JP2018013355A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor which is improved in measurement precision for a gas to be measured which has been introduced into a sensor element in a casing.SOLUTION: The present invention relates to a gas sensor comprising: a wiring board 50; a sensor element 40; and a casing 10 accommodating the wiring board, the casing having an introduction port 10g for introducing a measured gas G and a discharge port 10h for discharging the measured gas formed such that one-end sides 10g1, 10h1 of the introduction port and discharge port communicate with a storage space. The one end of the introduction port is located horizontally outside the sensor element and also arranged at a higher or lower position than the wiring board, and the one end of the discharge port is located horizontally outside the sensor element, and also arranged at a different position from the introduction port across the sensor element. The casing has a gas flow passage 10c connecting the introduction port and storage space to each other, the gas flow passage including an inner wall 10w2 which faces the one end of the introduction port, and changes a progress path of the gas introduced from the introduction port toward the storage space.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a gas sensor that detects the concentration of a specific gas.

Conventionally, as a metal oxide sensor, a configuration is known in which a sensor element is suspended and fixed in an opening of a wiring board by wire bonding or the like and accommodated in a case (housing) for each wiring board (Patent Document 1).
In this technology, the gas flow path in the case (case cap) arranged around the sensor element is made into a labyrinth, thereby generating an air flow, insulating the sensor element from the outside, and changing the ambient temperature. However, the operating temperature of the sensor element is kept constant. In addition, by fixing the sensor element in the air, it is possible to improve the gas detection accuracy and responsiveness by reducing the heat capacity of the sensor element and the surrounding thermal influence.

JP-A-9-84817 (FIG. 1)

By the way, depending on the flow of the gas to be measured introduced into the casing, the gas flow on the surface of the sensor element held on the wiring board becomes non-uniform, and depending on the position of the sensor element, the gas is hardly supplied and measurement is performed. There is a problem that accuracy decreases.
Therefore, an object of the present invention is to provide a gas sensor that improves the measurement accuracy of a gas to be measured in a gas sensor that introduces a gas to be measured into a sensor element in a casing.

In order to solve the above-mentioned problems, a gas sensor according to the present invention has a plate shape, a wiring board in which an opening penetrating in the thickness direction is formed, and a sensor in which a detection unit for detecting a specific gas is provided on a base substrate. A casing that is suspended in the opening by a plurality of current-carrying members and is electrically connected to the wiring board, and a casing that forms a housing space for housing the wiring board, An introduction port for introducing the gas to be measured into the accommodation space and an exhaust port for exhausting the gas to be measured from the accommodation space are formed in the casing side wall that surrounds the outer peripheral edge of the wiring substrate. A casing having one end of the outlet communicating with the accommodation space, and a gas sensor comprising:
In a state where the wiring board is installed in the casing so that the thickness direction of the wiring board is along the vertical direction, the one end of the introduction port is located on the outer side in the horizontal direction with respect to the sensor element, and the wiring While being arranged higher or lower than the substrate, the one end of the discharge port is located outside the sensor element in the horizontal direction, and is arranged at a position different from the introduction port across the sensor element. And
The casing is a gas flow path connecting the introduction port and the accommodation space, facing the one end of the introduction port, and converting a traveling path of the gas introduced from the introduction port toward the accommodation space. A gas flow path including an inner wall;

According to this gas sensor, one end of the inlet is formed in the gas flow path, and an inner wall facing the one end of the inlet is formed in the gas flow path. Thereby, the gas to be measured introduced from the introduction port first collides with the inner wall through the gas flow path, and the traveling path is converted toward the accommodation space.
At this time, one end of the introduction port is arranged higher or lower than the wiring board, that is, one end of the introduction port does not exist on the same plane as the wiring board (= sensor element). The gas to be measured collides with the surface of the sensor element and flows along the surface of the sensor element. And the to-be-measured gas which flowed along the surface of a sensor element is discharged | emitted from the discharge port arrange | positioned in the position different from the gas flow path facing one end of an inlet.
As a result, the flow of the gas to be measured along the surface of the sensor element becomes a laminar flow, and the difference in flow velocity due to the position on the surface of the sensor element is reduced, so that the gas to be measured is uniformly supplied to the entire sensor element. For this reason, the measurement accuracy of the gas to be measured can be improved.

