Gas sensor and sensor element housing

Abstract

To provide a gas sensor including a spacer that both suppresses a rise of the temperature and secures the heat resistance of a seal member.SOLUTION: A gas sensor for detecting a prescribed gas component included in the gas being measured, comprises a sensor element which is provided with a detection part on one end side, a casing in which the sensor element is accommodated and fixed in place, and a connector that is disposed inside of the casing and electrically connects the sensor element and the outside. The casing includes a main part in which a reference gas exists and a sealing part that is an end in reduced diameter than the main part, the main part being provided with an outer tube to which the other end side of the sensor element protrudes, a sealing member made of rubber that is fitted into the sealing part and seals the outer tube, and a spacer that is interposed between the sealing member and the connector in the inside of the outer tube, the spacer having a recess in an edge face on the side that is in contact with the connector and being designed to come into contact on the edge face, except the recess.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas sensor, and more particularly to suppressing heat transfer to a seal member that seals a casing that houses a sensor element. [Background technology]

[0002] Gas sensors in which a sensor element is formed using an oxygen ion conductive solid electrolyte ceramic such as zirconia (ZrO2) have been known for some time as devices for measuring the concentration of a specific gas component in a measurement gas such as combustion gas or exhaust gas from an internal combustion engine such as an automobile engine.

[0003] A widely used gas sensor has a long, plate-shaped sensor element (detection element) made primarily of oxygen-ion conductive ceramics (e.g., yttria-stabilized zirconia) housed in a metallic cylindrical housing (casing). Such a gas sensor is installed midway through the exhaust path of an internal combustion engine and is used to detect and measure the concentration of specific gas components contained in the exhaust gas.

[0004] One end of the casing is an opening into which a rubber seal is fitted. A protective cover is attached to the other end of the casing, allowing exhaust gas to pass in and out. The sensor element is housed inside the casing, with both ends sealed airtight. As a result, in the gas sensor, one end of the sensor element at one end of the casing comes into contact with a reference gas (usually the atmosphere) inside the casing, while the other end of the sensor element at the other end of the casing is exposed inside the protective cover and comes into contact with exhaust gas. Furthermore, the reference gas and exhaust gas do not come into contact with each other.

[0005] The rubber sealing member is fitted into the opening of the casing after lead wires for electrically connecting the sensor element to the outside have been inserted into the pre-installed through-holes, and the casing and the sealing member are crimped from the side of the fitting point to prevent water from entering from the outside through the opening.

[0006] Furthermore, the sensor element used in the gas sensor is usually equipped with a heater for heating and activating the oxygen ion conductive ceramics. Therefore, during use, the gas sensor becomes hot not only due to heat transferred through the piping generated by the operation of the internal combustion engine and heat received from the exhaust gas, but also due to heat generated by the heater provided in the gas sensor itself. For this reason, fluororubber, which has high heat resistance, is usually used for the rubber sealing member.

[0007] In recent years, there has been an increasing demand for shorter gas sensors due to the increasingly narrow space available for mounting components in internal combustion engines. While shortening the casing of conventional gas sensors would address this demand, the rubber sealing member that closes the opening of the casing would be closer to heat sources such as the piping and the exhaust gases inside the piping. Gas sensors designed to address this issue are already known (see, for example, Patent Document 1). The gas sensor disclosed in Patent Document 1 suppresses heat transfer to the sealing member by sandwiching a mica heat insulating member as a spacer between the sealing member and a ceramic contact holding member (a separator in Patent Document 1), thereby preventing excessive temperature rise of the sealing member. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-227227 Summary of the Invention [Problem to be solved by the invention]

[0009] The mica used as the spacer material in the gas sensor disclosed in Patent Document 1 has a layered structure, which raises concerns about its strength. For example, there are concerns that the mica spacer may partially fall off when the gas sensor is subjected to vibration, or that breakage during the manufacturing process of the gas sensor may reduce productivity.

[0010] Furthermore, it is difficult to replace the mica spacer with a resin spacer having a thermal conductivity as low as that of mica from the viewpoint of heat resistance.

[0011] From the viewpoint of strength and heat resistance, it is desirable to use a ceramic spacer, but ceramic materials are inferior to mica in terms of low thermal conductivity.

[0012] The present invention has been made in view of the above-mentioned problems, and has an object to provide a gas sensor including a spacer that suitably suppresses temperature rise in the sealing member while ensuring heat resistance. [Means for solving the problem]

[0013] In order to solve the above problems, a first aspect of the present invention is a gas sensor for detecting a predetermined gas component contained in a measurement gas, comprising: a sensor element having a detection portion on one end side; a casing in which the sensor element is housed and fixed; and a connector disposed inside the casing and electrically connecting the sensor element to the outside, wherein the casing has a main portion inside which a reference gas is present and a sealing portion which is an end portion having a smaller diameter than the main portion, an outer cylinder from which the other end side of the sensor element protrudes into the main portion, a rubber seal member fitted into the sealing portion to seal the outer cylinder, and a rubber seal member interposed inside the outer cylinder between the seal member and the connector. steatite and a spacer made of a material, wherein the spacer has a recess on an end surface that comes into contact with the connector, and the end surface excluding the recess comes into contact with the connector. where S0 is the smaller of the area of ​​the contact surface of the connector with the spacer and the area of ​​the entire end face including the recess of the spacer, and S is the contact area between the connector and the spacer, the contact area ratio S / S0 is 0.2≦S / S0≦0.5, and where a is the height of the spacer and b is the depth of the recess, the depth ratio b / a is 0.15≦b / a≦0.6. It is characterized by:

[0016] The present invention 2The embodiment is 1 of status Like In the gas sensor, the recessed portion has a linear, cross or circular shape when viewed from the end face side of the spacer.

