System for estimating mass of co2, method for estimating composition ratio of exhaust gas, and method for estimating mass of co2

Abstract

The present application provides a CO2 discharge mass estimation system. The CO2 mass estimation system includes: a detection value acquisition mechanism that acquires a detection value corresponding to the concentration of oxygen, H2O, and CO2 in engine exhaust gas, which is output by a gas sensor capable of outputting a detection value corresponding to the concentration of each of oxygen, H2O, and CO2 in a measured gas; an air-fuel ratio setting mechanism that sets the air-fuel ratio of the mixture; and a calculation mechanism that calculates the mass of CO2 in the exhaust gas, the calculation mechanism estimating the CO2 mass as follows: based on the sensor detection value, calculating the concentration of each of oxygen, H2O, and CO2 in the exhaust gas, acquiring the atmospheric concentration of each of oxygen and H2O and the air-fuel ratio, based on the concentration in the exhaust gas, the atmospheric concentration, and the air-fuel ratio, calculating the composition ratio of at least C atoms contained in the fuel, and based on the composition ratio and the injection amount of the fuel for the engine, estimating the mass of CO2 contained in the exhaust gas.

Description

Technical Field

[0001] This invention relates to the estimation of the mass of CO2 contained in exhaust gas from automobile engines. Background Technology

[0002] For the measurement of emissions from automobile exhaust, techniques for measuring the concentration of carbon dioxide (CO2) are known (see, for example, Patent Document 1 and Patent Document 2). The gas sensors disclosed in Patent Document 1 and Patent Document 2 are capable of measuring not only the carbon dioxide (CO2) component but also the water vapor (H2O) component.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 5918177

[0006] Patent Document 2: Japanese Patent No. 6469464 Summary of the Invention

[0007] In the management of automobile exhaust emissions, sometimes measuring the mass of emissions is more important than measuring the concentration (emission standard example: below 95g CO2 / km). Patent documents 1 and 2 provide methods for measuring CO2 concentration; however, they do not provide methods for measuring CO2 mass. Although mass can be calculated based on concentration, this requires measuring the mass flow rate of the exhaust gas. This is because the relationship is: CO2 concentration × mass flow rate = CO2 mass.

[0008] However, measuring the mass flow rate of exhaust gases while a car is in motion is not easy, and from a cost perspective, adding additional measurement equipment is impractical. It would be better to use existing components and information to estimate the CO2 emission mass.

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide a method for estimating the discharge mass of CO2 contained in exhaust gas without measuring the mass flow rate.

[0010] To address the aforementioned issues, a first aspect of the present invention is a system for estimating the mass of CO2 contained in exhaust gas from an engine of a vehicle, characterized by comprising: a gas sensor capable of outputting detection values ​​corresponding to the concentrations of oxygen, H2O, and CO2 in the gas being measured; a detection value acquisition mechanism that acquires the detection values ​​output by the gas sensor corresponding to the concentrations of oxygen, H2O, and CO2 in the exhaust gas from the engine; an air-fuel ratio setting mechanism that sets the air-fuel ratio of the mixture of fuel and atmosphere supplied to the engine; and a calculation mechanism that calculates the CO2 content in the exhaust gas. The calculation mechanism estimates the CO2 mass as follows: based on the detection value in the gas sensor when the measured gas is the exhaust gas, it calculates the respective concentrations of oxygen, H2O, and CO2 in the exhaust gas; obtains the respective atmospheric concentrations of oxygen and H2O; obtains the air-fuel ratio set in the air-fuel ratio setting mechanism; based on the respective concentrations of oxygen, H2O, and CO2 in the exhaust gas, the respective atmospheric concentrations of oxygen and H2O, and the air-fuel ratio obtained by the air-fuel ratio setting mechanism, it calculates the composition ratio of at least C atoms contained in the fuel; and based on the calculated composition ratio and the fuel injection amount for the engine, it estimates the CO2 mass contained in the exhaust gas.

[0011] The second aspect of the present invention is a method for estimating the composition ratio of C, H, and O atoms in exhaust gas from a vehicle engine, characterized by comprising the following steps: a detection value acquisition step, wherein a detection value corresponding to the concentrations of oxygen, H2O, and CO2 in the exhaust gas from the engine is acquired from a gas sensor capable of outputting detection values ​​corresponding to the respective concentrations of oxygen, H2O, and CO2 in the gas being measured; an exhaust gas concentration calculation step, wherein the respective concentrations of oxygen, H2O, and CO2 in the exhaust gas are calculated based on the detection values; and a further step... The process includes: an air concentration acquisition step, in which the atmospheric concentrations of oxygen and H2O are acquired; an air-fuel ratio acquisition step, in which the air-fuel ratio of the mixture of fuel and atmosphere supplied to the engine is acquired; and a composition ratio estimation step, in which the composition ratio of C, H, and O atoms contained in the fuel is estimated based on the exhaust gas concentrations of oxygen, H2O, and CO2 calculated in the exhaust gas concentration calculation step, the atmospheric concentrations of oxygen and H2O acquired in the atmospheric concentration acquisition step, and the air-fuel ratio acquired in the air-fuel ratio acquisition step.

[0012] The third aspect of the present invention is a method for estimating the mass of CO2 contained in the exhaust gas from an engine of a vehicle, characterized in that it includes a mass estimation step in which the mass of CO2 contained in the exhaust gas is estimated based on the composition ratio of C atoms contained in the fuel estimated by the exhaust gas composition ratio estimation method involved in the second aspect, and the amount of fuel injected for the engine.

[0013] Invention Effects

[0014] According to the first and third embodiments of the present invention, even without measuring the mass flow rate of the exhaust gas, it is possible to estimate the mass of CO2 contained in the exhaust gas when a certain mass of fuel has been injected.

[0015] Furthermore, according to the second aspect of the present invention, even without measuring the mass flow rate of the exhaust gas, it is possible to estimate the composition ratio of C atoms, H atoms, and O atoms contained in the exhaust gas when a certain mass of fuel has been injected. Attached Figure Description

[0016] Figure 1 This is a diagram that schematically illustrates an example of the configuration of a gas sensor 200.

[0017] Figure 2 This is a schematic diagram illustrating the configuration of the CO2 mass estimation system 1000.

