JP3962892B2 - Exhaust purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device, and more particularly to a technique for determining deterioration of a catalytic converter.
[0002]
[Related technology]
In the exhaust gas catalytic converter, the oxygen storage capacity added to the catalyst has a high correlation with the catalytic performance (HC purification performance), so that the catalytic converter particularly contains a large amount of oxygen storage material such as ceria (Ce). Is widely known as a method for detecting deterioration of a catalytic converter by detecting a change in the oxygen storage capacity.
[0003]
In this catalyst deterioration detection method, if the exhaust air-fuel ratio flowing into the catalytic converter is modulated with a predetermined period and amplitude between the lean air-fuel ratio and the rich air-fuel ratio, oxygen is stored in the catalytic converter if the oxygen storage capacity is high. The response of the exhaust air / fuel ratio downstream of the catalyst is slow, while if the oxygen storage capacity is low, oxygen is discharged without being stored in the catalytic converter so much that the response of the exhaust air / fuel ratio downstream of the catalyst is accelerated. For example, an oxygen sensor (O₂Sensor) or air-fuel ratio sensor (LAFS) detects the frequency or cycle of the oxygen concentration output value, and if the detected value is equal to or greater than a predetermined reference value, it is determined that the oxygen storage capacity is reduced, that is, the catalytic converter has deteriorated. Like to do.
[0004]
[Problems to be solved by the invention]
By the way, the catalyst deterioration detection method by the modulation of the air-fuel ratio as described above is effective for a catalytic converter that contains a large amount of oxygen storage material such as ceria and has sufficient oxygen storage capacity, but does not contain much ceria and the like. Catalytic converters with weak oxygen storage capacity that are originally low in capacity have a fast response to the exhaust air / fuel ratio downstream of the catalyst because oxygen is not stored much in the catalytic converter even if it has not deteriorated, making it difficult to detect deterioration. .
[0005]
In other words, in the case of a catalytic converter having an oxygen storage capability, a rich air-fuel ratio is obtained even when the lean air-fuel ratio is relatively long due to modulation of the exhaust air-fuel ratio due to a large amount of breakthrough (allowable oxygen storage amount of the catalytic converter). Oxygen continues to be occluded in the catalytic converter until it is switched to, and in the rich air-fuel ratio, the occluded oxygen will continue to be used for oxidation of HC and CO, and the oxygen concentration output value hardly fluctuates downstream of the catalyst. If the oxygen storage capacity declines and the oxygen concentration output value downstream of the catalyst begins to fluctuate, it can be determined that the amount of breakthrough has decreased and the catalytic converter has deteriorated. Because it is due to precious metals and the amount of breakthrough is small, the breakthrough amount is quickly exceeded, and even if the lean air-fuel ratio is assumed, surplus A large amount of oxygen is discharged from the catalytic converter, the oxygen concentration output value downstream of the catalyst changes, and even in the rich air-fuel ratio, the stored oxygen is immediately used up as an oxidant, and again the oxygen concentration output downstream of the catalyst There is a problem that the value changes and fluctuates, and the deterioration state cannot be clearly distinguished.
[0006]
This tendency is remarkable because the amount of oxygen flowing into the catalytic converter per unit time and the amount of HC and CO increase as the exhaust gas flow rate increases. Therefore, in the catalytic converter having a weak oxygen storage capacity, the exhaust gas flow rate is particularly large. It is very difficult to judge deterioration when the flow rate is high.
Therefore, in order to improve such problems, for example, in air-fuel ratio modulation of air-fuel ratio feedback control, the control coefficient for correction coefficient setting used for the air-fuel ratio feedback control is changed according to the oxygen storage amount at the time of specific deterioration diagnosis. An apparatus configured to do so is proposed in Japanese Patent Laid-Open No. 5-98945.
[0007]
However, the air-fuel ratio modulation of the air-fuel ratio feedback control disclosed in the publication is inherently unstable, and even if the correction coefficient setting control constant is changed, there is a high possibility that the breakthrough amount will be exceeded, and accurate deterioration will occur. Judgment may not be possible. In addition, the configuration disclosed in the publication has a drawback that the deterioration of the catalytic converter cannot be sufficiently monitored because the deterioration of the catalyst can be determined only at a specific timing set in advance.
[0008]
The present invention has been made to solve such problems, and an object of the present invention is to purify exhaust gas that can be easily and accurately determined for deterioration even with a catalytic converter having a low oxygen storage capacity. To provide an apparatus.