[0017] The present invention 3 The first aspect is or No. 2 attitude Like The gas sensor is characterized in that the thermal conductivity of the spacer is 32 W / m·K or less.

[0018] The present invention 4 The embodiment of the present invention is a casing that houses a sensor element having a detection unit at one end that detects a predetermined gas component contained in a gas to be measured, and a connector that electrically connects the sensor element to the outside, while fixing the sensor element inside, the casing having a main portion inside which a reference gas is present and a sealing portion that is an end portion having a smaller diameter than the main portion, and an outer cylinder arranged so that the other end side of the sensor element protrudes from the main portion, a rubber seal member that is fitted into the sealing portion to seal the outer cylinder, and a rubber seal member that is interposed inside the outer cylinder between the seal member and the connector. steatite and a spacer made of a material, wherein the spacer has a recess on an end surface that comes into contact with the connector, and the end surface excluding the recess comes into contact with the connector. where S0 is the smaller of the area of ​​the contact surface of the connector with the spacer and the area of ​​the entire end face including the recess of the spacer, and S is the contact area between the connector and the spacer, the contact area ratio S / S0 is 0.2≦S / S0≦0.5, and where a is the height of the spacer and b is the depth of the recess, the depth ratio b / a is 0.15≦b / a≦0.6. It is characterized by:

[0021] The present invention 5 The embodiment is 4 attitude Like The sensor element casing is characterized in that the recess has a linear, cross or circular shape when viewed from above from the end face side of the spacer.

[0022] The present invention 6 The embodiment is 4 or No. 5 attitude Like The sensor element casing is characterized in that the thermal conductivity of the spacer is 32 W / m·K or less. [Effects of the Invention]

[0023] The first to third aspects of the present invention 6 According to this aspect, heat transfer from the connector to the spacer and further to the sealing member can be suppressed, thereby ensuring the strength of the spacer and suppressing thermal deterioration of the sealing member. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view of a main part of a gas sensor 100 taken along the longitudinal direction. [Figure 2] 10 is a schematic perspective view of a spacer 7 showing an example of forming recesses 7b. FIG. [Figure 3] 10A to 10C are plan views illustrating various shapes of the recess 7b. [Figure 4] 10 is a diagram for explaining problems that may occur during assembly of the gas sensor 100 when the value of the contact portion area ratio S / S0 is small. FIG. [Figure 5] 10 is a diagram for explaining a problem that may occur during assembly of the gas sensor 100 when the value of the depth ratio b / a is large. FIG. [Figure 6] 1 is a cross-sectional view taken along the longitudinal direction of a sensor element 10 for detecting NOx. DETAILED DESCRIPTION OF THE INVENTION

[0025] <Gas sensor configuration> 1 is a longitudinal cross-sectional view of a main portion (more specifically, a main body portion) of a gas sensor 100 according to an embodiment of the present invention. More specifically, the cross-sectional view of the gas sensor 100 is shown above the broken line ZL, and only the external appearance of the gas sensor 100 is shown below the broken line ZL.

[0026] The gas sensor 100 detects a predetermined gas component (such as NOx) using a sensor element 10 provided therein. The gas sensor 100 generally has a long, columnar or thin-plate sensor element (detection element) 10 surrounded by a cylindrical body 1, a protective cover 2, a fixing bolt 3, and an outer cylinder 4. The cylindrical body 1, protective cover 2, and outer cylinder 4 together form a housing member (casing) that houses the sensor element 10 inside. Meanwhile, the fixing bolt 3 is annularly attached to the outer surface of the cylindrical body 1.

[0027] The sensor element 10 is arranged coaxially with the cylindrical body 1, protective cover 2, fixing bolt 3, and outer cylinder 4. The direction in which the central axis of the sensor element 10 extends is also referred to as the axial direction. In FIG. 1, the axial direction coincides with the vertical direction as viewed in the drawing.

[0028] More specifically, one end side of the sensor element 10 (for example, the first end E1 side in Figure 6) is surrounded by the protective cover 2, and the other end side protrudes into the outer cylinder 4, and the approximately central part between the two is fixed inside the cylindrical body 1 by a ceramic powder compact or ceramic part (not shown) in a manner that hermetically seals the space between both ends.

[0029] The sensor element 10 is provided with a detection section (for example, a gas inlet, an internal chamber, a detection electrode, etc.) on one end side surrounded by the protective cover 2. In addition, the sensor element 10 is provided with various electrodes and wiring patterns on the surface and inside of the element body.

[0030] For example, in one embodiment of the sensor element 10, the measurement gas 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 amount of oxygen ions flowing inside the element is proportional to the concentration of the target gas component in the measurement gas, and the concentration of the target gas component can be determined based on this.

