Patent Publication Number: US-2021172902-A1

Title: Metal terminal

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-222645 filed on Dec. 10, 2019, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a metal terminal, for example, a metal terminal that is suitable for use in a gas sensor. 
     Description of the Related Art 
     The invention described in Japanese Laid-Open Patent Publication No. 2018-132407 has the object of providing a gas sensor, which improves productivity by inserting, into a separator, a terminal fitting to which a lead wire has been connected beforehand, together with preventing detachment or pulling off of the terminal fitting toward a rear end side. 
     In order to achieve such an object, the terminal fitting of Japanese Laid-Open Patent Publication No. 2018-132407 includes a main body portion ( 21   a ), a locking portion ( 21   f ) that bends in a radial direction D along a surface S perpendicular to an axial direction O, and a collar portion ( 21   d ) having a first distal end facing surface ( 301 ). The separator further includes a shelf portion ( 166   a ) communicating with an insertion hole ( 166   h ) and having a first rear end facing surface ( 302 ), and a second distal end facing surface ( 303 ) communicating with the insertion hole. The locking portion protrudes toward an outer side in the radial direction more so than the insertion hole on the distal end side of the second distal end facing surface. A second rear end facing surface ( 304 ) of the locking portion abuts against the second distal end facing surface. The first distal end facing surface of the collar portion abuts against the first rear end facing surface of the shelf portion, and thereby prevents detachment of the terminal fitting toward the distal end or rear end. 
     The invention described in Japanese Laid-Open Patent Publication No. 2019-012010 provides a method for manufacturing a gas sensor in which damage or deformation of oppositely disposed terminal fittings is suppressed when the terminal fittings are attached to a separator. 
     In the above-described manufacturing method, a first jig ( 300 ) is used in which a planar surface portion ( 312 ) having a predetermined thickness and arranged at a position corresponding to facing surfaces of contact portions is erected from a bottom surface ( 300   b ) of an accommodation space ( 300   h ). The above-described manufacturing method includes a separator accommodating step, a terminal fitting retaining step, and a jig detachment step. In the separator accommodating step, the separator is accommodated in the first jig, and the planar surface portion is inserted into an insertion hole of the separator at a position corresponding to the facing surfaces. In the terminal fitting retaining step, the terminal fittings are inserted respectively into the insertion hole from a rear end side of the separator, in a manner so that the planar surface portion is interposed between the contact portions. In the jig detachment step, the first jig is detached from the separator. 
     The invention described in Japanese Laid-Open Patent Publication No. 2019-035646 has the object of improving an insulating property in the interior of a sensor. In order to achieve such an object, a metal terminal for use in a sensor is equipped with a terminal contact portion, a signal line connecting portion, and a closure portion. The closure portion is arranged between the terminal contact portion and the signal line connecting portion, and partially closes a through hole of a separator in a manner so that a core wire can be retained in the interior thereof. 
     SUMMARY OF THE INVENTION 
     Generally, in an automobile exhaust gas sensor, a metal terminal such as those described in the aforementioned prior art documents is used in order to provide an electrical contact between a gas concentration detection element and a lead wire. 
     The metal terminal includes a retaining member (for example, the crimp terminal part  211   c  of Japanese Laid-Open Patent Publication No. 2019-012010) that crimps and retains an inserted lead wire, and a positioning member (for example, the detachment preventing member  211   d  of Japanese Laid-Open Patent Publication No. 2019-012010) that locks the metal terminal inside a ceramic separator and fixes the position thereof. 
     However, due to vibrations and the like of an automobile, repetitive loads such as tension, compression, bending, and shearing or the like may be applied between the positioning member and the lead wire retaining member of the metal terminal, and there is a risk of damage occurring to the metal terminal. 
     An object of the present invention is to provide a metal terminal that can prevent damage from occurring to the metal terminal, even when the aforementioned various repetitive loads are applied between the positioning member and the lead wire retaining member of the metal terminal, or when put to use under a usage environment in which vibrations are intense, and that is capable of increasing the commercial value of a gas sensor. 
     A metal terminal according to one aspect of the present invention is a metal terminal, which is installed in a gas sensor including a sensor element and a ceramic housing configured to retain a rear end portion of the sensor element, the metal terminal being configured to electrically connect the sensor element and a lead wire, and comprising an element contacting portion disposed at one end of the metal terminal, and configured to be placed in contact with the sensor element, a lead wire retaining member disposed at another end of the metal terminal, and configured to crimp and retain the lead wire, a positioning member disposed between the one end and the another end, and extending in a direction intersecting one direction, the positioning member being configured to position the metal terminal on the ceramic housing, and a guide member provided integrally with the positioning member at a site between the positioning member and the lead wire retaining member. 
     According to the present invention, it is possible to prevent damage from occurring to the metal terminal, even when the aforementioned various repetitive loads are applied between the positioning member and the lead wire retaining member of the metal terminal, or when put to use under a usage environment in which vibrations are intense, and increase the commercial value of the gas sensor. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing an example of a gas sensor to which there is attached a metal terminal according to the present embodiment; 
         FIG. 2  is a schematic cross-sectional view schematically showing an example of the configuration of a sensor element; 
         FIG. 3  is a perspective view showing the metal terminal according to the present embodiment; 
         FIG. 4A  is a side view showing an example in which a rectangular guide member is disposed between a positioning member and a lead wire retaining member of the metal terminal; 
         FIG. 4B  is a side view showing an example in which a triangular guide member is provided; 
         FIG. 4C  is a side view showing an example in which a trapezoidal guide member is provided; 
         FIG. 5  is a first table (Table 1) in which there are shown evaluation results of experimental examples in which a conduction failure (contact failure) was confirmed in relation to Exemplary Embodiments 1 to 13; and 
         FIG. 6  is a second table (Table 2) in which there are shown evaluation results of experimental examples in which a conduction failure (contact failure) was confirmed in relation to Exemplary Embodiments 14 to 24 and Comparative Example 1. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of a metal terminal according to the present invention will be presented and described in detail below with reference to the accompanying drawings. 
     Initially, a description will be given with reference to  FIGS. 1 and 2  concerning a gas sensor  10  to which a metal terminal  18  according to the embodiment is applied. 
     As shown in  FIG. 1 , the gas sensor  10  includes a sensor element  12 . The sensor element  12  is of an elongated cuboid shape, the longitudinal direction of the sensor element  12  (the horizontal direction as shown in  FIG. 2 ) is defined as a front-rear direction, and the thickness direction of the sensor element  12  (the vertical direction as shown in  FIG. 2 ) is defined as an up-down direction. Further, the widthwise direction of the sensor element  12  (the direction perpendicular to the front-rear direction and the up-down direction) is defined as a left-right direction. 
