JP2017041431A - Ceramic heater, sensor element, and gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of a bent part of an exothermic body.SOLUTION: A heater part includes a heater 72, having a linear part 78 and a bent part 77. Resistance per unit length of the bent part 77 at any temperature in a temperature range of greater than or equal to 700°C and less than or equal to 900°C is lower than that of the linear part 78. When resistance per unit length of the bent part 77 is denoted as unit resistance R1, and resistance per unit length of the linear part 78 is denoted as unit resistance R2, a unit resistance ratio R1/R2 at least at any temperature of the temperature range is less than or equal to 0.87.SELECTED DRAWING: Figure 2

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). The heater pattern described in Patent Document 1 includes a linear conductor portion formed along the longitudinal direction and a folded conductor portion that connects the linear conductor portions. Moreover, what has a pattern provided with the linear part along a transversal direction and the folding | returning part which connects linear parts is 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 a problem, and a main object thereof is to suppress the deterioration of the bent portion 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 having a linear portion and a bent portion having a resistance value per unit length at a temperature in the temperature range of 700 ° C. or higher and 900 ° C. or lower lower than that of the linear portion;
A ceramic body surrounding the heating element;
It is equipped with.

  In this ceramic heater, the heating element has a straight portion and a bent portion. And the resistance value per unit length in the bending part at least in any temperature of the temperature range of 700 degreeC or more and 900 degrees C or less is low compared with a linear part. As a result, at least at a temperature of 700 ° C. to 900 ° C., the bent portion has a smaller heat generation density (a heat generation amount per unit length) than the straight portion, and the temperature is unlikely to rise. Since the heating element is more likely to deteriorate as the temperature becomes higher, it is difficult for the temperature of the bent portion to rise compared to the straight portion, so that deterioration of the bent portion can be suppressed.

  In the ceramic heater of the present invention, the resistance value per unit length of the bent portion is a unit resistance value R1 [μΩ / mm], and the resistance value per unit length of the linear portion is a unit resistance value R2 [μΩ / mm. ], The unit resistance value ratio R1 / R2 at at least one temperature in the temperature range may be 0.87 or less. If it carries out like this, the effect which suppresses deterioration of a bending 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 0.80 or less.

In the ceramic heater of the present invention, the bent portion may have a larger cross-sectional area perpendicular to the length direction than the straight portion. If it carries out like this, the resistance value per unit length of a bending part will become low easily compared with a linear part. In this case, the heating element may have a strip shape, and the bent portion may have a thickness greater than or equal to the thickness of the linear portion. The cross-sectional area ratio S2 / S1 between the cross-sectional area S1 [mm ² ] perpendicular to the length direction of the bent portion and the cross-sectional area S2 [mm ² ] perpendicular to the length direction of the straight portion is 0.87. The following is preferable. In this case, the unit resistance value ratio R1 / R2 at a temperature in at least one of the temperature ranges described above tends to be 0.87 or less. The cross-sectional area ratio S2 / S1 is more preferably 0.80 or less.

  In the ceramic heater of the present invention, the bent portion may have a lower volume resistivity at a temperature in at least one of the temperature ranges than the linear portion. If it carries out like this, the resistance value per unit length of a bending part will become low easily compared with a linear part. In this case, the volume resistivity which is a ratio of the volume resistivity ρ1 [μΩ · cm] of the bent portion and the volume resistivity ρ2 [μΩ · cm] of the linear portion at at least one temperature in the temperature range. The ratio ρ1 / ρ2 is preferably less than or equal to 0.87. In this case, the unit resistance value ratio R1 / R2 at a temperature in at least one of the temperature ranges described above tends to be 0.87 or less. Further, it is more preferable that the volume resistivity ratio ρ1 / ρ2 at a temperature in at least one of the temperature ranges is 0.80 or less.

  In the ceramic heater of the present invention, the ceramic body is a plate-like body having a longitudinal direction and a short direction, and the heating elements are arranged along the short direction as the linear portion and are in the length direction. Has four or more linear portions along the longitudinal direction, and the heating element has a plurality of one ends connecting the linear portions adjacent to each other in the lateral direction as the bent portions on one end side in the longitudinal direction. You may have a side bending part and the 1 or more other side bending part which connects the linear parts adjacent to the said transversal direction by the other end side of the said longitudinal direction.

  In the ceramic heater of the present invention, the ceramic body is a plate-like body having a longitudinal direction and a short direction, and the heating element as a whole is bent back and forth so that the folding direction is along the short direction. One or more regions each having a dense fold pitch along the short direction and a rough region are provided along the longitudinal direction so as to be folded along the longitudinal direction. The body exists as a part of the bent portion in the highest temperature region of the one or more dense regions that is the highest temperature when the heating element generates heat, and the folded vertices face each other in the short direction. The first bent portion may have a resistance value per unit length at a temperature in at least one of the temperature ranges lower than that of the linear portion. Here, the first bent portion is likely to be locally high in the highest temperature region due to heat transfer between the first bent portions facing each other. Therefore, among the bent portions, the first bent portion is particularly likely to become high temperature and easily deteriorates. On the other hand, the straight portion is less likely to be hot than the first bent portion. In this ceramic heater, since the resistance value per unit length at the temperature of at least one of the temperature ranges described above is lower than that of the linear portion, the first bent portion has a local area within the maximum temperature region of the heating element. Heating can be further reduced. That is, the temperature rise of the 1st bending part which tends to become high temperature can be suppressed more. Thereby, deterioration of the 1st bending part which is especially easy to deteriorate among bending parts can be controlled.

  In the ceramic heater of the present invention, the ceramic body is a plate-like body having a longitudinal direction and a short direction, and the heating element as a whole is bent back and forth so that the folding direction is along the short direction. One or more regions each having a dense fold pitch along the short direction and a rough region are provided along the longitudinal direction so as to be folded along the longitudinal direction. The body exists as a part of the bent portion in the highest temperature region of the one or more dense regions that is the highest temperature when the heating element generates heat, and the folded vertices face each other in the short direction. A first bent portion that is a portion and a third bent portion that exists in the highest temperature region and that exists outside the first bent portion in the short direction, the first bent portion being: Low temperature range And it may be lower than the resistance value per unit length also at any temperature between the third bend. Here, the first bent portion is likely to be locally high in the highest temperature region due to heat transfer between the first bent portions facing each other. Therefore, among the bent portions, the first bent portion is particularly likely to become high temperature and easily deteriorates. On the other hand, the third bent portion is located on the outer side of the ceramic body with respect to the first bent portion, and therefore, the third bent portion is less likely to reach a higher temperature than the first bent portion. In this ceramic heater, since the resistance value per unit length of the first bent portion is lower than that of the third bent portion at least in one of the above temperature ranges, the first bent portion is within the maximum temperature region of the heating element. The local heating can be further reduced. That is, the temperature rise of the 1st bending part which tends to become high temperature can be suppressed more. Thereby, deterioration of the 1st bending part which is especially easy to deteriorate among bending parts can be controlled.

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 suppressing deterioration of the bent portion of the heating element can be obtained.

The gas sensor of the present invention is
The sensor element of the present invention 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 ceramic heater or sensor element of the present invention described above, for example, an effect of suppressing deterioration of the bent portion 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 72B of a modification. Explanatory drawing of the heater 72C of a modification. The conceptual diagram of the temperature distribution along the left-right direction around the highest temperature area | region (1st area | region 90a) of the heat generating part 76. FIG.

  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 a suitable electrode outside the sensor element 101 is sufficient.

  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.

  Further, the heat generating portion 76 of the heater 72 is embedded over the entire area from the first internal space 20 to the second internal space 40, and the entire sensor element 101 is adjusted to a temperature at which the solid electrolyte is activated. Is possible.

  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 heating part 76 is a resistance heating element, and has a strip-like single-stroke shape in which both ends are connected to the lead part 79 as shown in FIG. The heat generating portion 76 has a plurality of (three in this embodiment) bent portions 77 and a plurality (four in this embodiment) straight portions 78. The plurality of bent portions 77 and the plurality of linear portions 78 are electrically connected in series. The heat generating portion 76 has a symmetrical shape.

  The plurality of linear portions 78 are arranged at equal intervals along the short direction (left-right direction) of the sensor element 101. In each of the plurality of linear portions 78, the length direction is along the longitudinal direction (front-rear direction) of the sensor element 101. In the present embodiment, the plurality of linear portions 78 are arranged so that the length direction is parallel to the front-rear direction. Of the plurality of straight line portions 78, the leftmost straight line portion 78 has a rear end connected to the first lead 79a. The rear end of the straight line portion 78 located on the rightmost side among the plurality of straight line portions 78 is connected to the second lead 79b.

