Concentration information acquisition device and concentration information acquisition method

Abstract

To provide a density information acquisition device and the like which can acquire accurate density information from output of a gas sensor regardless of a temperature condition and a pressure condition for the target gas contained in the exhaust gas.SOLUTION: A density information acquisition device 1 according to the present invention includes: a reception unit 41 which receives an output value of a detection cell 340 in a gas sensor 3; a temperature information acquisition unit 42 which acquires temperature information of the gas sensor 3; a pressure information acquisition unit 43 which acquires pressure information of the exhaust gas; a correction unit 44 which corrects the output value by using a correction formula to correct temperature dependency and pressure dependency of the output value; and a density information acquisition unit 42 which acquires density information on the basis of a correction formula that expresses a relationship between the density information related to density of the target gas and the output value, and the correction value of the output value corrected by the correction unit 44.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a concentration information acquisition device and a concentration information acquisition method. [Background technology]

[0002] Oxygen sensors are known that are attached to the exhaust pipe of internal combustion engines such as automobile engines to detect the oxygen concentration in the exhaust gas within the exhaust pipe (for example, Patent Document 1). One such oxygen sensor comprises a gas sensor element having a gas detection chamber for detecting the oxygen concentration in the exhaust gas, between an oxygen concentration detection cell and an oxygen pump cell. The oxygen concentration detection cell comprises a solid electrolyte and a pair of electrodes arranged to sandwich it, and an electromotive force corresponding to the oxygen concentration is generated between the two electrodes. The oxygen pump cell also comprises a solid electrolyte and a pair of electrodes arranged to sandwich it, and functions to draw oxygen into the gas detection chamber from the outside or to pump oxygen out of the gas detection chamber. In such a gas sensor element, the electromotive force generated between the two electrodes of the oxygen concentration detection cell is compared with a predetermined reference voltage (for example, 450mV), and the magnitude and direction of the current (pump current Ip) flowing between the two electrodes of the oxygen pump cell are controlled based on the comparison result. The oxygen sensor calculates the oxygen concentration in the exhaust gas and the air-fuel ratio λ based on this current (pump current Ip).

[0003] The relationship between the pump current Ip and oxygen information (air-fuel ratio λ, etc.) can be expressed by a predetermined relational equation. Therefore, oxygen information (air-fuel ratio λ, etc.) can be determined from this relational equation and the pump current Ip. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-15533 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The aforementioned relation is determined based on the assumption that the exhaust gas temperature and pressure are under predetermined standard conditions (e.g., 720°C, 1 atmosphere). In other words, the relation is valid only when the exhaust gas temperature and pressure are strictly speaking under the aforementioned standard conditions. However, since the pump current Ip is temperature-dependent and pressure-dependent, if, for example, the temperature or pressure conditions deviate from the standard conditions, it becomes difficult to accurately determine oxygen information (such as the air-fuel ratio λ) from the pump current Ip even when using the relation.

[0006] Conventionally, temperature correction was applied to the output value (pump current Ip) of the gas sensor to reduce the influence of temperature dependence, and pressure correction was applied to reduce the influence of pressure dependence. Temperature correction is performed using a correction formula that represents the temperature dependence of the pump current Ip at a predetermined reference pressure (e.g., 1 atmosphere), which has been known in advance. Pressure correction is performed using a correction formula that represents the pressure dependence of the pump current Ip at a predetermined reference temperature (e.g., 720°C), which has been known in advance.

[0007] However, these corrections (temperature correction, pressure correction) to the output value (pump current Ip) only considered the dependence on either temperature or pressure, and did not consider both temperature and pressure dependence simultaneously. For example, in the case of temperature correction, if the exhaust gas pressure deviated from the reference pressure, accurate temperature correction could not be performed. Similarly, in the case of pressure correction, if the exhaust gas temperature deviated from the reference temperature, accurate pressure correction could not be performed.

[0008] Generally, it is rare for only one of the exhaust gas temperature and pressure to deviate from the aforementioned reference conditions; more often, both temperature and pressure deviate from the reference conditions simultaneously. For example, when an internal combustion engine is under heavy load, the exhaust gas temperature becomes high and the exhaust gas pressure becomes high, causing both temperature and pressure to deviate significantly from the reference conditions. Therefore, there has been a need to combine and simultaneously perform temperature and pressure corrections on the gas sensor output (pump current Ip).

[0009] The object of the present invention is to provide a concentration information acquisition device and a concentration information acquisition method that can obtain accurate concentration information from the output of a gas sensor for a target gas contained in exhaust gas, regardless of temperature and pressure conditions. [Means for solving the problem]

[0010] The means to solve the aforementioned problem are as follows: <1> A concentration information acquisition device that acquires information relating to the concentration of a target gas contained in exhaust gas from a gas sensor having a detection cell having a solid electrolyte and a set of electrodes disposed on the solid electrolyte, the device comprising: a receiving unit that receives the output value of the detection cell; a temperature information acquisition unit that acquires the temperature information of the gas sensor; a pressure information acquisition unit that acquires the pressure information of the exhaust gas; a correction unit that corrects the output value using a correction formula for correcting the temperature dependence and pressure dependence of the output value; and a concentration information acquisition unit that acquires the concentration information based on a relational formula representing the relationship between the concentration information relating to the concentration of the target gas and the output value, and a corrected value of the output value corrected by the correction unit.

[0011] <2> The gas sensor has a detection chamber housing at least one of the pair of electrodes, and a porous diffusion layer that separates the outside from the detection chamber and introduces exhaust gas from the outside to the detection chamber, and the correction formula includes parameters based on the molecular diffusion coefficient of the diffusion layer, which depends on the type of gas moving inside the diffusion layer, and the Knudsen diffusion coefficient of the diffusion layer, which depends on the type of gas moving inside the diffusion layer and the pore size in the diffusion layer. <1> The concentration information acquisition device described above.

