JP2013015543A - Air flow rate measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air flow meter for stabilizing sensor output by suppressing turbulence of air flowing on a rear side of a sensor chip 12.SOLUTION: In a case 13 for holding a sensor chip 12, a recess 13a is formed on a surface along flow of air, the sensor chip 12 is housed in the recess 13a, and other end side of a sensor substrate 7 is fixed to a bottom surface of the recess 13a with an adhesive 14 to support the sensor chip 12 in a cantilever manner. In other words, one end side of the sensor substrate 7 in which a diaphragm 8 is formed is not stuck to the bottom surface of the recess 13a, so that a gap is disposed between the sensor substrate 7 and the recess 13a. The case 13 comprises a projection 13b that projects from the bottom surface of the recess 13a toward a cavity 7a of the sensor substrate 7 removed to form the diaphragm 8, and enters the cavity 7a, and a substantially uniform gap is formed between the recess 13a and the cavity 7a.

Description

  The present invention relates to an air flow rate measuring apparatus using a thin film type (chip type) flow rate measuring element for a sensor unit.

2. Description of the Related Art Conventionally, air flow meters (thermal flow meters) that measure the intake air amount of automobile engines have a chip-type flow rate detection element (hereinafter referred to as a sensor chip) in the sensor unit because of market requirements with high accuracy and high response. Is known (see Patent Document 1).
For example, as shown in FIGS. 10A and 10B, the sensor chip includes a diaphragm (thin film portion) 110 formed on a part of the sensor substrate 100, and a thin film resistor 120 is disposed on the surface of the diaphragm 110. It is comprised, is accommodated in the recessed part 140 formed in the surface of the resin case 130, and is being fixed with the adhesive agent 150. FIG.

  However, when the sensor substrate 100 is entirely bonded to the resin case 130, the linear expansion coefficients of the two differ greatly, so that stress is generated in the sensor substrate 100, and the sensor substrate 100 (particularly the portion where the diaphragm 110 is formed) due to the stress. ) Is distorted. As a result, it has been found that the resistance value of the thin film resistor 120 arranged on the surface of the diaphragm 110 changes and affects the flow rate detection accuracy. For this reason, as shown in FIG. 10A, the cantilever structure in which only one end in the longitudinal direction of the sensor substrate 100 (the end far from the portion where the diaphragm 110 is formed) is bonded to the resin case 130. Is common.

JP 2008-309623 A

However, if the sensor chip has a cantilever structure, a gap is formed between the back side of the sensor chip, that is, the recess 140 formed in the resin case 130 and the sensor substrate 100, so that when air flows through the air flow meter, Air also flows behind the chip.
However, the gap formed between the recess 140 of the resin case 130 and the sensor substrate 100 is not uniform as a whole, and the gap is large only in the portion where the diaphragm 110 is provided on the sensor substrate 100. That is, since the diaphragm 110 is formed by providing the cavity 111 on the back side of the sensor substrate 100 by etching or the like, the air flow passing through the back side of the sensor substrate 100 is disturbed by the influence of the cavity 111.

Specifically, as shown in FIG. 11A, since air also flows into the cavity 111, when the flow rate of air entering the back side of the sensor substrate 100 increases, FIGS. As shown in FIG. 4, a vortex is generated in the cavity 111, and the magnitude of the vortex changes according to the flow rate (naturally, the vortex increases as the flow rate increases). FIG. 11 shows a state in which the flow rate increases in the order of (a), (b), and (c), and the air turbulence increases.
As a result, the heat transfer to the thin film resistor 120 (see FIG. 10) disposed on the surface of the diaphragm 110 becomes unstable, and the characteristics change as the flow rate increases as shown in FIG. Therefore, there are problems that the output of the air flow meter is not stabilized (time fluctuation of the output becomes large), and the flow rate and voltage are not uniquely determined.
The present invention has been made based on the above circumstances, and an object of the present invention is to provide an air flow measuring device that can stabilize sensor output by suppressing turbulence of air flowing on the back side of the sensor chip. .

(Invention according to Claim 1)
In the present invention, a hollow portion is formed in a tapered shape from one back surface to the front side on one end side in the longitudinal direction of the sensor substrate, so that a diaphragm is provided on the surface of the sensor substrate corresponding to the hollow portion, and this A sensor chip having a heating resistor disposed on the surface of the diaphragm, and a recess formed to hold the sensor chip, and the other end of the sensor chip disposed in the recess is fixed with an adhesive A case where the sensor chip is cantilevered with a gap between the back surface and both side surfaces of the one end side of the sensor chip and the bottom surface and both side surfaces of the recess, and this case is disposed in the air passage, In the air flow measurement device that measures the air flow rate based on the heat exchange of the heating resistor, the case protrudes from the bottom surface of the recess to the hollow portion formed in the sensor substrate. Wherein the convex portion is provided Komu Ri.