[0018] Figure 3 It is a diagram that schematically illustrates the relationship between various parameters used to estimate the mass of CO2.

[0019] Explanation of reference numerals in the attached figures

[0020] 10…Gas inlet, 11…First diffusion rate control unit, 13…Second diffusion rate control unit, 14…Structure, 20…First cavity, 21…First pump unit, 22…First inner pump electrode, 24, 52, 46…Variable power supply, 30…Third diffusion rate control unit, 40…Second cavity, 41…Third pump unit, 42…Reference pump electrode, 43…Reference gas inlet space, 44…Third inner pump electrode, 50…Second pump unit, 51…Second inner pump electrode, 60…Fourth diffusion rate control unit, 61…Third cavity, 72…Heater, 80…Sensor unit for first cavity, 81…Sensor unit for second cavity, 82…Sensor unit for third cavity, 200…Gas sensor, 201…Sensor element, 301…Fuel injection device, 400…Inlet, 1000…CO2 mass estimation system. Detailed Implementation

[0021] <Composition of Gas Sensors>

[0022] Figure 1This is a summary representation of the CO2 mass estimation system 1000 involved in this embodiment. Figure 2 The diagram shows an example of the configuration of the gas sensor 200. The gas sensor 200 is a multi-gas sensor that monitors various gas components and measures their concentrations via sensor element 201. In this embodiment, at least water vapor (H2O) and carbon dioxide (CO2) are the main target gas components monitored in the gas sensor 200. Furthermore, the gas sensor 200 also includes a controller 210 that controls the operation of each component. As described later, in this embodiment, the gas sensor 200 is used by installing it in the exhaust path of an automobile engine and using the exhaust gas flowing through that exhaust path as the measured gas. Figure 1 A vertical cross-sectional view along the length direction including sensor element 201.

[0023] The sensor element 201 includes: a strip-shaped structure (substrate) 14 formed of an oxygen-ion-conducting solid electrolyte; a gas inlet 10 formed at one end of the structure 14 (the left end in the figure) for introducing the gas to be measured; and a buffer space 12, a first cavity 20, a second cavity 40, and a third cavity 61 formed within the structure 14, connected sequentially starting from the gas inlet 10. The buffer space 12 is connected to the gas inlet 10 via a first diffusion rate control unit 11. The first cavity 20 is connected to the buffer space 12 via a second diffusion rate control unit 13. The second cavity 40 is connected to the first cavity 20 via a third diffusion rate control unit 30. The third cavity 61 is connected to the second cavity 40 via a fourth diffusion rate control unit 60.

[0024] The structure 14 is constructed by stacking multiple substrates made of, for example, ceramic. Specifically, the structure 14 has a configuration in which six layers—a first substrate 1, a second substrate 2, a third substrate 3, a first solid electrolyte layer 4, an insulating layer 5, and a second solid electrolyte layer 6—are stacked in this order starting from the bottom. Each layer is made of a solid electrolyte with oxygen ion conductivity, such as zirconium oxide (ZrO2).

[0025] The gas inlet 10, the first diffusion rate control unit 11, the buffer space 12, the second diffusion rate control unit 13, the first cavity 20, the third diffusion rate control unit 30, the second cavity 40, the fourth diffusion rate control unit 60, and the third cavity 61 are formed sequentially on one end side of the structure 14, and are formed between the lower surface 6b of the second solid electrolyte layer 6 and the upper surface 4a of the first solid electrolyte layer 4. The portion from the gas inlet 10 to the third cavity 61 is also referred to as the gas flow section.

[0026] The gas inlet 10, buffer space 12, first cavity 20, second cavity 40, and third cavity 61 are formed such that they penetrate the isolation layer 5 along the thickness direction. In the above-mentioned cavities, the lower surface 6b of the second solid electrolyte layer 6 is exposed in the upper part of the attached drawing, and the upper surface 4a of the first solid electrolyte layer 4 is exposed in the lower part of the attached drawing. The sides of the above-mentioned cavities are divided by the isolation layer 5 or any diffusion rate control unit.

[0027] The first diffusion rate control unit 11, the second diffusion rate control unit 13, the third diffusion rate control unit 30, and the fourth diffusion rate control unit 60 each have two horizontally elongated slits. That is, they have openings that extend relatively long along a direction perpendicular to the drawing at the upper and lower parts.

[0028] Additionally, a reference gas inlet space 43 is provided at the other end of the sensor element 201 opposite to the end where the gas inlet 10 is provided (the right end in the attached figure). The reference gas inlet space 43 is formed between the upper surface 3a of the third substrate 3 and the lower surface 5b of the insulating layer 5. Furthermore, the side of the reference gas inlet space 43 is divided by the side of the first solid electrolyte layer 4. For example, oxygen (O2) and atmospheric air are introduced into the reference gas inlet space 43 as reference gases.

[0029] The gas inlet 10 is an open portion relative to the external space, through which the gas to be measured is introduced from the external space into the sensor element 201.

[0030] The first diffusion rate control unit 11 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the gas inlet 10 into the buffer space 12.

[0031] The purpose of providing the buffer space 12 is to eliminate the concentration fluctuation of the gas being measured caused by pressure changes in the gas being measured in the external space. Examples of such pressure fluctuations include, for instance, the pulsation of exhaust pressure in automobile exhaust.

[0032] The second diffusion rate control unit 13 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first cavity 20.

[0033] The first cavity 20 is configured such that oxygen is drawn from the gas to be measured, which is introduced through the second diffusion rate control unit 13, and then the H2O and CO2 components contained in the gas to be measured, which are the gas components to be monitored, are reduced (decomposed) to generate hydrogen (H2) and carbon monoxide (CO), so that the gas to be measured not only does not contain oxygen, but also substantially does not contain H2O and CO2. This reduction (decomposition) of H2O and CO2 is achieved by the operation of the first pump unit 21.

[0034] The first pump unit 21 is an electrochemical pump unit consisting of a first inner pump electrode 22, an outer pump electrode 23, and a solid electrolyte present in the portion of the structure 14 sandwiched between these two electrodes.

[0035] In the first pump unit 21, an oxygen pump current (oxygen ion current) Ip1 is generated by applying a voltage Vp1 between the first inner pump electrode 22 and the outer pump electrode 23 using a variable power supply 24 external to the sensor element 201. Accordingly, oxygen in the first cavity 20 can be drawn out to the external space.

