Gas sensor and sensor element housing

Abstract

This invention provides a gas sensor and a housing for housing the sensor element. The gas sensor includes an isolation member that effectively suppresses the temperature rise of the sealing component and ensures heat resistance. The gas sensor for monitoring a specified gas component contained in a measured gas includes: a sensor element having a monitoring portion at one end; a housing in which the sensor element is housed and fixed; and a connector disposed inside the housing for electrically connecting the sensor element to the outside. The housing includes: an outer cylinder having a main portion containing a reference gas and a sealing portion as an end portion with a reduced diameter compared to the main portion, the other end portion of the sensor element protruding towards the main portion; a rubber sealing member embedded in the sealing portion to seal the outer cylinder; and an isolation member located inside the outer cylinder between the sealing member and the connector, the isolation member having a recess on its end face that contacts the connector, and contacting the connector on its other end faces.

Description

Technical Field

[0001] This invention relates to gas sensors, and more particularly to suppressing heat transfer to a sealing component that seals a housing containing a sensor element. Background Technology

[0002] Previously, as a device for measuring the concentration of specified gas components in combustion gases and exhaust gases in internal combustion engines such as automobile engines, there is a well-known gas sensor that uses a sensor element formed from oxygen ion conductive solid electrolyte ceramics such as zirconium oxide (ZrO2).

[0003] As a gas sensor, a widely used gas sensor is constructed as follows: a strip-shaped sensor element (detection element) with oxygen ion-conducting ceramic (e.g., yttrium-stabilized zirconium oxide) as the main component is housed in a cylindrical metal housing. This gas sensor is positioned in the exhaust path of an internal combustion engine to monitor and determine the concentration of specified gas components in the exhaust gas.

[0004] One end of the housing is an opening, into which a rubber sealing component is embedded. Additionally, a protective cover allowing exhaust gas to enter and exit is provided at the other end of the housing. Inside the housing, the two ends are airtightly sealed, and a sensor element is housed there. Accordingly, in the gas sensor, at one end of the housing, one end of the sensor element is in contact with the reference gas (usually atmosphere) inside the housing, while at the other end of the housing, the other end of the sensor element is exposed within the protective cover and in contact with the exhaust gas. Furthermore, the reference gas and the exhaust gas do not come into contact with each other.

[0005] With the lead wire for making electrical connection between the sensor element and the outside passing through a pre-set through-hole, a rubber sealing member is embedded in the opening of the housing. From the side of the embedded part, the housing and the sealing member are pressed together, so that water cannot enter from the outside through the opening.

[0006] Furthermore, gas sensor elements typically include a heater for activating oxygen ion-conducting ceramics. Therefore, during operation, gas sensors become high-temperature components due to heat transfer through piping caused by the operation of the internal combustion engine, heat received from exhaust gases, and heat generated by the heater within the gas sensor itself. Consequently, rubber seals are typically made of heat-resistant materials such as fluororubber.

[0007] In recent years, the demand for miniaturization (shortening) of gas sensors has increased due to the need to reduce the installation space of components in internal combustion engines. To address this requirement, if the housing of conventional gas sensors is shortened, a rubber sealing member that closes the opening of the housing is placed near heat sources such as piping and exhaust gases within the piping. Gas sensors designed to address this problem are also known (see, for example, Patent Document 1). In the gas sensor disclosed in Patent Document 1, a mica heat-insulating member is sandwiched between the sealing member and a ceramic contact holding member (the partition in Patent Document 1) as an isolation element to suppress heat transfer to the sealing member and prevent excessive heating of the sealing member.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2005-227227 Summary of the Invention

[0011] In the gas sensor disclosed in Patent Document 1, the mica used as the insulating material is a layered material, which raises concerns about its strength. For example, if the gas sensor is subjected to vibration, the mica insulating material may partially detach, or the gas sensor may break during manufacturing, leading to decreased productivity.

[0012] Furthermore, from a heat resistance perspective, it is difficult to replace mica-based insulating materials with resin-based insulating materials that have the same low thermal conductivity as mica.

[0013] Considering strength and heat resistance, ceramic insulating components are preferred; however, ceramic materials are inferior to mica in terms of low thermal conductivity.

[0014] The present invention was made in view of the above-mentioned problems, and its object is to provide a gas sensor having an isolation element that effectively suppresses the temperature rise of the sealing component and ensures heat resistance.

[0015] To address the aforementioned issues, a first aspect of the present invention is a gas sensor for monitoring a specified gas component contained in a measured gas, characterized in that the gas sensor comprises: a sensor element having a monitoring portion at one end; a housing in which the sensor element is housed and fixed; and a connector disposed inside the housing for electrically connecting the sensor element to the outside. The housing comprises: an outer cylinder having a main portion containing a reference gas and a sealing portion as an end portion with a reduced diameter compared to the main portion, the other end portion of the sensor element protruding towards the main portion; a rubber sealing member embedded in the sealing portion to seal the outer cylinder; and a ceramic isolator located inside the outer cylinder between the sealing member and the connector, the isolator having a recess on one end face that contacts the connector, and contacting the connector on the other end face.

[0016] The second aspect of the present invention is based on the gas sensor involved in the first aspect, characterized in that, when the area of ​​the contact surface of the connector that contacts the isolator and the area of ​​the entire end face of the isolator including the recess are set as S0, and the contact area between the connector and the isolator is set as S, the contact area ratio S / S0 satisfies 0.2≤S / S0≤0.7.

