JP4069924B2 - Catalyst deterioration detection device for exhaust gas purification - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst deterioration detecting device that detects deterioration when an exhaust gas purifying catalyst installed in an exhaust system of an internal combustion engine deteriorates.

In a vehicle exhaust gas purification system, a catalyst deterioration detection device that detects catalyst deterioration has been developed in order to prevent the operation from being continued in a state where the catalyst has deteriorated and the exhaust gas purification capability has been reduced (for example, Patent Documents). 1 and Patent Document 2). All of the conventional catalyst deterioration detection devices detect the deterioration of the catalyst from the decrease in the exhaust gas purification ability after the catalyst is warmed up to the activation temperature (generally 300 to 400 ° C. or higher).
Japanese Patent Laid-Open No. 2-136538 JP-A-3-253714

  By the way, until the catalyst is warmed up to the activation temperature after the engine is started, the exhaust gas purification ability is low even with a normal catalyst, and even with a deteriorated catalyst, the exhaust gas purification ability is further reduced and harmful in the exhaust gas. Ingredients (emissions) will increase. However, all of the conventional catalyst deterioration detection methods detect catalyst deterioration from a decrease in exhaust gas purification capacity after catalyst activation, so it is not possible to detect catalyst deterioration taking into account the degree of increase in emissions before catalyst activation. It is difficult, and there is a possibility that the catalyst that should originally be determined to be in a deteriorated state may be determined as having no deterioration due to an increase in emissions before catalyst activation.

  When the engine is cold started, the activation of the catalyst proceeds from the exhaust gas inflow side (upstream side) with the lapse of time after the cold start, and finally the entire catalyst is activated. In general, since the capacity of the entire catalyst has some allowance, when the entire catalyst is activated, even if the catalyst is somewhat deteriorated, a purification rate close to that of a new catalyst can be obtained. The difference in purification rate between Therefore, as the activation of the catalyst progresses, it becomes more difficult to discriminate between a deteriorated catalyst and a new catalyst (that is, detection of catalyst deterioration). Therefore, if the deterioration of the catalyst is detected from the decrease in the exhaust gas purification capacity after the catalyst is activated, there is a risk that the catalyst that should originally be determined to be in a deteriorated state may be determined as having no deterioration due to the increase in the emission before the catalyst is activated. is there.

  The present invention has been made in view of such circumstances, and therefore the object of the present invention is to detect the catalyst deterioration in consideration of the increase in emission before the activation of the catalyst, and to improve the catalyst deterioration detection accuracy. An object of the present invention is to provide a catalyst deterioration detection device for purifying exhaust gas.

  In the invention according to claim 1, in the system in which the air-fuel ratio sensor is installed upstream of the exhaust gas purifying catalyst and the oxygen sensor is installed downstream, the catalyst saturation (downstream oxygen sensor) based on the output of the downstream oxygen sensor. Is determined by the saturation determination means, the area of the portion surrounded by the output waveform of the upstream air-fuel ratio sensor and the target air-fuel ratio is calculated by the first calculation means, and the catalyst inflow gas component amount And the amount of change in the output of the downstream oxygen sensor is integrated by the second computing means to determine the catalyst outflow gas component amount. Then, when the saturation is determined by the saturation determination means, the amount of the catalyst outflow gas component by the second calculation means is corrected by the saturation correction means based on the output of the upstream air-fuel ratio sensor, and the corrected catalyst outflow gas component is corrected. Based on the amount and the catalyst inflow gas component amount obtained by the first calculating means, the catalyst deterioration detecting means detects the catalyst deterioration.

  Here, as shown in FIG. 21, the output voltage of the downstream oxygen sensor changes linearly with respect to the excess air ratio λ (air-fuel ratio) in the vicinity of the stoichiometry, but in the region outside the stoichiometry, the excess air ratio λ Even if this changes, the output voltage of the downstream oxygen sensor does not change much, and the amount of gas component flowing out of the catalyst cannot be detected accurately. Therefore, it is considered that the catalyst is saturated in a region outside the stoichiometric range. In the catalyst saturation state, the rate of purification in the catalyst is low, and the catalyst outflow gas component amount is correlated with the catalyst inflow gas component amount. Therefore, if the catalyst outflow gas component amount is corrected based on the output of the upstream air-fuel ratio sensor when it is determined that the catalyst is saturated as in the first aspect, the catalyst outflow gas can be obtained even if the catalyst is saturated. The component amount can be determined with high accuracy, and the catalyst deterioration detection accuracy can be further improved.

  In this case, as in claim 2, when the area is integrated by the first calculating means, the area on either the lean side or the rich side from the target air-fuel ratio is canceled by the first canceling means. When the output change amount of the downstream oxygen sensor is integrated by the second calculation means, the output change direction of the downstream oxygen sensor is directed to the same side as the area canceled by the first cancellation means. Sometimes the output change amount in that direction may be canceled by the second canceling means. In this way, the catalyst inflow / outflow gas component amount can be calculated only for either the lean side or the rich side. For example, if the catalyst inflow / outflow gas component amount is calculated only for the rich side, The degree of deterioration of the HC purification rate can be determined.

  Further, as in claim 3, the catalyst deterioration detection process may be prohibited during the fuel cut and until a predetermined period elapses from the fuel cut return. Since fuel is not supplied during the fuel cut, the air-fuel ratio in the exhaust gas becomes lean and exceeds the range in which the air-fuel ratio can be correctly measured by the upstream air-fuel ratio sensor. In addition, the air-fuel ratio cannot be accurately detected until a predetermined period required for the air-fuel ratio feedback control to stabilize after the fuel cut is restored, that is, until the output value of the upstream air-fuel ratio sensor crosses the threshold value. . Therefore, as in the third aspect, the catalyst deterioration detection accuracy can be further improved by prohibiting the catalyst deterioration detection process when the fuel is being cut or until the predetermined period has elapsed after the fuel cut is restored. Here, the “predetermined period” during which the catalyst deterioration detection process is prohibited after returning from the fuel cut is a period required for the air-fuel ratio feedback to stabilize after the fuel cut is returned, and is set by the elapsed time after the fuel cut is returned. Alternatively, it may be a period until the output of the upstream air-fuel ratio sensor first crosses the threshold after returning from the fuel cut.

<< Reference Example (1) >>
A reference example (1) of the present invention will be described below with reference to FIGS. First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine. An intake air temperature sensor 14 that detects the intake air temperature Tam and an intake air flow rate Q are detected downstream of the air cleaner 13. An air flow meter 10 is provided. A throttle valve 15 and a throttle opening sensor 16 that detects the throttle opening TH are provided on the downstream side of the air flow meter 10. Further, an intake pipe pressure sensor 17 for detecting the intake pipe pressure PM is provided on the downstream side of the throttle valve 15, and a surge tank 18 is provided on the downstream side of the intake pipe pressure sensor 17. An intake manifold 19 that introduces air into each cylinder of the engine 11 is connected to the surge tank 18, and an injector 20 that injects fuel into each branch pipe portion of each cylinder of the intake manifold 19 is attached.

  The engine 11 is provided with a spark plug 21 for each cylinder, and a high-voltage current generated by the ignition circuit 22 is supplied to each spark plug 21 via a distributor 23. The distributor 23 is provided with a crank angle sensor 24 that outputs, for example, 24 pulse signals every 720 ° C. A (two rotations of the crankshaft), and the engine speed Ne is detected by the output pulse interval of the crank angle sensor 24. It is supposed to be. Further, a water temperature sensor 38 for detecting the engine cooling water temperature Thw is attached to the engine 11.

  On the other hand, an exhaust pipe (not shown) of the engine 11 is connected to an exhaust pipe 26 via an exhaust manifold 25. In the middle of the exhaust pipe 26, harmful components (CO, HC, NOx, etc.) in the exhaust gas are connected. A catalyst 27 such as a three-way catalyst is provided. An upstream air-fuel ratio sensor 28 that outputs a linear air-fuel ratio signal corresponding to the air-fuel ratio A / F of the exhaust gas is provided upstream of the catalyst 27. The upstream air-fuel ratio sensor 28 incorporates a heater (not shown) for promoting activation. A downstream oxygen sensor 29 is provided on the downstream side of the catalyst 27. The downstream oxygen sensor 29 reverses the output voltage VOX2 depending on whether the air-fuel ratio A / F of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio. The downstream oxygen sensor 29 has a built-in heater 39 for promoting activation of the oxygen sensor 29.

