JP2019211436A - Gas sensor - Google Patents

Abstract

To provide a gas sensor that can properly secure the introduction amount of the reference gas to the reference electrode and increase the heat transfer of the sensor element.SOLUTION: The sensor element 2 of a gas sensor 1 includes a solid electrolyte 31; a detection electrode 311; a reference electrode 312; insulators 33A, 33B; a heating element 34; and a reference gas duct 36. The reference gas duct 36 adjoins a second main surface 302 of the solid electrolyte 31 in a second insulator 33B and is formed from the rear end opening 360 of the long direction L of the reference gas duct 36 to the arrangement position of the reference electrode 312, introducing the reference gas A from the rear end opening 360 to the reference electrode 312. The cross-sectional area S1 of the cross-section perpendicular to the long direction L of the reference gas duct 36 at the rear end position 312A of the long direction L of the reference electrode 312 is less than 0.2 times or more and less than 1 time of the cross-sectional area S2 of the cross-section of the reference gas duct 36 in the rear end opening 360.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a gas sensor including a long plate-shaped sensor element.

  The gas sensor is disposed, for example, in an exhaust pipe of an internal combustion engine, and is used to detect the concentration of a specific gas component such as an oxygen concentration in the detection target gas using an exhaust gas flowing through the exhaust pipe as a detection target gas. The sensor element of the gas sensor includes a solid electrolyte body having oxygen ion conductivity, a detection electrode provided on the surface of the fixed electrolyte body and exposed to a detection target gas such as exhaust gas, and a surface provided on the surface of the solid electrolyte body. A reference electrode that is exposed to a reference gas such as In order to sufficiently supply the reference gas to the reference electrode, a reference gas duct into which the reference gas is introduced is formed in the sensor element.

  In addition, a heating element for heating the solid electrolyte body, the detection electrode, and the reference electrode to the activation temperature is embedded in the sensor element. The heating element includes a heating part that is disposed at a position facing the detection electrode and the reference electrode and generates heat when energized, and a pair of lead parts connected to both ends of the heating part.

  Further, for example, in the sensor element and the sensor of Patent Document 1, a device is devised to reduce the air supply amount to the reference electrode while reducing the power consumption for heating the sensor element. In Patent Document 1, the cross-sectional shape and cross-sectional area of an air introduction part for introducing air to the reference electrode are set within an appropriate range. When the air supply amount to the reference electrode is insufficient, particularly when the air-fuel ratio of the internal combustion engine is determined based on the composition of the exhaust gas exhausted from the internal combustion engine to the exhaust pipe by the gas sensor, compared to the stoichiometric air-fuel ratio. Occurs when detecting an air-fuel ratio rich condition where the fuel is excessive.

Japanese Patent Laying-Open No. 2015-34782

  In order to maintain a large amount of reference gas introduced into the reference electrode, it is preferable that the cross-sectional area of the cross section perpendicular to the longitudinal direction in the reference gas duct is large. On the other hand, when the cross-sectional area of the reference gas duct is increased, a heat insulating portion in the sensor element is increased, and heat conductivity when the sensor element is heated by the heating element is deteriorated.

  The reference gas duct for introducing the reference gas to the reference electrode is formed over a wide range in the longitudinal direction of the sensor element. Moreover, the gas detection part of the sensor element provided with the detection electrode, the reference electrode, and the heat generating part of the heating element is formed at the front end in the longitudinal direction of the sensor element. And the front-end | tip part of a sensor element becomes high temperature compared with a rear-end part, and the reference gas in a reference | standard gas duct also becomes high temperature in the front-end | tip part of a sensor element.

  According to the inventor's research, it is effective to provide a change in the cross-sectional area of the reference gas duct in the longitudinal direction in order to increase the heat transfer property of the sensor element while maintaining the amount of reference gas introduced to the reference electrode appropriately. It was found that there was. In the sensor element and sensor of Patent Document 1, no change is made in the cross-sectional area in the longitudinal direction of the reference gas duct (atmosphere introduction portion).

  The present invention has been made in view of such problems, and has been obtained in an attempt to provide a gas sensor that can appropriately secure the amount of reference gas introduced to the reference electrode and can enhance the heat transfer property of the sensor element. is there.

One aspect of the present invention is a gas sensor (1) including a long plate-shaped sensor element (2).
The sensor element is
A solid electrolyte body (31) having oxygen ion conductivity;
A detection electrode (311) provided at a front end side position in the longitudinal direction (L) of the sensor element on the first main surface (301) exposed to the detection target gas (G) in the solid electrolyte body;
A reference electrode (312) provided at the front end side position in the longitudinal direction on the second main surface (302) exposed to the reference gas (A) in the solid electrolyte body;
Insulators (33A, 33B) stacked on the solid electrolyte body;
A heat generating part (341) embedded in the insulator and disposed at a position facing the detection electrode and the reference electrode, and a lead connected to the rear end side in the longitudinal direction of the heat generating part. A heating element (34) having a portion (342);
The insulator is formed at a position adjacent to the second main surface of the solid electrolyte body from the rear end opening (360) in the longitudinal direction to the arrangement position of the reference electrode, and the rear end opening. A reference gas duct (36) into which the reference gas is introduced from the section,
The cross-sectional area (S1) of the cross section orthogonal to the longitudinal direction of the reference gas duct at the rear end position (312A) of the reference electrode in the longitudinal direction is the cross sectional area (S1) of the reference gas duct at the rear end opening. The gas sensor has a cross-sectional area (S2) of a cross section of 0.2 times or more and less than 1 time.

  In the gas sensor of the above aspect, the cross-sectional area of the reference gas duct at the rear end position in the longitudinal direction of the reference electrode is 0.2 times or more the cross-sectional area of the reference gas duct at the rear end opening. It is less than 1 time. With this configuration, it is possible to appropriately secure the amount of reference gas introduced to the reference electrode, and to increase the heat conductivity of the sensor element.

  Specifically, the cross-sectional area of the cross section at the rear end opening of the reference gas duct is set to a size that can sufficiently introduce the reference gas to the reference electrode. The cross-sectional area of the cross section of the reference gas duct at the rear end position of the reference electrode is such that when the solid electrolyte body, the detection electrode, and the reference electrode are heated by the heat generating part of the heat generating element, the reference gas duct becomes a heat insulating part. It can be set to a cross-sectional area that alleviates hindering heat transfer from the heat generating part to the solid electrolyte body or the like. Thereby, while ensuring the introduction amount of the reference gas to a reference electrode appropriately, the heat conductivity of a sensor element can be improved.

