JP2002174540A - Flow rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain initial characteristics even in prolonged use by preventing the accumulation of dirt in a clearance generated between a flow rate measuring element and a support. SOLUTION: It is so arranged that the position of the surface 14 of the support on the upstream side is higher than the position of the surface 16 of the flow rate measuring element and the position of the surface 15 of the support on the downstream side is lower than the position of the surface 16 of the flow rate measuring element with respect to the direction of a fluid to be measured flows. Thus, the fluid to be measured is kept from directly hitting the clearance 23 to prevent the accumulation of the dirt 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a flow rate of a fluid, and more particularly to a thermal type flow rate measuring apparatus for measuring a flow rate using a heating resistor. The present invention relates to a thermal air flow measuring device suitable for measurement.

[0002]

2. Description of the Related Art Conventionally, as a flow rate measuring device installed in an intake air passage of an internal combustion engine such as an automobile and measuring an intake air flow rate, a thermal type flow rate measuring apparatus has become mainstream because it can directly detect a mass flow rate. . In such a thermal type flow rate measuring device, a thermal type flow rate measuring device having a thin film sensor region is relatively easily manufactured on a semiconductor substrate such as silicon (Si) using a semiconductor fine processing technique, and is mass-produced. It is economical because it can be produced in a system, and has attracted attention because it can be driven with low power.

As a flow rate measuring device having such a thin film-shaped flow rate detecting region, for example, those described in JP-A-9-26343 and JP-A-2000-2573 are known. These flow rate measuring devices mainly include a flow rate measuring element, a support having a recess for installing the flow rate measuring element, a surface extending substantially parallel to the intake air flow, and a circuit section for driving the flow rate measuring element. And a casing on which these parts are mounted and attached to a pipeline through which intake air flows.

In the flow rate measuring element, an insulating layer is formed on a silicon substrate, a heating resistor is formed on the insulating layer, and a temperature measuring resistor is formed on both sides of the heating resistor, and is further protected on each of the resistors. A layer is formed, and the silicon substrate on the back surface of the heating resistor is removed to form a thin film portion. Here, the flow rate is detected by utilizing a change in the resistance value of the temperature measuring resistor when the intake air flows on the surface of the flow rate measuring element.

[0005]

Problems to be Solved by the Invention
In the flow measurement device according to the prior art described in Japanese Patent Application Laid-Open No. 2000-2573, the flow measurement element surface and the support surface are flush with each other or the flow measurement element surface is lower than the support surface. It is attached by an adhesive so as to be in the position. By making the surface of the flow measuring element and the surface of the support substantially the same, the turbulence of the air flowing on the surface of the flow measuring element is small, and the flow rate can be measured with high accuracy.

[0006] However, these prior arts are insufficient in the fouling resistance when used for a long time. The reason will be described below. As described above, the flow measurement element is installed in the depression provided in the support, but in mass production, the size of the depression of the support is always designed to be somewhat larger than the size of the flow measurement element. . As a result, a gap 23 is formed between the flow rate measuring element and the support recess as shown in FIG. Also, even if the surface of the flow rate measuring element is designed to coincide with the surface of the support, in mass production, the thickness variation of the flow rate measuring element, the processing variation of the support, the thickness variation of the adhesive, etc. As shown in FIG. 4, it is inevitable that the surface positions of the flow rate measuring element and the support do not match.

Here, when the surface of the flow measuring element is lower than the surface of the support as shown in FIG. 3, the downstream gap of the flow measuring element is higher than the surface of the support as shown in FIG. In such a case, a fouling substance accumulates in the gap on the upstream side of the flow rate measuring element.

[0008] In particular, in an example disclosed in Japanese Patent Application Laid-Open No. 2000-2573, the structure shown in FIG. 3 is adopted, and since the fouling substance is deposited on the surface of the flow rate measuring element, the flow rate characteristic changes easily.