  The outputs of the various sensors described above are read into the electronic control circuit 30 via the input port 31. The electronic control circuit 30 is mainly composed of a microcomputer, and includes a CPU 32, a ROM 33, a RAM 34, and a backup RAM 35, and calculates a fuel injection amount TAU, an ignition timing Ig, and the like using engine operation state parameters obtained from various sensor outputs. Then, a signal corresponding to the calculation result is output from the output port 36 to the injector 20 and the ignition circuit 22 to control the operation of the engine 11.

  The electronic control circuit 30 also stores a catalyst deterioration detection routine shown in FIG. 2 and a catalyst temperature estimation routine shown in FIG. 3 to be described later in the ROM 33 (storage medium), and executes these routines, so that the inside of the catalyst 27 is stored. It functions as a calculating means for calculating the amount of gas component to be purified (purified gas component amount) and a catalyst deterioration detecting means for detecting deterioration of the catalyst 27. When the deterioration of the catalyst 27 is detected, a lighting signal is output from the output port 36 to the warning lamp 37 to turn on the warning lamp 37 and warn the driver.

  Hereinafter, the flow of processing of the catalyst deterioration detection routine shown in FIG. 2 will be described. This routine functions as catalyst temperature estimation means in the claims, and is executed by interruption processing at predetermined time intervals (for example, every 64 msec). When the processing of this routine is started, first, at step 100, the catalyst temperature estimation routine shown in FIG. 3 is executed, and the catalyst temperature TCAT is estimated as follows.

  In the catalyst temperature estimation routine shown in FIG. 3, first, at step 101, it is determined whether or not the engine 11 has been started. If the engine 11 has not been started, the catalyst temperature TCAT = intake air temperature Tam (= outside air temperature) is set. End the routine.

  On the other hand, if the engine 11 has been started, the process proceeds to step 103 to determine whether or not the fuel is being cut. If not, the process proceeds to step 104 and the exhaust temperature TEX is estimated as follows. As shown in FIG. 4, a map for estimating the exhaust gas temperature TEX from the engine speed Ne and the intake air flow rate Q (= exhaust gas flow rate) is stored in the ROM 33 in advance. The exhaust temperature TEX is estimated from the map shown in FIG. 4 according to the engine speed Ne and the intake flow rate Q at the time. This estimation method utilizes the characteristic that the exhaust temperature TEX increases as the engine load (Ne, Q) increases.

  On the other hand, during the fuel cut, the combustion heat of the fuel disappears, and the exhaust temperature TEX rapidly decreases. Therefore, the exhaust temperature TEX cannot be estimated from the engine speed Ne and the intake flow rate Q. Therefore, if it is determined in step 103 that the fuel cut is in progress, the routine proceeds to step 105, where the exhaust temperature TEX is determined from the catalyst temperature TCAT (estimated value) at the start of fuel cut using the map shown in FIG. Is estimated. This estimation method utilizes the characteristic that the exhaust gas temperature TEX increases as the catalyst temperature TCAT increases due to the heat radiation of the catalyst 27.

  After the exhaust temperature TEX is estimated in step 104 or 105 as described above, the process proceeds to step 106 where the catalyst temperature TCAT (n-1) estimated in the previous process is compared with the exhaust temperature TEX, and the catalyst temperature tends to decrease. Or the upward trend. When the catalyst temperature TCAT tends to decrease (TCAT (n-1)> exhaust temperature TEX), the routine proceeds to step 107, where the current catalyst temperature TCAT (n) is calculated by the following equation.

TCAT (n) = TCAT (n−1) −K1 × | TCAT (n−1) −TEX |
Here, K1 is a coefficient set according to the intake air flow rate Q using the data table of FIG. It should be noted that K1 may be set to a different value when the fluctuation value of the engine speed Ne is large (non-steady state) and small (steady state).

  On the other hand, when the catalyst temperature TCAT tends to increase (TCAT (n−1) ≦ exhaust temperature TEX), the routine proceeds to step 108, where the current catalyst temperature TCAT (n) is calculated by the following equation.

TCAT (n) = TCAT (n−1) + K2 × | TCAT (n−1) −TEX |
Here, K2 is a coefficient set according to the intake air flow rate Q using the data table of FIG. During fuel cut, K1 and K2 may be fixed to a constant value.

  After estimating the catalyst temperature TCAT in step 107 or 108 as described above, the process returns to step 110 in FIG. 2 to determine whether or not the catalyst temperature TCAT has exceeded the deterioration detection start temperature, for example, 150 ° C. For example, this routine is terminated without performing the subsequent catalyst deterioration detection process. This is because, in a state where the catalyst temperature TCAT does not reach the deterioration detection start temperature, the temperature of the downstream oxygen sensor 29 is low and the sensor output VOX2 is not stable. Therefore, by prohibiting the catalyst deterioration detection process during this period, This is to prevent deterioration in accuracy of deterioration detection.

  Then, when the catalyst temperature TCAT exceeds the deterioration detection start temperature (for example, 150 ° C.), the process proceeds to step 120, the time counter 1 is incremented, and in the next step 130, data ΣV1 (downstream) reflecting the amount of the purified gas component The output voltage fluctuation locus of the side oxygen sensor 29 is calculated by the following equation (see FIG. 7).

ΣV1 (n) = ΣV1 (n−1) + | VOX2 (i) −VOX2 (i−1) |
Here, VOX2 (i) is the output voltage of the downstream oxygen sensor 29 during the current process, and VOX2 (i-1) is the output voltage of the downstream oxygen sensor 29 during the previous process. In other words, the above equation obtains the locus of the output voltage fluctuation of the downstream oxygen sensor 29 by integrating the change width of the output voltage VOX2 of the downstream oxygen sensor 29 at a predetermined sampling period (for example, 64 msec). The amount of the purified gas component is evaluated.

  Further, in step 130, data ΣΔA / F · Q1 obtained by quantifying the catalyst inflow gas component fluctuation is calculated by the following equation (see FIG. 8).

ΣΔA / F · Q1 (n) = ΣΔA / F · Q1 (n−1) + Q × | Target A / FA−F |
Here, Q is the intake flow rate Q detected by the air flow meter 10, and is used as data substituting the exhaust gas flow rate. The exhaust gas flow rate may be actually measured in place of the intake air flow rate, or may be estimated from other data. Of course, it may be estimated from the intake flow rate. A / F is the output voltage of the upstream air-fuel ratio sensor 28 (that is, the air-fuel ratio of the exhaust gas), and the target A / F is the air-fuel ratio (for example, stoichiometric air-fuel ratio) that is the target of air-fuel ratio control. The above equation is expressed as follows: deviation from target A / F of A / F detected by upstream air-fuel ratio sensor 28 in a predetermined sampling period (for example, 64 msec) | target A / F−A / F | and exhaust gas flow rate (= intake air) The data ΣΔA / F · Q1 of the catalyst inflow gas component variation is obtained by multiplying the flow rate Q) and integrating the multiplied value.

  Thereafter, in step 140, it is determined whether or not the count value of the time counter 1 has exceeded 10 seconds. If it has not exceeded 10 seconds, the processing in steps 110 to 130 is repeated. Thus, ΣV1 and ΣΔA / F · Q1 are calculated for 10 seconds. Then, when the count value of the time counter 1 exceeds 10 sec, the process proceeds to step 150, where it is determined whether or not the data ΣΔA / F · Q1 of the catalyst inflow gas component fluctuation for 10 sec is within a predetermined range. If so, the process proceeds to step 160, where the current ΣV1 is added to the previous ΣV1 integrated value ΣV to update ΣV, and the previous ΣΔA / F · Q1 integrated value ΣΔA / F · Q is changed to the current ΣΔA / ΣΔA / F · Q is updated by integrating F · Q1. Thereafter, the process proceeds to step 170, where both the time counter 1, ΣV1 and ΣΔA / F · Q1 are cleared.

  On the other hand, if it is determined in step 150 that the catalyst inflow gas component variation data ΣΔA / F · Q1 is not within the predetermined range, the process proceeds to step 170 without performing the integration process of step 160, and the time Counter 1, ΣV1 and ΣΔA / F · Q1 are all cleared (disabled). This is because when the catalyst inflow gas component fluctuation is too large or too small, the calculation accuracy of the purified gas component amount decreases, and therefore the catalyst inflow gas component fluctuation data ΣΔA / F · Q1 does not fall within the predetermined range. , ΣV1 and ΣΔA / F · Q1 are both cleared and integration processing is not performed, thereby preventing deterioration in deterioration detection accuracy due to catalyst inflow gas component fluctuations.