[0012] <3> The parameters include lean parameters, which are parameters when the exhaust gas in the detection chamber is in a lean state, and rich parameters, which are parameters when the exhaust gas in the detection chamber is in a rich state, and the correction formula includes a lean correction formula that includes the lean parameters as parameters, and a rich correction formula that includes the rich parameters as parameters, and the determination unit determines whether the detection chamber is in a lean state or a rich state based on the output value, and the selection unit selects the lean correction formula as the correction formula when the detection chamber is in a lean state, and selects the rich correction formula as the correction formula when the detection chamber is in a rich state. <2> The concentration information acquisition device described above.

[0013] <4> The aforementioned relational expression is under the conditions of a predetermined reference temperature and a predetermined reference pressure, and the correction expression is an expression based on the parameter, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure. <3> The concentration information acquisition device described above.

[0014] <5> The piping to which the gas sensor is attached is further fitted with a gas temperature detection device for detecting the temperature of the exhaust gas, and the temperature information acquisition unit acquires the higher of the control temperature of the gas sensor and the gas temperature received from the gas temperature detection device as the temperature information. <1> The concentration information acquisition device described above.

[0015] <6> A method for acquiring concentration information, comprising a concentration information acquisition step for acquiring information relating to the concentration of a target gas contained in exhaust gas from a gas sensor having a detection cell having a solid electrolyte and a set of electrodes disposed on the solid electrolyte, the method comprising a receiving step for receiving the output value of the detection cell, a temperature information acquisition step for acquiring temperature information of the gas sensor, a pressure information acquisition step for acquiring pressure information of the exhaust gas, and a correction step for correcting the output value using a correction formula for correcting the temperature dependence and pressure dependence of the output value, wherein in the concentration information acquisition step, the concentration information is acquired based on the corrected value of the output value corrected by the correction step and a relational formula representing the relationship between the concentration information relating to the concentration of the target gas and the output value.

[0016] <7> The gas sensor has a detection chamber housing at least one of the pair of electrodes, and a porous diffusion layer that separates the outside from the detection chamber and introduces exhaust gas from the outside to the detection chamber, and the correction formula includes parameters based on the molecular diffusion coefficient of the diffusion layer, which depends on the type of gas moving inside the diffusion layer, and the Knudsen diffusion coefficient of the diffusion layer, which depends on the type of gas moving inside the diffusion layer and the pore size in the diffusion layer. <6> The method for obtaining concentration information as described above.

[0017] <8> The parameters consist of lean parameters, which are parameters when the exhaust gas in the detection chamber is in a lean state, and rich parameters, which are parameters when the exhaust gas in the detection chamber is in a rich state, and the correction formula has a lean correction formula that includes the lean parameters as parameters and a rich correction formula that includes the rich parameters as parameters, and the determination step of determining whether the detection chamber is in a lean state or a rich state based on the output value, and the selection step of selecting the lean correction formula as the correction formula when the detection chamber is in a lean state, and selecting the rich correction formula as the correction formula when the detection chamber is in a rich state <7> The method for obtaining concentration information as described above.

[0018] <9> The aforementioned relational expression is under the conditions of a predetermined reference temperature and a predetermined reference pressure, and the correction expression is an expression based on the parameter, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure. <7> The method for obtaining concentration information as described above.

[0019] <10> The piping to which the gas sensor is attached is further fitted with a gas temperature detection device for detecting the temperature of the exhaust gas, and in the temperature information acquisition process, the higher of the control temperature of the gas sensor and the gas temperature received from the gas temperature detection device is acquired as the temperature information. <6> The method for obtaining concentration information as described above. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a concentration information acquisition device and a concentration information acquisition method that can obtain accurate concentration information from the output of a gas sensor for a target gas contained in exhaust gas, regardless of temperature and pressure conditions. [Brief explanation of the drawing]

[0021] [Figure 1] A schematic diagram illustrating the configuration of an engine equipped with a concentration information acquisition device according to Embodiment 1 and its peripheral equipment. [Figure 2] Diagram illustrating the schematic configuration of a gas sensor. [Figure 3] Perspective view of the gas sensor element of the gas sensor, seen from the tip side. [Figure 4] Cross-sectional view along line AA in Figure 3 [Figure 5] Flowchart of the process performed by the concentration information acquisition device [Modes for carrying out the invention]

[0022] <Embodiment 1> The concentration information acquisition device 1 and concentration information acquisition method according to Embodiment 1 will be described with reference to Figures 1 to 5. Figure 1 is a schematic diagram showing the configuration of the engine 2 and its peripheral equipment in which the concentration information acquisition device 1 according to Embodiment 1 is installed, and Figure 2 is a schematic diagram showing the general configuration of the gas sensor 3.

[0023] The concentration information acquisition device 1 is a device that acquires information related to the concentration of oxygen (an example of a target gas) contained in the exhaust gas (in this embodiment, the air-fuel ratio λ) from the output of the gas sensor 3.

[0024] While the air-fuel ratio usually refers to the mixture ratio (mass ratio) of air and gasoline, in this specification, the air-fuel ratio refers to the excess air ratio λ (= actual air-fuel ratio / stoichiometric air-fuel ratio), and an air-fuel ratio λ = 1 represents the stoichiometric air-fuel ratio.

[0025] The concentration information acquisition device 1 mainly comprises a receiving unit 41, a temperature information acquisition unit 42, a pressure information acquisition unit 43, a correction unit 44, and a concentration information acquisition unit 45. The concentration information acquisition device 1 further comprises a determination unit 46 and a selection unit 47.

[0026] The temperature information acquisition unit 42, pressure information acquisition unit 43, correction unit 44, concentration information acquisition unit 45, determination unit 46, and selection unit 47 are all configured by the CPU (Central Processing Unit) 401 within the ECU (Electronic Control Unit) 4. The receiving unit 41 consists of a communication circuit, including a receiving circuit, provided by the ECU 4. Details of the receiving unit 41, temperature information acquisition unit 42, pressure information acquisition unit 43, correction unit 44, concentration information acquisition unit 45, determination unit 46, and selection unit 47 will be described later.

[0027] The ECU4 is a device for electronically controlling the operation of the automobile's engine 2, and consists of a microcontroller chip equipped with a CPU 401, ROM 402, RAM 403, etc.