  Each of the plurality of bent portions 77 connects the linear portions 78 adjacent in the left-right direction. The bent portion 77 is a front end side bent portion 77a that connects the front end sides (one end side) of the adjacent linear portions 78 and a rear end side bent that connects the rear end sides (the other end side) of the adjacent straight portions 78. Part 77b. In this embodiment, the bent portion 77 has two front end side bent portions 77a and one rear end side bent portion 77b. The plurality of bent portions 77 are bent in a curved shape and have a semicircular arc shape. The bent portion 77 may be bent in a polygonal line shape.

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 bending portion 77 has a linear portion 78 having a resistance value per unit length at least in a temperature range of 700 ° C. or higher and 900 ° C. or lower, which is a temperature range in which the heat generating portion 76 may be heated during use. It is lower than In other words, when the resistance value per unit length of the bent portion 77 is a unit resistance value R1 [μΩ / mm], and the resistance value per unit length of the straight portion 78 is a unit resistance value R2 [μΩ / mm]. Further, the unit resistance value ratio R1 / R2 at a temperature in at least one of the above temperature ranges is less than 1. By doing so, at at least one of the temperatures of 700 ° C. to 900 ° C., the bent portion 77 has a smaller heat generation density (a heat generation amount per unit length) than the straight portion 78, and the temperature is unlikely to rise. Here, as the temperature rises, the heat generating portion 76 is more likely to be deteriorated due to oxidation (for example, oxidation of Pt, which is a noble metal component in the heat generating portion 76). By setting the unit resistance value ratio R1 / R2 to a value less than 1, the temperature rise of the bent portion 77 can be suppressed, and the bent portion 77 is deteriorated as compared with the case where the unit resistance value ratio R1 / R2 is 1 or more. Can be suppressed.

  The length direction of the bent portion 77 and the straight portion 78 is the axial direction of the bent portion 77 and the straight portion 78, in other words, the direction in which current flows. The unit resistance value R1 is an average value of resistance values per unit length of the bent portion 77. Similarly, the unit resistance value R2 is the average value of the resistance values per unit length of the linear portion 78. Therefore, even if there is a part where the resistance value per unit length is higher than that of the straight part 78 in a part of the bending part 77, the bending part 77 only needs to have a lower resistance value per unit length as a whole. However, it is preferable that the resistance value per unit length is lower than the unit resistance value R2 in any of the bent portions 77. Further, it is preferable that the unit resistance value ratio R1 / R2 is less than 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 any of the above temperature ranges is preferably a value of 0.87 or less, and more preferably a value of 0.80 or less. Further, the unit resistance value ratio R1 / R2 may be 0.5 or more at any temperature in the above temperature range.

In the present embodiment, the bent portion 77 and the straight portion 78 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 bent portion 77 is the length of the straight portion 78. The cross-sectional area S2 [mm ² ] perpendicular to the vertical direction is made larger. That is, the heat generating portion 76 has a cross-sectional area ratio S2 / S1 of less than 1. By doing so, the unit resistance value ratio R1 / R2 becomes less than the value 1 in any temperature range from 700 ° C. to 900 ° C. The cross-sectional area ratio S2 / S1 is preferably 0.87 or less, and more preferably 0.80 or less. The cross-sectional area ratio S2 / S1 is adjusted, for example, by making the width W1 of the bent portion 77 larger than the width W2 of the straight portion 78, or making the thickness D1 of the bent portion 77 larger than the thickness D2 of the straight portion 78. Or at least one of them. For example, when the width W1> the width W2, if the cross-sectional area ratio S2 / S1 is less than 1, the thickness D1 <thickness D2 may be satisfied, and the thickness D1 = thickness D2. Or thickness D1> thickness D2 may be sufficient. Similarly, when thickness D1> thickness D2, as long as the cross-sectional area ratio S2 / S1 is less than value 1, width W1 <width W2 may be satisfied, and width W1 = width W2 may be satisfied. Alternatively, width W1> width W2 may be satisfied. The values of the cross-sectional areas S1 and S2 are also average values of the bent portion 77 and the straight portion 78, similarly to the unit resistance values R1 and R2. In the present embodiment, the cross-sectional area of the straight portion 78 is the same value (= cross-sectional area S2) in any part. The bent portion 77 has the same cross-sectional area as that of the straight portion 78 at the connection portion with the straight portion 78, and has a shape in which the cross-sectional area increases as the position is away from the straight portion 78. That is, each of the plurality of bent portions 77 has a shape in which the cross-sectional area of the cross section of the left and right central portions (for example, the cross section passing through the most protruding portion in the case of the bent portions 77a) is the largest. The cross-sectional area ratio S2 / S1 may be 0.5 or more. The widths W1 and W2 may be 0.05 mm or more and 1.5 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 rear side of the heat generating portion 76 and a second lead 79b disposed on the right rear 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 and second leads 79a and 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 has a wider cross-sectional area than the heat generating portion 76. ing. Note that the width of the lead portion 79 in the left-right direction is the same as that of the straight portion 78 at the connection portion with the front straight portion 78, but the width becomes wider toward the rear.

  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 is less than 1, that is, the cross-sectional area ratio S2 / S1 is less than 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. Further, 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 bent portion 77 is made higher than the pattern of the portion that becomes the linear portion 78, or the bending For example, the number of times of printing at the time of forming the pattern of the portion to be the portion 77 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. Except for the point that the unit resistance value ratio R1 / R2 is less than 1, the manufacturing method of the gas sensor as described above is known and described in, for example, International Publication No. 2013/005491.

  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 easily oxidized and deteriorated as the temperature becomes high. Moreover, in general, the bent portion is more susceptible to stress due to thermal expansion than the straight portion, and therefore, disconnection due to deterioration is more likely to occur than the straight portion. 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 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. is less than 1. As a result, at at least one of the temperatures of 700 ° C. to 900 ° C., the bent portion 77 has a lower heat generation density at that temperature than the straight portion 78, and the temperature is unlikely to rise. Thereby, deterioration of the bending part 77 can be suppressed and the lifetime of the bending part 77 becomes long.

  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 this embodiment corresponds to a ceramic heater of the present invention, the heater 72 corresponds to a heating element, the bent portion 77 corresponds to a bent portion, the straight portion 78 corresponds to a straight portion, and the first substrate layer 1, the second substrate layer 2 and the third substrate layer 3 correspond to a ceramic body.

  According to the gas sensor 100 of the present embodiment described in detail above, the heater unit 70 includes the heater 72 having the straight part 78 and the bent part 77. And the bending part 77 has the resistance value per unit length in the temperature range of 700 degreeC or more and 900 degrees C or less lower than a linear part. Thereby, at at least one of the temperatures of 700 ° C. to 900 ° C., the bent portion 77 has a heat generation density lower than that of the straight portion 78, and deterioration of the bent portion 77 can be suppressed. For this reason, it becomes difficult to produce a disconnection etc. in the bending part 77, and the lifetime of the bending part 77 becomes long. In addition, the life of the bent portion 77, which is likely to cause disconnection due to deterioration, is extended, so that the life of the heat generating portion 76 as a whole is also extended.

  In addition, since the unit resistance value ratio R1 / R2 at the temperature in at least one of the above temperature ranges is 0.87 or less, the effect of suppressing the deterioration of the bent portion 77 is further enhanced. When the unit resistance value ratio R1 / R2 is 0.80 or less, the effect of suppressing the deterioration of the bent portion 77 is further enhanced. Since the bent portion 77 has a larger cross-sectional area perpendicular to the length direction than the straight portion 78, the resistance value (unit resistance value R1) per unit length of the bent portion 77 is equal to the unit resistance value R2 of the straight portion 78. Compared to low. The heat generating portion 76 has a strip shape, and the bent portion 77 has a thickness equal to or greater than the thickness of the linear portion 78. Since the cross-sectional area ratio S2 / S1 has a value of 0.87 or less, the unit resistance value ratio R1 / R2 at the temperature in at least one of the above temperature ranges tends to be 0.87 or less. Further, when the cross-sectional area ratio S2 / S1 is 0.80 or less, the unit resistance value ratio R1 / R2 at any temperature in the temperature range described above tends to be 0.80 or less.

