JP2024132120A - Concentration information acquisition device and concentration information acquisition method - Google Patents

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

The present invention relates to a concentration information acquisition device and a concentration information acquisition method.

Oxygen sensors that are attached to the exhaust pipe of an internal combustion engine such as an automobile engine and detect the oxygen concentration in the exhaust gas in the exhaust pipe are known (for example, Patent Document 1). For example, this type of oxygen sensor includes 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 includes a solid electrolyte body and a pair of electrodes arranged to sandwich the solid electrolyte body, and an electromotive force corresponding to the oxygen concentration is generated between the two electrodes. The oxygen pump cell includes a solid electrolyte body and a pair of electrodes arranged to sandwich the solid electrolyte body, and functions to pump oxygen into the gas detection chamber from the outside or pump oxygen out of the gas detection chamber to the outside. 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, 450 mV), and the magnitude and direction of the current (pump current Ip) flowing between the two electrodes of the oxygen pump cell is controlled based on the comparison result. The oxygen sensor calculates the oxygen concentration and air-fuel ratio λ in the exhaust gas based on that current (pump current Ip).

The relationship between the pump current Ip and oxygen information (air-fuel ratio λ, etc.) is expressed by a predetermined relational equation, and the oxygen information (air-fuel ratio λ, etc.) can be found from that relational equation and the pump current Ip.

JP 2022-15533 A

The above relational equation is determined based on the case where the temperature and pressure of the exhaust gas are at a predetermined reference condition (e.g., 720°C and 1 atmosphere). In other words, strictly speaking, the above relational equation is valid only when the temperature and pressure of the exhaust gas are at the above reference condition. However, since the pump current Ip has temperature dependency and pressure dependency, if, for example, the temperature conditions or pressure conditions deviate from the above reference conditions, it becomes difficult to accurately determine oxygen information (such as the air-fuel ratio λ) from the pump current Ip even when the above relational equation is used.

Therefore, conventionally, temperature correction is performed on the output value (pump current Ip) of the gas sensor to reduce the effect of temperature dependency, and pressure correction is performed to reduce the effect of pressure dependency. Temperature correction is performed using a correction equation that represents the temperature dependency of the pump current Ip at a predetermined reference pressure (e.g., 1 atmosphere) that is determined in advance. Pressure correction is performed using a correction equation that represents the pressure dependency of the pump current Ip at a predetermined reference temperature (e.g., 720°C) that is determined in advance.

However, these corrections (temperature correction, pressure correction) for the output value (pump current Ip) only considered the temperature or pressure dependency, and did not consider both temperature and pressure dependencies at the same time. For example, in the case of temperature correction, if the exhaust gas pressure deviates from the reference pressure, accurate temperature correction could not be performed. Similarly, in the case of pressure correction, if the exhaust gas temperature deviates from the reference temperature, accurate pressure correction could not be performed.

Generally, it is rare for only one of the exhaust gas temperature and pressure to deviate from the reference conditions, and it is common for both the temperature and pressure to deviate from the reference conditions at the same time. For example, when an internal combustion engine is under high load, the exhaust gas temperature becomes high and the exhaust gas pressure becomes high, causing both the temperature and pressure to deviate significantly from the reference conditions. For this reason, there has been a demand for temperature correction and pressure correction of the gas sensor output (pump current Ip) to be combined into one and performed simultaneously.

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.

The means for solving the above problems are as follows.
<1> A concentration information acquisition device that acquires information related to a concentration of a target gas contained in exhaust gas from a gas sensor including a detection cell having a solid electrolyte body and a set of electrodes arranged on the solid electrolyte body, the concentration information acquisition device comprising: a receiving unit that receives an output value of the detection cell; a temperature information acquisition unit that acquires temperature information of the gas sensor; a pressure information acquisition unit that acquires pressure information of the exhaust gas; a correction unit that corrects the output value using a correction equation for correcting temperature dependence and pressure dependence of the output value; and a concentration information acquisition unit that acquires the concentration information based on a relational equation expressing a relationship between concentration information related to the concentration of the target gas and the output value and a correction value of the output value corrected by the correction unit.

<2> 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, and the correction formula includes parameters based on the molecular diffusion coefficient of the diffusion layer that depends on the gas species moving inside the diffusion layer, and the Knudsen diffusion coefficient of the diffusion layer that depends on the gas species moving inside the diffusion layer and the pore size in the diffusion layer. The concentration information acquisition device described in <1>.

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

<4> The concentration information acquisition device described in <3>, in which the relational expression is based on a predetermined reference temperature and a predetermined reference pressure, and the correction expression is based on the parameters, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure.

<5> The concentration information acquisition device described in <1>, in which a gas temperature detection device that detects the temperature of the exhaust gas is further attached to the pipe to which the gas sensor is attached, and the temperature information acquisition unit acquires, as the temperature information, the higher of the control temperature of the gas sensor and the gas temperature received from the gas temperature detection device.

