Gas sensor manufacturing method and gas sensor

Abstract

To provide a gas sensor manufacturing method, which prevents adhesion of fumes to a protective cover and a housing and improves measurement accuracy of a sensor element, a gas sensor and a protective cover.SOLUTION: A manufacturing method for a gas sensor 10 includes connecting a housing 16 holding a sensor element 12 and a protective cover 14 so that a tip 24 of the sensor element 12 is covered by the protective cover 14. A first gas chamber 56, in which gas is introduced from outside, a sensor element chamber 58, and a second gas chamber 60 are formed between the protective cover 14 and housing 16. There is no welded joint in a gas introduction area, including the first gas chamber 56, sensor element chamber 58, and second gas chamber 60.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a gas sensor. and Gas Station To Regarding. [Background technology]

[0002] The gas sensor measures the concentration of a predetermined gas component in a gas to be measured. The gas sensor includes a housing, a sensor element, and a protective cover. The housing holds the sensor element. The tip of the sensor element protrudes from the tip of the housing. The protective cover is connected to the housing so as to cover the tip of the sensor element. The protective cover has an inner member and an outer member. The inner member is connected to the tip of the housing so as to surround the tip of the sensor element. The inner member is fixed to the tip of the housing by welding. The outer member is connected to the housing so as to cover the inner member and the tip of the sensor element. The connection point between the outer member and the housing is fixed by welding. Patent Document 1 discloses that the connection point between the protective cover and the housing is fixed by spot welding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-158572 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the inner member and the tip of the housing are welded together, fumes are generated. The fumes scatter and adhere to the inner member and the housing. If fumes adhere to the joint between the outer member and the housing, the accuracy of the joint between the outer member and the housing decreases. In addition, the tip of the sensor element is disposed in a space surrounded by the protective cover and the housing. Gas flows into this space from the outside. If fumes adhere to the inner member, the flow of gas is hindered. This reduces the measurement accuracy of the sensor element. If fumes adhere in this way, the defective rate of the gas sensor increases. In addition, since the inner member and the tip of the housing are welded together, manufacturing costs are high. Furthermore, since the adhesion of fumes is monitored, the number of management steps required for manufacturing the gas sensor increases.

[0005] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0006] A first aspect of the present invention is a manufacturing method for a gas sensor comprising a housing, a sensor element held in the housing, and a protective cover that protects a tip of the sensor element protruding from the housing, the method including a connecting step of connecting the housing and the protective cover so as to cover the tip of the sensor element with the protective cover, wherein gas is introduced from the outside into a space enclosed by the protective cover and the housing, and there are no welded joints in the parts of the protective cover and the housing that form the space.

[0007] A second aspect of the present invention is a gas sensor comprising a housing, a sensor element held in the housing, and a protective cover that protects a tip of the sensor element protruding from the housing, wherein the housing and the protective cover are connected so that the tip of the sensor element is covered by the protective cover, gas is introduced from the outside into a space enclosed by the protective cover and the housing, and there are no welded joints in the parts of the protective cover and the housing that form the space. Effect of the Invention

[0009] According to the present invention, no fume adheres to the protective cover and the housing. This improves the connection accuracy between the protective cover and the housing. Furthermore, gas flows smoothly through the space surrounded by the protective cover and the housing. This improves the measurement accuracy of the sensor element. Therefore, the present invention reduces the defect rate of the gas sensor. Furthermore, it is possible to reduce the manufacturing cost of the gas sensor. Furthermore, it is possible to reduce the management man-hours involved in manufacturing the gas sensor. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing the gas sensor of the present embodiment. [Diagram 2] FIG. 2A is a cross-sectional view showing the fitting of an outer member and an intermediate member, and FIG. 2B is a cross-sectional view showing the fitting of the outer member and the intermediate member with an inner member. [Diagram 3] FIG. 3A is a cross-sectional view showing the connection between the protective cover and the housing, and FIG. 3B is a cross-sectional view showing spot welding at the connection portion between the outer member and the housing. [Figure 4] FIG. 4 is a cross-sectional view showing a gas sensor according to a modified example. [Diagram 5] FIG. 5A is a cross-sectional view showing the fitting of an outer member and an intermediate member, and FIG. 5B is a cross-sectional view showing the fitting of the outer member and the intermediate member with the inner member. [Figure 6] FIG. 6A is a cross-sectional view showing the connection between the protective cover and the housing, and FIG. 6B is a cross-sectional view showing spot welding at the connection portion between the outer member and the housing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 1 is a cross-sectional view of a gas sensor 10 manufactured by the gas sensor manufacturing method according to this embodiment. The gas sensor 10 is installed, for example, in an exhaust pipe connected to an engine of a vehicle (not shown). The gas sensor 10 detects the concentration of gas components such as NOx contained in a measurement gas (exhaust gas) discharged from the engine.