Since the flow rate measuring element portion has a structure exposed to the inside of the intake pipe, a pollutant accumulates in the gap portion by using the structure for a longer time than the above structure. Because the manner of air flow on the flow measurement element surface changes due to this fouling substance accumulation,
Changes in the characteristics from the initial characteristics, fouling substances adhere to the surface of the flow rate measuring element, causing a change in the flow rate characteristics.Since the fouling substance contains water and oil, the flow rate measuring element and the drive circuit are connected through a gap. Problems such as easy corrosion of the connection portion occur.

As a prior art relating to a stain resistant substance, there is a technique described in Japanese Patent Application Laid-Open No. 57-208412. This technique suppresses the adhesion of fouling substances in a fluid by inclining a sensing element having a printed circuit board structure with respect to the flow direction of the fluid.
In the structure disclosed in Japanese Patent Application Laid-Open No. 9-263343 and Japanese Patent Application Laid-Open No. 2000-2573, there is no gap between the flow rate measuring element and the support as seen in the structures described in Japanese Patent Application Laid-Open Nos. 9-26343 and 2000-2573. No., JP-A-2000-2573
In the structure described in Japanese Patent Application Laid-Open Publication No. H10-27, the fluid directly hits the gap between the flow rate measuring element and the support body,
Rather, the structure is such that the fouling substance is easily deposited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide a highly reliable flow rate measuring device with little characteristic change even when used for a long time.

[0012]

According to the present invention, in order to solve the above-mentioned problems, the surface position of the support on the upstream side is higher than the surface position of the flow measurement element in the direction of air flow from the flow measurement element. It is characterized by having such a configuration.
With this configuration, there is no side surface against which the fluid flowing on the surface of the support collides in the flow direction of the fluid, so that no fouling substance accumulates in the gap formed between the flow rate measuring element and the support. Therefore, it is possible to provide a highly reliable flow rate measurement device with little change in characteristics even when used for a long time.

Further, by making the surface position of the downstream support lower than the surface position of the flow rate measuring element, even if the production is varied in mass production, (the surface height of the upstream surface of the support) is always maintained. (Flow measurement element surface height)>
Since the relationship (surface height on the downstream side of the support) is maintained, it is possible to reduce variation in flow rate characteristics. Further, since no fouling substance is deposited in any of the upper and lower gaps, it is possible to provide a highly reliable flow rate measuring device with less characteristic change.

[0014] Also, by inclining the support with respect to the direction of air flow, there is provided a flow rate measuring device in which pollutants are unlikely to adhere even when an air flow (backflow) flowing from the engine to the air cleaner is generated. can do.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 shows a cross-sectional view of the flow measuring device 1.

The flow measuring element 10 is bonded to a glass ceramic support 11 with an epoxy or silicone adhesive 12. A depression 13 is provided in a portion of the support 11 to which the flow rate measuring element 10 is adhered.
0 is adhered into the depression 13. FIG. 6 is a plan view of a support to which the flow rate measuring element 10 is adhered, and FIG. 1 is AA of FIG.
3 shows a cross section.

Here, the depression 13 corresponds to FIG.
As shown in the cross-sectional view, when the flow rate measuring element is mounted, (the height of the support upstream surface 14)> (the flow rate measuring element surface 16
Height)> (Height of surface 15 on the downstream side of the support). Although not shown here, the flow measuring element surface 16 and the support downstream surface 15 coincide with each other.
5 may be omitted. Hereinafter, each component in FIG. 5 will be described.

