Gas sensor and a method for measuring gas concentration

Abstract

Gas sensor (10) designed to measure the concentrations of a plurality of components present in the presence of oxygen, comprising: a structural body (14) formed from a solid electrolyte which has an oxygen ion conductivity; a gas inlet opening (16) which is formed in the structural body (14) and into which a gas to be measured is introduced; a pre-chamber (21) comprising a pre-pump electrode (82) and connected to the gas inlet opening (16); an oxygen concentration setting chamber (18) comprising a pump electrode (42) and connected to the prechamber (21); a measuring chamber (20) comprising a measuring electrode (62) and connected to the oxygen concentration setting chamber (18); an oxygen concentration control unit (106) designed to control an oxygen concentration within the pre-chamber (21) on the basis of a voltage of the pre-pump electrode (82); a unit for measuring a defined component (104) configured to detect a measuring pump current (Ip3) flowing through an outside pump electrode (44) and the measuring electrode (62) during operation of the oxygen concentration pilot unit (106); and a unit for detecting a target component (110) designed to detect a concentration of a target component within the gas to be measured on the basis of a change magnitude (ΔIp3) between a measuring pump flow (Ip3in) from the unit for measuring a defined component (104) at the time of a first operation of the oxygen concentration pilot unit (106) and a measuring pump flow (Ip3out) from the unit for measuring a defined component (104) at the time of a second operation of the oxygen concentration pilot unit (106), and one of the measuring pump flow (Ip3in) and the measuring pump flow (Ip3out); wherein the unit for measuring a defined component (104) is designed to determine a value of a steady state of the measuring pump current (Ip3in) or a value of a steady state of the measuring pump current (Ip3out) on the basis of a peak value of a rate of change of the measuring pump current (Ip3) over time when an operation of the oxygen concentration feedforward unit (106) is switched between the first operation and the second operation.

Description

BACKGROUND OF THE INVENTION: Field of invention:

[0001] The present invention relates to a gas sensor and a method for measuring a gas concentration in which an oxygen ion-conducting solid electrolyte is used. Description of the state of the art:

[0002] Traditionally, gas sensors have been proposed that measure the concentrations of a plurality of target components, such as nitrogen oxide (NO) and ammonia (NH3) and the like, which are present together in the presence of oxygen, such as in an exhaust gas.

[0003] For example, international publication No. WO 2017 / 222 002 A1 discloses a gas sensor in which a prechamber, a main chamber, an auxiliary chamber, and a measuring chamber, separated by diffusion resistance elements, are provided in an oxygen-ion-conducting solid electrolyte, along with pump electrodes arranged in each of the respective chambers. With such a gas sensor, the operation or cessation of an oxidation reaction of NH3 to NO, which takes place within the prechamber, is controlled by switching between activating (ON) or stopping (OFF) a pre-pump cell of the prechamber. Furthermore, the gas concentrations of NH3 and NO are measured based on a change in the pump current (hereinafter referred to as the measuring pump current Ip3) of a measuring electrode within the measuring chamber, which occurs due to a difference in the diffusion rate of NH3 and NO from the prechamber to the main chamber.Furthermore, DE 10 2019 002 274 A1, as a subsequently published prior art, relates to a gas sensor that can measure the respective concentrations of a plurality of target components in a gas to be measured, as well as a method for controlling such a gas sensor. Additionally, JP H10 - 206 371 A deals with an oxygen concentration sensor for detecting the oxygen concentration in the exhaust gas, e.g., of a motor vehicle engine, and an abnormality detection device for detecting an abnormality in the oxygen sensor using the frequency characteristics of the current and voltage of the oxygen concentration sensor. SUMMARY OF THE INVENTION

[0004] In the gas sensor described in international publication no. WO 2017 / 222 002 A1, the measuring pump current Ip3 is recorded while the pre-pump cell of the pre-chamber switches between ON and OFF at regular intervals. When the pre-pump cell switches between ON and OFF, the measuring pump current Ip3 changes temporarily and then reaches a steady-state value. Therefore, to record the measuring pump current Ip3, it is necessary to wait a certain period until the measuring pump current Ip3 reaches a steady-state value, and the switching period of the pre-pump cell's operating state is set to be longer than the period until the measuring pump current Ip3 reaches a steady-state value.

[0005] However, the state of the incoming exhaust gas is constantly changing. Therefore, if the concentration of the target gas varies during the switching period, the steady-state value of the measuring pump flow rate Ip3 also changes. As a result, there are cases where the concentration of the target component gas represented by the measuring pump flow rate Ip3in when the pre-pump cell is switched ON differs from the concentration of the target component gas represented by the measuring pump flow rate Ip3out when the pre-pump cell is switched OFF. Thus, if the concentration of the target component in the measuring chamber fluctuates significantly during the switching period of a pre-pump cell cycle, a problem arises in that the preconditions for measurement are not met, and the measurement accuracy is reduced.

[0006] The object of the present invention is to provide a gas sensor and a method for measuring a gas concentration which can prevent a reduction in measurement accuracy due to a delay in the measurement time of the measuring pump current Ip3.

[0007] One aspect of the present invention is characterized by a gas sensor configured for measuring the concentrations of a plurality of components present in the presence of oxygen, comprising a structural body formed from a solid electrolyte having oxygen ion conductivity, a gas inlet opening formed in the structural body into which a gas to be measured is introduced, a pre-chamber comprising a pre-pump electrode and connected to the gas inlet opening, an oxygen concentration adjustment chamber comprising a pump electrode and connected to the pre-chamber, a measuring chamber comprising a measuring electrode and connected to the oxygen concentration adjustment chamber, and an oxygen concentration control unit configured for controlling an oxygen concentration within the pre-chamber based on a voltage of the pre-pump electrode.a unit for measuring a specified component, configured to detect a measuring pump current (Ip3) flowing through an outside pump electrode and the measuring electrode during operation of the oxygen concentration pilot unit, and a unit for detecting a target component, configured to detect a concentration of a target component within the gas to be measured based on a rate of change (ΔIp3) between a measuring pump current (Ip3in) from the unit for measuring a specified component at the time of a first operation of the oxygen concentration pilot unit and a measuring pump current (Ip3out) from the unit for measuring a specified component at the time of a second operation of the oxygen concentration pilot unit,and is configured to measure one of the measuring pump current (Ip3in) and the measuring pump current (Ip3out); wherein the unit is configured to measure a defined component for determining a value of a steady state of the measuring pump current (Ip3in) or a value of a steady state of the measuring pump current (Ip3out) based on a peak value of a rate of change of the measuring pump current (Ip3) over time when an operation of the oxygen concentration feedforward unit is switched between the first operation and the second operation.

[0008] Another aspect of the present invention is characterized by a method for measuring a gas concentration in which a gas sensor is used, wherein the gas sensor comprises a structural body formed from a solid electrolyte having oxygen ion conductivity, a gas inlet opening formed in the structural body into which a gas to be measured is introduced, a pre-chamber comprising a pre-pump electrode and connected to the gas inlet opening, an oxygen concentration control chamber comprising a pump electrode and connected to the pre-chamber, a measuring chamber comprising a measuring electrode and connected to the oxygen concentration control chamber, an oxygen concentration control unit configured for controlling an oxygen concentration within the pre-chamber based on a voltage of the pre-pump electrode, and a unit for measuring a defined component.which is configured to detect a measuring pump current (Ip3) flowing through an outside pump electrode and the measuring electrode during operation of the oxygen concentration pilot unit, and comprises a unit for detecting a target component, which is configured to detect a concentration of a target component within the gas to be measured based on a magnitude of change (ΔIp3) between a measuring pump current (Ip3in) from the unit for measuring a specified component at the time of a first operation of the oxygen concentration pilot unit and a measuring pump current (Ip3out) from the unit for measuring a specified component at the time of a second operation of the oxygen concentration pilot unit, and one of the measuring pump current (Ip3in) and the measuring pump current (Ip3out),wherein the method for measuring a gas concentration comprises an operating switchover step of performing a control to switch between the first operation and the second operation of the oxygen concentration control unit, a determination step of determining a peak value of a rate of change of the measuring pump current (Ip3) over time by the unit for measuring a specified component, accompanied by the control to switch between the first operation and the second operation of the oxygen concentration control unit, a determination step of determining a value of a steady state of the measuring pump current (Ip3) from a previously determined correlation between the peak value of the rate of change of the measuring pump current (Ip3) over time and the value of a steady state of the measuring pump current (Ip3) by the unit for measuring a specified component,and includes a detection step of detecting the concentration of the target component within the gas to be measured by the target component detection unit based on the steady-state value of the measuring pump flow (Ip3) from the unit for measuring a specified component.