[0012] The gas sensor 10 includes a sensor element 12, a protective cover 14, and a housing 16. The sensor element 12 detects the concentration of a predetermined gas component in the gas to be measured. The housing 16 holds the sensor element 12. The housing 16 is a metal cylinder. Specifically, the housing 16 includes a housing 18, a fixing member 20, and a sensor support portion 22. The fixing member 20 is a cylindrical metal member. The fixing member 20 is connected to a pipe by welding, screwing, or the like. The housing 18 is a cylindrical metal member. The housing 18 is fixed to one surface (the surface close to the protective cover 14) of the fixing member 20. The sensor support portion 22 is fixed to the other surface of the fixing member 20. The housing 18, the fixing member 20, and the sensor support portion 22 are connected approximately coaxially. Note that "approximately coaxial" includes both a case where multiple objects are coaxial with each other and a case where multiple objects are slightly deviated from the coaxiality.

[0013] The sensor element 12 is in the form of a long plate. In the following description, the longitudinal direction of the sensor element 12 (left-right direction in FIG. 1) is referred to as the front-rear direction. The thickness direction of the sensor element 12 (up-down direction in FIG. 1) is referred to as the up-down direction. The width direction of the sensor element 12 (direction perpendicular to the left-right and up-down directions in FIG. 1) is referred to as the left-right direction. In the following description, the front end of the sensor element 12 etc. is referred to as the tip end. The rear end of the sensor element 12 etc. is referred to as the base end.

[0014] 1, the gas sensor 10 according to the present embodiment includes a sensor element 12. The sensor element 12 has a long rectangular parallelepiped shape, and the longitudinal direction of the sensor element 12 (left and right direction in FIG. 2) is defined as the front-rear direction, and the thickness direction of the sensor element 12 (up and down direction in FIG. 2) is defined as the up and down direction. The width direction of the sensor element 12 (direction perpendicular to the front-rear direction and the up and down direction) is defined as the left and right direction. The longitudinal direction of the sensor element 12 (left and right direction in FIG. 2) is defined as the front-rear direction, and the thickness direction of the sensor element 12 (up and down direction in FIG. 2) is defined as the up and down direction. The width direction of the sensor element 12 (direction perpendicular to the front-rear direction and the up and down direction) is defined as the left and right direction. The gas sensor 10 according to the present embodiment includes a sensor element 12 as shown in FIG. 1. The sensor element 12 has a long rectangular parallelepiped shape, and the longitudinal direction of the sensor element 12 (left and right direction in FIG. 2) is defined as the front-rear direction, and the thickness direction of the sensor element 12 (up and down direction in FIG. 2) is defined as the up and down direction. The width direction of the sensor element 12 (the direction perpendicular to the front-rear and up-down directions) is defined as the left-right direction. The sensor element 12 is held approximately coaxially with respect to the housing 16. That is, the sensor support portion 22 supports the base end portion of the sensor element 12 approximately coaxially. The sensor element 12 extends forward from the sensor support portion 22 and penetrates the fixing member 20 and the housing 18. Therefore, the tip portion 24 of the sensor element 12 protrudes forward from the housing 18.

[0015] The protective cover 14 is a metal cylinder with a bottom. The protective cover 14 is connected to the side (outer peripheral surface) of the housing 18 so as to cover the tip portion 24 of the sensor element 12 and the housing 18. The protective cover 14 is connected to the housing 18 approximately coaxially with the sensor element 12 and the casing 16.

[0016] Specifically, the protective cover 14 has an inner member 26 , a middle member 28 , and an outer member 30 .

