JP4092485B2 - Exhaust gas purification catalyst deterioration diagnosis device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst deterioration diagnosis device.
[0002]
[Prior art]
Conventionally, it is known to diagnose the deterioration state of an exhaust gas purification catalyst for exhaust improvement.
[0003]
Patent Document 1 discloses an internal combustion engine that includes a NOx trap catalyst provided in an exhaust passage of an internal combustion engine, and an intake / release control unit that makes the air-fuel ratio of exhaust gas rich so as to regenerate the NOx absorption capability of the NOx trap catalyst. An exhaust purification device for an engine, wherein the air-fuel ratio of exhaust gas flowing into the NOx trap catalyst is made richer than when the NOx trap capability is temporarily regenerated, and the air-fuel ratio of exhaust gas flowing out from the NOx trap catalyst at that time Discloses that the deterioration of the NOx trap catalyst is diagnosed based on the time during which the air-fuel ratio is rich.
[0004]
In Patent Document 2, a three-way catalyst, a binary O2 sensor, a NOx purification device, and a binary O2 sensor are arranged in this order in the exhaust system of the internal combustion engine. Then, when the air-fuel ratio is enriched, the timer measurement value tmMON2 from the upstream O2 sensor output change point to the downstream O2 sensor output change point and the upstream side when the air-fuel ratio is returned to lean It is disclosed that the corrected timer measurement value tmMON2C is calculated based on the timer measurement value tmMON3 from the O2 sensor output change point to the downstream O2 sensor output change point to diagnose the deterioration of the NOx purification device. ing.
[0005]
Further, in Patent Document 3, in order to check the inherent characteristics of the NOx trap catalyst, the air-fuel ratio of the exhaust gas is switched from lean to rich, and at least rich beyond the time required for complete desorption of NOx. After the rich phase is extended until the exhaust gas in the state has just passed through the catalyst, and the time interval Δt1 that occurs between the first switching and the breakthrough of the rich exhaust gas, and after switching from rich to lean operation again, Measuring the time interval Δt2 occurring between the switching of 2 and the passage of oxygen through the catalyst, and using the time differences Δt1 and Δt2 for separate evaluation of the oxygen trap function and the NOx trap function of the catalyst Has been.
[0006]
Further, in Patent Document 4, NOx emission from the NOx trap catalyst is made in order to prevent the output torque of the engine from changing when the average air-fuel ratio in the combustion chamber is switched from lean to rich so as to release NOx from the NOx trap catalyst. It is disclosed that sometimes the EGR control valve is opened or the intake control valve opening is decreased to reduce the intake air amount, and at the same time the fuel injection amount is increased so that the engine output torque does not change. .
[0007]
[Patent Document 1]
JP 2002-38929 A
[Patent Document 2]
JP 2001-73747 A
[Patent Document 3]
JP-A-11-324654
[Patent Document 4]
Japanese Patent Laid-Open No. 7-279718
[0008]
[Problems to be solved by the invention]
However, the above-described apparatus has a problem in terms of accuracy of deterioration diagnosis. That is, when variation occurs in the air-fuel ratio control during the rich spike operation, the output value of the air-fuel ratio changes with time, so that there is a problem that an erroneous deterioration diagnosis is made.
[0009]
Here, the improvement of the air-fuel ratio control accuracy of the rich spike control is of course important, but the control accuracy by feedback by a sensor (for example, an air-fuel ratio sensor) that detects the exhaust gas atmosphere at the time of the rich spike operation for several seconds at most. The improvement is naturally limited, and it has been necessary to diagnose catalyst deterioration on the assumption that there is always a predetermined amount of air-fuel ratio control error.
[0010]
In view of such a problem, an object of the present invention is to appropriately diagnose the degree of deterioration of an exhaust gas purification catalyst.
[0011]
[Means for Solving the Problems]
Therefore, in the present invention, during the rich spike control, the first exhaust gas atmosphere detection means detects a parameter related to the ratio of the oxidant and the reductant in the exhaust gas flowing in from the upstream of the exhaust gas purification catalyst, and the second The exhaust gas atmosphere detection means detects a parameter related to the ratio of the oxidizing agent and the reducing agent in the exhaust gas that has passed through the exhaust gas purification catalyst, while the output value of the first exhaust gas atmosphere detection means is The proportion of reducing agent is higher than the proportion of oxidizing agent Reached a predetermined value When the output value of the second exhaust gas atmosphere detection means is on the side where the ratio of the reducing agent is larger than the ratio of the oxidant than the output value of the first exhaust gas atmosphere detection means, The difference between the output value of the first exhaust gas atmosphere detection means and the output value of the second exhaust gas atmosphere detection means is calculated, and the deterioration of the exhaust gas purification catalyst is diagnosed based on this difference.
