Gas sensor

Abstract

A gas sensor includes a metal case in which a sensor element is inserted, and a metal outer tube that is welded to the outer periphery of the case, and pinholes are suppressed from being generated on the surface of the welded portion. In the gas sensor according to one aspect of the present invention, the length in the axial direction of the outer peripheral surface of the case that contacts the inner peripheral surface of the outer tube, that is, the contact distance Lg, at a position on the rear end side from the molten portion formed by welding, is equal to or less than the reference distance Lr.

Description

Technical Field

[0001] This invention relates to gas sensors. Background Technology

[0002] Conventionally, gas sensors for detecting the concentration of specific gases such as oxygen and NOx in gases such as automobile exhaust have been known, for example, those with the following configuration: a cylindrical metal housing with an elongated sensor element extending axially through it, and a metal outer cylinder welded to the outer periphery of the housing. For example, Patent Document 1 discloses a gas sensor manufactured by pressing a portion of the housing into the outer cylinder and then welding the overlapping portion of the housing and the outer cylinder circumferentially to join them together.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2002-174622 Summary of the Invention

[0006] The inventors of this invention have discovered that when welding a gas sensor having the above-described configuration, the following problem occurs when residual oil or the like adheres to the contact surface between the housing and the outer cylinder. Specifically, this residual oil or the like becomes volatile gas due to the heat during welding, and sometimes, due to mixing with the weld metal, manifests as bubbles (pinholes) on the surface of the welded portion (welded area surface).

[0007] Furthermore, the presence of such a pinhole can lead to corrosion originating from the pinhole, or the pinhole penetrating a component (such as the outer cylinder), resulting in reduced sealing. This possibility increases, especially when the gas sensor is used in harsh environments or for extended periods. To prevent this, it is considered to thoroughly clean both the housing and the outer cylinder to ensure no oil residue remains on their contact surfaces; however, it is difficult to completely eliminate any residual oil.

[0008] One aspect of the present invention was made in view of the above circumstances, and its object is to provide a gas sensor having a metal housing for inserting a sensor element, a metal outer cylinder welded to the outer periphery of the housing, and suppressing the generation of pinholes on the surface of the welded portion.

[0009] The present invention employs the following configuration to solve the aforementioned problems.

[0010] The gas sensor described in the first viewpoint comprises: a cylindrical and metal housing, an elongated sensor element extending axially through the interior of the housing; and a metal outer cylinder, a portion of the rear end of the housing in the axial direction being pressed into the outer cylinder, the outer cylinder being assembled onto the outer circumferential surface of the housing by circumferential welding of the overlapping portion of the outer cylinder and the pressed-in housing, the axial length of the outer circumferential surface of the housing in contact with the inner circumferential surface of the outer cylinder at a position closer to the rear end than the molten portion of the outer cylinder formed by the welding, i.e., the contact distance Lg, is a reference distance Lr or less, and the reference distance Lr is calculated by the following mathematical formula (1).

[0011] Lr=k×Da / (Tb×Tc)···Mathematical formula (1)

[0012] Here, in the mathematical formula (1), "k" represents a proportionality constant, "Da" represents the radial depth of the shell from its outer circumferential surface to the deepest part of the molten portion melted into the shell, "Tb" represents the difference between the outer diameter of the shell and the inner diameter of the outer cylinder, i.e., the reduction amount, and "Tc" represents the thickness of the outer cylinder. The molten portion can also be referred to as the part of the outer cylinder whose structure changes due to melting.

[0013] In this configuration, the gas sensor includes: a metal housing through which the sensor element passes; and a metal outer cylinder, into which the housing is pressed, and the outer cylinder is circumferentially welded at the overlapping portion of the outer cylinder and the housing, thereby fitting the outer cylinder to the outer circumferential surface of the housing. For example, laser welding is performed circumferentially at the overlapping portion of the housing and the outer cylinder, thereby fitting the outer cylinder to the outer circumferential surface of the housing. Furthermore, in the gas sensor, the contact distance Lg is less than or equal to the reference distance Lr, and the reference distance Lr is calculated using the mathematical formula (1).

[0014] Here, the reference distance Lr represents the maximum distance (reachable distance) that volatile gases, such as residual oil or other substances adhering to the contact surfaces of the housing and the outer cylinder, can travel under their own pressure due to the heat generated during welding. That is, when at least one of the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder is adhered to, the residual oil or other substances evaporate due to the heat generated during welding, thereby generating volatile gases. When the distance that such volatile gases can travel between the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder under their own pressure is called the "reachable distance of the volatile gases," the reference distance Lr is the maximum value of this reachable distance.

[0015] Furthermore, the reachable distance of the volatile gas has the following relationship with Da, Tb, and Tc: The larger Da, which represents the radial depth of the shell from its outer peripheral surface to the deepest part of the molten portion within the shell, the greater the thermal deformation of the shell and the outer cylinder. In other words, the larger Da is, the larger the gap between the outer peripheral surface of the shell and the inner peripheral surface of the outer cylinder. Therefore, the larger Da is, the smaller the diffusion resistance to the volatile gas, and the greater the reachable distance of the volatile gas moving between the outer peripheral surface of the shell and the inner peripheral surface of the outer cylinder. Additionally, the larger Tb, which represents the difference between the outer diameter of the shell and the inner diameter of the outer cylinder (i.e., the reduction), the greater the diffusion resistance to the volatile gas, and the smaller the reachable distance of the volatile gas moving between the outer peripheral surface of the shell and the inner peripheral surface of the outer cylinder. Furthermore, the larger the Tc, which represents the thickness of the outer cylinder, the easier it is for the heat during welding to diffuse, thus reducing the amount of volatile gas generated. Additionally, the thermal deformation of the shell and the outer cylinder is smaller. Therefore, the larger the Tc, the smaller the reachable distance of the volatile gas moving between the outer circumferential surface of the shell and the inner circumferential surface of the outer cylinder. Since Da, Tb, and Tc have the aforementioned relationship with respect to the reachable distance, the maximum value of the reachable distance, i.e., the reference distance Lr, can be expressed as a function of Da, Tb, and Tc. Furthermore, k, as a proportionality constant, can be determined through experiments, etc. Therefore, the reference distance Lr is calculated using the mathematical formula (1), which is a function of the proportionality constants k, Da, Tb, and Tc.

[0016] Furthermore, in the gas sensor, the contact distance Lg is less than or equal to the reference distance Lr, that is, "the axial length of the outer peripheral surface of the housing that contacts the inner peripheral surface of the outer cylinder at a position closer to the rear end of the molten portion" is less than or equal to the reference distance Lr. In other words, the length from the position of "the end point where the molten portion contacts the outer peripheral surface of the housing" (molten portion end) to "the position where the outer peripheral surface of the housing and the inner peripheral surface of the outer cylinder become non-contact in the entire circumferential direction" (release position) is less than or equal to the reference distance Lr.

[0017] Therefore, during the welding process, the volatile gas generated between the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder, which are in contact with each other, can move under its own pressure to a position where the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder become non-contact in the entire circumferential direction (release position). During the welding process, for example, the volatile gas at the molten portion can move under its own pressure to a position where "the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder become non-contact in the entire circumferential direction." That is, the volatile gas generated during the welding process can move towards the release position under its own pressure and be released there. Therefore, the gas sensor can reduce the possibility of volatile gas remaining in the molten portion and causing pinholes in the molten portion; that is, it can suppress the formation of pinholes in the molten portion.

[0018] Therefore, the gas sensor includes: a metal housing through which the sensor element is inserted, and a metal outer cylinder welded to the outer periphery of the housing, which can suppress the formation of pinholes in the molten portion.

[0019] Furthermore, in the gas sensor, by making the contact distance Lg less than or equal to the reference distance Lr calculated by the mathematical formula (1), pinholes can be suppressed in the molten portion. Moreover, as described above, the proportionality constant k in the mathematical formula (1) can be solved in advance through experiments, etc. Therefore, the structure for suppressing pinhole formation can be determined during the design phase of the gas sensor; for example, the value of the contact distance Lg can be determined during the design phase to be less than or equal to the reference distance Lr. Furthermore, by suppressing the formation of pinholes in the gas sensor, the possibility of corrosion and reduced sealing caused by pinholes can be suppressed. Moreover, since the structure for suppressing pinhole formation can be implemented during the design phase of the gas sensor, the formation of pinholes can be suppressed without changing welding conditions from previous gas sensors. Additionally, for the gas sensor, it is not necessary to thoroughly clean the housing and the outer cylinder separately to prevent oil residue from remaining on the contact surfaces of the housing and the outer cylinder; therefore, the time spent on management and processes that are necessary during manufacturing can be reduced.

[0020] The second viewpoint relates to a gas sensor that, based on the gas sensor described in the first viewpoint, allows the reference distance Lr to be greater than 1.2 times the contact distance Lg. In this configuration, the reference distance Lr in the gas sensor is greater than 1.2 times the contact distance Lg; that is, the contact distance Lg is less than 1 / 2 of the reference distance Lr. The inventors of this invention have experimentally confirmed that by making the contact distance Lg less than 1 / 2 of the reference distance Lr, the number of pinholes generated in the molten portion is drastically reduced. Therefore, for the gas sensor, by making the contact distance Lg less than 1 / 2 of the reference distance Lr, the generation of pinholes in the molten portion can be suppressed extremely effectively.

[0021] The gas sensor described in the third viewpoint, based on the gas sensor described in the first or second viewpoint above, allows for chamfering of the rear end of the outer peripheral surface of the housing. In this configuration, the rear end of the outer peripheral surface of the housing is chamfered; for example, the chamfer can be straight or curved. The rear end of the outer peripheral surface of the housing can be chamfered using at least one of C-shaped and R-shaped chamfering. This allows the gas sensor to use the chamfered rear end of the outer peripheral surface of the housing as a guide when pressing the housing into the outer cylinder, facilitating the pressing of the housing into the outer cylinder.

[0022] The fourth viewpoint relates to a gas sensor that, based on the gas sensor described in the third viewpoint, involves a chamfering process where the chamfering can be an R-shaped chamfer. In this configuration, the chamfering performed on the rear end of the outer peripheral surface of the housing in the gas sensor is an R-shaped chamfer. By employing an R-shaped chamfer as the chamfering process performed on the rear end of the outer peripheral surface of the housing, burr generation during processing can be suppressed, thereby preventing burr biting between the housing and the outer cylinder.

[0023] The gas sensor involved in the fifth viewpoint, based on the gas sensors involved in any of the first to fourth viewpoints mentioned above, may have a slit extending along the axial direction formed on at least one of the outer peripheral surface of the shell and the inner peripheral surface of the outer cylinder, which is closer to the rear end side than the molten portion.

[0024] In this configuration, in the gas sensor, at least one of the outer peripheral surface of the shell and the inner peripheral surface of the outer cylinder, located closer to the rear end of the molten portion, is formed along the axial direction of the outer cylinder and the housing, with slits extending along the axial direction. In the gas sensor, the slits may extend to the end face of the rear end of the housing. Furthermore, in the gas sensor, at least one of the outer peripheral surface of the housing and the inner peripheral surface of the outer cylinder may have a plurality of slits spaced apart from each other in the circumferential direction.

[0025] The inventors of this invention have confirmed that by forming a slit extending along the axial direction on at least one of the outer peripheral surface of the housing and the inner peripheral surface of the outer cylinder, the effect of suppressing pinhole formation can be improved compared to the case where the slit is not formed. Therefore, the gas sensor, by forming a slit extending along the axial direction, can further improve the effect of suppressing pinhole formation in the molten portion compared to the case where the slit is not formed.

[0026] Invention Effects

[0027] According to the present invention, a gas sensor is provided having a metal housing for sensor elements to pass through, and a metal outer cylinder welded to the outer periphery of the housing, and suppressing the generation of pinholes on the surface of the welded portion. Attached Figure Description

[0028] Figure 1 This is a partial cross-sectional schematic diagram illustrating an example of the main components of a gas sensor according to an embodiment.

[0029] Figure 2 It is shown schematically. Figure 1 An enlarged cross-sectional view of the relationship between the housing and the outer cylinder at the periphery of the welding position in the gas sensor.

[0030] Figure 3 This is an enlarged cross-sectional view schematically showing the relationship between the periphery of the welding position and the outer cylinder for the shell of modified Example 1.