[0028] In ECU4, the CPU401 executes various programs stored in ROM402, receives detection signals from various sensors (gas sensor 3, temperature sensor 8, etc.), and outputs control signals to operate injectors, etc. In this ECU4, the air-fuel ratio feedback control of engine 2 is performed based on the output of gas sensor 3.

[0029] The engine 2 in this embodiment is configured as a gasoline-fueled, inline four-cylinder, spark-ignition type engine. An intake pipe 5 is connected to the upstream side of the engine 2 through which air drawn in from the outside flows, and an exhaust pipe (piping) 6 is connected to the downstream side of the engine 2 through which exhaust gas produced by the combustion of fuel (gasoline) flows. A three-way catalytic converter 7 is installed in the middle of the exhaust pipe 6.

[0030] Multiple injectors (not shown) are installed in the intake manifold 5. The injectors are connected to the fuel tank and are provided for each of the multiple cylinders upstream of the engine 2, and they inject fuel in response to control signals from the ECU 4. Upstream of the injectors in the intake manifold 5, a throttle valve (not shown) is provided to adjust the amount of air taken into the engine 2, and the opening of this throttle valve is controlled by a control signal from the ECU 4.

[0031] External intake air moves through the intake manifold 5, passing through an air cleaner, throttle valve, etc. (not shown), and is mixed with fuel (gasoline) injected from the injector. This mixture is then supplied to each cylinder of the engine 2 as a fuel mixture with a predetermined air-fuel ratio. Each cylinder is equipped with a spark plug, which ignites the fuel mixture in each cylinder at a predetermined timing according to a control signal from the ECU 4. The exhaust gas produced after combustion is then discharged to the outside through the exhaust manifold 6.

[0032] The gas sensor 3 is located upstream of the purification device 7 in the exhaust pipe 6 and generates an output (an output value corresponding to the pump current Ip) corresponding to the oxygen concentration in the exhaust gas at that location. This output is transmitted to the ECU 4 via the gas sensor control device 31.

[0033] Here, the gas sensor 3 will be described with reference to Figure 1, etc. Figure 3 is a perspective view of the gas sensor element 30 of the gas sensor 3 as seen from the tip side, and Figure 4 is a cross-sectional view taken along line AA of Figure 3. The gas sensor 3 is a linear lambda sensor (limiting current type sensor) and is electrically connected to the gas sensor control device 31.

[0034] The gas sensor 3 comprises a gas sensor element 30 and a housing (not shown) that holds the gas sensor element 30 internally. The gas sensor element 30 in this embodiment is a two-cell type and comprises an oxygen pump cell 340 and an oxygen concentration detection cell 350, as will be described later.

[0035] As shown in Figure 3, the gas sensor element 30 is generally a long, slender plate shape, and a detection unit for detecting oxygen in the exhaust gas is provided at its tip. The tip of the gas sensor element 30 is covered with a protective layer M made of a porous material. Note that the protective layer M is omitted in Figure 4 and other figures for the sake of clarity. Furthermore, since the pore size of the porous material constituting the protective layer M is larger than that of the diffusion layer 315, which will be described later, the protective layer M does not restrict the amount of exhaust gas introduced.

[0036] The gas sensor element 30 comprises solid electrolytes 311 and 313 mainly composed of zirconia, and insulating substrates 312, 317, 318, and 324 mainly composed of alumina. These are all formed in the shape of elongated plates, and have a stacked structure in the order of insulating substrate 318, insulating substrate 317, solid electrolyte 313, insulating substrate 312, solid electrolyte 311, and insulating substrate 324.

[0037] A pair of electrodes 319 and 320, mainly made of platinum, are formed on both sides of the solid electrolyte 311. Similarly, a pair of electrodes 321 and 322 are formed on both sides of the solid electrolyte 313. Electrode 322 is embedded between the solid electrolyte 313 and the insulating substrate 317.

[0038] A hollow gas detection chamber (detection chamber) 323 is formed at one longitudinal end of the insulating substrate 312, with the solid electrolytes 311 and 313 forming a single wall, allowing exhaust gas to be introduced. The gas detection chamber 323 is formed between the solid electrolyte 313 and the solid electrolyte 311. At both ends of the gas detection chamber 323 in the width direction, porous diffusion layers (diffusion rate-limiting sections) 315 are provided to regulate the amount of exhaust gas introduced into the gas detection chamber 323. The diffusion layer 315 is interposed between the solid electrolyte 313 and the solid electrolyte 311 in the thickness direction (stacking direction) of the gas sensor element 30. The gas detection chamber 323 faces the diffusion layer 315, and external exhaust gas is introduced into the gas detection chamber 323 after passing through the diffusion layer 315. Furthermore, the electrode 320 on the solid electrolyte 311 and the electrode 321 on the solid electrolyte 313 are exposed within the gas detection chamber 323, respectively.

[0039] Furthermore, a platinum-based heat-generating resistor 326 is embedded between the insulating substrates 317 and 318. The insulating substrates 317 and 318 and the heat-generating resistor 326 function as heaters to heat and activate the solid electrolytes 311 and 313.

[0040] The electrode 319 on the solid electrolyte 311 is covered by a porous protective layer 325 whose surface is made of ceramics (e.g., alumina). The electrode 319 is protected by the protective layer 325 so as not to deteriorate due to toxic components (e.g., silicon, etc.) contained in the exhaust gas. The insulating substrate 324 laminated on the solid electrolyte 311 has an opening 324a so as not to cover the electrode 319, and the protective layer 325 is disposed within this opening 324a.

[0041] In the gas sensor element 30 configured in this way, the solid electrolyte 311 and the pair of electrodes 319 and 320 provided on both sides of it function as an oxygen pump cell 340 that draws oxygen into the gas detection chamber 323 from the outside or draws oxygen out of the gas detection chamber 323 to the outside. The pair of electrodes 319 and 320 are arranged so as to sandwich the solid electrolyte 311. One electrode 320 is placed in the gas detection chamber 323, and the other electrode 319 is placed in the opening of the insulating substrate 324. It is located within 324a. In this embodiment, the oxygen pump cell 340 corresponds to the "detection cell". The oxygen pump cell 340 has a solid electrolyte 311 and a pair of electrodes 319, 320 placed on the solid electrolyte 311.

