Intake temperature detection device and maximum heat generating amount components mounted on a single circuit board

The present invention reduces, by optimizing disposition of components on an electronic circuit board, heat transfer from other components mounted on the same board, and improves measurement accuracy of an intake air temperature detection element. A physical quantity detection device of the present invention has an electronic circuit board, which is provided with one or more intake air temperature detection elements (elements having intake air temperature detection function), and which processes electric signals. Furthermore, the physical quantity detection device has a configuration wherein the intake air temperature detection elements, and a power supply regulator having the maximum heat generation quantity are mounted on the same electronic circuit board. The physical quantity detection device is characterized in that the intake air temperature detection elements are disposed on the air flow upstream side of the power supply regulator.

TECHNICAL FIELD

The present invention relates to a physical quantity detection device of intake air of an internal combustion engine.

BACKGROUND ART

PTL 1 shows a structure in which a temperature measuring element is mounted on a sub air passage constituted by a part of a housing member, and a resin member constituting the sub-passage is formed with vent holes larger than the temperature measuring element on both side walls, and the temperature measuring element is disposed between the vent holes. In PTL 1, the temperature measuring element is installed at a position away from an electronic circuit board which drives the temperature measuring element.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

As shown in PTL 1, when the temperature measuring element and the driving circuit are not directly connected, the temperature measuring element and the driving circuit must be connected via a lead terminal or the like, which increases the number of assembling steps and the number of parts, leading to expansion of the module outer shape. On the other hand, in electronic circuit boards, the increase in the heat generation density is remarkable due to the high density mounting of many electronic components, and the circuit self heating causes a problem. Therefore, in a configuration in which a physical quantity detection element, a control IC, a power supply component, and the like are collectively mounted on the same circuit board, the influence of heat generation of other components is transmitted via the circuit board, so that the measurement accuracy of the physical quantity detection element is greatly affected. Therefore, it is necessary to reduce the circuit self-heating effect on the detection element.

The present invention has been made in view of the above issues, and it is an object of the present invention to provide a physical quantity detection device in which the heat transfer from other parts mounted on the same substrate is reduced by optimizing the arrangement of parts on the electronic circuit board, and in which the measurement accuracy of the intake temperature detection element is improved.

Solution to Problem

To solve the problem described above, a physical quantity detection device of the present invention includes one or more intake temperature detection elements and an electronic circuit board processing an electric signal, wherein the one or more intake temperature amount detection elements and a component having a maximum heat generation amount are configured to be mounted on the same electronic circuit board, and the one or more intake temperature detection elements are arranged at an air flow upstream portion with respect to the component having the maximum heat generation amount.

Advantageous Effects of Invention

According to the present invention, the heat transfer from other components mounted on the same substrate can be reduced by optimizing the arrangement of components on the electronic circuit board, and the measurement accuracy of the intake temperature detection element can be improved. The problems, configurations, and effects other than those described above will be clarified from the description of the following embodiments.

DESCRIPTION OF EMBODIMENTS

A mode for carrying out the invention (hereinafter referred to as an embodiment) described below solves various problems which are demanded as actual products, and solves various problems desirable for use as a detection device for detecting a physical quantity of intake air, in particular, of a vehicle, and achieve various effects. One of various problems solved by the following embodiment is the contents described in the Technical Problem described above, and one of the various effects exhibited by the following embodiments is the effect described in Advantageous Effects of Invention. Various problems solved by the following embodiments and various effects which are exerted by the following examples will be described in the description of the following embodiments. Accordingly, the problems and effects solved by the embodiments described in the following embodiments are also described with regard to the contents other than the contents of the Technical Problem and the Advantageous Effects of Invention.

In the following embodiments, the same reference numerals indicate the same elements and achieve the same operational effect even if they are in different drawings. For the elements already described, only the reference symbols are given in the drawings, and the explanation thereabout may be omitted in some cases.

1. One Embodiment Using Physical Quantity Detection Device According to the Present Invention in Internal Combustion Engine Control System

FIG. 1is a system diagram showing an embodiment using the physical quantity detection device according to the present invention in an internal combustion engine control system of an electronic fuel injection method. Based on the operation of an internal combustion engine110having an engine cylinder112and an engine piston114, the intake air is sucked from the air cleaner122as the measurement target gas30, and is taken through the main passage124, for example, an intake body, a throttle body126, and an intake manifold128and is guided to a combustion chamber of the engine cylinder112. The physical quantity of the measurement target gas30which is the intake air led to the combustion chamber is detected by a physical quantity detection device300according to the present invention. The fuel is supplied from the fuel injection valve152based on the detected physical quantity, and is led to the combustion chamber in an air-fuel mixture state with the intake air20. In the present embodiment, the fuel injection valve152is provided in the intake port of the internal combustion engine, and the fuel injected into the intake port forms an air-fuel mixture with the measurement target gas30which is the intake air, and it is led to the combustion chamber via the intake valve116to be combusted to generate mechanical energy.

The fuel and the air led to the combustion chamber form a mixed state of fuel and air, and explosively burn due to spark ignition of a spark plug154to generate mechanical energy. The gas generated by the combustion is guided from an exhaust valve118to the exhaust pipe and discharged as exhaust gas24from the exhaust pipe to the outside of the vehicle. The flow rate of the measurement target gas30, which is intake air led to the combustion chamber, is controlled by a throttle valve132of which opening degree varies on the basis of operation of an accelerator pedal. The fuel supply amount is controlled based on the flow rate of the intake air led to the combustion chamber. The driver can control the mechanical energy generated by the internal combustion engine by controlling the opening degree of the throttle valve132and controlling the flow rate of the intake air guided to the combustion chamber.

1.1 Overview of Control of Internal Combustion Engine Control System

The physical quantity such as the flow rate, temperature, humidity, pressure, and the like of the measurement target gas30which is taken in from the air cleaner122and flows through the main passage124is detected by the physical quantity detection device300, and an electric signal representing the physical quantity of the intake air is input into the control device200from the physical quantity detection device300. The output of the throttle angle sensor144for measuring the opening degree of the throttle valve132is input to the control device200. Further, the position and the state of the engine piston114of the internal combustion engine, the intake valve116, and the exhaust valve118are input to the control device200, and further, in order to measure the rotation speed of the internal combustion engine, the output of the rotation angle sensor146is input to the control device200. The output of the oxygen sensor148is input to the control device200in order to measure the state of the mixture ratio of the fuel quantity and the air quantity from the state of the exhaust gas24.

Based on the physical quantity of the intake air which is the output of the physical quantity detection device300and the rotation speed of the internal combustion engine measured based on the output of the rotation angle sensor146, the control device200calculates the fuel injection amount and the ignition timing. Based on these calculation results, the amount of fuel supplied from the fuel injection valve152and the ignition timing ignited by the spark plug154are controlled. The fuel supply amount and the ignition timing are actually controlled in details based on the temperature detected by the physical quantity detection device300, the change state of the throttle angle, the change state of the engine rotation speed, and the state of the air fuel ratio measured by the oxygen sensor148. The control device200further controls the amount of air bypassing the throttle valve132by an idle air control valve156in the idle operation state of the internal combustion engine, and controls the rotation speed of the internal combustion engine in the idle operation state.

