JP6584219B2 - Ceramic heater, sensor element and gas sensor - Google Patents

Description

  The present invention relates to a ceramic heater, a sensor element, and a gas sensor.

  2. Description of the Related Art Conventionally, as a ceramic heater, one having a ceramic sheet and a heater pattern formed by bending a plurality of times in the longitudinal direction of the ceramic sheet is known (for example, Patent Document 1). FIG. 4 is an explanatory diagram of such a conventional heater 372. The heater 372 includes a plurality of straight portions 378 and a plurality of bent portions 377 that connect adjacent straight portions 378 to each other. Moreover, what has the pattern provided with the return part which connects the linear part along the transversal direction of a ceramic sheet, and linear parts is also known (for example, patent document 2).

Japanese Patent No. 4826461 Japanese Patent No. 3571494

  By the way, in such a ceramic heater, the heat generating body may be deteriorated and disconnected due to oxidation of a conductor constituting the heat generating body at a high temperature. In particular, a bent portion such as a folded portion of the heater pattern is more susceptible to stress due to thermal expansion than the straight portion, and therefore, there is a problem that disconnection due to deterioration is more likely to occur than the straight portion.

  The present invention has been made to solve such problems, and has as its main object to prolong the life of the heating element.

  The present invention employs the following means in order to achieve the main object described above.

The ceramic heater of the present invention is
A heating element comprising: a lead portion having a first lead and a second lead; and a heat generating portion having a plurality of linear portions connecting between the first lead and the second lead;
A ceramic body surrounding the heating element;
It is equipped with.

  In this ceramic heater, the heat generating portion of the heating element does not include a bent portion that is likely to cause disconnection due to deterioration. Thereby, the lifetime of a heat generating body can be lengthened compared with the case where a heat generating part has a bending part.

  In the ceramic heater according to the aspect of the invention, the heat generating portion includes three or more straight portions, and the plurality of straight portions are arranged along a first direction intersecting a length direction of the straight portions and are electrically connected to each other. The linear portion located on one end side in the first direction and the straight portion located on the other end side are defined as outer straight portions, and the straight portion located between the outer straight portions is When the inner straight portion is formed, the resistance value of the inner straight portion per unit length at a temperature in the temperature range of 700 ° C. or higher and 900 ° C. or lower may be higher than that of the outer straight portion. By doing so, the heat generation density (heat generation amount per unit length) of the inner straight portion is smaller than that of the outer straight portion at at least one temperature of 700 ° C. to 900 ° C. Here, since the inner straight portion is located inside the outer straight portion, the temperature tends to increase, and the heating element tends to deteriorate as the temperature increases. By making the heat generation density of the inner straight line portion smaller than that of the outer straight line portion, it is possible to suppress the temperature rise of the inner straight line portion that tends to become high temperature, and to suppress the deterioration of the inner straight line portion. Therefore, the lifetime of the entire heating element can be extended.

  In the ceramic heater according to the aspect of the invention, the heat generating portion includes two straight portions, and the plurality of straight portions are arranged in a first direction intersecting a length direction of the straight portions and are electrically connected to each other. When the straight portion closer to the end of the ceramic body in the first direction is the outer straight portion and the far straight portion is the inner straight portion, the temperature is 700 ° C. or more and 900 The resistance value of the inner straight part per unit length at least in any temperature within a temperature range of 0 ° C. or less may be higher than that of the outer straight part. By doing so, the heat generation density of the inner straight portion is smaller than that of the outer straight portion at at least one of temperatures of 700 ° C. to 900 ° C. Here, since the inner straight portion is located farther from the end of the ceramic body than the outer straight portion, the inner straight portion is likely to become high temperature, and the heating element is likely to deteriorate as the temperature becomes higher. By making the heat generation density of the inner straight line portion smaller than that of the outer straight line portion, it is possible to suppress the temperature rise of the inner straight line portion that tends to become high temperature, and to suppress the deterioration of the inner straight line portion. Therefore, the lifetime of the entire heating element can be extended.

  In the ceramic heater of the present invention in which the resistance value per unit length of the inner straight portion is higher than that of the outer straight portion, the resistance value per unit length of the inner straight portion is defined as a unit resistance value R1 [μΩ / mm]. When the resistance value per unit length of the outer straight portion is the unit resistance value R2 [μΩ / mm], the unit resistance value ratio R1 / R2 at the temperature in at least one of the temperature ranges is 1.15. It is good also as above. If it carries out like this, the effect which suppresses deterioration of an inner side linear part will increase more. In this case, it is preferable that the unit resistance value ratio R1 / R2 at a temperature in at least one of the temperature ranges is a value of 1.25 or more.

In the ceramic heater of the present invention in which the resistance value per unit length of the inner straight portion is higher than that of the outer straight portion, the inner straight portion has a smaller cross-sectional area perpendicular to the length direction than the outer straight portion. May be. If it carries out like this, the resistance value per unit length of an inner side straight part will become high easily compared with an outer side straight part. In this case, the cross-sectional area ratio S2 / S1 between the cross-sectional area S1 [mm ² ] perpendicular to the length direction of the inner straight portion and the cross-sectional area S2 [mm ² ] perpendicular to the length direction of the outer straight portion is The value is preferably 1.15 or more. In this case, the unit resistance value ratio R1 / R2 at a temperature in at least one of the above temperature ranges tends to be a value of 1.15 or more. The cross-sectional area ratio S2 / S1 is more preferably a value of 1.25 or more.

  In the ceramic heater of the present invention in which the resistance value per unit length of the inner straight part is higher than that of the outer straight part, the inner straight part is at least at a temperature in the temperature range as compared with the outer straight part. The volume resistivity may be high. If it carries out like this, the resistance value per unit length of an inner side straight part will become high easily compared with an outer side straight part. In this case, the volume which is a ratio of the volume resistivity ρ1 [μΩ · cm] of the inner straight portion and the volume resistivity ρ2 [μΩ · cm] of the outer straight portion at at least one temperature in the temperature range. The resistivity ratio ρ1 / ρ2 is preferably a value of 1.15 or more. In this case, the unit resistance value ratio R1 / R2 at a temperature in at least one of the above temperature ranges tends to be a value of 1.15 or more. Further, it is more preferable that the volume resistivity ratio ρ1 / ρ2 at a temperature in at least one of the temperature ranges is a value of 1.25 or more.

The sensor element of the present invention is
The ceramic heater according to any one of the aspects described above is provided,
The specific gas concentration in the gas to be measured is detected.

  This sensor element includes the ceramic heater according to any one of the above-described aspects. Therefore, an effect similar to that of the ceramic heater of the present invention described above, for example, an effect of extending the life of the heating element can be obtained.

The gas sensor of the present invention is
The sensor element according to any one of the aspects described above is provided.

  This sensor element includes a sensor element including the ceramic heater according to any one of the aspects described above. Therefore, an effect similar to that of the above-described ceramic heater or sensor element of the present invention, for example, an effect of extending the life of the heating element can be obtained.

