JP2018115951A - Concentration calculating device and gas detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy of oxygen concentration.SOLUTION: A microcomputer 190 acquires a first pumping current Ip1 from an NOx detecting unit 101. The NOx detecting unit 101 outputs the first pumping current Ip1 whose value changes according to oxygen concentration in a first measurement chamber 121 into which an exhaust gas flows. The microcomputer 190 acquires a first ammonia electromotive force from a first ammonia detecting unit 102 and a second ammonia electromotive force from a second ammonia detecting unit 103. The first ammonia detecting unit 102 outputs the first ammonia electromotive force, and the second ammonia detecting unit 103 outputs the second ammonia electromotive force. The values of the first and second ammonia electromotive forces change according to concentration of the ammonia contained in the exhaust gas. The microcomputer 190 calculates the concentration of the oxygen contained in the exhaust gas on the basis of the first ammonia electromotive force, the second ammonia electromotive force, and the first pumping current Ip1.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a concentration calculation device and a gas detection device that calculate the concentration of oxygen.

  As in Patent Document 1, an oxygen sensor that detects the concentration of oxygen contained in a gas to be measured is known.

JP2015-148538A

In the oxygen sensor described in Patent Document 1, there is a problem in that the accuracy of detecting the oxygen concentration is lowered by the combustion of ammonia contained in the gas to be measured.
An object of the present disclosure is to improve the detection accuracy of the oxygen concentration.

One aspect of the present disclosure is a concentration calculation device that calculates the concentration of oxygen contained in a gas to be measured, and includes a first acquisition unit, a second acquisition unit, and a correction unit.
The first acquisition unit is configured to acquire a first concentration signal from the first detection unit. The first detector outputs a first concentration signal whose value changes according to the oxygen concentration in the measurement chamber into which the gas to be measured flows.

The second acquisition unit is configured to acquire the second concentration signal from the second detection unit that outputs a second concentration signal whose value changes according to the concentration of ammonia contained in the gas to be measured.
The correction unit is configured to obtain the concentration of oxygen contained in the gas to be measured based on the second concentration signal and the first concentration signal.

  In the first detection unit, ammonia and oxygen are introduced into the measurement chamber. For this reason, when ammonia contained in the gas to be measured is introduced into the measurement chamber of the first detection unit, oxygen is consumed by burning the ammonia. Thereby, when ammonia and oxygen are contained in the gas to be measured, the concentration of oxygen contained in the gas to be measured is different from the concentration of oxygen in the measurement chamber.

  On the other hand, the concentration calculation apparatus according to the present disclosure obtains the concentration of oxygen contained in the measurement gas based on the second concentration signal and the first concentration signal. For this reason, the concentration calculation device according to the present disclosure can calculate the amount of oxygen consumed by the combustion of ammonia based on the concentration of ammonia contained in the gas to be measured. Based on the concentration, the oxygen concentration before oxygen is consumed by the combustion of ammonia can be calculated. Thereby, the concentration calculation apparatus according to the present disclosure can improve the detection accuracy of the concentration of oxygen contained in the gas to be measured.

  In one aspect of the present disclosure, the first calculation unit and the second calculation unit are provided, and the correction unit corrects the first calculated concentration based on the second calculated concentration, thereby determining the oxygen contained in the measurement gas. The concentration may be obtained. The first calculation unit is configured to calculate a first calculated concentration based on the first concentration signal output from the first detection unit. The second calculation unit is configured to calculate a second calculated concentration based on the second concentration signal output from the second detection unit.

  In one aspect of the present disclosure, the correction unit may correct the first calculated density by adding the first calculated density and a multiplication value of a preset correction coefficient and the second calculated density. Good. Thereby, the density calculation device of the present disclosure can correct the first calculated density by a simple calculation of executing one multiplication and one addition, and can reduce the processing load of the density calculation device. it can.

  In one aspect of the present disclosure, the measurement chamber may be configured such that the gas to be measured flows through the diffusion resistor. Since the gas phase reaction occurs more stably due to the presence of the diffusion resistor, the concentration calculation device of the present disclosure can more accurately determine the concentration of oxygen contained in the gas to be measured.

  In one aspect of the present disclosure, the first detection unit and the second detection unit may be configured as an integrated gas sensor. Thereby, the concentration calculation apparatus according to the present disclosure can detect the oxygen concentration and the ammonia concentration in substantially the same region of the gas to be measured.

Another aspect of the present disclosure is a gas detection device including a first detection unit, a second detection unit, and the concentration calculation device according to one aspect of the present disclosure.
The gas detection device of the present disclosure configured as described above is a gas sensor including the concentration calculation device of one aspect of the present disclosure, and can obtain the same effects as the concentration calculation device of the present disclosure.

