check during an injection molding process whether or not there is a defect in the airflow detection section 602 or the processing unit 604 and the associated wiring for the resulting circuit assembly 400. In this embodiment, a test port 414 is provided for testing, and a test is performed for each individual circuit assembly 400 produced. Since the test port 414 is not used for measurement, the port is not connected to the inner socket of the external port 361, as described above. Furthermore, each connection port 412 is provided with a curved section 416 to increase mechanical elasticity.If a mechanical elastic force is provided in each connection port 412, it is possible to absorb stress caused by a difference in the coefficient of thermal expansion between the plastic of the first plastic forming process and the plastic of the second plastic forming process. This means that each connection port 412 is affected by the thermal expansion caused by the first plastic forming process, and the inner socket of the external port 361, which is connected to each connection port 412, is affected by the plastic of the second plastic forming process. It is therefore possible to absorb the generation of stress caused by the difference in the plastic. 4.4 Fastening of the circuit assembly 400 by the second plastic molding process and its effects

[0095] As in Fig. 5(B), Fig. As shown in Figure 6(B), the central section of the circuit assembly 400 and the like are a fixing section 372 and a thin section 376 for covering the circuit assembly 400 with the thermoplastic material used in the second plastic molding operation to attach the circuit assembly 400 to the housing 302 in the second plastic molding operation. Fig. 5(A), Fig. 5(B), Fig. 6(A) and Fig. As described in Figure 6(B), it is important to maintain high accuracy in order to provide a specific relationship between the measuring surface 430, the heat transfer surface exposure section 436 provided in the measuring surface 430, and the shape of the bypass passage. During the second plastic molding operation, the bypass passage is formed, and the circuit assembly 400 is attached to the housing 302 that forms the bypass passage. Therefore, it is possible to maintain a relationship between the bypass passage, the measuring surface 430, and the heat transfer surface exposure section 436 with remarkably high accuracy. Since the circuit assembly 400 is attached to the housing 302 in the second plastic molding operation, it is possible to position or fix the circuit assembly 400 with high accuracy in the die-casting mold used to form the housing 302 with the bypass passage.By injecting a high-temperature thermoplastic material into this die-casting mold, the bypass passage is formed with high accuracy and the circuit assembly 400 is fixed with high accuracy.

[0096] In this embodiment, not the entire surface of the circuit assembly 400 is covered by the plastic used to form the housing 302, but rather the front surface is exposed on the side of the connection terminal 412 of the circuit assembly 400. This means that a section is provided that is not covered by the plastic used to form the housing 302. In this embodiment, the area of ​​the front surface of the circuit assembly 400 that is not encased by the plastic used to form the housing 302, but remains uncovered by the plastic used to form the housing 302, is larger than the area of ​​the fixing section 372 and the thin section 376 that is encased by the plastic used to form the housing 302.

[0097] The coefficient of thermal expansion of the thermosetting plastic used to form the circuit assembly 400 differs from the coefficient of thermal expansion of the thermosetting plastic used to form the housing 302 with the fixing section 372. Preferably, any stress caused by this difference in coefficient of thermal expansion should not act on the circuit assembly 400 for as long as possible. The influence resulting from the difference in coefficient of thermal expansion can be reduced by decreasing the front surface area of ​​the circuit assembly 400, the mounting surface 432, and the thin section 376. For example, the mounting surface on the front surface of the circuit assembly 400 can be reduced by forming the width of the fixing section 372 and the thin section 376 into a band shape.

[0098] It is possible to increase the mechanical strength of the temperature detection unit 452 by providing the fixing section 372 and the thin section 376 at the base of the projection of the temperature detection unit 452. It is possible to further strengthen the fixation of the circuit assembly 400 and the housing 302 to one another by providing a band-shaped mounting surface along the flow axis of the target gas 30 and a mounting surface transverse to the flow axis of the target gas 30 on the front surface of the circuit assembly 400.On the mounting surface 432 and the thin section 376, a section that surrounds the circuit assembly 400 in ribbon form with a predetermined width along the measuring surface 430 is the mounting surface described above along the flow axis of the target gas 30, and a section that covers the base of the temperature detection unit 452 represents the mounting surface transverse to the flow axis of the target gas 30. 5. Mounting circuit components on the circuit assembly 5.1 Frame of the circuit assembly

[0099] As in Fig. As shown in Figures 8(A) to 8(C), a plate 532 is mounted in the center of the frame of the circuit assembly 400, and chips of the circuit components and the like are mounted on the plate 532. A conductor frame is mechanically connected to the frame that secures the plate 532. A chip-like airflow sensing section 602 and a processing unit 604, serving as an LSI circuit, are attached to the plate 532 mounted in the center of the frame. A membrane 672 is provided in the airflow sensing section 602, and this membrane corresponds to the heat transfer surface exposure section 436, which is formed by the molding process as described above, exposing the heat transfer surface 437 discussed above. Each terminal of the airflow sensing section 602 and the processing unit 604, described below, is connected by a wire 542.Furthermore, each terminal of the processing unit 604 and a corresponding conductor frame 514 are connected by means of a wire 543. In addition, the conductor frame (not shown), which is positioned between a section corresponding to the connection terminal of the circuit assembly 400 and the plate 532, is connected to the chip-like, intervening circuit component.

[0100] The airflow sensing section 602, which includes the membrane 672, is located at the frontmost end when the circuit assembly 400 is assembled in this manner. The processing unit 604 is located in an LSI state on the side corresponding to the connection port for the airflow sensing section 602. Furthermore, a connecting wire 543 is located on the connection side of the processing unit 604. By arranging the airflow sensing section 602, the processing unit 604, the wire 543, the circuit component 516, and the connecting wire frame 514 sequentially in this order, starting from the front end of the circuit assembly 400 and proceeding to the connection port, the entire circuit assembly 400 is simple and compact.

