JP2007010564A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent detection precision as a gas sensor from getting worse by a leak current in a heater. <P>SOLUTION: Since a heating pattern 12 in a heater pattern 10 is formed to avoid an area overlapped with a detection space 230 on a layered face, an electrode faced to at least the detection space 230, i.e. one electrode 22 in a sensor cell 20 is formed into structure not overlapped with the heating pattern 12 on the layered face. The one electrode 22 in the sensor cell 20 is a longer distant apart from the heating pattern 12 to bring high insulation resistance, compared with that when overlapped with the heating pattern 12 on the layered face, and the detection precision is hardly affected by the leak current from the heating pattern 12 as a result thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas sensor that detects the concentration of a specific component contained in a gas to be detected.

  Conventionally, a gas sensor used to detect the concentration of a specific component contained in a gas to be detected introduces the gas to be detected, in which oxygen is exhausted by a pump cell, into a detection space, and the energized state of a sensor cell provided in this detection space A corresponding parameter, specifically, a current value flowing between a pair of electrodes constituting the sensor cell is detected as a parameter indicating the concentration of a specific component contained in the gas to be detected.

At this time, in order for the pump cell and the sensor cell to function properly, it is necessary to heat the cell to a temperature at which these cells are activated. Therefore, the gas sensor must be provided with a heater portion formed with a heater pattern. Is common (see, for example, Patent Document 1).
JP 2004-157063 A

  However, when the heater unit is provided as described above, leakage current from the heater pattern formed in the heater unit adversely affects oxygen discharge by the pump cell and parameter detection by the sensor cell. There is a fear.

  For example, the pump cell has a structure in which the discharge of oxygen is controlled by energization between a pair of electrodes. Therefore, if the leakage current from the heater pattern is superimposed on this energization current, the discharge of oxygen is suppressed. There is a risk of being. In addition, since the sensor cell has a structure in which the current value flowing between the pair of electrodes is detected as a parameter, if the leakage current from the heater pattern is superimposed on this current, it is larger than the parameter that should be detected originally. Alternatively, a small parameter may be detected as the concentration of the specific component.

  This is because a pump cell has a current value on the order of mA and is generally large (or can be increased) so as not to be affected by the leakage current. Although not a problem, in the sensor cell, the current value at the time of detection is on the order of μA, which is much smaller than the current value in the pump cell, so even a slight leakage current is greatly affected.

  Thus, the leakage current due to the heater has a large effect on the current value upon detection by the sensor cell, resulting in a problem that the detection accuracy as a gas sensor is lowered.

  The present invention has been made to solve such a problem, and an object of the present invention is to prevent the detection accuracy of the gas sensor from being lowered due to the leakage current of the heater.

  In order to solve the above-mentioned problem, a gas sensor according to claim 1 has a first solid electrolyte part, a pump cell, a second solid electrolyte part, a sensor cell, and a heater part. Of these, the first solid electrolyte part is a layered member. The pump cell includes a pair of electrodes, and one of the electrodes faces an introduction space into which a gas to be detected is introduced from the outside, and the introduction is performed by energization between the pair of electrodes. Oxygen contained in the gas to be detected in the space can be discharged from the introduction space to the other electrode side through the first solid electrolyte portion. The second solid electrolyte part is the same layer as the first solid electrolyte part constituting the pump cell or a layer laminated on the first solid electrolyte part. The sensor cell includes a pair of electrodes, and one of the electrodes faces a detection space connected to the introduction space, and in the detection space based on an energization state between the pair of electrodes. The concentration of the specific component contained in the gas to be detected can be detected. And the heater part was comprised by the layered ceramic base | substrate laminated | stacked on the said 1st solid electrolyte part and the said 2nd solid electrolyte part by the heat_generation | fever pattern and a pair of lead pattern connected to the both ends. A heater pattern is embedded, and the heat generation pattern is formed so as to avoid a region overlapping the detection space on a surface intersecting with the stacking direction of each part.