[0017] The inner member 26 is a stepped cylindrical metal member. The inner member 26 is connected to the housing 18 approximately coaxially with the sensor element 12 and the housing 18. The inner member 26 has a large diameter portion 32, a stepped portion 34, and a small diameter portion 36. The large diameter portion 32 is a cylindrical portion that fits into the side surface of the housing 18. The small diameter portion 36 is a cylindrical portion having a smaller diameter than the large diameter portion 32 and a larger diameter than the sensor element 12. The small diameter portion 36 extends forward from the tip of the housing 18 approximately parallel to the sensor element 12. Therefore, the small diameter portion 36 is disposed so as to surround the tip 24 of the sensor element 12. The stepped portion 34 connects the large diameter portion 32 and the small diameter portion 36. The stepped portion 34 extends along the tip of the housing 18. The tip of the sensor element 12 slightly protrudes from the tip of the small diameter portion 36.

[0018] The outer member 30 is a stepped metal member. The outer member 30 is a cylindrical member with a bottom. The outer member 30 is connected to the housing 18 approximately coaxially with the sensor element 12 and the housing 18. The outer member 30 has a large diameter portion 38, a body portion 40, a stepped portion 42, and a small diameter portion 44. The large diameter portion 38 is a cylindrical portion that fits into the side surface of the housing 18. The large diameter portion 38 fits into the side surface of the housing 18 by press-fitting the outer member 30 into the housing 18. The large diameter portion 38 fits into the side surface of the housing 18 by press-fitting the inner member 26 into the outer member 30. The large diameter portion 32 of the inner member 26 fits into the inner surface (inner circumferential surface) of the large diameter portion 38 by press-fitting the inner member 26 into the outer member 30.

[0019] In addition, the fitting portion between the large diameter portion 38 and the side surface of the housing 18 is fixed by, for example, spot welding. The spot welding is performed at intervals of a predetermined angle in the circumferential direction of the outer member 30. Note that the spot welding includes various types of spot welding such as resistance spot welding and laser spot welding. In this embodiment, it is sufficient that the fitting portion between the large diameter portion 38 and the side surface of the housing 18 can be fixed by various types of welding such as resistance welding including resistance spot welding and laser welding including laser spot welding. Furthermore, even if fumes generated by welding adhere to the fitting portion between the large diameter portion 38 and the side surface of the housing 18, the fitting portion is not affected by the fumes. This is because there is no gas flow path near the fitting portion.

[0020] The body 40 extends forward from the large diameter portion 38 approximately parallel to the sensor element 12 and the small diameter portion 36 of the inner member 26. Thus, the body 40 is disposed so as to surround the tip end 24 of the sensor element 12 and the inner member 26. The step portion 42 extends forward from the body 40 and is connected to the small diameter portion 44. The small diameter portion 44 is a cylindrical portion having a smaller diameter than the large diameter portion 38 and the body 40, and a larger diameter than the small diameter portion 36 of the inner member 26. The small diameter portion 44 is a cylinder with a bottom that covers the tip end 24 of the sensor element 12.

[0021] The intermediate member 28 is disposed between the inner member 26 and the outer member 30. The intermediate member 28 is a cylindrical member made of metal and has a bottom. The intermediate member 28 has a tubular portion 46, an intermediate portion 48, and a truncated cone portion 50. The tubular portion 46 is a cylindrical portion having a larger diameter than the small diameter portion 36 of the inner member 26 and a smaller diameter than the body portion 40. A gap 52 is formed between the tubular portion 46 and the small diameter portion 36 of the inner member 26. The tubular portion 46 has a plurality of protruding portions 54 protruding radially inward. Each of the protruding portions 54 abuts against a side surface (outer peripheral surface) of the small diameter portion 36 of the inner member 26. That is, the inner member 26 is fitted to the inner surface of the tubular portion 46 by the small diameter portion 36 abutting against the plurality of protruding portions 54 due to the press-fitting of the inner member 26 into the intermediate member 28. Note that only one protruding portion 54 is shown in FIG. 1. The intermediate portion 48 connects the cylindrical portion 46 and the truncated cone portion 50. The intermediate portion 48 is connected to the inner surface of the stepped portion 42 of the outer member 30 by press-fitting the intermediate member 28 into the outer member 30. The truncated cone portion 50 is connected to the intermediate portion 48. The truncated cone portion 50 is disposed between the tip portion 24 of the sensor element 12 and the small diameter portion 44 of the outer member 30.

