Measuring device for determining the flow velocity of a sample gas

Abstract

Measuring device (300) for determining the flow velocity of a sample gas, comprising: a plate (400) having a flow velocity detection element (602) for detecting the flow velocity of the sample gas (30); and a housing (302) having a passage (305) receiving a portion of the sample gas and fixing the plate such that the flow velocity detection element is arranged in the passage, wherein the plate has a segmentation area (801) in the form of a notch provided at an edge (800) of the upstream side of a stream of the sample gas, with respect to the flow velocity detection element, and segmenting a portion of the edge, and wherein the notch is formed in a position where water accumulates on the upstream side of the stream of the sample gas in a boundary region between a wall surface of the housing forming the passage and the edge of the plate.

Description

Technical field The present invention relates to a measuring device for determining the flow velocity of a sample gas. State of the art An airflow measuring device for measuring the flow velocity of air including impurities, such as intake air of an internal combustion engine, is known. PTL 1 describes a thermal air flow meter. In the technique described in PTL 1, to prevent the adhesion of contaminants to a flow meter, the flow meter is positioned so that it is exposed to a surface located in a secondary passage in the direction of flow of the gas being measured. A step is formed in the exposed surface, surrounding the circumference of the flow meter. An inner region enclosed by the step is designed to project further than an outer region of the step. Bibliography Patent literature PTL 1: JP 2014-185868A A flow sensor arrangement with a sensor carrier, on the leading edge of which notches are provided towards the center of the passage to compensate for flow fluctuations, is disclosed in DE 10 2011 078 004 A1. Further arrangements of flow sensors that are connected with the measuring device of the present invention are disclosed in DE 10 2014 217 870 A1, DE 10 2008 042 155 A1 and WO 2016 / 017 300 A1. Technical problem The flow rate sensing part described in PTL 1 is surrounded by a stage, which blocks contaminants, such as oil mist containing carbon, on the outside of the stage to prevent the contaminants from adhering. However, in the technique described in PTL 1, the step is located on the same level as the flow meter. For this reason, the gas flow in the flow meter can be severely restricted, potentially leading to noise in the flow meter reading. Although the contaminants can be blocked, water droplets that flow in with the intake air can reach the flow rate measurement part and reduce the accuracy of the flow rate measurement. The present invention is based on the given facts. One object of the invention is to provide a measuring device for determining the flow velocity of air, with which disturbances in the flow of a gas to be measured (measuring gas) can be suppressed and a characteristic influence due to water droplets flowing in with the intake air can be reduced. Solution to the task To solve the aforementioned problem, the measuring device defined in claim 1 for determining the flow velocity of air is provided according to the invention. Further advantageous embodiments are described in the dependent claims. Advantageous effects of the invention According to the invention, it is possible to suppress disturbances in the flow of a gas being measured and to reduce the characteristic influence caused by water droplets flowing in with the intake air. This makes it possible to provide a measuring device for determining the flow velocity of air that ensures high measurement accuracy and has a simple design. Further tasks, configurations and effects of the invention will become apparent from the following description of embodiments. Brief description of the drawings [Fig. 1] Fig. 1 shows schematically how an embodiment of a measuring device according to the invention for determining the flow velocity of air in an internal combustion engine control system of the electronic fuel injection type is used. [Fig. 2] Fig. 2 is a front view of a measuring device for determining the flow velocity of air. [Fig. 3] Fig. 3 is a rear view of a measuring device for determining the flow velocity of air. [Fig. 4] Fig. 4 is a left side view of a measuring device for determining the flow velocity of air. [Fig. 5] Fig. 5 is a right side view of a measuring device for determining the flow velocity of air. [Fig. 6] Fig. 6 is a top view of a measuring device for determining the flow velocity of air. [Fig. 7] Fig. 7 is a bottom view of a measuring device for determining the flow velocity of air. [Fig. 8] Fig.Fig. 8 is a front view of a condition in which a front cover and a rear cover have been removed from a measuring device for determining the flow velocity of air. [Fig. 9] Fig. 9 is a rear view of a condition in which a front cover and a rear cover have been removed from a measuring device for determining the flow velocity of air. [Fig. 10] Fig. 10 is a left side view of a condition in which a front cover and a rear cover have been removed from a measuring device for determining the flow velocity of air. [Fig. 11] Fig. 11 is a right side view of a condition in which a front cover and a rear cover have been removed from a measuring device for determining the flow velocity of air. [Fig. 12] Fig. 12 is a cross-sectional view along line AA of Fig. 8. [Fig. 13]Fig. 13 shows another embodiment of a second side passage. [Fig. 14] Fig. 14 shows another embodiment of a second side passage. [Fig. 15] Fig. 15 shows a front cover. [Fig. 16] Fig. 16 shows a rear cover. [Fig. 17] Fig. 17 is a front view of a printed circuit board. [Fig. 18] Fig. 18 is a right side view of a printed circuit board. [Fig. 19] Fig. 19 is a rear view of a printed circuit board. [Fig. 20] Fig. 20 shows a circuit diagram of a measuring device for determining the flow velocity of air. [Fig. 21] Fig. 21 shows another example of a circuit arrangement of a measuring device for determining the flow velocity of air. [Fig. 22] Fig. 22 is a front view in the form of a housing, in which a front cover of a measuring device for determining the flow velocity of air is shown. has been removed. [Fig. 23] Fig. 23 shows a modification of the one in Fig.22. [Fig. 24] Fig. 24 shows a modification of the shape of a segmentation part. [Fig. 25] Fig. 25 shows a modification of the shape of a segmentation part. [Fig. 26] Fig. 26 shows a modification of the shape of a segmentation part. Description of the embodiments Embodiments of the present invention are described below with reference to the drawings. The embodiments of the present invention solve various problems that arise in actual products and, in particular, offer solutions for use as a detection device for measuring the physical quantity of intake air from a motor vehicle. Furthermore, various advantageous effects are achieved. Designs In the following embodiments, the same reference numerals denote the same elements in the different figures and result in the same functions and effects. For elements already described, reference is made only to the reference numerals shown in the figures, while an explanation of these elements is omitted. 1. Embodiment using a measuring device according to the invention for determining the flow velocity of air as a device for detecting a physical quantity in an internal combustion engine control system Fig. 1 shows schematically how an embodiment of a measuring device according to the invention is used to determine the flow velocity of air in an internal combustion engine control system of the type of electronic fuel injection. According to Fig. 1, based on the operation of an internal combustion engine 110, which comprises an engine cylinder 112 and an engine piston 114, intake air as measuring gas 30 is drawn from an air filter 122 and supplied to a combustion chamber of the engine cylinder 112 via a main passage 124, for example an intake body, a throttle body 126 and an intake manifold 128. A physical quantity of the measuring gas 30, which represents the intake air supplied to the combustion chamber, is detected by the measuring device 300 for determining the flow velocity of air according to an embodiment of the present invention, and fuel is supplied from a fuel injection valve 152 on the basis of the detected air quantity (physical quantity) and is directed into the combustion chamber together with the intake air 30 in the form of an air-fuel mixture. In the present embodiment, the fuel injection valve 152 is provided in an inlet opening of the internal combustion engine, and the fuel injected into the inlet opening together with the measuring gas 30, which represents the intake air, forms the air-fuel mixture, is supplied to the combustion chamber via an inlet valve 116 and is burned to generate mechanical energy. The fuel and the air supplied to the combustion chamber form a fuel-air mixture, which is explosively combusted by the spark of a spark plug 154 to generate mechanical energy. After combustion, the gas is directed through an exhaust valve 118 into an exhaust pipe and expelled from the vehicle as exhaust gas 24. The flow velocity of the sample gas 30, which is supplied to the combustion chamber as intake air, is controlled by a throttle valve 132, the opening of which is changed based on the application of the vehicle's accelerator pedal.The amount of fuel supplied is controlled based on the flow rate of the air introduced into the combustion chamber, and the driver controls the opening of the throttle valve 132 to control the flow rate of the intake air introduced into the combustion chamber, so that the mechanical energy generated by the internal combustion engine can be controlled. 