FIG. 3 is a schematic cross-sectional view schematically showing an example of the configuration of the gas sensor 100. AA sectional drawing of FIG. Explanatory drawing of the heater 72A of a modification. Explanatory drawing of the heater 372 of a prior art example.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view schematically showing an example of the configuration of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line AA of FIG. The gas sensor 100 detects the concentration of a specific gas such as NOx in a measured gas such as an exhaust gas of an automobile by the sensor element 101. The sensor element 101 has a long rectangular parallelepiped shape. The longitudinal direction of the sensor element 101 (left-right direction in FIG. 1) is the front-rear direction, and the thickness direction of the sensor element 101 (up-down direction in FIG. 1) is vertical. The direction. The width direction of sensor element 101 (the direction perpendicular to the front-rear direction and the up-down direction) is the left-right direction.

The sensor element 101 includes a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, and a first solid electrolyte layer 4 each made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). The spacer layer 5 and the second solid electrolyte layer 6 are elements having a structure in which the layers are laminated in this order from the bottom in the drawing. The solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured, for example, by performing predetermined processing and circuit pattern printing on a ceramic green sheet corresponding to each layer, stacking them, and firing and integrating them.

  One end of the sensor element 101, and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, is a gas inlet 10, a first diffusion rate limiting unit 11, and a buffer space. 12, the second diffusion rate limiting part 13, the first internal space 20, the third diffusion rate limiting part 30, and the second internal space 40 are adjacently formed in such a manner that they communicate in this order.

  The gas introduction port 10, the buffer space 12, the first internal space 20, and the second internal space 40 are provided on the lower surface of the second solid electrolyte layer 6 with the upper portion provided in a state in which the spacer layer 5 is cut out. The space inside the sensor element 101 is defined by the lower part being the upper surface of the first solid electrolyte layer 4 and the side parts being the side surfaces of the spacer layer 5.

  Each of the first diffusion rate controlling unit 11, the second diffusion rate controlling unit 13, and the third diffusion rate controlling unit 30 is provided as two horizontally long slits (the opening has a longitudinal direction in a direction perpendicular to the drawing). . In addition, the site | part from the gas inlet 10 to the 2nd internal space 40 is also called a gas distribution part.

  Further, at a position farther from the front end side than the gas circulation part, the side part is partitioned by the side surface of the first solid electrolyte layer 4 between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5. The reference gas introduction space 43 is provided at the position. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

  The air introduction layer 48 is a layer made of porous ceramics, and a reference gas is introduced into the air introduction layer 48 through the reference gas introduction space 43. The air introduction layer 48 is formed so as to cover the reference electrode 42.

  The reference electrode 42 is an electrode formed in such a manner that it is sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, the reference electrode 42 leads to the reference gas introduction space 43. An air introduction layer 48 is provided. Further, as will be described later, it is possible to measure the oxygen concentration (oxygen partial pressure) in the first internal space 20 and the second internal space 40 using the reference electrode 42.

  In the gas circulation part, the gas inlet 10 is a part opened to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion control unit 11 is a part that provides a predetermined diffusion resistance to the gas to be measured taken from the gas inlet 10. The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate controlling unit 11 to the second diffusion rate controlling unit 13. The second diffusion rate limiting unit 13 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20. When the gas to be measured is introduced from the outside of the sensor element 101 to the inside of the first internal space 20, the pressure fluctuation of the gas to be measured in the external space (exhaust pressure pulsation if the gas to be measured is an automobile exhaust gas) ), The gas to be measured that is suddenly taken into the sensor element 101 from the gas inlet 10 is not directly introduced into the first internal space 20, but the first diffusion control unit 11, the buffer space 12, the second After the concentration variation of the gas to be measured is canceled through the diffusion control unit 13, the gas is introduced into the first internal space 20. As a result, the concentration fluctuation of the gas to be measured introduced into the first internal space 20 becomes almost negligible. The first internal space 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate limiting unit 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21.

  The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode portion 22a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal space 20, and an upper surface of the second solid electrolyte layer 6. An electrochemical pump cell comprising an outer pump electrode 23 provided in a manner exposed to the external space in a region corresponding to the ceiling electrode portion 22a, and a second solid electrolyte layer 6 sandwiched between these electrodes. is there.

  The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that define the first inner space 20, and the spacer layer 5 that provides side walls. Yes. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal space 20, and a bottom portion is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. Spacer layers in which the electrode portions 22b are formed and the side electrode portions (not shown) constitute both side walls of the first internal space 20 so as to connect the ceiling electrode portions 22a and the bottom electrode portions 22b. 5 is formed on the side wall surface (inner surface), and is disposed in a tunnel-shaped structure at the portion where the side electrode portion is disposed.

The inner pump electrode 22 and the outer pump electrode 23 are formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO ₂ containing 1% of Au). The inner pump electrode 22 in contact with the gas to be measured is formed using a material that has a reduced reduction ability for the NOx component in the gas to be measured.

  In the main pump cell 21, a desired pump voltage Vp 0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and the pump current is positive or negative between the inner pump electrode 22 and the outer pump electrode 23. By flowing Ip0, oxygen in the first internal space 20 can be pumped into the external space, or oxygen in the external space can be pumped into the first internal space 20.

  Further, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The third substrate layer 3 and the reference electrode 42 constitute an electrochemical sensor cell, that is, a main pump control oxygen partial pressure detection sensor cell 80.

  By measuring the electromotive force V0 in the main pump control oxygen partial pressure detection sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be known. Further, the pump current Ip0 is controlled by feedback controlling the pump voltage Vp0 of the variable power source 24 so that the electromotive force V0 is constant. Thereby, the oxygen concentration in the first internal space 20 can be kept at a predetermined constant value.

  The third diffusion control unit 30 provides a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, and the gas under measurement is supplied to the gas under measurement. This is the part that leads to the second internal space 40.

  The second internal space 40 is provided as a space for performing a process related to the measurement of the nitrogen oxide (NOx) concentration in the gas to be measured introduced through the third diffusion control unit 30. The NOx concentration is measured mainly in the second internal space 40 in which the oxygen concentration is adjusted by the auxiliary pump cell 50, and further by measuring the pump cell 41 for measurement.

  In the second internal space 40, after the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal space 20, the auxiliary pump cell 50 is further supplied to the gas to be measured introduced through the third diffusion control unit 30. The oxygen partial pressure is adjusted by the above. Thereby, since the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, the gas sensor 100 can measure the NOx concentration with high accuracy.

  The auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, and an outer pump electrode 23 (outer pump electrode 23). The auxiliary electrochemical pump cell is configured by the second solid electrolyte layer 6 and the sensor element 101 and an appropriate electrode on the outside.

  The auxiliary pump electrode 51 is disposed in the second internal space 40 in the same tunnel configuration as the inner pump electrode 22 provided in the first internal space 20. That is, the ceiling electrode portion 51 a is formed on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and the first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40 is formed on the first solid electrolyte layer 4. The bottom electrode part 51b is formed, and the side electrode part (not shown) connecting the ceiling electrode part 51a and the bottom electrode part 51b is provided on the spacer layer 5 that provides the side wall of the second internal space 40. It has a tunnel-type structure formed on both wall surfaces. Note that the auxiliary pump electrode 51 is also formed using a material having a reduced reducing ability with respect to the NOx component in the gas to be measured, like the inner pump electrode 22.

