Patent Publication Number: US-9423368-B2

Title: Method for manufacturing gas sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2013-071829 filed in Japan on Mar. 29, 2013, the contents of which are hereby incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a gas sensor. 
     2. Description of the Related Art 
     Hitherto, there have been known gas sensors for detecting the concentration of a predetermined substance, such as NO x , in measured gas such as an automobile exhaust gas. For example, Japanese Unexamined Patent Application Publication No. 09-196885 describes a gas sensor including a sensor element which is placed in a tubular body made of metal and which detects the concentration of gas at the tip of the tubular body, a connector in contact with an electrode placed on the back end side of the sensor element, an elastic body (grommet) attached to a back open end of the tubular body, and a lead which is connected to the connector and which extends outward from an open end of the tubular body through a through-hole of the elastic body. 
     Japanese Unexamined Patent Application Publication No. 09-196885 proposes a method for manufacturing the gas sensor. In the method, the elastic body is fixed to the tubular body by multi-stage (two-stage) swaging in such a way that two sites spaced at a predetermined distance in an axial direction of the tubular body are swaged. 
     SUMMARY 
     In the case of fixing the elastic body by swaging as described above, if swaging excessively increases the axial elongation or misalignment of the elastic body, then sealing properties cannot be sufficiently ensured or a connection between the connector and the lead is misaligned; hence, electrical connectivity may possibly be adversely affected. 
     It is a main object of a method for manufacturing a gas sensor according to the present invention to ensure better sealing properties and electrical connectivity in the case of sealing an open end of a tubular body enclosing a sensor element by swaging an elastic body. 
     In order to achieve the above main object, the method for manufacturing the gas sensor according to the present invention has taken means below. 
     The present invention provides a method for manufacturing a gas sensor including a sensor element capable of detecting the concentration of measured gas; a connector electrically connected to the sensor element; a tubular body in which the sensor element and the connector are placed and which has an open end; leads which are connected to the connector and which extend outward from the open end of the tubular body; and an elastic body which is placed in the tubular body so as to seal the open end, in which connections between the connector and the leads are placed, and through which the leads extend, the method comprising: radially swaging the tubular body and the elastic body at a plurality of swaged sections including a swaged section located on the connection side and a swaged section located closer to the open end than the swaged section located on the connection side, wherein in the swaging, among the plurality of swaged sections, a swaged section other than the swaged section located on the connection side begins to be primarily swaged. 
     The method for manufacturing the gas sensor according to the present invention includes radially swaging the tubular body, which has the open end, and the elastic body, in which connections between the connector and the leads are placed and through which the leads extend, at the swaged sections, which include the swaged section located on the connection side and the swaged section located closer to the open end than the swaged section located on the connection side. In the swaging, among the swaged sections, a swaged section other than the swaged section located on the connection side begins to be primarily swaged. This allows strong force to be prevented from acting on the elastic body in a free state at a time and also allows the swaged section located on the connection side to begin to be swaged in such a state that the elastic body is aligned on the open end side as compared to the case where the swaged sections begin to be simultaneously swaged. Therefore, since the misalignment of the elastic body can be reduced during swaging as compared to the case where the swaged sections begin to be simultaneously swaged, the misalignment of the connections between the connector and the leads is reduced and therefore connection failure can be prevented. In addition, since the pressure in the elastic body can be increased by reducing the projection length of the swaged elastic body protruding from the open end, sealing properties can be enhanced. Thus, better sealing properties and electrical connectivity can be ensured. 
     Herein, the expression “among the swaged sections, a swaged section other than the swaged section located on the connection side begins to be primarily swaged” means that among the swaged sections, the swaged section located on the open end side may begin to be swaged prior to the swaged section located on the connection side or a swaged section located closest to the open end may begin to be primarily swaged. Alternatively, the swaged section located on the connection side may begin to be swaged in the course of swaging a swaged section other than the swaged section located on the connection side or the swaged section located on the connection side may begin to be swaged after the swaging of a swaged section other than the swaged section located on the connection side is finished. 
     In the method for manufacturing the gas sensor according to the present invention, in the swaging, two of the swaged sections that are a first swaged section located on the connection side and a second swaged section located on the open end side are swaged and among the two swaged sections, the second swaged section may begin to be swaged prior to the first swaged section. This allows better sealing properties and electrical connectivity to be ensured as compared to the case where the first swaged section and the second swaged section begin to be simultaneously swaged. 
     In the method for manufacturing the gas sensor according to the present invention, in the swaging, the elastic body may be swaged such that the inside diameter of a portion of the elastic body that corresponds to the first swaged section is greater than the inside diameter of a portion of the elastic body that corresponds to the second swaged section. This allows further better sealing properties and electrical connectivity to be ensured because the first swaged section is prevented from affecting electrical connectivity by inhibiting excessive force from acting on the connections and sealing properties can be enhanced by sufficiently swaging the second swaged section. 
     In the method for manufacturing the gas sensor according to the present invention, in the swaging, the elastic body may be swaged with a predetermined distance present between the first swaged section and the second swaged section in an axial direction of the elastic body. This allows the misalignment of the elastic body during swaging to be further reduced because the elongation of the elastic body can be absorbed by a portion corresponding to the predetermined distance in the case where the first swaged section begins to be swaged and the second swaged section then begins to be swaged. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the attached drawings which form a part of this original disclosure. 
         FIG. 1  is a sectional view of a gas sensor  10  according to an embodiment of the present invention. 
         FIG. 2  is a sectional view of swaged sections of the gas sensor  10 . 
         FIG. 3  is an illustration showing how an outer tube  46  and a rubber plug  60  are swaged in the course of manufacturing the gas sensor  10 . 