1.1 Overview of the control of the internal combustion engine control system Physical quantities, such as the flow velocity, temperature, humidity and pressure of the measuring gas 30, which represents the intake air taken from the air filter 122 and flowing through the main passage 124, are detected by the measuring device 300 for determining the flow velocity of air, and an electrical signal representing the flow velocity (physical quantity) of the intake air is input from the measuring device 300 for determining the flow velocity of air into a control device 200. Furthermore, an output from a throttle valve angle sensor 144 is input to the control device 200 to measure the opening of the throttle valve 132, and an output from a rotary angle sensor 146 is input to the control device 200 to measure the positions and states of the engine piston 114, the intake valve 116, and the exhaust valve 118 of the internal combustion engine, as well as the rotational speed of the internal combustion engine. An output from an oxygen sensor 148 is input to the control device 200 to measure the state of the mixture ratio of the fuel quantity and the quantity of air from the state of the exhaust gas 24. The control device 200 calculates the fuel injection quantity and the ignition timing based on the intake air flow velocity, which is the output of the measuring device 300 for determining the air flow velocity, and the rotational speed of the internal combustion engine, which is measured based on the output of the rotation angle sensor 146. The quantity of fuel supplied from the fuel injector 152 and the ignition timing of the spark plug 154 are controlled based on the calculation result. The fuel supply quantity and ignition timing are subject to fine control based on the temperature detected by the measuring device 300 for measuring the flow velocity, the change in the throttle angle, the change in engine speed, and the air-fuel ratio measured by the oxygen sensor 148. Furthermore, during idle operation of the internal combustion engine, the control device 200 controls the amount of air bypassing the throttle valve 132 through an idle air control valve 156 and controls the idle speed of the internal combustion engine. 1.2 Importance of improving the detection accuracy of the measuring device for determining the flow velocity of air and the mounting environment of the measuring device for determining the flow velocity of air Both the fuel quantity and the ignition timing, which are the main control parameters of the internal combustion engine, are determined using the output of the measuring device 300 for determining the air flow velocity as the primary parameter. Therefore, improving the detection accuracy of the measuring device 300 for determining the air flow velocity, suppressing temporary variations, and improving reliability are important for improving the control accuracy and reliability of the vehicle. In recent years, high demands have been placed on fuel efficiency and exhaust gas purification in motor vehicles. To meet these demands, it is extremely important to improve the accuracy of the measurement of the intake air velocity 20 by the measuring device 300. Furthermore, it is important to maintain the high reliability of the measuring device 300 for determining the air velocity. A motor vehicle in which the measuring device 300 for determining the air flow velocity is mounted is used in an environment with very strong changes in temperature or humidity. Preferably, the measuring device 300 for determining the air flow velocity is provided with measures to cope with temperature or humidity changes in the operating environment or with dust and contaminants. Furthermore, the measuring device 300 for determining the air flow velocity is attached to an intake pipe that is exposed to the heat generated by the internal combustion engine. The heat generated by the internal combustion engine is transferred to the measuring device 300 for determining the air flow velocity via the intake pipe, which constitutes the main passage 124. Since the measuring device 300 for determining the air flow velocity measures the flow velocity of the sample gas by transferring heat with the sample gas, it is important to suppress the influence of external heat as much as possible. As explained above, the measuring device 300, mounted in a motor vehicle, for determining the airflow velocity solves the problems described above in the section on the problem statement and achieves the effects described in the preceding section on the advantageous effects of the invention. As explained below, the measuring device 300 for determining the airflow velocity also fully addresses the problems described above that must be considered in the products and achieves various effects. Specific problems to be solved in the measuring device 300 for determining the flow velocity of air, and specific effects achieved by the measuring device 300 for determining the flow velocity of air, are explained below in the description of the following embodiments. 2. Setup of the measuring device 300 for determining the flow velocity of air 2.1 External structure of the measuring device 300 for determining the flow velocity of air Figures 2, 3, 4, 5, 6 to 7 show the measuring device 300 for determining the flow velocity of air. Figure 2 is a front view of the measuring device 300 for determining the flow velocity of air. Figure 3 is a rear view of the measuring device 300 for determining the flow velocity of air. Figure 4 is a left side view of the measuring device 300 for determining the flow velocity of air. Figure 5 is a right side view of the measuring device 300 for determining the flow velocity of air. Figure 6 is a top view of the measuring device 300 for determining the flow velocity of air. Figure 7 is a bottom view of the measuring device 300 for determining the flow velocity of air. According to Figs. 2, 3, 4, 5, 6 to 7, the measuring device 300 for determining the flow velocity of air comprises a housing 302, a front cover 303, and a rear cover 304. The housing 302 is formed from a synthetic resin material and has the following: a flange 311, which fixes the measuring device 300 for determining the flow velocity of air to the inlet body, which represents the main passage 124; an external connecting part 321 with a connector protruding from the flange 311 and providing the electrical connection to an external device; and a measuring part 331, which extends from the flange 311 to the center of the main passage 124. The measuring element 331 is provided with a printed circuit board 400 as an integral component by insert forming (compare Fig. 8 and Fig. 9). The printed circuit board 400 is provided with at least one sensing element for detecting the flow velocity of the measuring gas 30 flowing through the main passage 124, and a circuit element for processing the signal detected by the sensing element. The sensing element is arranged at a position exposed to the measuring gas 30, and the circuit element is arranged in a circuit chamber that is closed by the front cover 303. A secondary passage is provided in a surface and a rear surface of the measuring element 331, and a first secondary passage 305 is formed in conjunction with the front cover 303 and the rear cover 304. A first secondary passage inlet 305a for receiving a portion of the measuring gas 30, such as the air drawn into the first secondary passage 305, and a first secondary passage outlet 305b for returning the measuring gas 30 from the first secondary passage 305 to the main passage 124 are provided in a front end region of the measuring device 331. A portion of the circuit board 400 projects from the center of the passage of the first secondary passage 305. A flow velocity detection element 602 (see Fig. 8), which represents the detection element, is arranged in a detection area such that the flow velocity of the measuring gas 30 is detected. A second secondary passage 306 for extracting a portion of the sample gas 30, for example, air drawn into a sensor chamber Rs, is provided in a central region of the measuring section 331, which is located closer to the flange 311 than the first secondary passage 305. The second secondary passage 306 is formed by the interaction of the measuring section 331 and the rear cover 304. The second secondary passage 306 comprises a second secondary passage inlet 306a, which is open towards an upstream side of the outer wall 336 to receive the sample gas 30, and a second secondary passage outlet 306b, which is open towards a downstream side of the outer wall 338 to return the sample gas 30 from the second secondary passage 306 to the main passage 124. The second secondary passage 306 is connected to the sensor chamber Rs formed on the rear surface of the measuring element 331. Pressure sensors 421A and 421B and a humidity sensor 422 are arranged in the sensor chamber Rs as sensing elements, which are provided on the rear surface of the circuit board 400 (see Fig. 19). 