Sensor element and gas sensor

Abstract

To provide a sensor element and a gas sensor of which output is prevented from changing due to variations in the size of a diffusion resistance layer.SOLUTION: A sensor element 100 for detecting the concentration of a specific gas in a measurement target gas includes: a measurement room 107c arranged in a sensor element for measuring the concentration of a specific gas; and a diffusion resistance layer 115 leading to the measurement room from the outer surface of the sensor element, the diffusion resistance layer introducing the measurement gas into the measurement room. When the cross-sectional area of a first site 115a, which faces the outer surface of the sensor element, of the diffusion resistance layer is denoted by S1, the diffusion resistance layer has a second site 115b on the measurement room side, the second site having a smaller cross-sectional area than S1 at the side of the measurement room closer than the first site.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a sensor element and a gas sensor that are suitably used for detecting the concentration of a specific gas contained in, for example, combustion gas or exhaust gas from a combustor, an internal combustion engine, or the like. [Background technology]

[0002] Conventionally, gas sensors have been used to detect the concentration of specific components (oxygen, etc.) in exhaust gas from internal combustion engines. The gas sensor has a sensor element therein, and the sensor element has a cell made of, for example, a solid electrolyte and a pair of electrodes, and the cell is provided in a measurement chamber that forms the internal space of the sensor element. A porous diffusion resistance layer that realizes gas diffusion under a predetermined rate-limiting condition is disposed between the outside and the measurement chamber (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6809361 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the diffusion resistance layer is formed by printing and baking a paste for the diffusion resistance layer on the communication part between the outside and the measurement chamber. However, printing misalignment or the like can cause the dimensions of the diffusion resistance layer (particularly the cross-sectional area) to deviate from the set values, which changes the air resistance and causes the output of the sensor element to fluctuate. Therefore, the output of each sensor element after manufacture is measured, and sensor elements whose output is outside a set range are subjected to post-processing such as inserting a filler in the communication portion or removing part of the diffusion resistance layer.

[0005] However, this post-processing itself is troublesome, and since it is impossible to predict the number of sensor elements that will require post-processing, it is difficult to prepare processing equipment and personnel. SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a sensor element and a gas sensor in which output fluctuations caused by dimensional variations in the diffusion resistance layer are suppressed. [Means for solving the problem]

[0006] In order to solve the above problems, the sensor element of the present invention is a sensor element for detecting a concentration of a specific gas in a measured gas, comprising: a measurement chamber for measuring the concentration of the specific gas, which is disposed inside the sensor element; and a diffusion resistance layer communicating with the measurement chamber from an outer surface of the sensor element and introducing the measured gas into the measurement chamber, wherein when a cross-sectional area of ​​a first portion of the diffusion resistance layer facing the outer surface of the sensor element is S1, the diffusion resistance layer has a second portion on the measurement chamber side of the first portion and having a cross-sectional area smaller than S1.

[0007] Generally, the diffusion resistance layer is formed by printing and baking a paste for the diffusion resistance layer in the communication part between the outer surface of the sensor element and the measurement chamber. However, printing misalignment or other reasons may cause the dimensions of the diffusion resistance layer (especially the cross-sectional area) to deviate from the set values, which may change the air flow resistance and cause the output of the sensor element to fluctuate. In particular, printing misalignment during the formation of the diffusion resistance layer becomes greater on the outer surface side of the sensor element.

[0008] Therefore, if a second portion having a smaller cross-sectional area S2 than the cross-sectional area S1 of the first portion facing the outer surface of the sensor element is provided on the measurement chamber side (inner side of the sensor element), the gas diffusion in the diffusion resistance layer is rate-determined by the second portion having the smaller cross-sectional area S2. Furthermore, since the second portion is located on the inner side of the sensor element, printing misalignment is smaller than that of the first portion, and output fluctuations caused by dimensional variations in the diffusion resistance layer due to printing misalignment can be suppressed.

[0009] In the sensor element of the present invention, when a cross-sectional area of ​​a third portion of the diffusion resistance layer connected to the measurement chamber is designated as S3, the cross-sectional area S3 may be larger than the cross-sectional area S2 of the second portion. The printing misalignment during the formation of the diffusion resistance layer is largest in the third region, next to the first region. Therefore, by making S3>S2, the gas diffusion rate of the diffusion resistance layer is determined by the second portion, which has the smallest cross-sectional area S2. Since the second portion has a smaller printing misalignment than the first and third portions, it is possible to further suppress output fluctuations caused by dimensional variations in the diffusion resistance layer due to printing misalignment.