  In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere in the second internal space 40 is pumped to the external space, or It is possible to pump into the second internal space 40 from the space.

  Further, in order to control the oxygen partial pressure in the atmosphere in the second internal space 40, the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte. The layer 4 and the third substrate layer 3 constitute an electrochemical sensor cell, that is, an auxiliary pump control oxygen partial pressure detection sensor cell 81.

  The auxiliary pump cell 50 performs pumping by the variable power source 52 that is voltage-controlled based on the electromotive force V1 detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. Thereby, the oxygen partial pressure in the atmosphere in the second internal space 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

  At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor cell 80, and the electromotive force V0 is controlled, so that the third diffusion rate limiting unit 30 controls the second internal space. The gradient of the oxygen partial pressure in the gas to be measured introduced into the gas 40 is controlled so as to be always constant. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

  The measurement pump cell 41 measures the NOx concentration in the gas to be measured in the second internal space 40. The measurement pump cell 41 includes a measurement electrode 44 provided on a top surface of the first solid electrolyte layer 4 facing the second internal space 40 and spaced from the third diffusion rate-determining portion 30, an outer pump electrode 23, The electrochemical pump cell is constituted by the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4.

  The measurement electrode 44 is a porous cermet electrode. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere in the second internal space 40. Further, the measurement electrode 44 is covered with a fourth diffusion rate controlling part 45.

  The 4th diffusion control part 45 is a film | membrane comprised with a ceramic porous body. The fourth diffusion control unit 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44 and also functions as a protective film for the measurement electrode 44. In the measurement pump cell 41, oxygen generated by the decomposition of nitrogen oxides in the atmosphere around the measurement electrode 44 can be pumped out, and the generated amount can be detected as the pump current Ip2.

  In order to detect the oxygen partial pressure around the measurement electrode 44, an electrochemical sensor cell, that is, a first solid electrolyte layer 4, a third substrate layer 3, a measurement electrode 44, and a reference electrode 42, that is, A measurement pump control oxygen partial pressure detection sensor cell 82 is configured. The variable power supply 46 is controlled on the basis of the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82.

The gas to be measured introduced into the second internal space 40 reaches the measurement electrode 44 through the fourth diffusion rate-determining unit 45 under the condition where the oxygen partial pressure is controlled. Nitrogen oxide in the gas to be measured around the measurement electrode 44 is reduced (2NO → N ₂ + O ₂ ) to generate oxygen. The generated oxygen is pumped by the measurement pump cell 41. At this time, the variable power source is set so that the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 is constant. 46 voltage Vp2 is controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxide in the gas to be measured, the nitrogen oxide in the gas to be measured using the pump current Ip2 in the measurement pump cell 41. The concentration will be calculated.

  If the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detecting means as an electrochemical sensor cell, the measurement electrode The electromotive force according to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around 44 and the amount of oxygen contained in the reference atmosphere can be detected, whereby the NOx component in the gas to be measured It is also possible to determine the concentration of.

  The second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42 constitute an electrochemical sensor cell 83. The oxygen partial pressure in the gas to be measured outside the sensor can be detected by the electromotive force Vref obtained by the sensor cell 83.

  In the gas sensor 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx). A gas to be measured is supplied to the measurement pump cell 41. Therefore, the NOx concentration in the measurement gas is determined based on the pump current Ip2 that flows when oxygen generated by the reduction of NOx is pumped out of the measurement pump cell 41 in proportion to the NOx concentration in the measurement gas. You can know.

  Furthermore, the sensor element 101 includes a heater unit 70 that plays a role of temperature adjustment for heating and maintaining the sensor element 101 in order to increase the oxygen ion conductivity of the solid electrolyte. The heater unit 70 includes a heater connector electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure dissipation hole 75. The heater unit 70 includes a first substrate layer 1, a second substrate layer 2, and a third substrate layer 3 made of ceramics. The heater unit 70 is configured as a ceramic heater including a heater 72 and a second substrate layer 2 and a third substrate layer 3 surrounding the heater 72. As shown in FIG. 2, the heater 72 includes a heat generating portion 76 and a lead portion 79.

  The heater connector electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to an external power source, power can be supplied to the heater unit 70 from the outside.

  The heat generating part 76 of the heater 72 is an electric resistor formed in a form sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The lead portion 79 of the heater 72 is connected to the heater connector electrode 71 through the through hole 73, and the heat generating portion 76 generates heat by being supplied with electric power from the outside through the heater connector electrode 71, thereby forming the sensor element 101. Heat and heat the solid electrolyte.

  Moreover, the heat generating portion 76 of the heater 72 is embedded below the first internal space 20 and the second internal space 40, and the entire sensor element 101 can be adjusted to a temperature at which the solid electrolyte is activated. It has become.

  The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 by an insulator such as alumina. The heater insulating layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72 and electrical insulation between the third substrate layer 3 and the heater 72.

  The pressure dissipating hole 75 is a portion that is provided so as to penetrate the third substrate layer 3 and communicate with the reference gas introduction space 43, and is for the purpose of alleviating the increase in internal pressure accompanying the temperature increase in the heater insulating layer 74. Formed.

  The heat generating part 76 and the lead part 79 of the heater 72 will be described in detail. The heat generating portion 76 is a resistance heating element, and includes a plurality (three in this embodiment) of linear portions 78 as shown in FIG. In addition, the several linear part 78 is called the 1st-3rd linear part 78a-78c in order toward the back from the front. Each of the plurality of linear portions 78 connects the first lead 79 a and the second lead 79 b of the lead portion 79. That is, each of the plurality of linear portions 78 has a left end connected to the first lead 79a and a right end connected to the lead portion 79b. The plurality of linear portions 78 are all disposed such that the length direction is parallel to the short direction (left-right direction) of the sensor element 101. The length direction of the straight portion 78 is the axial direction of the straight portion 78, in other words, the direction in which current flows. The plurality of linear portions 78 are arranged along the front-rear direction orthogonal to the length direction (left-right direction). The front-rear direction is the longitudinal direction of the sensor element 101 and is also referred to as a first direction. The front-rear direction is also the flow direction of the gas to be measured in the gas flow section (portion extending from the gas inlet 10 to the second internal space 40). The plurality of linear portions 78 are arranged so as to be electrically parallel to each other. As described above, the heat generating portion 76 includes only a plurality of linear portions 78 and has no bent portion.

In the present embodiment, the heat generating portion 76 is a cermet containing noble metal and ceramics (for example, cermet of platinum (Pt) and alumina (Al ₂ O ₃ )). Note that the heat generating portion 76 is not limited to cermet, and may be anything including a conductive substance such as a noble metal. Examples of the noble metal used for the heat generating portion 76 include at least one metal of platinum, rhodium (Rh), gold (Au), palladium (Pd), or an alloy thereof.