[0017] The third embodiment of the present invention is based on the gas sensor involved in the first or second embodiment, characterized in that when the height of the isolation member is set as a and the depth of the recess is set as b, the depth ratio b / a satisfies 0.08≤b / a≤0.6.

[0018] The fourth aspect of the present invention is based on the gas sensor involved in any of the first to third aspects, characterized in that, when viewed from one side of the end face of the isolator, the recess is any one of a straight line, a cross shape, or a circle.

[0019] The fifth aspect of the present invention is based on the gas sensor involved in any of the first to fourth aspects, characterized in that the thermal conductivity of the insulating element is less than 32 W / m·K.

[0020] The sixth aspect of the present invention is a housing that houses a sensor element having a monitoring section at one end side for monitoring a specified gas component contained in a gas to be measured, and a connector for electrically connecting the sensor element to an external source. The housing is characterized by comprising: an outer cylinder having a main portion containing a reference gas and a sealing portion as an end portion with a reduced diameter compared to the main portion, and configured such that the other end of the sensor element protrudes towards the main portion; a rubber sealing member embedded in the sealing portion to seal the outer cylinder; and a ceramic isolator located inside the outer cylinder between the sealing member and the connector, the isolator having a recess on its end face on the side contacting the connector, and contacting the connector on the end face other than the recess.

[0021] The seventh aspect of the present invention is based on the sensor element housing involved in the sixth aspect, characterized in that, when the area of ​​the contact surface of the connector that contacts the isolator and the area of ​​the entire end face of the isolator including the recess are set as S0, and the contact area between the connector and the isolator is set as S, the contact area ratio S / S0 satisfies 0.2≤S / S0≤0.7.

[0022] The eighth embodiment of the present invention is based on the sensor element housing involved in the sixth or seventh embodiment, characterized in that when the height of the isolator is set to a and the depth of the recess is set to b, the depth ratio b / a satisfies 0.08≤b / a≤0.6.

[0023] The ninth aspect of the present invention is based on the sensor element housing involved in any of the sixth to eighth aspects, characterized in that, when viewed from the end face side of the isolator, the recess is any one of a straight line, a cross shape, or a circle.

[0024] The tenth aspect of the present invention is based on the sensor element housing involved in any of the sixth to ninth aspects, characterized in that the thermal conductivity of the insulating member is less than 32 W / m·K.

[0025] Invention Effects

[0026] According to the first to ninth aspects of the present invention, heat transfer from the connector toward the isolator and the sealing member can be suppressed. Accordingly, the strength of the isolator can be ensured, and thermal degradation of the sealing member can be suppressed. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of the main part of the gas sensor 100 along its length.

[0028] Figure 2 This is a simplified perspective view of the spacer 7 showing an example of the formation of the recess 7b.

[0029] Figure 3 This is a top view illustrating various shapes of the recess 7b.

[0030] Figure 4 This diagram illustrates potential malfunctions that may occur when assembling the gas sensor 100 if the contact area is smaller than the S / S0 value.

[0031] Figure 5 This diagram illustrates potential adverse events that may occur when assembling the gas sensor 100 with a depth ratio greater than b / a.

[0032] Figure 6 This is a cross-sectional view along the length of the sensor element 10 used for NOx detection.

[0033] Explanation of reference numerals in the attached figures

[0034] 1…Cylindrical body, 2…Protective cover, 3…Fixing bolt, 3a…Bolt part, 3b…Retaining part, 4…Outer cylinder, 4a…(outer cylinder)main part, 4b…(outer cylinder)sealing part, 5…Connector, 6…Sealing component, 7…Isolator, 8…Lead wire, 9…Through hole, 10…Sensor element, 11…Element substrate, 12…End protection layer, 13…Base layer, 51…Contact component, 100…Gas sensor, 101…Ceramic body, 106…Reference gas inlet, 150…Heater, 160…Electrode terminal, 170…Main surface protection layer. Detailed Implementation

[0035] <Composition of Gas Sensors>

[0036] Figure 1 This is a cross-sectional view of the main portion (more specifically, the main body portion) of the gas sensor 100 according to an embodiment of the present invention, along its length. More specifically, the cross-sectional view of the gas sensor 100 is shown above the break line ZL, while only the external appearance of the gas sensor 100 is shown below the break line ZL.

[0037] The gas sensor 100 is used to detect a specified gas component (e.g., NOx) via its internal sensor element 10. Generally, the gas sensor 100 is configured such that a long, cylindrical or thin-plate-shaped sensor element (detection element) 10 is surrounded by a cylindrical body 1, a protective cover 2, fixing bolts 3, and an outer cylinder 4. The cylindrical body 1, protective cover 2, and outer cylinder 4 together constitute a housing (shell) that houses the sensor element 10 internally. The fixing bolts 3 are mounted around the outer surface of the cylindrical body 1.

[0038] The sensor element 10 is configured to be coaxial with the cylindrical body 1, the protective cover 2, the fixing bolt 3, and the outer cylinder 4. The direction of extension of the central axis of the sensor element 10 is also referred to as the axial direction. Figure 1 In this diagram, the direction of the axis is consistent with the vertical direction in the attached diagram.