2.2 Effect based on the structure of the measuring device 300 for determining the flow velocity of air In the measuring device 300 for determining the flow velocity of air, the second secondary passage inlet 306a is provided in the middle part of the measuring section 331, which extends in a central direction from the flange 311 along the main passage 124, and the first secondary passage inlet 305a is provided in the front end region of the measuring section 331. Therefore, gas can be drawn from the first secondary passage 305 and the second secondary passage 306 in an area located near a central region at a distance from, but not near, an inner wall surface of the main passage 124. Thus, the measuring device 300 can measure a physical quantity of the gas in an area that is away from the inner wall surface of the main passage 124 for determining the flow velocity of air, and thus reduce the measurement error of the air flow velocity that arises from heat exposure or is due to a reduction in the flow velocity near the inner wall surface. The measuring element 331 has a shape extending along an axis from the outer wall of the main passage 124 towards the center, but with reduced thickness and width, as shown in Figures 4 and 5. This means that the measuring element 331 of the measuring device 300 for determining the air flow velocity has a shape in which the width of one side surface is small and the front surface is essentially rectangular. Thus, the measuring device 300 for determining the air flow velocity can include the first secondary passage 305 of sufficient length and reduce the fluid resistance for the measuring gas to a low value. Therefore, the measuring device 300 can reduce the fluid resistance to a low value and measure the flow velocity of the measuring gas 30 with high accuracy. 2.3 Structure and function of the flange 311 The flange 311 has a plurality of recesses 313 provided on a lower surface 312 facing the main passage 124 in order to reduce the heat transfer area between the flange 311 and the main passage 124, thereby making it more difficult for heat to affect the measuring device 300 for determining the air flow velocity. In the measuring device 300 for determining the air flow velocity, the measuring element 331 is inserted into an internal area through a mounting opening provided in the main passage 124, and the lower surface 312 of the flange 311 faces the main passage 124. The main passage 124, for example, is the intake manifold. The main passage 124 is often maintained at a high temperature. Conversely, it is evident that the main passage 124 has a very low temperature at startup in a cold environment. If such high or low temperatures of the main passage 124 affect the measurements of the various physical quantities, the measurement accuracy is reduced. The flange 311 has the recesses 313 on the lower surface 312, creating a space between the lower surface 312, which faces the main passage 124, and the main passage 124. This makes it possible to reduce the heat transfer from the main passage 124 to the measuring device 300 for determining the air flow velocity and to prevent a reduction in measurement accuracy due to heat. The screw holes 314 of the flange 311 are used to fix the measuring device 300 for determining the air flow velocity to the main passage 124. A space is created between each screw hole 314 and the main passage 124, such that the surface facing the main passage 124 around the screw hole 314 is located at a distance from the main passage 124. This design reduces heat transfer from the main passage 124 to the measuring device 300, thus minimizing the reduction in measurement accuracy due to heat. 2.4 Structure of the outer connection part 321 The outer connection part 321 has a connector 322, which is provided on an upper surface of the flange 311 and projects from the flange 311 towards the downstream side of the flow direction of the measuring gas 30. The connector 322 is provided with an insertion opening 322a for inserting a connecting cable for connection to the control device 200. Four external connections 323 are provided in the insertion opening 322a, as shown in Fig. 5. The external connections 323 represent a connection for outputting information about a physical quantity, which is a measurement result of the measuring device 300 for determining the flow velocity of air, and a power supply connection for supplying direct current for the operation of the measuring device 300 for determining the flow velocity of air. The connector 322 is designed such that it projects from the flange 311 towards the downstream side of the flow direction of the measuring gas 30 and is inserted from the downstream side of the flow direction to the upstream side. However, the present invention is not limited to the configuration described above. For example, the connector 322 can have a configuration in which it projects vertically from the upper surface of the flange 311 and is inserted along a direction of extension of the measuring element 331. Furthermore, various modifications can be made. Overall structure and effect of the housing 302 3.1 Overall structure The overall structure of the housing 302 is described below with reference to Figures 8, 9, 10, 11 to 12. Figures 8, 9, 10, 11 to 12 show a state of the housing 302 in which the front cover 303 and the rear cover 304 are removed from the measuring device 300 for determining the airflow velocity. Figure 8 is a front view of the housing 302, Figure 9 a rear view of the housing 302, Figure 10 a right side view of the housing 302, and Figure 11 a left side view of the housing 302. Figure 12 is a cross-section along line AA of Figure 8. The housing 302 is designed such that the measuring element 331 extends from the flange 311 towards the center of the main passage 124. The printed circuit board 400 is attached to the base end of the measuring element 331 by means of an insert forming process. The printed circuit board 400 is formed parallel to the surface of the measuring element 331 at a central position between the surface and the rear surface of the measuring element 331 and is firmly installed in the housing 302. The base end of the measuring element 331 is divided in the thickness direction into one side and another side. A circuit chamber Rc for receiving a circuit component of the printed circuit board 400 is formed on the surface side of the measuring component 331, and the sensor chamber Rs for receiving the pressure sensor 421 and the humidity sensor 422 is formed on the rear surface side. The circuit chamber Rc is closed by mounting the front cover 303 on the housing 302 and is completely insulated from the outside. The rear cover 304 is attached to the housing 302 in such a way that the second secondary passage 306 and the sensor chamber Rs, which forms an interior space for connection with the outside of the measuring component 331 via the second secondary passage 306, are created. A part of the circuit board 400 protrudes from a partition 335, which divides an area between the circuit chamber Rc of the measuring part 331 and the first secondary passage 305 into an inner area of ​​the first secondary passage 305, and the flow velocity detection part 602 is provided on a measuring flow passage surface 430 of a projection area. 3.2 Structure of the secondary passage groove A secondary passage groove for forming the first secondary passage 305 is provided on the front end face in the longitudinal direction of the measuring part 331. The secondary passage groove for forming the first secondary passage 305 has a front-side secondary passage groove 332 shown in Fig. 8 and a rear-side secondary passage groove 334 shown in Fig. 9. As shown in Fig. 8, the front-side secondary passage groove 332 is gradually curved towards the side of the flange 311, so that it forms the base end face of the measuring part 331 as it extends from the first secondary passage outlet 305b, which is open to the downstream side of the outer wall 338 of the measuring part 331, to the upstream side of the outer wall 336, and it is in contact with an opening 333, which penetrates the measuring part 331 in the thickness direction, in a position near the upstream side of the outer wall 336. The opening 333 is designed along the flow direction of the measuring gas 30 in the main passage 124 such that it is located between the upstream side of the outer wall 336 and the downstream side of the outer wall 338. As shown in Fig. 9, the rear-side secondary passage groove 334 extends from the upstream side of the outer wall 336 to the downstream side of the outer wall 338 and is divided into two parts in a midway position between the upstream and downstream sides of the outer wall 338. One of the two parts extends linearly as a drain passage and opens to a drain opening 305c on the downstream side of the outer wall 338, and the other part is gradually curved towards the side of the flange 311, which forms the base end of the measuring part 331, as it extends towards the downstream side of the outer wall 338 and is located near the downstream side of the outer wall 338 in conjunction with the opening 333. The rear-side secondary passage groove 334 forms an inlet groove into which the measuring gas 30 flows from the main passage 124, and the front-side secondary passage groove 332 forms an outlet groove for returning the measuring gas 30 taken from the rear-side secondary passage groove 334 to the main passage 124. Since the front-side secondary passage groove 332 and the rear-side secondary passage groove 334 are formed in the front end region of the housing 302, the gas can be taken as measuring gas 30 in an area far from the inner wall surface of the main passage 124; in other words, the gas flowing through the area near the central region of the main passage 124.The gas flowing near the inner wall surface of the main passage 124 is influenced by the wall surface temperature of the main passage 124 and often has a temperature that differs from the average temperature of the gas flowing through the main passage 124, such as the intake air 20. Furthermore, the gas flowing near the inner wall surface of the main passage 124 often exhibits a flow velocity that is lower than the average