[0009] According to the gas sensor and the method for measuring a gas concentration, as described above, by focusing attention on the rate of change of the pump current (measuring pump current) of the measuring electrode over time, which coincides with the switching of the operating state of the pre-pump cell in the pre-chamber, the predicted value of the steady-state pump current of the measuring electrode can be determined. Consequently, the steady-state pump current value can be determined before the pump current of the measuring electrode reaches a steady state. Therefore, the switching of the operating state of the pre-pump cell can be performed before the pump current of the measuring electrode reaches a steady state, and the switching period of the operating state of the pre-pump cell can be shortened.As a result, the delay in the measurement time of the measuring pump current Ip3 can be reduced and a reduction in measurement accuracy can be prevented.

[0010] The foregoing and other problems, features and advantages of the present invention will become clearer from the following description when it is taken together with the accompanying drawings, in which preferred embodiments of the present invention are shown by an illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a cross-sectional view showing a structural example of a gas sensor according to a first embodiment; Fig. 2 is a block diagram of the one in the Fig. 1 gas sensor shown; Fig. Figure 3 is an explanatory diagram that schematically shows reactions for a case where a pre-pump cell is located in the gas sensor of Fig. 1 is switched OFF; Fig. 4 is an explanatory diagram that schematically shows reactions for a case where a pre-pump cell is located in the gas sensor of Fig. 1 is switched ON; Fig. 5 is a flowchart illustrating a method for detecting a measuring pump current Ip3 in the gas sensor of Fig. 1 shows; Fig. Figure 6 is a diagram that schematically shows a change and rate of change of the measuring pump current Ip3 over time when the pre-pump cell is switched from OFF to ON; Fig. Figure 7 is a graph showing measurement results of a change in the measuring pump current Ip3 accompanied by the switching of the operating state of the pre-pump cell under a condition where the NO concentration of a gas to be measured is 0 ppm; Fig. Figure 8 is a graph showing the rate of change of the measuring pump current Ip3 over time, which is located in the Fig. 7 is shown; Fig. Figure 9 is a graph showing a correlation between the NH3 concentration and the rate of change of the measuring pump current Ip3 over time, which is shown in the Fig. 8 is shown; Fig. Figure 10 is a graph showing measurement results of a change in the measuring pump current Ip3 accompanied by the switching of the operating state of the pre-pump cell under a condition where the NO concentration of the gas to be measured is 500 ppm; Fig. Figure 11 is a graph showing the rate of change of the measuring pump current Ip3 over time, which is located in the Fig. 10 is shown; Fig. Figure 12 is a graph showing a correlation between the NH3 concentration and a peak value of the rate of change over time, which is shown in the Fig. 11 is shown; Fig. Figure 13 is a graph showing measurement results of a change in the NH3 concentration in a gas to be measured according to an FT-IR method and results (experimental example 3) of the determination of a detection value of the NH3 concentration by the gas sensor, which is located in the Fig. Figure 1 shows a simulation for a case where the operating switching period of the pre-pump cell has been set to 1 second (1 Hz); Fig. Figure 14 is a graph showing measurement results of a change in the NH3 concentration in a gas to be measured according to an FT-IR method and results (comparative example) of the determination of a detection value of the NH3 concentration by the gas sensor, which is located in the Fig. Figure 1 shows a simulation for a case where the operating switchover period of the pre-pump cell has been set to 4 seconds (0.25 Hz); and Fig. Figure 15 is a flowchart showing a method for detecting the measuring pump current Ip3 according to a second embodiment. DESCRIPTION OF PREFERRED EXECUTION FORMS

[0011] Exemplary embodiments of a gas sensor and a method for measuring a gas concentration according to the present invention are described below with reference to the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14 to Fig. 15 is illustrated and described. In the present embodiment, the term “to” when used to indicate a range of numbers is used with the implication that it includes the numerical values ​​indicated before and after the term as the lower limit or upper limit of the range of numbers. (First embodiment)

[0012] As it is in the Fig. 1 and Fig. As shown in Figure 2, a gas sensor 10 according to the present embodiment comprises a sensor element 12. The sensor element 12 comprises a structural body 14 formed from a solid electrolyte having at least one oxygen ion conductivity, a gas inlet opening 16 formed in the structural body 14 into which a gas to be measured is introduced, an oxygen concentration adjustment chamber 18 formed in the structural body 14 and connected to the gas inlet opening 16, and a measuring chamber 20 formed in the structural body 14 and connected to the oxygen concentration adjustment chamber 18.

[0013] The oxygen concentration adjustment chamber 18 comprises a main chamber 18a, located on the side of the gas inlet opening 16, and an auxiliary chamber 18b, which is connected to the main chamber 18a. The measuring chamber 20 is connected to the auxiliary chamber 18b. The oxygen concentration adjustment chamber 18 can consist solely of the main chamber 18a.

[0014] Furthermore, the gas sensor 10 includes a prechamber 21, which is provided between the gas inlet opening 16 and the main chamber 18a within the structural body 14. The main chamber 18a is connected to the gas inlet opening 16 via the prechamber 21.

[0015] The structural body 14, which has such a plurality of chambers 18a, 18b, 20, and 21, is formed by stacking a plurality of layers of substrates, which are, for example, made of a ceramic. In particular, the structural body 14 of the sensor element 12 is formed from several layers made of a first substrate 22a, a second substrate 22b, a third substrate 22c, a first solid electrolyte layer 24, a spacer layer 26, and a second solid electrolyte layer 28, which are stacked in this order from the bottom up. The respective layers are, for example, made of an oxygen-ion-conducting solid electrolyte, such as zirconium oxide (ZrO2) or the like.

[0016] The gas inlet opening 16 is provided at one end of the sensor element 12. The gas inlet opening 16 is formed between a lower surface 28b of the second solid electrolyte layer 28 and an upper surface 24a of the first solid electrolyte layer 24.

[0017] Furthermore, between the lower surface 28b of the second solid electrolyte layer 28 and the upper surface 24a of the first solid electrolyte layer 24, a first diffusion rate control element 30, the pre-chamber 21, a second diffusion rate control element 32, the oxygen concentration adjustment chamber 18, a third diffusion rate control element 34, and the measuring chamber 20 are provided. A fourth diffusion rate control element 36 is provided between the main chamber 18a and the auxiliary chamber 18b, which together form the oxygen concentration adjustment chamber 18.

[0018] The gas inlet opening 16, the first diffusion rate control element 30, the pre-chamber 21, the second diffusion rate control element 32, the main chamber 18a, the fourth diffusion rate control element 36, the auxiliary chamber 18b, the third diffusion rate control element 34, and the measuring chamber 20 are arranged adjacent to one another in such a way that they are interconnected in this order. The section from the gas inlet opening 16 leading to the measuring chamber 20 is also referred to as the gas flow section.

[0019] The gas inlet opening 16, the pre-chamber 21, the main chamber 18a, the auxiliary chamber 18b, and the measuring chamber 20 are configured such that they extend through the spacer layer 26 in the thickness direction. The lower surface 28b of the second solid electrolyte layer 28 is exposed on the upper portions of these chambers 18a, 18b, 20, and 21, and the upper surface 24a of the first solid electrolyte layer 24 is exposed on its lower portions. Furthermore, the side portions of the chambers 18a, 18b, 20, and 21 are divided by the spacer layer 26 or the diffusion rate control elements 30, 32, 34, and 36.

[0020] Each of the first diffusion rate control element 30, the third diffusion rate control element 34, and the fourth diffusion rate control element 36 is provided with two horizontally elongated slots. In particular, the slots in the upper and lower sections of these elements comprise slot-shaped openings that are elongated in a direction perpendicular to the surface of the drawing sheet. Furthermore, the second diffusion rate control element 32 is provided with a single horizontally elongated slot.