     The gas sensor  10  includes the sensor element  12 , a protective cover  14  for protecting a front end side of the sensor element  12 , and a sensor assembly  20  including a ceramic housing  16 . The ceramic housing  16  retains a rear end portion of the sensor element  12 , and a metal terminal  18  electrically connected to the sensor element  12  is installed in the ceramic housing  16 . The ceramic housing  16  thus functions as a connector  24 . 
     As shown in the figure, the gas sensor  10  is attached to a pipe  26  such as the exhaust gas pipe of a vehicle, and is used in order to measure the concentration of a specified gas such as NOx or O 2  contained in the exhaust gas which serves as a gas to be measured. 
     The protective cover  14  includes a bottomed tubular inner side protective cover  14   a  that covers the front end of the sensor element  12 , and a bottomed tubular outer side protective cover  14   b  that covers the inner side protective cover  14   a.  The inner side protective cover  14   a  and the outer side protective cover  14   b  are formed with a plurality of holes therein for allowing the gas to be measured to flow into the interior of the protective cover  14 . A sensor element chamber  28  is formed as a space surrounded by the inner side protective cover  14   a,  and the front end of the sensor element  12  is arranged inside the sensor element chamber  28 . 
     The sensor assembly  20  has an element sealing body  30  for sealing and fixing the sensor element  12 , a nut  32  attached to the element sealing body  30 , and an outer cylinder  34 . The sensor assembly  20  is equipped with the connector  24  which is in contact with as well as being electrically connected to non-illustrated electrodes formed on surfaces (upper and lower surfaces) of the rear end of the sensor element  12 . 
     The element sealing body  30  includes a tubular main metal fitting  40 , and a tubular inner cylinder  42  coaxially welded and fixed to the main metal fitting  40 . The element sealing body  30  is equipped with ceramic supporters  44   a  to  44   c,  compressed powder bodies  46   a  and  46   b,  and a metal ring  48  enclosed in a through hole on the inner side of the main metal fitting  40  and the inner cylinder  42 . The sensor element  12  is positioned on the central axis of the element sealing body  30 , and penetrates through the element sealing body  30  in the front-rear direction. A reduced diameter portion  42   a  for pressing the compressed powder body  46   b  in a direction toward the central axis of the inner cylinder  42  is formed on the inner cylinder  42 . Further, a reduced diameter portion  42   b  for pressing the ceramic supporters  44   a  to  44   c  and the compressed powder bodies  46   a  and  46   b  in a frontward direction via the metal ring  48  is formed on the inner cylinder  42 . Due to the pressing force from the reduced diameter portions  42   a  and  42   b,  the compressed powder bodies  46   a  and  46   b  are compressed between the main metal fitting  40  and the inner cylinder  42  and the sensor element  12 . Consequently, the compressed powder bodies  46   a  and  46   b  provide sealing between the sensor element chamber  28  inside the protective cover  14  and a space  50  inside the outer cylinder  34 , and fix the sensor element  12  in place. 
     The nut  32  is fixed coaxially with the main metal fitting  40 , and a male threaded portion is formed on the outer circumferential surface thereof. The male threaded portion of the nut  32  is inserted into a fixing member  52  which is welded to the pipe  26  and is provided with a female threaded portion on the inner circumferential surface thereof. Consequently, the gas sensor  10  is fixed to the pipe  26 , in a state with the front end of the sensor element  12 , and a portion of the protective cover  14  of the gas sensor  10  protruding into the pipe  26 . 
     The outer cylinder  34  covers the periphery of the inner cylinder  42 , the sensor element  12 , and the connector  24 , and a plurality of lead wires  54 , which are connected to the connector  24 , are drawn out from the rear end. The lead wires  54  are electrically connected to respective electrodes (to be described later) of the sensor element  12  via the connector  24 . A gap between the outer cylinder  34  and the lead wires  54  is sealed by an elastic insulating member  56  constituted by a grommet or the like. The space  50  inside the outer cylinder  34  is filled with a reference gas (an atmospheric gas according to the present embodiment). The rear end of the sensor element  12  is arranged in the space  50 . 
     On the other hand, as shown in  FIG. 2 , the sensor element  12  is an element having a stacked body in which six layers, each of which is formed of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO 2 ), are stacked on each other. The six layers include a first substrate layer  60 , a second substrate layer  62 , a third substrate layer  64 , a first solid electrolyte layer  66 , a spacer layer  68 , and a second solid electrolyte layer  70 , which are stacked in this order from the lower side in the drawing. 
     The solid electrolyte that forms these six layers is dense and possesses airtightness. For example, after having performed a predetermined process and printing of circuit patterns on ceramic green sheets corresponding to the respective layers, the sensor element  12  is manufactured by stacking, and furthermore, firing and integrating the respective layers. 
     A gas introduction port  80 , a first diffusion control member  82 , a buffer space  84 , a second diffusion control member  86 , a first internal vacancy  88 , a third diffusion control member  90 , a second internal vacancy  92 , a fourth diffusion control member  94 , and a third internal vacancy  96  are formed adjacent to each other in this order, at one end of the sensor element  12  (the left side in  FIG. 2 ) between a lower surface of the second solid electrolyte layer  70  and an upper surface of the first solid electrolyte layer  66 . 
     The gas introduction port  80 , the buffer space  84 , the first internal vacancy  88 , the second internal vacancy  92 , and the third internal vacancy  96  are spaces in the interior of the sensor element  12 . Such spaces are provided by way of hollowing out the spacer layer  68 , and the upper portions thereof are defined by lower surface of the second solid electrolyte layer  70 , the lower portions thereof are defined by upper surface of the first solid electrolyte layer  66 , and the side portions thereof are defined by side surfaces of the spacer layer  68 . 
     The first diffusion control member  82 , the second diffusion control member  86 , and the third diffusion control member  90  are each provided as two horizontally elongated slits (in which the openings thereof have a longitudinal direction in a direction perpendicular to the drawing). Further, the fourth diffusion control member  94  is provided as a single horizontally elongated slit (in which the opening thereof has a longitudinal direction in a direction perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer  70 . The portion from the gas introduction port  80  to the third internal vacancy  96  is also referred to as a gas-to-be-measured flow through section. 
