WO2023079791A1 - Control device and control method for internal combustion engine - Google Patents

Control device and control method for internal combustion engine Download PDF

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Publication number
WO2023079791A1
WO2023079791A1 PCT/JP2022/027297 JP2022027297W WO2023079791A1 WO 2023079791 A1 WO2023079791 A1 WO 2023079791A1 JP 2022027297 W JP2022027297 W JP 2022027297W WO 2023079791 A1 WO2023079791 A1 WO 2023079791A1
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exhaust gas
gas sensor
control device
way catalyst
catalyst
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PCT/JP2022/027297
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French (fr)
Japanese (ja)
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章広 小森
邦彦 鈴木
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日立Astemo株式会社
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Publication of WO2023079791A1 publication Critical patent/WO2023079791A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D45/00—Electrical control not provided for in groups F02D41/00 - F02D43/00

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  • the present invention relates to a control device for an internal combustion engine.
  • a control technology in which a three-way catalyst is provided in the exhaust pipe of an internal combustion engine, and the oxygen storage state in the three-way catalyst is detected by exhaust gas sensors installed in front and behind the catalyst, and the air-fuel ratio is corrected according to the result.
  • Patent Document 1 Japanese Patent Laid-Open No. 2011-174426 describes a first air-fuel ratio sensor provided upstream of a catalyst mounted in an exhaust passage of an internal combustion engine, and a second air-fuel ratio sensor provided downstream of the catalyst. and an air-fuel ratio control unit that estimates the amount of oxygen released from the catalyst with reference to at least the output of the first air-fuel ratio sensor and performs feedback control of the amount of oxygen released to a target value;
  • An air-fuel ratio control device is described that includes a learning unit that learns a learning parameter for reduction when a fuel cut occurs in an internal combustion engine.
  • the mapping data stored in the storage device 76 is input with time-series data of variables corresponding to the upstream air-fuel ratio and the downstream air-fuel ratio.
  • This is data that defines a neural network that outputs a deterioration degree variable, which is a variable that indicates the degree of deterioration of the side catalyst.
  • the CPU inputs time-series data of variables corresponding to the upstream air-fuel ratio and the downstream air-fuel ratio to the mapping defined by the mapping data, thereby calculating the deterioration degree variable of the upstream catalyst.
  • the oxygen storage capacity of the catalyst changes due to the deterioration of the three-way catalyst. Since the change in oxygen storage capacity affects the determination of air-fuel ratio correction control, it is necessary to accurately diagnose the degree of deterioration of the catalyst. If the deterioration state of the catalyst is erroneously determined, the air-fuel ratio cannot be corrected to the optimum, and the oxygen storage capacity cannot be maintained within an appropriate range.
  • the degree of deterioration of the catalyst is diagnosed from the correlation between the exhaust gas sensor signals before and after the catalyst. With a new catalyst, the amplitude of the downstream exhaust gas sensor signal is smaller than that of the upstream exhaust sensor. . The degree of deterioration of the catalyst is diagnosed using the correlation between the upstream and downstream sensor signals of the catalyst.
  • the prior art is based on the assumption that the air-fuel ratio is fluctuating at a steady state, and there is a problem that the opportunities are limited.
  • Patent Document 2 uses upstream average A/F, downstream average A/F, exhaust gas flow rate, rotation speed, A coefficient representing the degree of deterioration is obtained from a neural network with six inputs of filling efficiency and catalyst temperature. Then, the degree of deterioration of the catalyst is determined by comparing the coefficient with the threshold value. However, if the preconditions of the input data are changed due to disturbances such as the addition of devices or controls, the number of inputs will be increased, and the scale of the neural network will increase, which may make implementation difficult.
  • an object of the present invention is to provide a technique for accurately determining the degree of deterioration of a catalyst under various conditions using the frequency component of the output of an exhaust gas sensor.
  • a representative example of the invention disclosed in the present application is as follows. That is, a control device for controlling an internal combustion engine, wherein the internal combustion engine includes a three-way catalyst arranged in an exhaust flow path, an upstream exhaust gas sensor arranged upstream of the three-way catalyst, and a three-way catalyst. a frequency selector for extracting frequency components of an output signal of the upstream exhaust gas sensor and an output signal of the downstream exhaust gas sensor; and a frequency selector based on the output of the frequency selector.
  • a signal processing unit for estimating the state of the primary catalyst and a calculation unit for calculating the air-fuel ratio from the state of the three-way catalyst are provided.
  • FIG. 1 is a schematic configuration diagram of an entire system of an engine control device according to an embodiment of the present invention
  • FIG. 1 is a diagram showing the configuration of an aftertreatment system for purifying exhaust gas from an internal combustion engine
  • FIG. 4 is a diagram showing the tendency of the chemical species concentration of exhaust gas with respect to the equivalent ratio
  • FIG. 2 is a diagram showing the main reaction process of a three-way catalyst (ceria system) used in an aftertreatment system
  • FIG. 4 is a diagram showing the tendency of the purification efficiency of a three-way catalyst with respect to the exhaust gas equivalent ratio above the catalyst activation temperature.
  • FIG. 4 is a diagram showing the air-fuel ratios upstream and downstream of the catalyst and the output of an oxygen sensor installed downstream of the catalyst;
  • FIG. 4 is a diagram showing the hysteresis characteristic of an oxygen sensor;
  • FIG. 4 is a diagram showing temporal changes in NOx concentrations downstream of an oxygen sensor and a catalyst;
  • FIG. 4 is a diagram showing the relationship between the degree of catalyst deterioration and the oxygen storage capacity of a three-way catalyst;
  • FIG. 4 is a diagram showing the relationship between the oxygen storage ratio and the NOx purification efficiency;
  • FIG. 4 is a diagram showing the air-fuel ratios upstream and downstream of the catalyst and the output of an oxygen sensor installed downstream of the catalyst;
  • FIG. 4 is a schematic diagram showing spectral changes for each low to high frequency of a band-pass filter in new, centrally deteriorated, and completely deteriorated states.
  • FIG. 4 is a schematic diagram showing spectral changes for each low to high frequency of a band-pass filter in new, centrally deteriorated, and completely deteriorated states.
  • the intercooler 5 is provided downstream of the compressor 3a of the turbocharger 3, and cools the intake air whose temperature has been increased by being adiabatically compressed by the compressor 3a.
  • the supercharging temperature sensor 6 is provided downstream of the intercooler 5 and measures the temperature of the intake air cooled by the intercooler 5 (supercharging temperature).
  • the throttle valve 7 is provided downstream of the intercooler 5 and throttles the intake passage to control the amount of intake air flowing into the cylinders of the internal combustion engine 1 .
  • the throttle valve 7 is composed of an electronically controlled butterfly valve whose valve opening can be controlled independently of the amount of depression of the accelerator pedal by the driver.
  • An intake manifold 8 provided with a supercharging pressure sensor 9 communicates with an intake passage downstream of the throttle valve 7 .
  • the intake manifold 8 provided downstream of the throttle valve 7 and the intercooler 5 may be integrated. In this case, since the volume from the downstream of the compressor 3a to the cylinder can be reduced, the responsiveness of acceleration and deceleration can be improved, and the controllability can be improved.
  • the flow enhancement valve 10 is arranged downstream of the intake manifold 8 and enhances turbulence of the flow inside the cylinder by creating a bias in the intake air taken into the cylinder. Turbulent combustion is promoted and stabilized by closing the flow enhancing valve 10 when exhaust gas recirculation combustion, which will be described later, is performed.
  • the internal combustion engine 1 has an intake valve 11 and an exhaust valve 13 .
  • the intake valve 11 and the exhaust valve 13 each have a variable valve mechanism for continuously varying the valve opening/closing phase.
  • the variable valve mechanisms of the intake valve 11 and the exhaust valve 13 are provided with sensors 12 and 14, respectively, for detecting the opening/closing phases of the valves.
  • a cylinder of the internal combustion engine 1 is provided with a direct fuel injection valve 15 that injects fuel directly into the cylinder.
  • the fuel injection valve 15 may be of a port injection type that injects fuel into the intake port.
  • a cylinder of the internal combustion engine 1 is provided with a spark plug 16 that exposes an electrode portion inside the cylinder and ignites a combustible air-fuel mixture with a spark.
  • the knock sensor 17 is provided in the cylinder block and detects the presence or absence of knock by detecting cylinder block vibration caused by combustion pressure vibration generated in the combustion chamber.
  • the crank angle sensor 18 is provided on the crankshaft, and outputs a signal corresponding to the rotation angle of the crankshaft to the ECU 28, which will be described later, as a signal indicating the rotation speed.
  • the air-fuel ratio sensor 20 is provided in the exhaust passage downstream of the turbine 3b of the turbocharger 3, and outputs a signal indicating the detected exhaust gas composition, that is, the air-fuel ratio, to the ECU 28.
  • the exhaust purification catalyst 21 is a three-way catalyst, is provided downstream of the air-fuel ratio sensor 20, and purifies harmful exhaust gas components such as carbon monoxide, nitrogen compounds, and unburned hydrocarbons in the exhaust gas by catalytic reaction.
  • An oxygen sensor 22 is provided downstream of the exhaust purification catalyst 21 to detect the concentration of oxygen contained in the exhaust gas purified by the exhaust purification catalyst 21 .
  • the turbocharger 3 is provided with an air bypass valve 4 and a wastegate valve 19 .
  • the air bypass valve 4 is arranged on a bypass flow path connecting upstream and downstream of the compressor 3a in order to prevent an excessive increase in pressure from the downstream of the compressor 3a to the upstream of the throttle valve 7. As shown in FIG. When the throttle valve 7 is abruptly closed in the supercharging state, the air bypass valve 4 is opened under the control of the ECU 28, so that the compressed intake air in the downstream portion of the compressor 3a passes through the bypass passage to the compressor 3a. flows back upstream of the As a result, the supercharging pressure is immediately lowered to prevent the surging phenomenon and appropriately prevent damage to the compressor 3a.
  • the wastegate valve 19 is arranged on a bypass flow path that connects upstream and downstream of the turbine 3b.
  • the wastegate valve 19 is an electrically operated valve whose valve opening degree can be freely controlled with respect to the supercharging pressure under the control of the ECU 28 .
  • the opening degree of the waste gate valve 19 is adjusted by the ECU 28 based on the supercharging pressure detected by the supercharging pressure sensor 9, a part of the exhaust gas passes through the bypass flow path, thereby reducing the work given to the turbine 3b by the exhaust gas. can be reduced to maintain the boost pressure at the target pressure.
  • the EGR pipe 23 communicates with an exhaust passage downstream of the exhaust purification catalyst 21 and an intake passage upstream of the compressor 3a, and diverts the exhaust gas from the downstream of the exhaust purification catalyst 21 to the upstream of the compressor 3a. Reflux.
  • An EGR cooler 24 provided in the EGR pipe 23 cools the exhaust gas.
  • the EGR valve 25 is provided downstream of the EGR cooler 24 and controls the flow rate of exhaust gas.
  • the EGR pipe 23 is provided with a temperature sensor 26 that detects the temperature of the exhaust gas upstream of the EGR valve 25 and a differential pressure sensor 27 that detects a differential pressure between upstream and downstream of the EGR valve 25 .
  • the ECU 28 is an arithmetic circuit that has a CPU, ROM, RAM, A/D converter, driver circuit, etc., and controls each component of the engine control device and executes various data processing.
  • the various sensors and actuators described above are connected to the ECU 28 .
  • the ECU 28 controls the operations of actuators such as the throttle valve 7, the intake and exhaust valves 11 and 13 with variable valve mechanisms, the fuel injection valve 15, the EGR valve 25, and the like.
  • the ECU 28 also detects the operating state of the internal combustion engine 1 based on signals input from various sensors, and ignites the spark plug 16 at a timing determined according to the operating state.
  • FIG. 2(A) is a diagram showing the configuration of an aftertreatment system that purifies exhaust gas from an internal combustion engine.
  • a three-way catalyst is used as the exhaust gas purification catalyst.
  • sensors for detecting the exhaust gas composition are provided at each of the upstream and downstream portions of the three-way catalyst.
  • an air-fuel ratio sensor 20 is provided upstream, and an oxygen sensor 22 is provided downstream. According to this configuration, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst can be measured, and the presence or absence of oxygen contained in the exhaust gas after catalyst purification can be detected.
  • the air-fuel ratio sensor 20 is characterized in that it can accurately detect the equivalence ratio over a wide range from the exhaust gas lean state to the rich state by obtaining the relationship shown in FIG. 4 in advance.
  • FIG. 2(C) is a diagram showing the relationship between the equivalence ratio of the exhaust gas and the output of the oxygen sensor 22.
  • the oxygen sensor 22 outputs a signal according to the electromotive force associated with the concentration difference between the oxygen concentration contained in the exhaust gas and the oxygen concentration in the air.
  • the oxygen sensor 22 has a characteristic of outputting a generally minimum electromotive force under lean conditions, outputting a maximum electromotive force under rich conditions, and suddenly changing the output at a stoichiometric air-fuel ratio (equivalence ratio of 1.0). By capturing the change timing of the sensor output and feeding it back to the air-fuel ratio control, the exhaust gas equivalence ratio can be maintained near the theoretical air-fuel ratio.
  • FIG. 3 is a diagram showing the tendency of chemical species concentration in exhaust gas with respect to the equivalence ratio.
  • Combustion gas compositions of hydrocarbon-based fuels tend to increase CO (carbon monoxide) and H2 (hydrogen) on the rich side and O2 (oxygen) on the lean side of the stoichiometric air-fuel ratio.
  • NOx nitrogen oxides
  • NOx nitrogen oxides
  • HC unburned hydrocarbons
  • HC is a component that is emitted without being burned, and excessive lean or enrichment tends to result in HC being emitted without leading to normal combustion.
  • Fig. 4 is a diagram showing the main reaction process of a three-way catalyst (ceria-based) used in the post-treatment system.
  • the three-way catalytic reaction process mainly consists of an oxidation reaction, a NOx reduction reaction, and an oxygen storage/release reaction.
  • HC Unburned hydrocarbons
  • Unburned hydrocarbons (HC) include hydrocarbon components such as methane, propane, ethylene, and butane, which react at different rates.
  • the NOx reduction reaction is represented mainly by the reaction of CO and NO to produce harmless CO2 and N2.
  • the oxygen storage/release reaction the storage/release of oxygen and the oxidation and reduction reactions of HC, CO, and NO proceed via Ce (cerium), which is a catalyst material. That is, the reaction of cerium dioxide (CeO2) with CO and HC produces harmless CO2 and H2O, and the reaction of cerium trioxide (Ce2O3) with NO produces harmless N2.
  • the oxygen storage ratio of the three-way catalyst is defined by the balance between CeO2 and Ce2O3 that are produced at the same time. That is, when all of the Ce2O3 in the catalyst becomes CeO2, it cannot react with NO and cannot purify NO. In this way, in order to properly maintain the purification efficiency of the three-way catalyst, it is necessary to maintain the balance between CeO2 and Ce2O3, that is, the oxygen storage ratio, at a predetermined value. All of the reaction processes described above strongly depend on the catalyst temperature, and it is necessary to appropriately manage the catalyst temperature so that it reaches the activation temperature or higher in an early stage after starting. Although the system shown in this embodiment uses a ceria-based three-way catalyst, the present invention is not limited to this.
  • Catalysts using other materials exhibiting similar effects can also achieve similar effects by adjusting the constants of the control model without changing the configuration of the invention.
  • the catalytic reaction may also use the water-gas shift reaction or the like. These reaction mechanisms can also be handled by adjusting the control model constants.
  • FIG. 5 is a diagram showing the tendency of the purification efficiency of the three-way catalyst with respect to the exhaust gas equivalence ratio above the catalyst activation temperature.
  • the purification efficiency characteristics of the three-way catalyst change with the stoichiometric air-fuel ratio as a boundary. Under lean conditions, the CO and HC purification efficiency is generally maintained at 90% or more, and the NOx purification efficiency decreases as the equivalence ratio decreases. . On the other hand, on the rich side, the purification efficiency of HC and CO decreases as the equivalence ratio increases. In the vicinity of the theoretical air-fuel ratio, the purification efficiency of NOx, HC, and CO is 90% or more, and this point is called the ternary point.
  • the three-way catalyst is controlled to keep the purification efficiency at a high level by maintaining the equivalence ratio at the stoichiometric air-fuel ratio, which is the three-way point.
  • FIG. 6 shows the air-fuel ratio downstream of the catalyst and the oxygen sensor 22 installed downstream of the catalyst when the air-fuel ratio is varied stepwise to the lean side and the rich side over time, centering on the equivalence ratio of 1.0.
