Gas sensor

Abstract

Gas sensor (1), comprising: a housing (11A, 11B); an insulator (12) which is held by an inner periphery of the housing (11A, 11B); a detection device (10) comprising a solid electrolyte body (2) arranged in the insulator (12) and possessing an oxygen ion conductivity, wherein a front end section (100) projects in the longitudinal direction (L) of the gas sensor (1) from a front end face (121) of the insulator (12); and a protective cover (13A, 13B) which is attached to the front end section of the housing (11A, 11B) to cover the front end section (100) of the detection device (10), and which has cover inlet openings (131, 132) formed therein, which guide a measuring gas (G) towards the front end section (100) of the detection device (10), characterized by the fact that a pump electrode (21) and a sensor electrode (23) are arranged in the longitudinal direction (L) at a front end section (200) of the solid electrolyte body (2), wherein the pump electrode (21) is exposed to the measuring gas (G) and regulates an oxygen concentration in the measuring gas (G), and the sensor electrode (23) is exposed to the measuring gas (G) and measures a concentration of a predetermined gas component in the measuring gas (G) after the latter is regulated with respect to the oxygen concentration by the pump electrode (21), a complete sensor electrode (23) is arranged in the longitudinal direction (L) closer to a base end face of the gas sensor (1) than all cover inlet openings (131, 132) which are formed at an outer periphery of the protective cover (13A, 13B), and a base end (231) of the sensor electrode (23) is arranged in the longitudinal direction (L) closer to the base end face of the gas sensor (1) than a front end face (111) of the housing (11A, 11B).

Description

Technical area

[0001] The present invention generally relates to a gas sensor designed to measure a predetermined gas component contained in a measurement gas. General state of the art

[0002] Typical gas sensors that measure the concentration of a predetermined gas component such as NOx contained in a measurement gas such as exhaust gas emitted from an internal combustion engine operate to regulate the concentration of oxygen in the measurement gas using a pump cell and then measure, using a sensor cell, the concentration of the predetermined gas component in the measurement gas whose oxygen concentration has already been regulated.

[0003] An electrode forming the pump cell and an electrode forming the sensor cell must be operated within a suitable temperature range. In particular, the electrode forming the pump cell is operated within a temperature range in which it decomposes or breaks down oxygen, but does not decompose the specified gas component. The electrode forming the sensor cell is operated within a temperature range in which it decomposes the specified gas component, but does not decompose water.

[0004] For example, JP 2008-281583 A discloses a gas sensor equipped with a detection device that detects a predetermined gas component contained in a measurement gas, and inner and outer protective covers covering a front end portion of the detection device. The gas sensor is designed to have a ratio between a total opening area A1 of inner gas inlet ports of the inner protective cover and a total opening area A2 of outer gas inlet ports of the outer protective cover that satisfies a relationship of A1 / A2 ≥ 1, thereby reducing the flow velocity of the measurement gas introduced from the outer gas inlet ports into the outer protective cover and passing through the inner gas inlet ports.In other words, a ratio of the total opening areas of all gas inlet ports is regulated to minimize a temperature variation of the detection device caused by the entry of the measurement gas into the protective covers.

[0005] Furthermore, DE 10 2014 207 227 A1 discloses a gas sensor, wherein a protector is inserted into a metal shell in a state where at least a portion of each gas introduction hole is located on the lower end side with respect to the front end of the metal shell. The metal shell has a gas introduction space formed by an inner surface on the front end side of the metal shell and the outer surface of the protector, which introduces a gas to be detected (exhaust gas) from a region on the front end side of the metal shell into the gas introduction holes of the protector. The lower end of the front end portion of the sensing element is located on the lower end side with respect to the front end of each gas introduction hole, and the front end of the front end portion is located on the front end side with respect to the lower end of each gas introduction hole.

