JP2023044914A - Gas measurement device - Google Patents

Abstract

To provide a gas measurement device for easily and accurately measuring an ammonia concentration.SOLUTION: A gas measurement device 1 includes a sensor element 100 and a sensor control device 300. The sensor element 100 includes: a first measurement chamber R1 and second measurement chamber R2 to which exhaust gas is introduced; a pump cell 110; a Vs cell 120; and a detection cell 130. The sensor control device 300 includes: a CPU 331 and Vp3 application circuit 323 for applying, to the Vs cell 120, an oxidation voltage Vp31 which causes an ammonia oxidation reaction on a third electrode 122 and a non-oxidation voltage which is smaller than the oxidation voltage and does not cause the ammonia oxidation reaction on the third electrode 122; and the CPU 331 for calculating an ammonia concentration based on the value of a current Ip21 to be output from the detection cell 130 when the oxidation voltage is applied to the Vs cell 120 and the value of a current Ip22 to be output from the detection cell 130 when the non-oxidation voltage is applied to the Vs cell 120.SELECTED DRAWING: Figure 3

Description

The technology disclosed by this specification relates to a gas measuring device.

For example, it has recently become apparent that exhaust gases emitted from vehicles may contain ammonia, which is produced as a by-product of nitrogen compound purification. Due to growing interest in environmental protection, it is believed that ammonia discharged into the atmosphere will be subject to regulation in the future.

A gas sensor capable of measuring both the concentration of nitrogen oxides and the concentration of ammonia in exhaust gas has been proposed (see Patent Document 1). This gas sensor includes a preliminary adjustment chamber communicating with a gas introduction port into which a gas to be measured is introduced, an oxygen concentration adjustment chamber communicating with the preliminary adjustment chamber via a second diffusion rate controlling section, and a third diffusion rate controlling section. It has a measurement chamber communicating with the oxygen concentration adjustment chamber, a backup pump cell, a main pump cell, and a measurement pump cell.

The preliminary pump cell is composed of a preliminary pump electrode facing the preliminary adjustment chamber, an external pump electrode exposed to the external space, and a solid electrolyte layer. When the preliminary pump cell operates, oxygen is pumped in and out between the external space and the preliminary pump chamber, thereby adjusting the oxygen concentration in the atmosphere in the preliminary conditioning chamber and oxidizing ammonia on the preliminary pump electrode. A reaction occurs and ammonia is converted to nitric oxide. The main pump cell is composed of a main inner pump electrode facing the oxygen concentration adjusting chamber, an outer pump electrode exposed to the outer space, and a solid electrolyte layer. When the main pump cell operates, oxygen is pumped in and out between the outer space and the oxygen concentration pump chamber, thereby adjusting the oxygen concentration in the atmosphere in the oxygen concentration adjustment chamber and increasing the oxygen concentration on the main inner pump electrode. An oxidation reaction of ammonia occurs and ammonia is converted to nitric oxide. The measuring pump cell consists of a measuring electrode facing the measuring chamber, a reference electrode and a solid electrolyte layer. When the measuring pump cell is activated, nitric oxide is decomposed on the measuring electrode, the generated oxygen is pumped out, and a measuring pump current corresponding to the generated amount is output as a sensor output.

While the preliminary pump cell is being driven, ammonia contained in the gas to be measured is oxidized in the preliminary oxygen chamber, converted to nitrogen monoxide, and passed through the second diffusion control section. When the preliminary pump cell is stopped, the ammonia contained in the gas to be measured passes through the second diffusion control section as it is without being oxidized. Since nitrogen monoxide and ammonia have different diffusion coefficients, the difference in whether they pass through the second diffusion control section as nitrogen monoxide or as ammonia corresponds to the difference in the amount of nitrogen monoxide flowing into the measurement chamber. to change the measurement pump current flowing through the measurement pump cell. Therefore, the concentrations of nitrogen oxides and ammonia can be calculated based on the difference between the measured pump current when the standby pump cell is driven and the measured pump current when the standby pump cell is stopped.

International Publication No. 2017/222002

In the above configuration, an oxidation reaction of ammonia occurs in the preliminary oxygen chamber during operation of the preliminary pump cell. However, since the preliminary oxygen chamber is the most upstream chamber into which the gas to be measured directly flows, the oxygen concentration tends to fluctuate, and the ammonia oxidation reaction tends to vary. Therefore, further improvement was considered necessary to measure the concentration of ammonia with high accuracy.

A gas measuring device disclosed in the present specification is a gas measuring device that includes a sensor element and a control unit that controls the sensor element, and measures the concentration of ammonia in a measurement target gas containing ammonia, The sensor element comprises a gas space to be measured into which the gas to be measured is introduced, a first solid electrolyte body, and a first solid electrolyte body provided on the surface of the first solid electrolyte body and arranged inside the gas space to be measured. and a second electrode provided on the surface of the first solid electrolyte body and arranged outside the gas space to be measured. a pump cell for pumping or pumping, a second solid electrolyte body, a third electrode provided on the surface of the second solid electrolyte body and arranged inside the gas space to be measured, and the second solid electrolyte body an ammonia oxidation cell located downstream of the pump cell, a third solid electrolyte body, and a fourth electrode paired with the third electrode provided on the surface of a fifth electrode provided inside the gas space to be measured; and a sixth electrode provided on the surface of the third solid electrolyte body and paired with the fifth electrode. a detection cell whose concentration is adjusted and which outputs a current value corresponding to the concentration of nitrogen oxides in the gas to be measured after passing over the third electrode, wherein the control unit controls the ammonia oxidation cell and applying an oxidation voltage that causes an oxidation reaction of the ammonia on the third electrode and a non-oxidation voltage that is lower than the oxidation voltage and does not cause an oxidation reaction of the ammonia on the third electrode. a first current value output from the detection cell while the oxidation voltage is applied to the ammonia oxidation cell; and the detection cell while the non-oxidation voltage is applied to the ammonia oxidation cell. and a concentration calculation unit that calculates the concentration of the ammonia based on a second current value output from the.

