JP5209401B2 - Multi-gas sensor and gas sensor control device - Google Patents

Description

  The present invention relates to a gas sensor and a gas sensor control device suitable for detecting a nitrogen oxide concentration and an ammonia concentration in a gas to be measured.

As a gas sensor that measures the concentration of a specific gas in the exhaust gas of an automobile, a NO _x sensor that detects the NO _x concentration in the gas to be measured while using a solid electrolyte body, or a change in impedance or electromotive force between a pair of electrodes An ammonia sensor that detects the concentration of ammonia in a gas to be measured by using it is known.
Further, as a technique for simultaneously measuring the NO _x concentration and the ammonia concentration in the gas to be measured, a step of contacting the gas to be measured with an NH ₃ strong oxidation catalyst to convert ammonia into NO _x and measuring the total NO _x concentration; And measuring the NO _x concentration by contacting part of the gas to be measured with the NH ₃ weak oxidation catalyst to convert a part of ammonia into NO _x , and determining the NO _x concentration from the two detected values in these steps. A technique for calculating the ammonia concentration has been proposed (see Patent Document 1).
Furthermore, NO _x electrode in one sensor, reference electrode, selection electrode, provided the ammonia electrode constitute a plurality of cells (MultiCell), depending on the electromotive force between of the NO _x electrode and the reference electrode caused by the gas introduction There has been proposed an ammonia sensor for measuring an accurate ammonia concentration by changing the ammonia concentration calculation method (according to the presence state of NO _x ) (see Patent Document 2). More specifically, depending on the presence state of the NO _x, ammonia electrode - and the electromotive force between the reference electrode, NO _x poles - used to detect either the ammonia interpolar electromotive force.

JP 2001-133447 A (summary) US Patent Application Publication No. 2007/80074 (Abstract)

However, in the case of the technique described in Patent Document 1, since measurement is performed based on the difference in catalytic ability, the catalytic ability may change due to changes in the measurement environment (temperature, flow rate, pressure, etc.), and accurate measurement may not be possible. Further, when this apparatus is installed in a harsh environment such as in the exhaust gas of an automobile, it is difficult to stably maintain the catalytic ability over a long period of time.
The technique described in Patent Document 2 performs measurement by switching an electrode that detects ammonia. However, when the measurement environment changes, the detection electrode switching condition (switching timing and reference output point setting) that are initially set are changed. Etc.), and it may be difficult to accurately measure ammonia. Furthermore, complicated control of switching of detection electrodes is required.

In addition, when multiple types of gas concentrations are measured by separate sensors, measurement may be affected by differences in gas concentration, temperature distribution, etc. for each sensor.
Accordingly, the present invention has an object to provide a concentration of NO _x and measurable multi-gas sensor and the gas sensor control device of ammonia concentration in a single gas sensor.

In order to solve the above problems, a multi-gas sensor of the present invention is located inside and outside a first measurement chamber and has a pair of first electrodes provided on a first solid electrolyte layer, and the first measurement A first pumping cell for pumping or pumping oxygen in the gas to be measured introduced into the chamber; and a second solid electrolyte layer located inside and outside the NO _x measurement chamber communicating with the first measurement chamber A second pumping current corresponding to the NO _x concentration in the gas to be measured having a pair of second electrodes provided thereon, the oxygen concentration flowing into the NO _x measurement chamber from the first measurement chamber being adjusted; provided a NO _x sensor unit and a second pumping cell flowing between the pair of second electrodes, the ammonia sensor section formed in the NO _x outer surface of the sensor unit has at least a pair of electrodes together, The ammonia sensor The, the diffusion layer covering the pair of electrodes are formed, said a NO _x sensor of the detection start time, when the starting point either early detection starting detection start time of the ammonia sensor unit, the NO _x 90% response time of the sensor unit, the time difference between the 90% response time of the ammonia sensor unit, Ru der than 20% against 90% response time of any of the sensor unit.
With such a configuration, the NO _x sensor unit and the ammonia sensor unit are provided in one sensor, and each sensor unit has almost the same measurement environment (the composition, concentration, temperature, flow rate, pressure, etc. of the gas to be measured). Since it is under, the fall of the gas detection precision by a different measurement environment is suppressed.
That, NO by providing a _x sensor unit and the ammonia sensor unit to one sensor, concentration of NO _x and ammonia concentration without being affected by the measurement environment can be measured simultaneously, the detection of the NO _x concentration and the ammonia concentration Accuracy is improved. Further, since the measurement gas is brought into contact with one sensor, can be almost simultaneously detect NO _x and ammonia, reduction in detection accuracy due to a time lag of both detection is suppressed.
Furthermore, compared with the case where the NO _x sensor unit and the ammonia sensor unit are separate sensors, the cost and the size of the sensor can be reduced.

Further, the ammonia sensor unit, the diffusion layer covering the pair of electrodes are formed, origin and time of the NO _x sensor portion of the detection start, either early detection starting detection start time of the ammonia sensor unit In this case, the time difference between the 90% response time of the NO _x sensor unit and the 90% response time of the ammonia sensor unit is 20% or less with respect to the 90% response time of any sensor unit .
With such a configuration, it is possible to delay the diffusion of the gas to be measured to the ammonia sensor unit, the diffusion rate of the gas to be measured to the ammonia sensor unit located on the outer surface of the NO _x sensor unit, and the NO inside the sensor. _{Since the} measurement gas diffusion rate into the NO _x sensor unit having the _x measurement chamber becomes equal and the difference in detection responsiveness is reduced in each sensor unit, the measurement accuracy is improved.
In particular, even in an environment (transitional environment), such as concentration of NO _x and ammonia concentration in the measurement gas suddenly changes, to reduce the deviation of detection timing the response of the respective sensor portions due to the different, the measurement accuracy It can suppress that it falls.

Further, the ammonia sensor unit is formed with a diffusion layer covering the pair of electrodes, and starts from the detection start time which is the earlier of the detection start time of the NO _x sensor portion or the detection start time of the ammonia sensor portion. The time difference between the detection start time of the NO _x sensor unit and the detection start time of the ammonia sensor unit is 10% or less with respect to the 90% response time of any sensor unit. preferable.
With such a configuration, it is possible to delay the diffusion of the gas to be measured to the ammonia sensor unit, the diffusion rate of the gas to be measured to the ammonia sensor unit located on the outer surface of the NO _x sensor unit, and the NO inside the sensor. _{Since the} measurement gas diffusion rate into the NO _x sensor unit having the _x measurement chamber becomes equal and the difference in detection responsiveness is reduced in each sensor unit, the measurement accuracy is improved.
In particular, even in an environment (transitional environment), such as concentration of NO _x and ammonia concentration in the measurement gas suddenly changes, to reduce the deviation of detection timing the response of the respective sensor portions due to the different, the measurement accuracy It can suppress that it falls.