[0021] Furthermore, a reference gas introduction chamber 38 is provided at the other end (one end opposite the end where the gas introduction opening 16 is provided) of the sensor element 12. The reference gas introduction chamber 38 is formed between an upper surface 22c1 of the third substrate 22c and a lower surface 26b of the spacer layer 26. A side section of the reference gas introduction chamber 38 is also divided by a side surface of the first solid electrolyte layer 24. For example, oxygen or atmospheric air is introduced into the reference gas introduction chamber 38 as the reference gas.

[0022] The gas inlet opening 16 is a point that is open to the outside, and the target gas to be measured is drawn from the outside through the gas inlet opening 16 into the sensor element 12.

[0023] The first diffusion rate control element 30 is a point that exerts a predetermined diffusion resistance on the gas to be measured, which is introduced from the gas inlet opening 16 into the prechamber 21. Details concerning the prechamber 21 will be described later.

[0024] The second diffusion rate control element 32 is a point that exerts a predetermined diffusion resistance on the gas to be measured, which is introduced from the pre-chamber 21 into the main chamber 18a.

[0025] The main chamber 18a is provided as a space for adjusting the oxygen partial pressure within the gas to be measured, which is introduced through the gas inlet opening 16. The oxygen partial pressure is adjusted by operating a main pump cell 40.

[0026] The main pump cell 40 comprises an electrochemical pump cell, also referred to as the electrochemical main pump cell, which consists of a main pump electrode 42, an outer pump electrode 44, and an oxygen-ion-conducting solid electrolyte arranged sandwich-like between the two pump electrodes. The main pump electrode 42 is provided substantially on the entire surfaces of the upper surface 24a of the first solid electrolyte layer 24, the lower surface 28b of the second solid electrolyte layer 28, and the side surfaces of the spacer layer 26 that define the main chamber 18a. The outer pump electrode 44 is formed on the upper surface of the second solid electrolyte layer 28. The position of the outer pump electrode 44 is preferably arranged in a region corresponding to that of the main pump electrode 42, such that it is exposed to the outside.The main pump electrode 42 is preferably made of a material with a reduced reducing capacity with respect to the nitrogen oxide (NO) component within the gas to be measured. For example, the main pump electrode can be designed as a porous cermet electrode rectangular in plan view.

[0027] The main pump cell 40 applies a first pump voltage Vp1, which is supplied by a first variable current source 46 provided outside the sensor element 12, and by allowing a first pump current Ip1 to flow between the outside pump electrode 44 and the main pump electrode 42, oxygen inside the main chamber 18a can be pumped to the outside or alternatively, oxygen in the outside space can be pumped into the main chamber 18a.

[0028] Furthermore, the sensor element 12 comprises a first oxygen partial pressure detection sensor cell 50, which is an electrochemical sensor cell. The first oxygen partial pressure detection sensor cell 50 comprises the main pump electrode 42, a reference electrode 48, and the oxygen ion-conducting first solid electrolyte layer 24, which is sandwiched between these electrodes. The reference electrode 48 is formed between the first solid electrolyte layer 24 and the third substrate 22c and is made of the same porous cermet as the outer pump electrode 44. The reference electrode 48 has a rectangular shape in plan view. Furthermore, a reference gas introduction layer 52, made of porous aluminum oxide and connected to the reference gas introduction chamber 38, is provided around the circumference of the reference electrode 48.The reference gas in the reference gas introduction chamber 38 is supplied to the surface of the reference electrode 48 by means of the reference gas introduction layer 52. The first oxygen partial pressure detection sensor cell 50 generates a first electromotive force V1 between the main pump electrode 42 and the reference electrode 48, which is caused by the difference in oxygen concentration between the atmosphere inside the main chamber 18a and the reference gas in the reference gas introduction chamber 38.

[0029] The first electromotive force V1, generated in the first oxygen partial pressure sensing sensor cell 50, changes depending on the oxygen partial pressure of the atmosphere present in the main chamber 18a. Based on the aforementioned first electromotive force V1, the sensor element 12 controls the first variable current source 46 of the main pump cell 40. Consequently, the first pump voltage Vp1, applied to the main pump cell 40 by the first variable current source 46, can be controlled according to the oxygen partial pressure of the atmosphere in the main chamber 18a.

[0030] The fourth diffusion rate control element 36 exerts a predetermined diffusion resistance on the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 40 in the main chamber 18a, and is a point that directs the gas to be measured into the auxiliary chamber 18b.

[0031] The auxiliary chamber 18b serves as a space for further adjusting the oxygen partial pressure by means of an auxiliary pump cell 54 with respect to the gas to be measured, which is introduced through the fourth diffusion rate control element 36 after the oxygen concentration (oxygen partial pressure) has been preset in the main chamber 18a. According to this feature, the oxygen concentration within the auxiliary chamber 18b can be kept very precisely constant, and the NOx concentration can be measured with high accuracy.

[0032] The auxiliary pump cell 54 is an electrochemical pump cell and is formed from an auxiliary pump electrode 56, which is provided essentially over the entire surface facing the auxiliary chamber 18b in the lower surface 28b of the second solid electrolyte layer 28, the outer pump electrode 44, and the second solid electrolyte layer 28. Furthermore, the auxiliary pump electrode 56 is formed in the same way as the main pump electrode 42, also using a material with a reduced reducing capacity with respect to the NOx component within the gas to be measured.

[0033] The auxiliary pump cell 54 can, by applying a desired second pump voltage Vp2 between the auxiliary pump electrode 56 and the outside pump electrode 44, pump oxygen from the atmosphere inside the auxiliary chamber 18b out into the outside space or alternatively pump oxygen from the outside space into the auxiliary chamber 18b.

[0034] Furthermore, to control the oxygen partial pressure within the atmosphere inside the auxiliary chamber 18b, an electrochemical sensor cell is formed from the auxiliary pump electrode 56, the reference electrode 48, the second solid electrolyte layer 28, the spacer layer 26, and the first solid electrolyte layer 24. In particular, this forms a second oxygen partial pressure detection sensor cell 58 for controlling the auxiliary pump.

[0035] The second oxygen partial pressure detection sensor cell 58 generates a second electromotive force V2 between the auxiliary pump electrode 56 and the reference electrode 48, which is generated by a difference in oxygen concentration between the atmosphere inside the auxiliary chamber 18b and the reference gas in the reference gas introduction chamber 38. The second electromotive force V2 generated in the second oxygen partial pressure detection sensor cell 58 changes depending on the oxygen partial pressure of the atmosphere present in the auxiliary chamber 18b.

[0036] Based on the aforementioned second electromotive force V2, the sensor element 12 initiates pumping of the auxiliary pump cell 54 by controlling a second variable current source 60. Consequently, the oxygen partial pressure within the atmosphere inside the auxiliary chamber 18b is controlled to a low partial pressure that does not significantly affect the NOx measurement.

[0037] Furthermore, a second pump current Ip2 of the auxiliary pump cell 54 is used to control the second electromotive force V2 of the second oxygen partial pressure detection sensor cell 58. Specifically, the second pump current Ip2 is fed into the second oxygen partial pressure detection sensor cell 58 as a control signal. As a result, the second electromotive force V2 is controlled, and the gradient of the oxygen partial pressure within the gas to be measured, which is introduced into the auxiliary chamber 18b by the fourth diffusion rate control element 36, is controlled so that it remains constant. When the gas sensor 10 is used as a NOx sensor, the oxygen concentration within the auxiliary chamber 18b is maintained at a predetermined value with high accuracy for each of the respective conditions by the effects of the main pump cell 40 and the auxiliary pump cell 54.

[0038] The third diffusion rate control element 34 exerts a predetermined diffusion resistance on the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 54 in the auxiliary chamber 18b, and it is a point that directs the gas to be measured into the measuring chamber 20.