         FIGS. 4A and 4B  are illustrations showing how the outer tube  46  and the rubber plug  60  are swaged in the course of manufacturing the gas sensor  10 . 
         FIGS. 5A to 5C  are illustrations showing how two swaged sections begin to be simultaneously swaged. 
         FIGS. 6A to 6C  are illustrations showing how one of two swaged sections that is located on the open end side begin to be primarily swaged. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the attached drawings. 
       FIG. 1  is a sectional view of a gas sensor  10  according to an embodiment of the present invention. As shown in  FIG. 1 , the gas sensor  10  includes a sensor element  20  for measuring the concentration of a predetermined gas component in measured gas, a protective cover  30  protecting an end portion of the sensor element  20 , and a sensor assembly  40  including a rubber plug  60  and a connector  50  electrically connected to the sensor element  20 . The gas sensor  10  is attached to, for example, a vehicle&#39;s exhaust pipe and used to measure the concentration of a substance, such as NO x  or O 2 , contained in an exhaust gas which is measured gas. 
     The sensor element  20  is an element with a narrow elongated plate-like shape and is composed of, for example, six stacked ceramic substrates each including an oxygen-ion conducting solid electrolyte layer made of zirconia (ZrO 2 ) or the like. Herein, an end portion of the sensor element  20  that is located on the protective cover  30  side is referred to as a free end and an end portion of the sensor element  20  that is located on the connector  50  is referred to as a base end. The front and back surfaces of the base end of the sensor element  20  each have electrodes (not shown) for applying a voltage to the sensor element  20  or extracting the electromotive force or current generated depending on the concentration of a gas component detected by the sensor element  20 . The electrodes are arranged on the front and back surfaces of the sensor element  20  and are electrically connected to an electrode (not shown) placed in the free end of the sensor element  20  through a conducting path extending in the sensor element  20 . 
     The protective cover  30  is placed so as to surround the periphery of the free end of the sensor element  20 . The protective cover  30  includes an inner protective sub-cover  31  covering the free end of the sensor element  20  and an outer protective sub-cover  32  covering the inner protective sub-cover  31 . The inner protective sub-cover  31  is tube-shaped and has an inner protective cover hole  31   a  for introducing measured gas to the free end of the sensor element  20 . The outer protective sub-cover  32  has a bottomed cylindrical shape and also has, placed in the side surface, outer protective cover holes  32   a  for introducing measured gas. The inner protective sub-cover  31  and the outer protective sub-cover  32  are made of, for example, metal such as stainless steel. 
     The sensor assembly  40  includes a main fitting  41  made of metal, a cylindrical inner tube  42  welded to the main fitting  41 , a cylindrical outer tube  46  welded to the main fitting  41 , the connector  50 , the rubber plug  60 . The connector  50  is connected to the base end of the sensor element  20 . The rubber plug  60  is attached to the outer tube  46 . The main fitting  41  is attachable to, for example, automotive exhaust pipes using a male screw portion  41   a . The following members are enclosed in the main fitting  41  and the inner tube  42 : a plurality of ceramic supporters  43   a  to  43   c  and ceramic powders  44   a  and  44   b  such as talc powders. The ceramic powder  44   a  is placed between the ceramic supporters  43   a  and  43   b  and the ceramic powder  44   b  is placed between the ceramic supporters  43   b  and  43   c . The ceramic supporters  43   a  to  43   c  and the ceramic powders  44   a  and  44   b  are surrounded by a metal ring  45 , the inner wall of the main fitting  41 , and the inner wall of the inner tube  42  and are thereby sealed. The outer tube  46  covers surroundings of the inner tube  42 , the sensor element  20 , and the connector  50  and has an open end  46   a  (the upper end of the outer tube  46  shown in  FIG. 1 ). The rubber plug  60  is attached to the open end  46   a.    
     The connector  50  includes a housing  51  made of a ceramic such as sintered alumina and contact fittings  52  which are supported by the housing  51  and which are in contact with the electrodes of the sensor element  20 . The contact fittings  52  extend outside the connector  50  and are electrically connected to leads  48  through connections  52   a  which are crimp contacts. In the connector  50 , the number (for example, four, eight, or the like) of the contact fittings  52  corresponds to the number of the electrodes placed on the front and back surfaces of the sensor element  20 . Therefore, the number of the connections  52   a  is more than one (for example, four, eight, or the like) and the number of the leads  48  is also more than one (for example, four, eight, or the like). 
     The rubber plug  60  is located at the open end  46   a  of the outer tube  46 ; is a member, made of fluoro-rubber, for sealing gaps between the outer tube  46  and the leads  48  (the connections  52   a ); and has through-holes  60   a  extending therein. The connections  52   a  are placed in the through-holes  60   a  and the leads  48  are inserted in the through-holes  60   a . The plurality of through-holes are provided to accommodate the plurality of connections  52   a  and leads  48 . Since the gas sensor  10  is attached to a vehicle&#39;s exhaust pipe, the gas sensor  10  needs to be compact due to a limitation in installation space. Therefore, the connections  52   a  are placed in the through-holes  60   a , whereby the length (length in axial direction) of the rubber plug  60  is limited and the gas sensor  10  is made compact (the length of the outer tube  46  is limited). The rubber plug  60  contains a filler (aggregate) made of an inorganic material. The filler is an alumina (Al 2 O 3 ) or silica (SiO 2 ) powder with a particle size of 0.1 μm to 10 μm and the content of the filler is 1% to 30% by weight. The use of the filler allows the rubber plug  60  to have increased hardness. 
     The rubber plug  60  is radially swaged together with the outer tube  46  and is thereby fixed in the outer tube  46 .  FIG. 2  shows swaged sections thereof in cross section. As shown in  FIG. 2 , two swaged sections are arranged in an axial direction of the outer tube  46  (the rubber plug  60 ): one located on the connector  50  side (the sensor element  20  side) is referred to as a swaged section A ((A) in  FIG. 2 ) and the other located closer to the open end  46   a  than the swaged section A (on the side on which the leads  48  extend outward) is referred to as a swaged section B ((B) in  FIG. 2 ). The swaged section A is one formed by swaging the entire periphery of the outer tube  46  at sites (sites which correspond to the connections  52   a  in a radial direction of the outer tube  46  and which are located directly above and under the connections  52   a  as shown in  FIG. 2 ) corresponding to the connections  52   a  between the contact fittings  52  and the leads  48 . The swaging width LA (the length in the axial direction of the outer tube  46 ) of the swaged section A is within the width (within the length in the axial direction of the outer tube  46  at the connections  52   a ) of the connections  52   a . The swaged section B is apart from the swaged section A at a predetermined distance LS and has a swaging width LB equal to the swaging width LA. When the inside diameter of a portion of the outer tube  46  that corresponds to the swaged section A and the inside diameter of a portion of the outer tube  46  that corresponds to the swaged section B are expressed as inside diameter φA and inside diameter φB, respectively, the relation “inside diameter φA&gt;inside diameter φB” holds. That is, the swaged section B is one more heavily swaged than the swaged section A. In this embodiment, in the swaged sections A and B, the inside diameter and thickness of the unswaged outer tube  46  are invariant and therefore inside diameter φA and inside diameter φB correspond to the outside diameter of the swaged rubber plug  60 . 