[0036] The first inner pump electrode 22 is disposed in the form of a top electrode 22a and a bottom electrode portion 22b on the lower surface 6b of the second solid electrolyte layer 6 that defines the first cavity 20 and the upper surface 4a of the first solid electrolyte layer 4 that defines the first cavity 20, respectively.

[0037] The first inner pump electrode 22 is configured as a porous metal-ceramic electrode that is rectangular in shape when viewed from above, with platinum as the metal component, for example, containing platinum and zirconium oxide.

[0038] The outer pump electrode 23 is formed as a porous metal-ceramic electrode that is rectangular in top view, with platinum or a platinum-gold alloy (Pt-Au alloy) as the metal component, for example, containing platinum or Pt-Au alloy and zirconium oxide.

[0039] Furthermore, in sensor element 201, a first cavity sensor unit 80 is formed by the first inner pump electrode 22, the reference electrode 42, and the solid electrolyte present in the portion of structure 14 sandwiched between these two electrodes. The first cavity sensor unit 80 is an electrochemical sensor unit for measuring the oxygen partial pressure in the atmosphere within the first cavity 20.

[0040] The reference electrode 42 is an electrode formed between the first solid electrolyte layer 4 and the third substrate 3, for example, a porous metal-ceramic electrode that is rectangular in top view and includes platinum and zirconium oxide.

[0041] A reference gas introducing layer 48, formed of porous alumina and connected to the reference gas introducing space 43, is disposed around the reference electrode 42. The reference gas in the reference gas introducing space 43 is introduced to the surface of the reference electrode 42 through the reference gas introducing layer 48. That is, the reference electrode 42 is always in contact with the reference gas.

[0042] In the first cavity sensor unit 80, an electromotive force (Nernst electromotive force) V1 is generated between the first inner pump electrode 22 and the reference electrode 42. The electromotive force V1 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the first cavity 20 and the oxygen concentration (oxygen partial pressure) of the reference gas. Since the oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, the electromotive force V1 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the first cavity 20.

[0043] The third diffusion rate control unit 30 is a part that imparts a predetermined diffusion resistance to the gas to be measured, which contains H2 and CO but does not substantially contain H2O, CO2 and oxygen, introduced from the first cavity 20 into the second cavity 40.

[0044] The second cavity 40 is configured such that only the H2 contained in the gas to be measured, introduced through the third diffusion rate control unit 30, and the H2 in CO are selectively oxidized to regenerate H2O. This oxidation of H2 to generate H2O is achieved by the operation of the second pump unit 50.

[0045] The second pump unit 50 is an electrochemical pump unit consisting of a second inner pump electrode 51, an outer pump electrode 23, and a solid electrolyte present in the portion of the structure 14 sandwiched between these two electrodes.

[0046] In the second pump unit 50, an oxygen pump current (oxygen ion current) Ip2 is generated by applying a voltage Vp2 between the second inner pump electrode 51 and the outer pump electrode 23 using a variable power supply 52 external to the sensor element 201. Accordingly, oxygen can be drawn from the external space into the second cavity 40.

[0047] The second inner pump electrode 51 is disposed in the form of a top electrode 51a and a bottom electrode portion 51b on the generally entire surface of the lower surface 6b of the second solid electrolyte layer 6 that defines the second cavity 40 and the generally entire surface of the upper surface 4a of the first solid electrolyte layer 4 that defines the second cavity 40.

[0048] The second inner pump electrode 51 is configured as a porous metal-ceramic electrode that is rectangular in top view and has a Pt-Au alloy as its metal composition, for example, containing the Pt-Au alloy and zirconium oxide.

[0049] Furthermore, in sensor element 201, a second cavity sensor unit 81 is formed by the second inner pump electrode 51, the reference electrode 42, and the solid electrolyte present in the portion of structure 14 sandwiched between these two electrodes. The second cavity sensor unit 81 is an electrochemical sensor unit for measuring the partial pressure of oxygen in the atmosphere within the second cavity 40.

[0050] In the second cavity sensor unit 81, an electromotive force (Nernst electromotive force) V2 is generated between the second inner pump electrode 51 and the reference electrode 42. The electromotive force V2 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the second cavity 40 and the oxygen concentration (oxygen partial pressure) of the reference gas. Since the oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, the electromotive force V2 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the second cavity 40.

[0051] The fourth diffusion rate control unit 60 is a part that imparts a predetermined diffusion resistance to the gas to be measured, which contains H2O and CO but does not substantially contain CO2 and oxygen, introduced from the second cavity 40 into the third cavity 61.

[0052] The third cavity 61 is configured to oxidize all CO contained in the gas being measured, which is introduced through the fourth diffusion rate control unit 60, thereby regenerating CO2. This oxidation of CO to generate CO2 is achieved by the operation of the third pump unit 41.

[0053] The third pump unit 41 is an electrochemical pump unit consisting of the third inner pump electrode 44, the outer pump electrode 23, and the solid electrolyte present in the part of the structure 14 sandwiched between the two electrodes.

[0054] In the third pump unit 41, an oxygen pump current (oxygen ion current) Ip3 is generated by applying a voltage Vp3 between the third inner pump electrode 44 and the outer pump electrode 23 using a variable power supply 46 external to the sensor element 201. Accordingly, oxygen can be drawn from the external space into the third cavity 61.

[0055] The third inner pump electrode 44 is disposed on approximately the entire surface of the upper surface 4a of the first solid electrolyte layer 4 that defines the third cavity 61.

[0056] The third inner pump electrode 44 is configured as a porous metal-ceramic electrode that is rectangular in shape when viewed from above, with platinum as the metal component, for example, containing platinum and zirconium oxide.

[0057] Furthermore, in sensor element 201, a third cavity sensor unit 82 is formed by the solid electrolyte present in the third inner pump electrode 44, the reference electrode 42, and the portion of the structure 14 sandwiched between these two electrodes. The third cavity sensor unit 82 is an electrochemical sensor unit used to measure the partial pressure of oxygen in the atmosphere within the third cavity 61.