[0010] In the sensor element of the present invention, two or more of the diffusion resistance layers may be provided on one outer surface of the sensor element. The smaller the cross-sectional area S2 of the second portion, the more rate-determining the gas diffusion in the diffusion resistance layer becomes. For this reason, providing two diffusion resistance layers with a cross-sectional area S2 = 0.5 (arbitrary unit) per outer surface can further suppress output fluctuations due to printing misalignment, even if the total cross-sectional area of ​​the diffusion resistance layers is the same, than providing one diffusion resistance layer with a cross-sectional area S2 = 1 (arbitrary unit) per outer surface.

[0011] In the sensor element of the present invention, a length L2 of a portion where the cross-sectional area S2 is smallest along a direction from an outer surface of the sensor element toward the measurement chamber may be longer than a length L1 of a portion where the cross-sectional area is S1 along the first portion. According to this sensor element, the length L2 of the portion where the cross-sectional area S2 that determines the gas diffusion rate of the diffusion resistance layer is the smallest is sufficiently long, thereby further suppressing the influence of printing misalignment in the first portion and reliably suppressing fluctuations in the sensor output.

[0012] The gas sensor of the present invention is characterized in that, in the gas sensor comprising a sensor element for detecting the concentration of a specific gas component in a gas to be measured and a housing for holding the sensor element, the sensor element is used as described above. Effect of the Invention

[0013] According to the present invention, it is possible to obtain a sensor element and a gas sensor in which the output fluctuation caused by the dimensional variation of the diffusion resistance layer is suppressed. [Brief description of the drawings]

[0014] [Figure 1]1 is a cross-sectional view taken along the longitudinal direction of a gas sensor (oxygen sensor) according to an embodiment of the present invention. [Diagram 2] FIG. [Diagram 3] FIG. 2 is a schematic cross-sectional view perpendicular to the axial direction of the sensor element. [Figure 4] FIG. 2 is a plan view showing a measurement chamber and a diffusion resistance layer of the sensor element. [Diagram 5] FIG. 13 is a plan view showing a modified example of the diffusion resistance layer. [Figure 6] FIG. 13 is a plan view showing another modified example of the diffusion resistance layer. [Figure 7] FIG. 13 is a plan view showing still another modified example of the diffusion resistance layer. [Figure 8] FIG. 13 is a diagram showing the flow velocity in a simulation showing the change in sensor output when the width X of the second portion of the diffusion resistance layer is changed. [Figure 9] FIG. 13 is a diagram showing a simulation result. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view along the longitudinal direction (axis L direction) of a gas sensor (oxygen sensor) 1 according to a first embodiment of the present invention, FIG. 2 is a schematic exploded perspective view of a sensor element 100 (detection element portion 170 and heater portion 150), and FIG. 3 is a cross-sectional view perpendicular to the axis L direction of the sensor element 100.

[0016] 1, the gas sensor 1 includes a sensor element (oxygen sensor element) 100 including a detection element portion 170 and a heater portion 150 laminated on the detection element portion 170, a metal shell (housing) 30 that holds the sensor element 100 and the like therein, and a protector 24 that is attached to the tip of the metal shell 30. The sensor element 100 is disposed so as to extend in the direction of the axis L.

[0017] 2, the heater section 150 includes a first base 101 and a second base 103 mainly made of alumina, and a heating element 102 mainly made of platinum sandwiched between the first base 101 and the second base 103. The heating element 102 includes a heating portion 102a located at the tip side, and a pair of heater lead portions 102b extending from the heating portion 102a along the longitudinal direction of the first base 101. The terminals of the heater lead portions 102b are electrically connected to the heater side pads 120 via conductors formed in heater side through holes 101a provided in the first base 101. The first base 101 and the second base 103 are laminated to form an insulating ceramic body.