     The rubber plug  60  is used to the seal the open end  46   a  of the outer tube  46 . Therefore, if the rubber plug  60  is not sufficiently swaged, then sealing properties are not ensured and moisture and gases other than measured gas leak into the outer tube  46  to adversely affect the detection accuracy of the sensor element  20  in some cases. On the other hand, the leads  48  are inserted in the rubber plug  60  and the connections  52   a  between the contact fittings  52  and the leads  48  are placed in the rubber plug  60 . Therefore, if the whole of the rubber plug  60  is excessively swaged, then excessive force acts on the leads  48  and the connections  52   a . When excessive force acts on the leads  48  and the connections  52   a , the leads  48  are likely to be broken, the resistance of the leads  48  becomes unstable, the connections  52   a  become faulty, and/or the contact of the connections  52   a  cause shorts; hence, electrical connectivity may possibly be impaired. Alternatively, if a site corresponding to the swaged section A is not swaged, then the connections  52   a  are not secured in the through-holes  60   a  and therefore the misalignment of the connections  52   a  (the contact fittings  52 ) is likely to be caused by vibrations from vehicles. Hence, in this case, electrical connectivity may possibly be impaired. Therefore, in this embodiment, the swaged section B is more heavily swaged than the swaged section A, whereby sealing properties are ensured and leaking is prevented. Since the swaged section A is more lightly swaged than the swaged section B, excessive force is prevented from acting on the connections  52   a  with the connections  52   a  secured and good electrical connectivity is achieved. The reason why the inside diameter φA of the swaged section A and the inside diameter φB of the swaged section B are set such that the relation “inside diameter φA&gt;inside diameter φB” holds is that the prevention of leaking and the prevention of electrical connection failure are both achieved. 
     In the swaged section B, in order to ensure sealing properties, the swaging ratio is within the range of 8% to 14%, the swaging ratio being determined by dividing the difference (inside diameter before swaging−inside diameter φB after swaging) in inside diameter between the unswaged outer tube  46  and the swaged outer tube  46  by the inside diameter of the unswaged outer tube  46 . The inside diameter of the portion of the unswaged outer tube  46  that corresponds to the swaged section B, is used as the inside diameter before swaging. Instead, the inside diameter of a portion (an unswaged portion located between the swaged sections A and B) of the swaged outer tube  46 , the portion corresponding to the predetermined distance LS, may be used. Furthermore, in the swaged section A, the inside diameter φA is set to be slightly greater than the inside diameter φB such that swaging is slight and sealing properties are not significantly impaired. In particular, the inside diameter variance determined by dividing the difference between the inside diameter φA and the inside diameter φB by the inside diameter φB is 1% to 5%. That is, the inside diameter φA is 1% to 5% greater than the inside diameter φB. Furthermore, in this embodiment, since the hardness of the rubber plug  60  is increased by adding the filler to as described above, the durability of the rubber plug  60  can be increased. Therefore, the breakage of the rubber plug  60  can be reduced and obtained sealing properties can be maintained for a long period. In particular, the effect of adding the filler is significant because the gas sensor  10  is one used in vehicles and the rubber plug  60  is exposed to gas at a high temperature of higher than 250° C. and therefore is in a degradable environment. 
     A method for manufacturing the gas sensor  10  is described below. First, the main fitting  41  and the inner tube  42  are assembled by welding so as to be coaxial with each other. After the ceramic supporter  43   a , the ceramic powder  44   a , the ceramic supporter  43   b , the ceramic powder  44   b , and the ceramic supporter  43   c  are provided in the inner tube  42  in that order from the main fitting  41 , the metal ring  45  is inserted in the inner tube  42 . Next, the sensor element  20  is passed through the ceramic supporter  43   c , the ceramic powder  44   b , the ceramic supporter  43   b , the ceramic powder  44   a , and the ceramic supporter  43   a  in that order from the metal ring  45 . The ceramic supporters  43   a  to  43   c , the ceramic powders  44   a  and  44   b , and the metal ring  45  each have a hole through which the sensor element  20  can be passed. The metal ring  45  and the main fitting  41  are pressed in a direction in which the metal ring  45  and the main fitting  41  approach each other, whereby the ceramic powders  44   a  and  44   b  are compressed. In such a state, a portion (an upper portion in  FIG. 1 ) of the inner tube  42  that is located outside the metal ring  45  is reduced in diameter by swaging and a portion of the inner tube  42  that contains the ceramic powder  44   b  is also reduced in diameter by swaging, a primary assembly including the main fitting  41  and the sensor element  20  is obtained. 
     After the primary assembly is obtained as described above, the inner protective sub-cover  31  and the outer protective sub-cover  32  are welded to the main fitting  41 , whereby the protective cover  30  is formed. The outer tube  46  is welded to the main fitting  41 . Subsequently, the rubber plug  60  having the through-holes  60   a  is prepared. Herein, a rubber material for the rubber plug  60  is prepared in such a way that the filler, which is the alumina (Al 2 O 3 ) with a particle size of 0.1 μm to 10 μm, is added to a rubber component such as fluoro-rubber such that the content thereof is 1% to 30% by weight, followed by kneading with a mixer or the like. The filler is not limited to the alumina (Al 2 O 3 ) and may be a silica (SiO 2 ). The rubber material, prepared as described above, containing the filler is shaped so as to have a necessary form and size and is subjected to a step necessary to form the through-holes  60   a , whereby the rubber plug  60  is obtained. The leads  48  are passed through the through-holes  60   a  of the rubber plug  60  and the connections  52   a  of the contact fittings  52  are connected to the leads  48 , whereby the connector  50  is prepared. The connector  50  is connected to the base end of the sensor element  20 . The rubber plug  60  is inserted in the open end  46   a  of the outer tube  46 . Next, the outer tube  46  and the rubber plug  60  are reduced in diameter by swaging, whereby the rubber plug  60  is fixed to the outer tube  46 .  FIGS. 3 and 4  show how the outer tube  46  and the rubber plug  60  are swaged in the course of manufacturing the gas sensor  10 . 