[0058] In the sensor unit 82 of the third cavity, an electromotive force (Nernst electromotive force) V3 is generated between the third inner pump electrode 44 and the reference electrode 42. The electromotive force V3 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the third cavity 61 and the oxygen concentration (oxygen partial pressure) of the reference gas. Since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V3 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the third cavity 61.

[0059] In addition, the sensor element 201 also has an electrochemical sensor unit 83 consisting of an outer pump electrode 23, a reference electrode 42, and a solid electrolyte present in the portion of the structure 14 sandwiched between these two electrodes. In this sensor unit 83, the electromotive force Vref generated between the outer pump electrode 23 and the reference electrode 42 is a value corresponding to the oxygen partial pressure of the gas to be measured present outside the sensor element 201.

[0060] In addition to the components mentioned above, the sensor element 201 includes a heater 72 sandwiched between the second substrate 2 and the third substrate 3. The heater 72 is powered externally via heater electrodes 71 disposed on the lower surface 1b of the first substrate 1. The heater 72 is embedded throughout the buffer space 12 to the third cavity 61, enabling it to heat the sensor element 201 to a predetermined temperature and maintain that temperature. Heating by the heater 72 improves the oxygen ion conductivity of the solid electrolyte constituting the sensor element 201.

[0061] Above and below the heater 72, heater insulation layers 74 made of alumina or the like are formed for the purpose of obtaining electrical insulation with the second substrate 2 and the third substrate 3. Hereinafter, the heater 72, heater electrodes, and heater insulation layers 74 will be collectively referred to as the heater section. In addition, the heater section is provided with a pressure relief hole 75. The pressure relief hole 75 is provided to penetrate the third substrate 3 and communicate with the reference gas introduction space 43. The purpose of providing the pressure relief hole 75 is to mitigate the increase in internal pressure that accompanies the temperature rise within the heater insulation layer 74.

[0062] The controller 210 is composed of one or more electronic circuits, such as one or more CPUs (Central Processing Units) and storage devices. The electronic circuits are also software functional units that implement a predetermined function by the CPU executing a predetermined program stored in, for example, the storage device. Alternatively, it can be composed of integrated circuits such as an FPGA (Field-Programmable Gate Array) obtained by connecting multiple electronic circuits according to their function.

[0063] <Multi-gas monitoring and concentration determination>

[0064] Next, the monitoring of multiple gas types (multi-gas monitoring) and the method for determining the concentration of the monitored gas, implemented in the gas sensor 200 having the configuration described above, will be explained. In the following text, the gas to be measured is exhaust gas containing oxygen, H2O, and CO2.

[0065] In the gas sensor 200 of this embodiment, the gas to be measured introduced into the inside of the element from the gas inlet 10 is introduced into the first cavity 20 through the buffer space 12.

[0066] In the first cavity 20, oxygen is drawn from the introduced gas to be measured by the operation of the first pump unit 21. Accordingly, the H2O and CO2 contained in the gas to be measured undergo reduction (decomposition) reactions (2H2O→2H2+O2, 2CO2→2CO+O2), and H2O and CO2 are essentially completely decomposed into hydrogen (H2), carbon monoxide (CO), and oxygen, and the resulting oxygen is also drawn out. It should be noted that "essentially completely decomposed H2O and CO2" means that H2O and CO2 are not introduced into the second cavity 40.

[0067] The oxygen extraction described above is performed as follows: the controller 210 sets a target value (control voltage) for the electromotive force V1 in the first cavity sensor unit 80 based on the desired oxygen partial pressure (oxygen concentration) (preferably 1000mV) within the range of 1000mV to 1500mV, and performs feedback control on the voltage Vp1 applied by the variable power supply 24 to the first pump unit 21 based on the difference between the actual value of the electromotive force V1 and the target value, so as to achieve the aforementioned target value. In this case, the voltage Vp1 is the sum of the IR overvoltage and the reaction overvoltage.

[0068] When the gas to be measured, for example, contains a large amount of oxygen, arrives at the first cavity 20, the value of the electromotive force V1 deviates significantly from the target value. Therefore, the controller 210 controls the pump voltage Vp1 applied by the variable power supply 24 to the first pump unit 21 to reduce this deviation.

[0069] By setting the target value (control voltage) of the electromotive force V1 to a value within the range of 1000mV to 1500mV, the oxygen partial pressure in the first cavity 20 is sufficiently reduced. When V1 = 1000mV, this oxygen partial pressure is 10... -20 The gas to be measured in the first cavity 20 contains H2 and CO, but does not actually contain H2O, CO2, or oxygen. This gas is then introduced into the second cavity 40.

[0070] In the second cavity 40, oxygen is drawn in by the second pump unit 50, which oxidizes only the H2 contained in the introduced gas to be measured.

[0071] The oxygen intake described above is performed as follows: the controller 210 sets the target value (control voltage) of the electromotive force V2 in the second cavity sensor unit 81 according to the desired oxygen partial pressure (oxygen concentration) (preferably 350mV) within the range of 250mV to 450mV, and performs feedback control on the voltage Vp2 applied to the second pump unit 50 by the variable power supply 52 according to the difference between the actual value of the electromotive force V2 and the target value, so as to achieve the above target value.

[0072] The second pump unit 50 operates in the manner described above. Within the second cavity 40, the oxidation (combustion) reaction 2H₂ + O₂ → 2H₂O is promoted, and an amount of H₂O is regenerated that is correlated with the amount of H₂O introduced from the gas inlet 10. It should be noted that in this embodiment, "correlated" means that the amount of H₂O or CO₂ introduced from the gas inlet 10 is equal to or within a certain permissible error range for the sake of measurement accuracy, and that the amount of H₂ or CO₂ produced by their decomposition and the amount of H₂ or CO₂ regenerated by the oxidation of CO are equal to or within a certain permissible error range for the sake of measurement accuracy.

[0073] By setting the target value of the electromotive force V2 within the range of 250mV to 450mV, the oxygen partial pressure in the second cavity 40 is maintained at a value where H2 is almost completely oxidized but CO is not oxidized. For example, when V2 = 350mV, the oxygen partial pressure is 10. -7 Around ATM.