  Furthermore, the ceramic body (the first substrate layer 1, the second substrate layer 2, and the third substrate layer 3) is a plate-like body having a longitudinal direction and a short direction, and the heater 72 is a short portion as a straight portion 78. The heater 72 has four or more straight portions 78 that are arranged along the hand direction (left-right direction) and whose length direction is along the longitudinal direction (front-rear direction). A plurality of front end side bent portions 77a connecting the straight portions 78 to each other on the front end side in the longitudinal direction, and one or more rear end side bent portions connecting the straight portions 78 adjacent to each other in the short side direction on the rear end side in the longitudinal direction. 77b. 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 less than 1, but the unit resistance value ratio R1 / R2 at least in the temperature range of 700 ° C. to 900 ° C. is less than 1. That's fine. For example, the bent portion 77 may have a lower volume resistivity at least in one of the above temperature ranges than the straight portion 78. That is, the volume resistivity ratio, which is the ratio of the volume resistivity ρ1 [μΩ · cm] of the bent portion 77 and the volume resistivity ρ2 [μΩ · cm] of the linear portion 78 at least in any of the above temperature ranges. ρ1 / ρ2 may be less than 1. Even in this case, the unit resistance value ratio R1 / R2 at least in one of the above temperature ranges can be less than 1, and the deterioration of the bent portion 77 can be suppressed and the life of the heater 72 can be extended. The volume resistivity ratio ρ1 / ρ2 is preferably 0.87 or less, and more preferably 0.80 or less at least in any of the above temperature ranges. For example, the volume resistivity ρ1 can be made lower than the volume resistivity ρ2 by making the ratio of the noble metal (conductor) contained in the bent portion 77 higher than that of the straight portion 78. Alternatively, for example, the linear portion 78 is mainly composed of platinum, and the bent portion 77 can be obtained by adding a noble metal (rhodium, gold, etc.) having a lower volume resistivity than platinum in addition to or instead of platinum. The volume resistivity can be lower than ρ2. That is, the bent portion 77 may contain a noble metal having a volume resistivity lower than that of the noble metal contained in the straight portion 78 without being included in the straight portion 78. Alternatively, the bent portion 77 contains a material having a smaller temperature coefficient of resistance (unit: [% / ° C.]) than that of the main component noble metal, more than at least one of the above temperature ranges. The volume resistivity ρ1 at temperature can be made lower than the volume resistivity ρ2. Examples of such a material having a small resistance temperature coefficient include nichrome (an alloy containing nickel (Ni) and chromium (Cr)), Kanthal (registered trademark: an alloy containing iron, chromium, and aluminum), molybdenum disilicide (MoSi). ₂ ). Note that the values of the volume resistivity ρ1, ρ2 are also average values of the bent portion 77 and the straight portion 78, similarly to the unit resistance values R1, R2. Further, at any temperature in the above temperature range, the volume resistivity ratio ρ1 / ρ2 may be 0.5 or more.

  In the heater section 70, the cross-sectional area ratio S2 / S1 may be less than 1 and the volume resistivity ratio ρ1 / ρ2 may be less than 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 least at any temperature in the above temperature range is less than the value 1 and the value 0.87. Or less than 0.80. Even when the cross-sectional area ratio S2 / S1 is less than 1, the material of the bent portion 77 and the straight portion 78 may be different.

  The shape (pattern) of the heater 72 of the heater unit 70 is not limited to the above-described embodiment. The heater 72 only needs to have a bent portion 77 and a straight portion 78. For example, the linear part 78 may not be parallel as long as the length direction is along the longitudinal direction (front-rear direction) of the heater part 70. FIG. 3 is an explanatory diagram of a modified heater 72A. In the heater 72A, the two longitudinal directions of the four straight portions 78 are along the longitudinal direction, but are inclined with respect to the longitudinal direction. Specifically, the second straight portion 78 from the left is inclined so as to be located on the left side as it is rearward, and the second straight portion 78 from the right is inclined so that it is located on the right side as it is backward. By doing so, the radius (curvature radius) of the bent portion 77 can be increased as compared with the heater 72 having the shape of FIG. 2 described above. In other words, the width of the heat generating portion 76 in the left-right direction can be reduced without reducing the radius of curvature of the bent portion 77. Further, unlike FIG. 2, the lead portion 79 is wider than the straight portion 78 at the connecting portion with the straight portion 78 in the front. The shape of the lead portion 79 may be the same as that in FIG. 2, or the shape of the lead portion 79 in the heater 72 of FIG. 2 may be the same as that in FIG. Even with the heater 72 </ b> A of such a modification, the same effect as the above-described embodiment can be obtained. For example, the deterioration of the bent portion 77 can be suppressed by setting the unit resistance value ratio R1 / R2 at a temperature in the temperature range of 700 ° C. to 900 ° C. to be less than 1.

  In the above-described embodiment, the heat generating portion 76 includes the three bent portions 77 and the four straight portions 78, but is not limited thereto. For example, the number of the bent portions 77 may be three or more, one or two, and the number of the straight portions 78 may be four or more, or may be three or less. The straight line portion 78 may be four or more even numbers. Regarding the number of the front end side bent portions 77a and the rear end side bent portions 77b, the front end side bent portion 77a and the rear end side bent portion 77b are one in this embodiment, but It can be changed according to the number. For example, the number of the distal end side bent portions 77a may be one, or two or more as long as it is plural. The rear end side bent portion 77b may be one or more. When the number of the straight portions 78 is two and the number of the bent portions 77 is one, the heat generating portion 76 may not have the rear end side bent portion 77b.

  In the embodiment described above, the length direction of the straight portion 78 is along the longitudinal direction (front-rear direction), but the length direction of the straight portion 78 may be along the short direction of the heater portion 70. In this case, a plurality of linear portions 78 are arranged along the longitudinal direction of the heater portion 70, and the bent portion 77 connects the linear portions 78 adjacent to each other in the longitudinal direction at one end side or the other end side in the lateral direction. May be. FIG. 4 is an explanatory diagram of a heater 72B of a modified example in this case. Even with such a modified heater 72B, the same effects as those of the above-described embodiment can be obtained. For example, the deterioration of the bent portion 77 can be suppressed by setting the unit resistance value ratio R1 / R2 at a temperature in the temperature range of 700 ° C. to 900 ° C. to be less than 1.

  In the above-described embodiment, the bent portion 77 has a shape in which the cross-sectional area increases as the position is farther from the straight portion 78, but is not limited thereto. For example, the cross-sectional area of the bent portion 77 may be the same value (= cross-sectional area S1) in any part. In this case, a step may be generated at the connection portion between the straight portion 78 and the bent portion 77. However, since it is preferable that there is no step in the heat generating portion 76, when the cross-sectional area is made different between the bent portion 77 and the straight portion 78, the bent portion 77 has a shape in which the cross-sectional area gradually changes as shown in FIG. It is preferable to do. Moreover, although the cross-sectional area of the linear part 78 was made into the same value (= cross-sectional area S2) in any part, it is not restricted to this. For example, a portion where the cross-sectional area gradually changes may exist in the straight portion 78. Further, when the heat generating portion 76 has a plurality of bent portions 77, at least one of the plurality of bent portions 77 may have a cross-sectional area different from that of the other bent portions 77. The same applies to the plurality of linear portions 78.

  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 cross 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 instead of the two layers of 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.

  In a heater having a mode in which the length direction of the linear portion 78 is along the short direction of the heater portion 70, such as the heater 72B shown in FIG. FIG. 5 is an explanatory diagram of a modified heater 72C. As shown in FIG. 5, the heat generating portion 76 of the heater 72 </ b> C has a band-like zigzag one-stroke shape in which both ends are connected to the lead portion 79. The heat generating portion 76 includes a plurality (32 in FIG. 5) of bent portions 91 and a plurality (31 in FIG. 5) of linear portions 78. The plurality of bent portions 91 and the plurality of linear portions 78 are electrically connected in series. The heat generating part 76 has a left-right symmetric shape with the center axis (two-dot chain line in FIG. 5) of the sensor element 101 in the left-right direction as the axis of symmetry. The left portion of the heat generating portion 76 from the central axis is referred to as a left heat generating portion 76a, and the right portion symmetrical to the left heat generating portion 76a is referred to as a right heat generating portion 76b.

  Each of the left heat generating portion 76a and the right heat generating portion 76b is routed in the front-rear direction as a whole while being bent back and forth at the bent portion 91 so that the folding direction is along the left-right direction. Further, the left heat generating portion 76 a and the right heat generating portion 76 b are connected by a straight portion 78 a located at the foremost position among the plurality of straight portions 78. As a result, the heat generating portion 76 as a whole is turned from the rear to the front and then folded back toward the rear at the straight portion 78a (and the left outer bent portion 92b and the right outer bent portion 92d connected thereto). Has been routed. That is, the heat generating portion 76 is routed so as to be folded once along the longitudinal direction (front-rear direction) as a whole.