The flow measuring element 10 is manufactured by a semiconductor manufacturing technique. This is described below. A silicon dioxide layer is formed as an electrical insulating layer on a single crystal silicon substrate by a method such as thermal oxidation or CVD (Chemical Vapor Deposition), and a silicon nitride layer is formed by a method such as CVD. Next, a polycrystalline silicon layer is formed by a method such as CVD, and phosphorus (P) is doped as an impurity by thermal diffusion or ion implantation to obtain a desired resistance value. Thereafter, a heating resistor, an air temperature measuring resistor, a temperature measuring resistor, and the like are formed by patterning the polycrystalline silicon layer. Next, a silicon nitride layer and a silicon dioxide layer are formed as a protective layer by CVD.
And the like. After that, the protective layer is patterned to remove the protective layer at a portion where an electrode is to be formed. Next, an aluminum layer is formed and patterning is performed by etching. Finally, in order to form the cavity 26, a silicon nitride layer serving as a mask is formed on a surface of the single crystal silicon substrate on which the heating resistor 22 is not formed by a method such as CVD, and patterning is performed. Thereafter, a cavity is formed by anisotropic etching. By thus thermally insulating the heating resistor and the temperature measuring resistor by forming the cavity, it is possible to generate the resistor with power saving, and to measure the flow rate using heat transfer. Finally, the wafer is divided into chips by dicing. The divided flow measuring element 10 has a long side of about 5 mm and a short side of about 2.5 mm, for example.

Next, the support 1 on which the flow rate measuring element 10 is mounted
1 will be described. The support 11 of the present invention is formed by a glass ceramic laminated substrate 17. The manufacturing method will be described below. First, a desired number of glass ceramic substrates having the same flow rate measuring element surface 16 state are superimposed on a glass ceramic substrate having the same flow rate measuring element surface state 16 having a thickness of about 0.1 to 0.3 mm and pressurized. And stack them. At this time, the depression 1 for disposing the flow rate measuring element 10
3 is formed by punching a desired shape in a state of the flow rate measuring element surface 16 by a punching die or the like. Also,
A circuit for supplying power to the flow rate measuring element 10 and performing signal processing from the flow rate measuring element 10 is mounted on the support 11. On the front surface or the back surface of the laminated substrate, the support upstream surface 14 can be formed by printing or the like. The inner conductor 18 can be formed on the front and back surfaces and the inner layer of the laminated substrate 17 by printing or the like. The front and rear surfaces and the inner layer conductor 18 are connected by via holes 19. As described above, by configuring a circuit for controlling the flow rate measuring element 10 using the inner layer conductor 18 of the laminated substrate 17, the circuit can be downsized, and thus the flow rate measuring device 1 can be downsized. be able to. Flow measurement element 1
0 and the circuit are electrically connected by a connection line 20 such as a gold wire.

Here, the step 21 of the mounting portion of the actual flow rate measuring element 10 is formed by laminating the flow rate measuring element surface 16 on the outermost surface in the shape shown in FIG. Here, the thickness of the flow measurement element surface 16 after firing is 100 μm, the thickness of the adhesive 12 is about 20 μm, the thickness of the flow measurement element 10 is 330 μm, and the depth of the recess 13 for mounting the flow measurement element 10 from the upstream side of the support 11. 4
If the height is set to 00 μm, the step 21 between the upstream height position of the support 11 and the surface of the flow measurement element 10 is about 50 μm, and the step 21 between the surface of the flow measurement element 10 and the downstream position of the support 11 is 5 μm.
It is about 0 μm.

The height of the step 21 can be changed by selecting the thickness and the number of layers of the flow measuring element surface. By using a laminated substrate in this way,
A step can be formed with high accuracy, and a flow rate measuring device with little variation in flow rate characteristics can be provided even in mass production.

Since the air flow 2 flows as shown in FIG. 1 due to the step 21, no fouling substance is deposited in the gap between the flow rate measuring element 10 and the support 11, so that the characteristic changes with respect to the initial characteristic even when used for a long time. It is possible to provide a flow rate measurement device that does not use the flow. Here, (the height of the support upstream surface 14)> (the flow measurement element surface 16
In order to maintain the relationship of (height) ≧ (height of the surface 15 on the downstream side of the support), at least the thickness variation of the flow rate measuring element, the processing variation of the support,
It is necessary to have a step that is equal to or greater than the variation between the surface on the upstream side of the support and the surface of the flow rate measuring element caused by the variation in the thickness of the adhesive.
In the embodiment of the present invention, the thickness variation of the flow rate measuring element depends on the thickness variation of the silicon substrate. Further, the processing variation of the support depends on the variation of the depth of the depression formed in the laminated substrate. If the precision at the time of manufacturing is good, the sum of the above variations can be suppressed to about 10 to 20 μm, and in this case, a step of about 20 μm is sufficient.