[0022] The space surrounded by the inner member 26 and the outer member 30 is formed as a first gas chamber 56. The space surrounded by the intermediate member 28 and the inner member 26 is formed as a sensor element chamber 58. The space surrounded by the intermediate member 28 and the outer member 30 is formed as a second gas chamber 60. A plurality of first communication holes 62 that communicate the exhaust pipe and the first gas chamber 56 are formed in the body portion 40 and the step portion 42 of the outer member 30. Each of the first communication holes 62 is formed at intervals of a predetermined angle in the circumferential direction of the outer member 30. A plurality of second communication holes 64 that communicate the exhaust pipe and the second gas chamber 60 are formed in the small diameter portion 44 of the outer member 30. Each of the second communication holes 64 is formed at intervals of a predetermined angle in the circumferential direction of the outer member 30. A gas outlet 66 that communicates the sensor element chamber 58 and the second gas chamber 60 is formed in the truncated cone portion 50 of the intermediate member 28.

[0023] Here, the measurement gas flows into the first gas chamber 56 from the first communication hole 62, as indicated by the dashed arrow. The measurement gas in the first gas chamber 56 flows into the sensor element chamber 58 through the gap 52. The measurement gas in the sensor element chamber 58 flows out through the gas outlet 66, the second gas chamber 60, and the second communication hole 64. The tip 24 of the sensor element 12 extends into the sensor element chamber 58. Therefore, when the measurement gas temporarily stays in the sensor element chamber 58, a part of the measurement gas is taken into the sensor element 12. This allows the sensor element 12 to measure the concentration of a predetermined gas component in the measurement gas.

[0024] Next, the manufacturing method of this embodiment will be described with reference to FIGS. 2A to 3B.

[0025] First, as shown in Fig. 2A, with the inner surface of the outer member 30 and the truncated cone portion 50 of the intermediate member 28 facing each other, the intermediate portion 48 of the intermediate member 28 is press-fitted into the stepped portion 42 of the outer member 30. This causes the intermediate member 28 to be fitted approximately coaxially into the inner surface of the outer member 30, as shown in Fig. 2B.

[0026] Next, with the inner surface of the intermediate member 28 facing the small diameter portion 36 of the inner member 26, the small diameter portion 36 of the inner member 26 is press-fitted into the protruding portion 54 of the intermediate member 28. As a result, the inner member 26 is fitted approximately coaxially to the inner surface of the intermediate member 28, as shown in FIG. 3A. As a result, a cylindrical protective cover 14 with a bottom is formed. Therefore, each process in FIG. 2A and FIG. 2B corresponds to an assembly step for forming the protective cover 14. In this way, in the protective cover 14, the outer member 30, the intermediate member 28, and the inner member 26 are connected together in this order by fitting them together by press-fitting. In other words, there are no joints by welding in the protective cover 14.

[0027] Next, as shown in FIG. 3A, the tip portion 24 of the sensor element 12 held in the housing 16 and the inner member 26 of the protective cover 14 are faced to each other, and the large diameter portion 38 of the outer member 30 is press-fitted into the side of the housing 18 of the housing 16. As a result, as shown in FIG. 3B, the inner surface of the large diameter portion 38 is fitted into the side of the housing 18, and the inner surface of the large diameter portion 32 of the inner member 26 is fitted into the side of the housing 18. As a result, the protective cover 14 is connected to the housing 16 approximately coaxially with the sensor element 12 and the housing 16. The inner member 26 is disposed so as to surround the tip portion 24 of the sensor element 12. Furthermore, the intermediate member 28 is disposed so as to cover the tip portion 24 of the sensor element 12 and the small diameter portion 36 of the inner member 26. Furthermore, the outer member 30 is disposed so as to cover the tip portion 24 of the sensor element 12, the inner member 26, and the intermediate member 28. Also formed are a first gas chamber 56, a second gas chamber 60, and a sensor element chamber 58. By connecting the protective cover 14 and the housing 16, there are no joints between the protective cover 14 and the housing 16 due to welding.