  Each of the bent portions 91 is a folded portion in which the folded direction is along the left-right direction (short direction). Here, a plurality of bent portions 91 located on the inner side (right side) of the sensor element 101 in the left-right direction in the left heat generating portion 76a are referred to as left inner bent portions 92a. A plurality of bent portions 91 located on the outer side (left side) of the sensor element 101 in the left-right direction in the left heat generating portion 76a are referred to as left outer bent portions 92b. Similarly, a plurality of bent portions 91 respectively located on the inner side (left side) and the outer side (right side) of the sensor element 101 in the left-right direction in the right heat generating portion 76b are referred to as a right inner bent portion 92c and a right outer bent portion 92d. The heat generating portion 76 includes eight left inner bent portions 92a, left outer bent portions 92b, right inner bent portions 92c, and right outer bent portions 92d. The left inner bent portion 92a and the right outer bent portion 92d are folded portions that are turned leftward from the left (one in the short direction) toward the right (the other in the short direction). The left outer bent portion 92b and the right inner bent portion 92c are folded portions that are turned toward the right after moving from the right toward the left. The plurality of bent portions 91 are all bent in a curved shape and have a semicircular arc shape. The bent portion 91 may have a bent shape. The heat generating portion 76 is arranged so that the plurality of bent portions 91 and the plurality of linear portions 78 are alternately connected one by one. That is, each of the plurality of bent portions 91 connects the linear portions 78 adjacent in the front-rear direction. More specifically, the left inner bent portion 92a connects the right end sides of the adjacent linear portions 78 of the left heat generating portion 76a. The left outer bent portion 92b connects the left end sides of the adjacent straight portions 78 of the left heat generating portion 76a. Similarly, the right inner bent portion 92c and the right outer bent portion 92d connect the left end side and the right end side of the adjacent straight portions 78 of the right heat generating portion 76b, respectively. Of the plurality of bent portions 91 of the left heat generating portion 76a, the rearmost bent portion 91 (second bent portion 96c described later) has a rear end connected to the first lead 79a. Of the plurality of bent portions 91 of the right heat generating portion 76b, the rearmost bent portion 91 (second bent portion 96f described later) has a rear end connected to the second lead 79b.

  The plurality of linear portions 78 are spaced apart from each other along the longitudinal direction (front-rear direction) of the sensor element 101. In each of the plurality of linear portions 78, the length direction is along the short direction (left-right direction) of the sensor element 101. In the heater 72C of FIG. 5, the plurality of linear portions 78 are all arranged such that the length direction is parallel to the left-right direction. 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 same applies to the length direction of the bent portion 91.

  In addition, the heating portion 76 has a change in roughness in the folding pitch along the left-right direction, and is divided into first to fourth regions 90a to 90d in this order from the front to the rear due to the difference in pitch. Yes. In each of the first to fourth regions 90a to 90d, the folding pitch along the left-right direction is set to the pitches P1 to P4. Note that the turn-back pitch is the turn-back cycle, and the line width in the front-rear direction of the heat generating portion 76 (line width of the straight portion 78 in FIG. 5) and the portion adjacent to the front and rear in the heat generating portion 76 (in FIG. 5). It is the sum of the distance (distance) in the front-rear direction of the straight line portion 78). In the heater 72C of FIG. 5, P1 = P3 <P2 = P4. As described above, the heat generating portion 76 includes a region 88 (first and third regions 90a and 90c) having a dense turn-back pitch and a region 89 (second and fourth regions 90b and 90d) having a rough turn-back pitch. These regions are arranged along the front-rear direction. The first region 90a and the third region 90c have the same line width and the same distance between the front and rear of the linear portion 78. In addition, the third region 90c and the fourth region 90d have the same line width and the same distance before and after the linear portion 78. In each of the first to fourth regions 90a to 90d, the line width is changed at the connection part (before and after the boundary), but the line width is constant if the other parts are in the same region. is there. For example, the bent portions 91a and 91d extending over the first region 90a and the second region 90b have a gradually increasing (thicker) line width from the first region 90a side toward the second region 90b side. Similarly, the bent portions 91b and 91e extending over the second region 90b and the third region 90c and the bent portions 91c and 91f extending over the third region 90c and the fourth region 90d have a shape in which the line width gradually changes. ing.

  Thus, the heat generating part 76 has one or more dense regions 88 and one or more rough regions 89 along the front-rear direction, so that the temperature distribution in the front-rear direction of the sensor element 101 during heat generation is adjusted. Yes. In the heater 72C of FIG. 5, when the average temperatures of the periphery of each of the first to fourth regions 90a to 90d (portions positioned above and below the regions 90a to 90d in each layer 1 to 6) are compared along the front-rear direction. The periphery of the first region 90a is the highest temperature, and the periphery temperature decreases in the order of the second region 90b, the third region 90c, and the fourth region 90d. Basically, the area around the area where the turn-back pitch is dense tends to be higher, but in the heater 72C of FIG. 5, the area around the third area 90c is slightly lower than the area around the second area 90b. ing. This is because the third region 90c has a smaller occupied area (the length in the front-rear direction is smaller) than the first region 90a, and the periphery of the second region 90b is also heated by the first region 90a. It is. Further, when the heat generating portion 76 generates heat, the temperature (average temperature) of the first region 90 a in the dense region 88 becomes higher than the temperature (average temperature) of the third region 90 c, and the first region 90 a of the heat generating portion 76. Therefore, the first region 90a is referred to as the highest temperature region. The determination of which region is the highest temperature region among the dense regions 88 (the first region 90a and the third region 90c) is adjusted so that the average temperature of the entire heating unit 76 is 700 ° C. to 900 ° C. It is based on the average temperature of each region in the state.

  Further, in the dense region 88 and the rough region 89 of the heat generating portion 76, the positional relationship with the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 is adjusted. This will be described. In FIG. 5, the inner pump electrode projection region Ap, which is a region in which the inner pump electrode 22 is projected in the thickness direction (downward here) toward the heat generating portion 76, is indicated by a one-dot chain line frame. Similarly, the inner auxiliary pump electrode projection area Aq and the measurement electrode projection area Am in which the auxiliary pump electrode 51 and the measurement electrode 44 are respectively projected onto the heat generating portion 76 are also indicated by alternate long and short dash lines. As shown in FIG. 1, the ceiling electrode portion 51 a of the auxiliary pump electrode 51 exists immediately above the measurement electrode 44. Therefore, the inner auxiliary pump electrode projection area Aq and the measurement electrode projection area Am in FIG. 5 overlap each other, and more specifically, the measurement electrode projection area Am is included in the inner auxiliary pump electrode projection area Aq. As can be seen from FIG. 5, the first region 90 a of the dense region 88 is positioned so as to at least partially overlap the inner pump electrode projection region Ap. In other words, at least a part of the first region 90a is disposed so as to face the inner pump electrode 22 in the vertical direction (located directly below the inner pump electrode 22). In FIG. 5, the inner pump electrode projection region Ap is positioned so as to be included in the first region 90a. The second region 90b of the rough region 89 is located so as to overlap the inner auxiliary pump electrode projection region Aq, and the portion of the inner auxiliary pump electrode projection region Aq in front of the measurement electrode projection region Am is the second. It is included in the area 90b. The third region 90c of the dense region 88 is positioned so as to at least partially overlap the measurement electrode projection region Am, and the measurement electrode projection region Am protrudes before and after the third region 90c in the heater 72C of FIG. So both overlap.

  As described above, the positional relationship among the dense region 88 and the rough region 89, the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 is adjusted, so that the temperature distribution of each electrode and its surroundings can be adjusted. It has been adjusted. As described above, when the heat generating portion 76 generates heat, the periphery of the first region 90a has the highest temperature, and the peripheral temperature decreases in the order of the second region 90b, the third region 90c, and the fourth region 90d. Therefore, assuming that the temperatures of the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 are temperatures Tp, Tq, and Tm [° C.], respectively, temperature Tp> temperature Tq> temperature Tm. The measurement electrode projection area Am overlaps with the third area 90c of the dense area 88, so that although the temperature Tm is lower than the temperature Tq, the difference is slight and the temperature Tm does not become too low. It has become. Note that the folding pitch of the dense region 88 and the rough region 89 can be determined so that the temperatures Tp, Tq, and Tm when the heat generating portion 76 generates heat are set to desired values. Although not particularly limited thereto, the pitches P1 and P3 of the dense region 88 are each 0.4 mm to 0.7 mm, for example, and the pitches P2 and P4 of the rough region 89 are each 0.7 mm to 0.00 mm, for example. 9 mm.