     As shown in  FIG. 3 , swaging is performed using swaging tools  102  set to a swaging machine (not shown) and a pressing tool  104  pressing the back side of the swaging tools  102 . The swaging tools  102  each include a bump  102   a  for swaging the swaged section A and a bump  102   b  for swaging the swaged section B. As shown in an enlarged view in  FIG. 3 , the height ha of the bump  102   a  is slightly different from the height hb of the bump  102   b . The height hb is greater than the height ha by Δh (for example, 0.1 mm, 0.2 mm, or the like). The swaging tools  102  have such a form that a cylindrical member is divided into eight pieces at 45°. Therefore, in the case where eight of the swaging tools  102  are set to the swaging machine so as to direct the bumps  102   a  and  102   b  inward and the gas sensor  10  is set to the center surrounded by the swaging tools  102 , the swaging tools  102  are arranged around the outer tube  46 , which is cylindrical. An outside back surface  102   c  of each swaging tool  102  and an inside pressing surface  104   a  of the pressing tool  104  are tapered at substantially the same angle. Therefore, when the pressing tool  104  moves leftward to bring the pressing surface  104   a  into contact with the back surface  102   c  as shown in  FIG. 3 , the swaging tool  102  (the bumps  102   a  and  102   b ) are pressed by the pressing tool  104  and therefore move substantially in parallel from outside toward the center side (the outer tube  46  side). 
     When the pressing tool  104  further moves leftward from a state shown in  FIG. 3  and the swaging tool  102  move to the center side to abut the outer tube  46 , swaging starts (refer to  FIG. 4A ). Since the height ha of the bump  102   a  and the height hb of the bump  102   b  are slightly different from each other, the bump  102   b  abuts the outer tube  46  prior to the bump  102   a  as shown in an enlarged view in  FIG. 4A . That is, the bump  102   b  starts swaging prior to the bump  102   a . Therefore, the swaged section B begins to be swaged prior to the swaged section A. The pressing tool  104  further moves leftward and therefore the swaging tool  102  are moved (pressed) toward the center side (the outer tube  46  side), whereby swaging is performed. When the pressing tool  104  reaches a predetermined position, swaging ends (refer to  FIG. 4B ). Herein, since the height hb is greater than the height ha by Δh, the bump  102   b  is greater in indentation depth than the bump  102   a . Therefore, the bump  102   b  is greater in swaging depth than the bump  102   a ; hence, the inside diameter φB of the swaged section B is less than the inside diameter φA of the swaged section A. The gas sensor  10  in  FIG. 1  is obtained by such a manufacturing method including swaging. 
     As described above, in the method for manufacturing the gas sensor  10 , among the two swaged sections A and B, the swaged section B begins to be primarily swaged in the course of swaging the outer tube  46  and rubber plug  60 . For comparison,  FIGS. 5A to 5C  show how two swaged sections begin to be simultaneously swaged.  FIGS. 6A to 6C  show how one of two swaged sections that is located on the open end side begins to be primarily swaged like this embodiment. In  FIGS. 5A to 5C and 6A to 6C , the leads  48 , the connections  52   a , the through-holes  60   a , or the like are not shown. As shown in  FIGS. 5A to 5C , since the two swaged sections A and B begin to be simultaneously swaged ( FIG. 5A ), relatively strong force acts on the rubber plug  60  in a free state. Also, the elongation of rubber between (inside) the swaged sections A and B repels (inside elongation is restricted) and therefore rubber is likely to extend outward. That is, in the swaged section A, the rubber plug  60  relatively significantly extends leftward, and in the swaged section B, the rubber plug  60  relatively significantly extends rightward (in a direction in which the rubber plug  60  protrudes from the outer tube  46 ). Therefore, the projection length t0 of the rubber plug  60  protruding from the outer tube  46  is relatively large ( FIG. 5B ). The progression of swaging increases the elongation of the rubber plug  60  and also increases the projection length t of the rubber plug  60  protruding from the outer tube  46  ( FIG. 5C ). The connector  50 , which is not shown, is present on the left side in  FIGS. 5A to 5B  and therefore the leftward elongation of the rubber plug  60  is more likely to be restricted as compared to the rightward elongation thereof. On the other hand, as shown in  FIGS. 6A to 6C , among the two swaged sections A and B, the swaged section B is located on the open end side and begins to be primarily swaged ( FIG. 6A ); hence, the force acting on the rubber plug  60  at the start of swaging is less as compared to a comparative example and the leftward (inward) elongation of rubber in the swaged section B is unlikely to be restricted. Therefore, the projection length t0 of the rubber plug  60  protruding from the outer tube  46  is less as compared to a comparative example ( FIG. 6B ). When the swaged section A begins to be swaged, rubber in the swaged section B acts so as to restrict the elongation of the rubber plug  60  due to the swaging of the swaged section A because the swaged section B has already begun to be swaged. Since only the swaged section B begins to be primarily swaged, the swaged section A begins to be swaged in such a state that the rubber plug  60  is axially aligned at the swaged section B. Therefore, though swaging proceeds, the elongation of the rubber plug  60  is absorbed by the portion, located between the swaged sections A and B, corresponding to the predetermined distance LS; hence, the projection length t of the rubber plug  60  protruding from the outer tube  46  can be reduced as compared to the comparative example ( FIG. 6C ). Thus, the misalignment of the rubber plug  60  due to swaging is reduced and therefore the rubber plug  60  after swaging can be kept at substantially the same position. Since the projection length t of the rubber plug  60  protruding from the outer tube  46  is reduced without varying the indentation depth during swaging as described above, the pressure in the rubber plug  60  in the outer tube  46  can be increased. Therefore, sealing properties of the rubber plug  60  can be maintained for a long period. Since the position of the rubber plug  60  is not significantly varied before and after swaging (misalignment is reduced and substantially the same position is kept), the axial force (tensile force) applied to the leads  48  and the connections  52   a  during swaging is reduced and therefore the breakage of the leads  48  and the failure of the connections  52   a  can be prevented from occurring. These are the reasons why the swaged section B begins to be primarily swaged during swaging. 
     The correspondence between elements of this embodiment and elements of the present invention is described below. The sensor element  20  corresponds to a “sensor element” of the present invention, the connector  50  corresponds to a “connector” of the present invention, the outer tube  46  corresponds to a “tubular body” of the present invention, the leads  48  correspond to “leads” of the present invention, the rubber plug  60  corresponds to an “elastic body” of the present invention, the swaged section A corresponds to a “first swaged section” of the present invention, and the swaged section B corresponds to a “second swaged section” of the present invention. 