[0018] The detection element section 170 includes an oxygen concentration detection cell 130 and an oxygen pump cell 140 . The oxygen concentration detection cell 130 is formed of a first solid electrolyte body 105c, and a first electrode 104 and a second electrode 106 formed on both sides of the first solid electrolyte body 105c. The tip side of the first support 105, which is mainly made of alumina, is hollowed out in a rectangular shape, and the first solid electrolyte body 105c is embedded in this hollowed out portion. The outer dimensions of the first support 105 are the same as those of the gas sensor 1, and one first through-hole 105a is provided on the rear end side of the first support 105. The first electrode 104 is formed of a first electrode portion 104a and a first lead portion 104b extending from the first electrode portion 104a along the longitudinal direction of the first support 105. The second electrode 106 is formed of a second electrode portion 106a and a second lead portion 106b extending from the second electrode portion 106a along the longitudinal direction of the first support 105. The first electrode 104 and the second electrode 106 constitute a reference electrode and a detection electrode, respectively.

[0019] An end of the first lead portion 104b is electrically connected to the detection element side pad 121 via conductors formed in the first through hole 105a, the second through hole 107a provided in the insulating layer 107 described below, the fourth through hole 109a provided in the second solid electrolyte body 109, and the sixth through hole 111a provided in the protective layer 111. On the other hand, an end of the second lead portion 106b is electrically connected to the detection element side pad 121 via conductors formed in the third through hole 107b provided in the insulating layer 107 described below, the fifth through hole 109b provided in the second support 109 described below, and the seventh through hole 111b provided in the protective layer 111.

[0020] On the other hand, the oxygen pump cell 140 is formed of a second solid electrolyte body 109c, and a third electrode 108 and a fourth electrode 110 formed on both sides of the second solid electrolyte body 109c. The tip side of the second support 109 mainly made of alumina is hollowed out in a rectangular shape, and the second solid electrolyte body 109c is embedded in this hollowed out portion. The outer dimensions of the second support 109 are the same as those of the gas sensor 1, and a fourth through hole 109a and a fifth through hole 109b are provided on the rear end side of the second support 109. The third electrode 108 is formed of a third electrode portion 108a and a third lead portion 108b extending from the third electrode portion 108a along the longitudinal direction of the second support 109. The fourth electrode 110 is formed of a fourth electrode portion 110a and a fourth lead portion 110b extending from the fourth electrode portion 110a along the longitudinal direction of the second support 109.

[0021] An end of the third lead portion 108b is electrically connected to the detection element side pad 121 via a conductor formed in each of the fifth through hole 109b and the seventh through hole 111b provided in the protective layer 111. Meanwhile, an end of the fourth lead portion 110b is electrically connected to the detection element side pad 121 via a conductor formed in an eighth through hole 111c provided in the protective layer 111, which will be described later. The second lead portion 106b and the third lead portion 108b are at the same potential.

[0022] The first solid electrolyte body 105c and the second solid electrolyte body 109c are made of zirconia (ZrO 2 ) with yttria (Y 2 O 3 ) or calcia (CaO) is added to form a partially stabilized zirconia sintered body.

[0023] The heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side pad 120, and the detection element side pad 121 can be made of a platinum group element. Suitable platinum group elements for making these include Pt, Rh, Pd, etc., and these can be used alone or in combination of two or more kinds.

[0024] However, in consideration of heat resistance and oxidation resistance, it is more preferable that the heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side pad 120, and the detection element side pad 121 are mainly made of Pt. Furthermore, it is preferable that the heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater side pad 120, and the detection element side pad 121 contain a ceramic component in addition to the platinum group element that is the main component. From the viewpoint of adhesion, it is preferable that this ceramic component is the same component as the main material on the laminated side (for example, the main component of the first solid electrolyte body 105c and the second solid electrolyte body 109c).

[0025] An insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130. The insulating layer 107 is composed of an insulating portion 114 and a diffusion resistance layer 115. A hollow measurement chamber 107c is formed in the insulating portion 114 of the insulating layer 107 at a position corresponding to the second electrode portion 106a and the third electrode portion 108a. This measurement chamber 107c communicates with the outside in the width direction of the insulating layer 107, and a diffusion resistance layer 115 that realizes gas diffusion between the outside and the measurement chamber 107c under predetermined rate-limiting conditions is disposed in the communication portion.

[0026] The insulating portion 114 is not particularly limited as long as it is a ceramic sintered body having insulating properties, and examples thereof include oxide ceramics such as alumina and mullite.

[0027] The diffusion resistance layer 115 is a porous body made of alumina, and serves to regulate the flow rate of the measurement gas into the measurement chamber 107c. The sensor element 100 has four outer surfaces (side surfaces) along the axis L direction, and in this example, two opposing outer surfaces 100A, 100B (FIG. 3) are each provided with two diffused resistance layers 115.

