JP2019158572A - Method for producing gas sensor, method for securing sensor element protection cover, and welding device - Google Patents

Abstract

To provide a method for securing a sensor element protection cover with which a sputtering generation suppression, a securing of welding strength, and a longer life of a welding rod are realized when a cover for protecting a protrusion of the sensor element from a housing is secured by welding with respect to the housing that holds the sensor element.SOLUTION: A welding load having a predetermined load of 600 N or more is applied to a predetermined welding target region of the protective cover by a tungsten welding rod having a curved surface with a curvature radius of 1.5 to 6.0 mm, the welding current is increased from 0 with a constant current increase rate from the time of the start of energization until the welding current reaches the peak value, and after reaching the peak value, a spot welding is carried out by passing the welding current in accordance with the welding current profile set to reduce the welding current to 0 at a constant rate of current reduction and the total energization period to 200 to 300 msec, and the peak value to 1.8 to 2.5 kA.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of manufacturing a gas sensor including a sensor element made of ceramics, and more particularly to attachment of a protective cover that protects the sensor element.

Conventionally, oxygen ion conductive solid electrolyte ceramics such as zirconia (ZrO ₂ ) have been used as a device for measuring the concentration of a predetermined gas component in a measured gas such as combustion gas or exhaust gas in an internal combustion engine such as an automobile engine. Gas sensors in which sensor elements are formed using them are known.

  In such a gas sensor, normally, one end of a long plate-shaped sensor element (detection element) made of ceramics can be in contact with a gas to be measured, and moisture or contaminants adhere to the sensor element. In order to prevent this, a protective cover (protector) made of metal is provided to surround and protect one end of the sensor element (see, for example, Patent Document 1). The protective cover (protector) is welded and fixed to a housing (main metal fitting) that holds the sensor element inside, for example, as disclosed in Patent Document 1. Examples of the welding technique include spot welding (resistance welding) and laser welding.

JP 2010-164359 A

  For example, when a protective cover made of SUS stainless steel or the like is fixed to a housing constituting the gas sensor by spot welding, spatter (welding waste) may be generated by melting the welding rod (electrode rod). If such spatter adheres to the housing, sensor element, protective cover, etc., problems such as assembly failure in the subsequent process, abnormal characteristics of the produced gas sensor, and uneven wear of jigs and tools used for assembly and inspection may occur. May end up. In addition, welding under conditions where spatter is likely to occur may cause factors such as insufficient welding strength of the protective cover and shortening of the life of the welding rod. Therefore, there is a demand for gas sensor productivity and suppression of sputtering when the protective cover is fixed by welding.

  On the other hand, of course, the protective cover needs to be fixed to the housing with sufficient strength (welding strength).

  The present invention has been made in view of the above problems, and a method for fixing a sensor element protective cover in a gas sensor that suppresses the occurrence of spatter and ensures welding strength and extending the life of a welding rod. The purpose is to provide.

  In order to solve the above-mentioned problem, a first aspect of the present invention is a gas sensor manufacturing method, which protects one end of a sensor element protruding from the housing with respect to a housing holding the sensor element. And fitting the protective cover to the housing by spot welding according to a predetermined welding current profile to a predetermined welding target area of the protective cover fitted to the housing. A welding step, and in the welding step, a welding rod made of tungsten having a curved surface with a radius of curvature of 1.5 mm or more and 6.0 mm or less at a tip portion is brought into contact with the welding target region, whereby the welding is performed. In a state where a predetermined welding execution load of 600 N or more is applied to the target region, the welding power The welding current is increased from 0 at a constant current increasing rate until the time when the welding current reaches the peak value, and after the welding current reaches the peak value, the welding current is decreased to 0 at a constant current decreasing rate. The energization time from the start of energization to the end of energization is 200 msec or more and 300 msec or less, and the peak value is 1.8 kA or more and 2.5 kA or less. The spot welding is performed by flowing the welding current in accordance with a welding current profile.

  According to a second aspect of the present invention, there is provided a gas sensor manufacturing method according to the first aspect, wherein in the welding step, the two welding rods are used to cause the two protective rods to be opposed to each other in the two areas to be welded. The two places are welded simultaneously by applying the welding execution load at the same time.

  According to a third aspect of the present invention, there is provided a gas sensor manufacturing method according to the second aspect, wherein in the welding step, the load applied by the two welding rods to the two welding target regions is applied. The welding current is increased synchronously and continuously, and the welding current is passed between the two welding rods when the load reaches the welding execution load.