  In the next step 180, it is determined whether or not the catalyst temperature TCAT estimated in step 100 has exceeded a predetermined temperature of 550 ° C., and if not, the routine is executed without determining deterioration of the catalyst 27. finish. When the catalyst temperature TCAT exceeds a predetermined temperature of 550 ° C., the process proceeds to step 190, where data ΣV (the locus of fluctuations in the output voltage of the downstream oxygen sensor 29) reflecting the amount of purified gas component accumulated so far. Is compared with a predetermined deterioration determination value to determine whether or not the catalyst 27 has deteriorated.

  Here, the catalyst deterioration detection method will be described with reference to FIG. FIG. 9 shows an actual measurement of the relationship between the data ΣV reflecting the amount of the purified gas component and the data ΣΔA / F · Q of the catalyst inflow gas component fluctuation. In FIG. 9, ◯ indicates measured values for a new catalyst, □ indicates a deteriorated catalyst, and Δ indicates a dummy catalyst (only a ceramic carrier having no catalyst layer formed on the surface). With a new catalyst (marked with ◯), ΣV is small regardless of the magnitude of ΣΔA / F · Q, but with a deteriorated catalyst (marked with □), ΣV tends to increase as ΣΔA / F · Q increases. When the catalyst deterioration is extremely advanced and the catalytic action is lost, the state becomes the same as that of the dummy catalyst (Δ mark). Therefore, if ΣΔA / F · Q is the same, it means that the larger the ΣV, the more advanced the catalyst degradation.

Using this relationship, the deterioration determination value is set according to ΣΔA / F · Q using the data table shown in FIG. 10 stored in the ROM 33, and the catalyst 27 is determined by whether ΣV is larger than this deterioration determination value. The presence or absence of deterioration is determined. When ΣV is larger than the deterioration determination value, it is determined as deterioration (step 200), and when ΣV is equal to or lower than the deterioration determination value, it is determined as normal (step 210).

  In the present embodiment, the process for calculating ΣV corresponds to the calculation means, and the process for detecting catalyst deterioration based on ΣV and ΣΔA / F · Q corresponds to the catalyst deterioration detection means.

  In this case, when detecting the deterioration of the catalyst 27, in addition to the data ΣV reflecting the amount of the purified gas component, the data ΣΔA / F · Q of the catalyst inflow gas component fluctuation until the catalyst 27 reaches a predetermined temperature (550 ° C.) is also obtained. Therefore, highly accurate catalyst deterioration detection can be performed without the influence of fluctuations in the catalyst inflow gas component.

As described above, according to the present reference example , as shown in FIG. 12, the deterioration of the catalyst is detected based on the purification rate (purified gas component amount) before the catalyst is warmed up. That is, before the catalyst warms up, there is a large difference in the purification rate between the new catalyst and the deteriorated catalyst, so that the catalyst deterioration can be detected easily and accurately.

In this reference example , the deterioration determination value is changed according to ΣΔA / F · Q. However, ΣV may be corrected according to ΣΔA / F · Q.

  Further, as apparent from the relationship between ΣV and ΣΔA / F · Q shown in FIG. 9, the inclination of ΣV (ΣV ÷ ΣΔA / F · Q) tends to increase as the catalyst deterioration progresses. The presence or absence of catalyst deterioration may be determined based on the magnitude of the slope (ΣV ÷ ΣΔA / F · Q).

In this reference example , since the exhaust temperature is estimated from the engine load (Ne, Q) and the catalyst temperature is estimated based on the exhaust temperature, a temperature sensor for detecting the catalyst temperature becomes unnecessary, and the component cost is reduced. There is an advantage that can be reduced. However, the present invention may be configured such that a temperature sensor for detecting the exhaust temperature or the catalyst temperature is installed in the exhaust system, and even in this case, the intended object of the present invention can be sufficiently achieved.

Further, in this reference example , the catalyst deterioration is detected based on the amount of the purified gas component having a catalyst temperature of 150 ° C. to 550 ° C., but the calculation period of the purified gas component amount is not limited to this, and as shown in FIG. In addition, the period may be a period in which the difference in purification rate between the new catalyst and the deteriorated catalyst is large.

  2 is executed when the engine 11 is cold-started (that is, when the catalyst 27 is cold), and is not executed when the engine 11 in the warm-up state is restarted. That is, when restarting the engine 11 in the warm-up state, the catalyst temperature TCAT is already at the activation temperature or a temperature close to the activation temperature immediately after the start, and in this state, as shown in FIG. This is because there is little difference in the exhaust gas purification capacity between the new catalyst and it becomes difficult to distinguish the deteriorated catalyst from the new catalyst (that is, detection of catalyst deterioration). At this time, whether or not the engine is cold-started is determined by the engine coolant temperature Thw detected by the water temperature sensor 38 and the intake air temperature Tam detected by the intake air temperature sensor 14.

  For the same reason, the catalyst deterioration detection routine of FIG. 2 is not executed after the catalyst temperature TCAT becomes high (for example, 550 ° C.) even in the case of cold start. As described above, if the catalyst temperature TCAT is high, there is little difference in the exhaust gas purification capacity between the deteriorated catalyst and the new catalyst, and it becomes difficult to distinguish between the deteriorated catalyst and the new catalyst, and the catalyst deterioration detection accuracy decreases. It is to do.

<< Reference example (2) >>
In the reference example (1) , the downstream oxygen sensor 29 is installed on the downstream side of the catalyst 27. However, in the reference example (2) , instead of the downstream oxygen sensor 29, a downstream air-fuel ratio sensor is installed, and the catalyst An air-fuel ratio sensor is installed on both the upstream side and the downstream side.

  In this system, the deviation of the upstream A / F from the target A / F detected by the upstream air-fuel ratio sensor at a predetermined sampling period (for example, 64 msec period) | target A / F-upstream A / F | and exhaust gas The flow rate (= intake flow rate Q) is multiplied and the multiplied value is integrated to obtain catalyst inflow gas component fluctuation data ΣΔA / Fin · Q (this function is defined in claim 11 of the claims). As a means of accumulating

ΣΔA / Fin · Q (n) = ΣΔA / Fin · Q (n−1) + Q × | Target A / F−Upstream A / F |
Further, the deviation of the downstream A / F from the target A / F detected by the downstream air-fuel ratio sensor at the predetermined sampling period | target A / F−downstream A / F | and the exhaust gas flow rate (= intake flow rate Q ) And multiplying the multiplied value to obtain the data ΣΔA / Fout · Q of the catalyst outflow gas component variation (this function is the second integrating means in claim 11 of the claims) .

ΣΔA / Fout · Q (n) = ΣΔA / Fout · Q (n−1) + Q × | Target A / F−Downstream A / F |
Then, by subtracting the data ΣΔA / Fout · Q of the catalyst outflow gas component variation from the data ΣΔA / Fin · Q of the catalyst inflow gas component variation until the catalyst reaches a predetermined temperature, the purified gas component indicated by hatching in FIG. Calculate the amount.

Purified gas component amount = ΣΔA / Fin · Q−ΣΔA / Fout · Q
Thereafter, the amount of the purified gas component is compared with a predetermined deterioration determination value, and if the amount of the purified gas component is equal to or less than the deterioration determination value, it is determined that the catalyst is deteriorated. judge. Thereby, it is possible to detect the catalyst deterioration with high accuracy in consideration of the catalyst inflow gas component variation and the catalyst outflow gas component variation.

  In this case as well, when ΣΔA / Fin · Q or ΣΔA / Fout · Q does not fall within the predetermined range, the data calculated for detecting the catalyst deterioration is invalidated or the catalyst deterioration detection process is prohibited. It is preferable.

<< Reference example (3) >>
In this reference example (3) , the catalyst temperature estimation routine shown in FIG. 13 is executed (this catalyst temperature estimation routine serves as catalyst temperature estimation means in the claims). The system configuration of the reference example (3) is similar to the reference example (1) described above, in which the upstream air-fuel ratio sensor 28 is installed upstream of the catalyst 27 and the downstream oxygen sensor 29 is installed downstream of the catalyst 27. The configuration shown in FIG. In the reference example (1) described above, the catalyst temperature at the time of starting the engine is estimated as the intake air temperature. In this reference example (3) , a timer (stop time measuring means) for measuring the elapsed time after the engine is stopped is provided. In addition, the catalyst temperature TCATint at the time of starting the engine is set based on the elapsed time after the engine stop, the catalyst temperature at the time of engine stop and the intake air temperature (or the cooling water temperature), thereby improving the estimation accuracy of the catalyst temperature. .