According to the gas measuring device disclosed by this specification, the concentration of ammonia can be measured easily and accurately.

FIG. 1 is a cross-sectional view of the gas sensor of the embodiment. FIG. 2 is a cross-sectional view with a block diagram showing the configuration of the sensor element of the embodiment and the configuration of the sensor control device in the NOx measurement mode. FIG. 2 is a cross-sectional view with a block diagram showing the configuration of the sensor element of the embodiment and the configuration of the sensor control device in the ammonia measurement mode. FIG. 4 is a flow chart showing the flow of processing by the gas measuring device of the embodiment. FIG. 5 is a flow chart showing the flow of processing in the ammonia measurement mode in the embodiment.

[Overview of embodiment]
(1) A gas measuring device disclosed in the present specification is a gas measuring device that includes a sensor element and a control unit that controls the sensor element, and measures the concentration of ammonia in a measurement target gas containing ammonia. The sensor element comprises a gas space to be measured into which the gas to be measured is introduced, a first solid electrolyte body, and the sensor element provided on the surface of the first solid electrolyte body and arranged inside the gas space to be measured. and a second electrode provided on the surface of the first solid electrolyte body and arranged outside the gas space to be measured, and between the inside and the outside of the gas space to be measured. a second solid electrolyte body; a third electrode provided on the surface of the second solid electrolyte body and arranged inside the gas space to be measured; an ammonia oxidation cell provided on a surface of a solid electrolyte body and paired with the third electrode and positioned downstream of the pump cell; a third solid electrolyte body; and the third solid electrolyte body. and a sixth electrode provided on the surface of the third solid electrolyte body and paired with the fifth electrode, wherein the a detection cell that outputs a current value corresponding to the concentration of nitrogen oxides in the measurement target gas after passing over the third electrode, the oxygen concentration being adjusted by the pump cell; An oxidation voltage that causes an oxidation reaction of the ammonia on the third electrode and a non-oxidation voltage that is lower than the oxidation voltage and does not cause an oxidation reaction of the ammonia on the third electrode is applied to the ammonia oxidation cell. a first current value output from the detection cell while the oxidation voltage is applied to the ammonia oxidation cell; and a voltage application unit where the non-oxidation voltage is applied to the ammonia oxidation cell. and a concentration calculation unit that calculates the concentration of the ammonia based on a second current value output from the detection cell.

When an oxidation voltage is applied to the ammonia oxidation cell, ammonia in the gas to be measured is oxidized on the third electrode to produce nitrogen oxides and oxygen. Therefore, the first current value output from the detection cell corresponds to the sum of the concentration of nitrogen oxides originally contained in the gas to be measured and the concentration of nitrogen oxides generated by the oxidation of ammonia. . In a state in which a non-oxidizing voltage is applied to the ammonia oxidation cell, ammonia in the gas to be measured is not oxidized on the third electrode. Therefore, the second current value output from the detection cell corresponds to the concentration of nitrogen oxide originally contained in the gas to be measured. As described above, it is possible to easily and accurately calculate the concentration of ammonia in the gas to be measured based on the first current value and the second current value.

(2) In the gas measuring device of (1) above, the second electrode is a reference electrode exposed to a reference gas that serves as a reference for oxygen concentration, and the control section controls the measurement target in the gas space to be measured. between the first electrode and the second electrode so that the electromotive force generated between the first electrode and the second electrode is constant corresponding to the difference in oxygen concentration between the gas and the reference gas A current control section for controlling the flowing current may be provided.

According to such a configuration, there is no need to separately provide a cell for detecting the oxygen concentration, and the ammonia concentration in the gas to be measured can be accurately calculated with a simple configuration.

[Details of embodiment]
A specific example of the technology disclosed in this specification will be described below with reference to the drawings. The present invention is not limited to these exemplifications, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

<Embodiment>
An embodiment will be described with reference to FIGS. 1 to 5. FIG. The gas measuring device 1 of the present embodiment uses urea SCR (Selective Catalytic Reduction) to purify nitrogen oxides (NOx) contained in exhaust gas (an example of gas to be measured) emitted from a diesel engine of an automobile. It is used in the system. The urea SCR system is a system that purifies nitrogen oxides contained in exhaust gas by chemically reacting ammonia and nitrogen oxides to reduce the nitrogen oxides to nitrogen. In the urea SCR system, if the amount of ammonia supplied to nitrogen oxides becomes excessive, there is a risk that unreacted ammonia contained in the exhaust gas will be released to the outside. The gas measuring device 1 measures the concentrations of nitrogen oxides and ammonia contained in the exhaust gas.

The gas measuring device 1 includes a gas sensor 10 and a sensor control device 300 (an example of a control section) connected to the gas sensor 10 . The gas sensor 10 is installed downstream of the SCR catalyst device in an exhaust pipe connected to the diesel engine.

[Overall Configuration of Gas Sensor 10]
As shown in FIG. 1, the gas sensor 10 includes a sensor element 100, a metallic shell 11, an external protector 12, an internal protector 13, an outer cylinder 14, a holding member 18, and the like. The sensor element 100 is shaped like an elongated plate extending in the direction of the axis AX (vertical direction in FIG. 1) and is held inside the metal shell 11 . In the following description, the lower side of FIG. 1 is the leading end side, and the upper side of FIG. 1 is the rear end side.