  According to a fourth aspect of the present invention, there is provided a gas sensor manufacturing method according to any one of the first to third aspects, wherein the welding target area with which the welding rod abuts is convex with respect to the welding rod. It is curved in shape, and the foremost portion that is in contact with the welding target area of the welding rod is a circular flat portion orthogonal to the longitudinal direction of the welding rod. .

  A fifth aspect of the present invention is a sensor element protective cover fixing method for fixing a protective cover for protecting one end portion of a sensor element protruding from the housing to a housing for holding the sensor element in a gas sensor. Then, a tungsten welding rod having a curved surface with a radius of curvature of 1.5 mm or more and 6.0 mm or less at the tip is brought into contact with the welding target region, so that a predetermined welding target region of the protective cover is previously set. The welding current is increased from 0 at a constant current increasing rate from the start of energization to the time when the welding current reaches the peak value in a state where a predetermined welding execution load of 600 N or more is applied, and the welding current is After reaching the peak value, from the start of energization, the welding current is reduced to zero at a constant current reduction rate. By flowing the welding current according to a welding current profile determined so that the energization time until the end of electricity is 200 msec to 300 msec and the peak value is 1.8 kA to 2.5 kA, Spot welding is performed to fix the protective cover to the housing in the welding target area.

  A sixth aspect of the present invention is a method for fixing a sensor element protective cover according to the fifth aspect, wherein the welding is simultaneously performed on two welding target regions of the protective cover facing each other by two welding rods. By applying an effective load, the two locations are welded simultaneously.

  A seventh aspect of the present invention is a method for fixing a sensor element protective cover according to the sixth aspect, wherein the load applied by the two welding rods to the two welding target areas is synchronously performed. In addition, the welding current is continuously increased, and when the load reaches the welding execution load, the welding current is passed between the two welding rods.

  According to an eighth aspect of the present invention, there is provided a sensor element protective cover fixing method according to any one of the fifth to seventh aspects, wherein the welding target region with which the welding rod abuts is in contact with the welding rod. Curved in a convex shape, and the foremost portion that is in contact with the welding target area of the welding rod is a circular flat portion perpendicular to the longitudinal direction of the welding rod. Features.

  A ninth aspect of the present invention is a welding apparatus for fixing, by spot welding, a protective cover that protects one end of the sensor element protruding from the housing to a housing that holds the sensor element in the gas sensor. Two welding rods made of tungsten having a curved surface with a radius of curvature of 1.5 mm or more and 6.0 mm or less at the tip, and the two welding rods are welded at two positions opposite to each other predetermined in the protective cover By abutting each of the regions, a load applying means capable of applying a load to the corresponding welding target region from each of the two welding rods, and a welding current is passed between the two welding rods. Energizing means, and a welding current profile when the energizing means energizes the welding current from the start of energization to the welding The welding current is increased from 0 at a constant current increasing rate until the time when the current reaches the peak value, and after the welding current reaches the peak value, the welding current is increased at a constant current decreasing rate. It is determined so that the energization time from the start of energization to the end of energization is 200 msec or more and 300 msec or less and the peak value is 1.8 kA or more and 2.5 kA or less so as to decrease to 0. The load application means synchronously and continuously increase the load applied by the two welding rods to the two areas to be welded, and the energization means has the load determined in advance. Starting energization of the welding current according to the welding current profile between the two welding rods when reaching a welding execution load of 600 N or more. And features.

  A tenth aspect of the present invention is the welding apparatus according to the ninth aspect, wherein the welding target area with which the welding rod is in contact is curved in a convex shape with respect to the welding rod, The forefront portion of the welding rod that is in contact with the region to be welded is a circular flat portion orthogonal to the longitudinal direction of the welding rod.

  According to the first to tenth aspects of the present invention, the protective cover can be welded and fixed to the housing with sufficient welding strength without generating spatter. In addition, the life of the welding rod can be extended.

