JP6674211B2 - Ceramic heater, sensor element and gas sensor - Google Patents

Description

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

  BACKGROUND ART Conventionally, as a ceramic heater, a heater 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 Literature 1 includes a straight conductor portion formed along the longitudinal direction, and a folded conductor portion connecting the straight conductor portions. Further, there is also known a pattern having a pattern including a straight portion extending in a short direction and a folded portion connecting the straight portions (for example, Patent Document 2).

Japanese Patent No. 4826461 Japanese Patent No. 3571494

  By the way, in such a ceramic heater, the conductor constituting the heating element may be oxidized at a high temperature, and the heating element may be deteriorated and disconnected.

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

  The present invention employs the following means to achieve the above-mentioned main object.

The ceramic heater of the present invention
The outer heat generating portion, the resistance per unit length at least at any temperature in the temperature range of 700 ° C. or more and 900 ° C. or less is higher than the outer heat generating portion, and the inner side of the outer heat generating portion has the outer heat generating portion. A heating element having an inner heating portion electrically arranged in parallel with the heating element;
A ceramic body surrounding the heating element,
It is provided with.

  In this ceramic heater, the inner heating portion of the heating element is disposed electrically in parallel with the outer heating portion, and has a unit in at least one of a temperature range of 700 ° C. or more and 900 ° C. or less as compared with the outer heating portion. The resistance value per length is high. Thus, at least at any one of the temperatures of 700 ° C. to 900 ° C., the heat generation density (heat generation amount per unit length) of the inside heat generation part is smaller than that of the outside heat generation part. Here, the inside heat-generating portion is located on the inner side of the outside heat-generating portion, so that the temperature is likely to be high. In the ceramic heater according to the present invention, since the heat generation density of the inner heat generating portion is smaller than that of the outer heat generating portion, it is possible to suppress the temperature rise of the inner heat generating portion, which is likely to become high in temperature, and to suppress the deterioration of the inner heat generating portion. Therefore, the life of the heating element as a whole is prolonged.

  In the ceramic heater according to the present invention, the resistance value per unit length of the inner heating portion is defined as a unit resistance value R1 [μΩ / mm], and the resistance value per unit length of the outer heating portion is defined as a unit resistance value R2 [μΩ]. / Mm], the unit resistance ratio R1 / R2 at at least one of the temperatures in the above temperature range may be a value of 1.15 or more. In this case, the effect of suppressing the deterioration of the inner heat generating portion is further enhanced. In this case, it is preferable that the unit resistance value ratio R1 / R2 at at least one of the temperatures in the temperature range is 1.25 or more.

In the ceramic heater according to the aspect of the invention, the inner heating portion may have a smaller cross-sectional area perpendicular to the length direction than the outer heating portion. In this case, the resistance value per unit length of the inner heat generating portion tends to be higher than that of the outer heat generating portion. In this case, the cross-sectional area ratio S2 / S1 of the cross-sectional area S1 [mm ² ] perpendicular to the length direction of the inner heat generating portion and the cross-sectional area S2 [mm ² ] perpendicular to the length direction of the outer heat generating portion is obtained. Preferably the value is at least 1.15. In this case, the unit resistance ratio R1 / R2 at at least one of the temperatures in the above-described temperature range tends to be 1.15 or more. It is more preferable that the cross-sectional area ratio S2 / S1 is 1.25 or more.

  In the ceramic heater according to the aspect of the invention, the inner heat generating portion may have a higher volume resistivity at at least one of the temperatures in the temperature range than the outer heat generating portion. In this case, the resistance value per unit length of the inner heat generating portion tends to be higher than that of the outer heat generating portion. In this case, at least at any one of the temperatures in the temperature range, the volume is the ratio of the volume resistivity ρ1 [μΩ · cm] of the inner heating portion to the volume resistivity ρ2 [μΩ · cm] of the outer heating portion. It is preferable that the resistivity ratio ρ1 / ρ2 is equal to or greater than 1.15. In this case, the unit resistance ratio R1 / R2 at at least one of the temperatures in the above-described temperature range tends to be 1.15 or more. Further, it is more preferable that the volume resistivity ratio ρ1 / ρ2 at at least one of the temperatures in the temperature range is 1.25 or more.

  In the ceramic heater according to the aspect of the invention, each of the outer heat generating portion and the inner heat generating portion may include only one bent portion. In this case, for example, the number of bent portions is reduced or the radius of curvature of the bent portion is reduced as compared with the case where the inner heating portion and the outer heating portion are one heating portion electrically connected in series. Easy to enlarge. Here, the bent portion is more susceptible to the stress due to thermal expansion than the straight portion, for example, so that the bent portion is liable to be disconnected due to deterioration, and the life tends to be short. Therefore, the life of the heating element as a whole is prolonged due to at least one of the reduction in the number of the bent portions and the increase in the radius of curvature of the bent portion.

The sensor element of the present invention comprises:
Equipped with the ceramic heater of the present invention according to any one of the above-described embodiments,
It detects a specific gas concentration in the gas to be measured.

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

The gas sensor of the present invention
This is provided with the sensor element of the present invention described above.

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

FIG. 2 is a schematic cross-sectional view schematically illustrating 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.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view schematically illustrating an example of the configuration of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line AA of FIG. The gas sensor 100 detects the concentration of a specific gas such as NOx in a gas to be measured such as exhaust gas of an automobile by using the sensor element 101. The sensor element 101 has a long rectangular parallelepiped shape. The longitudinal direction of the sensor element 101 (horizontal direction in FIG. 1) is the front-back direction, and the thickness direction of the sensor element 101 (vertical direction in FIG. 1) is vertical. Direction. The width direction of the sensor element 101 (the direction perpendicular to the front-rear direction and the vertical direction) is defined as 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 ). , A spacer layer 5 and a second solid electrolyte layer 6 are elements having a structure in which the six layers are stacked in this order from below 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 printing a circuit pattern on a ceramic green sheet corresponding to each layer, and then laminating them, and further firing and integrating them.

  At one end of the sensor element 101, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet 10, a first diffusion-controlling portion 11, and a buffer space 12, the second diffusion control part 13, the first internal space 20, the third diffusion control part 30, and the second internal space 40 are formed adjacent to each other so as to communicate in this order.