[0042] Furthermore, the solid electrolyte 313 and the pair of electrodes 321 and 322 provided on both sides of it function as an oxygen concentration detection cell 350 that generates an electromotive force according to the oxygen concentration between the two electrodes. Electrode 322 functions as an oxygen reference electrode (reference chamber) that maintains a reference oxygen concentration for detecting the oxygen concentration in the gas detection chamber 323. The pair of electrodes 321 and 322 are arranged so as to sandwich the solid electrolyte 313. One electrode 321 is placed in the gas detection chamber 323, and the other electrode 322 is exposed to a reference atmosphere, which will be described later.

[0043] As shown in Figure 4, in this specification, the length of the diffusion rate-limiting portion 315 in the width direction of the gas sensor element 30 is denoted as "L". Also, the cross-sectional area of ​​the diffusion rate-limiting portion 315 as viewed from the width direction of the gas sensor element 30 is denoted as "S".

[0044] Next, the gas sensor control device 31 will be described. The gas sensor control device 31 mainly consists of a microcomputer 309 and a circuit unit 330. The microcomputer 309 consists of a known microcontroller chip equipped with a CPU 306, ROM 307, RAM 308, etc. The ROM 307 stores control programs and the like for causing the CPU 306 to execute various processes.

[0045] The circuit section 330 is implemented by a circuit (e.g., an ASIC: Application Specific Integrated Circuit) that drives the gas sensor 30. Such a circuit section 330 includes a pump current supply section 331, a reference voltage generation section 332, a minute current supply section 333, an AD conversion section 334, a PID calculation section 335, an Rpvs calculation section 336, a duty cycle calculation section 337, and a heater drive section 338. The circuit section 330 also includes a pump current terminal TIp electrically connected to the positive electrode side of the oxygen pump cell 340, a common terminal TCOM electrically connected to the negative electrode side of the oxygen pump cell 340 and the negative electrode side of the oxygen concentration detection cell 350, a voltage detection terminal TVs electrically connected to the positive electrode side of the oxygen concentration detection cell 350, and a heater terminal TH.

[0046] The reference voltage generation unit 332 generates a reference voltage applied to the common terminal TCOM. In this embodiment, the reference voltage is 2.7V. The minute current supply unit 333 is connected to the electrode 322 of the oxygen concentration detection cell 350 via the voltage detection terminals TVs. The minute current supply unit 333 supplies a minute current Icp to the oxygen concentration detection cell 350 via the voltage detection terminals TVs, thereby moving oxygen ions towards the electrode 322 and generating a reference atmosphere (oxygen partial pressure: approximately 2 atm). As a result, the electrode 322 functions as a reference oxygen reference electrode for detecting the oxygen concentration in the exhaust gas. The minute current supply unit 333 also supplies a pulse current Irpvs to the oxygen concentration detection cell 350 via the voltage detection terminals TVs to detect the internal resistance value of the oxygen concentration detection cell 350. The minute current supply unit 333 does not continuously supply the minute current Icp and pulse current Irpvs, but rather supplies the minute current Icp and pulse current Irpvs at appropriate times based on commands from the microcomputer 309.

[0047] The pump current supply unit 331 is connected to the electrode 319 of the oxygen pump cell 340 via the pump current terminal TIp. The pump current supply unit 331 supplies a pump current Ip, which is adjusted in size and orientation, to the oxygen pump cell 340.

[0048] The AD conversion unit 334 converts the voltage value of the analog signal input from the voltage detection terminal TVs into a digital signal and outputs it to the PID calculation unit 335 and the Rpvs calculation unit 336.

[0049] The PID calculation unit 335 performs feedback control to adjust the pump current Ip based on the digital signal input from the AD conversion unit 334, so that the voltage difference between the voltage at the voltage detection terminal TVs and the voltage at the common terminal TCOM becomes a preset target voltage (for example, 450mV). The PID calculation unit 335 performs PID (Proportional-Integral-Differential) calculation so that the voltage difference becomes the target voltage, and outputs the result obtained from the PID calculation (the current value of the digital signal) to the pump current supply unit 331. The pump current supply unit 331 converts the current value of the digital signal input from the PID calculation unit 335 into a pump current Ip and supplies the pump current Ip to the oxygen pump cell 340 as described above.

[0050] The Rpvs calculation unit 336 performs a calculation to calculate the internal resistance value Rpvs of the oxygen concentration detection cell 350 based on the digital signal input from the AD conversion unit 334 when the minute current supply unit 333 is supplying pulse current Irpvs, and outputs a digital signal indicating this internal resistance value Rpvs to the duty cycle calculation unit 337.

[0051] The duty cycle calculation unit 337 calculates the amount of heat generated by the heating resistor 326 required to maintain the temperature of the gas sensor element 30 at a preset target temperature (for example, 720°C) based on the digital signal input from the Rpvs calculation unit 336. The duty cycle calculation unit 337 then calculates the duty cycle of the power supplied to the heating resistor 326 based on the calculated amount of heat generated by the heating resistor 326, and outputs a PWM (Pulse Width Modulation) control signal corresponding to the calculated duty cycle to the heater drive unit 338. The heater drive unit 338 controls the voltage Vh supplied across the heating resistor 326 using PWM control based on the PWM control signal input from the duty cycle calculation unit 337, thereby generating heat in the heating resistor 326.

[0052] The CPU 306 of the microcomputer 309 executes a process to control the gas sensor element 30 based on a program stored in the ROM 307. For example, every time a preset acquisition period (e.g., 10ms) has elapsed, the CPU 306 acquires digital data (output values) from the circuit unit 330 that indicate the direction and magnitude of the pump current Ip, and transmits the acquired digital data to the ECU 2.

[0053] Using the gas sensor 3 described above, the concentration information acquisition device 1 acquires information on the concentration of oxygen contained in the exhaust gas.