flow velocity of the gas flowing through the main passage 124. In the device 300 for detecting the physical quantity according to the present embodiment, this influence is mitigated, thus making it possible to suppress a reduction in measurement accuracy. As shown in Fig. 9, a portion of the sample gas 30 flowing through the main passage 124 is drawn from the first secondary passage inlet 305a into the secondary passage groove 334 and flows into the rear-side secondary passage groove 334. Furthermore, high-mass foreign material contained in the sample gas 30 flows into the discharge passage, which extends linearly from a branch, along with a portion of the sample gas, and is discharged from the discharge opening 305c on the downstream side of the outer wall 338 into the main passage 124. The rear-side secondary passage groove 334 is shaped such that it deepens as it extends forward, and the measuring gas 30 gradually moves toward the front of the measuring element 331 as it flows along the rear-side secondary passage groove 334. Specifically, the rear-side secondary passage groove 334 is provided with a steep inclination region 334a that deepens rapidly before the opening 333. A portion of the air with low mass moves along the steep inclination region 334a and flows toward the side of the measuring flow passage surface 430 of the circuit board 400 in the opening 333. Conversely, foreign material with high mass flows toward the side of the rear surface 431 of the measuring flow passage, as a rapid change in course is hindered. As shown in Fig. 8, the measuring gas 30, which has moved towards the front at the opening 333, flows along the measuring flow passage surface 430 of the circuit board 400. Heat transfer is carried out by the flow velocity sensing element 602, which is provided in the measuring flow passage surface 430, and the flow velocity is measured. The air flowing from the opening 333 to the front-side secondary passage groove 332 flows along the front-side secondary passage groove 332 and is discharged from the first secondary passage outlet 305b, which opens towards the downstream side of the outer wall 338 of the main passage 124. Since material with a large mass, such as dust mixed with the measuring gas 30, has a large inertial force, it is difficult for it to rapidly change its course in the depth direction along a surface in the region of the steep inclination area 334a of the groove, where the groove deepens rapidly (shown in Fig. 9). For this reason, foreign material with a large mass moves to the side of the rear surface 431 of the measuring flow passage, and it becomes possible to prevent foreign material from passing near the flow velocity sensing part 602.In the present embodiment, the fact that numerous foreign materials with a large mass, different from the gas, move across the rear surface 431 of the measuring flow passage, which constitutes the rear surface of the measuring flow passage surface 430, makes it possible to reduce the influence of impurities due to foreign materials such as oil, carbon, and dust. Thus, it is possible to suppress a reduction in measurement accuracy. Since the device is designed in such a way that the course of the measuring gas 30 is rapidly changed along an axis crossing a flow axis of the main passage 124, it is possible to reduce the influence of foreign material mixed with the measuring gas 30. 3.3 Structures and effects of the second side passage and the sensor chamber The second secondary passage 306 is formed in a linear direction between the second secondary passage inlet 306a and the second secondary passage outlet 306b, parallel to the flange 311, so that it runs along the flow direction of the measuring gas 30. The second secondary passage inlet 306a is formed by cutting out a portion of the upstream side of the outer wall 336, and the second secondary passage outlet 306b is formed by cutting out a portion of the downstream side of the outer wall 338. Specifically, as shown in Figures 9 and 10, the second secondary passage inlet 306a and the second secondary passage outlet 306b are formed by cutting out a portion of the upstream side of the outer wall 336 and a portion of the downstream side of the outer wall 338 from the rear surface of the measuring element 331 at positions that run continuously along an upper surface of the partition 335. The second secondary passage inlet 306a and the second secondary passage outlet 306b are cut out at depth positions that are flush with the rear surface of the circuit board 400. Since the measuring gas 30 flows through the second secondary passage 306 along a rear surface of a plate body 401 (shown in Figure 19) of the circuit board 400, the second secondary passage 306 acts as a cooling channel for cooling the plate body 401.Numerous circuit boards 400 are heated by LSIs or microcomputers and transfer the heat to the rear surface of the board body 401, whereby the heat is radiated by the measuring gas 30, which flows through the second secondary passage 306. The sensor chamber Rs is located closer to the base end of the measuring element 331 than the second side passage 306. A portion of the measuring gas 30, flowing from the second side passage inlet 306a to the second side passage 306, flows into the sensor chamber Rs. The pressure and relative humidity are detected by the pressure sensor 421 and the humidity sensor 422 in the sensor chamber Rs. Because the sensor chamber Rs is located closer to the base end of the measuring element 331 than the second side passage 306, the influence of the dynamic pressure of the measuring gas 30 flowing through the second side passage 306 can be reduced. Therefore, the detection accuracy of the pressure sensor 421 in the sensor chamber Rs can be improved. The sensor chamber Rs is located closer to the base end of the measuring part 331 than the second side passage 306. Therefore, if, for example, the front end of the measuring part 331 is positioned at the inlet passage facing downwards, impurities and water droplets flowing in the second side passage 306 along with the measuring gas 30 can be prevented from adhering to the pressure sensor 421 and the humidity sensor 422, which are located on its downstream side. In the present embodiment, the pressure sensor 421, with a relatively large outer dimension, is arranged upstream in the sensor chamber Rs, and the humidity sensor 422, with a relatively small outer dimension, is arranged downstream of the pressure sensor 421. Therefore, impurities and water droplets flowing with the measuring gas 30 adhere to the pressure sensor 421 and are prevented from adhering to the humidity sensor 422. Consequently, it is possible to protect the humidity sensor 422, which has low resistance to impurities and water droplets. The pressure sensor 421 (421A and 421B) and the humidity sensor 422 are hardly affected by the flow of the sample gas 30, compared to the flow velocity sensing element 602. In particular, the humidity sensor 422 can only ensure a certain degree of moisture diffusion in the sample gas 30, so the humidity sensor 422 can be provided in the sensor chamber Rs next to the second side passage 306 with a linear shape. On the other hand, the flow velocity sensing element 602 requires a constant flow velocity or more, and it is necessary to keep out dust and impurities and to take into account the influence of pulsation. Therefore, the flow velocity sensing element 602 can be provided in the first side passage 305 with a loop shape. Figures 13 and 14 show another embodiment of the second side passage. In this embodiment, the second secondary passage inlet 306a and the second secondary passage outlet 306b are formed by providing through-holes 337 in the upstream side of the outer wall 336 and the downstream side of the outer wall 338 instead of cutting out the upstream side of the outer wall 336 and the downstream side of the outer wall 338. If the second secondary passage inlet 306a and the second secondary passage outlet 306b are formed by notching the upstream side of the outer wall 336 and the downstream side of the outer wall 338, as shown in Figs. 9, 10, 11 to 12, ....In the second secondary passage shown in Figure 12, the width of the upstream side of the outer wall 336 and the width of the downstream side of the outer wall 338 are locally reduced at the corresponding positions, so that the measuring part 331 can be distorted into a substantially V-shaped form with the notch as its starting point due to heat shrinkage or the like during forming. Since a through-hole is provided in place of the notch in this embodiment, it is possible to prevent the measuring part 331 from being bent into a substantially V-shaped form. Therefore, it is possible to prevent any impairment of the measurement accuracy due to a change in the position or direction of the sensing part in relation to the measuring gas 30 caused by distortion in the housing 302, so that no individual differences occur and a constant sensing accuracy can always be ensured. 