JPH112115A - Engine hc absorbent degradation diagnosing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve degradation judgment accuracy without a temperature sensor of high absolute value accuracy. SOLUTION: The internal temperature of the upper stream portion and the lower stream portion of an absorbent 21, which absorbs HC discharged from an engine when the engine temperature is low, is respectively detected with sensors 22, 23. Measurement means 25, 26 measure the peak time of the output of respective temperature sensors 22, 23 when the absorbent 21 in the condition of absorbing HC and a judgment means 27 judges whether the absorbent 21 is degraded or not by comparing the two peak times. In this case, it is not necessary to detect the temperature absolute value accurately with respective temperature sensors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for diagnosing deterioration of an HC adsorbent of an engine.

[0002]

2. Description of the Related Art Immediately after a cold start of an engine, the exhaust gas temperature is low and does not reach the temperature at which the three-way catalyst is activated (around 300 ° C.), so that HC (hydrocarbon) is hardly purified. For this reason, an adsorbent for HC is provided in the exhaust system, and HC discharged without being purified immediately after the cold start is adsorbed by the adsorbent, and thereafter, HC is desorbed from the adsorbent and burned. There is something that I did.

[0003] In this case, the adsorbent is deteriorated by being exposed to high-temperature exhaust gas or adhering and depositing oil contained in the exhaust gas. Heat generated during adsorption (heat of adsorption)
The temperature of the internal temperature of the adsorbent or the temperature of each exhaust gas at the inlet and outlet of the adsorbent is detected by a temperature sensor, and it is determined whether the adsorbent has deteriorated based on the detection result.

For example, in Japanese Unexamined Utility Model Publication No. 7-10418, unburned gas (e.g., unburned gas) generated in a fuel tank after a predetermined time has elapsed after the engine has stopped and the exhaust gas temperature has sufficiently decreased (the temperature of the adsorbent has stabilized). HC gas) was introduced to the adsorbent to detect the internal temperature of the adsorbent, and when the amount of increase in the internal temperature became smaller than a reference value, deterioration occurred. Under stable operating conditions such as idling, the temperature of each exhaust gas at the inlet and outlet of the adsorbent is detected, and the value obtained by multiplying this temperature difference by the amount of intake air is used as the amount of heat of adsorption per unit period and the total amount of heat of adsorption in a predetermined period. Is calculated, and it is determined that deterioration has occurred when the total heat of adsorption becomes equal to or less than the target total heat of adsorption.

[0005]

However, in the method of judging the deterioration of the adsorbent by comparing the temperature itself with a predetermined value as disclosed in Japanese Utility Model Application Laid-Open No. 7-10418, the accuracy of the deterioration judgment is determined by the temperature detection by a temperature sensor. Since the absolute value accuracy of the temperature determination is affected, a high-precision temperature sensor is required to increase the accuracy of the deterioration determination (cost is increased).

[0006] Further, as disclosed in JP-A-6-101452, when the deterioration is determined by comparing the total amount of heat of adsorption with the target total amount of heat of adsorption, the calculation accuracy of the amount of heat of adsorption is poor under the condition that the temperature is not stable. The accuracy of the judgment deteriorates. In other words, when the temperature of the adsorbent rises due to the heat of adsorption, under the condition that a temperature difference occurs between the temperature of the exhaust gas flowing into the adsorbent and the temperature of the adsorbent itself, the heat between the exhaust gas and the adsorbent Transfer occurs, and the temperature change due to the heat cannot be separated from the temperature change due to the heat of adsorption. To describe this in more detail, for example, when rapid acceleration is performed under the adsorption condition immediately after the cold start, the temperature of the exhaust gas flowing into the adsorbent becomes high, whereas the temperature of the adsorbent itself is still low. . In this case, the heat of the exhaust is transferred to the adsorbent and is taken away by the rise in the temperature of the adsorbent, so that the outlet exhaust temperature of the adsorbent is lower than the inlet exhaust temperature. Under conditions that are stable in temperature, the outlet exhaust gas temperature becomes higher than the inlet exhaust gas temperature of the adsorbent due to the heat of adsorption, and the difference corresponds to the heat of adsorption. Under these conditions, the difference between the exhaust gas temperature at the inlet and the outlet is not a value corresponding to the heat of adsorption. On the other hand, if the deterioration determination is performed only under conditions that are stable in terms of temperature, such as when idling is continued after starting, the opportunity for deterioration determination is narrowed.