     According to this embodiment, the outer tube  46  and the rubber plug  60  are swaged at two sites, that is, the swaged section A, which is located on the connections  52   a , and the swaged section B, which is located on the open end  46   a  side of the outer tube  46 , such that the inside diameter φA of the portion of the rubber plug  60  that corresponds to the swaged section A is greater than the inside diameter φB of the portion of the rubber plug  60  that corresponds to the swaged section B. Therefore, the swaged section B is more heavily swaged than the swaged section A, whereby sealing properties are ensured and leakage can be prevented. The swaged section A is more lightly swaged than the swaged section B, whereby the failure of the connections  52   a  and the like can be prevented. In the swaged section B, the swaging ratio is set within the range of 8% to 14% and therefore sealing properties can be reliably ensured. Furthermore, in the swaged section A, the swaged section A is set to be 1% to 5% greater than the swaged section B; hence, the swaged section A is more lightly swaged than the swaged section B and sealing properties can be prevented from being significantly impaired. Since the rubber plug  60  contains the filler, sealing properties can be maintained for a long period by increasing the pressure in the rubber plug  60 . These allow better sealing properties and electrical connectivity to be ensured. 
     According to this embodiment, in swaging, among the two swaged sections A and B, the swaged section B begins to be primarily swaged; hence, strong force can be prevented from acting on the rubber plug  60  in a free state at a time and the swaged section A can begin to be swaged in such a state that the portion of the rubber plug  60  that corresponds to the swaged section B is aligned as compared to the case where the swaged sections A and B begin to be simultaneously swaged. Therefore, the position of the rubber plug  60  can be prevented from being significantly varied and the rubber plug  60  can be prevented from protruding from the outer tube  46 ; hence, the breakage of the leads  48  and the failure of the connections  52   a  can be prevented from occurring and sealing properties can be maintained for a long period by increasing the pressure in the rubber plug  60 . In addition, the elongation of the rubber plug  60  can be absorbed by the portion, located between the swaged sections A and B, corresponding to the predetermined distance LS and therefore the pressure in the rubber plug  60  can be further increased. 
     The present invention is not limited to this embodiment and various modifications can be made within the technical scope of the present invention. 
     In this embodiment, the swaged section A is a site corresponding to the connections  52   a  and the swaging width LA of the swaged section A is within the width of the connections  52   a . Instead, the width of the connections  52   a  may be within the swaging width LA of the swaged section A or the swaging width LA of the swaged section A may partly overlap the width of the connections  52   a.    
     In this embodiment, the two swaged sections A and B are swaged. Instead, three or more sites may be swaged. In the case of swaging three or more sites, it is only necessary that the inside diameter φA of the swaged section A, which is the site corresponding to the connections  52   a , is greater than the inside diameter φA of a swaged section other than the swaged section A. In a step of swaging three or more sites, it is only necessary that a swaged section other than the swaged section A begins to be primarily swaged. 
     In this embodiment, the inside diameter φA of the portion of the rubber plug  60  that corresponds to the swaged section A is greater than the inside diameter φB of the portion of the rubber plug  60  that corresponds to the swaged section B. Instead, the inside diameter φA and the inside diameter φB may be the same. However, as described above, in order to ensure better sealing properties and electrical connectivity, the inside diameter φA is preferably greater than the inside diameter φB. 
     In this embodiment, the swaged section A begins to be swaged in the course of swaging the swaged section B. Instead, after the swaged section B is swaged, the swaged section A may begin to be swaged. 
     In this embodiment, the rubber plug  60  is the member made of fluoro-rubber. Instead, the rubber plug  60  may be made of another material, such as a heat-resistant resin, capable of sealing the open end  46   a  of the outer tube  46 . 
     In this embodiment, the rubber plug  60  contains the filler. Instead, the rubber plug  60  need not contain the filler. 
     In this embodiment, the swaged sections A and B are swaged with the swaging tools  102  common thereto. Instead, the swaged sections A and B may be separately swaged with separate swaging tools. 
     In this embodiment, the height ha of the bumps  102   a  of the swaging tools  102  is different from the height hb of the bumps  102   b  thereof. Instead, the height ha of the bumps  102   a  may be the same as the height hb of the bumps  102   b  and the swaging tools  102  may be different in indentation depth from each other. 
     In this embodiment, the predetermined distance LS is present between the swaged sections A and B. Instead, the swaged sections A and B may be stepwise connected with no distance therebetween. 
     In this embodiment, the swaging width LA of the swaged section A is the same as the swaging width LB of the swaged section B. Instead, the swaging width LA of the swaged section A may be different from the swaging width LB of the swaged section B. For example, the swaging width LB of the swaged section B may be greater than the swaging width LA of the swaged section A. This allows sealing properties to be further ensured and leakage to be further prevented because the swaging width LB of the swaged section B is large and also allows excessive force to be prevented from acting on the connections  52   a  because the swaging width LA of the swaged section A is small. 
     EXAMPLES 
     Preliminary Test 
     Before the gas sensor  10  shown in  FIG. 10  was manufactured, the following test was carried out: a preliminary test to determine the range of the swaging ratio of the inside diameter φB as the reference inside diameter of the swaged outer tube  46 . In the preliminary test, the following sensors were prepared: gas sensors subjected to single-stage swaging at a single swaged section and gas sensors subjected to two-stage swaging at two swaged sections. In the preliminary test, unlike the above embodiment, the gas sensors were swaged so as to have the same inside diameter. Seven of the gas sensors subjected to single-stage swaging and seven of the gas sensors subjected to two-stage swaging were prepared and were swaged such that the inside diameter before swaging was reduced from 11.8 mm to 11.0 mm (about 7%), 10.8 mm (about 8%), 10.6 mm (about 10%), 10.4 mm (about 12%), 10.2 mm (about 14%), 10.0 mm (about 15%), or 9.8 mm (about 17%) by swaging (each parenthesized value is the swaging ratio). The outside diameter of the unswaged rubber plug  60  was 11.0 mm. In the preliminary test, each prepared gas sensor was attached to a gas pipe similar to an automotive exhaust pipe. As shown in heating conditions in Table 1, a heating test was continuously carried out for 100 hours in such a way that the rubber plug  60  is exposed to high temperature, about 250° C., by introducing about 850° C. gas into the gas pipe using a gas burner. After the heating test was finished, a leakage test to check the leakage of air was carried out in such a way that air with a static pressure of 0.1 MPa was applied to the gas sensor from the lead  48  side. Subsequently, the rubber plug  60  was taken out of the gas sensor and was checked for the presence of cracks, whereby the rubber plug  60  was evaluated for durability. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 HEATING DEVICE 
                 C 3 H 8  BURNER 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 GAS TEMPERATURE 
                 850° 
                 C. 
               