[0009]
[Means for Solving the Problems]
  In order to achieve the above object, according to the first aspect of the present invention, the catalytic converter provided in the exhaust passage of the internal combustion engine and the air-fuel ratio are forcibly varied at a predetermined cycle and amplitude between the lean air-fuel ratio and the rich air-fuel ratio. Air-fuel ratio forced variation means, breakthrough amount detection means for detecting the current breakthrough amount or breakthrough amount correlation value for oxygen storage of the catalytic converter, and current breakthrough amount or breakthrough amount correlation detected by the breakthrough amount detection means Deterioration determining means for determining deterioration of the catalytic converter based on the value,The oxygen storage amount increases or decreases in correlation with the lean air-fuel ratio time or the rich air-fuel ratio time,The air-fuel ratio forced fluctuation means isThe lean air-fuel ratio time or the rich air-fuel ratio time is smaller than a breakthrough time corresponding to a predetermined breakthrough amount when the catalytic converter is not deteriorated and more than a breakthrough time corresponding to a breakthrough amount when the catalytic converter is deteriorated. bigThe air-fuel ratio is modulated so that
[0012]
  Therefore, the lean air-fuel ratio time or the rich air-fuel ratio time, which is the correlation value of the oxygen storage amount, isPredeterminedLess than the breakthrough time corresponding to the breakthrough amount at the time of non-degradation and the catalytic converterPredeterminedBy modulating the air-fuel ratio to be larger than the breakthrough time corresponding to the breakthrough amount at the time of deterioration, the lean air-fuel ratio time usually reaches the breakthrough time before the lean air-fuel ratio time reaches the breakthrough time. The air-fuel ratio is switched in advance, and the fluctuation of the exhaust air-fuel ratio downstream of the catalyst can be easily suppressed based on the time value. As a result, when the oxygen concentration in the downstream of the catalyst begins to change and the fluctuation of the exhaust air / fuel ratio downstream of the catalyst becomes large, these changes and fluctuations can be reliably detected, and the oxygen storage capacity of the catalytic converter decreases and the catalytic converter deteriorates. This makes it easy to make accurate determinations at all times.
[0013]
  Claims2In the invention, the air-fuel ratio forced fluctuation means has a lean air-fuel ratio time ratio or rich air-fuel ratio time ratio with respect to the predetermined cycle smaller than a time ratio corresponding to a predetermined amount of breakthrough when the catalytic converter is not deteriorated, and The air-fuel ratio is modulated so as to be larger than the time ratio corresponding to the breakthrough amount at the time of predetermined deterioration of the catalytic converter.
[0014]
  Therefore, the lean air-fuel ratio time ratio or the rich air-fuel ratio time ratio with respect to a predetermined period, which is the correlation value of the oxygen storage amount, isPredeterminedSmaller than the time ratio corresponding to the amount of breakthrough during non-degradation andPredeterminedBy modulating the air / fuel ratio to be larger than the time ratio corresponding to the breakthrough amount at the time of deterioration, the lean air / fuel ratio time ratio usually corresponds to the breakthrough amount, or the rich air / fuel ratio time ratio corresponds to the breakthrough amount. The air-fuel ratio is switched so that the time ratio becomes the same, and the fluctuation of the exhaust air-fuel ratio downstream of the catalyst can be easily suppressed based on the time ratio with respect to the cycle. As a result, as described above, when the oxygen concentration downstream of the catalyst starts to change and fluctuations in the exhaust air-fuel ratio downstream of the catalyst increase, these changes and fluctuations can be reliably detected, and the oxygen storage capacity of the catalytic converter decreases and the catalyst It is possible to easily determine that the converter has deteriorated and to always accurately determine.
[0015]
  PreferablyThe air-fuel ratio forced fluctuation means modulates the air-fuel ratio so that the lean air-fuel ratio time ratio or rich air-fuel ratio time ratio becomes 0.3 or less and 0.05 or more.Good.
  If you do thisBy modulating the air-fuel ratio so that the lean air-fuel ratio time ratio or the rich air-fuel ratio time ratio becomes 0.3 or less and 0.05 or more, the lean air-fuel ratio time ratio usually corresponds to the time ratio corresponding to the breakthrough amount ( 0.05 to 0.3), or the air-fuel ratio is switched so that the rich air-fuel ratio time ratio becomes a time ratio (0.05 to 0.3) corresponding to the breakthrough amount. Accordingly, the fluctuation of the exhaust air-fuel ratio downstream of the catalyst can be easily reduced. As a result, as described above, the catalytic converter can be easily deteriorated and can always be accurately determined.
