Sensor elements and gas sensors

Abstract

The present invention provides a sensor element and a gas sensor. The sensor element (101) has an element body and a heating portion (76), and a measured gas circulation portion is arranged inside the element body. A main pump chamber, an auxiliary pump chamber, and a measuring chamber are arranged in the measured gas circulation portion. The distance X1 in the left-right direction between the first inner straight portion (79a) and the second inner straight portion (79b) of the heating portion (76) at the portion overlapping with the main pump chamber projection area (Ap) is more than 1 / 3 of the width Wp in the left-right direction of the main pump chamber projection area (Ap). The distance X2 in the left-right direction between the first inner straight portion (79a) and the second inner straight portion (79b) at the portion overlapping with the auxiliary pump chamber projection area (Aq) is more than 0.4 times the width Wp.

Description

Technical Field

[0001] The present invention relates to a sensor element and a gas sensor. Background Art

[0002] In the past, there is a known sensor element for a gas sensor for detecting the concentration of a specific gas such as NOx in a measured gas such as automobile exhaust gas. For example, Patent Document 1 describes a sensor element comprising: a stack of multiple oxygen ion conductive solid electrolyte layers; an internal cavity, which is arranged inside the stack; a pump unit, which performs oxygen inlet and outlet of the internal cavity; and a measuring electrode, which is arranged inside the stack. When the concentration of NOx is detected using the sensor element, first, the oxygen concentration of the measured gas in the internal cavity is adjusted. Next, the NOx in the measured gas with the adjusted oxygen concentration is reduced around the measuring electrode. Then, based on the pump current flowing when the oxygen around the measuring electrode is extracted, the concentration of NOx in the measured gas is detected. In addition, the sensor element of Patent Document 1 has a heating element, which is responsible for the temperature adjustment function of heating and keeping the sensor element warm, so as to improve the oxygen ion conductivity of the solid electrolyte. The heating element has a straight portion and a curved portion. Furthermore, the resistance value per unit length of the curved portion is lower than that of the straight portion at at least any temperature in the temperature range of 700° C. to 900° C. This makes it difficult for the temperature of the curved portion, which is more susceptible to degradation than the straight portion, to rise, thereby suppressing degradation of the curved portion.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-041431 Summary of the invention

[0006] However, since the heating element heats the sensor element, stress may be generated around the inner cavity of the sensor element. This stress may cause cracks in the sensor element, so it is desirable to reduce the stress. Patent Document 1 does not consider the stress generated around the inner cavity.

[0007] The present invention has been made to solve the above-mentioned problems, and a main object of the present invention is to reduce stress generated around the inner cavity of a sensor element when a heating element generates heat.

[0008] In order to achieve the above-mentioned main object, the present invention adopts the following means.

[0009] [1] The sensor element of the present invention comprises:

[0010] A plate-shaped element body, the element body including a solid electrolyte layer having oxygen ion conductivity, a gas flow portion for introducing and flowing the gas to be measured, and having a long dimension direction, a short dimension direction, and a thickness direction perpendicular to the long dimension direction and the short dimension direction;

[0011] a main pump unit for adjusting the oxygen concentration of a main pump chamber in the measured gas flow section;

[0012] an auxiliary pump unit that adjusts the oxygen concentration of an auxiliary pump chamber disposed on a downstream side of the main pump chamber in the measured gas flow section;

[0013] a measurement pump unit that adjusts the oxygen concentration of a measurement chamber disposed downstream of the auxiliary pump chamber in the measured gas flow section; and

[0014] a heating element for heating the element body,

[0015] The heating element has:

[0016] A first outer straight portion and a second outer straight portion, the first outer straight portion and the second outer straight portion are arranged side by side along the short dimension direction and have a length direction along the long dimension direction;

[0017] a first inner straight portion and a second inner straight portion, wherein the first inner straight portion and the second inner straight portion are arranged between the first outer straight portion and the second outer straight portion in the short dimension direction and have a length direction along the long dimension direction;

[0018] a first curved portion connecting the first outer straight portion and the first inner straight portion at one end in the longitudinal direction;

[0019] a second curved portion connecting the first inner straight portion and the second inner straight portion at the other end side in the longitudinal direction; and

[0020] a third curved portion connecting the second inner straight portion and the second outer straight portion at one end in the longitudinal direction;

[0021] At least a portion of each of the first inner straight portion and the second inner straight portion overlaps with a main pump chamber projection area, wherein the main pump chamber projection area is an area obtained by projecting the main pump chamber toward the heating element in the thickness direction.

[0022] At least a portion of each of the first inner straight portion and the second inner straight portion overlaps with an auxiliary pump chamber projection area, wherein the auxiliary pump chamber projection area is an area obtained by projecting the auxiliary pump chamber toward the heating element in the thickness direction.

[0023] The distance X1 between the first inner straight portion and the second inner straight portion in the short dimension direction at the portion overlapping with the main pump chamber projection area is greater than 1 / 3 of the width Wp of the main pump chamber projection area in the short dimension direction.

[0024] A distance X2 in the short dimension direction between the first inner straight portion and the second inner straight portion at a portion overlapping with the auxiliary pump chamber projection region is equal to or greater than 0.4 times the width Wp.

[0025] In this sensor element, the positional relationship between the heating element and the internal cavity (main pump chamber, auxiliary pump chamber, and measuring chamber) of the sensor element satisfies the following conditions, namely, the distance X1 is more than 1 / 3 of the width Wp, and the distance X2 is more than 0.4 times the width Wp. The distance X1 is: the distance in the short dimension direction between the first inner straight line portion and the second inner straight line portion of the heating element at the parts where the main pump chamber projection area overlaps with the area obtained by projecting the main pump chamber toward the heating element in the thickness direction. The distance X2 is: the distance in the short dimension direction between the first inner straight line portion and the second inner straight line portion of the heating element at the parts where the auxiliary pump chamber projection area overlaps with the area obtained by projecting the auxiliary pump chamber toward the heating element in the thickness direction. The width Wp is the length in the short dimension direction of the main pump chamber projection area. By satisfying the above conditions, the stress generated around the internal cavity (main pump chamber, auxiliary pump chamber, and measuring chamber) when the heating element generates heat can be reduced.

[0026] [2] In the above sensor element (the sensor element described in [1]), the distance X1 may be larger than 0.4 times the width Wp. This improves the stress reduction effect.

[0027] [3] Based on the above-mentioned sensor element (the sensor element described in [1] or [2] above), the resistance value per unit length of the portion of the heating element that overlaps with the pump chamber projection area, i.e., the pump chamber overlapping portion, is set to a unit resistance value R1 [μΩ / mm], wherein the pump chamber projection area is an area obtained by projecting the main pump chamber and the auxiliary pump chamber toward the heating element and in the thickness direction, and the resistance value per unit length of the portion of the heating element that overlaps with the measurement chamber projection area, i.e., the measurement chamber overlapping portion, is set to a unit resistance value R3 [μΩ / mm], wherein the measurement chamber projection area is an area obtained by projecting the measurement chamber toward the heating element and in the thickness direction, and at this time, the unit resistance value ratio R3 / R1 at at least any temperature within the temperature range of 700°C to 900°C can be a value less than 1. Here, if the unit resistance value R3 is too large, the difference between the temperature around the main pump chamber and the auxiliary pump chamber and the temperature around the measurement chamber is too small, and sometimes the detection accuracy of the specific gas concentration is reduced. By setting the unit resistance value ratio R3 / R1 to a value less than 1, such a reduction in detection accuracy can be suppressed.

[0028] In this case, the measurement chamber overlapping portion may be at least a portion of the second curved portion. In other words, the second curved portion of the heating element may overlap with the measurement chamber projection area.

[0029] [4] The gas sensor of the present invention comprises the sensor element of any one of [1] to [3] above. Therefore, the gas sensor can obtain the same effects as the sensor element of the present invention, for example, the effect of reducing the stress generated around the internal cavity of the sensor element when the heating element generates heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic cross-sectional view schematically showing an example of the structure of the gas sensor 100 .

[0031] Figure 2 yes Figure 1 A-A cross-section diagram.

[0032] Figure 3 It is an explanatory diagram of a heater 72 according to a modified example.

[0033] Figure 4 It is an explanatory diagram of a heater 72 according to a modified example.

[0034] Figure 5 This is a graph in which the distances X1 and X2 of Experimental Examples 1 to 9 and the results of the stress evaluation of the internal cavity are plotted.

[0035] Figure 6 This is a graph in which the distances X1 and X2 of Experimental Examples 1 to 9 and the results of the stress evaluation of the outer peripheral portion are plotted.

[0036] Figure 7 This is an explanatory diagram of the heater 72 of Experimental Example 11. DETAILED DESCRIPTION

[0037] Next, embodiments of the present invention will be described with reference to the drawings. Figure 1 1 is a schematic cross-sectional view schematically showing an example of the structure of a gas sensor 100 as one embodiment of the present invention. Figure 2 yes Figure 1 The gas sensor 100 uses the sensor element 101 to detect the concentration of a specific gas such as NOx in a measured gas such as automobile exhaust gas. In addition, the sensor element 101 is in the shape of a long rectangular parallelepiped. Figure 1 The left-right direction) is set as the front-to-back direction, and the thickness direction ( Figure 1 In addition, the width direction of the sensor element 101 (a direction perpendicular to the front-rear direction and the up-down direction) is set as the left-right direction.