[0031] Figure 4 This is an enlarged cross-sectional view schematically showing the relationship between the periphery of the weld position and the outer cylinder for the shell of modified Example 2.

[0032] Figure 5 This is an enlarged cross-sectional view schematically showing the relationship between the periphery of the welding position and the outer cylinder for the shell of modified Example 3.

[0033] Figure 6 This is an enlarged cross-sectional view showing examples of various chamfering processes performed on the corners of the housing.

[0034] Symbol Explanation

[0035] 1…Gas sensor, 10…Sensor element, 20…Housing, 40…Outer cylinder, 210…Outer circumferential surface, 410…Inner circumferential surface, 420…Melted portion, AX…Axial direction, Lg…Contact distance, Lr…Reference distance, Da…Melting depth, Dp…Deepest part (deepest part of the molten portion), k…Proportional constant, Tb…Shrinkage, Tc…Thickness, Sl…Slit. Detailed Implementation

[0036] Hereinafter, based on the accompanying drawings, an embodiment of one aspect of the present invention (hereinafter also referred to as "this embodiment") will be described. However, the embodiments described below are merely examples of the present invention in all respects. Of course, various modifications and variations can be made without departing from the scope of the present invention. That is, when implementing the present invention, specific configurations corresponding to the embodiments can be appropriately adopted.

[0037] The gas sensor 1 described in detail below includes: a cylindrical housing 20, with an elongated sensor element 10 extending axially AX through its interior; and an outer cylinder 40 fitted onto the outer peripheral surface 210 of the housing 20. Both the housing 20 and the outer cylinder 40 are made of metal. After pressing the rear end of the housing 20 into the front end of the outer cylinder 40, circumferential welding is performed at the overlapping portion of the housing 20 and the outer cylinder 40, thereby fitting the outer cylinder 40 onto the outer peripheral surface 210 of the housing 20. With this configuration, during welding, if at least one of the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40 is present, the oil or similar substances will evaporate due to the heat generated during welding. Furthermore, if the volatile gas does not escape from between the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 but remains in the molten portion 420 of the outer cylinder 40 formed by welding, then bubbles of volatile gas, i.e., pinholes, are generated in the molten portion 420. The molten portion 420 can also be referred to as the portion whose structure changes due to melting.

[0038] The inventors of this invention explored a method for suppressing the generation of pinholes and confirmed that, regarding the gas sensor 1, the generation of pinholes can be suppressed by configuring it to have the following structure: Specifically, it was confirmed that, in the gas sensor 1, by allowing the volatile gas in the molten portion 420 to be discharged between the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40, which are in contact with each other, the generation of pinholes in the molten portion 420 can be suppressed.

[0039] Specifically, in gas sensor 1, the outer peripheral surface 210 of housing 20 and the inner peripheral surface 410 of outer cylinder 40 are in contact with each other. However, the volatile gas generated by the heat during welding can move between the outer peripheral surface 210 and the inner peripheral surface 410 by its own pressure. Therefore, in gas sensor 1, the distance (contact distance Lg) from the rear end of the molten portion 420 of outer cylinder 40 (molten portion end Ef) to the point where the outer peripheral surface 210 and the inner peripheral surface 410 become non-contact (non-contact position Np) is adjusted to satisfy the following condition: that is, in gas sensor 1, the contact distance Lg is adjusted to be "the distance that the volatile gas can move between the outer peripheral surface 210 and the inner peripheral surface 410 by its own pressure" (reachable distance) or less.

[0040] In gas sensor 1, by setting the contact distance Lg below the reachable distance, volatile gases in the molten portion 420 can be discharged between the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40. Therefore, gas sensor 1 can suppress the possibility that "volatile gases do not discharge between the outer peripheral surface 210 and the inner peripheral surface 410, and remain in the molten portion 420, causing pinholes in the molten portion 420".

[0041] The following uses Figure 1 The details of the gas sensor 1, which suppresses the generation of pinholes in the molten portion 420 by making the contact distance Lg below the reachable distance, especially the maximum value of the reachable distance, i.e., below the reference distance Lr, will be explained.

[0042] [Example of composition]

[0043] (Overall overview of the gas sensor)

[0044] Figure 1 This is a partial cross-sectional schematic diagram illustrating an example of the main components of the gas sensor 1 according to this embodiment. In this embodiment, to facilitate understanding of the relationship that the housing 20 and outer cylinder 40 of the gas sensor 1 should satisfy, particularly the condition that the contact distance Lg should satisfy, an example of a gas sensor 1 having the following configuration will be described. Specifically, an example of a gas sensor 1 having a sensor element 10, a housing 20, a sensor element holding member 30, an outer cylinder 40, and an outer protective cover 50 will be described. However, the gas sensor 1 of this embodiment may also have a configuration other than the sensor element 10, housing 20, sensor element holding member 30, outer cylinder 40, and outer protective cover 50.

[0045] The gas sensor 1 of this embodiment detects a specified target gas component (e.g., NOx) in a gas to be measured (e.g., exhaust gas) through a sensor element 10 disposed within it. The gas sensor 1 includes: a cylindrical housing 20, through which the sensor element 10 passes along the axial direction AX; and an outer cylinder 40, which is fitted onto the outer peripheral surface 210 of the housing 20. Figure 1 The gas sensor 1 illustrated also includes: a sensor element holding member 30 having an insertion hole for holding the sensor element 10 and being made of ceramic material; and a bottomed cylindrical outer protective cover 50 that surrounds (covers) the front end side of the sensor element 10. Figure 1 As illustrated, the outer side of the gas sensor 1 is mainly composed of an outer protective cover 50, a housing 20, and an outer cylinder 40.

[0046] For example, the central axes of the gas sensor 1, sensor element 10, housing 20, sensor element holding component 30, outer cylinder 40, and outer protective cover 50 are all coaxial. It should be noted that... Figure 1 The gas sensor 1 is shown in the figure with its central axis (axis) aligned with the left-right direction of the main body. In the following description, unless otherwise specified, the left side of the paper is referred to as the front end side of the gas sensor 1, and the right side as the rear end side. The front end side of the gas sensor 1 and the front end side of the sensor element 10 are on the same side, as are the rear end side of the gas sensor 1 and the rear end side of the sensor element 10.

[0047] (Sensor element)

[0048] The sensor element 10 is a long, columnar or thin plate-shaped component with a component body mainly composed of a zirconium oxide or other oxygen ion conductive solid electrolyte ceramic. The sensor element 10 can also be configured as a long, cylindrical or tubular component. The sensor element 10 has the following configuration: a gas inlet and an internal cavity are provided at the front end; and various electrodes and wiring patterns are provided on the surface and inside the component body.

[0049] In sensor element 10, the gas to be measured introduced into the internal cavity is reduced or decomposed within the internal cavity to generate oxygen ions. In gas sensor 1, the amount of oxygen ions flowing inside sensor element 10 is directly proportional to the concentration of a specified gas component in the gas being measured; based on this, the concentration of the gas component is determined.

[0050] like Figure 1As illustrated, a defined range along the length of the surface of sensor element 10, measured from its tip, can be covered by a protective film P. The protective film P is a porous membrane of approximately 10 μm to 2000 μm thickness, formed of materials such as Al₂O₃, and is used to protect the area near the tip of sensor element 10 from thermal shock; it is also called a thermal shock resistant protective layer. The protective film P is preferably formed to withstand forces up to approximately 50 N, depending on its intended purpose. The extent of the protective film P is appropriately determined based on the specific structure of sensor element 10.

[0051] The end of the sensor element 10, which is a long, columnar, or thin plate-like component, that is not covered by the protective film P is the rear end of the sensor element 10. In the gas sensor 1, the sensor element 10 extends axially AX through the interior of the cylindrical housing 20, with the front end covered by the protective film P and the rear end not covered by the protective film P protruding from the housing 20.

[0052] (case)

[0053] The housing 20 is a cylindrical component that extends through the sensor element 10 along the axial direction AX, and is made of metal. The housing 20 has a cylindrical storage space inside to house the sensor element 10, etc., and is used when fixing the gas sensor 1 at the measurement position.

[0054] The housing 20 has, for example, a radially projecting protrusion (flange), which may be provided throughout the circumference. This protrusion is a component that contacts an external component (e.g., an exhaust pipe) for mounting the gas sensor 1 (not shown) to prevent the gas to be measured from leaking out of the space defined by the external component (e.g., inside the exhaust pipe).

[0055] For example, a fixing bolt (not shown) is mounted around the outer periphery of the housing 20 in contact with the protrusion. This fixing bolt is made of, for example, metal and has external threads on its outer peripheral surface. The housing 20 is inserted into a fixing member (mounted portion, boss) that is welded to the exhaust pipe and has internal threads on its inner peripheral surface. Furthermore, the fixing bolt is inserted into the fixing member with the protrusion in contact with it. In this way, the housing 20 is fixed within the fixing member; that is, the gas sensor 1 is fixed within the exhaust pipe. The protrusion (particularly the front end face of the protrusion) abuts against the surface of the exhaust pipe (fixing member) to form a sealing surface, thereby preventing the measured gas from leaking out of the exhaust pipe.

[0056] It should be noted that... Figure 1 The front and rear ends of the housing 20 illustrated are configured as separate components. The housing 20 is formed by connecting and fixing the front and rear ends of the components using welding or the like. For example, the housing 20 may include a metal main body with protrusions (equivalent to...). Figure 1 The example shown is the component on the front end side of the housing 20, and the cylindrical inner cylinder (equivalent to) welded and fixed to the main metal part. Figure 1 (The component corresponding to the rear end of the housing 20 illustrated in the figure). In this embodiment, the housing 20 can be any cylindrical metal component through which the sensor element 10 passes along the axial direction AX. The housing 20 can be composed of a single cylindrical component or it can be constructed by coaxially connecting multiple cylindrical components.

[0057] As described above, the sensor element 10 is housed within a storage space inside the cylindrical housing 20. For example, in this storage space, the sensor element 10 is arranged such that its length direction aligns with the axial direction AX of the cylindrical housing 20; specifically, it is arranged so that the central axis of the sensor element 10 is coaxial with the central axis of the housing 20. The position of the sensor element 10, housed in this manner within the storage space of the housing 20, is maintained by the sensor element holding member 30.

[0058] (Sensor element holding component)

[0059] The sensor element holding member 30 is a component made of ceramic material that holds the sensor element 10 within the housing 20 for contact with the sensor element 10. Figure 1 The sensor element holding component 30 illustrated includes ceramic supports 310, 330, and 350, and powder compactors 320 and 340. The sensor element holding component 30 may further include washers (not shown). The ceramic supports 310, 330, and 350, and the powder compactors 320 and 340 each have through holes for holding the sensor element 10, and are coaxially mounted around it relative to the sensor element 10. That is, in the gas sensor 1, the ceramic supports 310, 330, and 350, and the powder compactors 320 and 340 are mounted around the central axis of the housing 20 (the central axis of the gas sensor 1) with the sensor element 10 positioned on it. Figure 1 The illustration shows an example where ceramic support 310, powder compaction body 320, ceramic support 330, powder compaction body 340, and ceramic support 350 are sequentially arranged around the sensor element 10 from the front end to the rear end. Furthermore, the aforementioned gasket can be arranged around the sensor element 10 at a position further rearward than the ceramic support 350, in contact with the ceramic support 350. It should be noted that in the following description, ceramic support 310, 330, 350, powder compaction body 320, 340, and the aforementioned gasket will be collectively referred to as "surrounding assembly components".

[0060] Ceramic support components 310, 330, and 350 are ceramic insulators. Additionally, powder compacts 320 and 340 are components formed from ceramic powders such as talc.