[0054] Furthermore, a temperature sensor (gas temperature detection device) 8 is attached to the exhaust pipe 6 to detect the temperature of the exhaust gas. The temperature sensor 8, like the gas sensor 3, is located upstream of the purification device 7. The temperature sensor 8 has a known configuration, for example, a temperature sensing element having a temperature sensing part whose electrical characteristics change according to the temperature, an electrode wire for outputting an electrical signal from the temperature sensing part to the outside, and a sheathed core wire (signal wire) electrically connected to the electrode wire. The tip of the sheathed core wire is electrically connected to the temperature sensing element. The rear end of the sheathed core wire is connected to a crimp terminal by resistance welding, and through the crimp terminal is connected to a lead wire for connecting to an external circuit. Such a temperature sensor 8 is electrically connected to an external circuit, the ECU 4, via the lead wire. The output of the temperature sensor 8 is transmitted to the ECU 4 via the lead wire.

[0055] Next, the receiving unit 41, temperature information acquisition unit 42, pressure information acquisition unit 43, correction unit 44, concentration information acquisition unit 45, determination unit 46, and selection unit 47 will be described.

[0056] The receiving unit 41 performs the process of receiving an output value corresponding to the pump current Ip flowing between a pair of electrodes 319, 320 of the oxygen pump cell (detection cell) 340. In this embodiment, based on instructions from the CPU 401 of the ECU 4, the receiving unit 41 receives digital data (output value) indicating the direction of the pump current Ip supplied to the oxygen pump cell 340 and the magnitude of the pump current Ip via the gas sensor control device 31 every time a preset acquisition cycle (for example, 10 ms) has elapsed.

[0057] The temperature information acquisition unit 42 executes a process to acquire temperature information from the gas sensor 3. In this embodiment, the temperature information acquisition unit 42 adopts the higher of the control temperature of the gas sensor 3 and the gas temperature received from the temperature sensor 8 as the temperature information of the gas sensor 3. The control temperature (target temperature) of the gas sensor 3 is supplied by the gas sensor control device 31. For example, the temperature information acquisition unit 42 receives the exhaust gas temperature (gas temperature) detected by the temperature sensor 8 every time a preset acquisition cycle (for example, 10 ms) has elapsed.

[0058] In other embodiments, the temperature information acquisition unit 42 may use the control temperature (target temperature) of the gas sensor 3 as temperature information, or it may use the gas temperature received from the temperature sensor 8 as temperature information. However, as in this embodiment, if the higher of the control temperature of the gas sensor 3 and the gas temperature received from the temperature sensor 8 is used as the temperature information of the gas sensor 3, the concentration information of oxygen (target gas) can be determined more accurately.

[0059] The pressure information acquisition unit 43 executes a process to acquire exhaust gas pressure information. The exhaust gas pressure (total pressure) can be determined, for example, using engine parameters (intake air volume, engine speed, throttle opening, etc.) 9. The pressure information acquisition unit 43 receives the engine parameters 9 at intervals of a preset acquisition cycle (for example, 10 ms) and acquires the exhaust gas pressure from those engine parameters 9 using a known method.

[0060] The correction unit 44 executes a process of correcting the output value by using a correction formula for correcting the temperature dependence and pressure dependence of the output value received by the receiving unit 41. Here, the output value (pump current Ip) received by the receiving unit 41 is defined as "Ip b ", and the corrected output value is defined as "Ip a ", the correction formula is expressed as follows.

[0061] [Mathematical Expression]

[0062] In formula (1), K M is a proportionality coefficient of the molecular diffusion coefficient when diffusion (molecular diffusion) occurs in the diffusion layer 315, and K K is a proportionality coefficient of the Knudsen diffusion coefficient when diffusion (Knudsen diffusion) occurs in the diffusion layer 315, and K M / K K is a parameter representing the degree of combination of two types of diffusion, molecular diffusion and Knudsen diffusion, when diffusing through the diffusion layer 315 (that is, a parameter representing the temperature dependence and pressure dependence of the pump current Ip). As will be described later, K M / K K is obtained in advance through experiments. K M / K K is stored in advance in the ROM 402 of the ECU 4.

[0063] Also, in formula (1), T a is a reference temperature in a reference state, and P a is a reference pressure in a reference state. In the case of the present embodiment, the reference temperature T a is set to 720°C, and the reference pressure (total pressure) P a is set to 1 atmosphere, respectively. The reference temperature T a and the reference pressure P a are stored in advance in the ROM 402 of the ECU 4. Note that the corrected output value Ip a is a value at the reference temperature T a and the reference pressure P a in the reference state.

[0064] Also, in formula (1), Tb The reference temperature T a This is a different temperature. In this embodiment, temperature T b This is the temperature of the gas sensor 3 obtained by the temperature information acquisition unit 42. Also, in equation (1), P b is the reference pressure P a This is a different pressure. In this embodiment, pressure P b This is the exhaust gas pressure (i.e., the actual exhaust gas pressure (total pressure)) acquired by the pressure information acquisition unit 43. Note that temperature T b and pressure P b This is the output value (pump current) Ip b These were obtained at the same time.

[0065] Here, we will explain how to derive the correction formula (1). The pump current Ip flowing between electrodes 319 and 320 of the oxygen pump cell 340 of the gas sensor 3 is expressed by the theoretical formula (2) shown below.

[0066]

number

[0067] In equation (2), F is the Faraday constant [C / mol], R is the gas constant [J / K / mol], T is the absolute temperature [K], and D O2 The diffusion coefficient of oxygen in the diffusion layer 315 is [m 2 [s], S is the cross-sectional area of ​​the diffusion layer 315 [m 2 ], L is the length of the diffusion layer 315 [m], Pe is the partial pressure of oxygen [Pa], and P is the total pressure of the exhaust gas [Pa].