[0028] Next, spot welding is performed on the connection portion between the large diameter portion 38 of the outer member 30 and the side surface of the housing 18. At this time, a spot welding jig 68 is brought into contact with the large diameter portion 38, and electricity is passed through the large diameter portion 38 and the housing 18, thereby joining the large diameter portion 38 and the housing 18. The spot welding is performed at a plurality of locations in the circumferential direction of the large diameter portion 38, spaced at predetermined angles. This fixes the protective cover 14 to the housing 16. As a result, the gas sensor 10 is completed. Therefore, the steps in FIGS. 3A and 3B correspond to a connecting step for connecting the protective cover 14 to the housing 16.

[0029] Next, a modified example of this embodiment will be described with reference to Figures 4 to 6B. Note that the same components as those described in Figures 1 to 3B will be denoted with the same reference numerals.

[0030] Fig. 4 shows a cross-sectional view of a gas sensor 80 according to a modified example. In comparison with the gas sensor 10 shown in Fig. 1, the gas sensor 80 does not have the gap 52. Furthermore, in the gas sensor 80, a plurality of through holes 82 are formed in the inner member 26. The plurality of through holes 82 are formed in the inner member 26 in the vicinity of the housing 18. The measurement gas flows from the first gas chamber 56 into the sensor element chamber 58 through the plurality of through holes 82, as indicated by the dashed arrows.

[0031] 1, the intermediate member 28 has a different shape. Specifically, the intermediate member 28 has a cylindrical portion 84, a truncated cone portion 50, and a diffusion portion 86. The cylindrical portion 84 is a cylindrical portion having a larger diameter than the small diameter portion 36 of the inner member 26 and a smaller diameter than the small diameter portion 44 of the outer member 30. The tip portion of the cylindrical portion 84 is fitted into the inner surface of the small diameter portion 44 of the outer member 30 by press-fitting the intermediate member 28 into the outer member 30. The small diameter portion 36 of the inner member 26 is fitted into the inner surface of the cylindrical portion 84 by press-fitting the inner member 26 into the intermediate member 28. The truncated cone portion 50 extends forward from the cylindrical portion 84.

[0032] The diffusion section 86 is formed at the rear end (base end) of the cylindrical section 84 so as to have a substantially U-shaped cross section. That is, the diffusion section 86 is formed by curving the base end of the cylindrical section 84 radially outward and folding it back forward. The diffusion section 86 prevents liquid such as water that has entered the first gas chamber 56 from passing through the multiple through holes 82. The diffusion section 86 also diffuses the measurement gas that has entered the gap between the outer member 30 and the inner member 26 in the first gas chamber 56. As a result, the measurement gas is guided to the multiple through holes 82 side of the first gas chamber 56.

[0033] Next, a manufacturing method of the modified example will be described with reference to FIGS. 5A to 6B.

[0034] First, as shown in Fig. 5A, with the inner surface of the outer member 30 and the truncated cone portion 50 of the intermediate member 28 facing each other, the cylindrical portion 84 of the intermediate member 28 is press-fitted into the small diameter portion 44 of the outer member 30. This causes the intermediate member 28 to be fitted approximately coaxially into the inner surface of the outer member 30, as shown in Fig. 5B.

[0035] Next, with the inner surface of the intermediate member 28 and the small diameter portion 36 of the inner member 26 facing each other, the small diameter portion 36 of the inner member 26 is press-fitted into the cylindrical portion 84 of the intermediate member 28. As a result, the inner member 26 is fitted approximately coaxially to the inner surface of the intermediate member 28, as shown in FIG. 6A. As a result, a cylindrical protective cover 14 with a bottom is formed. Therefore, the steps in FIGS. 5A and 5B correspond to the assembly steps for forming the protective cover 14. In the protective cover 14, the outer member 30, the intermediate member 28, and the inner member 26 are connected together in this order by fitting together through press-fitting. In other words, there are no welded joints in the protective cover 14.

