JP4729405B2 - Catalyst deterioration judgment device - Google Patents

Description

  The present invention relates to a catalyst deterioration determination device that is provided in an exhaust pipe of an internal combustion engine, and when a reducing agent is supplied, NOx in exhaust gas is reduced by the reducing agent to determine deterioration of the catalyst to be purified.

  Conventionally, for example, a device disclosed in Patent Document 1 is known as this type of deterioration determination device. This deterioration determination device determines the deterioration of the NOx catalyst on the assumption that the NOx catalyst has the following characteristics. Specifically, when the oxygen concentration in the exhaust gas is high, the NOx catalyst captures NOx in the exhaust gas, while the NOx catalyst recovers the NOx catalyst capture capability by increasing the amount of fuel supplied to the internal combustion engine. When the reducing agent is supplied into the exhaust gas and the exhaust gas is controlled in a reducing atmosphere, the trapped NOx is released as NO2. Hereinafter, controlling the exhaust gas to the reducing atmosphere in this way is referred to as “riching control”.

  In addition, this conventional deterioration determination device has a NOx concentration sensor on the downstream side of the NOx catalyst in the exhaust pipe, and the average value of the NOx concentration in the exhaust gas detected by this NOx concentration sensor during the enrichment control. Is calculated. When the calculated average value is smaller than the predetermined determination value, the NOx catalyst has deteriorated because the NOx amount trapped by the NOx catalyst until the enrichment control is small and the trapping capacity is reduced. It is determined that

  As described above, the conventional deterioration determination device determines the deterioration of the NOx catalyst based on the premise that the NOx catalyst releases NOx as NO2 during the enrichment control. However, in this type of NOx catalyst, not all of the trapped NOx is released as NO2 during the enrichment control, but at least a part of NOx is reduced by the reducing agent and released as N2. . Since this N2 is not detected by the NOx concentration sensor, the detected NOx concentration does not represent the amount of NOx trapped by the NOx catalyst, and as a result, the conventional deterioration determination device cannot accurately determine the deterioration of the catalyst. .

  In addition, in the NOx catalyst, NH3 may be generated due to the fact that NOx is not completely reduced during the enrichment control regardless of the deterioration. Further, the way NH3 is generated varies depending on the amount of reducing agent in the exhaust gas, the temperature of the catalyst, and the like. Furthermore, there is a type of NOx concentration sensor that detects the NOx concentration including the concentration of NH3 in the exhaust gas. With this type of NOx concentration sensor, when NH3 is generated, the NOx concentration apparently increases. End up. For this reason, when the deterioration is determined based on the NOx concentration detected by such a type of NOx concentration sensor, the determination accuracy may not be maintained due to the influence of NH3.

  The present invention has been made to solve the above-described problems, and can accurately determine deterioration of a catalyst without being affected by NH3 generated in the catalyst during supply of a reducing agent. An object of the present invention is to provide a catalyst deterioration determination device.

JP-A-11-294149

In order to achieve the above object, the invention according to claim 1 is provided in the exhaust system of the internal combustion engine 3 (the exhaust pipe 5 in the embodiment (hereinafter, the same in this section)), and when the reducing agent is supplied. 1 is a catalyst deterioration determination device 1 for determining deterioration of a catalyst (three-way catalyst 7) that reduces and purifies NOx in exhaust gas by a reducing agent, and the NOx concentration in the exhaust gas on the downstream side of the exhaust system catalyst. NOx concentration sensor 14 for detecting NO, reducing agent supply determining means (ECU 2, step 4) for determining whether or not the reducing agent is being supplied to the catalyst, and NH 3 is generated in the catalyst during the supply of the reducing agent. Based on the generation timing estimation means (ECU 2, steps 10, 31) for estimating the generation timing and the NOx concentration CNOx detected during the supply of the reducing agent and before the estimated generation timing, Catalyst deterioration determining means for determining deterioration of medium (ECU 2, step 11,13,14,16) and operating condition detecting means (airflow sensor 11, LAF sensor 12 for detecting the operating state of the internal combustion engine 3, exhaust gas temperature sensor 13, ECU 2, step 23), and the generation timing estimation means includes delay time calculation means (ECU 2, FIG. 3) that calculates the delay time τ of NH 3 generation in the catalyst according to the detected operating state. And the timing when the calculated delay time τ has elapsed after the start of the supply of the reducing agent to the catalyst (step 10: NO) is estimated as the generation timing .