Accordingly, the present invention measures the peak occurrence time of the internal temperature under the adsorption condition using a sensor for detecting the internal temperature of the upstream portion and the downstream portion of the adsorbent, and compares these two peak occurrence times. It is an object of the present invention to determine whether or not the adsorbent has deteriorated, thereby increasing the accuracy of the deterioration determination without using a temperature sensor having high absolute value accuracy.

[0008]

According to a first aspect of the present invention, as shown in FIG. 8, H discharged from the engine when the engine temperature is low.
Adsorbent 21 for adsorbing C, and sensors 22 and 23 for detecting the internal temperatures of the upstream portion and the downstream portion of the adsorbent 21, respectively.
Means 24 for determining whether or not the adsorbent 21 is in a condition for adsorbing the HC, and means 25 for measuring the peak occurrence timing of the temperature sensor outputs 22 and 23 when the adsorbent 21 is in the adsorption condition based on the determination result. , 26 and means 27 for determining whether or not the adsorbent 21 has deteriorated by comparing these two peak generation times.

According to the second invention, as shown in FIG. 9, an adsorbent 21 for adsorbing HC discharged from the engine when the engine temperature is low, and an internal temperature of an upstream portion and a downstream portion of the adsorbent 21 are detected. Sensors 22 and 23 and means 3 for differentiating the outputs of these temperature sensors 22 and 23 with time, respectively.
1, 32, means 24 for determining whether the adsorbent 21 is in a condition for adsorbing the HC, and based on the result of the judgment, the temperature sensor outputs 22, 23 when the adsorbent 21 is in the adsorption condition.
Means 33, 3 for measuring the peak occurrence time of the time derivative of
4 and means 27 for determining whether or not the adsorbent 21 has deteriorated based on a comparison of these two peak occurrence times.

According to a third aspect of the present invention, as shown in FIG. 10, an adsorbent 21 for adsorbing HC discharged from the engine when the engine temperature is low, and an internal temperature of an upstream portion and a downstream portion of the adsorbent 21 are detected. Sensors 22 and 23, means 31 and 32 for differentiating the outputs of the temperature sensors 22 and 23 with time, means 24 for determining whether or not the adsorbent 21 is in a condition for adsorbing the HC, Means 41 for determining whether or not the difference between the inlet exhaust gas temperature of the adsorbent and the upstream portion temperature is equal to or less than a predetermined value, and the difference between the inlet exhaust gas temperature of the adsorbent and the upstream portion temperature being in the adsorption condition based on these judgment results. When the temperature is equal to or less than a predetermined value, the temperature sensor output
2 and 23, and when the difference between the inlet exhaust gas temperature of the adsorbent and the upstream temperature exceeds the predetermined value under the adsorption condition, the time differential value of each of the temperature sensor outputs 22 and 23 is calculated. Means 42 for respectively measuring the peak occurrence time,
43, comparing the two peak generation times of the temperature sensor outputs 22 and 23 when the difference between the inlet exhaust gas temperature of the adsorbent and the upstream temperature is equal to or less than a predetermined value under the adsorption condition, When the difference between the inlet exhaust gas temperature of the adsorbent and the upstream temperature exceeds the predetermined value under the adsorption condition and the difference between the two peak occurrence times of the time differential values of the temperature sensor outputs 22 and 23, Means 44 for determining whether the adsorbent 21 has deteriorated is provided.

According to a fourth aspect of the present invention, in the first or third aspect, the peak generation timing of each of the temperature sensor outputs 22, 23 is different from the temperature sensor output 22,
23 is the time until the peak timing.

According to a fifth aspect of the present invention, in the first or third aspect, the peak occurrence time of the time differential value of each of the temperature sensor outputs 22 and 23 is different from that of the adsorption start timing by the time differential value of the temperature sensor 22 and 23 output. This is the time up to the peak.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects of the present invention, the deterioration judging means determines a time difference between the two peak occurrence times by comparing a time difference between the two peak occurrence times with a reference value. Is a means for determining that the adsorbent has deteriorated when is less than the reference value, and that the adsorbent has not deteriorated when the time difference between the two peak occurrence times is equal to or greater than the reference value.

