gas sensor

Abstract

To provide a gas sensor which comprises a metal housing designed to have a sensor element inserted there to, and a metal outer cylinder welded to an outer periphery of the housing, and which suppresses formation of pinholes on a weld surface.SOLUTION: A gas sensor according to an aspect of the present invention has a contact length Lg that is less than a reference length Lr, the contact length being defined as a length in an axial direction of an outer peripheral surface of a housing in contact with an inner peripheral surface of an outer cylinder on a rear end side of a weld portion formed by welding.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a gas sensor.

Background Art

[0002] Conventionally, for a gas sensor that detects the concentration of specific gases such as oxygen and NO in a measured gas such as automotive exhaust gas, for example, the following configuration is known. That is, a gas sensor is known that includes a cylindrical and metal housing through which a long sensor element axially penetrates internally, and a metal outer cylinder welded to the outer periphery of such a housing. For example, in Patent Document 1 listed below, a gas sensor manufactured by press-fitting a part of the housing into the outer cylinder and then welding the overlapping portion of the housing and the outer cylinder in the circumferential direction to join the two is disclosed. x

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventors of the present case have found that, for a gas sensor having the above-described configuration, when residual oil or the like adheres to the contact surface between the housing and the outer cylinder during the welding, the following problems occur. That is, such residual oil or the like becomes a volatile gas due to the heat during welding and may mix into the welded metal and appear as bubbles (pinholes) on the surface of the welded portion (welded joint surface).

[0005] Furthermore, if such pinholes occur, there is a possibility of malfunctions such as corrosion starting from the pinhole or the pinhole penetrating the component (for example, the outer cylinder) and reducing the sealing performance. In particular, the possibility of such malfunctions increases when the gas sensor is used in a harsh environment or for a long period of time. To prevent such malfunctions, it is conceivable to thoroughly clean the housing and the outer cylinder so that no oil or other substances remain on the contact surfaces between them, but it is difficult to completely eliminate residual oil or other substances.

[0006] In one respect, the present invention has been made in view of these circumstances, and its objective is to provide a gas sensor comprising a metal housing through which a sensor element is inserted, and a metal outer cylinder welded to the outer circumference of the housing, thereby suppressing the occurrence of pinholes on the welded surface. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention employs the following configuration.

[0008] The gas sensor relating to the first aspect comprises a cylindrical metal housing through which a long sensor element passes axially, and a metal outer cylinder attached to the outer surface of the housing by press-fitting a portion of the rear end of the housing in the axial direction, and welding in the circumferential direction at the overlapping portion with the press-fitted housing. The contact distance Lg, which is the length in the axial direction of the outer surface of the housing that is in contact with the inner surface of the outer cylinder beyond the molten portion of the outer cylinder formed by welding on the rear end side, is less than or equal to the reference distance Lr, and the reference distance Lr is calculated by the following formula (1). Lr = k × Da / (Tb × Tc) ... Formula (1)

[0009] Here, in formula (1) above, "k" represents the proportionality constant, "Da" represents the radial depth of the housing from the outer surface of the housing to the deepest part of the molten portion that has melted into the housing, "Tb" represents the interference fit, which is the difference between the outer diameter of the housing and the inner diameter of the outer cylinder, and "Tc" represents the thickness of the outer cylinder. The molten portion may also be described as the part of the outer cylinder whose structure has been altered by melting.

[0010] In this configuration, the gas sensor comprises a metal housing through which the sensor element is inserted, and a metal outer cylinder that is press-fitted into the housing and welded circumferentially at the overlapping portion with the housing, thereby being mounted on the outer surface of the housing. For example, the outer cylinder is mounted on the outer surface of the housing by laser welding circumferentially at the overlapping portion between the housing and the outer cylinder. 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 by formula (1).

[0011] Here, the reference distance Lr represents the maximum distance that volatile gas, formed when residual oil or other substances adhering to the contact surface between the housing and the outer cylinder volatilize due to the heat during welding, can reach by its own pressure (reachable distance). That is, if residual oil or other substances are adhering to at least one of the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder that are in contact with each other, volatile gas is generated when such residual oil or other substances volatilize due to the heat during welding. If the distance that such volatile gas can travel between the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder that are in contact with each other is referred to as the "reachable distance of the volatile gas," then the reference distance Lr is the maximum value of such reachable distance.

[0012] Furthermore, the reachable distance of the volatile gas has the following relationship with Da, Tb, and Tc, respectively. That is, the larger Da, which represents the radial depth of the housing from the outer circumferential surface of the housing to the deepest part of the molten portion melted into the housing, the greater the thermal deformation of the housing and the outer cylinder. In other words, the larger Da is, the larger the gap between the outer circumferential surface of the housing and the inner circumferential 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 circumferential surface of the housing and the inner circumferential surface of the outer cylinder. Also, the larger Tb, which represents the interference fit that is the difference between the outer diameter of the housing and the inner diameter of the outer cylinder, the larger the diffusion resistance to the volatile gas, and the smaller the reachable distance of the volatile gas moving between the outer circumferential surface of the housing and the inner circumferential 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 dissipate, thus reducing the amount of volatile gas generated and minimizing thermal deformation of the housing and the outer cylinder. Therefore, the larger the Tc, the smaller the reachable distance of the volatile gas traveling between the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder. Since Da, Tb, and Tc each have the above-described relationship with respect to the reachable distance, the reference distance Lr, which is the maximum value of the reachable distance, can be expressed as a function of Da, Tb, and Tc. In addition, the proportionality constant k can be determined by testing or other means. Therefore, the reference distance Lr is calculated by formula (1), which is a function of the proportionality constant k and Da, Tb, and Tc.

[0013] Furthermore, in the gas sensor, the contact distance Lg is less than or equal to the reference distance Lr, that is, "the length in the axial direction of the outer circumferential surface of the housing that is in contact with the inner circumferential surface of the outer cylinder on the rear end side of the molten portion" is less than or equal to the reference distance Lr. In other words, the length from "the endpoint where the molten portion contacts the outer circumferential surface of the housing" (molten portion end) to "the position where the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder are not in contact over the entire circumferential direction" (release position) is less than or equal to the reference distance Lr.

[0014] Therefore, during welding, 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 by its own pressure to a position (release position) where the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder are not in contact over the entire circumferential direction. During welding, for example, the volatile gas in the molten portion can move by its own pressure to a position where the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder are not in contact over the entire circumferential direction. In other words, the volatile gas generated during welding can move to the release position by its own pressure and is released (released) at the release position. Therefore, the gas sensor can reduce the possibility of the volatile gas being retained in the molten portion and causing pinholes in the molten portion, that is, it can suppress the occurrence of pinholes in the molten portion.

[0015] Therefore, the gas sensor comprises a metal housing through which the sensor element is inserted, and a metal outer cylinder welded to the outer circumference of the housing, thereby suppressing the occurrence of pinholes in the molten portion.

[0016] Furthermore, the gas sensor can suppress the occurrence of pinholes in the molten portion by setting the contact distance Lg to be less than or equal to the reference distance Lr calculated by formula (1). As mentioned above, the proportionality constant k in formula (1) can be determined in advance by testing or the like. Therefore, the gas sensor can have a structure that suppresses the occurrence of pinholes determined at the design stage, and for example, the value of the contact distance Lg can be determined at the design stage to be less than or equal to the reference distance Lr. Moreover, by suppressing the occurrence of pinholes, the gas sensor can suppress the possibility of problems such as corrosion and reduced sealing performance caused by the pinholes. In addition, since the gas sensor can realize a structure that suppresses the occurrence of pinholes at the design stage, the occurrence of pinholes can be suppressed without changing welding conditions or the like from previous ones. Furthermore, the gas sensor does not require processes such as thoroughly cleaning the housing and the outer cylinder to prevent oil and the like from remaining on the contact surface between the housing and the outer cylinder, so the amount of man-hours required in the management and processes during manufacturing can be reduced.

[0017] In the gas sensor relating to the second aspect, the reference distance Lr may be greater than 1.2 times the contact distance Lg in the gas sensor relating to the first aspect. 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 / 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 / 1.2 of the reference distance Lr, the number of pinholes generated in the molten portion decreases sharply. Therefore, the gas sensor can very effectively suppress the generation of pinholes in the molten portion by making the contact distance Lg less than 1 / 1.2 of the reference distance Lr.

[0018] A gas sensor relating to the third aspect may have a chamfered edge on the rear end of the outer circumferential surface of the housing, as described in the gas sensor relating to the first or second aspect above. In this configuration, the rear end of the outer circumferential surface of the housing of the gas sensor is chamfered, for example, the rear end of the outer circumferential surface of the housing may be chamfered in a straight line or a curved line. In the gas sensor, the rear end of the outer circumferential surface of the housing may be chamfered in at least one of C-chamfering and R-chamfering. The rear end of the outer circumferential surface of the housing, which has been chamfered, can be used as a guide when pressing the housing into the outer cylinder, making it easier to press the housing into the outer cylinder.

[0019] In the gas sensor relating to the fourth aspect, the chamfering process may be R-chamfering in the gas sensor relating to the third aspect. In this configuration, the chamfering process applied to the rear end of the outer peripheral surface of the housing in the gas sensor is R-chamfering. By adopting R-chamfering as the chamfering process applied to the rear end of the outer peripheral surface of the housing in the gas sensor, the generation of burrs during processing can be suppressed, and burr jamming between the housing and the outer cylinder can be suppressed.

[0020] The gas sensor according to the fifth viewpoint is a gas sensor according to any of the first to fourth viewpoints described above, in which at least one of the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder is formed in the axial direction of the outer cylinder and the housing, respectively, on the rear end side of the molten portion.

[0021] In this configuration, in the axial direction of each of the outer cylinder and the housing, on at least one of the outer peripheral surface of the housing and the inner peripheral surface of the outer cylinder on the rear end side of the molten portion, a slit extending in the axial direction is formed. In the gas sensor, the slit may extend to the end face on the rear end side of the housing. Also, in the gas sensor, a plurality of the slits provided at intervals in the circumferential direction may be formed on at least one of the outer peripheral surface of the housing and the inner peripheral surface of the outer cylinder.

[0022] The inventors of the present case have confirmed that by forming the slit extending in 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 the generation of pinholes can be improved as compared with the case where such a slit is not formed. Therefore, the gas sensor can further improve the effect of suppressing the generation of pinholes in the molten portion by the slit extending in the axial direction as compared with the case where the slit is not formed.

Effects of the Invention

[0023] According to the present invention, it is possible to provide a gas sensor including a metal housing through which a sensor element is inserted 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.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 is a partial cross-sectional schematic view schematically showing an example of the main configuration of a gas sensor according to an embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view schematically showing the relationship between the housing and the outer cylinder around the welding position in the gas sensor of FIG. 1. [Figure 3] FIG. 3 is an enlarged cross-sectional view schematically showing the relationship between the outer cylinder around the welding position with respect to the housing according to Modification 1. [Figure 4]Figure 4 is an enlarged cross-sectional view schematically showing the relationship between the housing according to Modified Example 2 and the outer cylinder around the welding position. [Figure 5] Figure 5 is an enlarged cross-sectional view schematically showing the relationship between the housing according to Modification 3 and the outer cylinder around the welding position. [Figure 6] Figure 6 is an enlarged cross-sectional view showing examples of various chamfering processes applied to the corners of the housing. [Modes for carrying out the invention]

[0025] Hereinafter, an embodiment relating to one aspect of the present invention (hereinafter also referred to as "this embodiment") will be described based on the drawings. However, this embodiment described below is merely illustrative in all respects of the present invention. Needless to say, various improvements and modifications can be made without departing from the scope of the present invention. In other words, in carrying out the present invention, specific configurations according to the embodiment may be appropriately adopted.

