Flow measuring device

A detection element portion is provided on an inner surface side of a plate as a wall surface portion defining a measurement passage in a flow measuring device. An intake-air temperature detection portion detecting a temperature of a fluid being measured is provided on one main surface of a substrate forming the detection element portion. A ventilation hole allowing a main passage in which the fluid being measured flows and the measurement passage to communicate is provided so as to penetrate through the plate. By achieving a state in which the substrate forming the detection element portion is installed so that an end thereof protrudes into the ventilation hole and a back surface of the end portion of the detection element portion where the intake-air temperature detection portion is formed is exposed toward the main passage, a response speed is enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flow measuring device, and, for example, to a device used to measure an intake-air flow rate and an intake-air temperature of an internal combustion engine.

2. Description of the Related Art

A flow measuring device in the related art is configured to have a measurement passage to let in a part of intake air flowing through a main passage, so that a flow rate detection element measuring a flow rate is installed in the measurement passage and further an intake-air temperature detection element measuring an intake-air temperature is installed in the measurement passage or the main passage.

A semiconductor device having a flow rate detection portion formed of a thin film with a thickness of a micron order is used as the flow rate detection element and a thermistor is used as the intake-air temperature detection element.

A support member is normally provided for installation of the intake-air temperature detection element. However, heat transmitted from the support member has an influence on detection accuracy of the intake-air temperature. Also, when a support member with low heat conductivity is used, a cost reduction becomes difficult.

To overcome such an inconvenience, a structure as follows is proposed as a flow measuring device capable of enhancing measurement accuracy of an intake-air temperature and reducing costs at the same time, and further achieving high robustness and high reliability.

The flow measuring device in the related art reduces influences of heat transmitted from the support member to the detection element by installing the intake-air temperature detection element in a bent measurement passage and thereby separating a connector terminal and a support terminal (see, for example, Patent Document 1).

Also, the flow measuring device in the related art reduces costs by installing the flow rate detection element and the intake-air temperature detection element on a single substrate and integrating the both into one piece.

Further, in the case of a detection element having the flow rate detection element and the intake-air temperature detection element formed on a single substrate, a speed of response to an intake-air temperature is enhanced by forming the intake-air temperature detection element on a diaphragm and reducing heat capacities of the intake-air temperature detection element and the support member including a substrate portion on which the intake-air temperature detection element is installed (see, for example, Patent Document 2).

Further, in the flow measuring device in the related art, a hole connecting the measurement passage and the main passage is provided to a cover portion near downstream of the detection element installed at a position on a plane same as one wall surface that defines the measurement passage (see, for example, Patent Document 3).

In addition, the flow measuring device in the related art has a hole provided upstream of the flow rate detection element installed in the measurement passage so as to penetrate through the measurement passage and the main passage. Hence, adhesion of water to the flow rate detection element is prevented by discharging water penetrating into the measurement passage to the main passage side (see, for example, Patent Document 4).

As has been described above, the structure to enhance detection accuracy of the detection element that detects an intake-air temperature is proposed for the flow measuring device in the related art. According to the techniques in Patent Documents 1 through 4, however, a heat capacity in the measurement passage in which to install the intake-air temperature detection element is so large that a response of a temperature detected in the measurement passage lags behind a response of the temperature in the main passage. Hence, the related art has a problem that even when measurement accuracy of the intake-air temperature detection element itself is enhanced, desired detection accuracy of the intake-air temperature cannot be obtained.

SUMMARY OF THE INVENTION

The invention was devised to solve the problems discussed above and has an object to provide a highly-accurate flow measuring device with excellent robustness and reliability by improving a speed of response to an intake-air temperature.

A flow measuring device according to one aspect of the invention includes: a main body portion extended into a main passage in which a fluid being measured flows and provided with a circuit storing portion internally; a measurement passage forming portion formed on an extension side of the circuit storing portion in the main body portion and provided with a measurement passage in which to let a part of the fluid being measured flow; a detection element portion provided on an inner surface side of a wall surface portion defining the measurement passage of the measurement passage forming portion, and provided with an intake-air temperature detection portion detecting a temperature of the fluid being measured and a flow rate detection portion detecting a flow rate, both of which are formed on one main surface of a same substrate; and a ventilation hole penetrating through the wall surface portion of the measurement passage forming portion and allowing the main passage and the measurement passage to communicate. The detection element portion is installed so that an end thereof protrudes into the ventilation hole. A back surface of the end of the detection element portion where the intake-air temperature detection portion is formed is exposed toward the main passage.