<6> A concentration information acquisition method including a concentration information acquisition step of acquiring information related to the concentration of a target gas contained in exhaust gas from a gas sensor including a detection cell having a solid electrolyte body and a pair of electrodes arranged on the solid electrolyte body, the concentration information acquisition method including a receiving step of receiving an output value of the detection cell, a temperature information acquisition step of acquiring temperature information of the gas sensor, a pressure information acquisition step of acquiring pressure information of the exhaust gas, and a correction step of correcting the output value using a correction formula for correcting the temperature dependency and pressure dependency of the output value, and the concentration information acquisition step acquires the concentration information based on a correction value of the output value corrected by the correction step and a relational formula expressing the relationship between the concentration information related to the concentration of the target gas and the output value.

<7> 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, and the correction formula includes parameters based on the molecular diffusion coefficient of the diffusion layer that depends on the gas species moving inside the diffusion layer, and the Knudsen diffusion coefficient of the diffusion layer that depends on the gas species moving inside the diffusion layer and the pore size in the diffusion layer. The concentration information acquisition method described in <6>.

<8> The parameters are lean parameters, which are parameters when the exhaust gas in the detection chamber is in a lean state, or 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 parameter as the parameter and a rich correction formula that includes the rich parameter as the parameter, and the concentration information acquisition method described in <7> is provided with a determination step of determining whether the inside of the detection chamber is in the lean state or the rich state based on the output value, and a selection step of selecting the lean correction formula as the correction formula when the inside of the detection chamber is in the lean state, and selecting the rich correction formula as the correction formula when the inside of the detection chamber is in the rich state.

<9> The concentration information acquisition method described in <7>, in which the relational expression is based on a predetermined reference temperature and a predetermined reference pressure, and the correction expression is based on the parameters, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure.

<10> The concentration information acquisition method described in <6>, in which a gas temperature detection device that detects the temperature of the exhaust gas is further attached to the pipe to which the gas sensor is attached, 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.

The present invention provides 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.

FIG. 2 is a schematic diagram illustrating the configuration of an engine provided with a concentration information acquisition device according to the first embodiment and its peripheral devices; FIG. 1 is an explanatory diagram showing a schematic configuration of a gas sensor; FIG. 2 is a perspective view of a gas sensor element of the gas sensor, viewed from the tip side; AA line cross-sectional view of FIG. Flowchart of a process executed by the concentration information acquisition device

<Embodiment 1>
A concentration information acquiring device 1 and a concentration information acquiring method according to the first embodiment will be described with reference to Fig. 1 to Fig. 5. Fig. 1 is an explanatory diagram showing a schematic configuration of an engine 2 provided with the concentration information acquiring device 1 according to the first embodiment and its peripheral devices, and Fig. 2 is an explanatory diagram showing a schematic configuration of a gas sensor 3.

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

Note that the air-fuel ratio usually refers to the mixture ratio (mass ratio) of air and gasoline, but in this specification, the air excess ratio λ (= actual air-fuel ratio/stoichiometric air-fuel ratio) is referred to as the air-fuel ratio, and an air-fuel ratio λ = 1 indicates the stoichiometric air-fuel ratio.

The concentration information acquisition device 1 mainly includes 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 includes a determination unit 46 and a selection unit 47.

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

The ECU 4 is a device for electronically controlling the operation of the engine 2 of the automobile, and is composed of a microcomputer chip equipped with a CPU 401, a ROM 402, a RAM 403, etc.

In the ECU 4, the CPU 401 executes various programs stored in the ROM 402, receives detection signals from various sensors (gas sensor 3, temperature sensor 8, etc.), and outputs control signals for operating the injectors, etc. In this manner, the ECU 4 performs feedback control of the air-fuel ratio of the engine 2 based on the output of the gas sensor 3.

The engine 2 of this embodiment is configured as an in-line 4-cylinder spark ignition type engine fueled by gasoline. An intake pipe 5 through which air drawn in from the outside flows is connected to the upstream side of the engine 2, and an exhaust pipe (piping) 6 through which exhaust gas generated by the combustion of fuel (gasoline) flows is connected to the downstream side of the engine 2. A three-way catalytic converter 7 is installed midway in the exhaust pipe 6.

Multiple injectors (not shown) are installed in the intake pipe 5. The injectors are connected to a fuel tank and provided for each of the multiple cylinders upstream of the engine 2, and inject fuel in response to a control signal from the ECU 4. A throttle valve (not shown) that adjusts the amount of air intake to the engine 2 is provided in the intake pipe 5 upstream of the injectors, and the opening degree of the throttle valve is controlled by a control signal from the ECU 4.

Intake air from the outside moves through the intake pipe 5 while passing through an air cleaner, throttle valve, etc. (not shown), and is mixed with fuel (gasoline) injected from an injector, and is supplied to each cylinder of the engine 2 as a fuel mixture with a specified air-fuel ratio. Each cylinder is provided with an ignition plug, which ignites the fuel mixture in each cylinder at a specified timing in response to a control signal from the ECU 4. Exhaust gas produced after combustion is discharged to the outside through the exhaust pipe 6.