2 is a cross-sectional view showing an internal structure of a multi-gas sensor 2. FIG. FIG. 2 is a diagram illustrating a schematic configuration of a sensor element unit 5 and a control unit 3. 3 is a cross-sectional view showing the structure of a first ammonia detector 102 and a second ammonia detector 103. FIG. It is a flowchart which shows a gas concentration calculation process. It is a graph which shows the ammonia concentration dependence of the oxygen concentration before correction | amendment.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
The multi-gas detection device 1 of the present embodiment is mounted on a vehicle and has an SCR (Selective Catalytic Reduction) catalyst installed to purify nitrogen oxides contained in exhaust gas discharged from an internal combustion engine, and urea as a reducing agent. Is used in a system including a NOx storage reduction catalyst, a diesel oxidation catalyst (DOC), and a diesel particulate removal device (DPF). More specifically, the multi-gas detection device 1 detects the concentrations of oxygen, ammonia, nitrogen dioxide, and nitrogen oxides contained in the exhaust gas downstream of the NOx storage reduction catalyst or SCR catalyst. Hereinafter, a vehicle equipped with the multi-gas detection device 1 is referred to as a host vehicle. Oxygen, ammonia, nitrogen dioxide and nitrogen oxides are also referred to as O ₂ , NH ₃ , NO ₂ and NOx, respectively.

The multi-gas detection device 1 includes a multi-gas sensor 2 shown in FIG. 1 and a control unit 3 shown in FIG.
As shown in FIG. 1, the multigas sensor 2 includes a sensor element unit 5, a metal shell 10, a separator 34, and a connection terminal 38. In the following description, the side where the sensor element unit 5 of the multi-gas sensor 2 is arranged (that is, the lower side in FIG. 1) is the tip side, and the side where the connection terminal 38 is arranged (ie, the upper side in FIG. 1). ) Is called the rear end side.

  The sensor element unit 5 has a plate shape extending in the axis O direction. Electrode terminal portions 5A and 5B are arranged at the rear end of the sensor element portion 5. In FIG. 1, for ease of illustration, the electrode terminal portions formed in the sensor element portion 5 are only the electrode terminal portion 5A and the electrode terminal portion 5B. A plurality of electrode terminal portions are formed according to the number of electrodes and the like included in the first ammonia detection unit 102 and the second ammonia detection unit 103.

  The metal shell 10 is a cylindrical member in which a screw portion 11 for fixing the multi-gas sensor 2 to an exhaust pipe of an internal combustion engine is formed on the outer surface. The metal shell 10 includes a through hole 12 that penetrates in the direction of the axis O, and a shelf 13 that protrudes radially inward of the through hole 12. The shelf portion 13 is formed as an inwardly tapered surface having an inclination that approaches the front end side from the radially outer side of the through hole 12 toward the center.

The metal shell 10 holds the sensor element portion 5 in a state where the front end side of the sensor element portion 5 protrudes from the through hole 12 toward the front end side and the rear end side of the sensor element portion 5 protrudes toward the rear end side of the through hole 12.
Inside the through hole 12 of the metal shell 10, a ceramic holder 14 that is a cylindrical member that surrounds the periphery of the sensor element portion 5 in the radial direction in order from the front end side to the rear end side, and a talc that is a powder-filled layer Rings 15 and 16 and ceramic sleeve 17 are laminated.

  A caulking packing 18 is disposed between the ceramic sleeve 17 and the end portion on the rear end side of the metal shell 10. A metal holder 19 is disposed between the ceramic holder 14 and the shelf 13 of the metal shell 10. The metal holder 19 accommodates the talc ring 15 and the ceramic holder 14 therein, and the talc ring 15 is compressed and filled so that the metal holder 19 and the talc ring 15 are integrated in an airtight manner. The end portion on the rear end side of the metal shell 10 is a portion that is caulked so as to press the ceramic sleeve 17 toward the front end side via the caulking packing 18. Further, the talc ring 16 is compressed and filled inside the metal shell 10, so that airtightness between the inner peripheral surface of the metal shell 10 and the outer peripheral surface of the sensor element portion 5 is ensured.

  An external protector 21 with a gas flow hole and an internal protector 22 with a gas flow hole are provided at the end of the metal shell 10 on the front end side. The external protector 21 and the internal protector 22 are cylindrical members formed of a metal material such as stainless steel whose end on the distal end side is closed. The internal protector 22 is welded to the metal shell 10 while covering the end of the sensor element portion 5 on the front end side, and the external protector 21 is welded to the metal shell 10 while covering the internal protector 22.

  On the outer periphery of the end portion on the rear end side of the metal shell 10, an end portion on the front end side of the outer cylinder 31 formed in a cylindrical shape is fixed by welding. Further, a grommet 32 that closes the opening is disposed in an opening that is an end portion on the rear end side of the outer cylinder 31.

  The grommet 32 is formed with a lead wire insertion hole 33 into which the lead wire 41 is inserted. The lead wire 41 is electrically connected to the electrode terminal portion 5A and the electrode terminal portion 5B of the sensor element portion 5.

  The separator 34 is a cylindrical member disposed on the rear end side of the sensor element unit 5. A space formed inside the separator 34 is an insertion hole 35 penetrating in the direction of the axis O. On the outer surface of the separator 34, a flange portion 36 that protrudes radially outward is formed.

The rear end portion of the sensor element portion 5 is inserted into the insertion hole 35 of the separator 34, and the electrode terminal portions 5 </ b> A and 5 </ b> B are disposed inside the separator 34.
Between the separator 34 and the outer cylinder 31, a metal holding member 37 formed in a cylindrical shape is disposed. The holding member 37 holds the separator 34 in a fixed state with respect to the outer cylinder 31 by contacting the flange 36 of the separator 34 and the inner surface of the outer cylinder 31.