In a seventh aspect based on the sixth aspect, the reference value is a value corresponding to the displacement during the HC adsorption period.

According to an eighth aspect, in any one of the first to fifth aspects, the comparison between the two peak occurrence times is a comparison between a ratio of the two peak occurrence times and a reference value.

In the ninth invention, in any one of the first to eighth inventions, if the desorption of HC from the adsorbent has not been completed during the previous operation, the deterioration determination is stopped.

[0017]

When the temperature of the exhaust gas flowing into the adsorbent is substantially equal to the temperature of the adsorbent, the adsorbent has a peak at its internal temperature under the adsorption condition. In this case, when the adsorbent is divided into an upstream portion and a downstream portion, the peak occurrence time of the internal temperature in the downstream portion is later than the peak occurrence time of the internal temperature in the upstream portion. Moreover, when the adsorbent is deteriorated, the peak of the internal temperature in the downstream portion occurs earlier than when no deterioration occurs.

By utilizing this property of the adsorbent, when the temperature of the exhaust gas flowing into the adsorbent is substantially equal to the temperature of the adsorbent, the first aspect of the present invention allows the upstream portion and the downstream portion of the adsorbent under the adsorption conditions. It is not necessary to accurately detect the absolute value of the temperature with each temperature sensor if the peak generation time of each temperature sensor output is measured, and therefore, the absolute value accuracy of the internal temperature detection of the adsorbent is high and expensive. The deterioration of the adsorbent can be determined with high accuracy without the need for a simple temperature sensor.

When the temperature of the exhaust gas flowing into the adsorbent is different from the temperature of the adsorbent, for example, when acceleration is performed under the adsorption conditions immediately after the cold start, the time differential of the internal temperature of the adsorbent is obtained under the adsorption conditions. A peak occurs in the value. In that case,
When the adsorbent is divided into an upstream portion and a downstream portion, the peak occurrence time of the time differential value of the internal temperature of the downstream portion is later than the peak occurrence time of the time differential value of the internal temperature of the upstream portion. Moreover, when the adsorbent is deteriorated, the peak of the time differential value of the internal temperature in the downstream portion occurs earlier than when no deterioration occurs.

By utilizing this property of the adsorbent, when the temperature of the exhaust gas flowing into the adsorbent is different from the temperature of the adsorbent, the second aspect of the present invention provides a method for adsorbing the adsorbent upstream and downstream of the adsorbent under adsorption conditions. Since the timing of each peak occurrence of the time derivative of the temperature sensor output is measured and the deterioration is determined by comparing the two, exhaust gas flowing into the adsorbent under adsorption conditions, such as when sudden acceleration is performed under adsorption conditions immediately after cold start, is performed. Even if there is a temperature difference between the adsorbent and the adsorbent, the deterioration of the adsorbent can be detected and determined with high accuracy without requiring an expensive temperature sensor.

According to the third aspect of the present invention, regardless of whether there is a temperature difference between the temperature of the exhaust gas flowing into the adsorbent and the temperature of the adsorbent itself, the adsorbent can be precisely formed without requiring an expensive temperature sensor. Can be determined.

In accordance with the seventh aspect of the present invention, the reference value is adsorbed in accordance with the fact that the larger the amount of exhaust gas during the adsorption period, the more the amount of HC flowing into the adsorbent, the earlier the timing at which the internal temperature of the adsorbent reaches a peak. Since the setting is made according to the average exhaust amount during the period, even if the exhaust amount during the adsorption period is different, the deterioration determination can be performed with high accuracy.

When the ratio between the two peak occurrence times is used, the reference value may be a constant value even if the exhaust amount during the adsorption period is different. It is not necessary to set in a table according to the amount, and thus the memory capacity can be reduced.

If the deterioration is determined while HC remains in the adsorbent during the previous operation, a peak in the internal temperature of the downstream portion occurs early, and it is erroneously determined that the deterioration has occurred even though the deterioration has not occurred. Although there is a possibility, at this time, in the ninth invention, since the deterioration determination is stopped, it is possible to avoid occurrence of an erroneous determination.

[0025]

FIG. 1 shows an engine body 1, an exhaust pipe 2, and a three-way catalyst 3.