It is a figure which shows the procedure which obtains the gas sensor 100 by welding and fixing the protective cover 2 with respect to the housing 1 in steps. It is a figure which shows the structure of the welding apparatus 1000 schematically. It is a figure which shows the shape of the welding rod 1101. FIG. It is a figure shown notionally about welding current profile PF. It is a figure which shows the relationship between a spot diameter and welding strength. It is a figure which shows the relationship between the welding current peak value and welding strength when spot welding of the protective cover 2 is performed with various welding current profiles PF in which the total energization time and the welding current peak value are different. It is a figure which illustrates welding current profile PF about conditions A-condition C. It is a figure which shows the relationship between welding execution load and welding strength when different welding execution load is performed and the protective cover 2 is spot-welded.

<Overview of gas sensor and protective cover welding>
FIG. 1 is a diagram showing step by step a procedure for obtaining a gas sensor 100 by welding and fixing a protective cover 2 to a housing 1. The gas sensor 100 is for detecting a predetermined gas component (for example, NOx) by the sensor element 10 provided in the inside thereof.

  The sensor element 10 is a long columnar or thin plate member made mainly of oxygen ion conductive solid electrolyte ceramics such as zirconia. The sensor element 10 includes, for example, a limiting current type sensor element having a configuration in which a gas introduction port and an internal space are provided on the one end portion 10a side and various electrodes and wiring patterns are provided on the surface and inside of the element body. It is. In the sensor element 10, the test gas introduced into the internal space is reduced or decomposed in the internal space to generate oxygen ions. In that case, in the gas sensor 100, the concentration of the 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 the gas component in the test gas. However, in the present embodiment, the configuration of the sensor element 10 is not limited to this. For example, a mixed potential for obtaining the concentration of a predetermined gas component based on a potential difference between two electrodes generated according to the concentration of the test gas. A mode in which a type of sensor element 10 is used may be used.

  In more detail, the gas sensor 100 is not necessarily completed by fixing the protective cover 2 to the housing 1, and other members may be assembled, but in the present embodiment, for convenience. A gas sensor 100 is a gas sensor 100 in which the protective cover 2 is fixed to the housing 1 by welding (all the welding target areas have been welded). Is assembled, but welding fixing is not completed is referred to as an unwelded gas sensor 100α.

  The housing 1 is a metallic cylindrical member made of SUS stainless steel or the like. As shown in FIG. 1A, the sensor element 10 is fixed inside the housing 1 by a predetermined fixing member (not shown) in such a manner that the one end 10a protrudes. Moreover, in the housing 1, the edge part (lower end part in FIG. 1) by which the one edge part 10a of the sensor element 10 protrudes is the cylindrical to-be-fitted part 1a.

  In addition, on the other end side of the housing 1 (not shown in FIG. 1), there are a configuration for holding and fixing the sensor element 10 inside the housing 1 and a configuration for obtaining an electrical connection between the sensor element 10 and the outside. , Provided.

  On the other hand, the protective cover 2 is a metal member made of, for example, SUS stainless steel, and one end (upper end in FIG. 1) 2a is open while the other end (lower end in FIG. 1). ) It has a bottomed cylindrical shape with the side closed. A plurality of through holes H are provided at equal intervals along the circumferential direction on the side peripheral surface of the protective cover 2, and the atmosphere inside and outside the protective cover 2 can be circulated through the through holes H. The shape and the number of arrangement of the plurality of through holes H may be appropriately determined. The protective cover 2 may have a two-layer structure. In that case, a through hole is also provided at an appropriate position in an internal cover (not shown).

  Further, one end 2a of the protective cover 2 is a fitting portion 2c that is fitted to the fitted portion 1a of the housing 1, and therefore, the fitting portion 2c is located outside the fitted portion 1a. It has an inner diameter commensurate with the diameter.

  In order to fix the protective cover 2 to the housing 1, first, the fitting portion 2 c of the protective cover 2 is fitted to the fitted portion 1 a of the housing 1 as indicated by an arrow AR 1 in FIG. . FIG. 1B shows an unwelded gas sensor 100α obtained by such fitting.

  When the unwelded gas sensor 100α is obtained, spot welding is performed to completely fix the protective cover 2 to the housing 1. As shown in FIG. 1B, a plurality of regions (welding target regions) RE to be spot-welded are determined in advance on the outer surface of the fitting portion 2c of the protective cover 2.

  The welding target area RE is defined at equal intervals and at even positions in the circumferential direction of the fitting portion 2c. For example, although it is preferable that the four welding target regions RE are determined by being separated by 90 ° in the circumferential direction of the fitting portion 2c, an aspect in which more welding target portions are provided may be employed. That is, the welding target region RE is determined so that a plurality of sets of two welding target regions RE that are separated from each other by 180 ° (opposite each other with the sensor element 10 interposed therebetween) can be formed.