  The diffusion layer may be made of at least one selected from the group consisting of alumina, spinel, silica alumina, and mullite.

Further, the ammonia sensor unit includes the pair of electrodes and a sensitive unit provided in contact with the pair of electrodes, and detects the ammonia concentration in the gas to be measured by changing the impedance between the pair of electrodes. Also good.
The ammonia sensor unit includes a solid electrolyte layer and the pair of electrodes laminated on both sides or one side of the solid electrolyte layer, and the ammonia concentration in the gas to be measured by the electromotive force change between the pair of electrodes. May be detected.

Furthermore, the gas sensor control device of the present invention includes a correction unit that is connected to the multi-gas sensor and corrects the NO _x concentration output from the NO _x sensor unit based on the ammonia concentration output from the ammonia sensor unit.
With such a configuration, it is possible to accurately measure the ammonia concentration and the NO _x concentration from the gas to be measured in which both ammonia and NO _x exist.

According to the present invention, the NO _x concentration and the ammonia concentration can be measured with one gas sensor.

Hereinafter, embodiments of the present invention will be described.
<First Embodiment>
FIG. 1 shows a cross-sectional view along the longitudinal direction of a multi-gas sensor 200A according to the first embodiment of the present invention. The multi-gas sensor 200A is an assembly in which a multi-gas sensor element unit 100A that detects ammonia concentration and NO _x concentration is assembled. The ammonia sensor 200A includes a plate-like multi-gas sensor element portion 100A extending in the axial direction, a cylindrical metal shell 138 having a screw portion 139 for fixing to the exhaust pipe, and a multi-gas sensor element portion 100A. The cylindrical ceramic sleeve 106 disposed so as to surround the periphery of the gas sensor and the inner wall surface of the contact insertion hole 168 penetrating in the axial direction surround the periphery of the rear end portion of the multi-gas sensor element portion 100A. An insulating contact member 166 and a plurality (only two are shown in FIG. 1) of connection terminals 110 disposed between the multi-gas sensor element unit 100A and the insulating contact unit 166 are provided.

  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 is arranged so that the front end side of the multi-gas sensor element portion 100A is disposed outside the front end side of the through hole 154, and the electrode terminal portions 80A and 82A are disposed outside the rear end side of the through hole 154. The element portion 100A is held in the through hole 154. 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 and powder filling layers 153 and 156 (hereinafter also referred to as talc rings 153 and 156) surrounding the radial direction of the multi-gas sensor element unit 100 </ b> A. ) And the above-described ceramic sleeve 106 are laminated in this order from the front end side to the rear end side. 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.

  On the other hand, as shown in FIG. 1, a metal (for example, stainless steel or the like) having a plurality of hole portions on the outer periphery of the front end side (lower side in FIG. 1) of the metal shell 138 covers the protruding portion of the multigas sensor element portion 100A. ) 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, a plurality of lead wires 146 (FIG. 1) that are electrically connected to the electrode terminal portions 80A and 82A of the multi-gas sensor element portion 100A, respectively, in the opening on the rear end side (upper side in FIG. 1) of the outer cylinder 144. A grommet 150 having lead wire insertion holes 161 into which only three wires are inserted is disposed. For simplicity, the front and back electrode terminal portions of the multi-gas sensor element portion 100A are represented by reference numerals 80A and 82A, respectively. However, in actuality, a NO _x sensor portion 30A and an ammonia detection portion 40A described later are used. A plurality of electrode terminal portions are formed according to the number of electrodes and the like.

  Further, an insulating contact member 166 is disposed on the rear end side (upper side in FIG. 1) of the multi-gas sensor element portion 100A protruding from the rear end portion 140 of the metal shell 138. The insulating contact member 166 is arranged around the electrode terminal portions 80A and 82A formed on the front and back surfaces of the rear end side of the multi-gas sensor element portion 100A. 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. The connection terminal 110 on the insulating contact member 166 side and the electrode terminal portions 80A and 82A of the multi-gas sensor element portion 100A are electrically connected, and are electrically connected to the outside by the lead wire 146.

FIG. 2 is a block diagram showing the configuration of the multi-gas sensor element unit 100A and the gas sensor control device (controller) 300 connected thereto according to the first embodiment of the present invention. In FIG. 2, only the cross section along the longitudinal direction of the multi-gas sensor element unit 100 </ b> A is displayed for convenience of explanation.
The multi-gas sensor 200A and the gas sensor control device 300 are mounted on a vehicle including an internal combustion engine (hereinafter also referred to as an engine) (not shown). The gas sensor control device 300 is electrically connected to a vehicle-side control device (hereinafter referred to as “ECU” as appropriate) 400. It is connected to the. The end of the lead wire 146 extending from the multi-gas sensor 200A is connected to a connector, and this connector is electrically connected to the connector on the gas sensor control device 300 side.
ECU400 the processing such as purification of receiving data ammonia concentration and NO _x concentration in the exhaust gas calculated by the gas sensor control unit 300, NO _x stored in the control and the catalyst operating conditions of the engine on the basis thereof Run.

Next, the configuration of the multi-gas sensor element unit 100A will be described. The multi-gas sensor element unit 100A includes a NO _x sensor unit 30A having a configuration similar to that of a known NO _x sensor and an ammonia sensor unit 40 having a configuration similar to that of a known ammonia sensor. The sensor unit 40 is formed on the outer surface of the NO _x sensor unit 30A.

First, the NO _x sensor unit 30A includes the insulating layer 23e, the first solid electrolyte layer 2a, the insulating layer 23d, the third solid electrolyte layer 6a, the insulating layer 23c, the second solid electrolyte layer 4a, and the insulating layers 23b and 23a. It has a stacked structure. A first measurement chamber S1 is defined between the first solid electrolyte layer 2a and the third solid electrolyte layer 6a, and the first diffusion resistor 8a is disposed at the left end (inlet) of the first measurement chamber S1. A gas to be measured is introduced from the outside. A porous protective layer 9 is disposed outside the first diffusion resistor 8a.
A second diffusion resistor 8b is disposed at the end of the first measurement chamber S1 opposite to the inlet, and communicates with the first measurement chamber S1 on the right side of the first measurement chamber S1 via the second diffusion resistor 8b. A second measurement chamber (corresponding to the “NO _x measurement chamber” of the present invention) S2 is defined. The second measurement chamber S2 penetrates the third solid electrolyte layer 6a and is formed between the first solid electrolyte layer 2a and the second solid electrolyte layer 4a.