[0101] Several conductor frames are provided to hold the plate 532, and this conductor frame is attached to the frame. It should be noted that a conductor frame surface (not shown) with the same area as that of the plate 532 connected to the conductor frame is provided on the underside of the plate 532, and the plate 532 is attached to this conductor frame surface. This conductor frame surface is grounded. As a result, it is possible to suppress noise by grounding the circuitry of the airflow detection section 602 or the processing unit 604 together via the conductor frame surface, thus improving the measurement accuracy of the target gas 30.Furthermore, a conductor frame is provided on the upstream side of the flow path, extending from the plate 532 in the direction of the temperature detection unit 452, such that it projects along an axis that runs transversely to the axis of the airflow sensing section 602, the processing unit 604, or the circuit component 516 described above. For example, a chip-like thermistor is connected to this conductor frame 544 as a temperature sensing element, forming the temperature detection unit. Additionally, a conductor frame is also provided in the immediate vicinity of the processing unit 604, which forms the basis of the temperature detection unit 452, and the conductor frames are electrically connected to each other by means of a thin conductor, such as a gold wire.If the conductor frames are directly connected, heat is transferred via the conductor frames to the temperature sensing element, such as the thermistor, making it difficult to accurately measure the temperature of the target gas 30. Therefore, it is possible to increase the thermal resistance between the conductor frames by connecting a wire with a small cross-sectional area and high thermal resistance. As a result, the temperature measurement accuracy of the target gas 30 can be improved, preventing the influence of heat from reaching the temperature sensing element of the temperature detection unit 452. 5.2 Construction of the connection void on the back surface of the membrane and opening

[0102] Fig. Figure 8 is a figure showing part of the cross-section along a line CC of Fig. Figure 5(B) illustrates a connecting opening 676 which connects a void 674 provided within the membrane 672 and the airflow sensing section (the flow sensing element) 602 to the opening 520.

[0103] As described below, the airflow sensing section 602 is equipped with a membrane 672 for measuring the flow rate of the target gas 30, and a void 674 is provided on the back surface of the membrane 672. Although not illustrated, the membrane 672 is provided with an element for heat exchange with the target gas 30 and for simultaneously measuring the flow rate. If the heat to the elements formed in the membrane 672 is transferred separately from the heat exchange with the target gas 30, it is difficult to measure the flow rate accurately. Therefore, it is necessary to increase the thermal resistance of the membrane 672 and to make the membrane 672 as thin as possible.

[0104] The airflow sensing section (the throughput sensing element) 602 is embedded in and fixed within the first plastic of the circuit assembly 400, which is formed by the first plastic molding process such that the heat transfer surface 437 of the membrane 672 is exposed. The surface of the membrane 672 is provided with the elements described above (not shown) (such as a heat generator 608, resistors 652 and 654 as upstream resistance temperature detectors, and resistors 656 and 658 as downstream resistance temperature detectors, which are located in Fig. (15 illustrated). Heat transfer to the target gas 30 (not shown) takes place at the elements via the heat transfer surface 437 on the surface of the elements in the heat transfer surface exposure section 436 corresponding to the membrane 672. The heat transfer surface 437 can be provided on the surface of each element or can be provided with a thin protective layer. Preferably, the heat transfer between the elements and the target gas 30 should be uniform, and direct heat transfers between the elements should be reduced as much as possible.

[0105] A section of the airflow sensing section (throughput sensing element) 602, in which the elements are provided, is arranged in the heat transfer surface exposure section 436 of the measuring surface 430, and the heat transfer surface 437 is recessed by the plastic used to form the measuring surface 430. The outer circumference of the airflow sensing element 602 is covered by the thermosetting plastic used in the first plastic forming operation to form the measuring surface 430. If only the side surface of the airflow sensing element 602 is covered by the thermosetting plastic and the surface side of the outer circumference of the airflow sensing element 602 (i.e.,Since the area around the membrane 672 is not covered by the thermosetting plastic, stress in the plastic used to form the measuring surface 430 is absorbed only by the side surface of the airflow sensing element 602, which can lead to distortion in the membrane 672 and a deterioration of its characteristic features. The distortion of the membrane 672 is reduced by covering the outer circumferential section of the airflow sensing element 602 with the thermosetting plastic, as shown in [reference]. Fig. Figure 8 illustrates this. If the height difference between the heat transfer surface 437 and the measuring surface 430, where the target gas 30 flows, is large, the flow of the target gas 30 is disturbed, thus impairing the measurement accuracy. It is therefore preferred that the height difference W between the heat transfer surface 437 and the measuring surface 430, where the target gas 30 flows, is small.

[0106] The membrane 672 is designed with a small thickness to minimize heat transfer between each element. This thin design is achieved by forming a void 674 on the rear surface of the airflow-sensing element 602. When this void 674 is tightly sealed, the pressure within the void 674, formed on the rear surface of the membrane 672, changes with temperature variations. As the pressure difference between the void 674 and the surface of the membrane 672 increases, the membrane 672 absorbs the pressure, causing distortion and making highly accurate measurement difficult. For this reason, a bore 520 is provided in the plate 532, connected to the outwardly opening 438, and a connecting opening 676 is provided to link this bore 520 to the void 674.This connecting opening 676 consists, for example, of a pair of plates, a first plate 532 and a second plate 536. The first plate 532 is provided with bores 520 and 521 and a channel for forming the connecting opening 676. The connecting opening 676 is formed by covering the channel and the bores 520 and 521 with the second plate 536. By means of the connecting opening 676 and the bore 520, the pressures acting on the front and back surfaces of the diaphragm 672 are made approximately equal, thus improving the measuring accuracy.