The metal shell 11 is a cylindrical member having a through hole 11A penetrating in the direction of the axis AX. The main metal fitting 11 protrudes the front end portion of the sensor element 100 to the outside of its front end side, and projects the rear end portion of the sensor element 100 to the outside of its rear end side. kept within.

Inside the through hole 11A of the metal shell 11, an annular ceramic holder 15, two talc rings 16A and 16B annularly filled with talc powder, and a ceramic sleeve 17 are arranged. Specifically, the ceramic holder 15, the talc rings 16A and 16B, and the ceramic sleeve 17 are arranged in this order so as to surround the sensor element 100, overlapping from the front end side to the rear end side of the metallic shell 11. .

An outer protector 12 and an inner protector 13 made of metal and having a plurality of holes are attached to the front end of the metal shell 11 by welding so as to cover the front end of the sensor element 100 . On the other hand, an outer cylinder 14 is attached to the rear end portion of the metallic shell 11 by welding. The outer cylinder 14 has a tubular shape extending in the direction of the axis AX and surrounds the rear end of the sensor element 100 .

A holding member 18 is arranged inside the outer cylinder 14 . The holding member 18 is a tubular member made of an insulating material (specifically, alumina) and having an insertion hole 18A penetrating in the direction of the axis AX. A rear end portion of the sensor element 100 and a plurality of terminal members 19 are arranged in the insertion hole 18A. The plurality of terminal members 19 are electrically connected to each of the plurality of electrode terminal portions provided on the surface of the sensor element 100 in elastic contact therewith. A plurality of terminal members 19 are connected to a plurality of lead wires 20, respectively.

An elastic sealing member 21 made of fluororubber is arranged in the opening on the rear end side of the outer cylinder 14 . A plurality of lead wires 20 pass through the elastic seal member 21 and are led out to the outside.

[Sensor element 100]
As shown in FIGS. 2 and 3, the sensor element 100 includes a pump cell 110, a Vs cell 120 (an example of an ammonia oxidation cell), a detection cell 130, a first measurement chamber R1 (an example of a gas space to be measured), and a second measurement chamber. It includes chamber R2 (an example of a gas space to be measured), reference oxygen chamber R3, and heater 170. FIG. The pump cell 110 , the Vs cell 120 , and the detection cell 130 are arranged in this order from the upstream side of the exhaust gas flow path provided inside the sensor element 100 .

The sensor element 100 includes a third dense layer 141C, a second dense layer 141B, a first dense layer 141A, a fifth insulating layer 144, a first insulating layer 142, a sixth insulating layer 145, a second insulating layer 143, and a seventh insulating layer. It has a structure in which a layer 146, a third insulating layer 171, and a fourth insulating layer 172 are laminated in this order. The fifth insulating layer 144 has a through hole H1, and the first solid electrolyte body 111 is embedded inside the through hole H1. The sixth insulating layer 145 has a through hole H2, and the second solid electrolyte body 121 is embedded inside the through hole H2. The seventh insulating layer 146 has a third through hole H3, and the third solid electrolyte body 131 is embedded inside the third through hole H3.

The first measurement chamber R1 is provided between a layer composed of the fourth insulating layer 144 and the first solid electrolyte body 111 and a layer composed of the fifth insulating layer 145 and the second solid electrolyte body 121. It is a small space penetrating the first insulating layer 142 . The first measurement chamber R1 is separated from the external space by a first diffusion resistor 151 through which gas can pass. The first diffusion resistor 151 limits the flow rate of the exhaust gas from the outside to the first measurement chamber R1 per unit time.

The second measurement chamber R2 is provided between a layer composed of the fourth insulating layer 144 and the first solid electrolyte body 111 and a layer composed of the seventh insulating layer 146 and the third solid electrolyte body 131. It is a small space that is separated and penetrates the first insulating layer 142 , the fifth insulating layer 145 and the second insulating layer 143 . The first measurement chamber R1 and the second measurement chamber R2 are separated by a second diffusion resistor 152 through which gas can pass. The second diffusion resistor 152 limits the flow rate of the exhaust gas per unit time from the first measurement chamber R1 to the second measurement chamber R2.

The reference oxygen chamber R3 is provided between a layer composed of the fifth insulating layer 145 and the second solid electrolyte body 121 and a layer composed of the seventh insulating layer 146 and the third solid electrolyte body 131. It is a small space that penetrates the second insulating layer 143 . A porous body 161 through which gas can pass is arranged inside the reference oxygen chamber R3.

The second dense layer 141B has voids 100G. The gap 100G is a small space provided between the first dense layer 141A and the third dense layer 141C and penetrating the second dense layer 141B. The third dense layer 141C has an air inlet 100h that communicates the space 100G and the external space of the sensor element 100 with each other. Air, which serves as a reference gas, is introduced into the gap 100G through the air inlet 100h. The first dense layer 141A has a through hole H4 communicating with the gap 10G, and the inside of the through hole H4 is filled with a porous body 162 through which gas can pass.

The pump cell 110 includes a first solid electrolyte body 111, a first electrode 112 disposed on the surface of the first solid electrolyte body 111 (lower surface in FIG. 2), and the other surface of the first solid electrolyte body 111 (lower surface in FIG. 2). It is provided with a first electrode 112 and a second electrode 113 arranged on the upper surface) and serving as a counter electrode. The first electrode 112 is arranged inside the first measurement chamber R<b>1 , and the second electrode 113 is arranged outside the first measurement chamber R<b>1 and is in contact with the porous body 162 .