[0016]
That is, referring to FIG. 4, the lean air-fuel ratio time ratio with respect to a predetermined cycle and O as a breakthrough amount detection means provided downstream of the catalyst.₂The relationship with the output amplitude of the sensor is shown. As described above, the time ratio (range of 0.05 to 0.3) corresponding to the breakthrough amount or the rich air / fuel ratio time ratio When the time ratio corresponding to the breakthrough amount is set (in the range of 0.05 to 0.3, that is, in the range of 0.7 to 0.95 in terms of the lean air-fuel ratio time ratio), it is usually O as shown by the solid line.₂The fluctuation of the output amplitude of the sensor, that is, the exhaust air / fuel ratio is suppressed to be small. In this range, if the catalytic converter deteriorates, O₂The output amplitude (broken line) of the sensor becomes conspicuous with respect to the output amplitude (solid line) at the time of non-deteriorating, and the catalytic converter can be easily deteriorated and can always be determined.
[0017]
  Claims3In this invention, the air-fuel ratio forced fluctuation means modulates the air-fuel ratio by shortening the predetermined period, which is the sum of the lean air-fuel ratio time and the rich air-fuel ratio time, as the exhaust flow rate or the exhaust flow rate correlation value is larger. It is characterized by.
  Therefore, as the exhaust flow rate or the exhaust flow rate correlation value increases, the oxygen amount and HC, CO amount flowing into the catalytic converter per unit time increase, and the oxygen storage amount reaches the breakthrough amount at an early stage. By adjusting the air-fuel ratio by shortening the predetermined period as the value of the air-fuel ratio increases, the air-fuel ratio is normally adjusted before the lean air-fuel ratio time reaches the breakthrough time or before the rich air-fuel ratio time reaches the breakthrough time. Therefore, regardless of the exhaust flow rate or the exhaust flow rate correlation value, the fluctuation of the exhaust air-fuel ratio downstream of the catalyst can be suppressed to a small value. As a result, as described above, the catalytic converter can be easily deteriorated and can always be accurately determined.
[0018]
That is, referring to FIG. 5, for example, the period of forced air-fuel ratio fluctuation when the lean air-fuel ratio time ratio is 0.3 and the O provided downstream of the catalyst.₂The relationship with the output amplitude of the sensor is indicated by a broken line and a solid line for each exhaust flow rate (at low flow rate and high flow rate). O compared to some cases₂Since the cycle at which the output amplitude of the sensor begins to increase is short, the cycle is shortened as the exhaust flow rate increases and the flow rate increases based on the map shown in FIG. As a result, O during normal non-deterioration₂The fluctuation in the output amplitude of the sensor, that is, the exhaust air-fuel ratio is suppressed to a small level, so that the catalytic converter can be easily deteriorated and can always be determined.
[0019]
  Also,PreferablyThe air-fuel ratio forced fluctuation means modulates the air-fuel ratio so that the predetermined period is 0.8 seconds or less.It is good.
  If you do thisAs the exhaust flow rate or the exhaust flow rate correlation value increases, the amount of oxygen flowing into the catalytic converter per unit time and the amount of HC and CO increase, and the oxygen storage amount reaches the breakthrough amount at an early stage. In general, the air-fuel ratio is switched before the lean air-fuel ratio time reaches the breakthrough time or before the rich air-fuel ratio time reaches the breakthrough time. Therefore, regardless of the exhaust flow rate or the exhaust flow rate correlation value, the fluctuation of the exhaust air-fuel ratio downstream of the catalyst is suppressed to a small value as shown in FIG. As a result, the deterioration of the catalytic converter can be facilitated and the determination can always be made with high accuracy.
[0020]
  Claims4In this invention, the breakthrough amount detecting means is an exhaust gas sensor that is provided downstream of the catalytic converter and detects an oxygen concentration.
  Therefore, when the oxygen concentration downstream of the catalyst begins to change and the exhaust air-fuel ratio fluctuations downstream of the catalyst increase, these changes and fluctuations are easily detected by the exhaust gas sensor downstream of the catalyst, and the oxygen storage capacity of the catalytic converter decreases and the catalyst It is possible to accurately and reliably determine that the converter has deteriorated with a simple configuration without providing a separate sensor.
[0021]
  Claims5In the invention, the deterioration determination means determines the deterioration of the catalytic converter using the fluctuation range of the output value from the exhaust gas sensor or the fluctuation range correlation value as a breakthrough amount correlation value.