  According to this catalyst deterioration determination device, the NOx concentration in the exhaust gas flowing downstream from the exhaust system catalyst is detected by the NOx concentration sensor, and whether or not the reducing agent for NOx reduction is being supplied. The determination is made by the reducing agent supply determining means, and the generation timing at which NH3 is generated in the catalyst during the supply of the reducing agent is estimated by the generation timing estimating means. Further, based on the NOx concentration detected during the supply of the reducing agent and before the estimated generation timing, the catalyst deterioration determining means determines the deterioration of the catalyst.

When the catalyst is deteriorated, the reducing ability of the catalyst is reduced. Therefore, during the supply of the reducing agent, the amount of NOx that is reduced and purified by the catalyst is reduced. As a result, in the exhaust gas flowing downstream of the catalyst, The NOx concentration, that is, the NOx concentration detected by the NOx concentration sensor increases. Therefore, as described above, the deterioration of the catalyst can be determined based on the NOx concentration detected by the NOx concentration sensor during the supply of the reducing agent. Further, as described above, during the supply of the reducing agent, the generation timing at which NH3 is generated in the catalyst is estimated, and the deterioration of the catalyst is determined based on the NOx concentration detected before the estimated generation timing. Even if NH 3 is generated in the catalyst, its influence can be eliminated, and therefore deterioration of the catalyst can be determined with high accuracy.
Furthermore, according to the above-described configuration, the delay time of NH3 generation in the catalyst is calculated by the delay time calculation means in accordance with the detected operating state of the internal combustion engine. Further, since the timing at which the calculated delay time has elapsed after the start of the supply of the reducing agent is estimated as the generation timing, the generation timing can be appropriately estimated according to the operating state of the internal combustion engine, thereby determining deterioration. The influence of NH3 on the can be surely eliminated.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a catalyst deterioration determination device 1 according to this embodiment and an internal combustion engine 3 to which the catalyst deterioration determination device 1 is applied. The internal combustion engine (hereinafter referred to as “engine”) 3 is a gasoline engine mounted on a vehicle (not shown).

  An intake pipe 4 and an exhaust pipe 5 (exhaust system) are connected to a cylinder head (not shown) of the engine 3, and a fuel injection valve (hereinafter referred to as “injector”) 6 is connected to a combustion chamber (not shown). ).

  The injector 6 is disposed at the center of the top wall of the combustion chamber, and injects fuel from the fuel tank into the combustion chamber. The fuel injection amount QINJ of the injector 6 is set by the ECU 2, and the valve opening time of the injector 6 is controlled so that the set fuel injection amount QINJ is obtained by a drive signal from the ECU 2.

  The intake pipe 4 is provided with an air flow sensor 11 (operating state detection means). The air flow sensor 11 detects an intake air amount QA and outputs a detection signal to the ECU 2.

  A three-way catalyst 7 (catalyst) is provided in the exhaust pipe 5. The three-way catalyst 7 is activated at a predetermined temperature (for example, 300 ° C.) or higher, oxidizes HC and CO in the exhaust gas with oxygen in the exhaust gas, and reduces NOx in the exhaust gas with HC and CO in the exhaust gas. , Purify the exhaust gas.

  The exhaust pipe 5 is provided with a LAF sensor 12 and an exhaust gas temperature sensor 13 on the upstream side of the three-way catalyst 7. The LAF sensor 12 linearly detects the oxygen concentration VLAF in the exhaust gas in a wide air-fuel ratio region from the rich region to the lean region. Based on the oxygen concentration VLAF detected by the LAF sensor 12, the ECU 2 calculates an actual air-fuel ratio A / FACT representing the air-fuel ratio of the air-fuel mixture burned in the combustion chamber. The exhaust gas temperature sensor 13 detects the exhaust gas temperature TEXG and outputs a detection signal to the ECU 2.

