JP2004176612A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform the optimum control even when change in environmental conditions such as atmospheric pressure occurs and change in amount of suction air occurs. <P>SOLUTION: This exhaust emission control device is provided with catalyst 32 purifying exhaust gas of an internal combustion engine, air-fuel ratio sensors 35, 36 detecting air-fuel ratio on the upstream side or the downstream side of the catalyst 32, an atmospheric pressure sensor 44 detecting atmospheric pressure, a means for calculating amount of oxygen occlusion of the catalyst 32 based on output values of the air-fuel ratio sensors 35, 36, and a means for compensating amount of oxygen occlusion based on atmospheric pressure. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and is particularly suitable for application to a device that performs control according to the oxygen storage amount of a catalyst.
[0002]
[Prior art]
Conventionally, there has been known a method of detecting an oxygen storage amount of an exhaust purification catalyst and performing control based on the oxygen storage amount. For example, Japanese Patent Application Laid-Open No. 2001-329832 discloses a control for forcibly changing the air-fuel ratio upstream of a catalyst to lean / rich (hereinafter referred to as active A / F control) to detect a maximum oxygen storage amount. A method for determining the deterioration state of the catalyst based on the above is described.
[0003]
The catalyst deterioration determination method based on active A / F control is based on the following considerations: when the air-fuel ratio is forcibly changed to lean / rich, the amount of gas flowing into the catalyst during the time when the stoichiometric air-fuel ratio is maintained, and the exhaust gas upstream of the catalyst. The maximum oxygen storage amount is calculated from the deviation amount (ΔA / F) of the air-fuel ratio from the stoichiometric air-fuel ratio. Then, the state of catalyst deterioration is determined based on the calculated maximum oxygen storage amount.
[0004]
[Patent Document 1]
JP 2001-329832 A
[Patent Document 2]
JP-A-5-133264
[Patent Document 3]
JP-A-5-195842
[0005]
[Problems to be solved by the invention]
However, when the oxygen storage amount is detected, the output of an air-fuel ratio sensor (A / F sensor) provided in an exhaust passage or the like is used. There is a problem that the output of the device fluctuates. This is because the air-fuel ratio sensor generates an output in accordance with the relative oxygen concentration difference between the atmosphere and the exhaust gas, and the reference oxygen concentration in the atmosphere fluctuates in an environment with a low atmospheric pressure. For this reason, in an environment with a low atmospheric pressure, an air-fuel ratio different from the actual air-fuel ratio is detected, and it becomes difficult to perform optimal control based on the detection value of the air-fuel ratio sensor.
[0006]
Also in the catalyst deterioration determination by the active A / F control described above, when the output of the air-fuel ratio sensor decreases, the difference (ΔA / F) between the exhaust air-fuel ratio detected upstream of the catalyst and the stoichiometric air-fuel ratio fluctuates. For this reason, the maximum oxygen storage amount calculated based on (ΔA / F) includes an error, and it has been difficult to determine the catalyst deterioration with high accuracy.
[0007]
Further, there is a problem that the output of the air-fuel ratio sensor fluctuates depending on conditions other than the atmospheric pressure, for example, engine operating conditions. For this reason, when engine operating conditions fluctuate, it has been difficult to perform optimal control based on the detection value of the air-fuel ratio sensor.
[0008]
The present invention has been made in order to solve the above-described problems, and performs optimal control even when various conditions such as environmental conditions such as atmospheric pressure and engine operating conditions change. With the goal.
[0009]
[Means for Solving the Problems]
According to a first aspect of the present invention, to achieve the above object, an exhaust purification catalyst that purifies exhaust gas of an internal combustion engine, an air-fuel ratio sensor that detects an air-fuel ratio upstream or downstream of the exhaust purification catalyst, and an atmospheric pressure are acquired. Atmospheric pressure obtaining means, oxygen storage amount calculating means for calculating the oxygen storage amount of the exhaust purification catalyst based on the output value of the air-fuel ratio sensor, and correction means for correcting the oxygen storage amount based on the atmospheric pressure And characterized in that:
[0010]
According to a second aspect of the present invention, there is provided an exhaust purification catalyst for purifying exhaust gas of an internal combustion engine, an air-fuel ratio sensor for detecting an air-fuel ratio upstream or downstream of the exhaust purification catalyst, and an intake air for the internal combustion engine. Intake air amount obtaining means for obtaining an amount, oxygen storage amount calculating means for calculating an oxygen storage amount of the exhaust purification catalyst based on an output value of the air-fuel ratio sensor, and oxygen storage based on the intake air amount. Correction means for correcting the amount.