[0026] The gas sensor 1, described in detail below, comprises a cylindrical housing 20 through which a long sensor element 10 penetrates in the axial direction AX, and an outer cylinder 40 mounted on the outer circumferential surface 210 of the housing 20. The housing 20 and the outer cylinder 40 are both made of metal. After press-fitting the rear end of the housing 20 into the front end of the outer cylinder 40, the outer cylinder 40 is attached to the outer circumferential surface 210 of the housing 20 by welding in the circumferential direction at the overlapping portion of the housing 20 and the outer cylinder 40. In the gas sensor 1 having this configuration, if oil or the like is present on at least one of the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40, which are in contact with each other during welding, such oil or the like will turn into a volatile gas due to the heat during welding. Furthermore, if the volatile gas in question cannot escape from between the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40, and remains trapped in the molten portion 420 of the outer cylinder 40 formed by welding, then bubbles of volatile gas, i.e., pinholes, will be generated in the molten portion 420. The molten portion 420 can also be described as the portion whose structure has been altered by melting.

[0027] The inventors of this case investigated a method to suppress the occurrence of such pinholes and confirmed that the occurrence of pinholes can be suppressed by configuring the gas sensor 1 to have the following configuration. Specifically, they confirmed that the occurrence of pinholes in the molten portion 420 of the gas sensor 1 can be suppressed by allowing the volatile gas in the molten portion 420 to escape from 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.

[0028] Specifically, in the gas sensor 1, the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are in contact with each other. However, volatile gases generated by the heat during welding can move between the outer circumferential surface 210 and the inner circumferential surface 410 due to their own pressure. Therefore, in the gas sensor 1, the distance (contact distance Lg) from the rear end of the molten portion 420 of the outer cylinder 40 (molten portion end Ef) to the position where the outer circumferential surface 210 and the inner circumferential surface 410 are not in contact (non-contact position Np) is adjusted to satisfy the following condition. That is, in the gas sensor 1, the contact distance Lg is adjusted to be less than or equal to "the distance that volatile gases can move between the outer circumferential surface 210 and the inner circumferential surface 410 due to their own pressure" (reachable distance).

[0029] In the gas sensor 1, by setting the contact distance Lg to be less than or equal to the reachable distance, the volatile gas in the molten portion 420 can escape from between the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40. Therefore, the gas sensor 1 can suppress the possibility that "volatile gas will remain in the molten portion 420 without escaping from between the outer peripheral surface 210 and the inner peripheral surface 410, causing a pinhole in the molten portion 420."

[0030] Below, we will explain in detail, using Figure 1 and other figures, a gas sensor 1 that suppresses the occurrence of pinholes in the molten portion 420 by setting the contact distance Lg to be less than or equal to the reachable distance, and in particular to be less than or equal to the reference distance Lr, which is the maximum reachable distance.

[0031] [Example Configuration] (Overall overview of gas sensors) Figure 1 is a schematic partial cross-sectional view illustrating an example of the main configuration of the gas sensor 1 according to this embodiment. In this embodiment, in order to facilitate understanding of the relationship that the housing 20 and the outer cylinder 40 of the gas sensor 1 must satisfy, and in particular the conditions that the contact distance Lg must satisfy, an example in which the gas sensor 1 has the following configuration will be described. That is, an example in which the gas sensor 1 comprises 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 according to this embodiment may also have configurations other than the sensor element 10, housing 20, sensor element holding member 30, outer cylinder 40, and outer protective cover 50.

[0032] The gas sensor 1 according to this embodiment uses a sensor element 10 located inside to detect a predetermined target gas component (e.g., NO) in the gas to be measured (e.g., exhaust gas). x The gas sensor 1 is used to detect (etc.). The gas sensor 1 comprises a cylindrical housing 20 through which a sensor element 10 penetrates in the axial direction AX, and an outer cylinder 40 mounted on the outer peripheral surface 210 of the housing 20. The gas sensor 1 illustrated in Figure 1 further comprises a sensor element holding member 30 made of ceramic material and having an insertion hole for holding the sensor element 10, and a bottomed cylindrical outer protective cover 50 that surrounds (covers) the tip side of the sensor element 10. As illustrated in Figure 1, the outside of the gas sensor 1 mainly consists of the outer protective cover 50, the housing 20, and the outer cylinder 40.

[0033] For example, the central axes of the gas sensor 1, sensor element 10, housing 20, sensor element holding member 30, outer cylinder 40, and outer protective cover 50 are coaxial. In Figure 1, the gas sensor 1 is shown in a manner in which the central axis (axis line) of the main body of the gas sensor 1 coincides with the left-right direction of the drawing. In the following description, unless otherwise specified, the right side of the page will be referred to as the front end of the gas sensor 1, and the left side of the page will be referred to as the rear end of the gas sensor 1. The front end of the gas sensor 1 and the front end of the sensor element 10 are on the same side, and the rear end of the gas sensor 1 and the rear end of the sensor element 10 are on the same side.

[0034] (Sensor element) The sensor element 10 is a long, columnar or thin plate-shaped member whose main constituent material is an element body made of an oxygen ion conductive solid electrolyte ceramic such as zirconia. The sensor element 10 may also be configured as a long, cylindrical or tubular member. The sensor element 10 has a gas inlet and an internal cavity at its tip, and has a configuration in which various electrodes and wiring patterns are provided on the surface and inside of the element body.

[0035] In the sensor element 10, the gas to be measured, introduced into the internal cavity, is reduced or decomposed within the cavity to generate oxygen ions. In the gas sensor 1, the concentration of a predetermined gas component is determined based on the fact that the amount of oxygen ions flowing inside the sensor element 10 is proportional to the concentration of that gas component in the gas to be measured.

[0036] As illustrated in Figure 1, for example, a predetermined area of ​​the surface of the sensor element 10 in the longitudinal direction from the tip may be covered with a protective film P. The protective film P is a porous film made of, for example, Al2O3, with a thickness of about 10 μm to 2000 μm, provided to protect the vicinity of the tip of the sensor element 10 from thermal shock, and is also called a thermal shock resistant protective layer. In light of its purpose, the protective film P is preferably formed to withstand forces up to about 50 N. The area in which the protective film P is formed is appropriately determined according to the specific structure of the sensor element 10.

[0037] The end of the sensor element 10, which is a long columnar or thin plate-shaped member, that is not covered with a protective film P is the rear end of the sensor element 10. In the gas sensor 1, the sensor element 10 penetrates the inside of the cylindrical housing 20 in the axial direction AX, with a front end covered with a protective film P and a rear end not covered with a protective film P protruding from the housing 20.

[0038] (housing) The housing 20 is a cylindrical member made of metal through which the sensor element 10 passes in the axial direction AX. The housing 20 has a cylindrical housing space inside which the sensor element 10 and the like are housed, and is used when fixing the gas sensor 1 to the measurement position.

[0039] The housing 20 may have, for example, radially projecting projections (flanges), and such projections may be provided along the entire circumferential direction. These projections are members that contact an external member (not shown) to which the gas sensor 1 is attached (for example, an exhaust pipe) and prevent the gas to be measured from leaking out of the space defined by the external member (for example, inside the exhaust pipe).

[0040] For example, fixing bolts (not shown) may be mounted around the outer circumference of the housing 20 in a manner that contacts the protruding portion. These fixing bolts are made of metal, for example, and have external threads on their outer surface. The housing 20 is inserted into a fixing member (mounting portion, boss) which is welded to the exhaust pipe and has internal threads on its inner surface. Furthermore, the fixing bolts are inserted into the fixing member while the protruding portion and the fixing member are in contact. 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 protruding portion (especially the tip side of the protruding portion) contacts the surface of the exhaust pipe (fixing member) to form a sealing surface, thereby preventing the gas to be measured from leaking out of the exhaust pipe.

[0041] In addition, the housing 20 exemplified in Figure 1 may be constructed by configuring the front end and rear end of the housing 20 as separate components, and connecting and fixing the front end component and the rear end component by welding or the like. For example, the housing 20 may include a metal main fitting with a protruding portion (a component corresponding to the front end of the housing 20 exemplified in Figure 1) and a cylindrical inner cylinder welded and fixed to the main fitting (a component corresponding to the rear end of the housing 20 exemplified in Figure 1). In this embodiment, the housing 20 may be a metal, cylindrical component through which the sensor element 10 passes in the axial direction AX, and the housing 20 may be constructed from a single cylindrical component, or from multiple cylindrical components connected coaxially.

[0042] As described above, the sensor element 10 is housed in the housing space provided inside the cylindrical housing 20. For example, in this housing space, the sensor element 10 is positioned such that its longitudinal direction coincides with the axial direction AX of the cylindrical housing 20, and specifically, the central axis of the sensor element 10 and the central axis of the housing 20 are coaxial. In this manner, the sensor element 10 housed in the housing space provided by the housing 20 is held in place by the sensor element holding member 30.

[0043] (Sensor element holding material) The sensor element holding member 30 is a member made of ceramic material that contacts the sensor element 10 and holds the sensor element 10 within the housing 20. The sensor element holding member 30 illustrated in Figure 1 includes ceramic supporters 310, 330, and 350, and compacted powder 320 and 340. The sensor element holding member 30 may further include washers (not shown). The ceramic supporters 310, 330, and 350, and the compacted powder 320 and 340 each have through holes for holding the sensor element 10 and are mounted coaxially around the sensor element 10. In other words, in the gas sensor 1, with the sensor element 10 positioned on the central axis of the housing 20 (the central axis of the gas sensor 1), the ceramic supporters 310, 330, and 350, and the compacted powder 320 and 340 are mounted along this central axis. Figure 1 shows an example in which the ceramic supporter 310, compacted powder 320, ceramic supporter 330, compacted powder 340, and ceramic supporter 350 are mounted around the sensor element 10 in this order from the front end to the rear end. Furthermore, the washer described above may be mounted around the sensor element 10 at a rear end of the ceramic supporter 350, in contact with the ceramic supporter 350. In the following description, the ceramic supporters 310, 330, and 350, the compacted powder 320 and 340, and the washer described above will be collectively referred to as "mounted components".

[0044] Ceramic supports 310, 330, and 350 are ceramic insulators. The compacted powder bodies 320 and 340 are molded from ceramic powder such as talc.

[0045] For example, as illustrated in Figure 1, a tapered portion is provided at the front end inside the housing 20, and the ceramic supporters 310, 330, and 350, which are mounted around the sensor element 10, along with the compacted powder bodies 320 and 340 and washers (not shown), are locked (fixed) to this tapered portion. This is achieved by fitting the housing 20 onto the outer circumference of the mounting components, which have already been mounted around the sensor element 10. Furthermore, after the aforementioned locking is achieved, a predetermined load is applied to the washers from the rear end to the front end, compressing the compacted powder bodies 320 and 340, thereby sealing the space between both ends of the sensor element 10 inside the housing 20. With this sealing in place, the mounting components are restrained by crimping the housing 20 at the rear end of the washers into a reduced diameter shape, ensuring airtightness between both ends of the sensor element 10. In other words, within the internal space of the housing 20, the ceramic supporters 310, 330, and 350, which are mounted around the sensor element 10, and the compacted powder bodies 320 and 340 are sealed by being sandwiched between the inner surface (inner wall) of the housing 20, particularly the inner wall in the tapered portion, and a washer. Here, the position of the housing 20 adjacent to the compacted powder body 340 may be crimped in a reduced diameter shape to further improve the airtightness between both ends of the sensor element 10.