  The gas inlet 10, the buffer space 12, the first internal space 20, and the second internal space 40 are formed such that an upper portion provided in a mode in which the spacer layer 5 is hollowed out is a lower surface of the second solid electrolyte layer 6. The lower part is the space inside the sensor element 101 defined by the upper surface of the first solid electrolyte layer 4 and the side part is defined by the side surface of the spacer layer 5.

  Each of the first diffusion-controlling portion 11, the second diffusion-controlling portion 13, and the third diffusion-controlling portion 30 is provided as two horizontally long slits (the openings have a longitudinal direction in a direction perpendicular to the drawing). . In addition, the part from the gas inlet 10 to the second internal space 40 is also referred to as a gas circulation part.

  Further, at a position farther from the distal end side than the gas flow portion, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, the side portion is partitioned by the side surface of the first solid electrolyte layer 4. The reference gas introduction space 43 is provided at a position where the reference gas is introduced. 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 so as to be sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and is connected to the reference gas introduction space 43 around the reference electrode 42 as described above. An air introduction layer 48 is provided. Further, as 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 flow section, the gas inlet 10 is a portion 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 part 11 is a part that gives a predetermined diffusion resistance to the gas to be measured taken in from the gas inlet 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion control part 11 to the second diffusion control part 13. The second diffusion control part 13 is a part that gives 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 (pulsation of the exhaust pressure if the gas to be measured is an exhaust gas of an automobile) The gas to be measured rapidly taken into the inside of the sensor element 101 from the gas inlet 10 by the above) is not directly introduced into the first internal space 20, but the first diffusion control part 11, the buffer space 12, the second After the fluctuation of the concentration of the gas to be measured is canceled through the diffusion control section 13, the gas is introduced into the first internal space 20. Thereby, 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 control part 13. The oxygen partial pressure is adjusted by operating the main pump cell 21.

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

  The inner pump electrode 22 is formed over the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that define the first internal space 20 and the spacer layer 5 that provides a side wall. I have. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 providing 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 providing the bottom surface. An electrode portion 22b is formed, and a side electrode portion (not shown) forms a spacer layer forming both side walls of the first internal space 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b. 5 is formed on the side wall surface (inner surface) and is disposed in a tunnel-shaped structure at a position where the side electrode portion is disposed.

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

  In the main pump cell 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and a pump current is applied between the inner pump electrode 22 and the outer pump electrode 23 in the positive or negative direction. 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.

  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, an oxygen partial pressure detection sensor cell 80 for controlling the main pump.

  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 determined. Further, the pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 of the variable power supply 24 so that the electromotive force V0 is constant. Thereby, the oxygen concentration in the first internal space 20 can be maintained at a predetermined constant value.

  The third diffusion control unit 30 applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, and It is a part leading to the second internal space 40.

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

  In the second internal space 40, after the oxygen concentration (oxygen partial pressure) is adjusted in the first internal space 20 in advance, the auxiliary pump cell 50 is further supplied to the gas to be measured introduced through the third diffusion-controlling section 30. The adjustment of the oxygen partial pressure is carried out. Thus, the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, so that 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 (the outer pump electrode 23). The auxiliary electrochemical pump cell is constituted by the sensor element 101 and an appropriate external electrode (sufficient), and the second solid electrolyte layer 6.

  The auxiliary pump electrode 51 is disposed in the second internal space 40 in the same tunnel-shaped structure as the inner pump electrode 22 provided in the first internal space 20. That is, the ceiling electrode portion 51 a is formed for 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 provided for the first solid electrolyte layer 4. , A bottom electrode portion 51b is formed, and a side electrode portion (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b is formed of a spacer layer 5 which provides a side wall of the second internal space 40. It has a tunnel-shaped structure formed on both wall surfaces. Note that, similarly to the inner pump electrode 22, the auxiliary pump electrode 51 is also formed using a material having a reduced ability to reduce NOx components in the gas to be measured.

  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 The space can be pumped into the second internal space 40.

  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 form an electrochemical sensor cell, that is, an auxiliary pump control oxygen partial pressure detection sensor cell 81.

  The auxiliary pump cell 50 performs pumping with the variable power supply 52 whose voltage is 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 for controlling the electromotive force of the main pump control oxygen partial pressure detection sensor cell 80. 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 controlling section 30 causes the second internal space to return. The gradient of the oxygen partial pressure in the gas to be measured introduced into 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 operation 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 the upper surface of the first solid electrolyte layer 4 facing the second internal space 40 and separated from the third diffusion-controlling portion 30, and the outer pump electrode 23. , A second solid electrolyte layer 6, a spacer layer 5, and a 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 existing 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 fourth diffusion control part 45 is a film composed of a ceramic porous body. The fourth diffusion control part 45 has a role of limiting the amount of NOx flowing into the measurement electrode 44, and also functions as a protective film of the measurement electrode 44. In the measurement pump cell 41, oxygen generated by the decomposition of nitrogen oxide in the atmosphere around the measurement electrode 44 is pumped out, and the generated amount can be detected as the pump current Ip2.

  In addition, in order to detect the oxygen partial pressure around the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42 make an electrochemical sensor cell, that is, An oxygen partial pressure detection sensor cell 82 for measuring pump control is configured. The variable power supply 46 is controlled based on 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 controlling part 45 under the condition where the oxygen partial pressure is controlled. Nitrogen oxides in the gas to be measured around the measurement electrode 44 are 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 supply is controlled so that the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 becomes constant. The voltage Vp2 of 46 is controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the amount of nitrogen oxides in the gas to be measured is determined using the pump current Ip2 in the pump cell 41 for measurement. 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 constitute oxygen partial pressure detection means as an electrochemical sensor cell, the measurement electrode The electromotive force corresponding 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 can be detected. Can also be determined.

  Further, an electrochemical sensor cell 83 is configured by 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. The partial pressure of oxygen 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). The gas to be measured is provided to the pump cell 41 for measurement. Therefore, the NOx concentration in the gas to be measured is changed substantially in proportion to the concentration of NOx in the gas to be measured, based on the pump current Ip2 flowing when the oxygen generated by the reduction of NOx is pumped from the pump cell 41 for measurement. You can now know.