  The heat generating portion 76 includes a first straight portion 78a located on one end side (front end side) in the first direction (front-rear direction) and a third straight portion located on the other end side (rear end side) among the plurality of straight portions 78. 78c is the outer straight portion 76b, and the second straight portion 78b located between the outer straight portions 76b is the inner straight portion 76a. The unit at a temperature in the temperature range of 700 ° C. to 900 ° C. The resistance value (unit: [μΩ / mm]) of the inner straight portion 76a per length is higher than that of the outer straight portion 76b. In other words, when the resistance value per unit length of the inner straight portion 76a is defined as a unit resistance value R1, and the resistance value per unit length of the outer straight portion 76b is defined as a unit resistance value R2, at least within the above temperature range. The unit resistance value ratio R1 / R2 at any temperature exceeds the value 1. By doing this, at least at a temperature of 700 ° C. to 900 ° C., the inner straight portion 76a has a smaller heat generation density (heat generation amount per unit length) than the outer straight portion 76b, and the temperature hardly rises. Become. Thereby, deterioration of the inner side straight part 76a can be suppressed.

  The unit resistance value R1 is an average value of the resistance values per unit length of the inner straight portion 76a. Similarly, the unit resistance value R2 is an average value of the resistance values per unit length of the outer straight portion 76b. Therefore, even when there is a portion where the resistance value per unit length is lower than that of the outer straight portion 76b in a part of the inner straight portion 76a, the inner straight portion 76a as a whole has a higher resistance value per unit length. Good. However, it is more preferable that the resistance value per unit length exceeds the unit resistance value R2 in any part of the inner straight portion 76a. Further, it is preferable that the unit resistance value ratio R1 / R2 is greater than the value 1 at any temperature in the above temperature range. Further, in the heat generating portion 76, the unit resistance value ratio R1 / R2 at least in one of the above temperature ranges is preferably a value of 1.15 or more, and more preferably a value of 1.25 or more. Further, the unit resistance value ratio R1 / R2 may be a value of 2.0 or less at any temperature in the above temperature range.

  In addition, the resistance value per unit length of the straight line portion on the front end side (the first straight line portion 78a in the present embodiment) of the outer straight line portion 76b is defined as a unit resistance value R3, and the straight line portion on the rear end side (in the present embodiment). A resistance value per unit length of the third linear portion 78c) is set as a unit resistance value R4. At this time, it is preferable that the unit resistance value R1 is higher than the unit resistance value R3 and higher than the unit resistance value R4 at least at any temperature of 700 ° C. to 900 ° C.

In the present embodiment, the inner straight portion 76a and the outer straight portion 76b are made of the same material (cermet containing platinum as described above), and the cross-sectional area S1 [mm ² ] perpendicular to the length direction of the inner straight portion 76a is the outer straight line. The cross-sectional area S2 [mm ² ] perpendicular to the length direction of the portion 76b is made smaller. That is, the heat generating portion 76 has a cross-sectional area ratio S2 / S1 exceeding the value 1. By doing so, the unit resistance value ratio R1 / R2 exceeds the value 1 in any temperature range from 700 ° C. to 900 ° C. The cross-sectional area ratio S2 / S1 is preferably 1.15 or more, and more preferably 1.25 or more. The cross-sectional area ratio S2 / S1 may be adjusted by, for example, making the width W1 of the inner straight portion 76a smaller than the width W2 of the outer straight portion 76b, or setting the thickness D1 of the inner straight portion 76a to the thickness of the outer straight portion 76b. The distance D2 may be smaller than at least one. For example, when the width W1 <the width W2, if the cross-sectional area ratio S2 / S1 exceeds the value 1, the thickness D1> the thickness D2 may be satisfied, and the thickness D1 = the thickness D2. Alternatively, the thickness D1 <thickness D2 may be satisfied. Similarly, when thickness D1 <thickness D2, as long as the cross-sectional area ratio S2 / S1 exceeds the value 1, width W1> width W2 may be satisfied, and width W1 = width W2 may be satisfied. Alternatively, the width W1 <the width W2 may be satisfied. The values of the cross-sectional areas S1 and S2 are also average values of the inner straight portion 76a and the outer straight portion 76b, similarly to the unit resistance values R1 and R2. In the present embodiment, the cross-sectional area of the inner straight portion 76a is the same value (= cross-sectional area S1) in any part. The same applies to the outer straight portion 76b. That is, the cross-sectional areas of the first straight part 78a and the second straight part 78b are the same value (= cross-sectional area S2) in any part. The cross-sectional area ratio S2 / S1 may be 2.0 or less. The widths W1 and W2 may be 0.05 mm or more and 2.0 mm or less. Thickness D1, D2 is good also as 0.003 mm or more and 0.1 mm or less.

  The lead portion 79 includes a first lead 79a disposed on the left side of the heat generating portion 76 and a second lead 79b disposed on the right side. The first and second leads 79 a and 79 b are leads for energizing the heat generating portion 76 and are connected to the heater connector electrode 71. The first lead 79a is a positive electrode lead, and the second lead 79b is a negative electrode lead. When a voltage is applied between the first lead 79a and the second lead 79b, a current flows through the heat generating portion 76, and the heat generating portion 76 generates heat. The lead portion 79 is a conductor and has a lower resistance value per unit length than the heat generating portion 76. Therefore, unlike the heat generating portion 76, the lead portion 79 hardly generates heat when energized. For example, the lead portion 79 is made of a material having a lower volume resistivity than the heat generating portion 76 or has a large cross-sectional area, so that the resistance value per unit length is low. In the present embodiment, the lead portion 79 has a lower volume resistivity due to a higher precious metal ratio than the heat generating portion 76, and is wider than the inner straight portion 76a and the outer straight portion 76b. The cross-sectional area is large.

  A method for manufacturing the gas sensor 100 thus configured will be described below. First, six green ceramic green sheets containing an oxygen ion conductive solid electrolyte such as zirconia as a ceramic component are prepared. In this green sheet, a plurality of sheet holes and necessary through holes used for positioning during printing and lamination are formed in advance. In addition, a space serving as a gas circulation portion is provided in advance in the green sheet serving as the spacer layer 5 by a punching process or the like. And each corresponding to each of the 1st substrate layer 1, the 2nd substrate layer 2, the 3rd substrate layer 3, the 1st solid electrolyte layer 4, the spacer layer 5, and the 2nd solid electrolyte layer 6, A pattern printing process and a drying process for forming various patterns on the ceramic green sheet are performed. Specifically, the pattern to be formed is, for example, a pattern of the above-described electrodes, lead wires connected to the electrodes, the air introduction layer 48, the heater 72, or the like. Pattern printing is performed by applying a pattern forming paste prepared according to the characteristics required for each object to be formed on a green sheet using a known screen printing technique. The pattern forming paste used for the heater 72 is a mixture of the raw material (for example, precious metal and ceramic particles) made of the material of the heater 72 described above, an organic binder, an organic solvent, and the like.