[0012]
【The invention's effect】
According to the present invention, since the difference between the output values of the first and second exhaust gas atmosphere detecting means is used as a diagnostic parameter, the exhaust gas purification catalyst is deteriorated even if the air-fuel ratio varies in rich spike control. Can be diagnosed appropriately.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an internal combustion engine (diesel engine) including an exhaust gas purification catalyst.
[0014]
In the intake system of the engine 1, an air cleaner 3 is disposed upstream of the intake passage 2, and on the downstream thereof, an air flow meter 4, an intake compressor 6 of a supercharger 5, an intercooler 7, an intake throttle valve 8, and a collector They are arranged in the order of 9.
[0015]
The engine 1 is provided with an injector 14 and a glow plug 15. The injector 14 is attached to an electronically controlled fuel injection device composed of a common rail 16, an injection pump 17 and the like, and controls the fuel injection timing, the fuel injection amount, etc. Oxidant in exhaust gas (O ₂ ) And the reducing agent (HC, CO) ratio (oxygen concentration, air-fuel ratio) can be changed, and rich spike control is also possible. The rich spike control method is known in Patent Document 1 and will not be described in detail. For example, there is a method of decreasing the opening of the intake throttle valve and increasing the fuel injection amount.
[0016]
Further, the exhaust passage 11 is provided with an exhaust turbine 12 of the supercharger 5, and an EGR pipe 20 for returning a part of the exhaust gas to the intake passage 2 is led out from the upstream thereof. The EGR pipe 20 is provided with an EGR valve 21 that controls the amount of EGR gas.
[0017]
Further, a NOx trap catalyst 13 as an exhaust gas purification catalyst is disposed downstream of the exhaust turbine 12 in order to purify the exhaust gas.
The NOx trap catalyst 13 has a function of trapping NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and reducing and purifying the trapped NOx when the air-fuel ratio is rich. It has an oxidation function and has an oxygen storage function.
[0018]
In order to detect parameters (oxygen concentration, air-fuel ratio) related to the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst 13 and the ratio of the oxidant and the reductant in the exhaust gas that has passed through the catalyst 13, A sensor 18 and an outlet atmosphere sensor 19 are respectively arranged. The atmosphere sensors 18 and 19 output a signal (voltage) corresponding to the air-fuel ratio in the exhaust gas. As the atmosphere sensors 18 and 19, it is preferable to use an O 2 sensor, a wide area air-fuel ratio sensor, a NOx sensor, or the like.
[0019]
The engine control device (not shown) receives signals from the air flow meter 4, the inlet atmosphere sensor 18, the outlet atmosphere sensor 19, and the like, and based on these signals, opens and closes the intake throttle valve 8 and the injection pump. 17 (fuel injection timing and fuel injection amount of the injector 14), EGR valve 21 and the like are controlled.
[0020]
Here, the necessity of regeneration of the NOx trap catalyst and a conventional method for diagnosing the degree of catalyst deterioration will be described.
Conventionally, in an internal combustion engine mounted on an automobile or the like, particularly a lean combustion type internal combustion engine (diesel engine) capable of combusting a lean (oxygen-rich) mixture, NOx (nitrogen) when the air-fuel ratio of the exhaust gas is lean As a technique for treating (oxide), an exhaust gas purification device in which a NOx trap catalyst is disposed in an exhaust passage of an internal combustion engine is known.
[0021]
The NOx trap catalyst is a technology for treating NOx when the air-fuel ratio of the exhaust gas is lean. The NOx trap catalyst traps NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean in the exhaust passage of the internal combustion engine. It has a function of releasing and purifying trapped NOx when the air-fuel ratio is rich.
[0022]
Since the NOx trap capacity of the NOx trap catalyst is limited, it is necessary to release and reduce NOx trapped in the NOx trap catalyst at an appropriate timing before the NOx absorption capacity of the NOx trap catalyst is saturated.
[0023]
Therefore, conventionally, in the exhaust gas purification device, the reducing agent is supplied to the exhaust gas upstream of the NOx trap catalyst 13 at a suitable timing in a short cycle, and the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst is temporarily set. So-called rich spike control is performed in which NOx trapped in the NOx trap catalyst is released and reduced and reduced.