A long plate-like heater 21 extending along the longitudinal direction of the multi-gas sensor element unit 100 is embedded between the insulating layers 23b and 23a. The heater 21 is used to raise the temperature of the gas sensor to the activation temperature and increase the conductivity of oxygen ions in the solid electrolyte layer to stabilize the operation.
The insulating layers 23a, 23b, 23c, 23d, and 23e are mainly made of alumina, and the first diffusion resistor 8a and the second diffusion resistor 8b are made of a porous material such as alumina. The heater 21 is made of platinum or the like.

The first pumping cell 2 includes a first solid electrolyte layer 2a mainly composed of zirconia having oxygen ion conductivity, an inner first pumping electrode 2b disposed so as to sandwich the first solid electrolyte layer 2a, and an outer first pumping electrode serving as a counter electrode. 2c (each electrode corresponds to the “first electrode” in the claims), and the inner first pumping electrode 2b faces the first measurement chamber S1. Both the inner first pumping electrode 2b and the outer first pumping electrode 2c are mainly made of platinum, and the surface of the inner first pumping electrode 2b is covered with a protective layer 11 made of a porous material.
Further, the insulating layer 23e corresponding to the upper surface of the outer first pumping electrode 2c is hollowed out and filled with the porous body 13, and the outer first pumping electrode 2c communicates with the outside to allow gas (oxygen) to enter and exit. Yes.

The oxygen concentration detection cell 6 includes a third solid electrolyte layer 6a mainly composed of zirconia, and a detection electrode 6b and a reference electrode 6c arranged so as to sandwich the third solid electrolyte layer 6a. The detection electrode 6b is an inner first pumping electrode 2b. It faces the first measurement chamber S1 further downstream. Both the detection electrode 6b and the reference electrode 6c are mainly made of platinum.
The insulating layer 23c is cut out so that the reference electrode 6c in contact with the third solid electrolyte layer 6a is disposed inside, and the cutout portion is filled with a porous material to form the reference oxygen chamber 15. . Then, a weak constant current is passed through the oxygen concentration detection cell 6 in advance using the Icp supply circuit 54, so that oxygen is sent from the first measurement chamber S1 into the reference oxygen chamber 15 to be an oxygen reference.

The second pumping cell 4 includes a second solid electrolyte layer 4a mainly composed of zirconia, an inner second pumping electrode 4b and a counter electrode disposed on the surface of the second solid electrolyte layer 4a facing the second measurement chamber S2. And a second pumping counter electrode 4c (each electrode corresponds to a “second electrode” in the claims). The inner second pumping electrode 4b and the second pumping counter electrode 4c are mainly composed of platinum.
The second pumping counter electrode 4c is disposed in a cutout portion of the insulating layer 23c on the second solid electrolyte layer 4a, and faces the reference oxygen chamber 15 so as to face the reference electrode 6c.

  The inner first pumping electrode 2b, the detection electrode 6b, and the inner second pumping electrode 4b are each connected to a reference potential and connected to a control circuit 59, which will be described later, included in the gas sensor control device 300.

Next, the ammonia sensor unit 40 is formed on the insulating layer 23e that forms the outer surface of the NO _x sensor unit 30A. More specifically, the ammonia sensor unit 40 includes a pair of comb-like electrodes 40a formed on the insulating layer 23e and a sensitive unit 40b that covers the pair of electrodes 40a, and changes the impedance between the pair of electrodes 40a. The ammonia concentration in the gas to be measured is detected.
Further, a porous diffusion layer 44A is formed so as to completely cover the sensitive portion 40b, and as will be described in detail later, the diffusion rate of the gas to be measured flowing into the sensitive portion 40b from the outside can be adjusted. .

FIG. 3 is a development view showing a configuration of the ammonia sensor unit 40. A pair of comb electrodes (a pair of electrodes) 40a is disposed on the insulating layer 23e, and leads 40ax and 40ay extend from the comb electrode 40a along the longitudinal direction of the insulating layer 23e, respectively, and are not shown on the leads 40ax and 40ay. An insulating layer is coated. However, the right ends of the leads 40ax and 40ay are exposed without being covered with this insulating layer, and form predetermined electrode terminal portions, respectively.
The comb-tooth electrode 40a has, for example, gold as a main component, and two comb-shaped electrodes are arranged apart from each other. Further, the leads 40ax and 40ay are made of, for example, a material whose main component is platinum.

The sensitive part 40b is a gas sensitive material whose impedance (Z) changes according to the ammonia concentration, and a solid acid substance can be used.
By applying an alternating current between the comb-tooth electrodes 40a, the impedance (Z) of the sensitive part 40b embedded between the comb-tooth electrodes 40a changes, so that it is possible to detect the ammonia concentration in the exhaust gas based on the impedance change. it can.
As the solid acid substance, a solid superacid substance described in JP 2005-114355 A (for example, paragraph 0066) is preferably used. As the solid acid substance, for example, one or more selected from the group of WO ₃ / ZrO ₂ , WO ₃ / YSZ, SO ₄ / ZrO ₂ , WO ₃ / TiO ₂ , and WO ₃ / Al ₂ O ₃ can be used. . Specifically, a composition of _{10wt% -WO 3 / 90wt% -YSZ} , which YSZ contains 4 wt% yttrium is exemplified.
Examples of the diffusion layer 44A that covers the sensitive portion 40b include at least one selected from the group consisting of alumina, spinel (MgAl ₂ O ₄ ), silica alumina, and mullite. And the gas diffusion time which reaches | attains the sensitive part 40b and the comb-tooth electrode 40a can be arbitrarily adjusted by adjusting the thickness of 44 A of diffusion layers, a particle size, a particle size distribution, a porosity, a compounding ratio, etc. suitably.