  At this time, the pattern serving as the heater 72 is formed so that the unit resistance value ratio R1 / R2 exceeds the value 1, that is, the cross-sectional area ratio S2 / S1 exceeds the value 1. For example, in order to satisfy the width W1 <the width W2, a mask having a shape capable of forming such a pattern is used. In order to satisfy the thickness D1 <thickness D2, for example, the viscosity of the paste that forms the pattern of the portion that becomes the inner straight portion 76a is made higher than the pattern of the portion that becomes the outer straight portion 76b. The number of times of printing when forming the pattern of the portion that becomes the inner straight portion 76a is increased.

  After forming various patterns in this way, the green sheet is dried. The drying process is also performed using a known drying means. When pattern printing / drying is completed, printing / drying processing of an adhesive paste for laminating / bonding the green sheets corresponding to each layer is performed. Then, the green sheets on which the adhesive paste is formed are stacked in a predetermined order while being positioned by the sheet holes, and are pressed by applying predetermined temperature and pressure conditions, thereby performing a pressing process to form a single laminate. The laminated body thus obtained includes a plurality of sensor elements 101. The laminated body is cut and cut into the size of the sensor element 101. Then, the cut laminate is fired at a predetermined firing temperature to obtain the sensor element 101.

   When the sensor element 101 is obtained in this manner, the gas sensor 100 is obtained by manufacturing a sensor assembly incorporating the sensor element 101 and attaching a protective cover or the like. The manufacturing method of the gas sensor as described above is known except that the shape of the heater 72 and the unit resistance value ratio R1 / R2 exceed the value 1, and is described in, for example, International Publication No. 2013/005491. Has been.

  In the gas sensor 100 configured in this way, when used, the heater 72 is connected to a power source (for example, an alternator of an automobile) via the heater connector electrode 71, and a DC voltage (for example, 12 to 14V) is connected between the first lead 79a and the second lead 79b. ) Is applied. Then, due to the applied voltage, a current flows through the heat generating portion 76 and the heat generating portion 76 generates heat. Thereby, the sensor element 101 whole is adjusted to the temperature (for example, 700 degreeC-900 degreeC) which the said solid electrolyte (each layer 1-6) activates. At this time, the heat generating portion 76 becomes high temperature, but the heat generating portion 76 is likely to be oxidized and deteriorated as the temperature increases (for example, platinum which is a noble metal component is oxidized). In particular, when the heat generating portion 76 has a bent portion, the bent portion is more susceptible to stress due to thermal expansion than the straight portion 78, and therefore, disconnection due to deterioration is more likely to occur than the straight portion 78. More specifically, the bent portion is likely to generate minute cracks due to the influence of stress due to thermal expansion. Then, the surface area of the bent portion is increased by the crack, whereby the oxidation is promoted or the crack is further extended, so that the bent portion is likely to be disconnected and has a short life. However, in the heater part 70 of this embodiment, since the heat generating part 76 does not include a bent part, the life of the heat generating element 76 becomes longer than when the heat generating part 76 has a bent part. In addition, when the heat generating portion 76 includes a plurality of straight portions 78, generally, the inner straight portion is located on the inner side as compared with the outer straight portion, so that the temperature tends to be high and the inner straight portion of the heat generating portion is likely to deteriorate. . However, in the heater unit 70 of the present embodiment, the unit resistance value ratio R1 / R2 at a temperature of at least one of 700 ° C. to 900 ° C. exceeds the value 1. Thus, at the temperature of at least one of 700 ° C. to 900 ° C., the inner straight portion 76a and the outer straight portion 76b that are electrically connected in parallel to each other have the same applied voltage and the inner straight portion 76a flows. Since the current decreases, the heat generation density at the temperature of the inner straight portion 76a decreases. Therefore, as compared with the case where the unit resistance value ratio R1 / R2 is 1 or less, the temperature increase of the inner straight portion 76a is suppressed. That is, the temperature rise of the inner straight portion 76a that tends to become high temperature is offset by reducing the heat generation density of the inner straight portion 76a. Thereby, deterioration of the inner side straight part 76a can be suppressed. For this reason, it becomes difficult to produce a disconnection etc. in the inner side linear part 76a, and the lifetime of the inner side linear part 76a becomes long. And the lifetime of the inner straight part 76a which is easy to deteriorate becomes longer, so that the lifetime of the heater 72 as a whole becomes longer. If the temperature of the inner straight portion 76a is smaller than that in the case where the unit resistance value ratio R1 / R2 is 1, the effect of suppressing the deterioration of the inner straight portion 76a can be obtained. Therefore, it is not essential that the temperature of the inner straight portion 76a is lower than the outer straight portion 76b. For example, even if the temperature of the inner straight portion 76a is higher than that of the outer straight portion 76b, if the heat uniformity of the entire heat generating portion 76 is improved as compared with the case where the unit resistance value ratio R1 / R2 is 1, the inner straight portion 76a The effect of suppressing the deterioration of the straight portion 76a and extending the life of the heater 72 can be obtained.

  Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. The heater portion 70 of the present embodiment corresponds to a ceramic heater of the present invention, the lead portion 79 corresponds to a lead portion, the straight portion 78 corresponds to a straight portion, the heat generating portion 76 corresponds to a heat generating portion, and the heater 72 The first substrate layer 1, the second substrate layer 2, and the third substrate layer 3 correspond to a heating element, and correspond to a ceramic body.

  According to the gas sensor 100 of the present embodiment described in detail above, the heat generating portion 76 of the heater 72 does not include a bent portion that is likely to cause disconnection due to deterioration. Thereby, the lifetime of the heater 72 can be extended compared with the case where the heat generating part 76 has a bent part.

  Further, the heat generating portion 76 has three or more straight portions 78, and the plurality of straight portions 78 are arranged along a first direction (front-rear direction) intersecting the length direction (left-right direction) of the straight portions 78. Are arranged electrically in parallel with each other. The resistance value of the inner straight portion 76a per unit length at at least one temperature in the temperature range of 700 ° C. or higher and 900 ° C. or lower is higher than the outer straight portion 76b (= the unit resistance value ratio R1 / R2 is a value). 1). Thereby, the heat generation density of the inner straight portion 76a is smaller than that of the outer straight portion 76b at at least one of the temperatures of 700 ° C. to 900 ° C., and deterioration of the inner straight portion 76a can be suppressed. Therefore, the lifetime of the heater 72 as a whole can be extended.

  In addition, since the unit resistance value ratio R1 / R2 at the temperature in at least one of the above temperature ranges is 1.15 or more, the effect of suppressing the deterioration of the inner straight portion 76a is further enhanced. When the unit resistance value ratio R1 / R2 is equal to or greater than 1.25, the effect of suppressing the deterioration of the inner straight portion 76a is further enhanced. Since the inner straight portion 76a has a smaller cross-sectional area perpendicular to the length direction than the outer straight portion 76b, the resistance value (unit resistance value R1) per unit length of the inner straight portion 76a is the unit of the outer straight portion 76b. It tends to be higher than the resistance value R2. When the cross-sectional area ratio S2 / S1 is a value of 1.15 or more, the unit resistance value ratio R1 / R2 at a temperature in at least one of the above temperature ranges tends to be a value of 1.15 or more. When the cross-sectional area ratio S2 / S1 is a value of 1.25 or more, the unit resistance value ratio R1 / R2 at a temperature in at least one of the above temperature ranges tends to be a value of 1.25 or more.