[0038] The sensor element 101 is an element having a laminated body obtained by laminating six layers in the following order from the bottom in the figure, the six layers being a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a separator 5, and a second solid electrolyte layer 6, each of which includes an oxygen ion conductive solid electrolyte layer such as zirconium oxide (ZrO2). In addition, the solid electrolyte forming these six layers is a dense and airtight solid electrolyte. The sensor element 101 is manufactured as follows: for example, ceramic green sheets corresponding to each layer are subjected to prescribed processing and circuit pattern printing, etc., and then they are laminated and then fired to achieve integration.

[0039] On the front end side of the sensor element 101 ( Figure 1 On the left end side) and 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 rate control part 11, a buffer space 12, a second diffusion rate control part 13, a first internal cavity 20, a third diffusion rate control part 30, a second internal cavity 40, a fourth diffusion rate control part 60, and a third internal cavity 61 are adjacently formed in a form connected in the following order.

[0040] The gas inlet port 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61 are: the internal space of the sensor element 101 formed by hollowing out the isolation layer 5, wherein the upper part of the internal space is divided by the lower surface of the second solid electrolyte layer 6, the lower part is divided by the upper surface of the first solid electrolyte layer 4, and the side part is divided by the side surface of the isolation layer 5.

[0041] The first diffusion rate control section 11, the second diffusion rate control section 13, and the third diffusion rate control section 30 are each provided as two horizontally long slits (the opening has a long dimension in a direction perpendicular to the drawing). In addition, the fourth diffusion rate control section 60 is provided as a horizontally long slit (the opening has a long dimension in a direction perpendicular to the drawing) formed in the form of a gap between the lower surface of the second solid electrolyte layer 6. In addition, the portion from the gas inlet 10 to the third internal cavity 61 is also referred to as a measured gas flow portion.

[0042] In addition, at a position farther from the terminal side than the measured gas flow portion, a reference gas introduction space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position defined by the side surface of the first solid electrolyte layer 4. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

[0043] The atmosphere introduction layer 48 is a layer made of porous ceramics, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43. The atmosphere introduction layer 48 is formed so as to cover the reference electrode 42.

[0044] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, an atmosphere introduction layer 48 connected to the reference gas introduction space 43 is provided around it. In addition, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous metal ceramic electrode (for example, a metal ceramic electrode of Pt and ZrO2).

[0045] In the measured gas flow portion, the gas inlet 10 is a portion open to the external space, and the measured gas is introduced from the external space into the sensor element 101 through the gas inlet 10. The first diffusion rate control portion 11 is a portion that applies a predetermined diffusion resistance to the measured gas introduced from the gas inlet 10. The buffer space 12 is a space provided to guide the measured gas introduced from the first diffusion rate control portion 11 to the second diffusion rate control portion 13. The second diffusion rate control portion 13 is a portion that applies a predetermined diffusion resistance to the measured gas introduced from the buffer space 12 to the first internal cavity 20. When the measured gas is introduced into the first internal cavity 20 from the outside of the sensor element 101, the measured gas that is rapidly introduced into the sensor element 101 from the gas inlet port 10 due to the pressure change of the measured gas in the external space (when the measured gas is automobile exhaust gas, it is the pulsation of the exhaust pressure) is not directly introduced into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure change of the measured gas is eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the pressure change of the measured gas introduced into the first internal cavity 20 reaches a level that can be almost ignored. The first internal cavity 20 is set as a space for adjusting the oxygen partial pressure in the measured gas introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust the oxygen partial pressure.

[0046] The main pump unit 21 is an electrochemical pump unit composed of an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 clamped by these electrodes, wherein the inner pump electrode 22 has: a top electrode portion 22a arranged on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and the outer pump electrode 23 is arranged in a form exposed to the external space in an area on the upper surface of the second solid electrolyte layer 6 corresponding to the top electrode portion 22a.

[0047] The inner pump electrode 22 is formed by: spanning the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that divide the first internal cavity 20 and the isolation layer 5 that provides the side wall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface, and a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the isolation layer 5 that constitutes the two side wall portions of the first internal cavity 20 to connect the top electrode portion 22a and the bottom electrode portion 22b, so that a tunnel-shaped structure is arranged at the arrangement position of the side electrode portion.

[0048] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (e.g., cermet electrodes containing 1% Au, Pt and ZrO2). In addition, the inner pump electrode 22 in contact with the measured gas is formed of a material that weakens the reducing ability of the NOx component in the measured gas.

[0049] In the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in a positive direction or a negative direction, thereby being able to draw oxygen in the first internal cavity 20 into the external space, or to draw oxygen in the external space into the first internal cavity 20.

[0050] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, namely, an oxygen partial pressure detection sensor unit 80 for main pump control, is composed of an inner pump electrode 22, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, a third substrate layer 3, and a reference electrode 42.

[0051] By measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20 can be known. In addition, the voltage Vp0 of the variable power supply 24 is feedback-controlled so that the voltage V0 becomes a target value, thereby controlling the pump current Ip0. In this way, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0052] The third diffusion rate control unit 30 is a portion that applies a predetermined diffusion resistance to the gas to be measured after the oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20 , and introduces the gas to be measured into the second internal cavity 40 .

[0053] The second internal cavity 40 is provided as a space for performing the following process: in the second internal cavity 40, the oxygen concentration (oxygen partial pressure) of the measured gas that has been previously adjusted in the first internal cavity 20 and then introduced through the third diffusion rate control unit 30 is adjusted again by the auxiliary pump unit 50. According to this, the oxygen concentration in the second internal cavity 40 can be kept constant with high accuracy, and therefore, in the gas sensor 100, the NOx concentration can be measured with high accuracy.

[0054] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit composed of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is a suitable electrode on the outside of the sensor element 101), and a second solid electrolyte layer 6, wherein the auxiliary pump electrode 51 has: a top electrode portion 51a that is arranged on the lower surface of the second solid electrolyte layer 6 and faces the second internal cavity 40.

[0055] The auxiliary pump electrode 51 is arranged in the second internal cavity 40 in a tunnel-shaped structure similar to the inner pump electrode 22 provided in the first internal cavity 20. That is, a top electrode portion 51a is formed on the second solid electrolyte layer 6 providing the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 providing the bottom surface of the second internal cavity 40, and a side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed on the two wall surfaces of the isolation layer 5 providing the side wall of the second internal cavity 40, thereby forming a tunnel-shaped structure. In addition, the auxiliary pump electrode 51 is formed of a material with a weakened reducing ability for the NOx component in the measured gas, similar to the inner pump electrode 22.

[0056] In the auxiliary pump unit 50 , a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23 , thereby allowing oxygen in the atmosphere in the second internal cavity 40 to be pumped out to the external space or pumped from the external space into the second internal cavity 40 .

[0057] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely, an auxiliary pump control oxygen partial pressure detection sensor unit 81, is formed by an auxiliary pump electrode 51, a reference electrode 42, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, and a third substrate layer 3.

[0058] Furthermore, the auxiliary pump unit 50 performs pumping using a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor unit 81. Thus, the oxygen partial pressure in the atmosphere in the second internal cavity 40 is controlled to a relatively low partial pressure that has substantially no effect on the measurement of NOx.

[0059] At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor unit 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control, and the target value of the voltage V0 is controlled, thereby controlling the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control unit 30 into the second internal cavity 40 to be constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm by the operation of the main pump unit 21 and the auxiliary pump unit 50.

[0060] The fourth diffusion rate control unit 60 is a portion that applies a predetermined diffusion resistance to the gas to be measured after the oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 50 in the second internal cavity 40, and introduces the gas to be measured into the third internal cavity 61. The fourth diffusion rate control unit 60 has the function of limiting the amount of NOx flowing into the third internal cavity 61.

[0061] The third internal cavity 61 is provided as a space for performing the following process: measuring the concentration of nitrogen oxides (NOx) in the measured gas which has been introduced after the oxygen concentration (oxygen partial pressure) has been adjusted in advance in the second internal cavity 40 through the fourth diffusion rate control unit 60. In the third internal cavity 61, the NOx concentration is measured mainly by the operation of the measurement pump unit 41.

[0062] The measuring pump cell 41 measures the NOx concentration in the measured gas in the third internal cavity 61. The measuring pump cell 41 is an electrochemical pump cell composed of a measuring electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4, wherein the measuring electrode 44 is provided on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61.

[0063] The measuring electrode 44 is a porous cermet electrode made of a material having a higher reducing ability for NOx components in the measured gas than the inner pump electrode 22. The measuring electrode 44 also functions as a NOx reducing catalyst for reducing NOx in the atmosphere in the third internal cavity 61.

[0064] The measuring pump unit 41 can extract oxygen generated by decomposition of nitrogen oxides in the atmosphere around the measuring electrode 44 and detect the generated amount as the pump current Ip2.