  Spot welding is performed on each welding target region RE, and a welded portion W is formed as shown in FIG. 1C, whereby the protective cover 2 is fixed to the housing 1 and the gas sensor 100 is obtained.

<Welding equipment>
Next, a welding apparatus 1000 used for welding and fixing the protective cover 2 to the housing 1 in the present embodiment will be described. FIG. 2 is a diagram schematically showing the configuration of the welding apparatus 1000.

  The welding apparatus 1000 includes two welding execution units 1100 (1100A, 1100B), a welding power source 1200, and a control unit 1300.

  The two welding execution units 1100A and 1100B are portions where welding is actually performed, and each has a welding rod 1101 (1101A and 1101B). The two welding execution units 1100A and 1100B are arranged so as to be symmetrical with each other in a state where the unwelded gas sensor 100α is held so as to have a longitudinal direction in the vertical direction by holding means (not shown). The welding power source 1200 is a power source for causing a current to flow between the welding rods 1101A and 1101B. The control unit 1300 controls the operation of each unit for realizing the welding process in the welding apparatus 1000, for example, the control of the advance / retreat operation of the welding execution unit 1100 and the applied voltage of the welding power source 1200 to control the current flowing during welding. Take control.

  In the welding apparatus 1000, two welding rods 1101 (1101A, 1101B) held by electrode holders 1102 provided in each of the two welding execution units 1100A, 1100B are roughly protected under the control of the control unit 1300. Two welds through the electrode holder 1102 are applied by applying a voltage from the welding power source 1200 in a state in which a predetermined load is applied to the two welding target regions RE facing each other (of the unwelded gas sensor 100α). By flowing a current (welding current) I having a predetermined magnitude between the rods 1101A and 1101B, the welded portion W can be formed simultaneously in the two welding target regions RE. If four welding target areas RE are defined in the unwelded gas sensor 100α, the protective cover 2 is completely fixed to the housing 1 by two welding processes, and the gas sensor 100 is obtained.

  The welding rod 1101 is made of tungsten from the viewpoint of heat resistance and spatter suppression. In addition, although the welding rod 1101 has comprised the round bar shape, the detail of the shape is mentioned later.

  More specifically, in each of the two welding execution units 1100A and 1100B, the welding rod 1101 (1101A and 1101B) is horizontally and one by the electrode holder 1102 electrically connected to the welding power source 1200. It is held so that it is located on the straight line.

  Further, the electrode holder 1102 is attached to a pressure follower 1103 that urges the welding rod 1101 so that the load (pressing load) applied to the welding target region RE by the welding rod 1101 at the time of performing welding is constant. Yes.

  The pressure follower 1103 is attached to an air cylinder 1104 whose movable portion 1104a is extendable in the horizontal direction. In the welding apparatus 1000, the electrode holder attached to the pressure follower 1103 is expanded and contracted by the movable part 1104 a of the air cylinder 1104 provided in the two welding execution parts 1100 A and 1100 B under the control of the control part 1300. The welding rods 1101 </ b> A and 1101 </ b> B held by 1102 can move forward and backward in the horizontal direction.

  A load cell 1105 is attached only to the pressure follower 1103 provided in the welding execution unit 1100A. The magnitude (load value) of the load applied to the welding target region RE by the welding rod 1101 (1101A), which is measured by the load cell 1105, is given to the control unit 1300, and is used for spot welding control by the control unit 1300.

  More specifically, the air cylinders 1104 provided in the two welding execution units 1100A and 1100B are controlled so that the two welding rods 1101A and 1101B advance and retract synchronously in opposite directions during the welding process. For example, when one is in contact with the welding target region RE where the unwelded gas sensor 100α is located, the other is controlled so as to contact the welding target region RE opposite to the welding target region RE.

  In spot welding in the welding apparatus 1000 having the above-described configuration, the two welding rods 1101A and 1101B are brought into contact with the corresponding welding target region RE, and a predetermined load is applied to the welding target region RE. This is realized by starting energization from the welding power source 1200 in the state of being made to occur.