The gas sensor 3 is disposed in the exhaust pipe 6 at a location upstream of the purification device 7, and produces an output corresponding to the oxygen concentration in the exhaust gas at that location (an output value corresponding to the pump current Ip). The output is transmitted to the ECU 4 via the gas sensor control device 31.

The gas sensor 3 will now be described with reference to FIG. 1 and other figures. FIG. 3 is a perspective view of the gas sensor element 30 of the gas sensor 3, seen from the tip side, and FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3. The gas sensor 3 is a linear lambda sensor (a limiting current type sensor), and is electrically connected to the gas sensor control device 31.

The gas sensor 3 includes a gas sensor element 30 and a housing (not shown) that holds the gas sensor element 30 inside. The gas sensor element 30 in this embodiment is of a two-cell type, and includes an oxygen pump cell 340 and an oxygen concentration detection cell 350, as described below.

As shown in FIG. 3, the gas sensor element 30 is generally in the shape of a long and thin plate, and a detection section for detecting oxygen in the exhaust gas is provided at the tip side of the gas sensor element 30. The tip side of the gas sensor element 30 is covered with a protective layer M made of a porous body. Note that the protective layer M is omitted as appropriate in FIG. 4 and other figures for the sake of convenience. In addition, the pore diameter of the porous body constituting the protective layer M is larger than the pore diameter of the diffusion layer 315 described below, so the protective layer M does not restrict the amount of exhaust gas introduced.

The gas sensor element 30 comprises solid electrolyte bodies 311 and 313 mainly made of zirconia, and insulating bases 312, 317, 318, and 324 mainly made of alumina. All of them are formed in a long, thin plate shape, and are structured such that insulating base 318, insulating base 317, solid electrolyte body 313, insulating base 312, solid electrolyte body 311, and insulating base 324 are layered in this order.

A pair of electrodes 319, 320, mainly made of platinum, are formed on both sides of the solid electrolyte body 311. Similarly, a pair of electrodes 321, 322 are formed on both sides of the solid electrolyte body 313. The electrode 322 is embedded and sandwiched between the solid electrolyte body 313 and the insulating base 317.

At one end of the insulating base 312 in the longitudinal direction, a hollow gas detection chamber (detection chamber) 323 into which exhaust gas can be introduced is formed, with the solid electrolyte bodies 311 and 313 as one wall surface. The gas detection chamber 323 is formed between the solid electrolyte body 313 and the solid electrolyte body 311. At both ends of the width direction of the gas detection chamber 323, a porous diffusion layer (diffusion rate control part) 315 is provided to regulate the amount of exhaust gas introduced (inflow amount) when introducing the exhaust gas into the gas detection chamber 323. The diffusion layer 315 is interposed between the solid electrolyte body 313 and the solid electrolyte body 311 in the thickness direction (stacking direction) of the gas sensor element 30. The gas detection chamber 323 faces the diffusion layer 315, and the external exhaust gas passes through the diffusion layer 315 and is introduced into the gas detection chamber 323. The electrode 320 on the solid electrolyte body 311 and the electrode 321 on the solid electrolyte body 313 are each exposed in the gas detection chamber 323.

A heating resistor 326 made mainly of platinum is embedded between the insulating bases 317 and 318. The insulating bases 317 and 318 and the heating resistor 326 function as a heater for heating and activating the solid electrolyte bodies 311 and 313.

The surface of the electrode 319 on the solid electrolyte body 311 is covered with a porous protective layer 325 made of ceramics (e.g., alumina). The electrode 319 is protected by the protective layer 325 to prevent deterioration by poisonous components (e.g., silicon, etc.) contained in the exhaust gas. The insulating base 324 laminated on the solid electrolyte body 311 has an opening 324a provided so as not to cover the electrode 319, and the protective layer 325 is disposed within the opening 324a.

In the gas sensor element 30 configured as described above, the solid electrolyte body 311 and the pair of electrodes 319, 320 provided on both sides thereof function as an oxygen pump cell 340 that pumps oxygen into the gas detection chamber 323 from the outside or pumps oxygen out from the gas detection chamber 323 to the outside. The pair of electrodes 319, 320 are arranged to sandwich the solid electrolyte body 311. One electrode 320 is arranged in the gas detection chamber 323, and the other electrode 319 is arranged in an opening 324a of the insulating base 324. In this embodiment, the oxygen pump cell 340 corresponds to the "detection cell". The oxygen pump cell 340 has the solid electrolyte body 311 and a pair of electrodes 319, 320 arranged on the solid electrolyte body 311.