[0006] Furthermore, JP 2011-227061 A discloses a gas sensor comprising a sensor element that has a solid electrolyte with oxygen ion conductivity as its main component and detects a predetermined gas component contained in a gas to be measured. The sensor element includes: an opening portion opened to an external space; an external connection portion for introducing the gas to be measured from the external space to provide the gas with a predetermined diffusion resistance; an internal space for connecting to the external connection portion; and a pump cell provided to pump oxygen into the internal space by applying a predetermined voltage between a first electrode formed on a surface of the internal space and a second electrode formed in a space other than the internal space.The thickness of the outer connecting section is designed to be greater than or equal to 50% and less than or equal to 100% of the thickness of the inner space. Summary of the inventionProblem to be solved by the invention

[0007] The above conventional gas sensor has a gas sensing portion of the detection device, where the pump electrode and the sensor electrode are arranged. The entirety of the gas sensing portion protrudes from a front end surface of a housing toward a front end of the gas sensor. The gas sensor is designed to promote the ease with which the measurement gas impinges on a region including a portion of the detection device where the pump electrode and the sensor electrode are arranged.

[0008] The gas sensor also controls the temperature of the sensing device by utilizing the fact that the impedance of the pump cell changes as a function of its temperature. Specifically, the temperature of the pump electrode is controlled as a function of the impedance of the pump cell to indirectly control the temperature of the sensor cell. This promotes the ease with which the temperature of the sensor electrode changes in a case where the gas sensor is designed to facilitate the impingement of the measurement gas around a portion of the sensing device in which the sensor electrode is disposed.

[0009] The invention was made in view of the above background with the object of providing a gas sensor that minimizes a temperature variation of a sensor electrode to improve the accuracy in measuring the concentration of a given gas component. Means of solving the problem

[0010] The above object is achieved by the subject matter of claim 1. Advantageous developments of the invention are the subject matter of the subsequent dependent claims.

[0011] An illustrative aspect of the present disclosure corresponds to a gas sensor comprising: a housing; an insulator held by an inner periphery of the housing; a sensing device including a solid electrolyte body disposed in the insulator and having oxygen ion conductivity, a front end portion in the longitudinal direction of the gas sensor protruding from a front end surface of the insulator; and a protective cover attached to the front end portion of the housing to cover the front end portion of the sensing device, and having a cover inlet port formed therein that guides a measurement gas toward the front end portion of the sensing device. A pump electrode and a sensor electrode are disposed at a front end portion of the solid electrolyte body in the longitudinal direction.The pump electrode is exposed to the measurement gas and regulates the oxygen concentration in the measurement gas. The sensor electrode is exposed to the measurement gas and measures the concentration of a specified gas component in the measurement gas after the oxygen concentration is regulated by the pump electrode. A base end of the sensor electrode in the longitudinal direction is positioned closer to a base end side of the gas sensor than a front end surface of the housing. Advantageous effects of the invention

[0012] The above gas sensor is constructed to have a designed positional relationship between the front end surface of the housing and the sensor electrode of the detecting device.

[0013] In particular, the base end of the sensor electrode of the detection device is arranged closer to the base end side in the longitudinal direction than the front end surface of the housing. A portion of the detection device where the sensor electrode is arranged is at least partially arranged in the housing.

[0014] When the gas sensor measures the concentration of the predetermined gas component in the measurement gas, the measurement gas is introduced into the protective cover via the cover inlet port and then comes into contact with the front end portion of the detection device (i.e., the solid electrolyte body) in the longitudinal direction. The base end of the detection device in the longitudinal direction is located closer to the base end than the front end surface of the housing, thereby minimizing a possibility of the measurement gas impinging on a region including a portion of the detection device where the sensor electrode is arranged, or reducing the flow velocity of the measurement gas impinging on a region including the portion of the detection device where the sensor electrode is arranged. This reduces a temperature variation of the sensor electrode in response to a temperature change of the measurement gas.

[0015] Accordingly, the above gas sensor has a reduced temperature variation of the sensor electrode and an increased accuracy in measuring the concentration of the given gas component. Short description of the figures Fig. 1 is an explanatory sectional view showing a front end portion of a gas sensor according to an embodiment. Fig. 2 is an explanatory sectional view illustrating a detection device according to an embodiment. Fig. Fig. 3 is a view showing a detection device according to an embodiment, and this corresponds to an explanatory sectional view taken along the line III-III in Fig. 2. Fig. 4 is an explanatory plan view illustrating configurations of a pump electrode and a sensor electrode of a detection device according to an embodiment. Fig. 5 is an explanatory sectional view showing a front end portion of another type of gas sensor according to an embodiment. Fig. 6 is an explanatory sectional view showing a front end portion of another type of gas sensor according to an embodiment. Fig. 7 is an explanatory sectional view showing a front end portion of another type of gas sensor according to an embodiment. Fig. 8 is a diagram illustrating a relationship between the position of a sensor electrode in a longitudinal direction and the flow velocity of a measurement gas coming into contact with a front end portion of a detection device in verification tests. Fig. 9 is a diagram showing a relationship between the position of a sensor electrode in a longitudinal direction and a temperature variation of the sensor electrode in verification tests. Embodiments for carrying out the invention

[0016] The gas sensor 1 according to this embodiment will be described below with reference to the drawings.