  Furthermore, a NOx concentration sensor 14 is provided in the exhaust pipe 5 on the downstream side of the three-way catalyst 7. The NOx concentration sensor 14 includes an oxygen pump cell that combines an oxygen ion conductive electrolyte layer and electrodes, and the concentration of NOx in the exhaust gas flowing downstream of the three-way catalyst 7 (hereinafter referred to as “NOx concentration”). CNOx is detected, and the detection signal is output to the ECU 2.

  Further, the ECU 2 outputs a detection signal representing the engine speed (hereinafter referred to as “engine speed”) NE of the engine 3 from the engine speed sensor 15 (operating state detecting means).

  The ECU 2 is composed of a microcomputer including an I / O interface, CPU, RAM, ROM, and the like. The detection signals from the various sensors 11 to 15 described above are each input to the CPU after A / D conversion and shaping by the I / O interface. Further, the ECU 2 determines the operating state of the engine 3 in accordance with these input signals in accordance with a control program stored in the ROM, etc., and includes engine control including control of the fuel injection amount QINJ in accordance with the determined operating state. Processing and deterioration determination processing for determining deterioration of the three-way catalyst 7 are executed. In the present embodiment, the ECU 2 corresponds to a reducing agent supply determination unit, a generation timing estimation unit, a catalyst deterioration determination unit, an operating state detection unit, and a delay time calculation unit.

  Next, the deterioration determination process according to the first embodiment of the present invention will be described with reference to FIG. This process is executed every predetermined time (for example, 10 msec). First, in step 1 (illustrated as “S1”, the same applies hereinafter), it is determined whether or not the determination end flag F_DONE is “1”. If the answer is YES and the deterioration determination described later is completed, the timer value TMRICH of the up-counting rich timer is reset to 0 (step 2), and the delay time calculation end flag F_τDONE is set to “0”. Reset (step 3) and end the process. The determination end flag F_DONE is reset to “0” when the engine 3 is started, and the deterioration determination is performed once for each operation cycle from the start to the stop of the engine 3.

  On the other hand, if the answer to step 1 is NO, it is determined whether or not the actual air-fuel ratio A / FACT is smaller than a predetermined threshold value α (eg, 0.9 × 14.7 (theoretical air-fuel ratio)) ( Step 4). If the answer is NO and the actual air-fuel ratio A / FACT is lean or weakly rich with respect to the stoichiometric air-fuel ratio, the deterioration is judged as not being supplied with a reducing agent such as HC or CO to the three-way catalyst 7. Rather, step 2 and the subsequent steps are executed. In this process, the deterioration is determined based on the purification rate of the three-way catalyst 7 as will be described later. On the other hand, when the reducing agent is not supplied, regardless of whether the three-way catalyst 7 is deteriorated or not, This is because NOx reduction / purification is not originally performed in the three-way catalyst 7, and therefore determination based on the purification rate cannot be performed appropriately.

  On the other hand, when the answer to step 4 is YES and the reducing agent is being supplied to the three-way catalyst 7, the state in which the first air-fuel ratio change amount DA / F1 is smaller than a predetermined threshold value ω is a predetermined time Tα ( For example, 1 sec), it is determined whether or not the process has been continued (step 5). The first air-fuel ratio change amount DA / F1 is an absolute value of the difference between the current value and the previous value of the actual air-fuel ratio A / FACT.

  If the answer to step 5 is NO, it is determined that the actual air-fuel ratio A / FACT is not stable, and the present process is terminated without determining deterioration. This is because when the actual air-fuel ratio A / FACT is not stable, the amount of reducing agent and the amount of NOx generated by the engine 3 are not stable, and the purification rate of the three-way catalyst 7 changes accordingly. This is because the determination accuracy of deterioration may decrease.

  On the other hand, if the answer to step 5 is YES, it is determined whether or not the delay time calculation end flag F_τDONE is “1” (step 6). If the answer is NO, the delay time τ is calculated (step 6). 7). This delay time τ corresponds to the time required for NH3 to be generated by incomplete reduction of NOx in the three-way catalyst 7 after the start of the supply of the reducing agent to the three-way catalyst 7.