[0031] The cylindrical body 1 is a metallic cylindrical member also called a metallic shell. The cylindrical body 1 is hardly exposed to the outside of the gas sensor 100, but is provided in a range from the upper end of the protective cover 2 as viewed in the drawing to the lower end of the outer cylinder 4 as viewed in the drawing. The cylindrical body 1 accommodates the sensor element 10 and a fixing part (a powder compact or a ceramic part) that is annularly mounted on the sensor element 10. In other words, the cylindrical body 1 is annularly mounted around an annular part that is annularly mounted around the sensor element 10.

[0032] The protective cover 2 is a substantially cylindrical exterior member that protects a predetermined area on the first end E1 side, which is the portion of the sensor element 10 that comes into direct contact with the gas to be measured during use. The protective cover 2 is fixed by welding to the end of the cylindrical body 1 on the lower side as viewed in the drawing.

[0033] The protective cover 2 is provided with a plurality of through holes H through which gas can pass. The measurement gas that flows into the protective cover 2 through the through holes H is directly detected by the sensor element 10. Note that the type, number, position, and shape of the through holes shown in FIG. 1 are merely examples, and may be determined appropriately taking into consideration the manner in which the measurement gas flows into the protective cover 2.

[0034] The fixing bolt 3 is an annular member used to fix the gas sensor 100 at a measurement position. The fixing bolt 3 has a threaded bolt portion 3a and a holding portion 3b that is held when the bolt portion 3a is screwed. The bolt portion 3a is screwed into a nut provided at the installation position of the gas sensor 100. This fixes the gas sensor 100 at the measurement position with the protective cover 2 side in contact with the gas to be measured. For example, by screwing the bolt portion 3a into a nut provided in an exhaust pipe of an automobile, the gas sensor 100 is fixed to the exhaust pipe with the protective cover 2 side exposed inside the exhaust pipe.

[0035] The outer cylinder 4 is a cylindrical member having one end (the lower end as viewed in the drawing) welded to the outer peripheral end of the upper part (not shown) of the cylindrical body 1. The outer cylinder 4 has a main portion 4a that extends axially from the welded fixed point to the cylindrical body 1 with the same diameter, and a sealing portion 4b that is continuous with the main portion 4a in the axial direction. The sealing portion 4b is an end portion having a smaller diameter than the main portion 4a.

[0036] The internal space of the outer cylinder 4 is filled with a reference gas (atmospheric atmosphere). A connector (also referred to as a contact holding member) 5 and a spacer 7 are disposed inside the main portion 4a.

[0037] On the other hand, the sealing portion 4b is a portion that seals the other end (the upper end as viewed in the drawing) of the outer tube 4 by being crimped from the side with the seal member 6 fitted therein.

[0038] This sealing is achieved by crimping the sealing portion 4b from the outside around its entire circumference at the crimping point 6s, which is a lateral position of the sealing member 6 as viewed in the drawing, thereby generating a reaction force that causes the sealing member 6 to move radially outward.

[0039] The sealing member 6 is made of rubber. Therefore, the sealing member 6 is also called a rubber stopper. The rubber used is typically fluororubber. The sealing member 6 has a uniform cylindrical shape before being fitted into the sealing portion 4b, but is deformed in the radial direction by fitting and further crimping.

[0040] The other end side (for example, the second end E2 side in FIG. 6 ) of the sensor element 10 is inserted into the connector 5. The connector 5 is provided with a plurality of metal contact members 51 that come into contact with a plurality of electrode terminals 160 (see FIG. 6 ) provided on the sensor element 10 when the sensor element 10 is inserted. One end (the lower end as viewed in the drawing) of the contact members 51 forms a hook portion 51a that hooks onto the connector 5, and the other end (the upper end as viewed in the drawing) forms a crimp portion 51b to which the lead wires 8 are crimped and fixed, with the portion therebetween forming a leaf spring shape. The contact members 51 are sandwiched and fixed between the connector 5 and the sensor element 10, thereby electrically connecting the electrode terminals 160 of the sensor element 10 and the contact members 51.

[0041] The spacer 7 is sandwiched (interposed) between the connector 5 and the seal member 6 inside the outer cylinder 4. The spacer 7 has a cylindrical shape with approximately the same diameter as the seal member 6 before crimping. The spacer 7 is provided for the purpose of suppressing a rise in temperature of the seal member 6 when the gas sensor 100 is in use. The spacer 7 will be described in detail later.

[0042] The lead wires 8 are inserted through through holes 9 formed continuously in the sealing member 6 and the spacer 7, one end of which is crimped and fixed to the crimping portion 51b of the contact member 51, and the other end of which is connected to the controller 50 and various power sources (see FIG. 6) external to the gas sensor 100. As a result, the sensor element 10 is electrically connected to the controller 50 and various power sources via the contact members 51 and the lead wires 8. Although FIG. 1 shows only two contact members 51 and two lead wires 8, this is merely for the sake of simplicity, and in reality, the number of lead wires required for the above electrical connections is provided.