[0036] Next, as shown in FIG. 6A, the tip portion 24 of the sensor element 12 held in the housing 16 and the inner member 26 of the protective cover 14 are faced to each other, and the large diameter portion 38 of the outer member 30 is press-fitted into the side of the housing 18 of the housing 16. As a result, as shown in FIG. 6B, the inner surface of the large diameter portion 38 is fitted into the side of the housing 18, and the inner surface of the large diameter portion 32 of the inner member 26 is fitted into the side of the housing 18. As a result, the protective cover 14 is connected to the housing 16 approximately coaxially with the sensor element 12 and the housing 16. The inner member 26 is disposed so as to surround the tip portion 24 of the sensor element 12. Furthermore, the intermediate member 28 is disposed so as to cover the tip portion 24 of the sensor element 12 and the small diameter portion 36 of the inner member 26. Furthermore, the outer member 30 is disposed so as to cover the tip portion 24 of the sensor element 12, the inner member 26, and the intermediate member 28. Further, a first gas chamber 56, a second gas chamber 60, and a sensor element chamber 58 are formed. Therefore, even in this modified example, there are no welded joints between the protective cover 14 and the housing 16.

[0037] Next, the large diameter portion of the outer member 30 38 and the side surface of the housing 16 are spot-welded. The spot welding is performed at a plurality of locations at intervals of a predetermined angle in the circumferential direction of the large diameter portion 38. In this way, the protective cover 14 is fixed to the case 16. As a result, the gas sensor 80 is completed. Therefore, the steps in FIGS. 6A and 6B correspond to a connecting step for connecting the protective cover 14 and the case 16.

[0038] 1 to 6B, the protective cover 14 and the housing 16 are fitted together by press-fitting. In this embodiment, any method may be used to connect the protective cover and the housing. For example, a groove may be formed in one of the protective cover and the housing, and a protrusion may be formed in the other. The protrusion fits into the groove, connecting the protective cover and the housing.

[0039] The manufacturing method of the gas sensor (10, 80) according to this embodiment and the modified example, the gas sensor (10, 80) and the protective cover (14) can be summarized as follows.

[0040] A manufacturing method for a gas sensor (10, 80) comprising a housing (16), a sensor element (12) held in the housing (16), and a protective cover (14) for protecting a tip portion (24) of the sensor element (12) protruding from the housing (16), the method includes a connecting step of connecting the housing (16) and the protective cover (14) so ​​as to cover the tip portion (24) of the sensor element (12) with the protective cover (14), wherein gas is introduced from the outside into a space (56, 58, 60) surrounded by the protective cover (14) and the housing (16), and no welded joints are present in the portions of the protective cover (14) and the housing (16) for forming the space (56, 58, 60).

[0041] A gas sensor (10, 80) comprising a housing (16), a sensor element (12) held in the housing (16), and a protective cover (14) that protects a tip portion (24) of the sensor element (12) protruding from the housing (16), wherein the housing (16) and the protective cover (14) are connected together so that the tip portion (24) of the sensor element (12) is covered with the protective cover (14), gas is introduced from the outside into a space (56, 58, 60) surrounded by the protective cover (14) and the housing (16), and there are no welded joints in the portions of the protective cover (14) and the housing (16) that form the space (56, 58, 60).

[0042] According to the present embodiment and its modified examples, no fume adheres to the protective cover (14) and the housing (16). This ensures the accuracy of connection between the protective cover (14) and the housing (16). Furthermore, gas flows smoothly through the space (56, 58, 60) surrounded by the protective cover (14) and the housing (16). This prevents a decrease in the measurement accuracy of the sensor element (12). Therefore, in the present embodiment and its modified examples, the defect rate of the gas sensor (10, 80) can be reduced. Furthermore, the manufacturing cost of the gas sensor (10, 80) can be reduced. Furthermore, the number of management steps required for manufacturing the gas sensor (10, 80) can be reduced.

[0043] In the connecting step, the protective cover (14) and the housing (16) are fitted together, thereby easily achieving the above-mentioned effects.

[0044] In the connecting step, the protective cover (14) and the housing (16) are fitted together by press fitting, thereby easily achieving the above-mentioned effects.

[0045] The protective cover (14) has an inner member (26) arranged in the housing (16) so as to surround the tip portion (24) of the sensor element (12), and an outer member (30) arranged in the housing (16) so as to cover the tip portion (24) of the sensor element (12) and the inner member (26). The manufacturing method of the gas sensor (10, 80) further includes, prior to the connecting step, an assembly step of fitting the inner member (26) and the outer member (30) by press-fitting to form the protective cover (14), and in the connecting step, the outer member (30) is connected to a side surface of the housing (16) and the inner member (26) is connected to a side surface of the housing (16).