  • FIG. 10 is a diagram showing the output; Even when the equivalence ratio is the stoichiometric air-fuel ratio, it is maintained in an intermediate state by discharging a very small amount of oxygen downstream of the catalyst. When the ratio is changed stepwise to the lean side, the rear equivalence ratio gradually changes, and the output of the oxygen sensor 22 rapidly changes to the minimum value side after a delay time.
  • FIG. 7 is a diagram showing the hysteresis characteristic of the oxygen sensor 22.
  • FIG. The static characteristics of the oxygen sensor 22 are shown in FIG.
  • the oxygen sensor 22 also uses a catalytic material and has hysteresis due to detection delay. That is, when the lean state changes rapidly to the rich state, the change timing of the sensor output shifts to the rich side of the equivalence ratio, and when the rich state changes suddenly to the lean state, the change timing of the sensor output shifts to the equivalence ratio. Shift to the lean side of the ratio. Furthermore, the behavior described above is affected by deterioration of the material properties of the sensor and temperature. In the control model, it is necessary to consider changes in dynamic characteristics including sensor deterioration and temperature effects in addition to catalyst deterioration.
  • FIG. 8 shows the oxygen sensor 22 and the NOx concentration downstream of the catalyst when the firing operation is performed again in the stoichiometric air-fuel ratio state after the motoring operation (fuel cut) period from the state controlled at the stoichiometric air-fuel ratio. It is a figure which shows a change. After the fuel cut, when the firing operation with the stoichiometric air-fuel ratio is started again, the detected value of the oxygen sensor 22 increases with a delay as shown in FIG.
  • the NOx concentration downstream of the catalyst shows a behavior in which NOx is discharged in a spike during the delay period until the oxygen sensor 22 is restored.
  • FIG. 9 is a diagram showing the relationship between the degree of catalyst deterioration and the oxygen storage capacity of the three-way catalyst.
  • Catalyst deterioration is a state in which the catalytic action is lowered due to the influence of heat and poisoning by sulfur contained in the fuel. As the catalyst deterioration progresses, the oxygen storage capacity decreases. The effect of changes in oxygen storage capacity on the purification action of the three-way catalyst will be described below.
  • FIG. 10 is a diagram showing the relationship between the oxygen storage ratio and the NOx purification efficiency.
  • NOx purification efficiency deteriorates significantly. This is because, as described in FIG. 4, Ce2O3 in the catalyst is important for purifying NOx, and if all Ce2O3 reacts and changes to CeO2, it cannot react with NO and cannot purify NO. be.
  • FIG. 5 in order to keep the catalyst purification efficiency at a high level, it is necessary not only to keep the exhaust gas air-fuel ratio at the catalyst inlet at the three-way point, but also to keep the oxygen storage ratio within a predetermined range. In addition, it is necessary to appropriately correct and control the exhaust gas air-fuel ratio at the catalyst inlet.
  • FIG. 11 shows the equivalence ratio downstream of the catalyst and the equivalence ratio installed downstream of the catalyst when the air-fuel ratio is changed stepwise to the lean side and the rich side over time with the equivalence ratio of 1.0 as the center for the new catalyst and the deteriorated catalyst.
  • FIG. 10 is a diagram showing an output of an oxygen sensor 22 (downstream exhaust gas sensor).
  • the deteriorated catalyst reduces the delay in change in the output of the oxygen sensor 22 with respect to changes in the air-fuel ratio to the lean and rich sides compared to the new catalyst.
  • This can be explained by the temporal transition of the oxygen storage rate of the catalyst. That is, the oxygen storage capacity of the catalyst decreases due to deterioration, and the oxygen storage rate reaches the maximum and minimum values more quickly, which accelerates the release of oxygen downstream and reduces the delay in change in the output of the oxygen sensor 22. It is from. Therefore, the rich correction period after returning from fuel cut described in FIG. 8 must be set in consideration of the deterioration state of the catalyst.
  • FIG. 12 is a schematic diagram showing spectral changes for each low to high frequency band-pass filter in new, centrally deteriorated, and completely deteriorated states.
  • the actual spectrum varies in various ways depending on the state of upstream exhaust gas.
  • the left side shows the signal of the upstream exhaust gas sensor (air-fuel ratio sensor 20) after band-pass filtering
  • the right side shows the signal of the downstream exhaust gas sensor (oxygen sensor 22) after band-pass filtering. Since the upstream exhaust gas sensor signal changes in synchronism with changes in the air-fuel ratio of the exhaust gas, it has the same spectrum regardless of the deterioration state of the catalyst. On the other hand, since the downstream exhaust gas sensor signal is affected by the oxygen storage capacity of the catalyst, the frequency spectrum differs for each deterioration state.
  • the catalyst has sufficient oxygen storage capacity, so the downstream exhaust gas sensor signal shows a small and gradual change, resulting in a low frequency spectrum.
  • the downstream exhaust gas sensor signal shows a change that swings more than in the new state due to the decrease in the oxygen storage capacity due to the decrease in Ce of the catalyst. Therefore, the spectrum is from frequencies lower to higher than those in the new state.
  • Ce decreases more than with a moderately degraded catalyst, so the change is similar to that of the upstream exhaust gas sensor signal.
  • the frequency change is greater than for the moderately aged catalyst and approaches the spectrum of the upstream exhaust gas sensor signal.
  • the catalyst deterioration level can be determined.
  • three frequencies of high frequency, medium frequency, and low frequency are used in order to divide into three levels of complete deterioration, moderate deterioration, and new product as an example, but the number of frequency bands that can be used is not limited. , more than three or less than three can be applied.
  • the degradation state of the catalyst may be determined based on two signals obtained by frequency-decomposing the upstream exhaust gas sensor signal and two signals obtained by frequency-decomposing the downstream exhaust gas sensor signal using two band-pass filters of high frequency and low frequency.
  • the frequency band set for each filter may not be a fixed value, but may be a variable that is adjusted according to the operating conditions of the internal combustion engine.
  • it is preferable to prepare a table that associates the pass frequency band of each bandpass filter with the rotational speed of the internal combustion engine refer to the outer table, and increase the frequency as the rotational speed increases.
  • the frequency characteristics of catalyst deterioration can be extracted from the frequency information of the exhaust gas sensor signal, the actual signal waveform does not have a constant shape, so signal processing is difficult. Therefore, in the present invention, the deterioration of the catalyst is diagnosed using the neural network 1301b that has been learned by associating the frequency information of the sensor with the deterioration of the catalyst.
  • the model for diagnosing deterioration of the catalyst may be a model other than the neural network 1301b (for example, a regression model) for diagnosing deterioration of the catalyst.
  • FIG. 13 is a block diagram of a control model that performs catalyst deterioration diagnosis from exhaust gas sensor signals upstream and downstream of the catalyst, and corrects and controls the air-fuel ratio in consideration of the oxygen storage amount.
  • a deterioration diagnosis unit 1301 receives exhaust gas sensor signals upstream and downstream of the catalyst, diagnoses the degree of deterioration of the catalyst, and is composed of a frequency selection unit 1301a and a neural network 1301b.
  • the frequency selector 1301a has a plurality of filters for extracting the frequency characteristics of the exhaust gas sensor signal as shown in FIG. In FIG. 13, as an example, three low-pass filters for each frequency are combined to form a band-pass filter.
  • the exhaust gas sensor signals upstream and downstream of the catalyst pass through low-pass filters with cutoff frequencies of high, medium, and low frequencies, are input to the calculation section to be decomposed into each frequency band, and are sent to the band-pass filter.
  • the band-pass filters are prepared for three frequency bands of high frequency, medium frequency, and low frequency, and each band-pass filter has 3 signals obtained by filtering the upstream exhaust gas sensor signal and 3 signals obtained by filtering the downstream exhaust gas sensor signal. Output a signal.
  • BPF3 (band pass filter 3) Original waveform-Signal after passing through LPF3 BPF2 (band pass filter 2) Signal after passing through LPF3 - Signal after passing through LPF2 BPF1 (band pass filter 1) Signal after passing LPF2 - Signal after passing LPF1
  • the frequency selection unit 1301a configures a band-pass filter by combining low-pass filters. You can use three. Also, the frequency selection unit 1301a may extract the frequency component of the exhaust gas sensor signal by Fourier transform instead of the filter.
  • the neural network 1301b learns frequency information associated with the deterioration state of the catalyst, receives the signal after passing through the band-pass filter output from the frequency selection unit 1301a, and determines whether the input signal is new, moderately deteriorated, or perfect.
  • a degradation diagnosis result (for example, the degree of certainty of each state) indicating which of the three states of degradation is present is output.
  • the neural network 1301b detects the relative relationship between the upstream and downstream exhaust gas sensor signals of the catalyst that have passed through the band-pass filter 1, the band-pass filter 2 , and the relative relationship between the upstream and downstream exhaust gas sensor signals of the catalyst that have passed through the band-pass filter 3 are learned as teacher data.
  • the OSC estimation model selection unit 1302 receives the deterioration diagnosis result and selects an OSC estimation model according to the deterioration diagnosis result.
  • the OSC estimator 1303 calculates an estimated oxygen storage capacity (estimated OSC) using the selected oxygen storage capacity (OSC) estimation model.
  • Catalyst control unit 1304 receives the estimated OSC and calculates an air-fuel ratio correction amount that does not lower the purification rate due to the estimated OSC, according to the operating conditions.
  • the operating conditions are, for example, throttle opening, engine load, engine speed, temperature, atmospheric pressure, and the like.
  • An air-fuel ratio correction amount calculation unit 1305 outputs a post-correction target air-fuel ratio based on the air-fuel ratio target value and the air-fuel ratio correction amount calculated by the catalyst control unit 1304 .
  • FIG. 14 is a diagram showing an overview of catalyst deterioration diagnosis by the deterioration diagnosis unit 1301.
  • the exhaust gas sensor signals upstream and downstream of the catalyst input to the deterioration diagnosis unit 1301 are frequency-decomposed by a bandpass filter.
  • the band-pass filters are three band-pass filters of high frequency, medium frequency, and low frequency, and each band-pass filter generates three signals obtained by frequency-resolving the upstream exhaust gas sensor signal and three signals obtained by frequency-resolving the downstream exhaust gas sensor signal. Input to neural network 1301b.
  • FIG. 15 is a diagram showing a method of realizing catalyst deterioration diagnosis based on the frequency of the exhaust gas sensor signal with the neural network 1301b.
  • a neural network model is a mathematical model that imitates the mechanism of human brain neural circuits, and weights and biases are set for each neuron that constitutes the model.
  • a function called an activation function is defined in a neuron.
  • a logistic function, a ramp function, or the like may be appropriately set as the activation function.
  • a plurality of neurons form one layer, and an intermediate layer is set between the input layer and the output layer. More complex input-output relationships can be approximated by increasing the number of neurons and the number of hidden layers.
  • FIG. 16 uses the control model shown in FIG. 13 to decompose the exhaust gas sensor signals upstream and downstream of the catalyst into three frequency bands using a band-pass filter, input them to the neural network 1301b, and output deterioration diagnosis results.
  • 4 is a flowchart of processing for executing air-fuel ratio correction
  • the deterioration diagnosis unit 1301 receives input of exhaust gas sensor signals upstream and downstream of the catalyst. disassemble.
  • the neural network 1301b receives input of exhaust gas sensor signals upstream and downstream of the catalyst resolved into frequency bands.
  • the neural network 1301b which has learned frequency information associated with the deterioration state of the catalyst, estimates the deterioration of the catalyst from the input exhaust gas sensor signals upstream and downstream of the catalyst.
  • the OSC estimation model selection unit 1302 selects an OSC model according to the deterioration state according to the deterioration diagnosis result.
  • a plurality of OSC models are prepared according to the state of deterioration of the catalyst (for example, the coefficients to be multiplied by ⁇ in the oxygen storage ratio formula in FIG. 4 are different), and an appropriate OSC model is selected according to the state of deterioration of the catalyst. selected.
  • the OSC estimator 1303 estimates the oxygen storage capacity (OSC) of the catalyst using the selected OSC model.
  • catalyst control unit 1304 calculates an air-fuel ratio correction amount based on the estimated oxygen storage amount.
  • the air-fuel ratio correction amount calculator 1305 uses the air-fuel ratio target value and the air-fuel ratio correction amount calculated at step 107 to calculate the post-correction target air-fuel ratio.
  • FIG. 17 is a diagram showing the effects of the control model shown in FIG.
  • the firing operation is performed again at the stoichiometric air-fuel ratio.
  • the rich correction is performed once, and then the stoichiometric air-fuel ratio control is performed to prevent NOx emissions downstream of the catalyst.
  • the deterioration state of the catalyst can be diagnosed with high accuracy, so the rich correction can be performed in an appropriate period, and NOx and HC emissions downstream of the catalyst can be reduced.
  • the control model of this embodiment may have an output sensor failure diagnosis function. For example, after the neural network 1301b learns the normal output signals of the upstream exhaust gas sensor and the downstream exhaust gas sensor, the output signal of the upstream exhaust gas sensor, the output signal of the downstream exhaust gas sensor, and the output signal of each exhaust gas sensor under normal conditions. An abnormality in the exhaust gas sensor may be diagnosed based on the degree of similarity between the two. Then, when it is determined that the exhaust gas sensor is abnormal, the neural network 1301b should stop estimating the state of the catalyst.
  • control model of this embodiment may have a heater failure diagnosis function.
  • the oxygen sensor 22, which is a downstream exhaust gas sensor, has a heater that maintains the temperature at which the material (zirconia) used for the sensor is activated.
  • the deterioration diagnosis unit 1301 monitors the heater temperature of the oxygen sensor 22, and after the neural network 1301b learns the heater energization state and normal heater temperature, You may diagnose the abnormality of a heater by the similarity of . Then, when it is determined that the heater is abnormal, the neural network 1301b should stop estimating the state of the catalyst.
  • FIG. 18 is a diagram showing the inspection procedure of the catalyst state estimation function of the ECU 28 of this embodiment.
  • the catalyst is new, moderate.
  • the upstream and downstream exhaust gas sensor signals of the catalyst at the time of deterioration and at the time of complete deterioration are connected, and test data simulating the signal after passing through the band-pass filter is input.
  • output signals of exhaust gas sensors upstream and downstream of the catalyst before being passed through a band-pass filter are created from the signal.
  • the generated signal is input to the ECU 28, and it is checked whether the amount of rich correction performed after the fuel cut changes in accordance with the deterioration state of the catalyst and whether the rich correction is performed within an assumed period.
  • FIG. 19 a configuration for estimating the effective Ce amount of the catalyst will be described with reference to FIGS. 19 and 20.
  • FIG. 19 is a block diagram of a control model that performs catalyst deterioration diagnosis from the signal of the exhaust gas sensor before and after the catalyst, and corrects and controls the air-fuel ratio in consideration of the effective Ce amount.
  • a deterioration diagnosis unit 1901 receives exhaust gas sensor signals upstream and downstream of the catalyst, estimates the amount of effective Ce, and is composed of a frequency selection unit 1901a and a neural network 1901b.
  • the frequency selection unit 1901a has the same configuration as the frequency selection unit 1301a shown in FIG. , three signals obtained by filtering the upstream exhaust gas sensor signal and three signals obtained by filtering the downstream exhaust gas sensor signal.
  • the neural network 1901b learns frequency information associated with the effective Ce amount of the catalyst, receives the signal after passing through the bandpass filter output from the frequency selection unit 1901a, and determines the effective Ce amount corresponding to the input signal. to estimate The estimated effective Ce amount is input to OSC estimation section 1903 .
  • the OSC estimator 1903 estimates the oxygen storage capacity (OSC) using the estimated available Ce amount.
  • the catalyst control unit 1304 and the air-fuel ratio correction amount calculation unit 1305 operate and output the post-correction target air-fuel ratio in the same procedure as in FIG.
  • FIG. 20 uses the control model shown in FIG. 19 to decompose the exhaust gas sensor signals upstream and downstream of the catalyst into three frequency bands using a band-pass filter, input them to the neural network 1301b, and output the effective Ce amount.
  • 4 is a flowchart of processing for executing air-fuel ratio correction
  • the deterioration diagnosis unit 1901 receives input of exhaust gas sensor signals upstream and downstream of the catalyst. disassemble.
  • the neural network 1301b receives input of exhaust gas sensor signals upstream and downstream of the catalyst resolved into frequency bands.
  • the neural network 1901b which has learned frequency information associated with the effective Ce amount of the catalyst, estimates the effective Ce amount from the input upstream and downstream exhaust gas sensor signals of the catalyst.
  • the OSC estimator 1303 estimates the oxygen storage capacity (OSC) of the catalyst according to the estimated effective Ce amount.