  FIG. 3 shows a calculation process of the delay time τ. First, in step 21, a basic value τBASE of the delay time τ is calculated. This basic value τBASE is calculated by searching the τBASE table shown in FIG. 4 according to the actual air-fuel ratio A / FACT. In the τBASE table, the basic value τBASE is set to a smaller value as the actual air-fuel ratio A / FACT is smaller and richer. This is because, as the air-fuel ratio A / FACT is richer, that is, as the amount of the reducing agent supplied to the three-way catalyst 7 is larger, the NOx reduction operation in the three-way catalyst 7 is performed faster. This is because the occurrence timing of the error also becomes earlier.

  In the next step 22 and subsequent steps, various correction coefficients for correcting the basic value τBASE are calculated. First, in step 22, the temperature correction coefficient KT is calculated by searching the KT table shown in FIG. 5 according to the exhaust gas temperature TEXG. In this KT table, the temperature correction coefficient KT is set to a larger value as TEXG is lower when the exhaust gas temperature TEXG is lower than a predetermined temperature TREF (for example, 200 ° C.), and is higher as TEXG is higher than TREF. It is set to a large value. This is because when the exhaust gas temperature TEXG is lower than the predetermined temperature TREF, the lower the TEXG, the lower the degree of activation of the three-way catalyst 7, and the reduction reaction in the three-way catalyst 7 is less likely to occur. This is to slow down. Further, when the exhaust gas temperature TEXG is equal to or higher than the predetermined temperature TREF, the generated three-way catalyst 7 is easily decomposed, so that the generated NH3 is easily decomposed. The higher the TEXG, the higher the degree of decomposition. This is because the generation timing is delayed.

  Next, the space velocity (hereinafter simply referred to as “space velocity”) SV of exhaust gas in the three-way catalyst 7 is calculated by searching a map (not shown) according to the intake air amount QA and the fuel injection amount QINJ ( Step 23).

  Next, the space velocity correction coefficient KSV is calculated by searching the KSV table shown in FIG. 6 according to the calculated space velocity SV (step 24). In this KSV table, the space velocity correction coefficient KSV is set to a larger value as the space velocity SV is larger. This is because, as the space velocity SV is larger and the exhaust gas flow velocity is larger, NOx is less likely to contact the wall surface of the three-way catalyst 7, and accordingly, the reduction reaction of NOx is less likely to be performed in the three-way catalyst 7. This is because the generation timing of NH3 is delayed.

  Next, the second air-fuel ratio change amount DA / F2 is calculated (step 25). This second air-fuel ratio change amount DA / F2 is obtained by subtracting the actual air-fuel ratio A / FACT just after the establishment from the actual air-fuel ratio A / FACT just before the establishment of A / FACT <α in the determination of step 4. Calculated.

  Next, the air-fuel ratio change correction coefficient KDA / F is calculated by searching the KDA / F table shown in FIG. 7 according to the calculated second air-fuel ratio change amount DA / F2 (step 26). In this KDA / F table, the air-fuel ratio variation correction coefficient KDA / F is set to a smaller value as the second air-fuel ratio variation DA / F2 is larger. This is because as the second air-fuel ratio change amount DA / F2 is larger, that is, as the rate of change to the rich air-fuel ratio is faster, NOx is more likely to be reduced incompletely in the three-way catalyst 7, thereby generating NH3. This is because the timing becomes early.

Next, as shown in the following equation (1), the temperature correction coefficient KT, space velocity correction coefficient KSV, and air-fuel ratio change amount correction coefficient KDA / By multiplying F, the delay time τ is calculated (step 27), and this process is terminated.
τ = τBASE / KT / KSV / KDA / F (1)

  Returning to FIG. 2, in Step 8 following Step 7, the delay time calculation end flag F_τDONE is set to “1” in order to indicate that the calculation of the delay time τ has ended, and the process proceeds to Step 9. By executing step 8, the answer to step 6 becomes YES. In this case, steps 7 and 8 are skipped and the process proceeds to step 9.