[0043] The gas sensor 100 having the above configuration can be fabricated using a conventional method. In brief, first, the connector 5, into which the sensor element 10 has been inserted and the contact member 51 and lead wire 8 have been connected, is placed in the main portion 4a of the outer tube 4 before the crimping portion 6s is crimped. Next, the lead wire 8 is inserted into the spacer 7 and the seal member 6, in that order, through their respective through-holes 9, and they are stacked on top of the connector 5. At the same time, the seal member 6 with the lead wire 8 inserted therein is fitted into the sealing portion 4b before crimping. Usually, air serving as a reference gas has already entered the outer tube 4 before the seal member 6 is fitted. After the seal member 6 is fitted, the crimping portion 6s is crimped using a predetermined crimping means.

[0044] In addition, it is a preferred example that the crimping is performed on the crimping point 6s that extends continuously around the entire outer periphery of the sealing portion 4b, but as long as good crimping fixation is achieved, the crimping point 6s may be discontinuous in the circumferential direction of the sealing portion 4b.

[0045] <Spacer structure and effects> Next, the structure of the spacer 7 and the effects obtained by providing such a structure will be described in detail.

[0046] First, ceramics are selected as the material for the spacer 7 in order to ensure strength. Preferably, ceramics with a thermal conductivity of 32 W / m K or less are selected, which are suitable in terms of heat resistance and low heat conductivity. More preferably, alumina (thermal conductivity: 32 W / m K) or steatite (thermal conductivity: 2 W / m K) is selected.

[0047] Additionally, in this embodiment, a recess 7b is provided on one end surface 7a of the spacer 7. FIG. 2 is a schematic perspective view of the spacer 7 showing an example of the formation of the recess 7b. Note that FIG. 2 illustrates an example in which the recess 7b is provided as a linear groove having a flat bottom surface 7c and a rectangular cross section perpendicular to the longitudinal direction. Note that in FIG. 2, four of the eight through holes 9 (9a) provided in the spacer 7 are present in the step portion between the one end surface 7a and the recess 7b, but this is merely an example, and the arrangement of the through holes 9a is not limited to this.

[0048] 3A and 3B are plan views illustrating various shapes of the recess 7b, with the through-hole 9a not shown.

[0049] Fig. 3(a) shows the same recess 7b as Fig. 2, in the case of a linear groove portion. In contrast, Fig. 3(b) shows recess 7b that is cross-shaped in plan view, with such linear groove portions intersecting at right angles. Fig. 3(c) shows recess 7b that is circular in plan view. The bottom surface 7c of these recess 7b may be flat or curved.

[0050] Regardless of the shape of the spacer 7, the connector 5 is in contact with the spacer 7 at a portion of one end face 7a excluding the recess 7b, as shown in FIG. 1, and is not in contact with the spacer 7 at the recess 7b.

[0051] By adopting such a configuration, in the gas sensor 100 according to this embodiment, heat transfer from the connector 5 to the spacer 7 and further to the sealing member 6 is suppressed compared to a gas sensor 100 having a configuration in which the entire connector 5 is in contact with one end surface 7a of the spacer 7. In other words, the risk of thermal degradation of the sealing member 6 is reduced. Specifically, in a configuration in which the connector 5 and the sealing member 6 are in direct contact with each other, thermal decomposition of the sealing member 6 may occur starting from the contact point with the connector 5, causing outgassing to diffuse and resulting in signal abnormalities. However, in the gas sensor 100 according to this embodiment, the spacer 7 having the recess 7b is interposed between the connector 5 and the sealing member 6, thereby suppressing a temperature rise at the end surface of the sealing member 6. As a result, the risk of signal abnormalities due to thermal decomposition is suitably reduced.

[0052] The shape of the recess 7b is not limited to that shown in Figure 3, and other shapes may be adopted as long as the spacer 7 is suitably held between the connector 5 and the sealing member 6 while heat transfer from the connector 5 to the sealing member 6 is suitably suppressed.

[0053] Preferably, when the smaller of the area of ​​the end face 5e of the connector 5, which is the contact surface with the spacer 7, and the area of ​​the entire one end face 7a including the recess 7b of the spacer 7 is defined as S0 and the contact area S between the connector 5 and the spacer 7, the smaller the ratio of the two (hereinafter also referred to as the contact area ratio) S / S0, the more likely it is that heat transfer from the connector 5 to the spacer 7 and further to the sealing member 6 is suppressed. Note that the area S0 is alternative because, although Figure 1 illustrates an example in which the area of ​​the end face 5e of the connector 5 is larger than the area of ​​the entire one end face 7a of the spacer 7, it is also possible to adopt a configuration in which the size relationship between the two areas is reversed.

[0054] Furthermore, the greater the ratio b / a of the depth b of the recess 7b to the height a of the spacer 7 (hereinafter also referred to as the depth ratio), the more likely it is that heat transfer from the connector 5 to the spacer 7 and further to the sealing member 6 is suppressed. Note that if the bottom surface 7c of the recess 7b is not flat, the distance to the deepest position may be taken as the depth b.

[0055] Although the heat transfer reduction effect should be realized when S / S0<1 or b / a>0, in practice, the substantial heat transfer reduction effect is expected when S / S0≦0.7 or b / a≧0.08. For example, if the spacer 7 is made of steatite, and S / S0≦0.5 and b / a≧0.15, If In this case, the temperature at the contact portion 6a of the sealing member 6 with the spacer 7 can be reduced by at least 2% compared to when the recess 7b is not provided. In particular, when S / S0≦0.5 and b / a≧0.5, the temperature reduction effect is about 3%. In the latter case, when the heat resistance limit temperature of the sealing member 6 is 300°C, a temperature reduction effect of at least 10°C can be expected.