[0074] Furthermore, when the electromotive force V2 remains at the target value, the oxygen pump current Ip2 flowing through the second pump unit 50 (hereinafter also referred to as the water vapor detection current Ip2) is approximately proportional to the concentration of H2O generated by the combustion of H2 in the second cavity 40 (there is a linear relationship between the water vapor detection current Ip2 and the concentration of generated H2O). The amount of H2O generated by this combustion is correlated with the amount of H2O in the measured gas that is temporarily decomposed in the first cavity 20 after being introduced from the gas inlet 10. Accordingly, by detecting the water vapor detection current Ip2, the H2O in the measured gas can be monitored.

[0075] Furthermore, a linear relationship exists between the water vapor detection current Ip2 and the water vapor concentration in the gas being measured. If data representing this linear relationship (water vapor characteristic data) is determined in advance using a sample gas with a known water vapor concentration, the value of the water vapor concentration corresponding to the water vapor detection current Ip2 can be determined by comparing the value of the water vapor detection current Ip2 obtained by the controller 210 with the water vapor characteristic data.

[0076] It should be noted that if the gas to be measured introduced from the gas inlet 10 does not contain H2O, then of course H2O will not decompose in the first cavity 20. Therefore, no H2 will be introduced into the second cavity 40, and thus the water vapor detection current Ip2 will be approximately zero.

[0077] H2 is oxidized to H2O, resulting in a gas containing H2O and CO but substantially free of CO2 and oxygen. This gas is then introduced into the third cavity 61. In the third cavity 61, oxygen is drawn in by the third pump unit 41, oxidizing the CO contained in the introduced gas.

[0078] The oxygen intake is performed as follows: the controller 210 sets the target value (control voltage) of the electromotive force V3 in the third cavity sensor unit 82 according to the desired oxygen partial pressure (oxygen concentration) (preferably 200mV) in the range of 100mV to 300mV, and performs feedback control on the voltage Vp3 applied to the third pump unit 41 by the variable power supply 46 according to the difference between the actual value of the electromotive force V3 and the target value, so as to achieve the target value.

[0079] The third pump unit 41 operates in the manner described above, and within the third cavity 61, the oxidation (combustion) reaction 2CO + O2 → 2CO2 is promoted, generating an amount of CO2 that is correlated with the amount of CO2 introduced from the gas inlet 10.

[0080] By setting the target value of the electromotive force V3 within the range of 100mV to 300mV, the oxygen partial pressure in the third cavity 61 is maintained at a value within which CO is approximately completely oxidized. For example, when V3 = 200mV, the oxygen partial pressure is 10. -4 Around ATM.

[0081] Furthermore, when the electromotive force V3 remains at the target value, the oxygen pump current Ip3 flowing through the third pump unit 41 (hereinafter also referred to as the carbon dioxide detection current Ip3) is approximately proportional to the concentration of CO2 generated by the combustion of CO in the third cavity 61 (the carbon dioxide detection current Ip3 and the concentration of generated CO2 have a linear relationship). The amount of CO2 generated by this combustion is correlated with the amount of CO2 in the measured gas that is temporarily decomposed in the first cavity 20 after being introduced from the gas inlet 10. Accordingly, by detecting the carbon dioxide detection current Ip3, the CO2 in the measured gas can be monitored.

[0082] Furthermore, a linear relationship exists between the carbon dioxide detection current Ip3 and the carbon dioxide concentration in the gas being measured. If data representing this linear relationship (carbon dioxide characteristic data) is determined in advance using a sample gas with a known carbon dioxide concentration, the value of the carbon dioxide concentration corresponding to the carbon dioxide detection current Ip3 can be determined by comparing the value of the carbon dioxide detection current Ip3 acquired by the controller 210 with the carbon dioxide characteristic data.

[0083] It should be noted that if there is no CO2 in the gas to be measured introduced through the gas inlet 10, then of course CO2 will not decompose in the first cavity 20. Therefore, no CO will be introduced into the third cavity 61, and thus the carbon dioxide detection current Ip3 will be approximately zero.

[0084] As described above, the gas sensor 200 according to this embodiment can accurately determine the concentration of water vapor and the concentration of carbon dioxide.

[0085] Furthermore, although indirect, the gas sensor 200 can still determine the oxygen concentration in the gas being measured. In short, the difference between the oxygen concentration drawn out of the first cavity 20 and the oxygen concentration drawn into the second cavity 40 and the third cavity 61 corresponds to the oxygen concentration in the gas being measured introduced through the gas inlet 10. Additionally, the concentrations of oxygen, H2O, and CO2 in the gas being measured are approximately proportional to the oxygen pump currents Ip1, Ip2, and Ip3, respectively. Therefore, when the concentrations of oxygen, H2O, and CO2 in the gas being measured are set as C... e_O2 C e_H2O C e_CO2 When the above values ​​are given, they can be expressed as follows. Specifically, regarding the oxygen pump currents Ip1, Ip2, and Ip3, the direction in which oxygen is drawn out is assumed to be positive, and a1 to a5 are proportionality constants determined experimentally.

[0086] C e_O2 =a1·Ip1+a2·Ip2+a3·Ip3····(1)

[0087] C e_H2O =a4·Ip2····(2)

[0088] C e_CO2 =a5·Ip3····(3)

[0089] If equation (1) is predetermined, the oxygen concentration in the gas being measured can be determined based on the detected values ​​of the oxygen pump currents Ip1, Ip2, and Ip3. Furthermore, equations (2) and (3) are simply expressions representing the characteristic data of water vapor and carbon dioxide, respectively.

[0090] <CO2 Mass Estimation System>

[0091] Next, the CO2 mass estimation system 1000 involved in this embodiment will be described. Figure 2 This is a schematic diagram illustrating the configuration of the CO2 mass estimation system 1000. In short, the CO2 mass estimation system 1000 is a system that estimates the mass of CO2 contained in the exhaust gas of a vehicle engine using a detection current in a gas sensor 200.

[0092] like Figure 2 As shown, the CO2 mass estimation system 1000 includes: a gas sensor 200; an ECU (electronic control unit) 100 that controls the operation of various parts of the vehicle; a fuel injection device 301 that injects fuel into the interior (combustion chamber) of the vehicle's engine 300; and an intake unit 400 provided in the air supply path P1 of the engine 300 to supply air to the engine 300. The gas sensor 200 is installed in the exhaust path P2 of the engine 300. That is, the CO2 mass estimation system 1000 according to this embodiment is configured to include the components of a vehicle and is assembled into a vehicle for use.