1.2 Importance of Improving the Detection Accuracy of Physical Quantity Detection Device and Mounting Environment of Physical Quantity Detection Device

Both the fuel supply amount and the ignition timing which are the main control amount of the internal combustion engine are calculated using the output of the physical quantity detection device300as the main parameter. Therefore, improvement of the detection precision of the physical quantity detection device300, suppression of change over time, and improvement of reliability are important for improving the control precision of the vehicle and ensuring reliability.

Particularly in recent years, the demand for fuel saving of vehicles has been very high, and the demand for purification of exhaust gas is very high. In order to satisfy these demands, it is extremely important to improve the detection accuracy of the physical quantity of the intake air20detected by the physical quantity detection device300. It is also important that the physical quantity detection device300maintains high reliability.

Vehicles equipped with the physical quantity detection device300are used in environments where the temperature and the humidity greatly change. It is desirable that the physical quantity detection device300is also designed to cope with changes in the temperature and the humidity in its use environment, and to deal with dust and contaminants.

The physical quantity detection device300is attached to an intake pipe which is affected by the heat generated from the internal combustion engine. Therefore, the heat generation of the internal combustion engine is transmitted to the physical quantity detection device300via the intake pipe which is the main passage124. Since the physical quantity detection device300detects the flow rate of the measurement target gas by performing heat transfer with the measurement target gas, it is important to suppress the influence of heat from the outside as much as possible.

As described below, the physical quantity detection device300installed in the car not only solves the problem described in the Technical Problem and exhibits the effects described in Advantageous Effects of Invention but also, as explained below, takes various problems mentioned above into consideration, solves various problems required as products, and achieves various effects. Specific problems to be solved by the physical quantity detection device300and concrete effects achieved thereby will be described in the description of the following embodiments.

2. Configuration of Physical Quantity Detection Device300

2.1 External Structure of Physical Quantity Detection Device300

FIG. 2AtoFIG. 2Fare views showing the appearance of the physical quantity detection device300.FIG. 2Ais a front view of the physical quantity detection device300.FIG. 2Bis a rear view.FIG. 2Cis a left side view.FIG. 2Dis a right side view.FIG. 2Eis a plan view.FIG. 2Fis a bottom view.

The physical quantity detection device300includes a housing302, a front cover303, and a back cover304. The housing302is formed by molding a synthetic resin material, and includes a flange311for fixing the physical quantity detection device300to the intake body which is the main passage124, an external connection unit321projecting from the flange311and having a connector for electrical connection with external devices, and a measurement unit331extending from the flange311so as to protrude toward the center of the main passage124.

In the measurement unit331, a circuit board400is integrally provided by insert molding when the housing302is molded (seeFIG. 3A,FIG. 3B). The circuit board400is provided with at least one detection unit for detecting the physical quantity of the measurement target gas30flowing through the main passage124and a circuit unit for processing the signal detected by the detection unit. The detection unit is placed at a position exposed to the measurement target gas30and the circuit unit is placed in the circuit chamber sealed by the front cover303.

A sub-passage groove is provided on the front and back surfaces of the measurement unit331, and a first sub-passage305is formed in cooperation with the front cover303and the back cover304. A first sub-passage entrance305afor taking a part of measurement target gas30such as intake air into first sub-passage305and a first sub-passage exit305bfor returning the measurement target gas30from the first sub-passage305to the main passage124are formed at the distal end portion of the measurement unit331. A part of the circuit board400protrudes in the middle of passage of the first sub-passage305. A flow rate detection unit602(seeFIG. 3A) which is a detection unit is arranged in the protruding portion, and the flow rate of the measurement target gas30is detected by the flow rate detection unit602.

A second sub-passage306for introducing a part of the measurement target gas30such as intake air into a sensor chamber Rs is provided in the middle part of the measurement unit331closer to the flange311than the first sub-passage305. The second sub-passage306is formed by cooperation of the measurement unit331and the back cover304. The second sub-passage306includes a second sub-passage entrance306aformed through the upstream side external wall336to capture the measurement target gas30and a second sub-passage exit306bformed through the downstream side external wall338to return the measurement target gas30from the second sub-passage306to the main passage124. The second sub-passage306is in communication with the sensor chamber Rs formed in the back side of the measurement unit331. In the sensor chamber Rs, a pressure sensor and a temperature and humidity sensor which are detection units provided on the back side of the circuit board400are arranged.

2.2 Effects Based on External Appearance Structure of Physical Quantity Detection Device300

In the physical quantity detection device300, the second sub-passage entrance306ais provided in the middle part of the measurement unit331extending from the flange311toward the center direction of the main passage124, and the first sub-passage entrance305ais provided at the distal end portion of the measurement unit331. Therefore, instead of from the vicinity of the inner wall surface of the main passage124, the gas from the vicinity of the center part away from the inner wall surface can be captured into in the first sub-passage305and the second sub-passage306. Therefore, the physical quantity detection device300can measure the physical quantity of the gas at a portion distant from the inner wall surface of the main passage124, and can reduce the measurement error of the physical quantity related to the heat and the flow velocity decrease near the inner wall surface.

The measurement unit331has a shape elongated along the axis extending from the external wall of the main passage124toward the center, but the thickness width is in a narrow shape as shown inFIG. 2CandFIG. 2D. More specifically, the measurement unit331of the physical quantity detection device300has a shape in which the side face is thin and the front face is substantially rectangular. Accordingly, the physical quantity detection device300can have the first sub-passage305of which length is sufficient, and the fluid resistance for the measurement target gas30can be suppressed to a small value. Therefore, the physical quantity detection device300can suppress the fluid resistance to a small value and measure the flow rate of the measurement target gas30with high accuracy.

2.3 Structure and Effect of Flange311

In the flange311, multiple dents313are provided on the lower surface312opposed to the main passage124to reduce the heat transfer surface with the main passage124, so that the physical quantity detection device300is less affected by heat. In the physical quantity detection device300, the measurement unit331is inserted into the mounting hole provided in the main passage124, and the lower surface312of the flange311is opposed to the main passage124. The main passage124is, for example, an intake body, and the main passage124is often maintained at a high temperature. Conversely, when starting up in cold climate, it is conceivable that the main passage124is at an extremely low temperature. If such a high temperature or low temperature state of the main passage124affects the measurements of various physical quantities, the measurement precision will be lowered. The flange311has the dents313in the lower surface312, and a space is formed between the lower surface312opposed to the main passage124and the main passage124. Therefore, it is possible to reduce the heat transfer from the main passage124to the physical quantity detection device300, and to prevent deterioration of measurement accuracy due to the heat.

A screw hole314of the flange311is for fixing the physical quantity detection device300to the main passage124, and a space is formed between the main passage124and the surface opposite the main passage124around each screw hole314, so that the surface opposing the main passage124around the screw hole314is away from the main passage124. In this configuration, the heat transfer from the main passage124to the physical quantity detection device300is reduced, and the structure is such that it is possible to prevent the deterioration of measurement accuracy due to heat.

2.4 Structure of External Connection Unit321

The external connection unit321has a connector322provided on the upper surface of the flange311and protruding from the flange311toward the flow-direction downstream side of the measurement target gas30. The connector322is provided with an insertion hole322afor inserting communication cables for connecting with the control device200. As shown inFIG. 2D, inside the insertion hole322a, four external terminals323are provided. The external terminal323is a terminal for outputting physical quantity information which is the measurement result of the physical quantity detection device300and power supply terminals for supplying DC power for the operation of the physical quantity detection device300.