3.4 Shape and function of the front cover 303 and the rear cover 304 Fig. 15 shows the appearance of the front cover 303. Fig. 15(a) is a front view and Fig. 15(b) is a cross-sectional view along line BB of Fig. 15(a). Fig. 16 shows the appearance of the rear cover 304. Fig. 16(a) is a front view and Fig. 16(b) is a cross-sectional view along line BB of Fig. 16(a). In Figures 15 and 16, the front cover 303 and the rear cover 304 close the front side passage groove 332 and the rear side passage groove 334 of the housing 302, forming the first side passage 305. Furthermore, the front cover 303 forms the closed circuit chamber Rc, and the rear cover 304 closes a concave area of ​​the rear surface of the measuring element 331, forming the second side passage 306 and the sensor chamber Rs, which is connected to the second side passage 306. As shown in Fig. 15(b), the front cover 303 includes a projecting area 356 in a position facing the flow velocity sensing part 602, for use in forming a diaphragm between the front cover 303 and the measuring flow passage surface 430 as shown in Fig. 8. This results in high shaping accuracy. Since the front cover 303 and the rear cover 304 are manufactured by a resin molding process involving the injection of a thermoplastic resin into a mold, they can be produced with high shaping accuracy. The front cover 303 and the rear cover 304 are provided with a plurality of fixing holes 351 into which a plurality of fixing pins 350 (shown in Figs. 8 and 9), protruding from the measuring part 331, are inserted accordingly. The front cover 303 and the rear cover 304 are attached to the surface and rear surface, respectively, of the measuring part 331. The fixing pins 350 are inserted into the fixing holes 351 and positioned accordingly. Furthermore, a connection is made by laser welding or the like along the edges of the front-side secondary passage groove 332 and the rear-side secondary passage groove 334. Likewise, a connection is made by laser welding or the like along the edges of the circuit chamber Rc and the sensor chamber Rs. 3.5 Fixing structure and effect of the housing 302 of the printed circuit board 400 The fixing of the printed circuit board 400 to the housing 302 by the resin forming process is described below. The printed circuit board 400 is entirely subjected to the forming process together with the housing 302, so that the flow velocity detection element 602 of the printed circuit board 400 is arranged at a predetermined location in the secondary passage groove forming the secondary passage, for example in the opening 331, which in the present embodiment represents a connection area between the front of the secondary passage groove 332 and the rear of the secondary passage groove 334. In the measuring section 331 of the housing 302, areas for embedding an outer circumferential edge region of a base region 402 of the printed circuit board 400 in the housing 302 are provided by resin molding and fixing as fixing areas 372 and 373 (Fig. 8 and Fig. 9). The fixing areas 372 and 373 sandwich-like enclose the outer circumferential edge region of the base region 402 of the printed circuit board 400 from the front and rear sides and fix it. The housing 302 is manufactured using a resin molding process. In this process, the printed circuit board 400 is embedded in the resin of the housing 302 and fixed to an inner area of ​​the housing 302 by resin molding. This allows for the highly accurate maintenance of positional or directional relationships, such as those relating to the shape of the secondary passage for measuring the flow velocity by heat transfer with the measuring gas 30 through the flow velocity sensing element 602, for example, the front-side secondary passage groove 332 or the rear-side secondary passage groove 334. Errors or variations occurring in the individual printed circuit boards 400 can be reduced to a very small value. As a result, the measurement accuracy of the printed circuit board 400 can be significantly improved.For example, the measurement accuracy can be significantly improved compared to a conventional fixing method using an adhesive. The measuring device 300 for determining the flow velocity of air is frequently manufactured by mass production, whereby improvements in measuring accuracy are severely limited when using an adhesive bonding method. In contrast, in the present embodiment, by fixing the circuit board 400 simultaneously with the formation of the secondary passage by the resin molding process for creating the secondary passage for the flow of the measuring gas 30, it is possible to significantly reduce variations in measuring accuracy, and the measuring accuracy of the measuring device 300 for determining the flow velocity of air can be considerably improved. The example shown in Figures 8, 9, 10, 11 to 12 is described in more detail below. The circuit board 400 can be fixed to the housing 302 with high precision, so that the relationship between the front-side secondary passage groove 332, the rear-side secondary passage groove 334 and the flow velocity sensing element 602 is as specified. As a result, the measuring devices 300 for determining the flow velocity of air can be mass-produced, whereby the positional relationship or the shape relationship between the flow velocity detection part 602 of the individual circuit boards 400 and the first secondary passage 305 can be maintained constantly with very high accuracy. For example, in the first side passage 305, in which the flow velocity sensing element 602 of the printed circuit board 400 is fixedly arranged, the front side passage groove 332 and the rear side passage groove 334 can be formed with very high precision. Therefore, the step to form the first side passage 305 from these side passage grooves 332 and 334 involves covering the two surfaces of the housing 302 with the front cover 303 and the rear cover 304. This step is very simple and involves few factors that could reduce measurement accuracy. Furthermore, the front cover 303 and the rear cover 304 are manufactured with high forming accuracy using a resin molding process.Therefore, the secondary passage, which is in a prescribed relationship to the flow velocity sensing section 602 of the printed circuit board 400, can be completed with high accuracy. This method allows for both improved measurement accuracy and high productivity. In contrast, conventional techniques produce a thermal flowmeter by creating a bypass and bonding a measuring element to it with adhesive. This method, using an adhesive, results in significant variations in adhesive thickness, and the bond position or angle varies between individual products. Therefore, it limits the potential for improving measurement accuracy. Furthermore, if this step is performed in a mass production process, improving measurement accuracy becomes very difficult. In the embodiment according to the invention, the circuit board 400 is fixed by the resin forming process, and simultaneously the secondary passage groove for shaping the first secondary passage 305 is formed by the resin forming process. In this way, the flow velocity sensing element 602 can be fixed to the shape of the secondary passage groove with extremely high accuracy. The area associated with measuring the flow velocity, for example, the flow velocity sensing element 602 or the measuring flow passage surface 430 (Fig. 8) to which the flow velocity sensing element 602 is attached, is provided on the surface of the printed circuit board 400. The flow velocity sensing element 602 and the measuring flow passage surface 430 are free of the resin used to form the housing 302. This means that the flow velocity sensing element 602 and the measuring flow passage surface 430 are not covered with the resin used to form the housing 302. The flow velocity sensing element 602 or the measuring flow passage surface 430 of the printed circuit board 400 are used in their original form even after the housing 302 has been formed with resin and are employed by the measuring device 300 to determine the flow velocity of air.This improves measurement accuracy. In the embodiment according to the invention, the printed circuit board 400 is fixed to the housing 302, with the first secondary passage 305 being fixed to the housing 302 by an integral shaping of the printed circuit board 400, thus ensuring secure fixation of the printed circuit board 400 to the housing 302. In particular, since a projecting area 403 of the printed circuit board 400 penetrates the partition 335 and projects towards the first secondary passage 305, a high degree of sealing is achieved between the first secondary passage 305 and the circuit chamber Rc, preventing the measuring gas 30 from escaping into the circuit chamber Rc from the first secondary passage 305. Furthermore, this prevents the circuit components or wiring of the printed circuit board 400 from contacting the measuring gas 30 and being subject to corrosion. 