[0028] As described above, the sensor element 100 has at least a detection cell (such as the oxygen concentration detection cell 130) that detects the concentration of a specific gas, and may further have other cells such as a pump cell (such as the oxygen pump cell 140). These cells have a solid electrolyte body and a pair of electrodes. One of a pair of electrodes of at least one cell faces the measurement chamber 107c.

[0029] A protective layer 111 is formed on the surface of the second solid electrolyte body 109c so as to sandwich the fourth electrode 110. The protective layer 111 is composed of a porous electrode protective portion 113a for protecting the fourth electrode portion 110a from poisoning by sandwiching the fourth electrode portion 110a, and a reinforcing portion 112 for protecting the second solid electrolyte body 109c by sandwiching the fourth lead portion 110b. In the sensor element 100 of this embodiment, the direction and magnitude of the current flowing between the electrodes of the oxygen pump cell 140 are adjusted so that the voltage (electromotive force) generated between the electrodes of the oxygen concentration detection cell 130 becomes a predetermined value (for example, 450 mV), and oxygen in the measurement chamber 107c is pumped. The sensor element 100 constitutes an oxygen sensor element that linearly detects the oxygen concentration in the measurement gas according to the current flowing through the oxygen pump cell 140.

[0030] Returning to FIG. 1, the metal shell 30 is made of SUS430 and has a male threaded portion 31 for mounting the gas sensor to the exhaust pipe and a hexagonal portion 32 to which a mounting tool is applied during mounting. The metal shell 30 is also provided with a metal side step 33 that protrudes radially inward, and this metal side step 33 supports a metal holder 34 for holding the sensor element 100. Inside the metal holder 34, a ceramic holder 35 and talc 36 are arranged in this order from the front end. The talc 36 is composed of a first talc 37 arranged in the metal holder 34 and a second talc 38 arranged across the rear end of the metal holder 34. The first talc 37 is compressed and filled in the metal holder 34, thereby fixing the sensor element 100 to the metal holder 34. The second talc 38 is compressed and filled in the metal shell 30, thereby ensuring sealing between the outer surface of the sensor element 100 and the inner surface of the metal shell 30. An alumina sleeve 39 is disposed on the rear end side of the second talc 38. This sleeve 39 is formed in a multi-stage cylindrical shape, has an axial hole 39a along the axis, and has the sensor element 100 inserted therein. The crimped portion 30a on the rear end side of the metal shell 30 is bent inward, and the sleeve 39 is pressed against the front end side of the metal shell 30 via a stainless steel ring member 40.

[0031] A metal protector 24 having a plurality of gas intake holes 24a and covering the tip portion of the sensor element 100 protruding from the tip of the metal shell 30 is attached by welding to the outer periphery on the tip side of the metallic shell 30. The protector 24 has a double structure, with a bottomed cylindrical outer protector 41 having a uniform outer diameter on the outside and a bottomed cylindrical inner protector 42 with a rear end 42a having an outer diameter larger than the outer diameter of a tip end 42b on the inside.

[0032] Meanwhile, the front end side of an outer tube 25 made of SUS430 is inserted into the rear end side of the metallic shell 30. The outer tube 25 has an expanded diameter front end portion 25a fixed to the metallic shell 30 by laser welding or the like. A separator 50 is disposed inside the rear end side of the outer tube 25, and a holding member 51 is interposed in the gap between the separator 50 and the outer tube 25. The holding member 51 engages with a protruding portion 50a of the separator 50, which will be described later, and is fixed to the outer tube 25 and the separator 50 by crimping the outer tube 25.

[0033] Further, the separator 50 has a through hole 50b extending from the front end side to the rear end side for inserting the lead wires 11-15 for the detection element section 170 and the heater section 150 (the lead wires 14 and 15 are not shown). The through hole 50b accommodates a connection terminal 16 for connecting the lead wires 11-15 to the detection element side pad 121 of the detection element section 170 and the heater side pad 120 of the heater section 150. Each of the lead wires 11-15 is connected to a connector (not shown) on the outside. Electrical signals are input and output between the external device such as an ECU and each of the lead wires 11-15 via this connector. Although not shown in detail, each of the lead wires 11-15 has a structure in which the conductor is covered with an insulating film made of resin.