According to the flow measuring device configured as above, by providing the ventilation hole penetrating through the measurement passage and the main passage, not only can let intake air on the main passage side flow to the intake-air temperature detection portion, but also a heat capacity in the measurement passage can be smaller. Further, by installing the detection element portion so that an end thereof protrudes into the ventilation hole, it becomes possible to achieve a state in which the back surface of the end of the detection element portion where the intake-air temperature detection portion is formed is exposed toward the main passage. Hence, a speed of response to an intake-air temperature can be improved by reducing thermal influences on the intake-air temperature detection portion from the wall surface portion. It thus becomes possible to obtain a highly-accurate flow measuring device with excellent robustness and reliability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A flow measuring device according to a first embodiment of the invention will be described usingFIG. 1throughFIG. 5.FIG. 1is a sectional side view perpendicular to a flow direction of a main passage2in a tube100in which a fluid being measured flows, and shows a state in which a flow measuring device1of the first embodiment is inserted into and attached to the main passage2so as to extend into the the main passage2.FIG. 2is a sectional side view along the flow direction of the main passage2and shows a major portion in a state in which the flow measuring device1is attached to the main passage2.FIG. 3is a circuit diagram schematically showing a configuration of a detection portion of the flow measuring device1.FIG. 4Ais a sectional side view of a major portion perpendicular to the flow direction of the main passage2and shows a detection element portion3ofFIG. 1and a periphery thereof.FIG. 4Bis a sectional side view of the major portion parallel to the flow direction of the main passage2and shows the detection element portion3and a periphery thereof.FIG. 5is a view used to describe an advantage of improving a response speed of an intake-air temperature detection portion6in the flow measuring device1of the first embodiment. For example, a main stream (flow direction) of the fluid being measured flows in a direction indicated by an arrow A ofFIG. 2.

As are shown inFIG. 1andFIG. 2, the flow measuring device1is fit to the tube100and used to measure a flow rate and a temperature of the fluid being measured in the tube100. The flow measuring device1is formed of a main body portion1anearer to a tube fixing portion, which is a flat plate portion inserted and extended in the tube100, and a measurement passage forming portion1b, which is a tip end side inserted into the tube100. The main body portion1ais extended into the main passage2in which the fluid being measured flows and provided with a circuit storing portion22internally. The measurement passage forming portion1bis formed on an extension side of the circuit storing portion22in the main body portion1aand provided with a measurement passage4in which to let a part of the fluid being measured flow. Further, a detection element portion3is provided on an inner surface side of a plate8, which is a wall surface portion defining the measurement passage4of the measurement passage forming portion1b. The detection element portion3has an intake-air temperature detection portion6detecting a temperature of the fluid being measured and a flow rate detection portion5detecting a flow rate, both of which are formed on one main surface of a same substrate15.

FIGS. 4A and 4Bare enlarged sectional side views of the major portion, that is, the detection element portion3and a periphery thereof. As are shown in these drawings, the flow measuring device1of the invention is characterized in that a ventilation hole34allowing the main passage2and the measurement passage4to communicate is provided so as to penetrate through the plate8, which is a wall surface portion of the measurement passage forming portion1b. It is configured in such a manner that an end (tip end side inserted into the tube100) of the detection element portion3is installed so as to protrude into the ventilation hole34, and that a back surface of the end of the detection element portion3where the intake-air temperature detection portion6is formed is exposed toward the main passage2.

Also, as is shown inFIG. 1andFIGS. 4A and 4B, a plane of the plate8, which is the wall surface portion defining the measurement passage4, is installed in the main passage2to be parallel to the flow direction of the main passage2and the ventilation hole34opens perpendicularly to the flow direction. Also, as are shown inFIG. 1andFIG. 2, the flow measuring device1is fixed to the tube100with the main body portion1aon an upper side and the measurement passage forming portion1bon a lower side.

Further, as is shown inFIG. 4B, an intake-air temperature detection resistor14forming the intake-air temperature detection portion6is installed on an extension of an opening of the ventilation hole34. The flow measuring device1is in a state in which a back surface (a measurement surface exposed to the measurement passage4is given as the main surface) of the substrate15on which to mount the intake-air temperature detection resistor14is exposed toward the main passage2via the ventilation hole34. For example, in order to prevent the intake-air temperature detection resistor14from being superimposed on the plate8via the substrate15, the substrate15is installed so that an entire region where the intake-air temperature detection resistor14is installed is superimposed on the ventilation hole34.