[0017] The Fig. The gas sensor 1 shown in Figure 1 includes the housing 11A and 11B, the insulator 12, the detection device 10, and the protective covers 13A and 13B. The housing 11A and 11B is made of metal. The insulator 12 is made of insulating ceramic and held inside an inner periphery of the housing 11A. The detection device 10 is arranged in the insulator 12 and equipped with the solid electrolyte body 2 having oxygen ion conductivity. The detection device 10 has a predetermined length and includes the front end portion 100. The front end portion 100 protrudes from the front end surface 121 of the insulator 12 along a longitudinal direction L of the detection device 10. The protective covers 13A and 13B are made of metal and are attached to a front end (i.e., a lower end as shown in the figure) of the housing 11A to cover the front end portion 100 of the detection device 10.The protective covers 13A and 13B have the cover inlet openings 131 and 132 formed therein, which guide the measurement gas G toward the front end portion 100 of the detection device 10.

[0018] The solid electrolyte body 2 has the front end portion 200. The front end portion 200 has the pump electrode 21 and the sensor electrode 23 arranged thereon. The pump electrode 21 is exposed to the measurement gas G to regulate the oxygen concentration in the measurement gas G. The sensor electrode 23 is exposed to the measurement gas G to measure the concentration of the predetermined gas component of the measurement gas G, whose oxygen concentration has been regulated by the pump electrode 21.

[0019] The sensor electrode 23, as in Fig. 1 and Fig. 4, has the base end edge 231 which is closer to the base end of the gas sensor 1 (i.e., the detection device 10) in the longitudinal direction L of the detection device 10 than the front end surface 111 of the housing 11A.

[0020] In this disclosure, a portion of the detection device 10 that protrudes from the insulator 12 is referred to as a front end side. In Fig. 1, a lower side corresponds to the front end side, while an upper side corresponds to the base end side. Fig. 2 to Fig. 4 schematically illustrate the detection device 10 and show the pump electrode 21 and the sensor electrode 23 shorter than in reality.

[0021] The gas sensor 1 is described below with reference to Fig. 1 to Fig. 7 explained in detail.

[0022] The gas sensor 1 is used to measure the concentration of NOx, which corresponds to the predetermined gas component contained in the measurement gas G, which corresponds to an exhaust gas flowing through an exhaust pipe of an internal combustion engine. The detection device 10 is, as shown in Fig. 2, is formed from a stack of the insulator 31 and the heater 5. The insulator 31 defines the measurement gas space 101 between itself and the solid electrolyte body 2. The heater 4 operates to heat the solid electrolyte body 2. The solid electrolyte body 2 has surfaces 201 and 202 opposite to each other in a thickness direction of the solid electrolyte body 2. The insulator 31 is arranged on the surface 201 via the spacer 33. The detection device 10 has the measurement gas space 101, which is surrounded by the surface 201 of the solid electrolyte body 2, the insulator 31, and the spacer 33, and into which the measurement gas G is guided.

[0023] The front end 103 of the detection device 10 has, as in Fig. 2, the inlet opening 331 formed therein, through which the measurement gas G is introduced into the measurement gas space 101 via the diffusion resistor 32. The inlet opening 331 is formed at a front end portion of the spacer 33. The diffusion resistor 32 is made of a porous material that provides a certain degree of diffusion resistance to a flow of the measurement gas G. The diffusion resistor 32 is arranged in the inlet opening 331. The pump electrode 21 and the sensor electrode 23 are mounted on the surface 201 of the solid electrolyte body 2 and are exposed to the measurement gas G flowing into the measurement gas space 101.

[0024] On the surface 201 of the solid electrolyte body 2, as shown in Fig. 3 and Fig. 4, the monitoring electrode 22 is arranged adjacent to the sensor electrode 22. The monitoring electrode 22 is exposed to the measurement gas G and operates to measure the oxygen concentration in the measurement gas G, the oxygen concentration of which has already been regulated by the pump electrode 21.