[0061] For example, such as Figure 1 As illustrated, a tapered portion is provided on the front end side inside the housing 20, which locks (fixes) the ceramic support members 310, 330, 350, powder compaction members 320, 340, and a washer (not shown) surrounding the sensor element 10. This is achieved by fitting the housing 20 into the outer periphery of the surrounding assembly members while they are already pre-assembled around the sensor element 10. Furthermore, after locking, a predetermined load is applied to the washer from the rear end side toward the front end side, compressing the powder compaction members 320 and 340 respectively, thereby sealing the space between the two ends of the sensor element 10 inside the housing 20. With this sealing achieved, the housing 20 on the rear end side of the washer is riveted to a reduced diameter shape, thereby constraining the surrounding assembly members and ensuring airtightness between the two ends of the sensor element 10. That is, within the internal space of the housing 20, the ceramic supports 310, 330, 350 and the powder compactors 320, 340 surrounding the sensor element 10 are sealed by the inner surface (inner wall) of the housing 20, particularly the inner wall at the conical portion, and the gaskets. Here, the position of the housing 20 adjacent to the powder compactor 340 can be riveted to a reduced diameter shape, thereby further improving the airtightness between the two ends of the sensor element 10.

[0062] It should be noted that, although the illustration is omitted, in the gas sensor 1, inside the outer cylinder 40 and located further rearward than the housing 20, a connector for electrical connection between the sensor element 10 and the outside can be connected to the multiple terminal electrodes of the sensor element 10. A wire extending from this connector can be led out from an opening provided at the rear end of the outer cylinder 40. This opening at the rear end of the outer cylinder 40 can be further used as an inlet / outlet for the reference gas, i.e., atmosphere.

[0063] The rear end of a cylindrical housing 20, which houses the sensor element 10 and the sensor element holding member 30 within its internal space, is pressed into the front end of an outer cylinder 40. Furthermore, the outer cylinder 40 is circumferentially welded to the overlapping portion of the housing 20, thereby assembling the outer cylinder 40 to the outer peripheral surface 210 of the housing 20. Figure 1 In the example shown, welding is performed circumferentially at the welding position Wp, thereby assembling the outer cylinder 40 onto the outer peripheral surface 210 of the shell 20.

[0064] (outer cylinder)

[0065] The outer cylinder 40 is a cylindrical metal component that surrounds and is fitted around the outer peripheral surface 210 (particularly the rear end side of the outer peripheral surface 210) of the housing 20, protecting the parts of the gas sensor 1 that are not in contact with the gas being measured. Specifically, the outer cylinder 40 is fixed to the housing 20 by a portion of the rear end side of the outer peripheral surface 210 being tightly fitted to the inner peripheral surface 410. The surrounding assembly of the outer cylinder 40 relative to the housing 20 and the tight fit between the outer cylinder 40 and the housing 20 are achieved by pressing a portion of the rear end side of the housing 20 into the outer cylinder 40.

[0066] The inner space of the outer cylinder 40 serves as the reference gas, i.e., the space where the reference gas, atmosphere, exists. The inner space of the outer cylinder 40 is isolated from the gas sensor 1 when it is installed inside a pipe, such as an engine exhaust pipe, containing the gas to be measured. However, the inner space of the outer cylinder 40 is not sealed; atmosphere can enter and exit through an opening (not shown) at the rear end of the outer cylinder 40 relative to the inner space of the outer cylinder 40.

[0067] (Outer protective cover)

[0068] The outer protective cover 50 is a bottomed cylindrical component, for example, made of metal, that surrounds (covers) the front end of the sensor element 10. The outer protective cover 50 protects the part of the gas sensor 1 that is in direct contact with the gas being measured, i.e., the front end of the sensor element 10 and its vicinity, during use. Figure 1 As illustrated, a through-hole 51 is formed in the outer protective cover 50 to allow the measured gas to flow from the outside to the inside. Figure 1 An example is shown where a through hole 51 is formed on the bottom surface (the surface on the front end side of the gas sensor 1) of the outer protective cover 50, which is a bottomed cylindrical component. However, Figure 1 The arrangement of the through holes 51 shown is merely an example. The location and number of through holes 51 can be appropriately determined by considering the flow pattern of the gas being measured toward the interior of the outer protective cover 50. For example, multiple through holes 51 can be formed on the side of the outer protective cover 50, which is a bottomed cylindrical component. Alternatively, multiple through holes 51 can be formed on the bottom surface of the outer protective cover 50.

[0069] The outer protective cover 50 is fitted to the outer peripheral surface 210 of the front end side of the housing 20. For example, the inner peripheral surface of the rear end side (opening edge) of the outer protective cover 50 abuts against the housing 20, thereby fixing the outer protective cover 50 to the housing 20.

[0070] Figure 1In the gas sensor 1 illustrated, the opening edge of the bottomed cylindrical outer protective cover 50 contacts the protrusion of the housing 20. However, for the gas sensor 1, contact between the opening edge of the outer protective cover 50 and the protrusion of the housing 20 is not necessary; a gap may exist between them. For example, a drainage channel (not shown) may be provided between the protrusion of the housing 20 and the opening edge of the bottomed cylindrical outer protective cover 50. This drainage channel extends circumferentially along the cylindrical housing 20, for example, it may be configured to surround the outer periphery of the housing 20.

[0071] The diameter of the bottom surface (bottom) of the aforementioned drainage ditch can be smaller (shorter) than the diameter of the opening edge of the outer protective cover 50. That is, the length of the bottom surface to the axis (central axis) of the housing 20 can be shorter than the length of the opening edge of the outer protective cover 50 to the axis of the housing 20. In other words, the length of the bottom surface (outer periphery of the bottom surface) of the aforementioned drainage ditch to the axis of the housing 20 can be shorter than the length of the opening edge of the outer protective cover 50 to the axis of the housing 20.

[0072] Figure 1 The outer protective cover 50 illustrated in the diagram has a cylindrical large-diameter portion and a bottomed cylindrical front end portion connected to the large-diameter portion and having a diameter smaller than the large-diameter portion. In other words, in this embodiment, the bottomed cylindrical outer protective cover 50 has a cylindrical body and a bottomed cylindrical front end portion with an inner diameter smaller than the body. The body includes a side portion having the side of the outer protective cover 50 along its central axis and a stepped portion that serves as the bottom of the body and connects the side portion and the front end portion. However, for the gas sensor 1, the outer protective cover 50 does not necessarily have the above-described configuration, nor does it necessarily have a body and a front end portion. In other words, for the gas sensor 1, it is not necessary for the outer protective cover 50 to have a configuration where the side of the cylindrical body and the bottomed cylindrical front end portion are connected by a stepped portion. For the gas sensor 1, the outer protective cover 50 only needs to have a bottomed cylindrical shape that covers the front end of the sensor element 10. For example, the outer protective cover 50 can be configured such that the sides of the cylindrical body and the bottomed cylindrical front end are directly connected without the aid of a step. Alternatively, the outer protective cover 50 may also have multiple steps. That is, the outer protective cover 50 may have: a cylindrical large-diameter portion, a cylindrical body connected to the large-diameter portion and having a diameter smaller than the large-diameter portion, and a bottomed cylindrical front end connected to the body and having an inner diameter smaller than the inner diameter of the body. In other words, in this embodiment, the outer protective cover 50 only needs to have a bottomed cylindrical shape that covers the front end (front end) of the sensor element 10. The shapes other than the bottomed cylindrical shape are appropriately selected based on the usage method and application location of the gas sensor 1.

[0073] With the above configuration, in the gas sensor 1, when installed in a specified position, the space around the front end of the sensor element 10 where the gas to be measured exists is completely isolated from the space around the rear end where the reference gas exists. Therefore, the gas sensor 1 can accurately measure the concentration of the target gas component in the gas being measured.

[0074] (A summary of information about gas sensors)

[0075] As previously described, the gas sensor 1 includes: a cylindrical, metal housing 20, with an elongated sensor element 10 extending axially AX through its interior; and a metal outer cylinder 40 fitted onto the outer peripheral surface 210 of the housing 20. A portion of the rear end of the housing 20 is pressed into the outer cylinder 40, and the overlapping portion with the pressed-in housing 20 is circumferentially welded, thereby fitting the outer cylinder 40 onto the outer peripheral surface 210 of the housing 20. Figure 1 In the example shown, welding is performed circumferentially at the welding position Wp, thereby assembling the outer cylinder 40 onto the outer peripheral surface 210 of the shell 20.

[0076] In gas sensor 1, the length along the axial direction AX of the outer peripheral surface 210 of the housing 20, which contacts the inner peripheral surface 410 of the outer cylinder 40, at a position further back than the molten portion 420 of the welded outer cylinder 40, is the contact distance Lg, which is less than or equal to the reference distance Lr. Hereinafter, using... Figure 2 The details of the contact distance Lg will be explained.

[0077] (Regarding contact distance)

[0078] Figure 2 It is an enlarged cross-sectional view schematically showing the relationship between the housing 20 and the outer cylinder 40 at the periphery of the welding position Wp in the gas sensor 1, and is a diagram that particularly illustrates the details of the contact distance Lg. Figure 2 In the diagram, the left-right direction of the paper is the axial direction AX.

[0079] like Figure 2 As illustrated, the molten portion 420 of the outer cylinder 40, formed by welding, is melted into the shell 20. Around this molten portion 420, the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 are in contact with each other. Furthermore, in Figure 2 In the example shown, the rear end embodiment of the outer peripheral surface 210 of the housing 20 is chamfered, that is, the corner of the rear end of the housing 20 is chamfered. Specifically, in Figure 2 In the housing 20 illustrated, a C-bevel is formed at the rear end of the outer peripheral surface 210, and a straight chamfer surface Af with a straight cross-sectional shape is formed between the outer peripheral surface 210 and the rear end surface 220 of the housing 20.

[0080] In the diagram, "Cf, the center of the molten portion" refers to the center along the axial direction AX of the molten portion 420 of the outer cylinder 40 formed by welding. The molten portion 420 can also be referred to as the part of the outer cylinder 40 whose structure changes due to melting.

[0081] In the diagram, "Molten End Ef" refers to the endpoint where the molten portion 420, located axially along the AX direction further rearward than the molten center Cf, contacts the outer peripheral surface 210 of the shell 20. The molten end Ef can also be referred to as the rear end of the molten portion 420 in contact with the shell 20 along the AX direction. Furthermore, the molten end Ef can also be referred to as the contact position of the outer peripheral surface 210 of the shell 20, the inner peripheral surface 410 of the outer cylinder 40, and the molten portion 420, axially along the AX direction further rearward than the molten center Cf. At this position axially along the AX direction, further rearward than the molten end Ef, the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 are in contact with each other.

[0082] In the diagram, "non-contact position Np" refers to the position in the axial direction AX where the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 become non-contact (no longer in contact) compared to the rearward side of the molten part center Cf. That is, non-contact position Np represents the position at the very front end where the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 become non-contact, also known as the "release position," located at the rearward side of the molten part center Cf. Non-contact position Np can also be described as the position where the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 become non-contact throughout the entire circumferential direction, located at the rearward side of the molten part center Cf. Furthermore, non-contact position Np can also be referred to as the rear end of the outer peripheral surface 210 of the shell 20. As described above, in Figure 2 In the example shown, a chamfer (C-chamfer) is performed on the rear end of the outer peripheral surface 210 of the housing 20. Therefore, the non-contact position Np can be referred to as the rear end of the outer peripheral surface 210 of the housing 20 after the chamfer is performed.

[0083] In the figure, "melt depth Da" represents the radial depth of the shell 20 from the outer peripheral surface 210 of the shell 20 to the deepest part Dp of the molten portion 420 melted into the shell 20. The deepest part Dp can also be referred to as the radial position of the shell 20 of the outer cylinder 40 melted into the shell 20 by welding, which is the deepest part 420 melted into the shell 20.

[0084] The “thickness Tc” in the figure represents the thickness of the outer cylinder 40, which is a cylindrical component made of metal, that is, the difference between the outer diameter and the inner diameter of the outer cylinder 40.

[0085] exist Figure 2In the example shown, between the molten end Ef and the non-contact position Np, the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 are in contact with each other, specifically, the outer peripheral surface 210 and the inner peripheral surface 410 are in contact with each other throughout the entire circumferential direction. Conversely, at a position in the axial direction AX further rearward than the non-contact position Np, the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40 are not in contact with each other, specifically, the outer peripheral surface 210 and the inner peripheral surface 410 are not in contact with each other throughout the entire circumferential direction.

[0086] Here, as described above, the contact distance Lg is the length along the axial direction AX of the outer peripheral surface 210 of the shell 20 that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end of the molten portion 420. Therefore, in Figure 2 In the example shown, the contact distance Lg can also be referred to as the distance between the molten end Ef and the non-contact position Np. That is, in Figure 2 In the example shown, the contact distance Lg can also be referred to as the length along the axial direction AX of the outer circumferential surface 210 of the shell 20 that contacts the inner circumferential surface 410 of the outer cylinder 40 in the entire circumferential direction at a position further back than the molten portion 420.