[0107] As previously described, the connection opening 676 can be formed by covering the channel and bores 520 and 521 with the second plate 536. Alternatively, the conductor frame can be used as the second plate 536. Inside the circuit assembly 400, which is connected to Fig. As described in Figure 5(B), the diaphragm 672 and the LSI circuit serving as the processing unit 604 are provided on the plate 532. A conductor frame is provided below the plate 532 for mounting the diaphragm 672 and the processing unit 604. Therefore, the construction is simplified when using the conductor frame. Furthermore, the conductor frame can be used as a ground electrode. If the conductor frame serves as the second plate 536 and the connecting opening 676 is formed by covering the bores 520 and 521 in the first plate 532 with the conductor frame, and the channel formed in the first plate 532 is thus covered by the conductor frame, the overall construction can be simplified. In addition, the influence of noise originating from the vicinity of the diaphragm 672 and the processing unit 604 can be reduced because the conductor frame serves as a ground electrode.

[0108] On the circuit assembly 400, the press impression 442 remains on the rear surface of the circuit assembly 400 where the heat transfer surface exposure section 436 is formed. In the first plastic molding process, to prevent the plastic from flowing into the heat transfer surface exposure section 436, a molding tool, such as an insertion mold, is inserted into a section of the heat transfer surface exposure section 436, and a molding tool is inserted into an opposite section of the press impression 442, thus preventing the plastic from flowing into the heat transfer surface exposure section 436. Because part of the heat transfer surface exposure section 436 is formed in this way, the flow rate of the target gas 30 can be measured with remarkably high accuracy. 6. Procedure for manufacturing the thermal flow meter 3006.1 Procedure for manufacturing the circuit assembly 400

[0109] Fig. 9(A) to 9(C) and Fig. Figure 10 illustrates a process for manufacturing the thermal flow meter 300, wherein Fig. 9(A) to 9(C) illustrates a method for manufacturing the circuit assembly 400 and Fig. Figure 10 illustrates a method for manufacturing the thermal flow meter. Fig. Figures 9(A) to 9(C) show step 1, a process for manufacturing the frame used for the circuit assembly 400. This frame is formed, for example, by press machining.

[0110] In step 2, the plate 532 is first mounted on the frame obtained in step 1, and then the airflow detection section 602 or the processing unit 604 is attached to the plate 532. Next, the temperature sensing element 518 and the circuit component, such as a chip capacitor, are mounted on it. In step 2, the electrical wiring is carried out between the circuit components, between the circuit component and the conductor frame, and between the conductor frames. In step 2, the conductor frames 544 and 548 are connected by means of a connecting line (not shown) to increase the thermal resistance. The connecting line is intended to receive an electrical signal from a temperature sensing element, which is used by the temperature detection unit 452.In step 2, the circuit component is placed on the frame, and the electrical wiring is then carried out, so that an electrical circuit is formed.

[0111] Then, in step 3, the first plastic molding process takes place, using a thermosetting plastic. In this state, the circuit component attached to the frame is covered with a molded plastic. Furthermore, in step 3, each of the connected conductor frames is separated from the frame 512, and the conductor frames are separated from each other, resulting in the circuit assembly 400. The measuring surface 430 and the heat transfer surface exposure section 436 are formed in this circuit assembly 400, although they are not shown in the drawing.

[0112] In step 4, a visual inspection or a functional test is performed on the resulting circuit assembly 400. In the first plastic molding operation of step 3, the electrical circuit obtained in step 2 is mounted inside the die-casting mold, and plastic is injected into the die-casting mold at high temperature and high pressure. Therefore, it is preferable to check whether or not there is a fault in the electrical component or the electrical wiring. For this test, the circuit obtained in step 2 is used. Fig. 5(A) and Fig. 6(B) used connection port 414 and the like. 6.2 Procedure for manufacturing the thermal flow meter 300 and calibrating the characteristic features

[0113] In the step of Fig. 10 is achieved by means of the as in Fig. The housing 302 is produced according to the second plastic molding operation in step 5, using the circuit assembly 400 and the external port 306 produced in steps 9(A) to 9(C). The bypass channel, flange 312, or external connector 305, formed from plastic, is created in the housing 302, and a section of the circuit assembly 400 is covered with plastic in the second plastic molding operation, thus fixing the circuit assembly 400 to the housing 302. The accuracy of the flow rate measurement is significantly improved by combining the production (step 3) of the circuit assembly 400 by the first plastic molding operation and the formation of the housing 302 of the thermal flow meter 300 by the second plastic molding operation. In step 6, the internal sockets of the external port 361 are separated, and in step 7, the connecting port 412 and the internal socket of the external port 361 are joined.

[0114] The housing 302 is obtained in step 7, and then in step 8 the front and rear covers 303 and 304 are installed in the housing 302 and the interior of the housing 302 is tightly sealed by means of the front and rear covers 303 and 304, so that the bypass passage for the flow of the target gas 30 is obtained. In addition, the one associated with Fig. 7(A), Fig. The muzzle assembly described in 7(B) is formed by the projection 356, which is provided on the front cover 303. Depending on requirements, the projection can also be provided on the rear cover 304. It should be noted that the front cover 303 is formed by the shaping of step 10 and the rear cover 304 by the shaping of step 11. Furthermore, the front and rear covers 303 and 304 are formed by separate operations using different die-casting molds.

[0115] In step 9, a feature test is performed by directing air to the bypass passage in practice. Since, as described above, a highly accurate relationship is maintained between the bypass passage and the airflow capture section, exceptionally high measurement accuracy is achieved by performing feature calibration via a feature test. Furthermore, because the molding is carried out with a positional or design relationship between the bypass passage and the airflow capture section, determined by the first and second plastic molding operations, the feature does not change significantly even with long-term use, and high reliability is maintained in addition to high accuracy. 7. Circuit design of the thermal flow meter 3007.1 Overall circuit design of the thermal flow meter 300

[0116] Fig. Figure 11 is a circuit diagram showing the flow rate sensing circuit 601 of the thermal flow meter 300. It should be noted that the measuring circuit described in the aforementioned embodiment, which relates to the temperature detection unit 452, is also provided in the thermal flow meter 300, but in Fig. Figure 11 is intentionally not illustrated. The flow sensing circuit 601 of the thermal flow meter 300 comprises the airflow sensing section 602 with the heat generator 608 and the processing unit 604. The processing unit 604 controls a quantity of heat from the heat generator 608 of the airflow sensing section 602 and, based on the output of the airflow sensing section 602, outputs a signal representing the flow rate via the terminal 662. For this processing, the processing unit 604 comprises a central processing unit (hereinafter referred to as the "CPU") 612, an input circuit 614, an output circuit 616, a memory 618 for storing data that represents 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 required circuit.The power circuit 622 is supplied with direct current energy from an external energy source, such as a battery installed in the vehicle, via a connection 664 and a ground connection (not shown).