The solid electrolyte body 313 and the pair of electrodes 321, 322 provided on both sides of it function as an oxygen concentration detection cell 350 that generates an electromotive force depending on the oxygen concentration between the two electrodes. The electrode 322 functions as an oxygen reference electrode (reference chamber) that maintains the oxygen concentration that serves as a reference for detecting the oxygen concentration in the gas detection chamber 323. The pair of electrodes 321, 322 are arranged to sandwich the solid electrolyte body 313. One electrode 321 is arranged in the gas detection chamber 323, and the other electrode 322 is exposed to a reference atmosphere described below.

As shown in FIG. 4, in this specification, the length of the diffusion-controlling portion 315 in the width direction of the gas sensor element 30 is represented as "L." Also, the cross-sectional area of the diffusion-controlling portion 315 as viewed in the width direction of the gas sensor element 30 is represented as "S."

Next, the gas sensor control device 31 will be described. The gas sensor control device 31 is mainly composed of a microcomputer 309 and a circuit section 330. The microcomputer 309 is made up of a microcomputer chip of a known configuration that includes a CPU 306, a ROM 307, a RAM 308, etc. The ROM 307 stores control programs and the like for causing the CPU 306 to execute various processes.

The circuit unit 330 is realized by a circuit (e.g., an ASIC: Application Specific Integrated Circuit) that drives the gas sensor 30. Such a circuit unit 330 includes a pump current supply unit 331, a reference voltage generation unit 332, a microcurrent supply unit 333, an AD conversion unit 334, a PID calculation unit 335, an Rpvs calculation unit 336, a duty calculation unit 337, and a heater drive unit 338. The circuit unit 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.

The reference voltage generating unit 332 generates a reference voltage to be applied to the common terminal TCOM. In this embodiment, the reference voltage is 2.7 V. The microcurrent supplying unit 333 is connected to the electrode 322 of the oxygen concentration detection cell 350 via the voltage detection terminal TVs. The microcurrent supplying unit 333 supplies a microcurrent Icp to the oxygen concentration detection cell 350 via the voltage detection terminal TVs, thereby moving oxygen ions to the electrode 322 side to generate a reference atmosphere (oxygen partial pressure: about 2 atm). As a result, the electrode 322 functions as an oxygen reference electrode that serves as a reference for detecting the oxygen concentration in the exhaust gas. In addition, the microcurrent supplying unit 333 supplies a pulse current Irpvs for detecting the internal resistance value of the oxygen concentration detection cell 350 to the oxygen concentration detection cell 350 via the voltage detection terminal TVs. The microcurrent supply unit 333 does not constantly supply the microcurrent Icp and the pulse current Irpvs, but supplies the microcurrent Icp and the pulse current Irpvs at appropriate times based on commands from the microcomputer 309.

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 whose magnitude and direction are adjusted to the oxygen pump cell 340.

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.

Based on the digital signal input from the AD conversion unit 334, the PID calculation unit 335 performs feedback control to adjust the pump current Ip 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 (e.g., 450 mV). The PID calculation unit 335 performs PID (Proportional-Integral-Differential) calculation so that the voltage difference becomes the target voltage, and outputs the result of the PID calculation (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 the pump current Ip, and supplies the pump current Ip to the oxygen pump cell 340 as described above.

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 microcurrent supply unit 333 is supplying the pulse current Irpvs, and outputs a digital signal indicating this internal resistance value Rpvs to the duty calculation unit 337.

Based on the digital signal input from the Rpvs calculation unit 336, the duty 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 (e.g., 720°C). Based on the calculated amount of heat generated by the heating resistor 326, the duty calculation unit 337 then calculates the duty ratio of the power to be supplied to the heating resistor 326, and outputs a PWM (Pulse Width Modulation) control signal according to the calculated duty ratio to the heater drive unit 338. Based on the PWM control signal input from the duty calculation unit 337, the heater drive unit 338 PWM controls the voltage Vh supplied to both ends of the heating resistor 326 to cause the heating resistor 326 to generate heat.

The CPU 306 of the microcomputer 309 executes a process for controlling the gas sensor element 30 based on a program stored in the ROM 307. For example, the CPU 306 acquires digital data (output values) indicating the direction of flow of the pump current Ip and values related to the magnitude of the pump current Ip from the circuit section 330 every time a preset acquisition period (e.g., 10 ms) elapses, and transmits the acquired digital data to the ECU 2.

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.

The exhaust pipe 6 is further fitted with a temperature sensor (gas temperature detector) 8 for detecting the temperature of the exhaust gas. The temperature sensor 8 is arranged upstream of the purification device 7, similar to the gas sensor 3. The temperature sensor 8 has a known configuration, and includes, for example, a temperature sensor having a temperature sensor whose electrical characteristics change according to temperature and an electrode wire for outputting an electrical signal from the temperature sensor to the outside, and a sheath core wire (signal wire) electrically connected to the electrode wire. The tip of the sheath core wire is electrically connected to the temperature sensor. The rear end of the sheath core wire is connected to a crimp terminal by resistance welding, and is connected to a lead wire for connecting an external circuit via the crimp terminal. Such a temperature sensor 8 is electrically connected to the ECU 4, which is an external circuit, via the lead wire. The output of the temperature sensor 8 is transmitted to the ECU 4 via the lead wire.