In the gas sensor according to the present invention, in the state where the wiring board is installed in the casing so that the plate thickness direction of the wiring board is along the vertical direction, the one end of the discharge port extends in the vertical direction in the wiring board. It may be arranged on the same side as the one end of the inlet.
According to this gas sensor, the gas to be measured whose traveling path has been converted by the inner wall collides with the surface of the sensor element and then flows to the discharge port. Therefore, the gas to be measured is smoothly discharged from the discharge port, and the gas to be measured The measurement accuracy is further improved.

In the gas sensor of the present invention, the other end side of the introduction port and the other end side of the discharge port are each configured by an internal space of a cylindrical portion that protrudes outward from the casing side wall. The cylindrical portion may be connected to a flow pipe for flowing the gas to be measured.
According to this gas sensor, since the gas to be measured is introduced from the flow pipe using the inner hole (internal space) of the introduction pipe as a guide, the gas to be measured is easily introduced into the gas flow path. Similarly, the gas to be measured discharged from the discharge port is discharged using the inner hole (internal space) of the discharge pipe as a guide, so that the gas to be measured is easily discharged. For this reason, the flow of the gas to be measured along the surface of the sensor element becomes more uniform, and the measurement accuracy of the gas to be measured is further improved.

  According to this invention, in the gas sensor that introduces the gas to be measured to the sensor element in the casing, a gas sensor with improved measurement accuracy of the gas to be measured can be obtained.

It is a disassembled perspective view of the gas sensor which concerns on embodiment of this invention. It is a top view of the gas sensor which concerns on embodiment of this invention. It is a bottom view of the engagement gas sensor according to the embodiment of the present invention. It is a perspective view which shows the wiring board accommodated in the casing. It is a perspective view of a casing. It is sectional drawing which follows the AA line of FIG. It is another perspective view of a casing. It is a top view of a casing. It is a perspective view of the casing of a comparative example. It is a figure which shows the fluid analysis simulation of the gas flow on the sensor element surface in the gas sensor which concerns on embodiment of this invention. It is a figure which shows the fluid analysis simulation of the gas flow on the sensor element surface in the gas sensor using the casing of FIG.

Hereinafter, the present invention will be described in detail with reference to the drawings. 1 is an exploded perspective view of a gas sensor 1 according to an embodiment of the present invention, FIGS. 2 and 3 are a top view and a bottom view of the gas sensor 1, respectively, and FIG. 4 is a perspective view showing a wiring board 50 accommodated in a casing 10. 5 is a perspective view of the casing 10, FIG. 6 is a cross-sectional view taken along line AA of FIG. 5, FIG. 7 is another perspective view of the casing 10, and FIG.
In FIG. 1, a gas sensor 1 is accommodated in a lower case 10 having a substantially rectangular box shape with an upper surface (a surface facing upward in FIG. 1) opened, a lid portion 20 that closes the opening of the lower case 10, and the lower case 10. Ceramic wiring board (hereinafter simply referred to as “wiring board”) 50, rectangular frame-shaped sealing materials (gaskets) 31, 32, sensor element 40 disposed in the opening 50 h of wiring board 50, and sensor element Current-carrying members 61, 63 for hanging and fixing 40 in the opening 50h. Although there are four energization members 61, in FIG. 1, one of them is not shown because it is disposed under the sealing material 31. In addition, there are two energizing members 63.
The lower case 10 and the lid 20 correspond to a “casing” in the claims.