[0011]
According to a third aspect of the present invention, an exhaust purification catalyst for purifying exhaust gas of an internal combustion engine, an air-fuel ratio sensor for detecting an air-fuel ratio upstream or downstream of the exhaust purification catalyst, and an atmospheric pressure are acquired. Atmospheric pressure obtaining means, intake air amount obtaining means for obtaining an intake air amount of the internal combustion engine, and oxygen storage amount calculating means for calculating an oxygen storage amount of the exhaust purification catalyst based on an output value of the air-fuel ratio sensor; Correction means for correcting the oxygen storage amount based on the atmospheric pressure and the intake air amount.
[0012]
In a fourth aspect based on any one of the first to third aspects, the oxygen storage amount calculation means includes integration means for integrating the oxygen storage amount for each minute time, and the correction means includes: It is characterized in that each of the oxygen storage amounts is corrected for each.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, some embodiments of the present invention will be described with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals, and redundant description will be omitted. The present invention is not limited by the following embodiments.
[0014]
Embodiment 1 FIG.
FIG. 1 is a diagram for explaining an exhaust gas purifying apparatus for an internal combustion engine and a structure around the exhaust gas purifying apparatus according to the first embodiment of the present invention. As shown in FIG. 1, an intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. The intake passage 12 includes an air filter 16 at an end on the upstream side. The air filter 16 is provided with an intake air temperature sensor 18 for detecting the intake air temperature THA (that is, the outside air temperature).
[0015]
An air flow meter 20 is arranged downstream of the air filter 16. The air flow meter 20 is a sensor that detects the amount of inflow of air (Ga) flowing through the intake passage 12. Downstream of the air flow meter 20, a throttle valve 22 is provided. In the vicinity of the throttle valve 22, there are arranged a throttle sensor 24 for detecting the throttle opening TA and an idle switch 26 which is turned on when the throttle valve 22 is fully closed.
[0016]
A surge tank 28 is provided downstream of the throttle valve 22. Further, a fuel injection valve 30 for injecting fuel into an intake port of the internal combustion engine 10 is disposed further downstream of the surge tank 28.
[0017]
An exhaust purification catalyst 32 is provided in the exhaust passage 14. When the inflowing exhaust air-fuel ratio is lean, the exhaust purification catalyst 32 selectively holds (occludes) oxygen in the exhaust by adsorption and / or absorption, and the inflowing exhaust air has a stoichiometric air-fuel ratio or rich air. When the fuel ratio is reached, the stored oxygen is reduced and purified using the reducing components (HC, CO) in the exhaust gas.
[0018]
In the exhaust passage 14, a first air-fuel ratio sensor 35 is disposed upstream of the exhaust purification catalyst 32, and a second air-fuel ratio sensor 36 is disposed downstream of the exhaust purification catalyst 32. The first air-fuel ratio sensor 35 and the second air-fuel ratio sensor 36 are both sensors that detect the oxygen concentration in the exhaust gas. According to the first air-fuel ratio sensor 35 and the second air-fuel ratio sensor 36, the air-fuel ratio upstream and downstream of the catalyst 32 can be detected based on the oxygen concentration in the exhaust gas.
[0019]
As shown in FIG. 1, the exhaust emission control device of the present embodiment includes an ECU (Electronic Control Unit) 40. The ECU 40 is connected to a water temperature sensor 42 for detecting a cooling water temperature of the internal combustion engine 10, an atmospheric pressure sensor 44, and the like, in addition to the various sensors and the fuel injection valve 30 described above. The atmospheric pressure sensor 44 detects an atmospheric pressure that fluctuates due to an environment such as altitude.
[0020]
In the system shown in FIG. 1, the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment detects the maximum oxygen storage amount (Cmax) of the catalyst 32 by active A / F control, and based on the atmospheric pressure and the intake air amount (Ga). The Cmax value is corrected by using the Cmax value, and the exhaust gas is purified based on the corrected Cmax value.
[0021]
First, a method of detecting Cmax by active A / F control will be described. FIG. 2 is a schematic diagram illustrating a method for detecting Cmax. 2, the solid line indicates the air-fuel ratio detected by the first air-fuel ratio sensor 35, and the broken line indicates the air-fuel ratio detected by the second air-fuel ratio sensor 36. FIG. 2 shows time t₁The air-fuel ratio of the mixture supplied to the engine cylinder at the lean air-fuel ratio (A / F)_LTo rich air-fuel ratio (A / F)_RAt time t₂The air-fuel ratio of the air-fuel mixture supplied to the engine cylinder at the rich air-fuel ratio (A / F)_RTo lean air-fuel ratio (A / F)_LThe case where the switching is forcibly performed is shown in FIG.