  Hereinafter, the processing content of the catalyst temperature estimation routine of FIG. 13 for estimating the catalyst temperature will be described. After the engine is stopped, the elapsed time is measured by a timer, and at the time of starting the engine, the process proceeds from step 301 to step 302. Whether the measured time Ttimer of the timer, that is, the elapsed time Ttimer from the engine stop to starting, exceeds a predetermined time ktimer. judge. Here, the predetermined time ktimer is set to a time required for the catalyst temperature to drop to the outside air temperature (or the cooling water temperature) after the engine is stopped. Therefore, if the elapsed time Ttimer after the engine stops exceeds the predetermined time ktimer, the process proceeds to step 303, and the catalyst temperature TCATint at the time of engine start is set to the intake air temperature Tam (or the outside air temperature). Alternatively, the catalyst temperature TCATint at the start of the engine may be set to the cooling water temperature THW. This is because the intake air temperature Tam (or the outside air temperature) and the cooling water temperature THW become substantially the same temperature when the engine 11 is completely cold (the temperature is completely lowered).

  On the other hand, if it is determined in step 302 that the elapsed time Ttimer after the engine has stopped does not exceed the predetermined time ktimer, the routine proceeds to step 304 where the catalyst temperature TCATend when the engine is stopped and the elapsed time after the engine is stopped. The catalyst temperature TCATint at the time of starting the engine is retrieved from the two-dimensional map of Table 1 below using Ttimer as a parameter according to TCATend and Ttimer at that time.

ここで、図１４は外気温度が２５℃の場合のエンジン停止後の触媒温度と冷却水温の挙動を測定したグラフであり、触媒温度の挙動については、エンジン停止時の触媒温度が６００℃と３８０℃の２つの例が測定されている。この測定結果から明らかなように、エンジン停止後の触媒温度の変化は、エンジン停止時の触媒温度とエンジン停止後の経過時間とに依存し、エンジン停止時の触媒温度が異なっても、ある程度の時間が経過すると、ほぼ一定の触媒温度に収束する。このような特性を考慮し、予め、エンジン停止時の触媒温度ＴＣＡＴｅｎｄとエンジン停止後の経過時間Ｔｔｉｍｅｒと触媒温度ＴＣＡＴｉｎｔとの関係を試験結果又はシミュレーションによりマップ化し、これをＲＯＭ３３に記憶して、上述したステップ３０４で利用する。

Here, FIG. 14 is a graph obtained by measuring the behavior of the catalyst temperature and the cooling water temperature after the engine stop when the outside air temperature is 25 ° C. The catalyst temperature behavior is 600 ° C. and 380 ° C. when the engine is stopped. Two examples of degrees Celsius have been measured. As is apparent from this measurement result, the change in the catalyst temperature after the engine stops depends on the catalyst temperature when the engine is stopped and the elapsed time after the engine is stopped. As time passes, it converges to a nearly constant catalyst temperature. In consideration of such characteristics, the relationship between the catalyst temperature TCATend when the engine is stopped, the elapsed time Ttimer after the engine is stopped, and the catalyst temperature TCATint is mapped by a test result or simulation, and this is stored in the ROM 33 and stored in the above-described manner. Used in step 304.

  Note that the change in the catalyst temperature after the engine is stopped depends on the outside air temperature in addition to TCATend and Ttimer. Incidentally, FIG. 15 is a graph in which the behavior of the catalyst temperature and the cooling water temperature after the engine stop when the outside air temperature is 15 ° C. is measured. The measurement result and the catalyst temperature when the outside air temperature is 25 ° C. shown in FIG. The degree of change is different. This is because, even if the catalyst temperature when the engine is stopped is the same, the lower the outside air temperature, the more the heat release from the catalyst 27 is promoted, and the catalyst temperature after the engine is stopped decreases more quickly. Therefore, the catalyst temperature TCATint retrieved from the map may be corrected by the outside air temperature. This correction may be performed by the following equation using a correction coefficient kam based on the outside air temperature (or intake air temperature), for example.

TCATint = TCATint × kam
Here, the correction coefficient kam based on the outside air temperature (or intake air temperature) is retrieved from the table shown in Table 2 below, for example.

以上のようにして、図１３のステップ３０３又は３０４で、エンジン始動時の触媒温度ＴＣＡＴｉｎｔを設定した後、ステップ３０５〜３０７の処理により、燃料カット中か否かを考慮して排気温度ＴＥＸを推定する。この排気温度ＴＥＸの推定方法は、前述した参考例（１）で説明した図３のステップ１０３〜１０５の処理と同じである。

As described above, after setting the catalyst temperature TCATint at the time of engine start in step 303 or 304 in FIG. 13, the exhaust temperature TEX is estimated by the processing in steps 305 to 307 in consideration of whether or not the fuel is being cut. To do. The method for estimating the exhaust gas temperature TEX is the same as the processing in steps 103 to 105 in FIG. 3 described in the reference example (1) described above.

  After the exhaust temperature TEX is estimated in step 306 or 307, the process proceeds to step 308, where the catalyst temperature TCAT (n-1) estimated in the previous process is compared with the exhaust temperature TEX, and the catalyst temperature tends to decrease or increase. Is determined. If the catalyst temperature TCAT tends to decrease (TCAT (n−1)> exhaust temperature TEX), the process proceeds to step 309, and the current catalyst temperature TCAT (n) is taken into account the catalyst temperature TCATint at the time of engine start. The following formula is used.

TCAT (n) = TCAT (n−1) −K1 × | TCAT (n−1) −TEX | + TCATint
Here, K1 is a coefficient set according to the intake air flow rate Q using the data table of FIG. It should be noted that K1 may be set to a different value when the fluctuation value of the engine speed Ne is large (non-steady state) and small (steady state).

  On the other hand, if the catalyst temperature TCAT tends to increase (TCAT (n−1) ≦ exhaust temperature TEX), the process proceeds to step 108, and the current catalyst temperature TCAT (n) is taken into consideration of the catalyst temperature TCATint at the start of the engine. The following formula is used.

TCAT (n) = TCAT (n−1) + K2 × | TCAT (n−1) −TEX | + TCATint
Here, K2 is a coefficient set according to the intake air flow rate Q using the data table of FIG. During fuel cut, K1 and K2 may be fixed to a constant value.

  After estimating the catalyst temperature TCAT in step 309 or 310 as described above, the process returns to step 110 in FIG. 2 to execute the catalyst deterioration detection process.

In this reference example (3) , the catalyst temperature TCATint at the time of starting the engine is estimated based on the elapsed time after the engine stop, the catalyst temperature at the time of the engine stop and the intake air temperature (or the cooling water temperature) by the processing of steps 302 to 303. In addition, since the catalyst temperature TCAT after engine start is estimated based on this TCATint, the estimation accuracy of the catalyst temperature can be improved, and the catalyst deterioration detection accuracy can be improved.

<< Embodiment (1) >>
In this embodiment (1) , the catalyst deterioration detection routine shown in FIGS. 16 and 17 is executed. In the system configuration of this embodiment (1) , the upstream air-fuel ratio sensor 28 is installed on the upstream side of the catalyst 27 and the downstream oxygen sensor 29 is installed on the downstream side of the catalyst 27, as in the reference example (1) described above. The configuration shown in FIG.

  The catalyst deterioration detection routine shown in FIGS. 16 and 17 is executed by interruption processing at predetermined time intervals (for example, every 64 msec). When the processing of this routine is started, first, in step 401, it is determined whether or not a catalyst deterioration determination calculation start condition is satisfied. Here, whether or not the catalyst deterioration determination calculation start condition is satisfied is determined by a catalyst deterioration determination calculation start condition determination routine shown in FIG.

  The catalyst deterioration determination calculation start condition determination routine shown in FIG. 18 is applied to a system that does not have a catalyst temperature sensor or a timer that measures an elapsed time after the engine is stopped. In this system, the catalyst temperature at the time of engine start cannot be estimated. Therefore, in this routine, first, in step 501, in order to determine whether or not the catalyst temperature has been sufficiently lowered when the engine is started, the difference between the coolant temperature THW and the intake air temperature Tam when starting the engine (THW−Tam). Is smaller than a predetermined value ktemp. If the catalyst temperature has dropped sufficiently when the engine is started, the cooling water temperature THW has also dropped sufficiently. Therefore, the cooling water temperature THW and the intake air temperature Tam at the time of starting the engine are substantially the same, and THW−Tam <ktemp. Become. Note that the outside air temperature may be used instead of the intake air temperature Tam.