The Vs cell 120 includes a second solid electrolyte body 121, a third electrode 122 arranged on the surface of the second solid electrolyte body 121 (the top surface in FIG. 2), and the other surface of the second solid electrolyte body 121 (the top surface in FIG. 2). and a fourth electrode 123 disposed on the lower surface of the . The third electrode 122 is arranged inside the first measurement chamber R1. The fourth electrode 123 is arranged inside the reference oxygen chamber R3. The first electrode 112 is arranged inside the first measurement chamber R1 at a position close to the entrance of the exhaust gas from the outside (the first diffusion resistor 151), that is, on the upstream side of the flow path of the exhaust gas. The three electrodes 122 are arranged in the first measurement chamber R1 at a position closer to the second diffusion resistor 152 than the first electrode 112, that is, at the downstream side of the exhaust gas flow path. In other words, the Vs cell 120 is arranged downstream of the pump cell 110 in the flow path of the exhaust gas, and the exhaust gas introduced from the outside through the first diffusion resistor 151 first passes through the pump cell 110 . It contacts the first electrode 112 and then the third electrode 122 of the Vs cell 120 .

The detection cell 130 includes a third solid electrolyte body 131, a fifth electrode 132 arranged on the surface of the third solid electrolyte body 131 (upper surface in FIG. 2), and a surface of the third solid electrolyte body 131 (upper surface in FIG. 2). ) and is provided with a fifth electrode 132 and a sixth electrode 133 serving as a counter electrode. The fifth electrode 132 is arranged inside the second measurement chamber R2. The sixth electrode 133 is arranged facing the fourth electrode 123 inside the reference oxygen chamber R3. The fifth electrode 132 is arranged downstream of the third electrode 122 in the flow path of the exhaust gas. That is, the sensing cell 130 is arranged downstream of the Vs cell 120 . After coming into contact with the third electrode 122 of the Vs cell 120, the exhaust gas passes through the second diffusion resistor 152 and is introduced into the second measurement chamber R2, where it comes into contact with the fifth electrode 132 of the detection cell 130. there is

As shown in FIGS. 2 and 3, the first electrode 112, the third electrode 122, and the fifth electrode 132 are each connected to a reference potential.

The heater 170 includes a third insulating layer 171, a fourth insulating layer 172, and a resistance heating element 173 that is embedded between the third insulating layer 171 and the fourth insulating layer 172 and generates heat when energized. . The heater 170 is used to heat the solid electrolyte bodies 111, 121, and 131 to a temperature at which they are activated and to increase the conductivity of oxygen ions in the solid electrolyte bodies 111, 121, and 131, thereby stabilizing the operation. .

Solid electrolyte bodies 111, 121, and 131 are mainly composed of zirconia having oxygen ion conductivity. The insulating layers 142, 143, 144, 145, 146, 171, 172, the porous bodies 161, 162, and the diffusion resistors 151, 152 are mainly composed of alumina. Electrodes 112, 113, 122, 123, 132, 133 and resistance heating element 173 are mainly composed of platinum. A main component means that the content is 50% by mass or more.

[Sensor control device 300]
Next, an example of the configuration of the sensor control device 300 will be described. The sensor control device 300 includes an electric circuit section 310 and a microcomputer 330, as shown in FIGS. The gas sensor 10 is controlled by the sensor control device 300 in two modes, a NOx measurement mode for measuring nitrogen oxides contained in the exhaust gas and an ammonia measurement mode for measuring ammonia contained in the exhaust gas.

The microcomputer 330 controls the entire sensor control device 300, and includes a CPU (Central Processing Unit) 331, a RAM 332, a ROM 333, a signal input/output unit 334, an A/D converter 335, and the like. The CPU 331 executes processing for controlling the sensor element 100 based on programs stored in the ROM 333 .

The electrical circuit section 310 is an analog circuit arranged on a circuit board. 2 and 3, the electric circuit section 310 includes a reference voltage comparison circuit 311, an Ip1 drive circuit 312, a Vs1 detection circuit 313, an Icp supply circuit 314, an Ip2 detection circuit 315, a Vp2 application circuit 316, and a heater drive circuit. 317 , a resistance detection circuit 318 , an Ip3 detection circuit 321 , a Vs2 application/detection circuit 322 and a Vp3 application circuit 323 . The reference voltage comparison circuit 311, the Icp supply circuit 314, the Ip2 detection circuit 315, the Vp2 application circuit 316, the heater drive circuit 317, and the resistance detection circuit 318 operate in a NOx measurement mode for measuring nitrogen oxides contained in the exhaust gas and an exhaust gas measurement mode. Used in both ammonia measurement modes to measure ammonia contained in gas. The Ip1 drive circuit 312 and the Vs1 detection circuit 313 are used in the NOx measurement mode. The Ip3 detection circuit 321, the Vs2 application/detection circuit 322, and the Vp3 application circuit 323 are used in the ammonia measurement mode.

The Ip1 drive circuit 312 supplies a current Ip1 between the first electrode 112 and the second electrode 113 and outputs the value of the supplied current Ip1 to the microcomputer 330 .

The Vs1 detection circuit 313 detects the voltage Vs1 between the third electrode 122 and the fourth electrode 123 and outputs it to the reference voltage comparison circuit 311 . The reference voltage comparison circuit 311 compares the reference voltage (eg, 425 mV) with the output (voltage Vs1) of the Vs1 detection circuit 313 and outputs the comparison result to the Ip1 drive circuit 312 . The Ip1 drive circuit 312 controls the direction and magnitude of the flow of the current Ip1 so that the voltage Vs1 becomes equal to the reference voltage, and the oxygen concentration in the first measurement chamber R1 is set to a predetermined value such that nitrogen oxides do not decompose. value.