[0022]
As shown in FIG.₁The air-fuel ratio supplied to the engine cylinder at the time is lean air-fuel ratio (A / F)_LTo rich air-fuel ratio (A / F)_R, The air-fuel ratio detected by the first air-fuel ratio sensor 35 is also a lean air-fuel ratio (A / F)._LTo rich air-fuel ratio (A / F)_RChanges to Further, the air-fuel ratio supplied into the engine cylinder is a rich air-fuel ratio (A / F)._RTo lean air-fuel ratio (A / F)_L, The air-fuel ratio detected by the first air-fuel ratio sensor 35 is also changed to the rich air-fuel ratio (A / F)._RTo lean air-fuel ratio (A / F)_LChanges to
[0023]
The air-fuel ratio detected by the second air-fuel ratio sensor 36 changes in a different pattern from that of the first air-fuel ratio sensor 35 as shown by a broken line in FIG. That is, the time t₁The air-fuel ratio supplied to the engine cylinder at the time is lean air-fuel ratio (A / F)_LTo rich air-fuel ratio (A / F)_RThe air-fuel ratio detected by the second air-fuel ratio sensor 36 when the air-fuel ratio changes to the lean air-fuel ratio (A / F)_LTo the stoichiometric air-fuel ratio, and T_RRich air-fuel ratio (A / F) after being maintained at stoichiometric air-fuel ratio for a period of time_RTo change. On the other hand, time t₂The air-fuel ratio supplied to the engine cylinder at the rich air-fuel ratio (A / F)_RTo lean air-fuel ratio (A / F)_LThe air-fuel ratio detected by the second air-fuel ratio sensor 36 when the air-fuel ratio changes to a rich air-fuel ratio (A / F)_RTo the stoichiometric air-fuel ratio, and T_LLean air-fuel ratio (A / F) after being maintained at stoichiometric air-fuel ratio for time_LTo change.
[0024]
The air-fuel ratio detected by the second air-fuel ratio sensor 36 is T_RTime or T_LThe stoichiometric air-fuel ratio is maintained over time because the O₂Depends on storage function. That is, the time t₁Previously, when the air-fuel ratio supplied to the engine cylinder was lean, excess oxygen was present in the exhaust gas, and the excess oxygen was adsorbed and held by the catalyst 32. Time t₁The air-fuel ratio of the mixture supplied to the engine cylinder at the lean air-fuel ratio (A / F)_LTo rich air-fuel ratio (A / F)_R, The amount of CO, HC, H corresponding to the air-fuel ratio is contained in the exhaust gas.₂And the like, and the oxygen adsorbed on the catalyst 32 is used to oxidize these unburned components. While the oxygen adsorbed and held by the catalyst 32 is oxidizing these unburned components, that is, T 2 in FIG._RDuring the time, the air-fuel ratio detected by the second air-fuel ratio sensor 36 is maintained at the stoichiometric air-fuel ratio. When the oxygen adsorbed and held in the catalyst 32 is exhausted, the oxidizing action of the unburned components is not performed._RBecomes
[0025]
Time t₂The air-fuel ratio of the air-fuel mixture supplied into the engine cylinder at_RTo lean air-fuel ratio (A / F)_L, The adsorption operation of oxygen by the catalyst 32 is started. While oxygen is being adsorbed, that is, T in FIG._LDuring the time, the air-fuel ratio detected by the second air-fuel ratio sensor 36 is maintained at the stoichiometric air-fuel ratio. Thereafter, when the ability of the catalyst 32 to adsorb oxygen is saturated, oxygen is no longer adsorbed by the catalyst 32, so that the air-fuel ratio detected by the second air-fuel ratio sensor 36 is a lean air-fuel ratio (A / F)._LBecomes While the oxygen adsorption operation is being performed, oxygen in the exhaust gas is deprived of the catalyst 32 and HC, CO, H contained in the exhaust gas is removed.₂Unburned components such as deprive NOx of oxygen to reduce NOx. When the ability of the catalyst 32 to adsorb oxygen is saturated, the unburned components in the exhaust gas are oxidized by the oxygen contained in the exhaust gas, so that the NOx reduction operation is not performed and NOx is discharged.
[0026]
There is an upper limit to the maximum oxygen storage amount (Cmax) that the catalyst 32 can adsorb and hold, and the absolute amount of Cmax is determined from the specifications of the catalyst 32. CO, HC, H that can be oxidized if the absolute amount of Cmax increases₂The amount of unburned components such as increases and the amount of reducible NOx increases, so that the purification rate of exhaust gas increases. If the absolute amount of Cmax decreases, the amount of oxidizable unburned components and the amount of reducible NOx decrease, and the exhaust gas purification rate decreases. Therefore, Cmax is a characteristic value indicating the degree of deterioration of the catalyst 32. FIG. 3 shows the relationship between Cmax and the degree of deterioration of the catalyst 32. As described above, if the Cmax of the catalyst 32 is detected, the degree of deterioration of the catalyst 32 can be accurately detected.