  In step 9, it is determined whether or not the calculated delay time τ is longer than a predetermined time Tβ (for example, 1.5 sec). When this answer is NO, the delay time τ is too short and NH3 is generated immediately after the start of the supply of the reducing agent. Therefore, the process is terminated without performing the deterioration determination.

On the other hand, if the answer to step 9 is YES, it is determined whether or not the timer value TMRICH of the rich timer set in the step 2 is smaller than the delay time τ (step 10). When the answer is YES, that is, when the delay time τ has not elapsed after the start of the supply of the reducing agent to the three-way catalyst 7, the purification rate ηNOx of the three-way catalyst 7 is calculated by the following equation (2) ( Step 11).
ηNOx = (UCNOx−CNOx) / UCNOx (2)
Here, UCNOx is the concentration of NOx upstream of the three-way catalyst 7 (hereinafter referred to as “upstream NOx concentration”), and is calculated as follows.

  That is, first, the basic value UCNOxB of the upstream NOx concentration is calculated by searching a map (not shown) according to the engine speed NE and the fuel injection amount QINJ. In this map, the basic value UCNOxB is such that the higher the engine speed NE and the larger the fuel injection amount QINJ, the higher the combustion gas temperature, and thus the greater the amount of NOx produced by the engine 3. Therefore, it is set to a larger value. Next, the upstream NOx concentration UCNOx is calculated by correcting the calculated basic value UCNOxB to a smaller value as the actual air-fuel ratio A / FACT is richer.

  Next, a determination value γ is calculated by searching a map (not shown) according to the engine speed NE and the fuel injection amount QINJ (step 12), and this process is terminated. In this map, the purification rate of the three-way catalyst 7 when it is not deteriorated is obtained by experiment according to the engine speed NE and the fuel injection amount QINJ, and is stored as the determination value γ.

  On the other hand, if the answer to step 10 is NO and the delay time τ has elapsed after the start of the supply of the reducing agent, it is assumed that it is the timing at which NH 3 is generated in the three-way catalyst 7, and the purification rate obtained so far It is determined whether or not ηNOx, that is, the purification rate ηNOx calculated immediately before the delay time τ elapses is larger than the determination value γ (step 13). When this answer is YES and the purification rate ηNOx is large, it is determined that the three-way catalyst 7 has not deteriorated because the NOx is sufficiently reduced and purified in the three-way catalyst 7, and this is indicated. Then, the catalyst deterioration flag F_NG is set to “0” (step 14). Next, the determination end flag F_DONE is set to “1” (step 15), and this process ends.

  On the other hand, if the answer to step 13 is NO and the purification rate ηNOx is small, it is determined that the three-way catalyst 7 has deteriorated because the three-way catalyst 7 has not sufficiently reduced NOx, and the catalyst deterioration flag F_NG is set to “1” (step 16), and step 15 is executed.

  FIG. 8 shows an example of transition of the NOx concentration CNOx, the purification rate ηNOx, and the like when the operation of the engine 3 is switched between a lean operation leaner than the stoichiometric air-fuel ratio and a rich rich operation. As shown in the figure, when the operation of the engine 3 shifts from lean operation to rich operation, the upstream NOx concentration UCNOx (shown by a one-dot chain line) slightly decreases and the actual air-fuel ratio A / FACT is reduced accordingly. It falls below the threshold value α (step 4: YES) (time point t1), and the supply of the reducing agent is started. Thereafter, when the state in which the first air-fuel ratio change amount DA / F1 is smaller than the threshold value ω continues for a predetermined time Tα (step 5: YES) (time point t2), the purification rate ηNOx and the determination value γ are Calculated (steps 11 and 12). Further, NOx is reduced in the three-way catalyst 7 by the supplied reducing agent, so that the NOx concentration CNOx on the downstream side of the three-way catalyst 7 becomes smaller than the upstream NOx concentration UCNOx.