     Further, at a position more distant from one end side than the gas-to-be-measured flow through section, and between an upper surface of the third substrate layer  64  and a lower surface of the spacer layer  68 , a reference gas introduction space  98  is provided such that the side portions thereof are defined by the side surfaces of the first solid electrolyte layer  66 . For example, the atmospheric gas (the atmosphere inside the space  50  shown in  FIG. 1 ) is introduced into the reference gas introduction space  98  as a reference gas when measurement of the NOx concentration is performed. 
     An atmospheric gas introduction layer  100  is a layer made of a ceramic such as porous alumina, and exposed to the reference gas introduction space  98 . The reference gas is introduced into the atmospheric gas introduction layer  100  through the reference gas introduction space  98 . Further, the atmospheric gas introduction layer  100  is formed in a manner so as to cover a reference electrode  102 . The atmospheric gas introduction layer  100  introduces the reference gas inside the reference gas introduction space  98  to the reference electrode  102 , while imparting a predetermined diffusion resistance to the reference gas. Further, the atmospheric gas introduction layer  100  is formed in a manner so as to be exposed to the reference gas introduction space  98  only at a position further to the rear end side (the right side shown in  FIG. 2 ) of the sensor element  12  than the reference electrode  102 . Stated otherwise, the reference gas introduction space  98  is not formed up to a location directly above the reference electrode  102 . However, the reference electrode  102  may also be formed directly below the reference gas introduction space  98  shown in  FIG. 2 . 
     The reference electrode  102  is formed so as to be sandwiched between the upper surface of the third substrate layer  64  and the first solid electrolyte layer  66 , and as described above, the atmospheric gas introduction layer  100  which is connected to the reference gas introduction space  98  is disposed around the periphery of the reference electrode  102 . Moreover, the reference electrode  102  is formed directly on the upper surface of the third substrate layer  64 , and a portion thereof other than the portion in contact with the upper surface of the third substrate layer  64  is covered by the atmospheric gas introduction layer  100 . Further, as will be discussed later, it is possible to measure the oxygen concentration (oxygen partial pressure) inside the first internal vacancy  88 , inside the second internal vacancy  92 , and inside the third internal vacancy  96 , by using the reference electrode  102 . The reference electrode  102  is formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO 2 ). 
     In the gas-to-be-measured flow through section, the gas introduction port  80  is a site that opens to the external space, and the gas to be measured is drawn into the sensor element  12  from the external space through the gas introduction port  80 . The first diffusion control member  82  is a site that imparts a predetermined diffusion resistance to the gas to be measured which is drawn in from the gas introduction port  80 . The buffer space  84  is a space provided in order to guide the gas to be measured that is introduced from the first diffusion control member  82  to the second diffusion control member  86 . The second diffusion control member  86  is a site that imparts a predetermined diffusion resistance to the gas to be measured which is drawn into the first internal vacancy  88  from the buffer space  84 . The operation, in which the gas to be measured is introduced from the exterior of the sensor element  12  to the interior of the first internal vacancy  88 , is carried out in the following manner. More specifically, the gas to be measured, which is suddenly drawn into the sensor element  12  from the gas introduction port  80  due to a pressure fluctuation of the gas to be measured in the external space, is not directly introduced into the first internal vacancy  88 . After a fluctuation in the concentration of the gas to be measured is canceled through the first diffusion control member  82 , the buffer space  84 , and the second diffusion control member  86 , the gas is introduced into the first internal vacancy  88 . Consequently, the fluctuation in the concentration of the gas to be measured that is introduced into the first internal vacancy  88  becomes almost negligible. The aforementioned fluctuation in pressure of the gas to be measured in the external space is a pulsation of the exhaust pressure in the case that the gas to be measured is an exhaust gas of an automobile. The first internal vacancy  88  is provided as a space for adjusting the oxygen partial pressure within the gas to be measured that is introduced through the second diffusion control member  86 . Such oxygen partial pressure is adjusted by operation of a main pump cell  110  described later. 
     The main pump cell  110  is an electrochemical pump cell, which is constituted by an interior side pump electrode  112 , an exterior side pump electrode  114 , and the second solid electrolyte layer  70  which is sandwiched between the two pump electrodes. The interior side pump electrode  112  is provided on an inner surface of the first internal vacancy  88 . The exterior side pump electrode  114  is provided in a region, corresponding to the interior side pump electrode  112 , on an upper surface of the second solid electrolyte layer  70  so as to be exposed to the external space (the sensor element chamber  28  of  FIG. 1 ). 
     The interior side pump electrode  112  spans over the upper and lower solid electrolyte layers (the second solid electrolyte layer  70  and the first solid electrolyte layer  66 ) that define the first internal vacancy  88 , and the spacer layer  68  that serves as the side walls of the first internal vacancy  88 . More specifically, a ceiling electrode portion  112   a  of the interior side pump electrode  112  is formed on the lower surface of the second solid electrolyte layer  70  that serves as a ceiling surface of the first internal vacancy  88 . Further, a bottom electrode portion  112   b  is directly formed on the upper surface of the first solid electrolyte layer  66  that serves as a bottom surface of the first internal vacancy  88 . In addition, side electrode portions (not shown) are formed so as to connect the ceiling electrode portion  112   a  and the bottom electrode portion  112   b.  More specifically, the side electrode portions are formed on side wall surfaces (inner surfaces) of the spacer layer  68  constituting both side wall portions of the first internal vacancy  88 , and the interior side pump electrode  112  is formed to have a structure like a tunnel at a site where the side electrode portions are disposed. The interior side pump electrode  112  and the exterior side pump electrode  114  are formed as porous cermet electrodes (for example, cermet electrodes of ZrO 2  and Pt containing 1% of Au). Moreover, the interior side pump electrode  112  in contact with the gas to be measured is formed using a material having a weakened reduction ability with respect to the NOx component within the gas to be measured. 
     The main pump cell  110  applies a desired pump voltage Vp 0  between the interior side pump electrode  112  and the exterior side pump electrode  114 , and thereby distributes a pump current Ip 0  in a positive direction or a negative direction between the interior side pump electrode  112  and the exterior side pump electrode  114 . Consequently, the oxygen inside the first internal vacancy  88  can be pumped out into the external space, or alternatively, the oxygen can be pumped in from the external space into the first internal vacancy  88 . 
     Further, an oxygen partial pressure detecting sensor cell  120  for main pump control is constituted by the interior side pump electrode  112 , the second solid electrolyte layer  70 , the spacer layer  68 , the first solid electrolyte layer  66 , and the reference electrode  102 . Such an electrochemical sensor cell detects the oxygen concentration (oxygen partial pressure) within the atmosphere in the first internal vacancy  88 . 