[0093] The gas sensor 200, having the above-described configuration, is originally intended for measuring the concentrations of H2O and CO2 in the exhaust gas flowing through the exhaust path P2 to determine the operating status of the engine 300. In this embodiment, the gas sensor 200 is used for estimating the CO2 mass in the CO2 mass estimation system 1000.

[0094] ECU 100 comprises electronic circuitry including at least one IC (integrated circuit). The electronic circuitry includes at least one processor (not shown). The various functions of ECU 100 can be implemented by the processor executing software. The software is recorded as a program and stored in a memory (not shown). The memory for storing the program may be included within ECU 100, and may be, for example, a non-volatile or volatile semiconductor memory.

[0095] The ECU100 mainly includes the following components as functional elements: a general control unit 110, a fuel injection control unit 120, an intake control unit 130, a sensor detection value acquisition unit 140, and a CO2 mass calculation unit 150.

[0096] The overall control unit 110 provides control instructions to each control unit of the ECU 100 based on the driver's operation of the vehicle, thereby performing overall control of the vehicle's movements.

[0097] The fuel injection control unit 120 controls the injection of fuel from the fuel injection device 301 under the control instruction from the general control unit 110. In addition, the fuel injection control unit 120 provides a signal indicating the measured value of the fuel injection quantity to the general control unit 110.

[0098] The intake control unit 130 controls the intake air from the intake unit 400 under the control instructions from the general control unit 110.

[0099] The fuel injection control unit 120 and the intake control unit 130 control the fuel injection device 301 and the intake unit 400 respectively, so as to perform fuel injection and intake in accordance with the air-fuel ratio A / F set by the overall control unit 110 according to the vehicle's operating conditions.

[0100] The sensor detection value acquisition unit 140 acquires signals representing various detection values ​​detected by the gas sensor 200. Examples of such detection values ​​include: oxygen pump current Ip1, oxygen pump current (water vapor detection current) Ip2, and oxygen pump current (carbon dioxide detection current) Ip3.

[0101] The CO2 mass calculation unit 150 calculates the estimated mass of CO2 contained in the exhaust gas based on the detection value of the gas sensor 200 obtained in the sensor detection value acquisition unit 140, the air-fuel ratio A / F given by the general control unit 110, and the value of the fuel injection quantity. The CO2 mass calculation unit 150 (more specifically, the memory, not shown, constituting the CO2 mass calculation unit 150) stores formulas (1) to (3) determined in advance through experiments (more specifically, the proportionality constants a1 to a5 of formulas (1) to (3) are given).

[0102] <Estimated order of CO2 mass>

[0103] Next, the processing sequence for estimating the mass of CO2 contained in the exhaust gas in the CO2 mass estimation system 1000 according to this embodiment will be described. Figure 3 This is a diagram schematically illustrating the relationship between various parameters used for estimating the mass of CO2 in the CO2 mass calculation unit 150 of the CO2 mass estimation system 1000.

[0104] In short, in this embodiment, based on the detected values ​​of the oxygen pump currents Ip1, Ip2, and Ip3 in the gas sensor 200 and the air-fuel ratio set by the general control unit 110 of the ECU 100, the composition of the fuel (at least the mass of C atoms per unit mass of fuel) is estimated. Based on this estimated fuel composition and the measured value of the fuel injection quantity in the fuel injection device 301, the mass of CO2 contained in the exhaust gas is estimated. However, the estimation of the CO2 mass in this embodiment is based on the premise that the fuel is completely burned in the engine 300 and that the exhaust gas does not contain unburned CO or HC.

[0105] First, under the condition that the exhaust gas generated by combustion flows through the exhaust path P2 inside the engine 300, the detected values ​​of the oxygen pump currents Ip1, Ip2, and Ip3 in the gas sensor 200 are compared with the concentrations C of oxygen, H2O, and CO2 contained in the measured gas, i.e., the exhaust gas. e_O2 C e_H2O C e_CO2 Between them, the relationship between equations (1) to (3) above holds.

[0106] Furthermore, the mass of C, H, and O atoms contained in a certain mass of waste gas is related to the concentrations of oxygen, H2O, and CO2 in the waste gas as expressed in equations (1) to (3), with the atomic mass ∝ Σ(concentration of the target gas × number of atoms of that type in one molecule of the target gas) × atomic weight. That is, the mass m of C, H, and O atoms contained in a certain mass of waste gas e_C m e_H m e_O The concentrations C of oxygen, H2O, and CO2 in the exhaust gas, as expressed by equations (1) to (3), are... e_O2 C e_H2O C e_CO2 The following relationship holds between them. Where k1 is an appropriate proportionality coefficient.

[0107] m e_C =k1·C e_CO2 ×1×12=k1·12·C e_CO2 ····(4)

[0108] m e_H =k1·C e_H2O ×2×1=k1·2·C e_H2O ····(5)

[0109] m e_O =k1·(C e_O2 ×2+C e_H2O ×1+C e_CO2 ×2)×16

[0110] =k1·(32·Ce_O2 +16·C e_H2O +32·C e_CO2 (6)

[0111] Furthermore, when there is no exhaust gas produced by combustion inside the engine 300, the air entering through the intake section 400 flows directly into the exhaust path P2. Therefore, if the detected values ​​of the oxygen pump currents Ip1, Ip2, and Ip3 detected by the gas sensor 200 under this condition are substituted into the following equations (1') and (2'), the concentrations C of oxygen and H2O in the atmosphere can be determined. a_O2 and C a_H2O .

[0112] C a_O2 =a1·Ip1+a2·Ip2+a3·Ip3 ····(1')

[0113] C a_H2O =a4·Ip2 ····(2')

[0114] It should be noted that the CO2 concentration can also be calculated; however, the atmospheric CO2 concentration is as low as around 300 ppm, therefore, it will be ignored and set to 0 in subsequent calculations. Alternatively, a separate gas sensor (separate from the gas sensor 200) can be used to measure the concentration at a location different from the exhaust path P2, thereby determining the CO2 concentration. a_O2 and C a_H2O .