  • catalyst control unit 1304 calculates an air-fuel ratio correction amount based on the estimated oxygen storage amount.
  • the air-fuel ratio correction amount calculation unit 1305 calculates the post-correction target air-fuel ratio using the air-fuel ratio target value and the air-fuel ratio correction amount calculated at step 116 .
  • the control device (ECU 28) of this embodiment performs frequency selection for extracting the frequency components of the output signal of the upstream exhaust gas sensor (air-fuel ratio sensor 20) and the output signal of the downstream exhaust gas sensor (oxygen sensor 22).
  • a signal processing unit (neural network 1301b) that estimates the state of the three-way catalyst (exhaust purification catalyst 21) based on the output of the frequency selection unit 1301a; and an air-fuel ratio that calculates the air-fuel ratio from the state of the three-way catalyst. Since the correction amount calculation unit 1305 is provided, the deterioration of the catalyst can be appropriately estimated using the frequency component of the output of the exhaust gas sensor, and appropriate engine control can be performed without increasing harmful components in the exhaust gas. In other words, it is possible to diagnose the deterioration of the catalyst based on the relationship between the relative relationship of each frequency after passing through the band-pass filter and the state of the catalyst. degree can be diagnosed.
  • the frequency selection unit 1301a includes a first filter that passes a first frequency band corresponding to the new state of the three-way catalyst and a second filter that passes a second frequency band corresponding to the deteriorated state of the three-way catalyst. is used to filter the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor, extracting the feature amount related to the deterioration of the catalyst, it is possible to perform highly accurate learning of the neural network 1301b.
  • the frequency selection unit 1301a includes a first filter that passes a first frequency band corresponding to the new state of the three-way catalyst and a second filter that passes a second frequency band corresponding to the deteriorated state of the three-way catalyst. and a third filter that passes a third frequency band between the first frequency and the second frequency to filter the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor. can be determined in three states, and the air-fuel ratio correction amount can be finely set.
  • the model selector is provided for selecting an oxygen storage capacity estimation model according to the state of deterioration of the three-way catalyst based on the output of the signal processor, the oxygen storage capacity can be accurately estimated according to the state of deterioration. It is possible to improve the correction accuracy of the air-fuel ratio.
  • the neural network 1301b determines whether the exhaust gas sensor is abnormal based on the degree of similarity between the output signal of the upstream exhaust gas sensor, the output signal of the downstream exhaust gas sensor, and the output signal of each exhaust gas sensor during normal operation. Together, sensor failure can be determined.
  • the neural network 1301b monitors the heater of the oxygen sensor 22 and determines whether the heater is abnormal based on the degree of similarity between the temperature change of the heater and the normal state. Therefore, it is possible to determine the deterioration of the catalyst as well as the failure of the heater.
  • the present invention is not limited to the above-described embodiments, and includes various modifications and equivalent configurations within the scope of the attached claims.
  • the above-described embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to those having all the described configurations.
  • part of the configuration of one embodiment may be replaced with the configuration of another embodiment.
  • the configuration of another embodiment may be added to the configuration of one embodiment.
  • additions, deletions, and replacements of other configurations may be made for a part of the configuration of each embodiment.
  • each configuration, function, processing unit, processing means, etc. described above may be realized by hardware, for example, by designing a part or all of them with an integrated circuit, and the processor realizes each function. It may be realized by software by interpreting and executing a program to execute.
  • control lines and information lines indicate those that are considered necessary for explanation, and do not necessarily indicate all the control lines and information lines necessary for implementation. In practice, it can be considered that almost all configurations are interconnected.

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Abstract

This control device is for controlling an internal combustion engine. The internal combustion engine is provided with: a three-way catalyst disposed in an exhaust flow passage; an upstream exhaust gas sensor disposed upstream of the three-way catalyst; and a downstream exhaust gas sensor disposed downstream of the three-way catalyst. The control device comprises: a frequency selection unit which extracts frequency components of output signals from the upstream exhaust gas sensor and the downstream exhaust gas sensor; a signal processing unit which estimates a condition of the three-way catalyst on the basis of the outputs from the frequency selection unit; and a calculation unit which calculates an air-fuel ratio from the condition of the three-way catalyst.

Description

内燃機関の制御装置及び制御方法CONTROL DEVICE AND CONTROL METHOD FOR INTERNAL COMBUSTION ENGINE 参照による取り込みImport by reference
　本出願は、令和３年（２０２１年）１１月４日に出願された日本出願である特願２０２１－１８０１４１の優先権を主張し、その内容を参照することにより、本出願に取り込む。 This application claims the priority of Japanese Patent Application No. 2021-180141, which was filed in Japan on November 4, 2021, and incorporates the contents thereof into the present application by reference.
　本発明は、内燃機関の制御装置に関する。 The present invention relates to a control device for an internal combustion engine.
　内燃機関の排気管に三元触媒を備え、その前後に組みつけられた排ガスセンサによって、三元触媒内の酸素貯蔵状態を捉え、その結果に応じて空燃比を補正する制御技術が知られている。 A control technology is known in which a three-way catalyst is provided in the exhaust pipe of an internal combustion engine, and the oxygen storage state in the three-way catalyst is detected by exhaust gas sensors installed in front and behind the catalyst, and the air-fuel ratio is corrected according to the result. there is
　本技術分野の背景技術として、以下の先行技術がある。特許文献１（特開２０１１－１７４４２６号公報）には、内燃機関の排気通路に装着された触媒の上流に設けられる第一の空燃比センサと、触媒の下流に設けられる第二の空燃比センサと、少なくとも第一の空燃比センサの出力を参照して触媒からの酸素放出量を推算しその酸素放出量を目標値にフィードバック制御する空燃比制御部と、推算される酸素放出量の誤差を縮小するための学習パラメータを内燃機関における燃料カット発生時に学習する学習部とを具備する空燃比制装置が記載されている。 As background technologies in this technical field, there are the following prior arts. Patent Document 1 (Japanese Patent Laid-Open No. 2011-174426) describes a first air-fuel ratio sensor provided upstream of a catalyst mounted in an exhaust passage of an internal combustion engine, and a second air-fuel ratio sensor provided downstream of the catalyst. and an air-fuel ratio control unit that estimates the amount of oxygen released from the catalyst with reference to at least the output of the first air-fuel ratio sensor and performs feedback control of the amount of oxygen released to a target value; An air-fuel ratio control device is described that includes a learning unit that learns a learning parameter for reduction when a fuel cut occurs in an internal combustion engine.
　また、特許文献２（特開２０２０－１３３４６７号公報）には、記憶装置７６に記憶された写像データは、上流側空燃比や下流側空燃比に応じた変数の時系列データを入力とし、上流側触媒の劣化度合いを示す変数である劣化度合い変数を出力するニューラルネットワークを規定するデータである。ＣＰＵは、写像データによって規定される写像に、上流側空燃比や下流側空燃比に応じた変数の時系列データを入力することによって、上流側触媒の劣化度合い変数を算出する触媒劣化検出装置が記載されている。 Further, in Patent Document 2 (Japanese Patent Laid-Open No. 2020-133467), the mapping data stored in the storage device 76 is input with time-series data of variables corresponding to the upstream air-fuel ratio and the downstream air-fuel ratio. This is data that defines a neural network that outputs a deterioration degree variable, which is a variable that indicates the degree of deterioration of the side catalyst. The CPU inputs time-series data of variables corresponding to the upstream air-fuel ratio and the downstream air-fuel ratio to the mapping defined by the mapping data, thereby calculating the deterioration degree variable of the upstream catalyst. Are listed.
　三元触媒の劣化によって、触媒の酸素貯蔵能が変化する。酸素貯蔵能の変化は空燃比補正制御の判定に影響を与えるため、触媒の劣化度合いを正確に診断する必要がある。触媒の劣化状態の判定を誤ると、最適な空燃比に補正できず、酸素貯蔵能を適切な範囲に維持できない。従来技術では、触媒の前後の排ガスセンサ信号の相関性から触媒の劣化度合いを診断する。新品の触媒では、下流の排ガスセンサ信号の振れ幅は上流の排ガスセンサよりも小さく、劣化した触媒では、下流の排ガスセンサ信号の振れ幅は新品時より大きく、上流の排ガスセンサと同様に変化する。このような触媒の上流及び下流のセンサ信号の相関を用いて、触媒の劣化度を診断する。しかしながら、従来技術は、定常かつ空燃比変動時を前提としており、機会が限定的という課題があった。 　The oxygen storage capacity of the catalyst changes due to the deterioration of the three-way catalyst. Since the change in oxygen storage capacity affects the determination of air-fuel ratio correction control, it is necessary to accurately diagnose the degree of deterioration of the catalyst. If the deterioration state of the catalyst is erroneously determined, the air-fuel ratio cannot be corrected to the optimum, and the oxygen storage capacity cannot be maintained within an appropriate range. In the prior art, the degree of deterioration of the catalyst is diagnosed from the correlation between the exhaust gas sensor signals before and after the catalyst. With a new catalyst, the amplitude of the downstream exhaust gas sensor signal is smaller than that of the upstream exhaust sensor. . The degree of deterioration of the catalyst is diagnosed using the correlation between the upstream and downstream sensor signals of the catalyst. However, the prior art is based on the assumption that the air-fuel ratio is fluctuating at a steady state, and there is a problem that the opportunities are limited.
　このような課題に対して、特許文献２に記載された技術では、劣化判定のため、触媒劣化の関連する時系列データの上流平均Ａ／Ｆ、下流平均Ａ／Ｆ、排ガス流量、回転数、充填効率、触媒温度の六つの入力としたニューラルネットワークにより劣化度合いを表す係数を求める。そして、その係数と閾値の比較によって、触媒の劣化度を判定する。しかし、デバイスや制御の追加等の外乱によって、入力データの前提条件が変更になった場合、入力数を増加させることになり、ニューラルネットワークの規模が拡大し、実装が困難になるおそれがある。 In order to solve such a problem, the technique described in Patent Document 2 uses upstream average A/F, downstream average A/F, exhaust gas flow rate, rotation speed, A coefficient representing the degree of deterioration is obtained from a neural network with six inputs of filling efficiency and catalyst temperature. Then, the degree of deterioration of the catalyst is determined by comparing the coefficient with the threshold value. However, if the preconditions of the input data are changed due to disturbances such as the addition of devices or controls, the number of inputs will be increased, and the scale of the neural network will increase, which may make implementation difficult.
　そこで、本発明は、排ガスセンサの出力の周波数成分を用いて、様々な条件下において触媒の劣化度を正確に判定する技術の提供を目的とする。 Therefore, an object of the present invention is to provide a technique for accurately determining the degree of deterioration of a catalyst under various conditions using the frequency component of the output of an exhaust gas sensor.
　本願において開示される発明の代表的な一例を示せば以下の通りである。すなわち、内燃機関を制御する制御装置であって、前記内燃機関は、排気流路に配置された三元触媒と、前記三元触媒の上流に配置される上流排ガスセンサと、前記三元触媒の下流に配置される下流排ガスセンサとを有し、前記上流排ガスセンサの出力信号及び前記下流排ガスセンサの出力信号の周波数成分を抽出する周波数選択部と、前記周波数選択部の出力に基づいて前記三元触媒の状態を推定する信号処理部と、前記三元触媒の状態から空燃比を演算する演算部とを備える。 A representative example of the invention disclosed in the present application is as follows. That is, a control device for controlling an internal combustion engine, wherein the internal combustion engine includes a three-way catalyst arranged in an exhaust flow path, an upstream exhaust gas sensor arranged upstream of the three-way catalyst, and a three-way catalyst. a frequency selector for extracting frequency components of an output signal of the upstream exhaust gas sensor and an output signal of the downstream exhaust gas sensor; and a frequency selector based on the output of the frequency selector. A signal processing unit for estimating the state of the primary catalyst and a calculation unit for calculating the air-fuel ratio from the state of the three-way catalyst are provided.
　本発明の一態様によれば、様々な条件下において触媒の劣化度を正確に判定できる。前述した以外の課題、構成及び効果は、以下の実施例の説明によって明らかにされる。 According to one aspect of the present invention, the degree of deterioration of the catalyst can be accurately determined under various conditions. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.
本発明の実施例のエンジン制御装置のシステム全体の概略構成図である。1 is a schematic configuration diagram of an entire system of an engine control device according to an embodiment of the present invention; FIG. 内燃機関の排ガスを浄化する後処理システムの構成を示す図であ。1 is a diagram showing the configuration of an aftertreatment system for purifying exhaust gas from an internal combustion engine; FIG. 排ガスの化学種濃度の当量比に対する傾向を示す図である。FIG. 4 is a diagram showing the tendency of the chemical species concentration of exhaust gas with respect to the equivalent ratio; 後処理システムで使用される三元触媒（セリア系）の主な反応過程を示す図である。FIG. 2 is a diagram showing the main reaction process of a three-way catalyst (ceria system) used in an aftertreatment system; 触媒活性化温度以上における排ガス当量比に対する三元触媒の浄化効率の傾向を示す図である。FIG. 4 is a diagram showing the tendency of the purification efficiency of a three-way catalyst with respect to the exhaust gas equivalent ratio above the catalyst activation temperature. 触媒の上流及び下流の空燃比、触媒下流に設置された酸素センサの出力を示す図である。FIG. 4 is a diagram showing the air-fuel ratios upstream and downstream of the catalyst and the output of an oxygen sensor installed downstream of the catalyst; 酸素センサの特性のヒステリシス性を示す図である。FIG. 4 is a diagram showing the hysteresis characteristic of an oxygen sensor; 酸素センサと触媒下流ＮＯｘ濃度の時間的変化を示す図である。FIG. 4 is a diagram showing temporal changes in NOx concentrations downstream of an oxygen sensor and a catalyst; 触媒劣化度合いと三元触媒の酸素貯蔵能力との関係を示す図である。FIG. 4 is a diagram showing the relationship between the degree of catalyst deterioration and the oxygen storage capacity of a three-way catalyst; 酸素貯蔵割合とＮＯｘ浄化効率との関係を示す図である。FIG. 4 is a diagram showing the relationship between the oxygen storage ratio and the NOx purification efficiency; 触媒の上流及び下流の空燃比、触媒下流に設置された酸素センサの出力を示す図である。FIG. 4 is a diagram showing the air-fuel ratios upstream and downstream of the catalyst and the output of an oxygen sensor installed downstream of the catalyst; 新品・中央劣化・完全劣化状態におけるバンドパスフィルタの低～高周波毎のスペクトル変化を示す模式図である。FIG. 4 is a schematic diagram showing spectral changes for each low to high frequency of a band-pass filter in new, centrally deteriorated, and completely deteriorated states. 触媒前後排ガスセンサ信号から触媒劣化診断を実施し、酸素貯蔵量を考慮して空燃比を補正制御する制御モデルのブロック図を示す図である。FIG. 10 is a block diagram of a control model that performs catalyst deterioration diagnosis based on signals from exhaust gas sensors before and after the catalyst, and corrects and controls the air-fuel ratio in consideration of the amount of stored oxygen. 劣化診断部による触媒劣化診断の概要を示す図である。FIG. 4 is a diagram showing an overview of catalyst deterioration diagnosis by a deterioration diagnosis unit; 排ガスセンサ信号の周波数に基づく触媒劣化診断をニューラルネットワークで実現する方法を示す図である。FIG. 10 is a diagram showing a method of realizing catalyst deterioration diagnosis based on the frequency of an exhaust gas sensor signal using a neural network; 図１３に示す制御モデルによる処理のフローチャートである。14 is a flowchart of processing by the control model shown in FIG. 13; 図１３に示す制御モデルによる効果を示す図である。FIG. 14 is a diagram showing the effect of the control model shown in FIG. 13; 本実施例のＥＣＵの検査手順を示す図である。It is a figure which shows the test|inspection procedure of ECU of a present Example. 触媒前後排ガスセンサ信号から触媒劣化診断を実施し、有効Ｃｅ量を考慮して空燃比を補正制御する制御モデルのブロック図を示す図である。FIG. 4 is a block diagram of a control model that performs catalyst deterioration diagnosis from signals from exhaust gas sensors before and after the catalyst, and corrects and controls the air-fuel ratio in consideration of the amount of effective Ce. 図１９に示す制御モデルによる処理のフローチャートである。FIG. 20 is a flowchart of processing by the control model shown in FIG. 19; FIG.
　図面を参照しながら、本発明の第１の実施例による内燃機関の制御装置について説明する。 A control device for an internal combustion engine according to a first embodiment of the present invention will be described with reference to the drawings.
　図１は、エンジン制御装置のシステム全体の概略構成図である。 FIG. 1 is a schematic configuration diagram of the entire system of the engine control device.