[0027]
In FIG. 2, T_R, The rich air-fuel ratio (A / F) in the engine cylinder_RIs supplied, and the amount of fuel supplied into the engine cylinder during this time is represented by F₁Then, the amount of air in the air-fuel mixture supplied into the cylinder is (A / F)_R・ F₁The amount of air required for combustion is (theoretical air-fuel ratio) · F₁Is represented by Therefore, in the engine cylinder, (theoretical air-fuel ratio− (A / F)_R) ・ F₁Assuming that the proportion of oxygen in the deficient air is 0.23, the deficient oxygen amount is 0.23 · (theoretical air-fuel ratio− (A / F)_R) ・ F₁Becomes The unburned portion of the fuel supplied to the engine cylinder is oxidized by oxygen adsorbed and held by the catalyst 32, and_RSince it is released from the catalyst 32 during the time, the oxygen amount of the shortage 0.23 · (theoretical air-fuel ratio− (A / F))_R) ・ F₁Is the absolute amount of oxygen adsorbed and held on the catalyst 32. Time t₁Previously, the output of the second air-fuel ratio sensor 36 was (A / F)_LAt time t₁At this point, the oxygen storage capacity of the catalyst 32 is saturated. Therefore, the oxygen amount is 0.23 · (theoretical air-fuel ratio− (A / F)_R) ・ F₁Is the maximum oxygen storage amount (Cmax) of the catalyst 32. Where T_RAir-fuel ratio (A / F) of the air-fuel mixture supplied to the engine cylinder within the time_RCan be detected from the output value of the first air-fuel ratio sensor 35. Therefore, the air-fuel ratio (A / F)_RAnd T_RFuel quantity F supplied into the engine cylinder during the time₁From this, the maximum oxygen storage amount (Cmax) of the catalyst 32 is known.
[0028]
Similarly, in FIG._L, The lean air-fuel ratio (A / F) in the engine cylinder_LIs supplied, and the amount of fuel supplied into the engine cylinder during this time is represented by F₂Then, the amount of air in the air-fuel mixture supplied into the cylinder is (A / F)_L-Expressed by F, the amount of air required for combustion is (theoretical air-fuel ratio)-F₂Is represented by Therefore, in the engine cylinder, ((A / F)_L−Theoretical air-fuel ratio) · F₂Assuming that the air amount becomes excessive and oxygen accounts for 0.23 of the excess air, the excess oxygen amount is 0.23 · ((A / F)_L−Theoretical air-fuel ratio) · F₂Becomes This excess amount of oxygen is T_LSince it is adsorbed by the catalyst 32 during the time, the excess oxygen amount is 0.23 · (A / F)_L−Theoretical air-fuel ratio) · F₂Is the absolute amount of oxygen adsorbed and held by the catalyst 32. T_RAfter a lapse of time, the output of the second air-fuel ratio sensor 36 becomes (A / F)_RAt time t₂At this point, all the oxygen stored by the catalyst 32 has been exhausted. Therefore, the amount of oxygen 0.23 · ((A / F)_L−Theoretical air-fuel ratio) · F₂Is the maximum oxygen storage amount (Cmax) of the catalyst 32. Where T_LAir-fuel ratio (A / F) of the air-fuel mixture supplied to the engine cylinder within the time_LCan be detected from the output value of the first air-fuel ratio sensor 35. Therefore, the air-fuel ratio (A / F)_LAnd T_LFuel quantity F supplied into the engine cylinder during the time₂From this, the maximum oxygen storage amount (Cmax) of the catalyst 32 is known. The fuel amount F₁, F₂Is T_RTime or T_LIt can be obtained from the fuel injection amount (injection valve opening degree) that the ECU 40 instructed to the fuel injection valve 30 during the time.
[0029]
T_RTime or T_LAir-fuel ratio ((A / F) detected by the first air-fuel ratio sensor 35 at time)_ROr (A / F)_L) Changes, T_RTime, T_LΔT that further divides time_RTime, ΔT_LThe oxygen storage amount ΔOSA is obtained for each time, and T_RTime or T_LBy integrating ΔOSA in time, the Cmax value can be obtained more accurately. In this case, ΔT_RTime or ΔT_LThe calculation formula of ΔOSA in time is as follows.