  Further, the sensor element 101 is provided with a heater section 70 which plays a role of temperature adjustment for heating the sensor element 101 and keeping it warm in order to increase the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes a heater connector electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure releasing hole 75. In addition, 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 section 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. The heater 72 includes a heating section 76 and a lead section 79, as shown in FIG.

  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 supply, power can be supplied to the heater unit 70 from outside.

  The heat generating portion 76 of the heater 72 is an electric resistor formed in a manner 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 power is supplied from the outside through the heater connector electrode 71 to generate heat, thereby forming the sensor element 101. The solid electrolyte is heated and kept warm.

  Further, the heat generating portion 76 of the heater 72 is buried from the first inner space 20 to the second inner space 40 so as to adjust the entire sensor element 101 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 with 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 release hole 75 is a portion provided to penetrate the third substrate layer 3 and communicate with the reference gas introduction space 43, and for the purpose of alleviating a rise in internal pressure due to a rise in temperature in the heater insulating layer 74. Be formed.

  The heating section 76 and the lead section 79 of the heater 72 will be described in detail. The heating section 76 is a resistance heating element, and includes an inner heating section 76a and an outer heating section 76b as shown in FIG. Each of the inner heat generating portion 76a and the outer heat generating portion 76b has a band-shaped single-stroke shape having both ends connected to the lead portion 79. Each of the inner heat generating portion 76a and the outer heat generating portion 76b has a symmetrical shape.

  The inner heat generating portion 76a is disposed inside the sensor element 101 in the left-right direction with respect to the outer heat generating portion 76b. The inner heat generating portion 76a is connected to the lead portion 79 so as to be electrically parallel to the outer heat generating portion 76b. The inner heat generating portion 76a has one bent portion 77a and two linear portions 78a. The two linear portions 78a are arranged along the short direction (left-right direction) of the sensor element 101. The length direction of each of the two straight portions 78a is along the longitudinal direction (front-back direction) of the sensor element 101. In the present embodiment, each of the two straight portions 78a is disposed so that the length direction is parallel to the front-rear direction. The rear end of the linear portion 78a located on the left side of the two linear portions 78a is connected to the first lead 79a. The rear end of the linear portion 78a located on the right side is connected to the second lead 79b. The bent portion 77a connects the front ends of the two straight portions 78a. The bent portion 77a is bent in a curved shape and has a semicircular arc shape. Note that the bent portion 77a may have a bent shape. The connecting portion between the inner heat generating portion 76a and the first and second leads 79a and 79b is closer to the inside of the sensor element 101 in the left and right direction than the connecting portion between the outer heat generating portion 76b and the first and second leads 79a and 79b. It is located in.

  The outer heat generating portion 76b has the same shape (pattern) as the inner heat generating portion 76a, and has one bent portion 77b and two linear portions 78b. The two linear portions 78b are arranged along the lateral direction (left and right direction) of the sensor element 101, and are disposed on both the left and right sides so as to sandwich the two linear portions 78a from the left and right. The length direction of each of the two straight portions 78b is along the longitudinal direction (front-back direction) of the sensor element 101. In the present embodiment, each of the two straight portions 78b is disposed so that the length direction is parallel to the front-rear direction. The rear end of the linear portion 78b located on the left side of the two linear portions 78b is connected to the first lead 79a. The rear end of the linear portion 78b located on the right side is connected to the second lead 79b. The bent portion 77b is disposed forward of the bent portion 77a, and connects the front ends of the two straight portions 78b. The bent portion 77b is bent in a curved shape and has a semicircular arc shape. The bent portion 77b has a larger radius of curvature than the bent portion 77a. Note that the bent portion 77b may have a bent shape.

In the present embodiment, the heat generating portion 76 is a cermet containing a noble metal and a ceramic (for example, a cermet of platinum (Pt) and alumina (Al ₂ O ₃ )). Note that the heat generating portion 76 is not limited to the cermet, and may be any material including a conductive material 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), and palladium (Pd), or an alloy thereof.

  The inner heat generating portion 76a has a resistance per unit length of at least one of a temperature range of 700 ° C. to 900 ° C. which is a temperature range in which the heat generating portion 76 may be heated during use. It is higher than the portion 76b. In other words, the resistance value per unit length of the inner heating portion 76a is defined as a unit resistance value R1 [μΩ / mm], and the resistance value per unit length of the outer heating portion 76b is defined as a unit resistance value R2 [μΩ / mm]. At this time, the unit resistance ratio R1 / R2 at least at any one of the above temperature ranges exceeds the value 1. By doing so, at at least one of the temperatures of 700 ° C. to 900 ° C., the heat generation density (heat generation per unit length) of the inner heat generating portion 76a is smaller than that of the outer heat generating portion 76b, and the temperature is hardly increased. Become. Thereby, the deterioration of the inner heat generating portion 76a can be suppressed.

  The length direction of the inner heat generating portion 76a and the outer heat generating portion 76b is the axial direction of the inner heat generating portion 76a and the outer heat generating portion 76b, in other words, the direction in which current flows. Further, the unit resistance value R1 is an average value of the resistance value per unit length of the inside heat generating portion 76a. Similarly, the unit resistance value R2 is an average value of the resistance value per unit length of the outer heat generating portion 76b. Therefore, even when a part of the inner heating part 76a has a lower resistance value per unit length than the outer heating part 76b, if the inner heating part 76a has a higher resistance value per unit length as a whole, Good. However, it is more preferable that the resistance value per unit length exceeds the unit resistance value R2 in any part of the inner heat generating portion 76a. Further, it is preferable that the unit resistance ratio R1 / R2 of the heat generating portion 76 exceeds the value 1 at any temperature in the above temperature range. Further, in the heat generating section 76, the unit resistance value ratio R1 / R2 at at least one of the above temperature ranges is preferably a value of 1.15 or more, more preferably a value of 1.25 or more. Further, at any temperature within the above temperature range, the unit resistance value ratio R1 / R2 may be set to a value of 2.0 or less.