In this embodiment, when the control temperature of the NO _x sensor unit 30A is 600 ° C., the position of the ammonia sensor unit 40 on the NO _x sensor unit 30A is such that the temperature of the ammonia sensor unit 40 is about 400 ° C. It has been decided. That is, in this embodiment, the ammonia sensor unit 40 is disposed on the rear end side of the sensor from the inner second pumping electrode 4b along the longitudinal direction of the sensor 100A so that the temperature is lower than that of the NO _x sensor unit 30A. This is because if the temperature of the ammonia sensor unit 40 is about 400 ° C., the ammonia detection ability of the solid acid substance constituting the sensitive unit 40b is enhanced.
More specifically, the temperature of the central portion of the inner second pumping electrode 4b of the NO _x sensor portion 30A is 600 ° C., and the temperature of the central portion of the comb electrode 40a of the ammonia sensor portion 40 is 400 ° C.

Next, returning to FIG. 2, the configuration of the gas sensor control device 300 will be described. The gas sensor control device 300 includes an (analog) control circuit 59 and a microcomputer 60 on a circuit board. The microcomputer 60 controls the entire gas sensor control device 300, and includes a CPU (central processing unit) 61, a RAM 62, a ROM 63, a signal input / output unit 64, an A / D converter 65, and a clock (not shown), and is stored in advance in a ROM or the like. The executed program is executed by the CPU.
The control circuit 59 includes a reference voltage comparison circuit 51, an Ip1 drive circuit 52, a Vs detection circuit 53, an Icp supply circuit 54, an Ip2 detection circuit 55, a Vp2 application circuit 56, a heater drive circuit 57, and an ammonia sensor unit impedance detection, which will be described in detail later. A circuit 58 is provided.
The control circuit 59 controls the NO _x sensor unit 30A, NO _x sensor unit first pumping current flowing through 30A Ip1, and outputs to the microcomputer 60 detects the second pumping current Ip2.
The control circuit 59 controls the ammonia sensor unit 40, applies a predetermined alternating voltage between the electrodes 40a of the ammonia sensor unit 40 (for example, 2 V, 400 Hz), detects the impedance from the current value flowing at that time, The impedance is converted into a voltage and then output to the microcomputer 60.

Specifically, the outer first pumping electrode 2c of the NO _x sensor unit 30A is connected to the Ip1 drive circuit 52, and the reference electrode 6c is connected in parallel to the Vs detection circuit 53 and the Icp supply circuit 54. The second pumping counter electrode 4 c is connected in parallel to the Ip2 detection circuit 55 and the Vp2 application circuit 56. The heater circuit 57 is connected to the heater 21.
A pair of electrodes 40 a of the ammonia sensor unit 40 is connected to the ammonia sensor unit impedance detection circuit 58.

Each circuit 51-57 has the following functions.
The Ip1 drive circuit 52 detects the first pumping current Ip1 at that time while supplying the first pumping current Ip1 between the inner first pumping electrode 2b and the outer first pumping electrode 2c.
The Vs detection circuit 53 detects the voltage Vs between the detection electrode 6 b and the reference electrode 6 c and outputs the detection result to the reference voltage comparison circuit 51.
The reference voltage comparison circuit 51 compares the reference voltage (for example, 425 mV) with the output (voltage Vs) of the Vs detection circuit 53 and outputs the comparison result to the Ip1 drive circuit 52. Then, Ip1 drive circuit 52 controls the direction and magnitude of flow voltage Vs of equal manner Ip1 current to the reference voltage, the predetermined value of the degree to which the oxygen concentration in the first measurement chamber S1 is NO _x does not decompose Adjust to.
The Icp supply circuit 54 causes a weak current Icp to flow between the detection electrode 6b and the reference electrode 6c, sends oxygen from the first measurement chamber S1 into the reference oxygen chamber 15, and a predetermined oxygen concentration based on the reference electrode 6c. To expose.
Vp2 application circuit 56, between the inner second pumping electrode 4b and the second pumping counter electrode 4c, a constant voltage of about decomposed into NO _x gas is oxygen and _{N 2} gas in a measurement gas Vp2 (e.g., 450 mV) Is applied to decompose NO _x into nitrogen and oxygen.
Ip2 detection circuit 55, when the oxygen generated by the decomposition of the NO _x is pumped into the second pumping counter electrode 4c side from the second measurement chamber S2 through the second solid electrolyte body 4a, the second pumping cell 4 The flowing second pumping current Ip2 is detected.

The Ip1 drive circuit 52 outputs the detected value of the first pumping current Ip1 to the A / D converter 65. The Ip2 detection circuit 55 outputs the detected second pumping current Ip2 value to the A / D converter 65.
The A / D converter 65 digitally converts these values and outputs them to the CPU 61 via the signal input / output unit 64.

Next, an example of control using the control circuit 59 will be described. First, when the engine is started and supplied with electric power from an external power source, the heater 21 is operated via the heater circuit 57, and the first pumping cell 2, the oxygen concentration detection cell 6, and the second pumping cell 4 are activated. Until heated. Further, the Icp supply circuit 54 causes a weak current Icp to flow between the detection electrode 6b and the reference electrode 6c, and sends oxygen from the first measurement chamber S1 into the reference oxygen chamber 15 to be an oxygen reference.
Further, when the NO _x sensor section 30A is heated to a suitable temperature by the heater 21, the ammonia sensor section 40 on the NO _x sensor portion 30A with it is also heated to the desired temperature.

When each cell is heated to the activation temperature, the first pumping cell 2 converts the oxygen in the gas to be measured (exhaust gas) flowing into the first measurement chamber S1 from the inner first pumping electrode 2b to the first outer pumping. Pump toward the electrode 2c.
At this time, the oxygen concentration in the first measurement chamber S1 corresponds to the interelectrode voltage (terminal voltage) Vs of the oxygen concentration detection cell 6, so that the interelectrode voltage Vs becomes the reference voltage. controls the first pumping current Ip1 to Ip1 drive circuit 52 flows through the first pumping cell 2, the oxygen concentration in the first measurement chamber S1 is nO _x adjusted so as not to decompose.

The gas to be measured whose oxygen concentration is adjusted further flows toward the second measurement chamber S2. Then, the Vp2 application circuit 56 uses a constant voltage Vp2 (oxygen concentration detection) as an interelectrode voltage (interterminal voltage) of the second pumping cell 4 such that the NO _x gas in the measurement gas is decomposed into oxygen and N ₂ gas. A voltage higher than the control voltage value of the cell 6 (for example, 450 mV) is applied to decompose NO _x into nitrogen and oxygen. Then, as the oxygen generated by the decomposition of the NO _x is pumped out from the second measurement chamber S2, the second pumping current Ip2 flows into the second pumping cell 4. At this time, since between the second pumping current Ip2 and concentration of NO _x is a linear relationship, by Ip2 detection circuit 55 detects the second pumping current Ip2, detecting the concentration of NO _x in the gas to be measured Can do.