In the air flow rate measuring device of the present invention, since the sensor chip is cantilevered by the case, at one end side of the sensor substrate that is not bonded to the bottom surface of the concave portion formed in the case, the concave portion of the case and the sensor substrate are Since a gap is generated between them, air flows not only on the front side of the sensor chip on which the heating resistor is disposed, but also on the back side of the sensor chip (a gap generated between the recess of the case and the sensor substrate). Therefore, in the present invention according to claim 1, a convex portion serving as a resistance is provided in the passage of air flowing on the back side of the sensor chip.
The convex portion protrudes from the bottom surface of the concave portion formed in the case with respect to the hollow portion provided in the sensor substrate and enters the hollow portion, so that the volume of the hollow portion is reduced and air turbulence is suppressed. The In addition, by reducing the gap between the hollow portion and the convex portion, it becomes difficult for air to flow into the back side of the sensor chip, and the flow rate of the air flowing through the back side of the sensor chip can be reduced to reduce the flow rate. As a result, the influence of the air flowing on the back side of the sensor chip can be made relatively small with respect to the air flowing on the front side of the sensor chip, so that the sensor output can be stabilized.

(A) It is sectional drawing of a case and a sensor chip along a longitudinal direction, (b) It is AA sectional drawing which shows the width direction of the same figure (a) (Example 1). It is sectional drawing which shows the state which attached the air flow meter to the intake duct. (A) The front view which looked at the air flow meter from the upstream side, (b) The side view of an air flow meter, (c) The back view which looked at the air flow meter from the downstream side. (A) Temperature distribution diagram illustrating the principle of flow rate measurement by the sensor unit, (b) a cross-sectional view of a sensor chip used in the sensor unit. It is a graph which shows the correlation with the temperature difference DTh of the detection temperature of an upstream temperature resistor, and the detection temperature of a downstream temperature resistor, and the flow volume and flow direction of air. It is sectional drawing which shows the modification of a convex-shaped part (Example 1). It is sectional drawing which shows the modification of a convex-shaped part (Example 1). It is sectional drawing which shows the modification of a convex-shaped part (Example 1). It is sectional drawing which shows the modification of a convex-shaped part (Example 1). (A) It is sectional drawing of a case and a sensor chip along a longitudinal direction, (b) It is BB sectional drawing which shows the width direction of the same figure (a) (prior art). It is sectional drawing which showed a mode that the state of the air which flows through the cavity part formed in the sensor board | substrate changed according to flow volume. It is a graph which shows the change of the output characteristic with respect to flow volume.

  The mode for carrying out the present invention will be described in detail with reference to the following examples.

Example 1
In the first embodiment, for example, an example in which the air flow measuring device of the present invention is applied to an air flow meter 1 that measures the amount of air taken into an engine of an automobile will be described.
As shown in FIG. 2, the air flow meter 1 includes a sensor housing 3 attached to the intake duct 2 and a sensor portion 4 incorporated in the sensor housing 3.
The intake duct 2 forms part of an intake passage connected to an intake port (not shown) of the engine. For example, an outlet pipe of an air cleaner arranged at the uppermost stream of the intake passage, or the outlet pipe An intake pipe or the like connected to the downstream side.
As shown in FIG. 3, the sensor housing 3 includes a flange portion 3 a fixed to the intake duct 2, a connector portion 3 b that electrically connects an ECU (not shown) that controls the operating state of the engine, an intake air A flow path forming body 3c and the like inserted into the duct 2 are formed.

In the flow path forming body 3c, a bypass flow path 5 for taking in the air flowing from the left side (air cleaner side) to the right side (engine side) in FIG. And a sub-bypass channel 6 for taking in part of the air flowing through the bypass channel 5 is formed.
The bypass flow path 5 is formed substantially linearly from the inlet 5 a that takes in air to the outlet 5 b that discharges air, and substantially parallel to the flow direction of the air flowing through the intake duct 2. The bypass channel 5 has a circular cross-sectional shape of the air channel, and the outlet side of the bypass channel 5 is formed in a tapered shape in which the channel cross-sectional area gradually decreases toward the outlet 5b.

The sub-bypass channel 6 is one of the Y-Y directions with respect to the bypass channel 5 when a predetermined direction (vertical direction in FIG. 2) orthogonal to the flow direction of the air flowing through the bypass channel 5 is called a Y-Y direction. An inlet 6 a of the sub bypass channel 6 that branches from the bypass channel 5 is formed on the side (the upper side in the drawing), and an annular outlet 6 b is formed around the outlet 5 b of the bypass channel 5. The sub-bypass channel 6 has a longer channel length than the bypass channel 5 and is formed with a bent portion whose direction changes greatly in the middle of the channel.
In addition, the inlet 6a of the sub-bypass channel 6 has a point A from the central axis of the bypass channel 5 when the upstream inlet end with respect to the bypass channel 5 is referred to as point A and the downstream inlet end is referred to as point B. It is formed so that the distance to point B is larger than the distance to (see FIG. 2). In other words, the inlet 6 a of the sub-bypass channel 6 is formed such that the opening surface including the points A and B is inclined toward the outlet side of the bypass channel 5.