[0065] In order to detect the oxygen partial pressure around the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42 constitute an electrochemical sensor unit, that is, a measuring pump control oxygen partial pressure detection sensor unit 82. Based on the electromotive force (voltage V2) detected by the measuring pump control oxygen partial pressure detection sensor unit 82, the variable power supply 46 is controlled.

[0066] The gas to be measured introduced into the second internal cavity 40 passes through the fourth diffusion rate control unit 60 under the condition that the oxygen partial pressure is controlled and reaches the measuring electrode 44 in the third internal cavity 61. The nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. And the generated oxygen is pumped by the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control is constant (target value). The amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured. Therefore, the pump current Ip2 in the measuring pump unit 41 is used to calculate the concentration of nitrogen oxides in the gas to be measured.

[0067] In addition, if the measuring 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 detection mechanism as an electrochemical sensor unit, it is possible to detect: the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around the measuring electrode 44 and the amount of oxygen contained in the reference atmosphere, thereby also being able to calculate the concentration of the NOx component in the measured gas.

[0068] In addition, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. The electromotive force (voltage Vref) obtained by the sensor unit 83 can be used to detect the oxygen partial pressure in the measured gas outside the sensor.

[0069] In the gas sensor 100 having such a configuration, the gas to be measured whose oxygen partial pressure is always kept at a constant low value (a value that has substantially no influence on the measurement of NOx) by operating the main pump unit 21 and the auxiliary pump unit 50 is supplied to the measurement pump unit 41. Therefore, the NOx concentration in the gas to be measured can be known based on the pump current Ip2 flowing due to the oxygen drawn from the measurement pump unit 41, which is substantially proportional to the NOx concentration in the gas to be measured and is generated by the reduction of NOx.

[0070] In addition, the sensor element 101 includes a heater portion 70, which is responsible for the temperature adjustment function of heating and keeping the sensor element 101 warm, so as to improve the oxygen ion conductivity of the solid electrolyte. The heater portion 70 includes: a heater connector electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure release hole 75. In addition, the heater portion 70 includes a first substrate layer 1, a second substrate layer 2 and a third substrate layer 3, all of which contain ceramics. The heater portion 70 is composed of a ceramic heater including a heater 72 and a second substrate layer 2 and a third substrate layer 3 surrounding the heater 72. Figure 2 As shown, the heater 72 includes a heat generating portion 76 and a lead portion 85 .

[0071] 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.

[0072] The heat generating portion 76 of the heater 72 is a resistor formed by being sandwiched from above and below by the second substrate layer 2 and the third substrate layer 3. The lead portion 85 of the heater 72 is connected to the heater connector electrode 71 via the through hole 73, and power is supplied from the outside through the heater connector electrode 71, thereby causing the heat generating portion 76 to generate heat, thereby heating and keeping the solid electrolyte forming the sensor element 101 warm.

[0073] Furthermore, the heat generating portion 76 of the heater 72 is buried from the first internal cavity 20 to the third internal cavity 61 , and the entire sensor element 101 can be adjusted to a temperature at which the solid electrolyte is activated.

[0074] Heater insulating layer 74 is an insulating layer formed of an insulator such as alumina on the upper and lower surfaces of heater 72. Heater insulating layer 74 is formed to obtain electrical insulation between second substrate layer 2 and heater 72, and between third substrate layer 3 and heater 72.

[0075] The pressure release hole 75 is a portion that penetrates the third substrate layer 3 and the atmosphere introduction layer 48 and is connected to the reference gas introduction space 43 . The purpose of forming the pressure release hole 75 is to alleviate the internal pressure increase associated with the temperature increase in the heater insulation layer 74 .

[0076] The heating portion 76 and the lead portion 85 of the heater 72 are described in detail. The heating portion 76 is a resistive heating element such as Figure 2As shown, it presents a strip-shaped one-stroke shape with both ends connected to the lead portion 85. The heating portion 76 has a curved portion 77 and a straight portion 78. The curved portion 77 has: a first curved portion 77a, a second curved portion 77b and a third curved portion 77c. The straight portion 78 has: a first outer straight portion 78a, a second outer straight portion 78b, a first inner straight portion 79a and a second inner straight portion 79b. A plurality of curved portions 77 and a plurality of straight portions 78 are electrically connected in series. Specifically, starting from the first lead 85a, the first outer straight portion 78a, the first curved portion 77a, the first inner straight portion 79a, the second curved portion 77b, the second inner straight portion 79b, the third curved portion 77c and the second outer straight portion 78b are connected in series with each other in the order, and the second outer straight portion 78b is connected to the second lead 85b. The heating portion 76 presents a left-right symmetrical shape.

[0077] A plurality of straight portions 78 are arranged side by side along the short dimension direction (left-right direction) of the sensor element 101. Specifically, from the left side to the right side of the sensor element 101, the first outer straight portion 78a, the first inner straight portion 79a, the second inner straight portion 79b, and the second outer straight portion 78b are arranged in this order. Therefore, the first inner straight portion 79a and the second inner straight portion 79b are arranged between the first outer straight portion 78a and the second outer straight portion 78b in the left-right direction. The first outer straight portion 78a, the second outer straight portion 78b, the first inner straight portion 79a, and the second inner straight portion 79b are all arranged so that the length direction is along the long dimension direction. The rear end of the first outer straight portion 78a is connected to the first lead 85a, and the rear end of the second outer straight portion 78b is connected to the second lead 85b. The first inner straight portion 79a includes a front portion 79a1, a rear portion 79a3 disposed behind the front portion 79a1, and a connecting portion 79a2 connecting the front portion 79a1 and the rear portion 79a3. The second inner straight portion 79b includes a front portion 79b1, a rear portion 79b3 disposed behind the front portion 79b1, and a connecting portion 79b2 connecting the front portion 79b1 and the rear portion 79b3.

[0078] Regarding the straight portion 78, "arranged so that the length direction is along the long dimension direction" includes: the case where the length direction is parallel to the long dimension direction (front-rear direction) of the sensor element 101, and the case where the length direction is inclined relative to the long dimension direction (front-rear direction) of the sensor element 101. For example, in the present embodiment, the length directions of the first outer straight portion 78a, the second outer straight portion 78b, the front side portion 79a1, the rear side portion 79a3, the front side portion 79b1, and the rear side portion 79b3 are parallel to the long dimension direction of the sensor element 101. The length directions of the connecting portions 79a2 and 79b2 are inclined relative to the long dimension direction of the sensor element 101.

[0079] The plurality of curved portions 77 connect the adjacent straight portions 78 in the left-right direction to each other. Specifically, the first curved portion 77a connects the first outer straight portion 78a and the first inner straight portion 79a at one end side (here, the front side) in the long dimension direction. The second curved portion 77b connects the first inner straight portion 79a and the second inner straight portion 79b at the other end side (here, the rear side) in the long dimension direction. The third curved portion 77c connects the second inner straight portion 79b and the second outer straight portion 78b at one end side (here, the front side) in the long dimension direction. The first to third curved portions 77a to 77c are all curved into a curve shape, in the shape of a semicircular arc. In addition, the first to third curved portions 77a to 77c may also be curved into a broken line shape.

[0080] Regarding the heating part 76, the positional relationship between it and the internal cavity of the measured gas flow part (here, the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61) is adjusted. This is explained. In addition, the first internal cavity 20 is an example of a main pump chamber, the second internal cavity 40 is an example of an auxiliary pump chamber, and the third internal cavity 61 is an example of a measuring chamber. Figure 2 In FIG. 1 , the area obtained by projecting the first internal cavity 20 toward the heat generating portion 76 in the thickness direction (here, downward), i.e., the main pump chamber projection area Ap, is indicated by a single-dot dashed line frame. Similarly, the auxiliary pump chamber projection area Aq and the measurement chamber projection area Am, obtained by projecting the second internal cavity 40 and the third internal cavity 61 toward the heat generating portion 76, are also indicated by single-dot dashed line frames. Figure 2 .like Figure 2 As shown, in this embodiment, the main pump chamber projection area Ap, the auxiliary pump chamber projection area Aq, and the measurement chamber projection area Am are all rectangular areas. That is, in this embodiment, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are each rectangular in shape when viewed from above.