  Therefore, if the exhaust gas sensor downstream of the catalyst is used, the fluctuation range of the exhaust air / fuel ratio downstream of the catalyst can be easily detected. Based on the fluctuation range, the oxygen storage capacity of the catalytic converter is reduced and the breakthrough amount is reduced. It is possible to accurately determine that the converter has deteriorated with a simple configuration without providing a separate sensor.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust emission control device according to the present invention mounted on a vehicle. Hereinafter, the configuration of the exhaust emission control device according to the present invention will be described based on the same drawing.
[0023]
As shown in the figure, the engine main body (hereinafter simply referred to as the engine) 1 includes, for example, fuel injection in the intake stroke (intake stroke injection) and fuel injection in the compression stroke (compression stroke) by switching the fuel injection mode. An in-cylinder injection type spark ignition gasoline engine capable of performing injection) is employed. This in-cylinder injection type engine 1 is easily operated at a stoichiometric air-fuel ratio (stoichiometric), an operation at a rich air-fuel ratio (rich air-fuel ratio operation), and an operation at a lean air-fuel ratio (lean air-fuel ratio operation). Is feasible.
[0024]
As shown in the figure, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, so that fuel can be directly injected into the combustion chamber. .
An ignition coil 8 that outputs a high voltage is connected to the spark plug 4. Further, a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. More specifically, the fuel supply device is provided with a low pressure fuel pump and a high pressure fuel pump, whereby fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure Pinj of the high-pressure fuel pump and the opening time of the fuel injection valve 6, that is, the fuel injection time Tinj.
[0025]
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of the intake manifold 10 is connected so as to communicate with each intake port. Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 12 is connected so as to communicate with each exhaust port.
[0026]
The in-cylinder injection type engine 1 is already known, and therefore, the detailed description of the configuration is omitted.
As shown in the figure, the intake manifold 10 is provided with an electromagnetic throttle valve 14 for adjusting the amount of intake air, and a throttle position sensor (TPS) 16 for detecting the opening θth of the throttle valve 14. An air flow sensor 18 for measuring the intake air amount is interposed upstream of the throttle valve 14. A Karman vortex airflow sensor is used as the airflow sensor 18.
[0027]
On the other hand, an exhaust pipe (exhaust passage) 20 is connected to the exhaust manifold 12, and a three-way catalyst (catalytic converter) 30 is interposed in the exhaust pipe 20 as an exhaust purification catalyst device.
The three-way catalyst 30 has copper (Cu), cobalt (Co), silver (Ag), or platinum (Pt) as an active noble metal on a support.
[0028]
The active noble metal has an oxygen storage function (O₂Storage function), that is, in an oxidizing atmosphere where the exhaust air-fuel ratio is a lean air-fuel ratio, oxygen (O₂) Is absorbed, the exhaust air-fuel ratio becomes rich and the reducing atmosphere becomes O.₂As a result, the three-way catalyst 30 is stored in a storage atmosphere even in a reducing atmosphere.₂Thus, HC (hydrocarbon) and CO (carbon monoxide) can be oxidized and removed. That is, the three-way catalyst 30 can purify HC and CO in an oxidizing atmosphere as well as stored O 2.₂Thus, not only NOx purification but also HC and CO can be purified even in a reducing atmosphere. However, these active noble metals have an oxygen content as high as oxygen storage materials such as ceria (Ce).₂Does not have storage capability. Such a three-way catalyst 30 is weak O₂Called a storage converter catalytic converter.
[0029]
Further, downstream of the three-way catalyst 30 of the exhaust pipe 20 is O₂A sensor (breakthrough amount detection means, exhaust gas sensor) 24 is disposed. O₂The sensor 24 has an output voltage that changes according to the oxygen concentration, and exhibits a low voltage value when the air-fuel ratio is a lean air-fuel ratio, while it rapidly increases near the theoretical air-fuel ratio and is high when the air-fuel ratio is a rich air-fuel ratio. It is a sensor that indicates a voltage value.
[0030]
An ECU (electronic control unit) 40 including an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like is installed. Comprehensive control of the combustion control device including 1 is performed.
On the input side of the ECU 40, the above-described TPS 16, air flow sensor 18, and O₂Various sensors such as the sensor 24 are connected, and detection information from these sensors is input.
[0031]
On the other hand, various output devices such as the fuel injection valve 6 and the ignition coil 8 described above are connected to the output side of the ECU 40, and the fuel injection calculated based on detection information from various sensors is connected to these various output devices. The amount, fuel injection timing, ignition timing, etc. are output, respectively, whereby an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and spark ignition is performed at an appropriate timing by the spark plug 4.