ΔOSA = 0.23 · (Theoretical air-fuel ratio− (A / F)_R) ・ F₁
ΔOSA = 0.23 · ((A / F)_L−Theoretical air-fuel ratio) · F₂
[0030]
In these ΔOSA calculation formulas, (A / F)_R, (A / F)_LIs ΔT_RTime or ΔT_LIt is an output value of the first air-fuel ratio sensor 35 for each time. Also, F₁, F₂Is ΔT_RTime or ΔT_LThis is the amount of fuel supplied into the engine cylinder over time. Thus, the minute time ΔT_R, ΔT_LΔOSA is calculated based on the output value of the first air-fuel ratio sensor 35 for each_RTime or T_LBy obtaining the sum of ΔOSA over time, the Cmax value can be obtained in consideration of the change in the air-fuel ratio upstream of the catalyst 32, and highly accurate Cmax calculation can be performed.
[0031]
Next, a method of correcting the Cmax value based on the atmospheric pressure and the intake air amount (Ga) will be described. First, a method of correcting the Cmax value based on the atmospheric pressure will be described. When the Cmax value is determined by the active A / F control, the output values of the first air-fuel ratio sensor 35 and the second air-fuel ratio sensor 36 are used as described above, but the output values of these air-fuel ratio sensors are large. It fluctuates according to the atmospheric pressure. Specifically, in an environment where the atmospheric pressure is low, such as high altitude, the output value of the sensor fluctuates toward the stoichiometric air-fuel ratio, and (theoretical air-fuel ratio− (A / F)_R) Or ((A / F)_L−theoretical air-fuel ratio) tends to decrease. Therefore, the Cmax value calculated under different atmospheric pressures includes an error.
[0032]
In the present embodiment, the Cmax value is corrected according to the atmospheric pressure based on the Cmax value calculated at the standard atmospheric pressure (for example, 760 mmHg). The ECU 40 stores a correction coefficient corresponding to the atmospheric pressure in advance, and corrects the Cmax value by multiplying the Cmax value calculated by the active A / F control by the correction coefficient. As the correction coefficient, a value calculated in advance based on the following equation is used.
Correction coefficient = (Cmax value at standard pressure) / (Cmax value under low pressure)
[0033]
Here, (Cmax value at standard pressure) is a Cmax value calculated under standard pressure using the system of FIG. The (Cmax value under low pressure) is a Cmax value calculated using the system in FIG. 1 under a low pressure environment. (Cmax value under low pressure) is calculated under a plurality of different atmospheric pressures, and the correction coefficient under each atmospheric pressure is calculated in advance. Thereby, the Cmax value can be corrected according to the atmospheric pressure of the environment where the engine is located. The ECU 40 selects a correction coefficient based on the output value of the atmospheric pressure sensor 44 and corrects the Cmax value. As a result, the Cmax value can be accurately obtained without the influence of the atmospheric pressure, and the catalyst deterioration determination by the active A / F control can be performed with high accuracy.
[0034]
Next, a method of correcting the Cmax value based on the intake air amount (Ga) will be described. Even if the environmental conditions such as the atmospheric pressure are the same, the output values of the first air-fuel ratio sensor 35 and the second air-fuel ratio sensor 36 fluctuate according to the intake air amount (Ga). This is due to factors such as an increase in the intake air amount (Ga), an increase in the probability that oxygen in the exhaust gas reaches these air-fuel ratio sensors (arrival probability). For this reason, the Cmax value calculated under different intake air amounts (Ga) includes an error.
[0035]
In the present embodiment, the correction according to the intake air amount (Ga) is performed to accurately obtain the Cmax value. The calculation of the correction coefficient according to the intake air amount (Ga) can be performed in the same manner as the calculation of the correction coefficient based on the atmospheric pressure, and is calculated based on, for example, the following equation.
Correction coefficient = (Cmax value at standard intake air amount) / (Cmax value at each intake air amount)
[0036]
Here, the (Cmax value at the standard intake air amount) is a Cmax value calculated when the intake air amount (Ga) is set to a reference standard value. The (Cmax value at each intake air amount) is a Cmax value calculated for each intake air amount with the intake air amount (Ga) set to a plurality of predetermined values. As described above, the Cmax value can be corrected in accordance with the intake air amount (Ga) by previously calculating the correction coefficient for each intake air amount from an experiment or the like. The catalyst temperature fluctuates according to the intake air amount (Ga), and the Cmax value fluctuates according to the catalyst temperature. It is desirable to conduct experiments and the like.
[0037]
The ECU 40 also stores the correction coefficient for each intake air amount (Ga) calculated in this way. The ECU 40 selects an optimum correction coefficient according to the intake air amount (Ga) from the stored correction coefficients based on the output value of the air flow meter 20, and corrects the Cmax value. As a result, the Cmax value can be accurately obtained, and the catalyst deterioration determination by active A / F control can be performed with high accuracy.