[0081] The first inner straight portion 79a and the second inner straight portion 79b of the heat generating portion 76 respectively overlap at least in part with the main pump chamber projection area Ap. Specifically, the front portion 79a1 in the first inner straight portion 79a and the front portion 79b1 in the second inner straight portion 79b respectively overlap at least in part with the main pump chamber projection area Ap. In other words, the first inner straight portion 79a and the second inner straight portion 79b (particularly the front portion 79a1 and the front portion 79b1) exist directly below the first internal cavity 20. In addition, the first inner straight portion 79a and the second inner straight portion 79b of the heat generating portion 76 respectively overlap at least in part with the auxiliary pump chamber projection area Aq. Specifically, the rear portion 79a3 in the first inner straight portion 79a and the rear portion 79b3 in the second inner straight portion 79b respectively overlap at least in part with the auxiliary pump chamber projection area Aq. In other words, there are the first inner straight portion 79a and the second inner straight portion 79b (particularly the rear portion 79a3 and the rear portion 79b3) directly below the second internal cavity 40. In addition, in the present embodiment, a portion of the second curved portion 77b, specifically the portion of the second curved portion 77b connected to the rear portion 79a3 and the rear portion 79b3, also overlaps with the auxiliary pump chamber projection area Aq. In addition, at least a portion of the heating portion 76 overlaps with the measurement chamber projection area Am. Specifically, at least a portion of the second curved portion 77b in the heating portion 76 overlaps with the measurement chamber projection area Am. In addition, in the present embodiment, the connecting portion 79a2 and the connecting portion 79b2 are arranged between the main pump chamber projection area Ap and the auxiliary pump chamber projection area Aq in the front-to-back direction, and the main pump chamber projection area Ap and the auxiliary pump chamber projection area Aq do not overlap. In addition, the first curved portion 77a, the third curved portion 77c, the first outer straight portion 78a and the second outer straight portion 78b do not overlap with the main pump chamber projection area Ap, the auxiliary pump chamber projection area Aq, and the measurement chamber projection area Am. In the present embodiment, the heating portion 76 is bilaterally symmetrical, and the left and right central axes of the heating portion 76, the left and right central axes of the main pump chamber projection area Ap, the left and right central axes of the auxiliary pump chamber projection area Aq, and the left and right central axes of the measurement chamber projection area Am are all consistent.

[0082] The distance X1 in the short dimension direction (left-right direction) between the first inner straight portion 79a and the second inner straight portion 79b of the heat generating portion 76 at the portion overlapping with the main pump chamber projection area Ap is greater than 1 / 3 of the width Wp in the short dimension direction of the main pump chamber projection area Ap. That is, X1 ≥ 1 / 3 × Wp is satisfied. In the present embodiment, the portions of the heat generating portion 76 overlapping with the main pump chamber projection area Ap are the front side portion 79a1 and the front side portion 79b1, and therefore, the distance in the left-right direction between the front side portion 79a1 and the front side portion 79b1 is the distance X1. In addition, in the present embodiment, the longitudinal directions of the front side portion 79a1 and the front side portion 79b1 are parallel to each other, and therefore, the distance in the left-right direction between the front side portion 79a1 and the front side portion 79b1 is a constant value (= distance X1). When the distance between the front side portion 79a1 and the front side portion 79b1 in the left-right direction is not constant, such as when the front side portion 79a1 and the front side portion 79b1 are not parallel to each other, the average value of the distances in the short dimension direction (left-right direction) between the portions of the first inner straight line portion 79a and the second inner straight line portion 79b that overlap with the main pump chamber projection area Ap is set to distance X1.

[0083] The distance X2 between the first inner straight portion 79a and the second inner straight portion 79b of the heating portion 76 in the short dimension direction (left-right direction) at the portion overlapping with the auxiliary pump chamber projection area Aq is 0.4 times or more the width Wp in the short dimension direction of the main pump chamber projection area Ap. That is, X2≥0.4Wp is satisfied. In the present embodiment, the portions of the heating portion 76 that overlap with the auxiliary pump chamber projection area Aq are the rear portion 79a3 and the rear portion 79b3, and therefore, the distance between the rear portion 79a3 and the rear portion 79b3 in the left-right direction is the distance X2. In addition, in the present embodiment, the longitudinal directions of the rear portion 79a3 and the rear portion 79b3 are parallel to each other, and therefore, the distance between the rear portion 79a3 and the rear portion 79b3 in the left-right direction is a constant value (=distance X2). In the case where the distance between the rear side portion 79a3 and the rear side portion 79b3 in the left-right direction is not constant, for example, when the rear side portion 79a3 and the rear side portion 79b3 are not parallel to each other, the average value of the distances in the short dimension direction (left-right direction) between the portions of the first inner straight line portion 79a and the second inner straight line portion 79b that overlap with the auxiliary pump chamber projection area Aq is set to the distance X2.

[0084] By satisfying the above-mentioned conditions, i.e., "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4Wp", it is possible to reduce the stress generated around the internal cavities (the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61) of the sensor element 101 when the heat generating portion 76 generates heat. In addition, the distance X1 is preferably greater than 0.4 times the width Wp, and more preferably greater than 0.4 times. The distance X1 may be greater than 2 / 3 times the width Wp. The distance X1 is preferably less than the width Wp and may be less than the width Wp. The distance X2 may be greater than 2 / 3 times the width Wp. In addition, when the width in the left-right direction of the auxiliary pump chamber projection area Aq is set to the width Wq, the distance X2 is preferably less than the width Wq and may be less than the width Wq. In addition, in the present embodiment, if Figure 2 As shown, the distance X2 is greater than the distance X1.

[0085] Furthermore, in the present embodiment, the heat generating portion 76 is symmetrical on both sides, and the left-right center axis of the heat generating portion 76 coincides with the left-right center axis of the main pump chamber projection area Ap. Therefore, the heat generating portion 76 does not exist in the area located in the left-right center of the main pump chamber projection area Ap and having a width equal to the distance X1. For example, when the above-mentioned X1>1 / 3×Wp is satisfied, the heat generating portion 76 does not exist in the area located in the left-right center of the main pump chamber projection area Ap and having a width of 1 / 3×Wp (i.e., the central area when the main pump chamber projection area Ap is divided into three equal parts in the left-right direction). In other words, the heat generating portion 76 does not exist directly below the area located in the left-right center of the main pump chamber (first internal cavity 20) and having a width of 1 / 3×Wp. Similarly, when X1>0.4Wp is satisfied, the heat generating portion 76 does not exist in the area located in the left-right center of the main pump chamber projection area Ap and having a width of 0.4Wp.

[0086] In addition, the heat generating portion 76 is symmetrical on the left and right, and the left and right center axes of the heat generating portion 76 are consistent with the left and right center axes of the main pump chamber projection area Ap. Therefore, if the distance X1 is less than the width Wp, the first inner straight line portion 79a and the second inner straight line portion 79b (here especially the front side portion 79a1 and the front side portion 79b1) respectively overlap with the main pump chamber projection area Ap in at least a portion.

[0087] In this embodiment, the heat generating portion 76 is bilaterally symmetrical, and the left and right central axes of the heat generating portion 76 coincide with the left and right central axes of the auxiliary pump chamber projection area Aq. Therefore, the heat generating portion 76 does not exist in the area located in the left and right center of the auxiliary pump chamber projection area Aq and having a width equal to the distance X2. In other words, the heat generating portion 76 does not exist directly below the area located in the left and right center of the auxiliary pump chamber (second internal cavity 40) and having a width of X2.

[0088] In addition, the heat generating portion 76 is symmetrical on the left and right, and the left and right center axes of the heat generating portion 76 are consistent with the left and right center axes of the auxiliary pump chamber projection area Aq. Therefore, if the distance X2 is less than the width Wq, the first inner straight line portion 79a and the second inner straight line portion 79b (here especially the rear portion 79a3 and the rear portion 79b3) respectively overlap with the auxiliary pump chamber projection area Aq in at least a portion.

[0089] In this embodiment, the heating portion 76 uses a metal ceramic containing a precious metal and a ceramic (for example, a metal ceramic of platinum (Pt) and aluminum oxide (Al2O3)). In addition, the heating portion 76 is not limited to a metal ceramic, and may contain, for example, a conductive material such as a precious metal. Examples of the precious metal used for the heating portion 76 include: platinum, rhodium (Rh), gold (Au), palladium (Pd) or at least one of the metals or their alloys.

[0090] Here, the resistance value per unit length of the portion of the heating portion 76 that overlaps with the main pump chamber projection area Ap and the auxiliary pump chamber projection area Aq, i.e., the pump chamber overlapping portion, is set to the unit resistance value R1 [μΩ / mm]. In addition, the resistance value per unit length of the portion of the heating portion 76 that overlaps with the measurement chamber projection area Am, i.e., the measurement chamber overlapping portion, is set to the unit resistance value R3 [μΩ / mm]. At this time, for the heating portion 76, at least any temperature in the temperature range of 700°C to 900°C in which the heating portion 76 may be heated during use, the unit resistance value ratio R3 / R1 is less than 1. In other words, at at least any temperature in the temperature range of 700°C to 900°C, the unit resistance value R3 is lower than the unit resistance value R1. In the present embodiment, the pump chamber repeating portion is composed of the portion of the front side portion 79a1 and the front side portion 79b1 that repeats with the main pump chamber projection area Ap, the portion of the rear side portion 79a3 and the rear side portion 79b3 that repeats with the auxiliary pump chamber projection area Aq, and the portion of the second curved portion 77b that repeats with the auxiliary pump chamber projection area Aq. In the present embodiment, the measurement chamber repeating portion is the portion of the second curved portion 77b that repeats with the measurement chamber projection area Am. In addition, the length direction of the heating portion 76 is the axial direction of the heating portion 76, in other words, the direction of current flow. In addition, the unit resistance value R1 is the average value of the resistance value per unit length of the pump chamber repeating portion. Similarly, the unit resistance value R3 is the average value of the resistance value per unit length of the measurement chamber repeating portion. Therefore, even if a part of the measurement chamber repeating portion has a portion with a higher resistance value per unit length than the pump chamber repeating portion, the resistance value per unit length of the measurement chamber repeating portion as a whole can be lower than the pump chamber repeating portion. However, it is preferred that the resistance value per unit length is lower than the unit resistance value R1 at any position of the measurement chamber repeating portion.