     By measuring an electromagnetic force V 0  in the oxygen partial pressure detecting sensor cell  120  for main pump control, it becomes possible to comprehend and determine the oxygen concentration (oxygen partial pressure) inside the first internal vacancy  88 . Furthermore, the pump current 
     Ip 0  is controlled by feedback-controlling the pump voltage Vp 0  of a variable power supply  122  in a manner so that the electromotive force V 0  becomes constant. Consequently, the oxygen concentration inside the first internal vacancy  88  can be maintained at a predetermined constant value. 
     The third diffusion control member  90  is a site that imparts a predetermined diffusion resistance to the gas to be measured, the oxygen concentration (oxygen partial pressure) of which is controlled by operation of the main pump cell  110  in the first internal vacancy  88 , and guides the gas to be measured into the second internal vacancy  92 . 
     The second internal vacancy  92  is provided as a space for further carrying out adjustment of the oxygen partial pressure by an auxiliary pump cell  124 , on the gas to be measured which is introduced through the third diffusion control member  90 , after the oxygen concentration (oxygen partial pressure) thereof has been adjusted beforehand in the first internal vacancy  88 . In accordance with this feature, the oxygen concentration inside the second internal vacancy  92  can be kept constant with high accuracy, and therefore, in the gas sensor  10 , it becomes possible to measure the NOx concentration with high accuracy. 
     The above-described auxiliary pump cell  124  is an auxiliary electrochemical pump cell, which is constituted by an auxiliary pump electrode  126  provided on an inner surface of the second internal vacancy  92 , the exterior side pump electrode  114 , and the second solid electrolyte layer  70 . The exterior side pump electrode  114  can be any other suitable electrode formed on the outer side of the sensor element  12 . 
     The auxiliary pump electrode  126  is arranged inside the second internal vacancy  92 , and has a tunnel-like structure similar to that of the interior side pump electrode  112  provided inside the first internal vacancy  88 . Stated otherwise, a ceiling electrode portion  126   a  is formed with respect to the second solid electrolyte layer  70  that serves as a ceiling surface of the second internal vacancy  92 . Further, a bottom electrode portion  126   b  is directly formed on the upper surface of the first solid electrolyte layer  66  that serves as a bottom surface of the second internal vacancy  92 . In addition, side electrode portions (not shown) connecting the ceiling electrode portion  126   a  and the bottom electrode portion  126   b  are formed respectively on both wall surfaces of the spacer layer  68  that serve as the side walls of the second internal vacancy  92 , whereby a tunnel-like structure is formed. Moreover, in the same manner as the interior side pump electrode  112 , the auxiliary pump electrode  126  is also formed using a material having a weakened reduction ability with respect to the NOx component within the gas to be measured. 
     The auxiliary pump cell  124  applies a desired voltage Vp 1  between the auxiliary pump electrode  126  and the exterior side pump electrode  114 . Consequently, the oxygen within the atmosphere inside the second internal vacancy  92  can be pumped out into the external space, or alternatively, the oxygen can be pumped in from the external space into the second internal vacancy  92 . 
     Further, an electrochemical sensor cell is constituted by the auxiliary pump electrode  126 , the reference electrode  102 , the second solid electrolyte layer  70 , the spacer layer  68 , and the first solid electrolyte layer  66 . An oxygen partial pressure detecting sensor cell  130  for auxiliary pump control controls the oxygen partial pressure within the atmosphere inside the second internal vacancy  92 . Moreover, the auxiliary pump cell  124  carries out pumping by a variable power supply  132 , the voltage of which is controlled based on an electromotive force V 1  detected by the oxygen partial pressure detecting sensor cell  130  for auxiliary pump control. Consequently, the oxygen partial pressure within the atmosphere inside the second internal vacancy  92  is controlled so as to become a low partial pressure that does not substantially influence the measurement of NOx. 
     In addition, a pump current Ip 1  thereof is used to control the electromotive force VO of the oxygen partial pressure detecting sensor cell  120  for main pump control. More specifically, the pump current Ip 1  is input as a control signal to the oxygen partial pressure detecting sensor cell  120  for main pump control, whereby the electromotive force VO thereof is controlled. Consequently, the gradient of the oxygen partial pressure within the gas to be measured, which is introduced from the third diffusion control member  90  into the second internal vacancy  92 , is controlled so as to always remain constant. When the gas sensor  10  is used as a NOx sensor, by the actions of the main pump cell  110  and the auxiliary pump cell  124 , the oxygen concentration in the second internal vacancy  92  is maintained at a constant value on the order of 0.001 ppm. 
     The fourth diffusion control member  94  is a site that imparts a predetermined diffusion resistance to the gas to be measured, the oxygen concentration (oxygen partial pressure) of which is controlled by operation of the auxiliary pump cell  124  in the second internal vacancy  92 , and guides the gas to be measured into the third internal vacancy  96 . The fourth diffusion control member  94  fulfills a role of limiting the amount of NOx that flows into the third internal vacancy  96 . 
     The third internal vacancy  96  is provided as a space for performing a process in relation to measurement of the nitrogen oxide (NOx) concentration within the gas to be measured, on the gas to be measured which is introduced through the fourth diffusion control member  94 , after the oxygen concentration (oxygen partial pressure) thereof has been adjusted beforehand in the second internal vacancy  92 . Measurement of the NOx concentration is primarily performed by operation of a measurement pump cell  140  in the third internal vacancy  96 . 
     The measurement pump cell  140  measures the NOx concentration in the gas to be measured in the interior of the third internal vacancy  96 . The measurement pump cell  140  is an electrochemical pump cell constituted by a measurement electrode  134 , the exterior side pump electrode  114 , the second solid electrolyte layer  70 , the spacer layer  68 , and the first solid electrolyte layer  66 . The measurement electrode  134  is provided directly on the upper surface of the first solid electrolyte layer  66  facing the third internal vacancy  96 . The measurement electrode  134 , for example, is a porous cermet electrode. The measurement electrode  134  also functions as an NOx reduction catalyst for reducing NOx existing within the atmosphere inside the third internal vacancy  96 . 
     In the measurement pump cell  140 , it is possible to pump out oxygen that is generated by the decomposition of nitrogen oxide within the atmosphere around the periphery of the measurement electrode  134 , and to detect the generated amount of oxygen as a pump current Ip 2 . 