[0046] Although not shown in the diagram, in the gas sensor 1, a connector for electrical connection between the sensor element 10 and the outside may be connected to a plurality of terminal electrodes on the sensor element 10, located inside the outer cylinder 40 and at the rear end of the housing 20. A cable extending from such a connector may be routed out from an opening provided at the rear end of the outer cylinder 40. The opening at the rear end of the outer cylinder 40 may also serve as an inlet and outlet for the reference gas, which is the atmosphere.

[0047] The rear end of the cylindrical housing 20, which houses the sensor element 10 and the sensor element holding member 30 in its internal space, is press-fitted into the front end of the outer cylinder 40. The outer cylinder 40 is then attached to the outer circumferential surface 210 of the housing 20 by welding in the circumferential direction at the overlapping portion of the outer cylinder 40 with the housing 20. In the example shown in Figure 1, the outer cylinder 40 is attached to the outer circumferential surface 210 of the housing 20 by welding in the circumferential direction at welding position Wp.

[0048] (Outer cylinder) The outer cylinder 40 is a cylindrical metal member that is fitted around the outer circumferential surface 210 of the housing 20 (particularly the outer circumferential surface 210 on the rear end side) and protects the portion of the gas sensor 1 that does not come into contact with the gas to be measured. Specifically, the outer cylinder 40 is fixed to the housing 20 by a portion of the outer circumferential surface 210 on the rear end side of the housing 20 being in close contact with the inner circumferential surface 410. The fitting of the outer cylinder 40 to the housing 20 and the close fixing of the outer cylinder 40 to the housing 20 at that time are achieved by press-fitting a portion of the rear end side of the housing 20 into the outer cylinder 40.

[0049] The inner space of the outer cylinder 40 is a reference gas space where the reference gas, which is the atmosphere, exists. The inner space of the outer cylinder 40 is separated from the piping, etc., where the gas to be measured exists, such as in the exhaust pipe of an engine, when the gas sensor 1 is attached to the piping, etc. However, the inner space of the outer cylinder 40 is not sealed, and the atmosphere can enter and exit the inner space of the outer cylinder 40 through an opening provided at the rear end portion (not shown) of the outer cylinder 40.

[0050] (Outer protective cover) The outer protective cover 50 is a bottomed cylindrical member that surrounds (covers) the tip of the sensor element 10, and is made of, for example, metal. The outer protective cover 50 protects the tip of the sensor element 10 and its vicinity, which are the parts that come into direct contact with the gas to be measured when the gas sensor 1 is in use. As illustrated in Figure 1, the outer protective cover 50 has through holes 51 that allow the flow of the gas to be measured from the outside to the inside. Figure 1 shows an example in which the through holes 51 are formed on the bottom surface (the surface on the tip side of the gas sensor 1) of the bottomed cylindrical member outer protective cover 50. However, the arrangement of the through holes 51 illustrated in Figure 1 is merely an example, and the arrangement position and number of through holes 51 may be appropriately determined considering the manner in which the gas to be measured flows into the inside of the outer protective cover 50. For example, multiple through holes 51 may be formed on the side surface of the bottomed cylindrical member outer protective cover 50. Alternatively, multiple through holes 51 may be formed on the bottom surface of the outer protective cover 50.

[0051] The outer protective cover 50 is attached to the outer peripheral surface 210 on the front end side of the housing 20. For example, the rear end side (opening edge) of the outer protective cover 50 has its inner peripheral surface in contact with the housing 20, thereby fixing the outer protective cover 50 to the housing 20.

[0052] In the gas sensor 1 illustrated in Figure 1, the opening edge of the bottomed cylindrical outer protective cover 50 is in contact with a protrusion of the housing 20. However, for the gas sensor 1, it is not essential that the opening edge of the outer protective cover 50 and the protrusion of the housing 20 are in contact, and there may be a gap between them. For example, a drainage groove (not shown) may be provided between the protrusion of the housing 20 and the opening edge of the bottomed cylindrical outer protective cover 50. Such a drainage groove extends in the circumferential direction of the cylindrical housing 20, and may, for example, be provided around the outer circumference of the housing 20.

[0053] The diameter of the bottom surface (bottom) of the aforementioned drainage groove may be smaller (shorter) than the diameter of the opening edge of the outer protective cover 50. In other words, the length from the bottom surface to the axis (central axis) of the housing 20 may be shorter than the length from the opening edge of the outer protective cover 50 to the axis of the housing 20. To put it another way, the length from the bottom surface (outer circumference of the bottom surface) of the aforementioned drainage groove to the axis of the housing 20 may be shorter than the length from the opening edge of the outer protective cover 50 to the axis of the housing 20.

[0054] The outer protective cover 50 illustrated in Figure 1 has a cylindrical large-diameter portion and a bottomed cylindrical tip portion connected to the large-diameter portion and having a smaller diameter than the large-diameter portion. In other words, in this embodiment, the bottomed cylindrical outer protective cover 50 has a cylindrical body portion and a bottomed cylindrical tip portion with a smaller inner diameter than the body portion. The body portion has a side portion having a surface along the central axis direction of the outer protective cover 50 and a stepped portion at the bottom of the body portion that connects the side portion and the tip portion. However, it is not essential for the gas sensor 1 that the outer protective cover 50 has such a configuration, and it is not essential that the outer protective cover 50 has a body portion and a tip portion. In other words, it is not essential for the gas sensor 1 that the outer protective cover 50 has a configuration in which the side of the cylindrical body portion and the bottomed cylindrical tip portion are connected by a stepped portion. For the gas sensor 1, it is sufficient that the outer protective cover 50 has a bottomed cylindrical shape that covers the tip of the sensor element 10. For example, the outer protective cover 50 may be configured such that the side surface of the cylindrical body and the bottomed cylindrical tip are directly connected without any stepped portion. Alternatively, the outer protective cover 50 may have multiple stepped portions. 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 smaller diameter than the large-diameter portion, and a tip connected to the body, having a smaller inner diameter than the body and being bottomed cylindrical. In other words, in this embodiment, the outer protective cover 50 only needs to have a bottomed cylindrical shape that covers the tip of the sensor element 10, and any other shapes it may include in addition to the bottomed cylindrical shape can be appropriately selected depending on the method of use, location of use, etc., of the gas sensor 1.

[0055] With the above configuration, when the gas sensor 1 is mounted in a predetermined position, the space where the gas to be measured is present around the tip of the sensor element 10 and the space where the reference gas is present around the rear end are completely separated. As a result, the gas sensor 1 can accurately measure the concentration of the target gas component in the gas to be measured.

[0056] (Summary of information on gas sensors) As described above, the gas sensor 1 comprises a cylindrical metal housing 20 through which a long sensor element 10 penetrates in the axial direction AX, and a metal outer cylinder 40 mounted on the outer circumferential surface 210 of the housing 20. The outer cylinder 40 is mounted on the outer circumferential surface 210 of the housing 20 by press-fitting a portion of the rear end of the housing 20 and welding in the circumferential direction at the overlapping portion with the press-fitted housing 20. In the example shown in Figure 1, the outer cylinder 40 is mounted on the outer circumferential surface 210 of the housing 20 by welding in the circumferential direction at welding position Wp.

[0057] In the gas sensor 1, the contact distance Lg, which is the length in the axial direction AX of the outer circumferential surface 210 of the housing 20 that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end of the molten portion 420 of the outer cylinder 40 formed by welding, is less than or equal to the reference distance Lr. The details of this contact distance Lg will be explained below using Figure 2 and other references.

[0058] (Regarding contact distance) Figure 2 is a schematic enlarged cross-sectional view showing the relationship between the housing 20 and the outer cylinder 40 around the welding position Wp of the gas sensor 1, and in particular, it is a figure that explains the details of the contact distance Lg. In Figure 2, the left-right direction of the paper is the axial direction AX.

[0059] As illustrated in Figure 2, the molten portion 420 of the outer cylinder 40 formed by welding is melted into the housing 20, and the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are in contact with each other around the molten portion 420. In addition, in the example shown in Figure 2, the rear end of the outer circumferential surface 210 of the housing 20 is chamfered, that is, the rear corner of the housing 20 is chamfered. Specifically, in the housing 20 illustrated in Figure 2, the rear end of the outer circumferential surface 210 is chamfered with a C-chamfer, and a corner surface Af with a straight cross-sectional shape is formed between the outer circumferential surface 210 of the housing 20 and the rear end surface 220 of the housing 20.

[0060] In the figure, "center of molten portion Cf" indicates the center in the axial direction AX of the molten portion 420 of the outer cylinder 40 formed by welding. The molten portion 420 can also be described as the part of the outer cylinder 40 whose structure has been altered by melting.

[0061] In the figure, "Molten portion end Ef" indicates the endpoint where the molten portion 420 contacts the outer circumferential surface 210 of the housing 20, located behind the center Cf of the molten portion in the axial direction AX. The molten portion end Ef can also be described as the rear end of the molten portion 420 in contact with the housing 20, in the axial direction AX. Alternatively, the molten portion end Ef can be described as the contact position between the outer circumferential surface 210 of the housing 20, the inner circumferential surface 410 of the outer cylinder 40, and the molten portion 420, located behind the center Cf of the molten portion in the axial direction AX. Behind the molten portion end Ef in the axial direction AX, the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are in contact with each other.

[0062] In the figure, "non-contact position Np" indicates the position in the axial direction AX, rearward from the molten area center Cf, where the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are not in contact (they no longer touch). In other words, non-contact position Np is the position furthest forward, rearward from the molten area center Cf, where the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are not in contact, and is also called the "release position". Non-contact position Np can also be described as the position, rearward from the molten area center Cf, where the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are not in contact over the entire circumferential direction. Alternatively, non-contact position Np can be described as the rear end of the outer circumferential surface 210 of the housing 20. As mentioned above, in the example shown in Figure 2, the rear end of the outer circumferential surface 210 of the housing 20 is chamfered (C-chamfering). Therefore, the non-contact position Np may be rephrased as the rear end of the outer peripheral surface 210 of the housing 20 after the chamfering process has been performed.

[0063] In the figure, "Penetration Depth Da" indicates the radial depth of the housing 20 from the outer circumferential surface 210 of the housing 20 to the deepest point Dp of the molten portion 420 that has melted into the housing 20. The deepest point Dp can also be described as the radial position of the molten portion 420 that is the deepest part of the molten portion 420 of the outer cylinder 40 that has melted into the housing 20 by welding.

[0064] In the figure, "thickness Tc" indicates the thickness of the outer cylinder 40, which is a cylindrical metal component; in other words, it represents the difference between the outer diameter and the inner diameter of the outer cylinder 40.

[0065] In the example shown in Figure 2, the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are in contact with each other between the molten end Ef and the non-contact position Np, and in particular, the outer circumferential surface 210 and the inner circumferential surface 410 are in contact with each other over the entire circumferential direction. Furthermore, in the axial direction AX, towards the rear end from the non-contact position Np, the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are not in contact with each other, and in particular, the outer circumferential surface 210 and the inner circumferential surface 410 are not in contact with each other over the entire circumferential direction.

[0066] Here, as mentioned above, the contact distance Lg is the length in the axial direction AX of the outer circumferential surface 210 of the housing 20 that is in contact with the inner circumferential surface 410 of the outer cylinder 40 on the rear end side of the molten portion 420. Therefore, in the example shown in Figure 2, the contact distance Lg can also be considered as the distance between the position of the molten portion end Ef and the non-contact position Np. In other words, in the example shown in Figure 2, the contact distance Lg can be rephrased as the length in the axial direction AX of the outer circumferential surface 210 of the housing 20 that is in contact with the inner circumferential surface 410 of the outer cylinder 40 over its entire length in the circumferential direction on the rear end side of the molten portion 420.

