JP2010271283A - NOx SENSOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NO<SB>x</SB>sensor that reduces the used amount of conductive material and improves the detection accuracy of the NO<SB>x</SB>concentration by individually controlling the temperatures of a first pumping cell and a second pumping cell by forming two heaters. <P>SOLUTION: This NO<SB>x</SB>sensor 200 includes a first measuring chamber 16, the first pumping cell 11, a second measuring chamber 18, a second pumping cell 13 for detecting a specific gas component, a first heater 51 including a first heating part 51a, a first positive electrode voltage supplying lead 51b, and a first negative electrode voltage supplying lead 51c, and a second heater 52 including a second heating part 52a, a second positive electrode voltage supplying lead 52b, and a second negative electrode voltage supplying lead 52c. The first pumping cell and the second pumping cell do not overlap in the direction perpendicular to the longitudinal direction, and at least a part of the first positive electrode voltage supplying lead and second positive electrode voltage supplying lead is common with at least a part 61 of the first negative electrode voltage supplying lead and second negative electrode voltage supplying lead. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a NO _x sensor that detects the concentration of NO _x contained in combustion gas and exhaust gas of, for example, a combustor or an internal combustion engine.

With the tightening of exhaust gas regulations for internal combustion engines such as automobiles, it is required to reduce the amount of nitrogen oxides (NO _x ) in the exhaust gas, and NO _x sensors that can directly measure the NO _x concentration have been developed.
The NO _x sensor includes a sensor element having one or more cells formed by forming a pair of electrodes on the surface of an oxygen ion conductive solid electrolyte body such as zirconia, and is in communication with a gas space to be measured. The oxygen concentration in the measurement chamber is measured, and the oxygen in the first measurement chamber is controlled (pumped and pumped out) by the first pumping cell so that the first measurement chamber has a predetermined oxygen concentration. Further, the gas to be measured whose oxygen concentration is controlled flows from the first measurement chamber to the second measurement chamber, and a constant voltage is applied to the second pumping cell to convert NO _x contained in the gas to be measured into N ₂ and O _2. Decompose into _two . At this time, the NO _x concentration in the gas to be measured is detected by measuring the second pump current flowing between the pair of electrodes of the second pumping cell.

Usually, one heater is provided in such a NO _x sensor, the temperature of the sensor element is controlled. Meanwhile, the first pumping cell and the second pumping cell are arranged so as not to overlap in the longitudinal direction of the sensor element, while the heater is arranged along the longitudinal direction of the sensor element. For this reason, in the longitudinal direction of the sensor element, there is a temperature gradient that becomes a low temperature from the first pumping cell toward the second pumping cell. Normally, in the NO _x sensor, the temperature of the second pumping cell is estimated by presuming the offset amount due to this temperature gradient and the NO _x concentration is detected, but the environment surrounding the NO _x sensor (exhaust gas) When the temperature gradient varies depending on the temperature and gas flow rate, etc.), there is a possibility that the detection error of the NO _x concentration temperature changes of the second pumping cell occurs.

  For this reason, a technique has been developed in which the first pumping cell and the second pumping cell are separately controlled by two heaters (see Patent Document 1).

JP 2000-206085 A

  However, in the case of the technique described in Patent Document 1, an additional conductive path (lead portion and electrode pad) is necessary to supply voltage to the two heaters, and an expensive conductive material such as Pt is consumed correspondingly. As a result, there was a problem of increasing costs.

That is, according to the present invention, by providing two heaters, the temperature of the first pumping cell and the second pumping cell is separately controlled to improve the detection accuracy of the NO _x concentration and reduce the amount of conductive material used. An object of the present invention is to provide a NO _x sensor capable of reducing the cost.

In order to solve the above-described problem, the NO _x sensor of the present invention includes a first measurement chamber that is partitioned between two layers of solid electrolyte bodies that are stacked with a gap therebetween and that introduces a gas to be measured from the outside, A first pump for controlling an oxygen partial pressure in the first measurement chamber, comprising an inner first pump electrode disposed facing the measurement chamber and a first counter electrode serving as a counter electrode of the inner first pump electrode A cell, a second measurement chamber that communicates with the first measurement chamber and is partitioned from the surroundings and introduces a gas to be measured with a controlled oxygen partial pressure from the first measurement chamber; and is provided in the second measurement chamber. A second pumping cell for detecting the NO _x concentration in the gas to be measured in the second measurement chamber, and the solid state second pump electrode and a second counter electrode serving as a counter electrode of the inner second pump electrode, and the solid Arranged in the stacking direction of the electrolyte body, the first heat generating portion and the same A first heater for heating the first pumping cell having a first positive voltage supply lead and a first negative voltage supply lead connected to each other, and disposed in the stacking direction of the solid electrolyte body. And a second heater for heating the second pumping cell, each having a second positive voltage supply lead and a second negative voltage supply lead connected to each other, wherein the stacking direction of the solid electrolyte body is a longitudinal direction. a NO _x sensor, formation region of the formation region and the second pumping cell of the first pumping cell does not overlap in the longitudinal direction perpendicular the first heating portion and the second heating section the The first heat generating portion and the first pumping cell forming region do not overlap in a direction perpendicular to the longitudinal direction, and have an overlap in a direction perpendicular to the longitudinal direction, and the second heat generating portion and the A region where two pumping cells are formed overlaps in a direction perpendicular to the longitudinal direction, and at least part of the first positive voltage supply lead and the second positive voltage supply lead, or the first negative voltage supply lead In addition, at least a part of the second negative voltage supply lead is common.