  When the three-way catalyst 7 is not deteriorated, the NOx concentration CNOx becomes very small as shown by the solid line by sufficiently reducing NOx in the three-way catalyst 7 during the supply of the reducing agent, and the purification rate. ηNOx greatly exceeds the determination value γ. Therefore, when ηNOx> γ, it can be determined that the three-way catalyst 7 has not deteriorated. On the other hand, when the three-way catalyst 7 is deteriorated, NOx is not sufficiently reduced in the three-way catalyst 7, so that the NOx concentration CNOx is larger than that when the three-way catalyst 7 is not deteriorated, as shown by a two-dot chain line. The purification rate ηNOx becomes lower than the determination value γ. Therefore, when ηNOx ≦ γ, it can be determined that the three-way catalyst 7 has deteriorated. When the supply of the reducing agent is completed and the lean operation is restarted (after time t3), the upstream NOx concentration UCNOx and the NOx concentration CNOx return to the original state.

  FIG. 9 shows an example of changes in the NOx concentration CNOx, the purification rate ηNOx, and the like when NH 3 is generated in the three-way catalyst 7 that is not deteriorated during the supply of the reducing agent by the rich operation. As shown in the figure, when NH3 is generated in the three-way catalyst 7 during the supply of the reducing agent (after time t4), the concentration of NH3 is included in the NOx concentration CNOx, so that the NOx concentration CNOx is correspondingly increased. Apparently increases. Accordingly, the purification rate ηNOx calculated based on the NOx concentration CNOx apparently decreases and falls below the determination value γ even though the three-way catalyst 7 has not deteriorated.

  In contrast, according to the present embodiment, as described above, after the start of the supply of the reducing agent, the delay time τ corresponding to the time required until NH3 is generated is calculated (step 7), and this delay time is also calculated. The purification rate ηNOx calculated immediately before τ elapses, that is, immediately before the timing at which NH 3 is generated, is used for deterioration determination (steps 10, 11, and 13). Therefore, it is possible to accurately determine the deterioration of the three-way catalyst 7 without being affected by NH3.

  Further, the delay time τ is calculated according to the actual air-fuel ratio A / FACT, the exhaust gas temperature TEXG, the space velocity SV, and the second air-fuel ratio change amount DA / F2. Therefore, the generation timing of NH3 can be appropriately estimated according to the operating state of the engine 3, the temperature state of the three-way catalyst 7, and the like, and thereby the influence of NH3 on the deterioration determination can be surely eliminated.

  In the present embodiment, the threshold value ω to be compared with the first air-fuel ratio change amount DA / F1 is set to a constant value in order to determine whether or not the actual air-fuel ratio A / FACT is stable. However, it may be set as follows. That is, the detection accuracy of the NOx concentration sensor 14 changes according to the operating state of the engine 3, for example, the engine speed NE, the fuel injection amount QINJ, the actual air-fuel ratio A / FACT, and the space velocity SV. The threshold value ω may be set accordingly.

  Next, the deterioration determination process according to the second embodiment of the present invention will be described with reference to FIG. This process differs from the process of FIG. 2 according to the first embodiment described above only in the method for estimating the generation timing of NH 3 in the three-way catalyst 7. For this reason, in FIG. 10, portions having the same execution contents as those in the first embodiment are given the same step numbers, and the following description will focus on execution contents different from those in the first embodiment.

  When the answer to step 1 is YES (F_DONE = 1), or when the answer to step 4 is NO (A / FACT ≧ α), the process is terminated. If the answer to step 5 is YES and the first air-fuel ratio change amount DA / F1 is smaller than the predetermined threshold value ω for a predetermined time Tα, the NOx concentration change amount DCNOx is a predetermined positive value. It is determined whether or not the threshold value is greater than DNOxREF (step 31). This NOx concentration change amount DCNOx is calculated by subtracting the previous value from the current value of the NOx concentration CNOx. When the answer to step 31 is NO, the step 11 and the subsequent steps are executed to calculate the purification rate ηNOx and the determination value γ.

  On the other hand, when the answer to step 31 is YES, that is, when the NOx concentration CNOx starts to increase, it is estimated that NH 3 has been generated. Next, the steps after step 13 are executed, and as described above, the deterioration is determined based on the purification rate ηNOx calculated immediately before NH 3 is generated.