[0087] In the gas sensor 1 of this embodiment, by making the contact distance Lg less than or equal to the reference distance Lr, the volatile gas in the molten portion 420 of the outer cylinder 40 can be discharged between the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40.

[0088] As described above, the reference distance Lr is, for example, the maximum reachable distance that "volatile gas can move between the outer peripheral surface 210 and the inner peripheral surface 410 by its own pressure". That is, the reference distance Lr represents the maximum distance (reachable distance) that volatile gas, such as residual oil adhering to the contact surface of the shell 20 and the outer cylinder 40, which evaporates due to the heat during welding, can reach by its own pressure. Furthermore, the reachable distance of the volatile gas has the following relationship with the penetration depth Da, the reduction amount Tb (which represents the difference between the outer diameter of the shell 20 and the inner diameter of the outer cylinder 40, i.e., the reduction amount), and the thickness Tc of the outer cylinder 40.

[0089] That is, the greater the penetration depth Da, which represents the radial depth of the shell 20 from the outer peripheral surface 210 of the shell 20 to the deepest part Dp of the molten portion 420 melted into the shell 20, the greater the thermal deformation of the shell 20 and the outer cylinder 40. In other words, the greater the penetration depth Da, the greater the gap between the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40. Therefore, the greater the penetration depth Da, the smaller the diffusion resistance of the volatile gas that wants to move between the outer peripheral surface 210 and the inner peripheral surface 410, and the greater the reachable distance of the volatile gas.

[0090] Furthermore, the larger the reduction amount Tb, which represents the difference between the outer diameter of the shell 20 and the inner diameter of the outer cylinder 40 (i.e., the reduction amount), the greater the diffusion resistance of the volatile gas that wants to move between the outer peripheral surface 210 and the inner peripheral surface 410. Therefore, the larger the reduction amount Tb, the smaller the reachable distance of the volatile gas.

[0091] Furthermore, the greater the thickness Tc, which represents the "thickness of the outer cylinder 40," the easier it is for heat to dissipate during welding. As a result, the amount of volatile gas generated is reduced, and the thermal deformation of the shell 20 and the outer cylinder 40 is also smaller. Therefore, the greater the thickness Tc, the shorter the reachable distance of volatile gas moving between the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40.

[0092] As explained above, the greater the penetration depth Da, the greater the reachable distance of the volatile gas; the greater the reduction Tb, the smaller the reachable distance of the volatile gas; and the greater the thickness Tc, the smaller the reachable distance of the volatile gas. Since the penetration depth Da, reduction Tb, and thickness Tc have the aforementioned relationships with respect to the reachable distance, the maximum reachable distance, i.e., the reference distance Lr, can be expressed as a function of the penetration depth Da, reduction Tb, and thickness Tc. That is, by setting "k" as a proportionality constant, the reference distance Lr can be calculated using the following mathematical formula (1).

[0093] Lr=k×Da / (Tb×Tc)···Mathematical formula (1)

[0094] (Calculation of the proportionality constant k)

[0095] Here, the inventors of this invention calculate the proportionality constant k in the above mathematical formula (1) as follows. First, the inventors of this invention manufacture a gas sensor 1 (Ref) with the following parameters: the depth of penetration Da is Da (Ref), the reduction amount Tb is Tb (Ref), the thickness Tc of the outer cylinder 40 is Tc (Ref), and the contact distance Lg is Lg (Ref). Regarding this gas sensor 1 (Ref), the inventors of this invention have confirmed that by changing at least one of the depth of penetration Da, the reduction amount Tb, and the thickness Tc of the outer cylinder 40 in a manner that increases the reference distance Lr, the number of pinholes generated in the molten portion 420 is reduced. In other words, regarding the gas sensor 1 (Ref), the inventors of this invention have confirmed that by changing at least one of the depth of penetration Da, the reduction amount Tb, and the thickness Tc of the outer cylinder 40 in a manner that increases the reachability distance of the volatile gas, the number of pinholes generated is reduced. Furthermore, regarding gas sensor 1 (Ref), the inventors of this invention have confirmed that by changing at least one of the melting depth Da, the reduction amount Tb, and the thickness Tc of the outer cylinder 40 in a manner that reduces the reference distance Lr, the number of pinholes generated in the molten portion 420 increases. In other words, regarding gas sensor 1 (Ref), the inventors of this invention have confirmed that by changing at least one of the melting depth Da, the reduction amount Tb, and the thickness Tc of the outer cylinder 40 in a manner that reduces the reachable distance of the volatile gas, the number of pinholes generated decreases. Based on these confirmations, the inventors of this invention have determined that in gas sensor 1 (Ref), the contact distance Lg is equal to the reference distance Lr. That is, the inventors of this invention have determined that in gas sensor 1 (Ref), the contact distance Lg (Ref) is equal to the reference distance Lr.

[0096] Therefore, the inventors of this invention substituted Da=Da(Ref), Tb=Tb(Ref), Tc=Tc(Ref), Lr=Lg(Ref) into the above mathematical formula (1) to calculate the proportionality constant k. Specifically, k(Ref) was calculated as the proportionality constant k.

[0097] (Specification of reference distance Lr and determination of contact distance Lg)

[0098] Since the proportionality constant k can be determined (i.e., the proportionality constant k can be determined as k(Ref)), the reference distance Lr can be calculated based on the melting depth Da, the reduction amount Tb, the thickness Tc of the outer cylinder 40, and the proportionality constant k, using mathematical formula (1). Furthermore, by making the contact distance Lg less than or equal to the calculated reference distance Lr, the gas sensor 1 can achieve the following effect: that is, the gas sensor 1 can suppress the possibility that "the volatile gas does not escape from between the outer peripheral surface 210 and the inner peripheral surface 410 but remains in the molten portion 420, causing pinholes in the molten portion 420", that is, it can suppress the formation of pinholes in the molten portion 420.

[0099] As explained above, regarding gas sensor 1, by making the contact distance Lg less than or equal to the reference distance Lr, gas sensor 1 can suppress the formation of pinholes in the molten portion 420. Furthermore, the inventors of this invention have confirmed through experiments that it is preferable to make the contact distance Lg less than the reference distance Lr, and more preferably, to make the contact distance Lg less than 1 / 2 of the reference distance Lr. Specifically, the inventors of this invention have confirmed through experiments that by making the contact distance Lg less than 1 / 2 of the reference distance Lr, the number of pinholes generated in the molten portion 420 is drastically reduced. The details of this experiment will be described below.

[0100] Therefore, in gas sensor 1, the reference distance Lr can be greater than 1.2 times the contact distance Lg, that is, the contact distance Lg can be less than 1 / 2 of the reference distance Lr. As described above, by making the contact distance Lg less than 1 / 2 of the reference distance Lr, the number of pinholes generated in the molten portion 420 is drastically reduced. Therefore, in gas sensor 1, by making the contact distance Lg less than 1 / 2 of the reference distance Lr, the generation of pinholes in the molten portion 420 can be suppressed extremely effectively.

[0101] (The shape of the corners of the shell)

[0102] As mentioned above, Figure 2 In the illustrated housing 20, the rear end (corner) of the outer peripheral surface 210 is chamfered; specifically, a C-shaped chamfer is performed. That is, Figure 2 The image shows an example where the corner (rear end corner) of the inner peripheral surface 410 of the shell 20 facing the outer cylinder 40 is chamfered, and a straight chamfered surface Af with a straight cross-sectional shape is formed between the outer peripheral surface 210 of the shell 20 and the rear end surface 220 of the shell 20.

[0103] In gas sensor 1, the rear end of the outer peripheral surface 210 of housing 20 can also be chamfered, for example, as... Figure 2As illustrated, the rear end of the outer peripheral surface 210 of the housing 20 is chamfered in a straight line. Specifically, Figure 2 In the gas sensor 1 illustrated, a C-shaped chamfer is applied to the rear end of the outer peripheral surface 210 of the housing 20. The gas sensor 1 can use the rear end of the chamfered outer peripheral surface 210 of the housing 20 as a guide when pressing the housing 20 toward the outer cylinder 40, making it easier to press the housing 20 toward the outer cylinder 40.

[0104] As explained above, Figure 2 An example of a gas sensor 1 in which a C-bevel is applied to the rear end of the outer peripheral surface 210 of the housing 20 is shown. That is, Figure 2 In the gas sensor 1 illustrated, the rear end of the outer peripheral surface 210 of the housing 20 is chamfered in a straight line. This chamfering process creates a more streamlined appearance on the rear end of the housing 20. Figure 2 As illustrated, a straight chamfered surface Af with a cross-sectional shape of a straight line is formed. However, for the gas sensor 1, it is not necessary for the cross-sectional shape of the straight chamfered surface Af formed on the rear end side of the "cylindrical and metal housing in which the sensor element penetrates axially" (e.g., housing 20) through chamfering to be a straight line. That is, for the gas sensor 1, it is not necessary for the cross-sectional shape of the straight chamfered surface Af formed by chamfering the rear end of the outer peripheral surface of the housing to be a straight line. The details will be explained below; by performing chamfering, a shape like... can be formed on the rear end side of the "cylindrical and metal housing in which the sensor element penetrates axially". Figure 6 The right-angled face Af is illustrated in (A) and (B) in the example. Figure 6 Examples of a right-beveled chamfered surface Af with a cross-sectional shape including multiple straight sections are shown in (A) and (B) of the paper. That is, in the gas sensor 1, the surface (right-beveled chamfered surface) formed on the rear end side of the "cylindrical and metal housing in which the sensor element is axially penetrated" by performing a chamfering process can include multiple straight sections in its cross-sectional shape.

[0105] Furthermore, for gas sensor 1, it is not necessary to perform chamfering on the rear end of the outer peripheral surface of the "cylindrical and metal housing through which the sensor element penetrates axially" (e.g., housing 20). Even if chamfering is performed on the rear end of the outer peripheral surface of the housing, it is not necessary for gas sensor 1 to use C-shaped chamfering as the chamfering process.

[0106] As described above, in this embodiment, for the gas sensor 1, the length along the axial direction AX of the outer peripheral surface 210 of the housing 20, which contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end of the molten portion 420 of the outer cylinder 40, i.e., the contact distance Lg, can be set to a reference distance Lr or less. For the gas sensor 1, whether to perform chamfering on the rear end of the outer peripheral surface 210 of the housing 20, and if so, which type of chamfering, is appropriately selected based on the usage method and application location of the gas sensor 1. That is, in a gas sensor 1 where the contact distance Lg is set to a reference distance Lr or less, the shape of the rear end corner (facing the inner peripheral surface 410 of the outer cylinder 40) of the "cylindrical metal housing in which the sensor element penetrates axially" can have various shapes. Hereinafter, a representative example will be described regarding the shape of the rear end corner of the "cylindrical metal housing in which the sensor element penetrates axially" in a gas sensor 1 where the contact distance Lg is set to a reference distance Lr or less.

[0107] (Shell of Modified Example 1)

[0108] Figure 3 The enlarged cross-sectional view schematically shows the relationship between the periphery of the welding position Wp and the outer cylinder 40 for the shell 20(1) of modified example 1. Figure 3 In the diagram, the left-right direction of the paper is the axial direction AX. Figure 2 In the illustrated shell 20, a C-bevel is applied to the rear corner (the corner facing the inner circumferential surface 410 of the outer cylinder 40). Specifically, a C-bevel is applied to the rear end (corner) of the outer circumferential surface 210 of the shell 20, forming a straight chamfer surface Af with a straight cross-section between the outer circumferential surface 210 and the rear end surface 220 of the shell 20. In contrast, Figure 3 In the shell 20(1) shown in the example, an R-shaped chamfer is applied to the corner of its rear end side (the corner of the inner peripheral surface 410 facing the outer cylinder 40). That is, an R-shaped chamfer is applied to the end (corner) of the rear end side of the outer peripheral surface 210(1) of the shell 20(1), and a curved surface Rf with a cross-sectional shape of a curve is formed between the outer peripheral surface 210(1) and the rear end surface 220(1) of the shell 20(1).