　エンジン制御装置は、内燃機関１、流量センサ２、ターボ過給機３、エアバイパス弁４、インタークーラ５、過給温度センサ６、スロットル弁７、吸気マニホールド８、過給圧センサ９、流動強化弁１０、吸気バルブ１１、排気バルブ１３、燃料噴射弁１５、点火プラグ１６、ノックセンサ１７、クランク角センサ１８、ウェイストゲート弁１９、上流排ガスセンサである空燃比センサ２０、排気浄化触媒（三元触媒）２１、下流排ガスセンサである酸素センサ２２、ＥＧＲ（Exhausted Gas Recirculation）管２３、ＥＧＲクーラ２４、ＥＧＲ弁２５、温度センサ２６、差圧センサ２７及びＥＣＵ（Electronic Control Unit）２８を有する。また、排気浄化触媒２１の下流に配置される下流排ガスセンサは、酸素センサ２２に加え、空燃比センサを設けてもよい。 The engine control device includes an internal combustion engine 1, a flow rate sensor 2, a turbocharger 3, an air bypass valve 4, an intercooler 5, a supercharging temperature sensor 6, a throttle valve 7, an intake manifold 8, a supercharging pressure sensor 9, and a flow enhancer. valve 10, intake valve 11, exhaust valve 13, fuel injection valve 15, spark plug 16, knock sensor 17, crank angle sensor 18, waste gate valve 19, air-fuel ratio sensor 20 which is an upstream exhaust gas sensor, exhaust purification catalyst (three-way catalyst) 21, an oxygen sensor 22 which is a downstream exhaust gas sensor, an EGR (Exhausted Gas Recirculation) pipe 23, an EGR cooler 24, an EGR valve 25, a temperature sensor 26, a differential pressure sensor 27 and an ECU (Electronic Control Unit) 28. Further, in addition to the oxygen sensor 22, an air-fuel ratio sensor may be provided as the downstream exhaust gas sensor arranged downstream of the exhaust purification catalyst 21.
　内燃機関１のシリンダには吸気流路及び排気流路が連通している。吸気流路には流量センサ２及び流量センサ２に内蔵された吸気温度センサが設けられる。ターボ過給機３は、吸気流路に接続されたコンプレッサ３ａと排気流路に接続されたタービン３ｂとによって構成される。タービン３ｂは、内燃機関１からの排出ガスが有するエネルギをタービン翼の回転エネルギに変換する。コンプレッサ３ａは、タービン翼と連結されたコンプレッサ翼の回転によって、吸入流路から流入した吸入空気を圧縮する。 An intake channel and an exhaust channel communicate with the cylinders of the internal combustion engine 1 . A flow rate sensor 2 and an intake temperature sensor incorporated in the flow rate sensor 2 are provided in the intake flow path. The turbocharger 3 is composed of a compressor 3a connected to an intake passage and a turbine 3b connected to an exhaust passage. The turbine 3b converts the energy of the exhaust gas from the internal combustion engine 1 into rotational energy of turbine blades. The compressor 3a compresses the intake air that has flowed in from the intake flow path by rotating the compressor blades that are connected to the turbine blades.
　インタークーラ５は、ターボ過給機３のコンプレッサ３ａの下流に設けられ、コンプレッサ３ａにより断熱圧縮されて温度が上昇した吸入空気を冷却する。過給温度センサ６は、インタークーラ５の下流に設けられ、インタークーラ５によって冷却された吸入空気の温度（過給温度）を計測する。スロットル弁７は、インタークーラ５の下流に設けられ、吸入流路を絞り、内燃機関１のシリンダに流入する吸入空気量を制御する。スロットル弁７は、ドライバによるアクセルペダル踏量と独立して弁開度の制御が可能な電子制御式バタフライ弁によって構成される。スロットル弁７の下流の吸気流路には、過給圧センサ９が設けられた吸気マニホールド８が連通している。 The intercooler 5 is provided downstream of the compressor 3a of the turbocharger 3, and cools the intake air whose temperature has been increased by being adiabatically compressed by the compressor 3a. The supercharging temperature sensor 6 is provided downstream of the intercooler 5 and measures the temperature of the intake air cooled by the intercooler 5 (supercharging temperature). The throttle valve 7 is provided downstream of the intercooler 5 and throttles the intake passage to control the amount of intake air flowing into the cylinders of the internal combustion engine 1 . The throttle valve 7 is composed of an electronically controlled butterfly valve whose valve opening can be controlled independently of the amount of depression of the accelerator pedal by the driver. An intake manifold 8 provided with a supercharging pressure sensor 9 communicates with an intake passage downstream of the throttle valve 7 .
　なお、スロットル弁７の下流に設けられた吸気マニホールド８とインタークーラ５とを一体化に構成してもよい。この場合、コンプレッサ３ａの下流からシリンダに至るまでの容積を小さくできるので、加減速の応答性を向上でき、制御性を向上できる。 The intake manifold 8 provided downstream of the throttle valve 7 and the intercooler 5 may be integrated. In this case, since the volume from the downstream of the compressor 3a to the cylinder can be reduced, the responsiveness of acceleration and deceleration can be improved, and the controllability can be improved.
　流動強化弁１０は、吸気マニホールド８の下流に配置され、シリンダに吸入される吸入空気に偏流を生じさせることによって、シリンダ内部の流れの乱れを強化する。後述する排ガス再循環燃焼を実施する際に、流動強化弁１０を閉じることで乱流燃焼を促進し、安定化する。内燃機関１は吸気バルブ１１及び排気バルブ１３を有する。吸気バルブ１１及び排気バルブ１３は、バルブ開閉の位相を連続的に可変するための可変動弁機構をそれぞれ有する。吸気バルブ１１及び排気バルブ１３の可変動弁機構は、バルブの開閉位相を検知するセンサ１２及び１４がそれぞれ設けられる。内燃機関１のシリンダには、シリンダ内に直接燃料を噴射する直接式の燃料噴射弁１５が設けられる。なお、燃料噴射弁１５は、吸気ポート内に燃料を噴射するポート噴射方式でもよい。 The flow enhancement valve 10 is arranged downstream of the intake manifold 8 and enhances turbulence of the flow inside the cylinder by creating a bias in the intake air taken into the cylinder. Turbulent combustion is promoted and stabilized by closing the flow enhancing valve 10 when exhaust gas recirculation combustion, which will be described later, is performed. The internal combustion engine 1 has an intake valve 11 and an exhaust valve 13 . The intake valve 11 and the exhaust valve 13 each have a variable valve mechanism for continuously varying the valve opening/closing phase. The variable valve mechanisms of the intake valve 11 and the exhaust valve 13 are provided with sensors 12 and 14, respectively, for detecting the opening/closing phases of the valves. A cylinder of the internal combustion engine 1 is provided with a direct fuel injection valve 15 that injects fuel directly into the cylinder. The fuel injection valve 15 may be of a port injection type that injects fuel into the intake port.
　内燃機関１のシリンダには、シリンダ内に電極部を露出させ、スパークによって可燃混合気を着火する点火プラグ１６が設けられる。ノックセンサ１７は、シリンダブロックに設けられ、燃焼室内で発生する燃焼圧力振動を起因として生じるシリンダブロック振動を検出して、ノックの有無を検出する。クランク角センサ１８は、クランク軸に設けられ、クランク軸の回転角度に応じた信号を、回転速度を示す信号として後述するＥＣＵ２８へ出力する。 A cylinder of the internal combustion engine 1 is provided with a spark plug 16 that exposes an electrode portion inside the cylinder and ignites a combustible air-fuel mixture with a spark. The knock sensor 17 is provided in the cylinder block and detects the presence or absence of knock by detecting cylinder block vibration caused by combustion pressure vibration generated in the combustion chamber. The crank angle sensor 18 is provided on the crankshaft, and outputs a signal corresponding to the rotation angle of the crankshaft to the ECU 28, which will be described later, as a signal indicating the rotation speed.
　空燃比センサ２０は、ターボ過給機３のタービン３ｂの下流の排気流路に設けられ、検出された排ガス組成、すなわち空燃比を示す信号をＥＣＵ２８へ出力する。排気浄化触媒２１は、三元触媒であり、空燃比センサ２０の下流に設けられ、排ガス中の一酸化炭素、窒素化合物及び未燃炭化水素等の有害排出ガス成分を触媒反応によって浄化する。排気浄化触媒２１の下流には、酸素センサ２２が設けられ、排気浄化触媒２１による浄化後の排ガスに含まれる酸素の濃度を検出する。 The air-fuel ratio sensor 20 is provided in the exhaust passage downstream of the turbine 3b of the turbocharger 3, and outputs a signal indicating the detected exhaust gas composition, that is, the air-fuel ratio, to the ECU 28. The exhaust purification catalyst 21 is a three-way catalyst, is provided downstream of the air-fuel ratio sensor 20, and purifies harmful exhaust gas components such as carbon monoxide, nitrogen compounds, and unburned hydrocarbons in the exhaust gas by catalytic reaction. An oxygen sensor 22 is provided downstream of the exhaust purification catalyst 21 to detect the concentration of oxygen contained in the exhaust gas purified by the exhaust purification catalyst 21 .
　ターボ過給機３には、エアバイパス弁４及びウェイストゲート弁１９が設けられる。エアバイパス弁４は、コンプレッサ３ａの下流からスロットル弁７の上流部までの圧力の過剰な上昇を防ぐために、コンプレッサ３ａの上流と下流とを結ぶバイパス流路上に配置される。過給状態でスロットル弁７が急激に閉止された場合に、ＥＣＵ２８の制御に従ってエアバイパス弁４が開かれることによって、コンプレッサ３ａの下流部の圧縮された吸入空気がバイパス流路を通ってコンプレッサ３ａの上流部に逆流する。その結果、過給圧を直ちに低下して、サージング現象を防止し、コンプレッサ３ａの破損を適切に防止する。 The turbocharger 3 is provided with an air bypass valve 4 and a wastegate valve 19 . The air bypass valve 4 is arranged on a bypass flow path connecting upstream and downstream of the compressor 3a in order to prevent an excessive increase in pressure from the downstream of the compressor 3a to the upstream of the throttle valve 7. As shown in FIG. When the throttle valve 7 is abruptly closed in the supercharging state, the air bypass valve 4 is opened under the control of the ECU 28, so that the compressed intake air in the downstream portion of the compressor 3a passes through the bypass passage to the compressor 3a. flows back upstream of the As a result, the supercharging pressure is immediately lowered to prevent the surging phenomenon and appropriately prevent damage to the compressor 3a.
　ウェイストゲート弁１９は、タービン３ｂの上流と下流とを結ぶバイパス流路上に配置される。ウェイストゲート弁１９は、ＥＣＵ２８の制御によって、過給圧に対して自由に弁開度が制御可能な電動弁である。過給圧センサ９が検知した過給圧に基づいてＥＣＵ２８によってウェイストゲート弁１９の開度が調整されると、排ガスの一部がバイパス流路を通過することによって、排ガスがタービン３ｂに与える仕事を減じて、過給圧を目標圧に保持できる。 The wastegate valve 19 is arranged on a bypass flow path that connects upstream and downstream of the turbine 3b. The wastegate valve 19 is an electrically operated valve whose valve opening degree can be freely controlled with respect to the supercharging pressure under the control of the ECU 28 . When the opening degree of the waste gate valve 19 is adjusted by the ECU 28 based on the supercharging pressure detected by the supercharging pressure sensor 9, a part of the exhaust gas passes through the bypass flow path, thereby reducing the work given to the turbine 3b by the exhaust gas. can be reduced to maintain the boost pressure at the target pressure.
　ＥＧＲ管２３は、排気浄化触媒２１の下流の排気流路と、コンプレッサ３ａの上流部の吸気流路とを連通し、排気浄化触媒２１の下流から排ガスを分流して、コンプレッサ３ａの上流部へ還流する。ＥＧＲ管２３に設けられたＥＧＲクーラ２４は、排ガスを冷却する。ＥＧＲ弁２５は、ＥＧＲクーラ２４の下流に設けられ、排ガスの流量を制御する。ＥＧＲ管２３には、ＥＧＲ弁２５の上流部の排ガスの温度を検出する温度センサ２６と、ＥＧＲ弁２５の上流と下流との差圧を検出する差圧センサ２７とが設けられている。 The EGR pipe 23 communicates with an exhaust passage downstream of the exhaust purification catalyst 21 and an intake passage upstream of the compressor 3a, and diverts the exhaust gas from the downstream of the exhaust purification catalyst 21 to the upstream of the compressor 3a. Reflux. An EGR cooler 24 provided in the EGR pipe 23 cools the exhaust gas. The EGR valve 25 is provided downstream of the EGR cooler 24 and controls the flow rate of exhaust gas. The EGR pipe 23 is provided with a temperature sensor 26 that detects the temperature of the exhaust gas upstream of the EGR valve 25 and a differential pressure sensor 27 that detects a differential pressure between upstream and downstream of the EGR valve 25 .
　ＥＣＵ２８は、ＣＰＵ、ＲＯＭ、ＲＡＭ、Ａ／Ｄ変換器、及びドライバ回路等を有し、エンジン制御装置の各構成要素を制御したり、各種データ処理を実行したりする演算回路である。ＥＣＵ２８には前述した各種センサと各種アクチュエータとが接続されている。ＥＣＵ２８は、スロットル弁７、可変動弁機構付き吸排気バルブ１１、１３、燃料噴射弁１５、ＥＧＲ弁２５等のアクチュエータの動作を制御する。また、ＥＣＵ２８は、各種センサから入力された信号に基づいて、内燃機関１の運転状態を検知して、運転状態に応じて決定したタイミングで点火プラグ１６を点火する。 The ECU 28 is an arithmetic circuit that has a CPU, ROM, RAM, A/D converter, driver circuit, etc., and controls each component of the engine control device and executes various data processing. The various sensors and actuators described above are connected to the ECU 28 . The ECU 28 controls the operations of actuators such as the throttle valve 7, the intake and exhaust valves 11 and 13 with variable valve mechanisms, the fuel injection valve 15, the EGR valve 25, and the like. The ECU 28 also detects the operating state of the internal combustion engine 1 based on signals input from various sensors, and ignites the spark plug 16 at a timing determined according to the operating state.
　図２（Ａ）は、内燃機関の排ガスを浄化する後処理システムの構成を示す図である。排ガス浄化触媒には三元触媒が用いられる。三元触媒の浄化効率を最適点に保持することを目的として、三元触媒の上流部と下流部とのそれぞれに排ガス組成を検出するセンサが設けられる。後処理システムでは、上流部に空燃比センサ２０、下流部に酸素センサ２２が設けられる。この構成によれば、三元触媒に流入する排ガスの空燃比を計測でき、触媒浄化後の排ガスに含まれる酸素の有無を検知できる。 FIG. 2(A) is a diagram showing the configuration of an aftertreatment system that purifies exhaust gas from an internal combustion engine. A three-way catalyst is used as the exhaust gas purification catalyst. For the purpose of maintaining the purification efficiency of the three-way catalyst at an optimum point, sensors for detecting the exhaust gas composition are provided at each of the upstream and downstream portions of the three-way catalyst. In the aftertreatment system, an air-fuel ratio sensor 20 is provided upstream, and an oxygen sensor 22 is provided downstream. According to this configuration, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst can be measured, and the presence or absence of oxygen contained in the exhaust gas after catalyst purification can be detected.
　図２（Ｂ）は、排ガスの当量比（＝理論空燃比÷空燃比）と空燃比センサ２０の出力との関係を示す図である。当量比が増加するほど（リッチ化するほど）、センサ出力は減少する傾向を示す。空燃比センサ２０は、図４の関係を予め取得することによって、排ガスのリーン状態からリッチ状態まで広範囲に精度良く当量比を検出できる点が特徴である。 FIG. 2(B) is a diagram showing the relationship between the equivalence ratio (=theoretical air-fuel ratio/air-fuel ratio) of the exhaust gas and the output of the air-fuel ratio sensor 20. FIG. As the equivalence ratio increases (richer), the sensor output tends to decrease. The air-fuel ratio sensor 20 is characterized in that it can accurately detect the equivalence ratio over a wide range from the exhaust gas lean state to the rich state by obtaining the relationship shown in FIG. 4 in advance.