               
                   
                 RUBBER PLUG 
                 250° 
                 C. 
               
               
                   
                 TEMPERATURE 
               
               
                   
                 HEATING TIME 
                 100 
                 hours 
               
               
                   
                   
               
            
           
         
       
     
     Table 2 shows results of the preliminary test. In the leakage test, the gas sensors, subjected to single-stage swaging, having an inside diameter φB of 10.6 mm to 11.0 mm had leaks and those having an inside diameter φB of 9.8 mm to 10.4 mm had no leaks. In Table 2, the symbol “B” denotes the absence of leaks and the symbol “D” denotes the presence of leaks problematic in practical use. The gas sensor, subjected to two-stage swaging, having an inside diameter φB of 11.0 mm had leaks and the others having an inside diameter φB of 9.8 mm to 10.8 mm had no leaks. In the evaluation of durability, the gas sensors, subjected to single- or two-stage swaging, having an inside diameter φB of 10.2 mm to 11.0 mm had no cracks (denoted by “B”) and were good in durability. However, those having an inside diameter φB of 9.8 mm or 10.0 mm had cracks (denoted by “D”) and were poor in durability. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 LEAKAGE TEST 
                 DURABILITY OF RUBBER PLUG 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 TWO-STAGE SWAGING 
                   
                 TWO-STAGE SWAGING 
               
               
                 REFERENCE INSIDE 
                   
                   
                 (TWO-STAGE WITH 
                   
                 (TWO-STAGE WITH 
               
               
                 DIAMETER 
                 SWAGING 
                 SINGLE-STAGE 
                 SAME INSIDE 
                 SINGLE-STAGE 
                 SAME INSIDE 
               
               
                 φB(mm) 
                 RATIO 
                 SWAGING 
                 DIAMETER) 
                 SWAGING 
                 DIAMETER) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 φ11.0 
                  7% 
                 D 
                 D 
                 B 
                 B 
               
               
                 φ10.8 
                  8% 
                 D 
                 B 
                 B 
                 B 
               
               
                 φ10.6 
                 10% 
                 D 
                 B 
                 B 
                 B 
               
               
                 φ10.4 
                 12% 
                 B 
                 B 
                 B 
                 B 
               
               
                 φ10.2 
                 14% 
                 B 
                 B 
                 B 
                 B 
               
               
                 φ10.0 
                 15% 
                 B 
                 B 
                 D 
                 D 
               
               
                 φ9.8 
                 17% 
                 B 
                 B 
                 D 
                 D 
               
               
                   
               
            
           
         
       
     
     The results of the preliminary test indicate the following. First, the reference inside diameter (inside diameter φB) capable of preventing leakage and keeping durability is preferably within the range of 10.2 mm to 10.8 mm, that is, the swaging ratio is preferably within the range of 8% to 14%. In the above embodiment, the inside diameter TA is greater than the inside diameter φB; hence, one having a high leakage prevention effect only by a single stage of the inside diameter φB is required. Therefore, the inside diameter φB is more preferably within the range of 10.2 mm to 10.4 mm, that is, the swaging ratio is more preferably within the range of 12% to 14%. 
     Evaluation Test 1 
     For the inside diameter φB determined as the reference inside diameter in the preliminary test, gas sensors for comparative examples in which the inside diameter φA was determined at an inside diameter variance of 0% (the same diameter) and gas sensors for examples in which the inside diameter φA was determined at an inside diameter variance within a predetermined range were prepared, followed by Evaluation Test 1. In the preliminary test, the preferred range of the inside diameter φB was 10.2 mm to 10.8 mm; hence, three sizes, 10.8 mm, 10.4 mm, and 10.2 mm, were used as values of the inside diameter φB. The inside diameter variance of the examples was within the range of 0.1% to 7% and was set to 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or 7%. In Evaluation Test 1, a heating test was carried out in substantially the same manner as that described in the preliminary test. After the heating test was finished, the above leakage test was carried out. Subsequently, the elongation ΔL of the whole rubber plug  60  was investigated. As the elongation ΔL of the whole rubber plug  60  as well as the projection length t of the rubber plug  60  increases, the tensile force acting on the leads  48  increases; hence, connection failure or disconnection is likely to occur and therefore electrical connectivity is reduced in some cases. The increase in elongation ΔL of the rubber plug  60  leads to the reduction of sealing properties because the pressure in the rubber plug  60  is reduced. Herein, it has been grasped that in the rubber plug  60  having an outside diameter of 11.0 mm and a length L of 14.5 mm in an initial state before swaging, electrical connectivity or sealing properties are affected in some cases when the elongation ΔL is 2.5 mm or more and such influence is significant when the elongation ΔL is 3.0 mm or more. Therefore, an elongation ΔL of less than 2.5 mm was rated as “B”, an elongation ΔL of 2.5 mm to less than 3.0 mm was rated as “C”, and an elongation ΔL of 3.0 mm or more was rated as “D”. In the manufacture of the gas sensor  10 , the projection length t of the rubber plug  60  protruding from the outer tube  46  is preferably about 1 mm and is aimed at the range of 1 mm plus/minus 0.5 mm (the range of a lower limit of 0.5 mm to an upper limit of 1.5 mm). 
     Table 3 shows results of Experimental Examples 1 to 10 in the case of an inside diameter φB of 10.8 mm. Experimental Example 1 corresponds to a comparative example and Experimental Example 2 to 10 correspond to examples. In the leakage test, Experimental Example 1 to 8 (an inside diameter variance of 0% or 0.1% to 5%) had no leaks and were rated as “B” and Experimental Examples 9 and 10 (an inside diameter variance of 6% or 7%) had slight leaks and were rated as “C”. In results of the leakage test, the symbol “B” denotes the absence of leaks as described above and the symbol “C” denotes the presence of slight leaks not problematic in practical use. For the elongation ΔL of the whole rubber plug  60 , Experimental Example 1 (an inside diameter variance of 0%) exhibited 2.5 mm and was rated as “C” and Experimental Examples 2 to 10 (an inside diameter variance of 0.1% to 7%) exhibited less than 2.5 mm and were rated as “B”. Therefore, for comprehensive evaluation in the case of an inside diameter φB of 10.8 mm, Experimental Examples 2 to 8 (an inside diameter variance of 0.1% to 5%) were rated as “A” and Experimental Examples 1, 9, and 10 were rated as “B”. For comprehensive evaluation, the symbol “A” denotes that both the leakage test and the elongation ΔL are rated as “B”, the symbol “B” denotes that one of the leakage test and the elongation ΔL is rated as “B” and the other is rated as “C”, and the symbol “D” denotes that one of the leakage test and the elongation ΔL is rated as “D”. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 INSIDE DIAMETER 
                   