The connector322protrudes from the flange311toward the flow-direction downstream side of the measurement target gas30and has a shape to be inserted from the flow-direction downstream side toward the upstream side. However, the connector322is limited to this shape. For example, the connector322may have a shape protruding perpendicularly from the upper surface of the flange311to be inserted along the extension direction of the measurement unit331, and various modifications are possible.

3. Entire Structure of Housing302and Effects Thereof

3.1 Structure of Housing

Subsequently, the entire structure of the housing302will be described with reference toFIGS. 3A to 3E.FIGS. 3A to 3Eare diagrams showing the state of the housing302in which the front cover303and the back cover304are removed from the physical quantity detection device300.FIG. 3Ais a front view of the housing302.FIG. 3Bis a rear view of the housing302.FIG. 3Cis a right side view of the housing302.FIG. 3Dis a left side view of the housing302.FIG. 3Eis a sectional view taken along line A-A ofFIG. 3A.

The housing302has a structure in which the measurement unit331extends from the flange311toward the center of the main passage124. A circuit board400is insert molded at the proximal end side of the measurement unit331. The circuit board400is disposed parallel to the surface of the measurement unit331at an intermediate position between the front surface and the back surface of the measurement unit331and molded integrally with the housing302, and the base end side of the measurement unit331is divided into thickness-direction one side and the other side.

On the front surface side of the measurement unit331, a circuit chamber Rc for accommodating the circuit unit of the circuit board400is formed. On the back surface side of the measurement unit331, a sensor chamber Rs for accommodating a pressure sensor421and a temperature and humidity sensor422are formed. The circuit chamber Rc is hermetically sealed by attaching the front cover303to the housing302and is completely isolated from the outside. On the other hand, by attaching the back cover304to the housing302, the second sub-passage306and the sensor chamber Rs which is a space inside the chamber in communication with the external of the measurement unit331via the second sub-passage306are formed. A part of the circuit board400protrudes from a partition wall335partitioning the circuit chamber Rc of the measurement unit331and the first sub-passage305toward the first sub-passage305, and a flow rate detection unit602is provided in the measurement flow path surface430of the protruded portion.

3.2 Structure of Sub-Passage Groove

At the length-direction distal end side of the measurement unit331, a sub-passage groove for forming the first sub-passage305is provided. The sub-passage groove for forming the first sub-passage305has a front side sub-passage groove332shown inFIG. 3Aand a back side sub-passage groove334shown inFIG. 3B. As shown inFIG. 3A, the front side sub-passage groove332gradually bends to the flange311which is the proximal end side of the measurement unit331as the front side sub-passage groove332extends from the first sub-passage exit305b, which is open through the downstream side external wall338of the measurement unit331, to the upstream side external wall336. The front side sub-passage groove332communicates with an opening unit333penetrating the measurement unit331in the thickness direction at a position near the upstream side external wall336. The opening unit333is formed along the flow-direction of the measurement target gas30of the main passage124so as to extend between the upstream side external wall336and the downstream side external wall338.

As shown inFIG. 3B, the backside sub-passage groove334moves from the upstream side external wall336to the downstream side external wall338, and is divided into two at the intermediate position between the upstream side external wall336and the downstream side external wall338, and one of them extends in straight line as a discharge passage and opens to an exhaust exit305cof the downstream side external wall338, and the other of them gradually bends to the flange311which is the proximal end side of the measurement unit331as it extends to the downstream side external wall338, and is in communication with the opening unit333in the vicinity of the downstream side external wall338.

The back side sub-passage groove334forms an entrance groove into which the measurement target gas30flows from the main passage124. The front side sub-passage groove332forms an exit groove for returning the measurement target gas30taken from the back side sub-passage groove334to the main passage124. Since the front side sub-passage groove332and the back side sub-passage groove334are provided in the distal end portion of the housing302, a gas in a portion away from the inner wall surface of the main passage124, i.e., a gas flowing in a portion close to the central portion of the main passage124, can be captured as the measurement target gas30. The gas flowing in the vicinity of the inner wall surface of the main passage124is affected by the wall surface temperature of the main passage124and often has a temperature different from the average temperature of the gas flowing through the main passage124such as intake air20. The gas flowing in the vicinity of the inner wall surface of the main passage124often shows a flow velocity lower than the average flow velocity of the gas flowing through the main passage124. Since the physical quantity detection device300according to the embodiment is hardly affected by such an influence, it is possible to suppress a decrease in the measurement accuracy.

As shown inFIG. 3B, a part of the measurement target gas30flowing through the main passage124is taken into the back side sub-passage groove334from the first sub-passage entrance305aand flows in the back side sub-passage groove334. A foreign substance having a large mass contained in the measurement target gas30flows into the discharge passage extending straight from the branch together with a part of the measurement target gas to be discharged from the exhaust exit305cof the downstream side external wall338to the main passage124.

The back side sub-passage groove334has a shape which becomes deeper as it advances and the measurement target gas30gradually moves to the front side of the measurement unit331as it flows along the back side sub-passage groove334. Particularly, the back side sub-passage groove334is provided with a sharply inclined portion334awhich is rapidly deepened before the opening unit333, and a part of the air having a small mass moves along the sharply inclined portion334aand, in the opening unit333, the part of the air having a small mass flows at the side of measurement flow path surface430of the circuit board400. On the other hand, a foreign substance having a large mass flows at the side of the measurement flow path surface back surface431because it is difficult to change the course suddenly.

As shown inFIG. 3A, the measurement target gas30moved to the front side in the opening unit333flows along the measurement flow path surface430of the circuit board, and heat transfer is performed with the flow rate detection unit602provided in the measurement flow path surface430so that the flow rate is measured. The air flowing from the opening unit333to the front side sub-passage groove332flows along the front side sub-passage groove332and is discharged to the main passage124from the first sub-passage exit305bthat is open to the downstream side external wall338.

A substance having a large mass such as dust mixed in the measurement target gas30has a large inertial force and therefore it is difficult for such a substance having a large mass such as dust mixed in the measurement target gas30to suddenly change the course in a deep direction of the groove along the front surface of a portion of the sharply inclined portion334awhere the depth of the groove rapidly increases. For this reason, a foreign substance having a large mass moves toward the measurement flow path surface back surface431, and it is possible to suppress a foreign substance from passing near the flow rate detection unit602. In this embodiment, many foreign substances having large masses other than the gas pass through the measurement flow path surface back surface431which is the back surface of the measurement flow path surface430, and therefore, it is possible to reduce the influence of contamination by foreign substances such as oil, carbon, and dust, and to suppress deterioration of measurement accuracy. More specifically, because of a shape that rapidly changes the course of the measurement target gas30along an axis transverse to the axis of the flow of the main passage124, the influence of foreign substances entering the measurement target gas30can be reduced.