  The ammonia sensor impedance detection circuit 58 detects the impedance of the pair of electrodes 40a, whereby the ammonia concentration in the gas to be measured can be detected. The ammonia concentration conversion value based on the impedance between the electrodes 40a (the rate of change (sensitivity) between the base impedance value and the impedance value in the presence of ammonia can also be used) is stored in the microcomputer 60, so that NH3 Calculate the concentration.

FIG. 4 is a processing flow for detecting the NO _x concentration and the ammonia concentration by the microcomputer 60 (CPU 61) of the gas sensor control device 300.
First, the microcomputer 60 operates the heater circuit 57 and determines whether or not the sensor has reached the activation temperature by the heater 21 (step S1). Usually, this determination is performed by monitoring the electrical resistance of the second solid electrolyte layer 4a of the second pumping cell 4. Next, the microcomputer 60 detects the ammonia concentration based on the voltage between the pair of electrodes 40a described above (step S3). Next, the microcomputer 60 on the basis of the second pumping current Ip2 described above, for detecting the concentration of NO _x (step S5).

Here, in the NO _x sensor unit 30A, ammonia also reacts (NO: NH ₃ = 1: 1), so the total concentration of the NO _x concentration and the ammonia concentration is detected. In the ammonia sensor unit 40A, only ammonia is selectively detected. Therefore, the microcomputer 60, NO _x from the sensor unit detected concentration of NO _x in 30A (ammonia concentration is superimposed), NO _x and ammonia by subtracting the ammonia concentration detected by the ammonia sensor section 40A Each gas concentration is calculated (step S7).
The microcomputer 60 corresponds to the “correction means” in the claims in that the correction process (calculation process) in step S7 is performed.
Next, the microcomputer 60 outputs the gas concentration calculated in step S7 to the ECU 400 (step S9), and repeats steps S3 to S9 until instructed to end the process (step S11).
7 and 8 show the outputs of the NO _x sensor unit 30A and the ammonia sensor unit 40A in the embodiment. The output of the ammonia sensor unit 40A is 0 at the output in 600-800 seconds when only the NO _x gas is introduced, but from the NO _x sensor unit 30A, only ammonia gas is introduced at 200-400 seconds. It can be seen that output is occurring.

As described above, in the present invention, the NO _x sensor unit 30A and the ammonia sensor unit 40A are provided in one multi-gas sensor 200A, and each sensor unit has almost the same measurement environment (composition, concentration, gas to be measured, Temperature, flow velocity, pressure, etc.), the gas detection accuracy is prevented from being lowered due to different measurement environments.
That is, by providing a NO _x sensor portion 30A and the ammonia sensor unit 40A in a single multi-gas sensor 200A, it is possible to simultaneously measure the concentration of NO _x and ammonia concentration without being affected by the measurement environment, the concentration of NO _x The detection accuracy of ammonia concentration is improved. Further, since the measurement gas is brought into contact with one of the multi-gas sensor 200A, can substantially simultaneously detect NO _x and ammonia, reduction in detection accuracy due to a time lag of both detection is suppressed.
Furthermore, compared with the case where the NO _x sensor unit 30A and the ammonia sensor unit 40A are separate sensors, the present invention can reduce the cost and the size of the sensor.

The multi-gas sensor 200A according to the present invention includes, for example, detection of deterioration of a catalyst provided as an auxiliary device of an engine device body, optimization of urea injection amount in a urea SCR system, and gas components discharged from a catalyst downstream (NO _x It can be applied to the accurate measurement of ammonia). For example, when only the NO _x sensor is used for sensing of the apparatus, when ammonia is discharged from the catalyst downstream, (i) ammonia discharge due to excessive urea addition, (ii) NO _x discharge due to excessive urea addition, (iii) Although it was not possible to clearly distinguish between ammonia emissions accompanying SCR catalyst deterioration, these determinations are possible using the multi-gas sensor of the present invention.

Next, the effect | action by providing 44 A of diffusion layers in the ammonia sensor part 40A is demonstrated. In the present invention, the NO _x sensor unit 30A introduces the gas to be measured into the internal measurement chambers (the first measurement chamber S1 and the NO _x measurement chamber S2), while the ammonia sensor unit 40A is exposed to the outside. doing. For this reason, there is a problem that the gas to be measured diffuses in the NO _x sensor unit 30A and the ammonia sensor unit 40A, and the detection responsiveness is different in each sensor unit.
In particular, the environment (transitional environment), such as concentration of NO _x and ammonia concentration in the measurement gas suddenly changes, shift the detection timing for the response of the respective sensor portions are different occurs (ammonia sensor unit responds faster ), The measurement accuracy tends to decrease. For example, if the measurement gas diffusion rate to each sensor unit is different, the ammonia sensor unit 40A detects a new measurement gas (in the NO _x sensor unit) while the NO _x sensor unit 30A detects the measurement gas. Gas that is later in time than the measured gas being detected) are detected one after another, making it impossible for each sensor unit to measure the measured gas in the same state.
Therefore, by providing a diffusion layer 44A in the ammonia sensor unit 40A, delaying the diffusion of the gas to be measured into the ammonia sensor unit 40A, and making it close to the diffusion rate into the NO _x sensor unit 30A, the difference in response of each sensor unit And the measurement accuracy can be improved.

From the viewpoint of reducing the difference in the response of each sensor unit, when a starting point and the detection start time of the NO _x sensor unit 30A, either early detection starting with the starting time of detection of the ammonia sensor portion 40A, NO _x sensor The time difference between the 90% response time of the part 30A and the 90% response time of the ammonia sensor part 40A is preferably 20% or less with respect to the 90% response time of any sensor part.
From the viewpoint of further reducing the difference in responsiveness of each sensor unit, when starting from the detection start time of the NO _x sensor unit 30A and the detection start time of the ammonia sensor unit 40A, which is the earlier detection point, NO _x If the time difference between the start of detection of the sensor unit 30A and the start of detection of the ammonia sensor unit 40A is 10% or less with respect to the 90% response time of any sensor unit, each sensor unit starts approximately the same Detection is possible at the timing, and the measurement accuracy is further improved.