  In addition, the duct portion of the reference gas duct located on the front end side of the rear end position of the reference electrode is located at a position facing the heat generating portion, and the reference gas in the duct portion located on the front end side is behind this. Compared with the reference gas in the duct part located on the end side, the heating part is heated to a higher temperature. The diffusion coefficient of the reference gas in the duct portion located on the front end side is larger than the diffusion coefficient of the reference gas in the duct portion located on the rear end side. The diffusion coefficient affects the amount of oxygen ions that move from the reference electrode to the detection electrode via the solid electrolyte body when the reference gas is supplied to the reference electrode. That is, the greater the diffusion coefficient, the greater the amount of oxygen ion movement.

  Therefore, even if the cross-sectional area of the cross section of the duct portion located on the distal end side becomes small, it is possible to appropriately secure the amount of oxygen ion movement from the reference electrode to the detection electrode. In particular, when the air-fuel ratio of the internal combustion engine obtained from the detection target gas is in a rich state, sufficient oxygen ions for chemically reacting unburned gas or the like in the detection electrode can be moved from the reference electrode to the detection electrode. . As a result, even if the cross-sectional area of the duct section located on the tip side is small, the movement of oxygen ions from the reference electrode to the detection electrode is not so restricted, and the electrochemical reaction in the sensor element is maintained well. Can do.

  Therefore, according to the gas sensor of the one aspect, it is possible to appropriately secure the introduction amount of the reference gas to the reference electrode and to enhance the heat conductivity of the sensor element.

  When the cross-sectional area of the cross section of the reference gas duct at the rear end position in the longitudinal direction of the reference electrode is less than 0.2 times the cross-sectional area of the cross section of the reference gas duct at the rear end opening, It becomes difficult to maintain a sufficient amount of reference gas introduced into the. On the other hand, when the cross-sectional area of the reference gas duct at the rear end position in the longitudinal direction of the reference electrode is greater than or equal to one times the cross-sectional area of the reference gas duct at the rear end opening, the sensor element It becomes difficult to increase the heat conductivity.

  Note that the reference numerals in parentheses of the constituent elements shown in one embodiment of the present invention indicate the correspondence with the reference numerals in the drawings in the embodiment, but the constituent elements are not limited only to the contents of the embodiments.

1 is a cross-sectional view showing a gas sensor according to a first embodiment. The perspective view which shows the sensor element before lamination | stacking concerning Embodiment 1. FIG. FIG. 3 is a cross-sectional view showing the sensor element according to the first embodiment. FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 3, showing the sensor element according to the first embodiment. FIG. 5 is a cross-sectional view taken along the line V-V in FIG. 3, showing the sensor element according to the first embodiment. Sectional drawing which shows the other sensor element concerning Embodiment 1. FIG. The graph which shows the change of the diffusion coefficient with respect to the change of the temperature of air | atmosphere concerning Embodiment 1. FIG. FIG. 4 is a cross-sectional view corresponding to the IV-IV section of FIG. 3 showing the sensor element according to the second embodiment. Sectional drawing which shows the sensor element concerning Embodiment 3. FIG. Sectional drawing which shows the sensor element concerning Embodiment 4. FIG. Sectional drawing which shows the other sensor element concerning Embodiment 4. FIG.

A preferred embodiment of the gas sensor described above will be described with reference to the drawings.
<Embodiment 1>
As shown in FIGS. 1 to 5, the gas sensor 1 of the present embodiment includes a long plate-shaped sensor element 2. The sensor element 2 includes a solid electrolyte body 31, a detection electrode 311, a reference electrode 312, insulators 33 </ b> A and 33 </ b> B, a heating element 34, and a reference gas duct 36. The solid electrolyte body 31 has oxygen ion conductivity at the activation temperature. The detection electrode 311 is provided on the first main surface 301 of the solid electrolyte body 31 that is exposed to the detection target gas G and on the front end side L1 in the longitudinal direction L of the sensor element 2. The reference electrode 312 is provided at a position on the distal end side L1 in the longitudinal direction L on the second main surface 302 exposed to the reference gas A in the solid electrolyte body 31.

  The insulators 33 </ b> A and 33 </ b> B have insulating properties, and are stacked on the first main body 301 </ b> A stacked on the first main surface 301 of the solid electrolyte body 31 and the second main surface 302 of the solid electrolyte body 31. There is a second insulator 33B. The heating element 34 is embedded in the second insulator 33B, and is disposed in a position facing the detection electrode 311 and the reference electrode 312. The heating element 341 that generates heat by energization and the heating element 341 in the longitudinal direction. And a heating element lead portion (lead portion) 342 connected to the rear end side of L. The reference gas duct 36 is adjacent to the second main surface 302 of the solid electrolyte body 31 in the second insulator 33B, and the rear end opening in the longitudinal direction L of the reference gas duct 36 (sensor element 2 and second insulator 33B). The reference gas A is formed from the portion 360 to the position where the reference electrode 312 is arranged, and is for introducing the reference gas A from the rear end opening 360 to the reference electrode 312.

  As shown in FIG. 3, the cross-sectional area S1 of the cross section perpendicular to the longitudinal direction L of the reference gas duct 36 at the rear end position 312A of the reference electrode 312 in the longitudinal direction L is the reference gas duct in the rear end opening 360. The cross-sectional area S2 of 36 cross sections is 0.2 times or more and less than 1 time.

Below, it explains in full detail about the gas sensor 1 of this form.
(Internal combustion engine)
The gas sensor 1 is disposed in an exhaust pipe or the like of an internal combustion engine (engine) of a vehicle, and is used to detect an oxygen concentration or the like in the detection target gas G using an exhaust gas flowing through the exhaust pipe as a detection target gas G. The gas sensor 1 can be used as an air-fuel ratio sensor for obtaining an air-fuel ratio in an internal combustion engine based on oxygen concentration, unburned gas concentration, etc. in exhaust gas. In addition to the air-fuel ratio sensor, the gas sensor 1 can be used for various purposes for obtaining the oxygen concentration.