  Further, the heat generating portion 76 includes a first bent portion 95, a second bent portion 96, and a third bent portion 97 as a part of the bent portion 91. Here, the 1st bending part 95 is the bending part 91 (folding part) which exists in the highest temperature area | region (1st area | region 90a), and the vertex of folding | turning mutually opposes in the left-right direction. That is, the first bent portions 95 are four bent portions 91 including first bent portions 95a and 95c and first bent portions 95b and 95d that face each other in the first region 90a. The second bent portion 96 is a bent portion 91 (folded portion) that exists in the rough area 89 and whose vertices of folding are opposed to each other in the left-right direction. That is, the second bent portion 96 includes second bent portions 96a and 96d facing each other in the second region 90b, second bent portions 96b and 96e facing each other in the fourth region 90d, and the second bent portion 96c. , 96f and six bent portions 91. The third bent portion 97 is a bent portion 91 (folded portion) that exists in the highest temperature region (first region 90 a) and that exists outside in the short direction (left-right direction) than the first bent portion 95. is there. That is, the third bent portion 97 includes three bent portions 91 existing in the first region 90a in the left outer bent portion 92b, and three bent portions present in the first region 90a in the right outer bent portion 92d. 91, and six bent portions 91. It should be noted that the bent portion 91 spanning the dense region 88 and the rough region 89 (overlapping both the dense region 88 and the rough region 89) is the first bent portion 95 and the second bent portion 96. It shall not be included in any of the above. That is, the bent portions 91a and 91d extending over the first and second regions 90a and 90b, the bent portions 91b and 91e extending over the second and third regions 90b and 90c, and the bent extending over the third and fourth regions 90c and 90d. The portions 91 c and 91 f are not included in the first bent portion 95 or the second bent portion 96. On the other hand, with respect to the third bent portion 97, the bent portion 91 extending over the highest temperature region (first region 90 a) and the other regions is also shorter than the first bent portion 95 (in the left-right direction). The bent portion 91 existing outside is included in the third bent portion 97. In the heater 72 </ b> C of FIG. 5, the distance X <b> 1 [mm] between the first bent portions 95 existing in the highest temperature region (first region 90 a) in the dense region 88 exists in the rough region 89. It is equal to the distance X2 [mm] between the second bent portions 96. However, the heater 72C is not limited to the case of X1 = X2, and may be X1> X2 or X1 <X2. In the heater 72C of FIG. 5, the distance between the first bent portions 95a and 95c and the distance between the first bent portions 95b and 95d are both equal (= distance X1). Similarly, the distance between the second bent portions 96a and 96d, the distance between the second bent portions 96b and 96e, and the distance between the second bent portions 96c and 96f are all equal (= distance X2). . However, when the distance between the first bent portions 95 is not constant, for example, the distance between the first bent portions 95a and 95c is different from the distance between the first bent portions 95b and 95d. The distance X1 is the average value of the distances facing each other. The same applies to the distance X2. Further, in the heater 72C of FIG. 5, the distance between the bent portions 91a to 91f not included in any of the first bent portion 95 and the second bent portion 96 is equal to the distance X2 (= distance X1). It was. The distances X1 and X2 may be, for example, 0.2 mm or more and less than 1.0 mm, respectively.

  In the heater 72C of this modified example, the resistance value per unit length of the first bent portion 95 is changed because the width Wa1 [mm] of the first bent portion 95 is larger than the width W2 of the linear portion 78. ing. In the heater 72C of this modified example, the unit resistance value Ra1 [μΩ / mm], which is the resistance value per unit length of the first bent portion 95, is at least in the temperature range of 700 ° C. or more and 900 ° C. or less. The unit resistance value R2 [μΩ / mm], which is the resistance value per unit length of the linear portion 78, is lower. In other words, the unit resistance value ratio Ra1 / R2 at a temperature in at least one of the above temperature ranges is less than 1. By doing so, the heat generation density (heat generation amount per unit length) of the first bent portion 95 is smaller than that of the straight portion 78 at at least one of the temperatures of 700 ° C. to 900 ° C. Although details will be described later, since the unit resistance value Ra1 is lower than the unit resistance value R2 (that is, the unit resistance value ratio Ra1 / R2 is less than 1), the temperature is high in the maximum temperature region (first region 90a). It is possible to suppress the temperature rise of the first bent portion 95 that is likely to become low, and it is possible to suppress the deterioration of the first bent portion 95 that is particularly easily deteriorated among the bent portions 91. In the heater 72C of FIG. 5, the bending portion 91 (including the third bending portion 97) other than the first bending portion 95 has the same cross-sectional area (thickness and line width) as the linear portion 78 in each region. The resistance value per unit length is also the same. However, as described in the above-described embodiment, the unit resistance value R1 and the unit resistance value R2 are average values of resistance values per unit length of the bent portion 91 and the straight portion 78, respectively. Therefore, also in the heater 72C of FIG. 5, the unit resistance value Ra1 of the first bent portion 95 is lower than the unit resistance value R2 of the linear portion 78, so that R1 <R2 (unit resistance value ratio R1 / R2 is less than 1). Meet.

The unit resistance value Ra1 is an average value of resistance values per unit length of the first bent portion 95. Therefore, even when a part of the first bent portion 95 has a higher resistance value per unit length than the straight portion 78, the first bent portion 95 as a whole has a lower resistance value per unit length. That's fine. However, it is preferable that the resistance value per unit length is lower than the unit resistance value R2 in any part of any of the first bent portions 95. Moreover, it is preferable that the unit resistance value ratio Ra1 / R2 is less than 1 at any temperature in the above temperature range. Further, in the heat generating portion 76, the unit resistance value ratio Ra1 / R2 at at least one temperature in the above temperature range is preferably a value of 0.87 or less, and more preferably a value of 0.80 or less. Further, at any temperature within the above temperature range, the unit resistance value ratio Ra1 / R2 may be 0.5 or more. Further, in the heater 72C of FIG. 5, the width Wa1 of the first bent portion 95 of the belt-like heater 72C is made larger (thicker) than the width W2 of the linear portion 78, whereby the cross-sectional area Sa1 [ mm ² ] is larger than the cross-sectional area S2 of the straight portion 78 (the cross-sectional area ratio S2 / Sa1 is less than 1), and thereby the unit resistance value ratio Ra1 / R2 is less than 1. The cross-sectional area Sa1 is a cross-sectional area perpendicular to the length direction of each of the first bent portions 95. By adjusting the cross-sectional area ratio S2 / Sa1 so that the unit resistance value ratio Ra1 / R2 is less than 1, the unit resistance value ratio Ra1 / R2 is 1 in any temperature range from 700 ° C. to 900 ° C. Less than. The cross-sectional area ratio S2 / Sa1 is preferably 0.87 or less, and more preferably 0.80 or less. In the heater 72C of FIG. 5, the cross-sectional area ratio S2 / Sa1 is adjusted by making the width Wa1 larger than the width W2. However, the width Wa1 is made larger than the width W2 or the thickness of the first bent portion 95 is increased. The cross-sectional area ratio S2 / Sa1 may be adjusted by making the length Da1 larger than the thickness D2 of the linear portion 78 or by at least one of them. The value of the cross-sectional area Sa1 is also the average value of the first bent portion 95, similarly to the unit resistance value Ra1. The first bent portion 95 has the same cross-sectional area as that of the straight portion 78 (and the third bent portion 97) at the connection portion with the straight portion 78, and the cross-sectional area is larger at a position away from the straight portion 78 (here, the width Wa1 is smaller). (Large). That is, each of the plurality of first bent portions 95 has the largest cross-sectional area of the cross section of the front and rear central portions (for example, the cross section passing through the most protruding portion to the right in the case of the first bent portions 95a and 95b). Shape. It should be noted that a step may be formed at the connection portion between the first bent portion 95 and the straight portion 78 so that the cross-sectional area of the first bent portion 95 is the same value (= cross-sectional area Sa1) in any portion. . The cross-sectional area ratio S2 / Sa1 may be 0.5 or more. The width Wa1 may be 0.05 mm or more and 1.5 mm or less. Thickness Da1 is good also as 0.003 mm or more and 0.1 mm or less.

  In the gas sensor 100 including the heater 72C of the modified example configured as described above, the roughness of the turn-back pitch of the heat generating portion 76 is adjusted, so that each electrode described above can be used during use (when the heat generating portion 76 generates heat). The temperature is Tp> temperature Tq> temperature Tm. Here, in the vicinity of the inner pump electrode 22, the gas to be measured before the adjustment of the oxygen concentration in the first internal space 20 by the main pump cell 21 flows in from the gas inlet 10 side, so that the oxygen concentration is high. Therefore, the inner pump electrode 22 and the surrounding solid electrolyte layer are more activated by setting the temperature Tp higher than the temperatures Tq and Tm so that the main pump cell 21 can pump a large amount of oxygen. On the other hand, the oxygen concentration around the auxiliary pump electrode 51 and the measurement electrode 44 is lower than that around the inner pump electrode 22. Therefore, for example, hydrogen or carbon monoxide may be generated due to reduction of water or carbon dioxide in the gas to be measured, and these may chemically react with oxygen in NOx, resulting in a decrease in measurement accuracy. Such reduction of components other than the specific gas (NOx) is likely to occur as the temperature increases. Therefore, such a decrease in measurement accuracy can be suppressed by making the temperatures Tq and Tm lower than the temperature Tp.