[0024]
On the other hand, in an exhaust gas purification apparatus as described in the prior art, high exhaust gas purification efficiency can be obtained, and therefore it is more important than ever to accurately detect abnormality of the NOx trap catalyst.
[0025]
In response to such a demand, as shown in Patent Documents 1 to 3, the air-fuel ratio of the exhaust gas flowing out from this catalyst is measured during rich spike control for releasing and purifying NOx trapped in the NOx trap catalyst. A method of diagnosing the deterioration of the NOx trap catalyst based on the time during which the measured air-fuel ratio is maintained near the stoichiometric air-fuel ratio has been proposed.
[0026]
FIG. 2 is a view showing deterioration diagnosis of a NOx trap catalyst in a conventional exhaust gas purifying device, and in the vicinity of the theoretical air fuel ratio when the air fuel ratio is changed during rich spike operation to the NOx trap catalyst in the same deterioration state. It is a figure which shows the mode of the change of the time (second) currently maintained by. Λ in the figure _F0 Is the target rich air-fuel ratio during rich spike control, λ _F Is the catalyst inlet (upstream) air-fuel ratio, λ _R Indicates the catalyst outlet (downstream) air-fuel ratio. FIG. 2A shows the target rich air-fuel ratio λ during the rich spike control. _F0 When (R) is richer than the reference, (B) shows the case of the reference, and (C) shows the case of leaner than the reference.
[0027]
As shown in the figure, when the actual air-fuel ratio shifts to the rich side with respect to the air-fuel ratio at the time of the rich spike, the time that is maintained in the vicinity of the theoretical air-fuel ratio is shortened, and conversely, it becomes longer when it is shifted to the lean side There is. Conventionally, using this property, the deterioration of the NOx trap catalyst has been diagnosed based on the time maintained near the theoretical air-fuel ratio.
[0028]
However, if the control of the target rich air-fuel ratio at the time of rich spike operation varies, the time that is maintained in the vicinity of the theoretical air-fuel ratio changes. Therefore, in the conventional technique for setting a predetermined time and judging deterioration, There is a problem that even a deteriorated catalyst is erroneously diagnosed as being deteriorated.
[0029]
Although it is important to improve the control accuracy of the target rich air-fuel ratio during the rich spike operation, feedback by a sensor (for example, an oxygen sensor or an air-fuel ratio sensor) that detects the exhaust gas atmosphere during the rich spike operation for several seconds at most. Therefore, it is necessary to diagnose the deterioration of the catalyst on the assumption that there is always a predetermined amount of air-fuel ratio control error.
[0030]
Therefore, in the present invention, the deterioration state of the catalyst 13 is diagnosed using the oxygen storage function of the NOx trap catalyst 13.
FIG. 3 is a diagram showing the time (seconds) when the lean operation and the rich spike operation are performed and the output voltage of the atmosphere sensor when performing the deterioration diagnosis of the catalyst in the first embodiment of the present invention. is there. Thin line VO2 shown in FIG. _F Is the output voltage of the inlet atmosphere sensor, thick line VO2 _R Indicates the output voltage of the outlet atmosphere sensor.
[0031]
In the first embodiment of the present invention, an inlet O2 sensor 18 as an inlet atmosphere sensor and an outlet O2 sensor 19 as an outlet atmosphere sensor are disposed upstream and downstream of the NOx trap catalyst 13, respectively.
[0032]
Here, the output voltage VO2 of the inlet O2 sensor 18 _F And the output voltage VO2 of the outlet O2 sensor 19 _R Will be described.
Since the amount of air supplied to the engine 1 increases during normal operation, the air-fuel ratio in the exhaust gas is lean. From this state, the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst 13 is a predetermined value VO2 on the rich side. _F0 In order to perform rich spike control so that the output voltage VO2 of the inlet O2 sensor 18 is _F Is the predetermined value VO2 _F0 (Time ac in FIG. 3).
[0033]
At this time, the output voltage VO2 of the outlet O2 sensor 19 _R Becomes the output voltage at stoichiometric (theoretical air-fuel ratio) for a predetermined time according to the deterioration state of the NOx trap catalyst 13 (time ab in FIG. 3). This is because the air-fuel ratio flowing into the NOx trap catalyst 13 is rich, that is, the ratio of reducing agents (HC, CO) in the exhaust gas is oxidant (O ₂ This is because the reducing agent undergoes a combustion reaction with the gas phase oxygen in the exhaust gas and the oxygen stored in the catalyst 13 even in a state where the ratio is greater than the ratio of
[0034]
Then, after all the oxygen stored in the catalyst 13 is consumed, the gas phase oxygen (oxidant) flowing into the catalyst 13 becomes the reducing agent. React with As a result, the amount of oxygen further decreases, so the output voltage VO2 of the outlet O2 sensor 19 _R Is the output voltage VO2 of the inlet O2 sensor 18 _F It further decreases (time b to c in FIG. 3).
