JP3409699B2 - Apparatus and method for diagnosing deterioration of HC adsorbent in internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for diagnosing deterioration of an HC adsorbent in an internal combustion engine equipped with an HC adsorbent for temporarily adsorbing HC in exhaust gas for purification of exhaust gas.

[0002]

2. Description of the Related Art A three-way catalyst device is generally used for purifying exhaust gas from an internal combustion engine. However, when the exhaust gas temperature is low, such as immediately after a cold start of the engine, the catalyst is inactive.
HC cannot be purified. For this reason, an HC adsorbent made of zeolite or the like is provided in the exhaust passage so that H
An exhaust emission control device that adsorbs C has been conventionally known.

The applicant of the present invention has previously proposed a diagnostic device for diagnosing the deteriorated state of the HC adsorbent (Japanese Patent Application Laid-Open No. 8-112232). This utilizes the characteristic that the HC adsorbent adsorbs HC at a low temperature and desorbs the adsorbed HC when the temperature becomes higher than a predetermined desorption temperature. Air-fuel ratio detection means such as air-fuel ratio sensors are arranged on both the upstream and downstream sides of
When desorbing HC, the total amount of desorbed HC is estimated by integrating the difference between the detected air-fuel ratios of the two with respect to the intake air amount,
The degree of deterioration is determined from the size.

[0004]

As described above, the HC
In many cases, the adsorbent is used together with the three-way catalyst device. For example, the three-way catalyst device is arranged upstream of the HC adsorbent. Further, since it is necessary to arrange the air-fuel ratio sensor on the upstream side of the three-way catalyst device for the air-fuel ratio feedback control, if two air-fuel ratio sensors are provided to diagnose the above HC adsorbent, Both the three-way catalyst device and the HC adsorbent are arranged between the upstream side air-fuel ratio sensor and the downstream side air-fuel ratio sensor.

In such a case, the three-way catalyst device has an oxygen storage function, and oxygen in the exhaust gas is absorbed or, conversely, oxygen is released into the exhaust gas. Since the air-fuel ratio difference occurs, the detection accuracy for the air-fuel ratio difference before and after the HC adsorbent due to the desorption of HC decreases.

If an air-fuel ratio sensor is further arranged between the three-way catalyst device and the HC adsorbent, it is necessary to provide the air-fuel ratio sensor at a total of three places, which is not preferable.

It is an object of the present invention to further improve the accuracy of diagnosis in an air-fuel ratio detecting means provided at two positions before and after the three-way catalyst device and the HC adsorbent.

[0008]

In order to solve the above-mentioned problems, a deterioration diagnosing device for an HC adsorbent in an internal combustion engine according to claim 1 is installed in an exhaust system of the internal combustion engine and has an adsorbing action at a low temperature. And an HC adsorbent having a desorption action at high temperature,
A three-way catalyst device arranged upstream of the HC adsorbent,
The upstream air-fuel ratio detecting means provided on the upstream side of the three-way catalyst device and the downstream air-fuel ratio detecting means provided on the downstream side of the HC adsorbent, and the upstream air-fuel ratio detecting means when the HC adsorbent is desorbed. An HC adsorbent comprising: a deterioration diagnosis means for diagnosing deterioration of the HC adsorbent from the desorbed HC amount estimated based on the detected air-fuel ratio in the fuel ratio detection means and the detected air-fuel ratio in the downstream side air-fuel ratio detection means. In the deterioration diagnosis device of
At the time of diagnosis, an oxygen supply means for bringing the oxygen storage capacity of the three-way catalyst device into a saturated state is provided.

Further, H in the internal combustion engine according to claim 8
A method for diagnosing deterioration of a C adsorbent is provided by an HC adsorbent that is interposed in an exhaust system of an internal combustion engine and that performs an adsorbing action at a low temperature and a desorbing action at a high temperature, and a three-component disposed on the upstream side of the HC adsorbent. The above-mentioned HC adsorbent, comprising a source catalyst device, upstream air-fuel ratio detection means provided upstream of the three-way catalyst device, and downstream air-fuel ratio detection means provided downstream of the HC adsorbent. At the time of desorption, the desorbed HC amount is estimated based on the detected air-fuel ratio in the upstream side air-fuel ratio detection means and the detected air-fuel ratio in the downstream side air-fuel ratio detection means, and the HC adsorbent deterioration from the desorbed HC amount. In the method for diagnosing deterioration of the HC adsorbent for diagnosing, the excess oxygen is applied to the three-way catalyst device to forcibly bring the oxygen storage capacity to a saturated state,
It is characterized in that deterioration diagnosis is performed based on the detected air-fuel ratio in both air-fuel ratio detection means.

As described above, if sufficient oxygen is supplied to the three-way catalyst device so that the oxygen storage capacity is saturated,
When HC is desorbed under the stoichiometric air-fuel ratio or lean air-fuel ratio, there is no change in the air-fuel ratio before and after the three-way catalyst device due to the oxygen storage action, and the upstream-side air-fuel ratio detecting means and the downstream-side air-fuel ratio detecting means are used. The difference in the air-fuel ratio detected in 1 is due only to the desorbed HC from the HC adsorbent. Therefore, even if the upstream side air-fuel ratio detecting means is on the upstream side of the three-way catalyst device, it is possible to accurately detect the amount of desorbed HC and thus the deterioration state of the HC adsorbent.