Thus, when a part of the first positive voltage supply lead and the second positive voltage supply lead, or the first negative voltage supply lead and the second negative voltage supply lead are common, a lead having a wide line width, The electrode pad at the base end of the lead can also be used as a common part, and the amount of conductive material (especially noble metal) used can be reduced correspondingly, thereby reducing the cost.
In addition, since the formation region of the first pumping cell and the formation region of the second pumping cell do not overlap in the direction perpendicular to the longitudinal direction, both the cells are separated in the longitudinal direction, and the first heater and the second heater respectively The temperature can be controlled separately, and the detection accuracy of the NO _x concentration can be improved.
Furthermore, in the direction perpendicular to the longitudinal direction, the first heat generating portion and the first pumping cell forming region overlap, and the second heat generating portion and the second pumping cell forming region overlap, Heat generated by the first heat generating portion and the second heat generating portion is efficiently transmitted to the first pumping cell and the second pumping cell, respectively, and the temperature of each cell can be accurately controlled.

The first heater and the second heater may be positioned on opposite sides of the first counter electrode and a direction perpendicular to the longitudinal direction with respect to the first measurement chamber.
If it does in this way, manufacture will become easy rather than providing a 1st heater and a 2nd heater in the 1st counter electrode side which needs to touch air. When the second pumping cell is opposite to the first counter electrode voltage with respect to the first measurement chamber, the first heater and the second heater are closer to the second pumping cell than the first pumping cell, and the NOx concentration is increased. Thus, the second pumping cell that performs the detection can be heated more accurately, and the detection accuracy of the NOx concentration can be improved.

The first heater and the second heater may be located on the same layer in the longitudinal direction.
In this way, since each heater can be manufactured on one layer at a time by a printing method or the like, productivity is improved. Further, since the heaters are not separated in the direction perpendicular to the longitudinal direction, a through hole for sharing a part of the lead of each heater becomes unnecessary, and the conductive material necessary for the through hole conductor can be reduced.

The first heater and the second heater are located on different layers in the longitudinal direction, and the second heater is separated from the second measurement chamber by the first heater in a direction perpendicular to the longitudinal direction. It may be in a distant position.
In this case, in the direction perpendicular to the longitudinal direction, the second heater is further away from the second measurement chamber than the first heater, thereby suppressing the leakage current of the second heater from affecting the second pumping cell. Can do.

The first heat generating portion and the formation region of the second pumping cell may not overlap with a direction perpendicular to the longitudinal direction.
In this case, since the first heat generating portion is far from the second pumping cell, the influence of the leakage current of the first heater on the second pumping cell is small, and the temperature control of each heater is less likely to interfere, and NO. The measurement accuracy of _x is improved.

According to the present invention, by providing two heaters, the temperature of the first pumping cell and the second pumping cell is separately controlled to improve the detection accuracy of the NO _x concentration, and the use amount of the conductive material is reduced. _{An x} sensor is obtained.

It is a sectional view taken along the longitudinal direction of the NO _x sensor according to the first embodiment of the present invention. It is a sectional view taken along the longitudinal direction of the NO _x sensor element and the heater. Is a sectional view taken along the longitudinal direction of the NO _x sensor element and the heater NO _x sensor has according to the second embodiment of the present invention. It is a figure which shows the positional relationship of the longitudinal direction of the formation area of a 1st pumping cell and a 2nd pumping cell, and a 1st heat generating part and a 2nd heat generating part.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 shows a cross-sectional view along the longitudinal direction of a NO _x sensor 200 according to the first embodiment of the present invention. The NO _x sensor 200 extends in the axial direction (longitudinal direction of the NO _x sensor 200: vertical direction in the figure) with a cylindrical metal shell 138 having a threaded portion 139 formed on the outer surface for fixing to the exhaust pipe. a NO _x sensor element 10 forming a plate-like shape, a NO _x cylindrical ceramic sleeve 106 which is disposed so as to surround the radial periphery of the sensor element 10, the inner wall surface of the contact insertion holes 168 penetrating in the axial direction NO an insulating contact member 166 is arranged in a state surrounding the periphery of the rear end portion of the _x sensor element, the six connection terminals 110 (FIG. 1 that is disposed between the NO _x sensor element 10 and the insulating contact portion 166, 2 are shown).

The metal shell 138 has a substantially cylindrical shape having a through hole 154 that penetrates in the axial direction, and a shelf 152 that protrudes radially inward of the through hole 154. Further, the metal shell 138 has the NO _x sensor element 10 at the front end side disposed outside the front end side of the through hole 154, and the electrode terminal portions 220 and 221 are disposed outside the rear end side of the through hole 154. keeping. Further, the shelf portion 152 is formed as an inwardly tapered surface having an inclination with respect to a plane perpendicular to the axial direction.

In addition, inside the through hole 154 of the metal shell 138, an annular ceramic holder 151, powder filling layers 153 and 156 (hereinafter also referred to as talc rings 153 and 156) surrounding the radial direction of the NO _x sensor element 10. ) And the above-described ceramic sleeve 106 are laminated in this order from the front end side (lower side in FIG. 1) to the rear end side (upper side in FIG. 1). A caulking packing 157 is disposed between the ceramic sleeve 106 and the rear end portion 140 of the metal shell 138, and a talc ring 153 is disposed between the ceramic holder 151 and the shelf 152 of the metal shell 138. In addition, a metal holder 158 for holding the ceramic holder 151 and maintaining hermeticity is disposed. Note that the rear end portion 140 of the metal shell 138 is crimped so as to press the ceramic sleeve 106 toward the distal end side via the crimping packing 157.
In this embodiment, the NO _x sensor element 10 is fixed by the ceramic holder 151 or the like that forms the casing of the NO _x sensor 200, and the NO _x sensor element 10 protrudes from the tip side of the ceramic holder 151. Accordingly, a portion of the NO _x sensor element 10 that is at the same position as the tip surface of the ceramic holder 151 is defined as a fixed end 10b.