[0032]
The operation of the exhaust emission control device according to the present invention configured as described above will be described below.
In the exhaust purification system of the present embodiment, in order to fully demonstrate the capability of the three-way catalyst 30, during normal operation, the ECU 40 forcibly alternates the air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio. ing. That is, here, as shown in FIG. 2, the air-fuel ratio A / F is modulated to be a lean air-fuel ratio for a certain period (lean time) and then to a rich air-fuel ratio for a certain period, and the lean air-fuel ratio and the rich air-fuel ratio are modulated. The fuel ratio is periodically repeated (air-fuel ratio forced variation means). The modulation waveform is a square wave here, but may be a triangular wave.
[0033]
As a result, when the exhaust air-fuel ratio is a lean air-fuel ratio, HC and CO are well purified and the three-way catalyst 30 O₂O by storage function₂Is stored, and when the exhaust air-fuel ratio is a rich air-fuel ratio, NOx is well purified and the stored O₂As a result, HC and CO are continuously purified.
In the exhaust purification system of this embodiment, it is possible to determine the deterioration of the three-way catalyst 30 at any time during normal operation.
[0034]
Referring to FIG. 3, a catalyst deterioration determination routine showing a procedure for determining catalyst deterioration is shown in a flow chart (deterioration determination means). Hereinafter, the catalyst deterioration determination according to the present invention will be described.
As described above, in the catalyst deterioration determination, it is necessary to change the air-fuel ratio between the lean air-fuel ratio and the rich air-fuel ratio. In this regard, in the present embodiment, as described above, the air-fuel ratio is forcibly changed in order to improve the exhaust purification efficiency during normal operation, and the catalyst deterioration can be determined.
[0035]
Then, under such forced air-fuel ratio variation, first, in step S10, catalyst optimization control is performed.
As shown in FIG. 7, an oxygen sensor provided downstream of the catalyst, that is, O₂Between the output value of the sensor 24 and the NOx purification efficiency, O₂It has been confirmed that there is a relationship that high NOx purification efficiency can be obtained if the air-fuel ratio is controlled in a balanced manner so that the output value of the sensor 24 falls within a predetermined range. Here, the degree of modulation is adjusted in this way. Thus, the exhaust purification efficiency of the three-way catalyst 30 is optimized.
[0036]
Specifically, for example, the air-fuel ratio is modulated and controlled in a balanced manner by adjusting the values of the lean air-fuel ratio and the rich air-fuel ratio while adjusting the average A / F to a predetermined value (near the stoichiometric range).₂The output value of the sensor 24 is set within a predetermined range.
At the same time, within the predetermined range of the output value, O of the three-way catalyst 30₂More than the breakthrough amount when the amount of storage is large (catalytic converter allowable oxygen storage amount) and less than the breakthrough amount when the catalyst deterioration is small ((catalyst large breakthrough amount) ≤ (O₂The modulation degree of the air-fuel ratio forced fluctuation is adjusted so that (storage amount) ≦ (passage amount when catalyst deterioration is small)).
[0037]
In other words, the air-fuel ratio is switched before the amount of oxygen stored at the lean air-fuel ratio reaches the breakthrough amount, or before the amount of oxygen released at the rich air-fuel ratio reaches the breakthrough amount, and at least the air-fuel ratio becomes lean. The oxygen concentration downstream of the three-way catalyst 30 does not change when the fuel ratio is at one of the fuel ratio and the rich air fuel ratio.₂Adjust the degree of modulation of the air-fuel ratio forced fluctuation so that the output of the sensor 24 does not fluctuate.₂Control the amount of storage.
[0038]
Specifically, O₂Since the storage amount and the lean air-fuel ratio time increase or decrease in correlation, the time ratio of the lean air-fuel ratio time or rich air-fuel ratio time to the modulation period ((lean air-fuel ratio time) based on FIG. 4 described above. / (Cycle)), that is, modulation is performed so that the air-fuel ratio duty is in a range not less than a value (0.05) corresponding to the overflow amount when the catalyst deterioration is large and not more than a value (0.3) corresponding to the overflow amount when the catalyst deterioration is small. Adjust the degree. In other words, the modulation is performed so that the time ratio of the lean air-fuel ratio time is in a range not less than (0.05) and not more than (0.3) or not less than (0.7) and not more than (0.95). Adjust the degree.