[0067] In this embodiment, the gas sensor 1 is configured such that the contact distance Lg is less than or equal to the reference distance Lr, allowing volatile gases in the molten portion 420 of the outer cylinder 40 to escape from between the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40.

[0068] As mentioned above, the reference distance Lr is the maximum reachable distance, which is, for example, "the distance that volatile gas can travel between the outer surface 210 and the inner surface 410 due to its own pressure." In other words, the reference distance Lr represents the maximum reachable distance that volatile gas, which is formed when residual oil etc. adhering to the contact surface between the housing 20 and the outer cylinder 40 volatilizes due to the heat during welding, can reach due to its own pressure. The reachable distance of the volatile gas has the following relationships with the penetration depth Da, the interference fit Tb which represents the difference between the outer diameter of the housing 20 and the inner diameter of the outer cylinder 40, and the thickness Tc of the outer cylinder 40.

[0069] In other words, the greater the penetration depth Da, which represents "the radial depth of the housing 20 from the outer peripheral surface 210 of the housing 20 to the deepest part Dp of the molten portion 420 melted into the housing 20," the greater the thermal deformation of the housing 20 and the outer cylinder 40. That is, the greater the penetration depth Da, the larger the gap between the outer peripheral surface 210 of the housing 20 and the inner peripheral surface 410 of the outer cylinder 40. Therefore, the greater the penetration depth Da, the smaller the diffusion resistance to volatile gases attempting to move between the outer peripheral surface 210 and the inner peripheral surface 410, and the greater the distance that volatile gases can reach.

[0070] Furthermore, the larger the interference fit Tb, which represents the difference between the outer diameter of the housing 20 and the inner diameter of the outer cylinder 40, the greater the diffusion resistance to volatile gases attempting to move between the outer surface 210 and the inner surface 410. Therefore, the larger the interference fit Tb, the smaller the reachable distance of the volatile gases.

[0071] Furthermore, the larger the thickness Tc, which represents the "thickness of the outer cylinder 40," the easier it is for heat to dissipate during welding, thus reducing the amount of volatile gas generated and minimizing thermal deformation of the housing 20 and the outer cylinder 40. Therefore, the larger the thickness Tc, the smaller the reachable distance of volatile gas between the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40.

[0072] As explained above, the greater the penetration depth Da, the greater the reachable distance of the volatile gas; the greater the overlap 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, overlap Tb, and thickness Tc each have the above-mentioned relationships with respect to the reachable distance, the reference distance Lr, which is the maximum reachable distance, can be expressed as a function of the penetration depth Da, overlap Tb, and thickness Tc. That is, the reference distance Lr is calculated by the following formula (1), where "k" is the proportionality constant. Lr = k × Da / (Tb × Tc) ... Formula (1)

[0073] (Calculation of the proportionality constant k) Here, the inventors of this case calculated the proportionality constant k in the above formula (1) as follows. First, the inventors of this case manufactured a gas sensor 1(Ref) with penetration depth Da as Da(Ref), overlap Tb as Tb(Ref), thickness Tc of the outer cylinder 40 as Tc(Ref), and contact distance Lg as contact distance Lg(Ref). With respect to the gas sensor 1(Ref), the inventors of this case confirmed that the number of pinholes generated in the molten portion 420 decreased by changing at least one of the penetration depth Da, overlap Tb, and thickness Tc of the outer cylinder 40 so that the reference distance Lr increases. In other words, the inventors of this case confirmed that the number of pinholes generated in the gas sensor 1(Ref) decreased by changing at least one of the penetration depth Da, overlap Tb, and thickness Tc of the outer cylinder 40 so that the reachable distance of the volatile gas increases. Furthermore, the inventors confirmed that by changing at least one of the following parameters of the gas sensor 1(Ref)—penetration depth Da, overlap Tb, and thickness Tc of the outer cylinder 40—to reduce the reference distance Lr, the number of pinholes in the molten portion 420 increased. In other words, the inventors confirmed that by changing at least one of the following parameters of the gas sensor 1(Ref)—penetration depth Da, overlap Tb, and thickness Tc of the outer cylinder 40—to reduce the reachable distance of the volatile gas, the number of pinholes decreased. Based on these confirmations, the inventors determined that in the gas sensor 1(Ref), the contact distance Lg is equal to the reference distance Lr. That is, the inventors determined that the contact distance Lg(Ref) in the gas sensor 1(Ref) is equal to the reference distance Lr in the gas sensor 1(Ref).

[0074] Therefore, the inventors of this case substituted Da=Da(Ref), Tb=Tb(Ref), Tc=Tc(Ref), and Lr=Lg(Ref) into the above-mentioned formula (1) to calculate the proportionality constant k, specifically calculating k(Ref) as the proportionality constant k.

[0075] (Identification of reference distance Lr, and determination of contact distance Lg) Since the proportionality constant k has been identified (i.e., it has been identified that the proportionality constant k is k(Ref)), the reference distance Lr for the gas sensor 1 can be calculated from the penetration depth Da, the overlap Tb, the thickness Tc of the outer cylinder 40, and the proportionality constant k, based on formula (1). Then, by setting the contact distance Lg for the gas sensor 1 to be 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 "volatile gas is trapped in the molten portion 420 without escaping from between the outer surface 210 and the inner surface 410, causing pinholes in the molten portion 420," in other words, it can suppress the occurrence of pinholes in the molten portion 420.

[0076] As explained above, by setting the contact distance Lg of the gas sensor 1 to be less than or equal to the reference distance Lr, the gas sensor 1 can suppress the generation of pinholes in the molten portion 420. Furthermore, the inventors have confirmed in experiments that it is desirable to make the contact distance Lg smaller than the reference distance Lr, and in particular, it is more desirable to make the contact distance Lg smaller than 1.2 times the reference distance Lr. Specifically, the inventors have confirmed through experiments that by making the contact distance Lg smaller than 1.2 times the reference distance Lr, the number of pinholes generated in the molten portion 420 decreases sharply. Details of this experiment will be described later.

[0077] Therefore, in the gas sensor 1, the reference distance Lr may be greater than 1.2 times the contact distance Lg, that is, the contact distance Lg may be less than 1 / 1.2 of the reference distance Lr. As described above, by making the contact distance Lg less than 1 / 1.2 of the reference distance Lr, the number of pinholes generated in the molten portion 420 decreases sharply. Therefore, by making the contact distance Lg less than 1 / 1.2 of the reference distance Lr, the gas sensor 1 can very effectively suppress the generation of pinholes in the molten portion 420.

[0078] (Shape of the corners of the housing) As described above, in the housing 20 illustrated in Figure 2, the rear end (corner) of the outer peripheral surface 210 is chamfered, specifically, a C-chamfer is applied. That is, Figure 2 shows an example in which the corner (rear end corner) of the housing 20 facing the inner peripheral surface 410 of the outer cylinder 40 is chamfered, and a corner Af having a linear cross-sectional shape is formed between the outer peripheral surface 210 of the housing 20 and the rear end surface 220 of the housing 20.

[0079] In the gas sensor 1, the rear end of the outer circumferential surface 210 of the housing 20 may be chamfered. For example, as illustrated in Figure 2, the rear end of the outer circumferential surface 210 of the housing 20 may be chamfered in a straight line. Specifically, in the gas sensor 1 illustrated in Figure 2, the rear end of the outer circumferential surface 210 of the housing 20 is chamfered with a C-chamfer. The rear end of the chamfered outer circumferential surface 210 of the housing 20 can be used as a guide when press-fitting the housing 20 into the outer cylinder 40, making it easier to press-fit the housing 20 into the outer cylinder 40.

[0080] As explained above, Figure 2 shows an example of a gas sensor 1 in which the rear end of the outer circumferential surface 210 of the housing 20 is chamfered in a straight line. That is, in the gas sensor 1 illustrated in Figure 2, the rear end of the outer circumferential surface 210 of the housing 20 is chamfered in a straight line. As a result of this chamfering, a single straight-line corner face Af is formed on the rear end of the housing 20, as illustrated in Figure 2. However, for the gas sensor 1, it is not essential that the corner face Af formed on the rear end of the "cylindrical, metal housing" (e.g., housing 20) through which the sensor element passes axially is made by chamfering has a single straight-line cross-section. In other words, for the gas sensor 1, it is not essential that the corner face Af formed by the chamfering applied to the rear end of the outer circumferential surface of the housing has a single straight-line cross-section. As will be explained in more detail later, by chamfering, a corner face Af may be formed on the rear end of the cylindrical metal housing through which the sensor element passes axially, as illustrated in Figures 6(A) and (B). Figures 6(A) and (B) show examples of corner faces Af whose cross-sectional shape includes multiple straight sections. In other words, in the gas sensor 1, the surface (corner face) formed on the rear end of the cylindrical metal housing through which the sensor element passes axially may include multiple straight sections in its cross-sectional shape.

[0081] Furthermore, for the gas sensor 1, it is not essential to chamfer the rear end of the outer surface of the cylindrical, metal housing (e.g., housing 20) through which the sensor element passes axially. Even if chamfering is applied to the rear end of the outer surface of the housing, it is not essential for the gas sensor 1 to use a C-chamfer for this chamfering process.

[0082] As described above, in this embodiment, the gas sensor 1 only needs to have a contact distance Lg, which is the length in the axial direction AX of the outer circumferential surface 210 of the housing 20 that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end side of the molten portion 420 of the outer cylinder 40, be less than or equal to the reference distance Lr. Whether or not to chamfer the rear end of the outer circumferential surface 210 of the housing 20, and if so, what kind of chamfer to apply, is appropriately selected according to the method of use and location of use of the gas sensor 1. That is, in a gas sensor 1 in which the contact distance Lg is less than or equal to the reference distance Lr, there can be various shapes for the rear end corner (the corner facing the inner circumferential surface 410 of the outer cylinder 40) of the "cylindrical metal housing through which the sensor element penetrates in the axial direction". Below, typical examples of the shape of the rear end corner of the "cylindrical metal housing through which the sensor element penetrates in the axial direction" of a gas sensor 1 in which the contact distance Lg is less than or equal to the reference distance Lr will be described.

[0083] (Housing relating to Modification 1) Figure 3 is an enlarged cross-sectional view schematically showing the relationship between the housing 20(1) according to Modification 1 and the outer cylinder 40 around the welding position Wp. In Figure 3, the left-right direction of the paper is the axial direction AX. The housing 20 exemplified in Figure 2 had a chamfered edge (C-chamfer) at the rear end corner (the corner facing the inner circumferential surface 410 of the outer cylinder 40). That is, the rear end (corner) of the outer circumferential surface 210 of the housing 20 had a chamfered edge, and a single straight corner Af was formed between the outer circumferential surface 210 and the rear end surface 220 of the housing 20. In contrast, the housing 20(1) exemplified in Figure 3 has an R-chamfered edge (R-chamfer) at the rear end corner (the corner facing the inner circumferential surface 410 of the outer cylinder 40). In other words, the rear end (corner) of the outer peripheral surface 210(1) of the housing 20(1) is chamfered with an R-chamfer, and a single curved rounded surface Rf is formed between the outer peripheral surface 210(1) and the rear end surface 220(1) of the housing 20.

[0084] Except for the fact that the rear corner is rounded instead of chamfered, the housing 20(1) shown in Figure 3 is the same as the housing 20 shown in Figure 2. That is, the housing 20(1) is a cylindrical metal component, similar to the housing 20, with a long sensor element 10 penetrating through its interior in the axial direction AX. As shown in Figure 3, a metal outer cylinder 40 is attached to the outer circumferential surface 210(1) of the housing 20(1). The outer cylinder 40 is attached to the outer circumferential surface 210(1) of the housing 20(1) by press-fitting a portion of the rear end of the housing 20(1) and welding in the circumferential direction at the overlapping portion with the press-fitted housing 20(1). The contact distance Lg, which is the length in the axial direction AX of the outer circumferential surface 210(1) of the housing 20(1) that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end side of the molten portion 420 of the outer cylinder 40 formed by welding, is less than or equal to the reference distance Lr.