The ventilation hole34opened in the plate8is formed in a size large enough to surround the region where the intake-air temperature detection resistor14of the detection element portion3is installed and a peripheral space. Herein, the ventilation hole34is opened wider than the substrate15forming the detection element portion3in the flow direction.

The flow measuring device1of the invention will now be described more in detail. Referring toFIG. 1throughFIG. 4B, the main passage2is an internal channel of the tube100of a cylindrical shape in which the fluid being measured passes by. In the case of an internal combustion engine for automobile, the main passage2is normally a channel in an intake duct formed integrally with an intake air filtering device (not shown) and the fluid being measured is air. The main passage2is provided with an insertion hole to plug in the flow measuring device1.

The flow measuring device1has the measurement passage4provided in the main passage2to let a part of the fluid being measured flow therein, the detection element portion3including the flow rate detection portion5detecting a flow rate of the fluid being measured flowing through the measurement passage4and the intake-air temperature detection portion6measuring a temperature of the fluid being measured, both of which are formed on the same substrate15, a circuit board7having a control circuit formed to process a flow rate detection signal and an intake-air temperature detection signal by driving the flow rate detection portion5and the intake-air temperature detection portion6, the plate8holding the detection element portion3and the circuit board7, a base9supporting the plate8, and a measurement passage defining cover10provided in close proximity to the base9and defining the measurement passage4in cooperation with the plate8.

As is shown in the sectional side view of the detection element portion3ofFIG. 4B, the detection element portion3includes the flow rate detection portion5and the intake-air temperature detection portion6. The flow rate detection portion5includes a heating resistor11used to detect a flow rate of the fluid being measured, heating temperature detection resistors12installed upstream and downstream of the heating resistor11in the flow direction of the fluid being measured, and a temperature compensation resistor13detecting a temperature of the fluid being measured and making a temperature compensation for a flow rate detection. The intake-air temperature detection portion6includes the intake-air temperature detection resistor14used to detect a temperature of the fluid being measured. The flow rate detection portion5and the intake-air temperature detection portion6are formed on the surface of the substrate15of a rectangular plate shape. Input and output terminals electrically connected to the heating resistor11, the heating temperature detection resistors12, the temperature compensation resistor13, and the intake-air temperature detection resistor14are formed on one side of the surface of the substrate15and connected to the circuit board7.

The heating resistor11, the heating temperature detection resistors12, the temperature compensation resistor13, the intake-air temperature detection resistor14, and the input and output terminals are formed by patterning a heat-sensitive resistance film made of platinum, nickel, iron, nickel alloy, or titanium and formed on the surface of the substrate15. The flow rate detection portion5, which is a region where the heating resistor11, the heating temperature detection resistors12, and the temperature compensation resistor13are formed, is of a diaphragm structure due to a cavity formed by eliminating the substrate15from the back surface side.

Further, an electrical insulating material, such as silicon and ceramic, is used as a material of the substrate15. As with the flow rate detection portion5, the intake-air temperature detection portion6, which is a region where the intake-air temperature detection resistor14is formed, may also be of a diaphragm structure due to a cavity formed by eliminating the substrate15from the back surface side.

As is shown in the circuit diagram of the flow measuring device1ofFIG. 3, the circuit board7forms an intake-air temperature detection circuit portion7a, a heating temperature control circuit portion7b, and a flow rate detection circuit7c(described in detail below) using a constant voltage power supply16, a transistor17, fixed resistors18, an operational amplifier19, and a constant current source20as components, and further includes a characteristic adjustment circuit21. The characteristic adjustment circuit21has an intake-air temperature signal adjustment portion21aand a flow rate signal adjustment portion21b.

The plate8is made of a plastic material shaped like a rectangular plate. The plate8cooperates with the measurement passage defining cover10laminated on the inner surface side, so that the circuit storing portion22(circuit board storing portion) and a detection element storing portion23are provided on the surface in a concave shape in close proximity to each other. The circuit board7is stored in the circuit storing portion22and fixed therein with an adhesive. The detection element portion3is stored in the detection element storing portion23with the input and output terminals positioned on the side of the circuit board7and fixed therein with an adhesive. It should be noted that the detection element storing portion23is a part of the measurement passage4and means a region where the detection element portion3is installed. In addition, the circuit board7and the detection element portion3are installed on a plane same as the surface (one main surface or inner surface) of the plate8.