  The connection terminal 38 is a member that is disposed in the insertion hole 35 of the separator 34, and is a conductive member that electrically connects the electrode terminal portion 5 </ b> A and the electrode terminal portion 5 </ b> B of the sensor element portion 5 and the lead wire 41 independently. It is a member. In FIG. 1, only two connection terminals 38 are shown for ease of illustration.

As shown in FIG. 2, the control unit 3 of the multi-gas detection device 1 is electrically connected to an electronic control device 200 mounted on the host vehicle. The electronic control device 200 receives data indicating the O ₂ concentration, NO ₂ concentration, NOx concentration and ammonia concentration (hereinafter referred to as NH ₃ concentration) in the exhaust gas calculated by the control unit 3, and based on the received data, the internal combustion engine 200 An engine operating state control process is executed, or a NOx purification process accumulated in the catalyst is executed.

  The sensor element unit 5 includes a NOx detector 101, a first ammonia detector 102, and a second ammonia detector 103. The second ammonia detector 103 is not shown in FIG. 2 but shown in FIG. The first ammonia detection unit 102 and the second ammonia detection unit 103 are arranged in the width direction of the NOx detection unit 101 (that is, at substantially the same position as the reference electrode 143 in the longitudinal direction of the NOx detection unit 101 (that is, the horizontal direction in FIG. 2). 2 are arranged in parallel so that their positions in the depth direction in FIG. 2 are different from each other. For this reason, FIG. 2 shows only the first ammonia detection unit 102 out of the first ammonia detection unit 102 and the second ammonia detection unit 103.

  The NOx detection unit 101 is configured by sequentially laminating an insulating layer 113, a ceramic layer 114, an insulating layer 115, a ceramic layer 116, an insulating layer 117, a ceramic layer 118, an insulating layer 119, and an insulating layer 120. The insulating layers 113, 115, 117, 119, 120 and the ceramic layers 114, 116, 118 are mainly formed of alumina.

  The NOx detection unit 101 includes a first measurement chamber 121 formed between the ceramic layer 114 and the ceramic layer 116. The NOx detection unit 101 exhausts from the outside to the inside of the first measurement chamber 121 via a diffusion resistor 122 disposed between the ceramic layer 114 and the ceramic layer 116 so as to be adjacent to the first measurement chamber 121. Introduce gas. The diffusion resistor 122 is made of a porous material such as alumina.

The NOx detection unit 101 includes a first pumping cell 130. The first pumping cell 130 includes a solid electrolyte layer 131 and pumping electrodes 132 and 133.
The solid electrolyte layer 131 is formed mainly of zirconia having oxygen ion conductivity. A portion of the ceramic layer 114 in the region in contact with the first measurement chamber 121 is removed, and a solid electrolyte layer 131 is embedded instead of the ceramic layer 114.

  The pumping electrodes 132 and 133 are formed mainly of platinum. The pumping electrode 132 is disposed on the surface that contacts the first measurement chamber 121 in the solid electrolyte layer 131. The pumping electrode 133 is disposed on the surface of the solid electrolyte layer 131 on the side opposite to the pumping electrode 132 with the solid electrolyte layer 131 interposed therebetween. The insulating layer 113 in the region where the pumping electrode 133 is disposed and the surrounding region is removed, and the porous body 134 is filled instead of the insulating layer 113. The porous body 134 allows gas (for example, oxygen) to enter and exit between the pumping electrode 133 and the outside.

The NOx detection unit 101 includes an oxygen concentration detection cell 140. The oxygen concentration detection cell 140 includes a solid electrolyte layer 141, a detection electrode 142, and a reference electrode 143.
The solid electrolyte layer 141 is formed mainly of zirconia having oxygen ion conductivity. A part of the ceramic layer 116 in the region on the rear end side (that is, the right side in FIG. 2) from the solid electrolyte layer 131 is removed, and the solid electrolyte layer 141 is embedded instead of the ceramic layer 116.

  The detection electrode 142 and the reference electrode 143 are formed mainly of platinum. The detection electrode 142 is disposed on the surface in contact with the first measurement chamber 121 in the solid electrolyte layer 141. The reference electrode 143 is disposed on the surface of the solid electrolyte layer 141 on the side opposite to the detection electrode 142 with the solid electrolyte layer 141 interposed therebetween.

  The NOx detection unit 101 includes a reference oxygen chamber 146. The reference oxygen chamber 146 is a through hole formed by removing the insulating layer 117 in the region where the reference electrode 143 is disposed and the surrounding region.

  The NOx detection unit 101 includes a second measurement chamber 148 on the downstream side of the first measurement chamber 121. The second measurement chamber 148 is formed through the solid electrolyte layer 141 and the insulating layer 117 on the rear end side of the detection electrode 142 and the reference electrode 143. The NOx detector 101 introduces exhaust gas discharged from the first measurement chamber 121 into the second measurement chamber 148.

The NOx detection unit 101 includes a second pumping cell 150. The second pumping cell 150 includes a solid electrolyte layer 151 and pumping electrodes 152 and 153.
The solid electrolyte layer 151 is formed mainly of zirconia having oxygen ion conductivity. The ceramic layer 118 in the region in contact with the reference oxygen chamber 146 and the second measurement chamber 148 and its peripheral region is removed, and a solid electrolyte layer 151 is embedded instead of the ceramic layer 118.