[0038]
When correcting the Cmax value, the correction may be performed based on only the atmospheric pressure or the intake air amount (Ga), or may be performed based on both the atmospheric pressure and the intake air amount (Ga). . When the correction is performed based on both the atmospheric pressure and the intake air amount (Ga), the ECU 40 stores a two-dimensional map that defines the relationship between the atmospheric pressure and the intake air amount and the correction coefficient.
[0039]
FIG. 4 is a schematic diagram showing an example of the two-dimensional map stored in the ECU 40. In FIG. 4, the horizontal axis represents the intake air amount (Ga), and the vertical axis represents the correction coefficient. A characteristic 50 indicates a characteristic when the atmospheric pressure is 625 mmHg, and a characteristic 52 indicates a characteristic when the atmospheric pressure is 570 mmHg. As described above, by using both the atmospheric pressure and the amount of intake air (Ga) as a parameter and calculating the correction coefficient in advance from an experiment or the like, the correction can be performed based on both the atmospheric pressure and the amount of intake air (Ga). Can be.
[0040]
As shown in FIG. 4, the value of the correction coefficient decreases as the intake air amount (Ga) increases. Further, the value of the correction coefficient decreases as the atmospheric pressure increases. The ECU 40 applies the output values of the atmospheric pressure sensor 44 and the air flow meter 20 to the map of FIG. 4 to determine an optimal correction coefficient. Note that FIG. 4 illustrates only the characteristics 50 and 52 when the atmospheric pressure is 625 mmHg and 570 mmHg. Can be obtained. When only the atmospheric pressure correction is performed based on the map of FIG. 4, the intake air amount (Ga) fluctuates in a range of about 5 g / sec to 25 g / sec by active A / F control, and thus is in the middle of the fluctuation range. It is desirable to use a correction coefficient for each atmospheric pressure at an intake air amount (Ga) of about 15 g / sec. When only the intake air amount correction is performed based on the map of FIG. 4, it is desirable to use the correction coefficient of each intake air amount at the standard atmospheric pressure (760 mmHg).
[0041]
Next, a procedure of processing in the exhaust gas purification apparatus of the present embodiment will be described based on the flowchart of FIG. First, in step S1, it is determined whether a calculation condition for determining catalyst deterioration by active A / F control has been satisfied. In the next step S2, active A / F control is executed to calculate a Cmax value. As described above, the Cmax value is equal to Tmax in FIG._RTime or T_LFuel supply F into the engine cylinder over time₁, F₂And the output value of the first air-fuel ratio sensor 35. In the next step S3, the atmospheric pressure and the intake air amount (Ga) are obtained based on the output values of the atmospheric pressure sensor 44 and the air flow meter 20.
[0042]
In the next step S4, a correction coefficient K corresponding to the atmospheric pressure and the intake air amount (Ga) is determined with reference to the map of FIG. In the next step S5, the Cmax value is corrected based on the correction coefficient K. Here, the Cmax value is corrected by the following calculation.
Cmax (after correction) = K · Cmax (before correction)
Here, the value of Cmax (before correction) is the value calculated in step S2.
[0043]
In the next step S6, catalyst deterioration determination is performed based on the corrected Cmax value obtained in step S5. Here, the predetermined threshold value is compared with the corrected Cmax value, and if the corrected Cmax value is equal to or greater than the threshold value, it is determined that the degree of deterioration of the catalyst 32 is small and normality is determined. If the corrected Cmax value is smaller than the threshold value, it is determined that the catalyst 32 has deteriorated and an abnormality is determined.
[0044]
Next, another processing procedure in the exhaust gas purification apparatus of the present embodiment will be described based on the flowchart of FIG. As described above, T in FIG._RTime, T_LΔT that further divides time_RTime, ΔT_LBy accumulating the oxygen storage amount ΔOSA for each time, the Cmax value can be obtained more accurately. In the processing in the flowchart of FIG. 6, a correction is performed according to the atmospheric pressure and the intake air amount (Ga) every time ΔOSA is calculated, and the corrected ΔOSA is calculated as T_RTime, T_LThe Cmax value is calculated by integrating the values in time.
[0045]
First, in step S11, it is determined whether a calculation condition for determining catalyst deterioration by active A / F control is satisfied. In the next step S12, active A / F control is executed, and ΔT_RTime or ΔT_LThe oxygen storage amount ΔOSA in time is calculated. In the next step S13, based on the output values of the atmospheric pressure sensor 44 and the air flow meter 20, ΔT_RTime or ΔT_LThe atmospheric pressure and the intake air amount (Ga) in time are obtained. In the next step S14, the atmospheric pressure and the intake air amount (Ga) are applied to the map of FIG._RTime or ΔT_LA correction coefficient K for each time is obtained.