The base9used to fix the flow measuring device1to the tube100has a joint portion with a flange portion36to ensure airtightness when the detection portion is inserted into the main passage2and a connector portion24provided to the other side of the junction portion and enabling signal transmissions between the circuit board7and the outside. The base9has a connection portion to the circuit storing portion22, which is provided from the joint portion toward the tube100. The forgoing members are molded in one piece of resin, such as polybutylene terephthalate.

The circuit storing portion22in which to store the circuit board7is defined by being surrounded by the plate8elongated to the extension side and a cover35. The plate8is bonded and fixed to the base9. Herein, the flow measuring device1is in a state in which the circuit board7and the detection element portion3are attached to the plate8, and the side of the plate8, on which the input and output terminals of the circuit board7and the detection element portion3are present, is exposed in the circuit storing portion22. The back surface of the tip end of the plate8is exposed toward the main passage2.

The measurement passage defining cover10that defines the measurement passage4in cooperation with the plate8is molded from resin, for example, polybutylene terephthalate. One surface of the measurement passage defining cover10is fixed to a region on the inner side of the plate8extended from the base9with an adhesive. The measurement passage4is formed in a concave shape in one surface of the measurement passage defining cover10. When the measurement passage defining cover10and the plate8are laminated, the both corporate with each other and define the measurement passage4having a rectangular passage cross section. The measurement passage defining cover10may be formed integrally with the base9from resin.

As is shown inFIG. 2, the measurement passage4includes an inlet25, a first passage portion26, a first bent portion27, a second passage portion28, a second bent portion29, a third passage portion30in which to install the detection element portion3, a third bent portion31, a fourth passage portion32, and an outlet33, and is formed in a bent shape. The inlet25opens toward an upper stream in the main stream flow direction A in close proximity to an end of the flow measuring device1on the opposite side to the connector portion24to let the fluid being measured flow into the measurement passage4. The outlet33opens in an end face of the flow measuring device1on the opposite side to the connector portion24to let the fluid being measured flow out from the measurement passage4to the main passage2. In other words, the end face of the flow measuring device1on the opposite side to the connector portion24is a surface substantially parallel to the main stream flow direction A.

A flow in the measurement passage4will now be described more in detail. The first passage portion26is extended from the outlet25in the main stream flow direction A so as to reach the first bent portion27. The second passage portion28is extended from the first bent portion27toward the circuit board7in a direction substantially orthogonal to the main stream flow direction A so as to reach the second bent portion29. The third passage portion30is provided in close proximity to the circuit storing portion22and extended from the second bent portion29in the main stream flow direction A so as to reach the third bent portion31. The fourth passage portion32is extended from the third bent portion31and away from the circuit board7in a direction substantially orthogonal to the main stream flow direction A so as to reach the outlet33. The first bent portion27, the second bent portion29, and the third bent portion31are formed to bend the flow direction of the fluid being measured by substantially 90°.

The ventilation hole34is provided so as to penetrate through the plate8at a position in the end of the substrate15nearer to the detection element portion3and the circuit board7so as to allow the third passage portion30and the main passage2to communicate. The regions of the detection element portion3where the heating resistor11, the heating temperature detection resistors12, and the temperature compensation resistor13of the flow rate detection portion5are formed, and where the intake-air temperature detection resistor14of the intake-air temperature detection portion6is formed are exposed in the third passage portion30of the measurement passage4.

As has been described, the ventilation hole34is formed at a position at which is installed the intake-air temperature detection resistor14, which is a part of the intake-air temperature detection portion6of the detection element portion3. Hence, when the ventilation hole34is looked inside from the side of the main passage2, the back surface of the detection element portion3on which is mounted the intake-air temperature detection resistor14is visible. The intake-air temperature detection resistor14is positioned on an extension of the opening of the ventilation hole34and protrudes into the ventilation hole34from the plate8. The intake-air temperature detection resistor14is therefore insusceptible to heat from the other portions. Hence, a response time required to detect a fluid temperature can be shorter than in a case where the ventilation hole34is absent.

Also, as is shown inFIG. 2, a plurality of insert conductors are provided to the base9by insert molding in such a manner that one end of each is exposed in the circuit storing portion22and the other end is exposed in the connector portion24. The input and output terminals of the detection element portion3and electrode terminals of the circuit board7are wire-bonded using wires, and the electrode terminals of the circuit board7and one ends of the insert conductors are wire-bonded using wires. Wire-bonding is described as an example of an electrical connection method. However, electrical connection methods, such as welding and soldering, may be used instead. Further, a resin cover is bonded by an adhesive applied to a groove along an outer periphery of the circuit storing portion22and thereby closes the circuit storing portion22. Bonding using an adhesive is described as an example of a closing method. However, other methods, such as fusing, may be used instead. Although it is not shown in the drawings, the circuit storing portion22is filled with encapsulation gel.