[0068] If the pore size of the diffusion layer 315 is larger than the mean free path of oxygen, oxygen diffuses by colliding with other molecules, just as it would in the absence of the diffusion layer 315 (so-called molecular diffusion). In contrast, if the pore size of the diffusion layer 315 is smaller than the mean free path of oxygen, collisions with the pore walls become dominant over collisions between oxygen molecules (so-called Knudsen diffusion). The actual diffusion in the diffusion layer 315 is thought to be a combination of these two types of diffusion (molecular diffusion and Knudsen diffusion). Therefore, D O2This is represented by equation (3) shown below.

[0069]

number

[0070] D in equation (3) M D is the molecular diffusion coefficient. K This is the Knudsen diffusion coefficient.

[0071] Molecular diffusion coefficient D M It is known that the molecular diffusion coefficient D is proportional to the 1.75th power of temperature T and inversely proportional to pressure P. M This is expressed by equation (4) shown below. Note that K in equation (4) M As mentioned above, the molecular diffusion coefficient D M This is the proportionality constant.

[0072]

number

[0073] Also, the Knudsen diffusion coefficient D K It is known that it is proportional to the 0.5 power of temperature. Therefore, the Knudsen diffusion coefficient D K This is expressed by equation (5) shown below. Note that K in equation (5) K As mentioned above, the Knudsen diffusion coefficient D K This is the proportionality constant.

[0074]

number

[0075] From equations (3), (4), and (5) above, D O2 This is represented by equation (6) shown below.

[0076]

number

[0077] From the obtained equation (6), the theoretical equation (2) above can be expressed by the following equation (7).

[0078]

number

[0079] Here, the reference state 1 (temperature T1, oxygen partial pressure P) is defined. e At a pressure (total pressure) P1), the pump current Ip flowing between electrodes 319 and 320 of the oxygen pump cell 340 of the gas sensor 3 is defined as "Ip1". Furthermore, the pump current Ip in state 2 (temperature T2, oxygen partial pressure Pe, pressure (total pressure) P2), which has different temperature and pressure conditions compared to state 1, is defined as "Ip2". The change in pump current Ip ΔIp when the temperature and pressure conditions change from state 1 to state 2 is expressed by equation (8) shown below, using equation (7). Note that the exhaust gas atmosphere is constant, so P e / P1 = Pe / P2.

[0080]

number

[0081] From equation (8), Ip2 / Ip1 is expressed by equation (9) shown below.

[0082]

number

[0083] Then, by rearranging equation (9), we obtain equation (10), which expresses the relationship between Ip1 in the reference state and Ip2 in a state different from the reference state.

[0084]

number

[0085] The equation (10) obtained in this way is used as the correction equation (1) described above.

[0086] The gas sensor 3 has a detection chamber 323 that houses at least one electrode 320 of a pair of electrodes 319, 320, and a porous diffusion layer 315 that separates the outside from the gas detection chamber (detection chamber) 323 and introduces exhaust gas from the outside to the gas detection chamber 323. The correction formula (1) described above depends on the molecular diffusion coefficient D of the diffusion layer 315, which depends on the type of gas moving inside the diffusion layer 315. M The Knudsen diffusion coefficient D of the diffusion layer 315 depends on the gas species moving within the diffusion layer 315 and the pore size r within the diffusion layer 315. K Parameters based on (K M / K K It includes ).

[0087] Molecular diffusion coefficient D M This is represented by equation (11) shown below.

[0088]

number

[0089] In formula (11), M A is the molecular weight of gas A (diffusive solute), and M B is the molecular weight of gas B (diffusion solvent), and (Σν) A is the diffusion volume of gas A, and (Σν) B is the diffusion volume of gas B, T is the temperature, and P is the pressure (total pressure). Note that the above K M Expressed by equation (12) shown below, the molecular diffusion coefficient D M This is given by equation (4) above.

[0090]

number

[0091] Also, the Knudsen diffusion coefficient D K This is represented by equation (13) shown below.

[0092]

number

[0093] In equation (13), r is the pore size of the diffusion layer 315, T is the temperature, and M A This is the molecular weight of gas A (diffusive solute). Note that K mentioned above... K Expressed by equation (14) shown below, the Knudsen diffusion coefficient D K This is given by equation (5) above.

[0094]

number

[0095] By the way, if we rearrange equation (8), K M / K K This is represented by equation (15) shown below.

[0096]

number

[0097] As shown in equation (15), K M / K K This is determined by the conditions of state 1 and state 2 (T1, T2, P1, P2, Ip1, Ip2). Therefore, K M / K K This can be determined in advance through experiments, for example, by appropriately changing the conditions of states 1 and 2.

[0098] Note that the parameter (K) included in the correction formula (1) M / K K) is used as either the lean parameter, which is the parameter when the exhaust gas in the gas detection chamber 323 is in a lean state, or the rich parameter, which is the parameter when the exhaust gas in the gas detection chamber 323 is in a rich state. When the exhaust gas is in a lean state, "gas A" in the above formula (11), etc., is oxygen and "gas B" is nitrogen. Therefore, in the case of a lean state, M A M is the molecular weight of oxygen. B This is the molecular weight of nitrogen. In contrast, when the exhaust gas is rich, "gas A" in the above equation (11), etc., is H2 or CO, and "gas B" is nitrogen. Therefore, in the case of a rich state, M A The molecular weights of H2 and CO, M B This represents the molecular weight of nitrogen.

[0099] The state of the exhaust gas in the gas detection chamber 323 is determined by the determination unit 46. The determination unit 46 determines whether the gas in the gas detection chamber 323 is lean or rich based on the output value (pump current Ip). The determination unit 46 determines whether it is lean or not by, for example, comparing the output value with a predetermined threshold.

[0100] Correction formula (1) is the parameter (K M / K K ) a lean correction formula including lean parameters, or the parameter (K M / K K A rich correction formula including rich parameters is used as the correction formula (1). For example, if the determination unit 46 determines that the state is lean, the selection unit 47 selects a lean correction formula including lean parameters as the correction formula (1). Conversely, if the determination unit 46 determines that the state is not lean (rich state), the selection unit 47 selects a rich correction formula including rich parameters as the correction formula (1).