[0109] An R-shaped chamfer was applied to the rear corner instead of a C-shaped chamfer. In addition, Figure 3 The shell 20(1) shown in the example is... Figure 2 The housing 20 illustrated is the same. That is, housing 20(1) is also a cylindrical and metal component, with a long strip-shaped sensor element 10 penetrating its interior along the axial direction AX. Figure 3As illustrated, a metal outer cylinder 40 is fitted onto the outer peripheral surface 210(1) of the housing 20(1). A portion of the rear end side of the housing 20(1) is pressed into the outer cylinder 40, and circumferential welding is performed on the overlapping portion with the pressed-in housing 20(1), thereby fitting the outer cylinder 40 onto the outer peripheral surface 210(1) of the housing 20(1). The length along the axial direction AX of the outer peripheral surface 210(1) of the housing 20(1) that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end side than the molten portion 420 of the welded outer cylinder 40, i.e., the contact distance Lg, is a reference distance Lr or less.

[0110] exist Figure 3 In the example shown, the molten end Ef represents the "end point where the molten portion 420 contacts the outer peripheral surface 210(1) of the shell 20(1)" located on the axial direction AX, further back than the center of the molten portion Cf. The molten end Ef can also be referred to as the "rear end of the molten portion 420 in contact with the shell 20(1) on the axial direction AX". In addition, the molten end Ef can also be referred to as the contact position of the outer peripheral surface 210(1) of the shell 20(1) on the axial direction AX, further back than the center of the molten portion Cf, the inner peripheral surface 410 of the outer cylinder 40, and the molten portion 420. The non-contact position Np represents the position where the outer peripheral surface 210(1) of the shell 20(1) and the inner peripheral surface 410 of the outer cylinder 40 become non-contact (the position where the two become non-contact at the very front end). The non-contact position Np can also be referred to as the position further back than the center Cf of the molten section, where the outer peripheral surface 210(1) of the shell 20(1) and the inner peripheral surface 410 of the outer cylinder 40 become non-contact positions throughout the circumferential direction. Furthermore, the non-contact position Np can also be referred to as the rear end of the outer peripheral surface 210(1) of the shell 20(1). As described above, in Figure 3 In the example shown, a chamfer (R-chamfer) is performed on the rear end of the outer peripheral surface 210(1) of the housing 20(1). Therefore, the non-contact position Np can be referred to as the rear end of the outer peripheral surface 210(1) of the housing 20(1) after the chamfering is performed. The penetration depth Da represents the radial depth of the housing 20(1) from the outer peripheral surface 210(1) to the deepest part Dp of the molten portion 420 that is melted into the housing 20(1). In addition, in Figure 3 In the example shown, the reduction Tb represents the difference between the outer diameter of the shell 20(1) and the inner diameter of the outer cylinder 40, i.e., the reduction amount. Furthermore, Figure 3 The center Cf of the molten part, the thickness Tc of the outer cylinder 40, etc. are related to Figure 2 The center Cf and thickness Tc of the molten part shown in the example are the same, so the description is omitted.

[0111] As described above, the contact distance Lg is the length along the axial direction AX of the outer peripheral surface 210(1) of the shell 20(1) that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end of the molten portion 420. Therefore, in Figure 3 In the example shown, the contact distance Lg can also be referred to as the distance between the position of the molten part end Ef and the non-contact position Np. Furthermore, the contact distance Lg is less than or equal to the reference distance Lr. In the gas sensor 1, by making the contact distance Lg less than or equal to the reference distance Lr, the volatile gas in the molten part 420 can be discharged between the outer peripheral surface 210(1) of the housing 20(1) and the inner peripheral surface 410 of the outer cylinder 40, thereby suppressing the generation of pinholes in the molten part 420.

[0112] As used before Figure 3 As explained, in the gas sensor 1, an R-shaped chamfer can be applied to the rear end of the outer peripheral surface 210(1) of the cylindrical metal housing 20(1) through which the elongated sensor element 10 passes along the axial direction AX. In the gas sensor 1, by using an R-shaped chamfer for the chamfering of the rear end of the outer peripheral surface 210 of the housing 20, burrs generated during processing can be suppressed, thereby suppressing burr biting between the housing 20 and the outer cylinder 40.

[0113] As explained above, Figure 3 An example of a gas sensor 1 in which an R-shaped chamfer is applied to the rear end of the outer peripheral surface 210(1) of the housing 20(1). That is, in Figure 3 In the gas sensor 1 illustrated, the rear end of the outer peripheral surface 210(1) of the housing 20(1) is chamfered in a curved shape. This chamfering process, as... Figure 3 As illustrated, a curved surface Rf with a cross-sectional shape of a single curve is formed. However, for the gas sensor 1, it is not necessary for the curved surface Rf formed on the rear end side of the "cylindrical metal housing in which the sensor element penetrates axially" through a chamfering process to have a curved cross-sectional shape. That is, for the gas sensor 1, it is not necessary for the curved surface Rf formed by chamfering the rear end of the outer peripheral surface of the housing to have a curved cross-sectional shape. The details will be explained below; it is also possible to form a curved surface Rf on the rear end side of the "cylindrical metal housing in which the sensor element penetrates axially" through a chamfering process. Figure 6 The surface Rf is illustrated in (C) above. Figure 6 Example of a surface Rf whose cross-sectional shape includes multiple curved portions is shown in (C). That is, in the gas sensor 1, the cross-sectional shape of the surface (curved surface) formed on the rear end side of the "cylindrical and metal housing in which the sensor element is axially penetrated" by performing a chamfering process may include multiple curved portions.

[0114] In gas sensor 1, the rear end of the outer peripheral surface of the "cylindrical and metal housing through which the sensor element extends axially" may be chamfered to form a surface with a cross-sectional shape including at least one of a straight portion and a curved portion. For example, the rear end of the outer peripheral surface of the "cylindrical and metal housing through which the sensor element extends axially" may be chamfered to form a right chamfered surface Af or a curved surface Rf with a cross-sectional shape including at least one of a straight portion and a curved portion. The cross-sectional shape of the surface formed on the rear end of the "cylindrical and metal housing through which the sensor element extends axially" by performing chamfering may include at least one of one or more straight portions and one or more curved portions. For example, as described later... Figure 6 (D) shows an example of a "cylindrical metal housing through which a sensor element is axially penetrated by a surface that has a cross-sectional shape consisting of one straight section and two curved sections, formed on the rear end side by performing a chamfering process."

[0115] (Shell of Modified Example 2)

[0116] Figure 4 The enlarged cross-sectional view schematically shows the relationship between the periphery of the welding position Wp and the outer cylinder 40 for the shell 20(2) of modified example 2. Figure 4 In the diagram, the left-right direction of the paper is the axial direction AX. Figure 2 and Figure 3 In the "cylindrical metal housing through which the sensor element extends axially" (i.e., housings 20, 20(1)) illustrated in the example, the corners on the rear end side (the corners facing the inner circumferential surface 410 of the outer cylinder 40) are chamfered. Specifically, a C-shaped chamfer is applied to the rear end (corner) of the outer circumferential surface 210 of housing 20, and an R-shaped chamfer is applied to the rear end (corner) of the outer circumferential surface 210(1) of housing 20(1). In contrast, Figure 4 In the shell 20(2) shown in the example, the corners on its rear end side (the corners facing the inner circumferential surface 410 of the outer cylinder 40) are not chamfered.

[0117] Apart from the fact that the corners on the rear side were not chamfered, Figure 4 The shell 20(2) shown in the example is... Figure 2 The shell 20 shown in the example and Figure 3 The housing 20(1) illustrated is the same. That is, the housing 20(2) is a cylindrical and metal component, similar to housings 20 and 20(1), with the elongated sensor element 10 penetrating its interior along the axial direction AX. Figure 4As illustrated, a metal outer cylinder 40 is fitted onto the outer peripheral surface 210(2) of the housing 20(2). A portion of the rear end side of the housing 20(2) is pressed into the outer cylinder 40, and circumferential welding is performed on the overlapping portion with the pressed-in housing 20(2), thereby fitting the outer cylinder 40 onto the outer peripheral surface 210(2) of the housing 20(2). The length along the axial direction of the outer peripheral surface 210(2) of the housing 20(2) that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end side than the molten portion 420 of the welded outer cylinder 40, i.e., the contact distance Lg, is a reference distance Lr or less.

[0118] exist Figure 4 In the example shown, the molten end Ef represents the "end point where the molten portion 420 contacts the outer peripheral surface 210(2) of the shell 20(2)" located on the axial direction AX, further back than the center of the molten portion Cf. The molten end Ef can also be referred to as the "rear end of the molten portion 420 in contact with the shell 20(2) on the axial direction AX". In addition, the molten end Ef can also be referred to as the contact position of the outer peripheral surface 210(2) of the shell 20(2) on the axial direction AX, further back than the center of the molten portion Cf, the inner peripheral surface 410 of the outer cylinder 40, and the molten portion 420. The non-contact position Np represents the position where the outer peripheral surface 210(2) of the shell 20(2) and the inner peripheral surface 410 of the outer cylinder 40 become non-contact (the position where the two become non-contact at the very front end). The non-contact position Np can also be referred to as the position further back than the center Cf of the molten section, where the outer peripheral surface 210(2) of the shell 20(2) and the inner peripheral surface 410 of the outer cylinder 40 become non-contact positions throughout the circumferential direction. Furthermore, the non-contact position Np can also be referred to as the rear end of the outer peripheral surface 210(2) of the shell 20(2). As described above, in Figure 4 In the example shown, the end of the rear end of the outer peripheral surface 210(2) of the housing 20(2) is not chamfered. Therefore, the non-contact position Np can also be referred to as the position where the outer peripheral surface 210(2) of the housing 20(2) and the rear end surface 220(2) are in contact. The penetration depth Da represents the radial depth of the housing 20(2) from the outer peripheral surface 210(2) to the deepest part Dp of the molten portion 420 that is melted into the housing 20(2). In addition, in Figure 4 In the example shown, the reduction Tb represents the difference between the outer diameter of the shell 20(2) and the inner diameter of the outer cylinder 40, i.e., the reduction amount. Furthermore, Figure 4 The center Cf of the molten part, the thickness Tc of the outer cylinder 40, etc. are related to Figure 2 and Figure 3 The center Cf and thickness Tc of the molten part shown in the example are the same, so the description is omitted.

[0119] As described above, the contact distance Lg is the length along the axial direction AX of the outer peripheral surface 210(2) of the shell 20(2) that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end of the molten portion 420. Therefore, in Figure 4 In the example shown, the contact distance Lg can also be referred to as the distance between the molten end Ef and the non-contact position Np. Furthermore, the contact distance Lg is less than or equal to the reference distance Lr.

[0120] As explained previously, in the gas sensor 1 of this embodiment, the contact distance Lg is set to be less than or equal to the reference distance Lr. With this configuration, the volatile gas in the molten portion 420 of the gas sensor 1 can be discharged between the outer peripheral surface of the cylindrical, metal housing in which the sensor element extends axially and the inner peripheral surface 410 of the outer cylinder 40. For the gas sensor 1 of this embodiment, if... Figure 4 As explained, it is not necessary to chamfer the end of the rear end of the outer peripheral surface of the "cylindrical and metal housing through which the sensor element is internally axially extended" (e.g., housing 20(2)).

[0121] (Shell of Modified Example 3)

[0122] Figure 5 The enlarged cross-sectional view schematically shows the relationship between the periphery of the welding position Wp and the outer cylinder 40 for the shell 20(3) of modified example 3. Figure 5 In the diagram, the left-right direction of the paper is defined by the axis AX. Previously used... Figures 2-4 The outer circumferential surface of the described "cylindrical, metallic housing through which the sensor element penetrates axially" contacts the inner circumferential surface 410 of the outer cylinder 40 throughout the entire circumferential direction between the molten end Ef and the non-contact position Np. That is, the outer circumferential surfaces of the housings 20, 20(1), and 20(2) contact the inner circumferential surface 410 of the outer cylinder 40 throughout the entire circumferential direction between the molten end Ef and the non-contact position Np. In contrast, in Figure 5 The outer peripheral surface 210(3) of the shell 20(3) illustrated herein has a slit Sl extending axially AX from the non-contact position Np toward the front end side. Therefore, a portion of the outer peripheral surface 210(3) of the shell 20(3) (specifically, the portion with the slit Sl) does not contact the inner peripheral surface 410 of the outer cylinder 40 between the molten end Ef and the non-contact position Np.