The lower case 10 includes an accommodation space 10r, a rectangular notch 10n extending downward from the upper end, and pipe-like introduction pipes 10a and discharge pipes 10b that serve as connection ports for the pipes. The introduction pipe 10a and the discharge pipe 10b protrude to the right from one side surface (the right side surface in FIG. 1) of the lower case 10, and the inner holes (the introduction port 10g and the discharge port 10h in FIG. 4) have an accommodation space 10r. Communicating with
The wiring board 50 includes a rectangular frame-shaped distal end portion 50a and a base end portion 50e that is narrower than the distal end portion 50a from one side of the distal end portion 50a and extends outward (left side in FIG. 1). .
The sealing materials 31 and 32 and the front end portion 50a of the wiring board 50 have dimensions that are just accommodated in the accommodating space 10r of the lower case 10, and the sealing material 31, the front end portion 50a, and the sealing material 32 are arranged in order from the lower case 10 side. It is accommodated in the accommodating space 10r. Further, the base end portion 50e of the wiring board 50 protrudes from the notch 10n to the outside of the lower case 10.

In this state, the sealing member 31 and 32 are pressed between the lower case 10 and the lid part 20 by bolting the lid part 20 onto the lower case 10 with bolts 25 from above the sealing material 32. A gap between the case 10 and the wiring board 50 is hermetically sealed.
As a result, the gas G to be measured introduced from the introduction pipe 10a into the accommodation space 10r comes into contact with the sensor element 40 to detect the concentration of the specific gas, and is then discharged to the outside from the discharge pipe 10b.

The sensor element 40 has a substantially rectangular plate shape, a heater portion 42 is disposed on the upper surface (surface facing upward in FIG. 1) of the base substrate 41, and a detection portion 43 is disposed on the lower surface side of the base substrate 41. In addition, the detection unit 43 and the heater unit 42 have an integrated structure in which the base substrate 41 is stacked above and below.
The detection unit 43 detects the concentration of the specific gas component by detecting an electric signal whose electrical characteristics change according to the concentration of the specific gas component and detecting the changed electric signal. The heater unit 42 heats the detection unit 43 to the operating temperature by energization heating. The output terminal of the detection unit 43 and the energization terminal of the heater unit 42 are suspended and fixed to the wiring board 50 by energization members 61 and 63 and electrically connected thereto.
The base substrate 41 can be a ceramic substrate, for example. Moreover, the detection part 43 can be formed, for example with an oxide semiconductor. The heater unit 42 may be a circuit that is formed on the surface of the base substrate 41 and serves as a heating resistor, for example.

  Here, a plurality of conductive pad portions 50p electrically connected to the detection portion 43 and the heater portion 42 via the current-carrying members 61 and 63 and the lead portions 50L are arranged on the front and back surfaces of the base end portion 50e of the wiring board 50. Has been. The electrical signal output from the detection unit 43 is output to the outside through the conductive pad unit 50p of the wiring board 50, and the heater unit 42 is energized and heated by the electric power supplied from the outside through the conductive pad unit 50p.

  Here, as shown in FIG. 2, the sensor element 40 is formed in a square shape in plan view, and the two energization members 61 a, straddling the first side 40 a (the left side in FIG. 2), 61 b is bonded to both end sides of the sensor element 40 and the wiring board 50. Similarly, another two energizing members 61c and 61d are connected to both ends of the sensor element 40 and the wiring board 50 so as to straddle the second side 40b (the right side in FIG. 2) facing the first side 40a. It is joined to.

Note that a plurality of (four in FIG. 2) element peripheral pads 50s are formed on the surface of the wiring board 50 so as to surround the opening 50h, and each element peripheral pad 50s is a conductive pad via a lead 50L. It is connected to the part 50p (three in FIG. 2).
Further, energization pads 42p are respectively formed at both ends of the heating resistor forming the heater section 42, and two element peripheral pads 0s are arranged so as to face the respective energization pads 42p. The energizing members 61a and 61d connect the energizing pads 42p facing the element peripheral pads 50s, respectively.
Further, a temperature sensor 44 is disposed along the heater portion 42, and energization pads 44p are formed at both ends of the temperature sensor 44, respectively. Two element peripheral pads 50s are arranged so as to oppose each energizing pad 44p, and the energizing members 61b and 61c connect each energizing pad 44p opposed to each element peripheral pad 50s. .
Note that a U-shaped conductive member 55 is connected to the element peripheral pad 50 s in the lower right of FIG. 2, and this conductive member 55 is connected to the element peripheral pad 50 s on the opposite surface of the wiring board 50 ( (See FIG. 3).