On the other hand, as shown in FIG. 1, a metal (for example, stainless steel or the like) having a plurality of holes and covering the protruding portion of the NO _x sensor element 10 on the outer periphery of the front end side (downward in FIG. 1) of the metallic shell 138 ) A double external protector 142 and an internal protector 143 are attached by welding or the like.

An outer cylinder 144 is fixed to the outer periphery of the rear end side of the metal shell 138. In addition, six lead wires 146 (FIG. 1) that are electrically connected to the electrode terminal portions 220 and 221 of the NO _x sensor element 10 are respectively provided in the opening on the rear end side (upper side in FIG. 1) of the outer cylinder 144. In this case, a grommet 150 in which a lead wire insertion hole 161 is formed is disposed.

An insulating contact member 166 is disposed on the rear end side (upper side in FIG. 1) of the NO _x sensor element 10 protruding from the rear end portion 140 of the metal shell 138. The insulating contact member 166 is disposed around the electrode terminal portions 220 and 221 formed on the rear end surface of the NO _x sensor element 10. The insulating contact member 166 is formed in a cylindrical shape having a contact insertion hole 168 penetrating in the axial direction, and is provided with a flange portion 167 protruding radially outward from the outer surface. The insulating contact member 166 is disposed inside the outer cylinder 144 by the flange portion 167 coming into contact with the outer cylinder 144 via the holding member 169.

Next, the structure of the NO _x sensor element 10 and the heaters (the first heater 51 and the second heater 52) will be described with reference to a sectional view 2 along the longitudinal direction. In the present invention, the term "longitudinal", a longitudinal direction of the NO _x sensor element, and a solid electrolyte body of the NO _x sensor element 10 (in this example, the first solid electrolyte body 11a~ third solid electrolyte A direction parallel to the stacking direction of the bodies 13a).
Also, the left side of FIG. 2 (the first pumping cell 11 side) is referred to as a "front end (side)" of the NO _x sensor element 10, the right side in FIG. 2 (second pumping cell 13 side) of the NO _x sensor element 10 ' This is referred to as “rear end (side)”.

2A, the NO _x sensor element 10 includes a first solid electrolyte body 11a, an insulating layer 14a, a second solid electrolyte body 12a, an insulating layer 14b, a third solid electrolyte body 13a, and insulating layers 14c and 14d. It has a structure laminated in this order. A first measurement chamber 16 is defined between the first solid electrolyte body 11a and the second solid electrolyte body 12a, and the first diffusion resistor 15a disposed at the left end (inlet) of the first measurement chamber 16 is interposed therebetween. A measurement gas GM is introduced from the outside.
A second diffusion resistor 15b is disposed at the end of the first measurement chamber 16 opposite to the inlet, and communicates with the first measurement chamber 16 on the right side of the first measurement chamber 16 via the second diffusion resistor 15b. A second measurement chamber 18 is defined. The second measurement chamber 18 passes through the second solid electrolyte body 12a and is formed between the first solid electrolyte body 11a and the third solid electrolyte body 13a.

As will be described in detail later, two elongated plate-like first heaters 51 and 52 extending along the longitudinal direction of the NO _x sensor element 10 are embedded on the same layer between the insulating layers 14c and 14d. Has been. The first heater 51, second heater 52, NO _x 2 one heater controller connected to the sensor 200 (not shown) each be separately controlled by a predetermined first pumping cell 11 and the second pumping cell 13, respectively The temperature is controlled (more specifically, the temperature gradient from the first pumping cell 11 to the second pumping cell 13 is constant).
The insulating layers 14a to 14d are mainly made of alumina, and the first diffusion resistor 15a and the second diffusion resistor 15b are made of a porous material such as alumina. The first heater 51 and the second heater 52 are made of platinum or the like. A known heater control unit (for example, a transistor and a resistor that is energized and controlled by pulse width modulation from the CPU of the controller) can be used.

  The first pumping cell 11 includes a first solid electrolyte body 11a mainly composed of zirconia having oxygen ion conductivity, an inner first pump electrode 11c disposed so as to sandwich the first solid electrolyte body 11a, and a first counter electrode serving as a counter electrode ( An outer first pump electrode 11 b, and the inner first pump electrode 11 c faces the first measurement chamber 16. Both the inner first pump electrode 11c and the outer first pump electrode 11b are mainly made of platinum, and the surface of each electrode is covered with a protective layer 11e, 11d made of a porous body.

The oxygen concentration detection cell 12 includes a second solid electrolyte body 12a mainly composed of zirconia, and a detection electrode 12b and a reference electrode 12c disposed so as to sandwich the second solid electrolyte body 12a. The detection electrode 12b is an inner first pump electrode 11c. It faces the first measurement chamber 16 on the rear end side. Both the detection electrode 12b and the reference electrode 12c are mainly made of platinum.
The insulating layer 14b is cut out so that the reference electrode 12c in contact with the second solid electrolyte body 12a is disposed inside, and the cutout portion is filled with a porous body to form the reference oxygen chamber 17. . Then, a weak constant value of current is passed through the oxygen concentration detection cell 12 in advance to send oxygen from the first measurement chamber 16 into the reference oxygen chamber 17 to be an oxygen reference.