[0035]
At this time, when the NOx trap catalyst 13 is deteriorated, the oxygen storage function of the catalyst 13 is lowered, and the reactivity between the reducing agent in the exhaust gas and the gas phase oxygen is lowered. 19 output voltage VO2 _R Is the output voltage VO2 of the inlet O2 sensor 18 _F There is a nature that approaches. And the output voltage difference VOBD at this time (time b to c in FIG. 3) _O2 To calculate this difference VOBD _O2 Based on the above, the degree of deterioration of the catalyst 13 is diagnosed. For this reason, the target output voltage (VO2 when performing rich spike control) _F0 ), The output voltage VO2 of the inlet O2 sensor 18 _F And the output voltage VO2 of the outlet O2 sensor 19 _R Output voltage difference with VOBD _O2 = VO2 _F -VO2 _R Based on the above, it is possible to diagnose whether or not the catalyst 13 exceeds the upper limit of deterioration.
[0036]
Next, the deterioration diagnosis process of the NOx trap catalyst 13 will be described with reference to the flowchart of FIG.
In step 1 (shown as “S1” in the figure, the same applies hereinafter), rich spike calculation flag F _rich Is checked to determine if the rich spike operation is in progress. This is for diagnosing the deterioration state of the NOx trap catalyst 13 during the rich spike operation. Operation flag F _rich Is true (F _rich = True), that is, when the rich spike operation is being performed, the process proceeds to Step 2. On the other hand, the calculation flag F _rich Is false (F _rich If not (True), the routine proceeds to step 14, where the exhaust gas processing diagnostic flag F_OBD_ATS is set to false (F_OBD_ATS = False), and the processing is terminated.
[0037]
In step 2, the output voltage VO2 of the inlet O2 sensor 18 _F Is the predetermined value VO2 on the rich side of the air-fuel ratio _F0 Is determined (VO2 in FIG. 3). _F0 reference). Voltage VO2 _F Is the predetermined value VO2 _F0 Is reached (VO2 _F = VO2 _F0 ) Go to Step 3. The predetermined value VO2 _F0 Is a target value of the air-fuel ratio in the exhaust gas flowing into the NOx trap catalyst 13 when performing the rich spike, and it is preferable to use a value determined in advance by experiments or the like. On the other hand, the output voltage VO2 _F Is the predetermined value VO2 _F0 Is not reached (VO2 _F ≠ VO2 _F0 ) Proceeds to step 14 described above.
[0038]
In step 3, the output voltage VO2 of the outlet O2 sensor 19 _R Is the predetermined value VO2 on the rich side of the air-fuel ratio _R0 Less than (VO2 _R <VO2 _R0 ), That is, whether or not the exhaust gas after passing through the NOx trap catalyst 13 is rich. The output voltage VO2 _R Is the predetermined value VO2 _R0 Less than (VO2 _R <VO2 _R0 ), Go to step 4. On the other hand, the output voltage VO2 _R Is the predetermined value VO2 _R0 (VO2 _R ≧ VO2 _R0 ), The process proceeds to step 14 described above. This is the output voltage VO2 of the outlet O2 sensor 19. _R This is for diagnosing the deterioration state of the catalyst 13 when the engine is rich. The predetermined value VO2 _R It is preferable to use a value predetermined by experiment or the like.
[0039]
In step 4, the exhaust gas processing diagnostic flag F_OBD_ATS is set to true (F_OBD_ATS = True).
In step 5, the output voltage VO2 of the inlet O2 sensor 18 and the outlet O2 sensor 19 is obtained. _F , VO2 _R Difference of VOBD _O2 = VO2 _F -VO2 _R Is calculated (see times b to c in FIG. 3).
[0040]
In step 6, the output voltage difference VOBD of the O2 sensors 18, 19 _O2 Is a positive value (+), that is, the H x is reduced by the reducing agent that flows into the NOx trap catalyst 13 during the rich operation. ₂ It is examined whether or not other reducing agents such as can be generated. Output voltage difference VOBD _O2 If is a positive value (+), go to Step 7. On the other hand, the output voltage difference VOBD _O2 Is negative value (−), the routine proceeds to step 13 where the exhaust gas processing diagnosis flag F_ATS_NG is set to the previous diagnosis result F_ATS_NG. _n-1 (F_ATS_NG = F_ATS_NG _n-1 ), The process is terminated.