     Further, in order to detect the oxygen partial pressure around the periphery of the measurement electrode  134 , an electrochemical sensor cell, and more specifically, an oxygen partial pressure detecting sensor cell  142  for measurement pump control, is constituted by the first solid electrolyte layer  66 , the measurement electrode  134 , and the reference electrode  102 . A variable power supply  144  is controlled based on an electromotive force V 2  detected by the oxygen partial pressure detecting sensor cell  142  for measurement pump control. 
     The gas to be measured which is guided into the second internal vacancy  92  reaches the measurement electrode  134  of the third internal vacancy  96  through the fourth diffusion control member  94  under a condition in which the oxygen partial pressure is controlled. Nitrogen oxide existing within the gas to be measured around the periphery of the measurement electrode  134  is reduced (2NO→N 2 +O 2 ) to thereby generate oxygen. Then, the generated oxygen is subjected to pumping by the measurement pump cell  140 . At this time, a voltage Vp 2  of the variable power supply  144  is controlled in a manner so that the electromotive force V 2  detected by the oxygen partial pressure detecting sensor cell  142  for measurement pump control becomes constant. The amount of oxygen generated around the periphery of the measurement electrode  134  is proportional to the nitrogen oxide concentration within the gas to be measured. Accordingly, the nitrogen oxide concentration within the gas to be measured can be calculated using the pump current Ip 2  of the measurement pump cell  140 . 
     Further, an electrochemical sensor cell  146  is constituted by the second solid electrolyte layer  70 , the spacer layer  68 , the first solid electrolyte layer  66 , the third substrate layer  64 , the exterior side pump electrode  114 , and the reference electrode  102 . In accordance with an electromotive force Vref obtained by the sensor cell  146 , it is possible to detect the oxygen partial pressure within the gas to be measured existing externally of the sensor. 
     Furthermore, an electrochemical reference gas adjusting pump cell  150  is constituted by the second solid electrolyte layer  70 , the spacer layer  68 , the first solid electrolyte layer  66 , the third substrate layer  64 , the exterior side pump electrode  114 , and the reference electrode  102 . The reference gas adjusting pump cell  150  carries out pumping by distributing a control current Ip 3  due to a voltage Vp 3  applied by a variable power supply  152 , which is connected between the exterior side pump electrode  114  and the reference electrode  102 . Consequently, the reference gas adjusting pump cell  150  draws in oxygen from the space around the periphery of the exterior side pump electrode  114  (the sensor element chamber  28  in  FIG. 1 ) into the space around the periphery of the reference electrode  102  (the atmospheric gas introduction layer  100 ). The voltage Vp 3  of the variable power supply  152  is predetermined as a DC voltage, in a manner so that the control current Ip 3  becomes a predetermined value (a DC current of a constant value). 
     In the gas sensor  10  having such a configuration, the main pump cell  110  and the auxiliary pump cell  124  are placed in operation. Consequently, the gas to be measured, in which the oxygen partial pressure is always maintained at a constant low value (a value that does not substantially exert an influence on the measurement of NOx), is imparted to the measurement pump cell  140 . Accordingly, the aforementioned pump current Ip 2  is distributed by pumping out the oxygen generated by the reduction of NOx from the measurement pump cell  140 , substantially proportionally to the concentration of NOx within the gas to be measured. As a result, the NOx concentration in the gas to be measured can be known based on the pump current Ip 2 . 
     Furthermore, in order to increase the oxygen ion conductivity of the solid electrolyte, the sensor element  12  is equipped with a heater unit  160  which plays a role in adjusting the temperature for heating and maintaining the temperature of the sensor element  12 . The heater unit  160  comprises a heater connector electrode  162 , a heater  164 , a through hole  166 , a heater insulating layer  168 , a pressure dissipation hole  170 , and a lead wire  172 . 
     The heater connector electrode  162  is formed so as to be in contact with a lower surface of the first substrate layer  60 . By the heater connector electrode  162  being connected to an external power supply, power can be supplied from the exterior to the heater unit  160 . 
     The heater  164  is an electric resistor formed in a state of being sandwiched from above and below between the second substrate layer  62  and the third substrate layer  64 . The heater  164  is connected to the heater connector electrode  162  via the lead wire  172  and the through hole  166 . The heater  164  generates heat by being supplied with electrical power from the exterior through the heater connector electrode  162 , and heats and maintains the temperature of the solid electrolyte that forms the sensor element  12 . 
     Further, the heater  164  is embedded over the entire area from the first internal vacancy  88  to the third internal vacancy  96 , whereby the entire sensor element  12  can be adjusted to a temperature at which the solid electrolyte is activated. 
     The heater insulating layer  168  is an insulating layer formed on upper and lower surfaces of the heater  164  and made of porous alumina formed of an insulator of alumina or the like. The heater insulating layer  168  is formed with the aim of obtaining electrical insulation between the second substrate layer  62  and the heater  164 , as well as electrical insulation between the third substrate layer  64  and the heater  164 . 
     The pressure dissipation hole  170  is a site that is provided so as to penetrate through the third substrate layer  64  and communicate with the reference gas introduction space  98 , and is formed with the aim of alleviating an increase in internal pressure accompanying a rise in the temperature inside the heater insulating layer  168 . 
     It should be noted that the variable power supplies  122 ,  144 ,  132 , and  152 , etc., shown in  FIG. 2  are actually connected to the respective electrodes via non-illustrated lead wires formed inside the sensor element  12 , and the connector  24  and the lead wires  54  shown in  FIG. 1 . 
     In addition, as shown in  FIG. 1 , in the present embodiment, the metal terminal  18  that rearwardly extends is electrically connected to a terminal pad  200  that is exposed from the rear end portion of the sensor element  12 . The ceramic housing  16  is installed around the periphery of the rear end portion of the sensor element  12 , and the metal terminal  18  is fitted between the above-described terminal pad  200  and the ceramic housing  16 . In accordance therewith, the terminal pad  200  of the sensor element  12  and the metal terminal  18  are crimped and electrically connected to each other. More specifically, the ceramic housing  16  is attached with the metal terminal  18  that is electrically connected to the sensor element  12 , and retains the rear end portion of the sensor element  12 . 
     A rear portion of the metal terminal  18  extends rearwardly of the ceramic housing  16 , and is electrically connected to the lead wires  54  that are inserted inside the elastic insulating member  56 . More specifically, in the elastic insulating member  56 , a plurality of through holes  202  are formed in the axial direction of the sensor element  12 . The lead wires  54  are inserted through the through holes  202 , and the metal terminal  18  extending from the sensor element  12  and the lead wires  54  are electrically connected in a later-described manner. 
     As shown in  FIG. 3 , the metal terminal  18  according to the present embodiment includes an element contacting portion  210 , a lead wire retaining member  212 , and a positioning member  214 . 