  The pumping electrodes 152 and 153 are formed mainly of platinum. The pumping electrode 152 is disposed on the surface in contact with the second measurement chamber 148 in the solid electrolyte layer 151. The pumping electrode 153 is disposed on the surface of the solid electrolyte layer 151 on the side opposite to the reference electrode 143 across the reference oxygen chamber 146. A porous body 147 is disposed inside the reference oxygen chamber 146 so as to cover the pumping electrode 153.

  The NOx detection unit 101 includes a heater 160. The heater 160 is a heating resistor that is formed mainly of platinum and generates heat when energized. The heater 160 is disposed between the insulating layer 119 and the insulating layer 120.

  The first ammonia detector 102 is formed on the outer surface of the NOx detector 101, more specifically, on the insulating layer 120. The first ammonia detection unit 102 is arranged at substantially the same position as the reference electrode 143 in the NOx detection unit 101 in the axis O direction (that is, the left-right direction in FIG. 2).

  The first ammonia detector 102 includes a first reference electrode 211 formed on the insulating layer 120, a first solid electrolyte body 212 that covers the surface and side surfaces of the first reference electrode 211, and the first solid electrolyte body 212. And a first detection electrode 213 formed on the surface. Similarly, as shown in FIG. 3, the second ammonia detection unit 103 includes a second reference electrode 221 formed on the insulating layer 120 and a second solid electrolyte body that covers the surface and side surfaces of the second reference electrode 221. 222 and a second detection electrode 223 formed on the surface of the second solid electrolyte body 222.

  The first reference electrode 211 and the second reference electrode 221 are mainly composed of platinum as an electrode material, and specifically, are composed of a material containing Pt and zirconium oxide. The first solid electrolyte body 212 and the second solid electrolyte body 222 are made of an oxygen ion conductive material such as yttria-stabilized zirconia. The first detection electrode 213 and the second detection electrode 223 are mainly composed of gold as an electrode material, and specifically, are composed of a material containing Au and zirconium oxide. The electrode materials of the first detection electrode 213 and the second detection electrode 223 are selected so that the ratio between the sensitivity to ammonia and the sensitivity to NOx is different in the first ammonia detection unit 102 and the second ammonia detection unit 103. Yes.

  The first ammonia detection unit 102 and the second ammonia detection unit 103 are integrally covered with a porous protective layer 230. The protective layer 230 prevents the poisonous substances from adhering to the first detection electrode 213 and the second detection electrode 223, and diffuses the ammonia flowing into the first ammonia detection unit 102 and the second ammonia detection unit 103 from the outside. Is to adjust. Thus, the first ammonia detection unit 102 and the second ammonia detection unit 103 function as a mixed potential type sensing unit.

As shown in FIG. 2, the control unit 3 includes a control circuit 180 and a microcomputer 190 (hereinafter, microcomputer 190).
The control circuit 180 is an analog circuit arranged on the circuit board. The control circuit 180 includes an Ip1 drive circuit 181, a Vs detection circuit 182, a reference voltage comparison circuit 183, an Icp supply circuit 184, a Vp2 application circuit 185, an Ip2 detection circuit 186, a heater drive circuit 187, and an electromotive force detection circuit 188.

  The pumping electrode 132, the detection electrode 142, and the pumping electrode 152 are connected to a reference potential. The pumping electrode 133 is connected to the Ip1 drive circuit 181. The reference electrode 143 is connected to the Vs detection circuit 182 and the Icp supply circuit 184. The pumping electrode 153 is connected to the Vp2 application circuit 185 and the Ip2 detection circuit 186. The heater 160 is connected to the heater drive circuit 187.

  The Ip1 drive circuit 181 supplies the first pumping current Ip1 by applying the voltage Vp1 between the pumping electrode 132 and the pumping electrode 133, and detects the supplied first pumping current Ip1.

The Vs detection circuit 182 detects the voltage Vs between the detection electrode 142 and the reference electrode 143, and outputs the detected result to the reference voltage comparison circuit 183.
The reference voltage comparison circuit 183 compares the reference voltage (for example, 425 mV) with the output of the Vs detection circuit 182 (that is, the voltage Vs), and outputs the comparison result to the Ip1 drive circuit 181. The Ip1 drive circuit 181 controls the flow direction of the first pumping current Ip1 and the magnitude of the first pumping current Ip1 so that the voltage Vs becomes equal to the reference voltage, and also controls the oxygen concentration in the first measurement chamber 121. , And adjust to a predetermined value that does not decompose NOx.

  The Icp supply circuit 184 flows a weak current Icp between the detection electrode 142 and the reference electrode 143. As a result, oxygen is sent from the first measurement chamber 121 to the reference oxygen chamber 146 via the solid electrolyte layer 141, so that the reference oxygen chamber 146 is set to a predetermined oxygen concentration as a reference.

  The Vp2 application circuit 185 applies a constant voltage Vp2 (for example, 450 mV) between the pumping electrode 152 and the pumping electrode 153. Thereby, in the second measurement chamber 148, NOx is dissociated by the catalytic action of the pumping electrodes 152 and 153 constituting the second pumping cell 150. Oxygen ions obtained by this dissociation move through the solid electrolyte layer 151 between the pumping electrode 152 and the pumping electrode 153, whereby a second pumping current Ip2 flows. The Ip2 detection circuit 186 detects the second pumping current Ip2.