　図２（Ｃ）は、排ガスの当量比と酸素センサ２２の出力との関係を示す図である。酸素センサ２２は、排ガスに含まれる酸素濃度と空気中の酸素濃度との濃度差にともなう起電力に従った信号を出力する。酸素センサ２２は、リーン条件では概ね最小起電力を出力し、リッチ条件では最大起電力を出力し、理論空燃比（当量比１．０）にて出力が急変する特性を有する。センサ出力の変化タイミングを捉え、これを空燃比制御へフィードバックすることで、排ガス当量比を理論空燃比近傍に保持できる。 FIG. 2(C) is a diagram showing the relationship between the equivalence ratio of the exhaust gas and the output of the oxygen sensor 22. FIG. The oxygen sensor 22 outputs a signal according to the electromotive force associated with the concentration difference between the oxygen concentration contained in the exhaust gas and the oxygen concentration in the air. The oxygen sensor 22 has a characteristic of outputting a generally minimum electromotive force under lean conditions, outputting a maximum electromotive force under rich conditions, and suddenly changing the output at a stoichiometric air-fuel ratio (equivalence ratio of 1.0). By capturing the change timing of the sensor output and feeding it back to the air-fuel ratio control, the exhaust gas equivalence ratio can be maintained near the theoretical air-fuel ratio.
　図３は、排ガスの化学種濃度の当量比に対する傾向を示す図である。炭化水素系燃料の燃焼ガス組成は、理論空燃比を境にしてリッチ側ではＣＯ（一酸化炭素）及びＨ２（水素）が増加し、リーン側ではＯ２（酸素）が増加する傾向を示す。さらに、ＮＯｘ（窒素酸化物）は、理論空燃比の若干リーン側に極大値を示し、そのリーン側及びリッチ側で減少する傾向を示す。ＨＣ（未燃炭化水素）は、燃焼に至らないで排出される成分であり、過剰にリーン化又はリッチ化すると正常燃焼に至らずにＨＣが排出される傾向がある。燃料と空気（酸素）が過不足なく供給される理論空燃比条件においても、高温な燃焼ガス中では、Ｈ２Ｏ（水）やＣＯ２（二酸化炭素）にならずにＣＯ（一酸化炭素）やＮＯｘ（窒素酸化物）が一定量排出されるために、後処理システムによる適切な浄化処理が必要となる。 FIG. 3 is a diagram showing the tendency of chemical species concentration in exhaust gas with respect to the equivalence ratio. Combustion gas compositions of hydrocarbon-based fuels tend to increase CO (carbon monoxide) and H2 (hydrogen) on the rich side and O2 (oxygen) on the lean side of the stoichiometric air-fuel ratio. Furthermore, NOx (nitrogen oxides) shows a maximum value slightly on the lean side of the stoichiometric air-fuel ratio, and tends to decrease on the lean and rich sides. HC (unburned hydrocarbons) is a component that is emitted without being burned, and excessive lean or enrichment tends to result in HC being emitted without leading to normal combustion. Even under the stoichiometric air-fuel ratio condition in which fuel and air (oxygen) are supplied in just the right amount, CO (carbon monoxide) and NOx (carbon monoxide) and NOx ( Nitrogen oxides) are emitted in a certain amount, so an appropriate purification treatment by an aftertreatment system is required.
　図４は、後処理システムで使用される三元触媒（セリア系）の主な反応過程を示す図である。三元触媒反応過程は主に、酸化反応、ＮＯｘ還元反応、酸素貯蔵・放出反応からなる。 Fig. 4 is a diagram showing the main reaction process of a three-way catalyst (ceria-based) used in the post-treatment system. The three-way catalytic reaction process mainly consists of an oxidation reaction, a NOx reduction reaction, and an oxygen storage/release reaction.
　酸化反応では、リッチ条件又は高温条件で生成するＣＯ、Ｈ２、ＨＣが酸素と反応し、無害なＣＯ２とＨ２Ｏを生成する。未燃炭化水素（ＨＣ）にはメタン、プロパン、エチレン、ブタンなどの炭化水素成分が含まれ、それぞれ異なる速度で反応が進行する。ＮＯｘ還元反応は、主にＣＯとＮＯとの反応で表され、無害なＣＯ２とＮ２が生成される。酸素貯蔵・放出反応では触媒材料であるＣｅ（セリウム）を介して、酸素の貯蔵・放出とＨＣ、ＣＯ及びＮＯの酸化反応及び還元反応が進行する。すなわち、二酸化セリウム（ＣｅＯ２）とＣＯ及びＨＣとの反応によって、無害なＣＯ２とＨ２Ｏが生成され、三酸化二セリウム（Ｃｅ２Ｏ３）とＮＯとの反応によって、無害なＮ２が生成される。このとき、同時に生成されるＣｅＯ２とＣｅ２Ｏ３とのバランスによって、三元触媒の酸素貯蔵割合が規定される。すなわち、触媒中のＣｅ２Ｏ３が全てＣｅＯ２となると、ＮＯと反応できず、ＮＯが浄化できない。この様に、三元触媒の浄化効率を適切に保持するためには、ＣｅＯ２とＣｅ２Ｏ３とのバランス、すなわち酸素貯蔵割合を所定値に保持する必要がある。前述の全ての反応過程は、触媒温度に強く依存しており、始動後早期に活性化温度以上となる様に、触媒温度を適切に管理する必要がある。なお、本実施例で示すシステムでは、セリア系の三元触媒を用いる構成としているが、本発明はこれに限定されない。同様の効果を示す他の材料を用いた触媒でも、制御モデルの定数を調整することによって、発明の構成を変えることなく、同様の効果を奏することができる。また、触媒反応には、図４で述べた反応機構以外にも、水性ガスシフト反応などが用いられる場合があるが、これらの反応機構についても、制御モデル定数の調整で対応できる。 In the oxidation reaction, CO, H2, and HC generated under rich or high temperature conditions react with oxygen to generate harmless CO2 and H2O. Unburned hydrocarbons (HC) include hydrocarbon components such as methane, propane, ethylene, and butane, which react at different rates. The NOx reduction reaction is represented mainly by the reaction of CO and NO to produce harmless CO2 and N2. In the oxygen storage/release reaction, the storage/release of oxygen and the oxidation and reduction reactions of HC, CO, and NO proceed via Ce (cerium), which is a catalyst material. That is, the reaction of cerium dioxide (CeO2) with CO and HC produces harmless CO2 and H2O, and the reaction of cerium trioxide (Ce2O3) with NO produces harmless N2. At this time, the oxygen storage ratio of the three-way catalyst is defined by the balance between CeO2 and Ce2O3 that are produced at the same time. That is, when all of the Ce2O3 in the catalyst becomes CeO2, it cannot react with NO and cannot purify NO. In this way, in order to properly maintain the purification efficiency of the three-way catalyst, it is necessary to maintain the balance between CeO2 and Ce2O3, that is, the oxygen storage ratio, at a predetermined value. All of the reaction processes described above strongly depend on the catalyst temperature, and it is necessary to appropriately manage the catalyst temperature so that it reaches the activation temperature or higher in an early stage after starting. Although the system shown in this embodiment uses a ceria-based three-way catalyst, the present invention is not limited to this. Catalysts using other materials exhibiting similar effects can also achieve similar effects by adjusting the constants of the control model without changing the configuration of the invention. In addition to the reaction mechanism described in FIG. 4, the catalytic reaction may also use the water-gas shift reaction or the like. These reaction mechanisms can also be handled by adjusting the control model constants.
　図５は、触媒活性化温度以上における排ガス当量比に対する三元触媒の浄化効率の傾向を示す図である。三元触媒の浄化効率特性は理論空燃比を境にして変化し、リーン条件下では、ＣＯとＨＣの浄化効率は概ね９０％以上に保持され、ＮＯｘ浄化効率は当量比が減少するに従って減少する。一方、リッチ側では、当量比が増加するに従ってＨＣ及びＣＯの浄化効率が減少する。理論空燃比近傍では、ＮＯｘ、ＨＣ、ＣＯのいずれの浄化効率も９０％以上であり、この点を三元点と呼ぶ。三元触媒では、三元点である理論空燃比に当量比を保つことによって浄化効率を高位に保つように制御される。 FIG. 5 is a diagram showing the tendency of the purification efficiency of the three-way catalyst with respect to the exhaust gas equivalence ratio above the catalyst activation temperature. The purification efficiency characteristics of the three-way catalyst change with the stoichiometric air-fuel ratio as a boundary. Under lean conditions, the CO and HC purification efficiency is generally maintained at 90% or more, and the NOx purification efficiency decreases as the equivalence ratio decreases. . On the other hand, on the rich side, the purification efficiency of HC and CO decreases as the equivalence ratio increases. In the vicinity of the theoretical air-fuel ratio, the purification efficiency of NOx, HC, and CO is 90% or more, and this point is called the ternary point. The three-way catalyst is controlled to keep the purification efficiency at a high level by maintaining the equivalence ratio at the stoichiometric air-fuel ratio, which is the three-way point.
　図６は、当量比１．０を中心にして、空燃比をリーン側及びリッチ側に時間経過に従ってステップ変動させた際の、触媒下流の空燃比、及び触媒下流に設置された酸素センサ２２の出力を示す図である。当量比が理論空燃比である場合にも、触媒下流にはごく微量の酸素が排出されることによって、中間状態に保持される。ステップ的にリーン側に変化させると、リア当量比は徐々に変化し、酸素センサ２２の出力は遅れ時間を経た後、最小値側に急激に変化する。一方、リーン側よりリッチ側に空燃比を変化させると、リア当量比は徐々に変化し、酸素センサ２２の出力は大きい遅れを経た後に急激に変化するステリシス性を示す。この様にリーンからリッチへの変化と、リッチからリーンへの変化では、遅れ時間が異なる傾向がある。これは、図４で述べた三元触媒のＣｅＯ２とＣｅ２Ｏ３の反応速度が異なることに起因する。反応速度は触媒温度や排ガス流量に依存するので、前述するヒステリシス性も触媒温度と排ガス流量によって変化する。 FIG. 6 shows the air-fuel ratio downstream of the catalyst and the oxygen sensor 22 installed downstream of the catalyst when the air-fuel ratio is varied stepwise to the lean side and the rich side over time, centering on the equivalence ratio of 1.0. FIG. 10 is a diagram showing the output; Even when the equivalence ratio is the stoichiometric air-fuel ratio, it is maintained in an intermediate state by discharging a very small amount of oxygen downstream of the catalyst. When the ratio is changed stepwise to the lean side, the rear equivalence ratio gradually changes, and the output of the oxygen sensor 22 rapidly changes to the minimum value side after a delay time. On the other hand, when the air-fuel ratio is changed from the lean side to the rich side, the rear equivalence ratio gradually changes, and the output of the oxygen sensor 22 exhibits steresis characteristics in which it rapidly changes after a large delay. In this way, the change from lean to rich and the change from rich to lean tend to have different delay times. This is due to the difference in reaction rate between CeO2 and Ce2O3 in the three-way catalyst described in FIG. Since the reaction rate depends on the catalyst temperature and exhaust gas flow rate, the hysteresis described above also changes depending on the catalyst temperature and exhaust gas flow rate.
　図７は、酸素センサ２２の特性のヒステリシス性を示す図である。酸素センサ２２の静特性は、図２に示す通りである。一方、酸素センサ２２にも触媒材料が使用されており、検出遅れによるヒステリシス性を有する。すなわち、リーンからリッチ状態に急激に変化する場合には、センサ出力の変化タイミングが当量比のリッチ側にシフトし、リッチからリーン状態に急激に変化する場合には、センサ出力の変化タイミングが当量比のリーン側にシフトする。さらに、前述した挙動は、センサを構成する材料特性劣化や温度の影響を受ける。制御モデルでは、触媒の劣化の他、センサの劣化や温度の影響を含んだ動特性の変化を考慮する必要がある。 FIG. 7 is a diagram showing the hysteresis characteristic of the oxygen sensor 22. FIG. The static characteristics of the oxygen sensor 22 are shown in FIG. On the other hand, the oxygen sensor 22 also uses a catalytic material and has hysteresis due to detection delay. That is, when the lean state changes rapidly to the rich state, the change timing of the sensor output shifts to the rich side of the equivalence ratio, and when the rich state changes suddenly to the lean state, the change timing of the sensor output shifts to the equivalence ratio. Shift to the lean side of the ratio. Furthermore, the behavior described above is affected by deterioration of the material properties of the sensor and temperature. In the control model, it is necessary to consider changes in dynamic characteristics including sensor deterioration and temperature effects in addition to catalyst deterioration.
　図８は、理論空燃比で制御された状態から、モータリング運転（燃料カット）期間を経て、再度理論空燃比状態でファイアリング運転を実施する場合の酸素センサ２２と触媒下流ＮＯｘ濃度の時間的変化を示す図である。燃料カット後、再度理論空燃比によるファイアリング運転を開始すると、酸素センサ２２の検出値は、図６に示すように遅れて増加する。触媒下流のＮＯｘ濃度は酸素センサ２２が復帰するまでの遅れ期間にスパイク的にＮＯｘが排出される挙動を示す。一方、燃料カット後、再度ファイアリング運転を開始する際に、一旦リッチ補正を実施した後に理論空燃比制御を実施する場合には、触媒下流のＮＯｘ排出を防止できる。酸素センサ２２は触媒の下流ガスの酸素状態を検出しているため、酸素センサ２２が反応する時点において、既に触媒内部状態は酸素貯蔵状態が最大又は最小状態にまで変化している。そのため、酸素センサ２２の反応後にリッチ補正制御を停止する制御方法では、触媒にとって制御タイミングの遅れ期間で酸素が不足するために、ＨＣを適切に防止できない。そのことから、内燃機関の空燃比制御においては、外部から直接観測できない触媒内部の状態を考慮して、適切な期間にリッチ補正を制御する必要がある。 FIG. 8 shows the oxygen sensor 22 and the NOx concentration downstream of the catalyst when the firing operation is performed again in the stoichiometric air-fuel ratio state after the motoring operation (fuel cut) period from the state controlled at the stoichiometric air-fuel ratio. It is a figure which shows a change. After the fuel cut, when the firing operation with the stoichiometric air-fuel ratio is started again, the detected value of the oxygen sensor 22 increases with a delay as shown in FIG. The NOx concentration downstream of the catalyst shows a behavior in which NOx is discharged in a spike during the delay period until the oxygen sensor 22 is restored. On the other hand, when the firing operation is started again after the fuel cut, if the stoichiometric air-fuel ratio control is performed after performing the rich correction once, NOx emissions downstream of the catalyst can be prevented. Since the oxygen sensor 22 detects the oxygen state of the gas downstream of the catalyst, the internal state of the catalyst has already changed to the maximum or minimum oxygen storage state at the time the oxygen sensor 22 reacts. Therefore, in the control method of stopping the rich correction control after the reaction of the oxygen sensor 22, HC cannot be prevented appropriately because oxygen is insufficient for the catalyst during the control timing delay period. Therefore, in the air-fuel ratio control of the internal combustion engine, it is necessary to consider the state inside the catalyst, which cannot be directly observed from the outside, and control the rich correction during an appropriate period.
　図９は、触媒劣化度合いと三元触媒の酸素貯蔵能力との関係を示す図である。触媒劣化とは、熱的な影響や燃料に含まれる硫黄による被毒の影響を受けて、触媒作用が低下した状態である。触媒劣化が進行するに従って、酸素貯蔵能力が低下する。以下、酸素貯蔵能力の変化が三元触媒の浄化作用に与える影響について述べる。 FIG. 9 is a diagram showing the relationship between the degree of catalyst deterioration and the oxygen storage capacity of the three-way catalyst. Catalyst deterioration is a state in which the catalytic action is lowered due to the influence of heat and poisoning by sulfur contained in the fuel. As the catalyst deterioration progresses, the oxygen storage capacity decreases. The effect of changes in oxygen storage capacity on the purification action of the three-way catalyst will be described below.
　図１０は、酸素貯蔵割合とＮＯｘ浄化効率との関係を示す図である。酸素貯蔵割合が所定値を超過するとＮＯｘ浄化効率が著しく悪化する。これは、図４で述べたように、ＮＯｘの浄化には、触媒中のＣｅ２Ｏ３が重要であり、Ｃｅ２Ｏ３が全て反応してＣｅＯ２に変化すると、ＮＯと反応ができず、ＮＯが浄化できないためである。このことから、図５で述べたように、触媒浄化効率を高位に保つためには、触媒入口の排ガス空燃比を三元点に保つだけでなく、酸素貯蔵割合が所定の範囲内となるように、触媒入口の排ガス空燃比を適宜補正制御する必要がある。 FIG. 10 is a diagram showing the relationship between the oxygen storage ratio and the NOx purification efficiency. When the oxygen storage ratio exceeds a predetermined value, NOx purification efficiency deteriorates significantly. This is because, as described in FIG. 4, Ce2O3 in the catalyst is important for purifying NOx, and if all Ce2O3 reacts and changes to CeO2, it cannot react with NO and cannot purify NO. be. For this reason, as described in FIG. 5, in order to keep the catalyst purification efficiency at a high level, it is necessary not only to keep the exhaust gas air-fuel ratio at the catalyst inlet at the three-way point, but also to keep the oxygen storage ratio within a predetermined range. In addition, it is necessary to appropriately correct and control the exhaust gas air-fuel ratio at the catalyst inlet.