  Specifically, when a spot welding start instruction is given to the control unit 1300, under the control of the control unit 1300, the synchronous part of the movable part 1104a of the air cylinder 1104 provided in each of the two welding execution parts 1100A and 1100B is synchronized. Expansion starts. As a result, the two welding rods 1101A and 1101B are synchronously moved in the direction approaching the corresponding welding target region RE. The expansion of the movable portion 1104a of the air cylinder 1104 continues even after the two welding rods 1101A and 1101B abut against the welding target region RE, whereby the load applied by the welding rods 1101A and 1101B to the welding target region RE. Gradually increases (continuously). At this time, the value of the load applied by the welding rod 1101A to the protective cover 2 (the value of the load applied by the welding rod 1101B to the protective cover 2 is also substantially the same) is measured in the load cell 1105.

  When the load value reaches the preset welding execution load, the control unit 1300 stops the movement of the two welding rods 1101A and 1101B due to the extension of the movable portion 1104a of the air cylinder 1104 and performs control. Part 1300 causes welding power source 1200 to be energized according to the welding current profile. Thereby, spot welding is performed in a state where the welding execution load is maintained, and a welded portion W is formed in the two welding target regions RE of the protective cover 2 that face each other. As the spot welding progresses, the tip of the welding rod 1101 may be shortened due to wear of the tip. In the welding apparatus 1000, the pressure follower 1103 keeps the welding execution load constant. It has become. As described above, in the case where the four welding target regions RE are determined by being separated by 90 ° in the circumferential direction of the fitting portion 2c of the protective cover 2, the welded portion W with respect to the first two welding target regions RE is determined. Then, the position of the unwelded gas sensor 100α in the horizontal plane is rotated by 90 °, and the welded portion W is formed on the remaining two welding target regions RE again in the same procedure.

  The welding execution load is preferably 600 N or more. In such a case, spot welding can be performed with sufficient welding strength without causing spatter. In the present embodiment, the magnitude of the torque (torsion torque) that causes the protective cover 2 to come off the housing 1 when the protective cover 2 of the gas sensor 100 after welding is fixed in the circumferential direction, Specified as welding strength. From the viewpoint of practicality, the inventors of the present invention have confirmed in advance that the weld cover 2 needs to have a weld strength of 29.4 N · m (approximately 30 N · m) or more. When the welding execution load is less than 600 N, sputtering is likely to occur, which is not preferable. In addition, the welding execution load should just be 1000 N or less.

  If it exceeds 1000 N, problems such as breakage of the welding rod 1101 and the electrode holder 1102 may occur.

<Shape of welding rod>
Next, the shape of the welding rod 1101 will be described. FIG. 3 is a view showing the shape of the welding rod 1101. As shown in FIG. 3 (a), the welding rod 1101 has a round bar shape, but as can be seen from FIG. 3 (b), which is an enlarged view of the portion A, the tip 1101a has an approximate curvature radius. R curved surface. This is intended to prevent the current flow during welding from being concentrated on a single point, and to suppress the occurrence of deformation and wear of the welding rod 1101 due to thermal effects and load application. is there. Actually, the wear amount of the welding rod 1101 made of tungsten having the above-mentioned shape used in the present embodiment per 1000 times of welding is as extremely low as 0.08 mm to 0.12 mm, and it is 7000 times by the same welding rod 1101. A degree of welding can be performed. This has, for example, about seven times the life of a welding rod made of beryllium copper.

  The size of the radius of curvature R of the tip 1101 a of the welding rod 1101 also affects the welding strength of the protective cover 2. If the value of the radius of curvature R of the tip 1101a is 1.5 mm or more, a welding strength of 30 N · m or more is realized.

  However, it is sufficient that the value of the radius of curvature R of the tip portion 1101a is 6.0 mm or less. This is because the welding strength tends to be saturated when R is larger than 6.0 mm.

  More specifically, as shown in FIG. 3B, the tip 1101a of the welding rod 1101 is not a uniform curved surface, and the most distal portion is orthogonal to the longitudinal direction of the welding rod 1101. This is a circular flat portion 1101b having a diameter d (smaller than the radius of curvature R). This is part of the surface of the protective cover 2 having a columnar shape, and thus stability when the welding rod 1101 is brought into contact with the welding target region RE that is curved in a convex shape with respect to the welding rod 1101. Is taken into account. The diameter d is preferably about 0.5 mm to 2.0 mm. The effect of providing the flat portion 1101b having a diameter d smaller than 0.5 mm cannot be suitably obtained. If the diameter d is larger than 2.0 mm, the effect of providing the tip portion 1101a is impaired, which is not preferable. .