Next, the receiving unit 41, the temperature information acquiring unit 42, the pressure information acquiring unit 43, the correcting unit 44, the concentration information acquiring unit 45, the determining unit 46, and the selecting unit 47 will be described.

The receiver 41 executes a 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, the receiver 41 receives digital data (output value) indicating the direction of flow of the pump current Ip supplied to the oxygen pump cell 340 and a value related to the magnitude of the pump current Ip, via the gas sensor control device 31, every time a preset acquisition period (e.g., 10 ms) elapses, based on an instruction from the CPU 401 of the ECU 4.

The temperature information acquisition unit 42 executes a process for acquiring temperature information of 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. The temperature information acquisition unit 42 receives the exhaust gas temperature (gas temperature) detected by the temperature sensor 8, for example, every time a preset acquisition period (for example, 10 ms) has elapsed.

In other embodiments, the temperature information acquisition unit 42 may use the control temperature (target temperature) of the gas sensor 3 as the temperature information, or may use the gas temperature received from the temperature sensor 8 as the 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, it is possible to more accurately grasp the concentration information of oxygen (target gas).

The pressure information acquisition unit 43 executes a process to acquire exhaust gas pressure information. The exhaust gas pressure (total pressure) can be grasped, 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, for example, every time a preset acquisition period (for example, 10 ms) elapses, and acquires the exhaust gas pressure from the engine parameters 9 using a known method.

The correction unit 44 executes a process of correcting the output value by using a correction formula for correcting the temperature dependency and pressure dependency of the output value received by the receiving unit 41. Here, if the output value (pump current Ip) received by the receiving unit 41 is "Ip _b " and the corrected output value is "Ip _a ", the correction formula is expressed as follows.

In formula (1), _KM is a proportional coefficient of the molecular diffusion coefficient when diffusing (molecular diffusion) in the diffusion layer 315, _KK is a proportional coefficient of the Knudsen diffusion coefficient when diffusing (Knudsen diffusion) in the diffusion layer 315, and _KM / _KK is a parameter representing the combined state of the two types of diffusion, molecular diffusion and Knudsen diffusion, when diffusing in the diffusion layer 315 (i.e., a parameter representing the temperature dependency and pressure dependency of the pump current Ip). As described later, _KM / _KK is obtained in advance by experiment. _KM / _KK is stored in advance in the ROM 402 of the ECU 4.

In addition, in formula (1), T _a is a reference temperature in the reference state, and P _a is a reference pressure in the reference state. In the case of this embodiment, the reference temperature T _a is set to 720° C., and the reference pressure (total pressure) P _a is set to 1 atmosphere. The reference temperature T _a and the reference pressure P _a are stored in advance in the ROM 402 of the ECU 4. The corrected output value Ip _a is at the reference temperature T _a and the reference pressure P _a .

In addition, in formula (1), _Tb is a temperature different from the reference temperature T _a . In this embodiment, the temperature T _b is the temperature of the gas sensor 3 acquired by the temperature information acquisition unit 42. In addition, in formula (1), _Pb is a pressure different from the reference pressure P _a . In this embodiment, the pressure _Pb is the pressure of the exhaust gas acquired by the pressure information acquisition unit 43 (i.e., the actual pressure (total pressure) of the exhaust gas). Note that the temperature T _b and the pressure P _b are acquired at the same time as the output value (pump current) Ip _b .

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

In equation (2), F is the Faraday constant [C/mol], R is the gas constant [J/K/mol], T is the absolute temperature [K], _DO2 is the diffusion coefficient of oxygen in the diffusion layer 315 [ ^m2 /s], S is the cross-sectional area of the diffusion layer 315 [ ^m2 ], L is the length of the diffusion layer 315 [m], Pe is the oxygen partial pressure [Pa], and P is the total pressure of the exhaust gas [Pa].

When the pore diameter of the diffusion layer 315 is larger than the mean free path of oxygen, oxygen diffuses while colliding with other molecules (so-called molecular diffusion) in the same way as when there is no diffusion layer 315. On the other hand, when the pore diameter of the diffusion layer 315 is smaller than the mean free path of oxygen, collisions with the pore walls become more prevalent than collisions between oxygen molecules (so-called Knudsen diffusion). The actual diffusion in the diffusion layer 315 is considered to be a combination of these two types of diffusion (molecular diffusion and Knudsen diffusion). Therefore, D _O2 is expressed by the following formula (3).

In equation (3), D _M is the molecular diffusion coefficient, and D _K is the Knudsen diffusion coefficient.

It is known that the molecular diffusion coefficient D _M is proportional to the 1.75th power of the temperature T and inversely proportional to the pressure P. Therefore, the molecular diffusion coefficient D _M is expressed by the following formula (4). Note that, as described above, K _M in formula (4) is the proportionality coefficient of the molecular diffusion coefficient D _M.