[0056] However, it is preferable that S / S0≧0.2. FIG. 4 is a diagram illustrating a problem that may occur during assembly of the gas sensor 100 when the value of the contact area ratio S / S0 is small. During assembly of the gas sensor 100, the spacer 7 is abutted on the end face 5e of the connector 5, which has the sensor element 10 inserted on the other end side, and the seal member 6 fitted into the sealing portion 4b of the outer tube 4 is abutted on the other end face 7e of the spacer 7 (the face opposite to the one end face 7a). Subsequently, the sealing portion 4b is crimped from the side at the crimping point 6s to reduce its diameter, thereby deforming the seal member 6. As the seal member 6 is deformed, a downward load F1 acts on the spacer 7, as shown in FIG. 4(a).

[0057] At this time, although the spacer 7 is constrained at the top and bottom end faces by the sealing member 6 and the connector 5, the outer periphery is not particularly constrained. Therefore, when the value of S / S0 is small, depending on how the load F1 acts, the spacer 7 may tilt as shown in Figure 4(b), resulting in a malfunction in which the spacer 7 is not properly held between the sealing member 6 and the connector 5, or even in which a force is applied to the sensor element 10 from the side, causing the sensor element 10 to break. When S / S0<0.2, the occurrence of such malfunctions becomes more pronounced.

[0058] Furthermore, it is preferable that b / a≦0.6. Fig. 5 is a diagram for explaining problems that may occur during assembly of the gas sensor 100 when the value of the depth ratio b / a is large.

[0059] As described above, during assembly of the gas sensor 100, a downward load F1 acts on the spacer 7 as the sealing portion 4b of the outer cylinder 4 is crimped and deformed. At the same time, an upward load F2 also acts on the spacer 7 from the connector 5. That is, compressive forces act on the spacer 7 from both above and below. Therefore, if the value of b / a is large and the recess 7b is deep, buckling fracture may occur near the edge portion 7d of the bottom surface 7c. When b / a>0.6, the occurrence of such a defect becomes significant.

[0060] As described above, according to this embodiment, by interposing a ceramic spacer between the connector, which is disposed inside the outer cylinder of the gas sensor and connected to the sensor element, and the seal member, which seals the end of the outer cylinder, and by providing a recess in the spacer where it comes into contact with the connector, it is possible to suppress heat transfer from the connector to the spacer and further to the seal member. This makes it possible to suppress thermal deterioration of the seal member while ensuring the strength of the spacer.

[0061] <Example of sensor element configuration> Finally, as an example of the sensor element 10, the configuration of a sensor element 10 for detecting NOx will be described. FIG. 6 is a longitudinal cross-sectional view of the sensor element 10 for detecting NOx. In this case, the sensor element 10 is a so-called limiting current type gas sensor element. In addition to the sensor element 10, FIG. 6 also shows a pump cell power supply 30, a heater power supply 40, and a controller 50 provided in the gas sensor 100.

[0062] As shown in Fig. 6, the sensor element 10 generally has a configuration in which a first end E1 side of a long, plate-shaped element substrate 11 is covered with a porous tip protective layer 12. The element substrate 11 has a long, plate-shaped ceramic body 101 as its main structure, and is provided with main surface protective layers 170 (170a, 170b) on two main surfaces of the ceramic body 101. Furthermore, the sensor element 10 is provided with tip protective layers 12 (inner tip protective layer 12a, outer tip protective layer 12b) on one end surface (tip surface 101e of the ceramic body 101) on the tip side and on the outside of the four side surfaces.

[0063] In this embodiment, for convenience, the ends of the ceramic body 101 and the sensor element 10 on the side where the first end E1 of the element base 11 is provided will also be referred to as the respective first end E1, and the ends on the side where the second end E2 of the element base 11 is provided will also be referred to as the respective second end E2.

[0064] The ceramic body 101 is made of ceramics containing zirconia (yttrium-stabilized zirconia), which is an oxygen ion conductive solid electrolyte, as its main component. The ceramic body 101 is dense and airtight.

[0065] 6 is a gas sensor element of a so-called serial three-chamber structure type having a first internal chamber 102, a second internal chamber 103, and a third internal chamber 104 inside a ceramic body 101. In other words, in the sensor element 10, the first internal chamber 102 is generally in communication with a gas inlet 105 that opens to the outside at the first end E1 side of the ceramic body 101 (strictly speaking, the gas inlet 105 communicates with the outside via the tip protective layer 12) through a first diffusion-controlling section 110 and a second diffusion-controlling section 120, the second internal chamber 103 is in communication with the first internal chamber 102 through a third diffusion-controlling section 130, and the third internal chamber 104 is in communication with the second internal chamber 103 through a fourth diffusion-controlling section 140. The path from the gas inlet 105 to the third internal chamber 104 is also referred to as a gas flow section. In the sensor element 10 according to this embodiment, the flow portion is provided in a straight line along the longitudinal direction of the ceramic body 101.