The Icp supply circuit 314 causes a weak current Icp to flow between the third electrode 122 and the fourth electrode 123 to pump out oxygen from the first measurement chamber R1 to the reference oxygen chamber R3.

The Vp2 application circuit 316 applies a constant voltage Vp2 (for example, 450 mV) that decomposes nitrogen oxides in the exhaust gas into oxygen and nitrogen between the fifth electrode 132 and the sixth electrode 133, thereby causing nitrogen oxidation. Decomposes matter into nitrogen and oxygen.

The Ip2 detection circuit 315 detects the fifth electrode 132 - the sixth electrode 133 when the oxygen generated by the decomposition of the nitrogen oxide on the fifth electrode 132 is pumped out to the sixth electrode 133 side through the third solid electrolyte body 131 . 133 is detected and output to the microcomputer 330 .

The heater driving circuit 317 applies a heater voltage Vh to the resistance heating element 173 of the heater 170 to cause the resistance heating element 173 to generate heat, thereby heating the sensor element 100 . The resistance heating element 173 is a single electrode pattern, one end of which is grounded and the other end of which is connected to the heater driving circuit 317 .

The Ip3 detection circuit 321 detects the value of the current Ip3 flowing between the first electrode 112 and the second electrode 113 and outputs it to the microcomputer 330 .

The Vs2 application/detection circuit 322 detects the voltage Vs2 between the first electrode 112 and the second electrode 113 and outputs it to the reference voltage comparison circuit 311 . The reference voltage comparison circuit 311 compares the reference voltage (for example, 425 mV) with the output (voltage Vs2) of the Vs2 application/detection circuit 322 and outputs the comparison result to the Vs2 application/detection circuit 322 . The Vs2 application/detection circuit 322 controls the voltage Vs2 to be constant near the reference voltage, and adjusts the oxygen concentration in the first measurement chamber R1 to a predetermined value at which nitrogen oxides do not decompose. . The Vs2 application/detection circuit 322 and the reference voltage comparison circuit 311 are examples of the current control section.

The CPU 331 outputs a drive signal to the Vp3 application circuit 323 via the signal input/output unit 334 and the A/D converter 335, so that the third electrode 122 oxidation control that applies an oxidation voltage Vp31 that causes an oxidation reaction of ammonia on the third electrode 122, and non-oxidation control that applies a non-oxidation voltage Vp32 that is lower than the oxidation voltage Vp31 and does not cause an oxidation reaction of ammonia on the selectively execute The CPU 331 and the Vp3 application circuit 323 are an example of a voltage application section.

The A/D converter 335 digitally converts the output values from the Ip2 detection circuit 315 and the Ip3 detection circuit 321 and outputs them to the CPU 331 via the signal input/output unit 334 . The CPU 331 reads various data from the ROM 333 and performs arithmetic processing to calculate the concentration of nitrogen oxides in the exhaust gas from the value of the current Ip2 and the concentration of oxygen in the exhaust gas from the value of the current Ip3. The CPU 331 is an example of a density calculator.

Further, the CPU 331 outputs a drive signal to the heater drive circuit 317 via the signal input/output unit 334 and the A/D converter 335, thereby controlling the power supplied to the heater 170 by pulse width modulation, thereby controlling the sensor element. 100 (more specifically, solid electrolyte bodies 111, 121, and 131) are brought to the activation temperature. The energization control of the heater 170 is based on a table in which the value indicating the amount of voltage change detected by the resistance detection circuit 318, the amount of change in the voltage Vs1 stored in the ROM 333, and the internal resistance value of the Vs cell 120 are associated in advance. Based on this, the internal resistance (impedance) of the Vs cell 120 is obtained, and the power supply amount is controlled so that the impedance becomes the target value.

[Operation Mode of Gas Measuring Device 1]
The process of measuring the concentration of nitrogen oxides and ammonia in the exhaust gas of a vehicle using the gas measuring device 1 will be described with reference to FIGS. 4 and 5. FIG.

When the diesel engine is started and power is supplied from the external power supply, the heater driving circuit 317 supplies a driving current to the resistance heating element 173 (step S10). The resistance heating element 173 is heated, and the solid electrolyte bodies 111, 121, 131 are heated and activated.

Exhaust gas is introduced into the first measurement chamber R1 while being restricted in the flow rate by the first diffusion resistor 151 .

Next, the Icp supply circuit 314 causes a weak current Icp to flow from the fourth electrode 123 to the third electrode 122 in the Vs cell 120 (step S20). As a result, the oxygen in the exhaust gas can receive electrons from the third electrode 122 in the first measurement chamber R1 on the negative electrode side, become oxygen ions, flow through the second solid electrolyte body 121, and become reference oxygen. Move into room R3. In other words, the oxygen in the first measurement chamber R1 is sent into the reference oxygen chamber R3 by the current Icp flowing between the third electrode 122 and the fourth electrode 123. As shown in FIG.

Next, the CPU 331 determines whether the voltage Vs1 detected by the Vs1 detection circuit 313 is equal to or less than a predetermined value (1.5 V) (step S30). When the CPU 331 determines that the voltage Vs1 is not equal to or lower than the predetermined value, the CPU 331 waits until the voltage Vs1 becomes equal to or lower than the predetermined value.

When the CPU 331 determines that the voltage Vs1 is equal to or lower than the predetermined value, it then determines whether or not it is necessary to switch to the ammonia measurement mode (step S40). This determination is made, for example, by determining whether injection of the urea aqueous solution into the exhaust gas by the SCR catalyst device has been detected.