  The heater driving circuit 187 drives the heater 160 by applying a positive voltage for energizing the heater to one end of the heater 160 that is a heating resistor and applying a negative voltage for energizing the heater to the other end of the heater 160. .

  The electromotive force detection circuit 188 includes an electromotive force between the first reference electrode 211 and the first detection electrode 213 (hereinafter referred to as a first ammonia electromotive force) and a second reference electrode 221 and the second detection electrode 223. An electromotive force (hereinafter, second ammonia electromotive force) is detected, and a signal indicating the detection result is output to the microcomputer 190.

  The microcomputer 190 includes a CPU 191, a ROM 192, a RAM 193, and a signal input / output unit 194. Various functions of the microcomputer are realized by the CPU 191 executing a program stored in a non-transitional physical recording medium. In this example, the ROM 192 corresponds to a non-transitional tangible recording medium that stores a program. Further, by executing this program, a method corresponding to the program is executed. The number of microcomputers constituting the control unit 3 may be one or more. Further, some or all of the functions executed by the microcomputer 190 may be configured by hardware using one or a plurality of ICs.

  The CPU 191 executes a process for controlling the sensor element unit 5 based on a program stored in the ROM 192. The signal input / output unit 194 is connected to the Ip1 drive circuit 181, the Vs detection circuit 182, the Ip2 detection circuit 186, the heater drive circuit 187, and the electromotive force detection circuit 188. The signal input / output unit 194 converts the voltage value of the analog signal from the Ip1 drive circuit 181, Vs detection circuit 182, Ip2 detection circuit 186 and electromotive force detection circuit 188 into digital data and outputs the digital data to the CPU 191.

  In addition, the CPU 191 outputs a drive signal to the heater drive circuit 187 via the signal input / output unit 194, thereby energizing the power supplied to the heater 160 by pulse width modulation so that the heater 160 reaches a target temperature. I have to. In addition, the energization control of the heater 160 is a known method of detecting the impedance of a cell (for example, the oxygen concentration detection cell 140) constituting the NOx detection unit 101 and controlling the amount of power supplied so that the detected impedance becomes a target value. It can be realized by a technique.

  Further, the CPU 191 reads various data from the ROM 192 and performs various arithmetic processes from the value of the first pumping current Ip1, the value of the second pumping current Ip2, the value of the first ammonia electromotive force, and the value of the second ammonia electromotive force.

The ROM 192 includes "first ammonia electromotive force-first ammonia concentration output relational expression", "second ammonia electromotive force-second ammonia concentration output relational expression", "first pumping current-oxygen concentration relational expression", "second ammonia "Pumping current-NOx concentration output relational expression", "First ammonia concentration output & second ammonia concentration output & oxygen concentration-corrected ammonia concentration relational expression", "First ammonia concentration output & second ammonia concentration output & oxygen concentration-correction" “NO ₂ concentration relational expression” and “NOx concentration output & corrected ammonia concentration & corrected NO ₂ concentration−corrected NOx concentration relational expression” are stored.

The “first ammonia concentration output & second ammonia concentration output & oxygen concentration−corrected ammonia concentration relational expression” corresponds to the following correction expression (1). “First ammonia concentration output & second ammonia concentration output & oxygen concentration−corrected NO ₂ concentration relational expression” corresponds to the following correction expression (2). “NOx concentration output & corrected ammonia concentration & corrected NO ₂ concentration−corrected NOx concentration relational expression” corresponds to the following correction formula (3).

  Further, the various data may be set as a predetermined relational expression as described above, or any data that calculates various gas concentrations from the output of the sensor, for example, may be set as a table. In addition, it may be a value obtained in advance using a gas model with a known gas concentration.

  The “first ammonia electromotive force—first ammonia concentration output relational expression” and “second ammonia electromotive force—second ammonia concentration output relational expression” are output from the first ammonia detection unit 102 and the second ammonia detection unit 103. It is a formula showing the relationship between ammonia electromotive force and ammonia concentration output.

The “first pumping current-oxygen concentration relational expression” is an expression representing the relation between the first pumping current and the oxygen concentration (that is, O ₂ concentration) in the exhaust gas. The “second pumping current-NOx concentration output relational expression” is an expression representing the relation between the second pumping current and the NOx concentration output.

The “first ammonia concentration output & second ammonia concentration output & oxygen concentration−corrected ammonia concentration relational expression” is the first and second ammonia concentration outputs affected by the oxygen concentration, ammonia concentration and NO ₂ concentration, the oxygen concentration and is an expression that represents the relationship between NO ₂ concentration effect correction ammonia concentration to remove the. “First ammonia concentration output & second ammonia concentration output & oxygen concentration−corrected NO ₂ concentration relational expression” is the first and second ammonia concentration outputs affected by the oxygen concentration, ammonia concentration and NO ₂ concentration, and the oxygen concentration And an equation representing the relationship with the corrected NO ₂ concentration from which the influence of the ammonia concentration has been removed. "NOx concentration output and correcting the ammonia concentration and correction NO ₂ concentration - correcting the NOx concentration relationship" includes a NOx concentration output affected by the ammonia concentration and NO ₂ concentration, correction to remove the effect of ammonia concentration and NO ₂ concentration It is a formula showing the relationship with the NOx concentration.

Next, a calculation process for obtaining the NO ₂ concentration, the NOx concentration, and the ammonia concentration from the first pumping current Ip1, the second pumping current Ip2, the first ammonia electromotive force, and the second ammonia electromotive force will be described. This calculation process is executed by the CPU 191 of the microcomputer 190.