[0115] When using the concentration C of oxygen and H2O in the atmosphere a_O2 and C a_H2O At that time, the mass m of C atoms, H atoms, and O atoms contained in a unit mass of atmosphere a_C m a_H m a_O The following is an example. Here, the average molecular weight of the atmosphere is set as M. air =28.8.

[0116] m a_C =0····(7)

[0117] m a_H =(C a_H2O ×2×1) / M air =2·C a_H2O / M air ····(8)

[0118] m a_O =(C a_O2 ×2+C a_H2O ×1)×16 / M air

[0119] =(32·C a_O2 +16·C a_H2O ) / M air ····(9)

[0120] On the other hand, assuming that fuel is composed primarily of C, H, and O atoms, the mass m of C, H, and O atoms contained in a unit mass of fuel is... f_C m f_H m f_O The following relationship holds true between them.

[0121] m f_C +m f_H +m f_O =1····(10)

[0122] Furthermore, the masses of C, H, and O atoms in the fuel-atmosphere mixture are the sum of the masses of these atoms in the fuel and the masses of these atoms in the atmosphere. The ratio of the mass of the atmosphere to the mass of the fuel in this mixture is the air-fuel ratio A / F. When the value of the air-fuel ratio A / F is set as r (=atmosphere mass / fuel mass), the mass m of C, H, and O atoms in a unit mass of fuel mixed with the atmosphere at this air-fuel ratio A / F is... m_C m m_H m m_O As shown below.

[0123] m m_C =m f_C +m a_C ·r····(11)

[0124] m m_H =m f_H +m a_H ·r····(12)

[0125] m m_O =m f_O +m a_O ·r····(13)

[0126] During complete combustion (when the engine is running normally), the composition of the air-fuel mixture is the same as that of the exhaust gas; therefore, the following relationship holds true.

[0127] m m_C =m e_C ····(14)

[0128] m m_H =m e_H ····(15)

[0129] m m_O =me_O ····(16)

[0130] Combining equations (4) to (16), the proportionality coefficient k1 in equations (4) to (6) is expressed as in equation (17) below.

[0131] k1={M air +(32·C a_O2 +18·C a_H2O )·r} / {M air ·(32·C e_O2 +18·C e_H2O +44·C e_CO2 )}

[0132] ····(17)

[0133] In equation (17), the average molecular weight of the atmosphere is M air It is a known fixed value. C a_O2 and C a_H2O The concentrations of oxygen and H2O in the atmosphere, as measured by gas sensor 200. (C) e_O2 C e_H2O and C e_CO2 Similarly, the concentrations of oxygen, H2O, and CO2 in the exhaust gas are measured by the gas sensor 200. Furthermore, the air-fuel ratio r is a value set by the overall control unit 110 according to the vehicle's operating conditions. Therefore, the proportional coefficient k1 can be specifically calculated using equation (17).

[0134] Using this proportionality coefficient k1, the mass m of C atoms per unit mass of fuel can be obtained from equations (4), (11), and (14). f_C The following formula (18).

[0135] m f_C =m m_C =m e_C =k1·12·C e_CO2 ····(18)

[0136] It should be noted that m represents the mass of H atoms per unit mass of fuel. f_H The mass m of the O atom f_O The formula can also be solved in the same way. In this case, the ratio m obtained from formula (18) and these two formulas is... f_C :m f_H :m f_O It represents the composition ratio of C, H, and O atoms in the fuel.

[0137] Furthermore, based on equation (10), m f_C The value also belongs to the composition ratio m f_C :mf_H :m f_O The composition of C atoms in the fuel, therefore, it can also be said that formula (18) is the formula for calculating the composition of C atoms in the fuel.

[0138] During complete combustion, all the carbon atoms in the fuel are converted into CO2; therefore, the injection mass M f The mass M of CO2 contained in the exhaust gas generated from fuel. e_CO2 M can be used f and m f_C The value of is obtained by the following equation (19).

[0139] M e_CO2 =M f ·m f_C • (Molecular weight of CO2 / atomic weight of C)

[0140] =M f ·m f_C ·(44 / 12)····(19)

[0141] Alternatively, the mass M of CO2 can be calculated by substituting equation (18) into equation (19) to obtain equation (20). e_CO2 .

[0142] M e_CO2 =44·M f ·k1·C e_CO2 ····(20)

[0143] In this embodiment, when the CO2 mass estimation system 1000 performs CO2 mass estimation at a predetermined time, it first acquires, via the sensor detection value acquisition unit 140, the detection values ​​of the oxygen pump current Ip1, Ip2, and Ip3 when the measured gas is exhaust gas, and the oxygen pump current Ip1 when the measured gas is atmospheric gas, either continuously or intermittently acquired from the gas sensor 200.

[0144] The detection values ​​of Ip2 and Ip3 are provided from the sensor detection value acquisition unit 140 to the CO2 mass calculation unit 150.

[0145] The CO2 mass calculation unit 150 uses these values ​​to calculate C. e_O2 C e_H2O C e_CO2 C a_O2 and C a_H2O It should be noted that the proportionality constants on the right side of each of equations (1) to (3) and equations (1') to (2') are the inherent proportionality constants of the gas sensor 200 used, which were determined in advance through experiments.

[0146] It should be noted that the composition of atmospheric gases varies less compared to that of exhaust gases. Furthermore, measurements may be performed using atmospheric gases at different times depending on the vehicle's operating conditions and the timing of the estimation. Therefore, it is also possible to use previously calculated and stored data in ECU100 or separately determined C... a_O2 and C a_H2O The value of .

[0147] In addition, the CO2 mass calculation unit 150 obtains the air-fuel ratio A / F value r from the overall control unit 110. Then, based on equation (17), the proportional coefficient k1 is calculated.

[0148] The CO2 mass calculation unit 150 also obtains the mass M of the fuel injected into the fuel injection device 301, which is provided to the general control unit 110 from the fuel injection control unit 120. f The value of is then calculated using equation (18). f_C Then, the mass M of CO2 was calculated using equation (19). e_CO2 Alternatively, based on equation (20), the mass M of CO2 can be calculated. e_CO2 .

[0149] In the CO2 mass estimation system 1000 of this embodiment, the composition ratio of C, H, and O atoms in the exhaust gas when a certain mass of fuel is injected can be estimated through the above sequence. Furthermore, the emission mass of CO2 can be estimated. Based on this sequence, even without measuring the mass flow rate of the exhaust gas, the emission mass of CO2 can be estimated based on the detection value in the gas sensor 200, the air-fuel ratio, and the value or set value in the ECU 100 during vehicle operation, which is called the fuel injection quantity.