On the other hand, as shown in FIG. 3, a plurality of (three in FIG. 3) lands 50s are formed on the back surface of the wiring board 50 so as to surround the opening 50h on the opposite surface of the sensor element 40, Each land 50s is connected to a conductive pad portion 50p (three in FIG. 3) via a lead portion 50L.
The two energization members 63 a and 63 b are joined between the two energization pads 43 p connected to the detection unit 43 of the sensor element 40 and the land 50 s of the opposing wiring board 50.

  The energization member 61 and the conductive member 55 can be formed of, for example, Pt, and the energization member 63 can be formed of, for example, Au, and are electrically connected to corresponding energization pads and element peripheral pads by welding or the like. be able to. Each energizing pad can be formed by printing a Pt paste or the like on the base substrate 41 of the sensor element 40 and then baking it. The element peripheral pad 50s, the lead portion 50L, and the conductive pad portion 50p can be formed by printing Au paste or the like on the wiring substrate 50 and then baking it.

Next, features of the present invention will be described with reference to FIGS.
As shown in FIGS. 4 to 7, the introduction pipe 10 a and the discharge pipe 10 b are attached to the casing side wall 10 s (the upper side of the casing 10 in FIGS. 4 and 5) surrounding the outer peripheral edge of the wiring board 50 in the casing 10. These inner holes serve as an inlet 10g and an outlet 10h.
Further, a raised portion 10L having a rectangular shape in plan view that is raised from the periphery is formed at the center of the bottom wall of the casing (lower case) 10 (FIG. 5), and is located at both ends of the raised portion 10L (left and right in FIG. 4). A part) is formed with an introduction-side gas flow path 10c and a discharge-side gas flow path 10d that are recessed in an oval shape as viewed from the surface of the raised portion 10L. The introduction side gas flow path 10c faces the introduction port 10c but does not face the discharge port 10h, and the introduction side gas flow path 10c is formed to extend on the extension line of the introduction port 10g. Further, the discharge side gas flow path 10d faces the discharge port 10h, and the discharge side gas flow path 10d is formed to extend on an extension line of the discharge port 10h.
Since the accommodation space 10r outside the outer peripheral edge of the raised portion 10L (hatched portion in FIG. 5) is closed by the sealing material 31, the portion directly above the introduction-side gas passage 10c and the discharge-side gas passage 10d, and A portion directly above the portion between the gas flow paths 10c and 10d in the raised portion 10L is a substantially effective accommodation space 10r. The introduction-side gas passage 10c is a gas passage disposed on the upstream side with respect to the accommodation space 10r, and corresponds to a “gas passage” in the claims.

Of the introduction-side gas flow path 10c and the discharge-side gas flow path 10d, an introduction port 10g and a discharge port 10h extending from the introduction tube 10a and the discharge tube 10b to the first side wall 10w1 on the introduction tube 10a and the discharge tube 10b side, respectively. Is open. Of the introduction port 10g and the discharge port 10h, the portion that faces the first side wall 10w1 and communicates with the accommodation space 10r through either the introduction side gas flow channel 10c or the discharge side gas flow channel 10d is respectively connected to the introduction port 10g. One end 10g1 and one end 10h1 of the discharge port 10h.
On the other hand, a second side wall 10w2 facing the one end 10g1 of the introduction port 10g is formed in the introduction side gas flow path 10c (FIG. 7).
The introduction pipe 10a and the discharge pipe 10b correspond to the “cylindrical portion” in the claims, and the second side wall 10w2 corresponds to the “inner wall” in the claims.