  In the gas sensor configured as described above, a region where the heating pattern of the heater section overlaps the detection space on the surface (hereinafter referred to as “laminated surface”) intersecting the stacking direction of each layer (solid electrolyte portion, heater portion) is avoided. Therefore, at least an electrode facing the detection space, that is, one electrode in the sensor cell does not overlap the heat generation pattern on the laminated surface.

  As a result, compared with the case where one electrode in the sensor cell overlaps the heat generation pattern on the laminated surface, the insulation resistance increases as the distance from the heat generation pattern increases, resulting in leakage current from the heater pattern. Can be less affected.

  The sensor cell in this configuration is capable of detecting the concentration of the specific component based on the energization state between the pair of electrodes. Here, in order to detect the concentration of the specific component based on the energization state, For example, a configuration may be employed in which a parameter corresponding to a current value energized between a pair of electrodes or a voltage value between the electrodes is detected as the concentration of the specific component.

  Also, the heat generation pattern of the heater part is formed so as to avoid the area that overlaps the detection space on the surface intersecting the stacking direction of each part. The heat generation pattern is detected when the gas sensor is projected in the stacking direction of each part. It is a state that does not overlap with space.

Moreover, the heater part mentioned above should just have the heat_generation | fever pattern formed avoiding the area | region which overlaps with detection space in a lamination | stacking surface, and the shape of the specific heat_generation | fever pattern is not specifically limited.
However, as described in claim 2, it is preferable that the heater portion is formed with the heat generation pattern avoiding a region overlapping with the detection space and the sensor cell on a surface intersecting a stacking direction of each portion. .

  With this configuration, since the heat generation pattern of the heater portion is formed so as to avoid a region overlapping the detection space and the sensor cell on the stacked surface, both the detection space and the sensor cell, that is, the electrode of the sensor cell, have a heat generation pattern on the stacked surface. It becomes a structure that does not overlap.

  As a result, the pair of electrodes in the sensor cell has not only one electrode but also the other electrode, because the insulation resistance increases as the distance from the heat generation pattern increases. It can be made difficult to receive.

  Further, in the gas sensor described above, if at least a part of each of the pump cell and the sensor cell is arranged so as not to overlap in a plane intersecting with the stacking direction of each part, Configure as described.

  4. The gas sensor according to claim 3, wherein the heat generation pattern in the heater portion is a position where a heat generation region of the heater portion on a surface intersecting a stacking direction of each portion is distributed around an electrode of a pump cell facing the introduction space. It is formed to be in a relationship.

  If comprised in this way, since the heat_generation | fever area | region of the heater part in a lamination | stacking surface distributes centering on introduction space, the temperature by the side of a pump cell becomes high between introduction space and detection space, ie, between a pump cell and a sensor cell. Such a temperature difference can be created.

  In general, in a gas sensor having a pump cell and a sensor cell, the pump cell generally requires a higher temperature in order to appropriately activate the sensor cell. This is because it is necessary to sufficiently secure the pumping capacity for discharging oxygen contained in the gas to be detected introduced into the introduction space in the pump cell. For this reason, providing a heater unit without taking this into consideration makes it impossible to make the relationship between the active state and temperature of each cell appropriate, resulting in a decrease in detection accuracy as a gas sensor. Will be a factor.

  For example, in the gas sensor (gas sensor element) of Patent Document 1, the heat generation pattern (heater electrode 14) regularly formed along the longitudinal direction of the heater portion (heater sheet) has a detection space (second internal space 7b) on the laminated surface. (See, for example, FIG. 5), the heat generation pattern generates heat so as to uniformly heat the entire laminated surface. Therefore, the pump cell (oxygen pump cell 2) and sensor cell (4) of the gas sensor are also heated uniformly, and there is a possibility that the relationship between the active state of each cell and the temperature cannot be made appropriate. This is because this Patent Document 1 does not consider that the pump cell requires a higher temperature than the sensor cell.

  In this regard, in the case of the present gas sensor that can realize the distribution of the heat generation area as described above, the heat generation area of the heater portion on the laminated surface is distributed around the introduction space, so that the introduction space, Since a temperature difference that increases the temperature on the pump cell side can be created, the relationship between the active state of each cell and the temperature can be made appropriate. Such a temperature difference can be increased as the overlap between the pump cell and the sensor cell is small, and as the pump cell and the sensor cell are separated from each other on the laminated surface.