In the present embodiment, the inner heat-generating portion 76a and the outer heat-generating portion 76b are made of the same material (cermet containing platinum as described above), and the cross-sectional area S1 [mm ² ] perpendicular to the longitudinal direction of the inner heat-generating portion 76a is equal to the outer heat-generating temperature. The cross-sectional area perpendicular to the length direction of the portion 76b is smaller than S2 [mm ² ]. That is, the heat generating portion 76 has a cross-sectional area ratio S2 / S1 exceeding the value 1. By doing so, the unit resistance ratio R1 / R2 exceeds the value 1 in any of the temperature ranges from 700 ° C. to 900 ° C. The value of the sectional area ratio S2 / S1 is preferably 1.15 or more, and more preferably 1.25 or more. The cross-sectional area ratio S2 / S1 is adjusted, for example, by making the width W1 of the inner heat generating portion 76a smaller than the width W2 of the outer heat generating portion 76b, or changing the thickness D1 of the inner heat generating portion 76a to the thickness of the outer heat generating portion 76b. It should be smaller than D2 or at least one of them. For example, when the width W1 <the width W2, if the cross-sectional area ratio S2 / S1 exceeds the value 1, the thickness D1> the thickness D2 may be satisfied, or the thickness D1 = the thickness D2. Or the thickness D1 <the thickness D2. Similarly, when the thickness D1 <the thickness D2, if the cross-sectional area ratio S2 / S1 exceeds the value 1, the width W1 may be greater than the width W2, or the width W1 may be greater than the width W2. Alternatively, the width W1 may be smaller than the width W2. Note that the values of the cross-sectional areas S1 and S2 are also average values of the inner heat generating portion 76a and the outer heat generating portion 76b, similarly to the unit resistance values R1 and R2. In the present embodiment, the cross-sectional area of the inner heat-generating portion 76a is the same value (= cross-sectional area S1) in any part. The same applies to the outer heat generating portion 76b. Further, the sectional area ratio S2 / S1 may be set to a value of 2.0 or less. The widths W1 and W2 may be 0.05 mm or more and 1.5 mm or less. The thicknesses D1 and D2 may be 0.003 mm or more and 0.1 mm or less.

  The lead portion 79 has 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 79a and 79b are leads for supplying electricity to the heat generating portion 76, and are connected to the heater connector electrode 71. The first lead 79a is a positive lead, and the second lead 79b is a negative lead. When a voltage is applied between the first lead 79a and the second lead 79b, a current flows through the heating section 76, and the heating section 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 sectional area, so that the resistance value per unit length is low. In the present embodiment, the lead portion 79 has a low volume resistivity due to a higher ratio of the noble metal than the heating portion 76, and has a wider width than the inner heating portion 76a and the outer heating portion 76b. The cross-sectional area is larger.

  A method for manufacturing the gas sensor 100 thus configured will be described below. First, six unfired 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. Further, a space serving as a gas flow section is provided in advance in the green sheet serving as the spacer layer 5 by a punching process or the like. Each of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second 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 each electrode described above, a lead wire connected to each electrode, the air introduction layer 48, the heater 72, and the like. The pattern printing is performed by applying a pattern forming paste prepared according to the characteristics required for each forming object on a green sheet using a known screen printing technique. As a paste for forming a pattern to be the heater 72, a mixture of a raw material (for example, a noble metal and ceramic particles) made of the above-described material of the heater 72, an organic binder, an organic solvent, and the like is used.

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

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

   When the sensor element 101 is obtained in this manner, a gas sensor 100 is obtained by manufacturing a sensor assembly incorporating the sensor element 101 and attaching a protective cover or the like. A method for manufacturing the above-described gas sensor is known, except that the shape of the heater 72 and the unit resistance value ratio R1 / R2 exceed a value of 1, and are described in, for example, International Publication 2013/005491. Have been.

  In the gas sensor 100 thus configured, the heater 72 is connected to a power supply (for example, an alternator of an automobile) via the heater connector electrode 71 during use, and a DC voltage (for example, 12 to 14 V) is applied between the first lead 79a and the second lead 79b. ) Is applied. Then, due to the applied voltage, a current flows through the heating section 76 and the heating section 76 generates heat. Thus, the temperature of the entire sensor element 101 is adjusted to a temperature (for example, 700 ° C. to 900 ° C.) at which the solid electrolyte (each of the layers 1 to 6) is activated. At this time, the temperature of the heat generating portion 76 becomes high. However, the higher the temperature becomes, the more easily the heat generating portion 76 is oxidized (for example, platinum as a noble metal component is oxidized) and deteriorated. In particular, since the inner heat generating portion 76a is located on the inner side as compared with the outer heat generating portion 76b, it tends to become hot, and the inner heat generating portion 76a of the heat generating portion 76 tends to deteriorate. However, in the heater section 70 of the present embodiment, the unit resistance ratio R1 / R2 at at least one of the temperatures of 700 ° C. to 900 ° C. exceeds the value 1. Accordingly, at at least one of the temperatures of 700 ° C. to 900 ° C., the applied voltage is the same between the inner heating portion 76 a and the outer heating portion 76 b which are electrically connected in parallel, and the inner heating portion 76 a flows. Since the current is reduced, the heat generation density of the inner heat generating portion 76a at that temperature is reduced. Therefore, as compared with the case where the unit resistance value ratio R1 / R2 is equal to or less than 1, the temperature rise of the inner heat generating portion 76a is suppressed. That is, a rise in the temperature of the inner heat generating portion 76a, which tends to be high, is offset by reducing the heat generation density of the inner heat generating portion 76a. Thereby, the deterioration of the inner heat generating portion 76a can be suppressed. For this reason, for example, it is difficult for the inner heat generating portion 76a to be disconnected, and the life of the inner heat generating portion 76a is extended. The life of the inner heat generating portion 76a, which is easily deteriorated, becomes longer, so that the life of the entire heater 72 becomes longer. Note that if the temperature of the inner heat generating portion 76a is lower than when the unit resistance value ratio R1 / R2 is 1, the effect of suppressing the deterioration of the inner heat generating portion 76a can be obtained. Therefore, it is not essential that the temperature of the inner heat generating portion 76a be lower than the temperature of the outer heat generating portion 76b. For example, even if the temperature of the inner heating portion 76a is higher than that of the outer heating portion 76b, if the uniformity of the entire heating portion 76 is improved as compared with the case where the unit resistance ratio R1 / R2 is 1, the heater is used. The effect of extending the life of the 72 is obtained.

  Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. The heater section 70 of the present embodiment corresponds to the ceramic heater of the present invention, the heater 72 corresponds to the heating element, the inner heating section 76a corresponds to the inner heating section, the outer heating section 76b corresponds to the outer heating section, 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 inner heating portion 76a of the heater 72 is disposed electrically in parallel with the outer heating portion 76b, and is 700 ° C. or more and 900 ° C. as compared with the outer heating portion 76b. The resistance value per unit length at at least one of the following temperature ranges is high. Accordingly, at least at any one of the temperatures of 700 ° C. to 900 ° C., the heat generation density of the inner heat generating portion 76a is smaller than that of the outer heat generating portion 76b, and the deterioration of the inner heat generating portion 76a can be suppressed. Therefore, the life of the entire heater 72 is prolonged. In addition, in order to make the resistance value per unit length different between the inner heating portion 76a and the outer heating portion 76b arranged in parallel, for example, the resistance value per unit length of a part of the heating portions connected in series The heater 72 is easier to manufacture than in the case of changing.

  Further, when the unit resistance value ratio R1 / R2 is at least 1.15 at at least one of the temperatures in the above temperature range, the effect of suppressing the deterioration of the inner heat generating portion 76a is further enhanced. When the unit resistance ratio R1 / R2 is equal to or greater than 1.25, the effect of suppressing the deterioration of the inner heat generating portion 76a is further enhanced. Since the inner heat generating portion 76a has a smaller cross-sectional area perpendicular to the length direction than the outer heat generating portion 76b, the resistance value (unit) of the inner heat generating portion 76a per unit length at at least one of the above-mentioned temperature ranges. The resistance value R1) tends to be higher than the unit resistance value R2 of the outer heat generating portion 76b. When the cross-sectional area ratio S2 / S1 is equal to or greater than 1.15, the unit resistance ratio R1 / R2 at at least one of the temperatures in the above-described temperature range tends to be equal to or greater than 1.15. When the cross-sectional area ratio S2 / S1 is equal to or greater than 1.25, the unit resistance value ratio R1 / R2 at least at any temperature in the above-described temperature range tends to be equal to or greater than 1.25.

  Further, each of the inner heating portion 76a and the outer heating portion 76b has only one bent portion 77a, 77b. Therefore, as compared with a case where the inner heat generating portion 76a and the outer heat generating portion 76b are one heat generating portion electrically connected in series, the number of the bent portions is reduced and the radius of curvature of the bent portion is reduced. Easy to make larger. For example, if it is attempted to form a heater 72 in a one-stroke pattern in which the inner heat generating portion 76a and the outer heat generating portion 76b are connected in series, an extra bent portion for connecting the inner heat generating portion 76a and the outer heat generating portion 76b is required. Is needed. Further, such a bent portion tends to have a small radius of curvature. Here, in general, a bent portion is more susceptible to stress due to thermal expansion than a straight portion, for example. More specifically, minute cracks are likely to occur in the bent portion under the influence of stress due to thermal expansion. Then, the cracks increase the surface area of the bent portion to promote oxidation, and furthermore, the cracks are extended, so that the bent portion is liable to be disconnected and the life tends to be short. Therefore, the life of the entire heater 72 is prolonged due to at least one of the reduction in the number of bent portions and the increase in the radius of curvature of the bent portion.

  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 at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

For example, in the above-described embodiment, the cross-sectional area ratio S2 / S1 is set to exceed the value 1. However, the unit resistance ratio R1 / R2 at least at any temperature in the temperature range of 700 ° C. to 900 ° C. may exceed the value 1. I just need. For example, the inner heat generating portion 76a may have a higher volume resistivity at at least one of the above-mentioned temperature ranges than the outer heat generating portion 76b. That is, at least at any one of the above temperature ranges, the volume resistivity is the ratio of the volume resistivity ρ1 [μΩ · cm] of the inner heating portion 76a to the volume resistivity ρ2 [μΩ · cm] of the outer heating portion 76b. The rate ratio ρ1 / ρ2 may exceed the value 1. Also in this case, the unit resistance ratio R1 / R2 at at least any one of the above temperature ranges can be made to exceed the value 1, the deterioration of the inner heat generating portion 76a can be suppressed, and the life of the heater 72 can be extended. At least one of the above temperature ranges, the volume resistivity ratio ρ1 / ρ2 is preferably at least 1.15, more preferably at least 1.25. For example, the volume resistivity ρ1 can be made higher than the volume resistivity ρ2 by making the ratio of the noble metal (conductor) included in the outer heating portion 76b higher than that of the inner heating portion 76a. Alternatively, for example, the inner heating portion 76a contains platinum as a main component, and the outer heating portion 76b adds a noble metal (rhodium, gold, or the like) having a lower volume resistivity than platinum in addition to or instead of platinum. ρ1 can be higher than the volume resistivity ρ2. That is, the outer heat generating portion 76b may include a noble metal that is not included in the inner heat generating portion 76a but has a lower volume resistivity than the noble metal included in the inner heat generating portion 76a. Alternatively, the outer heat generating portion 76b contains a material having a smaller temperature coefficient of resistance (unit: [% / ° C.]) than the noble metal as the main component more than the inner heat generating portion 76a, so that at least one of the above temperature ranges is obtained. The volume resistivity ρ1 at that temperature can be higher than the volume resistivity ρ2. Materials having such a low temperature coefficient of resistance include nichrome (an alloy containing nickel (Ni) and chromium (Cr)), Kanthal (registered trademark: an alloy containing iron, chromium, and aluminum), molybdenum disilicide (MoSi ₂ ) and the like. Note that the values of the volume resistivity ρ1 and ρ2 are also average values of the inner heating portion 76a and the outer heating portion 76b, similarly to the unit resistance values R1 and R2. At any temperature in the above temperature range, the volume resistivity ratio ρ1 / ρ2 may be set to a value of 2.0 or less.