  Furthermore, the sensor element 101 includes a heater unit 70 and detects a specific gas concentration in the gas to be measured. The gas sensor 100 includes a sensor element 101.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

For example, in the above-described embodiment, the cross-sectional area ratio S2 / S1 is set to exceed the value 1, but the unit resistance value ratio R1 / R2 at a temperature in the temperature range of 700 ° C. to 900 ° C. exceeds the value 1. That's fine. For example, the volume resistivity (unit: [μΩ · cm]) at the temperature in at least one of the above temperature ranges may be higher in the inner straight portion 76a than in the outer straight portion 76b. That is, the volume resistivity ratio ρ1 / ρ2, which is the ratio between the volume resistivity ρ1 of the inner straight portion 76a and the volume resistivity ρ2 of the outer straight portion 76b, is greater than 1 at any temperature in the above temperature range. There may be. Even in this case, the unit resistance value ratio R1 / R2 at at least one of the temperatures in the above temperature range can be exceeded by 1, and deterioration of the inner straight portion 76a can be suppressed and the life of the heater 72 can be extended. The volume resistivity ratio ρ1 / ρ2 is preferably a value of 1.15 or more, more preferably a value of 1.25 or more, at least in any of the above temperature ranges. For example, the volume resistivity ρ1 can be made higher than the volume resistivity ρ2 by increasing the ratio of the noble metal (conductor) included in the outer straight portion 76b as compared with the inner straight portion 76a. Alternatively, for example, the inner straight portion 76a has platinum as a main component, and the outer straight portion 76b can be added by adding a noble metal (rhodium, gold, etc.) having a lower volume resistivity than platinum in addition to or instead of platinum. ρ1 can be higher than the volume resistivity ρ2. That is, the outer straight portion 76b may contain a noble metal having a volume resistivity lower than that of the noble metal contained in the inner straight portion 76a without being included in the inner straight portion 76a. Alternatively, the outer straight portion 76b contains a material having a smaller temperature coefficient of resistance (unit: [% / ° C.]) than that of the main component noble metal more than the inner straight portion 76a. The volume resistivity ρ1 at such temperature can be made higher than the volume resistivity ρ2. Examples of such a material having a small resistance temperature coefficient include nichrome (alloy containing nickel (Ni) and chromium (Cr)), cantal (registered trademark: alloy containing iron, chromium, and aluminum), molybdenum disilicide (MoSi). ₂ ). The values of the volume resistivity ρ1, ρ2 are also average values of the inner straight portion 76a and the outer straight portion 76b, similarly to the unit resistance values R1, R2. Further, at any temperature within the above temperature range, the volume resistivity ratio ρ1 / ρ2 may be a value of 2.0 or less.

  In the above-described embodiment, as shown in FIG. 2, the cross-sectional area perpendicular to the length direction is the same at any location of the first linear portion 78a, but the present invention is not limited to this. For example, there may be a portion where the cross-sectional area changes, such as a part of the first straight portion 78a being wide. Thus, the average value of the cross-sectional areas of the first straight portions 78a can also be adjusted by changing the partial cross-sectional areas. The same applies to the second and third straight portions 78b and 78c. In addition, the linear portion 78 may have a shape in which at least one of both ends in the length direction becomes wider as it gets closer to the connection portion with the lead portion 79. FIG. 3 is an explanatory diagram of a heater 72A of a modified example in this case. In FIG. 3, both ends of the linear portion 78 have a shape that increases in a circular arc shape, but the present invention is not limited to this, and may have a shape that increases in a linear shape. As described above, since the end of the straight portion 78 becomes wider as the end of the straight portion 78 is closer to the connection portion with the lead portion 79, the end of the straight portion 78 becomes stronger against stress due to thermal expansion. Deterioration (disconnection, etc.) of the end portion of the straight portion 78 due to the influence of stress can be further suppressed. In particular, when the width of the straight portion 78 is narrow, it is preferable that the end portion has such a shape.

  In addition, in the heater part 70 of embodiment mentioned above, you may combine making cross-sectional area ratio S2 / S1 over value 1 and making volume resistivity ratio ρ1 / ρ2 over value 1. For example, the product (= unit resistance value ratio R1 / R2) of the cross-sectional area ratio S2 / S1 and the volume resistivity ratio ρ1 / ρ2 at a temperature in at least one of the above temperature ranges exceeds the value 1, and the value 1.15. Alternatively, the value may be 1.25 or more. Even when the cross-sectional area ratio S2 / S1 exceeds the value 1, the material of the inner straight portion 76a and the outer straight portion 76b may be different.

  In the embodiment described above, the heat generating portion 76 has the three straight portions 78, but is not limited thereto. For example, the heat generating part 76 may have two straight parts 78. In this case, the straight portion 78 closer to the end of the ceramic body in the first direction (front-rear direction) described above is the outer straight portion 76b, and the far straight portion 78 (closer to the center of the ceramic body) is the inner straight line. Let it be portion 76a. For example, when the heat generating portion 76 does not include the third straight portion 78c in FIG. 2, the first straight portion 78a is the outer straight portion 76b, and the second straight portion 78b is the inner straight portion 76a. In this case as well, the inner straight portion 76a is located farther from the end (front end) of the ceramic body, that is, from the outside, than the outer straight portion 76b, so that the temperature tends to be high. Therefore, the deterioration of the inner straight portion 76a can be suppressed by setting the unit resistance value R1 at the temperature in at least one of the above temperature ranges to be higher than the unit resistance value R2.

  In the embodiment described above, the number of straight portions 78 included in the heat generating portion 76 is not limited to three, and may be four or more. When there are four or more straight portions 78, the number of the straight portions 78 is divided into three, and the number of 1/3 each located on both sides (one end side and the other end side) in the first direction is defined as the outer straight portion 76b. The one-third number sandwiched between the outer straight portions 76b is defined as the inner straight portion 76a. In addition, when the remainder which remove | divided the number of the linear parts 78 by the value 3 arises, the number of remainders shall be included in the inner side linear part 76a. For example, when the heat generating unit 76 includes five straight portions 78, the outer straight portions 76b are two (one on each side in the first direction) and the inner straight portions 76a are three.

  In the above-described embodiment, the plurality of straight portions 78 have the same length in the left-right direction, but are not limited thereto. In the above-described embodiment, the plurality of linear portions 78 are disposed along the first direction (front-rear direction) orthogonal to the length direction (left-right direction), but the first direction is orthogonal to the length direction. It is not limited to the direction to be used, and any direction that intersects may be used.

  In the above-described embodiment, the plurality of linear portions 78 are connected between the same first lead 79a and second lead 79b, but are not limited thereto. For example, there are a plurality of first leads 79a (positive lead) and second leads 79b (negative lead), respectively, and the first lead 79a, second lead 79b to which the first straight portion 78a is connected, and the second straight line. The first lead 79a and the second lead 79b to which the portion 78b is connected may be different. In addition, when at least one of the plurality of straight portions 78 is connected to the first lead 79a and the second lead 79b different from the other straight portions 78, at least one of the plurality of straight portions 78 is The applied voltage may be different from that of the other straight part 78. However, for example, if the voltage applied to the inner straight portion 76b is too high compared to the outer straight portion 76b, the heat generation density of the inner straight portion 76a does not decrease compared to the outer straight portion 76b. Is preferably determined. Conversely, by reducing the voltage applied to the inner straight portion 76a as compared to the outer straight portion 76b, the heat generation density of the inner straight portion 76a can be reduced by that amount compared to the outer straight portion 76b.