[0117] The airflow detection section 602 is equipped with a heat generator 608 for heating the target gas 30. A voltage V1 is supplied by the power circuit 622 to a collector of a transistor 606, which is part of a current supply circuit of the heat generator 608, and a control signal is applied by the CPU 612 to a base of the transistor 606 via the output circuit 616. Based on this control signal, current is supplied from the transistor 606 to the heat generator 608 through terminal 624. The amount of current supplied to the heat generator 608 is controlled by a control signal applied by the CPU 612 to the transistor 606 of the current supply circuit of the heat generator 608 via the output circuit 616.The processing unit 604 controls the amount of heat from the heat generator 608 so that, starting from an initial temperature, the temperature of the target gas 30 increases by a predetermined temperature, for example 100 °C, by heating it using the heat generator 608.

[0118] The airflow sensing section 602 has a heating control bridge 640 for controlling the amount of heat from the heat generator 608 and an airflow sensing bridge circuit 650 for measuring the flow rate. A predetermined voltage V3 is supplied 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. A predetermined voltage V2 is also applied to one end of the airflow sensing bridge circuit 650 from the power circuit 622 via terminal 625, and the other end of the airflow sensing bridge circuit 650 is connected to the ground terminal 630.

[0119] The heating control bridge 640 includes a resistor 642, which is a resistance temperature detector with a resistance value that changes depending on the temperature of the heated target gas 30. Resistors 642, 644, 646, and 648 form a bridge circuit. A potential difference between node A (between resistors 642 and 646) and node B (between resistors 644 and 648) is input to the input circuit 614 via terminals 627 and 628. The CPU 612 controls the current supplied by transistor 606 to regulate the heat output of the heat generator 608 so that the potential difference between nodes A and B is set to a predetermined value, for example, zero voltage in this embodiment. Fig. Figure 11 illustrates the flow rate sensing circuit 601. This circuit heats the target gas 30 using the heat generator 608 such that the temperature always increases by a predetermined amount, for example, by 100 °C from an initial temperature of the target gas 30. To perform this heating control with high accuracy, the resistance values ​​of each resistor in the heating control bridge 640 are set such that the potential difference between nodes A and B always becomes zero when the temperature of the target gas 30 heated by the heat generator 608 increases by a predetermined amount, for example, by 100 °C from an initial temperature. Therefore, in the flow rate sensing circuit 601, the heating control bridge 640 controls the temperature of the target gas 30 by a predetermined amount. Fig. 11 the CPU 612 the electrical current supplied to the heat generator 608 so that the potential difference between nodes A and B becomes zero.

[0120] The bridge circuit of the airflow sensing device 650 comprises four resistance temperature detectors with resistors 652, 654, 656, and 658. The four resistance temperature detectors are arranged along the flow of the target gas 30 such that resistors 652 and 654 are located upstream in the flow path of the target gas 30 with respect to the heat generator 608, and resistors 656 and 658 are located downstream in the flow path of the target gas 30 with respect to the heat generator 608. Furthermore, to increase measurement accuracy, resistors 652 and 654 are arranged such that their distances to the heat generator 608 are approximately equal, and resistors 656 and 658 are also arranged such that their distances to the heat generator 608 are approximately equal.

[0121] A potential difference between node C (between resistors 652 and 656) and 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 in the bridge circuit of the airflow sensing unit 650 is adjusted, for example, so that the potential difference between nodes C and D becomes zero when the flow rate of the target gas 30 is zero. Therefore, when the potential difference between nodes C and D is set to zero, for example, the CPU 612 outputs an electrical signal at terminal 662 indicating that the flow rate in the main passage 124 is zero, based on the measurement result that the flow rate of the target gas 30 is zero.

[0122] If the target gas is 30 along the direction of the arrow in Fig. As the gas 11 flows, the upstream resistors 652 and 654 are cooled by the target gas 30, and the resistors 656 and 658, located on the downstream side of the target gas 30, are heated by the target gas 30 heated by the heat generator 608, causing the temperature of resistors 656 and 658 to rise. This generates a potential difference between nodes C and D of the airflow sensing bridge circuit 650, and this potential difference is fed into the input circuit 614 via terminals 631 and 632. Based on this potential difference between nodes C and D of the airflow sensing bridge circuit 650, the CPU 612 searches for data indicating a relationship between the main throughput 124 and the aforementioned potential difference stored in memory 618, in order to determine the main throughput 124.An electrical signal obtained in this way, indicating the throughput of the main passage 124, is output through terminal 662. Although the in . Fig. Note that the illustrated connections 664 and 662 are designated with new reference numbers in Figure 11; they are located in the connection connection 412 described above. Fig. 5(A), Fig. 5(B), Fig. 6(A), Fig. 6(B) and the like.