  If THW-Tam <ktemp, the routine proceeds to step 502, where it is determined whether or not the engine 11 is in a cold state based on whether or not the coolant temperature THW at the time of starting the engine is lower than a predetermined temperature khot. If there is, the process proceeds to step 503 to determine whether or not the catalyst temperature TCAT estimated by the above-described catalyst temperature estimation routine of FIG. 3 is higher than a predetermined temperature (a temperature at which a part of the catalyst 27 starts to be activated, for example, 150 ° C.). If “Yes”, the process proceeds to step 504, and after the upstream air-fuel ratio sensor 28 is completely activated (after the air-fuel ratio feedback is started), the predetermined time kactive required for the air-fuel ratio feedback to stabilize is It is determined whether or not it has elapsed. If “Yes”, the process proceeds to step 505, where it is determined that the catalyst deterioration determination calculation start condition is satisfied.

  On the other hand, if any one of the determinations in steps 501 to 504 is “No”, the process proceeds to step 506, where it is determined that the catalyst deterioration determination calculation start condition is not satisfied, and the catalyst deterioration determination calculation is prohibited.

  Here, as a catalyst deterioration determination calculation start condition, it is determined in step 504 whether or not a predetermined time kactive has elapsed after the upstream air-fuel ratio sensor 28 is completely activated (after the air-fuel ratio feedback is started). The reason is as follows. Immediately after the engine is started, until the air-fuel ratio feedback is started, the air-fuel ratio becomes rich due to the fuel increase at the time of starting. During this time, the catalyst temperature is still low, and rich components are adsorbed in the catalyst 27. As a result, the air-fuel ratio feedback is started in a state where many rich components are adsorbed in the catalyst 27. Therefore, the air-fuel ratio feedback is unstable immediately after the start of the air-fuel ratio feedback. Accordingly, in order to start the catalyst deterioration determination calculation after the air-fuel ratio feedback is stabilized, it is determined in step 504 whether or not the predetermined time kactive has elapsed.

  In this case, it is determined whether or not the air-fuel ratio feedback is stable depending on whether or not a predetermined time kactive has elapsed since the start of the air-fuel ratio feedback. It is determined whether or not the air-fuel ratio feedback is stable based on whether or not the output of the fuel ratio sensor 28 has crossed the target air-fuel ratio. The catalyst deterioration determination calculation may be prohibited until the fuel ratio is crossed. Even in this case, the catalyst deterioration determination calculation can be started after the air-fuel ratio feedback is stabilized.

  On the other hand, the catalyst deterioration determination calculation start condition determination routine shown in FIG. 19 is applied to a system equipped with a catalyst temperature sensor or a timer that measures an elapsed time after the engine is stopped. In this system, it is possible to estimate the catalyst temperature at the time of engine start by the output value of the catalyst temperature sensor or the above-described catalyst temperature estimation routine of FIG. Therefore, in this routine, first, in step 511, it is determined whether or not the engine is in a cold state based on whether or not the catalyst temperature TCAT at the time of engine start is lower than a predetermined temperature khotc. If “Yes”, the process proceeds to step 512. Then, it is determined whether or not the catalyst temperature TCAT is higher than a predetermined temperature (a temperature at which a part of the catalyst 27 starts to be activated, for example, 150 ° C.), and if “Yes”, the process proceeds to step 513 and the upstream air-fuel ratio sensor 28 is reached. Is fully activated (after starting air-fuel ratio feedback), it is determined whether or not a predetermined time kactive necessary for air-fuel ratio feedback to stabilize has elapsed. It is determined that the catalyst deterioration determination calculation start condition is established.

  On the other hand, if any one of the determinations in steps 511 to 513 is “No”, the process proceeds to step 515, where it is determined that the catalyst deterioration determination calculation start condition is not satisfied, and the catalyst deterioration determination calculation is prohibited.

  As described above, if it is determined by the catalyst deterioration determination calculation start condition determination routine of FIG. 18 or FIG. 19 that the catalyst deterioration determination calculation start condition is not satisfied, the catalyst deterioration detection routine of FIG. Is not done. Then, when the catalyst deterioration determination calculation start condition is satisfied, the process proceeds to step 402 in FIG. 16 to increment the time counter 1 and perform the processing of steps 403 to 409 until the time counter 1 reaches a predetermined time kdly (for example, 10 sec). repeat. Here, the predetermined time kdly can absorb the influence due to the delay time until the catalyst inflow gas is detected by the upstream air-fuel ratio sensor 28 and the gas is detected by the downstream oxygen sensor 29 through the reaction in the catalyst 27. Set to time.

  In step 403, the saturation determination of the catalyst is performed in consideration of the static characteristics of the downstream oxygen sensor 29 shown in FIG. 21 (this process serves as saturation determination means in the claims). The output voltage VOX2 of the downstream oxygen sensor 29 changes linearly with respect to the excess air ratio λ (air-fuel ratio) in the vicinity of the stoichiometry, but in the region outside the stoichiometry, even if the excess air ratio λ changes, the downstream side Since the output voltage VOX2 of the oxygen sensor 29 does not change so much and the amount of the catalyst outflow gas component cannot be accurately detected, it is considered that the catalyst is saturated in a region outside the stoichiometric range, that is, a region where VOX2> krich or VOX2 <klean. In the catalyst saturation state, the rate of purification in the catalyst 27 is low, and the catalyst outflow gas component amount is correlated with the catalyst inflow gas component amount.

  Therefore, if the catalyst is saturated, the routine proceeds to step 404 where the catalyst outflow gas component amount (hereinafter referred to as “catalyst saturation correction amount”) VSATU that cannot be detected from the output change amount of the downstream oxygen sensor 29 is converted to the upstream air-fuel ratio sensor 28. The output value is used to calculate by the following formula.

VSATU = | ΔA / F | × Q × k
Here, | ΔA / F | is the absolute value of the deviation between the output value (actual air-fuel ratio) of the upstream air-fuel ratio sensor 28 and the target air-fuel ratio, Q is the cylinder inflow air amount, and k is the upstream air-fuel ratio sensor 28. Is a conversion coefficient between the output value and the output value of the downstream oxygen sensor 29.

  On the other hand, if it is determined in step 403 that the catalyst is not saturated, that is, if klean ≦ VOX2 ≦ krich (stoichiometric region), the process proceeds to step 405 and the catalyst saturation correction amount VSATU is set to zero. This is because the catalyst outflow gas component amount can be calculated from the amount of change in the output voltage VOX2 of the downstream oxygen sensor 29.

An example of the catalyst saturation correction amount VSATU set in this way is shown in FIG. As is apparent from FIG. 22, when klean ≦ VOX2 ≦ krich, the catalyst saturation correction amount VSATU is maintained at zero. On the other hand, in the case of VOX2 <kleen or VOX2> krich, the catalyst saturation correction amount VSATU is obtained from the calculation of | ΔA / F | × Q × k. Therefore, the catalyst saturation correction amount VSATU
Is proportional to | ΔA / F | × Q, and as | ΔA / F | and the cylinder inflow air amount Q increase, the catalyst saturation correction amount VSATU increases.

  As described above, after setting the catalyst saturation correction amount VSATU in step 404 or 405 of FIG. 16, the process proceeds to step 406, where the catalyst inflow gas component amount GASin is calculated by the following equation (this processing is defined in the claims). It plays a role as a first computing means).

GASin (n) = GASin (n−1) + | ΔA / F | × Q
Here, GASin (n) is the current catalyst inflow gas component amount, and GASin (n−1) is the previously calculated catalyst inflow gas component amount.

  Thereafter, in step 407, the catalyst outflow gas component amount GASout is calculated by the following equation using the catalyst saturation correction amount VSATU.

GASout (n) = GASout (n−1) + | dV | × Q + VSATU
Here, GASout (n) is the current catalyst outflow gas component amount, GASout (n−1) is the previously calculated catalyst outflow gas component amount, and | dV | is the absolute value of the output voltage change amount of the downstream oxygen sensor 29. {| DV | = VOX2 (n) -VOX2 (n-1)}.

  The processing in step 407 serves as the second calculation means in the claims, and the processing in steps 404 and 407 also serves as the saturation correction means in the claims.