  In the embodiment described above, the unit resistance value ratio R1 / R2 may be 1 or less at any temperature in the temperature range of 700 ° C. or more and 900 ° C. or less. Even in such a case, since the heat generating portion 76 does not include the bent portion, an effect of extending the life of the heater 72 can be obtained.

  In the above-described embodiment, the first lead 79a and the second lead 79b have a linear shape. However, the first lead 79a and the second lead 79b do not reach a temperature as high as that of the heat generating portion 76, and thus have a bent portion. It may be.

  In the above-described embodiment, the plurality of linear portions 78 have a length direction parallel to the short direction (left-right direction) of the heater unit 70, but are not limited thereto. For example, the length direction of the plurality of linear portions 78 may be inclined from the left-right direction, and the length direction may be parallel to the longitudinal direction (front-rear direction) of the heater unit 70.

  In the above-described embodiment, the heater 72 has a belt shape, but is not limited thereto, and may have a linear shape (for example, a circle or an ellipse in section).

  In the above-described embodiment, the gas sensor 100 including the heater unit 70 has been described. However, the present invention may be the sensor element 101 alone or the heater unit 70 alone, that is, the ceramic heater alone. In addition, although the heater part 70 was provided with the 1st board | substrate layer 1, the 2nd board | substrate layer 2, and the 3rd board | substrate layer 3, it should just have the ceramic body which surrounds the heater 72. FIG. For example, the lower layer of the heater 72 may be only one layer, not the first substrate layer 1 and the second substrate layer 2. The heater unit 70 includes the heater insulating layer 74, but the ceramic body (for example, the first substrate layer 1 and the second substrate layer 2) surrounding the heater 72 is made of an insulating material (for example, alumina ceramic). If present, the heater insulating layer 74 may be omitted. The size of the sensor element 101 may be, for example, a length in the front-rear direction of 25 mm to 100 mm, a width in the left-right direction of 2 mm to 10 mm, and a thickness in the vertical direction of 0.5 mm to 5 mm.

  Hereinafter, an example in which a sensor element is specifically manufactured will be described as an example. Experimental Examples 1 to 12 correspond to examples of the present invention, and Experimental Example 13 corresponds to a comparative example. In addition, this invention is not limited to a following example.

[Experimental Examples 1-6]
According to the manufacturing method of the gas sensor 100 of the embodiment described above, the sensor element 101 shown in FIGS. Experimental Examples 1 to 6 have the same configuration except that the cross-sectional area ratio S2 / S1 is variously changed as shown in Table 1 below by changing the width W1 of the inner straight portion 76a (second straight portion 78b). did. The sensor element 101 has a length in the front-rear direction of 67.5 mm, a width in the left-right direction of 4.25 mm, and a thickness in the vertical direction of 1.45 mm. The width W1 of the inner straight portion 76a and the width W2 of the outer straight portion 76b (first and third straight portions 78a, 78c) in Experimental Example 1 were both 0.25 mm. Further, the thickness D1 of the inner straight portion 76a and the thickness D2 of the outer straight portion 76b in Experimental Example 1 were both set to 0.01 mm. In producing the sensor element 101, the ceramic green sheet was formed by mixing zirconia particles to which 4 mol% of a stabilizer yttria was added, an organic binder, and an organic solvent, and then forming a tape. The conductive paste for the heat generating part 76 of the heater part 70 was adjusted as follows. Preliminary mixing was performed by adding 4% by mass of alumina particles, 96% by mass of Pt, and a predetermined amount of acetone as a solvent to obtain a premixed solution. By adding and mixing the organic binder liquid obtained by dissolving 20% by mass of polyvinyl butyral in 80% by mass of butyl carbitol to the premixed solution, and adjusting the viscosity by adding butyl carbitol as appropriate. A conductive paste was obtained. In Experimental Example 1, the same conductive paste is used for the inner straight portion 76a and the outer straight portion 76b, and the volume resistivity ratio ρ1 / ρ2 is 1 at any temperature of 700 ° C. to 900 ° C. is there. The same applies to Experimental Examples 2 to 6.

[Experimental Examples 7 to 12]
Sensor elements 101 of Experimental Examples 7 to 12 were fabricated in the same manner as Experimental Example 1 except that the volume resistivity ratio ρ1 / ρ2 was variously changed as shown in Table 1 below. The volume resistivity ratio ρ1 / ρ2 was changed by changing the content ratio of Pt in the inner straight portion 76a. Note that the widths W1 and W2 and the thicknesses D1 and D2 of Experimental Examples 7 to 12 are all the same as those of Experimental Example 1, and the cross-sectional area ratio S2 / S1 of Experimental Examples 7 to 12 is a value of 1.00. . In Experimental Example 7 and Experimental Example 1, the value of the cross-sectional area ratio S2 / S1 and the value of the volume resistivity ratio ρ1 / ρ2 are the same.

  In addition, the measurement of volume resistivity (rho) 1 of Experimental Examples 7-12 was performed using the test piece produced as follows. First, the insulating paste used as the heater insulating layer 74 was printed on the ceramic green sheet used as the 2nd board | substrate layer 2 after baking. Next, the conductive paste for the inner straight portion 76a produced under the same conditions as in each of Experimental Examples 7 to 12 was printed in a rectangular parallelepiped shape on the insulating paste. Then, it baked on the same conditions as Experimental Examples 7-12, the rectangular parallelepiped heating part was formed, and each test piece of Experimental Examples 7-12 was obtained. And the lead for resistance value measurement was attached to the heat generating part of the rectangular parallelepiped shape, the test piece was heated to 700 ° C. to 900 ° C. with an electric furnace, and the resistance value of the heat generating part was measured in this state. And volume resistivity (rho) 1 was computed based on the length and cross-sectional area of a rectangular parallelepiped heat-emitting part, and the measured resistance value. Similarly, the volume resistivity ρ2 was calculated from the resistance value measured using a test piece. In addition, the value of volume resistivity ratio (rho) 1 / (rho) 2 of Experimental Examples 7-12 hardly changed in the range of 700 to 900 degreeC.

[Experimental Example 13]
A sensor element of Experimental Example 13 was produced in the same manner as in Experimental Example 1 except that the shape of the heater (the heat generating portion and the lead portion) was the same as that of the heater 372 shown in FIG. That is, in Experimental Example 13, the heat generating portion has a shape having four straight portions and three bent portions connected in series. The width and thickness of the heat generating part were also the same as in Experimental Example 1.