As shown in FIGS. 4 and 8, one end 10g1 of the inlet 10g in a state where the wiring board 50 is installed in the casing (lower case) 10 so that the thickness direction T of the wiring board 50 is along the vertical direction. The one end 10h1 of the discharge port 10h is located on the outer side in the horizontal direction than the sensor element 40. The discharge port 10h is arranged at a position different from the introduction port 10g with the sensor element 40 therebetween.
Here, “different positions across the sensor element” means that the line LX (see FIG. 8) connecting the one end 10g1 of the introduction port 10g and the one end 10h1 of the discharge port 10h satisfies the positional relationship across the sensor element 40. That is, the sensor element 40 does not necessarily exist on the line LX, and the sensor element 40 may be disposed at a position shifted from the line LX. In the present embodiment, the sensor element 40 is slightly displaced with respect to the line LX (in FIG. 8, the right side of the sensor element 40 is slightly displaced to the left with respect to the line LX).
Further, as shown in FIG. 6, one end 10g1 of the introduction port 10g and one end 10h1 of the discharge port 10h are disposed lower (lower side) than the position LE of the wiring board 50 in the vertical direction.

  As described above, the one end 10g1 of the introduction port 10g is formed on the first side wall 10w1 of the gas flow path 10c, and the second side wall 10w2 facing the one end 10g1 of the introduction port 10g is formed in the introduction side gas flow path 10c. Yes. As a result, as shown in FIG. 6, the measurement gas G introduced from the introduction port 10g first collides with the second side wall 10w2 facing the one end 10g1 of the introduction port 10g through the introduction side gas flow path 10c, The traveling path is converted toward the accommodation space 10r (that is, toward the upper sensor element 40 in FIG. 6).

At this time, one end 10g1 of the introduction port 10g is disposed lower (lower side) than the position LE of the wiring board 50. That is, the one end 10g1 of the introduction port 10g is flush with the wiring board 50 (= sensor element 40). Since the gas to be measured G whose traveling path is converted upward in FIG. 6 by the second side wall 10w2 of the introduction side gas flow path 10c is not present above, the surface of the sensor element 40 that is further above the second side wall 10w2. It collides with (detecting portion 43 on the lower surface side of the base substrate 41 in this example) and flows along the surface of the sensor element 40.
As a result, as shown in FIG. 8, the flow of the gas G to be measured along the surface of the sensor element 40 becomes a laminar flow, and the difference in flow velocity depending on the position on the surface of the sensor element 40 is reduced. The entire element 40 is supplied uniformly. For this reason, the measurement accuracy of the gas G to be measured can be improved.

  Further, in the above embodiment, the one end 10 h 1 of the discharge port 10 h is disposed on the same side (lower) in the vertical direction as the one end 10 g 1 of the introduction port 10 g than the wiring board 50. As a result, the gas to be measured G whose traveling path has been converted by the second side wall 10w2 collides with the surface of the sensor element 40 and then flows to the lower outlet 10h, so that the gas to be measured G smoothly flows into the outlet. The measurement accuracy of the gas G to be measured is further improved from 10h.

Moreover, in the said embodiment, the other end side of the inlet 10g and the outlet 10h is each comprised by the internal space of the inlet pipe 10a and the outlet pipe 10b which protrude toward the outer side from the casing 10 side wall. As shown in FIG. 4, the introduction pipe 10 a and the discharge pipe 10 b are connected to a circulation pipe 70 such as a rubber pipe through which the gas G to be measured is circulated.
In this way, the measurement gas G is introduced from the flow pipe 70 using the inner hole (internal space) of the introduction pipe 10a as a guide, so that the measurement gas G is easily introduced into the introduction-side gas flow path 10c. Similarly, the gas to be measured G discharged from the discharge port 10h is discharged using the inner hole (internal space) of the discharge pipe 10b as a guide, so that the gas to be measured G is easily discharged. For this reason, the flow of the measurement gas G along the surface of the sensor element 40 becomes more uniform, and the measurement accuracy of the measurement gas G is further improved.

It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention.
The casing, the inlet, the outlet, the gas flow path, the shape of the sensor element, and the like are not limited to the above embodiment. The structure and type of the heater unit and the detection unit are not limited.