  In the next step 408, the output change amount A / Flocs of the upstream air-fuel ratio sensor 28 within a predetermined time kdly (10 sec) is calculated by the following equation as a first cancellation determination criterion.

A / Flocs (n) = A / Flocs (n−1) + | dA / F |
Here, | dA / F | is the absolute value of the difference between the current output value of the upstream air-fuel ratio sensor 28 and the previous output value of the upstream air-fuel ratio sensor 28.

  Thereafter, in step 409, INamount is calculated by the following equation as the second cancellation criterion.

INamount (n) = INamount (n−1) + | ΔA / F | × Q
Here, INamount (n) is the same as the catalyst inflow gas component amount GASin calculated in step 406.

  The processing in steps 402 to 409 described above is repeated for a predetermined time kdly (10 sec), and after the predetermined time kdly has elapsed, the process proceeds from step 410 in FIG. 17 to step 411 and the upstream air-fuel ratio sensor within the predetermined time kdly calculated in step 408. It is determined whether the output change amount A / Flocs 28 is within a predetermined range (klmin <A / Flocs <klmax). If it is not within the predetermined range, it is not reflected in a catalyst deterioration index value to be described later, and step 417. Jump over to.

  When the output change amount A / Flocs of the upstream air-fuel ratio sensor 28 within the predetermined time kdly is equal to or less than the predetermined range (A / Flocs ≦ klmin), the output value of the upstream air-fuel ratio sensor 28 is stoichiometric. The upstream air-fuel ratio sensor 28 has a low resolution in the vicinity of the stoichiometry, and the calculation accuracy of the catalyst inflow gas component amount is deteriorated. Therefore, when A / Flocs ≦ klmin, it is not reflected in the catalyst deterioration index value.

  Further, when A / Flocs is equal to or greater than a predetermined range (A / Flocs ≧ klmax), it means that the control is performed in a region where the output value of the upstream air-fuel ratio sensor 28 is extremely deviated from the stoichiometry. If the output value of the upstream air-fuel ratio sensor 28 deviates extremely from the stoichiometry, the output of the upstream air-fuel ratio sensor 28 cannot maintain a linear relationship with respect to the excess air ratio λ (air-fuel ratio). Accordingly, even when A / Flocs ≧ klmax, the calculation accuracy of the catalyst inflow gas component amount is deteriorated, and thus is not reflected in the catalyst deterioration index value.

  On the other hand, when A / Flocs is within a predetermined range (klmin <A / Flocs <klmax), the resolution of the upstream air-fuel ratio sensor 28 is good and the linear characteristic of the output of the upstream air-fuel ratio sensor 28 is good. Therefore, the calculation accuracy of the catalyst inflow gas component amount can be sufficiently secured. Therefore, if A / Flocs is within the predetermined range, the process proceeds to step 412 to determine whether or not INamount calculated at step 409 is within the predetermined range (kamin <INamount <kamax). Otherwise, it is not reflected in the catalyst deterioration index value and jumps to step 417. Here, INamount corresponds to the amount of the catalyst inflow gas component that contributes to the catalytic reaction within the predetermined time kdly. When INamount is not more than the predetermined range (INamount ≦ kamin), the above-mentioned case of A / Flocs ≦ klmin For the same reason, it is not reflected in the catalyst deterioration index value.

  Further, when INamount is equal to or greater than a predetermined range (INamount ≧ kamax), the flow rate of the gas flowing into the catalyst 27 becomes too fast, so that the rate of adsorption to the catalyst 27 or contribution to the catalytic reaction becomes low. For this reason, even if the deviation ΔA / F between the output value (actual air-fuel ratio) of the upstream side air-fuel ratio sensor 28 and the target air-fuel ratio is the same, the air downstream of the catalyst is low when the cylinder inflow air amount Q is small and large. The fuel ratio will be different. Originally, if the catalyst has the same degree of deterioration, the calculation result of the catalyst deterioration index value must be the same value. However, if INamount ≧ kamax, the catalyst deterioration index value is deviated for the reason described above. Therefore, when INamount ≧ kamax, it is not reflected in the catalyst deterioration index value.

  On the other hand, if INamount is within the predetermined range (kamin <INamount <kamax), the process proceeds to step 413, whether the fuel cut (F / C) is not being performed, or after the fuel cut (F / C) is restored, a predetermined time kfcret. It is determined whether or not elapses. Since the fuel is not supplied during the fuel cut, the air-fuel ratio in the exhaust gas becomes lean and exceeds the range in which the air-fuel ratio can be measured correctly by the upstream air-fuel ratio sensor 28. Further, after the fuel cut is restored, the air-fuel ratio is accurately determined until a predetermined time kfcret necessary for air-fuel ratio feedback control to stabilize, that is, until the output value of the upstream air-fuel ratio sensor 28 crosses the target air-fuel ratio. It cannot be detected. Therefore, when the fuel cut is in progress, or when the predetermined time kfcret has not elapsed after the fuel cut is restored, it is not reflected in the catalyst deterioration index value.

  In this case, whether or not the air-fuel ratio feedback is stable is determined by whether or not the predetermined time kfcret has elapsed after the fuel cut is restored. Instead, after the fuel cut is restored, the upstream air-fuel ratio sensor 28 It is determined whether the air-fuel ratio feedback is stable depending on whether the output crosses the target air-fuel ratio, and catalyst deterioration determination is performed until the output of the upstream air-fuel ratio sensor 28 first crosses the target air-fuel ratio after returning from the fuel cut. You may make it prohibit a calculation. Even in this case, the catalyst deterioration determination calculation can be started after the air-fuel ratio feedback is stabilized after the fuel cut is restored.

  By the processing in steps 411 to 413 described above, (1) klmin <A / Flocs <klmax, (2) kamin <INamount <kamax, (3) the fuel cut is not in progress or a predetermined time kfcret has elapsed after the fuel cut is restored. In order to reflect the catalyst inflow / outflow gas component amount (integrated value) within the predetermined time kdly in the catalyst deterioration determination only when all of the following conditions are satisfied, that is, when the air-fuel ratio can be detected correctly, step 414 is performed. Proceed to In step 414, the catalyst inflow gas component amount GASin and the catalyst outflow gas component amount GASout for each predetermined time kdly calculated in steps 406 and 407 described above are integrated according to the following equations.

TGASin (n) = TGASin (n-1) + GASin (n)
TGASout (n) = TGASout (n-1) + GASout (n)
TGASin (n): integrated value of catalyst inflow gas component amount GASin up to this time TGASin (n-1): integrated value of catalyst inflow gas component amount GASin up to the previous time TGASout (n): catalyst outflow gas component amount GASout up to this time TGASout (n-1): Integrated value of the catalyst outflow gas component amount GASout up to the previous time After this, the routine proceeds to step 415, where the catalyst deterioration determination counter that counts the number of times reflected in the catalyst deterioration determination is incremented. In the next step 416, the time counter 1 for measuring the predetermined time kdly, the catalyst inflow gas component amount GASin and the catalyst outflow gas component amount GASout are both set to 0, and the process proceeds to step 417. If any one of the above-described steps 411 to 413 is determined as “No”, the processing of steps 414 to 416 is skipped and the process proceeds to step 417.

  In this step 417, it is determined whether or not a catalyst deterioration determination calculation end condition is satisfied. Here, whether or not the catalyst deterioration determination calculation end condition is satisfied is determined by the following procedure by the catalyst deterioration determination calculation end condition determination routine shown in FIG. First, in step 521, it is determined whether or not the catalyst temperature TCAT exceeds a predetermined temperature (for example, 550 ° C.). If not, the process proceeds to step 526, where it is determined that the catalyst deterioration determination calculation end condition is not satisfied.

  When the catalyst temperature TCAT exceeds a predetermined temperature (for example, 550 ° C.), the process proceeds from step 521 to step 522 to determine whether or not the catalyst deterioration determination counter that counts the number of times reflected in the catalyst deterioration determination exceeds a predetermined value kcatcount. If not, the process proceeds to step 525, where the catalyst deterioration determination counter is cleared and the process proceeds to step 526, where it is determined that the catalyst deterioration determination calculation end condition is not satisfied.

  When the catalyst deterioration determination counter exceeds the predetermined value kcatcount, the process proceeds from step 522 to step 523, the catalyst deterioration determination counter is cleared, the process proceeds to step 524, and it is determined that the catalyst deterioration determination calculation end condition is satisfied. .