The above-mentioned supply of oxygen can be achieved by, for example, an air-fuel ratio control means for temporarily making the air-fuel ratio lean. In addition, 2 in the exhaust system
It can also be realized by a secondary air supply device that supplies secondary air. Further, the supply of oxygen may be, for example, a fixed time or a fixed period sufficient to saturate the oxygen storage capacity,
Alternatively, a fixed amount may be performed, or, as described later, the oxygen storage amount of the three-way catalyst device at that time may be sequentially detected and performed until it is saturated.

Further, in the invention of claim 3 which further embodies the invention of claim 2, the air-fuel ratio control means keeps the air-fuel ratio lean until the end of the diagnosis by the deterioration diagnosis means.

If the HC is desorbed in the lean state and the deterioration of the HC adsorbent is diagnosed,
The deterioration of the diagnostic accuracy due to the oxygen storage action can be more surely avoided, and the desorbed HC can be satisfactorily purified.

A fourth aspect embodying the invention of the second aspect.
In the invention, the air-fuel ratio control means makes the air-fuel ratio lean until the oxygen storage capacity of the three-way catalyst device becomes saturated, and returns to the stoichiometric air-fuel ratio when the diagnosis by the deterioration diagnosis means is started.

After saturating the oxygen storage capacity in this way, HC is desorbed under the stoichiometric air-fuel ratio and the deterioration of the HC adsorbent is diagnosed. The increase is avoided.

Further, according to a fifth aspect of the present invention, the actual oxygen storage for sequentially estimating the actual oxygen storage amount in the three-way catalytic converter on the basis of the air-fuel ratio detected by the upstream side air-fuel ratio detection means and the intake air amount. An amount estimating means is provided, and the saturation of the oxygen storage capacity is determined based on the estimated actual oxygen storage amount.

That is, if lean exhaust gas flows into the three-way catalyst device, the oxygen storage amount of the three-way catalyst device increases, and conversely, if rich exhaust gas flows in, the oxygen storage amount decreases. Therefore, it is possible to sequentially estimate the actual oxygen storage amount based on the upstream air-fuel ratio and the exhaust gas amount, that is, the intake air amount. Then, the saturated state can be determined by whether or not this actual oxygen storage amount has reached a predetermined oxygen storage capacity.

Here, the oxygen storage capacity of the three-way catalytic converter, which is a criterion for determining whether or not it is saturated, may be treated as a fixed value, but in reality, the oxygen storage capacity is deteriorated as the catalyst deteriorates. Since it will decrease, it is desirable to consider this. The catalyst deterioration can be estimated, for example, by the operation history such as the operation time and the operation conditions (load, rotation speed) or the like, but can be detected as in claim 6.

That is, in the sixth aspect of the invention, during normal operation in which the three-way catalyst device is in the active state, the change in the detection signal of the upstream side air-fuel ratio detecting means and the detection signal of the downstream side air-fuel ratio detecting means are performed. The oxygen storage capacity estimation means for estimating the oxygen storage capacity of the three-way catalyst device from the relationship with the change of

When the air-fuel ratio of the internal combustion engine fluctuates cyclically by, for example, air-fuel ratio feedback control, the detection signal of the upstream side air-fuel ratio detecting means changes cyclically in response to this, but is downstream of the three-way catalytic converter. On the side, the air-fuel ratio change becomes very slow due to the oxygen storage effect. However, when the catalyst deteriorates and the oxygen storage capacity becomes low,
The change in the air-fuel ratio on the downstream side of the three-way catalyst device becomes close to the change in the air-fuel ratio on the upstream side. Therefore, it is possible to estimate the actual oxygen storage capacity from the relationship between the two. In particular, in this method, the oxygen storage capacity can be estimated using the upstream side air-fuel ratio detecting means and the downstream side air-fuel ratio detecting means for diagnosing the deterioration of the HC adsorbent as they are.

On the other hand, the deterioration diagnosing device for HC adsorbent in an internal combustion engine according to claim 7 is provided in an exhaust system of the internal combustion engine,
An HC adsorbent having an adsorbing action at a low temperature and a desorbing action at a high temperature, air-fuel ratio detecting means respectively provided on the upstream side and the downstream side of the HC adsorbent, and when desorbing the HC adsorbent, An actual oxygen storage amount estimating means for sequentially estimating the actual oxygen storage amount in the three-way catalyst device based on the air-fuel ratio detected by the upstream side air-fuel ratio detecting means and the intake air amount, and the estimated actual oxygen storage amount Is 0 or has reached the oxygen storage capacity saturation state, the air-fuel ratio detected by the upstream air-fuel ratio detection means, the theoretical air-fuel ratio when the actual oxygen storage amount is within the oxygen storage capacity, the HC adsorbent inlet Based on the adsorbent inlet side air-fuel ratio estimating means for outputting as the side air-fuel ratio and the estimated adsorbent inlet side air-fuel ratio and the detected air-fuel ratio in the downstream side air-fuel ratio detecting means. Estimate the amount of desorbed HC,
Deterioration diagnosis means for diagnosing the deterioration of the HC adsorbent from the C amount,
It is configured with.

The present invention estimates the air-fuel ratio on the HC adsorbent inlet side, that is, between the three-way catalyst device and the HC adsorbent without forcibly saturating the oxygen storage capacity of the three-way catalyst device. The detection accuracy of the amount of desorbed HC from the HC adsorbent is improved.