Embodiments of the present invention will be described below with reference to the drawings.
1. Overall configuration 1-1. First configuration (first embodiment)
The gas sensor 1 in the present embodiment is configured as a NOx sensor for detecting the concentration of nitrogen oxides (hereinafter referred to as “NOx”) contained in exhaust gas in an internal combustion engine of an automobile and various combustion devices (for example, a boiler). As shown in FIG. 1, the insulating layer 110, the insulating layer 120, and the solid electrolyte layer 130 constituting the sensor cell 20, the insulating layer 140, and the monitor cell 30 are formed as sheet-like members, respectively. The solid electrolyte layer 150, the insulating layer 160, and the solid electrolyte layer 170, and the insulating layer 180 that constitute the pump cell 40 are stacked in order (in order from bottom to top in FIG. 1). In addition, in the gas sensor of this embodiment, each layer 110,120,130,140,150,160,170,180 has the structure integrated by baking. In addition, the heater pattern 10 is embedded in the ceramic base composed of the insulating layer 110 and the insulating layer 120, thereby forming a heater portion 190.

  Among these, first, the solid electrolyte layer 170 is a sheet member made of a solid electrolyte body mainly composed of zirconia, and the upper and lower surfaces (upper side in FIG. 1) on the tip (left end in FIG. 1, the same applies hereinafter) side of this member. The pump cell 40 is formed by a pair of electrodes 42 and 44 provided so as to sandwich the lower surface (the same applies hereinafter). A lower electrode 42 in the pump cell 40 (the lower in FIG. 1, the same applies hereinafter) is coated with a protective layer 46 made of a porous material. A porous portion 182 made of a porous material is formed in the insulating layer 180 located around the upper electrode 44 (the same applies to the upper portion in FIG. 1 and the same hereinafter).

  Subsequently, the insulating layer 160 located below the solid electrolyte layer 170 is a sheet-like member made of an insulating ceramic such as alumina, and introduces a gas to be detected from the outside of the gas sensor 1 to the tip side thereof. And functions as a spacer for forming an introduction space 210 sandwiched between the solid electrolyte layers 170 and 150.

  The introduction space 210 is formed so that the entire lower electrode 42 of the pump cell 40 faces the leading end side of the introduction space 210. In addition, diffusion resistors 212 and 214 made of a porous body arranged along the direction from the outside of the gas sensor 1 to the introduction space 210 (see the arrow in FIG. 1) are provided at the tip of the introduction space 210. Is provided. In addition, two diffusion resistors 216 and 218 made of a porous body arranged along the longitudinal direction are provided in a region of the introduction space 210 on the rear end (right end in FIG. 1, the same applies hereinafter) side. Thus, the flow of the gas to be detected to the rear end side of the introduction space 210 is restricted.

  Subsequently, the solid electrolyte layer 150 located below the insulating layer 160 is a sheet member made of a solid electrolyte body mainly composed of zirconia, and sandwiches the upper and lower surfaces of the rear end side of the pump cell 40 in this member. A monitor cell 30 is formed by the pair of electrodes 32 and 34 provided. The upper electrode 32 in the monitor cell 30 faces the introduction space 210. Further, the solid electrolyte layer 150 penetrates in a vertical direction into a region corresponding to the space between the diffusion resistors 216 and 218 provided on the rear end side in the introduction space 210 on the rear end side from the monitor cell 30. A through hole 220 is formed.

  Subsequently, the insulating layer 140 located on the lower side of the solid electrolyte layer 150 is a sheet-like member made of an insulating ceramic such as alumina, and this penetrating region is formed in a region corresponding to the through hole 220 in the solid electrolyte layer 150. It functions as a spacer that forms a detection space 230 for detecting the concentration of a gas to be detected (a specific component contained therein) flowing between the introduction space 210 connected via the hole 220. In addition, a porous body 240 filled with a reference gas (oxygen in this embodiment) is provided in a region of the insulating layer 140 facing the lower electrode 34 in the monitor cell 30 as described later. ing. The porous body 240 is made of an insulating ceramic such as alumina.