[0085] In the example shown in Figure 3, the molten portion end Ef indicates the endpoint where the molten portion 420 contacts the outer circumferential surface 210(1) of the housing 20(1), located further rear than the molten portion center Cf in the axial direction AX. The molten portion end Ef can also be described as the rear end of the molten portion 420 in contact with the housing 20(1) in the axial direction AX. Alternatively, the molten portion end Ef can be described as the contact position between the outer circumferential surface 210(1) of the housing 20(1), the inner circumferential surface 410 of the outer cylinder 40, and the molten portion 420, located further rear than the molten portion center Cf in the axial direction AX. The non-contact position Np indicates the position where the outer circumferential surface 210(1) of the housing 20(1) and the inner circumferential surface 410 of the outer cylinder 40 are not in contact (the furthest forward position where they are not in contact), located further rear than the molten portion center Cf in the axial direction AX. The non-contact position Np can also be rephrased as the position where the outer circumferential surface 210(1) of the housing 20(1) and the inner circumferential surface 410 of the outer cylinder 40 are in non-contact over the entire circumferential direction, on the rear end side of the molten portion center Cf. Alternatively, the non-contact position Np can also be rephrased as the rear end of the outer circumferential surface 210(1) of the housing 20(1). As mentioned above, in the example shown in Figure 3, the rear end of the outer circumferential surface 210(1) of the housing 20(1) is chamfered (R chamfered). Therefore, the non-contact position Np can also be rephrased as the rear end of the outer circumferential surface 210(1) of the housing 20(1) after the chamfering process has been applied. The penetration depth Da indicates the radial depth of the housing 20(1) from the outer circumferential surface 210(1) of the housing 20(1) to the deepest part Dp of the molten portion 420 that has melted into the housing 20(1). Furthermore, in the example shown in Figure 3, the interference fit Tb represents the interference fit, which is the difference between the outer diameter of the housing 20(1) and the inner diameter of the outer cylinder 40. Other elements such as the molten zone center Cf and the thickness Tc of the outer cylinder 40 in Figure 3 are the same as those illustrated in Figure 2, so their explanation is omitted.

[0086] As described above, the contact distance Lg is the length in the axial direction AX of the outer circumferential surface 210(1) of the housing 20(1) that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end of the molten portion 420. Therefore, in the example shown in Figure 3, the contact distance Lg can also be considered as the distance between the position of the molten portion end Ef and the non-contact position Np. The contact distance Lg is less than or equal to the reference distance Lr. By setting the contact distance Lg to less than or equal to the reference distance Lr, the gas sensor 1 allows volatile gases in the molten portion 420 to escape from between the outer circumferential surface 210(1) of the housing 20(1) and the inner circumferential surface 410 of the outer cylinder 40, thereby suppressing the occurrence of pinholes in the molten portion 420.

[0087] As explained using Figure 3, in the gas sensor 1, the rear end of the outer circumferential surface 210(1) of the cylindrical metal housing 20(1), through which the elongated sensor element 10 penetrates in the axial direction AX, may be chamfered with an R-chamfer. By employing R-chamfering as the chamfering applied to the rear end of the outer circumferential surface 210 of the housing 20, the generation of burrs during processing can be suppressed, and burr jamming between the housing 20 and the outer cylinder 40 can be suppressed.

[0088] As explained above, Figure 3 shows an example of a gas sensor 1 in which the rear end of the outer peripheral surface 210(1) of the housing 20(1) is chamfered with an R-chamfer. That is, in the gas sensor 1 illustrated in Figure 3, the rear end of the outer peripheral surface 210(1) of the housing 20(1) is chamfered in a curved shape. This chamfering process creates a rounded surface Rf with a single curved cross-sectional shape, as illustrated in Figure 3. However, for the gas sensor 1, it is not essential that the rounded surface Rf formed on the rear end of the cylindrical metal housing through which the sensor element passes in the axial direction has been chamfered has a single curved cross-sectional shape. That is, for the gas sensor 1, it is not essential that the rounded surface Rf formed by the chamfering process applied to the rear end of the outer peripheral surface of the housing has a single curved cross-sectional shape. As will be explained in more detail later, by chamfering, a rounded surface Rf, as illustrated in Figure 6(C), may be formed on the rear end of the cylindrical metal housing through which the sensor element passes axially. Figure 6(C) shows an example of a rounded surface Rf whose cross-sectional shape includes multiple curved portions. In other words, in the gas sensor 1, the surface (rounded surface) formed on the rear end of the cylindrical metal housing through which the sensor element passes axially may include multiple curved portions in its cross-sectional shape.

[0089] In the gas sensor 1, the rear end of the outer surface of the cylindrical metal housing through which the sensor element passes axially may be chamfered so as to form a surface whose cross-sectional shape includes at least one of a straight portion and a curved portion. For example, the rear end of the outer surface of the cylindrical metal housing through which the sensor element passes axially may be chamfered so as to form an angular surface Af or a rounded surface Rf whose cross-sectional shape includes at least one of a straight portion and a curved portion. The surface formed on the rear end of the cylindrical metal housing through which the sensor element passes axially may include at least one of one or more straight portions and one or more curved portions in its cross-sectional shape. For example, Figure 6(D), described later, shows an example of a cylindrical metal housing through which a sensor element passes axially, in which a surface including one straight portion and two curved portions in its cross-sectional shape is formed on the rear end by chamfering.

[0090] (Housing relating to modified example 2) Figure 4 is an enlarged cross-sectional view schematically showing the relationship between the housing 20(2) according to Modification 2 and the outer cylinder 40 around the welding position Wp. In Figure 4, the left-right direction of the paper is the axial direction AX. The cylindrical metal housings (i.e., housings 20 and 20(1)) exemplified in Figures 2 and 3, in which a sensor element penetrates the interior axially, had chamfered edges at the rear end corners (corners facing the inner circumferential surface 410 of the outer cylinder 40). Specifically, the rear end corner of the outer circumferential surface 210 of housing 20 had a C-chamfer, and the rear end corner of the outer circumferential surface 210(1) of housing 20(1) had an R-chamfer. In contrast, the housing 20(2) exemplified in Figure 4 does not have chamfered edges at the rear end corners (corners facing the inner circumferential surface 410 of the outer cylinder 40).

[0091] Except for the fact that the rear end corner is not chamfered, the housing 20(2) illustrated in Figure 4 is the same as the housing 20 illustrated in Figure 2 and the housing 20(1) illustrated in Figure 3. That is, the housing 20(2), like the housings 20 and 20(1), is a cylindrical metal component, and a long sensor element 10 penetrates through its interior in the axial direction AX. As illustrated in Figure 4, a metal outer cylinder 40 is attached to the outer circumferential surface 210(2) of the housing 20(2). The outer cylinder 40 is attached to the outer circumferential surface 210(3) of the housing 20(2) by press-fitting a portion of the rear end of the housing 20(2) and welding in the circumferential direction at the overlapping portion with the press-fitted housing 20(2). The contact distance Lg, which is the length in the axial direction AX of the outer circumferential surface 210(2) of the housing 20(2) that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end side of the molten portion 420 of the outer cylinder 40 formed by welding, is less than or equal to the reference distance Lr.

[0092] In the example shown in Figure 4, the molten portion end Ef indicates the "endpoint where the molten portion 420 contacts the outer circumferential surface 210(2) of the housing 20(2)," located behind the molten portion center Cf in the axial direction AX. The molten portion end Ef can also be rephrased as "the rear end of the molten portion 420 in contact with the housing 20(2) in the axial direction AX." Alternatively, the molten portion end Ef can be rephrased as the contact position between the outer circumferential surface 210(2) of the housing 20(2), the inner circumferential surface 410 of the outer cylinder 40, and the molten portion 420, located behind the molten portion center Cf in the axial direction AX. The non-contact position Np indicates the position where the outer circumferential surface 210(2) of the housing 20(2) and the inner circumferential surface 410 of the outer cylinder 40 are not in contact (the furthest forward position where they are not in contact), located behind the molten portion center Cf in the axial direction AX. The non-contact position Np can also be rephrased as the position where the outer circumferential surface 210(2) of the housing 20(2) and the inner circumferential surface 410 of the outer cylinder 40 are in non-contact over the entire circumferential direction, on the rear end side of the molten portion center Cf. Alternatively, the non-contact position Np can also be rephrased as the rear end of the outer circumferential surface 210(2) of the housing 20(2). As mentioned above, in the example shown in Figure 4, the rear end of the outer circumferential surface 210(2) of the housing 20(2) is not chamfered. Therefore, the non-contact position Np can also be rephrased as the position where the outer circumferential surface 210(2) of the housing 20(2) and the rear end surface 220(3) are in contact. The penetration depth Da indicates the radial depth of the housing 20(2) from the outer circumferential surface 210(2) of the housing 20(2) to the deepest part Dp of the molten portion 420 that has melted into the housing 20(2). Furthermore, in the example shown in Figure 4, the interference fit Tb represents the interference fit, which is the difference between the outer diameter of the housing 20(2) and the inner diameter of the outer cylinder 40. Other elements such as the molten zone center Cf and the thickness Tc of the outer cylinder 40 in Figure 4 are the same as those illustrated in Figures 2 and 3, so their explanation is omitted.

[0093] As mentioned above, the contact distance Lg is the length in the axial direction AX of the outer circumferential surface 210(2) of the housing 20(2) that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end of the molten portion 420. Therefore, in the example shown in Figure 4, the contact distance Lg can also be considered as the distance between the position of the molten portion end Ef and the non-contact position Np. Furthermore, the contact distance Lg is less than or equal to the reference distance Lr.

[0094] As described above, the gas sensor 1 according to this embodiment has a contact distance Lg that is less than or equal to the reference distance Lr. By adopting this configuration, the gas sensor 1 allows the volatile gas in the molten portion 420 to escape from between the outer circumferential surface of the cylindrical metal housing through which the sensor element passes axially and the inner circumferential surface 410 of the outer cylinder 40. For the gas sensor 1 according to this embodiment, as explained with reference to Figure 4, it is not essential to chamfer the rear end of the outer circumferential surface of the cylindrical metal housing through which the sensor element passes axially (e.g., housing 20(2)).

[0095] (Housing relating to modified example 3) Figure 5 is an enlarged cross-sectional view schematically showing the relationship between the housing 20(3) according to the modified example 3 and the outer cylinder 40 around the welding position Wp. In Figure 5, the left-right direction of the paper is the axial direction AX. In the "cylindrical metal housing in which a sensor element penetrates the interior axially" that has been explained using Figures 2 to 4, the outer circumferential surface of the housing was in contact with the inner circumferential surface 410 of the outer cylinder 40 over the entire circumference between the molten end Ef and the non-contact position Np. That is, in housings 20, 20(1), and 20(2), the outer circumferential surface was in contact with the inner circumferential surface 410 of the outer cylinder 40 over the entire circumference between the molten end Ef and the non-contact position Np. In contrast, in the housing 20(3) illustrated in Figure 5, a slit Sl is formed on its outer circumferential surface 210(3) that extends in the axial direction AX from the non-contact position Np toward the tip. Therefore, a portion of the outer peripheral surface 210(3) of the housing 20(3) (specifically, the portion where the slit Sl is formed) is not in contact with the inner peripheral surface 410 of the outer cylinder 40 between the molten end Ef and the non-contact position Np.