  A catalyst for purifying harmful substances in the exhaust gas is arranged in the exhaust pipe, and the gas sensor 1 can be arranged either upstream or downstream of the catalyst in the flow direction of the exhaust gas in the exhaust pipe. . Moreover, the gas sensor 1 can also be arrange | positioned to piping at the suction side of the supercharger which raises the density of the air which an internal combustion engine inhales using waste gas. Moreover, the piping which arrange | positions the gas sensor 1 can also be used as piping in the exhaust gas recirculation mechanism which recirculates a part of exhaust gas exhausted from the internal combustion engine to the exhaust pipe to the intake pipe of the internal combustion engine.

  The air-fuel ratio sensor is quantitatively continuously air-fuel ratio from a fuel-rich state where the ratio of fuel to air is larger than the stoichiometric air-fuel ratio to a fuel-lean state where the ratio of fuel to air is smaller than the stoichiometric air-fuel ratio. Can be detected. In the air-fuel ratio sensor, when the diffusion rate of the detection target gas G guided to the gas chamber 35 by the diffusion resistance unit (diffusion rate controlling unit) 32 is reduced, oxygen ions are detected between the detection electrode 311 and the reference electrode 312. A predetermined voltage for indicating a limit current characteristic in which a current corresponding to the movement amount is output is applied.

  As shown in FIGS. 3 and 4, when the air-fuel ratio sensor detects the air-fuel ratio on the fuel lean side, oxygen contained in the detection target gas G becomes ions and is detected from the detection electrode 311 to the solid electrolyte body 31. The current generated when moving to the reference electrode 312 via the is detected. When the air-fuel ratio sensor detects an air-fuel ratio on the fuel-rich side, the reference electrode 312 is used to react with unburned gas (hydrocarbon, carbon monoxide, hydrogen, etc.) contained in the detection target gas G. Then, oxygen that has become ions moves to the detection electrode 311 through the solid electrolyte body 31, and a current generated when the unburned gas reacts with oxygen is detected.

(Sensor element 2)
As shown in FIGS. 3 and 4, the sensor element 2 is a laminated type in which insulators 33 </ b> A and 33 </ b> B and a heating element 34 are laminated on a solid electrolyte body 31. The solid electrolyte body 31 is made of a zirconia-based oxide, is composed of zirconia as a main component (containing 50% by mass or more), and is stabilized zirconia or a part in which a part of zirconia is substituted by a rare earth metal element or an alkaline earth metal element. Made of stabilized zirconia. A part of zirconia constituting the solid electrolyte body 31 can be replaced by yttria, scandia or calcia.

  Further, the detection electrode 311 and the reference electrode 312 contain platinum as a noble metal exhibiting catalytic activity against oxygen and a zirconia-based oxide as a co-material with the solid electrolyte body 31. The common material is a combination of the detection electrode 311 and the reference electrode 312 formed by the electrode material and the solid electrolyte body 31 when the paste-like electrode material is printed (applied) on the solid electrolyte body 31 and both are sintered. This is to maintain strength.

  A gas chamber 35 surrounded by the first insulator 33 </ b> A and the solid electrolyte body 31 is formed adjacent to the first main surface 301 of the solid electrolyte body 31. The gas chamber 35 is formed at the position where the detection electrode 311 is disposed in the first insulator 33A. A reference gas duct 36 surrounded by the second insulator 33 </ b> B and the solid electrolyte body 31 is formed adjacent to the second main surface 302 of the solid electrolyte body 31. The reference gas duct 36 is formed from the position where the reference electrode 312 is disposed to the rear end position of the sensor element 2 in the second insulator 33B. The first insulator 33 </ b> A is provided with a diffusion resistance portion 32 for introducing the detection target gas G into the gas chamber 35 at a predetermined diffusion rate in a state of communicating with the gas chamber 35.

  As shown in FIGS. 1 and 3, the sensor element 2 is formed in a long shape, and the detection electrode 311, the reference electrode 312, the gas chamber 35, the diffusion resistance unit 32, and the heat generation unit 341 of the heat generator 34 are long. It arrange | positions in the site | part of the front end side L1 of the scale direction L. FIG. At a portion of the sensor element 2 on the front end side L1 in the longitudinal direction L, there is a detection unit 21 including a detection electrode 311 and a reference electrode 312 and a portion of the solid electrolyte body 31 sandwiched between these electrodes 311 and 312. Is formed.

  The longitudinal direction L of the sensor element 2 refers to the direction in which the sensor element 2 is formed in a long shape. In addition, the direction in which the solid electrolyte body 31 and the insulators 33A and 33B are stacked in a cross section perpendicular to the longitudinal direction L, in other words, the solid electrolyte body 31, the insulators 33A and 33B, and the heating element 34 are formed. The stacked direction is referred to as a stacking direction D. In addition, the direction orthogonal to the stacking direction D in the cross section, in other words, the direction orthogonal to the longitudinal direction L and the stacking direction D is referred to as the width direction W. In the longitudinal direction L of the sensor element 2, the side on which the detection unit 21 is formed is referred to as a front end side L1, and the opposite side of the front end side L1 is referred to as a rear end side L2.

  As shown in FIG. 2, electrode lead portions 313 and 314 for electrically connecting these electrodes 311 and 312 to the outside of the gas sensor 1 are connected to the detection electrode 311 and the reference electrode 312. 313 and 314 are drawn out to a portion on the rear end side L2 in the longitudinal direction L. In FIG. 2, FIG. 3, FIG. 5, etc., the length of the sensor element 2 in the longitudinal direction L is shortened for easy understanding.

  As shown in FIGS. 2 and 5, the heating element 34 includes a heating part 341 that generates heat when energized, and a pair of heating element lead parts 342 connected to the heating part 341. The resistance value per unit length of the heat generating part 341 is larger than the resistance value per unit length of the heating element lead part 342. The heating element lead portion 342 is pulled out to the rear end side L2 of the longitudinal direction L. The heating element 34 contains a conductive metal material.

  The heat generating portion 341 is formed in a shape that meanders in the longitudinal direction L at the distal end portion of the heat generating body 34. Note that the heat generating portion 341 may be formed by meandering in the width direction W. The heat generating portion 341 is disposed at a position facing the detection electrode 311 and the reference electrode 312 in the stacking direction D orthogonal to the longitudinal direction L. When the heat generating part 341 generates heat by energization from the heat generating element lead part 342, the portion sandwiched between the electrodes 311 and 312 in the detection electrode 311, the reference electrode 312, and the solid electrolyte body 31 is a target temperature. To be heated.