  When the CPU 191 receives the first pumping current Ip1, the second pumping current Ip2, the first ammonia electromotive force, and the second ammonia electromotive force, the CPU 191 outputs the oxygen concentration, the NOx concentration output, the first ammonia concentration output, and the second ammonia concentration output. An arithmetic process for obtaining is performed. Specifically, from the ROM 192, “first ammonia electromotive force—first ammonia concentration output relational expression”, “second ammonia electromotive force—second ammonia concentration output relational expression”, “first pumping current Ip1—oxygen concentration relational expression. , "Second pumping current Ip2-NOx concentration output relational expression" is called, and the oxygen concentration and each concentration output are calculated using these relational expressions.

  The "first ammonia electromotive force-first ammonia concentration output relational expression" and the "second ammonia electromotive force-second ammonia concentration output relational expression" are used by the first ammonia detection unit 102 and the second ammonia detection unit 103. This is an equation set so that the ammonia concentration in the gas to be measured and the ammonia concentration output of the ammonia detector are in a substantially linear relationship over the entire range of ammonia electromotive force that can be output in the environment. By performing conversion using such a conversion formula, it is possible to perform calculation using changes in slope and offset in a later correction formula.

When the oxygen concentration, the NOx concentration output, the first ammonia concentration output, and the second ammonia concentration output are obtained, the CPU 191 performs an arithmetic operation using a correction formula described below to obtain the ammonia concentration in the exhaust gas, Determine the NO ₂ concentration and NOx concentration.

Correction formula (1): x = F (A, B, D)
= (EA-c) * (jB-h-fA + d) / (eA-c-iB + g) + fA-d
Correction formula (2): y = F ′ (A, B, D)
= (JB-h-fA + d) / (eA-c-iB + g)
Correction formula (3): z = C−ax + by
Here, x is the ammonia concentration, y is the NO ₂ concentration, and z is the NOx concentration. A is the first ammonia concentration output, B is the second ammonia concentration output, C is the NOx concentration output, and D is the oxygen concentration. F in equation (1) represents that x is a function of (A, B, D), and F ′ in equation (2) is that y is a function of (A, B, D). Represents. Further, a and b are correction coefficients, and c, d, e, f, g, h, i, and j are coefficients calculated using the oxygen concentration D (that is, coefficients determined by D).

The CPU 191 assigns the first ammonia concentration output, the second ammonia concentration output, the NOx concentration output, and the oxygen concentration to the correction equations (1) to (3) described above, thereby calculating the ammonia concentration in the exhaust gas, Determine the NO ₂ concentration and NOx concentration.

  The correction equation (1) and the correction equation (2) are equations that are determined based on the characteristics of the first ammonia detector 102 and the second ammonia detector 103, and the correction equation (3) is a characteristic of the NOx detector 101. This is a formula determined based on The correction expressions (1) to (3) are merely examples of the correction expression, and other correction expressions, coefficients, and the like may be used as appropriate according to the gas detection characteristics.

  And the microcomputer 190 of the control part 3 performs a gas concentration calculation process. The gas concentration calculation process is executed every time a preset execution cycle elapses after the heater 160 generates heat by supplying power to the heater 160 and the sensor element unit 5 reaches the activation temperature. It is.

Here, the procedure of the gas concentration calculation process will be described.
When the gas concentration calculation process is executed, the CPU 191 of the microcomputer 190 first, as shown in FIG. 4, in S10, the first pumping current Ip1, the second pumping current Ip2, the first ammonia electromotive force, and the second ammonia electromotive force. The detection result of power is acquired from the control circuit 180. In S20, the oxygen concentration is calculated. Specifically, the oxygen concentration is calculated using “first pumping current Ip1—oxygen concentration relational expression”.

Further, in S30, the ammonia concentration is calculated by the above calculation, that is, the calculation using the oxygen concentration calculated in S20 and the correction equation (1).
In S40, the oxygen concentration calculated in S20, “first ammonia electromotive force−first ammonia concentration output relational expression”, “second ammonia electromotive force−second ammonia concentration output relational expression”, “first ammonia electromotive force—second ammonia concentration output relational expression”, a second pumping current -NOx concentration output relationship "," first ammonia concentration output and the second ammonia concentration output and oxygen concentration - correction NO ₂ concentration relationship "," NOx concentration output and correcting the ammonia concentration and correction NO ₂ concentration Using the “corrected NOx concentration relational expression”, the NO ₂ concentration and the NOx concentration are calculated by the above calculation.

Next, in S50, the oxygen concentration calculated in S20 is corrected. Hereinafter, the oxygen concentration calculated in S20 is referred to as an uncorrected oxygen concentration. In S50, specifically, the oxygen concentration before correction calculated in S20 is C (O ₂ ), the ammonia concentration calculated in S30 is C (NH ₃ ), a preset correction coefficient is α, The corrected oxygen concentration is Cc (O ₂ ), and the oxygen concentration is corrected by the following equation (4). In the present embodiment, the correction coefficient α is set to 1.25.

Cc (O ₂ ) = C (O ₂ ) + α × C (NH ₃ ) (4)
The correction coefficient α is set based on the chemical reaction equation shown by the following equation (5). That is, the correction coefficient α is set based on the theoretical consumption of 5/4 (= 1.25) times as many oxygen molecules as ammonia molecules.