On the other hand, if the step is too large, the turbulence of the fluid flowing on the surface of the flow rate measuring element 10 becomes large. Therefore, the maximum value is about 150 μm.

As described above, the method using the laminated substrate 17 as a means for forming the step 21 has been described. As another method, although not shown here, machining or the like is performed on the metal support 11. As shown in FIG. 8, it is also possible to form the step 21 by providing a heating resistor 22 on the upstream side of the support 11 or the like.

Further, even when the step 21 is not provided on the surface of the support 11, the effect of the present invention can be obtained by mounting the flow rate measuring element 10 at an inclination as shown in FIG.

On the other hand, if the step 21 is increased, the air flow 2 becomes less likely to hit the surface of the flow rate measuring element 10, and there is a concern that the sensitivity of the flow rate measuring device 1 is reduced. In addition, depending on the driving state of the vehicle, air pulsation may occur, and air may flow from the direction opposite to the flow shown in FIG. 1, in which case the fouling substance is likely to adhere. In particular, this pulsation tends to occur in an engine equipped with a means for returning a part of the exhaust gas to the intake pipe in accordance with the recent exhaust gas regulation, an engine in which the valve timing is changed according to the operating state, and the like. .

FIG. 10 shows an embodiment of a flow rate measuring device provided with means for solving this problem. By inclining as shown in FIG. 10, in the case of the forward flow 3, the air flow easily hits the flow rate measuring element 10, so that it is possible to prevent the measurement sensitivity from lowering. Further, in the case of the backflow 4, since the airflow 2 is hard to hit directly, even in an engine in which pulsation is likely to occur, a pollutant is hardly attached, and a highly reliable flow measurement device can be provided.

Here, when the support 11 on which the flow rate measuring element 10 is mounted is disposed in the sub-passage 41, if the inclination angle is too large, it becomes difficult for air to flow, and the flow rate measuring element surface 1
The flow rate at 6 decreases. Accordingly, as shown in FIG. 12, when the inclination is made, as shown in FIG. 12, when the length of the support 11 in the air flow direction is w, the inclination angle is x, and the widest part width of the auxiliary passage is L, L ≧ 2 × If the width of the sub passage 41 is such that w × sin (x) is satisfied, it is possible to prevent the measurement performance of the flow rate measuring device 1 from being deteriorated due to a decrease in flow velocity. Here, FIG. 12 shows a BB cross section of FIG.

When the support 11 is inclined, as shown in FIG. 11, the inclination angle is x, the step 21 between the position of the support upstream surface 14 of the support 11 and the flow measurement element surface 16 is y, and When the gap 23 between the support 11 and the flow rate measuring element 10 is z, it is effective to design the step 21 so that y ≧ z × sin (x) holds. As a result, the air flow does not directly hit the gap 23, so that the accumulation of the fouling substance 30 in the gap 23 can be prevented. For example, if the gap 23 is about 200 μm and the inclination angle is 10 degrees, the airflow 2 does not directly hit the gap 23 if there is a step 21 of about 35 μm or more.

Although not shown, the flow rate measuring element surface 1
By making the above formula hold for the step 21 between the support 6 and the downstream surface 15 of the support, the reliability can be further improved.

[0031]

According to the present invention, it is possible to provide a flow rate measuring device which has a small characteristic change even when used for a long time. In addition, it is possible to provide a flow rate measuring device having a small flow rate characteristic variation even when a variation occurs during manufacturing.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a flow measuring device according to the present invention.