  As described above, the catalyst deterioration determination calculation end condition determination routine of FIG. 20 determines whether or not the catalyst deterioration determination calculation end condition is satisfied. If not, the catalyst deterioration detection process from step 418 onward in FIG. Without performing this, the catalyst deterioration detection routine is terminated.

  If the catalyst deterioration determination calculation end condition is satisfied, the process proceeds to step 418, where the catalyst inflow gas component amount integrated value TGASin and the catalyst outflow gas component amount integrated value TGASout calculated in step 414 described above are used. The deterioration index value JUDGE is calculated by the following equation.

JUDGE = TGASout / TGASin
The catalyst deterioration index value JUDGE is a ratio of the catalyst outflow gas component amount integrated value TGASout and the catalyst inflow gas component amount integrated value TGASin that contributes to the catalyst reaction between the catalyst temperature of 150 ° C. and 550 ° C. This is equivalent to the ratio of non-purification (non-purification rate). Therefore, as the catalyst deterioration index value JUDGE increases, it means that the catalyst deterioration has progressed.

  Therefore, in the next step 419, the catalyst deterioration index value JUDGE is compared with a predetermined deterioration determination value kjudge. If JUDGE> kjudge, it is determined that the catalyst has deteriorated (step 420). If JUDGE ≦ kjudge, normal ( It is determined that there is no catalyst deterioration (step 421). The processing in these steps 418 to 420 serves as catalyst deterioration detection means in the claims.

<< Embodiment (2) >>
The embodiment (2) shown in FIGS. 23 and 25 is obtained by changing a part of the processing of the embodiment (1) . In the above embodiment (1) , the catalyst outflow gas component amount integrated value TGASout and the catalyst inflow gas component amount integrated value TGASin are the rich component (reducing component such as HC, CO, H2, etc.) and lean component ( Both of the rich components and lean components are integrated to add the catalyst outflow gas component amount integrated value TGASout and the catalyst inflow gas component amount integrated value TGASin. And the catalyst deterioration determination may be performed.

In this embodiment (2) , in order to determine the degree of deterioration of the HC purification rate of the catalyst 27, only rich components are integrated, and a catalyst outflow rich gas component amount integrated value TGASout and a catalyst inflow rich gas component amount integrated value TGASin are obtained. Perform deterioration judgment.

This catalyst deterioration determination is performed by a catalyst deterioration detection routine shown in FIG. The processing portion different catalyst deterioration detection routine shown in FIGS. 16 and 17 of Embodiment (1) is only the processing of step 403a~403i surrounding 23 by a one-dot chain line, the other processes the embodiment ( Same as 1) .

In the catalyst deterioration detection routine shown in FIG. 23, the time counter 1 is incremented when the catalyst deterioration determination calculation start condition is satisfied (steps 401 and 402), and in the subsequent step 403a, the rich side is determined depending on whether or not VOX2> krich. Perform catalyst saturation determination. In the embodiment (1) , both the rich side / lean side catalyst saturation determination is performed, but in this embodiment (2) , only the rich component is integrated, and therefore, the rich side only catalyst saturation determination is performed. If the catalyst is not saturated (VOX2 ≦ krich), the process proceeds to step 403e, the catalyst saturation correction amount VSATU is set to 0, and the process proceeds to step 304f.

  On the other hand, if the catalyst is saturated (VOX2> krich), the process proceeds to step 403b, and the deviation ΔA / F (= target air-fuel ratio) between the target air-fuel ratio and the output value (actual air-fuel ratio) of the upstream air-fuel ratio sensor 28 is reached. It is determined whether or not the output value of the upstream air-fuel ratio sensor 28 is a negative value, that is, whether or not it is richer than the target air-fuel ratio, and if ΔA / F ≧ 0 (lean), step Proceeding to 403c, ΔA / F = 0, and ΔA / F is not reflected in the calculation of the catalyst inflow gas component amount GASin. Thus, only when ΔA / F <0 (rich), ΔA / F is reflected in the calculation of the catalyst inflow gas component amount GASin. The processing of these steps 403b and 403c serves as a first canceling means in the claims.

  In the next step 403d, the catalyst outflow gas component amount (catalyst saturation correction amount) VSATU that cannot be detected from the output change amount of the downstream oxygen sensor 29 is calculated by the following equation.

VSATU = | ΔA / F | × Q × k
Here, Q is the cylinder inflow air amount, and k is a conversion coefficient between the output value of the upstream air-fuel ratio sensor 28 and the output value of the downstream oxygen sensor 29. If ΔA / F ≧ 0 (lean), ΔA / F = 0 is set in step 403c, so this catalyst saturation correction amount VSATU becomes zero. Therefore, the catalyst saturation correction amount VSATU ≠ 0 only when ΔA / F <0 (rich).

  An example of the catalyst saturation correction amount VSATU set as described above is shown in FIG. As is apparent from FIG. 24, the condition for the catalyst saturation correction amount VSATU ≠ 0 is only when VOX2> krich and ΔA / F <0. When this condition is not satisfied, the catalyst saturation correction amount VSATU = 0.

  After setting the catalyst saturation correction amount VSATU in step 403d or 403e, the process proceeds to step 403f to determine again whether or not ΔA / F <0 (rich). If ΔA / F ≧ 0 (lean) In step 403g, ΔA / F = 0 is set, and the process proceeds to step 403h. If ΔA / F <0 (rich), the process proceeds to step 403h. In step 403h, it is determined whether the output voltage change amount dV of the downstream oxygen sensor 29 is a positive value, that is, whether the catalyst outflow gas is changing in the rich direction, and dV ≦ 0 (change in the lean direction). ), The process proceeds to step 403i, dV = 0 is set, and dV is not reflected in the calculation of the catalyst outflow gas component amount GASout. Only when dV> 0 (change in the rich direction), dV is reflected in the calculation of the catalyst outflow gas component amount GASout. The processing in steps 403h and 403i serves as second canceling means in the claims.

After performing the above processing, the process proceeds to step 406. The subsequent processing is the same as in the embodiment (1) . Therefore, when the process of FIG. 23 is completed, the process of FIG. 17 is executed. Also in this embodiment (2), the catalyst deterioration determining calculation start condition determining routine and the catalyst deterioration determining calculation ending condition determining routine of FIG. 20 in FIG. 18 used in the embodiment (1) (or FIG. 19) Execute. Further, when applied to a system having a timer for measuring the elapsed time after the engine is stopped, the catalyst temperature at the time of engine start is estimated by the catalyst temperature estimation routine of FIG.

In this embodiment (2) , only rich components out of the gas components contributing to the catalytic reaction are integrated, and the catalyst outflow rich gas component amount integrated value TGASout and the catalyst inflow rich gas component amount integrated value TGASin are obtained, and the rich gas component is not purified. The catalyst deterioration is determined from the rate (catalyst deterioration index value JUDGE = TGASout / TGASin). Thereby, the degree of deterioration of the HC purification rate of the catalyst 27 can be determined.

In this embodiment (2) , only the rich component is integrated, but on the contrary, only the lean component may be integrated and the catalyst deterioration determination may be made from the non-purification rate of the lean gas component.

<< Embodiment (3) >>
As the catalyst 27 deteriorates, the frequency at which the output value VOX2 of the downstream oxygen sensor 29 deviates from the stoichiometry increases. Since the catalyst outflow gas component amount cannot be detected by the output change amount of the downstream oxygen sensor 29 if it is out of the stoichiometry, in the above embodiments (1) and (2) , in step 403 in FIG. 16 and step 403a in FIG. It is determined whether or not the output value VOX2 of the downstream oxygen sensor 29 has deviated from the stoichiometry by the catalyst saturation determination. The calculation accuracy of the catalyst outflow gas component amount GASout is improved by calculating the saturation correction amount VSATU and correcting the catalyst outflow gas component amount GASout by the catalyst saturation correction amount VSATU. By doing so, it is possible to detect catalyst deterioration even after the catalyst is fully activated, in which the difference in the HC purification rate between the new catalyst and the deteriorated catalyst becomes small.

Therefore, in this embodiment (3) , the catalyst deterioration determination is performed after the catalyst 27 is fully activated by determining the catalyst deterioration determination calculation start / end conditions by the condition determination routines shown in FIGS. Hereinafter, this process will be described.