FIG. 1 shows the relationship between the air-fuel ratios on the upstream side and the downstream side of the three-way catalytic converter due to the oxygen storage action. In the figure, (A) shows the air-fuel ratio on the upstream side of the three-way catalyst device (usually equivalent to the air-fuel ratio of the internal combustion engine itself),
(B) shows the air-fuel ratio on the downstream side of the three-way catalyst device, and (C) shows the actual oxygen storage amount of the three-way catalyst device. As shown in this figure, when the air-fuel ratio on the upstream side becomes lean, the actual oxygen storage amount increases, but until the actual oxygen storage amount reaches the saturation level of the oxygen storage capacity, the three-way catalyst device is used. As a result of absorbing oxygen, the air-fuel ratio on the downstream side does not become lean but is maintained at the stoichiometric air-fuel ratio. Then, when the oxygen storage capacity is saturated, the air-fuel ratio on the downstream side becomes lean as well as the air-fuel ratio on the upstream side. In particular, while the oxygen storage capacity is saturated, the downstream air-fuel ratio becomes the same as the upstream air-fuel ratio.

Even when the air-fuel ratio on the upstream side becomes rich, oxygen is released from the three-way catalytic converter until the actual oxygen storage amount becomes 0, so that the air-fuel ratio on the downstream side becomes
It is not rich and is maintained at the stoichiometric air-fuel ratio. Then, as soon as the actual oxygen storage amount becomes 0, the downstream side air-fuel ratio also becomes rich. As long as the actual oxygen storage amount is 0, the downstream side air-fuel ratio becomes the same value as the upstream side air-fuel ratio.

In short, when the actual oxygen storage amount is increasing / decreasing within the range of oxygen storage capacity, the air-fuel ratio on the downstream side of the three-way catalyst device is the theoretical air-fuel ratio regardless of the air-fuel ratio on the upstream side. When the actual oxygen storage amount is 0 or saturated, the change in the upstream air-fuel ratio appears in the downstream air-fuel ratio as it is.

In the present invention, the actual oxygen storage amount estimating means similar to the above-mentioned claim 5 successively estimates the actual oxygen storage amount. Then, from the relationship between the actual oxygen storage amount and the predetermined oxygen storage capacity, the adsorbent inlet-side air-fuel ratio estimating means estimates the air-fuel ratio on the inlet side of the HC adsorbent. Therefore, the amount of desorbed HC can be detected while eliminating the effect of the oxygen storage action of the three-way catalyst device, and the accuracy of the deterioration diagnosis of the HC adsorbent becomes high.

[0027]

EFFECTS OF THE INVENTION H according to claims 1 to 6 or 8
According to the deterioration diagnosing device or the diagnosing method of the C adsorbent, H
Since the deterioration diagnosis based on the amount of desorbed C is performed, the influence of the oxygen storage action can be eliminated even in the exhaust system of the internal combustion engine in which the three-way catalyst device is arranged on the upstream side of the HC adsorbent. The deterioration diagnosis can be performed with higher accuracy based on the detection of the air-fuel ratios at two locations on the downstream side and the HC adsorbent downstream side.

Further, according to the invention of claim 5, since the actual oxygen storage amount is sequentially estimated, the supply of oxygen until the oxygen storage capacity is saturated, for example, the period of leaning,
It can be more appropriate without excess and deficiency, and diagnosis can be performed in a surely saturated state.

Further, according to the sixth aspect of the present invention, the oxygen storage capacity, which decreases with the deterioration of the catalyst, is detected by utilizing the upstream side air-fuel ratio detecting means and the downstream side air-fuel ratio detecting means. Can be determined more reliably.

Further, according to the invention of claim 7, means for forcibly saturating the oxygen storage capacity is not required, and for example, no trouble occurs due to lean air-fuel ratio, and a special sensor is used. Without needing to add
The accuracy of diagnosis can be improved.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows the structure of the exhaust system of the internal combustion engine 1 according to the present invention.
For example, the three-way catalyst device 3 is provided at the outlet of the exhaust manifold, and the HC adsorbent 4 is provided downstream of the three-way catalyst device 3. The HC adsorbent 4 is obtained by coating an adsorbent component such as zeolite with a catalyst component such as a noble metal on a carrier such as ceramics and supporting it at a predetermined desorption temperature (for example, 20
When the temperature is lower than 0 ° C), it has an adsorbing action to adsorb HC in exhaust gas, and at a high temperature above the desorption temperature, on the contrary, it has a desorbing action to desorb adsorbed HC. There is. Note that the HC adsorbent 4 may be one that does not contain a catalyst component. It is also possible to provide a second three-way catalyst device further downstream of the HC adsorbent 4.