[0123] Memory 618 stores data specifying the relationship between the potential difference between nodes C and D and the throughput in main passage 124, and stores calibration data to reduce measurement errors, such as deviations, based on the actual gas measurement after assembly of circuit 400. It should be noted that the actual gas measurement after assembly of circuit 400 and the resulting calibration value in memory 618 are determined using the data in Fig. 4(A) and Fig. The external connection 306 or calibration connection 307 illustrated in Figure 4(B) are stored. In this embodiment, the circuit assembly 400 is manufactured while maintaining a highly accurate and low-deviation arrangement between the bypass passage for the flow of the target gas 30 and the measuring surface 430, or between the bypass passage for the flow of the target gas 30 and the heat transfer surface exposure section 436. Therefore, a measurement result with remarkably high accuracy can be obtained by calibration using the calibration value. 7.2 Design of the throughput measurement circuit 601

[0124] Fig. Figure 12 is a diagram of a circuit layout, which represents a circuit arrangement of the throughput detection circuit 601 described above. Fig. Figure 11 shows the throughput measurement circuit 601, which is made from a rectangular semiconductor chip. The target gas 30 flows along the direction of the arrow from the left side to the right side of the [unclear text]. Fig. 12 illustrated throughput measurement circuit 601.

[0125] A rectangular membrane 672 with the thin semiconductor chip is formed in the airflow sensing section (throughput sensing element) 602, which is made from a semiconductor chip. The membrane 672 is provided with a thin area (i.e., with the aforementioned heat transfer surface) 603, which is indicated by the dotted line. The aforementioned void is formed on the rear surface side of the thin area 603 and is oriented with the Fig. 8(A) to 8(C) or 5 illustrated opening 438 in connection, so that the gas pressure inside the void depends on the pressure of the gas supplied from opening 438.

[0126] By reducing the thickness of the membrane 672, the thermal conductivity decreases, and the heat transfer through the membrane 672 to the resistors 652, 654, 658 and 656, which are provided in the thin area (in the heat transfer surface) 603 of the membrane 672, is prevented, so that the temperatures of the resistors are approximately adjusted by the heat transfer with the target gas 30.

[0127] The heat generator 608 is located in the center of the thin section 603 of the membrane 672, and the resistor 642 of the heating control bridge 640 is located around the heat generator 608. Furthermore, the resistors 644, 646, and 648 of the heating control bridge 640 are located on the outside of the thin section 603. The resistors 642, 644, 646, and 648 thus formed the heating control bridge 640.

[0128] Furthermore, resistors 652 and 654, acting as upstream resistance temperature detectors, and resistors 656 and 658, acting as downstream resistance temperature detectors, are arranged such that the heat generator 608 lies between them. Resistors 652 and 654, acting as upstream resistance temperature detectors, are located on the upstream side in the direction of the arrow, where the target gas 30 flows with respect to the heat generator 608. Resistors 656 and 658, acting as downstream resistance temperature detectors, are located on the downstream side in the direction of the arrow, where the target gas 30 flows with respect to the heat generator 608. In this way, the bridge circuit of the airflow sensing device 650 is formed by resistors 652, 654, 656, and 658 arranged in the thin section 603.

[0129] Both ends of the heat generator 608 are each connected to one of the connections 624 and 629, which are located in the lower half of Fig. 12 are illustrated. As in Fig. As shown in Figure 11, the current supplied by transistor 606 to heat generator 608 is applied to terminal 624, and terminal 629 is connected to ground.

[0130] Resistors 642, 644, 646, and 648 of the heating control bridge 640 are connected to each other and to terminals 626 and 630. As shown in Fig. As illustrated in Figure 11, terminal 626 is supplied with a predetermined voltage V3 from the power circuit 622, and terminal 630 is connected to ground. 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. As illustrated in Figure 12, 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 illustrated in Figure 11, terminal 625 is supplied with a predetermined voltage V2 from the power circuit 622, and terminal 630 is grounded as the ground terminal. Furthermore, a node between resistors 654 and 658 is connected to terminal 631, and terminal 631 outputs an electrical potential of node B. Fig. 11. The node between resistors 652 and 656 is connected to terminal 632, and terminal 632 outputs an electrical potential of the in Fig. 11 illustrated node C.

[0131] As in Fig. As illustrated in Figure 12, since the resistor 642 of the heating control bridge 640 is located in the immediate vicinity of the heat generator 608, the temperature of the gas heated by the heat from the heat generator 608 can be measured with high accuracy. The resistors 644, 646, and 648 of the heating control bridge 640, being located far from the heat generator 608, are not easily affected by the heat generated by the heat generator 608. The resistor 642 is designed to be sensitive to the temperature of the gas heated by the heat generator 608, and the resistors 644, 646, and 648 are designed to be unaffected by the heat generator 608.For this reason, the detection accuracy of the target gas 30 using the heating control bridge 640 is high, and the control to heat the target gas 30 by only a predetermined temperature starting from its initial temperature can be accomplished with high accuracy.

[0132] In this embodiment, a void is formed on the rear surface side of the membrane 672, which is connected to the Fig. The opening 438 illustrated in Figures 8(A) to 8(C) or 5(A) and 5(B) is connected in such a way that the difference between the pressure of the void on the back of the diaphragm 672 and the pressure on the front of the diaphragm 672 does not increase. It is possible to prevent warping of the diaphragm 672 caused by this pressure difference. This contributes to improving the measurement accuracy of the flow rate.

[0133] As described above, heat conduction through the membrane 672 is minimized by forming the thin region 603 and reducing the thickness of the section encompassing the thin region 603 within the membrane 672. While the influence of heat conduction through the membrane 672 is suppressed, the airflow sensing bridge circuit 650 or the heating control bridge 640 is therefore much more likely to operate according to the temperature of the target gas 30, thus improving the measurement process. For this reason, high measurement accuracy is achieved. 7.3 Design of the bypass passage of the circuit assembly and advantages

[0134] In the thermal flow meter 300 according to the present invention, the airflow detection section 602 of the circuit assembly 400 is arranged in the bypass passage in conjunction with the main passage 124 in order to measure the flow rate of the target gas 30, as previously described. As in Fig. 7(A) and Fig. As described in 7(B), in the measuring section 310 of the thermal flow meter 300 the measuring flow path is formed between the projection 356 of the front cover 303 and the rear cover 304, and the lower section of the circuit assembly 400 is arranged in the flow path in the surface direction.