  Subsequently, the solid electrolyte layer 130 positioned below the insulating layer 140 is a sheet member made of a solid electrolyte body mainly composed of zirconia, and is provided with a pair of gaps provided along the upper surface of the member. A sensor cell 20 is formed by the electrodes 22 and 24. Among these sensor cells 20, one electrode 22 is provided at a position facing the detection space 230, and the other electrode 24 is provided so that a part thereof is in contact with the porous body 240. Note that the sensor cell 20 has a surface (horizontal surface in FIG. 1; hereinafter referred to as “lamination surface”) orthogonal to the stacking direction (vertical direction in FIG. 1; hereinafter the same) of the layers (110 to 180) described above. Only a part of the electrode 24 overlaps the electrodes 42 and 44 of the pump cell 40. That is, one electrode 22 and the detection space 230 of the sensor cell 20 are in a positional relationship that does not overlap the pump cell 40 on the stacked surface.

Subsequently, the insulating layer 120 located below the solid electrolyte layer 130 is a sheet-like member made of an insulating ceramic such as alumina.
The insulating layer 110 located below the insulating layer 120 is obtained by forming the heater pattern 10 mainly composed of Pt on the upper surface of a sheet-like member made of an insulating ceramic such as alumina. As shown in FIG. 2, the heater pattern 10 is formed by bending a path extending along the longitudinal direction (left and right direction in FIG. 2) a plurality of times (in this embodiment, three times) in the width direction (up and down in FIG. 2). Direction) and a pair of lead patterns 18 connected to the end portions 14 and 16 of the heat generation pattern 12 and extending in the longitudinal direction. The heater pattern 10 is formed so that the resistance value per unit length is reduced by making the line width of the heat generation pattern 12 narrower than the line width of the lead pattern 18 in order to concentrate heat generation by the heat generation pattern 12. ing. Then, the rear end portion (the bent portion at the right end in FIG. 2) of the heat generation pattern 12 in the heater pattern 10 is formed so as to be located on the front end side of the region overlapping the detection space 230 on the laminated surface.

  Thus, when the heat generation pattern 12 has a positional relationship that does not overlap the detection space 230 on the stacking surface, the heater 22 has a structure in which one electrode 22 of the sensor cell 20 and the detection space 230 do not overlap the pump cell 40 on the stacking surface. The heat generation region is distributed around the electrode 42 of the pump cell 40 facing the introduction space 210. Thereby, when the heater pattern 10 is energized, the temperature on the pump cell 40 side can be made higher than the temperature on the sensor cell 20 side.

In addition, as the heat generation pattern 12 of the heater pattern 10 described above, a configuration in which the path extending along the longitudinal direction is a pattern extending over the entire width direction while being bent a plurality of times is exemplified, but the detection is performed on the laminated surface. A specific pattern is not particularly limited as long as it is formed so as to avoid a region overlapping with the space 230.
1-2. Second configuration (second embodiment)
The gas sensor in the present embodiment has the same configuration as the gas sensor 1 in the first configuration, but only the heater pattern 10 formed in the insulating layer 110 is different, so only this difference will be described.

  In this embodiment, the insulating layer 110 is obtained by forming the heater pattern 10 on the upper surface of a sheet-like member made of an insulating ceramic. As shown in FIG. 3, the heater pattern 10 includes a heating pattern 12 that extends over the entire width direction while bending a path extending along the longitudinal direction a plurality of times, and a pair of leads connected to the heating pattern 12. Although it is the same as that of 1st Embodiment by the point which has the pattern 18, the rear-end part (bending part of the right end in FIG. 3) of this heat generation pattern 12 is more distal than the area | region which overlaps with the electrode 24 of the sensor cell 20 in a lamination | stacking surface. It is formed to be located on the side. In FIG. 3, the gap between the rear end portion of the heat generation pattern 12 and the region overlapping the electrode 24 on the stacked surface is not provided, but this interval is wide (that is, the heat generation pattern 12 The shape may be such that the rear end portion is shifted to the front end side.