     The element contacting portion  210  is disposed at one end of the metal terminal  18 , and is placed in contact with the sensor element  12 . In the example shown in  FIG. 3 , a distal end portion  222  of an elongated extending portion  220  extending in one direction (the front-rear direction) has a rearwardly bent shape, and a top portion  224  thereof elastically contacts the terminal pad  200  of the sensor element  12  (see  FIG. 1 ). 
     The lead wire retaining member  212  is disposed at the other end of the metal terminal  18 , and crimps and retains the lead wires  54 . More specifically, the lead wire retaining member  212  includes a plurality of tubular parts  230 , and the metal terminal  18  and the lead wires  54  are electrically connected by inserting and crimping, inside the tubular parts  230 , the lead wires  54  in which the conductive wires are exposed. 
     The positioning member  214  serves as a site for positioning the metal terminal  18  on the ceramic housing  16 . The positioning member  214  is disposed between the one end and the other end of the metal terminal  18  in closest proximity to the lead wire retaining member  212 , and includes a pair of plate-shaped portions  240  that are bent in a direction that intersects the one direction (the front-rear direction). 
     In particular, according to the present embodiment, a guide member  242 , which is formed integrally with the positioning member  214 , is provided at a site between the positioning member  214  and the lead wire retaining member  212  of the metal terminal  18 . In the same manner as the positioning member  214 , the guide member  242  also includes a pair of plate-shaped portions  244  that are bent in a direction intersecting the one direction (the front-rear direction). 
     As examples of the side surface shape of the guide member  242 , as shown in  FIGS. 4A to 4C , there may be cited a rectangular shape, a triangular shape, a trapezoidal shape, or the like. Assuming that a length of the guide member  242  in a direction intersecting the one direction, in other words, a length of the guide member  242  (a length between the positioning member  214  and the lead wire retaining member  212 ) is given by L where the height thereof in closest proximity to the positioning member  214  is given by h 1  and the height thereof in closest proximity to the lead wire retaining member  212  is given by h 2 , the following combinations can be mentioned. 
     square shape: h 1 &gt;0, h 2 &gt;0, L&gt;0, h 1 =h 2 =L 
     rectangular shape (a): h 1 &gt;0, h 2 &gt;0, L&gt;0, h 1 =h 2 &gt;L 
     rectangular shape (b): h 1 &gt;0, h 2 &gt;0, L&gt;0, h 1 =h 2  &lt;L 
     triangular shape: h 1 &gt;0, h 2 =0, L&gt;0 
     trapezoidal shape: h 1 &gt;0, h 2 &gt;0, h 1 &gt;h 2 , L&gt;0 
       FIG. 4A  shows a representative diagram of the rectangular shape (b),  FIG. 4B  shows a representative diagram of the triangular shape, and  FIG. 4C  shows a representative diagram of the trapezoidal shape. Further, for the sake of convenience, a boundary portion between the positioning member  214  and the guide member  242  is indicated by the two-dot dashed line. 
     It goes without saying that these structures are simply offered as examples, and various alternative shapes may be considered. For example, in  FIGS. 4A to 4C , although an example is shown in which the boundary between the positioning member  214  and the guide member  242  is linear, such a boundary may also be curved. Further, in the aforementioned example, the thickness of the guide member  242  may be the same as or thicker than the thickness of the positioning member  214 . Of course, the thickness thereof may also be thinner, as long as no problem arises in relation to strength. 
     In the manner described above, by providing the guide member  242 , which is formed integrally with the positioning member  214 , at the site between the positioning member  214  and the lead wire retaining member  212 , the following advantageous effects are realized. More specifically, it is possible to prevent damage from occurring to the metal terminal  18 , even when repetitive loads such as tension, compression, bending, and shearing or the like are applied between the positioning member  214  and the lead wire retaining member  212  of the metal terminal  18 , or when put to use under a usage environment in which vibrations are intense, and the commercial value of the gas sensor  10  can be increased. 
     Exemplary Embodiments 
     Herein, in relation to Exemplary Embodiments 1 to 24 and Comparative Example 1, experimental examples will be presented in which the presence or absence of a conduction failure (contact failure) is confirmed after being subjected to a heating and vibration test. Further, the experimental results are shown in Table 1 and Table 2. 
     Exemplary Embodiment 1 
     The metal terminal  18  according to Exemplary Embodiment 1 includes the guide member  242  between the positioning member  214  and the lead wire retaining member  212 . In addition, the shape of the guide member  242  (indicated in Tables 1 and 2 as a “guide shape”) is a square shape (indicated by the word “square” in Tables 1 and 2). 
     Among the plurality of surfaces that constitute the guide member  242 , the area of the surface thereof along the surface of the positioning member  214  having the largest area (hereinafter, referred to as a “guide area”) is 0.01 mm 2 . 
     The height of the guide member  242  in closest proximity to the positioning member  214  (hereinafter, referred to as a “guide height h 1 ”) is 0.10 mm. Further, the height of the guide member  242  in closest proximity to the lead wire retaining member  212  (hereinafter, referred to as a “guide height h 2 ”) is 0.10 mm. The length of the guide member  242  (hereinafter, referred to as a “guide length L”) is 0.10 mm. 
     Exemplary Embodiment 2 
     The metal terminal  18  according to Exemplary Embodiment 2 also includes the guide member  242 , and the shape of the guide member  242  is a triangular shape (indicated by the word “triangular” in Tables 1 and 2). The guide area is 0.01 mm 2 , the guide height h 1  is 0.20 mm, the guide height h 2  is 0.00 mm, and the guide length L is 0.10 mm. 
     Exemplary Embodiment 3 
     The metal terminal  18  according to Exemplary Embodiment 3 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape (indicated by the word “trapezoidal” in Tables 1 and 2). The guide area is 0.01 mm 2 , the guide height h 1  is 0.07 mm, the guide height h 2  is 0.03 mm, and the guide length L is 0.10 mm. 
     Exemplary Embodiment 4 
     The metal terminal  18  according to Exemplary Embodiment 4 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape (indicated by the word “rectangular” in Tables 1 and 2). The guide area is 7.50 mm 2 , the guide height h 1  is 3.00 mm, the guide height h 2  is 3.00 mm, and the guide length L is 2.50 mm. 
     Exemplary Embodiment 5 
     The metal terminal  18  according to Exemplary Embodiment 5 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape. The guide area is 7.50 mm 2 , the guide height h 1  is 4.00 mm, the guide height h 2  is 2.00 mm, and the guide length L is 2.50 mm. 