3.3 Structure and Effects of Second Sub-Passage and Sensor Chamber

The second sub-passage306is formed in a straight line extending between the second sub-passage entrance306aand the second sub-passage exit306bin parallel with the flange311along the flow-direction of the measurement target gas30. The second sub-passage entrance306ais formed by cutting out a part of the upstream side external wall336. The second sub-passage exit306bis formed by cutting out a part of the downstream side external wall338. More specifically, as shown inFIG. 3C, at a position continuously along the upper surface of partition wall335, the second sub-passage entrance306aand the second sub-passage exit306bare formed by cutting out a portion of the upstream side external wall336and a portion of the downstream side external wall338from the back surface side of measurement unit331. The second sub-passage entrance306aand the second sub-passage exit306bare cut out to a depth position which is the same as the back surface and surface of the circuit board400. The second sub-passage306functions as a cooling channel for cooling a board main body401as the measurement target gas30passes along the back surface of the board main body401of the circuit board400. The circuit board400tends to have heat of an LSI and a microcomputer. The heat can be transferred to the back surface of the board main body401and dissipated by the measurement target gas30passing through the second sub-passage306.

The sensor chamber Rs is provided at the proximal end side of the measurement unit331with respect to the second sub-passage306. A part of the measurement target gas30flowing from the second sub-passage entrance306ainto the second sub-passage306flows into the sensor chamber Rs, and the temperature and humidity sensor422and the pressure sensor421in the sensor chamber Rs detect the relative humidity and the pressure, respectively. Since the sensor chamber Rs is located at the proximal end side of the measurement unit331with respect to the second sub-passage306, the influence of the dynamic pressure of the measurement target gas30passing through the second sub-passage306can be reduced. Therefore, the detection accuracy of the pressure sensor421in the sensor chamber Rs can be improved.

The sensor chamber Rs is located at the proximal end side of the measurement unit331with respect to the second sub-passage306, and therefore, when the measurement unit331is attached to the intake passage with the distal end side facing downward, for example, contaminants and water droplets flowing together with the measurement target gas30in the second sub-passage306can be prevented from adhering to the pressure sensor421and the temperature and humidity sensor422disposed upstream thereof.

The pressure sensor421and the temperature and humidity sensor422are less susceptible to the flow of the measurement target gas30compared to the flow rate detection unit602, and can be provided in the sensor chamber Rs adjacent to the second sub-passage306in a straight line. On the other hand, the flow rate detection unit602requires a certain flow rate or more, it is necessary to keep dust and contaminants away, and the influence on pulsation also needs to be considered. Therefore, the flow rate detection unit602is provided in the first sub-passage305having a loop shape.

FIG. 4AandFIG. 4Bare diagrams showing another mode of second sub-passage.

In this mode, instead of cutting out the upstream side external wall336and the downstream side external wall338, a through hole337is provided in the upstream side external wall336and the downstream side external wall338to form the second sub-passage entrance306aand the second sub-passage exit306b. Like the second sub-passage shown inFIG. 3BtoFIG. 3E, when the upstream side external wall336and the downstream side external wall338are respectively cut out to form the second sub-passage entrance306aand the second sub-passage exit306b, the width of the upstream side external wall336and the width of the downstream side external wall338are locally narrowed at such a position, so that the measurement unit331may be deformed in an almost angle shape from the notch being a starting point due to heat shrinkage or the like during molding. According to this mode, since the through hole is provided instead of the notch, it is possible to prevent the measurement unit331from being bent in a substantially square shape. Therefore, it is possible to prevent the position and direction of the detection unit with respect to the measurement target gas30from changing due to distortion in the housing302, thereby preventing the detection accuracy from being affected, and constant detection accuracy can always be secured without individual differences.

In the back cover304, a partition wall partitioning between the second sub-passage306and the sensor chamber Rs may be provided. According to such a configuration, it is possible to indirectly cause the measurement target gas30to flow from the second sub-passage306to the sensor chamber Rs, to reduce the influence of the dynamic pressure on the pressure sensor, and to suppress contaminants and water droplets adhered to the temperature and humidity sensor

3.4 Shape and Effect of Front Cover303and Back Cover304

FIGS. 5A and 5Bare figures showing an appearance of the front cover303.FIG. 5Ais a front view.FIG. 5Bis a B-B line sectional view ofFIG. 5A.FIGS. 6A and 6Bshow the appearance of the back cover304.FIG. 6Ais a front view, andFIG. 6Bis a B-B cross sectional view ofFIG. 6A.

InFIGS. 5A-5BandFIGS. 6A-6B, the front cover303and the back cover304close the front side sub-passage groove332and the back side sub-passage334of the housing302, thereby forming a first sub-passage305. In addition, the front cover303makes the hermetically sealed circuit chamber Rc, and the back cover304closes the recess of the back surface side of the measurement unit331to make the second sub-passage306and the sensor chamber Rs communicating with the second sub-passage306.

The front cover303has a protrusion unit356at a position facing the flow rate detection unit602and is used to form a stop between the flow rate detection unit602and the measurement flow path surface430. Therefore, it is desirable that molding accuracy is high. Since the front cover303and the back cover304are made by a resin molding process for injecting a thermoplastic resin into a mold, the front cover303and the back cover304can be made with high molding precision.

The front cover303and the back cover304are provided with multiple fixing holes351into which multiple fixation pins350protruding from the measurement unit331are inserted. The front cover303and the back cover304are respectively attached to the front surface and the back surface of the measurement unit331, and at this time, the fixing pin350is inserted into the fixing hole351and positioned. Then, bonding is performed by laser welding or the like along the edges of the front side sub-passage groove332and the back side sub-passage groove334, and likewise bonding is performed by laser welding or the like along edges of the circuit chamber Rc and the sensor chamber Rs.

3.5 Fixing Structure and Effects of Circuit Board400by Housing302

Next, fixing of the circuit board400to the housing302by the resin molding process will be described. The circuit board400is molded integrally with the housing302so that the flow rate detection unit602of the circuit board400is arranged in the predetermined place of the sub-passage groove forming the sub-passage, for example, in the present embodiment, the opening unit333which is the connection part between the front side sub-passage groove332and the back side sub-passage groove334.

In the measurement unit331of the housing302, parts for fixing the outer peripheral edge portion of the base unit402of the circuit board400by resin molding on the housing302are provided as fixing units372and373. The fixing units372and373fix the outer peripheral edge portions of the base unit402of the circuit board400by sandwiching them from the front side and the back side.

The housing302is manufactured by a resin molding process. In this resin molding process, the circuit board400is built in the resin of the housing302and fixed in the housing302by resin molding. Accordingly, the shape of the circuit board400of the sub flow passage for flow rate detection unit602to measure the flow rate by performing heat transfer with measurement target gas30, such as front side sub-passage groove332and back side sub-passage groove334, can be maintained with extremely high accuracy, and it is possible to suppress errors and variations occurring in each circuit board400to very small values. As a result, the measurement accuracy of the circuit board400can be greatly improved. For example, the measurement accuracy can be dramatically improved as compared with a method of fixing using a conventional adhesive.

The physical quantity detection device300is produced by mass production in many cases, and there is a limitation on the improvement of measurement accuracy in the method of adhesion with an adhesive while strictly performing measuring here. However, as in the present embodiment, the circuit board400is fixed at the same time as forming the sub-passage in the resin molding step for molding the sub-passage through which the measurement target gas30flows, so that the variation in the measurement accuracy can be greatly reduced, and it is possible to greatly improve the measurement accuracy of the physical quantity detection device300.