As shown in FIG. 4B, the sensor unit 4 includes, for example, a thin film resistor (a heating resistor 9 and side temperature resistors 10, 11) on the surface of a diaphragm 8 provided on a silicon sensor substrate 7. A circuit unit that controls the heat generation temperature of the formed sensor chip 12 and the heat generation resistor 9, and outputs a sensor signal corresponding to the flow rate and flow direction of air based on the resistance values of the side temperature resistors 10 and 11. (Not shown), and the sensor chip 12 is held by the case 13 and arranged at the bent portion of the sub-bypass channel 6.
The heating resistor 9 is energized and controlled to a reference temperature that is higher than the temperature of the air flowing through the sub-bypass passage 6 by a certain temperature. The side temperature resistors 10 and 11 are one side temperature resistor (hereinafter referred to as the upstream temperature resistor 10) disposed close to the upstream side of the heating resistor 9 and the downstream side of the heating resistor 9. Is the other side temperature resistor (hereinafter, referred to as the downstream temperature resistor 11) disposed in the vicinity.

Here, the measurement principle of the air flow rate by the sensor unit 4 will be described.
When the heating resistor 9 is energized and controlled to the reference temperature, a temperature distribution due to heat generated by the heating resistor 9 occurs. Here, when there is no air flow in the sub-bypass channel 6, as shown by the broken line graph in FIG. 4 (a), the temperature is increased between the upstream side and the downstream side around the position of the heating resistor 9. Since the distribution is symmetrical, the temperature detected by the upstream temperature resistor 10 is equal to the temperature detected by the downstream temperature resistor 11.
On the other hand, for example, when a forward air flow is generated in the sub-bypass channel 6, as shown by a solid line graph in FIG. 4A, the temperature distribution is shifted to the downstream side (the right side in the drawing) of the heating resistor 9. As a result, the detected temperature of the downstream temperature resistor 11 becomes higher than the detected temperature of the upstream temperature resistor 10.

On the other hand, when an air flow in the reverse flow direction is generated in the sub-bypass channel 6, a temperature distribution that is shifted toward the upstream side (the left side in the drawing) of the heating resistor 9 is generated, so that the upstream side of the detected temperature of the downstream temperature resistor 11. The detected temperature of the temperature resistor 10 is higher.
As described above, when a temperature difference DTh occurs between the detected temperature of the upstream temperature resistor 10 and the detected temperature of the downstream temperature resistor 11, the upstream temperature resistor 10 and the temperature difference DTh are determined according to the temperature difference DTh. Since the resistance value of the downstream temperature resistor 11 changes, the potential difference caused by the change in the resistance value is amplified and output to the ECU as a sensor signal (for example, an analog voltage). The sensor signal can also be output by converting an analog voltage into a frequency value. FIG. 5 is a graph showing the correlation between the temperature difference DTh between the detected temperature of the upstream temperature resistor 10 and the detected temperature of the downstream temperature resistor 11, and the flow rate and flow direction of air.

Next, the sensor chip 12 and the case 13 according to the present invention will be described.
As shown in FIG. 1A, the sensor chip 12 has a diaphragm 8 formed on one end side (right side in the figure) of the sensor substrate 7 in the longitudinal direction (left and right direction in the figure).
As shown in FIG. 4B, the diaphragm 8 is an insulating film formed on the surface of the sensor substrate 7 by a sputtering method or a CVD method. For example, the diaphragm 8 is formed from the back surface of the sensor substrate 7 by anisotropic etching. The sensor substrate 7 is provided by removing a part of the sensor substrate 7 up to the boundary surface with the insulating film and forming a cavity 7 a in the sensor substrate 7.
The hollow portion 7a is an opening of the hollow portion 7a from the back surface of the sensor substrate 7 to the front side in both the longitudinal direction of the sensor substrate 7 shown in FIG. 1A and the width direction shown in FIG. It is formed in a tapered shape with a gradually decreasing width.