The second pumping cell 13 includes a third solid electrolyte body 13a mainly composed of zirconia, an inner second pump electrode 13b and a counter electrode disposed on the surface of the third solid electrolyte body 13a facing the second measurement chamber 18. And a second counter electrode (counter electrode second pump electrode 13c). Both the inner second pump electrode 13b and the counter second pump electrode 13c are mainly composed of platinum.
In addition, the counter electrode 2nd pump electrode 13c is arrange | positioned at the cutout part of the insulating layer 14b on the 3rd solid electrolyte body 13a, and faces the reference | standard oxygen chamber 17 facing the reference electrode 12c.

  Further, the formation region 11S of the first pumping cell 11 and the formation region 13S of the second pumping cell 13 do not overlap in a direction perpendicular to the longitudinal direction. This is because the temperature of the first pumping cell 11 and the second pumping cell 13 can be separately controlled by the first heater 51 and the second heater 52 extending in the longitudinal direction, respectively. This is to separate them in the longitudinal direction.

Here, the formation region 11S of the first pumping cell 11 includes the inner first pump electrode 11c, the first counter electrode 11b, and the first solid electrolyte body 11a serving as a conductive path sandwiched between the electrodes 11c and 11b. This is the total area projected in the longitudinal direction. For example, in FIG. 2, the inner first pump electrode 11c and the first counter electrode 11b are opposed to the front and back of the first solid electrolyte body 11a, and the electrodes 11c and 11b are substantially the same size. The formation region 11S is equal to a region obtained by projecting the inner first pump electrode 11c (first counter electrode 11b) in the longitudinal direction.
Similarly, the formation region 13S of the second pumping cell 13 includes the inner second pump electrode 13b, the second counter electrode 13c, and the third solid electrolyte body 13a serving as a conductive path sandwiched between the electrodes 13c and 13b. This is the total area projected in the longitudinal direction. For example, in FIG. 2, since the inner second pump electrode 13b and the second counter electrode 13c are both separated from the back surface of the third solid electrolyte body 13a, oxygen ions are sandwiched between the electrodes 13c and 13b. It flows through the third solid electrolyte body 13a (becomes a conductive path). Therefore, formation area 13S of the second pumping cell 13, NO _x from the tip of the second counter electrode 13c on the front end side of the sensor element 10 (the left side in FIG. 2), NO _x sensor element the rear end of the inner second 10 The portion reaching the rear end (right side in FIG. 2) of the pump electrode 13b is equal to the region projected in the longitudinal direction.
And each formation area 11S and 13S is arrange | positioned at intervals in the longitudinal direction, and it turns out that the 1st pumping cell 11 and the 2nd pumping cell 13 are isolate | separated in the longitudinal direction.

FIG. 2B shows the planar shape and arrangement state of the first heater 51 and the second heater 52. Note that the straight line between FIGS. 2A and 2B corresponds to the positional relationship between each configuration of the NO _x sensor element 10 and each of the heaters 51 and 52.
2B, the first heater 51 includes a first heat generating portion 51a, and linear first positive voltage supply leads 51b and first negative voltage supply leads 51c that are connected to the first heating portions 51a and extend in the longitudinal direction. ing. The first heat generating portion 51a includes an outermost linear resistance portion 51a1 connected to the tip of the first positive voltage supply lead 51b, and a bent portion 51a2 bent in a U shape in the longitudinal direction opposite from the tip of the outermost linear resistance portion 51a1. And a meandering path 51a3 that reciprocates twice along the longitudinal direction from the bent part 51a2, a bent part 51a4 that is bent in a U-shape from the tip of the meandering path 51a3 in the longitudinal direction, and a rear end of the bent part 51a4. And an outermost linear resistance portion 51a5. The rear end of the outermost linear resistance portion 51a5 is connected to the front end of the first negative voltage supply lead 51c.
The rear end of the first positive voltage supply lead 51b forms a wide rectangular electrode pad 51d. On the other hand, the rear end of the first negative voltage supply lead 51c is connected to the second negative voltage supply lead 52c of the second heater 52, as will be described later, and both are integrated.
In the present invention, a conductor path other than the heat generating portion (that is, a portion having a lower resistance than the heat generating portion) in the heater is referred to as a “lead” including the electrode pad.

Since the first heat generating portion 51a is narrower than the first positive voltage supply lead 51b and the first negative voltage supply lead 51c, when the first heat generating portion 51a is energized between the first positive voltage supply lead 51b and the first negative voltage supply lead 51c. The first heat generating portion 51a having a high resistance generates heat.
The first heat generating portion 51a and the formation region 11S of the first pumping cell 11 overlap in a direction perpendicular to the longitudinal direction. Here, “having an overlap” means that at least a part of the first heat generating portion 51a and the formation region 11S need only overlap. Since the first heat generating portion 51a and the formation region 11S overlap each other, the heat generated by the first heat generating portion 51a is efficiently transmitted to the first pumping cell 11 so that the first pumping cell 11 can be heated (temperature control). ing.
In FIG. 2, the first heat generating portion 51a is located inside the formation region 11S.

Similarly, the second heater 52 includes a second heat generating portion 52a, and linear second positive voltage supply leads 52b and second negative voltage supply leads 52c that are connected to the second heating portions 52a and extend in the longitudinal direction. The second heater 52 is sandwiched between the first positive voltage supply lead 51b and the first negative voltage supply lead 51c, and is located on the rear end side of the first heat generating portion 51a and is surrounded by the first heater 51. Yes.
The second heat generating portion 52a includes an outermost linear resistance portion 52a1 connected to the tip of the second positive voltage supply lead 52b, and a bent portion 52a2 bent in a U-shape in the longitudinal direction opposite from the tip of the outermost linear resistance portion 52a1. And a meandering path 52a3 that reciprocates once in the longitudinal direction from the bent part 52a2, a bent part 52a4 that bends in a U-shape from the tip of the meandering path 52a3 in the longitudinal direction, and a rear end of the bent part 52a4. An outermost linear resistance portion 52a5. The rear end of the outermost linear resistance portion 52a5 is connected to the tip of the second negative voltage supply lead 52c. The rear end of the second positive voltage supply lead 52b forms a wide rectangular electrode pad 52d.
The second positive voltage supply lead 52b extends obliquely with respect to the longitudinal direction so that the rear end side faces inward so that the electrode pad 52d positioned inside the electrode pad 51d does not interfere with the electrode pad 51d.