For example, this will be further explained with the embodiment shown inFIG. 3AtoFIG. 3E. The circuit board400can be fixed to the housing302with high accuracy so that the relationship between the front side sub-passage groove332, the back side sub-passage groove334, and the flow rate detection unit602has a prescribed relationship. In this way, in the mass-produced physical quantity detection device300, the positional relationships between the flow rate detection unit602of each circuit board400and the first sub-passage305and the shapes thereof and the like can be obtained regularly and constantly with an extremely high accuracy.

With the first sub-passage305in which the flow rate detection unit602of the circuit board400is fixedly arranged, for example, the front side sub-passage groove332and the back side sub-passage groove334can be molded with extremely high precision, so that the operation of forming the first sub-passage305from these sub-passage grooves332and334is a work of covering both surfaces of the housing302with the front cover303and the back cover304. This work is very simple, and it is a work process involving few factors to lower the measurement accuracy. In addition, the front cover303and the back cover304are produced by process with resin molding with a high forming accuracy. Accordingly, it is possible to complete the sub-passage provided in a prescribed relationship with the flow rate detection unit602of the circuit board400with high accuracy. According to such a method, in addition to the improvement of the measurement accuracy, high productivity can be obtained.

In contrast to this, a thermal flow rate meter was manufactured by manufacturing a sub-passage and then attaching a measurement unit to the sub-passage with an adhesive. In the method of using the adhesive as described above, the thickness variation of the adhesive is large, and the bonding position and the bonding angle vary from product to product. Therefore, there was a limitation on the increase of the measurement accuracy. Furthermore, when these tasks are performed in a mass production process, it is extremely difficult to improve the measurement accuracy.

In the embodiment according to the present invention, the sub-passage groove for molding the first sub-passage305with a resin mold is formed at the same time as fixing the circuit board400by resin molding. Therefore, the flow rate detection unit602can be fixed to the shape of the sub-passage groove and the sub-passage groove with an extremely high accuracy.

The parts related to the flow rate measurement, for example, the flow rate detection unit602and the measurement flow path surface430to which the flow rate detection unit602is attached, are provided on the front surface of the circuit board400. The flow rate detection unit602and the measurement flow path surface430are exposed from the resin molding the housing302. More specifically, the flow rate detection unit602and the measurement flow path surface430are not covered with the resin molding the housing302. The flow rate detection unit602of the circuit board400and the measurement flow path surface430are used as they are even after resin molding of the housing302and used for the flow rate measurement of the physical quantity detection device300. As a result, the measurement accuracy improves.

In the embodiment according to the present invention, the circuit board400is fixed to the housing302having the first sub-passage305by integrally molding the circuit board400with the housing302, the circuit board400can be reliably fixed to the housing302. In particular, since the protrusion unit403of the circuit board400protrudes into the first sub-passage305through the partition wall335, the sealing property between the first sub-passage305and the circuit chamber Rc is high, and it is possible to prevent the measurement target gas30from leaking from the first sub-passage305to the circuit chamber Rc and to prevent the circuit component, the wiring, and the like of the circuit board400from coming into contact with the measurement target gas30and corroding.

3.6 Structure and Effects of Terminal Connection Unit320

Next, the structure of the terminal connection unit will be described below with reference toFIG. 9AtoFIG. 9E.FIG. 9Ais a diagram for explaining the structure of the terminal connection unit.FIG. 9Bis a diagram for explaining the structure of the terminal connection unit.FIG. 9Cis a line F-F sectional view ofFIG. 9A.FIGS. 9D and 9Eare line G-G sectional views ofFIG. 9B.

In the terminal connection unit320, the inner end unit361of the external terminal323and the connection terminal412of the circuit board400are connected by an aluminum wire or a gold wire413. As shown inFIG. 9A, the inner end unit361of each external terminal323protrudes from the side of the flange311into the circuit chamber Rc and arranged side by side with a predetermined distance from each other according to the position of the connection terminal412of the circuit board400.

As shown inFIG. 9C, the inner end unit361is disposed at a position approximately on the surface of the front surface of the circuit board400. The distal end thereof is bent in a substantially L shape from the front surface to the back surface side of the measurement unit331and protrudes to the back surface of the measurement unit331. As shown inFIG. 9D, a distal end of each inner end unit361is connected by a connecting portion365, and as shown inFIG. 9E, after the molding, the connecting portions365are separated and divided individually.

Each inner end unit361is fixed to the housing302by a resin mold in a molding process so that the inner end unit361and the circuit board400are arranged on the same plane. Each inner end unit361is fixed to the housing302by a resin molding process in a state in which they are joined together by the connecting portion365so as to prevent deformation and dislocation. After being fixed to the housing302, the connecting portion365is disconnected.

The inner end unit361is molded in a state sandwiched between the front surface side and the back surface side of the measurement unit331. At that time, the front surface of the inner end unit361is brought into contact with the mold over the entire surface and the fixing pin is brought into contact with the back surface of the inner end unit361. Accordingly, the front surface of the inner end unit361to which the aluminum wire or the gold wire is welded can be completely exposed without being covered with the mold resin due to resin leakage, and it is easy to weld the gold wire. A pin hole340formed by holding the inner end unit361with the fixing pin is formed in the measurement unit331.

The distal end of the inner end unit361protrudes into the recessed unit341formed in the back surface of the measurement unit331. The recessed unit341is covered with the back cover304, and the periphery of the recessed unit341is joined to the back cover304continuously by laser welding or the like to form a hermetically sealed chamber inner space. Therefore, it is possible to prevent the inner end unit361from coming into contact with the measurement target gas30and corroding.

4. External Appearance of Circuit Board400

4.1 Formation of Measurement Flow Path Surface430Having Flow Rate Detection Unit602

The appearance of the circuit board400is shown inFIG. 7AtoFIG. 7F. The hatched portion on the external appearance of the circuit board400indicates the fixing surface432and the fixing surface434which cover and fix the circuit board400by the resin when the housing302is molded in the resin molding process.

FIG. 7Ais a front view of the circuit board.FIG. 7Bis a right side surface diagram of the circuit board.FIG. 7Cis a back surface diagram of the circuit board.FIG. 7Dis a left side surface diagram of the circuit board.FIG. 7EandFIG. 7Fare B-B line sectional views showing the cross-section of the LSI portion ofFIG. 7A.FIG. 7Gis a line C-C sectional view of the detection unit ofFIG. 7A.

The circuit board400has a board main body401. The circuit unit and the flow rate detection unit602which is a sensing element are provided on the front surface of the board main body401. The pressure sensor421and the temperature and humidity sensor422which are sensing elements are provided on the back surface of the board main body401. The board main body401is made of a material made of glass epoxy resin. As compared with the ceramic material board, the board main body401has a value close to the thermal expansion coefficient of the thermoplastic resin molding the housing302. Therefore, stress caused by a difference in thermal expansion coefficient can be reduced when insert molding is performed on the housing302, and distortion of the circuit board400can be reduced.

The circuit unit is configured by mounting electronic components such as an LSI414, a microcomputer415, a power supply regulator416, and a chip component417such as a resistance and a capacitor on a circuit wiring, not shown.