An upstream air-fuel ratio sensor 5 is arranged as upstream air-fuel ratio detecting means on the upstream side of the three-way catalyst device 3, and a downstream air-fuel ratio is provided downstream of the HC adsorbent 4. A downstream air-fuel ratio sensor 6 is arranged as a detection means. These air-fuel ratio sensors 5, 6 are, for example, oxygen pump type sensors that can continuously detect the value of the air-fuel ratio, and as will be described later, the air-fuel ratio detected by the upstream side air-fuel ratio sensor 5 is used. The air-fuel ratio feedback control is performed based on Then, the detection signal of the downstream side air-fuel ratio sensor 6 is
In order to improve the accuracy of the air-fuel ratio control using the upstream side air-fuel ratio sensor 5, it is used for learning correction of deviation of the control system, and as will be described later, deterioration of the three-way catalyst device 3, that is, oxygen storage. It is used for estimating the capacity and diagnosing the deterioration of the HC adsorbent 4. Instead of the upstream air-fuel ratio sensor 5, an O ₂ sensor that detects whether the air-fuel ratio is lean or rich can be used.

The detection signals of the both air-fuel ratio sensors 5 and 6 are input to the engine control unit 7. Further, various sensors such as an air flow meter 8, a crank angle sensor 9 and a water temperature sensor 10 are provided to detect the operating conditions of the engine, and respective detection signals are similarly input to the engine control unit 7. Has been done.

In the intake passage 11 of the internal combustion engine 1,
A fuel injection valve 12 for injecting and supplying fuel to the intake valve of each cylinder is provided, and the engine control unit 7 controls the fuel injection amount and injection timing of the fuel injection valve 12 or the ignition timing of an ignition plug (not shown). Etc. are controlled comprehensively.

The exhaust gas purification of the internal combustion engine 1 is basically performed by the three-way catalyst device 3, and the air-fuel ratio is basically maintained at the stoichiometric air-fuel ratio by the feedback control, and the three-way catalyst device 3 is used. Oxidation and reduction are performed by the catalytic action of. The three-way catalyst device 3 cannot exert its catalytic action unless the catalyst activation temperature is reached, but the HC discharged from the internal combustion engine 1 at a low temperature such as immediately after cold start is adsorbed by the HC adsorbent 4. And removed.
The once adsorbed HC is desorbed again when the HC adsorbent 4 reaches a high temperature and reaches a predetermined desorption temperature.

When the HC adsorbent 4 deteriorates, the amount of HC adsorbed in the cold state decreases, but the amount of adsorbed HC basically becomes the amount of HC desorbed thereafter. Therefore, the degree of deterioration can be diagnosed by estimating the desorbed HC amount from the change in the air-fuel ratio.

Next, a concrete deterioration diagnosis of the HC adsorbent 4 will be described with reference to the flow charts of FIG. 3 and thereafter.

First, FIGS. 3 and 4 are flowcharts of a portion related to the basic control of the fuel injection amount, and these routines are repeatedly executed in time synchronization or crank angle synchronization. FIG. 3 is a routine for determining the feedback correction coefficient α, and it is determined in step 1 whether or not the predetermined feedback control condition is satisfied based on the engine operating condition, the cooling water temperature, and the like. If it is not the control condition, the process proceeds to step 3 to fix the correction coefficient α to 1, and if it is the feedback control condition, the process proceeds to step 2 to correct the correction coefficient α.
Is calculated. In this embodiment, the upstream air-fuel ratio sensor 5
The deviation between the actual air-fuel ratio detected by and the set air-fuel ratio (target air-fuel ratio) is divided by the set air-fuel ratio to obtain a minute correction amount, which is added to the previous correction coefficient α (αold) Correction coefficient α (αnew). Thereby, the feedback correction according to the deviation is added. In addition, in the figure, all "air-fuel ratios" are abbreviated as "A / F".

FIG. 4 is a routine for calculating the fuel injection amount. In step 11, the output signal of the air flow meter 8 is set to A /
Intake air amount Q with D conversion and linearization
Find a. Next, in step 12, the basic fuel injection amount Tp
Using the intake air amount Qa and the engine speed N,
It is determined as p = Qa × K / N. Note that K is a constant. Then, in step 13, the actual injection pulse width Ti given to the fuel injection valve 12 is Ti = Tp × COEF × α
Calculate as + Ts. Here, COEF is various increase correction coefficients based on water temperature and the like, and Ts is a voltage correction amount with respect to the battery voltage.

Next, FIG. 5 shows the maximum oxygen storage amount in consideration of the deterioration of the three-way catalyst device 3, that is, the oxygen storage capacity a.
Is a routine for obtaining. This routine is executed by the internal combustion engine 1
Is executed under steady operating conditions after the completion of the warm-up of the above, and it may be performed only once for each operation,
Alternatively, it may be repeatedly executed.

In step 21, the upstream air-fuel ratio sensor 5
The rich / lean reversal number L of the detected air-fuel ratio of the downstream side air-fuel ratio sensor 6 is counted while the detected air-fuel ratio is reversed to the rich / lean predetermined number of times (M times). Then, in step 22, the oxygen storage capacity a corresponding to the number L of inversions is obtained based on a predetermined table of characteristics as shown in FIG. In other words, if the catalyst of the three-way catalyst device 3 is not deteriorated, even if the air-fuel ratio changes on the upstream side, it changes very slowly on the downstream side, so the number of reversals L is small. On the other hand, when the catalyst of the three-way catalyst device 3 is deteriorated, the same change in the air-fuel ratio as in the upstream side appears on the downstream side as well, so the reversal number L approaches the reversal number M on the upstream side. By using such characteristics, the actual oxygen storage capacity a of the three-way catalyst device 3 can be obtained.