  In the heater section 70, combining the cross-sectional area ratio S2 / S1 with a value exceeding 1 and the volume resistivity ratio ρ1 / ρ2 with a value exceeding 1 may be combined. For example, the product of the cross-sectional area ratio S2 / S1 and the volume resistivity ratio ρ1 / ρ2 (= unit resistance ratio R1 / R2) at at least one of the temperatures in the above temperature range exceeds the value 1, the value 1.15. Alternatively, the value may be 1.25 or more. Even when the cross-sectional area ratio S2 / S1 exceeds the value 1, the material of the inner heat generating portion 76a and the material of the outer heat generating portion 76b may be different.

  In the above-described embodiment, the heater 72 includes the inner heat generating portion 76a and the outer heat generating portion 76b. However, the heater 72 includes a heat generating portion electrically arranged in parallel with the inner heat generating portion 76a and the outer heat generating portion 76b. Furthermore, one or more may be provided. FIG. 3 is an explanatory diagram of a heater 72A of a modified example in this case. The heating section 76 of the heater 72A includes an intermediate heating section 76c in addition to the inner heating section 76a and the outer heating section 76b. The intermediate heating portion 76c is disposed outside the inner heating portion 76a and inside the outer heating portion 76b, and is connected to the lead portion 79 so as to be electrically parallel to the inner heating portion 76a and the outer heating portion 76b. ing. The intermediate heating portion 76c has one bent portion 77c and two straight portions 78c, like the inner heating portion 76a and the outer heating portion 76b. With the heater 72A of such a modification, the same effects as those of the above-described embodiment can be obtained. For example, when the unit resistance ratio R1 / R2 at least at any temperature in the temperature range of 700 ° C. to 900 ° C. exceeds 1, the deterioration of the inner heat generating portion 76a can be suppressed, and the life of the heater 72A can be extended. . Further, assuming that the resistance value per unit length of the intermediate heating portion 76c is the unit resistance value R3, the unit resistance value R3 is preferably equal to or less than the unit resistance value R1, and more preferably less than the unit resistance value R1. Further, the unit resistance value R3 is preferably equal to or more than the unit resistance value R2, and may be greater than the unit resistance value R2. The temperature of the intermediate heat generating portion 76c is likely to be higher than that of the outer heat generating portion 76b, and is less likely to be higher than that of the inner heat generating portion 76a. Therefore, it is preferable that R2 <R3 <R1 because the uniformity of the heat generating portion 76 as a whole is easily increased and the life of the heater 72A is easily elongated. When the heating elements have three or more heating elements connected in parallel with each other, such as the heater 72A, the outermost heating element is defined as an outer heating element, and the innermost heating element is defined as an inner heating element. The other heating parts are defined as intermediate heating parts.

  In the above-described embodiment, the inner heat generating portion 76a and the outer heat generating portion 76b are both connected to the same lead portion 79, but are not limited thereto. For example, a lead portion connected to the inside heat generating portion 76a and a lead portion connected to the outside heat generating portion 76b may exist separately. In this case, the voltages applied to the inner heating section 76a and the outer heating section 76b may be different. However, if the voltage applied to the inner heat generating portion 76a is too high compared to the outer heat generating portion 76b, the heat generation density of the inner heat generating portion 76a does not become lower than that of the outer heat generating portion 76b. Must be determined. Conversely, by lowering the voltage applied to the inner heat generating portion 76a as compared to the outer heat generating portion 76b, the heat generation density of the inner heat generating portion 76a can be reduced by that much compared to the outer heat generating portion 76b. Further, the inner heat generating portion 76a and the outer heat generating portion 76b may not be directly connected to the lead portion 79. For example, the inner heat generating portion 76a and the outer heat generating portion 76b may be connected in parallel so as to branch off from the heat generating portion connected to the lead portion 79.

  In the above-described embodiment, each of the inner heat generating portion 76a and the outer heat generating portion 76b has only one bent portion and two linear portions. However, the present invention is not limited to this. Shape may be used. For example, the inner heat generating portion 76a and the outer heat generating portion 76b may include more bent portions and linear portions. FIG. 4 is an explanatory diagram of a heater 72B of a modified example in this case. The inner heating portion 76a of the heater 72B includes three bent portions 77a and four straight portions 78a. Two bent portions 77a are provided on the front end side of the straight portion 78a, and one is provided on the rear end side of the straight portion 78a. Each of the three bent portions 77a connects two linear portions 78a. The outer heat generating portion 76b also has three bent portions 77b and four linear portions 78b, similarly to the inner heat generating portion 76a. With the heater 72B of such a modification, the same effects as those of the above-described embodiment can be obtained. For example, when the unit resistance ratio R1 / R2 at least at any temperature in the temperature range of 700 ° C. to 900 ° C. exceeds 1, the deterioration of the inner heat generating portion 76a can be suppressed and the life of the heater 72B can be extended. .

  In the embodiment described above, the length direction of the straight portions 78a and 78b is parallel to the longitudinal direction (front-back direction) of the heater unit 70. However, if the length direction is along the front-back direction, they are not parallel. Is also good. For example, at least one of the linear portions 78a and 78b may have a length direction inclined with respect to the front-rear direction. Further, the length direction of the linear portions 78a and 78b may be along the short direction (left-right direction) of the heater unit 70. FIG. 5 is an explanatory diagram of a heater 72C of a modified example in this case. The inner heat generating portion 76a of the heater 72C includes a plurality of (15 in FIG. 5) linear portions 78a whose length directions are parallel to the left-right direction and are arranged in the front-rear direction. Further, the inner heat generating portion 76a connects a plurality of linear portions 78a adjacent to each other in the front-rear direction, and connects between the linear portion 78a arranged at the rearmost end and the lead portion 79 (16 in FIG. 5). ) Bent portions 77a. Similarly to the inner heat generating portion 76a, the outer heat generating portion 76b includes 16 bent portions 77b and 15 linear portions 78b. With the heater 72C of such a modification, the same effects as those of the above-described embodiment can be obtained. For example, by making the unit resistance ratio R1 / R2 at least one of the temperatures in the temperature range of 700 ° C. to 900 ° C. more than 1, the deterioration of the inner heat generating portion 76a can be suppressed and the life of the heater 72C can be extended. .