[0046] Since no welding is performed in the assembly step, the number of manufacturing steps can be reduced. This reduces the cost of the gas sensor (10, 80). In addition, the accuracy of assembling the inner member (26) and the outer member (30) is improved. In addition, the accuracy of assembling the protective cover (14) and the housing (16) is improved. Furthermore, it is possible to prevent a decrease in the measurement accuracy of the sensor element (12) due to the adhesion of fumes.

[0047] The protective cover (14) is disposed between the inner member (26) and the outer member (30) and further includes an intermediate member (28) that covers the tip portion (24) of the sensor element (12), and in the assembly step, the intermediate member (28) is fitted to the inner surface of the outer member (30) by press fitting, and then the inner member (26) is fitted to the inner surfaces of the outer member (30) and the intermediate member (28) by press fitting. This makes it easy to obtain the above-mentioned effects.

[0048] The outer member (30), the intermediate member (28), and the inner member (26) are fitted together approximately coaxially, and in the connecting step, the housing (16) and the protective cover (14) are connected together so that the sensor element (12), the housing (16), and the protective cover (14) are approximately coaxially arranged. This improves the accuracy of assembling the components constituting the gas sensor (10, 80) and the measurement accuracy of the sensor element (12).

[0049] In the connecting step, the connecting portion between the outer member (30) and the side surface of the housing (16) is fixed by welding. Since the welding is performed after the protective cover (14) is attached to the housing (16), it is possible to prevent fumes from entering.

[0050] In the connecting step, the connecting portions between the outer member 30 and the side surface of the housing 16 are fixed by resistance welding, thereby making it possible to inexpensively fix the protective cover 14 to the housing 16.

[0051] In the connecting step, the connecting portions between the outer member 30 and the side surface of the housing 16 are fixed by laser welding, thereby enabling the protective cover 14 to be fixed to the housing 16 with high accuracy in a short time.

[0052] In the connecting step, the connecting portions between the outer member 30 and the side surface of the housing 16 are fixed by spot welding, which makes it possible to fix the protective cover 14 to the housing 16 at a lower cost.

[0053] A protective cover (14) for protecting a tip portion (24) of a sensor element (12) held in a housing (16), the protective cover (14) comprising an inner member (26) arranged in the housing (16) so as to surround the tip portion (24) of the sensor element (12), and an outer member (30) arranged in the housing (16) so as to cover the tip portion (24) of the sensor element (12) and the inner member (26), the inner member (26) and the outer member (30) being joined by fitting.

[0054] Even in this case, no fumes adhere to the protective cover (14) and the housing (16). This ensures the accuracy of connection between the protective cover (14) and the housing (16). As a result, the gas flows smoothly through the space (56, 58, 60) surrounded by the protective cover (14) and the housing (16). This prevents a decrease in the measurement accuracy of the sensor element (12). The rate of defects of the gas sensor (10, 80) can be reduced. Furthermore, the number of management steps required for manufacturing the gas sensor (10, 80) can be reduced. Moreover, since no welding is performed, the number of manufacturing steps can be reduced. As a result, the cost of the gas sensor (10, 80) can be reduced. Furthermore, the accuracy of assembly between the inner member (26) and the outer member (30) is improved. Furthermore, the accuracy of assembly between the protective cover (14) and the housing (16) is improved.

[0055] The sensor further includes an intermediate member (28) that is disposed between the inner member (26) and the outer member (30) and covers the tip portion (24) of the sensor element (12), the intermediate member (28) being fitted to the inner surface of the outer member (30), and the inner member (26) being fitted to the inner surfaces of the outer member (30) and the intermediate member (28). This makes it easy to obtain the above-mentioned effects.

[0056] The outer member (30), the intermediate member (28) and the inner member (26) are fitted together approximately coaxially, thereby improving the accuracy of assembling the components constituting the gas sensor (10, 80) and the measurement accuracy of the sensor element (12).

[0057] The outer member 30, the intermediate member 28 and the inner member 26 are fitted together by press fitting, thereby easily achieving the above-mentioned effects.