It is also known that the Knudsen diffusion coefficient _DK is proportional to the 0.5 power of temperature. Therefore, the Knudsen diffusion coefficient _DK is expressed by the following formula (5). Note that, as described above, _KK in formula (5) is the proportionality coefficient of the Knudsen diffusion coefficient _DK .

From the above formulas (3), (4), and (5), _DO2 is expressed by the following formula (6).

From the obtained formula (6), the above theoretical formula (2) can be expressed as the following formula (7).

Here, the pump current Ip flowing between the electrodes 319, 320 of the oxygen pump cell 340 of the gas sensor 3 in the reference state 1 (temperature _T1 , oxygen partial pressure _Pe , pressure (total pressure) _P1 ) is defined as " _Ip1 ". The pump current Ip in state 2 (temperature _T2 , oxygen partial pressure Pe, pressure (total pressure) _P2 ) in which the temperature and pressure conditions are different from those in state 1 is defined as " _Ip2 ". The amount of change ΔIp in the pump current Ip when the temperature and pressure conditions change from state 1 to state 2 is expressed by the following formula (8) using formula (7). Note that since the exhaust gas atmosphere is constant, _Pe / _P1 = Pe/ _P2 .

From equation (8), Ip ₂ /Ip ₁ is expressed by equation (9) shown below.

Then, by modifying equation (9), equation (10) is obtained, which expresses the relationship between _Ip1 in the reference state and _Ip2 which is different from the reference state.

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

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 gas detection chamber (detection chamber) 323 from the outside and introduces exhaust gas from the outside to the gas detection chamber 323. The above-mentioned correction formula (1) includes a parameter (K M /K K ) based on a molecular diffusion coefficient D _M of the diffusion layer 315 that depends on the gas species moving inside the diffusion layer 315, and a Knudsen diffusion coefficient D _{K of} the diffusion layer 315 that depends on the gas species moving inside the diffusion layer 315 and a pore radius r in the diffusion _layer 315.

The molecular diffusion coefficient D _M is expressed by the following equation (11).

In formula (11), M _A is the molecular weight of gas A (diffusing solute), M _B is the molecular weight of gas B (diffusing solvent), (Σν) _A is the diffusion volume of gas A, (Σν) _B is the diffusion volume of gas B, T is the temperature, and P is the pressure (total pressure). When the above-mentioned K _M is expressed by the following formula (12), the molecular diffusion coefficient D _M becomes the above-mentioned formula (4).

The Knudsen diffusion coefficient _DK is expressed by the following formula (13).

In formula (13), r is the pore size of the diffusion layer 315, T is the temperature, and M _A is the molecular weight of gas A (diffusing solute). When the above-mentioned K _K is expressed by the following formula (14), the Knudsen diffusion coefficient D _K becomes the above-mentioned formula (5).

By the way, by modifying the formula (8), K _M /K _K is expressed by the following formula (15).

As expressed in formula (15), _KM / _KK is determined _from the conditions ( _T1 , T2, _P1 , _P2 , _Ip1 , _Ip2 ) of states 1 and 2. Therefore, _KM / _KK can be determined in advance, for example, by experiment while appropriately changing the conditions of states 1 and 2.

As the parameter (K _M /K _K ) included in the correction formula (1), a lean parameter, which is a parameter when the exhaust gas in the gas detection chamber 323 is in a lean state, or a rich parameter, which is a parameter when the exhaust gas in the gas detection chamber 323 is in a rich state, is used. 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 lean state, M _A is the molecular weight of oxygen, and M _B is the molecular weight of nitrogen. On the other hand, when the exhaust gas is in a rich state, "gas A" in the above formula (11) etc. is H ₂ or CO, and "gas B" is nitrogen. Therefore, in the rich state, M _A is the molecular weight of H ₂ or CO, and M _B is the molecular weight of nitrogen.

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 inside of the gas detection chamber 323 is in a lean state or a rich state based on the output value (pump current Ip). The determination unit 46 determines whether the inside of the gas detection chamber 323 is in a lean state or a rich state, for example, by comparing the output value with a predetermined threshold value.

As the correction formula (1), a lean correction formula including a lean parameter as the parameter ( _KM / _KK ), or a rich correction formula including a rich parameter as the parameter ( _KM / _KK ) is used. For example, when the determination unit 46 determines that the fuel consumption is lean, the selection unit 47 selects the lean correction formula including the lean parameter as the correction formula (1). On the other hand, when the determination unit 46 determines that the fuel consumption is not lean (rich), the selection unit 47 selects the rich correction formula including the rich parameter as the correction formula (1).

The concentration information acquisition unit 45 executes a process of acquiring the concentration information (air-fuel ratio λ) based on a relational expression that expresses the relationship between concentration information (air-fuel ratio λ in this embodiment) 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., correction value) Ip _a corrected by the correction unit 44.