On the other hand, the second negative voltage supply lead 52c extends obliquely with respect to the longitudinal direction so that the rear end side faces outward, and approaches the first negative voltage supply lead 51c. The rear ends of the second negative voltage supply lead 52c and the first negative voltage supply lead 51c are in contact with each other to form a wide common pad 61.
Thus, since at least a part (the rear end portion in the example of FIG. 2) of the first negative voltage supply lead 51c and the second negative voltage supply lead 52c is common, the lead portion or electrode pad having a wide line width is used. Thus, the amount of expensive conductive material such as Pt can be reduced by that amount, thereby reducing the cost. For example, in the example of FIG. 2, the first negative voltage supply lead 51c and the second negative voltage supply lead 52c are in contact with each other in the longitudinal direction to form a common pad 61, and the line width of the common pad 61 is the first negative voltage supply. Since the line width of the lead 51c and the second negative voltage supply lead 52c is the sum, only the common pad 61 functions as an external connection terminal (electrode pad). Therefore, it is not necessary to separately provide a wide electrode pad at the rear end of the first negative voltage supply lead 51c or the second negative voltage supply lead 52c, and the amount of conductive material used is reduced by the amount of these unnecessary electrode pads. It will be.

Since the second heat generating part 52a is narrower than the second positive voltage supply lead 52b and the second negative voltage supply lead 52c, it is between the second positive voltage supply lead 52b and the second negative voltage supply lead 52c. By energizing, the second heat generating part 52a having a high resistance generates heat.
The second heat generating portion 52a and the formation region 13S of the second pumping cell 13 overlap in a direction perpendicular to the longitudinal direction. Here, “having an overlap” means that at least a part of the second heat generating portion 52a and the formation region 13S need only overlap. Since the second heat generating portion 52a and the formation region 13S overlap, the heat generated by the second heat generating portion 52a is efficiently transmitted to the second pumping cell 13 so that the second pumping cell 13 can be heated (temperature control). ing.
In FIG. 2, the second heat generating portion 52a is located inside the formation region 13S.

In addition, the first heater 51 and the second heater 52 have the first negative voltage supply lead 51c and the second negative voltage supply lead 52c serving as the ground as a common potential (ground), respectively, and the first positive voltage supply lead 51b. And the second positive voltage supply lead 52b are separated. For this reason, the first positive voltage supply lead 51b and the second positive voltage supply lead 52b are connected to different heater control units, and the ground is shared, so that the first heater 51 and the second heater 52 are connected. Thus, the temperature of the first pumping cell and the second pumping cell can be controlled separately to improve the detection accuracy of the NO _x concentration.
More specifically, by controlling the first heater 51 and the second heater 52 separately, the temperature gradient from the first pumping cell 11 to the second pumping cell 13 can be controlled to be constant. In this case, the temperature of the NO _x sensor element 10 is measured based on the internal resistance (impedance) of the oxygen concentration detection cell 12, and the first heater 51 and the second heater 52 are controlled according to this temperature.
The first pumping cell 11 has a large area and is on the tip side of the NO _x sensor element 10 and is easily cooled by the gas to be measured. For this reason, the heat generation amount of the first heat generating portion 51a of the first heater 51 is increased so that the first pumping cell 11 can be controlled independently (specifically, the first heat generating portion 51a is reciprocated three times in the longitudinal direction). (I fold it in three and make it meander).
In contrast, since the oxygen concentration detection cell 12 and the second pumping cell 13 are smaller than the first pumping cell 11, the temperatures of the oxygen concentration detection cell 12 and the second pumping cell 13 are collectively controlled by the second heater 52. ing.

  In the first embodiment, the first heater 53 and the second heater 54 are both located on the same layer in the longitudinal direction (between the insulating layers 14c and 14d). For this reason, since each heater 53 and 54 can be manufactured on one layer at a time by the printing method etc., productivity improves. Further, since the heaters 53 and 54 are not separated in the direction perpendicular to the longitudinal direction, a through hole for conducting the heater is not necessary, and the conductive material necessary for the through hole conductor can be reduced.

Next, an example of the operation of the NO _x sensor element 10 will be described. First, when the engine is started and supplied with electric power from an external power source, the heaters 51 and 52 are operated via a predetermined control circuit, and the first pumping cell 11, the oxygen concentration detection cell 12, and the second pumping cell 13 are connected. Heat to activation temperature. When each of the cells 11 to 13 is heated to the activation temperature, the first pumping cell 11 converts excess oxygen in the gas to be measured (exhaust gas) GM flowing into the first measurement chamber 16 into the inner first pump electrode. Pump from 11c toward the first counter electrode 11b.
At this time, the oxygen concentration in the first measurement chamber 16 corresponds to the interelectrode voltage (inter-terminal voltage) Vs of the oxygen concentration detection cell 12, so that the interelectrode voltage Vs is a constant voltage V1 (for example, 425 mV). By controlling the inter-electrode voltage (inter-terminal voltage) Vp1 of the first pumping cell 11 so as to become, the oxygen concentration in the first measurement chamber 16 is adjusted to such an extent that NO _x is not decomposed.