[0039] More specifically, one end side of the sensor element 10 (e.g. Figure 6 The first end (E1 side) is surrounded by a protective cover 2, and the other end protrudes into the outer cylinder 4. The roughly central portion between the two ends is fixed inside the cylindrical body 1 by means of ceramic powder or ceramic components (not shown) to airtightly seal the two ends.

[0040] The sensor element 10 has a monitoring section (e.g., a gas inlet, an internal cavity, a monitoring electrode, etc.) on one end side surrounded by the protective cover 2. In addition, various electrodes and wiring patterns are provided on the surface and inside the sensor element 10.

[0041] For example, in one embodiment of the sensor element 10, the gas to be measured introduced into the element is reduced or decomposed inside the element to generate oxygen ions. In a gas sensor 100 equipped with such a sensor element 10, the concentration of the gas component is determined based on the fact that the amount of oxygen ions flowing inside the element is directly proportional to the concentration of the target gas component in the measured gas.

[0042] The cylindrical body 1 is a metal cylindrical component, also referred to as the main body fitting. The cylindrical body 1 is almost entirely concealed from the exterior of the gas sensor 100 and is fitted over the entire range from the upper end of the protective cover 2 (see attached drawing) to the lower end of the outer cylinder 4 (see attached drawing). Inside the cylindrical body 1 are housed the sensor element 10 and a fixing component (powder-pressed or ceramic component) surrounding and fitted to the sensor element 10. In other words, the cylindrical body 1 is further surrounded by a surrounding mounting component that is mounted around the sensor element 10.

[0043] The protective cover 2 is a generally cylindrical external component that protects the portion of the sensor element 10 that is in direct contact with the gas being measured during use, namely, a defined area on the first end E1 side. The protective cover 2 is welded and fixed to the lower end of the cylindrical body 1 as shown in the attached drawing.

[0044] The protective cover 2 is provided with multiple through holes H through which gas can pass. The gas to be measured flowing into the protective cover 2 through these through holes H becomes the direct monitoring object in the sensor element 10. It should be noted that... Figure 1 The types, number, location, and shape of the through holes shown are merely examples and can be appropriately determined by considering the flow pattern of the gas being measured into the interior of the protective cover 2.

[0045] The fixing bolt 3 is an annular component used to fix the gas sensor 100 to the measuring position. The fixing bolt 3 includes a threaded bolt portion 3a and a retaining portion 3b that is held in place when the bolt portion 3a is screwed in. The bolt portion 3a is screwed into a nut installed at the mounting position of the gas sensor 100. Accordingly, the gas sensor 100 is fixed to the measuring position such that the side facing the protective cover 2 is in contact with the gas to be measured. For example, by screwing the bolt portion 3a into a nut provided on the exhaust pipe of a car, the gas sensor 100 is fixed to the exhaust pipe such that the side facing the protective cover 2 is exposed inside the exhaust pipe.

[0046] The outer cylinder 4 is a cylindrical component whose one end (the lower end in the attached drawing) is welded and fixed to the outer peripheral end of the upper part (not shown) of the cylindrical body 1. The outer cylinder 4 includes: a main portion 4a extending along the axial direction with the same diameter from the welded and fixed portion to the cylindrical body 1; and a sealing portion 4b continuous with the main portion 4a in the axial direction. The sealing portion 4b is an end portion with a reduced diameter compared to the main portion 4a.

[0047] The interior space of the outer cylinder 4 is filled with a reference gas (atmosphere) atmosphere. Additionally, a connector (also called a contact holding component) 5 and an isolator 7 are disposed inside the main body 4a.

[0048] On the other hand, the sealing part 4b is a part that is pressed from the side in a state where the sealing member 6 is embedded, thereby sealing the other end (the upper end in the attached figure) of the outer cylinder 4.

[0049] In the pressing portion 6s located on the side in the attached drawing of the sealing member 6, the sealing part 4b is pressed from the outside in its entire circumference, so that the sealing member 6 generates a reaction force toward the radially outward, thereby achieving the above-mentioned seal.

[0050] The sealing component 6 is made of rubber. Therefore, the sealing component 6 is also called a rubber plug. The rubber used is typically fluororubber. The sealing component 6 is uniformly cylindrical before being inserted into the sealing part 4b, however, it deforms radially through insertion and compression.

[0051] On the other end side where the sensor element 10 is inserted into connector 5 (e.g.) Figure 6 The second end (E2 side). The connector 5 has multiple electrode terminals 160 (see reference) of the sensor element 10 in the inserted state. Figure 6Multiple metal contact components 51 are used in contact with the connector 5. One end of the contact component 51 (the lower end in the figure) is a hook portion 51a that is hooked onto the connector 5, and the other end (the upper end in the figure) is a crimping portion 51b that crimps and fixes the lead wire 8. The portion in between is spring-shaped. The contact component 51 is clamped and fixed between the connector 5 and the sensor element 10, thereby electrically connecting the electrode terminal 160 of the sensor element 10 and the contact component 51.

[0052] The isolator 7 is sandwiched (intervened) inside the outer cylinder 4 between the connector 5 and the sealing member 6. The isolator 7 is cylindrical with approximately the same diameter as the sealing member 6 before compression. The purpose of the isolator 7 is to suppress the temperature rise of the sealing member 6 when the gas sensor 100 is in use. The details of the isolator 7 are described below.