On the other hand, when the diffusion layer 44A is not provided in the ammonia sensor unit 40A, the diffusion rate of the gas to be measured into the ammonia sensor unit 40A becomes too high, especially in a transient environment (the composition, concentration, temperature, flow rate, pressure of the gas to be measured). Etc.), the measurement accuracy may be reduced.
As a method of reducing the difference in response of each sensor unit by lowering the diffusion rate of the gas to be measured to the ammonia sensor unit 40A, the gap of the diffusion layer 44A is reduced or the thickness of the diffusion layer 44A is increased. Thus, it is possible to increase air resistance.

10 and 12 show the outputs of the NO _x sensor unit 30A and the ammonia sensor unit 40A in the case of the example (with a diffusion layer) and the comparative example (without the diffusion layer), respectively. If not provided diffusion layer 44A to the ammonia sensor portion 40A as shown in FIG. 12, 90% response time with NO _x sensor portion 30A and the ammonia sensor portion 40A is it differs greatly, by providing the diffusion layer 44A, FIG. As shown in FIG. 10, the 90% response time of each sensor unit can be made equal.

The multi-gas sensor 200A of the present invention can be manufactured in the same manner as a known NO _x sensor or ammonia sensor. For example, in the same manner as a known NO _x sensor, the solid electrolyte layer of the NO _x sensor part is formed from a green sheet, and each electrode, lead, and insulating layer are paste-printed, whereby the non-sintered body of the NO _x sensor part Form. Next, the green body of the ammonia sensor unit is formed at a predetermined position on the surface of the green body of the NO _x sensor unit. The unsintered body of the ammonia sensor part can be formed by paste printing the electrodes, leads, sensitive parts, solid electrolyte layer, diffusion layer, etc. constituting the sensor part.
Then, the green body of the NO _x sensor section green body of the ammonia sensor portion is formed on the surface and baked at a predetermined temperature as a whole, to produce a sensor element of the multi-gas sensor, a housing so A multi-gas sensor can be obtained by assembling to.

<Second Embodiment>
Next, a multi-gas sensor 200B according to a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the configuration of the gas sensor control device (controller) connected to the multi-gas sensor 200B and the control process of the gas sensor are the same as those in the first embodiment, and thus the description thereof is omitted. Further, in the multi-gas sensor 200B of the second embodiment, the same parts as those of the multi-gas sensor 200A according to the first embodiment are denoted by the same reference numerals and description thereof is omitted.
FIG. 5 shows a cross section along the longitudinal direction of the multi-gas sensor element unit 100B in the multi-gas sensor 200B of the second embodiment.

In FIG. 5, the ammonia sensor part 42 is not formed on the insulating layer 23e, the solid electrolyte layer 25 is formed on the insulating layer 23e, the insulating layer 23f is formed on the solid electrolyte layer 25, and the insulating layer 23f is formed. Constitutes the surface of the NO _x sensor unit 30B. However, a part of the insulating layer 23f is cut out in a rectangular shape to expose the solid electrolyte layer 25, and the ammonia sensor part 42 is formed on the exposed part. More specifically, the ammonia sensor unit 42 includes a pair of electrodes 42a formed on the solid electrolyte layer 25 and a selective reaction layer 42b that covers the pair of electrodes 42a, and is covered by an electromotive force change between the pair of electrodes 42a. The ammonia concentration in the measurement gas is detected.
A porous diffusion layer 44B is formed so as to completely cover the selective reaction layer 42b, and the diffusion rate of the gas to be measured flowing into the ammonia sensor unit 42 from the outside can be adjusted.

FIG. 6 is a development view showing the configuration of the ammonia sensor unit 42. A pair of electrodes 42a1 and 42a2 (collectively referred to as a pair of electrodes 42a) are disposed on the solid electrolyte layer 25, and leads 42ax and 42ay are provided from the electrodes 42a1 and 42a2 along the longitudinal direction of the solid electrolyte layer 25, respectively. The leads 42ax and 42ay are extended and covered with insulating layers 23f (not shown). However, the right ends of the leads 42ax and 42ay are exposed without being covered with this insulating layer, and form predetermined electrode terminal portions, respectively.
The electrodes 42a1 and 42a2 are spaced apart from each other along the short direction of the solid electrolyte layer 25. The electrode 42a1 is made of a material mainly composed of gold and functions as a detection electrode. The electrode 42a2 is composed mainly of platinum. It is made of material and acts as a reference electrode. Since the detection electrode 42a1 is more reactive with ammonia than the reference electrode 42a2, an electromotive force is generated between the detection electrode 42a1 and the reference electrode 42a2.
The solid electrolyte layer 25 is made of an oxygen ion conductive material such as ZrO ₂ , and the leads 42ax and 42ay are made of a material containing platinum as a main component, for example.

The selective reaction layer 42b has a role of burning combustible gas components other than ammonia in the gas to be measured. When the selective reaction layer 42b exists, the ammonia in the gas to be measured is not affected by the combustible gas components. Can be detected. The selective reaction layer 42b usually contains a metal oxide as a main component, but in particular, a material (for example, bismuth vanadium oxide: BiVO ₄ ) containing vanadium oxide (V ₂ O ₅ ) and bismuth oxide (Bi ₂ O ₃ ) in a predetermined ratio. ).
Even if the selective reaction layer 42b covers only the detection electrode 42a1, the above-described effects can be exhibited.
Examples of the diffusion layer 44B include at least one selected from the group consisting of alumina, spinel (MgAl ₂ O ₄ ), silica alumina, and mullite.

In this embodiment, when the control temperature of the NO _x sensor unit 30A is 600 ° C., the position of the ammonia sensor unit 40 is determined on the NO _x sensor unit 30A so that the temperature of the ammonia sensor unit 40 is also equal. ing. That is, in this embodiment, the ammonia sensor unit 40 is disposed in the vicinity of the midpoint (heat generation center) of the heater 21 along the longitudinal direction of the sensor 100A. This is because the vicinity of the middle point of the heater 21 (heat generation center) is the region where the temperature is the highest near the control temperature, and the temperature of the ammonia sensor unit 40 is also close to the control temperature (600 ° C.).

  Also in the second embodiment, the same effect as in the first embodiment can be obtained by providing a diffusion layer in the ammonia sensor section.