<Welding current profile>
Next, the relationship between the current profile (hereinafter referred to as a welding current profile) PF, the welding strength, and the occurrence of spatter during spot welding will be described.

  FIG. 4 is a diagram conceptually showing the welding current profile PF. In the present embodiment, the welding current profile PF means a change in welding current over time from the start of energization to the end of energization. In the present embodiment, as shown in FIG. 4, the time change is constant from the start of energization (t = 0) to the time (t = tp) at which the welding current reaches a predetermined peak value (welding current peak value) Ip. The welding current is increased from 0 at a rate (current increasing speed), and after the welding current reaches the welding current peak value Ip, the welding current is decreased to 0 at a constant rate of time change (current decreasing speed). It is assumed that the welding current profile PF is used. When the welding current becomes zero (t = te), the welding is finished. However, the welding current may be maintained for a certain period of time at the welding current peak value Ip. The welding current profile PF is realized by the control unit 1300 controlling the applied voltage of the welding power source 1200.

  In the welding current profile PF, a period during which the welding current is increased from 0 to the welding current peak value Ip at a predetermined current increase rate is referred to as upslope, and the welding current is a welding current at a predetermined current decrease rate. The period during which the peak value Ip is reduced to 0 is also referred to as downslope.

  In the present embodiment, the welding current profile PF is set so that the total energization time is 200 msec or more and the welding current peak value Ip is 1.8 kA or more. In such a case, the protective cover 2 can be welded and fixed to the housing 1 with sufficient welding strength.

  However, since the welding strength tends to be saturated when the total energization time exceeds 200 msec, the total energization time is at most 300 msec at most. If the total energization time is the same, the welding strength tends to increase as the welding current peak value Ip increases. However, if the welding current peak value Ip exceeds 2.5 kA, spatter is generated, which is not preferable.

  As described above, in the present embodiment, a protective cover that protects one end of the sensor element protruding from the housing is fixed to the housing that holds the sensor element in the gas sensor by spot welding. , A tungsten welding rod having a curved surface with a curvature radius of 1.5 mm or more and 6.0 mm or less is used, the welding load is 600 N or more, the energization time is 200 msec or more and 300 msec or less, and welding is performed. The peak value of the welding current in the current profile is set to 1.8 kA or more and 2.5 kA or less. Accordingly, the protective cover can be welded and fixed to the housing with sufficient welding strength without causing spatter. In addition, the life of the welding rod can be extended.

Example 1
FIG. 5 is a diagram showing the relationship between the spot diameter, which is the diameter of the welded portion W formed by welding fixation, and the weld strength, which is the strength of the welded portion W. In order to obtain the results shown in FIG. 5, a welding rod 1101 having a diameter of 6 mm was used, the welding current peak value was 1.9 kA, the applied load (welding execution load) from the welding rod 1101 was 600 N, and the total energization time. Is set to 300 msec.

  As shown in FIG. 5, the welding strength of the protective cover 2 varies depending on the spot diameter. FIG. 5 shows that a welding strength of 30 N · m or more can be obtained if the spot diameter is 1.5 mm or more.

  Here, the spot diameter is a value determined according to the radius of curvature R of the tip 1101a. For example, the value of the radius of curvature R of the tip 1101a when the spot diameter is 1.5 mm is 1.5 mm, and the value of the radius of curvature R of the tip 1101a when the spot diameter is 3.0 mm is 6. It has been confirmed in advance that it is 0 mm.

  Therefore, it can be said that the value of the radius of curvature R of the tip 1101a is preferably 1.5 mm or more. Further, since the welding strength tends to be saturated when the spot diameter is 3.0 mm or more, it is sufficient that the value of the radius of curvature R of the tip 1101a is 6.0 mm or less.

(Example 2)
FIG. 6 shows that the total energization time is different from three levels of 100 msec (Condition A), 200 msec (Condition B), and 300 msec (Condition C), and the welding current peak value is 7 levels within the range of 1.4 kA to 2.5 kA ( 1.4 kA, 1.6 kA, 1.7 kA, 1.8 kA, 2.0 kA, 2.1 kA, 2.5 kA), when spot welding of the protective cover 2 was performed with various welding current profiles PF. It is a figure which shows the relationship between welding current peak value and welding strength about each of the conditions A-condition C. In addition, the curvature radius R of the front-end | tip part 1101a was 4 mm, and the welding execution load was 600N.