[0053] The lead wire 8 is inserted through the through hole 9 continuously provided in the sealing member 6 and the isolator 7. One end is crimped and fixed to the crimping part 51b of the contact member 51, and the other end is connected to the controller 50 and various power supplies (see reference) outside the gas sensor 100. Figure 6 The sensor element 10, controller 50, and various power supplies are electrically connected via contact parts 51 and leads 8. It should be noted that... Figure 1 In the diagram, only two contact components 51 and two leads 8 are shown, simply for the sake of simplicity. In reality, the number of leads required for the aforementioned electrical connection is much greater.

[0054] It should be noted that the gas sensor 100 with the above configuration can be manufactured using the same method as before. In general, firstly, before the clamping part 6s is clamped, the connector 5, in which the sensor element 10 is inserted and the contact member 51 is connected to the lead wire 8, is pre-positioned in the main part 4a of the outer cylinder 4. Next, the lead wire 8 is inserted sequentially through the respective through holes 9 in the order of the isolator 7 and the sealing member 6, and stacked sequentially on top of the connector 5. Then, the sealing member 6, through which the lead wire 8 passes, is inserted into the sealing part 4b before clamping. Normally, atmospheric air, serving as a reference gas, has already been introduced into the outer cylinder 4 before the sealing member 6 is inserted. When the sealing member 6 is inserted, the clamping part 6s is clamped using a prescribed clamping mechanism.

[0055] It should be noted that, for the purpose of clamping, it is preferable to clamp the clamping portion 6s which extends continuously over the entire outer periphery of the sealing portion 4b. However, as long as good clamping and fixing can be achieved, the clamping portion 6s may be discontinuous in the circumferential direction of the sealing portion 4b.

[0056] <Composition and Function of the Isolator>

[0057] Next, the composition of the isolation element 7 and the effects obtained by having this composition will be explained in detail.

[0058] First, ceramic is chosen as the material for the insulating element 7 to ensure strength. Preferably, it is a ceramic with a thermal conductivity of 32 W / m·K or less, which is optimal in terms of heat resistance and low thermal conductivity. More preferably, it is alumina (thermal conductivity: 32 W / m·K) or block talc (thermal conductivity: 2 W / m·K).

[0059] Furthermore, in this embodiment, a recess 7b is provided on one end face 7a side of the isolation member 7. Figure 2 This is a simplified perspective view of the spacer 7 showing an example of the formation of the recess 7b. It should be noted that... Figure 2 The illustration shows a case where the recess 7b is configured as a straight groove with a flat bottom surface 7c and a rectangular cross-section perpendicular to the length direction. It should be noted that... Figure 2 In this example, four of the eight through holes 9 (9a) of the spacer 7 are located in the stepped portion of an end face 7a and a recess 7b, but this is just an example and the configuration of the through holes 9a is not limited to this.

[0060] in addition, Figure 3 This is a top view illustrating various shapes of the recess 7b. However, the illustration of the through hole 9a is omitted.

[0061] Figure 3 (a) shows the relationship with Figure 2 The same recess 7b is a straight groove. In contrast, Figure 3 (b) shows the cross-shaped recess 7b when viewed from above, formed by the orthogonal straight grooves described above. Additionally, Figure 3 (c) shows a circular recess 7b when viewed from above. The bottom surface 7c of the recess 7b can be flat or curved.

[0062] Regardless of the shape of the isolator 7, the connector 5 is as follows: Figure 1 As shown, the portion of one end face 7a, excluding the recess 7b, contacts the spacer 7, while the portion of the recess 7b does not contact the spacer 7.

[0063] By adopting the above configuration, the gas sensor 100 according to this embodiment, compared with the gas sensor 100 with the connector 5 in contact with one end face 7a of the isolator 7, suppresses heat transfer from the connector 5 to the isolator 7 and the sealing member 6. That is, the risk of thermal degradation of the sealing member 6 is reduced. Specifically, in the case of a structure where the connector 5 and the sealing member 6 are in direct contact, the sealing member 6 may sometimes undergo thermal decomposition starting from the contact portion with the connector 5, resulting in exhaust diffusion and signal abnormalities. However, in the gas sensor 100 according to this embodiment, by clamping the isolator 7 with the recess 7b, the temperature rise of the end face of the sealing member 6 is suppressed, and as a result, the risk of signal abnormalities caused by thermal decomposition is appropriately reduced.

[0064] It should be noted that the shape of the recess 7b is not limited to Figure 3 The shape shown can be any other shape, as long as the spacer 7 is well held between the connector 5 and the sealing member 6 and the heat transfer from the connector 5 to the sealing member 6 is well suppressed.

[0065] Preferably, when the smaller of the area of ​​the contact surface with the isolator 7, i.e., the area of ​​the end face 5e of the connector 5, and the area of ​​the entire end face 7a of the isolator 7, including the recess 7b, is set as S0, and the contact area between the connector 5 and the isolator 7 is set as S, the following trend occurs: the smaller the value of the ratio of the two (hereinafter also referred to as the contact area ratio) S / S0, the more the heat transfer from the connector 5 to the isolator 7 and the sealing member 6 is suppressed. It should be noted that the area S0 is chosen because: considering that although Figure 1 The example illustrates a case where the area of ​​one end face 7a of the isolator 7 is larger than the area of ​​the end face 5e of the connector 5, but it is also possible to use a configuration where the size relationship between the two areas is reversed.