In this method, since the actual oxygen storage capacity a can be detected by utilizing both air-fuel ratio sensors 5 and 6,
Very easy to achieve. In addition, for the rich / lean reversal of the upstream side air-fuel ratio, the change due to the above-mentioned air-fuel ratio feedback control may be used as it is, or under a specific operating condition, the air-fuel ratio is forcibly changed for a certain period. You may do it.

The value of the oxygen storage capacity a thus obtained is used in the diagnosis of the HC adsorbent 4 after the next start, as described later.

The degree of deterioration of the three-way catalytic converter 3 can be estimated to some extent based on the operating history of the internal combustion engine 1, the total operating time, etc., and the oxygen storage capacity a can be determined based on these.

Next, FIG. 6 is a flowchart showing a routine for calculating the actual oxygen storage amount O2S of the three-way catalyst device 3. This routine is repeatedly executed in synchronization with time.

That is, the excess / deficiency of oxygen in the exhaust gas flowing into the three-way catalyst device 3 is repeatedly added / subtracted in step 31 to obtain the actual oxygen storage amount O2 at that time.
S is estimated. Specifically, in step 31, the difference between the actual air-fuel ratio detected by the upstream side air-fuel ratio sensor 5 and the stoichiometric air-fuel ratio is multiplied by the intake air amount Qa at that time and a predetermined constant k, and this is calculated as Actual oxygen storage amount (O2
Sold) to add a new actual oxygen storage amount (O
2Snew). That is, if the lean state of the actual air-fuel ratio continues, the actual oxygen storage amount O2S gradually increases, and conversely, if the rich state continues, the actual oxygen storage amount O2S gradually decreases.

Then, in step 32, the calculated value is compared with the oxygen storage capacity a which is the upper limit of the actual oxygen storage amount O2S. If the calculated value is more than this, in step 33, Actual oxygen storage amount O
The upper limit value a is set as 2S. Similarly, when the calculated value is a negative value, 0 is set as the actual oxygen storage amount O2S (steps 34 and 3).
5). At the stage immediately after the start of diagnosing the HC adsorbent 4, there is a possibility that the oxygen storage capacity can not be sufficiently estimated according to the flowchart of FIG. 5, so the value of the oxygen storage capacity a is as described above. , It is recommended to use the value obtained at the previous driving.

Next, FIG. 7 shows a routine for judging whether or not the condition is that HC is desorbed from the HC adsorbent 4 (desorption condition). This routine is also repeatedly executed in synchronization with time. Since the desorption of HC mainly depends on the temperature of the HC adsorbent 4, in this embodiment, the temperature of the HC adsorbent 4 is estimated by estimating the exhaust gas temperature and the temperature rise of the HC adsorbent 4 due to the exhaust gas temperature. When it is within a certain range, it is determined that the condition is desorption. Specifically, at step 41, the exhaust temperature T1 is calculated from the engine speed N and the basic fuel injection amount Tp corresponding to the load by using calculation or a predetermined table.
To estimate. Then, in step 42, the exhaust temperature T1 is subjected to a weighted average processing using the weighting factors G and H to obtain the adsorbent temperature T. That is, the previous adsorbent temperature is T
old, and the new adsorbent temperature is Tnew, Tne
It is sequentially calculated as w = (Told × G + T1 × H) / (G + H). Note that the adsorbent temperature T (T
The initial value of (old) may be given according to, for example, the cooling water temperature, or a fixed value may be used.

Further, the HC adsorbent 4 may be provided with a temperature sensor for directly detecting the temperature T of the HC adsorbent 4, and the desorption condition may be determined based on the detected temperature.

In step 43, the estimated adsorbent temperature T is set to the lower limit value (corresponding to the desorption start temperature) I and the upper limit value (corresponding to the temperature at which desorption is considered completed).
Compared with J, if I ≦ T ≦ J, it is determined that the desorption condition is satisfied (step 44), and otherwise, it is determined that the desorption condition is not satisfied (that is, the desorption condition or the desorption completion state). (Step 45). The result of the determination as to whether or not this desorption condition is set is indicated by a flag (not shown).

Next, FIG. 8 is a flow chart showing the main part of the diagnostic processing, and this routine is repeatedly executed in synchronization with time. The flag F1 is a diagnostic flag indicating whether or not the diagnosis is being performed, and is reset to 0 each time the engine is started.

First, in step 51, it is determined whether or not the HC desorption condition is satisfied based on the flag indicating the determination result of the routine of FIG. 7 described above. While the temperature of the HC adsorbent 4 is low (that is, while adsorbing HC), NO is obtained here, so the routine proceeds to the step 52 side. Step 5
In 2, the theoretical air-fuel ratio is set as the set air-fuel ratio. The value of this set air-fuel ratio is reflected in step 2 of FIG. 3 as described above, and the fuel injection amount Ti is feedback-controlled with this set air-fuel ratio as the target value. Then, in step 53, the diagnosis flag F1 is determined, but the initial value is 0.
Therefore, the determination result is NO, and the series of routines ends.