[0039]
Further, as described above with reference to FIG.₂Since the storage amount reaches the breakthrough amount, according to the map of FIG. 6, the modulation cycle is shortened and the air-fuel ratio is changed as the exhaust flow rate increases ((cycle) = f (exhaust flow rate)). At this time, the exhaust flow rate may be actually measured, but the exhaust flow rate correlation value (for example, vehicle speed, volumetric efficiency, intake air amount, net average effective pressure, air valve opening, engine rotation speed) Etc.).
[0040]
Further, as is apparent from FIG. 5, if the modulation period is 0.8 seconds or less, O₂In order to suppress the output fluctuation of the sensor 24 sufficiently small, the modulation period may be fixed to 0.8 seconds or less. However, if the modulation period is too short, the modulation is blurred in the upstream of the three-way catalyst 30 and the degree of air-fuel ratio modulation is reduced. Therefore, the modulation period is at least 0. It is good to set it as 3 seconds or more and the said 0.3 second or more and 0.8 second or less range. However, when the air-fuel ratio modulation upstream of the catalyst is estimated in advance as a map value as a function of frequency, the catalyst is determined by the amplitude rate (catalyst downstream air-fuel ratio amplitude / catalyst upstream air-fuel ratio amplitude) instead of the catalyst downstream air-fuel ratio amplitude. By performing the deterioration determination, the lower limit of 0.3 seconds can be removed.
[0041]
The time ratio of the lean air-fuel ratio time and the modulation period when adjusting the modulation degree may be instantaneous values or average values.
O₂If the degree of modulation is adjusted so that the output amplitude of the sensor 24 becomes small, then the breakthrough amount decreases and the oxygen concentration downstream of the three-way catalyst 30 begins to change, and O₂When the output fluctuation of the sensor 24 becomes large, the output fluctuation can be reliably detected.₂It becomes possible to easily detect that the storage capacity is reduced.
[0042]
In step S11, it is determined whether or not catalyst deterioration determination is to be started. In this embodiment, for example, the deterioration determination is performed every predetermined period or every predetermined traveling distance. Here, it is determined whether the predetermined period has elapsed or the predetermined traveling distance has been reached. It should be noted that the catalyst deterioration determination can always be performed during the air-fuel ratio forced fluctuation, and in this case, the determination in step S11 may be omitted.
[0043]
If the determination result in step S11 is true (Yes), the process proceeds to step S12, and O₂The output value of the sensor 24 is inspected and the O₂Based on the output value of the sensor 24, the O of the three-way catalyst 30₂It is determined whether or not the storage capacity is reduced.
When the amount of breakthrough decreases and the oxygen concentration downstream of the three-way catalyst 30 begins to change, as shown in FIG.₂The amplitude (variation width) W of the output fluctuation of the sensor 24 is O shown in FIG.₂It becomes larger than the amplitude Wmin when the storage capacity is high. Therefore, specifically, by determining whether or not any of the following conditions 1) to 4) is satisfied, O₂It is determined whether or not the storage capacity is reduced. 1) (O₂Sensor output amplitude) ≧ (predetermined value A)
2) ((O₂Sensor output) ≤ (predetermined value B1) time) ≤ (predetermined value B2)
3) (((O₂(Sensor output) ≦ (predetermined value C1) time) / ((O₂Sensor output)
≧ (time when predetermined value C2))) ≦ predetermined value C3
4) ((O₂Sensor output amplitude) / (air-fuel ratio forced modulation width)) ≧ predetermined value D
And as mentioned above, O₂Since the storage capacity and the catalyst performance (HC purification performance) of the three-way catalyst 30 are highly correlated, the determination result is true (Yes), and any of the above conditions 1) to 4) is satisfied, and O₂When it is determined that the storage capacity has decreased, the process proceeds to step S13, and it is determined that the three-way catalyst 30 has deteriorated.
[0044]
On the other hand, if the determination result in step S12 is false (No),₂When it is considered that the storage capacity has not decreased, it is determined that the three-way catalyst 30 has not yet deteriorated and is in a normal state.
In this way, the catalyst deterioration determination is performed. However, in the exhaust gas purification apparatus of the present invention, as described above, when the three-way catalyst 30 is not yet deteriorated,₂In order to positively control the storage amount, the modulation degree of the air-fuel ratio fluctuation is adjusted according to the breakthrough amount of the three-way catalyst 30, and when the three-way catalyst 30 is not deteriorated, the downstream of the three-way catalyst 30₂The output value fluctuation of the sensor 24 is kept small.