[0066] Furthermore, there is a trend that the larger the ratio (hereinafter also referred to as the depth ratio) b / a of the recess 7b to the height a of the spacer 7, the more the heat transfer from the connector 5 to the spacer 7 and the sealing member 6 is suppressed. It should be noted that when the bottom surface 7c of the recess 7b is not flat, the distance to the deepest position can be set as the depth b.

[0067] It should be noted that, ideally, a heat transfer reduction effect would be observed if S / S0 < 1 or b / a > 0. However, in practice, a substantial heat transfer reduction effect is expected only when S / S0 ≤ 0.7 or b / a ≥ 0.08. For example, when the spacer 7 is made of talc, the temperature at the contact portion 6a between the sealing member 6 and the spacer 7 is reduced by at least 2% compared to the case without the recess 7b, when S / S0 ≤ 0.5 and b / a ≥ 0.15. In particular, the temperature reduction effect is approximately 3% when S / S0 ≤ 0.5 and b / a ≥ 0.5. Based on the latter, a temperature reduction effect of at least 10°C can be foreseen when the heat resistance limit temperature of the sealing member 6 is 300°C.

[0068] However, it is preferable that S / S0 ≥ 0.2. Figure 4 This diagram illustrates potential adverse situations that may occur when assembling the gas sensor 100 if the contact area is smaller than the S / S0 value. During assembly of the gas sensor 100, with the isolator 7 abutting against the end face 5e of the connector 5 to which the sensor element 10 is inserted at the other end, the sealing member 6, embedded in the sealing portion 4b of the outer cylinder 4, abuts against the other end face 7e of the isolator 7 (the opposite side of one end face 7a). Next, at the pressing portion 6s, the sealing portion 4b is pressed from the side, causing it to shrink in diameter. This causes the sealing member 6 to deform. As the sealing member 6 deforms, as... Figure 4 As shown in (a), the downward load F1 acts on the isolation member 7.

[0069] At this point, the isolator 7 is restricted at its upper and lower end faces by the sealing component 6 and the connector 5; however, its outer periphery is not particularly restricted. Therefore, when the value of S / S0 is small, such as Figure 4 As shown in (b), the isolator 7 tilts due to the action of load F1, which may result in it not being able to hold accurately between the sealing member 6 and the connector 5, or the sensor element 10 being broken due to the force applied from the side. This defect becomes significant when S / S0 < 0.2.

[0070] In addition, b / a ≤ 0.6 is preferred. Figure 5 This diagram illustrates potential adverse events that may occur when assembling the gas sensor 100 when the depth ratio b / a is large.

[0071] As described above, during the assembly of the gas sensor 100, as the sealing portion 4b of the outer cylinder 4 is compressed and deformed, a downward load F1 acts on the isolator 7. At the same time, an upward load F2 from the connector 5 also acts on the isolator 7. That is, compressive forces in both the vertical and horizontal directions act on the isolator 7. Therefore, if the value of b / a is large and the recess 7b is deep, buckling failure may occur near the end edge 7d of the bottom surface 7c. When b / a > 0.6, this defect becomes significant.

[0072] As explained above, according to this embodiment, by placing a ceramic insulating member between a connector disposed inside the outer cylinder of the gas sensor and connected to the sensor element, and a sealing member that seals the end of the outer cylinder, and by providing a recess at the contact portion between the insulating member and the connector, heat transfer from the connector to the insulating member and the sealing member can be suppressed. Accordingly, the strength of the insulating member can be ensured, and thermal degradation of the sealing member can be suppressed.

[0073] <Example of Sensor Element Configuration>

[0074] Finally, as an example of sensor element 10, the configuration of sensor element 10 for NOx detection will be described. Figure 6 This is a cross-sectional view along the length of the sensor element 10 used for NOx detection. In this case, the sensor element 10 is a so-called limiting current type gas sensor element. It should be noted that... Figure 6 In addition to showing the sensor element 10, the pump unit power supply 30, heater power supply 40, and controller 50 of the gas sensor 100 are also shown.

[0075] like Figure 6 As shown, generally speaking, the sensor element 10 is configured such that the first end E1 side of the elongated plate-shaped element substrate 11 is covered by a porous end protective layer 12. The element substrate 11 has an elongated plate-shaped ceramic body 101 as its main structure, and the ceramic body 101 has main surface protective layers 170 (170a, 170b) on two main surfaces. In addition, in the sensor element 10, end protective layers 12 (inner end protective layer 12a, outer end protective layer 12b) are provided on the end face (end face 101e of ceramic body 101) on one end portion side and on the outer sides of the four sides.

[0076] It should be noted that, in this embodiment, for ease of explanation, the end on the side where the first end E1 of the element base 11 is located in the ceramic body 101 and the sensor element 10 is also referred to as the respective first end E1, and the end on the side where the second end E2 of the element base 11 is located is also referred to as the respective second end E2.

[0077] The ceramic body 101 is formed of a ceramic with zirconium oxide (yttrium-stabilized zirconium oxide) as the main component, which is an oxygen ion-conducting solid electrolyte. The ceramic body 101 is dense and airtight.