[0135] In particular, the circuit assembly 400 is configured such that the measuring surface 430 and the rear side of the measuring surface 431 are arranged at its rear surface in the bypass passage, and the bypass passage is designed such that the target gas 30 can flow when it is divided into the side of the measuring surface 430 of the circuit assembly 400 and the side of the rear side of the measuring surface 431 at its rear surface, which is arranged in the bypass passage. According to this configuration, the target gas 30 passes from the inlet channel 351, which forms the bypass passage, through the front bypass passage channel 332 and, when divided, flows into the flow path 386 on the side of the measuring surface 430 of the circuit assembly 400 and into the flow path 387 on the rear side of the measuring surface 431 at its rear surface. The target gas 30 then passes through the rear bypass channel 334 and is discharged from the outlet channel 353.

[0136] The thermal flow meter 300 according to the present invention is characterized in that the target gas 30 is designed such that, after dividing, it flows into the side of the measuring surface 430 of the circuit assembly 400 and the rear side of the measuring surface 431, and is characterized by the shape of the end surface for dividing the gas on the inlet side of the circuit assembly 400. In particular, the upstream end surface of the circuit assembly 400 for dividing the target gas 30 to be measured has different shapes at the end surface on the side of the measuring surface 430 and at the end surface on the rear side of the measuring surface 431 in order to consistently divide the flow of the target gas 30 to the side of the measuring surface 430 and the rear side of the measuring surface 431.

[0137] In a circuit assembly 401 according to the first embodiment, as in Fig. As shown in Figure 13(A), the upstream end surface is formed with a reference line 700, which has a front end edge for dividing the target gas 30. An end surface 701a, inclined on the side of the measuring surface 430 of the reference line 700, and an end surface 701b, inclined on the side of the rear of the measuring surface 431, have different shapes to consistently divide the flow of the target gas 30 to the measuring surface 430 and the rear of the measuring surface 431. Accordingly, the end surfaces 701a and 701b are designed to be asymmetrical with respect to the reference line 700. It should be noted that the first embodiment serves to illustrate the invention and to facilitate understanding of the technical teaching.If the end surface 701a, which is inclined on the side of the measuring surface 430 of the reference line 700, and the end surface 701b, which is inclined on the side of the back of the measuring surface 431, have asymmetrical shapes, the target gas 30 flowing into the bypass passage will not necessarily be divided in the same ratio when the flow of the target gas 30 is divided, and the flow division ratio will become unstable, causing a problem insofar as this can affect the measurement accuracy. In contrast, the end surface on the outflow side of the circuit assembly 401 also has this characteristic. largely the same shape as the oncoming end surface with regard to the effect of the backflow from the outlet of the bypass passage and an asymmetrically tapered shape with regard to the reference line 700.

[0138] The end surface 701a facing the flow is an inclined surface with a large height h1 from the reference line 700 and a large angle of inclination θ1. The end surface 701b is an inclined surface with a low height h2 from the reference line 700 and an angle of inclination θ2 equal to or less than θ1. The end surface 701 extending from the leading edge of the reference line 700 to the measuring surface 430 is an inclined surface with an angle of inclination of 20 to 45 degrees. The end surface 701b extending from the leading edge to the trailing edge of the measuring surface 431 is an inclined surface with an angle of inclination of 0 to 45 degrees. The inclination angle θ1 on the side of the end surface 701a is so high that it forms a shape which has less resistance in terms of flow and can direct more target gas 30 to the side of the measuring surface 430, so that this is preferred from the point of view of measuring a very low throughput.The horizontal direction length L11 of the measuring surface 430 is designed such that it is less than the horizontal direction length of the back of the measuring surface 431.

[0139] An arc segment R is located at the intersection of the end surface 701a, which is on the upper side in Fig. 13(A) is inclined, and the measuring surface 430 of the upper surface is formed, so that the end surface 701a and the measuring surface 430 are seamlessly connected and no turbulence is generated. An arc segment R is also formed at the intersection of the end surface 701b, which is located on the underside in Fig. 13(A) is included, and the back of the measuring surface 431 of the lower surface is formed, so that the end surface 701b and the back of the measuring surface 431 are seamlessly connected and no turbulence is generated. The outlet-side end surface is also connected to the upper surface and the lower surface at the arc section like the upstream end surfaces 701a, 701b, so that no turbulence is generated when the target gas 30 flows out.

[0140] In the circuit assembly 401 according to the first embodiment, a metal substrate 501, which forms a guide frame for attaching a device for measuring the flow rate of the target gas 30, is embedded during the forming process, resulting in an airflow detection section 602. The metal substrate 501 corresponds to the first plate 531 or the second plate 536. The membrane 672, which forms the airflow detection section 602, is provided on the upper surface of the metal substrate 501. The void 674 is provided on the rear surface of the metal substrate 501. The upper surface of the metal substrate 501 and the reference line 700, which forms the front end edge, are on the same plane, resulting in a parting line PL of the die-casting mold.Therefore, there is no undercut section of the die-casting mold, and the die-casting mold can be simplified. Furthermore, the die-casting mold can be easily divided during the molding process. The airflow sensing section 602 has a membrane 672 for transferring heat to / from the target gas 30, and the surface of the membrane 672 is flush with the measuring surface 430, so that the target gas 30 flows uniformly and no turbulence is generated.

[0141] As previously described, it is located in circuit assembly 401 of Fig. 13(A) A large quantity of target gas 30 is designed to flow steadily towards the flow path 386 at the end surface 701 above the reference line 700, and on both the end surface 701a and end surface 701b sides, the inlet airflow is designed so that it does not collide with the end surface, thus preventing turbulence, and the laminar flow is designed to ensure that the split flow becomes steady. Furthermore, a sufficiently large quantity of target gas 30 is generated to actively flow towards the side of the measuring surface 430, thus preventing binarization and achieving a highly accurate measurement.A substance with a heavy mass, such as an impurity mixed into the target gas 30, flows to the flow path 375 on the side of the back of the measuring surface 431 on the side of the end surface 701b, and impurities and the like do not flow to the side of the measuring surface 430 where the throughput sensing element 602 is located, thus enabling a highly accurate throughput measurement.