4. Appearance of the printed circuit board 400 4.1 Shaping of the measuring flow passage surface 430 including the flow velocity detection part 602 Figures 17, 18 to 19 depict the printed circuit board 400. A hatched area in the design of the printed circuit board 400 shows a fixing surface 432 and a fixing surface 434, where the printed circuit board 400 is covered and fixed with resin during the resin forming process of the housing 302. Fig. 17 is a front view of the circuit board, Fig. 18 is a right side view of the circuit board and Fig. 19 is a rear view of the circuit board. The printed circuit board 400 comprises the board body 401. The circuit area and the flow velocity sensing element 602, which is a sensor element, are located on the surface of the board body 401. The pressure sensor 421 and the humidity sensor 422, which are sensor elements, are located on the rear surface of the board body 401. The board body 401 is manufactured using a glass-epoxy resin material and has a coefficient of thermal expansion that is close to that of the thermoplastic resin used to form the housing 302, compared to a board made of a ceramic material. Therefore, if the insert forming is carried out on the housing 302, stresses due to different coefficients of thermal expansion and distortions of the printed circuit board 400 can be reduced. The plate body 401 has the form of a flat plate of uniform thickness and, in plan view, essentially a T-shaped form with a substantially rectangular base region 402 and a substantially rectangular projecting region 403, which projects from one side of the base region 402 and is smaller than the base region 402. The circuit region is provided on the surface of the base region 402. The circuit region is configured by mounting electronic components, such as an LSI 414, a microcomputer 415, a power supply regulator 416, and a chip component 417, such as a resistor and a capacitor, with wiring not shown in the drawings. The power supply regulator 416 has a higher caloric value compared to the other electronic components, such as the microcomputer 415 and the LSI 414, so it is arranged relatively upstream in the circuit chamber Rc.The entire LSI 414 is sealed with a synthetic resin material 419, so that gold wires are enclosed, thereby improving the handling of the printed circuit board 400 at the time of insert forming. As shown in Fig. 17, a concave region 402a, into which the LSI 414 is fitted, is formed on the surface of the substrate 401. The concave region 402a can be formed by laser processing of the substrate 401. The substrate 401, made of glass-epoxy resin, is easier to process than a ceramic substrate, and the concave region 402a can be provided in a simple manner. The concave region 402a has a depth such that the surface of the LSI 414 is flush with the surface of the substrate 401. By adjusting the height of the surface of the LSI 414 to the height of the surface of the substrate 401 in the manner described above, the wire contacting for connecting the LSI 414 and the substrate 401 with the gold wires is facilitated, thus simplifying the fabrication of the printed circuit board 400. For example, as shown in Fig.17. The LSI 414 can be provided directly on the surface of the circuit board body 401. In the case of the aforementioned structure, the resin material 419, which covers the LSI 414, protrudes further. Machining to form the concave area 402 in the circuit board 401 is therefore unnecessary, and manufacturing can be simplified. When the circuit board 400 is inserted into the housing 302, the projecting area 403 is provided in the first secondary passage 305, and the measuring flow passage surface 430, which is the surface of the projecting area 403, extends along the flow direction of the measuring gas 30. The flow velocity sensing element 602 is provided on the measuring flow passage surface 430 of the projecting area 403. The flow velocity sensing element 602 performs heat transfer with the measuring gas 30, measures the state of the measuring gas 30, for example, the flow velocity of the measuring gas 30, and outputs an electrical signal that represents the flow velocity of the gas flowing through the main passage 124. To measure the state of the sample gas 30 with high accuracy through the flow velocity sensing element 602, it is desirable that the gas flow near the measuring flow passage surface 430 is laminar and exhibits few disturbances. Therefore, it is desirable that the surface of the flow velocity sensing element 602 and the surface of the measuring flow passage surface 430 are flush with each other, or that the level difference corresponds to or is below a predetermined value. As shown in Fig. 17, a concave region 403a is provided in the surface of the measuring flow passage surface 430, and the flow velocity sensing element 602 is fitted into this region. The concave region 403a can also be formed by laser machining. The concave region 403a has a depth such that the surface of the flow velocity sensing element 602 is flush with the surface of the measuring flow passage surface 430. The flow velocity sensing element 602 and its wiring area are covered with a synthetic resin material 418 to prevent electrolytic corrosion caused by adhering salt water. As shown in Fig. 19, the two pressure sensors 421A and 421B and a humidity sensor 422 are provided on the rear surface of the plate body 401. The two pressure sensors 421A and 421B are separated into upstream and downstream sides and arranged in a row. Furthermore, the humidity sensor 422 is arranged on the downstream side of the pressure sensor 421B. The two pressure sensors 421A and 421B and the humidity sensor 422 are arranged in the sensor chamber Rs. In the printed circuit board 400, the second secondary passage 306 is arranged on the rear surface of the board body 401. Therefore, it is possible to cool the entire board body 401 with the measuring gas 30 flowing through the second secondary passage 306. 4.2 Structure of the temperature sensing unit 451 As shown in Fig. 17 and Fig. 18, a temperature sensing part 451 is provided at an edge of the upstream side of the base region 402 and in a corner region of the side of the projecting region 403. The temperature sensing part 451 represents one of the sensing parts for sensing the physical quantity of the measuring gas 30, which flows through the main passage 124, and is provided in the circuit board 400. The circuit board 400 has a projecting area 450 that extends from the second secondary passage inlet 306a of the second secondary passage 306 towards the upstream side of the measuring gas 30, and the temperature sensing element 451 has a temperature sensor 453 designed as a chip, which is provided on the rear surface of the circuit board 400 at the projecting area 450. The temperature sensor 453 and its wiring area are covered with a synthetic resin material to prevent electrolytic corrosion from adhering salt water. For example, as shown in Fig. 9, in the central region of the measuring area 331, which is provided with the second secondary passage inlet 306a, the upstream side of the outer wall 336 in the measuring area 331, which forms the housing 302, is provided with a recess facing downstream, and the projecting area 450 (shown in Fig. 17) of the circuit board 400 projects upstream from the upstream side of the outer wall 336 with the recess. The front end of the projecting area 450 is arranged in a position where a recess is provided on the surface of the most upstream side of the upstream side of the outer wall 336. The temperature sensing part 451 is arranged in the projecting area 450 such that it faces the rear surface of the circuit board 400, i.e. the side of the second secondary passage 306. Since the second secondary passage inlet 306a is located on the downstream side of the temperature sensing section 451, the measuring gas 30, which flows from the second secondary passage inlet 306a into the second secondary passage 306, contacts the temperature sensing section 451 and flows into the second secondary passage inlet 306a. When the measuring gas 30 contacts the temperature sensing section 451, the temperature is detected. The measuring gas 30, which contacts the temperature sensing section 451, flows from the second secondary passage inlet 306a into the second secondary passage 306, passes through the second secondary passage 306, and is discharged from the second secondary passage outlet 306b into the main passage 123. 4.4 Fixing of the printed circuit board 400 by the resin molding process and its effects A hatched area in Fig. 19 shows the fixing surface 432 (Fig. 17) and the fixing surface 434 for covering the circuit board 400 with the thermoplastic resin used in the resin molding process to fix the circuit board 400 to the housing 302 during the resin molding process. It is important to maintain the relationship between the measuring flow passage surface 430 and the flow velocity sensing element 602 in the measuring flow passage surface, as well as the shape of the secondary passage, with high accuracy in order to achieve a prescribed relationship. Since the printed circuit board 400 is fixed to the housing 302 forming the secondary passage simultaneously with the formation of the secondary passage during the resin molding process, it is possible to maintain a relationship between the secondary passage and the measuring flow passage surface 430, as well as the flow velocity sensing element 602, with extremely high accuracy. This means that, due to the fixing of the printed circuit board 400 to the housing 302 during the resin molding process, it is possible to position and fix the printed circuit board 400 with high accuracy in a mold for forming the housing 302, including the secondary passage. By injecting the thermoplastic resin into the mold at high temperature, the secondary passage is formed with high accuracy and the printed circuit board 400 is fixed with high accuracy. Therefore, errors and variations occurring in individual printed circuit boards (PCBs) can be reduced to very low values. As a result, the measurement accuracy of the PCB can be significantly improved. 