                 LEAKAGE 
                 ELONGATION 
                 COMPREHENSIVE 
               
               
                 VARIANCE 
                 REFERENCE INSIDE DIAMETER φB: 10.8 mm 
                 TEST 
                 ΔL 
                 EVALUATION 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0% 
                 EXPERIMENTAL EXAMPLE 1 
                 φA: 10.8 mm 
                 B 
                 2.5 mm(Δ) 
                 B 
               
               
                 0.1%     
                 EXPERIMENTAL EXAMPLE 2 
                 φA: 10.81 mm 
                 B 
                 2.0 mm(∘) 
                 A 
               
               
                 0.5%     
                 EXPERIMENTAL EXAMPLE 3 
                 φA: 10.85 mm 
                 B 
                 1.9 mm(∘) 
                 A 
               
               
                 1% 
                 EXPERIMENTAL EXAMPLE 4 
                 φA: 10.91 mm 
                 B 
                 1.8 mm(∘) 
                 A 
               
               
                 2% 
                 EXPERIMENTAL EXAMPLE 5 
                 φA: 11.02 mm 
                 B 
                 1.6 mm(∘) 
                 A 
               
               
                 3% 
                 EXPERIMENTAL EXAMPLE 6 
                 φA: 11.12 mm 
                 B 
                 1.4 mm(∘) 
                 A 
               
               
                 4% 
                 EXPERIMENTAL EXAMPLE 7 
                 φA: 11.23 mm 
                 B 
                 1.3 mm(∘) 
                 A 
               
               
                 5% 
                 EXPERIMENTAL EXAMPLE 8 
                 φA: 11.34 mm 
                 B 
                 1.1 mm(∘) 
                 A 
               
               
                 6% 
                 EXPERIMENTAL EXAMPLE 9 
                 φA: 11.45 mm 
                 C 
                 1.0 mm(∘) 
                 B 
               
               
                 7% 
                 EXPERIMENTAL EXAMPLE 10 
                 φA: 11.56 mm 
                 C 
                 0.8 mm(∘) 
                 B 
               
               
                   
               
            
           
         
       
     
     Table 4 shows results of Experimental Examples 11 to 20 in the case of an inside diameter φB of 10.4 mm. Experimental Example 11 corresponds to a comparative example and Experimental Examples 12 to 20 correspond to examples. In the leakage test, Experimental Examples 11 to 19 (an inside diameter variance of 0% or 0.1% to 6%) had no leaks and were rated as “B” and Experimental Example 20 (an inside diameter variance of 7%) had slight leaks and were rated as “C”. For the elongation ΔL of the whole rubber plug  60 , Experimental Example 11 (an inside diameter variance of 0%) exhibited 3.5 mm and was rated as “D”, Experimental Example 12 (an inside diameter variance of 0.1%) exhibited 2.5 mm and was rated as “C”, and Experimental Examples 13 to 20 (an inside diameter variance of 0.5% to 7%) exhibited less than 2.5 mm and were rated as “B”. Therefore, for comprehensive evaluation in the case of an inside diameter φB of 10.4 mm, Experimental Examples 13 to 19 (an inside diameter variance of 0.5% to 6%) were rated as “A”, Experimental Examples 12 and 20 (an inside diameter variance of 0.1% or 7%) were rated as “B”, and Experimental Example 11 (an inside diameter variance of 0%) was rated as “D”. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 INSIDE DIAMETER 
                   
                 LEAKAGE 
                 ELONGATION 
                 COMPREHENSIVE 
               
               
                 VARIANCE 
                 REFERENCE INSIDE DIAMETER φB:10.4 mm 
                 TEST 
                 ΔL 
                 EVALUATION 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0% 
                 EXPERIMENTAL EXAMPLE 11 
                 φA: 10.4 mm 
                 B 
                 3.5 mm(x) 
                 D 
               
               
                 0.1%     
                 EXPERIMENTAL EXAMPLE 12 
                 φA: 10.41 mm 
                 B 
                 2.5 mm(Δ) 
                 B 
               
               
                 0.5%     
                 EXPERIMENTAL EXAMPLE 13 
                 φA: 10.45 mm 
                 B 
                 2.2 mm(∘) 
                 A 
               
               
                 1% 
                 EXPERIMENTAL EXAMPLE 14 
                 φA: 10.50 mm 
                 B 
                 2.0 mm(∘) 
                 A 
               
               
                 2% 
                 EXPERIMENTAL EXAMPLE 15 
                 φA: 10.61 mm 
                 B 
                 1.8 mm(∘) 
                 A 
               
               
                 3% 
                 EXPERIMENTAL EXAMPLE 16 
                 φA: 10.71 mm 
                 B 
                 1.6 mm(∘) 
                 A 
               
               
                 4% 
                 EXPERIMENTAL EXAMPLE 17 
                 φA: 10.82 mm 
                 B 
                 1.4 mm(∘) 
                 A 
               
               
                 5% 
                 EXPERIMENTAL EXAMPLE 18 
                 φA: 10.92 mm 
                 B 
                 1.2 mm(∘) 
                 A 
               
               
                 6% 
                 EXPERIMENTAL EXAMPLE 19 
                 φA: 11.02 mm 
                 B 
                 1.1 mm(∘) 
                 A 
               
               
                 7% 
                 EXPERIMENTAL EXAMPLE 20 
                 φA: 11.13 mm 
                 C 
                 1.0 mm(∘) 
                 B 
               
               
                   
               
            
           
         
       
     
     Table 5 shows results of Experimental Examples 21 to 30 in the case of an inside diameter φB of 10.2 mm. Experimental Example 21 corresponds to a comparative example and Experimental Examples 22 to 30 correspond to examples. In the leakage test, all of Experimental Examples 21 to 30 (an inside diameter variance of 0% or 0.1% to 7%) had no leaks and were rated as “B”. For the elongation ΔL of the whole rubber plug  60 , Experimental Example 21 (an inside diameter variance of 0%) exhibited 4.0 mm and was rated as “D”, Experimental Examples 22 and 23 (an inside diameter variance of 0.1% or 0.5%) exhibited 2.5 mm to less than 3.0 mm and were rated as “C”, and Experimental Examples 24 to 30 (an inside diameter variance of 1% to 7%) exhibited less than 2.5 mm and were rated as “B”. Therefore, for comprehensive evaluation in the case of an inside diameter φB of 10.2 mm, Experimental Examples 24 to 30 (an inside diameter variance of 1% to 7%) were rated as “A”, Experimental Examples 22 and 23 (an inside diameter variance of 0.1% or 0.5%) were rated as “B”, and Experimental Example 21 was rated as “D”. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 INSIDE DIAMETER 
                   