[0091] If the unit resistance value R3 is too large, the difference between the temperature around the first internal cavity 20 and the second internal cavity 40 and the temperature around the third internal cavity 61 is too small, and the detection accuracy of the NOx concentration is sometimes reduced. By setting the unit resistance value ratio R3 / R1 to a value less than 1, such a reduction in detection accuracy can be suppressed. The unit resistance value ratio R3 / R1 at at least any temperature within the above-mentioned temperature range is preferably a value of 0.8 or less, more preferably a value of 0.7 or less, and further preferably a value of 0.65 or less. The unit resistance value ratio R3 / R1 at at least any temperature within the above-mentioned temperature range can be a value of 0.5 or more.

[0092] In this embodiment, the first inner straight portion 79a, the second inner straight portion 79b and the second curved portion 77b are made of the same material (the above-mentioned metal ceramic containing platinum), and the cross-sectional area S1 [mm] perpendicular to the length direction of the repeated portion of the pump chamber in the heating portion 76 2 ] is smaller than the cross-sectional area S3[mm 2 ]. That is, the cross-sectional area ratio S1 / S3 of the heating portion 76 is a value less than 1. Accordingly, at any temperature in the temperature range of 700°C to 900°C, the unit resistance value ratio R3 / R1 is a value less than 1. The cross-sectional area ratio S1 / S3 is preferably a value less than 0.8, more preferably a value less than 0.7, and further preferably a value less than 0.65. The cross-sectional area ratio S1 / S3 can be a value greater than 0.5. In addition, the cross-sectional area ratio S1 / S3 can be adjusted by, for example, making the width W1 of the pump chamber repeating part smaller than the width W3 of the measuring chamber repeating part, or making the thickness D1 of the pump chamber repeating part smaller than the thickness D3 of the measuring chamber repeating part. In addition, all values ​​of the cross-sectional areas S1, S3, widths W1, W3, and thicknesses D1, D3 are set to the average values ​​of the pump chamber repeating part and the measuring chamber repeating part, respectively, in the same way as the unit resistance values ​​R1, R3.

[0093] In this embodiment, the first inner straight portion 79a, the second inner straight portion 79b and the second curved portion 77b have the same thickness in any part. The first inner straight portion 79a and the second inner straight portion 79b have the same width in any part. In addition, for the second curved portion 77b, the width increases as the distance from the first inner straight portion 79a and the second inner straight portion 79b increases in the connection part with the first inner straight portion 79a and the second inner straight portion 79b, and the width is constant in the part other than the connection part (including the part overlapping with the measurement chamber projection area Am). Therefore, corresponding to the fact that a part of the second curved portion 77b is included in the pump chamber overlapping part, the width W1 of this embodiment becomes a value slightly larger than the width of the first inner straight portion 79a and the second inner straight portion 79b. In addition, the width W3 is the same value as the width of the part other than the connection part with the first inner straight portion 79a and the second inner straight portion 79b in the second curved portion 77b. Furthermore, by making the width W1 smaller than the width W3, the cross-sectional area ratio S1 / S3 is a value less than 1. The ratio W1 / W3 of the width W1 to the width W3 is preferably a value less than 0.8, more preferably a value less than 0.7, and further preferably a value less than 0.65. The ratio W1 / W3 may be a value greater than 0.5. The widths W1 and W3 may be greater than 0.05 mm and less than 1.5 mm. The thicknesses D1 and D3 may be greater than 0.003 mm and less than 0.1 mm. The width W1 may be greater than 0.3 mm and less than 0.4 mm. The width W3 may be greater than 0.5 mm and less than 0.6 mm.

[0094] The distance X1 may be greater than 0.67 mm, greater than 0.8 mm, or greater than 0.86 mm. The distance X1 may be less than 2 mm, less than 2 mm, less than 1.67 mm, or less than 1.34 mm. The distance X2 may be greater than 0.8 mm, or greater than 0.86 mm. The distance X2 may be less than 2 mm, less than 2 mm, or less than 1.34 mm. The width Wp of the main pump chamber projection area Ap (=the width of the first internal cavity 20) is, for example, greater than 1.5 mm and less than 3 mm. The width Wq of the auxiliary pump chamber projection area Aq (=the width of the second internal cavity 40) is, for example, greater than 1.2 mm and less than 2.4 mm. The width Wm of the measurement chamber projection area Am (=the width of the third internal cavity 61) is, for example, greater than 0.9 mm and less than 1.8 mm. The length from the front end of the sensor element 101 to the rear end of the third internal cavity 61, that is, the length of the measured gas flow portion is, for example, greater than 7.5 mm and less than 9 mm. In addition, in the present embodiment, Wp>Wq>Wm is satisfied.

[0095] The lead portion 85 includes: a first lead 85a disposed at the left rear of the heating portion 76, and a second lead 85b disposed at the right rear. The first and second leads 85a and 85b are leads for energizing the heating portion 76, and are connected to the heater connector electrode 71. The first lead 85a is a positive lead, and the second lead 85b is a negative lead. By applying a voltage between the first lead 85a and the second lead 85b, a current flows in the heating portion 76, and the heating portion 76 generates heat. The lead portion 85 is a conductor, and its resistance per unit length is lower than that of the heating portion 76. Therefore, the lead portion 85 is different from the heating portion 76 and hardly generates heat when energized. For example, the lead portion 85 is made of a material with a lower volume resistivity than the heating portion 76, or has a larger cross-sectional area, so that the resistance per unit length is reduced. In the present embodiment, the lead portion 85 has a higher ratio of noble metal than the heat generating portion 76 , thereby reducing volume resistivity, and has a larger width than the heat generating portion 76 , thereby increasing cross-sectional area.

[0096] The manufacturing method of the gas sensor 100 of the above-mentioned structure is described below. First, six unfired ceramic green sheets containing oxygen ion conductive solid electrolytes such as zirconium oxide as ceramic components are prepared. A plurality of sheet holes and necessary through holes for positioning during printing and lamination are formed in advance on the green sheets. In addition, a space for the gas to be measured is set in advance on the green sheet that becomes the isolation layer 5 by punching treatment. Then, pattern printing treatment and drying treatment for forming various patterns are performed on each ceramic green sheet corresponding to the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6, respectively. Specifically, the pattern to be formed is, for example, a pattern of each of the above-mentioned electrodes and leads connected to each electrode, an atmosphere introduction layer 48, and a heater 72. The pattern printing is performed as follows: a pattern forming paste prepared according to the characteristics required for each formation object is applied to the green sheet using a known screen printing technique. The paste used for patterning the heater 72 is prepared by mixing raw materials (such as noble metal and ceramic particles) containing the material of the heater 72 , an organic binder, an organic solvent, and the like.

[0097] At this time, the pattern of the heater 72 is formed so that the unit resistance value ratio R3 / R1 is less than 1, for example, the cross-sectional area ratio S1 / S3 is less than 1. For example, in order to make the width W1 < the width W3, a mask having a shape that can form the pattern is used. In addition, in order to make the thickness D1 < the thickness D3, for example, the viscosity of the paste forming the pattern of the portion that becomes the repeating portion of the measuring chamber (for example, the second curved portion 77b) is increased compared with the pattern of the portion that becomes the repeating portion of the pump chamber (for example, the first inner straight portion 79a and the second inner straight portion 79b), or the number of printing times when forming the pattern of the portion that becomes the repeating portion of the measuring chamber is increased.

[0098] After various patterns are formed as described above, the raw sheet is dried. The drying process is also carried out using a known drying method. After the pattern printing and drying are completed, the bonding paste used to stack and bond the raw sheets corresponding to each layer is printed and dried. Then, a crimping process is performed, that is, the raw sheets formed with the bonding paste are positioned using the sheet holes, and stacked in a specified order, and crimped by applying specified temperature and pressure conditions to form a stack. The stack obtained in this way contains a plurality of sensor elements 101. The stack is cut and divided into the size of the sensor element 101. Then, the cut stack is fired at a specified firing temperature to obtain the sensor element 101.

[0099] After the sensor element 101 is obtained as described above, a sensor assembly in which the sensor element 101 is assembled is manufactured, and a protective cover and the like are attached, thereby obtaining the gas sensor 100 .

[0100] When the gas sensor 100 thus constructed is used, the heater 72 is connected to a power source (e.g., an alternator of a car) via the heater connector electrode 71, and a DC voltage (e.g., 12 to 14 V) is applied between the first lead 85a and the second lead 85b. Then, due to the applied voltage, a current flows in the heating portion 76, and the heating portion 76 generates heat. Accordingly, the entire sensor element 101 is adjusted to a temperature (e.g., 700° C. to 900° C.) at which the solid electrolyte (each layer 1 to 6) is activated. In this state, when the measured gas is introduced from the gas inlet 10 to the measured gas flow portion, the measured gas passes through the first diffusion rate control portion 11, the buffer space 12, and the second diffusion rate control portion 13 and reaches the first internal cavity 20. Next, the oxygen concentration of the measured gas is adjusted in the first internal cavity 20 and the second internal cavity 40 by the main pump unit 21 and the auxiliary pump unit 50, and the adjusted measured gas reaches the third internal cavity 61. Then, the NOx concentration in the gas to be measured is detected based on the pump current Ip2 when the oxygen in the third internal cavity 61 is pumped out by the measurement pump cell 41 .