5. Circuit configuration of device 300 for determining the flow velocity of air 5.1 Overall configuration of the circuit of the measuring device 300 for determining the flow velocity of air Fig. 20 is a circuit diagram of the measuring device 300 for determining the flow velocity of air. The measuring device 300 for determining the flow velocity of air has a circuit 601 for detecting the flow velocity and a circuit 701 for detecting the temperature / humidity. The circuit 601 for sensing the flow velocity comprises a flow velocity sensing section 602 with a heating element 608 and a processing section 604. The processing section 604 controls the amount of heat generated by the heating element 608 of the flow velocity sensing section 602 and outputs a signal representing the flow velocity to the microcomputer 415 via a terminal 662 based on an output from the flow velocity sensing section 602. To perform the aforementioned processing, the processing unit 604 comprises a central processing unit (hereinafter referred to as CPU) 612, an input circuit 614, an output circuit 616, a memory 618 for storing data representing the relationship between a correction value or a measured value and the flow velocity, and a power supply circuit 622 for supplying each of the necessary circuits with a constant voltage. Direct current is supplied to the power supply circuit 622 from an external power supply, for example a vehicle battery, via a terminal 664 and a ground terminal (not shown in the drawings). The flow velocity sensing unit 602 is equipped with a heating element 608 for heating the measuring gas 30. A voltage V1 is applied by the power supply circuit 622 to a collector of a transistor 606, which represents a power supply circuit for the heating element 608. A control signal is output by the CPU 612 via the output circuit 616 to a base of the transistor 606, and a current is supplied by the transistor 606 to the heating element 608 via a terminal 624 on the base of the control signal. The amount of current supplied to the heating element 608 is controlled by the control signal supplied by the CPU 612 to the transistor 606, which represents the power supply circuit for the heating element 608, via the output circuit 616. The processing part 604 controls the amount of heat generated by the heating element 608, so that the temperature of the measuring gas 30 is higher than the initial temperature by a predetermined temperature amount, for example 100°C, by carrying out a heating process with the heating element 608. The flow velocity sensing unit 602 comprises a heat generation control bridge 640 for controlling the amount of heat generated by the heating element 608 and a flow velocity sensing bridge 650 for measuring the flow velocity. A constant voltage V3 is applied by the power supply circuit 622 to one end of the heat generation control bridge 640 via a terminal 626, and the other end of the heat generation control bridge 640 is connected to the ground terminal 630. Furthermore, the constant voltage V3 is applied by the power supply circuit 622 to one end of the flow velocity sensing bridge 650 via a terminal 625, and the other end of the flow velocity sensing bridge 650 is connected to the ground terminal 630. The heat generation control bridge 640 includes a resistor 642, which acts as a resistance temperature detector. The resistance of this detector changes based on the temperature of the heated measuring gas 30. The resistor 642, a resistor 644, a resistor 646, and a resistor 648 form a bridge circuit. A potential difference between an intersection A of resistor 642 and resistor 646 and an intersection B of resistor 644 and resistor 648 provides the input to the input circuit 614 via terminals 627 and 628. The CPU 612 controls the amount of heat generated by the heating element 608 by controlling the current supplied by transistor 606, such that the potential difference between intersection A and intersection B reaches a predetermined value, which in this embodiment is 0 volts. The flow velocity sensing circuit 601 shown in Fig. 20 heats the sample gas 30 with the heating element 608 so that the temperature is always a constant temperature, for example 100°C, higher than the original temperature of the sample gas 30. To control the heating with high accuracy when the temperature of the sample gas 30 heated by the heating element 608 is always a constant temperature, for example 100°C, higher than the original temperature, the resistance value of each resistor, which represents the heat generation control bridge 640, is set such that the potential difference between junction A and junction B is 0 volts. Therefore, in the flow velocity sensing circuit 601, the CPU 612 controls the current supplied to the heating element 608 such that the potential difference between junction A and junction B is 0 volts. The flow velocity sensing bridge 650 comprises four resistance temperature detectors, namely resistors 652, 654, 656, and 658. These four resistance temperature detectors are arranged along the flow of the sample gas 30. Resistors 652 and 654 are located upstream of the flow path of the sample gas 30 with respect to the heating element 608, and resistors 656 and 658 are located downstream of the flow path of the sample gas 30 with respect to the heating element 608. To improve measurement accuracy, resistors 652 and 654 are arranged such that their distances to the heating element 608 are substantially equal, and resistors 656 and 658 are also arranged such that their distances to the heating element 608 are substantially equal. A potential difference between an intersection point C of resistor 652 and resistor 656 and an intersection point D of resistor 654 and resistor 658 is input to the input circuit 614 via terminals 631 and 632. To improve measurement accuracy, each resistor of the flow velocity sensing bridge 650 is adjusted such that the potential difference between intersection C and intersection D is, for example, 0 when the flow rate of the sample gas 30 is 0. Therefore, in a state where the potential difference between intersection C and intersection D is, for example, 0 volts, the CPU 612 outputs an electrical signal from terminal 662 indicating that the flow velocity of the main passage 124 is 0, based on the measurement result showing that the flow velocity of the sample gas 30 is 0. When the sample gas 30 flows in the direction of the arrow in Fig. 20, the resistors 652 and 654, which are arranged upstream, are cooled by the sample gas 30, and the resistors 656 and 658, which are arranged on the downstream side of the sample gas 30, are heated by the sample gas 30 heated by the heating element 608, and the temperatures of the resistors 656 and 658 rise. Therefore, a potential difference is generated between the intersection point C and the intersection point D of the flow velocity sensing bridge 650, and this potential difference is fed into the input circuit 614 via terminals 631 and 632.The CPU 612 searches for data that represents a relationship between the potential difference stored in memory 618 and the flow velocity of the main passage 124, based on the potential difference between intersection C and intersection D of the flow velocity detection bridge 650, and obtains the value for the flow velocity of the main passage 124. An electrical signal representing the flow velocity of the main passage 124, obtained in the manner described above, is output via the terminal 662. Although new reference numerals have been given to terminals 664 and 662 in Fig. 20, these terminals fall under the connecting terminals 412 shown in Fig. 17 described above. Data representing the relationship between the potential difference between intersection point C and intersection point D and the flow velocity of the main passage 124 are stored in memory 618. After the production of the circuit board 400, correction data to reduce measurement errors, such as variations obtained based on actual gas measurements, are stored in memory. The temperature / humidity sensing circuit 701 comprises an input circuit, such as an A / D amplifier for inputting sensing signals from the temperature sensor 453 and the humidity sensor 422; an output circuit; a memory for storing data representing the relationship between the correction value or temperature and absolute humidity; and a power supply circuit 622 that provides each required circuit with a constant voltage. Signals output by the flow velocity sensing circuit 601 and the temperature / humidity sensing circuit 701 are input to the microcomputer 415. The microcomputer 415 has a flow velocity processing unit, a temperature processing unit, and an absolute humidity processing unit.It calculates the flow rate, temperature and absolute humidity, which represent the physical quantities of the measuring gas 30, based on the signals and outputs them to an ECU 200. The measuring device 300 for determining the air flow velocity and the control device (ECU) 200 are connected by a communication cable, and communication using a digital signal is carried out according to a communication standard such as SENT, LIN, and CAN. In the present embodiment, a signal is transmitted from the microcomputer 415 to a LIN driver 420, and LIN communication is carried out by the LIN driver 420. Information output by the LIN driver 420 of the measuring device 300 for determining the air flow velocity to the control device (ECU) 200 is superimposed and output via digital communication using a single-wire or two-wire communication cable. The processing unit of the microcomputer 415 for calculating absolute humidity performs a process to calculate absolute humidity based on the relative humidity and temperature information output by sensor 422, and to correct the absolute humidity based on errors. The corrected absolute humidity calculated by the processing unit is used for various engine operation controls by the control device 200, which is the ECU. Furthermore, the control device 200 can directly use information about total errors for various engine operation controls. In the embodiment described above, shown in Fig. 20, the case was described in which the measuring device 300 for determining the air flow velocity includes the LIN driver 420 and performs LIN communication. However, the present invention is not limited to this. As shown in Fig. 21, the measuring device for determining the air flow velocity does include the controller 416, but the device can also perform direct communication with the microcomputer 415 without using LIN communication. 