                 LEAKAGE 
                 ELONGATION 
                 COMPREHENSIVE 
               
               
                 VARIANCE 
                 REFERENCE INSIDE DIAMETER φB: 10.2 mm 
                 TEST 
                 ΔL 
                 EVALUATION 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0% 
                 EXPERIMENTAL EXAMPLE 21 
                 φA: 10.2 mm 
                 B 
                 4.0 mm(x) 
                 D 
               
               
                 0.1%     
                 EXPERIMENTAL EXAMPLE 22 
                 φA: 10.21 mm 
                 B 
                 2.8 mm(∘) 
                 B 
               
               
                 0.5%     
                 EXPERIMENTAL EXAMPLE 23 
                 φA: 10.25 mm 
                 B 
                 2.6 mm(∘) 
                 B 
               
               
                 1% 
                 EXPERIMENTAL EXAMPLE 24 
                 φA: 10.30 mm 
                 B 
                 2.4 mm(∘) 
                 A 
               
               
                 2% 
                 EXPERIMENTAL EXAMPLE 25 
                 φA: 10.40 mm 
                 B 
                 2.0 mm(∘) 
                 A 
               
               
                 3% 
                 EXPERIMENTAL EXAMPLE 26 
                 φA: 10.51 mm 
                 B 
                 1.9 mm(∘) 
                 A 
               
               
                 4% 
                 EXPERIMENTAL EXAMPLE 27 
                 φA: 10.61 mm 
                 B 
                 1.8 mm(∘) 
                 A 
               
               
                 5% 
                 EXPERIMENTAL EXAMPLE 28 
                 φA: 10.71 mm 
                 B 
                 1.5 mm(∘) 
                 A 
               
               
                 6% 
                 EXPERIMENTAL EXAMPLE 29 
                 φA: 11.81 mm 
                 B 
                 1.3 mm(∘) 
                 A 
               
               
                 7% 
                 EXPERIMENTAL EXAMPLE 30 
                 φA: 11.91 mm 
                 B 
                 1.1 mm(∘) 
                 A 
               
               
                   
               
            
           
         
       
     
     The results of Evaluation Test 1 indicate the following. Comparative examples (Experimental Examples 1, 11, and 21) with an inside diameter variance of 0% were rated as “B” in the case of an inside diameter φB of 10.8 mm or were rated as “D” in the case of an inside diameter φB of 10.4 mm or 10.2 mm because the elongation ΔL of the whole rubber plug  60  was large. Therefore, it is conceivable that an inside diameter variance of 0% adversely affects electrical connectivity with relatively high probability. On the other hand, examples (Experimental Examples 2 to 10, 12 to 20, and 22 to 30) with an inside diameter variance of 0.1% to 7% were all rated as “A” or “B”. Therefore, in these examples, leaks and the reduction of electrical connectivity can be well prevented. In particular, examples (Experimental Examples 4 to 8, 14 to 18, and 24 to 28) with an inside diameter variance of 1% to 5% were all rated as “A”. That is, in the examples with an inside diameter variance of 1% to 5%, leaks and the reduction of electrical connectivity can be further well prevented regardless of the value of the inside diameter φB. 
     The above results of the preliminary test and Evaluation Test 1 indicate that for the inside diameter φB, the swaging ratio is preferably within the range of 8% to 14% (the range of 10.2 mm to 10.8 mm) and more preferably within the range of 12% to 14% (the range of 10.2 mm to 10.4 mm). The inside diameter variance determined by dividing the difference between the inside diameter φA and the inside diameter φB by the inside diameter φB is preferably within the range of 1% to 5%. Therefore, as an example of the size of a swaged section in an example, it is conceivable that the inside diameter φB is adjusted to 10.4 mm within the range of 10.2 mm and 10.4 mm and the inside diameter variance is adjusted to 2% in the range of 1% to 5%. That is, the inside diameter φB was adjusted to 10.4 mm, the inside diameter variance was adjusted to 2% with respect to an inside diameter φB of 10.4 mm, and the inside diameter φA was adjusted to 10.6 mm. Furthermore, the swaging width LA and the swaging width LB were both adjusted to 2.5 mm and the swaging distance LS was adjusted to 3.5 mm. 
     Evaluation Test 2 
     Thirty gas sensors  10  including swaged sections having a size determined as described above were manufactured by a method in which a the swaged section B begins to be swaged prior to the swaged section A as described in the above embodiment, followed by measuring the projection length t of each rubber plug  60 . Table 6 shows the measurement results. The projection length t ranged from 0.84 mm at minimum to 1.19 mm at maximum and was 1.04 mm on average. The projection length t was within the range of 1.0±0.5 mm, which is a target value as described above. This result was better than a result obtained by allowing the swaged sections A and B to begin to be simultaneously swaged. Therefore, in the gas sensors  10  manufactured by the method described in the above embodiment, the effect of preventing leaks and the effect of preventing the reduction of electrical connectivity are high. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                 PROJECTION 
               
               
                   
                 No. 
                 LENGTH t(mm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 1 
                 1.19 
               
               
                   
                 2 
                 0.84 
               
               
                   
                 3 
                 1.08 
               
               
                   
                 4 
                 0.91 
               
               
                   
                 5 
                 0.89 
               
               
                   
                 6 
                 0.99 
               
               
                   
                 7 
                 1.12 
               
               
                   
                 8 
                 1.00 
               
               
                   
                 9 
                 1.05 
               
               
                   
                 10 
                 1.10 
               
               
                   
                 11 
                 1.05 
               
               
                   
                 12 
                 1.13 
               
               
                   
                 13 
                 1.06 
               
               
                   
                 14 
                 0.98 
               
               
                   
                 15 
                 1.02 
               
               
                   
                 16 
                 1.14 
               
               
                   
                 17 
                 0.89 
               
               
                   
                 18 
                 0.92 
               
               
                   
                 19 
                 1.03 
               
               
                   
                 20 
                 1.11 
               
               
                   
                 21 
                 1.06 
               
               
                   
                 22 
                 1.16 
               
               
                   
                 23 
                 1.16 
               
               
                   
                 24 
                 1.10 
               
               
                   
                 25 
                 1.05 
               
               
                   
                 26 
                 1.00 
               
               
                   
                 27 
                 1.12 
               
               
                   
                 28 
                 0.98 
               
               
                   
                 29 
                 1.10 
               
               
                   
                 30 
                 1.02 
               
               
                   
                 MAX 
                 1.19 
               
               
                   
                 MIN 
                 0.84 
               
               
                   
                 AVE 
                 1.04