[0025] The pump electrode 21 is arranged on the front end of the solid electrolyte body 2 of the detection device 10, which is close to the inlet port 331. The sensor electrode 23 and the monitor electrode 22 are arranged adjacent to the base end side of the pump electrode 21 at the same distance from the pump electrode 21. In other words, the sensor electrode 23 and the monitor electrode 22 are arranged at equal distances from a base end edge of the pump electrode 21 in the longitudinal direction L.

[0026] The heating device 5 is, as in Fig. 2 and Fig. 3, is arranged on the surface 202 of the solid electrolyte body 2 via the spacer 34. The heater 5 is constructed of a pair of ceramic supports 51 and a heating layer 52 interposed between the ceramic supports 51. The detection device 10 has the reference gas space 102, which is surrounded by the surface 202 of the solid electrolyte body 2, the heater 5, and the spacer 34, and into which a reference gas (i.e., atmospheric gas) A is introduced. The reference electrode 25, which is exposed to the reference gas A that has entered the reference gas space 102, is arranged on a region of the surface 202 where the pump electrode 21, the monitor electrode 22, and the sensor electrode 23 protrude in the thickness direction of the solid electrolyte body 2, that is, the reference electrode 25 faces the pump electrode 21, the monitor electrode 22, and the sensor electrode 23 via the solid electrolyte body 2.

[0027] The reference electrode 25 occupies the entire area of ​​the surface 202, from which three electrodes protrude: the pump electrode 21, the monitoring electrode 22, and the sensor electrode 23. Alternatively, the reference electrode 25 can be provided individually for each electrode of the pump electrode 21, the monitoring electrode 22, and the sensor electrode 23.

[0028] The detection device 10, as in Fig. 2 and Fig. 3, the detection device 10 includes the pump cell 41, which applies a voltage across the solid electrolyte body 2 between the pump electrode 21 and the reference electrode 25 to adjust the oxygen concentration in the measurement gas G in the measurement gas space 101 to below a predetermined concentration. The detection device 10 also includes the monitoring cell 42, which measures an oxygen ion current flowing between the monitoring electrode 22 and the reference electrode 25 via the solid electrolyte body 2 to determine the oxygen concentration contained in the measurement gas G in the measurement gas space 101, which has already been regulated in terms of oxygen concentration by the pump cell 41.The detection device 10 also has the sensor cell 43, which measures an oxygen ion current flowing between the sensor electrode 23 and the reference electrode 25 via the solid electrolyte body 2 to determine concentrations of NOx and oxygen contained in the measurement gas G in the measurement gas chamber 101, which has already been regulated in terms of oxygen concentration by the pump cell 41. The gas sensor 1 subtracts a value of the oxygen ion current in the monitoring cell 42 from a value of the oxygen ion current in the sensor cell 43 to determine the concentration of NOx in the measurement gas G.

[0029] The housing 11A and 11B corresponds, as can be seen from Fig. 1, the first housing 11A disposed on an outer periphery of the insulator 12, and a second housing 11B disposed on an outer periphery of the first housing 11A. The first housing 11A has a front end portion protruding from the front end of the second housing 11B toward the front end side of the gas sensor 1.

[0030] An arrangement of the protective covers 13A and 13B has a double-wall structure. The protective covers 13A and 13B correspond to the first protective cover 13A, which is attached to the outer periphery of the front end portion of the first housing 11A, and the second protective cover 13B, which is fixed to the outer periphery of the first protective cover 13A, respectively. The cover inlet openings 131 and 132, which guide the measurement gas G toward the front end portion 100 of the detection device 10, correspond to the cover inlet openings 131 formed at an outer periphery and a front end of the first protective cover 13A, and the cover inlet openings 132 formed at an outer periphery and a front end of the second protective cover 13B, respectively.The measurement gas G first passes through the outer periphery of the first protective cover 13A and the outer periphery of the second protective cover 13B, flows into the second protective cover 13B, comes into contact with the front end portion 100 of the detection device 10, passes through the front end of the first protective cover 13A and the front end of the second protective cover 13B, and then reaches the outside of the protective covers 13A and 13B.

[0031] The front end of the first protective cover 13A is, as shown in Fig. 1, is disposed within the cover inlet opening 132 formed at the front end of the second protective cover 13B. The measurement gas G, which has passed through the cover inlet openings 131 in the outer periphery of the first protective cover 13A and flows toward the base end side, comes into contact with the front end portion 100 of the detection device 10 disposed in the first protective cover 13A.