The gas to be measured GN whose oxygen concentration is adjusted further flows toward the second measurement chamber 18. Then, as the interelectrode voltage (terminal voltage) Vp2 of the second pumping cell 13, a constant voltage Vp2 (control of the oxygen concentration detection cell 12) such that the NO _x gas in the measurement gas GN is decomposed into oxygen and N ₂ gas. By applying a voltage higher than the voltage value (for example, 450 mV), NO _x is decomposed into nitrogen and oxygen. Then, the second pump current Ip2 flows through the second pumping cell 13 so that oxygen generated by the decomposition of NO _x is pumped out of the second measurement chamber 18. In this case, between the second pump current Ip2 and the concentration of NO _x because there is a linear relationship, it is possible to detect the concentration of NO _x in the gas to be measured by detecting the Ip2.

Next, the NO _x sensor 200C according to the second embodiment of the present invention will be described. Since the NO _x sensor 200C is the same as that of the first embodiment except that the configuration of the NO _x sensor element 10C is different, the description of the NO _x sensor 200C is omitted.
FIG. 3 is a cross-sectional view along the longitudinal direction showing the structure of the NO _x sensor element 10C and the heaters (the first heater 55 and the second heater 56). Since the NO _x sensor element 10C other than the first heater 55 and the second heater 56 is the same as the NO _x sensor element 10 in the first embodiment, the same reference numerals are given to the same components. Description is omitted.

In FIG. 3A, an insulating layer 14h is laminated under the insulating layer 14d, and the insulating layers 14c, 14d, and 14h are in this order in the second pumping cell 13 (more specifically, the third solid electrolyte body 13a). It is laminated on the lower surface.
A long plate-shaped first heater 55 extending along the longitudinal direction of the NO _x sensor element 10C is embedded between the insulating layers 14c and 14d, and the first pumping cell 11 positioned above the first heater 55 is disposed. It comes to heat.
On the other hand, a long plate-like second heater 56 extending along the longitudinal direction of the NO _x sensor element 10 _{</ b} > C is embedded between the insulating layers 14 d and 14 h, and the second pumping cell located above the second heater 56. 13 is heated.
The first heater 55 and the second heater 56 are separately controlled by two heater control units (not shown) connected to the NO _x sensor 200C, and each of the first pumping cell 11 and the second pumping cell 13 is determined in advance. The temperature is controlled (more specifically, the temperature gradient from the first pumping cell 11 to the second pumping cell 13 is constant).
Furthermore, a through hole 71 extending from the first heater 55 to the second heater 56 (that is, penetrating the insulating layer 14d) is drilled in a direction perpendicular to the longitudinal direction (the stacking direction of the layers). As will be described later, the first negative voltage supply lead 55 c of the first heater 55 and the second negative voltage supply lead 56 c of the second heater 56 are electrically connected via a through-hole conductor formed in the through hole 71. Connected.

FIG. 3B shows the planar shape and arrangement state of the first heater 55 and the second heater 56. Note that the straight line between FIGS. 3A and 3B corresponds to the positional relationship between each component of the NO _x sensor element 10C and each of the heaters 55 and 56.
In FIG. 3B, the first heater 55 has substantially the same shape as the first heater 51 in the first embodiment, and is connected to the first heat generating portion 55 a and the same as the first heater 51. The first positive voltage supply lead 55b and the first negative voltage supply lead 55c are provided. In the same manner as the first heater 51, the first heat generating portion 55a has an outermost linear resistance portion 55a1 connected to the tip of the first positive voltage supply lead 55b, and a longitudinal direction opposite from the tip of the outermost linear resistance portion 55a1. A bent portion 55a2 bent in a U shape, a meandering path 55a3 reciprocating in the longitudinal direction from the bent portion 55a2, a bent portion 55a4 bent in a U shape in the longitudinal direction opposite from the tip of the meandering path 55a3, and a bent portion And an outermost linear resistance portion 55a5 connected to the rear end of 55a4. The rear end of the outermost linear resistance portion 55a5 is connected to the front end of the first negative voltage supply lead 55c.
The rear end of the first positive voltage supply lead 55b forms a wide rectangular electrode pad 55d. On the other hand, the rear end of the first negative voltage supply lead 55c is connected to the second negative voltage supply lead 56c of the second heater 56, as will be described later.

Since the first heat generating portion 55a is narrower than the first positive voltage supply lead 55b and the first negative voltage supply lead 55c, if the first heat generating portion 55a is energized between the first positive voltage supply lead 55b and the first negative voltage supply lead 55c. The first heat generating portion 55a having a high resistance generates heat.
Further, the first heat generating portion 55a and the formation region 11S of the first pumping cell 11 overlap in a direction perpendicular to the longitudinal direction, and the heat generated by the first heat generating portion 55a is efficiently transmitted to the first pumping cell 11. The first pumping cell 11 can be heated (temperature control).
In FIG. 3, the front end side of the first heat generating portion 55a protrudes outside (the front end side) from the front end of the forming region 11S, while the rear end side of the first heat generating portion 55a is inward from the rear end of the forming region 11S. positioned.