4NH ₃ + 5O ₂ → 4NO + 6H ₂ O (5)
FIG. 5 is a graph showing the dependence of the oxygen concentration before correction on the ammonia concentration when the concentration of oxygen contained in the gas to be measured is 15% and 7%. The upper graph in FIG. 5 shows the ammonia concentration dependency when the oxygen concentration is 15%, and the lower graph in FIG. 5 shows the ammonia concentration dependency when the oxygen concentration is 7%.

As shown in FIG. 5, the pre-correction oxygen concentration decreases as the concentration of ammonia contained in the gas to be measured increases.
As shown by the straight line L1 and the straight line L2 in the graph of FIG. 5, respectively, the ammonia concentration dependence of the oxygen concentration before correction when the concentration of oxygen contained in the gas to be measured is 15% and 7%, respectively, ) And the following formula (7). In the following formulas (6) and (7), Y [%] is the oxygen concentration before correction, and X [%] is the ammonia concentration.

Y = −1.30X + 14.9 (6)
Y = −1.28X + 7.03 (7)
The absolute values of the slopes in the linear expressions of the above formulas (6) and (7) are 1.30 and 1.28, respectively, and the oxygen molecule consumption rate calculated theoretically based on the above formula (5) (that is, , 1.25).

When the process of S50 ends, the gas concentration calculation process is temporarily ended as shown in FIG.
The microcomputer 190 configured as described above calculates the concentration of oxygen contained in the exhaust gas.
Then, the microcomputer 190 acquires the first pumping current Ip1 from the NOx detection unit 101.

The NOx detector 101 outputs a first pumping current Ip1 whose value changes according to the oxygen concentration in the first measurement chamber 121 into which exhaust gas flows.
The microcomputer 190 acquires the first ammonia electromotive force and the second ammonia electromotive force from the first ammonia detection unit 102 and the second ammonia detection unit 103, respectively. The first ammonia detector 102 and the second ammonia detector 103 each output a first ammonia electromotive force and a second ammonia electromotive force whose values change according to the concentration of ammonia contained in the exhaust gas.

The microcomputer 190 obtains the concentration of oxygen contained in the exhaust gas based on the first ammonia electromotive force, the second ammonia electromotive force, and the first pumping current Ip1.
In the NOx detection unit 101, ammonia and oxygen are introduced into the first measurement chamber 121. For this reason, when ammonia contained in the exhaust gas is introduced into the first measurement chamber 121 of the NOx detector 101, oxygen is consumed by burning the ammonia. Thereby, when ammonia and oxygen are contained in the exhaust gas, the concentration of oxygen contained in the exhaust gas is different from the concentration of oxygen in the first measurement chamber 121.

  In contrast, the microcomputer 190 obtains the concentration of oxygen contained in the exhaust gas based on the first ammonia electromotive force, the second ammonia electromotive force, and the first pumping current Ip1. Therefore, the microcomputer 190 can calculate the amount of oxygen consumed by the combustion of ammonia based on the concentration of ammonia contained in the exhaust gas, and the calculation result and the oxygen concentration in the first measurement chamber 121 can be calculated. Based on the above, it is possible to calculate the oxygen concentration before oxygen is consumed by the combustion of ammonia. Thereby, the microcomputer 190 can improve the detection accuracy of the concentration of oxygen contained in the exhaust gas.

  Further, the microcomputer 190 calculates the oxygen concentration based on the first pumping current Ip1 output from the NOx detector 101. The microcomputer 190 calculates the ammonia concentration based on the first ammonia electromotive force and the second ammonia electromotive force output from the first ammonia detection unit 102 and the second ammonia detection unit 103, respectively. And the microcomputer 190 calculates | requires the density | concentration of oxygen contained in exhaust gas by correct | amending oxygen concentration based on ammonia concentration.

  Further, the microcomputer 190 corrects the oxygen concentration by adding the oxygen value and the multiplication value of the preset correction coefficient α and the ammonia concentration. Thereby, the microcomputer 190 can correct the oxygen concentration by a simple calculation of executing one multiplication and one addition, and the processing load on the microcomputer 190 can be reduced.

  The first measurement chamber 121 is configured such that exhaust gas flows through the diffusion resistor 122. Since the gas phase reaction occurs more stably due to the presence of the diffusion resistor 122, the microcomputer 190 can more accurately determine the concentration of oxygen contained in the exhaust gas.

  The NOx detector 101, the first ammonia detector 102, and the second ammonia detector 103 are configured as an integrated multi-gas sensor 2. Thereby, the microcomputer 190 can detect the oxygen concentration and the ammonia concentration in substantially the same region of the exhaust gas.

  In the embodiment described above, the microcomputer 190 corresponds to the concentration calculation device, S10 corresponds to the processing as the first acquisition unit and the second acquisition unit, and S50 corresponds to the processing as the correction unit.

S20 corresponds to processing as the first calculation unit, and S30 corresponds to processing as the second calculation unit.
The first measurement chamber 121 corresponds to a measurement chamber, the NOx detection unit 101 corresponds to a first detection unit, and the first ammonia detection unit 102 and the second ammonia detection unit 103 correspond to a second detection unit.