  The cross-sectional area of the heat generating portion 341 is smaller than the cross-sectional area of the heat generating lead portion 342, and the resistance value per unit length of the heat generating portion 341 is higher than the resistance value per unit length of the heat generating lead portion 342. This cross-sectional area refers to the cross-sectional area of the surface orthogonal to the direction in which the heat generating part 341 and the heat generating lead part 342 extend. When a voltage is applied to the pair of heating element lead portions 342, the heating portion 341 generates heat due to Joule heat, and the periphery of the detection unit 21 is heated by this heat generation.

  The first insulator 33A forms the gas chamber 35, and the second insulator 33B forms the reference gas duct 36 and embeds the heating element 34 therein. The first insulator 33A and the second insulator 33B are made of alumina (aluminum oxide). Each of the insulators 33A and 33B is formed as a dense body through which the detection target gas G or the reference gas A cannot permeate. In each of the insulators 33A and 33B, almost all pores through which gas can pass are formed. It has not been.

  As shown in FIGS. 2 and 3, the first insulator 33 </ b> A is stacked on the insulating spacer 331 and the insulating spacer 331 having a through hole 332 that is penetrated in the stacking direction D in order to form the gas chamber 35. An insulating plate 334 for closing the through hole 332 is formed. The diffusion resistance portion 32 of this embodiment is formed adjacent to the distal end side L1 of the gas chamber 35 in the longitudinal direction L. The diffusion resistance portion 32 is disposed in the introduction spacer 331 of the first insulator 33A in the introduction port 333 opened adjacent to the distal end side L1 in the longitudinal direction L of the gas chamber 35.

  The gas chamber 35 is formed as a space portion closed by the first insulator 33 </ b> A, the diffusion resistance portion 32, and the solid electrolyte body 31. The detection target gas G, which is exhaust gas flowing in the exhaust pipe, passes through the diffusion resistance portion 32 and is introduced into the gas chamber 35.

  The diffusion resistance portion 32 may be formed adjacent to both sides of the gas chamber 35 in the width direction W. In this case, the diffusion resistance portion 32 is disposed in the inlet 333 opened adjacent to both sides in the width direction W of the gas chamber 35 in the insulating spacer 331 of the first insulator 33A.

  The diffusion resistance portion 32 is formed of porous ceramics such as alumina. The diffusion speed (flow rate) of the detection target gas G introduced into the gas chamber 35 is determined by limiting the speed at which the detection target gas G passes through the pores in the diffusion resistance portion 32.

  In addition, the diffusion resistance part 32 can also be formed using a pin hole which is a small through hole communicating with the gas chamber 35 in addition to using a porous body.

  As shown in FIGS. 2 and 3, the second insulator 33 </ b> B includes an insulating spacer 335 in which a notch 336 constituting the reference gas duct 36 is formed, a first heater plate 337 stacked on the insulating spacer 335, A heating element 34 is sandwiched between the first heater plate 337 and a second heater plate 338 stacked on the first heater plate 337.

  In the insulating spacer 331 of the first insulator 33A and the insulating spacer 335 of the second insulator 33B, the through hole 332 or the notch 336 can be formed by various methods such as molding, cutting, and paste application. .

  The reference gas duct 36 is formed as a duct of the reference gas A in which the rear end side L2 of the longitudinal direction L is opened. The reference gas duct 36 is formed from a rear end position in the longitudinal direction L of the sensor element 2 to a position facing the gas chamber 35 via the solid electrolyte body 31. The reference electrode 312 is disposed at the front end side L1 in the reference gas duct 36. Atmosphere as the reference gas A is introduced into the reference gas duct 36 from the rear end side L2 of the sensor element 2.

  As shown in FIG. 1, a porous layer for capturing poisonous substances to the detection electrode 311, condensed water generated in the exhaust pipe, and the like around the entire periphery of the sensor element 2 on the tip side L <b> 1 in the longitudinal direction L. 37 is provided. The porous layer 37 is formed of porous ceramics such as alumina. The porosity of the porous layer 37 is larger than the porosity of the diffusion resistance portion 32, and the flow rate of the detection target gas G that can permeate the porous layer 37 is the detection target that can permeate the diffusion resistance portion 32. More than the flow rate of gas G.

(Reference gas duct 36)
As shown in FIGS. 3 and 5, the reference gas duct 36 is formed by changing the cross-sectional area of the cross section perpendicular to the longitudinal direction L of the sensor element 2 in the longitudinal direction L. The reference gas duct 36 has a duct boundary portion 363 whose cross-sectional area changes in the position of the rear end side L2 in the longitudinal direction L from the rear end position 312A of the reference electrode 312. In the present embodiment, a portion of the reference gas duct 36 that is located on the distal end side L1 in the longitudinal direction L from the duct boundary portion 363 is referred to as a distal end side duct portion 361, and the reference gas duct 36 is longer in the longitudinal direction than the duct boundary portion 363. A portion located on the rear end side L2 of L is referred to as a rear end side duct portion 362.

  The reference gas duct 36 has a shape in which the cross-sectional area of the front end side duct portion 361 that is easily heated to a high temperature by the heat generating portion 341 of the heat generating element 34 is smaller than that of the rear end side duct portion 362. The duct boundary portion 363 of the present embodiment is formed as a stepped portion in which the cross-sectional area of the cross section of the front end side duct portion 361 is rapidly reduced from the cross sectional area of the cross section of the rear end side duct portion 362. The wall surface 339 in the stacking direction D located on the side opposite to the solid electrolyte body 31 in the front end side duct portion 361 is the wall surface in the stacking direction D located on the side opposite to the solid electrolyte body 31 in the rear end side duct portion 362. It is at a position closer to the solid electrolyte body 31 than 339. And the cross-sectional area of the cross section in the full length of the elongate direction L of the front end side duct part 361 is smaller than the cross sectional area of the cross section in the full length of the elongate direction L of the rear end side duct part 362.