[0041]
In step 7, the output voltage difference VOBD of the O2 sensors 18 and 19 _O2 Is the predetermined value VOBD _O20 (VOBD) _O2 > VOBD _O20 ). Output voltage difference VOBD _O2 Is the predetermined value VOBD _O20 Exceeds VOBD (VOBD _O2 > VOBD _O20 ) Go to Step 8. On the other hand, the output voltage difference VOBD of the O2 sensors 18 and 19 _O2 Is the predetermined value VOBD _O20 If (VOBD) _O2 ≦ VOBD _O20 ) Proceeds to step 13 described above.
[0042]
In step 8, the final output voltage difference VOBD _F Output voltage difference VOBD _O2 To the same value (VOBD _F = VOBD _O2 ). Thus, the final output voltage difference VOBD of the O2 sensors 18 and 19 _F Confirm.
[0043]
In step 9, the output voltage difference VOBD of the O2 sensors 18, 19 _O2 Clear (VOBD _O2 = 0).
In step 10, the final output voltage difference VOBD _F Is the deterioration diagnosis threshold value VOBD of the catalyst 13 _FSL Greater than (VOBD) _F > VOBD _FSL ). Thereby, it is diagnosed whether the NOx trap catalyst 13 exceeds the deterioration upper limit. Final output voltage difference VOBD _F Is the deterioration diagnosis threshold VOBD _FSL Greater than (VOBD _F > VOBD _FSL ), It is diagnosed that the deterioration of the catalyst 13 has not reached the upper limit, and the routine proceeds to step 11. On the other hand, VOBD _F Is the deterioration diagnosis threshold VOBD _FSL Below (VOBD _F ≦ VOBD _FSL ), The process proceeds to step 12 where it is diagnosed that the deterioration of the catalyst 13 exceeds the upper limit, the exhaust gas treatment diagnosis flag F_ATS_NG is set to true (F_ATS_NG = True), and the process is terminated.
[0044]
In step 11, it is diagnosed that the deterioration of the NOx trap catalyst 13 is within the upper limit range, the exhaust gas treatment diagnosis flag F_ATS_NG is set to false (F_ATS_NG = False), and the process is terminated.
[0045]
According to the present embodiment, an oxidant (O in the exhaust gas that is disposed upstream of the exhaust gas purification catalyst (NOx trap catalyst) 13 and flows into the catalyst 13. ₂ ) And a reducing agent (HC, CO) ratio (oxygen concentration) related to the first exhaust gas atmosphere detection means (inlet O2 sensor) 18 for detecting a parameter, and a catalyst disposed downstream of the exhaust gas purification catalyst 13 A second exhaust gas atmosphere detection means (exit O2 sensor) 19 for detecting a parameter (oxygen concentration) related to the ratio of the oxidant and the reductant in the exhaust gas that has passed through 13, and a first exhaust gas atmosphere detection Output value (output voltage) VO2 of means 18 _F Is the predetermined value VO2 _F0 (Step 2), the output value VO2 of the first exhaust gas atmosphere detection means 18 is reached. _F And the output value VO2 of the second exhaust gas atmosphere detection means 19 _R Difference VOBD _O2 (Step 5), and this difference VOBD _O2 And a diagnostic means (step 10) for diagnosing deterioration of the exhaust gas purification catalyst 13 based on the above. Therefore, the output value VO2 of the inlet O2 sensor 18 _F And the output value VO2 of the outlet O2 sensor 19 _R Difference VOBD _O2 Can be used as a diagnostic parameter, and the target rich air-fuel ratio VO2 in the rich spike control _F0 Even if this variation occurs, the deterioration of the NOx trap catalyst 13 can be properly diagnosed.