[0123] Specifically, in Figure 5 The outer peripheral surface 210(3) of the shell 20(3) illustrated in the example has a slit Sl formed at a position closer to the rear end side than the molten portion 420 of the outer cylinder 40 formed by welding. Figure 5 In the example shown, the slit Sl extends axially AX from the non-contact position Np toward the front end side.

[0124] A slit Sl extending axially AX is formed on the outer peripheral surface, in addition to this. Figure 5 The shell 20(3) shown in the example is... Figure 2 The housing 20 shown in the example is the same. That is, the housing 20(3) is also a cylindrical and metal component, like the housing 20, with the elongated sensor element 10 penetrating its interior along the axial direction AX. Figure 5 As illustrated, a metal outer cylinder 40 is fitted onto the outer peripheral surface 210(3) of the shell 20(3). A portion of the rear end side of the shell 20(3) is pressed into the outer cylinder 40, and circumferential welding is performed on the overlapping portion with the pressed-in shell 20(3), thereby fitting the outer cylinder 40 onto the outer peripheral surface 210(3) of the shell 20(3). The length along the axial direction of the outer peripheral surface 210(3) of the shell 20(3) that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position further back than the molten portion 420 of the welded outer cylinder 40, i.e., the contact distance Lg, is less than or equal to the reference distance Lr. That is, the length along the axial direction of the portion of the outer peripheral surface 210(3) of the shell 20(3) that does not form a slit Sl at a position further back than the molten portion 420 that contacts the inner peripheral surface 410 of the outer cylinder 40, i.e., the contact distance Lg, is less than or equal to the reference distance Lr.

[0125] In addition, similarly to the outer shell 20, the rear corner of the shell 20(3) (the corner of the inner circumferential surface 410 facing the outer cylinder 40) is chamfered. That is, the rear end (corner) of the outer circumferential surface 210(3) of the shell 20(3) is chamfered, and a straight chamfer surface Af with a straight cross-sectional shape is formed between the outer circumferential surface 210(3) and the rear end surface 220(3) of the shell 20(3).

[0126] exist Figure 5 In the example shown, the molten part end Ef refers to the "end point where the molten part 420 contacts the outer peripheral surface 210(3) of the shell 20(3)" located on the axial direction AX, further back than the center of the molten part Cf. The molten part end Ef can also be referred to as "the rear end of the molten part 420 in contact with the shell 20(3) on the axial direction AX". In addition, the molten part end Ef can also be referred to as the contact position of the outer peripheral surface 210(3) of the shell 20(3), the inner peripheral surface 410 of the outer cylinder 40, and the molten part 420 on the axial direction AX, further back than the center of the molten part Cf.

[0127] The non-contact position Np represents the position where the outer peripheral surface 210(3) of the shell 20(3) and the inner peripheral surface 410 of the outer cylinder 40 become non-contact (the position where the two become non-contact at their most foremost points) on the axial direction AX, which is further rearward than the center Cf of the molten portion. Here, as described above, a slit Sl is formed on the outer peripheral surface 210(3) of the shell 20(3), specifically at a position further rearward than the molten portion 420. Therefore, Figure 5 The non-contact position Np illustrated in the example can be referred to as the portion of the outer peripheral surface 210(3) of the shell 20(3) that does not form a slit Sl on the axial direction AX, which is located on the rear end side of the molten part center Cf, and the position where the inner peripheral surface 410 of the outer cylinder 40 does not contact. That is, Figure 5 The non-contact position Np illustrated in the example can be referred to as the position where the outer peripheral surface 210(3) of the shell 20(3) and the inner peripheral surface 410 of the outer cylinder 40 become non-contact in the entire circumferential direction, located on the rear end side of the shell 20(3) further from the center Cf of the molten section in the axial direction AX. Furthermore, the non-contact position Np can be referred to as the rear end of the outer peripheral surface 210(3) of the shell 20(3). As described above, in Figure 5 In the example shown, a chamfer (C-chamfer) is performed on the rear end of the outer peripheral surface 210(3) of the housing 20(3). Therefore, the non-contact position Np can be referred to as the rear end of the outer peripheral surface 210(3) of the housing 20(3) after the chamfer is performed.

[0128] The penetration depth Da represents the radial depth of the shell 20(3) from the outer peripheral surface 210(3) to the deepest part Dp of the molten portion 420 that is melted into the shell 20(3). Additionally, in Figure 5 In the example shown, the reduction Tb represents the difference between the outer diameter of the shell 20(3) and the inner diameter of the outer cylinder 40, i.e., the reduction amount. Furthermore, Figure 5 The center Cf of the molten part, the thickness Tc of the outer cylinder 40, etc. are related to Figures 2-4 The center Cf and thickness Tc of the molten part shown in the example are the same, so the description is omitted.

[0129] As described above, the contact distance Lg is the length along the axial direction AX of the outer peripheral surface 210(3) of the shell 20(3) that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end of the molten portion 420. Specifically, regarding the outer peripheral surface 210(3) with the slit Sl formed, the contact distance Lg is the length along the axial direction AX of the portion of the outer peripheral surface 210(3) that does not have the slit Sl formed, which contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end of the molten portion 420. Figure 5In the example shown, the contact distance Lg can also be referred to as the distance between the position of the molten part end Ef and the non-contact position Np where the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40 become non-contact in the entire circumferential direction. Furthermore, the contact distance Lg is less than or equal to the reference distance Lr. In the gas sensor 1, by making the contact distance Lg less than or equal to the reference distance Lr, the volatile gas in the molten part 420 can be discharged between the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40, thus suppressing the generation of pinholes in the molten part 420.

[0130] As previously explained, in the gas sensor 1, a slit Sl extending along the axial direction AX is formed on the outer peripheral surface 210(3) of the housing 20(3) located further rearward than the molten portion 420. Here, details will be provided below. The inventors of this invention have confirmed that by forming the slit Sl extending along the axial direction AX on the outer peripheral surface 210(3) of the housing 20(3), the effect of suppressing pinhole formation can be improved compared to the case where the slit Sl is not formed. For example, it is believed that the slit Sl increases the distance that the volatile gas can move between the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40 by its own pressure. Therefore, in the gas sensor 1, by forming the slit Sl extending along the axial direction AX, the effect of suppressing pinhole formation in the molten portion 420 can be further improved compared to the case where the slit Sl is not formed.

[0131] As explained earlier, in Figure 5 In the illustrated housing 20(3), a slit Sl is formed on the outer peripheral surface 210(3) of the housing 20(3) at a position further from the rear end of the molten portion 420, extending axially from the non-contact position Np toward the front end. Furthermore, a C-bevel is applied to the end of the outer peripheral surface 210(3) of the housing 20(3). However, for the gas sensor 1, it is not necessary for the slit Sl to extend from the non-contact position Np toward the front end. The slit Sl only needs to extend axially along the AX at a position further from the rear end of the molten portion 420. It can be considered that even if the slit Sl does not extend from the non-contact position Np, if it extends axially along the AX, the reachable distance of the volatile gas can be increased through the slit Sl, that is, it can be considered that the effect of suppressing pinhole formation can be improved.

[0132] Similarly, for the gas sensor 1, it is not necessary for the slit Sl to be formed on the outer peripheral surface 210(3) of the housing 20(3). The slit Sl can also be formed on the inner peripheral surface 410 of the outer cylinder 40. The slit Sl only needs to be formed on at least one of the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40.

[0133] Alternatively, at least one of the outer peripheral surface 210(3) of the shell 20(3) and the inner peripheral surface 410 of the outer cylinder 40 may be formed with a plurality of slits Sl that are spaced apart from each other in the circumferential direction of the shell 20(3) and the outer cylinder 40.

[0134] Furthermore, if a slit Sl is formed on at least one of the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40, it is not necessary to perform C-beveling on the rear end of the outer peripheral surface 210(3). Alternatively, R-beveling may be performed on the rear end of the outer peripheral surface 210(3), or chamfering may be omitted. For example, the gas sensor 1 may also... Figure 3 The outer peripheral surface 210(1) of the housing 20(1) illustrated herein forms a slit Sl. Additionally, the gas sensor 1 may include: Figure 3 The example shown includes the outer peripheral surface 210(1) of the housing 20(1) and the outer cylinder 40 with a slit S1 formed on its inner peripheral surface 410. Similarly, the gas sensor 1 can be... Figure 4 The outer peripheral surface 210(2) of the housing 20(2) illustrated herein forms a slit Sl. Additionally, the gas sensor 1 may include: Figure 4 The outer peripheral surface 210(2) of the shell 20(2) shown in the example, and the outer cylinder 40 with a slit Sl formed on the inner peripheral surface 410.

[0135] That is, in the gas sensor 1, at least one of the outer peripheral surface 210(3) of the housing 20(3) located further rearward than the molten portion 420 and the inner peripheral surface 410 of the outer cylinder 40, can be formed with a slit Sl extending along the axial direction AX. In the gas sensor 1, the slit Sl can extend to the end face (rear face 220(3)) of the rear end of the housing 20(3), that is, it can extend to the non-contact position Np. In addition, in the gas sensor 1, at least one of the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40 can also be formed with a plurality of slits Sl spaced apart from each other in the circumferential direction.

[0136] As described above, the inventors of this invention have confirmed that by forming a slit Sl extending along the axial direction AX on at least one of the outer peripheral surface 210(3) and the inner peripheral surface 410, the effect of suppressing pinhole formation can be improved compared to the case where the slit Sl is not formed. Therefore, in the gas sensor 1, by forming a slit Sl extending along the axial direction AX, the effect of suppressing pinhole formation in the molten portion 420 can be further improved compared to the case where the slit Sl is not formed.

[0137] (Other examples of chamfering processes performed on the corners of the housing)

[0138] Figure 6This is an enlarged cross-sectional view showing examples of various chamfering processes performed on the corners (rear-side corners) of the "cylindrical, metal housing through which the sensor element extends axially" of the gas sensor 1. Specifically, Figure 6 An example of chamfering is shown for the corners of housings 20(4) to 20(7), which are respectively “cylindrical and metal housings through which sensor elements are axially inserted”. Figure 6 In the diagram, the left-right direction of the paper is the axial direction AX.

[0139] exist Figure 6 In the housing 20(4) illustrated in (A), a chamfered surface Af with a cross-sectional shape including multiple straight sections is formed on the rear end side of the housing 20(4) by performing chamfering on its corners (the corners on the rear end side). Specifically, an example is shown where a chamfered surface Af with a cross-sectional shape including two straight sections is formed on the rear end side of the housing 20(4) by performing chamfering. A gas sensor 1 with a contact distance Lg of less than or equal to a reference distance Lr can have a chamfered surface Af formed on the rear end side of a cylindrical and metal housing in which the sensor element is axially penetrated. Figure 6 The straight chamfer surface Af illustrated in (A).

[0140] exist Figure 6 In the housing 20(5) illustrated in (B), a chamfered surface Af with a cross-sectional shape including multiple straight sections is formed on the rear end side of the housing 20(5) by performing chamfering on its corners (the corners on the rear end side). Specifically, an example is shown where a chamfered surface Af with a cross-sectional shape including three straight sections is formed on the rear end side of the housing 20(5) by performing chamfering. A gas sensor 1 with a contact distance Lg of less than or equal to a reference distance Lr can have a chamfered surface Af formed on the rear end side of a cylindrical and metal housing in which the sensor element is axially penetrated. Figure 6 The straight chamfer surface Af illustrated in (B).

[0141] As used before Figure 6 As described in (A) and (B), in the gas sensor 1, a chamfered surface Af with a cross-sectional shape including multiple straight sections can be formed on the rear end side of the "cylindrical and metal housing in which the sensor element is axially penetrated".