  The thickness in the stacking direction D in the entire length in the longitudinal direction L of the front end side duct portion 361 is smaller than the thickness in the stacking direction D in the entire length in the longitudinal direction L of the rear end side duct portion 362. Accordingly, the thickness in the stacking direction D of the reference gas duct 36 at the rear end position 312A of the reference electrode 312 is smaller than the thickness in the stacking direction D of the reference gas duct 36 at the rear end opening 360.

  Further, as shown in FIGS. 3 and 5, the width in the width direction W in the entire length in the longitudinal direction L of the front end side duct portion 361 is equal to the width in the width direction W in the entire length in the length direction L of the rear end side duct portion 362. It is almost the same as the width. And the cross-sectional area of the cross section of the front end side duct part 361 is reduced by making the thickness of the front end side duct part 361 in the stacking direction D smaller than the thickness of the rear end side duct part 362 in the stacking direction D. The cross-sectional area of the cross section of the portion 362 is made smaller. Further, the length in the longitudinal direction L of the front end side duct portion 361 is shorter than the length of the rear end side duct portion 362 in the longitudinal direction L. The volume of the front end side duct portion 361 is smaller than the volume of the rear end side duct portion 362.

  The thickness in the stacking direction D and the width in the width direction W of the rear end side duct portion 362 of this embodiment are constant in the longitudinal direction L. Further, the cross-sectional area of the transverse section of the rear end side duct portion 362 is constant in the longitudinal direction L. On the other hand, the width in the width direction W of the distal end side duct portion 361 is constant in the longitudinal direction L, and the thickness in the stacking direction D of the distal end side duct portion 361 is increased toward the distal end side L1 in the longitudinal direction L. It is shrinking. And the cross-sectional area of the cross section of the front end side duct part 361 is reducing as it goes to the front end side L1 of the elongate direction L. As shown in FIG.

  As shown in FIG. 3, the wall surface 339 in the stacking direction D located on the opposite side of the solid electrolyte body 31 in the distal end side duct portion 361 of the present embodiment is formed in a curved shape that swells away from the solid electrolyte body 31. ing. The front end side duct portion 361 may be formed in a shape in which the cross sectional area S1 of the cross section is constant. Further, only the end portion on the distal end side L1 of the distal end side duct portion 361 may be formed in a curved shape, and the portion other than the end portion on the distal end side L1 may be formed in a planar shape.

  In addition, as shown in FIG. 6, the duct boundary portion 363 has a wall surface 339 in the stacking direction D located on the opposite side of the solid electrolyte body 31 in the front end side duct portion 361, and a solid surface in the rear end side duct portion 362. You may form as a bending part bent with respect to the wall surface 339 of the lamination direction D located in the opposite side to the electrolyte body 31. FIG. In this case, the wall surface 339 in the stacking direction D located on the side opposite to the solid electrolyte body 31 in the front end side duct portion 361 approaches the solid electrolyte body 31 as it goes to the front end side L1 in the longitudinal direction L. It can be formed as a tapered surface.

  Further, the volume of the reference gas duct 36 is larger than the volume of the gas chamber 35. The length of the reference gas duct 36 in the longitudinal direction L is longer than the length of the gas chamber 35 in the longitudinal direction L, and the thickness of the reference gas duct 36 in the stacking direction D is greater than the thickness of the gas chamber 35 in the stacking direction D. Is also big.

(Other configurations of the gas sensor 1)
As shown in FIG. 1, in addition to the sensor element 2 and the like, the gas sensor 1 includes a first insulator 42 that holds the sensor element 2, a housing 41 that holds the first insulator 42, and a second insulator connected to the first insulator 42. A contact terminal 44 that is held by the insulator 43 and the second insulator 43 and contacts the sensor element 2 is provided. Further, the gas sensor 1 includes a front end side cover 45 attached to the front end side L1 portion of the housing 41, a rear end side attached to the rear end side L2 portion of the housing 41 and covering the second insulator 43, the contact terminal 44, and the like. A bush 47 for holding the lead wire 48 connected to the cover 46 and the contact terminal 44 to the rear end side cover 46 is provided.

  The front end side cover 45 is disposed in the exhaust pipe of the internal combustion engine. The front end cover 45 is formed with a gas passage hole 451 for allowing the exhaust gas as the detection target gas G to pass therethrough. The front end side cover 45 can have a double structure or a single structure. The exhaust gas as the detection target gas G flowing into the tip side cover 45 from the gas passage hole 451 of the tip side cover 45 passes through the porous layer 37 and the diffusion resistance part 32 of the sensor element 2 and is guided to the detection electrode 311. It is burned.

  As shown in FIG. 1, the rear end side cover 46 is disposed outside the exhaust pipe of the internal combustion engine. The rear end cover 46 is formed with an atmosphere introduction hole 461 for introducing the atmosphere as the reference gas A into the rear end cover 46. The air introduction hole 461 is provided with a filter 462 that does not allow liquid to pass while allowing gas to pass. The reference gas A introduced into the rear end side cover 46 from the atmosphere introduction hole 461 is guided to the reference electrode 312 through the gap in the rear end side cover 46 and the reference gas duct 36.

  As shown in FIGS. 1 and 2, the contact terminal 44 is connected to the electrode lead part 313 of the detection electrode 311, the electrode lead part 314 of the reference electrode 312, and the heating element lead part 342 of the heating element 34, respectively. A plurality of second insulators 43 are arranged. Further, the lead wire 48 is connected to each of the contact terminals 44.

  As shown in FIGS. 1 and 3, the lead wire 48 in the gas sensor 1 is electrically connected to a sensor control device 6 that controls gas detection in the gas sensor 1. The sensor control device 6 performs electrical control in the gas sensor 1 in cooperation with an engine control device that controls combustion operation in the engine. The sensor control device 6 includes a measurement circuit 61 that measures a current flowing between the detection electrode 311 and the reference electrode 312, an application circuit 62 that applies a voltage between the detection electrode 311 and the reference electrode 312, and a heating element 34. An energization circuit for energizing is formed. The sensor control device 6 may be constructed in the engine control device.

(Production method)
In manufacturing the sensor element 2, the solid electrolyte body 31, the insulators 33 </ b> A and 33 </ b> B, the diffusion resistance portion 32, the heating element 34, and the like are laminated to form a laminated body, and this laminated body is heated and sintered. The detection electrode 311 and the reference electrode 312 are formed by printing (applying) a paste material containing platinum, a solid electrolyte, a solvent or the like on the solid electrolyte body 31 and sintering the laminate of the sensor element 2. Is formed by sintering.