　図１１は、新品触媒と劣化触媒において当量比１．０を中心にして、空燃比をリーン側及びリッチ側に時間経過に従ってステップ変動させた際の、触媒下流の当量比、触媒下流に設置された酸素センサ２２（下流排ガスセンサ）の出力を示す図である。 FIG. 11 shows the equivalence ratio downstream of the catalyst and the equivalence ratio installed downstream of the catalyst when the air-fuel ratio is changed stepwise to the lean side and the rich side over time with the equivalence ratio of 1.0 as the center for the new catalyst and the deteriorated catalyst. FIG. 10 is a diagram showing an output of an oxygen sensor 22 (downstream exhaust gas sensor).
　劣化した触媒は、新品触媒と比較して空燃比のリーン及びリッチ側への変化に対する酸素センサ２２の出力の変化の遅れが減少している。これは、触媒の酸素貯蔵割合の時間的推移で説明できる。すなわち、劣化によって触媒の酸素貯蔵能力の減少によって、より早く酸素貯蔵割合が最大値、最小値に達することで、下流への酸素放出が早められ、酸素センサ２２の出力の変化の遅れが減少するからである。従って、図８で説明した燃料カット復帰後のリッチ補正期間は、触媒の劣化状態を考慮して設定される必要がある。 The deteriorated catalyst reduces the delay in change in the output of the oxygen sensor 22 with respect to changes in the air-fuel ratio to the lean and rich sides compared to the new catalyst. This can be explained by the temporal transition of the oxygen storage rate of the catalyst. That is, the oxygen storage capacity of the catalyst decreases due to deterioration, and the oxygen storage rate reaches the maximum and minimum values more quickly, which accelerates the release of oxygen downstream and reduces the delay in change in the output of the oxygen sensor 22. It is from. Therefore, the rich correction period after returning from fuel cut described in FIG. 8 must be set in consideration of the deterioration state of the catalyst.
　図１２は、新品・中央劣化・完全劣化状態におけるバンドパスフィルタの低～高周波毎のスペクトル変化を示す模式図である。実際のスペクトルは、上流の排ガス状態によって様々に変化する。 FIG. 12 is a schematic diagram showing spectral changes for each low to high frequency band-pass filter in new, centrally deteriorated, and completely deteriorated states. The actual spectrum varies in various ways depending on the state of upstream exhaust gas.
　上段から下段へ新品、中程度劣化、完全劣化状態の順で示す。また、左に上流排ガスセンサ（空燃比センサ２０）の信号のバンドパスフィルタ通過化後の信号、右に下流排ガスセンサ（酸素センサ２２）の信号のバンドパスフィルタ通過化後の信号を示す。上流排ガスセンサ信号は、排ガスの空燃比変化と同期して変化するため、触媒の劣化状態にかかわらず、同様のスペクトルとなる。一方、下流排ガスセンサ信号は、触媒の酸素貯蔵能に影響されるため、劣化状態毎に周波数のスペクトルが異なる。 From top to bottom, new, moderately deteriorated, and completely deteriorated are shown in that order. The left side shows the signal of the upstream exhaust gas sensor (air-fuel ratio sensor 20) after band-pass filtering, and the right side shows the signal of the downstream exhaust gas sensor (oxygen sensor 22) after band-pass filtering. Since the upstream exhaust gas sensor signal changes in synchronism with changes in the air-fuel ratio of the exhaust gas, it has the same spectrum regardless of the deterioration state of the catalyst. On the other hand, since the downstream exhaust gas sensor signal is affected by the oxygen storage capacity of the catalyst, the frequency spectrum differs for each deterioration state.
　新品触媒において、触媒は十分な酸素貯蔵能を有することから、下流排ガスセンサ信号は小さく緩やかな変化を示すため、低い周波数のスペクトルとなる。中程度劣化した触媒において、触媒のＣｅの減少による酸素貯蔵能の減少によって、下流排ガスセンサ信号は新品状態より大きく振れる変化を示す。そのため、新品状態より低い周波数から高い周波数のスペクトルとなる。完全に劣化した触媒では、中程度劣化触媒より更にＣｅが減少するため、上流排ガスセンサ信号と近い変化となる。周波数変化は中程度劣化触媒より大きくなり、上流排ガスセンサ信号のスペクトルに近づく。 　In a new catalyst, the catalyst has sufficient oxygen storage capacity, so the downstream exhaust gas sensor signal shows a small and gradual change, resulting in a low frequency spectrum. In the moderately deteriorated catalyst, the downstream exhaust gas sensor signal shows a change that swings more than in the new state due to the decrease in the oxygen storage capacity due to the decrease in Ce of the catalyst. Therefore, the spectrum is from frequencies lower to higher than those in the new state. With a completely degraded catalyst, Ce decreases more than with a moderately degraded catalyst, so the change is similar to that of the upstream exhaust gas sensor signal. The frequency change is greater than for the moderately aged catalyst and approaches the spectrum of the upstream exhaust gas sensor signal.
　このような触媒劣化状態毎の様々な減衰パターンと触媒劣化の関係性を予めニューラルネットワーク１３０１ｂに学習させることで、触媒劣化レベルを判定できる。本実施例では、一例として完全劣化、中程度劣化、新品の３水準に分けるため、高周波、中周波、低周波の三つの周波数を用いるが、使用できる周波数帯の個数を限定するのものではなく、三つより多い又は三つより少なくても適用できる。例えば、高周波、低周波の二つのバンドパスフィルタによって、上流排ガスセンサ信号を周波数分解した２信号と、下流排ガスセンサ信号を周波数分解した２信号によって触媒の劣化状態を判定してもよい。 By making the neural network 1301b learn in advance the relationship between various attenuation patterns for each catalyst deterioration state and the catalyst deterioration, the catalyst deterioration level can be determined. In this embodiment, three frequencies of high frequency, medium frequency, and low frequency are used in order to divide into three levels of complete deterioration, moderate deterioration, and new product as an example, but the number of frequency bands that can be used is not limited. , more than three or less than three can be applied. For example, the degradation state of the catalyst may be determined based on two signals obtained by frequency-decomposing the upstream exhaust gas sensor signal and two signals obtained by frequency-decomposing the downstream exhaust gas sensor signal using two band-pass filters of high frequency and low frequency.
　また、各フィルタに設定される周波数帯は固定的な値ではなく、内燃機関の運転条件などに従って調整される変数でもよい。例えば、各バンドパスフィルタの通過周波数帯域と内燃機関の回転数を関連付けたテーブルを準備し、外テーブルを参照して、回転数が上がると周波数を高くするとよい。排ガスセンサ信号の周波数情報から触媒劣化の周波数特性を抽出できるが、実際の信号波形は一定の形状ではないため、信号処理が困難である。そのため、本発明では、センサの周波数情報と触媒劣化とを関連付けて学習させたニューラルネットワーク１３０１ｂを用いて、触媒の劣化を診断する。 Also, the frequency band set for each filter may not be a fixed value, but may be a variable that is adjusted according to the operating conditions of the internal combustion engine. For example, it is preferable to prepare a table that associates the pass frequency band of each bandpass filter with the rotational speed of the internal combustion engine, refer to the outer table, and increase the frequency as the rotational speed increases. Although the frequency characteristics of catalyst deterioration can be extracted from the frequency information of the exhaust gas sensor signal, the actual signal waveform does not have a constant shape, so signal processing is difficult. Therefore, in the present invention, the deterioration of the catalyst is diagnosed using the neural network 1301b that has been learned by associating the frequency information of the sensor with the deterioration of the catalyst.
　また、触媒の劣化を診断するモデルは、ニューラルネットワーク１３０１ｂではなく、他のモデル（例えば、回帰モデル）を用いて、触媒の劣化を診断してもよい。 Also, the model for diagnosing deterioration of the catalyst may be a model other than the neural network 1301b (for example, a regression model) for diagnosing deterioration of the catalyst.
　図１３は、触媒の上流及び下流の排ガスセンサ信号から触媒劣化診断を実施し、酸素貯蔵量を考慮して空燃比を補正制御する制御モデルのブロック図を示す図である。 FIG. 13 is a block diagram of a control model that performs catalyst deterioration diagnosis from exhaust gas sensor signals upstream and downstream of the catalyst, and corrects and controls the air-fuel ratio in consideration of the oxygen storage amount.
　図１３に示す制御モデルは、劣化診断部１３０１、ＯＳＣ推定モデル選択部１３０２、ＯＳＣ推定部１３０３、触媒制御部１３０４及び空燃比補正量演算部１３０５を有する。 　The control model shown in FIG.
　劣化診断部１３０１は、触媒の上流及び下流の排ガスセンサ信号が入力され、触媒の劣化度合いを診断し、周波数選択部１３０１ａ及びニューラルネットワーク１３０１ｂによって構成される。周波数選択部１３０１ａは、図１２に示すような排ガスセンサ信号の周波数特性を抽出するために、複数のフィルタを有する。図１３は、一例として周波数毎の三つのローパスフィルタを組み合わせてバンドパスフィルタを構成する。 A deterioration diagnosis unit 1301 receives exhaust gas sensor signals upstream and downstream of the catalyst, diagnoses the degree of deterioration of the catalyst, and is composed of a frequency selection unit 1301a and a neural network 1301b. The frequency selector 1301a has a plurality of filters for extracting the frequency characteristics of the exhaust gas sensor signal as shown in FIG. In FIG. 13, as an example, three low-pass filters for each frequency are combined to form a band-pass filter.
　触媒の上流及び下流の排ガスセンサ信号は、高周波、中周波、低周波のカットオフ周波数が設定されているローパスフィルタを通過し、各周波数帯に分解するため演算部に入力され、バンドパスフィルタにてフィルタ処理される。例えば、バンドパスフィルタは、高周波、中周波、低周波の三つの周波数帯が用意され、各バンドパスフィルタは、上流排ガスセンサ信号をフィルタ処理した３信号と、下流排ガスセンサ信号をフィルタ処理した３信号を出力する。
ＢＰＦ３(バンドパスフィルタ３)
　元の波形－ＬＰＦ３通過後信号
ＢＰＦ２（バンドパスフィルタ２）
　ＬＰＦ３通過後信号－ＬＰＦ２通過後信号
ＢＰＦ１（バンドパスフィルタ１）
　ＬＰＦ２通過後信号－ＬＰＦ１通過後信号 The exhaust gas sensor signals upstream and downstream of the catalyst pass through low-pass filters with cutoff frequencies of high, medium, and low frequencies, are input to the calculation section to be decomposed into each frequency band, and are sent to the band-pass filter. filtered by For example, the band-pass filters are prepared for three frequency bands of high frequency, medium frequency, and low frequency, and each band-pass filter has 3 signals obtained by filtering the upstream exhaust gas sensor signal and 3 signals obtained by filtering the downstream exhaust gas sensor signal. Output a signal.
BPF3 (band pass filter 3)
Original waveform-Signal after passing through LPF3 BPF2 (band pass filter 2)
Signal after passing through LPF3 - Signal after passing through LPF2 BPF1 (band pass filter 1)
Signal after passing LPF2 - Signal after passing LPF1
　周波数選択部１３０１ａは、ローパスフィルタを組み合わせてバンドパスフィルタを構成したが、ハイパスフィルタを組み合わせてバンドパスフィルタを構成したり、高周波のハイパスフィルタと中周波のバンドパスフィルタと低周波のローパスフィルタの三つを使用してもよい。また、周波数選択部１３０１ａは、フィルタではなく、フーリエ変換によって排ガスセンサ信号の周波数成分を抽出してもよい。 The frequency selection unit 1301a configures a band-pass filter by combining low-pass filters. You can use three. Also, the frequency selection unit 1301a may extract the frequency component of the exhaust gas sensor signal by Fourier transform instead of the filter.
　ニューラルネットワーク１３０１ｂは、触媒の劣化状態と関連付けられた周波数情報を学習しており、周波数選択部１３０１ａから出力されるバンドパスフィルタ通過後の信号を受信し、入力信号が新品、中程度劣化、完全劣化の３状態のいずれであるかを示す劣化診断結果（例えば、各状態の確信度）を出力する。例えば、ニューラルネットワーク１３０１ｂは、触媒の新品状態、中程度劣化状態、及び完全劣化状態の各状態において、バンドパスフィルタ１を通過した触媒の上流及び下流の排ガスセンサ信号の相対関係、バンドパスフィルタ２を通過した触媒の上流及び下流の排ガスセンサ信号の相対関係、バンドパスフィルタ３を通過した触媒の上流及び下流の排ガスセンサ信号の相対関係を教師データとして学習したモデルである。 The neural network 1301b learns frequency information associated with the deterioration state of the catalyst, receives the signal after passing through the band-pass filter output from the frequency selection unit 1301a, and determines whether the input signal is new, moderately deteriorated, or perfect. A degradation diagnosis result (for example, the degree of certainty of each state) indicating which of the three states of degradation is present is output. For example, the neural network 1301b detects the relative relationship between the upstream and downstream exhaust gas sensor signals of the catalyst that have passed through the band-pass filter 1, the band-pass filter 2 , and the relative relationship between the upstream and downstream exhaust gas sensor signals of the catalyst that have passed through the band-pass filter 3 are learned as teacher data.
　ＯＳＣ推定モデル選択部１３０２は、劣化診断結果を受信し、劣化診断結果に応じたＯＳＣ推定モデルを選択する。ＯＳＣ推定部１３０３は、選択された酸素ストレージ能（ＯＳＣ）推定モデルを用いて推定酸素貯蔵量（推定ＯＳＣ）を算出する。触媒制御部１３０４は、推定ＯＳＣを受信し、運転条件に従って、推定ＯＳＣによって浄化率が低下しない空燃比の補正量を算出する。運転条件は、例えば、スロットル開度、エンジン負荷、エンジン回転数、温度、気圧などである。空燃比補正量演算部１３０５は、空燃比目標値と触媒制御部１３０４が算出した空燃比の補正量によって補正後目標空燃比を出力する。 The OSC estimation model selection unit 1302 receives the deterioration diagnosis result and selects an OSC estimation model according to the deterioration diagnosis result. The OSC estimator 1303 calculates an estimated oxygen storage capacity (estimated OSC) using the selected oxygen storage capacity (OSC) estimation model. Catalyst control unit 1304 receives the estimated OSC and calculates an air-fuel ratio correction amount that does not lower the purification rate due to the estimated OSC, according to the operating conditions. The operating conditions are, for example, throttle opening, engine load, engine speed, temperature, atmospheric pressure, and the like. An air-fuel ratio correction amount calculation unit 1305 outputs a post-correction target air-fuel ratio based on the air-fuel ratio target value and the air-fuel ratio correction amount calculated by the catalyst control unit 1304 .
　図１４は、劣化診断部１３０１による触媒劣化診断の概要を示す図である。劣化診断部１３０１に入力された触媒の上流及び下流の排ガスセンサ信号は、バンドパスフィルタによって周波数分解される。バンドパスフィルタは、高周波、中周波、低周波の三つのバンドパスフィルタであり、各バンドパスフィルタは、上流排ガスセンサ信号を周波数分解した３信号と、下流排ガスセンサ信号を周波数分解した３信号をニューラルネットワーク１３０１ｂへ入力する。ニューラルネットワーク１３０１ｂは、各周波数の強度と触媒の劣化度とを関連付けて学習しており、入力信号から触媒の劣化状態を完全劣化、中程度劣化、新品の３水準に分別して、劣化診断結果を出力する。 FIG. 14 is a diagram showing an overview of catalyst deterioration diagnosis by the deterioration diagnosis unit 1301. FIG. The exhaust gas sensor signals upstream and downstream of the catalyst input to the deterioration diagnosis unit 1301 are frequency-decomposed by a bandpass filter. The band-pass filters are three band-pass filters of high frequency, medium frequency, and low frequency, and each band-pass filter generates three signals obtained by frequency-resolving the upstream exhaust gas sensor signal and three signals obtained by frequency-resolving the downstream exhaust gas sensor signal. Input to neural network 1301b. The neural network 1301b learns by associating the intensity of each frequency with the degree of deterioration of the catalyst, classifies the deterioration state of the catalyst from the input signal into three levels of complete deterioration, moderate deterioration, and new condition, and outputs the deterioration diagnosis result. Output.