[0039] The measurement of the NOx concentration is primarily carried out by operating a measuring pump cell 61, which is provided in the measuring chamber 20. The measuring pump cell 61 is an electrochemical pump cell consisting of a measuring electrode 62, the outer pumping electrode 44, the second solid electrolyte layer 28, the spacer layer 26, and the first solid electrolyte layer 24. The measuring electrode 62 is, for example, located on the upper surface 24a of the first solid electrolyte layer 24 within the measuring chamber 20 and is made of a material with an increased reducing capacity with respect to the NOx component in the gas to be measured, which is higher than that of the main pumping electrode 42. The measuring electrode 62 can, for example, be a porous cermet electrode. Furthermore, a material is preferably used for the measuring electrode 62 that also acts as an NOx reduction catalyst for reducing NOx present in the atmosphere.

[0040] The measuring pump cell 61 generates oxygen by decomposing nitrogen oxide in the vicinity of the measuring electrode 62 within the measuring chamber 20. Furthermore, the measuring pump cell 61 can pump out the oxygen generated at the measuring electrode 62 and record the amount of oxygen generated as the measuring pump current Ip3, or in other words, as the sensor output.

[0041] Furthermore, to detect the oxygen partial pressure in the vicinity of the measuring electrode 62 within the measuring chamber 20, an electrochemical sensor cell, and in particular a third oxygen partial pressure detection sensor cell 66 for controlling the measuring pump, is formed from the first solid electrolyte layer 24, the measuring electrode 62, and the reference electrode 48. A third variable current source 68 is controlled on the basis of a third electromotive force V3, which is detected by the third oxygen partial pressure detection sensor cell 66.

[0042] The gas to be measured, introduced into the auxiliary chamber 18b, reaches the measuring electrode 62 within the measuring chamber 20 through the third diffusion rate control element 34 under a condition in which the oxygen partial pressure is controlled. Nitrogen oxide present in the vicinity of the measuring electrode 62 within the gas to be measured is reduced, thus generating oxygen. The generated oxygen is then pumped through the measuring pump cell 61. A third pump voltage Vp3 of the third variable current source 68 is controlled such that the third electromotive force V3, detected by the third oxygen partial pressure sensing sensor cell 66, remains constant. The amount of oxygen generated in the vicinity of the measuring electrode 62 is proportional to the nitrogen oxide concentration within the gas to be measured.Accordingly, the nitrogen oxide concentration within the gas to be measured can be calculated using the measuring pump flow rate Ip3 of the measuring pump cell 61. In particular, the measuring pump cell 61 forms a unit for measuring a defined component 104, which measures the concentration of a defined component (NO) within the measuring chamber 20.

[0043] Furthermore, the gas sensor 10 comprises an electrochemical sensor cell 70. The sensor cell 70 is formed from the second solid electrolyte layer 28, the spacer layer 26, the first solid electrolyte layer 24, the third substrate 22c, the outer pump electrode 44, and the reference electrode 48. According to the electromotive force Vref, which is obtained by the sensor cell 70, the oxygen partial pressure within the gas to be measured, which is located outside the sensor, can be detected.

[0044] Furthermore, a heating element 72 is configured in the sensor element 12 such that it is sandwiched between the second substrate 22b and the third substrate 22c from above and below. The heating element 72 generates heat by being supplied with current from an external source via a heating element electrode (not shown) located on a lower surface 22a2 of the first substrate 22a. As a result of the heat generated by the heating element 72, the oxygen ion conductivity of the solid electrolyte forming the sensor element 12 is increased. The heating element 72 is embedded across the entire area of ​​the pre-chamber 21, the oxygen concentration adjustment chamber 18, and the measuring chamber 20, and a predetermined location of the sensor element 12 can be heated to and maintained at a predetermined temperature.Furthermore, a heating element insulating layer 74, made of aluminum oxide or the like, is formed above and below the heating element 72 to provide electrical insulation from the second substrate 22b and the third substrate 22c. Hereinafter, the heating element 72, the heating element electrode, and the heating element insulating layer 74 may collectively be referred to as the heating element section.

[0045] Furthermore, the pre-chamber 21 is controlled by an operating control unit 108 described later (see the Fig. 2) is operated and, while in operation, functions as a chamber for adjusting the oxygen partial pressure within the gas to be measured, which is introduced through the gas inlet opening 16. The oxygen partial pressure is adjusted by operating a pre-pump cell 80.

[0046] The pre-pump cell 80 is an electrochemical pump cell consisting of a pre-pump electrode 82, which is provided substantially over the entire area directed towards the pre-chamber 21 in the lower surface 28b of the second solid electrolyte layer 28, the outer pump electrode 44 and the second solid electrolyte layer 28.

[0047] Furthermore, in the same way as the main pump electrode 42, the pre-pump electrode 82 is also formed using a material with a reduced reduction capacity with respect to the NOx component within the gas to be measured.

[0048] The pre-pump cell 80 can, by applying a desired pre-voltage Vp0 between the pre-pump electrode 82 and the outside pump electrode 44, pump oxygen from the atmosphere inside the pre-chamber 21 into the outside space, or alternatively, it can pump oxygen from the outside space into the pre-chamber 21.

[0049] Furthermore, the gas sensor 10 includes a pre-oxygen partial pressure sensing sensor cell 84 for controlling the backing pump in order to control the oxygen partial pressure within the atmosphere inside the pre-chamber 21. The pre-oxygen partial pressure sensing sensor cell 84 comprises the backing pump electrode 82, the reference electrode 48, the second solid electrolyte layer 28, the spacer layer 26, and the first solid electrolyte layer 24. The pre-oxygen partial pressure sensing sensor cell 84 detects, as an electromotive pre-force V0, the electromotive force between the backing pump electrode 82 and the reference electrode 48, which is generated by a difference between the oxygen concentration within the atmosphere inside the pre-chamber 21 and the oxygen concentration in the reference gas.

[0050] Furthermore, the pre-pump cell 80 performs pumping through a variable pre-current source 86, the voltage of which is controlled based on an electromotive pre-force V0, which has been detected by the pre-oxygen partial pressure sensing sensor cell 84. Consequently, the oxygen partial pressure within the atmosphere inside the pre-chamber 21 is controlled to be a low partial pressure that does not significantly affect the NOx measurement.

[0051] Furthermore, a pre-pump current Ip0 is used to control the electromotive pre-force V0 of the pre-oxygen partial pressure detection sensor cell 84. In particular, the pre-pump current Ip0 is fed into the pre-oxygen partial pressure detection sensor cell 84 as a control signal, and by controlling the electromotive pre-force V0, the gradient of the oxygen partial pressure within the gas to be measured, which is introduced into the pre-chamber 21 by the first diffusion rate control element 30, is controlled so that it always remains constant.

[0052] The pre-chamber 21 also acts as a buffer chamber. In particular, it can eliminate fluctuations in the concentration of the gas being measured, which occur due to pressure fluctuations of the gas being measured in the external chamber. Such pressure fluctuations of the gas being measured could include, for example, pulsations in the exhaust pressure of a vehicle.

[0053] Furthermore, the gas sensor comprises 10, as shown schematically in the Fig. Figure 2 shows an oxygen concentration control unit 100 (main oxygen concentration control unit) which controls the oxygen concentration within the oxygen concentration setting chamber 18, a temperature control unit 102 which controls the temperature of the sensor element 12, the unit for measuring a specified component 104 which measures the concentration of a specified component (NO or NH3) within the measuring chamber 20, an oxygen concentration pre-control unit 106, the operating control unit 108 and a unit for detecting a target component 110.

[0054] Furthermore, the oxygen concentration control unit 100, the temperature control unit 102, the unit for measuring a specified component 104, the oxygen concentration pre-control unit 106, the operating control unit 108, and the unit for detecting a target component 110 are formed from one or more electronic circuits, which include, for example, one or more CPUs (central processing units), storage devices, and the like. The electronic circuits are software-based functional units in which predefined functions are implemented, such as by the CPUs executing programs stored in the storage device. Naturally, the electronic circuits can be formed from an integrated circuit, such as…an FPGA (field-programmable gate array) in which the majority of electronic circuits are connected according to their functions.

[0055] By being equipped with the pre-chamber 21, the oxygen concentration pre-control unit 106, the operating control unit 108 and the unit for detecting a target component 110 in addition to the oxygen concentration setting chamber 18, the oxygen concentration control unit 100, the temperature control unit 102 and the unit for measuring a specified component 104 described above, the gas sensor 10 can detect the respective concentrations of NO (nitric oxide) and NH3 (ammonia).