[0045]
Therefore, according to the exhaust gas purification apparatus, the amount of breakthrough is reduced and the three-way catalyst 30 O₂It is possible to easily and reliably detect that the storage capacity has deteriorated, and it is possible to always determine the deterioration of the three-way catalyst 30 with high accuracy.
Further, in the exhaust purification device of the present invention, the upstream side of the three-way catalyst 30 is O₂Without providing a sensor, O downstream of the three-way catalyst 30₂Only the sensor 24 determines the deterioration of the three-way catalyst 30. Accordingly, it is possible to perform the catalyst deterioration determination with high accuracy with simple and low cost.
[0046]
In the above embodiment, weak O₂Although the three-way catalyst 30 with storage capacity has been described as an example, even in a three-way catalyst containing ceria (Ce), the content of ceria (Ce) may be low, and the present invention is effectively applied. However, the catalytic converter is not limited to a three-way catalyst.
In the above embodiment, O₂The sensor 24 is used to₂Detected a drop in storage capacity, but O₂Instead of the sensor 24, an air-fuel ratio sensor (LAFS or the like) may be used.
[0047]
In the above embodiment, the air-fuel ratio is forcibly changed during normal operation. For example, air-fuel ratio feedback control is performed during normal operation, and the air-fuel ratio is forcibly changed only at the time of catalyst deterioration determination. Also good.
[0048]
【The invention's effect】
  As explained in detail above, according to the exhaust emission control device of claim 1 of the present invention,The lean air-fuel ratio time or rich air-fuel ratio time, which is the correlation value of the oxygen storage amount, is smaller than the breakthrough time corresponding to the predetermined breakthrough amount of the catalytic converter and corresponds to the breakthrough amount at the predetermined deterioration of the catalytic converter By changing the air / fuel ratio to be greater than the breakthrough time, it is usually possible to switch the air / fuel ratio before the lean air / fuel ratio reaches the breakthrough time or before the rich air / fuel ratio reaches the breakthrough time. Thus, the fluctuation of the exhaust air-fuel ratio downstream of the catalyst can be easily suppressed based on the time value. As a result, it is possible to easily determine that the catalytic converter has deteriorated due to a decrease in the oxygen storage capacity of the catalytic converter and to always accurately determine the catalytic converter.
[0049]
As a result, when it is observed that the current breakthrough amount or the breakthrough amount correlation value for the oxygen storage of the catalytic converter, that is, the allowable oxygen storage amount is decreased, the oxygen concentration downstream of the catalyst starts to change, and the downstream of the catalyst Although fluctuations in the exhaust air-fuel ratio increase, such changes and fluctuations can be reliably detected, and it is possible to always stably and accurately determine that the catalytic converter has deteriorated due to a decrease in the oxygen storage capacity of the catalytic converter. .
[0051]
  Claims2According to the exhaust gas purification apparatus of the present invention, the lean air-fuel ratio time ratio or rich air-fuel ratio time ratio with respect to a predetermined period, which is a correlation value of the oxygen storage amount, is smaller than the time ratio corresponding to the predetermined breakthrough amount of the catalytic converter. In addition, by modulating the air-fuel ratio so as to be larger than the time ratio corresponding to the breakthrough amount at the time of the predetermined deterioration of the catalytic converter, the lean air-fuel ratio time ratio is usually set to the time ratio corresponding to the breakthrough amount or the rich air-fuel ratio time. The air-fuel ratio is switched so that the ratio becomes a time ratio corresponding to the breakthrough amount, and the fluctuation of the exhaust air-fuel ratio downstream of the catalyst can be easily suppressed based on the time ratio with respect to the cycle. As a result, as described above, it is possible to easily determine that the oxygen storage capacity of the catalytic converter has deteriorated and the catalytic converter has deteriorated, and to always accurately determine.
[0053]
  Claims3According to this exhaust gas purification apparatus, the larger the exhaust gas flow rate or the exhaust gas flow rate correlation value, the larger the oxygen amount and HC, CO amount flowing into the catalytic converter per unit time, and the oxygen storage amount reaches the breakthrough amount early. By adjusting the air-fuel ratio by shortening the predetermined cycle as the flow rate or exhaust flow correlation value increases, the lean air-fuel ratio time usually reaches the breakthrough time before the lean air-fuel ratio time reaches the breakthrough time. The air-fuel ratio is switched before reaching, and fluctuations in the exhaust air-fuel ratio downstream of the catalyst can be kept small regardless of the exhaust flow rate or the exhaust flow rate correlation value. As a result, as described above, the catalytic converter can be easily deteriorated and can always be accurately determined.