[0101] At this time, since the heat generating portion 76 becomes high temperature, stress is sometimes generated around the internal cavity (first internal cavity 20, second internal cavity 40 and third internal cavity 61) of the sensor element 101. It is believed that this is caused by the temperature difference between the lower side of the internal cavity and the upper side of the internal cavity in the sensor element 101. However, in the sensor element 101 of the present embodiment, by satisfying the above-mentioned "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4Wp", the stress generated around the internal cavity of the sensor element 101 when the heat generating portion 76 generates heat can be reduced. It is believed that this is because: by satisfying the above-mentioned conditions by the distances X1 and X2, overheating near the left and right centers of the lower side of the internal cavity can be suppressed, thereby reducing the temperature difference between the lower side of the internal cavity and the upper side of the internal cavity. In addition, if the distance X1 is greater than 0.4 times the width Wp, the effect of reducing the above-mentioned stress is improved.

[0102] In addition, by satisfying "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4 Wp", it is also possible to reduce stress generated in the outer peripheral portion of the sensor element 101 (particularly, the outer peripheral surface of the sensor element 101 close to the heater 72, that is, the lower surface). This is considered to be because by satisfying the above conditions of the distances X1 and X2, it is possible to suppress overheating near the left and right center of the lower surface of the sensor element 101, thereby reducing the temperature difference between the left and right center of the lower surface and other parts.

[0103] In addition, in the present embodiment, the distance X1 is less than the width Wp, and the first inner straight portion 79a and the second inner straight portion 79b (particularly the front portion 79a1 and the front portion 79b1 here) each overlap at least a portion with the main pump chamber projection area Ap. Therefore, the solid electrolyte around the main pump chamber (here, the first internal cavity 20) can be fully heated by the heating portion 76, so that the main pump unit 21 can fully function. Similarly, the distance X2 is less than the width Wq, and the first inner straight portion 79a and the second inner straight portion 79b (particularly the rear portion 79a3 and the rear portion 79b3 here) each overlap at least a portion with the auxiliary pump chamber projection area Aq. Therefore, the solid electrolyte around the auxiliary pump chamber (here, the second internal cavity 40) can be fully heated by the heating portion 76, so that the auxiliary pump unit 50 can fully function. When the functions of the main pump unit 21 and the auxiliary pump unit 50 are insufficient, the oxygen concentration in the measured gas cannot be fully adjusted, and sometimes the detection accuracy of the NOx concentration will be reduced. However, in this embodiment, the reduction in the detection accuracy of the NOx concentration can be suppressed by making the distance X1 less than the width Wp and the distance X2 less than the width Wq.

[0104] In addition, in the present embodiment, at least a portion of the heat generating portion 76 (here, the second curved portion 77b) overlaps with the measurement chamber projection area Am, so that the solid electrolyte around the measurement chamber (here, the third internal cavity 61) can be sufficiently heated, thereby enabling the measurement pump unit 41 to fully function. Accordingly, it is also possible to suppress a decrease in the detection accuracy of the NOx concentration.

[0105] In addition, by making the unit resistance value ratio R3 / R1 at at least any temperature in the temperature range of 700°C to 900°C less than 1, it is possible to suppress the reduction in the detection accuracy of the NOx concentration. This will be described in detail. First, when the temperatures around the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are set to temperatures Tp, Tq, and Tm [°C], respectively, when the heat generating portion 76 generates heat, it is preferred that (temperature Tp and temperature Tq)>temperature Tm, and it is more preferred that temperature Tp>temperature Tq>temperature Tm. The reason is as follows. Since the gas to be measured before the oxygen concentration is adjusted by the main pump unit 21 flows in from the gas inlet port 10 side, the oxygen concentration around the inner pump electrode 22, that is, the first internal cavity 20 is higher than the oxygen concentration around the measuring electrode 44. In addition, since the gas to be measured before the oxygen concentration is adjusted by the auxiliary pump unit 50 flows in from the first internal cavity 20 side, the oxygen concentration around the auxiliary pump electrode 51, that is, the second internal cavity 40 is higher than the oxygen concentration around the measuring electrode 44. Therefore, it is preferable to make the temperature Tp around the first internal cavity 20 and the temperature Tq around the second internal cavity 40 higher than the temperature Tm, so as to further activate the solid electrolyte layer around the inner pump electrode 22, the auxiliary pump electrode 51 and the surrounding thereof, so that the main pump unit 21 and the auxiliary pump unit 50 extract a large amount of oxygen. On the other hand, the oxygen concentration around the measuring electrode 44, that is, the third internal cavity 61, is lower than that of the first internal cavity 20 and the second internal cavity 40. Therefore, for example, hydrogen and carbon monoxide are sometimes generated due to the reduction of water and carbon dioxide in the measured gas, and these substances sometimes react chemically with oxygen in NOx, resulting in a decrease in measurement accuracy. In addition, the higher the temperature, the easier it is for the reduction of components other than the specific gas (NOx) to occur. Therefore, the temperature Tm is preferably not too high. Considering the above content, it is preferable that (temperature Tp and temperature Tq)>temperature Tm. In addition, the first internal cavity 20 is located at a position closer to the upstream side of the measured gas flow portion than the second internal cavity 40, and the oxygen concentration of the first internal cavity 20 is higher than the oxygen concentration of the second internal cavity 40. Therefore, it is preferred to make the temperature Tp around the first internal cavity 20 higher than the temperature Tq around the second internal cavity 40, so as to further activate the solid electrolyte layer of the inner pump electrode 22 and its periphery. Therefore, it is more preferred that the temperature Tp>temperature Tq>temperature Tm. In addition, if the unit resistance value R3 is too large, the temperature Tm is too high, and the relationship of (temperature Tp and temperature Tq)>temperature Tm is not satisfied, and the measurement accuracy of the NOx concentration may be reduced. By making the unit resistance value ratio R3 / R1 less than 1, since the unit resistance value R3 is not too large, such a reduction in detection accuracy can be suppressed.In addition, if the temperature Tm is high, the temperature Tq around the second inner cavity 40 near the third inner cavity 61 is also likely to rise, so that the temperature Tp < temperature Tq > temperature Tm, and the relationship of temperature Tp > temperature Tq > temperature Tm is not satisfied, and the pumping capacity of the main pump unit 21 is sometimes insufficient. In contrast, if the unit resistance value ratio R3 / R1 is less than 1, the pumping capacity of the main pump unit 21 is likely to be sufficiently increased.

[0106] Here, the correspondence between the components of the present embodiment and the components of the present invention is clarified. Each layer 1 to 6 of the present embodiment is equivalent to the element body of the present invention, the first internal cavity 20 is equivalent to the main pump chamber, the main pump unit 21 is equivalent to the main pump unit, the second internal cavity 40 is equivalent to the auxiliary pump chamber, the auxiliary pump unit 50 is equivalent to the auxiliary pump unit, the third internal cavity 61 is equivalent to the measurement chamber, the measurement pump unit 41 is equivalent to the measurement pump unit, the heating portion 76 is equivalent to the heating element, the first outer straight portion 78a is equivalent to the first outer straight portion, the second outer straight portion 78b is equivalent to the second outer straight portion, the first inner straight portion 79a is equivalent to the first inner straight portion, the second inner straight portion 79b is equivalent to the second inner straight portion, the first to third curved portions 77a to 77c are equivalent to the first to third curved portions, the main pump chamber projection area Ap is equivalent to the main pump chamber projection area, and the auxiliary pump chamber projection area Aq is equivalent to the auxiliary pump chamber projection area.

[0107] According to the gas sensor 100 of the present embodiment described in detail above, by making the distance X1 greater than 1 / 3 of the width Wp and the distance X2 greater than 0.4 times of the width Wp, it is possible to reduce the stress generated around the internal cavity (main pump chamber, auxiliary pump chamber, and measurement chamber) when the heating element generates heat. In addition, by making the distance X1 greater than 0.4 times of the width Wp, the above-mentioned stress reduction effect is improved. In addition, by making the unit resistance value ratio R3 / R1 less than 1 at at least any temperature in the temperature range of 700°C to 900°C, it is possible to suppress the reduction in the detection accuracy of the NOx concentration.

[0108] In addition, the present invention is not limited to the above-mentioned embodiment at all, and it is needless to say that the present invention can be implemented in various forms as long as it belongs to the technical scope of the present invention.

[0109] For example, in the above embodiment, the distance X2 is greater than the distance X1, but it is not limited thereto. Figure 3 As shown, the distance X1 and the distance X2 may be the same size. In this case, by satisfying "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4 Wp", the effect of reducing the stress generated around the internal cavity of the sensor element 101 when the heat generating portion 76 generates heat can also be obtained. In addition, Figure 3In the case of , since X1=X2, "X1≥0.4Wp" is also satisfied. In addition, Figure 3 In the example of FIG. 1 , the front portion 79a1, the connecting portion 79a2, and the rear portion 79a3 of the first inner straight portion 79a are arranged in a straight line, so that the front portion 79a1, the connecting portion 79a2, and the rear portion 79a3 have shapes that cannot be distinguished from each other. The same is true for the front portion 79b1, the connecting portion 79b2, and the rear portion 79b3 of the second inner straight portion 79b.