[0056] Based on the preset oxygen concentration condition and the first electromotive force V1 generated in the first oxygen partial pressure detection sensor cell 50 (see the Fig. 1) The oxygen concentration control unit 100 regulates the first variable power source 46 and adjusts the oxygen concentration within the oxygen concentration setting chamber 18 to a concentration according to the condition described above.

[0057] The temperature control unit 102 controls the heating device 72 on the basis of a preset sensor temperature condition and the measured value from a temperature sensor (not shown) that measures the temperature of the sensor element 12, thereby setting the temperature of the sensor element 12 to a temperature according to the condition described above.

[0058] Through the oxygen concentration control unit 100 and the temperature control unit 102, the gas sensor 10 controls the condition within the oxygen concentration setting chamber 18 in such a way that all the NH3 is converted into NO without causing decomposition of NO within the oxygen concentration setting chamber 18.

[0059] The unit for measuring a defined component 104 detects and outputs the measuring pump current Ip3 flowing between the measuring electrode 62 and the outer pump electrode 44. Furthermore, after the switching of the pre-pump cell 80 has been carried out, the unit for measuring a defined component 104 determines a rate of change dlp3 / dt of the measuring pump current Ip3 over time and records its peak value. Furthermore, the unit for measuring a defined component 104 refers to a second characteristic map 114 and determines a change magnitude ΔIp3 from the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3 over time until the value of a steady state of the measuring pump current Ip3 is reached, and obtains a steady state value (predicted value) of the measuring pump current Ip3 by adding the change magnitude ΔIp3 to the measuring pump current Ip3 before switching.Furthermore, the second characteristic curve 114 includes a data group in which a relationship with the rate of change ΔIp3, until the value of a steady state of the measuring pump flow Ip3 is reached, is recorded for each of points defined by peak values ​​of the rate of change dlp3 / dt of the measuring pump flow Ip3 over time, coinciding with switching operations of the pre-pump cell 80 between ON and OFF. In addition, the second characteristic curve 114 can also be provided with a data group in which a relationship with the NH3 concentration within the gas to be measured is recorded for each of the respective points defined by the peak values ​​of the rate of change dlp3 / dt of the measuring pump flow Ip3 over time, coinciding with switching operations of the pre-pump cell 80 between ON and OFF.With regard to the data groups registered in the second characteristic field 114, information (relationships) is used that was obtained beforehand through an experiment or a simulation.

[0060] Based on the preset oxygen concentration condition and the electromotive pre-force V0, which is generated in the pre-oxygen partial pressure detection sensor cell 84 (see the Fig. 1) The oxygen concentration control unit 106 regulates the variable pre-current source 86, thereby adjusting the oxygen concentration within the pre-chamber 21 to a concentration according to the condition.

[0061] Furthermore, the unit for detecting a target component 110 records the respective concentrations of NO and NH3 on the basis of a difference between the sensor output from the unit for measuring a defined component 104 according to a first operation of the oxygen concentration control unit 106 and the sensor output from the unit for measuring a defined component 104 according to a second operation of the oxygen concentration control unit 106.

[0062] In this case, the NO and the NH3 within the gas to be measured are changed in the following manner according to a bias voltage Vp0, which is applied to the pre-pump electrode 82 by the oxygen concentration control unit 106.

[0063] First, in a first voltage region, the NH3 within the prechamber 21 is maintained in the form of NH3. While remaining in the form of NH3, the NH3 within the prechamber 21 passes through the second diffusion rate control element 32 and arrives at the interior of the oxygen concentration adjustment chamber 18. Furthermore, the NO within the prechamber 21, while remaining in the form of NO, passes through the second diffusion rate control element 32 and arrives at the interior of the oxygen concentration adjustment chamber 18.

[0064] In a second voltage region, the NH3 is oxidized to NO within the pre-chamber 21, passes through the second diffusion rate control element 32, and arrives at the oxygen concentration adjustment chamber 18. Furthermore, the NO, while remaining in the form of NO, passes through the second diffusion rate control element 32 and arrives at the oxygen concentration adjustment chamber 18.

[0065] The oxygen concentration control unit 106 applies the first voltage Va as the bias voltage Vp0 at the time of the first operation and outputs the second voltage Vb as the bias voltage Vp0 at the time of the second operation. Furthermore, depending on the oxygen concentration of the gas being measured, oxygen can be pumped into the pre-chamber 21, and in such a case, the first voltage Va can have a negative value. In cases where oxygen is neither pumped out of nor into the pre-chamber 21, the first voltage Va can be set to Vaus.

[0066] As described above, during the first operation, the NH3 component, in the form of NH3, passes through the second diffusion rate control element 32 and is represented in the measurement pump flow (sensor output) Ip3. Furthermore, during the second operation, the NH3 component, in the form of NO, passes through the second diffusion rate control element 32 and is also represented in the measurement pump flow (sensor output) Ip3. Since NH3 diffuses through the second diffusion rate control element 32 more rapidly than NO, the measurement pump flow (sensor output) Ip3 changes between the time of the first operation and the time of the second operation. The magnitude of this difference represents the concentration of NH3 within the gas being measured. In particular, the measurement pump flow (sensor output) Ip3 can be decomposed into an NO component flow and an NH3 component flow by means of the difference in the diffusion rates of NH3 and NO.Accordingly, the gas sensor 10 determines the concentrations of NO and NH3 on the basis of the difference between the sensor outputs from the unit for measuring a defined component 104 according to the first and second operation of the oxygen concentration pilot unit 106.

[0067] Next, processing operations of the gas sensor 10 will also be described with reference to the Fig. 3 and Fig. 4 described.

[0068] First achieved, as it is in the Fig. Figure 3 shows that the NH3, introduced through the gas inlet opening 16, enters the oxygen concentration adjustment chamber 18 during a period in which the oxygen concentration pre-control unit 106 performs its initial operation via the operating control unit 108. Within the oxygen concentration adjustment chamber 18, the operation of the oxygen concentration control unit 100 ensures that all the NH3 is converted to NO. Therefore, the NH3 flowing from the pre-chamber 21 into the oxygen concentration adjustment chamber 18 causes a reaction in which NH3 is oxidized to NO within the oxygen concentration adjustment chamber 18, and all the NH3 within the oxygen concentration adjustment chamber 18 is converted to NO.Accordingly, the NH3, which has been introduced through the gas inlet opening 16, passes through the first diffusion rate control element 30 and the second diffusion rate control element 32 at the NH3 diffusion coefficient (e.g. 2.2 cm). 2 / s) through, and, after being converted into NO within the oxygen concentration setting chamber 18, passes through the third diffusion rate control element 34 at the NO diffusion coefficient (e.g. 1.8 cm). 2 / s) through and moves into the adjacent measuring chamber 20.

[0069] On the other hand, during a period in which the oxygen concentration pre-control unit 106 performs the second operation by the operating control unit 108, as described in the Fig. As shown in Figure 4, the oxidation reaction of NH3 to NO takes place within the prechamber 21, and all the NH3 introduced through the gas inlet opening 16 is converted to NO. Accordingly, although the NH3 passes through the first diffusion rate control element 30 at the NH3 diffusion coefficient, after passing through the second diffusion rate control element 32 on the innermost side of the prechamber 21, it moves into the measuring chamber 20 at the NO diffusion coefficient.

[0070] In other words, by switching the oxygen concentration control unit 106 from the first operating state to the second operating state, the point where the oxidation reaction of NH3 takes place is moved from the oxygen concentration setting chamber 18 to the pre-chamber 21.

[0071] The movement of the point where the NH3 oxidation reaction takes place, from the oxygen concentration control chamber 18 to the pre-chamber 21, implies that the state of the NH3 within the gas being measured changes from NH3 to NO when the NH3 passes through the second diffusion rate control element 32. Furthermore, since NO and NH3 have different diffusion coefficients, the difference between passing through the second diffusion rate control element 32 with NO or passing through it with NH3 results in a difference in the amount of NO flowing into the measuring chamber 20, and consequently causes the measuring pump flow rate Ip3 flowing to the measuring pump cell 61 to change.