The exhaust pipe 2 is connected to the main passage 2a downstream of the three-way catalyst 3.
And a bypass passage 2b. A valve 4 for switching the flow of exhaust gas between the main passage 2a and the bypass passage 2b is provided at a branch portion of the two passages. The switching valve 4 is driven directly by the control unit 11 or via an actuator (not shown).

In the bypass passage 2b, the HC adsorbent 5 and the electrothermal catalyst 6 supply air in this order from the upstream side, and supply air just upstream of the adsorbent 5, so that the air supply passage 8
And a secondary air supply device comprising an air pump 9.

Here, the adsorbent 5 is obtained by coating a single honeycomb with a slurry containing zeolite powder as a main component.
(0 ° C. to 300 ° C.), there is a property of desorbing HC. The adsorbent is not limited to the one based on zeolite, and activated carbon or the like may be used as the adsorbent.

In order to detect the exhaust gas temperature downstream of the three-way catalyst,
A temperature sensor 12 is provided upstream of the switching valve 4. The temperature signal from the sensor 12 is input to a control unit 11 composed of a microcomputer, and the control unit 11 controls the switching valve 4, the electrothermal catalyst 6, and the air pump 9 based on the temperature signal, thereby adsorbing and desorbing HC. The three processes of purifying the separated and desorbed HC are performed.

Since methods for adsorbing and desorbing HC and purifying HC are well known, see JP-A-6-1014.
52, the description based on the flowchart is omitted, and the contents are outlined.

Three-way catalyst 3 provided upstream of exhaust pipe 2
Is a catalyst that carries noble metals (platinum, rhodium, etc.) or other metals, and simultaneously purifies HC, CO, and NOx, which are harmful components in exhaust gas, when activated at around 300 ° C. (while oxidizing HC and CO, , Reducing NOx).

However, immediately after the cold start of the engine 1, the temperature of the exhaust gas is low and the activation temperature of the three-way catalyst 3 (300 ° C.)
), HC in the exhaust gas flows to the downstream in the exhaust pipe 2 without being substantially purified by the three-way catalyst 3. The exhaust gas temperature at this time is detected by the temperature sensor 12 and input to the control unit 11. The control unit 11 compares the exhaust temperature detected by the sensor 12 with a predetermined temperature (for example, 300 ° C.), and when the exhaust temperature is lower than the predetermined temperature, closes the main passage 2a with respect to the switching valve 4 and closes the bypass passage 2b. Outputs a drive signal to open. As a result, the entire amount of exhaust gas flows into the bypass passage 4, and the adsorbent 5 traps HC. At this time, the electrothermal catalyst 6 is in a non-energized state, and the air pump 9 is in a non-operated state.

Thereafter, when the three-way catalyst 3 is activated, the exhaust gas temperature downstream of the three-way catalyst 3 increases. When the exhaust gas temperature exceeds the predetermined temperature, the control unit 11 outputs a drive signal to the switching valve 4 to close the bypass passage 2b and open the main passage 2a. Start energization. By this operation, the exhaust gas purified by the three-way catalyst 3 is discharged through the main passage 2a. At this time, the adsorbent 5 is in a state where HC is trapped.

When the electrothermal catalyst 6 rises to an activation temperature (for example, 350 ° C.) by energization, the switching valve 4 is controlled so that the bypass passage 2 b is partially (or entirely) opened to desorb HC from the adsorbent 5. High-temperature exhaust gas is caused to flow into the bypass passage 2b. At the same time, the air pump 9 is operated,
Secondary air is introduced into the bypass passage 2b via the air supply passage 8. The high-temperature exhaust gas is introduced to desorb HC from the adsorbent 5, and the desorbed HC is purified by oxidation treatment in the electrothermal catalyst 6 using oxygen which is present in a large amount in the secondary air. The process of desorbing the HC from the adsorbent and the process of purifying with the electrothermal catalyst are terminated when a predetermined time has elapsed.

Whether or not the electrothermal catalyst 6 has been activated is determined by the duration of power supply to the electrothermal catalyst 6. Of course, the temperature of the electrothermal catalyst 6 is detected by a temperature sensor provided inside or downstream of the electrothermal catalyst 6, and whether the electrothermal catalyst 6 is activated is determined by comparing the detected temperature with a predetermined temperature. It is also possible.

Here, the fact that the exhaust gas temperature detected by the sensor 12 is lower than the predetermined temperature and the bypass passage 2b is opened is an adsorption condition described later.
Is raised to the activation temperature and the bypass passage 2b is opened again, which is a desorption condition described later.