[0101] The concentration information acquisition unit 45 obtains a relational expression representing the relationship between concentration information (in this embodiment, air-fuel ratio λ) related to the concentration of oxygen (an example of a target gas) and the output value (pump current Ip), and the output value (i.e., the corrected value) Ip corrected by the correction unit 44. aBased on this, the process of obtaining the concentration information (air-fuel ratio λ) is executed.

[0102] The "relational expression that shows the relationship between the air-fuel ratio λ and the output value (pump current Ip)" is based on the above-mentioned reference conditions (reference temperature T a =720℃, reference pressure P a This is based on a pressure of 1 atmosphere (=1 atmosphere) and is predetermined through experiments, etc. This relationship is stored in the ROM 402 of the ECU 4. The concentration information acquisition unit 45 corrects the output value (corrected value) Ip based on this relationship. a This is converted to the corresponding air-fuel ratio λ.

[0103] Thus, in the concentration information acquisition unit 45, the output from the gas sensor 3 (pump current Ip) received by the receiving unit 41 is obtained from the concentration information acquisition unit 45. b ) is not used as is, but the correction value Ip is corrected by the correction unit 44. a To utilize the above output temperature T b and pressure P b Regardless of the source, accurate concentration information (air-fuel ratio λ) can be obtained.

[0104] Next, referring to Figure 5, we will explain the process (i.e., the method for acquiring concentration information) that the concentration information acquisition device 1 performs when acquiring oxygen concentration information (air-fuel ratio λ) in the exhaust gas.

[0105] Figure 5 is a flowchart of the process performed by the concentration information acquisition device 1 (ECU4). First, in step S100, the concentration information acquisition device 1 determines whether or not it is time to sample the Ip output (pump current Ip) of the gas sensor 3. In this embodiment, for example, the Ip output is sampled every 10ms (i.e., the acquisition period for the Ip output is 10ms). If it is time to sample the Ip output in step S100, the process moves to step S110; if it is not time to sample the Ip output, the process returns to step S100.

[0106] In step S110, the receiving unit 41 of the concentration information acquisition device 1 receives the output value (Ip) of the oxygen pump cell (detection cell) 340.b output (reception step). The receiving unit 41 receives the pump current Ip supplied to the oxygen pump cell 340 b flow direction and the pump current Ip b digital data (output value) indicating a value related to the magnitude of is received via the gas sensor control device 31.

[0107] Next, in step S120, the determination unit 46 executes a process of determining whether the inside of the gas detection chamber 323 is in a lean state or a rich state based on the output value (the pump current Ip b ) (determination step). The determination unit 46 determines whether the state is lean or not, for example, by comparing the output value with a predetermined threshold value. If it is determined to be the lean state, the process proceeds to step S130; if it is determined to be a non-lean state (rich state), the process proceeds to step S140.

[0108] After the determination unit 46 determines the lean state, in step S130, the selection unit 47 selects a lean parameter K for lean M / K K ) (selection step). Thereafter, the process proceeds to step S150. On the other hand, after the determination unit 46 determines that the state is not lean (rich state), in step S140, the selection unit 47 selects a rich parameter K for rich M / K K ) (selection step). Thereafter, the process proceeds to step S150.

[0109] In step S150, a temperature information acquisition unit 42 acquires the temperature Tb of the gas sensor element 30 (temperature information acquisition step), and a pressure information acquisition unit 43 acquires the pressure Pex of exhaust gas (pressure information acquisition step).

[0110] In the temperature information acquisition step in step S150, as the temperature information of the gas sensor 3 (gas sensor element 30), the higher temperature among the control temperature of the gas sensor 3 (gas sensor element 30) and the gas temperature received from the temperature sensor 8 is adopted.

[0111] Thereafter, the process proceeds to step S160, where the correction unit 44 corrects the output value (Ip b output) by using correction formula (1) for correcting the temperature dependence and pressure dependence of the output, the above output value (Ip b output) is corrected (correction step). As for correction formula (1), when a lean parameter is selected in step S130, a lean correction formula including the lean parameter (lean K M / K K ) is used; when a rich parameter is selected in step S140, a rich correction formula including the rich parameter (rich K M / K K ) is used. After the output value (Ip b output) is corrected by the correction unit 44, a corrected Ip a output (corrected value) is obtained.

[0112] Next, the process proceeds to step S170, where the concentration information acquisition unit 45 executes processing for acquiring the air-fuel ratio λ based on a relational expression representing the relationship between the air-fuel ratio λ and the output value (pump current Ip) and the output value (corrected value) Ip corrected by the correction unit 44 (concentration information acquisition step). In this way, the concentration information acquisition unit 45 does not directly use the output (output value, pump current Ip a ) from the gas sensor 3 received by the reception unit 41, and uses the corrected value Ip corrected by the correction unit 44. Therefore, accurate concentration information (air-fuel ratio λ) can be obtained regardless of the temperature T b and the pressure P a at the time of the output. b and pressure P b irrespective of, accurate concentration information (air-fuel ratio λ) can be obtained.

[0113] As described above, according to the concentration information acquisition device 1 and concentration information acquisition method of this embodiment, temperature correction and pressure correction of the gas sensor output (pump current Ip) are performed simultaneously using correction formula (1). Therefore, accurate concentration information of oxygen (target gas) contained in the exhaust gas can be obtained from the output of the gas sensor 3 (pump current Ip) regardless of temperature and pressure conditions. In this embodiment, the air-fuel ratio feedback control of the engine 2 is performed using the accurate oxygen concentration information (air-fuel ratio λ) obtained by the concentration information acquisition device 1.

[0114] <Other Embodiments> The present invention is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included in the technical scope of the present invention.

[0115] (1) In the above embodiment, a gas sensor including a two-cell type gas sensor element was used, but in other embodiments, a gas sensor including a known one-cell type gas sensor element may be used.