(Function and effect)
In the gas sensor 1 of this embodiment, the cross-sectional area of the cross-section of the front end side duct portion 361 including the rear end position 312A in the longitudinal direction L of the reference electrode 312 is that of the rear end side duct portion 362 including the rear end opening 360. The cross-sectional area of the cross section is 0.2 times or more and less than 1 time. With this configuration, it is possible to appropriately secure the amount of the reference gas A introduced into the reference electrode 312 and to increase the heat conductivity of the sensor element 2.

  Specifically, the cross-sectional area S2 of the cross section in the rear end opening 360 of the rear end side duct portion 362 is set to a size that can sufficiently introduce the reference gas A to the reference electrode 312. Then, the cross-sectional area S1 of the front end side duct portion 361 including the rear end position 312A of the reference electrode 312 heats the solid electrolyte body 31, the detection electrode 311 and the reference electrode 312 by the heat generating portion 341 of the heat generating body 34. At this time, the reference gas duct 36 is set as a heat insulating portion, and the cross-sectional area is set so as to alleviate the heat transfer from the heat generating portion 341 to the solid electrolyte body 31 and the like. Thereby, while ensuring the introduction amount of the reference gas A to the reference electrode 312 appropriately, the heat conductivity of the sensor element 2 can be improved.

  At the distal end portion of the sensor element 2 of the present embodiment, the volume of the second insulator 33B is increased by the smaller volume of the distal end side duct portion 361, and the detection electrode 311 and the reference electrode 312 are increased by the heating portion 341 of the heating element 34. And the part of the solid electrolyte body 31 located between each electrode 311 and 312 becomes easy to be heated. Thereby, the time for activating the sensor element 2 by the heating element 34 can be shortened.

  Further, the front end side duct part 361 is located at a position facing the heat generating part 341, and the reference gas A in the front end side duct part 361 is generated by the heat generating part 341 compared to the reference gas A in the rear end side duct part 362. Heated to high temperature. The diffusion coefficient of the reference gas A in the front end side duct portion 361 is larger than the diffusion coefficient of the reference gas A in the rear end side duct portion 362. The diffusion coefficient determines the amount of oxygen ions that move from the reference electrode 312 to the detection electrode 311 via the solid electrolyte body 31 when the reference gas A is supplied to the reference electrode 312. That is, the greater the diffusion coefficient, the greater the amount of oxygen ion movement.

  Therefore, even if the cross-sectional area of the cross section of the distal end side duct portion 361 is reduced, it is possible to appropriately ensure the amount of oxygen ion movement from the reference electrode 312 to the detection electrode 311. In particular, when the air-fuel ratio of the internal combustion engine obtained from the detection target gas G is in a rich state, sufficient oxygen ions for chemically reacting unburned gas or the like in the detection electrode 311 are transferred from the reference electrode 312 to the detection electrode 311. Can be made. Thereby, even if the cross-sectional area of the cross-section of the distal end side duct portion 361 is small, the movement of oxygen ions from the reference electrode 312 to the detection electrode 311 is not so restricted, and the electrochemical reaction in the sensor element 2 is maintained well. be able to.

  Therefore, according to the gas sensor 1 of the present embodiment, the amount of the reference gas A introduced into the reference electrode 312 can be appropriately ensured, and the heat conductivity of the sensor element 2 can be enhanced.

(Cross sectional area S1, S2)
The cross-sectional area S1 of the cross section at the rear end position 312A of the reference electrode 312 of the front end side duct part 361 is 0.2 times or more the cross sectional area S2 of the cross section of the rear end opening 360 of the rear end side duct part 362. . When the ratio S1 / S2 of the cross-sectional areas is less than 0.2 times, it is difficult to sufficiently maintain the introduction amount of the reference gas A to the reference electrode 312. The value “0.2 times or more” is obtained based on the following reason.

The value “0.2 times or more” is based on a difference in diffusion coefficient due to a temperature difference between the atmosphere as the reference gas A in the front duct portion 361 and the atmosphere as the reference gas A in the rear end opening 360. Asked. The diffusion coefficient of gas is mainly determined as a function of temperature. When gas diffusion coefficient is D [m ² / s], Boltzmann constant is k [JK ⁻¹ ], temperature is T [K], and molecular radius is a [nm], D = 2 / (3a ² ) × (KT / π) ^3/2 .

  FIG. 7 shows the result of calculating the diffusion coefficient D when the temperature T of the atmosphere as the reference gas A is changed from normal temperature (20 ° C.) to 700 ° C. using this diffusion coefficient equation. In the gas sensor 1, air at normal temperature (about 20 ° C.) is introduced from the rear end opening 360 of the rear end side duct portion 362, and the air in the front end side duct portion 361 is heated to 700 ° C. by the heat generating portion 341 of the heating element 34. Heated to a degree.

  In the figure, the horizontal axis represents the temperature of the atmosphere introduced into the reference gas duct 36, and the vertical axis represents the diffusion coefficient ratio to show how much the diffusion coefficient changes with respect to the atmospheric temperature. . The diffusion coefficient ratio indicates how many times the diffusion coefficient at each temperature is higher than the reference diffusion coefficient with the atmospheric diffusion coefficient at 20 ° C. as the reference diffusion coefficient.

  When the change of the diffusion coefficient was confirmed, the atmospheric diffusion coefficient at 700 ° C. was about 5.2 times the atmospheric diffusion coefficient at 20 ° C. As a result, the cross-sectional area S1 of the front end side duct portion 361 at the rear end position 312A of the reference electrode 312 is 1/5 of the cross sectional area S2 of the rear end opening portion 360 of the rear end side duct portion 362. The value “0.2 times or more” was derived.

<Embodiment 2>
In the present embodiment, a form of the sensor element 2 different from that of the first embodiment is shown.
As shown in FIG. 8, the width in the width direction W of the front end side duct portion 361 including the rear end position 312A of the reference electrode 312 is larger than the width in the width direction W of the rear end side duct portion 362 including the rear end opening 360. Can also be formed small. The cross-sectional area of the cross section of the front end side duct portion 361 is such that the width in the width direction W of the front end side duct portion 361 is smaller than the width in the width direction W of the rear end side duct portion 362. It becomes smaller than the cross-sectional area of the cross section.