[0046]
Further, according to the present embodiment, the diagnosis means outputs the output value VO2 of the first exhaust gas atmosphere detection means (inlet O2 sensor) 18. _F Is the predetermined value VO2 _F0 (Step 2), the output value VO2 of the second exhaust gas atmosphere detection means (exit O2 sensor) 19 is reached. _R Is the output value VO2 of the first exhaust gas atmosphere detection means 18 _F Output value VO2 of the first exhaust gas atmosphere detection means 18 (step 6). _F And the output value VO2 of the second exhaust gas atmosphere detection means 19 _R Difference VOBD _O2 (Step 5), and this difference VOBD _O2 Based on this, the deterioration of the exhaust gas purification catalyst 13 is diagnosed (step 10). Therefore, the output value VO2 of the outlet O2 sensor 19 _R Is the output value VO2 of the inlet O2 sensor 18 _F The NOx trap catalyst 13 from the reducing agent (HC, CO) to hydrogen (H ₂ ) Is considered to generate a reducing agent that affects the detection output, and the reaction capability of the catalyst 13 is determined by the difference between the output values before and after the catalyst 13 (the ratio between the oxidizing agent and the reducing agent). VOBD _O2 In this manner, deterioration of the catalyst 13 can be diagnosed by using it as a diagnostic parameter.
[0047]
Further, according to the present embodiment, the first and second exhaust gas atmosphere detection means are means for detecting the oxygen concentration in the exhaust gas (inlet O2 sensor 18 and outlet O2 sensor 19). For this reason, it is possible to detect the oxygen release at the NOx trap catalyst 13 and the generation of the reducing agent (HC, CO) at the catalyst 13 after the end of the oxygen release, and the deterioration of the catalyst 13 can be diagnosed. Then, the deterioration state of the catalyst 13 can be diagnosed while maintaining the usage for purifying NOx by the NOx trap catalyst 13 without making the air-fuel ratio of the exhaust gas stoichiometric.
[0048]
FIG. 5 is a flowchart showing a deterioration diagnosis process of the exhaust gas purification catalyst 13 according to the second embodiment. In the present embodiment, an inlet air-fuel ratio sensor 18 as an inlet atmosphere sensor and an outlet air-fuel ratio sensor 19 as an outlet atmosphere sensor are arranged upstream and downstream of the NOx trap catalyst 13, respectively, and the difference in air-fuel ratio (excess air ratio). VOBDλ is obtained, and the deterioration of the catalyst 13 is diagnosed based on this. In FIG. 3, a thin line indicates the inlet air-fuel ratio (inlet air excess ratio) λ _F , Outlet air-fuel ratio (exit air excess ratio) λ _R Respectively.
[0049]
FIG. 6 shows the air-fuel ratio λ by the air-fuel ratio sensors 18 and 19. _F , Λ _R It is a flowchart which shows the arithmetic processing of. The calculation processes of these sensors 18 and 19 are the same.
In step 21 of FIG. 6, the pump current values of the air-fuel ratio sensors 18 and 19 are read.
[0050]
In step 22, the actual air-fuel ratio Rlamb0 is obtained by a table or calculation of the pump currents of the air-fuel ratio sensors 18 and 19 and the actual air-fuel ratio Rlamb0 shown in FIG.
[0051]
In step 23, the weighted average processing of the actual air-fuel ratio Rlamb0 is performed upstream and downstream of the catalyst 13, and the inlet air-fuel ratio λ _F And outlet air-fuel ratio λ _R Are calculated respectively.
And these air-fuel ratio λ _F , Λ _R Based on the above, the deterioration diagnosis process of the catalyst 13 according to the flowchart of FIG.
[0052]
In step 1 of FIG. 5, the rich spike calculation flag F _rich Is checked to determine if the rich spike operation is in progress. Operation flag F _rich Is true (F _rich = True) Go to step 2. On the other hand, the calculation flag F _rich Is false (F _rich If not (True), the routine proceeds to step 14, where the exhaust gas processing diagnostic flag F_OBD_ATS is set to false (F_OBD_ATS = False), and the processing is terminated.
[0053]
In step 2, the inlet air-fuel ratio λ _F Is the predetermined value λ on the rich side of the air-fuel ratio _F0 Is determined (λ in FIG. 3). _F0 reference). Inlet air-fuel ratio λ _F Is the predetermined value λ _F0 Is reached (λ _F = Λ _F0 ) Go to Step 3. On the other hand, the predetermined value λ _F0 Is not reached (λ _F ≠ λ _F0 ) Proceeds to step 14 described above.
[0054]
In step 3, the outlet air-fuel ratio λ _R Is the predetermined value λ on the rich side of the air-fuel ratio _R0 Less than (λ _R <Λ _R0 ) Or not. Predetermined value λ _R0 Less than (λ _R <Λ _R0 ), Go to step 4. On the other hand, the predetermined value λ _R0 (Λ _R ≧ λ _R0 ), The process proceeds to step 14 described above.
[0055]
In step 4, the exhaust gas processing diagnostic flag F_OBD_ATS is set to true (F_OBD_ATS = True).