When the injection of the aqueous urea solution into the exhaust gas by the SCR catalyst device is not detected, the CPU 331 determines that it is not necessary to switch to the ammonia measurement mode, and measures the concentration of nitrogen oxides in the exhaust gas in the NOx measurement mode. (Step S50). Measurement can be performed, for example, by a known procedure shown below.

A Vs1 detection circuit 313 detects a voltage Vs1 between the third electrode 122 and the fourth electrode 123 . The voltage Vs1 is a voltage corresponding to the oxygen concentration difference between the first measurement chamber R1 and the reference oxygen chamber R3. The Vs1 detection circuit 313 compares the detected voltage Vs1 with the reference voltage (425 mV) using the reference voltage comparison circuit 311 and outputs the comparison result to the Ip1 drive circuit 312 . Here, if the oxygen concentration in the first measurement chamber R1 is adjusted so that the voltage Vs1 becomes constant around 425 mV, the oxygen concentration in the exhaust gas in the first measurement chamber R1 will be a predetermined value (for example, 10 ⁻⁸ ~10 ^-9 atm).

When the oxygen concentration of the exhaust gas introduced into the first measurement chamber R1 is lower than a predetermined value, the Ip1 drive circuit 312 causes the current Ip1 to flow through the pump cell 110 so that the second electrode 113 side becomes the negative electrode, thereby causing the second electrode 110 to flow from the gap 100G. 1 Pump oxygen into the measuring chamber R1. On the other hand, when the oxygen concentration of the exhaust gas introduced into the first measurement chamber R1 is higher than the predetermined value, the Ip1 drive circuit 312 causes the current Ip1 to flow through the pump cell 110 so that the first electrode 112 side becomes the negative electrode. Oxygen is pumped out from the measurement chamber R1 to the gap 100G. That is, the pump cell 110 pumps oxygen between the inside and outside of the first measurement chamber R1 so that the oxygen concentration in the first measurement chamber R1 is constant.

The exhaust gas, the oxygen concentration of which has been adjusted in the first measurement chamber R1, is introduced into the second measurement chamber R2 while being restricted by the second diffusion resistor 152 in the flow rate. A voltage Vp2 is applied between the fifth electrode 132 and the sixth electrode 133 by the Vp2 application circuit 316, and the nitrogen oxides in the exhaust gas contacting the fifth electrode 132 in the second measurement chamber R2 are It is decomposed into nitrogen and oxygen on the fifth electrode 132 . The decomposed oxygen turns into oxygen ions, flows through the third solid electrolyte body 131, and moves into the reference oxygen chamber R3. The current Ip2 flowing through the sensing cell 130 at this time indicates a value corresponding to the nitrogen oxide concentration. The CPU 331 calculates the concentration of nitrogen oxides in the exhaust gas based on the value of the current Ip2.

When the injection of the urea aqueous solution into the exhaust gas by the SCR catalyst device is detected, the CPU 331 determines that it is necessary to switch to the ammonia measurement mode, and measures the concentration of ammonia in the exhaust gas in the ammonia measurement mode (step S60). The measurement procedure is as follows.

In the ammonia measurement mode, the second electrode 113 serves as a reference electrode exposed to a reference gas that serves as a reference for oxygen concentration. Air as a reference gas is introduced into the gap 100G through the air inlet 100h, passes through the porous body 162, and comes into contact with the second electrode 113. As shown in FIG. A Vs2 application/detection circuit 322 applies a voltage Vs2 between the first electrode 112 and the second electrode 113 of the pump cell 110 . The voltage Vs2 is set to a voltage value (for example, 280 mV) that does not substantially dissociate nitrogen oxides in the gas to be measured and allows measurement of a limiting current corresponding to the oxygen concentration in the first measurement chamber R1. Then, the Ip3 detection circuit 321 measures the current Ip3 flowing between the first electrode 112 and the second electrode 113 . When the oxygen concentration of the exhaust gas introduced into the first measurement chamber R1 is lower than a predetermined value, the current Ip3 flows through the pump cell 110 so that the second electrode 113 side becomes the negative electrode, and the current Ip3 flows from the gap 100G into the first measurement chamber R1. oxygen pumping takes place. On the other hand, when the oxygen concentration of the exhaust gas introduced into the first measurement chamber R1 is higher than the predetermined value, the current Ip3 flows through the pump cell 110 so that the first electrode 113 side becomes the negative electrode, and the current Ip3 flows from the first measurement chamber R1. Oxygen is pumped into the air gap 100G. That is, the pump cell 110 pumps oxygen between the inside and outside of the first measurement chamber R1 so that the oxygen concentration in the first measurement chamber R1 is constant (step S61).

The exhaust gas after the oxygen concentration has been adjusted by the pump cell 110 inside the first measurement chamber R1 flows toward the second diffusion resistor 152 and contacts the third electrode 122 . The CPU 331 outputs a drive signal to the Vp3 application circuit 323, and applies an oxidation voltage Vp31 that causes an oxidation reaction of ammonia on the third electrode 122 between the third electrode 122 and the fourth electrode 123 of the Vs cell 120. Control and non-oxidation control of applying a non-oxidation voltage Vp32 that is lower than the oxidation voltage Vp31 and that does not cause an oxidation reaction of ammonia on the third electrode 122 are selectively executed.