[0142] exist Figure 6In the housing 20(6) illustrated in (C), a curved surface Rf with a cross-sectional shape including multiple curved portions is formed on the rear end side of the housing 20(6) by chamfering its corners (rear end corners). Specifically, an example is shown where a curved surface Rf with a cross-sectional shape including two curved portions is formed on the rear end side of the housing 20(6) by chamfering. A gas sensor 1 with a contact distance Lg less than or equal to a reference distance Lr can have a curved surface Rf formed on the rear end side of a "cylindrical and metal housing in which the sensor element is axially penetrated." Figure 6 The surface Rf illustrated in (C) is as follows. That is, in the gas sensor 1, a surface Rf with a cross-sectional shape including multiple curved portions can be formed on the rear end side of the "cylindrical and metal housing in which the sensor element is axially penetrated".

[0143] exist Figure 6 In the housing 20(7) illustrated in (D), a surface ARf with a cross-sectional shape including a straight portion and a curved portion is formed on the rear end side of the housing 20(7) by chamfering its corner (the corner on the rear end side). Specifically, an example is shown where a surface ARf with a cross-sectional shape including one straight portion and two curved portions is formed on the rear end side of the housing 20(7) by chamfering is shown. A gas sensor 1 with a contact distance Lg less than or equal to a reference distance Lr can have a surface ARf formed on the rear end side of a "cylindrical and metal housing in which the sensor element is axially penetrated." Figure 6 The surface ARf is illustrated in (D) in the example. That is, in the gas sensor 1, a surface with a cross-sectional shape including at least one of one or more straight portions and one or more curved portions can be formed on the rear end side of the "cylindrical and metal housing in which the sensor element is axially penetrated".

[0144] As previously explained, the gas sensor 1 includes a cylindrical, metallic housing in which a sensor element extends axially, and a metallic outer cylinder 40 fitted onto the outer peripheral surface of the housing. Furthermore, in the gas sensor 1, the length along the axial direction AX of the outer peripheral surface of the housing that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position closer to the rear end of the molten portion 420 is set to be less than or equal to the reachable distance of the volatile gas in the molten portion 420, for example, less than or equal to a reference distance Lr.

[0145] In the gas sensor 1 described above, the rear end of the outer peripheral surface of the housing can be chamfered. For example, the rear end of the outer peripheral surface of the housing can be chamfered in a straight line or a curve. Specifically, in the gas sensor 1, at least one of C-shaped chamfering and R-shaped chamfering can be performed on the rear end of the outer peripheral surface of the housing. The rear end of the outer peripheral surface of the housing with the chamfered finish can be used as a guide when pressing the housing toward the outer cylinder 40, thereby pressing the housing toward the outer cylinder 40.

[0146] [feature]

[0147] As previously explained, the gas sensor 1 of this embodiment includes: a cylindrical, metal housing with an elongated sensor element 10 extending through it along the axial direction AX; and a metal outer cylinder 40 fitted onto the outer peripheral surface 210 of the housing. The "cylindrical, metal housing with an elongated sensor element 10 extending through it along the axial direction AX" in the gas sensor 1 is any of the housings 20, 20(1) to 20(7) previously described, such as housing 20. A portion of the rear end of the housing 20 along the axial direction AX is pressed into the outer cylinder 40, and circumferential welding is performed at the overlapping portion with the pressed-in housing 20, thereby fitting the outer cylinder 40 onto the outer peripheral surface 210 of the housing 20. For example, at the overlapping portion of the housing 20 and the outer cylinder 40 (as an example, ... Figure 1 The welding position Wp in the middle is laser welded along the circumferential direction, and the outer cylinder 40 is assembled onto the outer circumferential surface 210 of the shell 20.

[0148] In the gas sensor 1, the length along the axial direction AX of the outer peripheral surface 210 of the housing 20 that contacts the inner peripheral surface 410 of the outer cylinder 40, which is located at a position further back than the molten portion 420 of the welded outer cylinder 40, i.e., the contact distance Lg, is less than or equal to the reference distance Lr. The reference distance Lr is calculated using the following mathematical formula (1) using the proportionality constant k, the molten depth Da, the reduction amount Tb, and the thickness Tc.

[0149] Lr=k×Da / (Tb×Tc)···Mathematical formula (1)

[0150] As described above, the penetration depth Da represents the radial depth of the shell 20 from its outer peripheral surface 210 to the deepest part Dp of the molten portion 420 within the shell 20. The reduction amount Tb represents the difference between the outer diameter of the shell 20 and the inner diameter of the outer cylinder 40, i.e., the reduction amount. The thickness Tc represents the thickness of the outer cylinder 40. The molten portion 420 can also be referred to as the part of the outer cylinder 40 whose structure changes due to melting.

[0151] Furthermore, the reference distance Lr represents, for example, the maximum distance (reachable distance) that a volatile gas can reach under its own pressure, that is, the maximum value of the reachable distance. Specifically, the reference distance Lr is, for example, the maximum distance (reachable distance) that a volatile gas can move between the outer peripheral surface 210 of the shell 20 and the inner peripheral surface 410 of the outer cylinder 40, which are in contact with each other, under its own pressure. In addition, the reachable distance of the volatile gas has the following relationship with the penetration depth Da, the reduction amount Tb, and the thickness Tc: that is, the larger the penetration depth Da, the larger the reachable distance of the volatile gas; the larger the reduction amount Tb, the smaller the reachable distance of the volatile gas; and the larger the thickness Tc, the smaller the reachable distance of the volatile gas. Therefore, the maximum value of the reachable distance, i.e., the reference distance Lr, can be expressed as a function of the penetration depth Da, the reduction amount Tb, and the thickness Tc. Furthermore, the proportionality constant k can be determined through experiments, etc. Therefore, the reference distance Lr is calculated by using k, which is a proportional constant, the fusion depth Da, the reduction amount Tb, and the thickness Tc as a function of the above mathematical formula (1).

[0152] In gas sensor 1, the contact distance Lg is less than or equal to the reference distance Lr, that is, "the length along the axial direction AX of the outer peripheral surface 210 of the housing 20 that contacts the inner peripheral surface 410 of the outer cylinder 40 at a position further back than the molten portion 420" is less than or equal to the reference distance Lr. The contact distance Lg can also be referred to as the length along the axial direction AX from the position of the molten portion end Ef to the non-contact position Np. As described above, the molten portion end Ef is the endpoint of the molten portion 420 that contacts the outer peripheral surface 210 of the housing 20 at a position further back than the center (molten portion center Cf) of the molten portion 420 in the axial direction. In addition, the non-contact position Np is the position where the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40 become non-contact in the entire circumferential direction at a position further back than the molten portion center Cf, for example, the rear end of the outer peripheral surface 210 of the housing 20.

[0153] In gas sensor 1, the contact distance Lg is less than or equal to the reference distance Lr. Therefore, the volatile gas generated between the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40 during welding can move to the non-contact position Np by its own pressure. That is, in gas sensor 1, the volatile gas can move to a position where the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40 become non-contact in the entire circumferential direction (e.g., the rear end of the outer peripheral surface 210 of the housing 20) by its own pressure. During welding, for example, the volatile gas in the molten portion 420 can move to a position where "the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40 become non-contact in the entire circumferential direction" by its own pressure. That is, in gas sensor 1, the volatile gas generated during welding can move towards the non-contact position Np by its own pressure and be released at the non-contact position Np. Therefore, the gas sensor 1 can reduce the possibility of volatile gas remaining in the molten part 420 and causing pinholes in the molten part 420, that is, it can suppress the formation of pinholes in the molten part 420.

[0154] Therefore, the gas sensor 1 includes a metal housing 20 through which the sensor element 10 is inserted, and a metal outer cylinder 40 welded to the outer periphery of the housing 20, which can suppress the generation of pinholes in the molten portion 420.

[0155] Furthermore, in gas sensor 1, by making the contact distance Lg less than or equal to the reference distance Lr calculated by mathematical formula (1), pinholes in the molten portion 420 can be suppressed. Moreover, as described above, the proportionality constant k in mathematical formula (1) can be solved in advance through experiments, etc. Therefore, the structure for suppressing pinhole formation can be determined during the design phase of gas sensor 1; for example, the value of the contact distance Lg can be determined during the design phase by making the value of the contact distance Lg less than or equal to the reference distance Lr. In addition, by suppressing pinhole formation in gas sensor 1, the possibility of corrosion and reduced sealing caused by the pinhole can be suppressed. Furthermore, since the structure for suppressing pinhole formation can be implemented during the design phase of gas sensor 1, pinhole formation can be suppressed without changing welding conditions from previous gas sensors. Furthermore, for gas sensor 1, it is not necessary to thoroughly clean the housing 20 and the outer cylinder 40 separately to prevent oil residue from remaining on the contact surfaces of the housing 20 and the outer cylinder 40; therefore, the time spent on management and processes necessary during manufacturing can be reduced.

[0156] [Variation Example]

[0157] The embodiments of the present invention have been described above; however, the foregoing description of the embodiments is merely an example of the present invention in all respects. Various modifications and variations can be made to the above embodiments. Regarding the constituent elements of the above embodiments, constituent elements can be omitted, substituted, or added as appropriate. Furthermore, the shape and size of the constituent elements of the above embodiments can be appropriately changed accordingly. For example, the following changes can be made. It should be noted that the same reference numerals are used below for the same constituent elements as in the above embodiments, and appropriate descriptions are omitted for the same points as in the above embodiments. The following variations can be appropriately combined.

[0158] (Regarding the components of a gas sensor)

[0159] Previously, an example of a gas sensor 1 according to this embodiment including a sensor element holding member 30 and an outer protective cover 50 was described. However, for the gas sensor 1 of this embodiment, including the sensor element holding member 30 and the outer protective cover 50 is not necessary, and the gas sensor 1 may not include at least one of the sensor element holding member 30 and the outer protective cover 50. In addition, the gas sensor 1 may have a configuration other than the sensor element 10, the housing 20, the sensor element holding member 30, the outer cylinder 40, and the outer protective cover 50.

[0160] For example, in addition to having a bottomed cylindrical outer protective cover 50 that surrounds the front end of the sensor element 10, the gas sensor 1 may further have a bottomed cylindrical inner protective cover that covers the front end of the sensor element 10. That is, the gas sensor 1 may be configured such that the inner protective cover covering the front end of the sensor element 10 is further covered by the outer protective cover 50. This inner protective cover may be made of metal. In addition to having the aforementioned inner and outer protective covers 50, the gas sensor 1 may further have another protective cover. For example, in addition to having the inner and outer protective covers 50, the gas sensor 1 may further have an intermediate protective cover disposed between the two. That is, the gas sensor 1 can protect the vicinity of the front end of the sensor element 10 by multiple protective covers (such as the inner cover mentioned above, in addition to the outer protective cover 50).

[0161] (Regarding the slit)

[0162] use Figure 5An example of a gas sensor 1 in which at least one of the outer peripheral surface 210(3) of the shell 20(3) located further rearward than the molten portion 420 and the inner peripheral surface 410 of the outer cylinder 40 is formed along the axial direction AX is described. However, the slit Sl formed on at least one of the outer peripheral surface 210(3) of the shell 20(3) located further rearward than the molten portion 420 and the inner peripheral surface 410 of the outer cylinder 40 may not extend along the axial direction AX. For example, at least one of the outer peripheral surface 210(3) of the shell 20(3) located further rearward than the molten portion 420 and the inner peripheral surface 410 of the outer cylinder 40 may form a circumferentially extending slit Sl. That is, at least one of the outer peripheral surface 210(3) between the molten end Ef and the non-contact position Np (the rear end of the outer peripheral surface 210(3) of the shell 20(3)) and the inner peripheral surface 410 of the outer cylinder 40 can be formed with a circumferentially extending slit Sl. It can be considered that by the circumferentially extending slit Sl, the distance that the volatile gas can move between the outer peripheral surface 210(3) and the inner peripheral surface 410 by its own pressure can be increased, that is, it can be considered that the generation of pinholes can be suppressed.

[0163] [Example]

[0164] To verify the effectiveness of the present invention, gas sensors with the following settings 1 to 7 and a Ref gas sensor were manufactured. However, the present invention is not limited to the gas sensors with the following settings and the Ref gas sensor.

[0165] Table 1

[0166]

[0167] In Table 1, for gas sensors at positions 1-2, the contact distance Lg is greater than the reference distance Lr. In addition, they possess the same... Figure 1 The gas sensor 1 illustrated in the example has the same configuration. The gas sensor in Ref. is a reference gas sensor used to verify the effectiveness of the present invention, and has the same... Figure 1 The gas sensor 1 shown in the example has the same configuration, with the contact distance Lg equal to the reference distance Lr. Gas sensors with settings 3 to 7 have the same... Figure 1 The gas sensor 1 illustrated in the example has the same configuration, but the contact distance Lg is less than the reference distance Lr.