As shown inFIG. 7E, a recessed unit402ainto which the LSI414is fitted is formed in a recessed manner on the front surface of the board main body401. The recessed unit402acan be formed by subjecting the board main body401to laser processing. The board main body401made of the glass epoxy resin is easier to process than the main body made of ceramic and the recessed unit402can be easily provided. The recessed unit402has a depth such that the front surface of the LSI414is flush with the front surface of the board main body401. By making the front surface of the LSI414and the front surface of the board main body401to be the same as each other in this manner, wire bonding for connecting the LSI414and the board main body401with the gold wire411becomes easy, and the circuit board400can be easily manufactured. The LSI414can be provided directly on the front surface of the board main body401as shown inFIG. 7F, for example. With such a structure, the synthetic resin material419covering the LSI414protrudes more greatly, but the processing for forming the recessed unit402in the board main body401becomes unnecessary and manufacturing can be simplified.

The protrusion unit403is disposed in the first sub-passage305when the circuit board400is insert molded in the housing302, and the measurement flow path surface430which is the front surface of the protrusion unit403is placed in the flow direction of the measurement target gas30. In the measurement flow path surface430of the protrusion unit403, the flow rate detection unit602is provided. The flow rate detection unit602performs heat transfer with the measurement target gas30, measures the state of the measurement target gas30, for example, the flow rate of measurement target gas30, and outputs an electric signal representing the flow rate flowing through the main passage124. In order for the flow rate detection unit602to measure the state of the measurement target gas30with high accuracy, it is desirable that the gas flowing in the vicinity of the measurement flow path surface430is a laminar flow and less disordered. Therefore, it is desirable that the front surface of the flow rate detection unit602and the surface of the measurement flow path surface430are flush with each other or the difference is equal to or smaller than a predetermined value.

As shown inFIG. 7G, a recessed unit403ais formed in a recessed manner on the front surface of the measurement flow path surface430, and the flow rate detection unit602is fitted therein. The recessed unit403acan also be formed by laser processing. The recessed unit403ahas a depth such that the front surface of the flow rate detection unit602is flush with the front surface of the measurement flow path surface430. The flow rate detection unit602and its wiring portion are covered with a synthetic resin material418to prevent electrolytic corrosion due to adhesion of salt water.

On the back surface of the board main body401, two pressure sensors421A and421B and one temperature and humidity sensor422are provided. The two pressure sensors421A and421B are arranged in a row separated into an upstream side and a downstream side. The temperature and humidity sensor422is arranged on the upstream side of the pressure sensor421B. These two pressure sensors421A and421B and one temperature and humidity sensor422are arranged in the sensor chamber Rs. In the example shown inFIG. 7C, the case of having two pressure sensors421A and421B and one temperature and humidity sensor422has been described, but only the pressure sensor421B and the temperature and humidity sensor422may be provided, or only the temperature and humidity sensor422may be provided.

In the circuit board400, the second sub-passage306is arranged on the back surface side of the board main body401. Therefore, the measurement target gas30passing through the second sub-passage306can cool the entire board main body401.

4.2 Structure of Temperature Detection Unit451

The temperature detection unit451is provided at the edge of the upstream side of the base unit402and at the corner of the protrusion unit403. The temperature detection unit451constitutes one of detection units for detecting the physical quantity of the measurement target gas30flowing through the main passage124, and is provided in the circuit board400. The circuit board400has a protrusion unit450protruding from the second sub-passage entrance306aof the second sub-passage306toward upstream of the measurement target gas30. The temperature detection unit451has a chip type temperature sensor453provided on the back surface of the circuit board400as a protrusion unit450. The temperature sensor453and its wiring portion are covered with a synthetic resin material and prevent electrolytic corrosion due to adhesion of salt water.

For example, as shown inFIG. 3B, in the central part of the measurement unit331provided with the second sub-passage entrance306a, the upstream side external wall336in the measurement unit331constituting the housing302is recessed toward the downstream side. From the dent-shaped upstream side external wall336, the protrusion unit450of the circuit board400protrudes toward the upstream side. The distal end of the protrusion unit450is arranged at a position more recessed than the surface of the most upstream side of the upstream side external wall336. The temperature detection unit451is provided in the protrusion unit450on the back surface of the circuit board400, and more specifically, provided in the protrusion unit450so as to face the second sub-passage306.

Since the second sub-passage entrance306ais formed on the downstream side of the temperature detection unit451, the measurement target gas30flowing from the second sub-passage entrance306ato the second sub-passage306comes into contact with the temperature detection unit451, and then flows to the second sub-passage entrance306a, and when the measurement target gas30comes into contact with the temperature detection unit451, the temperature is detected. The measurement target gas30in contact with the temperature detection unit451directly flows from the second sub-passage entrance306ato the second sub-passage306, and passes through the second sub-passage306, and then the measurement target gas30is discharged from the second sub-passage exit306bto the main passage123.

4.4 Fixing of Circuit Board400by Resin Molding Process and Effects Thereof

The hatched portion inFIG. 8Aindicates the fixing surface432and the fixing surface434for covering the circuit board400with the thermoplastic resin used in the resin molding process in order to fix the circuit board400to the housing302in the resin molding process. It is important that the relationship with the shape of the sub-passage and the flow rate detection unit602provided on the measurement flow path surface430and the measurement flow path surface430is maintained with high accuracy so as to be a predetermined relationship.

In the resin molding process, simultaneously with molding the sub-passage, the circuit board400is fixed to the housing302which molds the sub-passage. Therefore, the relationship between the sub-passage, the measurement flow path surface430, and the flow rate detection unit602can be maintained with extremely high accuracy. More specifically, since the circuit board400is fixed to the housing302in the resin molding process, it is possible to position and fix the circuit board400with high precision in a mold for molding the housing302having the sub-passage. By injecting high temperature thermoplastic resin into this mold, the sub-passage is molded with high precision and the circuit board400is fixed with high accuracy. Therefore, errors and variations occurring in each circuit board400can be suppressed to very small values. As a result, measurement accuracy of the circuit board400can be greatly improved.

In this embodiment, the outer circumference of the base unit402of the board main body401is covered with the fixing units372and373of the mold resin molding the housing302to make the fixing surfaces432and434. In the embodiment shown inFIG. 8A, the through hole404is provided in the board main body401of the circuit board400as a fixing means for further strengthening fixing, and by filling the through hole404with the mold resin, the fixing force of the board main body401is increased. The through hole404is provided at a location fixed by the partition wall335, and the partition wall335is connected to the front side and the back side via the through hole404.

The through hole404is preferably provided at a position corresponding to the partition wall335. Since the mold resin is a thermoplastic resin and the board main body401is made of glass epoxy, the chemical bonding action is low, and it is difficult to make adhesion tightly. The partition wall335has a long length with respect to the width, and has a structure that is easily spread in a direction away from the board main body401. Therefore, by providing the through hole404at a position corresponding to the partition wall335, the partition walls335sandwiching the board main body401can be physically coupled to each other via the through hole404. Therefore, the circuit board400can be more firmly fixed to the housing302, and a gap can be prevented from being formed between the circuit board400and the protrusion unit403. Therefore, the measurement target gas30can be prevented from entering the circuit chamber Rc through the gap between the partition wall335and the protrusion unit403, and the inside of the circuit chamber Rc can be completely sealed.

In the embodiment shown inFIG. 8B, in addition to the through hole404, round hole shaped through holes405are provided on each of the edge side of the upstream side and the edge side of the downstream side of the base unit402, and the through hole405is filled with a mold resin to further increase the fixing force of the board main body401. The edge side of the upstream side and the edge side of the downstream side of the base unit402are sandwiched from both sides in the thickness direction by the fixing units372and373, and the front side and the back side are further connected via the through hole405. Therefore, the circuit board400can be more firmly fixed to the housing302.