The adsorbent 5 may be deteriorated by being exposed to high-temperature exhaust gas or by adhering and depositing oil contained in the exhaust gas, and the adsorbing performance may be reduced. It has been proposed to detect the internal temperature of the adsorbent or each exhaust gas temperature at the inlet and outlet of the adsorbent with a temperature sensor and determine whether the adsorbent has deteriorated based on the detection result. In the method of judging deterioration by comparison of the above, since the accuracy of the deterioration judgment depends on the absolute value accuracy of the temperature detection by the temperature sensor, a high-precision temperature sensor is required to improve the accuracy of the deterioration judgment. In the case where the deterioration is determined by comparing the total amount of heat of adsorption with the target total amount of heat of adsorption, the calculation accuracy of the amount of heat of adsorption is poor under the condition that the temperature is not stable, and the accuracy of the deterioration determination is deteriorated.

In order to cope with this, in the present invention, a sensor for detecting the internal temperature of the upstream portion and the downstream portion of the adsorbent is used.
The occurrence timing of the temperature peak under the adsorption condition or the peak of the time differential value of the temperature is measured, and it is determined whether or not the adsorbent has deteriorated by comparing these two peak occurrence times.

Here, the principle of the deterioration judgment according to the present invention will be described with reference to FIGS.

The present invention also utilizes the change in the internal temperature of the adsorbent due to the heat of adsorption. That is, FIG.
As shown in the upper part, when the adsorbent has not deteriorated, the internal temperature of the upstream portion of the adsorbent (hereinafter simply referred to as the upstream portion temperature) is changed simultaneously with the start of adsorption (deterioration determination start) under the adsorption condition. , And thereafter approaches the temperature of the exhaust gas flowing into the adsorbent (inlet exhaust temperature), so that a temperature peak occurs at a predetermined time. This is for the following reason. Considering the specific portion of the adsorbent (in this case, the temperature measuring portion on the upstream side), in the initial state where HC is hardly adsorbed to the specific portion, the inflowing HC is adsorbed very well, so that the heat of adsorption is large. On the other hand, when the adsorption proceeds to some extent after the passage of time, the adsorption amount of the specific portion does not increase so much. In addition, since the temperature of the specific portion is higher than the temperature of the exhaust gas due to the heat of adsorption, heat transfer from the adsorbent to the exhaust gas occurs due to the temperature difference between the temperature of the specific portion and the temperature of the exhaust gas. Since the temperature of the part approaches the exhaust temperature (that is, the temperature of the specific part of the adsorbent starts to decrease), a temperature peak appears. The internal temperature of the downstream portion of the adsorbent (hereinafter simply referred to as the downstream portion temperature) also starts to decrease after being raised to a certain time for the same reason as described above, so that a temperature peak occurs.

It should be noted that the timing at which the downstream temperature peak occurs is later than the timing at which the upstream temperature peak occurs. This is because when HC flows into the adsorbent, most of it is first adsorbed in the upstream part, so that HC is not so much present in the downstream part at the initial stage of adsorption, and the generation of heat of adsorption in the downstream part is small. . Thereafter, when the adsorption of the upstream portion is saturated to some extent, HC also flows to the downstream portion, so that the adsorption is performed in the downstream portion, and the heat of adsorption is generated. The time of occurrence is delayed.

On the other hand, when the adsorbent deteriorates,
A change occurs when the temperature peak occurs. The deterioration of the adsorbent is caused by the exposure of the adsorbent to high-temperature exhaust gas or the attachment of oil contained in the exhaust gas to the adsorbent. In the initial stage of adsorption, a large amount of HC flows into the downstream part even if the amount that can be adsorbed decreases. As a result, as shown in the lower part of FIG. 2, a temperature peak in the downstream portion occurs early.

As described above, the peak generation time of the upstream temperature and the peak generation time of the downstream temperature are different between the case where the adsorbent has not deteriorated and the case where the adsorbent has deteriorated. By comparing the peak occurrence time with the peak occurrence time of the downstream temperature, it is possible to estimate whether or not the adsorbent has deteriorated. In this case, the absolute value of the temperature is not a problem, and even if the absolute value of the temperature deviates slightly from the true value, it is only necessary to know the temperature peak occurrence time, so it is not necessary to accurately detect the absolute value of the temperature. Thus, no expensive temperature sensors are required.