[0066] The first diffusion rate-limiting section 110, the second diffusion rate-limiting section 120, the third diffusion rate-limiting section 130, and the fourth diffusion rate-limiting section 140 are each provided as two slits, one above the other, as viewed in the drawing. The first diffusion rate-limiting section 110, the second diffusion rate-limiting section 120, the third diffusion rate-limiting section 130, and the fourth diffusion rate-limiting section 140 provide a predetermined diffusion resistance to the measurement gas passing through them. A buffer space 115 is provided between the first diffusion rate-limiting section 110 and the second diffusion rate-limiting section 120, and has the effect of buffering pulsation of the measurement gas.

[0067] 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 chamber 102. Furthermore, an auxiliary pump electrode 143 is provided in the second internal chamber 103, and a measurement electrode 145, which is a direct detector for the gas component to be measured, is provided in the third internal chamber 104. In addition, a reference gas inlet 106, which is connected to the outside and through which a reference gas is introduced, is provided on the second end E2 side of the ceramic body 101, and a reference electrode 147 is provided within the reference gas inlet 106.

[0068] In the gas sensor 100 including the sensor element 10, the NOx gas concentration in the measurement gas is calculated by the following process.

[0069] First, the measurement gas flows into the protective cover 2 through the through-hole H and is introduced into the first internal chamber 102 through the gas inlet 105. The oxygen concentration of the measurement gas is adjusted to a substantially constant level by the pumping action (oxygen inflow or outflow) of the main pump cell P1, and then the measurement gas is introduced into the second internal chamber 103. The main pump cell P1 is an electrochemical pump cell composed of an outer pump electrode 141, an inner pump electrode 142, and a ceramic layer 101a, which is a part of the ceramic body 101 located between the two electrodes. In the second internal chamber 103, oxygen in the measurement gas is pumped out of the element by the pumping action of the auxiliary pump cell P2, which is also an electrochemical pump cell, to achieve a sufficiently low oxygen partial pressure in the measurement gas. The auxiliary pump cell P2 is composed of an outer pump electrode 141, an auxiliary pump electrode 143, and a ceramic layer 101b, which is a part of the ceramic body 101 located between the two electrodes.

[0070] The outer pump electrode 141, the inner pump electrode 142, and the auxiliary pump electrode 143 are formed as porous cermet electrodes (for example, a cermet electrode of Pt and ZrO containing 1% Au). The inner pump electrode 142 and the auxiliary pump electrode 143, which come into contact with the measurement gas, are made of a material that has a weakened or no reducing ability for the NOx component in the measurement gas.

[0071] The NOx in the measurement gas, which has been brought to a low-oxygen partial pressure state by the auxiliary pump cell P2, is introduced into the third internal chamber 104 and reduced or decomposed at the measurement electrode 145 provided in the third internal chamber 104. The measurement electrode 145 is a porous cermet electrode that also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere within the third internal chamber 104. During this reduction or decomposition, the potential difference between the measurement electrode 145 and the reference electrode 147 is maintained constant. Oxygen ions generated by the reduction or decomposition are pumped to the outside of the element by the measurement pump cell P3. The measurement pump cell P3 is composed of the external pump electrode 141, the measurement electrode 145, and the ceramic layer 101c, which is part of the ceramic body 101 located between the two electrodes. The measurement pump cell P3 is an electrochemical pump cell that pumps out oxygen generated by the decomposition of NOx in the atmosphere surrounding the measurement electrode 145.

[0072] Pumping (pumping of oxygen in or out) in the main pump cell P1, the auxiliary pump cell P2, and the measurement pump cell P3 is achieved by applying a voltage required for pumping between the electrodes of each pump cell by a pump cell power supply (variable power supply) 30 under the control of a controller 50. In the case of the measurement pump cell P3, a voltage is applied between the external pump electrode 141 and the measurement electrode 145 so that the potential difference between the measurement electrode 145 and the reference electrode 147 is maintained at a predetermined value. A pump cell power supply 30 is usually provided for each pump cell.

[0073] The controller 50 detects the pump current Ip2 flowing between the measurement electrode 145 and the external pump electrode 141 in accordance with the amount of oxygen pumped out by the measurement pump cell P3, and calculates the NOx concentration in the measured gas based on the fact that there is a linear relationship between the current value (NOx signal) of this pump current Ip2 and the concentration of decomposed NOx.

[0074] Preferably, the gas sensor 100 includes a plurality of electrochemical sensor cells (not shown) that detect the potential difference between each pump electrode and the reference electrode 147, and the controller 50 controls each pump cell based on the detection signals of these sensor cells.

[0075] Furthermore, in the sensor element 10, a heater 150 is embedded inside the ceramic body 101. The heater 150 is provided on the lower side of the gas flow section as viewed in FIG. 6 , extending from the vicinity of the first end E1 to at least the positions where the measurement electrode 145 and the reference electrode 147 are formed. The heater 150 generates heat by receiving power from a heater power supply 40 under the control of a controller 50. The heater 150 is provided mainly for the purpose of heating the sensor element 10 to increase the oxygen ion conductivity of the solid electrolyte constituting the ceramic body 101 when the sensor element 10 is in use. The sensor element 10 is heated so that the temperature in at least the range from the first internal chamber 102 to the second internal chamber 103 reaches 500°C or higher.