[0116] (2) In the above embodiment, the target gas was oxygen, but the present invention is not limited thereto, and in other embodiments, for example, NO x NO may also be used as the target gas. x A known gas sensor (for example, Japanese Patent Publication No. 2020-3286) can be used to measure the concentration. This gas sensor consists of a solid electrolyte and NO formed on the solid electrolyte. x It comprises a cell with a set of electrodes for detection, and NO flows between the electrodes. x Based on the current (output value, second pump current) corresponding to the oxygen (oxygen ions) of origin, NO x The concentration can be measured. In other embodiments, such NO x Temperature and pressure corrections are applied simultaneously to the output value of the detection gas sensor using a predetermined correction formula, and based on the obtained correction value, accurate NO is calculated. x You may also calculate the concentration.

[0117] (3) In the above embodiment, the receiving unit, temperature information acquisition unit, pressure information acquisition unit, correction unit, concentration information acquisition unit, determination unit and selection unit were configured by an ECU, but the present invention is not limited thereto, and in other embodiments, they may be configured by, for example, a gas sensor control device or a dedicated control device consisting of a microcomputer or the like.

[0118] (4) In other embodiments, some of the configurations that were implemented by software may be replaced by hardware. [Explanation of Symbols]

[0119] 1...Concentration information acquisition device, 2...Engine, 3...Gas sensor, 31...Gas sensor control device, 4...ECU, 41...Receiver, 42...Temperature information acquisition unit, 43...Pressure information acquisition unit, 44...Correction unit, 45...Concentration information acquisition unit, 46...Determination unit, 47...Selection unit, 5...Intake pipe, 6...Exhaust pipe (piping), 7...Purification device (catalyst unit), 8...Temperature sensor, 9...Engine parameters

Claims

1. A concentration information acquisition device that acquires information related to the concentration of a target gas contained in exhaust gas from a gas sensor comprising a detection cell having a solid electrolyte and a set of electrodes disposed on the solid electrolyte, A receiving unit that receives the output value of the detection cell, A temperature information acquisition unit that acquires temperature information from the gas sensor, A pressure information acquisition unit that acquires the pressure information of the exhaust gas, A correction unit that corrects the output value using a correction formula for correcting the temperature dependence and pressure dependence of the output value, A concentration information acquisition unit acquires the concentration information based on a relational expression representing the relationship between the concentration information related to the concentration of the target gas and the output value, and a corrected value of the output value corrected by the correction unit. The determination unit, A selection unit and, The gas sensor has a detection chamber that houses at least one of the pair of electrodes, and a porous diffusion layer that separates the outside from the detection chamber and introduces exhaust gas from the outside to the detection chamber. The correction formula includes parameters based on the molecular diffusion coefficient of the diffusion layer, which depends on the gas species moving within the diffusion layer, and the Knudsen diffusion coefficient of the diffusion layer, which depends on the gas species moving within the diffusion layer and the pore size within the diffusion layer. The parameters include lean parameters, which are parameters when the exhaust gas in the detection chamber is in a lean state, and rich parameters, which are parameters when the exhaust gas in the detection chamber is in a rich state. The correction formula comprises a lean correction formula that includes the lean parameter as a parameter, and a rich correction formula that includes the rich parameter as a parameter. The determination unit determines, based on the output value, whether the inside of the detection chamber is in the lean state or the rich state. The selection unit is a concentration information acquisition device that selects the lean correction formula as the correction formula when the detection chamber is in a lean state, and selects the rich correction formula as the correction formula when the detection chamber is in a rich state.

2. The above relational expression is based on the conditions of a predetermined reference temperature and a predetermined reference pressure. The concentration information acquisition device according to claim 1, wherein the correction formula is an expression based on the parameter, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure.

3. The piping to which the gas sensor is attached is further equipped with a gas temperature detection device for detecting the temperature of the exhaust gas. The concentration information acquisition device according to claim 1, wherein the temperature information acquisition unit acquires the higher of the control temperature of the gas sensor and the gas temperature received from the gas temperature detection device as the temperature information.

4. A method for acquiring concentration information, comprising a concentration information acquisition step, which acquires information related to the concentration of a target gas contained in exhaust gas from a gas sensor having a detection cell having a solid electrolyte and a set of electrodes disposed on the solid electrolyte, A receiving step of receiving the output value of the detection cell, A temperature information acquisition step for acquiring temperature information from the gas sensor, A pressure information acquisition step for acquiring the pressure information of the exhaust gas, A correction step of correcting the output value using a correction formula for correcting the temperature dependence and pressure dependence of the output value, The judgment process, A selection process, and In the concentration information acquisition step, the concentration information is acquired based on the corrected value of the output value corrected in the correction step and a relational expression representing the relationship between the concentration information related to the concentration of the target gas and the output value. The gas sensor has a detection chamber that houses at least one of the pair of electrodes, and a porous diffusion layer that separates the outside from the detection chamber and introduces exhaust gas from the outside to the detection chamber. The correction formula includes parameters based on the molecular diffusion coefficient of the diffusion layer, which depends on the gas species moving within the diffusion layer, and the Knudsen diffusion coefficient of the diffusion layer, which depends on the gas species moving within the diffusion layer and the pore size within the diffusion layer. The aforementioned parameters consist of lean parameters, which are the parameters when the exhaust gas in the detection chamber is in a lean state, or rich parameters, which are the parameters when the exhaust gas in the detection chamber is in a rich state. The correction formula comprises a lean correction formula that includes the lean parameter as a parameter, and a rich correction formula that includes the rich parameter as a parameter. In the determination step, based on the output value, it is determined whether the inside of the detection chamber is in the lean state or the rich state. A method for acquiring concentration information, wherein in the selection step, when the detection chamber is in a lean state, the lean correction formula is selected as the correction formula, and when the detection chamber is in a rich state, the rich correction formula is selected as the correction formula.

5. The above relational expression is based on the conditions of a predetermined reference temperature and a predetermined reference pressure. The method for acquiring concentration information according to claim 4, wherein the correction formula is an expression based on the parameter, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure.

6. The piping to which the gas sensor is attached is further equipped with a gas temperature detection device for detecting the temperature of the exhaust gas. The method for acquiring concentration information according to claim 4, wherein in the temperature information acquisition step, the higher of the control temperature of the gas sensor and the gas temperature received from the gas temperature detection device is acquired as the temperature information.

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