  As described above, according to the present embodiment, the timing at which the NOx concentration CNOx starts to increase during the supply of the reducing agent is estimated as the timing at which NH3 is generated in the three-way catalyst 7, so that NH3 is actually generated. The timing can be estimated appropriately. Further, the determination of the timing at which the NOx concentration CNOx begins to increase is made when the answer to Steps 4 and 5 is YES, that is, the actual air-fuel ratio A / FACT is stable, the amount of reducing agent and the generated NOx. Therefore, the NH3 generation timing can be estimated with higher accuracy.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, the embodiment is an example in which the three-way catalyst 7 is used as a catalyst. However, any other suitable catalyst, for example, an exhaust gas, may be used as long as it is a catalyst that reduces and purifies NOx in exhaust gas with a supplied reducing agent. A NOx catalyst that captures NOx when the oxygen concentration therein is high and reduces the captured NOx under a reducing atmosphere may be used. In the embodiment, the reducing agent is supplied by controlling the actual air-fuel ratio A / FACT to be richer than the stoichiometric air-fuel ratio. However, by supplying the fuel as the reducing agent directly to the catalyst. You may go.

  Furthermore, in the embodiment, the purification rate ηNOx is used as a parameter for determining deterioration, but other appropriate parameters, for example, the NOx concentration CNOx detected before NH 3 is generated during the supply of the reducing agent. May be used as they are. Further, in the embodiment, the NH3 generation timing is estimated based on the delay time τ calculated according to the operating state of the engine 3 and the actual increase start timing of the NOx concentration CNOx. You may perform based on a suitable parameter. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 is a diagram schematically showing a catalyst deterioration determination device according to an embodiment and an internal combustion engine to which the device is applied. FIG. It is a flowchart which shows the deterioration determination process by 1st Embodiment of this invention. It is a flowchart which shows the subroutine of (tau) calculation process of step 7 of FIG. 4 is an example of a τBASE table used in the process of FIG. 3. It is an example of the KT table used by the process of FIG. It is an example of the KSV table used by the process of FIG. It is an example of the KDA / F table used by the process of FIG. It is a timing chart which shows an example of transition of NOx concentration etc. accompanying switching of operation of an engine about the time of degradation of a three way catalyst, and non-degradation. It is a timing chart which shows an example of changes, such as NOx concentration accompanying change of operation of an engine, about the case where NH3 occurs in a three way catalyst. It is a flowchart which shows the deterioration determination process by 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Degradation determination apparatus 2 ECU (reducing agent supply determination means, generation timing estimation means, catalyst deterioration determination means, operation
(State detection means, delay time calculation means)
3 Engine 5 Exhaust pipe (exhaust system)
7 Three-way catalyst (catalyst)
11 Air flow sensor (Operating state detection means)
12 LAF sensor (operating state detection means)
13 Exhaust gas temperature sensor (operating state detection means)
14 NOx concentration sensor CNOx NOx concentration τ Delay time

Claims (1)

A catalyst deterioration determination device that is provided in an exhaust system of an internal combustion engine, and when a reducing agent is supplied, reduces NOx in exhaust gas by the reducing agent and determines deterioration of the catalyst to be purified,
A NOx concentration sensor for detecting the NOx concentration in the exhaust gas downstream of the catalyst in the exhaust system;
Reducing agent supply determining means for determining whether or not the reducing agent is being supplied to the catalyst;
A generation timing estimation means for estimating a generation timing at which NH3 is generated in the catalyst during the supply of the reducing agent;
Catalyst deterioration determination means for determining deterioration of the catalyst based on the NOx concentration detected during the supply of the reducing agent and before the estimated generation timing;
Operating state detecting means for detecting the operating state of the internal combustion engine,
The generation timing estimation means includes
A delay time calculating means for calculating a delay time of generation of NH3 in the catalyst according to the detected operating state;
An apparatus for determining deterioration of a catalyst , wherein the timing at which the calculated delay time has elapsed after the start of the supply of the reducing agent to the catalyst is estimated as the generation timing .

Images