The flow measuring device1as above is formed of the main body portion1ain which a base portion of the extension portion extended from the base9is formed of the plate8and the cover35laminated thereto, and the measurement passage forming portion1bformed of the plate8used commonly and the measurement passage defining cover10laminated thereto. The base portion of the extension portion is shaped like a rectangular prism and the main body portion1a(also the measurement passage forming portion1b) has a rectangular cross section orthogonal to the extension direction. The main body portion1aand the measurement passage forming portion1bare enclosed within a projection plane of the joint portion in the extension direction.

As has been described, the main body portion1aand the measurement passage forming portion1bhave rectangular cross sections orthogonal to the extension direction, and one wall surface as a long side of the rectangular outer periphery corresponds to the back surface of the plate8and the other wall surface corresponds to the outer surfaces of the cover35and the measurement passage defining cover10. Further, the inlet25of the measurement passage4is provided to a short side of the rectangular outer periphery of the cross section of the measurement passage forming portion1borthogonal to the extension direction in the end face in the upper stream of the passage in close proximity to the tip end of the plate8in the upper stream of the passage. The outlet33of the measurement passage4is provided to the end face located downstream of the same tip end portion in the passage.

As is shown inFIG. 1, the flow measuring device1is attached as the main body portion1ais inserted into the insertion hole so as to extend into the main passage2and the flange portion36of the joint portion is fastened and fixed to the flange portion36of the main passage2with screws37. The flow measuring device1is plugged in the main passage2in such a manner that the wall surface formed of the long side of the rectangular outer periphery of the cross section orthogonal to the extension direction of the main body portion1a(also the measurement passage forming portion1b) is substantially parallel to the main stream flow direction A of the fluid being measured flowing through the main passage2while the other wall surface formed of the short side of the rectangular outer periphery of the cross section of the main body portion1ais oriented toward the upper stream so as to be orthogonal to the flow direction A. An O-ring is interposed between the joint portion and the insertion hole to ensure airtightness. Herein, the outlet25of the measurement passage4opens in close proximity to the end of the surface orthogonal to the main stream flow direction A on the extension side into the main passage2. The outlet33opens in the end face on the extension side into the main passage2, which is a plane parallel to the main stream flow direction A.

The fluid being measured flowing through the main passage2flows into the measurement passage4from the inlet25. The fluid being measured flows through the first passage portion26along the main stream flow direction A until the flow direction is bent by substantially 90° at the first bent portion27and flows through the second passage portion28in a direction orthogonal to the main stream flow direction A. Subsequently, the flow direction of the fluid being measured is bent by substantially 90° at the second bent portion29and the fluid being measured flows through the third passage portion30, in which the measurement position is set, in the main stream flow direction A and flows along the surface of the detection element portion3. Thereafter, the flow direction of the fluid being measured is bent by substantially 90° at the third bent portion31and the fluid being measured is discharged into the main passage2from the outlet33.

As is shown inFIG. 2, power from the outside is supplied to the control circuit formed in the circuit board7from the connector portion24via the insert conductors. As is shown inFIG. 3, the control circuit is formed of the intake-air temperature detection circuit portion7a, the heating temperature control circuit portion7b, and the flow rate detection circuit portion7c.

As is shown inFIG. 3, the intake-air temperature detection circuit portion7asupplies a current to the intake-air temperature detection resistor14of the detection element portion3from the constant current source20and supplies a voltage across the intake-air temperature detection resistor14to the intake-air temperature signal adjustment portion21a. The voltage is adjusted to have a predetermined characteristic in the intake-air temperature signal adjustment portion21aand outputted from the output terminal as an intake-air temperature signal.

Also, the heating temperature control circuit portion7bforms a bridge circuit from the heating resistor11and the temperature compensation resistor13of the detection element portion3, and the fixed resistors18of the circuit board7. The heating temperature control circuit portion7bperforms feedback control to maintain the heating temperature constant by detecting a differential signal of the bridge circuit using the operational amplifier19and supplying a current via the transistor17.