     Exemplary Embodiment 6 
     The metal terminal  18  according to Exemplary Embodiment 6 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape. The guide area is 1.50 mm 2 , the guide height h 1  is 1.00 mm, the guide height h 2  is 1.00 mm, and the guide length L is 1.50 mm. 
     Exemplary Embodiment 7 
     The metal terminal  18  according to Exemplary Embodiment 7 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape. The guide area is 0.80 mm 2 , the guide height h 1  is 0.80 mm, the guide height h 2  is 0.80 mm, and the guide length L is 1.00 mm. 
     Exemplary Embodiment 8 
     The metal terminal  18  according to Exemplary Embodiment 8 also includes the guide member  242 , and the shape of the guide member  242  is a triangular shape. The guide area is 0.80 mm 2 , the guide height h 1  is 1.60 mm, the guide height h 2  is 0.00 mm, and the guide length L is 1.00 mm. 
     Exemplary Embodiment 9 
     The metal terminal  18  according to Exemplary Embodiment 9 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape. The guide area is 0.80 mm 2 , the guide height h 1  is 1.00 mm, the guide height h 2  is 0.60 mm, and the guide length L is 1.00 mm. 
     Exemplary Embodiment 10 
     The metal terminal  18  according to Exemplary Embodiment 10 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape. The guide area is 0.38 mm 2 , the guide height h 1  is 0.46 mm, the guide height h 2  is 0.46 mm, and the guide length L is 0.82 mm. 
     Exemplary Embodiment 11 
     The metal terminal  18  according to Exemplary Embodiment 11 also includes the guide member  242 , and the shape of the guide member  242  is a triangular shape. The guide area is 0.41 mm 2 , the guide height h 1  is 1.00 mm, the guide height h 2  is 0.00 mm, and the guide length L is 0.82 mm. 
     Exemplary Embodiment 12 
     The metal terminal  18  according to Exemplary Embodiment 12 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape. The guide area is 0.37 mm 2 , the guide height h 1  is 0.60 mm, the guide height h 2  is 0.30 mm, and the guide length L is 0.82 mm. 
     Exemplary Embodiment 13 
     The metal terminal  18  according to Exemplary Embodiment 13 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape. The guide area is 0.18 mm 2 , the guide height h 1  is 0.30 mm, the guide height h 2  is 0.30 mm, and the guide length L is 0.61 mm. 
     Exemplary Embodiment 14 
     The metal terminal  18  according to Exemplary Embodiment 14 also includes the guide member  242 , and the shape of the guide member  242  is a triangular shape. The guide area is 0.18 mm 2 , the guide height h 1  is 0.60 mm, the guide height h 2  is 0.00 mm, and the guide length L is 0.61 mm. 
     Exemplary Embodiment 15 
     The metal terminal  18  according to Exemplary Embodiment 15 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape. The guide area is 0.18 mm 2 , the guide height h 1  is 0.40 mm, the guide height h 2  is 0.20 mm, and the guide length L is 0.61 mm. 
     Exemplary Embodiment 16 
     The metal terminal  18  according to Exemplary Embodiment 16 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape. The guide area is 0.11 mm 2 , the guide height h 1  is 0.22 mm, the guide height h 2  is 0.22 mm, and the guide length L is 0.49 mm. 
     Exemplary Embodiment 17 
     The metal terminal  18  according to Exemplary Embodiment 17 also includes the guide member  242 , and the shape of the guide member  242  is a triangular shape. The guide area is 0.10 mm 2 , the guide height h 1  is 0.40 mm, the guide height h 2  is 0.00 mm, and the guide length L is 0.49 mm. 
     Exemplary Embodiment 18 
     The metal terminal  18  according to Exemplary Embodiment 18 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape. The guide area is 0.10 mm 2 , the guide height h 1  is 0.30 mm, the guide height h 2  is 0.10 mm, and the guide length L is 0.49 mm. 
     Exemplary Embodiment 19 
     The metal terminal  18  according to Exemplary Embodiment 19 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape. The guide area is 0.05 mm 2 , the guide height h 1  is 0.15 mm, the guide height h 2  is 0.15 mm, and the guide length L is 0.30 mm. 
     Exemplary Embodiment 20 
     The metal terminal  18  according to Exemplary Embodiment 20 also includes the guide member  242 , and the shape of the guide member  242  is a triangular shape. The guide area is 0.05 mm 2 , the guide height h 1  is 0.30 mm, the guide height h 2  is 0.00 mm, and the guide length L is 0.30 mm. 
     Exemplary Embodiment 21 
     The metal terminal  18  according to Exemplary Embodiment 21 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape. The guide area is 0.05 mm 2 , the guide height h 1  is 0.20 mm, the guide height h 2  is 0.10 mm, and the guide length L is 0.30 mm. 
     Exemplary Embodiment 22 
     The metal terminal  18  according to Exemplary Embodiment 22 also includes the guide member  242 , and the shape of the guide member  242  is a rectangular shape. The guide area is 0.08 mm 2 , the guide height h 1  is 0.13 mm, the guide height h 2  is 0.13 mm, and the guide length L is 0.60 mm. 
     Exemplary Embodiment 23 
     The metal terminal  18  according to Exemplary Embodiment 23 also includes the guide member  242 , and the shape of the guide member  242  is a triangular shape. The guide area is 0.08 mm 2 , the guide height h 1  is 0.25 mm, the guide height h 2  is 0.00 mm, and the guide length L is 0.60 mm. 
     Exemplary Embodiment 24 
     The metal terminal  18  according to Exemplary Embodiment 24 also includes the guide member  242 , and the shape of the guide member  242  is a trapezoidal shape. The guide area is 0.09 mm 2 , the guide height h 1  is 0.20 mm, the guide height h 2  is 0.10 mm, and the guide length L is 0.60 mm. 
     Comparative Example 1 
     In the metal terminal  18  according to Comparative Example 1, the guide member  242  is not provided. 
     [Evaluation Method] 
     Confirmations were made concerning the presence or absence of a conduction failure (contact failure) after being subjected to a heating and vibration test. 
     [Experimental Method] 
     A gas sensor was attached to a chamber through which a high-temperature gas at 850° C. flows, and a test was carried out for 500 hours under the following vibratory conditions. 
     number of cycles: 50, 100, 150, and 250 Hz 
     acceleration: 30 G, 40 G, and 50 G 
     sweep time: 30 min/sweep cycle 
     testing time period: 500 hours 
     gas temperature: 850° C. 