[0076] More specifically, the heater 150 is a resistance heating element made of, for example, platinum, and is provided in such a manner that its periphery is surrounded by an insulating layer 151 .

[0077] A plurality of electrode terminals 160 for establishing electrical connection between the sensor element 10 and the outside are formed on each main surface of the ceramic body 101 near the second end E2. These electrode terminals 160 are electrically connected in a predetermined correspondence to the five electrodes, both ends of the heater 150, and internal wiring (not shown) for detecting heater resistance, via internal wiring (not shown) provided inside the ceramic body 101. As described above, the electrode terminals 160 are connected to the lead wires 8 via the contact members 51. Application of voltage from the pump cell power supply 30 to each pump cell of the sensor element 10 and heating of the heater 150 by power supply from the heater power supply 40 are performed via the lead wires 8, the contact members 51, and the electrode terminals 160.

[0078] The main surface protection layer 170 is a layer made of alumina, has a thickness of about 5 μm to 30 μm, and has pores with a porosity of about 20% to 40%, and is provided for the purpose of preventing foreign matter and poisonous substances from adhering to the two main surfaces of the ceramic body 101 and the external pump electrode 141. Therefore, one of the main surface protection layers 170a also functions as a pump electrode protection layer that protects the external pump electrode 141.

[0079] The tip protective layer 12 is provided on the outermost periphery of the element substrate 11 within a predetermined range from the first end E1. The tip protective layer 12 is provided to surround a portion of the element substrate 11 that becomes hot (up to approximately 700°C to 800°C) when the gas sensor 100 is in use, thereby ensuring water resistance at that portion and preventing cracks (water-induced cracking) in the element substrate 11 from occurring due to thermal shock caused by a local temperature drop caused by direct exposure of that portion to water.

[0080] In addition, the tip protection layer 12 is provided to prevent poisoning substances such as Mg from entering the inside of the sensor element 10, thereby ensuring poison resistance.

[0081] The inner tip protective layer 12a is made of alumina and has a porosity of 45% to 60% and a thickness of 450 μm to 650 μm. The outer tip protective layer 12b is made of alumina and has a porosity of 10% to 40%, which is lower than that of the inner tip protective layer 12a, and a thickness of 50 μm to 300 μm. The inner tip protective layer 12a is provided as a layer with low thermal conductivity, and has the function of suppressing heat conduction from the outside to the element base 11.

[0082] The inner tip protective layer 12a and the outer tip protective layer 12b are formed by sequentially spraying (plasma spraying) the respective constituent materials onto the element substrate 11 on the surface of which the underlayer 13 is formed.

[0083] 6, an underlayer 13 is provided between the inner tip protective layer 12a and the element substrate 11 to ensure adhesion of the inner tip protective layer 12a. The underlayer 13 is provided on at least two main surfaces of the element substrate 11. The underlayer 13 is made of alumina, has a porosity of 30% to 60%, and is formed to a thickness of 15 μm to 50 μm.

[0084] <Modification> In the above-described embodiment, a limiting current type sensor element having three internal chambers and detecting NOx as a gas component is exemplified as the sensor element 10. However, the number of internal chambers does not have to be three in the sensor element 10 provided in the gas sensor 100, and a gas component other than NOx may be detected as a detection target. Alternatively, the sensor element may be a mixed potential type sensor element or other sensor element having a structure without an internal chamber. [Example]

[0085] A gas sensor 100 having a fluororubber sealing member 6 and a steatite spacer 7 was attached to a pipe through which a high-temperature gas to be measured flows, and a CAE simulation was performed to determine the temperature (steady-state temperature) at the contact portion 6a of the sealing member 6 with the spacer 7, thereby determining the temperature reduction effect of the spacer 7.

[0086] The temperature of the gas flowing through the pipe was set to 850°C, and the flow rate was set to 4.85 m / sec. The gas sensor 100 was attached to the pipe by screwing the bolt portion 3a into a nut provided at a predetermined attachment position. The temperature outside the pipe (the temperature around the gas sensor 100) was set to 25°C. The operating temperature of the sensor element 10 (the set heating temperature of the heater 150) was set to 850°C.

[0087] The gas sensor 100 used had a larger area for the entire one end face 7a of the spacer 7, including the recess 7b, than the area for the end face 5e of the connector 5, and the recess 7b of the spacer 7 formed a linear groove as shown in Figures 2 and 3(a), but the depth ratio b / a was set to two different levels (Example 1 and Example 2). Specifically, the value was set to 0.15 (Example 1) and 0.5 (Example 2). The contact area ratio S / S0 was set to 0.459.

[0088] As a comparative example for obtaining a reference for the steady-state temperature, a simulation was also performed under the same conditions for a gas sensor 100 having the same configuration as in Examples 1 and 2 except that it did not have the recess 7b.

[0089] Table 1 lists the contact area ratio S / S0 and depth ratio b / a for Examples 1 and 2 (these are also shown for Comparative Example 1), the evaluation results of the temperature reduction effect based on the maximum temperature of the contact part 6a, and the ratio of the temperature of the contact part 6a when the value for Comparative Example 1 is set to 1.