  In the catalyst deterioration determination calculation start condition determination routine shown in FIG. 25, first, in step 601, whether or not the catalyst 27 has been fully activated depending on whether or not the cooling water temperature THW has exceeded the water temperature (for example, 80 ° C.) when the engine is completely warmed up. If “Yes”, the process proceeds to step 602, and whether or not the predetermined time kactive has elapsed after the upstream air-fuel ratio sensor 28 is completely activated (after the air-fuel ratio feedback is started). If “Yes”, the process proceeds to step 603 to determine that the catalyst deterioration determination calculation start condition is satisfied. Here, the reason why the predetermined time kactive after the full activation is required is that the air-fuel ratio feedback is stable even when the water temperature is high (the upstream air-fuel ratio sensor 28 is fully activated) at the time of restart. This is to prevent the catalyst deterioration determination calculation from being started in a state where it is not.

  In this case, after the upstream side air-fuel ratio sensor 28 is fully activated (after the start of air-fuel ratio feedback), it is determined whether or not the air-fuel ratio feedback is stable depending on whether or not the predetermined time kactive has elapsed. After the start of air-fuel ratio feedback, it is determined whether the air-fuel ratio feedback is stable based on whether the output of the upstream air-fuel ratio sensor 28 has crossed the target air-fuel ratio. The catalyst deterioration determination calculation may be prohibited until the output of the fuel ratio sensor 28 first crosses the target air fuel ratio.

  When the catalyst deterioration determination calculation start condition is satisfied by the processing of steps 601 to 603 described above, the processing after step 402 of the catalyst deterioration detection routine of FIG. 16 or FIG. 23 is executed.

  On the other hand, if “No” is determined in either step 601 or 602, the process proceeds to step 604, where it is determined that the catalyst deterioration determination calculation start condition is not satisfied, and the catalyst deterioration determination calculation is prohibited.

  In the catalyst deterioration determination calculation end condition determination routine shown in FIG. 26, first, in step 611, it is determined whether or not the catalyst deterioration determination counter that counts the number of times reflected in the catalyst deterioration determination has reached a predetermined value kcatcount2. If not, the process proceeds to step 614, and it is determined that the catalyst deterioration determination calculation end condition is not satisfied.

When the catalyst deterioration determination counter reaches the predetermined value kcatcount2, the process proceeds from step 611 to step 612, the catalyst deterioration determination counter is cleared, the process proceeds to step 613, and the catalyst deterioration determination calculation end condition is satisfied. judge. When the catalyst deterioration determination calculation end condition is satisfied, the processing after step 418 in FIG. 17 is executed to calculate the catalyst deterioration index value JUDGE (= TGASout / TGASin), and this catalyst deterioration index value JUDGE is set to a predetermined deterioration determination value. Compared with kjudge, if JUDGE> kjudge, it is determined that the catalyst is deteriorated, and if JUDGE ≦ kjudge, it is determined that the catalyst is normal (no catalyst deterioration). The deterioration determination value kjudge is set to a smaller value than in the embodiments (1) and (2) where deterioration is determined during the catalyst activity. As a result, catalyst deterioration can be detected even after the catalyst is fully activated in which the difference in the HC purification rate between the new catalyst and the deteriorated catalyst is small.

Schematic configuration diagram of the entire engine control system in Reference Example (1) of the present invention Flowchart showing the process flow of the catalyst deterioration detection routine Flow chart showing the process flow of the catalyst temperature estimation routine The figure which shows notionally the map which estimates exhaust temperature TEX from engine speed Ne and the intake air flow rate Q The figure which shows the data table which prescribes | regulates the relationship between the catalyst temperature TCAT at the time of a fuel cut start, and exhaust gas temperature TEX The figure which shows the data table which prescribes | regulates the relationship between the intake air flow rate Q and the coefficient K1, K2. The figure explaining the calculation method of the data (SIGMA) V (trajectory of the output voltage fluctuation | variation of a downstream oxygen sensor) reflecting the amount of purification gas components The figure explaining the calculation method of data (SIGMA) deltaA / FQ which digitized the catalyst inflow gas component fluctuation | variation The figure which measured the relationship between the data ΣV reflecting the amount of the purified gas component and the data ΣΔA / F · Q of the catalyst inflow gas component fluctuation The figure which shows the data table which prescribes | regulates the relationship between the data ΣΔA / F · Q of the catalyst inflow gas component fluctuation and the deterioration judgment value The figure explaining the catalyst deterioration detection method in the reference example (2) of this invention The figure which shows an example of a time-dependent change of the HC purification rate after a cold start about a new catalyst and a deterioration catalyst The flowchart which shows the flow of a process of the catalyst temperature estimation routine in the reference example (3) of this invention. Time chart showing an example of the behavior of catalyst temperature and cooling water temperature after engine stop when the outside air temperature is 25 ° C Time chart showing an example of the behavior of catalyst temperature and cooling water temperature after engine stop when the outside air temperature is 15 ° C The flowchart which shows the flow of the process of the first half of the catalyst deterioration detection routine in Embodiment (1) of this invention. The flowchart which shows the flow of the process of the second half part of the catalyst deterioration detection routine of FIG. A flowchart showing the flow of processing of a catalyst deterioration determination calculation start condition determination routine used in a system without a catalyst temperature sensor or a timer for measuring an elapsed time after engine stop. A flowchart showing the flow of processing of a catalyst deterioration determination calculation start condition determination routine used in a system having a catalyst temperature sensor or a timer for measuring an elapsed time after engine stop. The flowchart which shows the flow of a process of a catalyst deterioration determination calculation end condition determination routine The figure which shows the static characteristic of the downstream oxygen sensor Time chart for explaining the relationship among the output value of the upstream air-fuel ratio sensor, the catalyst saturation correction amount VSATU, and the output value of the downstream oxygen sensor in the embodiment (1) of the present invention The flowchart which shows the flow of the process of the first half of the catalyst deterioration detection routine in Embodiment (2) of this invention. Time chart explaining the relationship between the output value of the upstream air-fuel ratio sensor, the catalyst saturation correction amount VSATU, and the output value of the downstream oxygen sensor in the embodiment (2) of the present invention The flowchart which shows the flow of a process of the catalyst deterioration determination calculation start condition determination routine in Embodiment (3) of this invention. The flowchart which shows the flow of a process of a catalyst deterioration determination calculation end condition determination routine

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Air flow meter, 11 ... Engine (internal combustion engine), 14 ... Intake air temperature sensor,
17 ... Intake pipe pressure sensor, 24 ... Crank angle sensor, 26 ... Exhaust pipe, 27 ... Catalyst,
28 ... upstream air-fuel ratio sensor, 29 ... downstream oxygen sensor, 30 ... electronic control circuit (calculation means, catalyst deterioration detection means, saturation determination means, first calculation means, second calculation means, saturation correction means, first 1 canceling means, second canceling means, first integrating means, second integrating means),
37 ... warning lamp, 38 ... water temperature sensor, 39 ... heater for downstream oxygen sensor.

Claims (3)

In a system in which an air-fuel ratio sensor is installed upstream of the exhaust gas purification catalyst and an oxygen sensor is installed downstream,
Saturation determination means for determining saturation of the catalyst based on the output of the downstream oxygen sensor;
First calculating means for calculating an area of a portion surrounded by an output waveform of the upstream air-fuel ratio sensor and a target air-fuel ratio to obtain a catalyst inflow gas component amount;
A second computing means for integrating the output change amount of the downstream oxygen sensor to obtain the catalyst outflow gas component amount;
Saturation correction means for correcting the catalyst outflow gas component amount by the second calculation means based on the output of the upstream air-fuel ratio sensor when the saturation determination means determines the saturation of the catalyst;
And a catalyst deterioration detecting means for detecting deterioration of the catalyst based on the catalyst outflow gas component amount corrected by the saturation correction means and the catalyst inflow gas component amount determined by the first calculation means. A catalyst deterioration detection device for purifying exhaust gas. First canceling means for canceling the area on either the lean side or the rich side from the target air-fuel ratio when integrating the area by the first calculating means;
When the output change amount of the downstream oxygen sensor is accumulated by the second calculation means when the output change direction of the downstream oxygen sensor is directed to the same side as the area canceled by the first cancellation means 2. The exhaust gas purifying catalyst deterioration detecting device according to claim 1, further comprising: a second canceling unit that cancels an output change amount in the direction. 3. The exhaust gas purifying catalyst deterioration detecting device according to claim 1, further comprising means for prohibiting the catalyst deterioration detecting process during the fuel cut and until a predetermined period of time has elapsed since the fuel cut was recovered.

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