　図１５は、排ガスセンサ信号の周波数に基づく触媒劣化診断をニューラルネットワーク１３０１ｂで実現する方法を示す図である。ニューラルネットワークモデルは、人間の脳神経回路の仕組みを模した数学モデルであり、モデルを構成する各ニューロンには、重みとバイアスが設定される。また、ニューロンには活性化関数と呼ばれる関数が定義される。活性化関数には、ロジスティック関数やランプ関数などが適宜設定されるとよい。複数のニューロンで一つの層が形成され、入力層と出力層との間に中間層が設定される。ニューロン数や中間層の層数の増加によって、より複雑な入出力関係を近似できる。近似精度とモデル規模との間にはトレードオフの関係があり、双方の要求を満足する両立点が選定される。排ガスセンサ信号の周波数を入力層に、触媒劣化診断を出力層に、それぞれ設定し、各ニューロンの重みとバイアスを（教師有り）機械学習することによって、入出力関係を近似できる。機械学習のアルゴリズムには、誤差逆伝播法を適用できる。 FIG. 15 is a diagram showing a method of realizing catalyst deterioration diagnosis based on the frequency of the exhaust gas sensor signal with the neural network 1301b. A neural network model is a mathematical model that imitates the mechanism of human brain neural circuits, and weights and biases are set for each neuron that constitutes the model. A function called an activation function is defined in a neuron. A logistic function, a ramp function, or the like may be appropriately set as the activation function. A plurality of neurons form one layer, and an intermediate layer is set between the input layer and the output layer. More complex input-output relationships can be approximated by increasing the number of neurons and the number of hidden layers. There is a trade-off relationship between approximation accuracy and model scale, and a compatible point that satisfies both requirements is selected. By setting the frequency of the exhaust gas sensor signal in the input layer and the catalyst deterioration diagnosis in the output layer, and performing (supervised) machine learning on the weight and bias of each neuron, the input/output relationship can be approximated. Backpropagation can be applied to machine learning algorithms.
　図１６は、図１３に示す制御モデルにより、触媒の上流及び下流の排ガスセンサ信号をバンドパスフィルタにより三つの周波数帯に分解し、それらをニューラルネットワーク１３０１ｂに入力し、出力された劣化診断結果から空燃比補正を実行する処理のフローチャートである。 FIG. 16 uses the control model shown in FIG. 13 to decompose the exhaust gas sensor signals upstream and downstream of the catalyst into three frequency bands using a band-pass filter, input them to the neural network 1301b, and output deterioration diagnosis results. 4 is a flowchart of processing for executing air-fuel ratio correction;
　ステップ１０１では、劣化診断部１３０１が、触媒の上流及び下流の排ガスセンサ信号の入力を受け、ステップ１０２では、周波数選択部１３０１ａが、入力された排ガスセンサ信号をバンドパスフィルタによって三つの周波数帯に分解する。ステップ１０３では、ニューラルネットワーク１３０１ｂが、周波数帯に分解された触媒の上流及び下流の排ガスセンサ信号の入力を受ける。ステップ１０４では、触媒の劣化状態と関連付けられた周波数情報を学習済のニューラルネットワーク１３０１ｂが、入力された触媒の上流及び下流の排ガスセンサ信号から触媒の劣化を推定する。ステップ１０５では、ＯＳＣ推定モデル選択部１３０２が、劣化診断結果に従って、劣化状態に応じたＯＳＣモデルを選択する。ＯＳＣモデルは、触媒の劣化状態に応じて複数用意されており（例えば、図４の酸素貯蔵割り合いの式のΨに乗じる係数が異なるもの）、触媒の劣化状態に応じて適切なＯＳＣモデルが選択される。ステップ１０６では、ＯＳＣ推定部１３０３が、選択したＯＳＣモデルを用いて、触媒の酸素貯蔵量（ＯＳＣ）を推定する。ステップ１０７では、触媒制御部１３０４が、推定酸素貯蔵量に基づいて空燃比補正量を算出する。ステップ１０８では、空燃比補正量演算部１３０５が、空燃比目標値とステップ１０７で算出された空燃比補正量を用いて、補正後目標空燃比を算出する。 In step 101, the deterioration diagnosis unit 1301 receives input of exhaust gas sensor signals upstream and downstream of the catalyst. disassemble. In step 103, the neural network 1301b receives input of exhaust gas sensor signals upstream and downstream of the catalyst resolved into frequency bands. In step 104, the neural network 1301b, which has learned frequency information associated with the deterioration state of the catalyst, estimates the deterioration of the catalyst from the input exhaust gas sensor signals upstream and downstream of the catalyst. At step 105, the OSC estimation model selection unit 1302 selects an OSC model according to the deterioration state according to the deterioration diagnosis result. A plurality of OSC models are prepared according to the state of deterioration of the catalyst (for example, the coefficients to be multiplied by Ψ in the oxygen storage ratio formula in FIG. 4 are different), and an appropriate OSC model is selected according to the state of deterioration of the catalyst. selected. At step 106, the OSC estimator 1303 estimates the oxygen storage capacity (OSC) of the catalyst using the selected OSC model. At step 107, catalyst control unit 1304 calculates an air-fuel ratio correction amount based on the estimated oxygen storage amount. At step 108 , the air-fuel ratio correction amount calculator 1305 uses the air-fuel ratio target value and the air-fuel ratio correction amount calculated at step 107 to calculate the post-correction target air-fuel ratio.
　図１７は、図１３に示す制御モデルによる効果を示す図である。 FIG. 17 is a diagram showing the effects of the control model shown in FIG.
　理論空燃比で制御された状態から、モータリング運転（燃料カット）期間を経て、再度理論空燃比状態でファイアリング運転を実施する。燃料カット後、再度ファイアリング運転を開始する際に、一旦リッチ補正を実施した後、理論空燃比制御を実施し、触媒の下流へのＮＯｘ排出を防止する。本実施例によって、触媒の劣化状態を高精度で診断できるため、リッチ補正を適切な期間に実施でき、触媒下流へのＮＯｘ及びＨＣの排出を低減できる。 From the state controlled at the stoichiometric air-fuel ratio, after the motoring operation (fuel cut) period, the firing operation is performed again at the stoichiometric air-fuel ratio. When the firing operation is started again after the fuel cut, the rich correction is performed once, and then the stoichiometric air-fuel ratio control is performed to prevent NOx emissions downstream of the catalyst. According to this embodiment, the deterioration state of the catalyst can be diagnosed with high accuracy, so the rich correction can be performed in an appropriate period, and NOx and HC emissions downstream of the catalyst can be reduced.
　ここまで、上流及び下流の排ガスセンサ信号からの劣化推定について説明したが、上流排ガスセンサの出力値の変化は小さいので、下流排ガスセンサ（酸素センサ２２）の出力だけから触媒の劣化を推定してもよい。 Up to this point, the deterioration estimation from the upstream and downstream exhaust gas sensor signals has been explained. However, since the change in the output value of the upstream exhaust gas sensor is small, the deterioration of the catalyst is estimated only from the output of the downstream exhaust gas sensor (oxygen sensor 22). good too.
　本実施例の制御モデルは、出力センサ故障診断機能を有してもよい。例えば、ニューラルネットワーク１３０１ｂが、上流排ガスセンサ及び下流排ガスセンサの正常時の出力信号を学習した後、上流排ガスセンサの出力信号及び下流排ガスセンサの出力信号と、正常時の各排ガスセンサの出力信号との類似度によって、排ガスセンサの異常を診断してもよい。そして、排ガスセンサが異常であると判定された場合、ニューラルネットワーク１３０１ｂによる触媒の状態の推定を停止するとよい。 The control model of this embodiment may have an output sensor failure diagnosis function. For example, after the neural network 1301b learns the normal output signals of the upstream exhaust gas sensor and the downstream exhaust gas sensor, the output signal of the upstream exhaust gas sensor, the output signal of the downstream exhaust gas sensor, and the output signal of each exhaust gas sensor under normal conditions. An abnormality in the exhaust gas sensor may be diagnosed based on the degree of similarity between the two. Then, when it is determined that the exhaust gas sensor is abnormal, the neural network 1301b should stop estimating the state of the catalyst.
　さらに、本実施例の制御モデルは、ヒータ故障診断機能を有してもよい。下流排ガスセンサである酸素センサ２２は、センサに使用される物質（ジルコニア）が活性化する温度を維持するヒータを有している。例えば、劣化診断部１３０１が酸素センサ２２のヒータ温度を監視しており、ニューラルネットワーク１３０１ｂが、ヒータの通電状態と正常時のヒータ温度を学習した後、ヒータの通電状態と温度変化の正常時との類似度によって、ヒータの異常を診断してもよい。そして、ヒータが異常であると判定された場合、ニューラルネットワーク１３０１ｂによる触媒の状態の推定を停止するとよい。 Furthermore, the control model of this embodiment may have a heater failure diagnosis function. The oxygen sensor 22, which is a downstream exhaust gas sensor, has a heater that maintains the temperature at which the material (zirconia) used for the sensor is activated. For example, the deterioration diagnosis unit 1301 monitors the heater temperature of the oxygen sensor 22, and after the neural network 1301b learns the heater energization state and normal heater temperature, You may diagnose the abnormality of a heater by the similarity of . Then, when it is determined that the heater is abnormal, the neural network 1301b should stop estimating the state of the catalyst.
　図１８は、本実施例のＥＣＵ２８の触媒状態推定機能の検査手順を示す図である。 FIG. 18 is a diagram showing the inspection procedure of the catalyst state estimation function of the ECU 28 of this embodiment.
　学習済のニューラルネットワーク１３０１ｂに、理論空燃比で制御された状態から、モータリング運転（燃料カット）期間を経て、再度理論空燃比状態でファイアリング運転を実施した時の触媒が新品時、中程度劣化時、及び完全劣化時の触媒の上流及び下流の排ガスセンサ信号を連結して、バンドパスフィルタに通した後の信号を模擬したテストデータを入力する。そして、該信号からバンドパスフィルタに通す前の触媒の上流及び下流の排ガスセンサの出力信号を作成する。作成した信号をＥＣＵ２８に入力し、燃料カット後に実施されるリッチ補正量が触媒の劣化状態に合わせて変化し、想定した期間でリッチ補正が実施されているかを検査する。 When the learned neural network 1301b is under control with the stoichiometric air-fuel ratio, after a period of motoring operation (fuel cut), firing operation is performed again with the stoichiometric air-fuel ratio, the catalyst is new, moderate. The upstream and downstream exhaust gas sensor signals of the catalyst at the time of deterioration and at the time of complete deterioration are connected, and test data simulating the signal after passing through the band-pass filter is input. Then, output signals of exhaust gas sensors upstream and downstream of the catalyst before being passed through a band-pass filter are created from the signal. The generated signal is input to the ECU 28, and it is checked whether the amount of rich correction performed after the fuel cut changes in accordance with the deterioration state of the catalyst and whether the rich correction is performed within an assumed period.
　次に、図１９及び図２０を参照して、触媒の有効Ｃｅ量を推定する構成について説明する。 Next, a configuration for estimating the effective Ce amount of the catalyst will be described with reference to FIGS. 19 and 20. FIG.
　図１９は、触媒前後排ガスセンサ信号から触媒劣化診断を実施し、有効Ｃｅ量を考慮して空燃比を補正制御する制御モデルのブロック図を示す図である。 FIG. 19 is a block diagram of a control model that performs catalyst deterioration diagnosis from the signal of the exhaust gas sensor before and after the catalyst, and corrects and controls the air-fuel ratio in consideration of the effective Ce amount.
　図１９に示す制御モデルは、劣化診断部１９０１、ＯＳＣ推定部１９０３、触媒制御部１３０４及び空燃比補正量演算部１３０５を有する。 　The control model shown in FIG.
　劣化診断部１９０１は、触媒の上流及び下流の排ガスセンサ信号が入力され、有効Ｃｅ量を推定し、周波数選択部１９０１ａ及びニューラルネットワーク１９０１ｂによって構成される。周波数選択部１９０１ａは、図１３に示す周波数選択部１３０１ａと同じ構成を有し、入力された触媒の上流及び下流の排ガスセンサ信号を、高周波、中周波、低周波の各周波数帯に分解して、上流排ガスセンサ信号をフィルタ処理した３信号と、下流排ガスセンサ信号をフィルタ処理した３信号を出力する。 A deterioration diagnosis unit 1901 receives exhaust gas sensor signals upstream and downstream of the catalyst, estimates the amount of effective Ce, and is composed of a frequency selection unit 1901a and a neural network 1901b. The frequency selection unit 1901a has the same configuration as the frequency selection unit 1301a shown in FIG. , three signals obtained by filtering the upstream exhaust gas sensor signal and three signals obtained by filtering the downstream exhaust gas sensor signal.
　ニューラルネットワーク１９０１ｂは、触媒の有効のＣｅ量と関連付けられた周波数情報を学習しており、周波数選択部１９０１ａから出力されるバンドパスフィルタ通過後の信号を受信し、入力信号に対応する有効Ｃｅ量を推定する。推定された有効Ｃｅ量は、ＯＳＣ推定部１９０３に入力される。ＯＳＣ推定部１９０３は、推定された有効Ｃｅ量を用いて酸素貯蔵量（ＯＳＣ）を推定する。 The neural network 1901b learns frequency information associated with the effective Ce amount of the catalyst, receives the signal after passing through the bandpass filter output from the frequency selection unit 1901a, and determines the effective Ce amount corresponding to the input signal. to estimate The estimated effective Ce amount is input to OSC estimation section 1903 . The OSC estimator 1903 estimates the oxygen storage capacity (OSC) using the estimated available Ce amount.
　以後、触媒制御部１３０４及び空燃比補正量演算部１３０５は、図１３と同様の手順によって補正後目標空燃比を演算子、出力する。 After that, the catalyst control unit 1304 and the air-fuel ratio correction amount calculation unit 1305 operate and output the post-correction target air-fuel ratio in the same procedure as in FIG.
　図２０は、図１９に示す制御モデルにより、触媒の上流及び下流の排ガスセンサ信号をバンドパスフィルタにより三つの周波数帯に分解し、それらをニューラルネットワーク１３０１ｂに入力し、出力された有効Ｃｅ量から空燃比補正を実行する処理のフローチャートである。 FIG. 20 uses the control model shown in FIG. 19 to decompose the exhaust gas sensor signals upstream and downstream of the catalyst into three frequency bands using a band-pass filter, input them to the neural network 1301b, and output the effective Ce amount. 4 is a flowchart of processing for executing air-fuel ratio correction;
　ステップ１１１では、劣化診断部１９０１が、触媒の上流及び下流の排ガスセンサ信号の入力を受け、ステップ１１２では、周波数選択部１９０１ａが、入力された排ガスセンサ信号をバンドパスフィルタによって三つの周波数帯に分解する。ステップ１１３では、ニューラルネットワーク１３０１ｂが、周波数帯に分解された触媒の上流及び下流の排ガスセンサ信号の入力を受ける。ステップ１１４では、触媒の有効Ｃｅ量と関連付けられた周波数情報を学習済のニューラルネットワーク１９０１ｂが、入力された触媒の上流及び下流の排ガスセンサ信号のから有効Ｃｅ量を推定する。ステップ１１５では、ＯＳＣ推定部１３０３が、推定された有効Ｃｅ量に従って、触媒の酸素貯蔵量（ＯＳＣ）を推定する。ステップ１１６では、触媒制御部１３０４が、推定酸素貯蔵量に基づいて空燃比補正量を算出する。ステップ１１７では、空燃比補正量演算部１３０５が、空燃比目標値とステップ１１６で算出された空燃比補正量を用いて、補正後目標空燃比を算出する。 In step 111, the deterioration diagnosis unit 1901 receives input of exhaust gas sensor signals upstream and downstream of the catalyst. disassemble. In step 113, the neural network 1301b receives input of exhaust gas sensor signals upstream and downstream of the catalyst resolved into frequency bands. In step 114, the neural network 1901b, which has learned frequency information associated with the effective Ce amount of the catalyst, estimates the effective Ce amount from the input upstream and downstream exhaust gas sensor signals of the catalyst. At step 115, the OSC estimator 1303 estimates the oxygen storage capacity (OSC) of the catalyst according to the estimated effective Ce amount. At step 116, catalyst control unit 1304 calculates an air-fuel ratio correction amount based on the estimated oxygen storage amount. At step 117 , the air-fuel ratio correction amount calculation unit 1305 calculates the post-correction target air-fuel ratio using the air-fuel ratio target value and the air-fuel ratio correction amount calculated at step 116 .