The second heater 56 has substantially the same shape as the second heater 52 in the first embodiment. The second heater 56a and the second positive voltage supply lead 56b and the second negative voltage supply lead connected to the second heat generator 56a, respectively. 56c. The second heater 56 is sandwiched between the first positive voltage supply lead 55b and the first negative voltage supply lead 55c, and is located on the rear end side of the first heat generating portion 55a, and is surrounded by the first heater 55. Yes.
The second heat generating portion 56a includes an outermost straight resistance portion 56a1 connected to the tip of the second positive voltage supply lead 56b, and a bent portion 56a2 bent in a U shape in the longitudinal direction opposite from the tip of the outermost straight resistance portion 56a1. And a meandering path 56a3 that reciprocates once in the longitudinal direction from the bent part 56a2, a bent part 56a4 that is bent in a U-shape from the tip of the meandering path 56a3 in the longitudinal direction, and a rear end of the bent part 56a4. An outermost linear resistance portion 56a5. The rear end of the outermost linear resistance portion 56a5 is connected to the front end of the second negative voltage supply lead 56c. The rear end of the second positive voltage supply lead 56b forms a wide rectangular electrode pad 56d.
The second positive voltage supply lead 56b extends obliquely with respect to the longitudinal direction so that the rear end side faces inward so that the electrode pad 56d located inside the electrode pad 55d does not interfere with the electrode pad 55d.

On the other hand, the second negative voltage supply lead 56c extends obliquely with respect to the longitudinal direction so that the rear end side faces outward, and overlaps the first negative voltage supply lead 55c in a direction perpendicular to the longitudinal direction. A through-hole connection is made between the rear end of the first negative voltage supply lead 55c and the second negative voltage supply lead 56c located immediately below the first negative voltage supply lead 55c. A common pad 65 having a wide base end 56c is formed.
In this way, a part of the first negative voltage supply lead 55c and the second negative voltage supply lead 56c (in the example of FIG. 3, the rear end from the through-hole connecting portion) is common, so that the lead portion having a wide line width is used. The electrode pad can also be used, and the amount of expensive conductive material such as Pt used can be reduced by that amount to reduce the cost. For example, in the example of FIG. 3, the first negative voltage supply lead 55c and the second negative voltage supply lead 56c are through-hole connected, and one common pad 65 is formed on the rear end side from the through-hole connection portion. Therefore, it is not necessary to separately provide a wide electrode pad on the rear end side of the first negative voltage supply lead 55c, and the amount of conductive material used is reduced by the amount of electrode pads that are no longer necessary.

Since the second heat generating portion 56a is narrower than the second positive voltage supply lead 56b and the second negative voltage supply lead 56c, it is between the second positive voltage supply lead 56b and the second negative voltage supply lead 56c. By energizing, the second heat generating portion 56a having a high resistance generates heat.
Further, the second heat generating portion 56a and the formation region 13S of the second pumping cell 13 overlap in a direction perpendicular to the longitudinal direction, and the heat generated by the second heat generating portion 56a is efficiently transmitted to the second pumping cell 13. The second pumping cell 13 can be heated (temperature control).
Further, the front end side of the second heat generating portion 56a protrudes outside (the front end side) from the front end of the forming region 13S, while the rear end side of the second heat generating portion 56a is located inside the rear end of the forming region 13S. .

The first heater 55 and the second heater 56 have the first negative voltage supply lead 55c and the second negative voltage supply lead 56c serving as the ground as a common potential (ground), respectively, and the first positive voltage supply lead 55b and the second negative voltage supply lead 56c, respectively. Two positive voltage supply leads 56b are separated. For this reason, the first positive voltage supply lead 55b and the second positive voltage supply lead 56b are connected to different heater control units, and the ground is shared, so that the first heater 55 and the second heater 56 are connected. Thus, the temperature of the first pumping cell and the second pumping cell can be controlled separately to improve the detection accuracy of the NO _x concentration.
More specifically, by controlling the first heater 55 and the second heater 56 separately, the temperature gradient from the first pumping cell 11 to the second pumping cell 13 can be controlled to be constant.

In the second embodiment, the second heater 56 and the first heater 55 are on the same side in the direction perpendicular to the longitudinal direction across the first measurement chamber 16 (below the first measurement chamber 16 in FIG. 3). ). Further, in the direction perpendicular to the longitudinal direction, the second heater 56 is positioned below the first heater 55 and is far from the second measurement chamber 18.
In this way, the second heater 56 and the first heater 55 are positioned on the same side across the first measurement chamber 16, thereby shortening the length of the through hole 71 and using a conductive material used for the through hole conductor. The amount can be reduced. Further, the leakage current of the second heater 56 is prevented from affecting the second pumping cell 13 by moving the second heater 56 away from the second measurement chamber 18 from the first heater 55 in the direction perpendicular to the longitudinal direction. can do.

Next, referring to FIG. 4, in the first embodiment, the positional relationship in the longitudinal direction between the formation regions 11S and 13S of the cells 11 and 13 and the first and second heat generating portions 51a and 52a is changed. The operation of the case will be described.
FIG. 4A shows a case where the front and rear ends of the first heat generating portion 51a protrude from the formation region 11S and the rear end of the first heat generating portion 51a extends to the inside of the formation region 13S. On the other hand, in Fig.4 (a), the front-and-rear end of the 2nd heat generating part 52a is located inside the formation area 13S. In the case of FIG. 4A, since the first heat generating portion 51a is wider than the formation region 11S, the first pumping cell 11 can be sufficiently heated, but the first heat generating portion 51a is close to the formation region 13S (first Since one heat generating portion 51a overlaps the formation region 13S in a direction perpendicular to the longitudinal direction), the influence of the leakage current of the first heater 51 on the second pumping cell 13 may increase.

In FIG. 4B, the front and rear ends of the first heat generating portion 51a are all located inside the forming region 11S, while the tip of the second heat generating portion 52a protrudes from the forming region 13S and extends to the inside of the forming region 11S. Indicates the case. In the case of FIG. 4B, since the second heat generating part 52a is wider than the formation region 13S, the second pumping cell 13 can be sufficiently heated. Further, since the first heat generating portion 51a is far from the formation region 13S (because the first heat generating portion 51a does not overlap the formation region 13S in the direction perpendicular to the longitudinal direction), the second pumping cell 13 due to the leakage current of the first heater 51 is used. The measurement accuracy of NO _x is improved.
Although the second heat generating part 52a extends to the inside of the formation region 11S, since a relatively large current flows through the first pumping cell 11 itself, the leakage current of the second heater 52 causes the first pumping cell 11 to The impact is small.