FIG. 2 is a partial plan view showing a flow measurement device according to the related art.

FIG. 3 is a partial plan view showing a flow measurement device according to the related art.

FIG. 4 is a partial plan view showing a flow measurement device according to the related art.

FIG. 5 is a sectional view showing a flow measuring device according to the present invention.

FIG. 6 is a partial plan view showing a support on which the flow rate measuring element according to the present invention is mounted.

FIG. 7 is a bird's-eye view showing a support 11 of the flow measuring device according to the present invention.

FIG. 8 is a partial sectional view showing a flow rate measuring device according to the present invention.

FIG. 9 is a partial sectional view showing a flow rate measuring device according to the present invention.

FIG. 10 is a partial sectional view showing a flow rate measuring device according to the present invention.

FIG. 11 is a partial sectional view showing a flow rate measuring device according to the present invention.

FIG. 12 is a partial cross-sectional view showing a flow measuring device according to the present invention.

[Explanation of symbols]

1: Flow rate measuring device, 2: Air flow, 3: Forward flow, 4: Reverse flow,
10 flow rate measuring element, 11 support, 12 adhesive, 1
Reference numeral 3: recess, 14: upstream surface of the support, 15: downstream surface of the support, 16: surface of the flow rate measuring element, 17: laminated substrate, 1
8 inner conductor, 19 via hole, 20 connection line, 21
... steps, 22 ... heating resistors, 23 ... gaps, 30 ... fouling substances, 41 ... sub-passages, 42 ... covers, 43 ... housing cases, 44 ... ducts.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Izumi Watanabe 2477 Takaba, Hitachinaka-shi, Ibaraki Prefecture Inside Hitachi Car Engineering Co., Ltd. Within the automotive equipment group (72) Inventor Kei Ueyama 2520 Oaza Takaba, Hitachinaka-shi, Ibaraki F-term in the automotive equipment group, Hitachi, Ltd. (reference) 2F035 AA02 EA08

Claims (7)

[Claims] 1. A flow measuring device comprising at least a flow measuring element having a heating resistor and a support on which the flow measuring element is mounted, wherein the support is located upstream with respect to the flow direction of the fluid to be measured. The flow rate measuring device, wherein the flow rate measuring element is mounted on the support so that a surface position is higher than a surface position of the flow rate measuring element. 2. The flow measuring device according to claim 1, wherein
The flow rate measuring device, wherein the flow rate measuring element is mounted on the support so that the surface position of the support body on the downstream side is lower than the surface position of the flow rate measuring element. 3. The flow rate measuring device according to claim 1, wherein the surface of the upstream side support and the surface of the flow rate measuring element and / or the surface of the downstream side support and the thermal type air flow measuring element are arranged. Step between the surfaces is from 20 μm to 150 μm
A thermal type flow measuring device, characterized in that: 4. A flow rate measuring apparatus according to claim 1, wherein said support is attached to said housing case at an angle to a flow direction of a fluid to be measured. Measuring device. 5. The flow measuring device according to claim 4, wherein
When the width of the widest part of the sub passage in which the support is inserted is L, the angle of inclination of the support is x, and the width of the support in the air flow direction is w, L ≧ 2 × w × sin ( x) The flow rate measuring device characterized by the following relationship: 6. The flow measuring device according to claim 4, wherein a step y between the surface of the flow measuring element and the surface of the support, an inclination angle x between the fluid to be measured and the support, A flow rate measuring device, wherein a relationship of y ≧ z × sin (x) is established between a gap z generated between the flow rate measuring element and the support. 7. The flow rate measuring device according to claim 1, wherein the support on which the flow rate measuring element is mounted is formed by laminating two or more layers of members, and is provided upstream in the flow direction of the fluid to be measured. The support surface on the side is constituted by the outermost surface layer of the laminated member, and the support surface on the downstream side with respect to the flow direction of the fluid to be measured is constituted by the inner layer member surface. Measuring device.