[0078] Figure 6 The sensor element 10 shown is a so-called tandem three-chamber gas sensor element having a first internal cavity 102, a second internal cavity 103, and a third internal cavity 104 inside a ceramic body 101. Specifically, in the sensor element 10, the first internal cavity 102 is connected to a gas inlet 105 (strictly speaking, connected to the outside via an end protective layer 12) that is open to the outside at the first end E1 side of the ceramic body 101 via a first diffusion rate control unit 110 and a second diffusion rate control unit 120; the second internal cavity 103 is connected to the first internal cavity 102 via a third diffusion rate control unit 130; and the third internal cavity 104 is connected to the second internal cavity 103 via a fourth diffusion rate control unit 140. It should be noted that the path from the gas inlet 105 to the third internal cavity 104 is also referred to as a gas flow section. In the sensor element 10 of this embodiment, this flow section is arranged in a straight line along the length direction of the ceramic body 101.

[0079] The first diffusion rate control unit 110, the second diffusion rate control unit 120, the third diffusion rate control unit 130, and the fourth diffusion rate control unit 140 are all configured as two upper and lower slits as shown in the attached figure. The first diffusion rate control unit 110, the second diffusion rate control unit 120, the third diffusion rate control unit 130, and the fourth diffusion rate control unit 140 apply a predetermined diffusion resistance to the gas being measured. It should be noted that a buffer space 115 is provided between the first diffusion rate control unit 110 and the second diffusion rate control unit 120, which has the effect of buffering the pulsation of the gas being measured.

[0080] Furthermore, an external pump electrode 141 is provided on the outer surface of the ceramic body 101, and an internal pump electrode 142 is provided in the first internal cavity 102. Additionally, an auxiliary pump electrode 143 is provided in the second internal cavity 103, and a measuring electrode 145, serving as a direct monitoring unit for the gas composition to be measured, is provided in the third internal cavity 104. Furthermore, a reference gas inlet 106, communicating with the outside and allowing reference gas to be introduced, is provided on the second end E2 side of the ceramic body 101, and a reference electrode 147 is disposed within this reference gas inlet 106.

[0081] In the gas sensor 100 equipped with the above-mentioned sensor element 10, the NOx gas concentration in the gas to be measured is calculated by the following steps.

[0082] First, the oxygen concentration of the gas to be measured, which flows into the protective cover 2 through the through-hole H and is introduced into the first internal cavity 102 through the gas inlet 105, is adjusted to be approximately constant by the pumping action (oxygen intake or exhaust) of the main pump unit P1. Then, it is introduced into the second internal cavity 103. The main pump unit P1 is an electrochemical pump unit consisting of an external pump electrode 141, an internal pump electrode 142, and a ceramic body 101 portion, i.e., a ceramic layer 101a, between these two electrodes. In the second internal cavity 103, the oxygen in the gas to be measured is drawn out of the element by the pumping action of the auxiliary pump unit P2, which is also an electrochemical pump unit, thereby bringing the gas to be measured to a sufficiently low oxygen partial pressure. The auxiliary pump unit P2 consists of an external pump electrode 141, an auxiliary pump electrode 143, and a ceramic body 101 portion, i.e., a ceramic layer 101b, between these two electrodes.

[0083] The external pump electrode 141, internal pump electrode 142, and auxiliary pump electrode 143 are formed as porous metal-ceramic electrodes (e.g., metal-ceramic electrodes containing 1% Au, Pt, and ZrO2). It should be noted that the internal pump electrode 142 and auxiliary pump electrode 143, which are in contact with the gas being measured, are formed using materials that have reduced or no reducing ability for NOx components in the gas being measured.

[0084] NOx in the gas to be measured, which is in a low oxygen partial pressure state through the auxiliary pump unit P2, is introduced into the third internal cavity 104, where it is reduced or decomposed at the measuring electrode 145 disposed in the third internal cavity 104. The measuring electrode 145 is a porous metal-ceramic electrode that also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere within the third internal cavity 104. During this reduction or decomposition, the potential difference between the measuring electrode 145 and the reference electrode 147 remains constant. Then, the oxygen ions generated by the reduction or decomposition are drawn out of the element through the measuring pump unit P3. The measuring pump unit P3 consists of an external pump electrode 141, a measuring electrode 145, and a ceramic body 101 portion, i.e., a ceramic layer 101c, between these two electrodes. The measuring pump unit P3 is an electrochemical pump unit that draws out oxygen generated by the decomposition of NOx in the atmosphere surrounding the measuring electrode 145.

[0085] Under the control of the controller 50, the voltage required for pumping is applied between the electrodes of each pump unit via the pump unit power supply (variable power supply) 30, thereby realizing pumping (oxygen intake or exhaust) in the main pump unit P1, auxiliary pump unit P2, and measuring pump unit P3. In the case of the measuring pump unit P3, a voltage is applied between the external pump electrode 141 and the measuring electrode 145 in a manner that maintains the potential difference between the measuring electrode 145 and the reference electrode 147 at a predetermined value. Typically, a pump unit power supply 30 is provided for each pump unit.

[0086] The controller 50 detects the pump current Ip2 and calculates the NOx concentration in the gas being measured based on the linear relationship between the current value (NOx signal) of the pump current Ip2 and the concentration of decomposed NOx. The pump current Ip2 flows between the measuring electrode 145 and the external pump electrode 141 in a manner corresponding to the amount of oxygen drawn out by the measuring pump unit P3.

[0087] It should be noted that, preferably, the gas sensor 100 includes: a plurality of electrochemical sensor units (not shown) that monitor the potential difference between each pump electrode and the reference electrode 147, and the controller 50 controls each pump unit based on the detection signals of these sensor units.