　以上に説明したように、本実施例の制御装置（ＥＣＵ２８）は、上流排ガスセンサ（空燃比センサ２０）の出力信号及び下流排ガスセンサ（酸素センサ２２）の出力信号の周波数成分を抽出する周波数選択部１３０１ａと、周波数選択部１３０１ａの出力に基づいて三元触媒（排気浄化触媒２１）の状態を推定する信号処理部（ニューラルネットワーク１３０１ｂ）と、三元触媒の状態から空燃比を演算する空燃比補正量演算部１３０５とを備えるので、排ガスセンサの出力の周波数成分を用いて、触媒の劣化を適切に推定でき、排ガス中の有害成分を増大させない適切なエンジン制御ができる。すなわち、バンドパスフィルタ通過後の周波数毎のそれぞれの相対関係に触媒の状態との関連によって、触媒の劣化を診断でき、エンジン状態、デバイスや制御の追加等の様々な条件下においても正確に劣化度を診断できる。 As described above, the control device (ECU 28) of this embodiment performs frequency selection for extracting the frequency components of the output signal of the upstream exhaust gas sensor (air-fuel ratio sensor 20) and the output signal of the downstream exhaust gas sensor (oxygen sensor 22). a signal processing unit (neural network 1301b) that estimates the state of the three-way catalyst (exhaust purification catalyst 21) based on the output of the frequency selection unit 1301a; and an air-fuel ratio that calculates the air-fuel ratio from the state of the three-way catalyst. Since the correction amount calculation unit 1305 is provided, the deterioration of the catalyst can be appropriately estimated using the frequency component of the output of the exhaust gas sensor, and appropriate engine control can be performed without increasing harmful components in the exhaust gas. In other words, it is possible to diagnose the deterioration of the catalyst based on the relationship between the relative relationship of each frequency after passing through the band-pass filter and the state of the catalyst. degree can be diagnosed.
　また、周波数選択部１３０１ａは、三元触媒の新品状態に対応する第１周波数の帯域を通過する第１フィルタと、三元触媒の劣化状態に対応する第２周波数の帯域を通過する第２フィルタとを用いて、上流排ガスセンサの出力信号と前記下流排ガスセンサの出力信号をフィルタリング処理するので、触媒の劣化に関する特徴量を抽出して、ニューラルネットワーク１３０１ｂの高精度な学習が可能となる。 Further, the frequency selection unit 1301a includes a first filter that passes a first frequency band corresponding to the new state of the three-way catalyst and a second filter that passes a second frequency band corresponding to the deteriorated state of the three-way catalyst. is used to filter the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor, extracting the feature amount related to the deterioration of the catalyst, it is possible to perform highly accurate learning of the neural network 1301b.
　また、周波数選択部１３０１ａは、三元触媒の新品状態に対応する第１周波数の帯域を通過する第１フィルタと、三元触媒の劣化状態に対応する第２周波数の帯域を通過する第２フィルタと、第１周波数と第２周波数の間の第３周波数の帯域を通過する第３フィルタとを用いて、上流排ガスセンサの出力信号と下流排ガスセンサの出力信号をフィルタリング処理するので、触媒の劣化を３状態に判定でき、空燃比補正量を細かく設定できる。 Further, the frequency selection unit 1301a includes a first filter that passes a first frequency band corresponding to the new state of the three-way catalyst and a second filter that passes a second frequency band corresponding to the deteriorated state of the three-way catalyst. and a third filter that passes a third frequency band between the first frequency and the second frequency to filter the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor. can be determined in three states, and the air-fuel ratio correction amount can be finely set.
　また、信号処理部の出力に基づいて、三元触媒の劣化状態に応じた酸素ストレージ能推定モデルを選択するモデル選択部を設けたので、劣化状態に応じた酸素ストレージ能を正確に推定でき、空燃比の補正精度を向上できる。 In addition, since the model selector is provided for selecting an oxygen storage capacity estimation model according to the state of deterioration of the three-way catalyst based on the output of the signal processor, the oxygen storage capacity can be accurately estimated according to the state of deterioration. It is possible to improve the correction accuracy of the air-fuel ratio.
　また、ニューラルネットワーク１３０１ｂは、上流排ガスセンサの出力信号及び下流排ガスセンサの出力信号と、正常時の各排ガスセンサの出力信号との類似度によって、排ガスセンサの異常を判定するので、触媒の劣化判定と共に、センサの故障を判定できる。 In addition, the neural network 1301b determines whether the exhaust gas sensor is abnormal based on the degree of similarity between the output signal of the upstream exhaust gas sensor, the output signal of the downstream exhaust gas sensor, and the output signal of each exhaust gas sensor during normal operation. Together, sensor failure can be determined.
　また、ニューラルネットワーク１３０１ｂは、酸素センサ２２のヒータを監視し、ヒータの温度変化の正常時との類似度によって、ヒータの異常を判定するので、触媒の劣化判定と共に、ヒータの故障を判定できる。 In addition, the neural network 1301b monitors the heater of the oxygen sensor 22 and determines whether the heater is abnormal based on the degree of similarity between the temperature change of the heater and the normal state. Therefore, it is possible to determine the deterioration of the catalyst as well as the failure of the heater.
　第１フィルタの通過周波数、第２フィルタの通過周波数、及び第３フィルタの通過周波数の少なくとも一つを、内燃機関の動作点に従って変更するので、空燃比補正の精度を向上できる。 Since at least one of the pass frequency of the first filter, the pass frequency of the second filter, and the pass frequency of the third filter is changed according to the operating point of the internal combustion engine, the accuracy of air-fuel ratio correction can be improved.
　なお、本発明は前述した実施例に限定されるものではなく、添付した特許請求の範囲の趣旨内における様々な変形例及び同等の構成が含まれる。例えば、前述した実施例は本発明を分かりやすく説明するために詳細に説明したものであり、必ずしも説明した全ての構成を備えるものに本発明は限定されない。また、ある実施例の構成の一部を他の実施例の構成に置き換えてもよい。また、ある実施例の構成に他の実施例の構成を加えてもよい。また、各実施例の構成の一部について、他の構成の追加・削除・置換をしてもよい。 It should be noted that the present invention is not limited to the above-described embodiments, and includes various modifications and equivalent configurations within the scope of the attached claims. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to those having all the described configurations. Also, part of the configuration of one embodiment may be replaced with the configuration of another embodiment. Moreover, the configuration of another embodiment may be added to the configuration of one embodiment. Further, additions, deletions, and replacements of other configurations may be made for a part of the configuration of each embodiment.
　また、前述した各構成、機能、処理部、処理手段等は、それらの一部又は全部を、例えば集積回路で設計する等により、ハードウェアで実現してもよく、プロセッサがそれぞれの機能を実現するプログラムを解釈し実行することにより、ソフトウェアで実現してもよい。 In addition, each configuration, function, processing unit, processing means, etc. described above may be realized by hardware, for example, by designing a part or all of them with an integrated circuit, and the processor realizes each function. It may be realized by software by interpreting and executing a program to execute.
　各機能を実現するプログラム、テーブル、ファイル等の情報は、メモリ、ハードディスク、ＳＳＤ（Ｓｏｌｉｄ　Ｓｔａｔｅ　Ｄｒｉｖｅ）等の記憶装置、又は、ＩＣカード、ＳＤカード、ＤＶＤ等の記録媒体に格納することができる。 Information such as programs, tables, and files that implement each function can be stored in storage devices such as memory, hard disks, SSDs (Solid State Drives), or recording media such as IC cards, SD cards, and DVDs.
　また、制御線や情報線は説明上必要と考えられるものを示しており、実装上必要な全ての制御線や情報線を示しているとは限らない。実際には、ほとんど全ての構成が相互に接続されていると考えてよい。 In addition, the control lines and information lines indicate those that are considered necessary for explanation, and do not necessarily indicate all the control lines and information lines necessary for implementation. In practice, it can be considered that almost all configurations are interconnected.

Claims (14)

  1. 　内燃機関を制御する制御装置であって、
    　前記内燃機関は、排気流路に配置された三元触媒と、前記三元触媒の上流に配置される上流排ガスセンサと、前記三元触媒の下流に配置される下流排ガスセンサとを有し、
    　前記上流排ガスセンサの出力信号及び前記下流排ガスセンサの出力信号の周波数成分を抽出する周波数選択部と、
    　前記周波数選択部の出力に基づいて前記三元触媒の状態を推定する信号処理部と、
    　前記三元触媒の状態から空燃比を演算する演算部とを備える制御装置。     A control device for controlling an internal combustion engine,
    The internal combustion engine has a three-way catalyst arranged in an exhaust passage, an upstream exhaust gas sensor arranged upstream of the three-way catalyst, and a downstream exhaust gas sensor arranged downstream of the three-way catalyst,
    a frequency selection unit that extracts frequency components of the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor;
    a signal processing unit that estimates the state of the three-way catalyst based on the output of the frequency selection unit;
    and a computing unit that computes an air-fuel ratio from the state of the three-way catalyst.
  2. 　請求項１に記載の制御装置であって、
    　前記周波数選択部は、前記三元触媒の新品状態に対応する第１周波数の帯域を通過する第１フィルタと、前記三元触媒の劣化状態に対応する第２周波数の帯域を通過する第２フィルタとを用いて、前記上流排ガスセンサの出力信号と前記下流排ガスセンサの出力信号をフィルタリング処理する制御装置。     The control device according to claim 1,
    The frequency selection unit includes a first filter that passes a first frequency band corresponding to the new state of the three-way catalyst and a second filter that passes a second frequency band corresponding to the deteriorated state of the three-way catalyst. and filtering the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor.
  3. 　請求項２に記載の制御装置であって、
    　前記周波数選択部は、前記第１フィルタと、前記第２フィルタと、前記第１周波数と前記第２周波数の間の第３周波数の帯域を通過する第３フィルタとを用いて、前記上流排ガスセンサの出力信号と前記下流排ガスセンサの出力信号をフィルタリング処理する制御装置。     The control device according to claim 2,
    The frequency selection unit uses the first filter, the second filter, and a third filter that passes a third frequency band between the first frequency and the second frequency to select the upstream exhaust gas sensor. and the output signal of the downstream exhaust gas sensor.
  4. 　請求項１に記載の制御装置であって、
    　前記信号処理部は、前記周波数選択部から出力された信号の振幅情報を入力変数とし、前記三元触媒の劣化状態を出力変数とするニューラルネットワークモデルによって前記三元触媒の状態を推定する制御装置。     The control device according to claim 1,
    The signal processing unit is a control device for estimating the state of the three-way catalyst using a neural network model having amplitude information of the signal output from the frequency selection unit as an input variable and a deterioration state of the three-way catalyst as an output variable. .
  5. 　請求項３に記載の制御装置であって、
    　前記信号処理部は、前記第１フィルタでフィルタリング処理された前記上流排ガスセンサの出力信号と、前記第１フィルタでフィルタリング処理された前記下流排ガスセンサの出力信号と、前記第２フィルタでフィルタリング処理された前記上流排ガスセンサの出力信号と、前記第２フィルタでフィルタリング処理された前記下流排ガスセンサの出力信号と、前記第３フィルタでフィルタリング処理された前記上流排ガスセンサの出力信号と、前記第３フィルタでフィルタリング処理された前記下流排ガスセンサの出力信号とを入力とし、前記三元触媒が新品状態であることを示す第１値と、前記三元触媒の完全劣化状態であることを示す第２値と、前記三元触媒が中程度劣化状態であることを示す第３値とを前記三元触媒の推定状態として出力する制御装置。     The control device according to claim 3,
    The signal processing unit outputs an output signal of the upstream exhaust gas sensor filtered by the first filter, an output signal of the downstream exhaust gas sensor filtered by the first filter, and an output signal filtered by the second filter. The output signal of the upstream exhaust gas sensor filtered by the second filter, the output signal of the downstream exhaust gas sensor filtered by the second filter, the output signal of the upstream exhaust gas sensor filtered by the third filter, and the third filter and the output signal of the downstream exhaust gas sensor filtered by a first value indicating that the three-way catalyst is in a new state and a second value indicating that the three-way catalyst is in a completely deteriorated state. and a third value indicating that the three-way catalyst is in a moderately deteriorated state as an estimated state of the three-way catalyst.
  6. 　請求項１に記載の制御装置であって、
    　前記演算部は、前記信号処理部の出力に基づいて、前記三元触媒の劣化状態に応じた酸素ストレージ能推定モデルを選択するモデル選択部を有する制御装置。     The control device according to claim 1,
    The control device, wherein the calculation unit has a model selection unit that selects an oxygen storage capacity estimation model according to the deterioration state of the three-way catalyst based on the output of the signal processing unit.
  7. 　請求項６に記載の制御装置であって、
    　前記演算部は、前記選択された酸素ストレージ能推定モデルによって推定された酸素ストレージ能に基づいて、補正された空燃比を演算する制御装置。     A control device according to claim 6,
    The computing unit computes a corrected air-fuel ratio based on the oxygen storage capacity estimated by the selected oxygen storage capacity estimation model.
  8. 　請求項１に記載の制御装置であって、
    　前記信号処理部は、前記上流排ガスセンサの出力信号及び前記下流排ガスセンサの出力信号と、正常時の各排ガスセンサの出力信号との類似度によって、前記上流排ガスセンサ及び前記下流排ガスセンサの異常を判定する制御装置。     The control device according to claim 1,
    The signal processing unit detects an abnormality of the upstream exhaust gas sensor and the downstream exhaust gas sensor based on the degree of similarity between the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor and the output signal of each exhaust gas sensor during normal operation. Control device to judge.
  9. 　請求項８に記載の制御装置であって、
    　前記上流排ガスセンサ又は前記下流排ガスセンサが異常であると判定された場合、前記三元触媒の状態の推定を停止する制御装置。     A control device according to claim 8,
    A control device that stops estimating the state of the three-way catalyst when it is determined that the upstream exhaust gas sensor or the downstream exhaust gas sensor is abnormal.
  10. 　請求項１に記載の制御装置であって、
    　前記下流排ガスセンサは、温度を維持するヒータを有し、
    　前記信号処理部は、前記ヒータを監視し、前記ヒータの温度変化の正常時との類似度によって、前記ヒータの異常を判定する制御装置。     The control device according to claim 1,
    The downstream exhaust gas sensor has a heater that maintains the temperature,
    The signal processing unit monitors the heater and determines whether the heater is abnormal based on the degree of similarity between the temperature change of the heater and the normal state.
  11. 　請求項１０に記載の制御装置であって、
    　前記ヒータが異常であると判定された場合、前記三元触媒の状態の推定を停止する制御装置。     A control device according to claim 10,
    A control device that stops estimating the state of the three-way catalyst when it is determined that the heater is abnormal.
  12. 　請求項１に記載の制御装置であって、
    　前記三元触媒が新品状態、中程度劣化状態、及び完全劣化状態の前記上流排ガスセンサの出力信号及び前記下流排ガスセンサの出力信号を模擬したテストデータを、前記信号処理部に入力し、適切な空燃比が出力されるかを検査する機能を有する制御装置。     The control device according to claim 1,
    Test data simulating the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor when the three-way catalyst is in a new state, a moderately deteriorated state, and a completely deteriorated state are input to the signal processing unit, and an appropriate A control device that has a function to check whether the air-fuel ratio is output.
  13. 　請求項３に記載の制御装置であって、
    　前記第１フィルタの通過周波数、前記第２フィルタの通過周波数、及び前記第３フィルタの通過周波数の少なくとも一つを、前記内燃機関の動作点に従って変更する制御装置。     The control device according to claim 3,
    A control device that changes at least one of the pass frequency of the first filter, the pass frequency of the second filter, and the pass frequency of the third filter according to the operating point of the internal combustion engine.
  14. 　制御装置が実行する内燃機関の制御方法であって、
    　前記内燃機関は、排気流路に配置された三元触媒と、前記三元触媒の上流に配置される上流排ガスセンサと、前記三元触媒の下流に配置される下流排ガスセンサとを有し、
    　前記制御方法は、
    　前記制御装置が、前記上流排ガスセンサの出力信号及び前記下流排ガスセンサの出力信号の周波数成分を抽出し、
    　前記制御装置が、前記抽出された周波数成分の振幅に基づいて前記三元触媒の状態を推定し、
    　前記制御装置が、前記三元触媒の状態から空燃比を演算する制御方法。     A control method for an internal combustion engine executed by a control device, comprising:
    The internal combustion engine has a three-way catalyst arranged in an exhaust passage, an upstream exhaust gas sensor arranged upstream of the three-way catalyst, and a downstream exhaust gas sensor arranged downstream of the three-way catalyst,
    The control method is
    The control device extracts frequency components of the output signal of the upstream exhaust gas sensor and the output signal of the downstream exhaust gas sensor,
    the control device estimating the state of the three-way catalyst based on the amplitude of the extracted frequency component;
    A control method in which the control device calculates an air-fuel ratio from the state of the three-way catalyst.
PCT/JP2022/027297 2021-11-04 2022-07-11 Control device and control method for internal combustion engine WO2023079791A1 (en)

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