It is preferable to provide the through hole404in the partition wall335, but when the partition wall335is fixed to the board main body401with a predetermined fixing force, the through hole404can be omitted. In the embodiment shown inFIG. 8C, the through hole404is omitted, and the through holes405are provided on the edge side of the upstream side and the edge side of the downstream side of the base unit402. With such a configuration, the board main body401of the circuit board400can be firmly fixed to the housing302.

The through hole is not limited to the round hole shape, but it may be an elongated through hole406as shown inFIG. 8D, for example. In the present embodiment, the long hole shaped through hole406is provided so as to extend along the edge side of the upstream side and the edge side of the downstream side of the base unit402. The through hole406has a larger amount of resin connecting the front side and the back side of the measurement unit331as compared with the through hole406, so that a higher fixing force can be obtained.

In each of the above-mentioned embodiments, the case of the through holes404,405, and406has been described as an example of the fixing means, but the fixing means is not limited to the through hole. For example, in the embodiment shown inFIG. 8E, a large notch portion407extending over its length-direction is provided in the edge side of the upstream side and the edge side of the downstream side of the base unit402. In the embodiment shown inFIG. 8F, a notch portion408is provided between the base unit402and the protrusion unit403. In the embodiment shown inFIG. 8G, multiple notch portions409are provided so as to be aligned at a predetermined interval in the edge side of the upstream side and the edge side of the downstream side of the base unit402. In the embodiment shown inFIG. 8H, a pair of notch portions410cut out from both sides of the protrusion unit403toward the base unit402is provided. With these configurations, the board main body401of the circuit board400can also be firmly fixed to the housing302.

7. Circuit Configuration of Physical Quantity Detection Device300

7.1 Entire Circuit Configuration of Physical Quantity Detection Device300

FIG. 10Ais a circuit diagram of the physical quantity detection device300. The physical quantity detection device300has a flow rate detection circuit601and a temperature and humidity detection circuit701.

The flow rate detection circuit601includes a flow rate detection unit602having a heating element608and a processing unit604. The processing unit604controls the amount of heat generated by the heating element608of the flow rate detection unit602and outputs a signal indicating the flow rate to the microcomputer415via the terminal662based on the output of the flow rate detection unit602. In order to perform the processing, the processing unit604includes a Central Processing Unit (hereinafter referred to as CPU)612, an input circuit614, an output circuit616, a memory618for holding data representing the relationship between the correction value and measured value and flow rate, and a power supply circuit622for supplying a constant voltage to each required circuit. ADC power is supplied to the power supply circuit622from an external power supply such as a vehicle battery via a terminal664and a ground terminal (not shown).

The flow rate detection unit602is provided with a heating element608for heating the measurement target gas30. From the power supply circuit622, a voltage V1is supplied to the collector of a transistor606constituting the electric current supply circuit of the heating element608, and a control signal is applied from the CPU612via the output circuit616to the base of the transistor606, and an electric current is supplied to the heating element608from the transistor606via the terminal624based on the control signal. The electric current amount supplied to the heating element608is controlled by the control signal applied to the transistor606which constitutes the electric current supply circuit of the heating element608from the CPU612via the output circuit616. The processing unit604controls the heat generation amount of the heating element608so that the temperature of the measurement target gas30is increased by a predetermined temperature, for example, 100 degrees Celsius, from the initial temperature by being heated by the heating element608.

The flow rate detection unit602has a heat generation control bridge640for controlling the heat generation amount of the heating element608and a flow rate detection bridge650for measuring the flow rate. A constant voltage V3is supplied from the power supply circuit622to one end of the heat generation control bridge640via the terminal626. The other end of the heat generation control bridge640is connected to the ground terminal630. A constant voltage V2is supplied from the power supply circuit622to one end of the flow rate detection bridge650via the terminal625. The other end of the flow rate detection bridge650is connected to the ground terminal630.

The heat generation control bridge640has a resistance642which is a temperature measuring resistance member whose resistance value varies based on the temperature of the heated measurement target gas30. The resistance642, the resistance644, the resistance646, and the resistance648constitute the bridge circuit. The potential difference between the intersection A of the resistance642and the resistance646and the intersection B of the resistance644and the resistance648is input to the input circuit614through the terminal627and the terminal628. The CPU612controls the electric current supplied from the transistor606so that the potential difference between the intersection A and the intersection B becomes a predetermined value (i.e., zero volts in this embodiment), thereby setting the heat generation amount of the heating element608. The flow rate detection circuit601described inFIG. 10Aheats the measurement target gas30with the heating element608so that the temperature of the measurement target gas30is higher by a certain temperature (for example, always 100 degrees Celsius) with respect to the original temperature of the measurement target gas30. In order to perform this heating control with high accuracy, the resistance value of each resistance constituting the heat generation control bridge640is set so that the potential difference between the intersection A and the intersection B becomes zero volts when the temperature of the measurement target gas30heated by the heating element608rises by a certain temperature (for example, always 100 degrees Celsius) with respect to the initial temperature. Therefore, in the flow rate detection circuit601, the CPU612controls the supply electric current to the heating element608so that the potential difference between the intersection A and the intersection B becomes zero volts.

The flow rate detection bridge650is constituted by four resistance temperature detectors, i.e., a resistance652, a resistance654, a resistance656, and a resistance658. These four resistance temperature detectors are arranged along the flow of measurement target gas30. The resistance652and the resistance654are arranged on the upstream side in the flow path of the measurement target gas30with respect to the heating element608. The resistance656and the resistance658are arranged on the downstream side in the flow path of the measurement target gas30with respect to the heating element608. In order to improve the measurement accuracy, the resistance652and the resistance654are arranged so that the distances to the heating element608are substantially equal to each other. The resistance656and the resistance658are arranged such that distances to the heating element608are substantially equal to each other.

The potential difference between the intersection C of the resistance652and the resistance656and the intersection D of the resistance654and the resistance658is input to the input circuit614via the terminal631and the terminal632. In order to increase the measurement accuracy, each resistance of the flow rate detection bridge650is set so that the potential difference between the intersection C and the intersection D becomes zero when, for example, the flow of the measurement target gas30is zero. Therefore, in the state where the potential difference between the intersection C and the intersection D is, for example, zero volts, the CPU612outputs an electric signal, indicating that the flow rate of the main passage124is zero, from the terminal662based on the measurement result that the flow rate of the measurement target gas30is zero.

When the measurement target gas30flows in the direction of the arrow inFIG. 10A, the resistance652and the resistance654disposed on the upstream side are cooled by the measurement target gas30, and the resistance656and the resistance658located on the downstream side of the measurement target gas30are warmed by the measurement target gas30warmed by the heating element608, and the temperature of these resistance656and resistance658rises. Therefore, a potential difference occurs between the intersection C and the intersection D of the flow rate detection bridge650, and the potential difference is input to the input circuit614via the terminal631and the terminal632. Based on the potential difference between the intersection C and the intersection D of the flow rate detection bridge650, the CPU612searches for data representing the relationship between the potential difference stored in the memory618and the flow rate of the main passage124, and derives the flow rate of main passage124. An electric signal representing the flow rate of the main passage124obtained in this manner is output via the terminal662. Note that the terminal664and the terminal662shown inFIG. 10Ahave new reference numbers. However, the terminal664and the terminal662are included in the connection terminal412shown inFIG. 8Adescribed above.