Further, the exhaust gas corresponds to the measurement gas, the first pumping current Ip1 corresponds to the first concentration signal, and the oxygen concentration calculated in S20 corresponds to the first calculated concentration.
The first ammonia electromotive force and the second ammonia electromotive force correspond to the second concentration signal, and the ammonia concentration calculated in S30 corresponds to the second calculated concentration.

The correction coefficient α corresponds to a correction coefficient, the multi-gas sensor 2 corresponds to an integrated gas sensor, and the multi-gas detection device 1 corresponds to a gas detection device.
As mentioned above, although one embodiment of this indication was described, this indication is not limited to the above-mentioned embodiment, and can carry out various modifications.

  For example, in the above embodiment, the oxygen concentration is calculated based on the signal output from the NOx detection unit 101. A sensor that outputs a signal whose value changes according to the concentration of oxygen is not limited to the NOx detector. For example, in addition to the measurement chamber and the oxygen concentration detection cell, a full-range air-fuel ratio comprising a pumping cell that pumps oxygen into or out of the measurement chamber in response to a pumping current energized from the outside. One that calculates the oxygen concentration based on the signal output from the sensor is mentioned.

  In the above embodiment, the correction coefficient α is set to 1.25 based on the chemical reaction equation represented by the above equation (5). However, it is considered that the consumption ratio at which oxygen molecules are consumed by ammonia molecules varies depending on the degree of diffusion of exhaust gas controlled by the diffusion resistor 122. Similarly, the consumption rate depends on the position where the gas inlet for introducing the exhaust gas is arranged inside the first measurement chamber 121 and the position where the first measurement chamber 121 is arranged in the sensor element unit 5. It will change. For this reason, for example, as shown in FIG. 5, the ammonia concentration dependence of the oxygen concentration before correction may be actually measured, and the correction coefficient α may be set based on the measurement result.

  In the above embodiment, the ammonia concentration is corrected using the oxygen concentration before correction. However, oxygen correction may be performed using the ammonia concentration before correction. However, the ammonia concentration can be calculated more accurately by performing the process of correcting the ammonia concentration using the oxygen concentration.

  In the above embodiment, the diffusion resistor 122 controls the diffusion of the exhaust gas. However, the diffusion resistance is not limited to the porous diffusion resistor, and any diffusion resistance may be provided on the path through which the gas to be measured flows into the measurement chamber, such as the slit and the protective layer of the element. By setting the structure of the protector and the position of the sensor, diffusion resistance can be given.

  The functions of one component in each of the above embodiments may be shared by a plurality of components, or the functions of a plurality of components may be exhibited by one component. Moreover, you may abbreviate | omit a part of structure of each said embodiment. In addition, at least a part of the configuration of each of the above embodiments may be added to or replaced with the configuration of the other above embodiments. In addition, all the aspects included in the technical idea specified from the wording described in the claims are embodiments of the present disclosure.

  In addition to the above-described microcomputer 190, a system including the microcomputer 190 as a constituent element, a program for causing the computer to function as the microcomputer 190, a non-transition actual recording medium such as a semiconductor memory storing the program, a concentration calculation method, and the like The present disclosure can be realized in various forms.

  DESCRIPTION OF SYMBOLS 1 ... Multi gas detection apparatus, 2 ... Multi gas sensor, 3 ... Control part, 101 ... Detection part, 102 ... 1st ammonia detection part, 103 ... 2nd ammonia detection part, 121 ... 1st measurement chamber, 122 ... Diffusion resistor 140 ... oxygen concentration detection cell, 190 ... microcomputer

Claims (6)

A concentration calculation device for calculating the concentration of oxygen contained in a gas to be measured,
A first acquisition unit configured to acquire the first concentration signal from a first detection unit that outputs a first concentration signal whose value changes according to the concentration of oxygen in the measurement chamber into which the measurement gas flows;
A second acquisition unit configured to acquire the second concentration signal from a second detection unit that outputs a second concentration signal whose value changes according to the concentration of ammonia contained in the gas to be measured;
A concentration calculation device comprising: a correction unit configured to obtain a concentration of oxygen contained in the measurement gas based on the second concentration signal and the first concentration signal. The concentration calculation apparatus according to claim 1,
A first calculator configured to calculate a first calculated density based on the first density signal output from the first detector;
A second calculation unit configured to calculate a second calculated concentration based on the second concentration signal output from the second detection unit;
The concentration calculating device obtains the concentration of oxygen contained in the gas to be measured by correcting the first calculated concentration based on the second calculated concentration. The concentration calculation apparatus according to claim 2,
The correction unit corrects the first calculated density by adding a multiplication value of a preset correction coefficient and the second calculated density and the first calculated density. It is the density | concentration calculation apparatus of any one of Claims 1-3,
The concentration calculation device is configured such that the measurement chamber flows in the measurement gas through a diffusion resistor. It is the density | concentration calculation apparatus of any one of Claims 1-4, Comprising:
The concentration calculation apparatus in which the first detection unit and the second detection unit are configured as an integrated gas sensor. A first detector that outputs a first concentration signal whose value changes according to the concentration of oxygen in the measurement chamber into which the gas to be measured flows;
A second detection unit that outputs a second concentration signal whose value changes according to the concentration of ammonia contained in the gas to be measured;
A gas detection apparatus comprising: the concentration calculation apparatus according to any one of claims 1 to 5.

Images