[0032] The front end of the first protective cover 13A can, as shown in Fig. 7, the measurement gas G may be arranged away from the front end of the second protective cover 13B toward the base end side of the gas sensor 1 to form a space between the front end of the first protective cover 13A and the front end of the second protective cover 13B. With this structure, the measurement gas G, after flowing from the cover inlet openings 132 in the outer periphery of the second protective cover 13B into the space between the front end of the first protective cover 13A and the front end of the second protective cover 13B, enters the cover inlet openings 131 in the outer periphery of the first protective cover 13A. The measurement gas G, which has entered the first protective cover 13A through the cover inlet openings 131 and flows within the inner periphery of the first protective cover 13A, then comes into contact with the front end portion 100 of the detection device 10.

[0033] The arrangement of the protective covers 13A and 13B may be designed such that it has a single-wall structure.

[0034] The gas sensor 1 is designed to measure the temperature of the detection device 10. Specifically, the gas sensor 1 is configured to measure an impedance between the pump electrode 21 and the reference electrode 25 via the solid electrolyte body 2 in the pump cell 41 and to control the amount of heat generated by the heater 5 to adjust the impedance to a predetermined value. The pump electrode 21 is heated to a temperature between 830 and 920°C, at which oxygen is decomposed while NOx is not decomposed. The sensor electrode 23 is heated to a temperature between 650 and 740°C, at which NOx is decomposed while water is not decomposed.

[0035] The insulator 12 fixes the detection device 10 to the first housing 11A and electrically insulates the detection device 10 from the first housing 11A, as shown in Fig. 1. The front end surface 121 of the insulator 12 is arranged closer to the base end of the gas sensor 1 than the front end surface 111 of the first housing 11A. The base end edge 231 of the sensor electrode 23 in the longitudinal direction L and the base end edge 221 of the monitoring electrode 22 in the longitudinal direction L are, as shown in Fig. 4, are located closer to the base end of the gas sensor 1 than the front end surface 111 of the first housing 11A, and are disposed within the recess 14 defined by the first end surface 121 of the insulator 12 and the inner peripheral surface 112 of the first housing 11A. The sensor electrode 23 and the monitor electrode 22 have the centers 232 and 222 in the longitudinal direction L, which are located closer to the base end side of the gas sensor 1 than the first end surface 111 of the first housing 11A.

[0036] The gas sensor 1 is configured to have the front end portion 100 of the detection device 10, at which the pump electrode 21, the sensor electrode 23, the monitor electrode 22, and the reference electrode 25 are arranged, and which is arranged as close as possible to the base end side of the gas sensor 1 relative to the first housing 11A.

[0037] When the gas sensor 1 measures the NOx concentration in the measurement gas G, the measurement gas G is introduced into the protective covers 13A and 13B via the cover inlet openings 131 and 132, and then comes into contact with the front end portion 100 of the detection device 10. The measurement gas G then flows into the measurement gas chamber 101 via the inlet opening 331 formed at the front end 103 of the detection device 10.

[0038] The flow of the measurement gas G introduced into the protective covers 13A and 13B is slowed down in the recess 14 formed by the front end surface 121 of the insulator 12 and the inner peripheral surface 112 of the first housing 11A. The centers 232 and 222 of the sensor electrode 23 and the monitoring electrode 22 are located closer to the base end side of the gas sensor 1 than the front end surface 111 of the first housing 11A in the longitudinal direction L, and are at least partially disposed in the recess 14.This minimizes a probability that the measurement gas G hits an area including a portion of the detection device 10 in which the sensor electrode 23 and the monitor electrode 22 are arranged, or reduces the flow velocity of the measurement gas G hitting an area including the portion of the detection device 10 in which the sensor electrode 23 and the monitor electrode 22 are arranged, thereby reducing a temperature variation of the sensor electrode 23 and the monitor electrode 22 in response to a temperature change of the measurement gas G.

[0039] Accordingly, the gas sensor 1 has a reduced temperature variation of the sensor electrode 23 to improve the accuracy in measuring the concentration of NOx.