  It is to be noted that the inner heating portion 76a and the outer heating portion 76b each having only one bent portion 77a and 77b, respectively, like the heater 72 of FIG. 2 described above, are different from the heaters 72B and 72C shown in FIGS. Since the number of bends can be reduced and the radius of curvature of the bends can be increased, the life of the heater 72 can be prolonged, which is preferable.

  In the above-described embodiment, the inner heat-generating portion 76a and the outer heat-generating portion 76b are shaped such that the cross-sectional area has the same value in any part, but the present invention is not limited to this. For example, a portion having a different cross-sectional area from the others may be present in the inner heat generating portion 76a. In this case, a step may be generated in the inside heat generating portion 76a, or a portion whose cross-sectional area gradually changes along the length direction may exist in the inside heat generating portion 76a. However, it is preferable that there is no step in the inside heat generating portion 76a. The same applies to the outer heat generating portion 76b.

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

  In the above-described embodiment, the gas sensor 100 including the heater unit 70 has been described. However, the present invention may be a single sensor element 101 or a single heater unit 70, that is, a single ceramic heater. Although the heater unit 70 includes the first substrate layer 1, the second substrate layer 2, and the third substrate layer 3, the heater unit 70 may have a ceramic body surrounding the heater 72. For example, the lower layer of the heater 72 may be a single layer instead of the two layers of the first substrate layer 1 and the second substrate layer 2. Although the heater section 70 includes the heater insulating layer 74, 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 so, the heater insulating layer 74 may be omitted. Further, the size of the sensor element 101 may be, for example, a length in the front-rear direction of 25 mm or more and 100 mm or less, a width in the left-right direction of 2 mm or more and 10 mm or less, and a thickness in the vertical direction of 0.5 mm or more and 5 mm or less.

  Hereinafter, an example in which a sensor element is specifically manufactured will be described as an example. Experimental Examples 2 to 9, 11 to 18 correspond to Examples of the present invention, and Experimental Examples 1 and 10 correspond to Comparative Examples. Note that the present invention is not limited to the following embodiments.

[Experimental Examples 1 to 9]
According to the manufacturing method of the gas sensor 100 of the above-described embodiment, the sensor elements 101 shown in FIGS. Experimental examples 1 to 9 had the same configuration except that the cross-sectional area ratio S2 / S1 was variously changed as shown in Table 1 below by changing the width W1 of the inner heat generating portion 76a. The size of the sensor element 101 was such that the length in the front-rear direction was 67.5 mm, the width in the left-right direction was 4.25 mm, and the thickness in the up-down direction was 1.45 mm. In Example 1, the width W1 of the inner heat generating portion 76a and the width W2 of the outer heat generating portion 76b were both set to 0.25 mm. Further, both the thickness D1 of the inner heat generating portion 76a and the thickness D2 of the outer heat generating portion 76b in Experimental Example 1 were 0.01 mm. In manufacturing the sensor element 101, the ceramic green sheet was formed by mixing zirconia particles to which 4 mol% of yttria as a stabilizer was added, an organic binder, and an organic solvent, and then forming the tape by tape molding. The conductive paste for the heating section 76 of the heater section 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 liquid. An organic binder solution obtained by dissolving 20% by mass of polyvinyl butyral in 80% by mass of butyl carbitol was added to the premixed liquid, mixed, and then appropriately added with butyl carbitol to adjust the viscosity. A conductive paste was obtained. In Experimental Example 1, the same conductive paste was used for the inner heating portion 76a and the outer heating portion 76b, and the volume resistivity ratio ρ1 / ρ2 was 1 at any temperature from 700 ° C. to 900 ° C. is there. The same applies to Experimental Examples 2 to 9.

[Experimental Examples 10 to 18]
Sensor elements 101 of Experimental Examples 10 to 18 were produced in the same manner as in Experimental Example 1 except that the volume resistivity ratio ρ1 / ρ2 was variously changed as shown in Table 1 below. The volume resistivity ratio ρ1 / ρ2 was changed by changing the content ratio of Pt in the inner heat generating portion 76a. The widths W1 and W2 and the thicknesses D1 and D2 of Experimental Examples 10 to 18 are the same as those of Experimental Example 1, and the cross-sectional area ratios S2 / S1 of Experimental Examples 10 to 18 are all 1.00. . Further, 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.

  The measurement of the volume resistivity ρ1 in Experimental Examples 10 to 18 was performed using a test piece manufactured as follows. First, an insulating paste to be the heater insulating layer 74 was printed on a ceramic green sheet to be the second substrate layer 2 after firing. Next, a conductive paste for the inside heat generating portion 76a, which was manufactured 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, and formed the heat generating part of a rectangular parallelepiped shape, and obtained each test piece of Experimental Examples 10-18. Then, a resistance measuring lead was attached to the heat generating portion having a rectangular parallelepiped shape, the test piece was heated to 700 ° C. to 900 ° C. in an electric furnace, and the resistance value of the heat generating portion was measured in this state. Then, the volume resistivity ρ1 was calculated based on the length and the cross-sectional area of the rectangular heating element and the measured resistance value. The volume resistivity ρ2 was similarly calculated from the resistance value measured using a test piece. The values of the volume resistivity ratios ρ1 / ρ2 of Experimental Examples 10 to 18 hardly changed in the range of 700 ° C to 900 ° C.