[0096] Specifically, on the outer circumferential surface 210(3) of the housing 20(3) illustrated in Figure 5, a slit Sl is formed on the rear end side of the molten portion 420 of the outer cylinder 40 formed by welding. In the example shown in Figure 5, the slit Sl extends axially AX from the non-contact position Np toward the tip.

[0097] Except for the fact that a slit Sl extending in the axial direction AX is formed on the outer circumferential surface, the housing 20(3) illustrated in Figure 5 is the same as the housing 20 illustrated in Figure 2. That is, the housing 20(3), like the housing 20, is a cylindrical, metal member, and a long sensor element 10 penetrates through its interior in the axial direction AX. As illustrated in Figure 5, a metal outer cylinder 40 is attached to the outer circumferential surface 210(3) of the housing 20(3). The outer cylinder 40 is attached to the outer circumferential surface 210(3) of the housing 20(3) by press-fitting a portion of the rear end side of the housing 20(3) and welding in the circumferential direction at the overlapping portion with the press-fitted housing 20(3). The contact distance Lg, which is the length in the axial direction AX of the outer circumferential surface 210(3) of the housing 20(3) that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end side of the molten portion 420 of the outer cylinder 40 formed by welding, is less than or equal to the reference distance Lr. In other words, the contact distance Lg, which is the length in the axial direction AX of the outer circumferential surface 210(3) of the housing 20(3) that is in contact with the inner circumferential surface 410 of the outer cylinder 40, on the rear end side of the molten portion 420, is less than or equal to the reference distance Lr.

[0098] Furthermore, similar to the housing 20, the housing 20(3) has a chamfered edge at its rear end corner (the corner facing the inner circumferential surface 410 of the outer cylinder 40). That is, the rear end (corner) of the outer circumferential surface 210(3) of the housing 20(3) is chamfered, and a straight corner surface Af is formed between the outer circumferential surface 210(3) and the rear end surface 220(3) of the housing 20(3).

[0099] In the example shown in Figure 5, the molten portion end Ef indicates the endpoint where the molten portion 420 contacts the outer circumferential surface 210(3) of the housing 20(3), located further back than the molten portion center Cf in the axial direction AX. The molten portion end Ef can also be described as the rear end of the molten portion 420 in contact with the housing 20(3) in the axial direction AX. Alternatively, the molten portion end Ef can be described as the contact point between the outer circumferential surface 210(3) of the housing 20(3), the inner circumferential surface 410 of the outer cylinder 40, and the molten portion 420, located further back than the molten portion center Cf in the axial direction AX.

[0100] The non-contact position Np is the position in the axial direction AX that is behind the center Cf of the molten portion, where the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40 are not in contact (the position closest to the tip where both are not in contact). As mentioned above, a slit Sl is formed on the outer circumferential surface 210(3) of the housing 20(3) on the rear side of the molten portion 420. Therefore, the non-contact position Np illustrated in Figure 5 can be rephrased as the position in the axial direction AX that is behind the center Cf of the molten portion, where the portion of the outer circumferential surface 210(3) of the housing 20(3) where the slit Sl is not formed is not in contact with the inner circumferential surface 410 of the outer cylinder 40. In other words, the non-contact position Np illustrated in Figure 5 can be rephrased as the position where the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40 are in non-contact over the entire circumferential direction, located on the rear end side of the molten portion center Cf in the axial direction AX. Alternatively, the non-contact position Np can be rephrased as the rear end of the outer circumferential surface 210(3) of the housing 20(3). As mentioned above, in the example shown in Figure 5, the rear end of the outer circumferential surface 210(3) of the housing 20(3) is chamfered (C-chamfering). Therefore, the non-contact position Np can be rephrased as the rear end of the outer circumferential surface 210(3) of the housing 20(3) after the chamfering has been applied.

[0101] The penetration depth Da indicates the radial depth of the housing 20(3) from the outer circumferential surface 210(3) of the housing 20(3) to the deepest part Dp of the molten portion 420 that has melted into the housing 20(3). In the example shown in Figure 5, the interference fit Tb represents the interference fit, which is the difference between the outer diameter of the housing 20(3) and the inner diameter of the outer cylinder 40. Other details such as the center of the molten portion Cf and the thickness Tc of the outer cylinder 40 in Figure 5 are the same as those illustrated in Figures 2 to 4, so their explanation is omitted.

[0102] As described above, the contact distance Lg is the length in the axial direction AX of the outer circumferential surface 210(3) of the housing 20(3) that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end of the molten portion 420. In particular, for the outer circumferential surface 210(3) in which the slit Sl is formed, the contact distance Lg is the length in the axial direction AX of the outer circumferential surface 210(3) that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end of the molten portion 420, in the portion where the slit Sl is not formed. In the example shown in Figure 5, the contact distance Lg can also be considered as the distance between the position of the molten portion end Ef and the non-contact position Np where the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40 are not in contact over the entire circumferential direction. The contact distance Lg is less than or equal to the reference distance Lr. The gas sensor 1 ensures that the contact distance Lg is less than or equal to the reference distance Lr, thereby allowing volatile gases in the molten portion 420 to escape from between the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40, and suppressing the occurrence of pinholes in the molten portion 420.

[0103] As explained above, in the gas sensor 1, a slit Sl extending in the axial direction AX is formed on the outer peripheral surface 210(3) of the housing 20(3) on the rear end side of the molten portion 420 in the axial direction AX. Here, although the details will be described later, the inventors have confirmed that by forming a slit Sl extending in the axial direction AX on the outer peripheral surface 210(3) of the housing 20(3), the effect of suppressing pinhole generation can be improved compared to when such a slit Sl is not formed. For example, it is thought that the slit Sl can increase the distance that volatile gas can travel between the outer peripheral surface 210(3) of the housing 20(3) and the inner peripheral surface 410 of the outer cylinder 40 due to its own pressure. Therefore, the gas sensor 1 can further improve the effect of suppressing pinhole generation in the molten portion 420 by forming a slit Sl extending in the axial direction AX compared to when the slit Sl is not formed.

[0104] As explained above, on the outer circumferential surface 210(3) of the housing 20(3) illustrated in Figure 5, a slit Sl is formed on the rear end side of the molten portion 420, extending axially AX from the non-contact position Np towards the tip. In addition, the rear end of the outer circumferential surface 210(3) of the housing 20(3) is chamfered. However, for the gas sensor 1, it is not essential that the slit Sl extends from the non-contact position Np towards the tip. The slit Sl only needs to extend axially AX on the rear end side of the molten portion 420. Even if the slit Sl does not extend from the non-contact position Np, if it extends axially AX, it is thought that the slit Sl can increase the reachable distance of the volatile gas, that is, it is thought that the effect of suppressing pinhole generation can be improved.

[0105] Similarly, for the gas sensor 1, it is not essential that the slit Sl be formed on the outer circumferential surface 210(3) of the housing 20(3). The slit Sl may be formed on the inner circumferential surface 410 of the outer cylinder 40, and it is sufficient that the slit Sl be formed on at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40.

[0106] Furthermore, at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40 may have a plurality of slits Sl provided at intervals from each other in the circumferential direction of the housing 20(3) and the outer cylinder 40, respectively.

[0107] Furthermore, when a slit Sl is formed on at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40, it is not essential that the rear end of the outer circumferential surface 210(3) is chamfered. The rear end of the outer circumferential surface 210(3) may or may not be chamfered. For example, the gas sensor 1 may have a slit Sl formed on the outer circumferential surface 210(1) of the housing 20(1) as illustrated in Figure 3. Alternatively, the gas sensor 1 may comprise the outer circumferential surface 210(1) of the housing 20(1) as illustrated in Figure 3 and an outer cylinder 40 with a slit Sl formed on its inner circumferential surface 410. Similarly, the gas sensor 1 may have a slit Sl formed on the outer circumferential surface 210(2) of the housing 20(2) as illustrated in Figure 4. Furthermore, the gas sensor 1 may also include an outer circumferential surface 210(2) of the housing 20(2) as illustrated in Figure 4, and an outer cylinder 40 with a slit Sl formed on its inner circumferential surface 410.

[0108] In other words, in the gas sensor 1, a slit Sl extending in the axial direction AX may be formed on at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40, on the rear end side of the molten portion 420 in the axial direction AX. In the gas sensor 1, the slit Sl may extend to the rear end surface (rear end surface 220(3)) of the housing 20(3), that is, it may extend to the non-contact position Np. Furthermore, in the gas sensor 1, a plurality of slits Sl may be formed on at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40, spaced apart from each other in the circumferential direction.

[0109] As described above, the inventors of this case have confirmed that by forming a slit Sl extending in the axial direction AX on at least one of the outer circumferential surface 210(3) and the inner circumferential surface 410, the effect of suppressing pinhole generation can be improved compared to when the slit Sl is not formed. Therefore, the gas sensor 1 can further improve the effect of suppressing pinhole generation in the molten portion 420 by forming a slit Sl extending in the axial direction AX compared to when the slit Sl is not formed.

[0110] (Regarding other examples of chamfering applied to the corners of the housing) Figure 6 is an enlarged cross-sectional view showing examples of various chamfering processes applied to the corners (rear end corners) of the cylindrical, metal housing through which the sensor element passes axially, which comprises the gas sensor 1. Specifically, Figure 6 shows examples of chamfering processes applied to the corners of housings 20(4) to 20(7), each of which is an example of a cylindrical, metal housing through which the sensor element passes axially. In Figure 6, the left-right direction of the paper is the axial direction AX.

[0111] In the housing 20(4) illustrated in Figure 6(A), chamfering is applied to its corner (the corner on the rear end side), thereby forming a corner surface Af with a cross-sectional shape including multiple straight sections on the rear end side of the housing 20(4). Specifically, an example of a corner surface Af with a cross-sectional shape including two straight sections, formed on the rear end side of the housing 20(4) by chamfering, is shown. In a gas sensor 1 where the contact distance Lg is less than or equal to the reference distance Lr, the corner surface Af illustrated in Figure 6(A) may be formed on the rear end side of a cylindrical, metal housing through which the sensor element penetrates in the axial direction.

[0112] In the housing 20(5) illustrated in Figure 6(B), a chamfered edge (the rear end corner) is formed on the rear end of the housing 20(5), creating a corner surface Af with a cross-sectional shape including multiple straight sections. Specifically, an example of a corner surface Af with a cross-sectional shape including three straight sections, formed on the rear end of the housing 20(5) by chamfering, is shown. In a gas sensor 1 where the contact distance Lg is less than or equal to the reference distance Lr, a corner surface Af illustrated in Figure 6(B) may be formed on the rear end of a cylindrical, metal housing through which the sensor element penetrates in the axial direction.

[0113] As explained using Figures 6(A) and (B), in the gas sensor 1, a rectangular surface Af having a cross-sectional shape including multiple straight sections may be formed on the rear end side of the cylindrical metal housing through which the sensor element penetrates in the axial direction.

[0114] In the housing 20(6) illustrated in Figure 6(C), a rounded 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 corner (the corner on the rear end side). Specifically, an example of a rounded surface Rf with a cross-sectional shape including two curved portions, formed on the rear end side of the housing 20(6) by chamfering, is shown. In a gas sensor 1 where the contact distance Lg is less than or equal to the reference distance Lr, a rounded surface Rf illustrated in Figure 6(C) may be formed on the rear end side of the "cylindrical, metal housing through which the sensor element penetrates in the axial direction." That is, in the gas sensor 1, a rounded surface Rf with a cross-sectional shape including multiple curved portions may be formed on the rear end side of the "cylindrical, metal housing through which the sensor element penetrates in the axial direction."