The above is the case where the temperature of the exhaust gas flowing into the adsorbent under the adsorption conditions is almost equal to the temperature of the adsorbent.

Next, the case where the temperature of the exhaust gas flowing into the adsorbent is different from the temperature of the adsorbent under the adsorption conditions will be described.
The upper part of FIG. 3 shows the temperature change between the upstream temperature and the downstream temperature of the adsorbent when relatively high-temperature exhaust gas flows into the adsorbent in a low-temperature state by performing acceleration, for example, immediately after a cold start under adsorption conditions. It is shown. As shown,
After the upstream temperature is increased by the heat of adsorption in the initial stage of the adsorption, the temperature rise becomes small and approaches the inlet exhaust temperature. However, the temperature of the adsorbent does not decrease due to the high exhaust gas temperature, and thus no temperature peak occurs. Similarly, no temperature peak occurs at the downstream temperature.

However, the rapid temperature rise due to the heat of adsorption at the downstream temperature is delayed. Then, under such conditions, when each temperature is differentiated with respect to time, a peak occurs in the time differential value of each temperature as shown in the lower part of FIG. In other words, these time differential values also show a rapid rise in temperature due to heat of adsorption, and when the adsorbent deteriorates, the peak of the differential value of the downstream temperature shows no deterioration in the adsorbent. It occurs earlier than the time (not shown). Therefore, when the temperature of the exhaust gas flowing into the adsorbent is different from the temperature of the adsorbent under the adsorption conditions, the peak generation time of the differential value of each temperature is measured, and the two are compared, thereby deteriorating the adsorbent. Can be determined. In addition, in this case, it is not necessary to limit the deterioration determination to a temperature stable condition.

According to the present invention, when the temperature of the exhaust gas flowing into the adsorbent is substantially equal to the temperature of the adsorbent under the adsorption conditions, the peak occurrence timings of the upstream portion temperature and the downstream portion temperature are measured, and both of them are measured. By comparing the temperature, the deterioration of the adsorbent can be determined with high accuracy without being affected by the absolute value accuracy of the temperature detection of each temperature sensor. When the temperature of the exhaust gas differs, the peak differential time of the upstream part temperature and the time differential value of the downstream part temperature are measured, and the two are compared, so that the temperature difference between the exhaust gas flowing into the adsorbent and the adsorbent is obtained. Regardless, the deterioration of the adsorbent can be determined with high accuracy without requiring an expensive temperature sensor.

This concludes the description of the principle of determining the deterioration of the adsorbent according to the present invention.

The contents of this control executed by the control unit 11 will be described with reference to the following flowchart.

The flowchart of FIG. 4 is for determining the deterioration of the adsorbent on the assumption that the temperature of the exhaust gas flowing into the adsorbent is substantially equal to the temperature of the adsorbent. FIG.
Is started at the same time as the start of HC adsorption, and is executed at regular intervals (for example, every one second).

The upstream and downstream portions of the adsorbent 5 are provided with sensors 13 and 14 for detecting the internal temperature of the adsorbent 5, respectively.
(See FIG. 1), and these outputs are input to the control unit 11.

In step 0, whether or not the start is being determined is determined by checking the start determination flag. If the start is being determined, the process proceeds to steps 3, 4, and 5, and 0 is set in the timer TM.
The upstream temperature T1 of the adsorbent is set in a variable T1MAX, and the downstream temperature T2 of the adsorbent is set in a variable T2MAX, and the process ends. Steps 3, 4, and 5 are for setting initial values.

In steps 1 and 2, the diagnosis experience flag (initial setting to "0" at startup) is checked. This flag is set to "1" in step 16 described later when the adsorbent is judged to be deteriorated during the current operation.

If the adsorbent has not been judged to have deteriorated after the start-up, the diagnostic experience flag is set to "0".
Then, it is determined from the deterioration diagnosis permission flag whether the condition is a deterioration judgment permission condition. The setting of the deterioration determination permission flag will be described with reference to the flowchart of FIG.

In step 21, it is determined whether or not HC adsorption has started. Whether or not the adsorption has started is determined, for example, by comparing the inlet exhaust gas temperature of the adsorbent (using the exhaust gas temperature detected by the sensor 12) with a predetermined value (approximately 300 ° C.) after the start-up. If it is below, it is determined that the adsorption has started).