Thus, if the heat generation pattern 12 does not overlap with the electrode 24 of the sensor cell 20 on the stacking surface, most of the sensor cell 20 except for the other electrode 24 of the sensor cell 20 does not overlap with the pump cell 40 on the stacking surface. The heat generation area is distributed around the tip end side of the electrode 22 in the pump cell 40 facing the introduction space 210. Thereby, when the heater pattern 10 is energized, the temperature on the pump cell 40 side can be made higher than the temperature on the sensor cell 20 side.
2. Operation Principle Next, the operation of the gas sensor 1 in the detected gas (NOx gas) atmosphere will be described.

First, the heater unit 190 is heated to a temperature at which each of the pump cell 40, the monitor cell 30, and the sensor cell 20 is activated by energization of the heater pattern 10.
In this state, after the gas to be detected is introduced into the introduction space 210 via the diffusion resistors 212 and 214 (see the arrow in FIG. 2), the upper electrode 44 is connected to the positive electrode between the electrodes 42 and 44 of the pump cell 40. By applying such a voltage, oxygen in the gas to be detected in the introduction space 210 is reduced to oxygen ions, and these oxygen ions are transferred from the lower electrode 42 through the solid electrolyte layer 170 to the upper electrode 44. Discharged to the side.

  At this time, the magnitude of the voltage applied between the electrodes 42 and 44 is controlled based on the operating state of the monitor cell 30. To describe this control in detail, first, by flowing a certain weak current in the direction from the electrode 32 to the electrode 34, oxygen moves from the introduction space 210 to the porous body 240 through the solid electrolyte layer 150, and the porous structure becomes porous. The body 240 becomes a reference oxygen reservoir. The voltage applied between the electrodes 42 and 44 is adjusted so that the electromotive force (voltage value) generated between the electrodes 32 and 34 becomes a predetermined value. That is, based on the voltage output from the monitor cell 30, the value of the current flowing through the pump cell 40 is controlled.

  Thus, the gas to be detected introduced from the outside of the gas sensor 1 reaches the detection space 230 through the through hole 220 of the solid electrolyte layer 150 in a state where oxygen is discharged in the introduction space 210.

Then, by applying a constant voltage between the electrodes 22 and 24 of the sensor cell 20 so that the electrode 24 facing the porous body 240 becomes a positive electrode, a specific component in the gas to be detected in the detection space 230, specifically Specifically, NOx is dissociated into nitrogen (N ₂ ) and oxygen (O ₂ ), and the oxygen is in contact with the porous body 240 through the solid electrolyte layer 130 from the electrode 22 facing the detection space 230. Pumped out. At this time, since the magnitude of the pump current flowing through the sensor cell 20 is proportional to NOx contained in the gas to be detected, if the current value of the pump current flowing through the sensor cell 20 is detected as a parameter indicating the NOx concentration, NOx concentration can be calculated.
3. In the gas sensor 1 configured as described above, since the heat generation pattern 12 of the heater pattern 10 is formed so as to avoid a region overlapping the detection space 230 on the laminated surface, at least an electrode facing the detection space 230 That is, one electrode 22 in the sensor cell 20 has a structure that does not overlap the heat generation pattern 12 on the laminated surface.

  As a result, the one electrode 22 in the sensor cell 20 has a higher insulation resistance due to a greater distance from the heat generation pattern 12 than the case where it overlaps the heat generation pattern 12 on the laminated surface. Can be made less susceptible to the leakage current from

  In particular, when the heater pattern 10 is configured as in the second embodiment, the heat generation pattern 12 is formed so as to avoid a region that overlaps the detection space 230 and the sensor cell 20 on the stacked surface. In addition, the sensor cell 20, that is, both the electrodes of the sensor cell 20, have a structure that does not overlap the heat generation pattern 12 on the laminated surface. For this reason, the pair of electrodes 22 and 24 in the sensor cell 20 also increase the insulation resistance when the distance from the heat generating pattern 12 is increased with respect to the other electrode 24, and as a result, the influence of the leakage current from the heat generating pattern 12 is further increased. It can be made difficult to receive.