The flow rate detection circuit portion7cforms abridge circuit from the constant voltage power supply16, the heating temperature detection resistors12installed upstream and downstream of the heating resistor11in the flow direction of the fluid being measured, resistance values of which vary with thermal influences of the heating resistor11, and the fixed resistors18. A differential signal corresponding to the flow rate is detected by the bridge circuit and the detected differential signal is supplied to the flow rate signal adjustment portion21b. The differential signal is adjusted to have a predetermined characteristic in the flow rate signal adjustment portion21band outputted from the output terminal as a flow rate signal.

FIG. 5is a view showing response characteristics of the intake-air temperature detection portion6in the flow measuring device1according to the first embodiment of the invention, and shows a change of a detection temperature of the intake-air temperature detection portion6in response to a temperature change of the fluid being measured.

InFIG. 5, a solid line (A) indicates an internal temperature of the main passage2when a temperature of the fluid being measured changes and shows a target waveform to be measured in the measurement passage4. Data indicated by a rough broken line (B) ofFIG. 5is the data obtained by the flow measuring device1provided with the ventilation hole34of the invention. A fine broken line (C) ofFIG. 5indicates comparative data when the ventilation hole34is absent. The data reveals that a time until an equilibrium is established is longer than in the cases of the lines (A) and (B) and a temperature when the equilibrium is established is the lowest. In other words, the flow measuring device1of the invention provided with the ventilation hole34can obtain data close to an actual temperature change of the fluid being measured.

As is indicated by the fine broken line (C) ofFIG. 5, in the fluid measuring device without the ventilation hole34, an internal temperature of the measurement passage4rises gradually in comparison with an internal temperature of the main passage2. This is because a heat capacity in the measurement passage4formed by molding is so large that a response lags behind a temperature change of the fluid being measured in the main passage2and an exact intake-air temperature cannot be detected.

Even when a heat capacity of the intake-air temperature detection portion6is reduced, for example, by adopting a diaphragm structure to the substrate portion of the intake-air temperature detection portion6and a response speed of the intake-air temperature detection portion6to a temperature change is enhanced, an exact intake-air temperature cannot be detected, either, because there is an error in the internal temperature of the measurement passage4.

According to the first embodiment, however, the ventilation hole34allowing the main passage2and the third passage portion30of the measurement passage4to communicate is provided so as to penetrate through the plate8and a part of the intake-air temperature detection portion6of the detection element portion3is installed in the ventilation hole34. When this structure is adopted, the fluid being measured on the side of the main passage2is allowed to pass by the intake-air temperature detection portion6of the detection element portion3from the ventilation hole34. When configured in this manner, as is indicated by the line (B) ofFIG. 5, a measurement error of a temperature of the intake-air temperature detection portion6from a true value, that is, the internal temperature of the main passage2indicated by the line (A), can be reduced. Hence, a speed of response to a temperature change of the fluid being measured can be improved.

With reference toFIG. 2andFIG. 4B, the above has described, by way of example, that an opening dimension of the ventilation hole34is set to a size large enough to surround the region of the detection element portion3where the intake-air temperature detection resistor14is installed and a peripheral space and that the opening is formed in a rectangular shape. It goes without saying, however, that the ventilation hole34can be of any shape other than a rectangle.

Second Embodiment

The first embodiment above has described a case where the ventilation hole34opens in a direction perpendicular to the plane of the plate8while maintaining a constant opening dimension in a thickness direction of the plate8. A second embodiment will describe a modification of the ventilation hole34usingFIGS. 6A and 6B.FIG. 6Ais an enlarged view of a major portion when a ventilation hole34of the second embodiment and a periphery thereof are viewed from the side of the main passage2.FIG. 6Bis a cross section taken along a line B-B ofFIG. 6A.

As is shown inFIGS. 6A and 6B, the ventilation hole34is configured in such a manner that the inner sides of the ventilation hole34form inclined surfaces34aso that an opening area becomes larger on the side of the main passage2, that is, the back surface side of the plate8, than the side of the measurement passage4(one main surface side) of the plate8where the detection element portion3is formed. In a case shown inFIGS. 6A and 6B, of the inner surfaces of the ventilation hole34having a rectangular cross section, a top surface and a bottom surface form the inclined surface34a. Inclined directions are vertically symmetrical. The rest of the configuration is the same as that of the first embodiment above.