In step 5, the inlet air-fuel ratio λ _F And outlet air-fuel ratio λ _R Difference VOBDλ = λ _F −λ _R Is calculated (see times b to c in FIG. 3).
[0056]
In step 6, it is determined whether or not the air-fuel ratio difference VOBDλ is a positive value (+). When the air-fuel ratio difference VOBDλ is a positive value (+), the routine proceeds to step 7. On the other hand, if it is a negative value (−), the routine proceeds to step 13 where the exhaust gas processing diagnosis flag F_ATS_NG is set to the previous diagnosis result F_ATS_NG. _n-1 (F_ATS_NG = F_ATS_NG _n-1 ), The process is terminated.
[0057]
In step 7, the air-fuel ratio difference VOBDλ is a predetermined value VOBDλ. ₀ (VOBDλ> VOBDλ) ₀ ). Predetermined value VOBDλ ₀ (VOBDλ> VOBDλ) ₀ ) Go to Step 8. On the other hand, the predetermined value VOBDλ ₀ In the following case (VOBDλ ≦ VOBDλ ₀ ) Proceeds to step 13 described above.
[0058]
In step 8, the final air-fuel ratio difference VOBD _F The value of the air-fuel ratio difference VOBDλ is substituted as λ (VOBD) _F λ = VOBDλ).
In step 9, the air-fuel ratio difference VOBDλ is set to 0 (VOBDλ = 0).
[0059]
In step 10, the final air-fuel ratio difference VOBD _F λ is a deterioration diagnosis threshold value VOBDλ of the catalyst 13 _FSL Greater than (VOBD) _F λ> VOBDλ _FSL ). Thereby, it is diagnosed whether the NOx trap catalyst 13 exceeds the deterioration upper limit. Final air-fuel ratio difference VOBD _F λ is a deterioration diagnosis threshold value VOBDλ of the catalyst 13 _FSL Greater than (VOBD _F λ> VOBDλ _FSL ), It is diagnosed that the deterioration of the catalyst 13 has not reached the upper limit, and the routine proceeds to step 11. On the other hand, VOBD _F λ is a deterioration diagnosis threshold value VOBDλ _FSL Below (VOBD _F λ ≦ VOBDλ _FSL ), The process proceeds to step 12 where it is diagnosed that the deterioration of the catalyst 13 exceeds the upper limit, the exhaust gas treatment diagnosis flag F_ATS_NG is set to true (F_ATS_NG = True), and the process is terminated.
[0060]
In step 11, the exhaust gas processing diagnosis flag F_ATS_NG is set to false (F_ATS_NG = False), and the process is terminated.
According to the present embodiment, an oxidant (O in the exhaust gas that is disposed upstream of the exhaust gas purification catalyst (NOx trap catalyst) 13 and flows into the catalyst 13. ₂ ) And a reducing agent (HC, CO), a first exhaust gas atmosphere detection means (inlet air / fuel ratio sensor) 18 for detecting a parameter (air / fuel ratio) related to the ratio of the reducing agent (HC, CO) and an exhaust gas purification catalyst 13. A second exhaust gas atmosphere detection means (exit air / fuel ratio sensor) 19 for detecting a parameter (air / fuel ratio) related to the ratio of the oxidizing agent and the reducing agent in the exhaust gas that has passed through the catalyst 13, and the first exhaust gas. Output value λ of atmosphere detecting means 18 _F Is the predetermined value λ _F0 (Step 2), the output value λ of the first exhaust gas atmosphere detection means 18 _F And the output value λ of the second exhaust gas atmosphere detection means 19 _R And a diagnosing means (step 10) for diagnosing the deterioration of the exhaust gas purification catalyst 13 based on the difference VOBDλ. Therefore, the output value λ of the inlet air-fuel ratio sensor 18 _F And the output value λ of the outlet air-fuel ratio sensor 19 _R VOBDλ can be used as a diagnostic parameter, and the target rich air-fuel ratio λ in rich spike control _F0 Even if this variation occurs, the deterioration of the NOx trap catalyst 13 can be properly diagnosed.
[0061]
Further, according to the present embodiment, the first and second exhaust gas atmosphere detection means are configured to detect the air-fuel ratio λ in the exhaust gas. _F , Λ _R (Inlet air / fuel ratio sensor 18, outlet air / fuel ratio sensor 19). For this reason, oxygen (O ₂ ) And the generation of the reducing agent (HC, CO) in the catalyst 13 after the end of the oxygen release can be estimated as the air-fuel ratio difference VOBDλ, and based on this, the deterioration of the catalyst 13 can be properly diagnosed.