  Thus, in the heater part 70 provided with the heater 72C of the modified example, the dense region 88 and the rough region 89 (first to fourth regions 90a to 90d) are provided in the front-rear direction of the sensor element 101. Temperature distribution is generated. Apart from this, a temperature distribution may occur in each of the first to fourth regions 90a to 90d. For example, in general, the temperature of the heat generating portion 76 is likely to be higher in the left inner bent portion 92a and the right inner bent portion 92c than in the left outer bent portion 92b and the right outer bent portion 92d. Heat transfer occurs between the left inner bent portion 92a and the right inner bent portion 92c facing each other, and the left inner bent portion 92a and the right inner bent portion 92c are more than the left outer bent portion 92b and the right outer bent portion 92d. This is because the sensor element 101 is positioned on the left and right sides of the sensor element 101. Therefore, in general, the first bent portion 95 among the left inner bent portion 92a and the right inner bent portion 92c is likely to become locally higher in the highest temperature region (first region 90a). That is, among the bent portions 91, the first bent portion 95 is particularly likely to have a high temperature and easily deteriorates. On the other hand, the straight portion 78 is less likely to be hot than the first bent portion 95. In the heater 72C of the modified example, the resistance value per unit length of the first bent portion 95 at a temperature in at least one of the above temperature ranges is lower than that of the straight portion 78 (unit resistance value ratio Ra1 / R2 is less than 1). Therefore, local heating in the maximum temperature region (first region 90a) of the heater 72C can be further reduced. That is, the temperature rise of the 1st bending part 95 which tends to become high temperature can be suppressed more. Thereby, deterioration of the 1st bending part 95 which is easy to deteriorate among the bending parts 91 can be suppressed. In addition, the life of the first bent portion 95 that is likely to cause disconnection or the like due to deterioration becomes longer, so that the life of the heater 72C as a whole also becomes longer. FIG. 6 is a conceptual diagram of a temperature distribution along the left-right direction around the maximum temperature region (first region 90a) of the heat generating portion 76. The right side of FIG. 6 is a view showing the periphery of the first region 90a in FIG. 5, and the left side of FIG. 6 is the third substrate layer 3 along the line BB shown on the right side of FIG. 1) is a graph of the temperature distribution on the upper surface. As shown in the graph of FIG. 6, when the unit resistance value Ra1 = unit resistance value R2 (thick broken line in the graph), the vicinity of the first bent portion 95, that is, the left and right central portions of the sensor element 101 are locally heated. It tends to be hot. On the other hand, when the unit resistance value Ra1 is lower than the unit resistance value R2 (thick solid line in the graph) as in the heater 72C of the modified example, the temperature decrease around the first bent portion 95 is larger than the temperature decrease in other portions. And local heating is reduced.

  In the heater 72C of FIG. 5, the cross-sectional area ratio S2 / Sa1 is less than 1, but the unit resistance value ratio Ra1 / R2 is adjusted by adjusting the volume resistivity of the first bent portion 95 and the straight portion 78. It may be less than 1. For example, at a temperature of at least one of 700 ° C. to 900 ° C., the volume resistivity ratio ρa1 / which is the ratio of the volume resistivity ρa1 [μΩ · cm] of the first bent portion 95 to the volume resistivity ρ2 of the linear portion 78. ρ2 may be less than 1. Even in this case, the unit resistance value ratio Ra1 / R2 at at least one temperature in the above temperature range can be less than 1. The volume resistivity ratio ρa1 / ρ2 is preferably a value of 0.87 or less, more preferably a value of 0.80 or less, at least in any of the above temperature ranges. The volume resistivity ρa1 and the volume resistivity ρ2 can be adjusted in the same manner as the volume resistivity ρ1 and the volume resistivity ρ2 described above. Note that the value of the volume resistivity ρa1 is also the average value of the first bent portions 95, similarly to the unit resistance value Ra1. Further, at any temperature in the above temperature range, the volume resistivity ratio ρa1 / ρ2 may be a value of 0.5 or more.

  Further, in the heater 72C of FIG. 5, the width Wa1 of the first bent portion 95 is larger than the width Wa3 [mm] of the third bent portion 97. Thereby, as for the heater 72C, unit resistance value ratio Ra1 / Ra3 in the temperature of at least any one of 700 to 900 degreeC is less than the value 1. Here, the unit resistance value Ra3 [μΩ / mm] is a resistance value per unit length of the third bent portion 97. As described above, the first bent portion 95 is deteriorated even when the resistance value per unit length at a temperature in at least one of the above temperature ranges is lower than that of the third bent portion 97. Can be suppressed. In general, as described above, the first bent portion 95 is likely to be locally high in the maximum temperature region (the first region 90a) and is likely to deteriorate. On the other hand, the third bent portion 97 is located on the outer side of the heater portion 70 with respect to the first bent portion. Therefore, by setting the unit resistance value ratio Ra1 / Ra3 to a value less than 1, local heating in the maximum temperature region (first region 90a) can be further reduced. That is, the temperature rise of the 1st bending part 95 which tends to become high temperature can be suppressed more. As a result, as in the case where the unit resistance value ratio Ra1 / R2 is less than 1, it is possible to suppress the deterioration of the first bent portion 95 that is particularly easily deteriorated among the bent portions 91, and the life of the heater 72C as a whole is also extended. . The unit resistance value Ra3 is an average value of resistance values per unit length of the third bent portion 97. Further, in the heater 72C of FIG. 5, the unit resistance value ratio Ra1 / R2 is less than a value 1 and the unit resistance value ratio Ra1 / Ra3 is less than a value 1 at least in any one of the temperatures described above. However, if at least one of the two is satisfied, an effect of suppressing the deterioration of the first bent portion 95 can be obtained. For example, in any of the plurality of bent portions 91, when the resistance value per unit length is made to be lower than that of the straight portion 78 in the same region of the first region 90a to the fourth region 90d, the unit resistance value ratio Ra1 / R2 may be less than 1 and the unit resistance value ratio Ra1 / Ra3 may be 1 (the unit resistance values of the first bent portion 95 and the third bent portion 97 are the same). Even in such a case, the effect of suppressing the deterioration of the first bent portion 95 can be obtained as compared with the case where the unit resistance value ratio Ra1 / R2 is 1.

Similarly to the case where the unit resistance value ratio Ra1 / R2 is less than 1, when the unit resistance value ratio Ra1 / Ra3 is less than 1, the cross-sectional area Sa1 of the first bent portion 95 is set to, for example, What is necessary is just to make it larger than the cross-sectional area Sa3 [mm < ² >] of the 3 bending part 97 (cross-sectional area ratio Sa3 / Sa1 is less than 1). When the cross-sectional area ratio Sa3 / Sa1 is less than 1, the width Wa1 of the first bent portion 95 is made larger than the width Wa3 of the third bent portion 97, or the thickness Da1 of the first bent portion 95 is set to the first value. It is sufficient that at least one of the thicknesses Da3 of the three bent portions 97 is made larger. Alternatively, the volume resistivity ratio ρa1 which is the ratio of the volume resistivity ρa1 of the first bent portion 95 and the volume resistivity ρa3 [μΩ · cm] of the third bent portion 97 at least in one of the above temperature ranges. By making / ρa3 less than 1, the unit resistance value ratio Ra1 / Ra3 may be less than 1. The value of the cross-sectional area Sa3 and the value of the volume resistivity ρa3 are also set to the average value of the third bent portion 97, like the unit resistance value Ra3 described above. In the heater 72C of FIG. 5, the cross-sectional area of the third bent portion 97 is the same value (= cross-sectional area Sa3) in any part.