[0040] The gas sensor 1 can, as in Fig. 5, may be designed to have the sensor electrode 23 disposed in its entirety closer to the base end side of the gas sensor 1 than the front end surface 111 of the first housing 11A. This further reduces a temperature change of the sensor electrode 23 and the monitor electrode 22.

[0041] The gas sensor 1 can, as in Fig. 6, the front end 103 of the detection device 10 may be configured to be closer to the base end side of the gas sensor 1 than the front end surface 111 of the first housing 11A. In other words, the entirety of the detection device 10 is disposed within the recess 14 formed by the front end surface 121 of the insulator 12 and the inner peripheral surface 112 of the first housing 11A. This further reduces temperature variation of the sensor electrode 23 and the monitor electrode 22. Verification tests

[0042] Tests were conducted to examine a relationship between the position of the sensor electrode 23 in the longitudinal direction L and a variation in the temperature of the sensor electrode 23. Such a temperature variation was determined by simulations on a test sample 1 using the protective covers 13A and 13B of Fig. 1 and a test pattern 2 using the Fig. 7. The simulations were performed under a condition where the measurement gas G flows into the gas sensor 1 at 20 m / s from a direction in which the measurement gas G moves in the exhaust duct where the gas sensor 1 is installed, that is, a direction perpendicular to the longitudinal direction L of the detection device 10. The flow velocity of the measurement gas G and a temperature change of the sensor electrode 23 when the measurement gas G enters the protective covers 13A and 13B and then comes into contact with the front end portion 100 of the detection device 10 were measured. Changes in the flow velocity and temperature were also derived for different positions of the sensor electrode 23 in the longitudinal direction L.

[0043] Fig. 8 illustrates relationships between the position of the sensor electrode 23 in the longitudinal direction L and the flow velocity of the measurement gas G when it comes into contact with the front end portion 100 of the detection device 10. When the position of the base end edge 231 of the sensor electrode 23 in the longitudinal direction L is equal to that of the front end surface 111 of the housing 11A, the position of the sensor electrode 23 in the longitudinal direction L is defined as 0 mm. When the position of the base end edge 231 of the sensor electrode 23 in the longitudinal direction L is closer to the base end of the gas sensor 1 than the front end surface 111 of the housing 11A, the position of the sensor electrode 23 in the longitudinal direction L is defined to have a negative value.When the position of the base end edge 231 of the sensor electrode 23 in the longitudinal direction L is closer to the front end of the gas sensor 1 than the front end surface 111 of the housing 11A, the position of the sensor electrode 23 in the longitudinal direction L is defined to have a positive value.

[0044] Fig. 8 shows that in each of Test Samples 1 and 2, when the base end edge 231 of the sensor electrode 23 is located closer to the base end of the gas sensor 1 in the longitudinal direction L than the front end surface 111 of the housing 11A (that is, the negative value), the flow velocity of the measurement gas G is low, and that the farther the base end edge 231 of the sensor electrode 23 is located in the longitudinal direction L from the front end surface 111 of the housing 11A toward the base end of the gas sensor 1, the lower the flow velocity of the measurement gas G is.

[0045] Fig. 9 illustrates relationships between the position of the sensor electrode 23 in the longitudinal direction L and a temperature variation of the sensor electrode 23. Such a temperature variation is defined as a reference variation when the sensor electrode 23 has a predetermined temperature and the flow velocity of the measurement gas G is 0 mm / s. Fig. Figure 9 indicates a variation of the temperature of the sensor electrode 23 when the flow velocity of the measurement gas G is 20 mm / s, compared to the reference variation when the flow velocity is 0 mm / s. The position of the sensor electrode 23 in the longitudinal direction L is equal to the value shown in Fig. 8. Fig. 9 shows that in each of Test Samples 1 and 2, when the base end edge 231 of the sensor electrode 23 is located closer to the base end of the gas sensor 1 in the longitudinal direction L than the front end surface 111 of the housing 11A (that is, the negative value), a variation in the temperature of the sensor electrode 23 is small, and that the farther the base end edge 231 of the sensor electrode 23 is located from the front end surface 111 of the housing 11A in the longitudinal direction L toward the base end of the gas sensor 1, the smaller a temperature variation of the sensor electrode 23 is.