When the adsorption is started, the routine proceeds to step 22, where it is determined from the flag FD whether or not HC has been completely desorbed under the conditions for desorbing HC in the previous operation.

Here, the flag FD = 1 indicates that HC has been completely desorbed under the desorption conditions of the previous operation, and the flag FD = 0 indicates that HC has not been desorbed under the desorption conditions of the previous operation. Indicates completion. Although the flow for setting the flag FD is omitted, the desorption time of HC is measured under desorption conditions, and the desorption time is longer than a predetermined value by comparing the desorption time with a predetermined value. Time (that is, HC
When the desorption is completed), the flag FD is set to "1". When the desorption time is shorter than a predetermined value (that is, when the desorption of HC is not completed), the flag FD is set to "0". By setting and storing the setting result in the backup RAM, it is possible to determine whether HC has been completely desorbed under the desorption conditions of the previous operation when the flag FD is viewed during the current operation.

When FD = 1, the process proceeds to step 23 to permit the deterioration judgment, and the deterioration judgment permission flag is set to "1".
Set to. That is, the deterioration determination is performed only when the adsorbent has completely completed the desorption of HC under the desorption conditions of the previous operation.

On the other hand, when FD = 0, the routine proceeds to step 24, where the deterioration determination permission flag is set to "0".
That is, even if the adsorption is started, the deterioration determination is not permitted when the desorption of HC is not completed during the previous operation. This is H
If the deterioration determination is performed while HC remains in the C adsorbent, there is a possibility that the deterioration may be erroneously determined even though the HC has not deteriorated. This is to avoid this.

Even when the adsorption of HC has not been started, the routine proceeds to step 24, where the deterioration judgment permission flag is set to "0".
It goes without saying that it is set to.

Returning to FIG. 4, if it is determined in step 2 that the condition for permitting deterioration determination is not satisfied, the current processing is terminated as it is when the diagnostic experience flag = 1.

When the condition for permitting the deterioration determination is reached, the process proceeds from step 2 to step 6 where the timer TM is incremented. This timer TM is for measuring the elapsed time after the deterioration determination is permitted.

In step 7, the current upstream temperature T1 of the adsorbent is compared with a variable T1MAX, and T1MAX ≧ T1
If so, the process proceeds to step 8 and the value of the timer TM at that time is transferred to the variable TM1MAX. If T1MAX <T1, step 8 is skipped.

As shown in the upper part of FIG. 2, the upstream portion temperature T1 gradually increases from the start of the deterioration judgment, reaches a peak, and thereafter decreases, so that the upstream portion temperature T1 only increases while T1 increases. The value of timer TM is stored in variable T1MAX. That is, T1MAX represents the time from the deterioration determination start timing to the timing at which T1 reaches a peak (see the upper part of FIG. 2).

In the following steps 9 and 10, steps 7 and
Similarly to 8, the downstream temperature T2 of the adsorbent is compared with the variable T2MAX, and the value of the timer TM is transferred to the variable TM2MAX only when T2MAX ≧ T2. TM2M
The time from the deterioration determination start timing to the timing when T2 reaches a peak is stored in AX (see the upper part of FIG. 2).

In steps 11 and 12, it is checked whether the current condition is the suction condition and whether the previous condition was the suction condition. The process proceeds to step 13 only when the adsorption condition is not the current adsorption condition and the previous time was the adsorption condition (that is, when the adsorption was completed), and the difference DTM between the variables TM1MAX and TM2MAX is calculated.
Compare with TM1.

Here, DTM1 is a value for judging the deterioration of the adsorbent, and is a value previously obtained by an experiment or the like. If DTM <DTM1, it is determined that the adsorbent has deteriorated, and the routine proceeds to step 15, in which a warning lamp is lit to notify the driver of the deterioration of the adsorbent, and DTM ≧ DT
If it is M1, it is determined that the adsorbent has not deteriorated, and step 15 is skipped.

In step 16, the diagnostic experience flag is set to "1".
To end the current process. By setting this flag to "1", it is impossible to proceed to step 2 from the next time. That is, the determination of the deterioration of the adsorbent is performed once per operation.