[0072] In this case, the measuring pump flow rate Ip3(Vb) during the second operation of the pre-pump cell 80, and the rate of change ΔIp3 in the measuring pump flow rate Ip3(Va) at the time of the first operation of the pre-pump cell 80, are uniquely determined by the concentration of NH3 within the gas being measured. Therefore, the respective concentrations of NO and NH3 can be calculated from the measuring pump flow rate Ip3(Vb) or Ip3(Va) and the rate of change ΔIp3 in the measuring pump flow rate Ip3.

[0073] The unit for detecting a target component 110 obtains the respective concentrations of NO and NH3 based on a first characteristic curve 112 of the measuring pump flow rate Ip3(Va) at the time of the first operation of the pre-pump cell 80 and the rate of change ΔIp3 in the measuring pump flows Ip3 at the time of the first operation and at the time of the second operation. The first characteristic curve 112 is a data set that indicates a correlation between the rate of change ΔIp3 and the NH3 concentration, which is obtained beforehand by an experiment or a simulation, and is formed from a plurality of sets of data sets corresponding to a plurality of different NO concentrations.Based on the measuring pump current Ip3 off at the time when the pre-pump cell 80 is switched OFF, the unit for detecting a target component 110 determines which of the correlations between the change magnitude ΔIp3 and the NH3 concentration should be used according to the NO concentration, and identifies the NH3 concentration based on the corresponding change magnitude ΔIp3.

[0074] Furthermore, the unit for detecting a target component 110 can obtain a relationship between the rate of change ΔIp3 and the NH3 concentration in advance through an experiment or simulation, and can obtain the NH3 concentration from the rate of change ΔIp3 at the time when the pre-pump cell 80 is switched ON and at the time when the pre-pump cell 80 is switched OFF. Then, the NO concentration can be obtained by subtracting the NH3 concentration obtained in the above manner from the NO concentration obtained from the sensor output at the time when the pre-pump cell 80 was switched OFF, or in other words, the total NO concentration obtained by converting the total concentrations of NO and NH3 to NO.

[0075] Next, with reference to the flowchart of Fig. 5 and the schematic diagram of Fig. 6 a method of detecting the measuring pump current Ip3 (sensor output) and a method of detecting the target component by the unit for detecting a target component 110, which are carried out in the unit described above for measuring a specified component 104 of the gas sensor 10, are described.

[0076] First, in step S10 of Fig. 5. The gas sensor 10 switches the pre-pump cell 80 ON (second operation). Consequently, the NH3 within the gas to be measured is converted into NO within the pre-chamber 21, passes through the second diffusion rate control element 32, and based on a difference in the diffusion coefficients between NO and NH3 in the second diffusion rate control element 32, the measuring pump current Ip3, which flows through the measuring pump cell 61, changes.

[0077] In this case, this is achieved when the operating state of the pre-pump cell 80 is switched from OFF to ON, as described in the Fig. As shown in Figure 6, the measuring pump current Ip3 represents a steady-state value after a temporary change, due to the diffusion resistance of the NO gas, an electrode reaction resistance on the surface of the measuring electrode, and delays in the respective pump voltage controls. The rate of change dlp3 / dt of the measuring pump current Ip3 over time is large immediately after switching and is subject to change, eventually reaching a constant value. Furthermore, the rate of change dlp3 / dt of the measuring pump current Ip3 over time is approximately proportional to the magnitude of the change ΔIp3, which is the difference between the measuring pump current Ip3in at the time when the pre-pump cell 80 is switched ON and the measuring pump current Ip3off at the time when the pre-pump cell 80 is switched OFF.Consequently, according to the present embodiment, attention is focused on the rate of change dlp3 / dt of the measuring pump current Ip3 over time.

[0078] Specifically recorded in step S20 of Fig. 5 the unit for measuring a defined component 104 the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3ein over time. As stated in the Fig. As shown in Figure 6, the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3ein appears over time within 0.5 seconds of the switching of the operating state of the pre-pump cell 80, and the result is obtained faster than a period on the order of 2 seconds until the measuring pump current Ip3ein reaches a steady-state value.

[0079] Then, in step S30, it receives Fig. 5 based on a temporary peak value of the rate of change dlp3 / dt of the measuring pump current Ip3ein over time, which was recorded in step S20, and a correlation which has been determined in advance by an experiment or a simulation, between the peak value of the rate of change over time dlp3 / dt and the value of a steady state of the measuring pump current Ip3ein, the unit for measuring a specified component 104 a predicted value of the value of a steady state of the measuring pump current Ip3ein.

[0080] Then, in step S40, the gas sensor 10 switches the pre-pump cell 80 to OFF (first operation). The period during which the pre-pump cell 80 remains in the ON state from step S10 to step S30, e.g., a period on the order of 0.5 seconds, can be made shorter than the period (e.g., on the order of 2 seconds) until the measuring pump current Ip3 reaches a steady-state value.

[0081] By switching the operating state of the pre-pump cell 80 from ON to OFF, the NH3 within the gas to be measured within the pre-chamber 21 passes directly through the second diffusion rate control element 32 without alteration and is, as described in the Fig. Figure 3 shows that the oxygen concentration is converted into NO in the oxygen concentration control chamber 18. Based on a difference in the diffusion coefficients between NO and NH3 in the second diffusion rate control element 32, the measuring pump current Ip3, which flows through the measuring pump cell 61, changes.

[0082] When the operating state of the pre-pump cell 80 is switched from ON to OFF, the measuring pump current Ip3 reaches a steady-state value after a temporary change, due to the diffusion resistance of the NO gas, the electrode reaction resistance on the surface of the measuring electrode, and delays in the respective pump voltage controls. Furthermore, the rate of change dlp3 / dt of the measuring pump current Ip3 over time is approximately proportional to the magnitude of the change ΔIp3, which is the difference between the measuring pump current Ip3off at the time the pre-pump cell 80 is switched OFF and the measuring pump current Ip3in at the time the pre-pump cell 80 is switched ON. In step S50, the unit for measuring a defined component 104 measures a temporary peak value of the rate of change dlp3 / dt of the measuring pump current Ip3off over time.

[0083] Next, in step S60, based on the temporary peak value of the rate of change dlp3 / dt of the measuring pump current Ip3 over time, which was obtained in step S50, and a correlation determined beforehand by an experiment or simulation between the peak value of the rate of change dlp3 / dt over time and the value of a steady state of the measuring pump current Ip3, the unit for measuring a specified component 104 receives a predicted value of the value of a steady state of the measuring pump current Ip3.

[0084] In the following step S70, the unit for detecting a target component 110 detects the NH3 concentration and the NO concentration, which are the target components, on the basis of the measuring pump flow rate Ip3in obtained in step S30, the measuring pump flow rate Ip3out obtained in step S60, and the change magnitude ΔIp3 in between.

[0085] In particular, the unit for detecting a target component 110 determines, based on the measuring pump current Ip3 at the time when the pre-pump cell 80 is switched OFF, which of the correlations of the first characteristic map 112 between the rate of change ΔIp3 and the NH3 concentration corresponding to the NO concentration is to be used, and identifies the NH3 concentration based on the corresponding rate of change ΔIp3. The unit for detecting a target component 110 then obtains the NO concentration by subtracting the NH3 concentration obtained in the manner described above from the NO concentration obtained from the sensor output at the time when the pre-pump cell 80 was switched OFF, or in other words, the total NO concentration obtained by converting the total concentrations of NO and NH3 into NO.

[0086] In step S80, gas sensor 10 then checks whether an input to end the measurement has been made. If no input to end the measurement has been made, the procedure continues to step S10. In this case, the time required to switch from step S40 to step S10 can be shorter than the time until the measuring pump current Ip3 reaches a steady-state value, and can be, for example, on the order of 0.5 seconds.

[0087] On the other hand, if it has been determined in step S80 that an input to end the measurement has been made, the gas sensor 10 terminates the measurement procedure.