[0150] Example

[0151] Using gasoline passenger cars as the target, the CO2 mass estimation system 1000 is used to estimate the CO2 mass in the exhaust gas.

[0152] First, using a sample gas, the oxygen pump currents Ip1, Ip2, and Ip3 [unit: mA] in the gas sensor 200 and the concentrations C of oxygen, H2O, and CO2 in the exhaust gas were determined experimentally. e_O2 C e_H2O C e_CO2 The proportionality constants a1 to a5 [unit: % / mA] of equations (1) to (3) are as follows.

[0153] C e_O2 =20.0·Ip1+22.0·Ip2+57.1·Ip3;

[0154] C e_H2O= -10.0 Ip2;

[0155] C e_CO2 = -71.4·Ip3.

[0156] The gas sensor 200 is installed in the tailpipe of a gasoline passenger vehicle. The vehicle is operated under the following conditions, and the exhaust gas is measured using the gas sensor 200.

[0157] Passenger vehicle speed: 60 km / h, constant;

[0158] Measurement time: 60 seconds;

[0159] Fuel injection rate per unit time: 0.34 g / s;

[0160] Air-fuel ratio r: 14.3.

[0161] As a result, the values ​​of the oxygen pump currents Ip1, Ip2, and Ip3 are as follows.

[0162] Ip1 = 1.63mA;

[0163] Ip2 = -1.04mA;

[0164] Ip3 = -0.17mA.

[0165] In addition, the predetermined concentration C of oxygen in the atmosphere a_O2 and the concentration C of H2O a_H2O The details are as follows.

[0166] Atmospheric oxygen concentration C a_O2 20.7%;

[0167] Atmospheric H2O concentration C a_H2O 1.0%.

[0168] Using these values, the value of the proportionality constant k1 is obtained using equation (17).

[0169] k1 = 0.60669

[0170] On the other hand, the concentration C of CO2 in the exhaust gas e_CO2 The calculation is as follows:

[0171] C e_CO2 =-71.4·Ip3=-71.4×(-0.17)=12.1%.

[0172] Substituting these values ​​into equation (18), the mass m of C atoms per unit mass of fuel is... f_C for:

[0173] m f_C =k1·12·Ce_CO2 =0.60669×12×12.1=88%.

[0174] It should be noted that the fuel composition ratio is:

[0175] m f_C :m f_H :m f_O =88:12:0.

[0176] Finally, the estimated mass of CO2 in the exhaust gas (when fuel is injected at 0.34 g / s for 60 seconds) is M. e_CO2 The calculation is as follows:

[0177] M e_CO2 =M f ·m f_C (44 / 12)

[0178] = (0.34 × 60) · (88 / 100) · (44 / 12)

[0179] =66g.

[0180] It should be noted that, for comparison, the value of the CO2 emission mass simultaneously measured in the quantitative dilution sampling device is compared with the estimated value M. e_CO2 Both weigh approximately 64g. The difference between the two is about 3%.

[0181] This result demonstrates that the mass of CO2 emitted can be estimated even without measuring the mass flow rate.

Claims

1. A CO2 mass estimation system for estimating the mass of CO2 contained in exhaust gas from an engine of a vehicle. Its features are, have: A gas sensor that can output detection values ​​corresponding to the concentrations of oxygen, H2O and CO2 in the gas being measured. The detection value acquisition mechanism acquires the detection values ​​output by the gas sensor, which correspond to the respective concentrations of oxygen, H2O, and CO2 contained in the exhaust gas from the engine. An air-fuel ratio setting mechanism that sets the air-fuel ratio of the mixture of fuel and air supplied to the engine; as well as The mass of CO2 contained in the exhaust gas from the computing unit. The arithmetic mechanism estimates the CO2 mass as follows: Based on the detection value of the gas sensor when the measured gas is the waste gas, the concentrations of oxygen, H2O, and CO2 in the waste gas are calculated. Obtain the atmospheric concentrations of oxygen and H2O. Obtain the air-fuel ratio set in the air-fuel ratio setting mechanism. Based on the respective concentrations of oxygen, H2O, and CO2 in the exhaust gas, the respective concentrations of oxygen and H2O in the atmosphere, and the air-fuel ratio obtained by the air-fuel ratio setting mechanism, the composition ratio of at least C atoms contained in the fuel is calculated. Based on the calculated composition ratio and the fuel injection amount for the engine, the mass of CO2 contained in the exhaust gas is estimated.

2. A method for estimating the composition ratio of exhaust gas, which estimates the composition ratio of C atoms, H atoms, and O atoms in exhaust gas from a vehicle engine. Its features are, Includes the following steps: The detection value acquisition step involves acquiring detection values ​​corresponding to the concentrations of oxygen, H2O, and CO2 in the exhaust gas from the engine from a gas sensor capable of outputting detection values ​​corresponding to the concentrations of oxygen, H2O, and CO2 in the gas being measured. The waste gas concentration calculation step involves calculating the concentrations of oxygen, H2O, and CO2 in the waste gas based on the detected values. The atmospheric concentration acquisition step involves acquiring the atmospheric concentrations of oxygen and H2O, respectively. An air-fuel ratio acquisition step, in which the air-fuel ratio of the mixture of fuel and atmosphere supplied to the engine is acquired; as well as The composition ratio estimation step involves estimating the composition ratio of C, H, and O atoms in the fuel based on the concentrations of oxygen, H2O, and CO2 in the exhaust gas calculated in the exhaust gas concentration calculation step, the concentrations of oxygen and H2O in the atmosphere obtained in the atmosphere concentration acquisition step, and the air-fuel ratio obtained in the air-fuel ratio acquisition step.

3. A method for estimating the mass of CO2, which estimates the mass of CO2 contained in the exhaust gas from an engine of a vehicle. Its features are, The method includes a mass estimation step in which the mass of CO2 contained in the exhaust gas is estimated based on the composition ratio of C atoms in the fuel estimated by the exhaust gas composition ratio estimation method of claim 2, and the amount of fuel injected for the engine.

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