The "relational expression expressing the relationship between the air-fuel ratio λ and the output value (pump current Ip)" is for the above-mentioned reference state (reference temperature T _a =720° C., reference pressure P _a =1 atm) and is determined in advance through experiments or the like. This relational expression is stored in the ROM 402 of the ECU 4. The concentration information acquisition unit 45 converts the corrected output value (corrected value) Ip _a into the air-fuel ratio λ corresponding thereto using this relational expression.

In this way, the concentration information acquisition unit 45 does not directly use the output (pump current Ip _b ) from the gas sensor 3 received by the receiving unit 41, but uses the correction value Ip _a corrected by the correction unit 44, so that accurate concentration information (air-fuel ratio λ) can be obtained regardless of the temperature T _b and pressure P _b at the time of the output.

Next, with reference to FIG. 5, the process (i.e., the concentration information acquisition method) that the concentration information acquisition device 1 executes when acquiring oxygen concentration information (air-fuel ratio λ) in exhaust gas will be described.

Figure 5 is a flowchart of the process executed by the concentration information acquisition device 1 (ECU 4). First, in step S100, the concentration information acquisition device 1 determines whether it is time to sample the Ip output (pump current Ip) of the gas sensor 3. In the case of this embodiment, for example, the Ip output is sampled every 10 ms (i.e., the Ip output acquisition period is 10 ms). In step S100, if it is time to sample the Ip output, the process proceeds to step S110, and if it is not time to sample the Ip output, the process returns to step S100 again.

In step S110, the receiving unit 41 of the concentration information acquiring device 1 receives the output value (Ip _b output) of the oxygen pump cell (detection cell) 340 (receiving step). The receiving unit 41 receives digital data (output value) indicating the direction of flow of the pump current Ip _b supplied to the oxygen pump cell 340 and the value related to the magnitude of the pump current Ip _b via the gas sensor control device 31.

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 (pump current Ip _b ) (determination step). The determination unit 46 determines whether the inside of the gas detection chamber 323 is in a lean state or a rich state, for example, by comparing the output value with a predetermined threshold value. If it is determined that the inside of the gas detection chamber 323 is in a lean state, the process proceeds to step S130, and if it is determined that the inside of the gas detection chamber 323 is not in a lean state (rich state), the process proceeds to step S140.

After the determination unit 46 determines that the mixture is in a lean state, in step S130, the selection unit 47 selects a lean correction formula including lean parameters ( _KM / _KK for lean) (selection process). Then, the process proceeds to step S150. On the other hand, after the determination unit 46 determines that the mixture is not in a lean state (rich state), in step S140, the selection unit 47 selects a rich correction formula including rich parameters ( _KM / _KK for rich) (selection process). Then, the process proceeds to step S150.

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

In the temperature information acquisition process in step S150, the higher of the control temperature of the gas sensor 3 (gas sensor element 30) and the gas temperature received from the temperature sensor 8 is used as the temperature information of the gas sensor 3 (gas sensor element 30).

Then, the process proceeds to step S160, where the correction unit 44 executes a process of correcting the output value (Ip _b output) using a correction formula (1) for correcting the temperature dependency and pressure dependency of the output value (Ip _b output) (correction step). Note that, as the correction formula (1), if lean parameters are selected in step S130, a lean correction formula including lean parameters (K _M /K _K for lean) is used, and if rich parameters are selected in step S140, a rich correction formula including rich parameters (K _M /K _K for rich) is used. When the output value (Ip _b output) is corrected by the correction unit 44, a corrected Ip _a output (corrected value) is obtained.

Next, the process proceeds to step S170, where the concentration information acquisition unit 45 executes a process of acquiring the air-fuel ratio λ based on the relational expression expressing the relationship between the air-fuel ratio λ and the output value (pump current Ip) and the output value (correction value) Ip _a 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 _b ) from the gas sensor 3 received by the receiving unit 41, but uses the correction value Ip _a corrected by the correction unit 44, so that accurate concentration information (air-fuel ratio λ) can be obtained regardless of the temperature T _b and pressure P _b at the time of the output.

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

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

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

(2) In the above embodiment, the target gas is oxygen, but the present invention is not limited to this, and in other embodiments, for example, NO _x or the like may be the target gas. A known gas sensor (for example, JP 2020-3286 A) is used as a gas sensor for measuring the NO _x concentration. This gas sensor is provided with a cell including a solid electrolyte body and a pair of electrodes for detecting NO _x formed on the solid electrolyte body, and the NO _x concentration can be measured based on a current (output value, second pump current) corresponding to oxygen (oxygen ions) derived from NO _x flowing between the electrodes. In other embodiments, the temperature correction and pressure correction in the output value of such a gas sensor for detecting NO _x may be performed simultaneously by combining them into one using a predetermined correction formula, and an accurate NO _x concentration may be obtained based on the obtained correction value.