[0055]
  Claims4According to this exhaust gas purification apparatus, when the oxygen concentration downstream of the catalyst begins to change and fluctuations in the exhaust air / fuel ratio downstream of the catalyst increase, these changes and fluctuations can be easily detected by the exhaust gas sensor downstream of the catalyst, It is possible to accurately and reliably determine that the storage capacity is reduced, the amount of breakthrough is reduced, and the catalytic converter is deteriorated without providing a separate sensor.
[0056]
  Claims5According to this exhaust gas purification apparatus, if the exhaust gas sensor downstream of the catalyst is used, especially the fluctuation range of the exhaust air-fuel ratio downstream of the catalyst can be easily detected. Based on the fluctuation range, the oxygen storage capacity of the catalytic converter is reduced. It is possible to accurately determine that the amount of breakthrough has decreased and the catalytic converter has deteriorated with a simple configuration without providing a separate sensor.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust emission control device according to the present invention mounted on a vehicle.
FIG. 2 is a diagram showing a modulation waveform of an air-fuel ratio (A / F).
FIG. 3 is a flowchart showing a catalyst deterioration determination routine.
FIG. 4 shows a lean air-fuel ratio time ratio with respect to a predetermined period and O provided downstream of the catalyst.₂It is a figure which shows the relationship with the output amplitude of a sensor.
FIG. 5 shows the period of forced air-fuel ratio fluctuation and O provided downstream of the catalyst.₂It is the figure which showed the relationship with the output amplitude of a sensor for every exhaust gas flow rate (at the time of the low flow rate and the high flow rate).
FIG. 6 is a map showing a relationship between an exhaust flow rate and a cycle.
FIG. 7 shows O provided downstream of the catalyst.₂It is a figure which shows the relationship between the output value of a sensor, and NOx purification efficiency.
FIG. 8₂O as storage capacity declines₂It is a figure which shows the change of the output fluctuation of a sensor.
[Explanation of symbols]
1 Engine body
24 O₂Sensor (breakthrough amount detection means, exhaust gas sensor)
30 Three-way catalyst (catalytic converter)
40 ECU (Electronic Control Unit)

Claims (5)

A catalytic converter provided in an exhaust passage of the internal combustion engine;
An air-fuel ratio forcibly varying means for forcibly varying the air-fuel ratio with a predetermined period and amplitude between a lean air-fuel ratio and a rich air-fuel ratio;
Breakthrough amount detection means for detecting a current breakthrough amount or a breakthrough amount correlation value for oxygen storage of the catalytic converter;
Deterioration determining means for determining deterioration of the catalytic converter based on a current breakthrough amount or a breakthrough amount correlation value detected by the breakthrough amount detection means,
The oxygen storage amount increases or decreases in correlation with the lean air-fuel ratio time or the rich air-fuel ratio time,
The air-fuel ratio forced variation means has a lean air-fuel ratio time or a rich air-fuel ratio time that is shorter than a breakthrough time corresponding to a predetermined breakthrough amount when the catalytic converter is not deteriorated and is broken when the catalytic converter is deteriorated. An exhaust emission control device that modulates an air-fuel ratio so as to be longer than a breakthrough time corresponding to an excessive amount . The air-fuel ratio forced variation means is configured such that the lean air-fuel ratio time ratio or the rich air-fuel ratio time ratio with respect to the predetermined cycle is smaller than a time ratio corresponding to a predetermined amount of breakthrough when the catalytic converter is not deteriorated and the predetermined ratio of the catalytic converter. exhaust gas purification device in which the is characterized by modulating the air-fuel ratio to be greater than the time ratio corresponding to the breakthrough amount of time deterioration, according to claim 1. The air-fuel ratio forcibly changing means modulates the air-fuel ratio by shortening the predetermined period, which is the sum of the lean air-fuel ratio time and the rich air-fuel ratio time, as the exhaust flow rate or the exhaust flow rate correlation value increases. The exhaust emission control device according to claim 1 . The exhaust gas purification device according to any one of claims 1 to 3, wherein the breakthrough amount detection means is an exhaust gas sensor that is provided downstream of the catalytic converter and detects an oxygen concentration. 5. The exhaust emission control device according to claim 4 , wherein the deterioration determination means determines deterioration of the catalytic converter using a fluctuation range or fluctuation range correlation value of an output value from the exhaust gas sensor as a breakthrough amount correlation value.

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