FIG. 4C shows a case where the front and rear ends of the first heat generating portion 51a and the front and rear ends of the second heat generating portion 52a are located inside the formation regions 11S and 13S, respectively. Also in the case of FIG. 4C, since the first heat generating portion 51a is far from the formation region 13S (because the first heat generating portion 51a does not overlap the formation region 13S in the direction perpendicular to the longitudinal direction), the leakage of the first heater 51 The influence of the current on the second pumping cell 13 is small, and the measurement accuracy of NO _x is improved. Further, since the first heat generating part 51a and the second heat generating part 52a do not protrude outside the formation regions 11S and 13S, the first pumping cell 11 and the second pumping cell 13 are moved by the first heater 51 and the second heater 52, respectively. Individual control with high accuracy.

It goes without saying that the present invention is not limited to the above-described embodiment, and extends to various modifications and equivalents included in the spirit and scope of the present invention. For example, the planar shape of the heater is not limited to the above. Further, at least a part of the first positive voltage supply lead and the second positive voltage supply lead may be made common instead of the first negative voltage supply lead and the second negative voltage supply lead.
In the above embodiment, the solid electrolyte layer constituting the NO _x sensor element is three layers, but the solid electrolyte layer may be two layers. A NO _x sensor element structure having two solid electrolyte layers is described in, for example, Japanese Patent Application Laid-Open No. 2004-354400 (FIG. 3).
In the above embodiment, by converting the second pump current Ip2 when the control voltage of the second pumping cell Vp2 to concentration of NO _x, but to measure the voltage Vp2 of the second pumping cell, the second measurement the Vp2 indicating the electromotive force corresponding to the oxygen partial pressure in the chamber may be in terms of concentration of NO _x. Further, the detection electrode of the oxygen concentration detection cell may also be used as the inner electrode of the first pump cell.

200, 200C NO _x sensor 10, 10C NO _x sensor element 11 First pumping cell 11S First pumping cell formation region 12 Oxygen concentration detection cell 13 Second pumping cell 13S Second pumping cell formation region 11a to 13a First solid Electrolyte body to third solid electrolyte body 11b First counter electrode (outer first pump electrode)
11c Inner first pump electrode 13b Inner second pump electrode 13c Counter electrode second pump electrode 16 First measurement chamber 18 Second measurement chamber 51, 55 First heater 51a, 55a First heating part 51b, 55b First positive voltage supply lead 51c, 55c First negative voltage supply lead 52, 56 Second heater 52a, 56a Second heating part 52b, 56b Second positive voltage supply lead 52c, 56c Second negative voltage supply lead 61, 65 Common pad (common part of lead) )

Claims (5)

A first measurement chamber that is partitioned between two layers of solid electrolyte bodies that are stacked at an interval and introduces a gas to be measured from the outside;
An inner first pump electrode disposed facing the first measurement chamber; and a first counter electrode serving as a counter electrode of the inner first pump electrode; and for controlling an oxygen partial pressure in the first measurement chamber A first pumping cell;
A second measurement chamber that communicates with the first measurement chamber and that is partitioned from the surroundings and introduces a gas to be measured with the oxygen partial pressure controlled from the first measurement chamber;
And a second counter electrode serving as a counter electrode of the second inner provided in the measurement chamber a second pumping electrode and the inner second pump electrode, for detecting the concentration of NO _x in the measurement gas in said second measurement chamber A second pumping cell;
A first heater disposed in the stacking direction of the solid electrolyte body and provided with a first heat generating part and a first positive voltage supply lead and a first negative voltage supply lead connected to the first heat generating part, and heating the first pumping cell; ,
A second heater disposed in the stacking direction of the solid electrolyte body and provided with a second heat generating part and a second positive voltage supply lead and a second negative voltage supply lead connected to the second heat generating part, respectively, and heating the second pumping cell; the a, a stacking direction of the solid electrolyte body a NO _x sensor whose longitudinal direction,
The formation region of the first pumping cell and the formation region of the second pumping cell do not overlap in a direction perpendicular to the longitudinal direction,
The first heat generating part and the second heat generating part do not overlap in a direction perpendicular to the longitudinal direction, and the first heat generating part and the formation region of the first pumping cell overlap in a direction perpendicular to the longitudinal direction. The second heat generating portion and the formation region of the second pumping cell are overlapped in a direction perpendicular to the longitudinal direction,
An NO _x sensor in which at least a part of the first positive voltage supply lead and the second positive voltage supply lead, or at least a part of the first negative voltage supply lead and the second negative voltage supply lead are common.   2. The NOx sensor according to claim 1, wherein the first heater and the second heater are located on a side opposite to the first counter electrode and a direction perpendicular to the longitudinal direction with respect to the first measurement chamber. Wherein the first heater and the second heater, NO _x sensor according to claim 1 or claim 2 positioned in the longitudinal direction of the same layer. The first heater and the second heater are located on different layers in the longitudinal direction, and the second heater is separated from the second measurement chamber by the first heater in a direction perpendicular to the longitudinal direction. NO _x sensor according to claim 1 or claim 2 located far. 5. The NO _x sensor according to claim 1, wherein the first heat generating portion and the formation region of the second pumping cell do not overlap in a direction perpendicular to the longitudinal direction.

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