[0088] In the manner described above, according to the gas sensor 10 of the present embodiment, since the switching period between the operating modes of the pre-pump cell 80 can be shortened, a reduction in measurement accuracy due to a delay in the measurement time of the measuring pump current Ip3 can be prevented. (Experimental Example 1)

[0089] An experimental example is described in which the gas sensor 10 of the present embodiment is used. In experimental example 1, six types of the gas to be measured, with NO concentrations of 0 ppm and NH3 concentrations of 0 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm respectively, were supplied to the gas sensor 10, and when the operating state of the pre-pump cell 80 was switched from OFF to ON, the rate of change of the measuring pump current Ip3 was determined over time.

[0090] As it is in the Fig. As shown in Figure 7, in experimental example 1 the operating state of the pre-pump cell 80 was switched at 15 seconds. It was confirmed that the measuring pump flow rate Ip3 converged to a steady-state value within a period of approximately 2 seconds, regardless of the NH3 concentration in the gas being measured. Furthermore, it was confirmed that the slope of the measuring pump flow rate Ip3 tends to increase as the NH3 concentration increases.

[0091] After obtaining the rate of change of the measuring pump current Ip3 over time for each of the gases to be measured, as described in the Fig. Figure 8 shows that the peak values ​​of the rate of change over time occur approximately 0.5 seconds after the switchover time at 15 seconds of the pre-pump cell 80, and that the peak values ​​are larger when the change in the measuring pump current Ip3 after switching increases. Furthermore, it was confirmed that there is a correlation between the rate of change of the measuring pump current Ip3 over time and the magnitude of change ΔIp3 of the measuring pump current Ip3 after switching. Accordingly, by recording the rate of change of the measuring pump current Ip3 over time, the value of a steady state can be determined before the measuring pump current Ip3 converges to the value of a steady state.

[0092] As it is in the Fig. As shown in Figure 9, the rate of change dlp3 / dt of the measuring pump flow rate Ip3 changes over time essentially proportionally to the NH3 concentration within the gas being measured. Therefore, the NH3 concentration within the gas being measured can be directly determined from the rate of change dlp3 / dt of the measuring pump flow rate Ip3 over time. (Experimental Example 2)

[0093] Next, in experimental example 2, six types of the gas to be measured, with NO concentrations of 500 ppm and NH3 concentrations of 0 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm and 500 ppm respectively, were supplied to the gas sensor 10, and when the operating state of the pre-pump cell 80 was switched from OFF to ON, the rate of change of the measuring pump current Ip3 was determined over time.

[0094] As it is in the Fig. As shown in Figure 10, even in the case where the NO concentration was 500 ppm, it could be confirmed that the slope of the measuring pump flow Ip3 tends to increase as the NH3 concentration increases. Furthermore, as shown in the Fig. As shown in Figure 11, it can be confirmed that the peak values ​​of the rate of change dlp3 / dt of the measuring pump current Ip3 exhibit larger values ​​over time when the change in the measuring pump current Ip3ein after switching is greater. Therefore, according to experimental Example 2, it could be confirmed that even when the gas to be measured is mixed with NO, the measuring pump current Ip3ein (steady-state value) can be determined from the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3 over time. Furthermore, the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3 over time can be determined within a period on the order of 0.5 seconds, and the measuring pump current Ip3ein can be determined without having to wait for the measuring pump current Ip3 to converge to the steady-state value.

[0095] Furthermore, as can be seen in the Fig. As shown in Figure 12, it can be confirmed that even when the gas to be measured is mixed with NO, there is a correlation between the peak value of the rate of change dlp3 / dt of the measuring pump flow Ip3 over time and the NH3 concentration within the gas to be measured. Therefore, based on the correlation shown in Figure 12, it can be determined that the NH3 concentration in the gas to be measured is 12. Fig. Figure 12 shows that NH3 together with 500 ppm NO can be obtained directly from the rate of change dlp3 / dt of the measuring pump current Ip3 over time. (Experimental Example 3 and Comparative Example)

[0096] To confirm the advantages realized by the gas sensor 10 and the concentration measurement method of the present embodiment, differences in measurement results were confirmed by means of a simulation calculation for a case in which the switching period of the operating state of the pre-pump cell 80 was set to 4 seconds (0.25 Hz) (comparative example) and a case in which the switching period was set to 1 second (1 Hz) (experimental example 3). Regarding the NO concentration and the NH3 concentration of the gas to be measured, the results obtained by an FT-IR method are shown by the solid lines in the Fig. 13 and Fig. 14 shown.

[0097] In this case, the measuring pump flow rate Ip3in and the measuring pump flow rate Ip3out were approximated by multiplying each of the NO and NH3 concentrations obtained by the FT-IR method by a single coefficient and adding them together. Specifically, the measuring pump flow rate Ip3out was determined by multiplying the NO concentration (t1) and the NH3 concentration (t1), obtained by the FT-IR method at a desired measurement time t1, by predetermined coefficients and adding them together. Furthermore, the measuring pump flow rate Ip3in was determined by multiplying the NO concentration (t2) and the NH3 concentration (t2), obtained by the FT-IR method at a desired measurement time t2 at half the time before t1, by predetermined coefficients and adding them together.Furthermore, in this case, to account for variations in the measuring pump flow rate Ip3in and the measuring pump flow rate Ip3out, the values ​​of the coefficients themselves, which are multiplied by the NO concentration and the NH3 concentration, can be selected in a suitable manner. The NO concentration and the NH3 concentration, which were determined on the basis of the first characteristic map 112, are in the . Fig. 13 and Fig. 14 plotted with respect to the measuring pump current Ip3out and the measuring pump current Ip3in, which were obtained by the method described above.

[0098] In the case where the switching period is 1 second (1 Hz), as in experimental example 3 of Fig. 13. In this case, it is evident that the delay in the measurement time of the NO concentration and the NH3 concentration is limited to 0.5 seconds and any reduction in measurement accuracy is suppressed.

[0099] On the other hand, in the case where the switching period is 4 seconds (0.25 Hz), as in the comparative example of Fig. 14 In this case, it is evident that the delay in the measurement time of the NO concentration and the NH3 concentration is on the order of 2 seconds and that significant errors occur with regard to the measurement results obtained by the FT-IR method.

[0100] The gas sensor 10 and the method for measuring a gas concentration according to the present embodiment as described above have the following advantages.

[0101] In the gas sensor 10 and the method for measuring a gas concentration of the present embodiment, the oxygen concentration control unit 106 (pre-pump cell 80) performs switching operations between the first operation (OFF) and the second operation (ON) within a period shorter than a standby time, until the measuring pump current Ip3 converges to a steady-state value. Consequently, since the measurement period is shortened, a reduction in measurement accuracy due to a delay in the measurement time can be suppressed. (Second embodiment)

[0102] Another example of a method for detecting the measuring pump current Ip3 (sensor output) performed by the unit for measuring a specified component 104 and a method for detecting a target component by the unit for detecting a target component 110 of the gas sensor 10 is described.

[0103] As it is in the Fig. 9 and Fig. As shown in Figure 12, the peak value of the rate of change dlp3 / dt of the measuring pump flow Ip3 over time correlates with the NH3 concentration in the gas being measured. Consequently, according to the present embodiment, the unit for measuring a defined component 104 determines the NH3 concentration directly from the correlation between the peak value of the rate of change dlp3 / dt of the measuring pump flow Ip3 over time and the NH3 concentration in the gas being measured.

[0104] As shown in the flowchart of Fig. As shown in Figure 15, in step S110 the gas sensor 10 switches the operating state of the pre-pump cell 80 to ON. Then, in step S120, the unit for measuring a defined component 104 receives the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3 over time.

[0105] Then, in step S130, the unit for measuring a defined component 104 determines the NH3 concentration within the gas to be measured from the peak value of the rate of change dlp3 / dt of the measuring pump flow Ip3 over time, with reference to the second characteristic map 114.

[0106] Next, in step S140, the gas sensor 10 switches the operating state of the pre-pump cell 80 to OFF. Then, in step S150, the unit for measuring a defined component 104 records the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3aus over time.

[0107] Next, in step S160, the unit for measuring a specified component 104 determines the value of a steady state of the measuring pump current Ip3aus (predicted value) from the peak value of the rate of change dlp3 / dt of the measuring pump current Ip3 over time, which was recorded in step S150.