[0046]
In the next step S15, correction is performed based on the correction coefficient K. In the process of step S15, the correction is performed by multiplying ΔOSA by the correction coefficient K, and the sum of ΔOSA calculated so far is obtained. At this stage, ΔOSA is calculated n times, and assuming that the sum of n ΔOSAs is Cmax (n), Cmax (n) is represented by the following equation.
Cmax (n) = Cmax (n−1) + K · ΔOSA
[0047]
In the next step S16, the number of times ΔOSA is calculated is T_RTime, or T_LΔT in time_RTime, ΔT_LIt is determined whether or not the number of time divisions N has been reached. That is, it is determined here whether n = N. If n = N, the process proceeds to step S17, and a catalyst deterioration determination is performed as in the case of FIG. If n ≠ N in step S16, the processes in steps S12 to S15 are continuously performed to calculate Cmax (n).
[0048]
In the process of FIG. 6, each time ΔOSA is calculated, a correction coefficient K is obtained from the atmospheric pressure and the intake air amount (Ga) to perform the correction._RTime, or T_LEven if the atmospheric pressure and the intake air amount (Ga) fluctuate during the time, the minute time ΔT_R, T_LEach ΔOSA obtained for each can be corrected. Therefore, according to the process of FIG. 6, it is possible to correct the Cmax value with higher accuracy.
[0049]
As described above, according to the first embodiment, the Cmax value is corrected based on one of the atmospheric pressure and the intake air amount (Ga), or both the atmospheric pressure and the intake air amount (Ga). The Cmax value can be accurately obtained by eliminating the influence of the atmospheric pressure and the intake air amount (Ga). Therefore, it is possible to determine the catalyst deterioration by the active A / F control with high accuracy.
[0050]
Embodiment 2 FIG.
Next, a second embodiment of the present invention will be described. In the first embodiment, an example in which the present invention is applied to the determination of catalyst deterioration by active A / F control is shown. The example which applied the invention is shown. Note that the configuration of the exhaust gas purification apparatus according to the second embodiment is the same as that of FIG.
[0051]
FIG. 7 is a flowchart illustrating a procedure of a process in the exhaust gas purification device for an internal combustion engine according to the second embodiment. First, in step S21, it is determined whether a condition for calculating the oxygen storage amount OSA is satisfied. In the next step S22, the oxygen storage amount OSA of the catalyst 32 is calculated. Here, the oxygen storage amount OSA is calculated from the amount of fuel supplied into the engine cylinder, the amount of intake air (Ga), the output values of the first air-fuel ratio sensor 35, the second air-fuel ratio sensor 35, and the like. T in FIG._RIt may be calculated from the output value of the first air-fuel ratio sensor 35 only during the time and the supplied fuel amount during that time. In the next step S23, the atmospheric pressure and the intake air amount (Ga) are obtained based on the output values of the atmospheric pressure sensor 44 and the air flow meter 20.
[0052]
In the next step S24, a correction coefficient K corresponding to the atmospheric pressure and the intake air amount (Ga) is determined with reference to the map of FIG. In the next step S25, the oxygen storage amount OSA is corrected based on the correction coefficient K. Here, the oxygen storage amount is corrected by the following calculation.
OSA (after correction) = K · OSA (before correction)
Here, the value of OSA (before correction) is the value calculated in step S22.
[0053]
In the next step S26, feedback control of the air-fuel ratio is performed based on the corrected oxygen storage amount OSA obtained in step S25. Here, the predetermined threshold value is compared with the corrected oxygen storage amount OSA, and when the corrected OSA is equal to or larger than the threshold value, the air-fuel ratio is increased so that the oxygen storage amount OSA of the catalyst 32 decreases. Change to the side. If the corrected OSA is smaller than the threshold value, the air-fuel ratio is changed to the lean side so that the catalyst 32 increases the oxygen storage amount OSA.
[0054]
As described above, according to the second embodiment, since the oxygen storage amount OSA of the catalyst 32 can be kept constant, the saturation of the oxygen storage capacity of the catalyst 32 can be suppressed. Therefore, the exhaust gas purifying function of the catalyst 32 can be maximized.
[0055]
In the above-described embodiments, the method of correcting the Cmax value and the OSA value according to the atmospheric pressure or the intake air amount (Ga) has been described. The output value of the air-fuel ratio sensor 35 or the second air-fuel ratio sensor 36 may be directly corrected. In this case, a map defining the relationship between the atmospheric pressure, the intake air amount (Ga) and the sensor output is stored in the ECU 40 based on the fluctuation characteristics of the sensor output depending on the atmospheric pressure and the intake air amount (Ga). , The sensor output value can be directly corrected.