The CPU 331 first executes oxidation control (step S62). When the oxidation voltage Vp31 is applied between the third electrode 122 and the fourth electrode 123, ammonia contained in the exhaust gas is oxidized on the third electrode 122 to produce nitrogen monoxide and water. The exhaust gas after being subjected to the ammonia oxidation treatment by the third electrode 122 is introduced into the second measurement chamber R2 while being subject to the restriction of the flow rate by the second diffusion resistor 152, and comes into contact with the fifth electrode 132. The voltage Vp2 is applied between the fifth electrode 132 and the sixth electrode 133 by the Vp2 application circuit 316, so that nitrogen oxides in the exhaust gas are decomposed into nitrogen and oxygen on the fifth electrode 132. . Oxygen generated by the decomposition becomes oxygen ions, flows through the third solid electrolyte body 131, and moves into the reference oxygen chamber R3. The value of the current Ip21 flowing through the detection cell 130 at this time (an example of the first current value) indicates a value corresponding to the concentration of nitrogen oxides.

Under oxidation control, the nitrogen oxides decomposed on the fifth electrode 132 are composed of nitrogen oxides originally contained in the exhaust gas and nitrogen monoxide derived from ammonia in the exhaust gas (ammonia is added to the third electrode 122). Nitric oxide produced by being oxidized above). Therefore, the value of the current Ip21 becomes a value corresponding to the total amount of nitrogen oxides originally contained in the exhaust gas and nitrogen monoxide derived from ammonia in the exhaust gas.

Next, the CPU 331 executes non-oxidation control (step S63). When the non-oxidizing voltage Vp32 is applied between the third electrode 122 and the fourth electrode 123, the ammonia is not oxidized and is contained in the exhaust gas as it is. The exhaust gas that has passed over the third electrode 122 is introduced into the second measurement chamber R2 while being restricted in the flow rate by the second diffusion resistor 152 . As in the case of oxidation control, nitrogen oxides in the exhaust gas are decomposed into nitrogen and oxygen on the fifth electrode 132, and the oxygen generated by the decomposition becomes oxygen ions and moves into the reference oxygen chamber R3. do. At this time, a current Ip22 flows through the sensing cell 130 .

Under non-oxidizing control, the nitrogen oxides decomposed on the fifth electrode 132 contain nitrogen oxides originally contained in the exhaust gas, but do not contain nitrogen monoxide derived from ammonia in the exhaust gas. Therefore, the value of the current Ip22 flowing through the sensing cell 130 (an example of the second current value) corresponds to the amount of nitrogen oxide originally contained in the exhaust gas.

The CPU 331 calculates the concentration of nitrogen oxides in the exhaust gas based on the value of the current Ip22, and calculates the concentration of ammonia contained in the exhaust gas based on the difference between the value of the current Ip21 and the value of the current Ip22. (step S64).

After step S50 or step S60, the CPU 331 determines whether or not there is a request to end the measurement process (step S70). If it is determined that there is no end request, the processing from step S40 to step S60 is repeated. If it is determined that there is an end request, the measurement process is ended.

[Effect]
As described above, according to the present embodiment, the gas measuring device 1 includes the sensor element 100 and the sensor control device 300 that controls the sensor element 100, and measures the concentration of ammonia in exhaust gas containing ammonia. The sensor element 100 includes a first measurement chamber R1 and a second measurement chamber R2 into which exhaust gas is introduced, a first solid electrolyte body 111, and a first solid electrolyte body 111 provided on the surface of the first solid electrolyte body 111. A first electrode 112 arranged inside the measurement chamber R1, and a second electrode 113 provided on the surface of the first solid electrolyte body 111 and arranged outside the first measurement chamber R1. a pump cell 110 for pumping or pumping oxygen between the inside and outside of the chamber R1; a second solid electrolyte body 121; a Vs cell 120 located downstream of the pump cell 110, comprising a third electrode 122 disposed and a fourth electrode 123 provided on the surface of the second solid electrolyte body 121 and paired with the third electrode 122; a third solid electrolyte body 131; a fifth electrode 132 provided on the surface of the third solid electrolyte body 131 and arranged inside the second measurement chamber R2; Equipped with five electrodes 132 and a sixth electrode 133 paired with each other, the oxygen concentration is adjusted by the pump cell 110, and a current value corresponding to the concentration of nitrogen oxides in the exhaust gas after passing over the third electrode 122 is output. the sensor control device 300 provides the Vs cell 120 with an oxidation voltage Vp31 that causes an oxidation reaction of ammonia on the third electrode 122 and an oxidation voltage Vp31 that is lower than the oxidation voltage Vp31 and on the third electrode 122 A CPU 331 and a Vp3 application circuit 323 that apply a non-oxidizing voltage Vp32 that does not cause an oxidation reaction of ammonia at , a value of a current Ip21 that is output from the detection cell 130 while the oxidation voltage Vp31 is being applied to the Vs cell 120, and , the value of the current Ip22 output from the detection cell 130 while the non-oxidizing voltage Vp32 is being applied to the Vs cell 120, and a CPU 331 for calculating the concentration of ammonia based on the current Ip22.

When the oxidation voltage Vp31 is applied to the Vs cell 120, ammonia in the exhaust gas is oxidized on the third electrode 122 to produce nitrogen oxides and oxygen. Therefore, the value of the current Ip21 output from the detection cell 130 corresponds to the sum of the concentration of nitrogen oxides originally contained in the exhaust gas and the concentration of nitrogen oxides produced by the oxidation of ammonia. . Ammonia in the exhaust gas is not oxidized on the third electrode 122 when the non-oxidizing voltage Vp32 is applied to the Vs cell 120 . Therefore, the value of the current Ip22 output from the detection cell 130 corresponds to the concentration of nitrogen oxide originally contained in the exhaust gas. As described above, the concentration of ammonia in the exhaust gas can be easily and accurately calculated based on the value of the current Ip21 and the value of the current Ip22.