(3) In the above embodiment, the receiving unit, the temperature information acquiring unit, the pressure information acquiring unit, the correction unit, the concentration information acquiring unit, the determining unit, and the selecting unit are configured by an ECU, but the present invention is not limited to this. In other embodiments, they may be configured by, for example, a gas sensor control unit, a dedicated control unit configured by a microcomputer, etc.

(4) In other embodiments, some of the configuration implemented by software may be replaced by hardware.

1...concentration information acquisition device, 2...engine, 3...gas sensor, 31...gas sensor control device, 4...ECU, 41...receiving unit, 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 (10)

A concentration information acquisition device that acquires information related to a concentration of a target gas contained in exhaust gas from a gas sensor including a detection cell having a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body,
a receiving unit for receiving an output value of the detection cell;
a temperature information acquiring unit for acquiring temperature information of the gas sensor;
a pressure information acquisition unit that acquires pressure information of the exhaust gas;
a correction unit that corrects the output value by using a correction formula for correcting the temperature dependency and the pressure dependency of the output value;
A concentration information acquisition device comprising: a concentration information acquisition unit that acquires the concentration information based on a relational equation that represents the relationship between concentration information related to the concentration of the target gas and the output value, and a correction value of the output value corrected by the correction unit. the gas sensor includes a detection chamber that houses at least one of the pair of electrodes, and a porous diffusion layer that separates the detection chamber from the outside and introduces exhaust gas from the outside to the detection chamber;
2. The concentration information acquisition device according to claim 1, wherein the correction formula includes parameters based on a molecular diffusion coefficient of the diffusion layer that depends on the gas species moving inside the diffusion layer, and a Knudsen diffusion coefficient of the diffusion layer that depends on the gas species moving inside the diffusion layer and a pore size in 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 includes a lean correction formula including the lean parameter as the parameter, and a rich correction formula including the rich parameter as the parameter,
a determination unit that determines whether the inside of the detection chamber is in the lean state or the rich state based on the output value;
3. The concentration information acquisition device according to claim 2, further comprising a selection unit that selects the lean correction formula as the correction formula when the inside of the detection chamber is in the lean state, and selects the rich correction formula as the correction formula when the inside of the detection chamber is in the rich state. The above-mentioned relationship is under the conditions of a predetermined reference temperature and a predetermined reference pressure,
The concentration information acquiring device according to claim 3 , wherein the correction formula is based on the parameter, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure. A gas temperature detector for detecting the temperature of the exhaust gas is further attached to the pipe to which the gas sensor is attached,
2 . The concentration information acquiring device according to claim 1 , wherein the temperature information acquiring unit acquires, as the temperature information, a higher temperature out of a control temperature of the gas sensor and a gas temperature received from the gas temperature detection device. A concentration information acquiring method comprising: a concentration information acquiring step of acquiring information related to a concentration of a target gas contained in exhaust gas from a gas sensor including a detection cell having a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body,
a receiving step of receiving an output value of the detection cell;
a temperature information acquiring step of acquiring temperature information of the gas sensor;
a pressure information acquiring step of acquiring pressure information of the exhaust gas;
and a correction step of correcting the output value by using a correction formula for correcting the temperature dependency and the pressure dependency of the output value,
A concentration information acquisition method in which, in the concentration information acquisition process, the concentration information is acquired based on a correction value of the output value corrected in the correction process and a relational equation that represents the relationship between concentration information related to the concentration of the target gas and the output value. the gas sensor includes a detection chamber that houses at least one of the pair of electrodes, and a porous diffusion layer that separates the detection chamber from the outside and introduces exhaust gas from the outside to the detection chamber;
7. The concentration information acquisition method according to claim 6, wherein the correction formula includes parameters based on a molecular diffusion coefficient of the diffusion layer that depends on the type of gas moving inside the diffusion layer, and a Knudsen diffusion coefficient of the diffusion layer that depends on the type of gas moving inside the diffusion layer and a pore size in the diffusion layer. the parameters include lean parameters which are parameters when the exhaust gas in the detection chamber is in a lean state, or rich parameters which are parameters when the exhaust gas in the detection chamber is in a rich state,
The correction formula includes a lean correction formula including the lean parameter as the parameter, and a rich correction formula including the rich parameter as the parameter,
a determination step of determining whether the inside of the detection chamber is in the lean state or the rich state based on the output value;
The concentration information acquisition method according to claim 7, further comprising a selection step of selecting the lean correction formula as the correction formula when the inside of the detection chamber is in the lean state, and selecting the rich correction formula as the correction formula when the inside of the detection chamber is in the rich state. The above-mentioned relationship is under the conditions of a predetermined reference temperature and a predetermined reference pressure,
The concentration information acquiring method according to claim 7 , wherein the correction formula is an equation based on the parameter, the output value, the temperature information, the pressure information, the reference temperature, and the reference pressure. A gas temperature detector for detecting the temperature of the exhaust gas is further attached to the pipe to which the gas sensor is attached,
7. The concentration information acquiring method according to claim 6, wherein in the temperature information acquiring step, a higher temperature out of a 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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