[0142] Like the circuit assembly 401 according to the first embodiment, which is described in Fig. As shown in 13(A), the circuit assembly 402 according to the second embodiment, which is shown in Fig. As shown in Figure 13(B), such a configuration is formed in which the upstream end surface is formed with reference line 700 for dividing the target gas 30, and the end surface 702a on the side of the measuring surface with respect to reference line 700 and the end surface 702b on the back side of the measuring surface with respect to reference line 700 have different shapes in order to consistently divide the flow of the target gas 30 into the measuring surface 430 and the back side of the measuring surface 431, and the end surface 702a on the side of the measuring surface with respect to reference line 700 and the end surface 702b on the back side of the measuring surface with respect to reference line 700 are designed to be asymmetrical with respect to reference line 700. The outlet-side end surface of the circuit assembly 402 also has the same shape as the upstream end surface.The inclination angles θ1, θ2, the heights of the end surfaces 702a, 702b, the length L1 of the measuring surface 430 and the length L2 of the back of the measuring surface 431 are formed such that they are equal to those of the first embodiment.

[0143] In the circuit assembly 402 according to the second embodiment, a metal substrate 502, forming the conductor frame, is bent to form an upper layer section 502 and a lower layer section 502b. The membrane 672 and the void 674, which form the flow-sensing element 602, are formed on the upper layer section 502a of the metal substrate 502. It should also be noted that the second embodiment serves to illustrate the invention and facilitate understanding of the technical teaching. The lower surface of the lower layer section 502b of the metal substrate 502 is exposed in the same plane as the lower surface of the circuit assembly 402. In this circuit assembly 402, the reference line 700, which forms the front end edge, becomes the parting line of the die-casting mold during the forming process.

[0144] The circuit assembly 402 of this second embodiment achieves the same effects as the circuit assembly 401 of the first embodiment. Since the height difference between the upper layer section 502a and the lower layer section 502b of the metal substrate 502 is formed with plastic, the metal substrate and the forming plastic are in close contact with each other, and the quality of the circuit assembly 402 can be improved. The lower layer section 502b of the metal substrate 502 is free of the forming plastic, so that the thermal radiation properties of a semiconductor chip and the like, which are implemented on the metal substrate 502, can be improved, and the performance can be stabilized.

[0145] Like the first and second embodiments, the circuit assembly 403 of the third embodiment is located in Fig. Figure 13(C) shows the third embodiment configured such that the end surface 703a, which is inclined towards the upper side of the reference line 700 forming the front end edge, and the end surface 703b, which is inclined towards the lower side of the reference line 700, differ in shape and have asymmetrical forms with respect to the reference line 700. It is also noted that the third embodiment serves to illustrate the invention and to facilitate understanding of the technical teaching.The target gas 30 flowing in the measuring flow path is designed such that the height h3 of end surface 703a is greater than the height h4 of end surface 703b, so that more gas flows continuously to the measuring surface 430 with end surface 703 on the side of the flow path 386. A substance with a heavier mass, such as an impurity, flows to the side of the rear of measuring surface 431 on the side of end surface 703b, and impurities and the like do not flow to the side of measuring surface 430 where the flow sensing element 602 is located. Turbulence can be prevented by the shape of the upstream end surface of the circuit assembly 403, and a stable laminar flow can be formed, so that the measurement can be carried out with high accuracy.

[0146] In the circuit assembly 403 of this third embodiment, the metal substrate 503, which forms the conductor frame, has a flat plate shape, and the entire lower surface is exposed by the molded plastic forming the circuit assembly. The bottom surface of the molded plastic and the bottom surface of the metal substrate coincide and form the same bottom surface. In the circuit assembly 403 of the third embodiment, the thermal radiation from a component located on the metal substrate 503 can be emitted and dissipated, the thickness can be reduced, and the resistance to the flow of the target gas 30 can be reduced. Therefore, this can prevent the generation of turbulence in the section of the circuit assembly 403, and the flow rate can be measured with high accuracy.

[0147] In the circuit assembly 404 of the fourth embodiment, which is in Fig. As shown in Figure 14(A), the upstream end surface of the target gas 30 comprises an end surface 704a inclined in the longitudinal direction above the reference line 700, and a vertical surface 704b below the reference line 700. In particular, the end surface 704a at the measuring surface 430 is an inclined surface with an inclination angle of 20 to 45 degrees, and the end surface on the back side of the measuring surface 431 is a vertical surface 704b perpendicular to the measuring surface 430 and parallel to the flow direction, and the inclined surface 704a and the vertical surface 704b are continuous with the reference line 700 between them.

[0148] The horizontal direction length L3 of the measuring surface 430 on the upper side is designed to be shorter than the horizontal direction length L4 of the back of the measuring surface 431 on the lower side. The height h5 of the inclined end surface 704a is designed to be greater than the height h6 of the vertical end surface 704b, and the end surface inclined towards the upper side is seamless, allowing a larger quantity of target gas 30 to flow towards the flow path 386. In this example, the metal substrate 504 of the conduit frame is designed to be flat, and the upper surface on which a flow-measuring component is formed corresponds to the corner section of the reference line where the inclined surface and the vertical surface coincide, and this corner section serves as the parting line during forming.

[0149] If the circuit group 404 of the fourth embodiment is arranged in the measuring flow path, as in Fig. As shown in Figure 14(B), a large quantity of target gas 30 flows to flow path 386 on the side of the measuring surface 430 along the inclined end surface 704a in the upper section of the reference line 700, and less target gas 30 flows to flow path 387 on the side of the back of the measuring surface 431 in the lower section of the reference line 700. In particular, there is a region S in flow path 387 below the circuit assembly 404 where a rotating flow is generated, and no air flows, as shown by a dashed line, on the side of the vertical surface 704b, and the size of the region of the flow path decreases (airflow resistance increases), so that the flow velocity of the gas decreases.Therefore, a large quantity of target gas 30 can be passed through on the side of the flow path 386 on the side of the measuring surface 430 above the circuit assembly 404, and the flow rate of the flow path 387 can be reduced on the side of the back of the measuring surface 431.