     During testing, a sensor signal (the pump current Ip 2 ) was monitored, and it was investigated whether or not the sensor signal changed in excess of a predetermined threshold value. When the sensor signal exceeds the predetermined threshold value, it implies that a conduction failure is occurring. 
     The judgment criteria are as follows: 
     A: The sensor signal did not exceed the predetermined threshold value during a durability test. 
     B: The sensor signal was in excess of the predetermined threshold value during a period from 50 to 500 hours. 
     C: The sensor signal was in excess of the predetermined threshold value during a period of less than or equal to 50 hours. 
     The evaluation results of Exemplary Embodiments 1 to 13 are shown in Table 1 of  FIG. 5 , and the evaluation results of Exemplary Embodiments 14 to 24 and Comparative Example 1 are shown in Table 2 of  FIG. 6 . From the evaluation results shown in Table 1 and Table 2, it can be understood that favorable determination results are obtained by providing the guide member  242 , which is formed integrally with the positioning member  214 , at the site between the positioning member  214  and the lead wire retaining member  212  of the metal terminal  18 . 
     In particular, the area of the guide member  242  preferably lies within a range of being greater than or equal to 0.01 mm 2  and less than or equal to 7.50 mm 2 , and more preferably, lies within a range of being greater than or equal to 0.05 mm 2  and less than or equal to 7.50 mm 2 . The height h 1  of the guide member  242  preferably lies within a range of being greater than or equal to 0.07 mm and less than or equal to 4.00 mm, and more preferably, lies within a range of being greater than or equal to 0.13 mm and less than or equal to 4.00 mm. The height h 2  of the guide member  242  preferably lies within a range of being greater than or equal to 0.00 mm and less than or equal to 3.00 mm. The length L of the guide member  242  preferably lies within a range of being greater than or equal to 0.10 mm and less than or equal to 2.50 mm, and more preferably, lies within a range of being greater than or equal to 0.30 mm and less than or equal to 2.50 mm. 
     Further, the ratio (h 0 /h 1 ) of a height h 0  of the positioning member  214  (see  FIG. 4A ) to the maximum height (h 1 ) of the guide member  242  preferably lies within a range of being greater than or equal to 1.33 and less than or equal to 30.00. The ratio (L 0 /L) of a length L 0  of the positioning member  214  (see  FIG. 4A ) to the length L of the guide member  242  preferably lies within a range of being greater than or equal to 1.2 and less than or equal to 20.00. 
     [Inventions Obtained from the Present Embodiment] 
     A description will be given below concerning the inventions that can be grasped from the above-described embodiment. 
     [1] The metal terminal ( 18 ) according to the present embodiment is installed in the gas sensor ( 10 ) including the sensor element ( 12 ) and the ceramic housing ( 16 ) configured to retain the rear end portion of the sensor element ( 12 ), and electrically connects the sensor element ( 12 ) and the lead wires ( 54 ), the metal terminal ( 18 ) comprising the element contacting portion ( 210 ) disposed at one end of the metal terminal ( 18 ), and configured to be placed in contact with the sensor element ( 12 ), the lead wire retaining member ( 212 ) disposed at the other end of the metal terminal ( 18 ), and configured to crimp and retain the lead wires ( 54 ), the positioning member ( 214 ) disposed between the one end and the other end and extending in a direction intersecting the one direction, the positioning member ( 214 ) being configured to position the metal terminal ( 18 ) on the ceramic housing ( 16 ), and the guide member ( 242 ) provided integrally with the positioning member ( 214 ) at a site between the positioning member ( 214 ) and the lead wire retaining member ( 212 ). 
     In accordance with such features, it is possible to prevent damage from occurring to the metal terminal  18 , even when repetitive loads such as tension, compression, bending, and shearing or the like are applied between the positioning member  214  and the lead wire retaining member  212  of the metal terminal  18 , or when put to use under a usage environment in which vibrations are intense, and the commercial value of the gas sensor  10  can be increased. 
     [2] In the present embodiment, among the plurality of surfaces constituting the guide member ( 242 ), the area of the surface thereof along a surface of the positioning member ( 214 ) having a largest area preferably lies within a range of being greater than or equal to 0.01 mm 2  and less than or equal to 7.50 mm 2 . 
     [3] In the present embodiment, among the plurality of surfaces constituting the guide member ( 242 ), the area of the surface thereof along a surface of the positioning member ( 214 ) having a largest area preferably lies within a range of being greater than or equal to 0.05 mm 2  and less than or equal to 7.50 mm 2 . 
     [4] In the present embodiment, the height (h 1 ) of the guide member ( 242 ) preferably lies within a range of being greater than or equal to 0.07 mm and less than or equal to 4.00 mm in closest proximity to the positioning member ( 214 ). 
     [5] In the present embodiment, the height (h 1 ) of the guide member ( 242 ) preferably lies within a range of being greater than or equal to 0.13 mm and less than or equal to 4.00 mm in closest proximity to the positioning member ( 214 ). 
     [6] In the present embodiment, the height (h 2 ) of the guide member ( 242 ) preferably lies within a range of being greater than or equal to 0.00 mm and less than or equal to 3.00 mm in closest proximity to the lead wire retaining member ( 212 ). 
     [7] In the present embodiment, the length (L) of the guide member ( 242 ) along the one direction preferably lies within a range of being greater than or equal to 0.10 mm and less than or equal to 2.50 mm. 
     [8] In the present embodiment, the length (L) of the guide member ( 242 ) along the one direction preferably lies within a range of being greater than or equal to 0.30 mm and less than or equal to 2.50 mm. 
     [9] In the present embodiment, the ratio (h 0 /h 1 ) of the height (h 0 ) of the positioning member ( 214 ) to the maximum height (h 1 ) of the guide member ( 242 ) preferably lies within a range of being greater than or equal to 1.33 and less than or equal to 30.00. 
     [10] In the present embodiment, the ratio (L 0 /L) of the length (L 0 ) of the positioning member ( 214 ) (see  FIG. 4A ) to the length (L) of the guide member ( 242 ) preferably lies within a range of being greater than or equal to 1.2 and less than or equal to 20.00. 
     In the above-described embodiments, the sensor element  12  detects the NOx concentration within the gas to be measured. However, the present invention is not limited to this feature, so long as the sensor element  12  detects the concentration of a specific gas existing within the gas to be measured. For example, the sensor element  12  may detect the oxygen concentration within the gas to be measured. 
     In practicing the present invention, various configurations for improving reliability may be added as components for an automotive vehicle to such an extent that the concept of the present invention is not impaired.