The case 13 is made of, for example, resin, and as shown in FIG. 1B, a concave portion 13a is formed on the surface along the air flow, and the sensor chip 12 is arranged in the concave portion 13a. The other end side of the sensor chip 12 is fixed to the bottom surface of the concave portion 13 a with an adhesive 14 to support the sensor chip 12 in a cantilever manner. That is, since one end side of the sensor substrate 7 on which the diaphragm 8 is formed is not bonded to the bottom surface of the recess 13a, there is a gap between the back surface and both side surfaces of the sensor substrate 7 and the bottom surface and both side surfaces of the recess 13a. have.
As shown in FIGS. 1A and 1B, the case 13 has a convex shape that protrudes from the bottom surface of the recess 13 a and enters the cavity 7 a with respect to the cavity 7 a that is removed to provide the diaphragm 8. A portion 13b is provided. For example, the convex portion 13b is provided in a tapered shape having substantially the same shape as the hollow portion 7a, and a substantially uniform gap is formed between the convex portion 13b and the hollow portion 7a. In addition, although the case 13 is not limited to resin, in this embodiment, it is preferable that the case 13 is made of resin.

(Operation and Effect of Example 1)
In the air flow meter 1 of this embodiment, the sensor chip 12 is cantilevered by the case 13. In this structure, a gap is formed between the recess 13a of the case 13 and the sensor substrate 7 on one end side of the sensor substrate 7 that is not bonded to the bottom surface of the recess 13a formed in the case 13. Not only on the front side of the sensor chip 12 on which the resistor 9, the upstream temperature resistor 10, and the downstream temperature resistor 11) are arranged, but also on the back side of the sensor chip 12 (between the recess 13a of the case 13 and the sensor substrate 7). Air also flows through the gap. On the other hand, the case 13 described in the first embodiment is provided with a convex portion 13b that serves as a resistance in the passage of air that flows on the back side of the sensor chip 12.

  As shown in FIG. 1B, the convex portion 13b protrudes from the bottom surface of the concave portion 13a formed in the case 13 with respect to the hollow portion 7a provided in the sensor substrate 7, and enters the hollow portion 7a. As a result, the volume of the cavity 7a is reduced and air turbulence is suppressed. Moreover, since the clearance gap between the cavity part 7a and the convex-shaped part 13b can be made small, it becomes difficult for air to flow into the back side of the sensor chip 12, and the flow velocity of the air which flows through the back side of the sensor chip 12 can be reduced. As a result, the influence of the air flowing on the back side of the sensor chip 12 can be made relatively small with respect to the air flowing on the front side of the sensor chip 12, so that the characteristics do not change and the sensor output is stabilized (time fluctuations are reduced). Small).

The convex portion 13b shown in FIG. 1 is provided in substantially the same shape (tapered shape) as the hollow portion 7a of the sensor substrate 7, but is not limited to this shape, and flows on the back side of the sensor chip 12. Any shape that resists the passage of air, in other words, any shape that makes it difficult for air to flow through the back side of the sensor chip 12 and that can reduce the flow velocity of the air may be used.
For example, the shapes shown in FIGS.
The convex portion 13b shown in FIG. 6 is an example provided at a position biased to the upstream side (the left side in the drawing) of the cavity portion 7a with respect to the flow direction of the air flowing on the back side of the sensor chip 12.

The convex portion 13b shown in FIG. 7 is an example that is provided at a substantially central portion of the hollow portion 7a and that protrudes from the bottom surface of the concave portion 13a into a prismatic shape or a cylindrical shape. And a substantially constant gap is formed between the cavity portion 7a and the ceiling surface (the upper surface in the drawing).
The convex portion 13b shown in FIG. 8 is an example in which the shape of the tip portion entering the inside of the hollow portion 7a is a convex curved surface having a predetermined curvature (a hemispherical shape in FIG. 8).
The convex portion 13b shown in FIG. 9 is an example having a flat surface at the tip that enters the inside of the hollow portion 7a, and R is provided at the peripheral edge of the flat surface.

1 Air flow meter (air flow measuring device)
2 Intake duct (air passage) 7 Sensor board 7a Sensor board cavity 8 Diaphragm 9 Heating resistor 12 Sensor chip 13 Case 13a Concave part formed in the case 13b Convex part provided in the case 14 Adhesive

Claims (1)

A surface of the sensor substrate (7) corresponding to the cavity (7a) is formed on one end side in the longitudinal direction of the sensor substrate (7) by forming a cavity (7a) in a tapered shape from the back surface to the front side. A sensor chip (12) provided with a diaphragm (8) and a heating resistor (9) disposed on the surface of the diaphragm (8);
The sensor chip (12) has a recess (13a) formed to hold the sensor chip (12), and the other end of the sensor chip (12) disposed in the recess (13a) is fixed with an adhesive (14). A case in which the sensor chip (12) is cantilevered with a gap between the back surface and both side surfaces on one end side of the sensor chip (12) and the bottom surface and both side surfaces of the recess (13a) ( 13)
In the air flow rate measuring device (1) which arranges the case (13) in the air passage (2) and measures the air flow rate based on the heat exchange of the heating resistor (9),
The case (13) protrudes from the bottom surface of the recess (13a) with respect to the cavity (7a) formed in the sensor substrate (7) and protrudes into the cavity (7a) (13b). ) Is provided.

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