The second embodiment has a structure that allows the fluid being measured to readily flow from the main passage2to the measurement passage4by forming a passage sectional area of the ventilation hole34in such a manner so as to increase from the measurement passage4toward the main passage2. Hence, a flow rate of the fluid being measured in the ventilation hole34can be increased in comparison with a case where the inclined surfaces34aare not provided. Further, in order to provide the inclined surface34a, a part of the plate8on the periphery of the intake-air temperature detection portion6is scraped off. Hence, a heat capacity on the periphery of the detection portion can be smaller than in the case of the ventilation hole34having a uniform opening dimension as in the first embodiment above. In this manner, the intake-air temperature detection portion6can enhance a speed of response to a temperature change of the fluid being measured. It goes without saying, however, that a modification, such as forming only one of a plurality of inner surfaces forming the ventilation hole34as the inclined surface34a, can be made.

Third Embodiment

The first and second embodiments above have described the technique of exposing the back surface of the intake-air temperature detection resistor14toward the main passage2by providing the ventilation hole34penetrating through the plate8(wall surface portion) serving as the mount surface, so that the intake-air temperature detection resistor14of the detection element portion3is insusceptible to heat from the other components.

The flow measuring device1, however, has another problem to be solved other than an improvement of a response speed. The problem is penetration of rain water into the measurement passage4.

For example, assume that the flow measuring device1is mounted to an automobile. When the automobile runs in the rain behind a vehicle running by splashing up a large volume of water drops from the wheels or runs in heavy rain, fine water drops readily penetrate into the flow measuring device1measuring intake air of the automobile by way of an intake air filtering device. When the water drops adhere onto the flow rate detection portion5and the intake-air temperature detection portion6, an output becomes abnormal until the water drops evaporate.

The flow measuring device described in the related art (Patent Document 3 and Patent Document 4) is configured in such a manner that water penetrating into the measurement passage is discharged to the main passage through a hole penetrating though the measurement passage and the main passage. However, no consideration is given to a configuration that prevents water adhering to the wall surface on the main passage side from penetrating into the measurement passage from this penetrating hole.

A third embodiment will describe a flow measuring device capable of preventing penetration of water into the measurement passage4from the side of the main passage2besides being capable of improving a response speed of the intake-air temperature detection portion6to an intake-air temperature.

The flow measuring device1of the third embodiment is shown inFIG. 7andFIG. 8.FIG. 7is an enlarged view of a major portion on the side of the main passage2, that is, the ventilation hole34and a periphery thereof.FIG. 8is a cross section taken on the line C-C ofFIG. 7. As are shown in these drawings, a convex portion38protruding toward the main passage2to prevent penetration of water into the ventilation hole34is provided to an opening end of the ventilation hole34on the side of the main passage2in the measurement passage forming portion1b. The convex portion38can be formed by upraising a part of the wall surface of the plate8in close proximity to the opening on the side of the main passage2. Alternatively, the convex portion38can be formed by another method, such as bonding and fixing a separate member.

According to the third embodiment, even when fine water drops penetrate into the measurement tube100by way of the intake air filtering device and adhere onto the wall surface of the flow measuring device1on the side of the main passage2, because the convex portion38is formed so as to rise up on the periphery of the opening of the ventilation hole34, the water drops cannot penetrate into the measurement passage4from the ventilation hole34. Hence, because water in the tube100does not adhere onto the intake-air temperature detection portion6of the detection element portion3, an error does not occur in an intake-air temperature detection. The ventilation hole34is not closed with water, either.

As has been described, when the flow measuring device1of the third embodiment is used, penetration of water into the ventilation hole34can be prevented by an action of the convex portion38provided to the wall surface in close proximity to the opening of the ventilation hole34on the side of the main passage2. Hence, not only can a flow rate and an intake-air temperature be detected with high accuracy, but also high robustness and high reliability can be ensured.

As are shown inFIG. 7andFIG. 8, by taking a flow of the fluid being measured into consideration, the convex portion38is formed in an U shape conforming to the ventilation hole34having a rectangular opening shape along one side on the upper stream side of the main passage2and two sides connected to this one side and extending along the passage. The convex portion38is not formed along one side on the lower stream side of the passage. It goes without saying, however, that a modification can be made in this regard and an opening shape of the ventilation hole34can be changed, too.

Fourth Embodiment

A flow measuring device1according to a fourth embodiment of the invention will now be described. The convex portion38preventing penetration of rain water described in the third embodiment above is of a protruding shape protruding from the back surface of the plate8while maintaining a uniform dimension. The fourth embodiment will describe a modification of the convex portion38.FIG. 9is an enlarged view of a major portion on the side of the main passage2, that is, a ventilation hole34and a periphery thereof in the flow measuring device1of the fourth embodiment.FIG. 10is a cross section taken along the line D-D ofFIG. 9.