[0168] In Table 1, "Lr / Lg" represents the ratio of the reference distance Lr to the contact distance Lg. For example, in the gas sensor of position 1, the ratio of the reference distance Lr to the contact distance Lg is "0.37", meaning that the reference distance Lr is 0.37 times the contact distance Lg, and the contact distance Lg is greater than the reference distance Lr. Similarly, in the gas sensor of position 2, the reference distance Lr is 0.71 times the contact distance Lg, and the contact distance Lg is greater than the reference distance Lr. Additionally, in the gas sensor of position Ref, the reference distance Lr and the contact distance Lg are equal. In the gas sensor of position 3, the reference distance Lr is 1.11 times the contact distance Lg, and the contact distance Lg is less than the reference distance Lr. In the gas sensors of positions 4 and 5, the reference distance Lr is 1.23 times the contact distance Lg, and the contact distance Lg is less than the reference distance Lr. In the gas sensor of position 6, the reference distance Lr is 1.35 times the contact distance Lg, and the contact distance Lg is less than the reference distance Lr. In the gas sensor with gear 7, the reference distance Lr is 1.92 times the contact distance Lg, and the contact distance Lg is less than the reference distance Lr.

[0169] Table 1 shows the "slit structure": for gas sensors at positions 1 to 7, whether at least one of the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40 is formed. Figure 5 The slit Sl is illustrated in the diagram. The slit structure is indicated by "having": for example, a slit Sl extending axially AX is formed on the outer peripheral surface 210 of the shell 20. Conversely, the slit structure is indicated by "not having": no slit Sl is formed on either the outer peripheral surface 210 of the shell 20 or the inner peripheral surface 410 of the outer cylinder 40.

[0170] In Table 1, the "Pinhole Count Ratio" represents the ratio of the number of pinholes detected in the molten portion 420 by the gas sensor for each setting to the number of pinholes detected by the gas sensor for the Ref. In other words, the "Pinhole Count Ratio" indicates how many times the number of pinholes detected by the gas sensor for each setting is greater than the number of pinholes detected by the gas sensor for the Ref where the contact distance Lg is equal to the reference distance Lr.

[0171] In Table 1, "Pinhole Reduction Effect" indicates the degree of pinhole reduction effect confirmed for each gas sensor position, relative to the pinhole suppression effect confirmed for the Ref gas sensor. "Pinhole suppression effect" can also be referred to as "the effect of reducing the number of pinholes." A pinhole reduction effect of "× (Poor)" indicates that the pinhole reduction effect confirmed for each gas sensor position is worse than the pinhole reduction effect of the Ref gas sensor where the contact distance Lg is equal to the reference distance Lr. A pinhole reduction effect of "〇 (Good)" indicates that the pinhole reduction effect confirmed for each gas sensor position is the same as the pinhole reduction effect confirmed for the Ref gas sensor where the contact distance Lg is equal to the reference distance Lr. A pinhole reduction effect of "◎ (Excellent)" indicates that the pinhole reduction effect confirmed for each gas sensor position is even better than the pinhole reduction effect confirmed for the Ref gas sensor where the contact distance Lg is equal to the reference distance Lr.

[0172] That is, the "pinhole generation ratio" of the gas sensor for position 1 is "1.07", and the "number of pinholes generated in the molten portion 420" confirmed for the gas sensor for position 1 is more than the number confirmed for the gas sensor for Ref. Therefore, the "pinhole reduction effect" of the gas sensor for position 1 is "× (defect)".

[0173] The "pinhole generation ratio" of the gas sensor for position 2 is "1.08". The number of pinholes generated in the molten portion 420 confirmed for the gas sensor for position 2 is greater than the number confirmed for the gas sensor for Ref. Therefore, the "pinhole reduction effect" of the gas sensor for position 2 is "× (defective)".

[0174] The "pinhole generation ratio" of the gas sensor in position 3 is "0.92". The "number of pinholes generated in the molten portion 420" confirmed for the gas sensor in position 3 is slightly less than the number confirmed for the gas sensor in Ref. That is, the gas sensor in position 3 can achieve the same pinhole reduction effect as the pinhole reduction effect confirmed for the gas sensor in Ref, and the "pinhole reduction effect" of the gas sensor in position 3 is "0 (good)".

[0175] The "pinhole generation ratio" of the gas sensor at position 4 is "0.89". The "number of pinholes generated in the molten portion 420" confirmed for the gas sensor at position 4 is slightly less than the number confirmed for the gas sensor at position Ref. That is, the gas sensor at position 4 can achieve the same pinhole reduction effect as the pinhole reduction effect confirmed for the gas sensor at position Ref, and the "pinhole reduction effect" of the gas sensor at position 4 is "0 (good)".

[0176] The "pinhole generation ratio" of the gas sensor at position 5 is "0.80". The "number of pinholes generated in the molten portion 420" confirmed for the gas sensor at position 5 is slightly less than the number confirmed for the gas sensor at position Ref. That is, the gas sensor at position 5 can achieve the same pinhole reduction effect as the pinhole reduction effect confirmed for the gas sensor at position Ref, and the "pinhole reduction effect" of the gas sensor at position 5 is "0 (good)".

[0177] The "pinhole generation ratio" of the gas sensor at position 6 is "0.60". The number of pinholes generated in the molten portion 420 confirmed by the gas sensor at position 6 is extremely low compared to the number confirmed by the gas sensor for Ref. In other words, the gas sensor at position 6 can achieve a better pinhole reduction effect than the pinhole reduction effect confirmed by the gas sensor for Ref. The "pinhole reduction effect" of the gas sensor at position 6 is "◎ (very good)".

[0178] The "pinhole generation ratio" of the gas sensor for setting 7 is "0.25". The number of pinholes generated in the molten portion 420 confirmed by the gas sensor for setting 7 is extremely low compared to the number confirmed by the gas sensor for Ref. In other words, the gas sensor for setting 7 can achieve a better pinhole reduction effect than the pinhole reduction effect confirmed by the gas sensor for Ref. The "pinhole reduction effect" of the gas sensor for setting 7 is "◎ (very good)".

[0179] (Item 1 that can be identified from Table 1)

[0180] As shown in Table 1, the "pinhole reduction effect" of gas sensors at positions 1-2, where the contact distance Lg is greater than the reference distance Lr, is "× (poor)". In contrast, the "pinhole reduction effect" of gas sensors at positions 3-7, where the contact distance Lg is less than the reference distance Lr, is "〇 (good)" or "◎ (very good)". Furthermore, the "pinhole reduction effect" of gas sensors at positions Ref, where the contact distance Lg is equal to the reference distance Lr, is "〇". Therefore, the inventors of this invention have confirmed that, for a gas sensor 1 having a housing 20 through which the sensor element 10 is inserted and an outer cylinder 40 welded to the outer peripheral surface of the housing 20, by making the contact distance Lg less than or equal to the reference distance Lr, the following effect can be achieved. That is, the inventors of this invention have confirmed that, with respect to the gas sensor 1, by making the contact distance Lg less than or equal to the reference distance Lr, pinholes in the molten portion 420 can be suppressed.

[0181] Furthermore, the "pinhole generation ratio" of gas sensors at positions 3 to 7, where the contact distance Lg is less than the reference distance Lr, is all less than "1.00". That is, compared to gas sensors at positions 3 to 7, where the contact distance Lg and reference distance Lr are equal, gas sensors at positions 3 to 7, where the contact distance Lg is less than the reference distance Lr, can suppress pinhole generation. Therefore, for a gas sensor 1 having a housing 20 through which the sensor element 10 is inserted and an outer cylinder 40 welded to the outer peripheral surface of the housing 20, it is preferable that the contact distance Lg is shorter than the reference distance Lr.

[0182] (Item 2 that can be confirmed from Table 1)

[0183] Based on the relationship between "the ratio of pinhole occurrences" and "Lr / Lg (the ratio of reference distance Lr to contact distance Lg)" shown in Table 1, the inventors of this invention have confirmed that the ratio of reference distance Lr to contact distance Lg exhibits the following trend: Specifically, the inventors have confirmed that adjusting the contact distance Lg so that the reference distance Lr is greater than 1.2 times the contact distance Lg dramatically increases the pinhole reduction effect (the effect of suppressing pinhole occurrence). For example, by plotting the results of Table 1 on a graph with "Lr / Lg" on the horizontal axis and "the ratio of pinhole occurrences" on the vertical axis, and obtaining approximate curves from the points corresponding to gear positions 1-7 and Ref respectively, the inventors of this invention have confirmed the following trend regarding these approximate curves: Specifically, the inventors have confirmed that the slope of these approximate curves increases dramatically near the point where the reference distance Lr is greater than 1.2 times the contact distance Lg.

[0184] Therefore, for the gas sensor 1, which has a cylindrical metal housing in which the sensor element extends axially and an outer cylinder 40 welded to the outer circumferential surface of the housing, the following trend can be confirmed. That is, for the gas sensor 1, it can be confirmed that by making the reference distance Lr greater than 1.2 times the contact distance Lg, the generation of pinholes in the molten portion 420 can be suppressed extremely effectively.

[0185] (Item 3 that can be confirmed from Table 1)

[0186] Both the gas sensor at position 4 and the gas sensor at position 5 have an Lr / Lg ratio of 1.23. However, the gas sensor at position 4 has no slit structure, while the gas sensor at position 5 has a slit structure. That is, the gas sensors at positions 4 and 5 have the same configuration, except for whether or not a slit Sl is formed on at least one of the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40. Furthermore, the pinhole generation ratio of the gas sensor at position 4 is 0.89, while that of the gas sensor at position 5 is 0.80. In other words, compared to the gas sensor at position 4, the gas sensor at position 5 is able to suppress pinhole generation. Therefore, the inventors of this invention have confirmed that, for the gas sensor 1, forming a slit Sl on at least one of the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40 improves the effect of suppressing pinhole formation compared to the case where the slit Sl is not formed. Therefore, for the gas sensor 1 having a "cylindrical, metallic housing in which a sensor element extends axially along the interior" and an outer cylinder 40 welded to the outer peripheral surface of the housing," the following trend has been confirmed: That is, it has been confirmed that, by forming a slit Sl on at least one of the outer peripheral surface of the housing and the inner peripheral surface 410 of the outer cylinder 40, the effect of suppressing pinhole formation in the molten portion 420 is improved compared to the case where the slit Sl is not formed.

Claims

1. A gas sensor, comprising: A cylindrical, metal housing with a long, strip-shaped sensor element extending axially through its interior; and A metal outer cylinder, a portion of the rear end of the axially extending housing is pressed into the outer cylinder, and the outer cylinder is assembled to the outer circumferential surface of the housing by circumferential welding of the overlapping portion of the outer cylinder and the pressed-in housing. At a position closer to the rear end of the molten portion of the outer cylinder formed by the welding, the axial length of the outer peripheral surface of the shell that contacts the inner peripheral surface of the outer cylinder, i.e., the contact distance Lg, is less than or equal to the reference distance Lr. The reference distance Lr is calculated using the following mathematical formula (1). Lr=k×Da / (Tb×Tc)···Mathematical formula (1) Here, in the mathematical formula (1), "k" represents the proportionality constant. "Da" represents the radial depth of the shell from its outer peripheral surface to the deepest part of the molten portion that is melted into the shell. "Tb" represents the difference between the outer diameter of the shell and the inner diameter of the outer cylinder, i.e., the reduction amount. "Tc" indicates the thickness of the outer cylinder.

2. The gas sensor according to claim 1, wherein, The reference distance Lr is greater than 1.2 times the contact distance Lg.

3. The gas sensor according to claim 1 or 2, wherein, The rear end of the outer peripheral surface of the housing was chamfered.

4. The gas sensor according to claim 3, wherein, The chamfering process is an R-shaped chamfer.

5. The gas sensor according to claim 1 or 2, wherein, In the axial direction of the outer cylinder and the shell, at least one of the outer peripheral surface of the shell and the inner peripheral surface of the outer cylinder, which are closer to the rear end side than the molten portion, is formed with a slit extending along the axial direction.

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