[0056]
Further, in each of the above-described embodiments, the intake air amount (Ga) is directly detected from the air flow meter 20. May be estimated. Further, in each of the above-described embodiments, the atmospheric pressure is directly detected from the atmospheric pressure sensor 44. The atmospheric pressure may be estimated from the difference.
[0057]
Further, in the above-described embodiment, an example is shown in which the present invention is applied to the determination of catalyst deterioration by active A / F control or the feedback control of the air-fuel ratio, but the present invention is not limited to this. The present invention can be widely applied when obtaining the oxygen storage amount of the catalyst, and the concept of correcting the oxygen storage amount of the catalyst according to the atmospheric pressure and the intake air amount belongs to the category of the present invention.
[0058]
【The invention's effect】
Since the present invention is configured as described above, it has the following effects.
[0059]
According to the first aspect, since the oxygen storage amount can be corrected based on the atmospheric pressure, the oxygen storage amount of the catalyst can be calculated with high accuracy. Therefore, it is possible to perform optimal control according to the oxygen storage amount.
[0060]
According to the second aspect, since the oxygen storage amount can be corrected based on the intake air amount, the oxygen storage amount of the catalyst can be calculated with high accuracy. Therefore, it is possible to perform optimal control according to the oxygen storage amount.
[0061]
According to the third aspect, since the oxygen storage amount can be corrected based on the atmospheric pressure and the intake air amount, the oxygen storage amount of the catalyst can be calculated with extremely high accuracy. Therefore, it is possible to perform optimal control according to the oxygen storage amount.
[0062]
According to the fourth aspect, since each of the oxygen storage amounts is corrected for each minute time, the optimum correction can be performed for each minute time. Therefore, the oxygen storage amount of the catalyst can be calculated with higher accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a structure of a catalyst deterioration determination device according to a first embodiment of the present invention and a peripheral structure thereof;
FIG. 2 is a schematic diagram illustrating a method of detecting a maximum oxygen storage amount (Cmax) by active A / F control.
FIG. 3 is a characteristic diagram showing a relationship between a maximum oxygen storage amount (Cmax) and a degree of catalyst deterioration.
FIG. 4 is a schematic diagram illustrating a two-dimensional map that defines a relationship between an atmospheric pressure and an intake air amount and a correction coefficient.
FIG. 5 is a flowchart illustrating a processing procedure in the exhaust emission control device according to the first embodiment of the present invention.
FIG. 6 is a flowchart illustrating another processing procedure in the exhaust gas purification device according to the first embodiment of the present invention.
FIG. 7 is a flowchart illustrating a processing procedure in the exhaust gas purification device according to the second embodiment of the present invention.
[Explanation of symbols]
20 Air flow meter
32 catalyst
35 first air-fuel ratio sensor
36 Second air-fuel ratio sensor
40 ECU
44 Atmospheric pressure sensor

Claims (4)

An exhaust purification catalyst for purifying exhaust of the internal combustion engine;
An air-fuel ratio sensor that detects an air-fuel ratio upstream or downstream of the exhaust purification catalyst;
An atmospheric pressure obtaining means for obtaining an atmospheric pressure;
Oxygen storage amount calculation means for calculating an oxygen storage amount of the exhaust purification catalyst based on an output value of the air-fuel ratio sensor;
Correction means for correcting the oxygen storage amount based on the atmospheric pressure,
An exhaust gas purification device for an internal combustion engine, comprising: An exhaust purification catalyst for purifying exhaust of the internal combustion engine;
An air-fuel ratio sensor that detects an air-fuel ratio upstream or downstream of the exhaust purification catalyst;
Intake air amount obtaining means for obtaining an intake air amount of the internal combustion engine,
Oxygen storage amount calculation means for calculating an oxygen storage amount of the exhaust purification catalyst based on an output value of the air-fuel ratio sensor;
Correction means for correcting the oxygen storage amount based on the intake air amount,
An exhaust gas purification device for an internal combustion engine, comprising: An exhaust purification catalyst for purifying exhaust of the internal combustion engine;
An air-fuel ratio sensor that detects an air-fuel ratio upstream or downstream of the exhaust purification catalyst;
An atmospheric pressure obtaining means for obtaining an atmospheric pressure;
Intake air amount obtaining means for obtaining an intake air amount of the internal combustion engine,
Oxygen storage amount calculation means for calculating an oxygen storage amount of the exhaust purification catalyst based on an output value of the air-fuel ratio sensor;
Correction means for correcting the oxygen storage amount based on the atmospheric pressure and the intake air amount,
An exhaust gas purification device for an internal combustion engine, comprising: The oxygen storage amount calculation means includes integration means for integrating the oxygen storage amount for each minute time,
The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the correction unit corrects each of the oxygen storage amounts for each of the minute times.

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