  Further, the duct boundary portion 363 is formed as a portion where the wall surface 339A in the width direction W of the reference gas duct 36 changes in a step shape. The duct boundary portion 363 can also be formed as an end portion on the distal end side L1 in the longitudinal direction L of a portion where the wall surface 339A in the width direction W of the reference gas duct 36 changes in an inclined manner. Further, the distal end side duct portion 361 can be formed as a portion where both the thickness in the stacking direction D and the width in the width direction W of the reference gas duct 36 are reduced.

  Other configurations, operational effects, and the like in the gas sensor 1 of the present embodiment are the same as those of the first embodiment. Also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those in the first embodiment.

<Embodiment 3>
This embodiment also shows a form of the sensor element 2 different from the first embodiment.
As shown in FIG. 9, the thickness in the stacking direction D of the front end portion of the sensor element 2 can be made smaller than the thickness in the stacking direction D of the rear end portion. Specifically, the sensor element 2 may have the element boundary portion 24 in which the cross-sectional area of the cross section changes in the vicinity of the rear end position 312A of the reference electrode 312 in the longitudinal direction L or on the rear end side L2. Good. The cross-sectional area of the cross section of the distal end side element portion 22 located on the distal end side L1 in the longitudinal direction L from the element boundary portion 24 is the rear end located on the rear end side L2 in the longitudinal direction L from the element boundary portion 24 The cross sectional area of the lateral cross section of the side element portion 23 can be made smaller.

  The element boundary portion 24 can be formed as a step portion in which the cross-sectional area of the cross section of the front end side element portion 22 abruptly decreases from the cross sectional area of the cross section of the rear end side element portion 23. The outer surface 330 in the stacking direction D of the second insulator 33B in the front end side duct portion 361 is more solid than the outer surface 330 in the stacking direction D of the second insulator 33B in the rear end side duct portion 362. It is formed in the position near. In other words, the cross-sectional area of the cross section of the front end side element portion 22 is such that the outer surface 330 of the second insulator 33B in the front end side element portion 22 is the second insulator in the rear end side element portion 23 in the stacking direction D. By being closer to the solid electrolyte body 31 than the outer surface 330 of 33B, the cross-sectional area of the cross section of the rear end side element part 23 can be made smaller.

  Further, as shown in the figure, the cross-sectional area of the cross section of the front end side element portion 22 is such that the thickness of the front end side element portion 22 in the stacking direction D is smaller than the thickness of the rear end side element portion 23 in the stacking direction D. Thus, the cross-sectional area of the transverse section of the rear end side element portion 23 can be made smaller. In other words, the thickness in the stacking direction D of the front end side element portion 22 is larger than the thickness in the stacking direction D of the rear end side element portion 23 by the notch 221 formed in the outer surface 330 of the second insulator 33B. It can be formed small. The heat generating part 341 can be embedded in the second insulator 33B at a position adjacent to the stacking direction D where the cutout part 221 is formed.

  In this embodiment, the volume of the second insulator 33B in the distal end side element portion 22 is reduced, and the heat capacity of the sensor element 2 is reduced. Therefore, the power consumption when heating the solid electrolyte body 31 etc. by the heat generating body 34 can be reduced. Further, the heat generating portion 341 of the heat generating element 34 can be disposed at a position close to the detection electrode 311 and the reference electrode 312, so that the sensor element 2 can be activated early by the heat generating element 34.

  Other configurations, operational effects, and the like in the gas sensor 1 of the present embodiment are the same as those of the first embodiment. Also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those in the first embodiment.

<Embodiment 4>
This embodiment also shows a form of the sensor element 2 different from the first embodiment.
As shown in FIG. 10, the heating element 34 can also be embedded in the first insulator 33A. Thereby, the heat generating part 341 of the heat generating body 34 can be arranged at a position closer to the detection electrode 311 and the reference electrode 312. Therefore, it is possible to further reduce the power consumption when heating the solid electrolyte body 31 and the like by the heating element 34, and to further accelerate the sensor element 2 by the heating element 34. Further, even when the heating element 34 is embedded in the first insulator 33A, the notch 221 can be formed in the second insulator 33B at the tip of the sensor element 2, and the notch 221 is formed. You can not.

  Further, as shown in FIG. 11, between the front end side duct portion 361 and the rear end side duct portion 362 of the reference gas duct 36, the wall surface 339 of the front end side duct portion 361 in the stacking direction D and the rear end side duct portion 362. A duct inclined surface 364 that is connected to the wall surface 339 in the stacking direction D and is inclined with respect to the longitudinal direction L may be formed. In this case, the duct boundary portion 363 can be an end portion on the distal end side L1 in the longitudinal direction L of the duct inclined surface 364 as a bent portion.

  Further, as shown in the figure, between the front end side element portion 22 and the rear end side element portion 23 of the sensor element 2, the outer side surface 330 of the front end side element portion 22 in the stacking direction D and the rear end side element portion. The element inclination surface 25 which inclines with respect to the elongate direction L which connects the outer side surface 330 of the lamination direction D of 23 may be formed. In this case, the element boundary portion 24 can be an end portion on the distal end side L1 in the longitudinal direction L of the element inclined surface 25 as a bent portion.

  Moreover, although illustration is abbreviate | omitted, the edge part of the duct inclined surface 364 and the duct boundary part 363 are good also as a curved-surface-shaped edge part besides making it a bending part. Further, the end portion of the element inclined surface 25 and the element boundary portion 24 may be curved end portions in addition to the bent portion. The curved end indicates that a corner that becomes a bent portion is rounded into an R shape.

  Other configurations, operational effects, and the like in the gas sensor 1 of the present embodiment are the same as those of the first embodiment. Also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those in the first embodiment.

  The structure of the sensor element 2 shown in the first to fourth embodiments is an example of a structure that the sensor element 2 can take. The structure of the sensor element 2 can be a structure by various combinations shown in the first and second embodiments. Further, depending on the application of the gas sensor 1, the sensor element 2 in which the gas chamber 35 and the diffusion resistance portion 32 are not provided can be used.