  Preferred modes and values (numerical ranges) of the unit resistance value ratio Ra1 / Ra3, the cross-sectional area ratio Sa3 / Sa1, and the volume resistivity ratio ρa1 / ρa3 will be described when the unit resistance value ratio Ra1 / R2 is less than 1. The same aspect and value (numerical range) as those described above can be applied. For example, even when a part of the first bent portion 95 has a portion with a higher resistance value per unit length than the third bent portion 97, the first bent portion 95 as a whole has a resistance value per unit length. Should be low. In any part of any first bent portion 95, the resistance value per unit length is preferably lower than the unit resistance value Ra3. Further, it is preferable that the unit resistance value ratio Ra1 / Ra3 is less than 1 at any temperature in the above temperature range. Further, in the heat generating portion 76, the unit resistance value ratio Ra1 / Ra3 at least in any of the above temperature ranges is preferably 0.87 or less, and more preferably 0.80 or less. The unit resistance value ratio Ra1 / Ra3 may be 0.5 or more at any temperature in the above temperature range. The same applies to the cross-sectional area ratio Sa3 / Sa1 and the volume resistivity ratio ρa1 / ρa3. The width Wa3 may be 0.05 mm or more and 1.5 mm or less. Thickness Da3 is good also as 0.003 mm or more and 0.1 mm or less.

  As described above, in the heater 72C of FIG. 5, the bending portion 91 (including the third bending portion 97) other than the first bending portion 95 has a straight portion 78 and a cross-sectional area (thickness and thickness) in each region. The line width is the same, and the resistance value per unit length is also the same. However, it is preferable that the bending portion 91 other than the first bending portion 95 has a resistance value per unit length lower than the unit resistance value R2 (for example, the bending portion 91 is thicker than the straight portion 78). By so doing, the deterioration of the bent portions 91 other than the first bent portion 95 can also be suppressed. Further, the resistance value per unit length of the bent portion 91 (including the third bent portion 97) other than the first bent portion 95 is made lower than the unit resistance value R2 (for example, thicker than the straight portion 78). The first bent portion 95 may have a lower resistance value per unit length than the third bent portion 97 (eg, thicker than the third bent portion 97). If it carries out like this, local heating in the highest temperature area | region (1st area | region 90a) will be suppressed, suppressing deterioration of the whole bending part 91, and deterioration about the 1st bending part 95 can be suppressed more.

  Similarly to the case where the unit resistance value ratio R1 / R2 is less than 1 in the above-described embodiment, when the unit resistance value ratio Ra1 / R2 is less than 1 in the heater 72C of FIG. The ratio S2 / Sa1 may be less than 1 and the volume resistivity ratio ρa1 / ρ2 may be less than 1. Similarly, when the unit resistance value ratio Ra1 / Ra3 is less than 1 in the heater 72C of FIG. 5, the cross-sectional area ratio Sa3 / Sa1 is less than 1 and the volume resistivity ratio ρa1 / ρa3 is a value. You may combine making it less than one. Similarly to the relationship between the unit resistance value Ra1 and the unit resistance value R2, the unit resistance value Ra1 exists in the maximum temperature region (first region 90a) and is a straight portion 78 (see FIG. 5 may be lower than the unit resistance value Ra4 [μΩ / mm], which is the resistance value per unit length of the eight straight portions 78). Note that the straight portion 78 closest to the first bent portion 95 means a straight portion 78 that is directly connected to the first bent portion 95. Instead of setting the unit resistance value ratio Ra1 / R2 to less than 1, the unit resistance value ratio Ra1 / Ra4 may be set to less than 1, or the unit resistance value ratio Ra1 / R2 is set to less than 1. In addition, the unit resistance value ratio Ra1 / Ra4 may be less than 1.

  In the heater 72C of the modified example of FIG. 5, the dense region 88 and the rough region 89 of the heat generating portion 76 are as shown in FIG. 5 in the positional relationship with the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44. However, the present invention is not limited to this. The point where temperature Tp> temperature Tq> temperature Tm is also not particularly limited. However, it is preferable that at least a part of the maximum temperature region (first region 90a) overlaps with the inner pump electrode projection region Ap.

  The number of the bent portions 91 and the straight portions 78 may be increased or decreased as compared with the pattern of the heater 72C shown in FIG. In this case, the heat generating portion 76 includes two or more first bent portions 95 (one or more pairs of first bent portions 95 facing each other) and two or more second bent portions 96 (one facing each other) as the bent portions 91. And at least a pair of second bent portions 96). When the unit resistance value ratio Ra1 / Ra3 is less than 1, the heat generating portion 76 only needs to have one or more third bent portions 97, and may have a plurality of third bent portions 97. Good. Further, the left heat generating portion 76a and the right heat generating portion 76b may not be symmetrical.

  The arrangement of the dense area 88 and the coarse area 89 (first to fourth areas 90a to 90d) is not limited to the heater 72C in FIG. For example, all of the areas other than the first area 90a may be rough areas 89, such that the pitch P3 of the third area 90c is equal to the pitches P2 and P4. If there is only one dense region 88 as described above, that region becomes the maximum temperature region. Further, in the heater 72C of FIG. 5, the heat generating portion 76 has two dense regions 88 and two rough regions 89, respectively. However, when the heater is turned up and down, the heat generating portion 76 is 1 What is necessary is just to have the above dense area | region 88 and the 1 or more rough area | region 89. FIG. In the heater 72C of FIG. 5, the dense region 88 is smaller in both the line width and the front-rear direction interval than the rough region 89, but the dense region 88 is folded back compared to the rough region 89. As long as the pitch is dense (the pitch is small). That is, the dense region 88 only needs to have at least one of the line width and the front-rear direction interval smaller than that of the rough region 89.

  In the heater 72C of FIG. 5, the linear portion 78 has a length direction parallel to the short direction (left and right direction) of the heater portion 70. However, if the length direction is along the short direction, the straight portion 78 may not be parallel. Good. For example, the length direction of the straight portion 78 may be inclined (but less than 45 °) from the short direction.

  Hereinafter, an example in which a sensor element is specifically manufactured will be described as an example. Experimental examples 2 to 9 and 11 to 18 correspond to examples of the present invention, and experimental examples 1 and 10 correspond to comparative examples. Experimental example 1A corresponds to a comparative example, and experimental example 2A corresponds to an example of the present invention. In addition, this invention is not limited to a following example.

[Experimental Examples 1-9]
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 9 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 bent portion 77. 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 bent portion 77 and the width W2 of the straight portion 78 in Experimental Example 1 were both 0.25 mm. In addition, the thickness D1 of the bent portion 77 and the thickness D2 of the straight portion 78 in Experimental Example 1 were both 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 bent portion 77 and the linear portion 78, and the volume resistivity ratio ρ1 / ρ2 is 1 at any temperature of 700 ° C to 900 ° C. The same applies to Experimental Examples 2 to 9.

[Experimental Examples 10 to 18]
Sensor elements 101 of Experimental Examples 10 to 18 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 bent portion 77. Note that the widths W1 and W2 and the thicknesses D1 and D2 of Experimental Examples 10 to 18 are all the same as Experimental Example 1, and the cross-sectional area ratios S2 / S1 of Experimental Examples 10 to 18 are all 1.00. . In Experimental Example 10 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 10-18 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 bent portion 77 produced under the same conditions as in each of Experimental Examples 10 to 18 was printed in a rectangular parallelepiped shape on the insulating paste. Then, it baked on the same conditions as Experimental Examples 10-18, the rectangular parallelepiped heat generating part was formed, and each test piece of Experimental Examples 10-18 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 10-18 hardly changed in the range of 700 to 900 degreeC.

[Evaluation test]
About Experimental Examples 1-18, durability (life) of the heat generating part 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, there was a tendency that the smaller the value of the unit resistance value ratio R1 / R2, the harder the disconnection of the heat generating portion 76 occurred. As the value of the unit resistance value ratio R1 / R2 is smaller, there is a tendency that disconnection of the heat generating portion 76 is less likely to occur even at a higher temperature. In Experimental Examples 4 to 9, 13 to 18, where the unit resistance value ratio R1 / R2 is 0.87 or less, the evaluation is A (excellent) or B (good) at any temperature of 700 ° C. to 900 ° C. Met. In Experimental Examples 6 to 9, 15 to 18 in which the unit resistance value ratio R1 / R2 is 0.80 or less, the evaluation was A (excellent) at any temperature of 700 ° C. to 900 ° C. In all of the experimental examples in which the evaluation was B (good) or C (impossible), the bent portion 77 was disconnected. Further, from comparison between Experimental Examples 1-9 and Experimental Examples 10-18, 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 bent portion 77, the same results as in Experimental Examples 1 to 9 were obtained.