Example: A model of a structure in which a wiring board 50 in which a sensor element 40 is suspended and fixed as shown in FIGS. 1 to 3 is installed in a casing (lower case) 10 shown in FIGS. First, a fluid analysis simulation was performed with STAR-CCM + (CD-adapco) for the gas flow flowing on the lower surface of the sensor element 40 (detection unit 43 side) when the gas G was introduced from the introduction port 10g. In addition, the fluid analysis simulation was carried out by setting the inner diameters of the inlet 10a and the outlet 10b to 1.5 mm and allowing air to flow into the casing 10 from the inlet 10a at a flow rate of 160 cc / min.
Comparative Example: A fluid analysis simulation was performed in the same manner as in the example except that the casing (lower case) 100 shown in FIG. 9 was used. The lower case 100 scrapes between the two introduction-side gas passages 10c and the discharge-side gas passage 10d of the lower case 10 of the embodiment, and gas passages are arranged on the upstream side and the downstream side with respect to the accommodation space 100r. This is a large storage space 100r. And the accommodation space 100r (hatching part of FIG. 9) outside the outer peripheral edge of the raised portion 100L is closed with a sealing material. Accordingly, the lower case 100 does not have a gas flow path, and the measurement gas G is directly introduced into the accommodation space 100r from the introduction port 100g, and is discharged to the outside through the discharge port 100h.

The obtained results are shown in FIGS.
In the case of FIG. 10 showing the embodiment, a laminar flow from the upper left to the lower right of FIG. 10 is formed on the lower surface of the sensor element 40, thereby reducing the difference in flow velocity depending on the position on the surface of the sensor element 40. It can be seen that G is uniformly supplied to the entire sensor element 40.
On the other hand, in the case of FIG. 11 showing the comparative example, a strong flow is generated in the upper left corner and above of the sensor element 40, thereby generating a vortex on the surface of the sensor element 40, and depending on the position of the sensor element 40, the gas G may be generated. It can be seen that almost no gas is supplied and the gas flow is uneven.

DESCRIPTION OF SYMBOLS 1 Gas sensor 10, 20 Casing 10a, 10b Cylindrical part 10c Introduction side gas flow path (gas flow path)
10d discharge side gas flow path 10w2 inner wall 10r accommodation space 10g introduction port 10g1 one end of introduction port 10h discharge port 10h1 one end of discharge port 10s casing side wall 40 sensor element 41 base substrate 43 detection unit 50 wiring substrate 50h opening unit 61, 63 energization member 70 Flow pipe G Gas to be measured T Thickness direction

Claims (3)

A wiring board having a plate shape and having an opening penetrating in the thickness direction;
A detection element for detecting a specific gas is a sensor element provided on the base substrate, the sensor element is suspended in the opening by a plurality of current-carrying members, and is electrically connected to the wiring board,
A casing that forms a housing space for housing the wiring board, and an inlet for introducing a gas to be measured into the housing space on a casing side wall that surrounds an outer peripheral edge of the wiring board, and the measurement target from the housing space A gas sensor having a discharge port for discharging gas, and a casing in which one end of the introduction port and the discharge port communicates with the accommodation space,
In a state where the wiring board is installed in the casing so that the thickness direction of the wiring board is along the vertical direction, the one end of the introduction port is located on the outer side in the horizontal direction with respect to the sensor element, and the wiring While being arranged higher or lower than the substrate, the one end of the discharge port is located outside the sensor element in the horizontal direction, and is arranged at a position different from the introduction port across the sensor element. And
The casing is a gas flow path connecting the introduction port and the accommodation space, facing the one end of the introduction port, and converting a traveling path of the gas introduced from the introduction port toward the accommodation space. A gas sensor comprising a gas flow path including an inner wall. The gas sensor according to claim 1,
In the state where the wiring board is installed in the casing so that the thickness direction of the wiring board is along the vertical direction, the one end of the discharge port is more than the one end of the introduction port in the vertical direction than the wiring board. Gas sensor located on the same side. The gas sensor according to claim 1 or 2,
The other end side of the introduction port and the other end side of the discharge port are each configured by an internal space of a cylindrical portion protruding outward from the casing side wall. A gas sensor to which a flow pipe for flowing a gas to be measured is connected.