  FIG. 7 is a diagram illustrating a welding current profile PF for conditions A to C. Specifically, in FIG. 7, the welding current profile PF for each of the conditions A to C when the welding current peak value is 2.0 kA and the conditions when the welding current peak value is 1.4 kA. The welding current profile PF about A is illustrated.

  In addition, as shown in FIG. 7, in all the welding current profiles PF, the down slope time is set to 30 msec. Therefore, for condition A, the welding current profile PF changes from upslope to downslope when 100-30 = 70 msec has elapsed from the start of energization, regardless of the value of the welding current peak value, and for conditions B and C, respectively. When 170 msec and 270 msec have elapsed from the start of energization, the welding current profile PF turns from an up slope to a down slope.

  FIG. 6 confirms that the welding strength varies depending on the welding current and the energization time, and that if the welding time is the same, the welding strength increases as the welding current peak value increases. Further, when the welding current peak value is the same value, the condition A has a lower welding strength than the conditions B and C, and the welding current peak value is 2.5 kA in the conditions B and C. It is confirmed that the welding strength is almost the same if the welding current peak value is the same except for. In addition, it is thought that the welding strength is small in the condition A because the pre-heating is not given to the protective cover 2 during welding because the up slope time is short.

  More specifically, in condition A, the welding strength is 30 N · m or more in the range where the welding current peak value is 2.0 kA or more, and in conditions B and C, the welding strength is in the range where the welding current peak value is 1.8 kA or more. Was over 30 N · m. However, in any of the conditions A to C, when a welding current profile having a welding current peak value exceeding 2.5 kA was employed, spatter was generated in the vicinity of the welded portion W.

  From the above results, if the total energization time is 200 msec or more and the welding current peak value is 1.8 kA or more and 2.5 kA or less, the protective cover 2 can be fixed with sufficient welding strength without generating spatter. I understand.

(Example 3)
FIG. 8 is a diagram showing the relationship between the welding execution load and the welding strength when spot welding of the protective cover 2 is performed with the welding execution load being changed to four levels of 430N, 570N, 680N, and 710N. In addition, spot welding is performed 10 times for each welding execution load. In FIG. 8, the minimum value of the welding strength under each load condition is indicated by “−” mark, and the maximum value is indicated by “●” mark or It is indicated by “X” mark. The welding current peak value was 1.9 kA, the total energization time was 300 msec, and the curvature radius R of the tip 1101a was 4 mm.

  In the case where the welding execution load was 430 N and 570 N using the “x” mark, spatter occurred in 7 times and 2 times out of 10 spot welds. On the other hand, in the case where the welding execution load was 680N and 710N using the “●” mark, no spatter occurred.

  From the results, it was confirmed that no spatter was generated at least when the welding execution load was 600 N or more.

DESCRIPTION OF SYMBOLS 1 Housing 1a (Housing) fitting part 2 Protective cover 2c (Protective cover) fitting part 10 Sensor element 10a (Sensor element) one end part 100 Gas sensor 100 (alpha) Unwelded gas sensor 1100 (1100A, 1100B) Welding execution part 1101 (1101A, 1101B) Welding rod 1101a (welding rod) tip 1101b (welding rod) flat portion 1102 electrode holder 1103 pressure follower 1104 air cylinder 1104a (air cylinder) movable portion 1105 load cell 1200 welding power source 1300 control portion H Through hole RE Welding target area W Welded part

Claims (10)