[0115] In the housing 20(7) illustrated in Figure 6(D), chamfering is applied to its corner (the corner on the rear end side), thereby forming a surface ARf on the rear end side of the housing 20(7) that includes a straight portion and a curved portion in its cross-sectional shape. Specifically, an example of a surface ARf formed on the rear end side of the housing 20(7) by chamfering is shown, which has a cross-sectional shape including one straight portion and two curved portions. In a gas sensor 1 where the contact distance Lg is less than or equal to the reference distance Lr, the surface ARf illustrated in Figure 6(D) may be formed on the rear end side of the "cylindrical, metal housing through which the sensor element penetrates in the axial direction." That is, in the gas sensor 1, a surface may be formed on the rear end side of the "cylindrical, metal housing through which the sensor element penetrates in the axial direction" that includes at least one of one or more straight portions and one or more curved portions in its cross-sectional shape.

[0116] As described above, the gas sensor 1 comprises a cylindrical metal housing through which a sensor element penetrates in the axial direction, and a metal outer cylinder 40 attached to the outer circumferential surface of the housing. The gas sensor 1 is configured such that the length of the outer circumferential surface of the housing that contacts the inner circumferential surface 410 of the outer cylinder 40 at the rear end of the molten portion 420, in the axial direction AX, is less than or equal to the reachable distance of the volatile gas in the molten portion 420, for example, less than or equal to the reference distance Lr.

[0117] In the gas sensor 1 described above, the rear end of the outer circumferential surface of the housing may be chamfered. For example, the rear end of the outer circumferential surface of the housing may be chamfered in a straight line or in a curved line. Specifically, in the gas sensor 1, at least one of C-chamfering and R-chamfering may be applied to the rear end of the outer circumferential surface of the housing. The rear end of the outer circumferential surface of the housing, which has been chamfered, can be used as a guide when pressing the housing into the outer cylinder 40, making it easier to press the housing into the outer cylinder 40.

[0118] [Features] As described above, the gas sensor 1 according to this embodiment comprises a cylindrical metal housing through which a long sensor element 10 penetrates in the axial direction AX, and a metal outer cylinder 40 mounted on the outer circumferential surface 210 of the housing. The "cylindrical metal housing through which a long sensor element 10 penetrates in the axial direction AX" of the gas sensor 1 is one of the housings 20, 20(1) to 20(7) described above, for example, housing 20. The outer cylinder 40 is mounted on the outer circumferential surface 210 of the housing 20 by press-fitting a portion of the rear end side of the housing 20 in the axial direction AX, and welding in the circumferential direction at the overlapping portion with the press-fitted housing 20. For example, the outer cylinder 40 is mounted on the outer circumferential surface 210 of the housing 20 by laser welding in the circumferential direction at the overlapping portion of the housing 20 and the outer cylinder 40 (for example, at the welding position Wp in Figure 1).

[0119] In the gas sensor 1, the contact distance Lg, which is the length in the axial direction AX of the outer circumferential surface 210 of the housing 20 that is in contact with the inner circumferential surface 410 of the outer cylinder 40 at the rear end of the molten portion 420 of the outer cylinder 40 formed by welding, is less than or equal to the reference distance Lr. The reference distance Lr is calculated using the following formula (1) with respect to the proportionality constant k, the penetration depth Da, the overlap Tb, and the thickness Tc. Lr = k × Da / (Tb × Tc) ... Formula (1)

[0120] As mentioned above, the penetration depth Da represents the radial depth of the housing 20, from the outer surface 210 of the housing 20 to the deepest part Dp of the molten portion 420 that has melted into the housing 20. The interference fit Tb represents the interference fit, which is the difference between the outer diameter of the housing 20 and the inner diameter of the outer cylinder 40. The thickness Tc represents the thickness of the outer cylinder 40. The molten portion 420 can also be described as the part of the outer cylinder 40 whose structure has been altered by melting.

[0121] The reference distance Lr represents the maximum distance that a volatile gas can reach due to its own pressure (reachable distance), that is, the maximum reachable distance. In other words, the reference distance Lr is the maximum distance that a volatile gas can travel between the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40, which are in contact with each other, due to its own pressure (reachable distance). Furthermore, the reachable distance of the volatile gas has the following relationship with the penetration depth Da, the overlap Tb, and the thickness Tc, respectively. That is, the larger the penetration depth Da, the larger the reachable distance of the volatile gas; the larger the overlap 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 reference distance Lr, which is the maximum reachable distance, can be expressed as a function of the penetration depth Da, the overlap Tb, and the thickness Tc. In addition, the proportionality constant k can be determined by testing, etc. Therefore, the reference distance Lr is calculated by the above-mentioned formula (1), which is a function of the proportionality constant k, the penetration depth Da, the overlap Tb, and the thickness Tc.

[0122] In the gas sensor 1, the contact distance Lg is less than or equal to the reference distance Lr, that is, "the length in the axial direction AX of the outer circumferential surface 210 of the housing 20 that is in contact with the inner circumferential surface 410 of the outer cylinder 40 on the rear end side of the molten portion 420" is less than or equal to the reference distance Lr. The contact distance Lg can also be rephrased as the length in the axial direction AX from the position of the molten portion end Ef to the non-contact position Np. As mentioned above, the molten portion end Ef is the endpoint where the molten portion 420 is in contact with the outer circumferential surface 210 of the housing 20, located on the rear end side of the center of the molten portion 420 (molten portion center Cf) in the axial direction AX. The non-contact position Np is a position where the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are not in contact over the entire circumferential direction, located on the rear end side of the center of the molten portion Cf, for example, the rear end of the outer circumferential surface 210 of the housing 20.

[0123] In the gas sensor 1, since the contact distance Lg is less than or equal to the reference distance Lr, the volatile gas generated during welding between the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40, which are in contact with each other, can move to a non-contact position Np due to its own pressure. In other words, in the gas sensor 1, the volatile gas can move by its own pressure to a position where the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are not in contact over the entire circumferential direction (for example, the rear end of the outer circumferential surface 210 of the housing 20). During welding, for example, the volatile gas in the molten portion 420 can move by its own pressure to a position where the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 are not in contact over the entire circumferential direction. In other words, in the gas sensor 1, the volatile gas generated during welding can move to a non-contact position Np due to its own pressure and is released at the non-contact position Np. Therefore, the gas sensor 1 can reduce the possibility of volatile gases being retained in the molten portion 420 and causing pinholes in the molten portion 420, in other words, it can suppress the occurrence of pinholes in the molten portion 420.

[0124] Therefore, the gas sensor 1 comprises a metal housing 20 through which the sensor element 10 is inserted, and a metal outer cylinder 40 welded to the outer circumference of the housing 20, thereby suppressing the occurrence of pinholes in the molten portion 420.

[0125] Furthermore, the gas sensor 1 can suppress the occurrence of pinholes in the molten portion 420 by setting the contact distance Lg to be less than or equal to the reference distance Lr calculated by formula (1). As mentioned above, the proportionality constant k in formula (1) can be determined in advance by testing or other means. Therefore, the structure of the gas sensor 1 that suppresses the occurrence of pinholes can be determined at the design stage, and for example, the value of the contact distance Lg can be determined at the design stage to be less than or equal to the reference distance Lr. Moreover, by suppressing the occurrence of pinholes, the gas sensor 1 can suppress the possibility of problems such as corrosion and reduced sealing performance caused by the pinholes. In addition, since the gas sensor 1 can realize a structure that suppresses the occurrence of pinholes at the design stage, the occurrence of pinholes can be suppressed without changing welding conditions or other conditions from the conventional ones. Furthermore, since the gas sensor 1 does not require processes such as thoroughly cleaning the housing 20 and the outer cylinder 40 to prevent oil and other substances from remaining on the contact surface between the housing 20 and the outer cylinder 40, the number of man-hours required in the management and processes during manufacturing can be reduced.

[0126] [Differentiation] The embodiments of the present invention have been described above, but the descriptions of the embodiments described so far are merely illustrative in all respects of the present invention. Various improvements and modifications may be made to the above embodiments. With respect to each component of the above embodiments, components may be omitted, replaced, or added as appropriate. Furthermore, the shape and dimensions of each component of the above embodiments may be changed as appropriate depending on the embodiment. For example, the following changes are possible. In the following, the same reference numerals are used for components that are the same as in the above embodiments, and explanations of the same points as in the above embodiments have been omitted as appropriate. The following modifications can be combined as appropriate.

[0127] (Regarding the configuration of the gas sensor) Up to this point, we have described an example in which the gas sensor 1 according to this embodiment includes a sensor element holding member 30 and an outer protective cover 50. However, the inclusion of the sensor element holding member 30 and the outer protective cover 50 is not essential for the gas sensor 1 according to this embodiment, and the gas sensor 1 may not include at least one of the sensor element holding member 30 and the outer protective cover 50. Furthermore, the gas sensor 1 may include components other than the sensor element 10, housing 20, sensor element holding member 30, outer cylinder 40, and outer protective cover 50.

[0128] For example, the gas sensor 1 may further include a bottomed cylindrical inner protective cover that covers the tip of the sensor element 10, in addition to the bottomed cylindrical outer protective cover 50 that surrounds the tip of the sensor element 10. That is, the gas sensor 1 may be configured such that the inner protective cover that covers the tip of the sensor element 10 is further covered by the outer protective cover 50. The inner protective cover may be made of metal. In addition to the above-described inner protective cover and outer protective cover 50, the gas sensor 1 may further include another protective cover. For example, in addition to the inner protective cover and outer protective cover 50, the gas sensor 1 may further include an intermediate protective cover placed between them. That is, the gas sensor 1 may protect the vicinity of the tip of the sensor element 10 with multiple protective covers (for example, the inner cover described above, in addition to the outer protective cover 50).

[0129] (Regarding the slit) Using Figure 5, an example of a gas sensor 1 in which a slit Sl extending in the axial direction AX is formed on at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40, on the rear end side of the molten portion 420 in the axial direction AX. However, the slit Sl formed on at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40, on the rear end side of the molten portion 420 in the axial direction AX, does not have to extend in the axial direction AX. For example, a slit Sl extending in the circumferential direction may be formed on at least one of the outer circumferential surface 210(3) of the housing 20(3) and the inner circumferential surface 410 of the outer cylinder 40, on the rear end side of the molten portion 420 in the axial direction AX. In other words, a circumferentially extending slit Sl may be formed on at least one of the outer circumferential surface 210(3) and the inner circumferential surface 410 of the outer cylinder 40, between the molten edge Ef and the non-contact position Np (the rear end of the outer circumferential surface 210(3) of the housing 20(3)). It is thought that the circumferentially extending slit Sl can also increase the distance over which volatile gases can travel between the outer circumferential surface 210(3) and the inner circumferential surface 410 due to their own pressure, and thus can suppress the occurrence of pinholes.

[0130] [Examples] To verify the effects of the present invention, gas sensors corresponding to levels 1 to 7 and Ref were fabricated. However, the present invention is not limited to the gas sensors corresponding to each of the following levels and Ref. [Table 1]

[0131] In Table 1, the gas sensors for levels 1 and 2 have the same configuration as gas sensor 1 illustrated in Figure 1, except that the contact distance Lg is greater than the reference distance Lr. The gas sensor for level Ref is the gas sensor used as a reference when verifying the effects of the present invention, and has the same configuration as gas sensor 1 illustrated in Figure 1, with a contact distance Lg equal to the reference distance Lr. The gas sensors for levels 3 to 7 have the same configuration as gas sensor 1 illustrated in Figure 1, with a contact distance Lg smaller than the reference distance Lr.