[0090] [Table 1]

[0091] In assessing the temperature reduction effect, it was determined that the gas sensor 100 in which the temperature of the contact portion 6a was 6°C or more lower than that of Comparative Example 1 had a good temperature reduction effect on the sealing member 6 due to the provision of the recess 7b in the spacer 7. Example 2, which met this criteria, is marked with a circle (◯) in the evaluation result column of Table 1.

[0092] On the other hand, for the gas sensor 100 in which the temperature of the contact portion 6a was 1°C or more but less than 6°C lower than that of Comparative Example 1, it was determined that the temperature reduction effect of the sealing member 6 due to the provision of the recess 7b in the spacer 7 was achieved to a certain extent. For Example 1 that fell into this category, a "△" (triangle mark) is marked in the judgment result column of Table 1.

[0093] In addition, for gas sensors 100 in which the temperature of the contact portion 6a is less than 1°C lower than that of Comparative Example 1 or is equal to or higher than that of Comparative Example 1, it was determined that the temperature reduction effect of the sealing member 6 due to the provision of the recess 7b in the spacer 7 was not obtained, but this did not apply to either the gas sensors 100 of Example 1 or Example 2.

[0094] The results shown in Table 1 confirm that the gas sensor 100 of Example 1, which has recesses 7b that satisfy 0.2≦S / S0≦0.5 and 0.15≦b / a≦0.6, can reduce the temperature of the contact portion 6a of the sealing member 6 with the spacer 7 by a little more than 2%. Furthermore, the gas sensor 100 of Example 2, which has recesses 7b that satisfy 0.2≦S / S0≦0.5 and 0.5≦b / a≦0.6, can reduce the temperature of the contact portion 6a of the sealing member 6 with the spacer 7 by a little more than 3%. [Explanation of symbols]

[0095] 1. Cylindrical body 2 Protective Cover 3 Fixing bolts 3a Bolt section 3b Holding part 4 outer cylinder 4a (Main part of the outer tube) 4b (Outer cylinder) sealing part 5 Connectors 6 Sealing material 7 spacers 8 Lead Wires 9 through holes 10 Sensor element 11 Element substrate 12 Tip protection layer 13 Base layer 51 Contact parts 100 Gas Sensor 101 Ceramic body 106 Reference gas inlet 150 heater 160 Electrode terminal 170 Main surface protective layer

Claims

1. A gas sensor for detecting a predetermined gas component contained in a measurement gas, a sensor element having a detection portion on one end side; a casing in which the sensor element is housed and fixed; a connector disposed inside the casing and electrically connecting the sensor element to the outside; Equipped with The casing is an outer cylinder including a main portion in which a reference gas is present and a sealing portion which is an end portion having a smaller diameter than the main portion, and the other end side of the sensor element protruding from the main portion; a rubber seal member that is fitted into the sealing portion to seal the outer cylinder; a spacer made of steatite interposed between the seal member and the connector inside the outer cylinder; Equipped with the spacer has a recess on an end surface that contacts the connector, and the end surface excluding the recess contacts the connector; When the smaller of the area of ​​the contact surface of the connector with the spacer and the area of ​​the entire end face including the recess of the spacer is defined as S0 and the contact area between the connector and the spacer is defined as S, the contact area ratio S / S0 is as follows: 0.2≦S / S0≦0.5 and When the height of the spacer is a and the depth of the recess is b, the depth ratio b / a is as follows: 0.15≦b / a≦0.6 A gas sensor characterized by:

2. 2. The gas sensor according to claim 1, The recess has a linear, cross, or circular shape in a plan view from the end face side of the spacer. A gas sensor characterized by:

3. 3. The gas sensor according to claim 1, The thermal conductivity of the spacer is 32 W / m K or less. A gas sensor characterized by:

4. A casing that houses a sensor element having a detection unit at one end thereof that detects a predetermined gas component contained in a measurement gas, and a connector that electrically connects the sensor element to the outside, while fixing the sensor element therein, an outer cylinder including a main portion in which a reference gas is present and a sealing portion which is an end portion having a smaller diameter than the main portion, the other end side of the sensor element being disposed so as to protrude from the main portion; a rubber seal member that is fitted into the sealing portion to seal the outer cylinder; a spacer made of steatite interposed between the seal member and the connector inside the outer cylinder; Equipped with the spacer has a recess on an end surface that contacts the connector, and the end surface excluding the recess contacts the connector; When the smaller of the area of ​​the contact surface of the connector with the spacer and the area of ​​the entire end face including the recess of the spacer is defined as S0 and the contact area between the connector and the spacer is defined as S, the contact area ratio S / S0 is as follows: 0.2≦S / S0≦0.5 and When the height of the spacer is a and the depth of the recess is b, the depth ratio b / a is as follows: 0.15≦b / a≦0.6 A sensor element accommodating casing, characterized in that:

5. 5. The sensor element accommodating casing according to claim 4, The recess has a linear, cross, or circular shape in a plan view from the end face side of the spacer. A sensor element accommodating casing.

6. 6. The sensor element accommodating casing according to claim 4 or claim 5, The thermal conductivity of the spacer is 32 W / m K or less. A sensor element accommodating casing.

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