[Evaluation test]
For Experimental Examples 1 to 13, the durability (life) of the heat generating portion 76 was evaluated. Specifically, a voltage is applied to the lead portion 79 so that the heater 72 is energized so that the average value of the temperature of the heat generating portion 76 becomes a predetermined temperature. In this state, it was determined whether or not a disconnection occurred in the heat generating portion 76 within 2000 hours. The case where disconnection did not occur after 2000 hours was designated as “A (excellent, practical level or higher)”, and the case where disconnection occurred within 2000 hours after 1000 hours was designated as “B (good, practical level)”. The case where disconnection occurred within 1000 hours was defined as “C (impossible, less than practical level)”. The durability of the heat generating portion 76 was evaluated for each case where the average temperature of the heat generating portion 76 was 700 ° C., 750 ° C., 800 ° C., 850 ° C., and 900 ° C. The temperature of the heat generating portion 76 was adjusted by changing the voltage applied to the lead portion 79. Moreover, the temperature of the heat generating part 76 was indirectly measured by measuring the temperature of the lower surface of the sensor element 101 with a radiation thermometer. The results of the evaluation test are shown in Table 1. Table 1 also shows values of the unit resistance value ratio R1 / R2, the cross-sectional area ratio S2 / S1, and the volume resistivity ratio ρ1 / ρ2 of each experimental example. The value of the unit resistance value ratio R1 / R2 was calculated as the product of the cross-sectional area ratio S2 / S1 and the volume resistivity ratio ρ1 / ρ2.

  As shown in Table 1, in Experimental Examples 1 to 12 having no bent portion, disconnection was less likely to occur than in Experimental Example 13 having a bent portion at any temperature of 700 ° C. to 900 ° C. Moreover, when Experimental Examples 1-12 were compared, the tendency for the disconnection of the heat generating part 76 to become hard to produce was seen, so that the value of unit resistance value ratio R1 / R2 was large. As the value of the unit resistance value ratio R1 / R2 is larger, there is a tendency that disconnection of the heat generating portion 76 is less likely to occur even at a higher temperature. In Examples 4 to 6 and 10 to 12, in which the unit resistance value ratio R1 / R2 is 1.15 or more, the evaluation is A (excellent) or B (good) at any temperature of 700 ° C. to 900 ° C. Met. In Experimental Examples 6 and 12 in which the unit resistance value ratio R1 / R2 was 1.25 or more, the evaluation was A (excellent) at any temperature of 700 ° C. to 900 ° C. In Experimental Examples 1 to 12, in the experimental examples where the evaluation was B (good) or C (impossible), the inner straight portion 76a was disconnected. In Experimental Example 12, the bent portion was disconnected at any temperature. Further, from comparison between Experimental Examples 1-6 and Experimental Examples 7-12, if the unit resistance value ratio R1 / R2 is the same, the volume resistivity ratio ρ1 is the same as when the cross-sectional area ratio S2 / S1 is changed. It was found that the same result was obtained when / ρ2 was changed. In addition, when the cross-sectional area ratio S2 / S1 was changed by changing the thickness D1 of the inner straight portion 76a, the same results as in Experimental Examples 1 to 6 were obtained.

  DESCRIPTION OF SYMBOLS 1 1st board | substrate layer, 2nd board | substrate layer, 3rd board | substrate layer, 4th 1st solid electrolyte layer, 5 spacer layer, 6 2nd solid electrolyte layer, 10 gas inlet, 11 1st diffusion control part, 12 buffer Space, 13 Second diffusion limiting part, 20 First internal space, 21 Main pump cell, 22 Inner pump electrode, 22a Ceiling electrode part, 22b Bottom electrode part, 23 Outer pump electrode, 24 Variable power supply, 30 Third diffusion limiting part , 40 2nd internal space, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 45 4th diffusion control part, 46 Variable power supply, 48 Air introduction layer, 50 Auxiliary pump cell, 51 Auxiliary pump Electrode, 51a Ceiling electrode part, 51b Bottom electrode part, 52 Variable power supply, 70 Heater part, 71 Heater connector electrode, 72, 72A Heater, 73 Through hole, 7 4 Heater insulation layer, 75 Pressure dissipation hole, 76 Heat generating part, 76a Inner straight part, 76b Outer straight part, 78 Straight part, 78a-78c First to third straight part, 79 Lead part, 79a, 79b First, first 2-lead, 80 oxygen partial pressure detection sensor cell for main pump control, 81 oxygen partial pressure detection sensor cell for auxiliary pump control, 82 oxygen partial pressure detection sensor cell for measurement pump control, 83 sensor cell, 100 gas sensor, 101 sensor element, 372 heater, 377 Bending part, 378 Straight part.

Claims (11)

A heating element comprising: a lead portion having a first lead and a second lead; and a heat generating portion having a plurality of linear portions connecting between the first lead and the second lead;
A ceramic body surrounding the heating element;
Equipped with a,
The heat generating portion has three or more straight portions,
The plurality of straight portions are arranged along a first direction intersecting the length direction of the straight portions, and are arranged in parallel with each other, and the straight portions located on one end side in the first direction; At least one temperature in the temperature range of 700 ° C. or more and 900 ° C. or less when the straight portion located on the other end side is defined as the outer straight portion and the straight portion located between the outer straight portions is defined as the inner straight portion. The resistance value of the inner straight portion per unit length is higher than that of the outer straight portion.
Ceramic heater. When the resistance value per unit length of the inner straight portion is a unit resistance value R1 [μΩ / mm], and the resistance value per unit length of the outer straight portion is a unit resistance value R2 [μΩ / mm]. The unit resistance value ratio R1 / R2 at a temperature in at least one of the temperature ranges is 1.15 or more.
The ceramic heater according to claim 1 . The unit resistance value ratio R1 / R2 at a temperature in at least one of the temperature ranges is a value of 1.25 or more.
The ceramic heater according to claim 2 . The inner straight portion has a smaller cross-sectional area perpendicular to the length direction than the outer straight portion,
The ceramic heater according to any one of claims 1 to 3 . The cross-sectional area ratio S2 / S1 between the cross-sectional area S1 [mm ² ] perpendicular to the length direction of the inner straight portion and the cross-sectional area S2 [mm ² ] perpendicular to the length direction of the outer straight portion is 1.15. That's it,
The ceramic heater according to claim 4 . The cross-sectional area ratio S2 / S1 is a value of 1.25 or more,
The ceramic heater according to claim 5 . The inner straight portion has a higher volume resistivity at a temperature in at least one of the temperature ranges than the outer straight portion.
The ceramic heater according to any one of claims 1 to 6 . The volume resistivity ratio ρ1 which is the ratio of the volume resistivity ρ1 [μΩ · cm] of the inner straight portion to the volume resistivity ρ2 [μΩ · cm] of the outer straight portion at at least one temperature in the temperature range. / Ρ2 is a value of 1.15 or more,
The ceramic heater according to claim 7 . The volume resistivity ratio ρ1 / ρ2 at a temperature in at least one of the temperature ranges is a value of 1.25 or more,
The ceramic heater according to claim 8 . Comprising a ceramic heater according to any one of claims 1 to 9 sensor element for detecting a specific gas concentration in the measurement gas. A gas sensor comprising the sensor element according to claim 10 .

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