[0132] In Table 1, "Lr / Lg" indicates the ratio of the reference distance Lr to the contact distance Lg. For example, in a gas sensor for Level 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 a gas sensor for Level 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. Also, in a gas sensor for Ref, the reference distance Lr is equal to the contact distance Lg. In a gas sensor for Level 3, the reference distance Lr is 1.11 times the contact distance Lg, and the contact distance Lg is smaller than the reference distance Lr. In gas sensors for Levels 4 and 5, the reference distance Lr is 1.23 times the contact distance Lg, and the contact distance Lg is smaller than the reference distance Lr. In a gas sensor at level 6, the reference distance Lr is 1.35 times the contact distance Lg, and the contact distance Lg is smaller than the reference distance Lr. In a gas sensor at level 7, the reference distance Lr is 1.92 times the contact distance Lg, and the contact distance Lg is smaller than the reference distance Lr.

[0133] In Table 1, "Slit structure" indicates whether a slit Sl, as illustrated in Figure 5, is formed on at least one of the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 for each gas sensor relating to levels 1 to 7. "Present" for a slit structure means, for example, that a slit Sl extending in the axial direction AX is formed on the outer circumferential surface 210 of the housing 20. "Absent" for a slit structure means that no slit Sl is formed on either the outer circumferential surface 210 of the housing 20 or the inner circumferential surface 410 of the outer cylinder 40.

[0134] In Table 1, the "Ratio of Pinhole Occurrences" shows the ratio of the "Number of Pinhole Occurrences" confirmed for each level's gas sensor to the "Number of Pinhole Occurrences in the Melted Portion 420" confirmed for the gas sensor related to Ref. In other words, the "Ratio of Pinhole Occurrences" indicates how many times greater the number of pinholes confirmed for each level's gas sensor was compared to the number of pinholes confirmed for the gas sensor related to Ref where the contact distance Lg is equal to the reference distance Lr.

[0135] In Table 1, "Pinhole Reduction Effect" indicates the degree of pinhole reduction effect observed for each level of gas sensor, relative to the pinhole suppression effect observed for the gas sensor related to Ref. "Pinhole Suppression Effect" can also be rephrased as "Effect of Reducing the Number of Pinholes." A "× (Poor)" pinhole reduction effect indicates that the pinhole reduction effect observed for each level of gas sensor is inferior to the pinhole reduction effect of the gas sensor related to Ref where the contact distance Lg is equal to the reference distance Lr. A "〇 (Good)" pinhole reduction effect indicates that for each level of gas sensor, a pinhole reduction effect similar to that observed for the gas sensor related to Ref where the contact distance Lg is equal to the reference distance Lr was observed. A "◎ (Excellent)" pinhole reduction effect indicates that for each level of gas sensor, an even better pinhole reduction effect was observed than that observed for the gas sensor related to Ref where the contact distance Lg is equal to the reference distance Lr.

[0136] In other words, the "number of pinholes" for the gas sensor at Level 1 is "1.07," and the "number of pinholes in the molten portion 420" confirmed for the gas sensor at Level 1 is greater than the number confirmed for the gas sensor at Ref. Therefore, the "pinhole reduction effect" of the gas sensor at Level 1 is "× (defective)."

[0137] The ratio of pinhole occurrences for gas sensors at Level 2 is 1.08, and the number of pinholes observed in the molten portion 420 of the Level 2 gas sensor is greater than the number observed for the Ref gas sensor. Therefore, the pinhole reduction effect of the Level 2 gas sensor is marked as "× (defective)".

[0138] The ratio of pinhole occurrences for the gas sensor at Level 3 is 0.92, and the number of pinholes observed in the molten portion 420 for the Level 3 gas sensor is slightly less than the number observed for the gas sensor at Ref. In other words, the Level 3 gas sensor is able to achieve the same pinhole reduction effect as the gas sensor at Ref, and the pinhole reduction effect of the Level 3 gas sensor is rated as "○ (good)".

[0139] The ratio of pinhole occurrences for the gas sensor at Level 4 is 0.89, and the number of pinholes observed in the molten portion 420 for the Level 4 gas sensor is slightly less than the number observed for the gas sensor at Ref. In other words, the Level 4 gas sensor is able to achieve the same pinhole reduction effect as the gas sensor at Ref, and the pinhole reduction effect of the Level 4 gas sensor is rated as "○ (good)".

[0140] The ratio of pinhole occurrences for the gas sensor at Level 5 is 0.80, and the number of pinholes observed in the molten portion 420 for the gas sensor at Level 5 is slightly less than the number observed for the gas sensor at Ref. In other words, the gas sensor at Level 5 is able to achieve the same pinhole reduction effect as the gas sensor at Ref, and the pinhole reduction effect of the gas sensor at Level 5 is rated as "○ (good)".

[0141] The ratio of pinhole occurrences for the gas sensor at Level 6 is 0.60, and the number of pinholes observed in the molten portion 420 for the gas sensor at Level 6 is significantly lower than the number observed for the gas sensor at Reference. In other words, the gas sensor at Level 6 achieves an even better pinhole reduction effect than the gas sensor at Reference, and the pinhole reduction effect of the gas sensor at Level 6 is rated as "◎ (exceptionally good)".

[0142] The ratio of pinhole occurrences for the gas sensor at Level 7 is 0.25, and the number of pinholes observed in the molten portion 420 for the gas sensor at Level 7 is significantly lower than the number observed for the gas sensor at Reference. In other words, the gas sensor at Level 7 achieves an even better pinhole reduction effect than the gas sensor at Reference, and the pinhole reduction effect of the gas sensor at Level 7 is rated as "◎ (exceptionally good)".

[0143] (Item confirmed from Table 1) As shown in Table 1, the "pinhole reduction effect" of gas sensors at levels 1 to 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 levels 3 to 7, where the contact distance Lg is smaller than the reference distance Lr, is "〇 (good)" or "◎ (exceptionally good)". Furthermore, for gas sensors at level Ref, where the contact distance Lg and the reference distance Lr are equal, the "pinhole reduction effect" is "〇". Therefore, the inventors of this case have confirmed that the following effect can be achieved by setting the contact distance Lg to be less than or equal to the reference distance Lr in a gas sensor 1 comprising a housing 20 through which a sensor element 10 is inserted and an outer cylinder 40 welded to the outer circumferential surface of the housing 20. Specifically, the inventors of this case have confirmed that the occurrence of pinholes in the molten portion 420 can be suppressed by setting the contact distance Lg to be less than or equal to the reference distance Lr in the gas sensor 1.

[0144] Furthermore, the "ratio of pinhole occurrences" for gas sensors in levels 3 to 7, where the contact distance Lg is smaller than the reference distance Lr, is less than "1.00" in all cases. In other words, gas sensors in levels 3 to 7, where the contact distance Lg is smaller than the reference distance Lr, are able to suppress pinhole occurrence more effectively than gas sensors in level Ref, where the contact distance Lg and the reference distance Lr are equal. For this reason, it is more desirable to make the contact distance Lg shorter than the reference distance Lr for a gas sensor 1 comprising a housing 20 through which the sensor element 10 is inserted and an outer cylinder 40 welded to the outer surface of the housing 20.

[0145] (Items confirmed from Table 1, Part 2) The inventors of this case confirmed the following trend in the ratio of the reference distance Lr to the contact distance Lg, based on the relationship between the "ratio of pinhole occurrences" and "Lr / Lg (ratio of reference distance Lr to contact distance Lg)" shown in Table 1. Specifically, the inventors confirmed that the pinhole reduction effect (pinhole occurrence suppression effect) improves dramatically by adjusting the size of the contact distance Lg so that the reference distance Lr is greater than 1.2 times the contact distance Lg. For example, plotting the results from Table 1 on a graph with "Lr / Lg" on the horizontal axis and "ratio of pinhole occurrences" on the vertical axis, the inventors confirmed the following trend in the approximation curves obtained from points corresponding to levels 1 to 7 and Ref. Specifically, the inventors confirmed that the slope of the approximation curve increases sharply when the reference distance Lr is greater than 1.2 times the contact distance Lg.

[0146] Therefore, with respect to the gas sensor 1 comprising a cylindrical metal housing through which a sensor element penetrates axially, and an outer cylinder 40 welded to the outer surface of the housing, the following trend was confirmed. Specifically, it was confirmed that by making the reference distance Lr greater than 1.2 times the contact distance Lg, the occurrence of pinholes in the molten portion 420 can be suppressed very effectively.

[0147] (Item confirmed from Table 1, item 3) The gas sensors for Level 4 and Level 5 share the common characteristic of having a "Lr / Lg" ratio of "1.23," but the Level 4 gas sensor has "no" slit structure, while the Level 5 gas sensor has a slit structure. In other words, the Level 4 gas sensor and the Level 5 gas sensor have similar configurations, except for whether or not the slit Sl is formed on at least one of the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40. Furthermore, the ratio of pinhole occurrences for the Level 4 gas sensor is "0.89," while the ratio of pinhole occurrences for the Level 5 gas sensor is "0.80." This means that the Level 5 gas sensor is better able to suppress pinhole occurrence than the Level 4 gas sensor. Therefore, the inventors of this case confirmed that by forming a slit Sl on at least one of the outer circumferential surface 210 of the housing 20 and the inner circumferential surface 410 of the outer cylinder 40 of the gas sensor 1, the effect of suppressing pinhole generation can be improved compared to when the slit Sl is not formed. Accordingly, the following trend was confirmed for the gas sensor 1 comprising a cylindrical metal housing through which a sensor element penetrates in the axial direction, and an outer cylinder 40 welded to the outer circumferential surface of the housing. That is, by forming a slit Sl on at least one of the outer circumferential surface of the housing and the inner circumferential surface 410 of the outer cylinder 40, the effect of suppressing pinhole generation in the molten portion 420 can be improved compared to when the slit Sl is not formed. [Explanation of symbols]

[0148] 1...Gas sensor, 10...Sensor element, 20...Housing, 40...Outer cylinder 210...Outer surface, 410...Inner surface, 420...Molten portion, AX...Axial direction, Lg...Contact distance, Lr...Reference distance, Da...Penetration depth, Dp...Deepest part (deepest part of the molten portion), k...Proportionality constant, Tb...Interlocking allowance, Tc...Thickness, Sl...Slit

Claims

1. A cylindrical metal housing through which a long sensor element passes axially, A portion of the rear end of the housing is press-fitted in the axial direction, and welding is performed in the circumferential direction at the overlapping portion with the press-fitted housing, thereby attaching a metal outer cylinder to the outer circumferential surface of the housing, Equipped with, The contact distance Lg, which is the axial length of the outer circumferential surface of the housing that is in contact with the inner circumferential surface of the outer cylinder at the rear end side of the molten portion of the outer cylinder formed by the welding, is less than or equal to the reference distance Lr. The aforementioned reference distance Lr is calculated by the following formula (1): Gas sensor. Lr = k × Da / (Tb × Tc) ... Formula (1) Here, in the above formula (1), "k" represents the constant of proportionality. "Da" represents the radial depth of the housing, from the outer surface of the housing to the deepest part of the molten portion that has melted into the housing. "Tb" represents the interference fit, which is the difference between the outer diameter of the housing and the inner diameter of the outer cylinder. "Tc" represents the thickness of the outer cylinder.

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

3. The rear end of the outer surface of the housing is chamfered. The gas sensor according to claim 1 or 2.

4. The aforementioned chamfering process is an R-chamfering process. The gas sensor according to claim 3.

5. In the axial direction of the outer cylinder and the housing, at least one of the outer circumferential surface of the housing and the inner circumferential surface of the outer cylinder, on the rear end side of the molten portion, is formed a slit extending in the axial direction. The gas sensor according to claim 1 or 2.

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