[0088] Additionally, a heater 150 is embedded inside the ceramic body 101 in the sensor element 10. The heater 150 is located in the gas flow section. Figure 6 The lower side, as shown in the attached diagram, is located across the entire range from near the first end E1 to the formation positions of at least the measuring electrode 145 and the reference electrode 147. Under the control of the controller 50, the heater 150 heats up due to power supplied from the heater power supply 40. The main purpose of providing the heater 150 is to heat the sensor element 10 when it is in use, thereby improving the oxygen ion conductivity of the solid electrolyte constituting the ceramic body 101. The sensor element 10 is heated until the temperature of at least the range from the first internal cavity 102 to the second internal cavity 103 reaches 500°C or higher.

[0089] More specifically, the heater 150 is a resistance heating element formed, for example, from platinum, and is configured such that it is surrounded by an insulating layer 151.

[0090] On the second end E2 side of each main surface of the ceramic body 101, a plurality of electrode terminals 160 are formed for electrical connection between the sensor element 10 and the outside. These electrode terminals 160 are electrically connected to the five electrodes, the two ends of the heater 150, and the internal wiring for heater resistance detection (not shown) in a predetermined correspondence through internal wiring (not shown) provided inside the ceramic body 101. As described above, the electrode terminals 160 are connected to the lead wire 8 via the contact member 51, and through the lead wire 8, the contact member 51, and the electrode terminals 160, voltage is applied from the pump unit power supply 30 to each pump unit of the sensor element 10, and heating of the heater 150 is achieved by power supply from the heater power supply 40.

[0091] The main surface protective layer 170 is a layer formed of alumina with a thickness of about 5 μm to 30 μm and a porosity of about 20% to 40%. The purpose of providing the main surface protective layer 170 is to prevent foreign objects or poisoning substances from adhering to the two main surfaces of the ceramic body 101 or the external pump electrode 141. Therefore, one main surface protective layer 170a also functions as a pump electrode protective layer to protect the external pump electrode 141.

[0092] The end protective layer 12 is provided at the outermost periphery of a predetermined range, starting from the first end E1 of the component substrate 11. The purpose of providing the end protective layer 12 is to ensure the water resistance of the gas sensor 100 in the component substrate 11 when it becomes hot (up to about 700°C to 800°C) during use, and to suppress the thermal shock caused by the local temperature drop due to direct water spray on that part, which could cause the component substrate 11 to crack (water spray cracking).

[0093] In addition, the purpose of setting the end protective layer 12 is to prevent poisonous substances such as Mg from entering the interior of the sensor element 10, that is, to ensure resistance to poisoning.

[0094] The inner end protective layer 12a is made of alumina, has a porosity of 45% to 60%, and a thickness of 450 μm to 650 μm. The outer end protective layer 12b is also made of alumina, has a porosity 10% to 40% lower than that of the inner end protective layer 12a, and a thickness of 50 μm to 300 μm. The inner end protective layer 12a is configured as a layer with low thermal conductivity, thereby suppressing heat conduction from the outside to the component substrate 11.

[0095] The inner end protective layer 12a and the outer end protective layer 12b are formed as follows: each constituent material is sequentially sprayed (plasma spraying) onto the element substrate 11 on which the base layer 13 is formed, thereby forming the aforementioned protective layers.

[0096] In addition, such as Figure 6 As shown, a base layer 13 is provided between the inner end protective layer 12a and the component substrate 11 to ensure the adhesion of the inner end protective layer 12a. The base layer 13 is provided on at least two main surfaces of the component substrate 11. The base layer 13 is made of alumina and is formed to have a porosity of 30% to 60% and a thickness of 15 μm to 50 μm.

[0097] <Variation Example>

[0098] In the above embodiments, the sensor element 10 is exemplified as a limiting current type sensor element with three internal cavities, which is a sensor element that detects NOx as a gas component. However, the number of internal cavities in the sensor element 10 of the gas sensor 100 may not be three, and other gas components besides NOx may be used as the monitoring target. Alternatively, a sensor element without internal cavities, such as a mixed potential type sensor element, may also be used.

[0099]

Example

[0100] CAE simulation was performed on the temperature (stable temperature) at the contact portion 6a between the sealing component 6 and the isolation component 7 when the gas sensor 100, which has a fluororubber sealing component 6 and a talc isolation component 7, is installed in a high-temperature piping through which the measured gas flows. The temperature reduction effect caused by the isolation component 7 was determined.

[0101] The temperature of the gas flowing through the piping is set to 850°C, and the flow rate is set to 4.85 m / sec. The gas sensor 100 is installed on the piping by screwing the bolt part 3a into the nut located at the specified installation position. Furthermore, the external temperature of the piping (the temperature around the gas sensor 100) is set to 25°C. Additionally, the driving temperature of the sensor element 10 (the set heating temperature of the heater 150) is set to 850°C.

[0102] As a gas sensor 100, the area of ​​one end face 7a of the isolator 7, including the recess 7b, is larger than the area of ​​the end face 5e of the connector 5, and the recess 7b of the isolator 7 is... Figure 2 and Figure 3 (a) shows a gas sensor with a straight groove, and the depth ratio b / a is set to two different levels (Example 1, Example 2). Specifically, it is set to 0.15 (Example 1) and 0.5 (Example 2). The contact area ratio S / S0 is 0.459, which is common.