[Evaluation test]
With respect to Experimental Examples 1 to 18, the durability (life) of the heat generating portion 76 was evaluated. Specifically, a voltage was applied to the lead portion 79 so that the average value of the temperature of the heating portion 76 became a predetermined temperature, and the heater 72 was energized. Then, it was determined whether or not the heat generating portion 76 was disconnected within 2000 hours in that state. A case where no disconnection occurred for more than 2000 hours is referred to as “A (excellent, practical level or more)”, and a case where disconnection occurs for more than 1000 hours and within 2000 hours is “B (good, practical level)” The case where disconnection occurred within 1000 hours was designated as "C (impossible, less than practical level)". When the average temperature of the heat generating portion 76 was 700 ° C., 750 ° C., 800 ° C., 850 ° C., and 900 ° C., the durability of the heat generating portion 76 was evaluated. The temperature of the heating section 76 was adjusted by changing the voltage applied to the lead section 79. The temperature of the heat generating portion 76 was measured indirectly by measuring the temperature of the lower surface of the sensor element 101 with a radiation thermometer. Table 1 shows the results of the evaluation test. Table 1 also shows values of the unit resistance ratio R1 / R2, the sectional area ratio S2 / S1, and the volume resistivity ratio ρ1 / ρ2 of each experimental example. The value of the unit resistance 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 as the value of the unit resistance value ratio R1 / R2 was larger, disconnection of the heat generating portion 76 was less likely to occur. As the value of the unit resistance value ratio R1 / R2 was larger, there was a tendency that disconnection of the heat generating portion 76 was less likely to occur even at a higher temperature. Further, in Experimental Examples 4 to 9, 13 to 18 in which the unit resistance value ratio R1 / R2 was 1.15 or more, the evaluation was A (excellent) or B (good) at any temperature from 700 ° C. to 900 ° C. Met. In Experimental Examples 6 to 9, and 15 to 18 in which the unit resistance value ratio R1 / R2 was 1.25 or more, the evaluation was A (excellent) at any temperature from 700 ° C to 900 ° C. In each of the experimental examples in which the evaluation was B (good) or C (impossible), disconnection occurred in the inner heat generating portion 76a. From a comparison between Experimental Examples 1 to 9 and Experimental Examples 10 to 18, if the values of the unit resistance value ratios R1 / R2 are the same, the case where the cross-sectional area ratio S2 / S1 is changed and the case where the volume resistivity ratio ρ1 It was found that the same result was obtained when / ρ2 was changed. The same results as in Experimental Examples 1 to 9 were obtained when the cross-sectional area ratio S2 / S1 was changed by changing the thickness D1 of the inner heat generating portion 76a.

  REFERENCE SIGNS LIST 1 first substrate layer, 2 second substrate layer, 3 third substrate layer, 4 first solid electrolyte layer, 5 spacer layer, 6 second solid electrolyte layer, 10 gas inlet, 11 first diffusion-controlling part, 12 buffer Space, 13 second diffusion control 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 source, 30 third diffusion control part , 40 second internal space, 41 measurement pump cell, 42 reference electrode, 43 reference gas introduction space, 44 measurement electrode, 45 fourth diffusion control part, 46 variable power supply, 48 atmosphere introduction layer, 50 auxiliary pump cell, 51 auxiliary pump Electrode, 51a ceiling electrode section, 51b bottom electrode section, 52 variable power supply, 70 heater section, 71 heater connector electrode, 72, 72A to 72C heater, 73 through electrode , 74 heater insulating layer, 75 pressure release hole, 76 heating section, 76a inside heating section, 76b outside heating section, 76c intermediate heating section, 77a to 77c bent section, 78a to 78c linear section, 79 lead section, 79a, 79b First and second leads, 80 oxygen partial pressure detection sensor cell for main pump control, 81 oxygen partial pressure detection sensor cell for auxiliary pump control, 82 oxygen partial pressure detection sensor cell for pump control for measurement, 83 sensor cells, 100 gas sensor, 101 sensor element.

Claims (13)

The outer heat generating portion, the resistance per unit length at least at any temperature in the temperature range of 700 ° C. or more and 900 ° C. or less is higher than the outer heat generating portion, and the inner side of the outer heat generating portion has the outer heat generating portion. A heating element having an inner heating portion electrically arranged in parallel with the heating element;
A ceramic body surrounding the heating element,
With
The outer heat generating portion includes a straight portion,
The inner heating portion includes a linear portion is high resistance value per unit length in at least one of the temperature of the temperature range in comparison with the linear portion of the outer heat generating portion,
The cross-sectional area of the inner heating portion is the same value in any portion,
The cross-sectional area of the outer heating portion has the same value in any portion,
Ceramic heater. The outer heat generating portion, the resistance per unit length at least at any temperature in the temperature range of 700 ° C. or more and 900 ° C. or less is higher than the outer heat generating portion, and the inner side of the outer heat generating portion has the outer heat generating portion. A heating element having an inner heating portion electrically arranged in parallel with the heating element;
A ceramic body surrounding the heating element,
With
The outer heat generating portion and the inner heat generating portion each include a linear portion,
At least at any one of the temperatures in the temperature range, the inner heating portion has a higher resistance value per unit length in any portion than the average value of the resistance value per unit length of the outer heating portion. ,
Ceramic heater. When the resistance value per unit length of the inner heating part is unit resistance R1 [μΩ / mm], and the resistance value per unit length of the outer heating part is unit resistance R2 [μΩ / mm]. The unit resistance ratio R1 / R2 at at least one of the temperatures in the temperature range is not less than 1.15;
The ceramic heater according to claim 1. The unit resistance ratio R1 / R2 at least at any one of the temperature ranges is equal to or greater than 1.25;
The ceramic heater according to claim 3. The inner heating portion has a smaller cross-sectional area perpendicular to the length direction than the outer heating portion,
The ceramic heater according to claim 1. The cross-sectional area ratio S2 / S1 of the cross-sectional area S1 [mm ² ] perpendicular to the length direction of the inner heat generating portion and the cross-sectional area S2 [mm ² ] perpendicular to the length direction of the outer heat generating portion is 1.15. That's it,
The ceramic heater according to claim 5. The cross-sectional area ratio S2 / S1 is not less than 1.25,
The ceramic heater according to claim 6. The inner heating portion has a higher volume resistivity at at least one of the temperatures in the temperature range than the outer heating portion,
The ceramic heater according to any one of claims 1 to 7. A volume resistivity ratio ρ1 that is a ratio of a volume resistivity ρ1 [μΩ · cm] of the inner heating portion and a volume resistivity ρ2 [μΩ · cm] of the outer heating portion at at least one temperature in the temperature range. / Ρ2 is greater than or equal to 1.15,
A ceramic heater according to claim 8. The volume resistivity ratio ρ1 / ρ2 at at least one of the temperatures in the temperature range is equal to or greater than 1.25;
The ceramic heater according to claim 9. The outer heat generating portion and the inner heat generating portion each include only one bent portion,
The ceramic heater according to any one of claims 1 to 10.   A sensor element comprising the ceramic heater according to claim 1, wherein the sensor element detects a specific gas concentration in a gas to be measured.   A gas sensor comprising the sensor element according to claim 12.

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