Further, the second electrode 113 is a reference electrode that is exposed to a reference gas serving as a reference of oxygen concentration, and the sensor control device 300 responds to the difference in oxygen concentration between the exhaust gas and the reference gas in the first measurement chamber R1. and a Vs2 application/detection circuit 322 that controls the current Ip1 flowing between the first electrode 112 and the second electrode 113 so that the electromotive force generated between the first electrode 112 and the second electrode 113 is constant. and a reference voltage comparison circuit 311 .

According to such a configuration, there is no need to separately provide a cell for detecting the oxygen concentration, and the ammonia concentration in the exhaust gas can be accurately calculated with a simple configuration.

<Other embodiments>
(1) The positional relationship between the pump cell and the ammonia oxidation cell should be such that the exhaust gas after the oxygen concentration has been adjusted by the pump cell is in contact with the third electrode of the ammonia oxidation cell. In the above embodiment, as shown in FIGS. 2 and 3, the second electrode 113 and the third electrode 122 overlap when viewed from the plate thickness direction of the sensor element 100 (from the upper side or the lower side in FIGS. 2 and 3). However, for example, it is sufficient if the third electrode is positioned downstream of the second electrode when viewed in the plate thickness direction of the sensor element, and the second electrode and the third electrode partly overlap. It doesn't matter if you do.
(2) In the above embodiment, non-oxidation control is performed after oxidation control, but the order of oxidation control and non-oxidation control is arbitrary, and oxidation control may be performed after non-oxidation control.
(3) In the above embodiment, the first measurement chamber R1 and the second measurement chamber R2 are separated by the second diffusion resistor 152, but the inside of one measured gas space not separated by the diffusion resistor The first electrode, the third electrode, and the fifth electrode may be arranged in the .

1: Gas measuring device 10: Gas sensor 11: Metal shell 11A: Through hole 12: External protector 13: Internal protector 14: Outer cylinder 15: Ceramic holders 16A, 16B: Talc ring 17: Ceramic sleeve 18: Holding member 18A: Insertion hole 19: Terminal member 20: Lead wire 21: Elastic seal member 100: Sensor element 100G: Gap 100h: Atmosphere inlet 110: Pump cell 111: First solid electrolyte body 112: First electrode 113: Second electrode 120: Vs cell ( ammonia oxidation cell)
121: Second solid electrolyte body 122: Third electrode 123: Fourth electrode 130: Detection cell 131: Third solid electrolyte body 132: Fifth electrode 133: Sixth electrode 141A: First dense layer 141B: Second dense layer 141C: Third Dense Layer 142: First Insulating Layer 143: Second Insulating Layer 144: Third Insulating Layer 145: Fourth Insulating Layer 146: Fifth Insulating Layer 151: First Diffusion Resistor 152: Second Diffusion Resistor 161: porous body 162: porous body 170: heater 171: third insulating layer 172: fourth insulating layer 173: resistance heating element 300: sensor control device (control unit)
310: Electric circuit section 311: Reference voltage comparison circuit (current control section)
312: Ip1 drive circuit 313: Vs1 detection circuit 314: Icp supply circuit 315: Ip2 detection circuit 316: Vp2 application circuit 317: Heater drive circuit 318: Resistance detection circuit 321: Ip3 detection circuit 322: Vs2 application/detection circuit (current control part)
323: Vp3 application circuit (voltage application unit)
330: Microcomputer 331: CPU (voltage application section, density calculation section)
332: RAM
333: ROM
334: Signal input/output unit 335: A/D converter AX: Axis lines H1, H2, H3, H4: Through hole R1: First measurement chamber (gas space to be measured)
R2: Second measurement chamber (measured gas space)
R3: Reference oxygen chamber

Claims (2)

A gas measuring device for measuring the concentration of ammonia in a measurement target gas containing ammonia, comprising a sensor element and a control unit for controlling the sensor element,
The sensor element is
a gas space to be measured into which the gas to be measured is introduced;
a first solid electrolyte body; a first electrode provided on the surface of the first solid electrolyte body and disposed inside the gas space to be measured; and a first electrode provided on the surface of the first solid electrolyte body and the measurement subject a pump cell for pumping oxygen between the inside and outside of the gas space to be measured, and a second electrode arranged outside the gas space;
a second solid electrolyte body; a third electrode provided on the surface of the second solid electrolyte body and arranged inside the gas space to be measured; an ammonia oxidation cell located downstream of the pump cell, comprising a fourth electrode paired with an electrode;
a third solid electrolyte body; a fifth electrode provided on the surface of the third solid electrolyte body and arranged inside the gas space to be measured; An electrode and a sixth electrode paired with each other are provided, and the oxygen concentration is adjusted by the pump cell, and a current value corresponding to the concentration of nitrogen oxides in the gas to be measured after passing over the third electrode is output. a sensing cell;
The control unit
The ammonia oxidation cell is provided with an oxidation voltage that causes an oxidation reaction of the ammonia on the third electrode and a non-oxidation voltage that is lower than the oxidation voltage and does not cause an oxidation reaction of the ammonia on the third electrode. a voltage applying unit that applies
A first current value output from the detection cell while the oxidation voltage is applied to the ammonia oxidation cell and a first current value output from the detection cell while the non-oxidation voltage is applied to the ammonia oxidation cell and a concentration calculator that calculates the concentration of the ammonia based on the second current value. wherein the second electrode is a reference electrode exposed to a reference gas serving as a reference for oxygen concentration;
The control unit makes the electromotive force generated between the first electrode and the second electrode constant corresponding to the difference in oxygen concentration between the measurement object gas and the reference gas in the gas space to be measured. 2. The gas measuring device according to claim 1, further comprising a current control section for controlling current flowing between said first electrode and said second electrode.

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