[0110] Or, if Figure 4 As shown, the distance X1 may be greater than the distance X2. In this case, by satisfying "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4 Wp", the effect of reducing the stress generated around the internal cavity of the sensor element 101 when the heat generating portion 76 generates heat can also be obtained. In addition, Figure 4 In the case of , since X1>X2, “X1>0.4Wp” is also satisfied.

[0111] In the above embodiment, the unit resistance value ratio R3 / R1 is made to be less than 1 by making the cross-sectional area ratio S1 / S3 a value less than 1, but the present invention is not limited thereto. For example, at at least any temperature within the above temperature range, the ratio of the volume resistivity ρ1 [μΩ·cm] of the pump chamber repeating portion to the volume resistivity ρ3 [μΩ·cm] of the measuring chamber repeating portion, i.e., the volume resistivity ratio ρ3 / ρ1, may be a value less than 1. Even so, the unit resistance value ratio R3 / R1 at at least any temperature within the above temperature range can be made to be less than 1, thereby suppressing the reduction in the detection accuracy of the NOx concentration. At at least any temperature within the above temperature range, the volume resistivity ratio ρ3 / ρ1 is preferably a value less than 0.8, more preferably a value less than 0.7, and further preferably a value less than 0.65. The volume resistivity ratio ρ3 / ρ1 may be a value greater than 0.5. For example, by making the proportion of the noble metal (conductor) contained in the measuring chamber repeating portion of the heat generating portion 76 higher than that in the pump chamber repeating portion, the volume resistivity ρ3 can be made lower than the volume resistivity ρ1. In addition, the values ​​of the volume resistivities ρ1 and ρ3 are respectively the average values ​​of the pump chamber overlapping portion and the measurement chamber overlapping portion, similarly to the unit resistance values ​​R1 and R3.

[0112] In the above embodiment, the unit resistance value R3 / R1 is set to a value less than 1, but the present invention is not limited thereto. Figure 2 In the embodiment, the width of the second curved portion 77b can be made equal to the widths of the first inner straight portion 79a and the second inner straight portion 79b, so that the unit resistance value R3 / R1 is 1. In this case, if "X1 ≥ 1 / 3×Wp" and "X2 ≥ 0.4Wp" are satisfied, the effect of reducing the stress generated around the internal cavity of the sensor element 101 when the heat generating portion 76 generates heat can also be obtained.

[0113] In the above-mentioned embodiment, the heating portion 76 is symmetrical on the left and right, and the left and right central axes of the heating portion 76, the left and right central axes of the main pump chamber projection area Ap, the left and right central axes of the auxiliary pump chamber projection area Aq, and the left and right central axes of the measurement chamber projection area Am are all consistent, but are not particularly limited to this. For example, the heating portion 76 may be asymmetrical on the left and right, and any one of the above-mentioned central axes may deviate from the other central axes. In this case, at least a portion of each of the first inner straight portion 79a and the second inner straight portion 79b overlaps with the main pump chamber projection area Ap, and at least a portion of each of the first inner straight portion 79a and the second inner straight portion 79b overlaps with the auxiliary pump chamber projection area Aq, and "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4Wp" are satisfied.

[0114] In the above embodiment, the shape of the main pump chamber projection area Ap, that is, the shape of the first internal cavity 20 in a top view, is a rectangle. Figure 2 As shown, the width of the main pump chamber projection area Ap in the short dimension direction is a constant value (= width Wp), but is not limited to this. For example, there may be a portion with a larger width in the short dimension direction of the main pump chamber projection area Ap and a portion with a smaller width, and the width of the main pump chamber projection area Ap in the short dimension direction is not constant. In such a case, the maximum value of the width of the main pump chamber projection area Ap in the short dimension direction is set to width Wp. The same is true for the width Wq of the auxiliary pump chamber projection area Aq and the width Wm of the measurement chamber projection area Am.

[0115] Example

[0116] Hereinafter, a specific example of manufacturing a sensor element will be described. Experimental Examples 3 to 6, 8, 9, and 10 correspond to the embodiments of the present invention, and Experimental Examples 1, 2, 7, and 11 correspond to comparative examples. In addition, the present invention is not limited to the following embodiments.

[0117] [Experimental Example 1]

[0118] Does not satisfy "X1 ≥ 1 / 3 × Wp", otherwise, Figure 1 , 2The same sensor element as the sensor element 101 shown is set as Experimental Example 1. For the size of the sensor element of Experimental Example 1, the length in the front-to-back direction is 67.5 mm, the width in the left-to-right direction is 4.25 mm, and the thickness in the up-down direction is 1.45 mm. The width of the first outer straight portion 78a and the second outer straight portion 78b is 0.28 mm. The width of the first inner straight portion 79a and the second inner straight portion 79b is 0.33 mm. The width of the second curved portion 77b other than the connecting portion with the first inner straight portion 79a and the second inner straight portion 79b is 0.53 mm. The width Wp of the main pump chamber projection area Ap is 2 mm. The width Wq of the auxiliary pump chamber projection area Aq is 1.6 mm. The width Wm of the measurement chamber projection area Am is 1.2 mm. The length of the measured gas flow portion is 8.3 mm. The distance X1 is 0.26 mm (= 0.13 Wp), and the distance X2 is 0.86 mm (= 0.43 Wp). Therefore, Experimental Example 1 satisfies “X2 ≥ 0.4 Wp”, but does not satisfy “X1 ≥ 1 / 3×Wp”.

[0119] [Experimental Examples 2 and 3]

[0120] Experimental Example 2 was an experiment in which the same sensor element as in Experimental Example 1 was used except that the distance X1 was 0.46 mm (= 0.23 Wp). Experimental Example 3 was an experiment in which the same sensor element as in Experimental Example 1 was used except that the distance X1 was 0.67 mm (= 1 / 3×Wp).

[0121] [Experimental Example 4]

[0122] The pattern of the heater 72 will be Figure 3 The sensor element of the shape shown is used as Experimental Example 4. In Experimental Example 4, the distance X1 and the distance X2 are both set to 0.86 mm (= 0.43 Wp). The other dimensions are the same as those of Experimental Example 1.

[0123] [Experimental Examples 5 and 6]

[0124] The pattern of the heater 72 will be Figure 4 The sensor element of the shape shown is used in Experimental Examples 5 and 6. In Experimental Example 5, the distance X1 is set to 1.34 mm (= 2 / 3 × Wp), and the distance X2 is set to 0.86 mm (= 0.43 Wp). In Experimental Example 6, the distance X1 is set to 1.67 mm (= 0.84 Wp), and the distance X2 is set to 0.86 mm (= 0.43 Wp). The dimensions of Experimental Examples 5 and 6 other than these are the same as those of Experimental Example 1.

[0125] [Experimental Examples 7 to 9]

[0126] The pattern of the heater 72 will be Figure 3The sensor element of the shape shown is set as Experimental Examples 7 to 9. In Experimental Example 7, the distance X1 and the distance X2 are both set to 0.67 mm (= 1 / 3 × Wp). In Experimental Example 8, the distance X1 and the distance X2 are both set to 1.34 mm (= 2 / 3 × Wp). In Experimental Example 9, the distance X1 and the distance X2 are both set to 0.8 mm (= 0.4 Wp). The dimensions of Experimental Examples 7 to 9 other than these are the same as those of Experimental Example 1.

[0127] [Evaluation of stress]

[0128] For the sensor elements of Experimental Examples 1 to 9, the stress of the internal cavity and the stress of the peripheral portion generated in the sensor element when the heat generating portion 76 was heated to 800°C were investigated respectively. The stress of the internal cavity was set as the maximum value of the stress generated around the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61 of the sensor element, and the evaluation was performed in four stages of "excellent (A)", "good (B)", "qualified (C)" and "unqualified (F)" according to the size of the maximum value. The stress of the peripheral portion was set as the maximum value of the stress generated on the lower surface of the sensor element, and the evaluation was performed in four stages of "excellent (A)", "good (B)", "qualified (C)" and "unqualified (F)" according to the size of the maximum value. In the above evaluation, the maximum value of the stress is the smallest in the case of "excellent (A)", and the maximum value of the stress is the largest in the case of "unqualified (F)".

[0129] The distances X1 and X2 of Experimental Examples 1 to 9, the results of the stress evaluation of the internal cavity, and the results of the stress evaluation of the outer periphery are shown in Tables 1 and 2. Figure 5 , 6 . Figure 5 shows the results of the stress evaluation of the internal cavity, Figure 6 The results of stress evaluation of the outer periphery are shown. Figure 5 , 6 The numbers 1 to 9 in the table represent the numbers of the experimental examples. For the results of the stress evaluation, "excellent (A)" is represented by a circle, "good (B)" is represented by a white square, "qualified (C)" is represented by a hatched square, and "unqualified (F)" is represented by a black square.