  Further, the gas sensor control device in the second embodiment is replaced with an electromotive force detection circuit generated between the electrodes 42a instead of the ammonia sensor unit impedance detection circuit 58 in the gas sensor control device 300 shown in FIG. Instead of the ammonia concentration conversion value based on the impedance stored in the computer 60, the ammonia concentration conversion value based on the electromotive force is replaced and controlled. Other control functions are the same as those in the first embodiment.

It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention. For example, in the above embodiment, the solid electrolyte layer constituting the NO _x sensor unit 30A is three layers, but the solid electrolyte layer may be two layers. The element structure of the NO _x sensor unit having two solid electrolyte layers is described in, for example, Japanese Patent Application Laid-Open No. 2004-354400 (FIG. 3).
In this case, the second measurement chamber S2 is defined between the solid electrolyte layers 2a and 6a in FIG. 2, and the first measurement chamber S1 and the second measurement chamber S2 are partitioned by the diffusion rate controlling portion 8b. The inner second pump electrode 4 b is disposed on the upper surface of the solid electrolyte layer 6. The lower surface of the solid electrolyte layer 6 is exposed to the outside, and the second pump counter electrode 4c is disposed on the exposed surface.

(1) Production of Sensor Example 1 A multi-gas sensor 200A according to the first embodiment was produced. In this multi-gas sensor 200A, the ammonia sensor unit 40 is an impedance type (solid acid type). The solid acid contained in the sensitive part 40b of the ammonia sensor 40 and _{10wt% -WO 3 / 90wt% -YSZ} , YSZ is intended to include 4 wt% yttrium. Further, a porous layer of spinel (MgAl ₂ O ₄ ) was formed as the diffusion layer 44A covering the sensitive part 40b.
Example 2: A multi-gas sensor 200B according to the second embodiment was manufactured. In this multi-gas sensor 200B, the ammonia sensor unit 42 is an electromotive force type. A pair of electrodes 42a of the ammonia sensor 42, sensing electrode 42a1 each containing gold, using a reference electrode 42a2 composed mainly of platinum, selective reaction layer 42b was set BiVO _4. A porous layer of spinel (MgAl ₂ O ₄ ) was formed as a diffusion layer 44B covering the pair of electrodes 42a and the selective reaction layer 42b.
Comparative Example 1: In the multi-gas sensor 200A according to the first embodiment, the ammonia layer 40A was not provided with the diffusion layer 44A.
Comparative Example 2: In the multi-gas sensor 200B according to the second embodiment, the diffusion layer 44B was not provided in the ammonia sensor unit 42.

(2) Sensor characteristic evaluation A (detection of ammonia concentration and NO _x concentration by the sensors of Examples 1 and 2 and calculation of each concentration)
Sensor characteristics were evaluated using a model gas generator. The base gas composition of the model gas generator was O ₂ = 10% CO ₂ = 5% H ₂ O = 5% N ₂ = bal. And the sensor was arrange | positioned in the gas flow of a model gas generator. The gas temperature was 280 ° C.
The heater control temperature of the NO _X sensor unit was set to 600 ° C. At this time, when the temperature of the center part of the pair of electrodes of the ammonia sensor part was measured, Example 1 and Comparative Example 1 were about 400 ° C., and Example 2 and Comparative Example 2 were about 650 ° C.
The multi-gas sensor of Example 1 and Example 2 is arranged in the gas flow of the model gas generator, and the components in the gas flow are arranged in order (i) the base gas and (ii) 100 ppm NH in the base gas. ₃ plus, (iii) the base gas plus NO of 100ppm in (iv) above base gas, The pattern was switched to (v) the base gas, and (vi) the base gas added with 100 ppm NH ₃ and 100 ppm NO, and the NO _x and NH ₃ concentrations in the measured gas were measured.

7 and 8 show the outputs of the NO _x sensor units 30A and 30B and the ammonia sensor units 40A and 42 in the sensors of the first and second embodiments. 7 and 8, a gas containing 100 ppm NH ₃ is detected in 200-400 seconds, a gas containing 100 ppm NO _x is detected in 600-800 seconds, and 100 ppm NH ₃ and 100 ppm are detected in 1000-1200 seconds. so that the gas is detected containing and NO _x.
In the detection principle, in the case of the NO _x sensor units 30A and 30B, NH ₃ flowing into the measurement chamber changes to NO, and therefore both NO _x and NH ₃ are detected (as the total concentration of both components). On the other hand, the ammonia sensor units 40A and 42 selectively detect NH ₃ . Therefore, the output of the ammonia sensor units 40A and 42 is 0 at the output in 600 to 800 seconds including only NO _x, but the NO _x sensor is in spite of the gas containing only NH _{3 in} 200 to 400 seconds. It can be seen that outputs are generated from the parts 30A and 30B.

Table 1 shows the results of calculating the concentrations of NO _x and NH ₃ in the test gas in step S7 of the flow of FIG. 4 based on the output of FIG.

In Table 1, the ammonia concentration was calculated by directly adopting the output of the ammonia sensor section. On the other hand, in the NO _x sensor units 30A and 30B, ammonia reacts (NO: NH ₃ = 1: 1), so the total concentration of the NO _x concentration and the ammonia concentration is detected. Therefore, NO _x sensor section 30A, from the detected concentration of NO _x (ammonia concentration is superimposed) at 30B, to calculate the concentration of NO _x by subtracting the ammonia concentration detected by the ammonia sensor unit 40A, 42 .

(3) Sensor characteristic evaluation B (Evaluation of responsiveness of each sensor unit with or without diffusion layer)
Using the model gas generator, the sensors of Example 1 and Comparative Example 1 are arranged in a gas flow in which 50 ppm of NH ₃ is added to the base gas, and the responsiveness of each sensor unit (output with respect to measurement time) Evaluated. The gas temperature was 280 ° C., and the control temperature of the sensor was the same as in the characteristic evaluation A.
9 and 10 are graphs showing the responsiveness (output with respect to the measurement time) of the sensor of Example 1, FIG. 9 shows the total measurement time, and FIG. 10 is the reference point (0) when the ammonia sensor unit 40A starts detection. FIG.
Similarly, FIGS. 11 and 12 are graphs showing the responsiveness (output with respect to the measurement time) of the sensor of Comparative Example 1, FIG. 11 shows the total measurement time, and FIG. 12 shows the detection start time of the ammonia sensor unit 40A. It is the elements on larger scale made into the base point. Table 2 shows the 90% response time of each sensor unit calculated from FIGS. 10 and 12, respectively.