[0062]
In the above embodiment, when the NOx trap catalyst 13 having an oxygen storage function is provided as the exhaust gas purification catalyst, the deterioration diagnosis of the catalyst 13 is performed. However, as shown in FIG. A diesel particulate filter (shown as “DPF” in the figure) 24 for collecting exhaust particulates may be disposed downstream of the exhaust gas to further purify the exhaust gas.
[0063]
Further, as shown in FIG. 9, the oxidation catalyst 23 is separated from the NOx trap catalyst 13 and arranged upstream, and the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 23 is detected by the inlet air-fuel ratio sensor 18, The air-fuel ratio of the exhaust gas that has passed through the NOx trap catalyst 13 may be detected by the outlet air-fuel ratio sensor 19. In this case, even if the NOx trap catalyst 13 does not have an oxygen storage function, the oxidation catalyst 23 stores and supplies oxygen, so that the output value λ of the inlet air-fuel ratio sensor 18 is similar to the above-described processing. _F And the output value λ of the outlet air-fuel ratio sensor 19 _R The deterioration state of the NOx trap catalyst 13 can be diagnosed based on the difference VOBDλ.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an internal combustion engine provided with an exhaust gas purification catalyst.
FIG. 2 is a diagram showing deterioration diagnosis of a conventional NOx trap catalyst.
FIG. 3 is a diagram showing time and output values of an inlet atmosphere sensor and an outlet atmosphere sensor.
FIG. 4 is a flowchart showing catalyst deterioration diagnosis processing by an O2 sensor.
FIG. 5 is a flowchart showing catalyst deterioration diagnosis processing by an air-fuel ratio sensor.
FIG. 6 is a flowchart showing a weighted average process of the air-fuel ratio sensor.
FIG. 7 is a table showing pump current and actual air-fuel ratio of an air-fuel ratio sensor.
FIG. 8 is a diagram in which a DPF is disposed downstream of a NOx trap catalyst.
FIG. 9 is a diagram in which an oxidation catalyst is disposed upstream of a NOx trap catalyst and a DPF is disposed downstream.
[Explanation of symbols]
1 engine
2 Intake passage
5 turbochargers
8 Inlet throttle valve
11 Exhaust passage
13 NOx trap catalyst
14 Injector
17 Injection pump
18 Inlet atmosphere sensor (O2 sensor, air-fuel ratio sensor)
19 Outlet atmosphere sensor (O2 sensor, air-fuel ratio sensor)
21 EGR valve

Claims (3)

Exhaust gas atmosphere variable means for changing the ratio of oxidant and reducing agent in the exhaust gas atmosphere discharged from the internal combustion engine, and nitrogen oxides in the exhaust gas are adsorbed by the exhaust gas atmosphere changed by the exhaust gas atmosphere variable means Or an exhaust gas purifying apparatus comprising an exhaust gas purifying catalyst having a function of reducing and purifying exhaust gas,
First exhaust gas atmosphere detection means that is disposed upstream of the exhaust gas purification catalyst and detects a parameter related to a ratio of an oxidizing agent and a reducing agent in the exhaust gas flowing into the catalyst;
Second exhaust gas atmosphere detection means for detecting a parameter related to the ratio of the oxidizing agent and the reducing agent in the exhaust gas that is disposed downstream of the exhaust gas purification catalyst and has passed through the catalyst;
The output value of the first exhaust gas atmosphere detection means reaches a predetermined value where the ratio of the reducing agent is larger than the ratio of the oxidant, and the output value of the second exhaust gas atmosphere detection means is the first exhaust gas. When the ratio of the reducing agent is larger than the ratio of the oxidizing agent than the output value of the atmosphere detection means, the output value of the first exhaust gas atmosphere detection means and the second exhaust gas atmosphere detection means An exhaust gas purification catalyst deterioration diagnosing device, comprising: a diagnosis unit that calculates a difference from an output value and diagnoses deterioration of the exhaust gas purification catalyst based on the difference. 2. The exhaust gas purification catalyst deterioration diagnosis device according to claim 1, wherein the first and second exhaust gas atmosphere detection means are means for detecting an oxygen concentration in the exhaust gas. 2. The exhaust gas purification catalyst deterioration diagnosis device according to claim 1, wherein the first and second exhaust gas atmosphere detection means are means for detecting an air-fuel ratio in the exhaust gas.

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