[0034] Furthermore, a substantially cylindrical rubber cap 52 is disposed on the rear end side of the separator 50 to close the opening 25b on the rear end side of the outer tube 25. This rubber cap 52 is fixed to the outer tube 25 by crimping the outer periphery of the outer tube 25 radially inward while attached inside the rear end of the outer tube 25. Through holes 52a for inserting the lead wires 11 to 15 are also formed through the rubber cap 52 from the front end side to the rear end side.

[0035] Next, a characteristic feature of the present invention will be described with reference to Fig. 4. Fig. 4 is a plan view showing the measurement chamber 107c and the diffusion resistance layer 115 of the sensor element 100. As shown in FIG. 4, a total of four diffusion resistance layers 115 are provided, and each diffusion resistance layer 115 is formed in a substantially H-shape. When the cross-sectional area of ​​the first portion 115a of the diffusion resistance layer 115 facing the outer surface 100A (100B) of the sensor element 100 is S1, the diffusion resistance layer 115 has a second portion 115b on the measurement chamber 107c side from the first portion 115a, the second portion 115b having a cross-sectional area S2 smaller than S1.

[0036] Generally, the diffusion resistance layer 115 is formed by printing and baking a paste for the diffusion resistance layer in the communication part between the outer surface 100A (100B) of the sensor element 100 and the measurement chamber 107c. However, printing misalignment or the like may cause the dimensions (particularly the cross-sectional area) of the diffusion resistance layer 115 to deviate from the set values, which may change the air resistance and cause the output of the sensor element to fluctuate. In particular, printing misalignment during the formation of the diffusion resistance layer 115 becomes large on the outer surface 100A side of the sensor element 100.

[0037] Therefore, if a second portion 115b having a smaller cross-sectional area S2 than the cross-sectional area S1 of the first portion 115a facing the outer surface 100A of the sensor element 100 is provided on the measurement chamber 107c side (the inner side of the sensor element 100), the gas diffusion of the diffusion resistance layer 115 is rate-determined by the second portion 115b having the smaller cross-sectional area S2. Since the second portion 115b is located inside the sensor element 100, printing misalignment is smaller than that of the first portion 115a, and output fluctuations caused by dimensional variations in the diffusion resistance layer 115 due to printing misalignment can be suppressed.

[0038] In this example, when the cross-sectional area of ​​the third portion 115c of the diffusion resistance layer 115 connected to the measurement chamber 107c is S3, S3 is larger than S2. The printing misalignment during the formation of the diffusion resistance layer 115 is largest in the third portion 115c after the first portion 115a. Therefore, by making S3>S2, the rate of gas diffusion in the diffusion resistance layer 115 is determined by the second portion 115b, which has the smallest cross-sectional area S2. Since the second portion 115b has smaller printing misalignment than the first portion 115a and the third portion 115c, it is possible to further suppress output fluctuations caused by dimensional variations in the diffusion resistance layer 115 due to printing misalignment.

[0039] In this example, two (or more) diffusion resistance layers 115 are provided on each outer surface 100A (100B) of the sensor element 100. The smaller the cross-sectional area S2 of the second portion 115b, the more rate-determining the gas diffusion in the diffusion resistance layer 115. For this reason, providing two diffusion resistance layers 115 with a cross-sectional area S2 = 0.5 (arbitrary unit) per outer surface 100A (100B) can further suppress output fluctuations due to printing misalignment, even if the total cross-sectional area of ​​the diffusion resistance layers 115 is the same, rather than providing one diffusion resistance layer 115 with a cross-sectional area S2 = 1 (arbitrary unit) per outer surface 100A (100B).

[0040] Furthermore, in this example, along the direction from the outer surface 100A of the sensor element 100 toward the measurement chamber 107c, the length L2 of the portion where the cross-sectional area S2 is the smallest (in this example, the entire second portion 115b) is longer than the length L1 of the portion along the first portion 115a where the cross-sectional area is S1 (in this example, the entire first portion 115a). In this way, the length L2 of the portion where the cross-sectional area S2 that determines the rate of gas diffusion in the diffusion resistance layer 115 is the smallest becomes sufficiently long, thereby further suppressing the effects of printing misalignment in the first portion 115a and reliably suppressing fluctuations in the sensor output.

[0041] The present invention is not limited to the above-described embodiments. The shape of the diffusion resistance layer is not limited. For example, as shown in FIG. 5, the diffusion resistance layer 215 may be U-shaped in plan view, with the first portion 215a and the third portion 215c being the longest.