6. Circuit board structure 400 Fig. 22 is a front view to show the shape of the housing 302, in which the front cover 303 has been removed from the measuring device 300 for determining the flow velocity of air. The measuring gas 30 flowing from the inlet 305a of the secondary passage 305 of the housing 302 may contain water droplets. The measuring gas 30 then passes through the secondary passage 305 and reaches the flow velocity sensing unit 602 together with the water droplets. The flow velocity sensing unit 602 comprises a heat generation control bridge for controlling the amount of heat generated by the heating element and a flow velocity sensing bridge for measuring the flow velocity. If adhering water droplets are present, a problem arises insofar as the bridge equilibrium collapses and the characteristic values ​​change. If a few water droplets on When numerous water droplets arrive at the flow velocity sensing unit 602, output noise occurs. If numerous water droplets arrive at the flow velocity sensing unit 602, a discrepancy arises between the detected flow velocity and the actual flow velocity, thus impairing the accuracy of the flow velocity sensing. In a region of the edge 800 of the circuit board 400, where the flow velocity sensing element 602 is attached, a segmentation area 801 is formed on the side where the measuring gas 30 arrives upstream of the flow velocity sensing element 602. The measuring gas 30, which has passed through the secondary passage 305, can transport water droplets flowing with the measuring gas 30 in a direction away from the flow velocity sensing element 602 by means of vortices generated by the segmentation area 801. Thus, the number of water droplets arriving at the flow velocity sensing element 602 can be reduced. When water droplets flow from the inlet 305a of the secondary passage 305 of the housing 302, they concentrate at the edge 800 of the outer circumference of the circuit board 400 and the secondary passage 305, across the outer wall of the secondary passage 305. If the segmentation area 801 is not formed, the water droplets concentrate at the edge 800, forming large droplets, and flow into the flow velocity sensing element 602. If the segmentation area 801 is formed at the edge 800, water droplets that have reached the circuit board 400 flow in a direction away from the flow velocity sensing element 602, due to the vortices generated by the segmentation area 801. The number of water droplets arriving at the flow velocity sensing element 602 can thus be reduced. During the forming of the housing 302, the printed circuit board 400 is inserted into the housing 302 and fixed by the housing 302. By fixing the segmentation structure area 801, which is formed in the printed circuit board 400 by the mold, the outer circumference of the secondary passage 305 and the edge of the segmentation structure 801 can be substantially aligned with each other, so that the water droplets flowing together with the measuring gas 30 flow in a direction away from the flow velocity sensing part 602. Fig. 23 is a front view of the shape of the housing 302, in which the front cover 304 has been removed from the device 300 for detecting a physical quantity. It represents a modification of the example shown in Fig. 22. In Fig. 23, in addition to the segmentation area 801 shown in Fig. 22, a segmentation area 802 is formed for segmenting an edge of the downstream side of the circuit board 400 on which the flow velocity sensing element 602 is mounted. Depending on the internal combustion engine in which the device is to be mounted, the measuring device 300 for determining the air flow velocity may be subject to strong back pressure from the engine, and water droplets may be contained in the back pressure. For this reason, by forming the segmentation area 802 on the downstream side, output noise and output deviations can be suppressed. The segmentation areas 801 and 802 can be described as water droplet trapping areas. Figures 24, 25 to 26 show modifications of the shape of the segmentation area 801. The segmentation area 801 is not limited to the semicircular shape shown in Figures 22 and 23; it can have a polygonal shape, for example, a triangular, a rectangular, or a pentagonal shape. When the segmentation area 801 is located at the edge 800, water droplets that have reached the circuit board 400 flow in a direction away from the flow velocity sensing element 602, due to the vortices generated by the segmentation area 801. The number of water droplets reaching the flow velocity sensing element 602 can thus be reduced. As shown in Fig. 23, these triangular, rectangular and polygonal segmentation areas can be formed on the upstream and downstream sides. As described above, according to this embodiment of the present invention, due to the fact that the segmentation area 801, which has the semicircular notch structure for segmenting the edge 800, is formed on the edge 800 of the upstream side through which the air flows in the circuit board 400 and on which the flow velocity detection part 602 is attached, it is possible to suppress the arrival of water droplets at the flow velocity detection part 602 by intercepting the water droplets flowing with the measuring gas 30 through the segmentation area 801. Thus, it is possible to design the measuring device for determining the flow velocity of air in such a way that it suppresses flow disturbances of the measuring gas and reduces the characteristic influence of water droplets that flow in with the intake air. For example, if the width of the plate on which the flow velocity sensing element 602 is mounted is approximately 10.8 mm, the segmentation area 801 can be a semicircular notch with a radius of approximately 1.5 mm, thereby suppressing disturbances in the flow of the measuring gas 30. Furthermore, in the case of the semicircular notch, the radius can be approximately 0.5 mm up to a longitudinal boundary point of the front end region of the printed circuit board 400. The above example describes how the printed circuit board 400 is integrated during the forming of the housing 302 (an example of an integrating forming process). However, the printed circuit board 400 and the housing 302 can also be provided without an integrating forming process, but rather by separate manufacturing. Furthermore, the segmentation area 801 is formed near the edge region between the wall surface of the housing 302, which forms the first side passage 305, and the edge of the plate 400. However, the segmentation area 801 can also be formed near the center of the end region 800 of the plate 400, or it can also be formed on the front end face. If the shape is such that the water droplets flowing through the first secondary passage 305 flow at a distance from the flow velocity detection part 602, the segmentation area 801 may also have a shape that differs from the shape described above; for example, a groove and a plurality of concave areas may be formed in an end face of the plate 400. Reference symbol list 30 Measuring gas 124 Main passage 300 Measuring device for determining the flow velocity of air 302 Housing 305 First secondary passage 400 Circuit board 404, 405, 406 Through hole 407, 408 Notch area 421A, 421B Pressure sensor 422 Humidity sensor 602 Flow velocity detection part 801 Segmentation area

Claims

Measuring device (300) for determining the flow velocity of a sample gas, comprising: a plate (400) having a flow velocity detection element (602) for detecting the flow velocity of the sample gas (30); and a housing (302) having a passage (305) receiving a portion of the sample gas and fixing the plate such that the flow velocity detection element is arranged in the passage, wherein the plate has a segmentation area (801) in the form of a notch provided at an edge (800) of the upstream side of a stream of the sample gas, with respect to the flow velocity detection element, and segmenting a portion of the edge, and wherein the notch is formed in a position where water accumulates on the upstream side of the stream of the sample gas in a boundary region between a wall surface of the housing forming the passage and the edge of the plate. Measuring device (300) for determining the flow velocity of a measuring gas according to claim 1, wherein a further notch (802) is also formed on an edge of the downstream side of the flow of the measuring gas (30), with respect to the flow velocity detection part (602). Measuring device (300) for determining the flow velocity of a measuring gas according to claim 1 or 2, wherein the notch (801, 802) has a semicircular shape. Measuring device (300) for determining the flow velocity of a measuring gas according to claim 1 or 2, wherein the notch (801, 802) has a triangular shape. Measuring device (300) for determining the flow velocity of a measuring gas according to claim 1 or 2, wherein the notch (801, 802) has a rectangular shape. Measuring device (300) for determining the flow velocity of a measuring gas according to claim 1 or 2, wherein the notch (801, 802) has a polygonal shape with at least five corners. Measuring device (300) for determining the flow velocity of a measuring gas according to claim 1, wherein the notch (801) has a shape in which water droplets flowing through the passage (305) are far away from the flow velocity detection part (602). Measuring device (300) for determining the flow velocity of a measuring gas according to claim 7, wherein the notch (801) has a water droplet trapping area that traps the water droplets flowing through the passage (305). Measuring device (300) for determining the flow velocity of a measuring gas according to claim 1, wherein the plate (400) has been fixed to the housing (302) by integrated shaping.

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