After that, when the temperature of the HC adsorbent 4 rises and it is judged in step 51 that the desorption condition is satisfied, the routine proceeds from step 51 to step 54, where an appropriate value C on the lean side is set as the set air-fuel ratio. Given. The value of the set air-fuel ratio C may be a fixed value or may be a slightly different value depending on engine operating conditions. By thus setting the set air-fuel ratio to the lean side, the actual air-fuel ratio also becomes lean with the air-fuel ratio C as the target value by the routines of FIGS. 3 and 4. Then, in such a state where the air-fuel ratio is lean, it is determined in step 55 whether or not the actual oxygen storage amount O2S successively calculated in the routine of FIG. 6 has reached a saturation state, that is, O2S = a. Judgment in. The first time immediately after the desorption condition is reached, step 55 is NO, but steps 51, 54,
When the process of step 55 is repeated, the actual oxygen storage amount O2S eventually reaches a saturated state.

If YES at step 55, the routine proceeds to step 56, at which the diagnosis flag F1 is judged. In the first time when the diagnosis flag F1 is 0, the steps 56 to 57 are performed.
In step 58, the flag F1 is set to 1, and in step 58, the value of the total HC desorption amount σHC is initialized to 0. Then, the routine proceeds to step 59, where the total desorption amount σHC is integrated. From the next time onward, the process proceeds from step 56 to step 59.

At step 59, the upstream air-fuel ratio sensor 5
Difference (R / F) between the upstream air-fuel ratio (FA / F) detected by and the downstream air-fuel ratio (RA / F) detected by the downstream air-fuel ratio sensor 6.
A / F-FA / F) and the total intake air amount Qa are sequentially calculated based on the intake air amount Qa. Specifically, if the previous value is σHCold and the new value is σHCnew, σHCnew = σHCold−Qa × (RA / F−
The total desorption amount σHC is calculated as FA / F). That is, the air-fuel ratio difference is related to the concentration of desorbed HC, and the amount of desorbed HC can be estimated by multiplying this by the gas flow rate, that is, the amount of intake air. The accumulation in step 59 is continued until the desorption is completed, that is, until it is determined in step 51 that the desorption condition is completed.

When the desorption is completed and the desorption condition is not satisfied in step 51, the process proceeds to step 52, but since the diagnosis flag F1 is 1 at this time, the process proceeds to step 61 and the total desorption accumulated during the desorption is performed. It is determined whether or not the amount σHC is equal to or greater than the determination reference value e. If the judgment reference value e or more, it means that a sufficiently large amount of HC can be adsorbed, so the routine proceeds to step 62, where it is judged that the HC adsorbent 4 is normal, that is, in a non-deteriorated state. If it is less than the judgment reference value e, HC
It means that the adsorption capacity of
Then, it is determined that the HC adsorbent 4 is in a deteriorated state.
Then, after this determination, in step 64, the diagnosis flag F1
Is reset to 0, and a series of diagnostic processing ends.

As described above, in this embodiment, since the diagnosis based on the air-fuel ratio difference is carried out while the lean state is continued, the three-way catalyst device 3 is certainly kept in the oxygen saturated state, and the accuracy is deteriorated by the oxygen storage action. There is no. Further, since the inside of the exhaust system is lean during the desorption of HC, the desorbed HC is satisfactorily oxidized, and the amount of HC finally discharged to the outside is extremely small.

In this embodiment, the air-fuel ratio is made lean after the desorption condition is reached, and the desorption HC amount is started to be integrated after the oxygen storage capacity is saturated. Since the period from when the fuel ratio becomes lean to the saturation is extremely short (for example, about 1 to 2 seconds), this delay does not pose a problem. Further, it is possible to set the lower limit temperature of the desorption condition (see step 43) in consideration of this period in advance.

Next, FIG. 9 is a flow chart showing a second embodiment of the present invention. Similar to FIG. 8, this routine shows the main part of the diagnostic processing, and instead of the routine of FIG. 8, it is adapted to be combined with other routines of FIGS. 3 to 7. The flowchart of FIG. 9 is basically the same as the flowchart of FIG. 8 except for the steps 71 to 73, and thus the duplicate description will be omitted. Figure 8
The step having the same number as the step of (1) basically performs the same processing.

In the second embodiment, when it is determined in step 51 that the desorption condition is satisfied, it is determined in step 71 whether the actual oxygen storage amount O2S has reached the saturated state, and the saturated state is reached. Until it reaches step 72
Then, the process proceeds to and the set air-fuel ratio is set to the predetermined value D on the lean side. The value of the set air-fuel ratio D may also be a fixed value, or may be a slightly different value depending on engine operating conditions. When the actual oxygen storage amount O2S reaches the saturated state, step 71
To step 73, the set air-fuel ratio is returned to the stoichiometric air-fuel ratio, and under this stoichiometric air-fuel ratio, steps 56 to 5 are performed.
9. Total desorption amount σHC by step 9 and steps 61 to
Diagnosis by 63 is performed.

Even if the diagnosis based on the air-fuel ratio difference is performed in the state where the stoichiometric air-fuel ratio is returned to the stoichiometric air-fuel ratio, the oxygen storage capacity of the three-way catalyst device 3 is saturated in advance. No change in fuel ratio occurs. Therefore, sufficiently high diagnostic accuracy can be obtained. In addition, in this embodiment, the period forcibly leaning for diagnosis is minimized, so that there is an advantage that the generation of NOx accompanying leaning can be suppressed.

Next, FIGS. 10 and 11 are flow charts showing a third embodiment in which the diagnostic accuracy is improved without forcibly leaning. It should be noted that these routines are also combined with the routines shown in FIGS.