[0042] 6, the diffusion resistance layer 315 may be gradually narrowed from the outer surface 100A of the sensor element 100 toward the measurement chamber 107c in a plan view. In the case of this diffusion resistance layer 315, the portion of the diffusion resistance layer 315 connected to the measurement chamber 107c is the second portion 315b, and the third portion 115c does not exist. However, the lengths L1 and L2 are not clear for the diffusion resistance layer 315. Therefore, the length L1 is set to a position from the first portion 315a toward the measurement chamber 107c where the cross-sectional area is S1×0.8. Similarly, the length L2 is set to a position from the position where the cross-sectional area of ​​the diffusion resistance layer 315 is the minimum SS to a position where the cross-sectional area is SS×1.2. The above coefficients of 0.8 and 1.2 mean that the areas covered are those that change by 20% from the cross-sectional areas S1 and SS.

[0043] Also, as shown in FIG. 7, when viewed from above, the diffusion resistance layer 415 may be gradually narrowed from the outer surface 100A of the sensor element 100 toward the measurement chamber 107c, forming a neck portion with a minimum cross-sectional area SS, and then expanding toward the measurement chamber 107c. In the case of the diffusion resistance layer 415, the lengths L1 and L2 are not clear, so they are determined in the same manner as in the case of the diffusion resistance layer 315. However, the length L2 is the distance between the position where the cross-sectional area SS changes by 20% toward the first portion (the outer surface of the sensor element) and the position where the cross-sectional area SS changes by 20% toward the measurement chamber 107c.

[0044] The present invention is applicable to any gas sensor (sensor element) having a measurement chamber and a diffusion resistance layer, and can be applied to the oxygen sensor (oxygen sensor element) of the present embodiment, but it goes without saying that the present invention is not limited to these applications and covers various modifications and equivalents that fall within the spirit and scope of the present invention. For example, the present invention may be applied to a NOx sensor (NOx sensor element) that detects the NOx concentration in a measurement gas. EXAMPLES

[0045] A change in sensor output when the width X of the second portion 115b of the diffusion resistance layer 115 shown in Fig. 4 is changed was obtained by simulation. The width X was expressed as a relative value with respect to the difference Y in width between the first portion 115a and the third portion 115c and the second portion 115b. In addition, the first portion 115a and the third portion 115c were changed at a predetermined rate to reproduce printing misalignment. The simulation was performed by calculating two-dimensional diffusion of a model gas entering the diffusion resistance layer 115 . FIG. 8 is a diagram showing the flow velocity in a simulation showing the change in sensor output when the width X of the second portion is changed, and FIG. 9 is a diagram showing the simulation results. As is clear from FIG. 9, the narrower the width X, the smaller the rate of change in the sensor output, and it is found that the rate of gas diffusion in the diffusion resistance layer 115 is determined by the second portion 115b. [Explanation of symbols]

[0046] 1 Gas sensor 30 Housing 100 Sensor element 100A, 100B Outer surface of sensor element 107c Measurement room 115, 215, 315, 415 Diffusion resistance layer 115a, 215a, 315a 1st part 115b, 215b, 315b 2nd part 115c, 215c 3rd part

Claims

1. A sensor element for detecting a specific gas concentration in a measurement gas, a measurement chamber disposed inside the sensor element for measuring the concentration of the specific gas; a diffusion resistance layer communicating with the measurement chamber from an outer surface of the sensor element and introducing the measurement gas into the measurement chamber, a second portion of the diffusion resistance layer facing an outer surface of the sensor element, the second portion having a cross-sectional area smaller than S1, the second portion being closer to the measurement chamber than the first portion.

2. 2. The sensor element according to claim 1, wherein a cross-sectional area S3 of a third portion of said diffusion resistance layer connected to said measurement chamber is larger than a cross-sectional area S2 of said second portion.

3. 3. The sensor element according to claim 1, wherein two or more of the diffusion resistance layers are provided on one outer surface of the sensor element.

4. A sensor element as described in claim 1 or 2, characterized in that a length L2 of a portion where the cross-sectional area S2 is the smallest along a direction from the outer surface of the sensor element toward the measurement chamber is longer than a length L1 of a portion where the cross-sectional area is S1 along the first portion.

5. A gas sensor comprising a sensor element for detecting a concentration of a specific gas in a measurement gas and a housing for holding the sensor element, 3. A gas sensor comprising the sensor element according to claim 1 or 2.

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