The memory618stores data indicating the relationship between the potential difference between the intersection C and the intersection D and the flow rate of the main passage124, and stores correction data for reducing the measurement error such as variation, which is obtained based on the measured value of gas after production of the circuit board400.

The temperature and humidity detection circuit701includes an input circuit such as an amplifier and A/D which input a detection signal from the temperature sensor453and the temperature and humidity sensor422, an output circuit, a memory that holds data representing the relationship between the absolute humidity and the temperature and the correction values, and a power supply circuit622supplying a constant voltage to each required circuit. The signal output from the flow rate detection circuit601and the temperature and humidity detection circuit701is input to the microcomputer415. The microcomputer415has a flow rate calculation unit, a temperature calculation unit, and an absolute humidity calculation unit. The microcomputer415calculates the flow rate, temperature, absolute humidity which are the physical quantities of the measurement target gas30based on the signal, and outputs them to the ECU200.

The physical quantity detection device300and the ECU200are connected via a communication cable, and communication using a digital signal is performed according to a communication standard such as SENT, LIN, or CAN. In the present embodiment, a signal is input from the microcomputer415to the LIN driver420, and LIN communication is performed from the LIN driver420. Information output from the LIN driver of the physical quantity detection device300to the ECU200is superimposed and output by digital communication using a single or two-wire communication cable.

The absolute humidity calculation unit of the microcomputer415calculates the absolute humidity based on the information of the relative humidity output from the temperature and humidity sensor422and the temperature information and corrects the absolute humidity based on the error. The corrected absolute humidity calculated by the absolute humidity calculation unit is used for various engine operation control in the control unit62of the ECU18. Further, the ECU18can directly use information about total error for various engine operation controls.

In the above-described embodiment shown inFIGS. 10A and 10B, the physical quantity detection device300has the LIN driver420and the LIN communication is performed, but the present invention is not limited thereto. Alternatively, as shown inFIG. 10B, direct communication with microcomputer415may be performed without using LIN communication.

4.5 Component Arrangement on Circuit Board400

FIGS. 11A and 11Bshow a mode showing the present invention.FIG. 11Ais a front view of the circuit board.FIG. 11Bis a back surface diagram of the circuit board.

On the back surface of the circuit board400, a second sub-passage306is formed to extend between the second sub-passage entrance306aand the second sub-passage exit306bto take in the measurement target gas30flowing through the main passage124. A temperature sensor453is provided in the protrusion unit450. The temperature sensor453directly comes into contact with the measurement target gas30and detects the intake temperature. The temperature and humidity sensor422is mounted on the back surface of the circuit board400to directly come into contact with the measurement target gas30flowing in from the second sub-passage306and detects the intake temperature.

In the present embodiment, since the signal transmission from the physical quantity detection device300to the ECU is performed in LIN communication, the battery voltage is supplied to the physical quantity detection element300. The power supply regulator416steps down the battery voltage from 12 V to 5 V used for normal sensor drive. Therefore, the heat generation by the power supply regulator416becomes large, and the power supply regulator416has the maximum heat generation amount on the circuit board400. The heat is transferred along the air flow, and therefore, the power supply regulator416is arranged in the air flow downstream portion from the temperature and humidity sensor422and the temperature sensor453, so that the heat generated in the power supply regulator416is suppressed from being transmitted to the temperature and humidity sensor422and the temperature sensor453arranged in the air flow upstream portion. In order to further reduce the influence of the heat generated by the power supply regulator416on the temperature and humidity sensor422and the temperature sensor453, it is preferable that the distance from the power supply regulator is long. By placing the power supply regulator416in the air flow downstream portion, it is possible to increase the distance between the temperature sensor453arranged near the second sub-passage entrance306aand also to suppress the heat conduction.

In the embodiment ofFIGS. 11A and 11B, the heat generation amount decreases in the following order: the power supply regulator416, the LSI414, and the microcomputer415, and the power supply regulator416, the LSI414, and the microcomputer415are arranged in this order from the air flow downstream portion. Components generating large amount of heat are configured to be arranged farther from the temperature and humidity sensor422and the temperature sensor453, thereby reducing heat conduction. In addition, by placing another electronic component between the temperature and humidity sensor422or the temperature sensor453and the power supply regulator416which is the component having the maximum heat generation amount, the effect of suppressing the heat conduction to the temperature and humidity sensor422and the temperature sensor453is also obtained.

Further, the power supply regulator416is disposed on the side opposite to the second sub-passage306with the circuit board400interposed therebetween. More specifically, the second sub-passage306is formed on the back surface which is a surface of one side where the temperature and humidity sensor422of the circuit board400and the temperature sensor453(an element having the intake temperature detection function) are mounted. The entire or a part of the power supply regulator41which is the component having the maximum heat generation amount is arranged on the front surface which is a surface of the other side of the circuit board400and is at the position on the opposite side of the second sub-passage306with the circuit board400interposed therebetween. For this reason, the flow velocity is high within the hermetically sealed circuit chamber Rc, the heat generated by the power supply regulator416is transmitted to the back surface of the board main body401, and the effect of dissipating the heat with the measurement target gas30passing through the second sub-passage306is improved.

In the present embodiment, the circuit board400is molded integrally with the housing302. On the other hand, conventionally, the circuit board was fixed on the metal base with an adhesive. Therefore, the metal base functioned as a heat sink, enhancing the effect of dissipating the heat generated in the circuit board to the surroundings. In the present embodiment, the heat affecting the temperature and humidity sensor422and the temperature sensor453due to the heat generation of the power supply regulator416can be reduced by the above configuration. For this reason, the metal base can be eliminated, and both-surface-mounting of the circuit board and the integrally-molded configuration with the housing can be realized.

When installed in the intake system of the internal combustion engine, the inside of the intake pipe is heated to a high temperature by being subjected to the thermal influence emitted by the internal combustion engine. For this reason, in the state where a temperature difference is present between the temperature of the measurement target gas30and the temperature in the intake pipe, a heat distribution is generated inside the module, which tends to cause a deterioration in measurement accuracy. Particularly, when the temperature and humidity sensor422is heated to a high temperature, both the relative humidity output and the temperature output are likely to shift to a condition with low measurement accuracy, and it is desirable to arrange the temperature and humidity sensor422at a position where the thermal influence of the internal combustion engine can be minimized. In the sensor chamber Rs, the flow velocity is stronger at a position closer to the second sub-passage entrance306a, and therefore, the arrangement of the temperature sensor453according to the present embodiment also has the effect of suppressing the heat influence from the internal combustion engine.

Although the embodiments of the present invention have been described in details above, the present invention is not limited to the above-described embodiments, but various changes and modifications may be made without departing from the spirit of the present invention as set forth in the claims. For example, the mode of operation described above has been described in details in order to explain the present invention in an easy-to-understand manner and is not necessarily limited to having all the configurations described. It is possible to replace some of the configurations of one embodiment with the configurations of another embodiment, and it is also possible to add a configuration of an embodiment to a configuration of another embodiment. Further, it is possible to add, delete, or replace some of the configurations of each embodiment with other configurations.

REFERENCE SIGNS LIST