The routine of FIG. 10 is, as already described with reference to FIG. 1, the inlet side air-fuel ratio (IA /
F) is estimated and is repeatedly executed in synchronization with time. At step 81, the actual oxygen storage amount O2S sequentially obtained by the process of FIG. 6 is 0 <O2.
It is determined whether or not it is within the range of <a. That is, it is determined whether the actual oxygen storage amount O2S is not 0 or is not saturated. If it is in the range of 0 <O2 <a, the air-fuel ratio on the outlet side of the three-way catalyst device 3 becomes the stoichiometric air-fuel ratio due to the oxygen storage action, so in step 82, the stoichiometric air-fuel ratio (IA / F) is set as the theoretical air-fuel ratio. Is substituted. If the actual oxygen storage amount O2S is 0 or is in the saturated state, the actual air-fuel ratio at that time detected by the upstream air-fuel ratio sensor 5 is substituted as the inlet side air-fuel ratio (IA / F) in step 83. .

FIG. 11 is a routine showing the main part of the diagnosis using the inlet side air-fuel ratio (IA / F) thus estimated. This is similar to the routines of FIGS. 8 and 9, and is also repeatedly executed in synchronization with time. The flag F1 is a diagnostic flag indicating whether or not the diagnosis is being performed, as in each of the above-described embodiments, and is reset to 0 each time the engine is started.

First, in step 91, similarly to step 51 described above, it is determined whether or not the HC desorption condition is satisfied based on the flag indicating the determination result of the routine of FIG. While the temperature of the HC adsorbent 4 is low (that is, while HC is being adsorbed), NO is given here, so the routine proceeds to the step 92 side. In step 92, the diagnosis flag F1 is judged, but since the initial value is 0, it becomes NO, and the series of routines is finished as it is.

After that, when the temperature of the HC adsorbent 4 rises and it is judged at step 91 that the desorption condition is satisfied, the routine proceeds from step 91 to step 93, and the diagnosis flag F1 is judged. The first time when the diagnosis flag F1 is 0, step 93 is executed.
From step 94 to step 95, flag F
While 1 is set to 1, the value of the total desorption amount σHC of HC is initialized to 0. Then, the routine proceeds to step 96, where the total desorption amount σHC is integrated. From the next time onward, the process proceeds from step 93 to step 96.

Total desorption amount σHC in step 96
The calculation of is basically the step 5 of each embodiment described above.
9, but in this embodiment, the inlet side air-fuel ratio (IA / F) estimated by the routine of FIG.
The calculation is performed as the air-fuel ratio upstream of the C adsorbent 4. Specifically, the previous value is σHCold and the new value is σHCne.
w, and the intake air amount is Qa, σHCnew = σHC
The total desorption amount σHC is calculated as old-Qa × (RA / F-IA / F). The accumulation in step 96 is continued until the desorption is completed, that is, until it is determined in step 91 that the desorption condition is completed.

When desorption is completed and the desorption condition is not satisfied in step 91, the process proceeds to step 92. At this time, however, the diagnosis flag F1 is 1, so the procedure proceeds to step 97 and the total desorption accumulated during the desorption is performed. It is determined whether or not the amount σHC is equal to or greater than the determination reference value e. If the judgment reference value e or more, it means that a sufficiently large amount of HC can be adsorbed. Therefore, the routine proceeds to step 98, where it is judged that the HC adsorbent 4 is normal, that is, in a non-deteriorated state. If it is less than the judgment reference value e, HC
It means that the adsorption capacity of
Then, it is determined that the HC adsorbent 4 is in a deteriorated state.
Then, after this determination, in step 100, the diagnosis flag F
1 is reset to 0, and a series of diagnostic processing ends.

As described above, in this embodiment, the air-fuel ratio difference before and after the HC adsorbent 4 is determined in consideration of the oxygen storage function of the three-way catalyst device 3 without making the air-fuel ratio lean. Since the deterioration diagnosis of No. 4 is performed, it is possible to improve the accuracy of the diagnosis without causing any trouble such as an increase in NOx due to a temporary lean air-fuel ratio.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between an actual oxygen storage amount of a three-way catalyst device and air-fuel ratios on an upstream side and a downstream side.

FIG. 2 is a structural explanatory view of an internal combustion engine according to the present invention.

FIG. 3 is a flowchart showing a calculation routine of a feedback correction coefficient α.

FIG. 4 is a flowchart showing a calculation routine of a fuel injection amount.

FIG. 5 is a flowchart showing a routine for estimating oxygen storage capacity.

FIG. 6 is a flowchart showing a routine for estimating the actual oxygen storage amount.

FIG. 7 is a flowchart showing a desorption condition determination routine.

FIG. 8 is a flowchart showing a deterioration diagnosis routine of the first embodiment.

FIG. 9 is a flowchart showing a deterioration diagnosis routine of the second embodiment.

FIG. 10 is a flowchart showing an inlet side air-fuel ratio estimation routine in the third embodiment.

FIG. 11 is a flowchart showing a deterioration diagnosis routine of a third embodiment.

FIG. 12 is a characteristic diagram showing the relationship between the number of inversions on the downstream side and the oxygen storage capacity.