As is clear from Table 2, in Example 1 in which the diffusion layer was provided in the ammonia sensor part, the difference in 90% response time of each sensor part was small, and the difference at the start of detection of each sensor part was small. .
On the other hand, in the case of Comparative Example 1 in which the diffusion layer is not provided in the ammonia sensor unit, the difference r between the 90% response times of the sensor units is 90% response time of each sensor unit (represented by a subscript τ). Also exceeded 20%. In the case of Comparative Example 1, the time difference d at the start of detection of each sensor unit exceeded 10% with respect to the 90% response time of each sensor unit (represented by subscript τ, respectively). That is, the detection timing of each sensor unit was shifted, and the NO _x sensor unit responded quickly.
If NO _x and NH _{3 in the} gas to be measured can be detected almost simultaneously, urea injection control for suppressing NO _x emission in the gas to be measured, SCR catalyst deterioration, detection accuracy of slip NH _{3 and the} like are remarkably high. Get higher. Meanwhile, various operation control and sensor control of the motor vehicle are generally each about several hundreds msec, the error of the NO _x detection and NH ₃ response time of detection exceeds 20%, highly accurate control becomes difficult. For this reason, it is not preferable that the difference r between the 90% response times of the sensor units exceeds 20% with respect to the 90% response time of each sensor unit (represented by the subscript τ). I saw it.

  Note that the 90% response described above is used in order to improve the detection accuracy at each sensor unit and reduce the effect on measurement accuracy due to fluctuations in the measurement environment (gas composition, concentration, temperature, flow rate, pressure, etc.). It is most preferable that the time difference r and the time difference d at the start of detection are each 0, but it is practically difficult. If these differences r and d are within 1 second, the influence on the detection accuracy is affected. Is small and can be used.

It is sectional drawing in alignment with the longitudinal direction of the multi-gas sensor which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the multi gas sensor and gas sensor control apparatus which concern on the 1st Embodiment of this invention. It is an expanded view which shows the structure of the ammonia sensor part in 1st Embodiment. Is a process flow of detecting the concentration of NO _x and ammonia concentration by the gas sensor control unit (microcomputer). It is sectional drawing which follows the longitudinal direction of a multi-gas sensor element part among the multi-gas sensors of 2nd Embodiment. It is an expanded view which shows the structure of the ammonia sensor part in 2nd Embodiment. In the sensor of Example 1 is a diagram showing the output of the NO _x sensor section and the ammonia sensor unit for detecting time. In the sensor of Example 2 is a diagram showing the output of the NO _x sensor section and the ammonia sensor unit for detecting time. It is a figure which shows the responsiveness (output with respect to measurement time) of the sensor of Example 1. FIG. FIG. 10 is a partially enlarged view of FIG. 9 with a detection start time of the ammonia sensor unit as a base point (0 seconds). It is a figure which shows the responsiveness (output with respect to measurement time) of the sensor of the comparative example 1. It is the elements on larger scale of FIG. 11 which made the ammonia sensor part the detection start time as a base point (0 second).

Explanation of symbols

2a First solid electrolyte layer 2b, 2c First electrode (inner first pumping electrode, outer first pumping electrode)
2 1st pumping cell 4a 2nd solid electrolyte layer 4b, 4c 2nd electrode (inner side 2nd pumping electrode, 2nd pumping counter electrode)
4 Second pumping cell 25 Solid electrolyte layer (Ammonia sensor part) 30A, 30B NO _x sensor part 40, 42 Ammonia sensor part 40a, 42a A pair of electrodes 40b Sensing part 42b Selective reaction layer 44A, 44B Diffusion layer 60 Correction means ( Microcomputer)
100A, 100B Multi-gas sensor element section 200A Multi-gas sensor 300 Gas sensor control device S1 First measurement chamber S2 NO _x measurement chamber Ip2 Second pumping current

Claims (6)

Pumping oxygen in the gas to be measured, which is located inside and outside the first measurement chamber and has a pair of first electrodes provided on the first solid electrolyte layer, or introduced into the first measurement chamber has a first pumping cell for pumping insertion, with located inside and outside of the NO _x measurement chamber communicating with the first measurement chamber, a pair of second electrodes provided on the second solid electrolyte layer, a second pumping cell in which the second pumping current oxygen concentration flowing into the NO _x measurement chamber from said first measurement chamber in accordance with the concentration of NO _x in the measurement gas is adjusted to flow between the pair of second electrode A NO _x sensor unit comprising:
A multi-gas sensor having at least a pair of electrodes and an ammonia sensor part formed on the outer surface of the NO _x sensor part ,
In the ammonia sensor part, a diffusion layer covering the pair of electrodes is formed,
When starting from the detection start earlier of the detection start of the NO _x sensor unit and the detection start of the ammonia sensor unit,
And 90% response time of the NO _x sensor unit, the time difference between the 90% response time of the ammonia sensor section, multi-gas sensor also below 20% 90% response time of any of the sensor unit. In the ammonia sensor part, a diffusion layer covering the pair of electrodes is formed,
When starting from the detection start earlier of the detection start of the NO _x sensor unit and the detection start of the ammonia sensor unit,
The multi time according to claim 1 , wherein a time difference between the detection start time of the NO _x sensor unit and the detection start time of the ammonia sensor unit is 10% or less with respect to a 90% response time of any sensor unit. Gas sensor. The multi-gas sensor according to claim 1, wherein the diffusion layer is made of at least one selected from the group consisting of alumina, spinel, silica alumina, and mullite . The ammonia sensor unit includes the pair of electrodes and a sensitive unit provided in contact with the pair of electrodes, and detects the ammonia concentration in the gas to be measured based on an impedance change between the pair of electrodes. The multi-gas sensor according to any one of? The ammonia sensor unit includes a solid electrolyte layer and the pair of electrodes stacked on both sides or one side of the solid electrolyte layer, and detects the ammonia concentration in the gas to be measured by a change in electromotive force between the pair of electrodes. multi-gas sensor according to any one of claims 1 to 3 for. Is connected to the multi-gas sensor according to any one of claims 1 to 5, based on the ammonia concentration output from the ammonia sensor section, the gas sensor control having a correction means for correcting the concentration of NO _x output from the NO _x sensor unit Equipment .

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