[0058] The present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0059] 10, 80...Gas sensor 12...Sensor element 14…Protective cover 16…Housing 24...Tip 26…Inner member 28...Intermediate part 30...Outer member 56…First Gas Chamber 58…Sensor element chamber 60…Second gas chamber

Claims

1. 1. A method for manufacturing a gas sensor comprising: a housing; a sensor element held in the housing; and a protective cover for protecting a tip portion of the sensor element protruding from the housing, the method comprising the steps of: the protective cover includes an inner member disposed in the housing so as to surround a tip portion of the sensor element, an outer member disposed in the housing so as to cover the tip portion of the sensor element and the inner member, and an intermediate member disposed between the inner member and the outer member and covering the tip portion of the sensor element and a tip side of the inner member, The method for manufacturing the gas sensor includes the steps of: an assembly step of fitting an outer surface of the intermediate member to an inner surface of the outer member by press fitting, and then fitting an outer surface of the inner member to the inner surfaces of the outer member and the intermediate member by press fitting to form the protective cover; a connecting step of connecting an inner surface of the outer member to a side surface of the housing and connecting an inner surface of the inner member to a side surface of the housing so as to cover a tip portion of the sensor element with the protective cover, and fixing only a portion of the inner surface of the outer member that directly contacts the side surface of the housing and only a portion of the side surface of the housing that directly contacts the inner surface of the outer member by welding; having A gas is introduced from the outside into a space surrounded by the protective cover and the housing, The method for manufacturing a gas sensor, wherein the protective cover has no welded joints other than the welded parts welded in the connecting step.

2. 2. The method for manufacturing the gas sensor according to claim 1, In the connecting step, the protective cover and the housing are fitted together.

3. 3. The method for manufacturing a gas sensor according to claim 2, further comprising the steps of: In the connecting step, the protective cover and the housing are fitted together by press fitting.

4. The method for manufacturing the gas sensor according to any one of claims 1 to 3, the outer member, the intermediate member and the inner member are fitted together substantially coaxially, In the connecting step, the housing and the protective cover are connected to each other so that the sensor element, the housing, and the protective cover are substantially coaxial with each other.

5. The method for manufacturing the gas sensor according to any one of claims 1 to 4, further comprising the steps of: A method for manufacturing a gas sensor, wherein in the connecting step, only a portion of the inner surface of the outer member that directly contacts the side surface of the housing and only a portion of the side surface of the housing that directly contacts the inner surface of the outer member are fixed by resistance welding.

6. The method for manufacturing the gas sensor according to any one of claims 1 to 4, further comprising the steps of: A method for manufacturing a gas sensor, wherein in the connecting step, only a portion of the inner surface of the outer member that is in direct contact with the side surface of the housing and only a portion of the side surface of the housing that is in direct contact with the inner surface of the outer member are fixed by laser welding.

7. 7. The method for producing a gas sensor according to claim 5, further comprising the steps of: In the connecting step, only a portion of the inner surface of the outer member that directly contacts the side surface of the housing and only a portion of the side surface of the housing that directly contacts the inner surface of the outer member are fixed by spot welding.

8. A gas sensor comprising a housing, a sensor element held in the housing, and a protective cover for protecting a tip portion of the sensor element protruding from the housing, the protective cover includes an inner member disposed in the housing so as to surround a tip portion of the sensor element, an outer member disposed in the housing so as to cover the tip portion of the sensor element and the inner member, and an intermediate member disposed between the inner member and the outer member and covering the tip portion of the sensor element and a tip side of the inner member, the protective cover is configured by fitting an outer surface of the intermediate member to an inner surface of the outer member by press fitting, and fitting an outer surface of the inner member to the inner surfaces of the outer member and the intermediate member by press fitting, an inner surface of the outer member and a side surface of the housing are connected, and an inner surface of the inner member and a side surface of the housing are connected, and only a portion of the inner surface of the outer member that directly contacts the side surface of the housing and only a portion of the side surface of the housing that directly contacts the inner surface of the outer member are fixed by welding, so that a tip portion of the sensor element is covered with the protective cover, A gas is introduced from the outside into a space surrounded by the protective cover and the housing, The gas sensor according to claim 1, wherein the protective cover has no welded joints other than the welded portions.

Images