[0103] In addition, as a comparative example for obtaining a stable temperature, a gas sensor 100 that does not have the recess 7b but otherwise has the same configuration as in Examples 1 and 2 was simulated under the same conditions.

[0104] Table 1 shows in summary the contact area ratio S / S0 and depth ratio b / a of Examples 1 and 2 (these values ​​are also shown for Comparative Example 1), the determination results of the temperature reduction effect based on the highest temperature of the contact portion 6a, and the ratio of the temperature of the contact portion 6a when the value of Comparative Example 1 is set to 1.

[0105] Table 1

[0106]

[0107] When judging the temperature reduction effect, for the gas sensor 100 whose temperature at the contact portion 6a is more than 6°C lower than that of Comparative Example 1, it is determined that the temperature reduction effect of the sealing component 6 achieved by providing the recess 7b in the isolation member 7 is good. For Example 2, which falls under this category, "〇" (circled) is marked in the judgment result column of Table 1.

[0108] On the other hand, regarding the gas sensor 100 whose temperature at the contact portion 6a is 1°C lower than or equal to 6°C lower than that in Comparative Example 1, it is determined that the temperature reduction effect of the sealing component 6 achieved by providing the recess 7b in the isolation member 7 has been obtained to a certain extent. For Example 1, which falls under this category, "Δ" (triangle mark) is marked in the determination result column of Table 1.

[0109] It should be noted that for gas sensors 100 whose temperature of the contact portion 6a is less than 1°C lower than that of Comparative Example 1, or is higher than that of Comparative Example 1, it is determined that the temperature reduction effect of the sealing component 6 caused by providing the recess 7b in the isolation member 7 is not obtained. However, the gas sensors 100 of Examples 1 and 2 are not in this case.

[0110] The results shown in Table 1 confirm that the gas sensor 100 of Embodiment 1, which has a recess 7b satisfying 0.2≤S / S0≤0.5 and 0.15≤b / a≤0.6, achieves a temperature reduction effect of more than 2% at the contact portion 6a between the sealing member 6 and the insulating member 7. Furthermore, it was confirmed that the gas sensor 100 of Embodiment 2, which has a recess 7b satisfying 0.2≤S / S0≤0.5 and 0.5≤b / a≤0.6, achieves a temperature reduction effect of more than 3% at the contact portion 6a between the sealing member 6 and the insulating member 7.

Claims

1. A gas sensor for monitoring a specified gas component contained in a measured gas, characterized in that, The gas sensor includes: A sensor element having a monitoring section at one end; Housing, in which the sensor element is housed and secured; and A connector, disposed inside the housing, electrically connects the sensor element to the external environment. The housing includes: The outer cylinder has a main part in which a reference gas is contained, and a sealing part as an end that is reduced in diameter compared to the main part, and the other end of the sensor element protrudes laterally toward the main part; A rubber sealing component is embedded in the sealing portion to seal the outer cylinder; as well as A ceramic spacer is located inside the outer cylinder, between the sealing component and the connector. The isolator has a recess on its end face that contacts the connector, and the other end faces of the isolator contact the connector. When the smaller of the area of ​​the contact surface of the connector that contacts the isolator and the area of ​​the entire end face of the isolator, including the recess, is defined as S0, and the contact area between the connector and the isolator is defined as S, the contact area ratio S / S0 satisfies 0.2 ≤ S / S0 ≤ 0.

7. When the height of the spacer is set to 'a' and the depth of the recess is set to 'b', The depth ratio b / a satisfies 0.08 ≤ b / a ≤ 0.

6.

2. The gas sensor according to claim 1, characterized in that, When viewed from one side of the end face of the spacer, the recess is any one of a straight line, a cross shape, and a circle.

3. The gas sensor according to claim 1 or 2, characterized in that, The thermal conductivity of the insulating element is below 32 W / m·K.

4. A sensor element housing, wherein a sensor element and a connector for electrically connecting the sensor element to an external source are fixed and housed inside the sensor element housing, and one end of the sensor element has a monitoring section for monitoring a predetermined gas component contained in the gas to be measured, characterized in that, The housing includes: The outer cylinder has a main part in which a reference gas is contained, and a sealing part as an end that is reduced in diameter compared to the main part, and is configured such that the other end of the sensor element protrudes laterally toward the main part; A rubber sealing component is embedded in the sealing portion to seal the outer cylinder; as well as A ceramic spacer is located inside the outer cylinder, between the sealing component and the connector. The isolator has a recess on its end face that contacts the connector, and the other end faces of the isolator contact the connector. When the smaller of the area of ​​the contact surface of the connector that contacts the isolator and the area of ​​the entire end face of the isolator, including the recess, is defined as S0, and the contact area between the connector and the isolator is defined as S, the contact area ratio S / S0 satisfies 0.2 ≤ S / S0 ≤ 0.

7. When the height of the spacer is set to 'a' and the depth of the recess is set to 'b', The depth ratio b / a satisfies 0.08 ≤ b / a ≤ 0.

6.

5. The sensor element housing according to claim 4, characterized in that, When viewed from one side of the end face of the spacer, the recess is any one of a straight line, a cross shape, and a circle.

6. The sensor element housing according to claim 4 or 5, characterized in that, The thermal conductivity of the insulating element is below 32 W / m·K.

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