The convex portion38located upstream of the ventilation hole34in the main passage2has an inclined portion38a. The inclined portion38ais of a shape with an inclined surface so that an amount of protrusion smoothly increases toward downstream of the ventilation hole34. The rest of the configuration is the same as that of the third embodiment above.

In addition to the advantages of the third embodiment described above, the flow measuring device1of the fourth embodiment can suppress a disturbance of the flow of the fluid being measured occurring upstream of the convex portion38owing to the inclined portion38aprovided to the convex portion38formed upstream of the ventilation hole34penetrating through the measurement passage4and the main passage2in the wall surface in close proximity to the opening on the side of the main passage2. Further, a disturbance of the flow of the fluid being measured flowing from the main passage2into the measurement passage4via the ventilation hole34can be suppressed. Hence, a flow rate can be detected with high accuracy.

Fifth Embodiment

A flow measuring device1according to a fifth embodiment of the invention will be now be described usingFIG. 11andFIG. 12. The fourth embodiment above has described a case where the convex portion38preventing penetration of rain water includes the inclined portion38awith a varying protrusion height. The third and fourth embodiments above have described a case where the convex portion38with a uniform width is provided on the periphery (three sides except for one downstream side) of the ventilation hole34on the side of the main passage2and an outer peripheral shape of the convex portion38is one size larger than the opening shape of the ventilation hole34. The fifth embodiment will describe a case where an outer peripheral shape of the convex portion38provided on the periphery of the ventilation hole34is inclined on an upper stream side of the passage.

FIG. 11is an enlarged view of a major portion on the side of the main passage2, that is, a ventilation hole34and a periphery thereof in the flow measuring device1of the fourth embodiment.FIG. 12is a cross section taken along the line E-E ofFIG. 11. As are shown inFIG. 11andFIG. 12, the flow measuring device1of the fifth embodiment is characterized in that when the measurement passage forming portion1bis installed downward so as to extend into the tube100from the main body portion1a, an outer peripheral shape of the convex portion38located upstream of the ventilation hole34in the main passage2is of a shape having an inclined portion38bthat inclines downward from upstream to downstream in the main passage2. The rest of the configuration is the same as that of the first embodiment above.

In the fifth embodiment, by providing the convex portion38with the inclined portion38bwhose outer peripheral shape on the upper stream side in the passage is inclined, when water splashed to the ventilation hole34from upstream in the main passage2adheres onto the convex portion38, the water is guided to the outside of the ventilation hole34along the inclined portion38binclined from upstream to downstream. Hence, penetration of water into the ventilation hole34can be prevented. Further, not only can a disturbance of a flow of the fluid being measured occurring at the inclined portion38blocated upstream of the ventilation hole34be suppressed, but also a disturbance of a flow of the fluid being measured flowing from the ventilation hole34into the measurement passage4can be suppressed. Hence, a flow rate can be detected with high accuracy.

Sixth Embodiment

The third through fifth embodiments above have described a case where the convex portion38is provided on the periphery of the opening of the ventilation hole34on the side of the main passage2. A different structure also capable of suppressing penetration of rain water into the measurement passage4will be described usingFIGS. 13A and 13Bas a sixth embodiment.FIG. 13Ais an enlarged view of a major portion when a ventilation hole34of the sixth embodiment and a periphery thereof are viewed from the side of the main passage2.FIG. 13Bis a cross section taken along the line F-F ofFIG. 13A. In the flow measuring device1of the sixth embodiment, the measuring passage forming portion1bincludes a concave portion39recessed from the surface of the plate8(wall surface portion) on the periphery of an opening end of the ventilation hole34on the side of the main passage2. The rest of the configuration is the same as the configuration of the first embodiment above.

According to the flow measuring device1of the sixth embodiment, by providing the concave portion39in the wall surface in close proximity to the opening of the ventilation hole34on the side of the main passage2, a state in which water drops are collected in the concave portion39and allowed to flow downstream along the flow of the fluid can be achieved. Hence, penetration of water into the ventilation hole34can be prevented. Because a protruding portion like the convex portion38is not formed on the back surface of the plate8, neither a flow of the fluid being measured is disturbed nor a pressure loss is increased. Hence, a flow rate and an intake-air temperature can be detected with high accuracy and high robustness can be ensured.

It should be appreciated that the respective embodiments of the invention can be combined without any restriction and the respective embodiments can be modified or omitted appropriately within the scope and sprit of the invention.