  Moreover, in the said embodiment, as a result of arrange | positioning so that most each of the pump cell 40 and the sensor cell 20 may become the positional relationship which does not overlap in a lamination | stacking surface, the heat_generation | fever area | region of the heater part 190 faces the introduction space 210. It is distributed around the electrode 22 of the pump cell 40. Therefore, it is possible to create a temperature difference between the introduction space 210 and the detection space 230, that is, between the pump cell 40 and the sensor cell 20 so that the temperature on the pump cell 40 side becomes high.

  In general, in a gas sensor having a pump cell and a sensor cell, the pump cell generally requires a higher temperature in order to appropriately activate the sensor cell. In the gas sensor of the present embodiment, when the temperature on the sensor cell 20 side is set to 650 ° C. to 770 ° C., the temperature on the pump cell 40 side needs to be higher than this by about 80 ° C. to 130 ° C. Therefore, providing the heater unit 190 without taking such matters into consideration makes it impossible to make the relationship between the active state and temperature of each cell appropriate, and as a result, the detection accuracy as a gas sensor is improved. It will be a factor to reduce.

  However, in the case of the present gas sensor 1 that can realize the distribution of the heat generation area as described above, the heat generation area of the heater unit 190 on the laminated surface is distributed around the introduction space 210, so that the detection space 230, that is, the sensor cell 20 side. Since a temperature difference that increases the temperature on the introduction space 210, that is, on the pump cell 40 side can be created, the relationship between the active state of each cell and the temperature can be made appropriate.

The figure which shows the internal structure of the gas sensor (main part sectional view) The figure which shows the heater pattern of a heater layer (1st Embodiment). The figure which shows the heater pattern of a heater layer (2nd Embodiment).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gas sensor, 10 ... Heater pattern, 12 ... Heat generation pattern, 18 ... Lead pattern, 20 ... Sensor cell, 22, 24 ... Electrode, 30 ... Monitor cell, 32, 34 ... Electrode, 40 ... Pump cell, 42, 44 ... Electrode, 46 ... Protective layer, 110 ... Insulating layer, 120 ... Insulating layer, 130 ... Solid electrolyte layer, 140 ... Insulating layer, 150 ... Solid electrolyte layer, 160 ... Insulating layer, 170 ... Solid electrolyte layer, 180 ... Insulating layer, 182 ... Porous The material part, 190 ... heater part, 210 ... introduction space, 212-218 ... diffusion resistor, 220 ... through-hole, 230 ... detection space, 240 ... porous body.

Claims (3)

A first solid electrolyte portion having a layer shape;
It consists of a pair of electrodes, and one of the electrodes faces the introduction space into which the gas to be detected is introduced from the outside, and the gas to be detected in the introduction space is energized between the pair of electrodes. A pump cell capable of discharging oxygen contained in the other electrode side from the introduction space through the first solid electrolyte part;
A second solid electrolyte part which is the same layer as the first solid electrolyte part constituting the pump cell or a layer laminated on the first solid electrolyte part;
It consists of a pair of electrodes, and one of the electrodes faces the detection space connected to the introduction space, and is included in the gas to be detected in the detection space based on the energization state between the pair of electrodes. A sensor cell capable of detecting the concentration of a specific component
A heater pattern composed of a heat generation pattern and a pair of lead patterns connected to both ends thereof is embedded in a layered ceramic substrate laminated on the first solid electrolyte part and the second solid electrolyte part. And the heater pattern is formed so as to avoid a region overlapping with the detection space on a surface intersecting with the stacking direction of each part. 2. The gas sensor according to claim 1, wherein the heater part is formed with the heat generation pattern avoiding a region overlapping with the detection space and the sensor cell on a surface intersecting a stacking direction of each part. At least a part of each of the pump cell and the sensor cell is arranged so as to be in a positional relationship that does not overlap in a plane intersecting the stacking direction of each part,
The heat generation pattern in the heater section is formed such that the heat generation area of the heater section on the surface intersecting the stacking direction of each section is in a positional relationship distributed around the electrode of the pump cell facing the introduction space. The gas sensor according to claim 1, wherein the gas sensor is provided.

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