[Explanation of symbols]

3 ... Three-way catalyst device 4 ... HC adsorbent 5 ... Upstream air-fuel ratio sensor 6 ... Downstream air-fuel ratio sensor

Continuation of front page (51) Int.Cl. ⁷ identification code FI F02D 45/00 314 F02D 45/00 314Z (56) References JP-A-8-121148 (JP, A) JP-A-7-208149 (JP, A) JP 7-26947 (JP, A) JP 6-66131 (JP, A) JP 7-63046 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) ) F01N 3/08-3/24 F02D 45/00 F02D 41/14

Claims (8)

(57) [Claims] 1. An HC adsorbent which is interposed in an exhaust system of an internal combustion engine and has an adsorbing action at a low temperature and a desorbing action at a high temperature,
A three-way catalyst device arranged upstream of the HC adsorbent,
The upstream air-fuel ratio detecting means provided on the upstream side of the three-way catalyst device and the downstream air-fuel ratio detecting means provided on the downstream side of the HC adsorbent, and the upstream air-fuel ratio detecting means when the HC adsorbent is desorbed. HC adsorption comprising deterioration diagnosis means for diagnosing the deterioration of the HC adsorbent from the desorbed HC amount estimated based on the detected air-fuel ratio in the fuel ratio detection means and the detected air-fuel ratio in the downstream side air-fuel ratio detection means. An apparatus for diagnosing deterioration of an HC adsorbent in an internal combustion engine, comprising: an oxygen supply unit that saturates the oxygen storage capacity of the three-way catalyst apparatus during diagnosis. 2. The deterioration diagnosing device for an HC adsorbent in an internal combustion engine according to claim 1, wherein the oxygen supply means comprises air-fuel ratio control means for temporarily making the air-fuel ratio lean. 3. The deterioration diagnosis of the HC adsorbent in an internal combustion engine according to claim 2, wherein the air-fuel ratio control means holds the air-fuel ratio lean until the diagnosis by the deterioration diagnosis means ends. apparatus. 4. The air-fuel ratio control means leans the air-fuel ratio until the oxygen storage capacity of the three-way catalyst device becomes saturated, and returns to the stoichiometric air-fuel ratio when the deterioration diagnosis means starts the diagnosis. The deterioration diagnosing device for an HC adsorbent in an internal combustion engine according to claim 2. 5. An actual oxygen storage amount estimating means for sequentially estimating an actual oxygen storage amount in the three-way catalytic converter based on the air-fuel ratio detected by the upstream side air-fuel ratio detecting means and the intake air amount is provided. The deterioration diagnostic apparatus for an HC adsorbent in an internal combustion engine according to any one of claims 1 to 4, wherein saturation of the oxygen storage capacity is determined based on the estimated actual oxygen storage amount. 6. A normal operation of the three-way catalytic converter in an active state, a change in the detection signal of the upstream side air-fuel ratio detection means and a change in the detection signal of the downstream side air-fuel ratio detection means The deterioration diagnosing device for an HC adsorbent in an internal combustion engine according to claim 5, further comprising oxygen storage capacity estimating means for estimating an oxygen storage capacity of the original catalyst device. 7. An HC adsorbent which is interposed in an exhaust system of an internal combustion engine and has an adsorbing action at a low temperature and a desorbing action at a high temperature, and a three-way catalyst device arranged upstream of the HC adsorbent. And an upstream air-fuel ratio detecting means provided on the upstream side of the three-way catalyst device and a downstream air-fuel ratio detecting means provided on the downstream side of the HC adsorbent, and at the time of desorption of the HC adsorbent, An actual oxygen storage amount estimating means for sequentially estimating the actual oxygen storage amount in the three-way catalyst device based on the air-fuel ratio and the intake air amount detected by the upstream side air-fuel ratio detecting means, and the estimated actual oxygen storage amount. Is 0 or has reached the oxygen storage capacity saturation state, the detected air-fuel ratio by the upstream air-fuel ratio detection means, and the theoretical air-fuel ratio when the actual oxygen storage amount is within the oxygen storage capacity, H
C adsorbent inlet side air-fuel ratio estimating means for outputting as the air-fuel ratio on the adsorbent inlet side, and desorption based on the estimated adsorbent inlet side air-fuel ratio and the detected air-fuel ratio in the downstream side air-fuel ratio detecting means A deterioration diagnosing device for an HC adsorbent in an internal combustion engine, comprising: a deterioration diagnosing means for estimating the amount of HC and diagnosing deterioration of the HC adsorbent from the amount of desorbed HC. 8. An HC adsorbent which is interposed in an exhaust system of an internal combustion engine and performs an adsorbing action at a low temperature and a desorbing action at a high temperature, and a three-way catalyst device arranged upstream of the HC adsorbent. An upstream side air-fuel ratio detecting means provided on the upstream side of the three-way catalyst device and a downstream side air-fuel ratio detecting means provided on the downstream side of the HC adsorbent at the time of desorption of the HC adsorbent. HC that estimates the desorbed HC amount based on the detected air-fuel ratio in the upstream side air-fuel ratio detecting means and the detected air-fuel ratio in the downstream side air-fuel ratio detecting means, and diagnoses the deterioration of the HC adsorbent from the desorbed HC amount. In the method of diagnosing deterioration of an adsorbent, performing deterioration diagnosis based on the detected air-fuel ratio in both air-fuel ratio detection means after giving excess oxygen to the three-way catalyst device to forcibly saturate the oxygen storage capacity. Internal combustion engine characterized by Degradation diagnosis method of the HC adsorbent in.