[0108] Then, in step S170, the unit for detecting a target component 110 determines the total NO concentration from the measuring pump flow Ip3 (predicted value) and then subtracts the NH3 concentration obtained in step S130 from the total NO concentration, thereby determining the concentration of NO, which is the target component, within the gas to be measured.

[0109] Next, in step S180, the gas sensor 10 detects whether an input to end the measurement has been made or not, and in the case where an input to end the measurement has not been made, the procedure returns to step S110 and the measurement is continued, whereas in the case where an input to end the measurement has been made, the measurement procedure is terminated.

[0110] In the above manner, in the gas sensor 10 and the method for measuring a gas concentration of the present embodiment, the unit for measuring a defined component 104 can utilize the second characteristic map 114, which registers a relationship between the concentration of the defined component within the gas to be measured, which is measured experimentally in advance, and a point defined by the peak values ​​of the rate of change dlp3 / dt of the measuring pump current Ip3 over time, which is measured experimentally in advance, accompanied by switching operations between the time of the first operation and the time of the second operation of the oxygen concentration pre-control unit 106 (pre-pump cell 80).and it can determine the concentration of the specified component (NH3) within the gas to be measured by comparing the peak values ​​of the rate of change dlp3 / dt of the measuring pump flow Ip3 over time from the unit for measuring a specified component 104 with the second characteristic curve 114 during switching operations of the oxygen concentration pre-control unit 106 (pre-pump cell 80) during its actual use.

Claims

[1] Gas sensor (10) designed to measure the concentrations of a plurality of components present in the presence of oxygen, comprising: a structural body (14) formed from a solid electrolyte which has an oxygen ion conductivity; a gas inlet opening (16) which is formed in the structural body (14) and into which a gas to be measured is introduced; a pre-chamber (21) comprising a pre-pump electrode (82) and connected to the gas inlet opening (16); an oxygen concentration setting chamber (18) comprising a pump electrode (42) and connected to the prechamber (21); a measuring chamber (20) comprising a measuring electrode (62) and connected to the oxygen concentration setting chamber (18); an oxygen concentration control unit (106) designed to control an oxygen concentration within the pre-chamber (21) on the basis of a voltage of the pre-pump electrode (82); a unit for measuring a defined component (104) configured to detect a measuring pump current (Ip3) flowing through an outside pump electrode (44) and the measuring electrode (62) during operation of the oxygen concentration pilot unit (106); and a unit for detecting a target component (110) designed to detect a concentration of a target component within the gas to be measured on the basis of a change magnitude (ΔIp3) between a measuring pump flow (Ip3in) from the unit for measuring a defined component (104) at the time of a first operation of the oxygen concentration pilot unit (106) and a measuring pump flow (Ip3out) from the unit for measuring a defined component (104) at the time of a second operation of the oxygen concentration pilot unit (106), and one of the measuring pump flow (Ip3in) and the measuring pump flow (Ip3out); wherein the unit for measuring a defined component (104) is designed to determine a value of a steady state of the measuring pump current (Ip3in) or a value of a steady state of the measuring pump current (Ip3out) on the basis of a peak value of a rate of change of the measuring pump current (Ip3) over time when an operation of the oxygen concentration feedforward unit (106) is switched between the first operation and the second operation. [2] Gas sensor according to claim 1, wherein the oxygen concentration control unit (106) performs switching operations between the first operation and the second operation within a period shorter than a standby time, until the measuring pump current converges to the value of a steady state. [3] Gas sensor according to claim 1 or 2, wherein the unit is configured to measure a defined component (104) for: Utilizing a characteristic map (114) that records a relationship between a concentration of a defined component within the gas to be measured, which is measured experimentally beforehand, and a point defined by the peak value of the rate of change of the measuring pump current (Ip3) over time, which is measured experimentally beforehand, accompanied by the switching process between the first operation and the second operation of the oxygen concentration pilot unit (106); and Determining the concentration of the specified component within the gas to be measured by comparing a peak value of a rate of change of the measuring pump current (Ip3) over time from the unit for measuring a specified component (104) with the characteristic curve during a switching operation of the oxygen concentration control unit (106) during its actual use. [4] Gas sensor according to claim 3, wherein the specified component is NH3. [5] Gas sensor according to any one of claims 1 to 4, wherein the oxygen concentration setting chamber (18) comprises a main chamber (18a) and an auxiliary chamber (18b), wherein the main chamber (18a) is connected to the pre-chamber (21) and the auxiliary chamber (18b) is connected to the measuring chamber (20). [6] Method for measuring a gas concentration in which a gas sensor (10) is used, wherein the gas sensor (10) comprises a structural body (14) formed from a solid electrolyte having an oxygen ion conductivity, a gas inlet opening (16) formed in the structural body (14) into which a gas to be measured is introduced, a pre-chamber (21) comprising a pre-pump electrode (82) and connected to the gas inlet opening (16), an oxygen concentration control chamber (18) comprising a pump electrode (42) and connected to the pre-chamber (21), a measuring chamber (20) comprising a measuring electrode (62) and connected to the oxygen concentration control chamber (18), and an oxygen concentration control unit (106) configured to control an oxygen concentration within the pre-chamber (21) based on a voltage of the pre-pump electrode (82).a unit for measuring a specified component (104) configured to detect a measuring pump current (Ip3) flowing through an outside pump electrode (44) and the measuring electrode (62) during operation of the oxygen concentration pilot unit (106), and a unit for detecting a target component (110) configured to detect a concentration of a target component within the gas to be measured based on a magnitude of change (ΔIp3) between a measuring pump current (Ip3in) from the unit for measuring a specified component (104) at the time of a first operation of the oxygen concentration pilot unit (106) and a measuring pump current (Ip3out) from the unit for measuring a specified component (104) at the time of a second operation of the oxygen concentration pilot unit (106), and one of the measuring pump current (Ip3in) and the measuring pump current (Ip3out); wherein the method for measuring a gas concentration comprises: an operating switching step of performing a control to switch between the first operation and the second operation of the oxygen concentration pilot control unit (106); a determination step of determining a peak value of a rate of change of the measuring pump current (Ip3) over time by the unit for measuring a defined component (104) accompanied by the control for switching between the first operation and the second operation of the oxygen concentration pilot control unit (106); a determination step of determining a value of a steady state of the measuring pump current (Ip3) from a pre-determined correlation between the peak value of the rate of change of the measuring pump current (Ip3) over time and the value of a steady state of the measuring pump current (Ip3) by the unit for measuring a specified component (104); and a detection step of detecting the concentration of the target component within the gas to be measured by the unit for detecting a target component on the basis of the value of a steady state of the measuring pump flow (Ip3) from the unit for measuring a specified component (104). [7] Method for measuring a gas concentration according to claim 6, wherein the control for switching between the first operation and the second operation of the oxygen concentration pre-control unit (106) is repeatedly carried out in a period of time that is shorter than the time until the measuring pump current (Ip3) converges to the value of a steady state. [8] Method for measuring a gas concentration according to claim 6, wherein the method for measuring a gas component comprises a step for detecting a defined component, in which the unit for measuring a defined component (104) utilizes a characteristic map (114) that registers a relationship between a concentration of a defined component within the gas to be measured, which is measured experimentally in advance, and a point defined by the peak value of the rate of change of the measuring pump current (Ip3) over time, which is measured experimentally in advance, accompanied by a switching process between the first operation and the second operation of the oxygen concentration feedforward unit (106),and the unit for measuring a specified component (104) determines the concentration of the specified component within the gas to be measured by comparing a peak value of a rate of change of the measuring pump flow (Ip3) over time from the unit for measuring a specified component (104) during a switching operation of the oxygen concentration pilot unit (106) during its actual use with the characteristic curve (114). [9] Method for measuring a gas concentration according to claim 8, wherein the specified component is NH3. [10] Method for measuring a gas concentration according to any one of claims 6 to 9, wherein the oxygen concentration setting chamber (18) comprises a main chamber (18a) and an auxiliary chamber (18b), wherein the main chamber (18a) is connected to the pre-chamber (21) and the auxiliary chamber (18b) is connected to the measuring chamber (20).

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