A method for manufacturing a gas sensor, comprising:
A fitting step of fitting a protective cover that protects one end of the sensor element protruding from the housing to the housing holding the sensor element;
A welding step of fixing the protective cover to the housing by performing spot welding on a predetermined welding target region of the protective cover fitted to the housing according to a predetermined welding current profile;
With
In the welding process,
Execution of welding of 600 N or more predetermined with respect to the welding target area by bringing a tungsten welding rod having a curved surface with a curvature radius of 1.5 mm or more and 6.0 mm or less at the tip part into contact with the welding target area. With the load applied,
The welding current is increased from 0 at a constant current increasing speed until the time when the welding current reaches the peak value from the start of energization, and after the welding current reaches the peak value, the constant current decreasing speed is reached. In order to reduce the welding current to 0, the energization time from the start of energization to the end of energization is 200 msec to 300 msec, and the peak value is 1.8 kA to 2.5 kA. The spot welding is performed by flowing the welding current in accordance with the welding current profile determined as follows:
A method for producing a gas sensor. It is a manufacturing method of the gas sensor according to claim 1,
In the welding process, the two places are welded simultaneously by applying the welding execution load simultaneously to the two areas to be welded of the protective cover that are opposed to each other by the two welding rods.
A method for producing a gas sensor. A method for manufacturing a gas sensor according to claim 2,
In the welding step, the load applied by the two welding rods to the two areas to be welded is synchronously and continuously increased, and when the load reaches the welding execution load, Passing the welding current between the two welding rods;
A method for producing a gas sensor. A method of manufacturing a gas sensor according to any one of claims 1 to 3,
The welding target area with which the welding rod is in contact is curved in a convex shape with respect to the welding rod;
The most distal portion that is in contact with the welding target area of the welding rod is a circular flat portion orthogonal to the longitudinal direction of the welding rod,
A method for producing a gas sensor. A sensor element protective cover fixing method for fixing a protective cover for protecting one end of a sensor element protruding from the housing to a housing holding a sensor element in a gas sensor,
A tungsten welding rod having a curved surface with a curvature radius of 1.5 mm or more and 6.0 mm or less at the tip is brought into contact with the welding target area, so that the predetermined welding target area of the protective cover is predetermined. With a welding execution load of 600 N or more applied,
The welding current is increased from 0 at a constant current increasing speed until the time when the welding current reaches the peak value from the start of energization, and at a constant current decreasing speed after the welding current reaches the peak value. In order to reduce the welding current to zero, the energization time from the start of energization to the end of energization is from 200 msec to 300 msec, and the peak value is from 1.8 kA to 2.5 kA. In accordance with the welding current profile defined in the above, spot welding is performed to fix the protective cover to the housing in the welding target region by flowing the welding current.
A method for fixing a sensor element protective cover. A method for fixing the sensor element protective cover according to claim 5,
By simultaneously applying the welding execution load to the two welding target areas of the protective cover facing each other by the two welding rods, the two places are welded simultaneously.
A method for fixing a sensor element protective cover. A sensor element protective cover fixing method according to claim 6,
The load applied by the two welding rods to the two welding target regions is synchronously and continuously increased, and when the load reaches the welding execution load, the two welding rods Energizing the welding current during
A method for fixing a sensor element protective cover. A sensor element protective cover fixing method according to any one of claims 5 to 7,
The welding target area with which the welding rod is in contact is curved in a convex shape with respect to the welding rod;
The most distal portion that is in contact with the welding target area of the welding rod is a circular flat portion orthogonal to the longitudinal direction of the welding rod,
A method for fixing a sensor element protective cover. A welding device for fixing, by spot welding, a protective cover that protects one end of the sensor element protruding from the housing to a housing that holds the sensor element in the gas sensor,
Two welding rods made of tungsten having a curved surface with a radius of curvature of 1.5 mm or more and 6.0 mm or less at the tip,
The two welding rods are respectively brought into contact with two predetermined welding target regions facing each other predetermined in the protective cover, so that the welding target regions corresponding to the two welding rods correspond to each other. A load applying means capable of applying a load;
Energization means for energizing a welding current between the two welding rods;
With
The welding current profile when the energization means energizes the welding current increases the welding current from 0 at a constant current increase rate from the start of energization to the time when the welding current reaches a peak value, and the welding After the current reaches the peak value, the energization time from the start of energization to the end of energization is 200 msec or more and 300 msec or less so that the welding current is decreased to 0 at a constant current decrease rate. And the peak value is determined to be 1.8 kA or more and 2.5 kA or less,
The load application means synchronously and continuously increase the load applied by the two welding rods to the two areas to be welded,
The energization means starts energization of the welding current according to the welding current profile between the two welding rods when the load reaches a predetermined welding execution load of 600 N or more.
A welding apparatus characterized by that. The welding apparatus according to claim 9,
The welding target area with which the welding rod is in contact is curved in a convex shape with respect to the welding rod;
The most distal portion that is in contact with the welding target area of the welding rod is a circular flat portion orthogonal to the longitudinal direction of the welding rod,
A welding apparatus characterized by that.

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