[0150] In circuit assembly 405 of the fifth embodiment, as in Fig. As shown in Figure 15(A), the downstream end surface of the target gas 30 is formed by an end surface 705a, which is formed by means of an arcuate cross-section with a large radius of curvature and is located above the reference line 700, and an end surface 705b, which is formed by means of an arcuate cross-section with a small radius of curvature and is located below the reference line 700. It should also be noted that the fifth embodiment serves to illustrate the invention and to facilitate understanding of the technical teaching. The arcuate surface is formed by a quarter circle.

[0151] The upper end surface 705a and the lower end surface 705b are continuous with respect to the measuring surface 430. The lower end surface 705b is continuous with respect to the back side of the measuring surface 431, and both are smoothly continuous. The horizontal direction length L5 of the upper measuring surface 430 is configured to be shorter than the horizontal direction length L6 of the lower back side of the measuring surface 431. The height h7 of the end surface 705a is configured to be greater than the height h8 of the end surface 705b, and the upper end surface is smooth where a large quantity of target gas 30 is intended to flow. A flat, plate-like metal substrate 505 is contained within the molded plastic of the circuit assembly 405, and the airflow sensing section 602 is provided on the substrate.

[0152] When the circuit assembly 405 of the fifth embodiment is arranged in the bypass passage, a large airflow is generated on the side of the flow path 386 along the end surface 705a, which is strongly curved above the reference line 700, and a small airflow is generated on the side of the flow path 387 along the end surface 705b, which has a lesser curvature. Contaminants and the like flow to the side of the flow path 387 on the lower side, thus improving the accuracy with respect to the measurement of the throughput. In the fifth embodiment, the end surfaces 705a and 705b are smoothly continuous, so that a clear line from a leading edge and the like is not formed at the section of the reference line 700 that is continuous with respect to both arc-shaped surfaces.

[0153] In circuit assembly 406 of the sixth embodiment, as in Fig.As shown in Figure 15(B), the upstream end surface of the target gas 30 is formed by an end surface 706a, which is inclined rearward toward the outlet side above the reference line 700 that divides the target gas 30, and an end surface 706b, which is inclined such that it projects further toward the upstream side than the end surface 706a. It should also be noted that the sixth embodiment serves to illustrate the invention and to facilitate understanding of the technical teaching. The angle of inclination of the end surface 706a is greater than the angle of inclination of the end surface 706b, and the end surface 706b has such a shape that it projects forward with respect to the reference line 700. The horizontal direction length of the measuring surface 430 on the side of the end surface 706a is designed as L7, and the horizontal direction length L8 of the back of the measuring surface 431 on the side of the end surface 706b is designed to be greater than L7.The height h7 of the end surface 706a is designed to be greater than the height h8 of the end surface 706b. A flat, plate-like metal substrate 506 is contained in the molded plastic of the circuit assembly 406, and the airflow capture section 602 is provided on the substrate.

[0154] In the circuit assembly 406 of this sixth embodiment, the upstream end surface of the target gas 30 is formed by two inclined surfaces 706a, 706b, and one of the end surfaces, i.e., end surface 706b, projects further forward than the other end surface, i.e., end surface 706a, thus blocking the flow of the target gas 30 into the side of the flow path 387. A large quantity of the target gas 30 then flows to the side of the flow path 386, where the diaphragm 672 and the void 674 are provided, forming the flow rate sensing element 602. Impurities and the like flow to the side of the flow path 387, allowing the flow rate to be measured with high accuracy. The circuit assembly 406 of the sixth embodiment has different shapes on the upstream end surface and the outlet end surface.Alternatively, the circuit assembly 406 of the sixth embodiment can have a shape such that it projects towards the lower side in the same way. In this sixth embodiment, the parting line of the die-casting mold for forming the circuit assembly 406 is preferably the back side of the measuring surface 431.

[0155] As previously described, the embodiments have been described in detail, but the present invention is not limited to these embodiments. Various design modifications can be made to the embodiments without departing from the essence of the present invention as described in the claims. For example, the embodiments described above have been explained in detail for the present invention in an easily understandable manner, and the embodiments are not necessarily limited to those that incorporate all the components described above. A part of the design of a particular embodiment can be replaced by a design of another embodiment. It is possible to add, delete, or replace any part of the design of an embodiment from other embodiments.

[0156] Control lines and information lines are shown that are deemed necessary for explanation; however, not all control lines and information lines required in relation to the products are necessarily shown. Essentially, most of the component elements can be considered interconnected in reality. Industrial availability

[0157] The present invention is applicable to a measuring device described above for measuring a gas flow rate. Reference symbol list 30 Target gas (intake air) 300 thermal flow meters 302 Cases 303 front cover 304 rear cover 305 external connector 306 external connection 307 Calibration port 310 Measuring section 320 connectors 332 front bypass passage 334 rear bypass passage 356 lead 372 Fixation section 400, 401 to 406 Circuit assembly 412 Connection port 414 connection 424 lead 430 measuring area 432 Mounting surface 436 Heat transfer surfaces - exposure section 438 Opening 452 Temperature detection unit 501 to 505 Metal substrate 502a upper layer section 502b lower layer section 590 Press fit opening 594 Incline section 596 Incline section 601 Throughput measurement circuit 602 Airflow Capture Section 604 processing units 608 Heat generators 640 Heating control bridge 650 Bridge circuit for airflow detection 672 Membran 700 reference line 701a to 706a End surfaces on the measuring surface 701b to 706b End faces on the back of the measuring surface

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