[0130] Table 1

[0131]

[0132] From Table 1 and Figure 5It can be seen that the stress evaluation of the internal cavity of Experimental Examples 1 and 2 that do not satisfy "X1≥1 / 3×Wp", and Experimental Example 7 that does not satisfy "X2≥0.4Wp" are all "unqualified (F)". In contrast, the stress evaluation of the internal cavity of Experimental Examples 3 to 6, 8, and 9 that satisfy both "X1≥1 / 3×Wp" and "X2≥0.4Wp" are all "qualified (C)" or above. From these results, it can be confirmed that by satisfying "X1≥1 / 3×Wp" and "X2≥0.4Wp" at the same time, the stress of the internal cavity can be reduced. In addition, the stress evaluation of the internal cavity of Experimental Examples 4 to 6 and 8 that further satisfy "X1>0.4Wp" are all "good (B)" or above. In addition, Figure 5 The following trend is confirmed: the larger the distances X1 and X2, the more the markers Figure 5 In the upper right experimental example, the stress evaluation of the internal cavity is higher.

[0133] The stress evaluation of the outer periphery also showed the same trend as the stress evaluation of the inner cavity. Figure 6 It can be seen that the stress evaluation of the peripheral part of Experimental Examples 1 and 2 that do not satisfy "X1 ≥ 1 / 3 × Wp" and Experimental Example 7 that does not satisfy "X2 ≥ 0.4Wp" are all "unqualified (F)". In contrast, the stress evaluation of the peripheral part of Experimental Examples 3 to 6, 8, and 9 that satisfy both "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4Wp" are all "qualified (C)" or above. These results confirm that by satisfying both "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4Wp", the stress of the peripheral part can be reduced. In addition, Figure 6 The following trend is confirmed: the larger the distances X1 and X2, the more the markers Figure 6 In the upper right experimental example, the stress evaluation of the outer periphery is higher.

[0134] [Experimental Example 10]

[0135] The pattern of the heater 72 will be Figure 3 The sensor element of the shape shown is used as Experimental Example 10. In Experimental Example 10, the distance X1 and the distance X2 are both set to 0.86 mm (= 0.43 Wp) as in Experimental Example 4. The other dimensions are the same as those in Experimental Example 1. Therefore, Experimental Example 10 satisfies both "X1 ≥ 1 / 3 × Wp" and "X2 ≥ 0.4 Wp".

[0136] [Experimental Example 11]

[0137] The pattern of the heater 72 will be Figure 7 The sensor element of the shape shown in FIG. 1 is set as Experimental Example 11. In Experimental Example 11, Figure 7As shown, the width of the first inner straight portion 79a and the second inner straight portion 79b presents a partially large shape, and the width of the portion overlapping with the auxiliary pump chamber projection area Aq is the largest. The front side portion 79a1 of the first inner straight portion 79a has a portion whose length direction is inclined relative to the long dimension direction (front-back direction) of the sensor element and a portion parallel to the long dimension direction (front-back direction). The same is true for the front side portion 79b1 of the second inner straight portion 79b. The portion inclined relative to the front-back direction in the front side portion 79a1 and the portion inclined relative to the front-back direction in the front side portion 79b1 are arranged so that the closer to the front end of the sensor element, the greater the distance between them in the left-right direction. The distance between the front side portion 79a1 and the front side portion 79b1 in the left-right direction is not constant, and the distance between the portion parallel to the front-back direction in the front side portion 79a1 and the portion parallel to the front-back direction in the left-right direction in the left-right direction is the minimum distance X1min between the front side portion 79a1 and the front side portion 79b1 in the left-right direction. The minimum distance X1min is 0.47 mm. The distance X1 is the average value of the distances in the short dimension direction (left-right direction) between the portions of the first inner straight portion 79a and the second inner straight portion 79b that overlap with the main pump chamber projection area Ap. The distance X1 is 0.49 mm, which is greater than the minimum distance X1min. The distance in the left-right direction between the rear portion 79a3 and the rear portion 79b3 is constant, and is the same as the minimum distance X1min. Therefore, the distance X2 is 0.47 mm, which is the same as the minimum distance X1min. The width of the second curved portion 77b is 0.33 mm. The other dimensions are the same as those in Experimental Example 1, and the width Wp of the main pump chamber projection area Ap is 2 mm. Therefore, in Experimental Example 11, neither "X1 ≥ 1 / 3 × Wp" nor "X2 ≥ 0.4Wp" is satisfied.

[0138] [Evaluation of cracking incidence]

[0139] For the sensor elements of Experimental Examples 10 and 11, the cracking incidence when the heating portion 76 is heated is measured. Specifically, first, 10 sensor elements of each of Experimental Examples 10 and 11 are prepared. Next, for each sensor element, a certain voltage is applied to the heater 72 to heat the heating portion 76 so that the heater 72 reaches the target temperature (800°C). Then, it is confirmed whether each sensor element has cracked. In addition, the heating condition is a condition in which the heater 72 is heated to the target temperature in a shorter time than when the sensor element is normally used, and accordingly, a certain degree of cracking occurs in the sensor element. In Experimental Example 10, 4 of the 10 sensor elements cracked, and the cracking incidence was 40%. In Experimental Example 11, all 10 sensor elements cracked, and the cracking incidence was 100%. From these results, it was confirmed that the cracking rate was lower in Experimental Example 10, which satisfied both "X1≥1 / 3×Wp" and "X2≥0.4Wp", than in Experimental Example 11, which satisfied neither "X1≥1 / 3×Wp" nor "X2≥0.4Wp". It is considered that Experimental Example 10 was able to reduce the stress of the internal cavity by satisfying both "X1≥1 / 3×Wp" and "X2≥0.4Wp", and therefore the cracking rate was lower.

[0140] This application claims priority based on Japanese Patent Application No. 2021-137151 filed on August 25, 2021, the entire contents of which are incorporated herein by reference.

Claims

1. A sensor element, wherein: have: A plate-shaped element body, the element body including a solid electrolyte layer having oxygen ion conductivity, a gas flow portion for introducing and flowing the gas to be measured, and having a long dimension direction, a short dimension direction, and a thickness direction perpendicular to the long dimension direction and the short dimension direction; a main pump unit for adjusting the oxygen concentration of a main pump chamber in the measured gas flow section; an auxiliary pump unit that adjusts the oxygen concentration of an auxiliary pump chamber disposed on a downstream side of the main pump chamber in the measured gas flow section; a measurement pump unit that adjusts the oxygen concentration of a measurement chamber disposed downstream of the auxiliary pump chamber in the measured gas flow section; and a heating element for heating the element body, The heating element has: A first outer straight portion and a second outer straight portion, the first outer straight portion and the second outer straight portion are arranged side by side along the short dimension direction and have a length direction along the long dimension direction; a first inner straight portion and a second inner straight portion, wherein the first inner straight portion and the second inner straight portion are arranged between the first outer straight portion and the second outer straight portion in the short dimension direction and have a length direction along the long dimension direction; a first curved portion connecting the first outer straight portion and the first inner straight portion at one end in the longitudinal direction; a second curved portion connecting the first inner straight portion and the second inner straight portion at the other end side in the longitudinal direction; as well as a third curved portion connecting the second inner straight portion and the second outer straight portion at one end in the longitudinal direction; At least a portion of each of the first inner straight portion and the second inner straight portion overlaps with a main pump chamber projection area, wherein the main pump chamber projection area is an area obtained by projecting the main pump chamber toward the heating element in the thickness direction. At least a portion of each of the first inner straight portion and the second inner straight portion overlaps with an auxiliary pump chamber projection area, wherein the auxiliary pump chamber projection area is an area obtained by projecting the auxiliary pump chamber toward the heating element in the thickness direction. The distance X1 between the first inner straight portion and the second inner straight portion in the short dimension direction at the portion overlapping with the main pump chamber projection area is greater than 1 / 3 of the width Wp of the main pump chamber projection area in the short dimension direction. A distance X2 in the short dimension direction between the first inner straight portion and the second inner straight portion at a portion overlapping with the auxiliary pump chamber projection region is equal to or greater than 0.4 times the width Wp.

2. The sensor element according to claim 1, wherein: The distance X1 is greater than 0.4 times the width Wp.

3. The sensor element according to claim 1 or 2, wherein: The resistance value per unit length of the repeated portion of the pump chamber in the heating element is set to a unit resistance value R1, wherein the repeated portion of the pump chamber is a portion that overlaps with the pump chamber projection area, and the pump chamber projection area is an area obtained by projecting the main pump chamber and the auxiliary pump chamber toward the heating element and in the thickness direction. The resistance value per unit length of the repeated portion of the measuring chamber in the heating element is set to a unit resistance value R3, wherein the repeated portion of the measuring chamber is a portion that overlaps with the projection area of ​​the measuring chamber, and the projection area of ​​the measuring chamber is an area obtained by projecting the measuring chamber toward the heating element in the thickness direction. At this time, the unit resistance value ratio R3 / R1 at at least any temperature in the temperature range of 700°C to 900°C is smaller than 1, wherein the unit resistance values ​​R1 and R3 are expressed in μΩ / mm.

4. A gas sensor, wherein: A sensor element according to claim 1 or 2.

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