[0046] In Fig.In Fig. 9, broken lines represent a case where the center 232 of the sensor electrode 23 in the longitudinal direction L is located at the same position as that of the front end surface 111 of the housing 11A (the position of the sensor electrode 23 in the longitudinal direction L is -0.8 mm in this embodiment), and a case where the front end of the sensor electrode 23 in the longitudinal direction L is located at the same position as that of the front end surface 111 of the housing 11A (the position of the sensor electrode 23 in the longitudinal direction L is -1.6 mm in this embodiment). The test results show that the closer the sensor electrode 23 is to the base end of the gas sensor 1 in the longitudinal direction L compared to the front end surface 111 of the housing 11A, the smaller the temperature variation of the sensor electrode 23 is.

[0047] Explanation of reference symbols 1 gas sensor 10 Detection device 11A, 11B housing 12 Insulator 13A, 13B protective cover 131, 132 Cover inlet opening 2 solid electrolyte bodies 21 Pump electrode 22 Monitoring electrode 23 Sensor electrode 31 Base end edge

Claims

[1] Gas sensor (1), comprising: a housing (11A, 11B); an insulator (12) held by an inner periphery of the housing (11A, 11B); a detection device (10) comprising a solid electrolyte body (2) arranged in the insulator (12) and having oxygen ion conductivity, wherein a front end portion (100) in the longitudinal direction (L) of the gas sensor (1) protrudes from a front end surface (121) of the insulator (12); and a protective cover (13A, 13B) which is attached to the front end portion of the housing (11A, 11B) to cover the front end portion (100) of the detection device (10), and has cover inlet openings (131, 132) formed therein which guide a measurement gas (G) toward the front end portion (100) of the detection device (10), characterized by , that a pump electrode (21) and a sensor electrode (23) are arranged in the longitudinal direction (L) at a front end portion (200) of the solid electrolyte body (2), wherein the pump electrode (21) is exposed to the measurement gas (G) and regulates an oxygen concentration in the measurement gas (G), and the sensor electrode (23) is exposed to the measurement gas (G) and measures a concentration of a predetermined gas component in the measurement gas (G) after it is regulated with regard to the oxygen concentration by the pump electrode (21), an entirety of the sensor electrode (23) is arranged in the longitudinal direction (L) closer to a base end side of the gas sensor (1) than all of the cover inlet openings (131, 132) formed at an outer periphery of the protective cover (13A, 13B), and a base end (231) of the sensor electrode (23) is arranged closer to the base end side of the gas sensor (1) in the longitudinal direction (L) than a front end surface (111) of the housing (11A, 11B). [2] Gas sensor (1) according to claim 1, characterized by that the entirety of the sensor electrode (23) is arranged closer to the base end side of the gas sensor (1) than the front end surface (111) of the housing (11A, 11B) and is arranged within a recess (14) which is formed by the front end surface (121) of the insulator (12) and an inner peripheral surface (112) of the housing (11A). [3] Gas sensor (1) according to claim 1, characterized bythat a front end (103) of the detection device (10) is arranged closer to the base end side of the gas sensor (1) in the longitudinal direction (L) than the front end surface (111) of the housing (11A, 11B) and is arranged within a recess (14) which is formed by the front end surface (121) of the insulator (12) and an inner peripheral surface (112) of the housing (11A). [4] Gas sensor (1) according to one of claims 1 to 3, characterized by that the detection device (10) has a measuring gas chamber (101) which introduces the measuring gas (G) towards a surface of the solid electrolyte body (2), that the pump electrode (21) and the sensor electrode (23) are exposed to the measuring gas (G) guided towards the measuring gas chamber (101), and that a front end (103) of the detection device (10) has an inlet opening (331) formed therein which guides the measuring gas (G) via a diffusion resistor (32) into the measuring gas chamber (101). [5] The gas sensor (1) according to claim 1, wherein the entirety of the sensor electrode (23) is arranged closer to the base end side of the gas sensor (1) than a base end of the protective cover (13A, 13B). [6] The gas sensor (1) according to claim 1, wherein the protective cover (13A, 13B) comprises a first protective cover (13A) and a second protective cover (13B), the first protective cover (13A) being fixed to an outer periphery of the front end portion of the housing (11A, 11B), the second protective cover (13B) being fixed to the outer periphery of the first protective cover (13A), and the cover inlet openings (131) formed at the outer periphery of the first protective cover (13A) being arranged closer to a front end side of the gas sensor (1) in the longitudinal direction (L) than the cover inlet openings (132) formed at an outer periphery of the second protective cover (13B).

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