[Experimental examples 1A, 2A]
According to the method for manufacturing the gas sensor 100 of the embodiment described above, the sensor element 101 including the heater 72C illustrated in FIG. However, in Experimental Example 1A, the width Wa1 of the first bent portion 95 is the same line width as the straight portion 78 and the third bent portion 97 in the first region 90a, and the thickness is also the same. Thus, in Experimental Example 1A, the unit resistance value ratio R1 / R2 is set to the value 1.00, the unit resistance value ratio Ra1 / R2 is set to the value 1.29, and the unit resistance value ratio Ra1 / Ra3 is set to the value 1.00. . In Experimental Example 1A, the line widths of the dense regions 88 in the heat generating portion 76 are all 0.26 mm, and the line widths of the coarse regions 89 are all 0.41 mm (the dense regions 88 and the coarse regions 88 are coarse). Except for the connection with the region 89). The folding pitches P1 and P3 were both 0.56 mm. The folding pitches P2 and P4 were both 0.82 mm. Experimental Example 2A was the same as Experimental Example 1A except that the width Wa1 of the first bent portion 95 was 0.46 mm and the line width of the first bent portion 95 was increased as shown in FIG. Thus, in Experimental Example 2A, the unit resistance value ratio R1 / R2 is set to a value of 0.92, the unit resistance value ratio Ra1 / R2 is set to a value of 0.73, and the unit resistance value ratio Ra1 / Ra3 is set to a value of 0.57. .

[Evaluation test]
For Experimental Examples 1A and 2A, the temperature and durability (lifetime) of the heater 72C during heat generation were evaluated. Specifically, a voltage of 12 W was applied to the lead portion 79 to energize the heater 72C. Then, the temperature distribution in the maximum temperature region (first region 90a) in a state where the temperature of the sensor element 101 was stable after 3 minutes or more after voltage application was measured. The temperature distribution of the first region 90a is indirectly measured by measuring the temperature of the rectangular region directly below the first region 90a of the lower surface of the sensor element 101 with a radiation thermometer. The temperature, the minimum temperature, and the difference between the maximum temperature and the average temperature were derived. Further, as an evaluation of durability, it was determined whether or not a disconnection occurred in the heat generating portion 76 within 2000 hours in a state where a voltage was applied to the heater 72C. 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)”.

  Unit resistance value ratios R1 / R2, Ra1 / R2, Ra1 / Ra3 of experimental examples 1A and 2A, temperature distribution of first region 90a (maximum temperature, average temperature, minimum temperature, difference between maximum temperature and average temperature), and The durability evaluation is summarized in Table 2.

  As shown in Table 2, in Example 2A in which the values of the unit resistance value ratios R1 / R2, Ra1 / R2, and Ra1 / Ra3 were less than 1, the evaluation of durability was A (excellent). On the other hand, in the experimental example 1A in which these values are 1 or more, the durability evaluation was C (impossible). From this, the lifetime of the heater 72C as a whole is reduced by reducing the unit resistance value Ra1 of the first bent portion 95 (and thereby reducing the unit resistance value ratios R1 / R2, Ra1 / R2, and Ra1 / Ra3). It is thought that it can be extended. In Experimental Example 1A, the first bent portion 95 was disconnected. In Experimental Example 2A, the maximum temperature in the maximum temperature region (first region 90a) was lower than in Experimental Example 1A, and the difference between the maximum temperature and the average value was also small. On the other hand, the minimum temperature in the maximum temperature region was hardly different between Experimental Examples 1A and 2A. That is, in Experimental Example 2A, local heating of the first bent portion 95 in the maximum temperature region could be reduced. Therefore, in Experimental Example 2A, it is possible to suppress the deterioration of the first bent portion 95 that is particularly easily deteriorated, thereby suppressing the deterioration of the first bent portion 95 and extending the life of the heater 72C. It is done.

  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, 72B, 72C Heater, 73 Through hole, 74 Heater insulating layer, 75 Pressure dissipation hole, 76 Heat generating part, 76a Left heat generating part, 76b Right heat generating part, 77 Bent part, 77a Front end side bent part, 77b Rear end side bent part, 78, 78a Linear part, 79 Lead part, 79a, 79b First and second lead, 80 Main pump control oxygen partial pressure detection sensor cell, 81 Auxiliary pump control oxygen partial pressure detection sensor cell, 82 Measurement pump control oxygen partial pressure detection sensor cell, 83 Sensor cell , 88 dense region, 89 rough region, 90a to 90d first to fourth regions, 91, 91a to 91f bent portion, 92a left inner bent portion, 92b left outer bent portion, 92c right inner bent portion, 92d right outer Bent part, 95, 95a to 95d First bent part, 96, 96a to 96f Second bent part, 97 Third bent part, 100 Gas sensor, 10 Sensor element, Am measuring electrode projection area, Ap inner pumping electrode projection area, Aq inner auxiliary pumping electrode projection region.

Claims (15)

A heating element having a linear portion and a bent portion having a resistance value per unit length at a temperature in the temperature range of 700 ° C. or higher and 900 ° C. or lower lower than that of the linear portion;
A ceramic body surrounding the heating element;
Ceramic heater with   When the resistance value per unit length of the bent portion is a unit resistance value R1 [μΩ / mm] and the resistance value per unit length of the linear portion is a unit resistance value R2 [μΩ / mm], The ceramic heater according to claim 1, wherein the unit resistance value ratio R1 / R2 at a temperature in at least one of the temperature ranges is 0.87 or less. The unit resistance value ratio R1 / R2 at a temperature in at least one of the temperature ranges is 0.80 or less,
The ceramic heater according to claim 2. The bent portion has a larger cross-sectional area perpendicular to the length direction than the straight portion,
The ceramic heater according to any one of claims 1 to 3. The heating element is strip-shaped,
The bent portion has a thickness equal to or greater than the thickness of the linear portion.
The ceramic heater according to claim 4. The cross-sectional area ratio S2 / S1 between the cross-sectional area S1 [mm ² ] perpendicular to the length direction of the bent part and the cross-sectional area S2 [mm ² ] perpendicular to the length direction of the straight part is 0.87 or less. is there,
The ceramic heater according to claim 4 or 5. The cross-sectional area ratio S2 / S1 is 0.80 or less,
The ceramic heater according to claim 6. The bent portion has a lower volume resistivity at a temperature in at least one of the temperature ranges than the linear portion,
The ceramic heater according to any one of claims 1 to 7. The volume resistivity ratio ρ1 / ρ2 which is the ratio of the volume resistivity ρ1 [μΩ · cm] of the bent portion and the volume resistivity ρ2 [μΩ · cm] of the linear portion at at least one temperature in the temperature range. Is less than or equal to 0.87,
The ceramic heater according to claim 8. The volume resistivity ratio ρ1 / ρ2 at a temperature of at least one of the temperature ranges is 0.80 or less,
The ceramic heater according to claim 9. The ceramic body is a plate-like body having a longitudinal direction and a short direction,
The heating element has four or more straight portions that are arranged along the short direction as the straight portions and whose length direction is along the long direction,
The heating element includes, as the bent portion, a plurality of one-end-side bent portions that connect the straight portions adjacent in the short direction on one end side in the longitudinal direction, and the straight portions adjacent in the short direction. One or more other side bent portions connected at the other end side in the longitudinal direction,
The ceramic heater of any one of Claims 1-10. The ceramic body is a plate-like body having a longitudinal direction and a short direction,
The heating element is routed so as to be folded back along the longitudinal direction as a whole while being folded a plurality of times so that the folding direction is along the short direction, and the folding pitch along the short direction is dense. One or more regions and coarse regions are provided along the longitudinal direction,
The heating element is present as a part of the bent portion in the highest temperature region of the one or more dense regions where the heating element generates the highest temperature when the heating element generates heat, and the vertices of folding are opposed to each other in the lateral direction. A first bent portion that is a folded portion
The first bent portion has a lower resistance value per unit length at at least one temperature in the temperature range than the linear portion.
The ceramic heater according to any one of claims 1 to 11. The ceramic body is a plate-like body having a longitudinal direction and a short direction,
The heating element is routed so as to be folded back along the longitudinal direction as a whole while being folded a plurality of times so that the folding direction is along the short direction, and the folding pitch along the short direction is dense. One or more regions and coarse regions are provided along the longitudinal direction,
The heating element is present as a part of the bent portion in the highest temperature region of the one or more dense regions where the heating element generates the highest temperature when the heating element generates heat, and the vertices of folding are opposed to each other in the lateral direction. A first bent portion that is a folded portion, and a third bent portion that exists in the highest temperature region and that is present outside in the short direction from the first bent portion,
The first bent portion has a lower resistance value per unit length at at least one temperature in the temperature range than the third bent portion.
The ceramic heater according to any one of claims 1 to 12.   A sensor element comprising the ceramic heater according to claim 1 and detecting a specific gas concentration in a gas to be measured.   A gas sensor comprising the sensor element according to claim 14.