<Confirmation test>
In this confirmation test, a conventional sensor element (comparative product) in which the front end side duct portion 361 and the rear end side duct portion 362 are not formed in the reference gas duct 36 and the sensor element 2 shown in the first embodiment (implemented product 1). ), And the sensor element 2 (embodiment 2) in which the heating element 34 is embedded in the second insulator 33B and the notch 221 is formed in the second insulator 33B, as shown in the third embodiment. The power consumption required for the heating element 34 was compared for the sensor element 2 (embodiment 3) in which the heating element 34 was embedded in the first insulator 33A shown in the fourth embodiment.

  Each sensor element was heated by the heating element 34 so that the operating temperature at the time of use of the gas sensor 1 was 700 ° C. As a result of confirming the power consumption of the heating element 34, the power consumption of the comparative sensor element was 9.3W, whereas the power consumption of the implementation product 1 was 8.5W and the power consumption of the implementation product 2 was 7. The power consumption of 2W and the implementation product 3 was 5.8W. In the working products 1 to 3, it was found that the effect of reducing the power consumption of the sensor element 2 can be obtained by forming the reference gas duct 36 in a state in which the cross-sectional area of the cross section changes. Further, in the products 2 and 3, it was found that the power consumption of the heating element 34 is further reduced by bringing the heating part 341 of the heating element 34 closer to the detection electrode 311 and the reference electrode 312.

  The present invention is not limited only to each embodiment, and further different embodiments can be configured without departing from the scope of the invention. Further, the present invention includes various modifications, modifications within an equivalent range, and the like.

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Sensor element 31 Solid electrolyte body 311 Detection electrode 312 Reference electrode 312A Rear end position 33A, 33B Insulator 34 Heat generating element 36 Reference gas duct 360 Rear end opening

Claims (11)

In the gas sensor (1) including the long plate-shaped sensor element (2),
The sensor element is
A solid electrolyte body (31) having oxygen ion conductivity;
A detection electrode (311) provided at a front end side position in the longitudinal direction (L) of the sensor element on the first main surface (301) exposed to the detection target gas (G) in the solid electrolyte body;
A reference electrode (312) provided at the front end side position in the longitudinal direction on the second main surface (302) exposed to the reference gas (A) in the solid electrolyte body;
Insulators (33A, 33B) stacked on the solid electrolyte body;
A heat generating part (341) embedded in the insulator and disposed at a position facing the detection electrode and the reference electrode, and a lead connected to the rear end side in the longitudinal direction of the heat generating part. A heating element (34) having a portion (342);
The insulator is formed at a position adjacent to the second main surface of the solid electrolyte body from the rear end opening (360) in the longitudinal direction to the arrangement position of the reference electrode, and the rear end opening. A reference gas duct (36) into which the reference gas is introduced from the section,
The cross-sectional area (S1) of the cross section perpendicular to the longitudinal direction of the reference gas duct at the rear end position (312A) of the reference electrode in the longitudinal direction is the cross sectional area (S1) of the reference gas duct at the rear end opening. A gas sensor having a cross-sectional area (S2) of a cross section of 0.2 times or more and less than 1 time. When the direction in which the solid electrolyte body and the insulator are stacked in the cross section is the stacking direction (D),
2. The gas sensor according to claim 1, wherein a thickness of the reference gas duct in the stacking direction at the rear end position of the reference electrode is smaller than a thickness of the reference gas duct in the stacking direction at the rear end opening. In the cross section, when the direction in which the solid electrolyte body and the insulator are laminated is a lamination direction (D), and a direction orthogonal to the lamination direction is a width direction (W),
The gas sensor according to claim 1 or 2, wherein a width in the width direction of the reference gas duct at the rear end position of the reference electrode is smaller than a width in the width direction of the reference gas duct at the rear end opening. . The reference gas duct has a duct boundary part (363) in which the cross-sectional area of the cross section changes at a position on the rear end side in the longitudinal direction from the rear end position of the reference electrode,
The cross-sectional area of the cross section of the front end side duct portion (361) located on the front end side in the longitudinal direction from the duct boundary portion is a rear end located on the rear end side in the longitudinal direction from the duct boundary portion. The gas sensor according to any one of claims 1 to 3, wherein the gas sensor is smaller than a cross-sectional area of the cross-section of the end duct portion (362).   The said duct boundary part is formed as a level | step-difference part which the cross-sectional area of the said cross section of the said front end side duct part reduces rapidly from the cross-sectional area of the said cross section of the said rear end side duct part. Gas sensor.   The gas sensor according to claim 4, wherein the duct boundary portion is formed as a bent portion in which a wall surface (339) of the front end side duct portion is bent with respect to a wall surface (339) of the rear end side duct portion. The cross-sectional area of the transverse section of the rear end side duct portion is constant in the longitudinal direction,
The gas sensor according to any one of claims 4 to 6, wherein a cross-sectional area of the cross section in at least a part of the front end side duct portion is reduced toward the front end side in the longitudinal direction. The sensor element has an element boundary (24) in which a cross-sectional area of the cross section changes in the vicinity of the rear end position of the reference electrode in the longitudinal direction or on the rear end side,
The cross-sectional area of the cross-section of the distal-side element portion (22) located on the distal end side in the longitudinal direction from the element boundary portion is a rear end located on the rear end side in the longitudinal direction from the element boundary portion. The gas sensor of any one of Claims 1-7 smaller than the cross-sectional area of the said cross section of an end side element part (23). The sensor element is
A gas chamber (35) formed at a position adjacent to the first main surface of the solid electrolyte body in the insulator and at a position where the detection electrode is disposed;
A diffusion resistance portion (32) provided in the insulator in communication with the gas chamber, for introducing the detection target gas into the gas chamber at a predetermined diffusion rate;
The insulator includes a first insulator (33A) stacked on the first main surface of the solid electrolyte body, and a second insulator (33B) stacked on the second main surface of the solid electrolyte body. Consists of
The cross-sectional area (S3) of the cross section of the tip side element part is the outer surface (330) of the second insulator in the tip side element part in the stacking direction (D) of the solid electrolyte body and the insulator. ) Is closer to the solid electrolyte body than the outer surface (330) of the second insulator in the rear end side element portion, and thus, more than the cross sectional area (S4) of the transverse section of the rear end side element portion. The gas sensor according to claim 8, which is small.   The gas sensor according to claim 9, wherein the heat generating portion is embedded in the second insulator in the tip side element portion.   The gas sensor according to claim 9, wherein the heat generating portion is embedded in the first insulator in the tip side element portion.

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