As described above, in the first embodiment, on the assumption that the temperature of the exhaust gas flowing into the adsorbent under the adsorption conditions is substantially equal to the temperature of the adsorbent, the temperature of the upstream portion and the downstream portion of the adsorbent is determined. Measure each peak occurrence time,
Since the deterioration is determined by comparing the two, it is not necessary to accurately detect the absolute value of the temperature with the temperature sensors 13 and 14. Therefore, an expensive temperature sensor having high absolute value accuracy of the temperature detection is required. It is possible to determine the deterioration of the adsorbent with high accuracy without performing.

FIG. 6 is a flowchart of the second embodiment.
Corresponding to FIG. The same steps as those in FIG. 4 are denoted by the same step numbers.

The second embodiment is based on the premise that the temperature of the exhaust gas flowing into the adsorbent and the temperature of the adsorbent under the adsorption conditions are different.

Mainly the differences from FIG. 4 will be described. During the start determination, the process proceeds from step 0 to steps 31 and 32, where the initial value 0 is set in the variables DT1MAX and DT2MAX.

When the diagnostic experience flag = 0 and the condition for permitting deterioration determination are satisfied, the time differential value DT1 of the current upstream temperature T1 of the adsorbent is compared with the variable DT1MAX in step 33, and only when DT1MAX ≧ DT1, step 8 is executed. And the value of the timer TM at that time is set to the variable TM1MAX.
Transfer to The time from the deterioration determination start timing to the time when the time differential value of T1 reaches a peak is stored in TM1MAX (see the lower part of FIG. 3).

Similarly, at step 34, the time differential value DT2 of the current downstream temperature T2 of the adsorbent and the variable DT2
The process proceeds to step 10 only when DT2MAX ≧ DT2, and the value of the timer TM at that time is transferred to the variable TM1MAX, so that the time differential value of T2 reaches a peak at TM2MAX from the deterioration determination start timing. Is stored (see the lower part of FIG. 3).

As described above, in the second embodiment, the time differential value of the time differential value of the upstream temperature of the adsorbent and the time differential value of the time differential value of the downstream temperature are measured, and the two are compared to degrade the adsorbent. Is determined, the cost is high even if there is a temperature difference between the exhaust gas flowing into the adsorbent and the adsorbent under the adsorption conditions, such as when sudden acceleration is performed under the adsorption conditions immediately after cold start. It is possible to detect and determine the deterioration of the adsorbent with high accuracy without requiring a special temperature sensor.

If the temperature of the exhaust gas detected by the sensor 12 becomes 300 ° C. or more due to acceleration under the adsorption condition immediately after the cold start, the adsorption condition is not satisfied (this point is not included in the flow of FIG. 5). No deterioration determination is performed.

It is also effective to select either the first embodiment or the second embodiment according to the comparison result between the inlet exhaust gas temperature of the adsorbent at the start of the deterioration judgment and the internal temperature of the adsorbent. Means (third embodiment). That is, at the start of the deterioration determination, a difference DT (= TEXH-T1) between the inlet exhaust gas temperature TEXH and the upstream temperature T1 of the adsorbent is calculated, and the temperature difference DT is compared with a predetermined value (for example, 50 ° C.). If DT is equal to or less than a predetermined value, a peak occurs in the internal temperature of the adsorbent. Therefore, the deterioration determination of the first embodiment is performed. In some cases, the deterioration determination of the second embodiment using the peak occurrence time of the time differential value of the internal temperature is performed. Thereby, in the third embodiment, regardless of whether there is a temperature difference between the temperature of the exhaust gas flowing into the adsorbent and the temperature of the adsorbent itself, the adsorbent can be accurately detected without requiring an expensive temperature sensor. Deterioration determination can be performed.

FIG. 7 is a characteristic diagram of the fourth embodiment. While the reference value DTM1 of the above three embodiments (the first, second, and third embodiments) was a constant value, the fourth embodiment uses DTM1 as the average exhaust flow rate during the adsorption period. It is set according to. DTM as shown in FIG.
The reason why the value of 1 is made smaller as the amount of exhaust gas increases is that the amount of HC flowing into the adsorbent increases as the amount of exhaust gas increases, and the timing at which the upstream portion temperature T1 and the downstream portion temperature T2 of the adsorbent reaches a peak is earlier. Because.

As described above, in the fourth embodiment, the reference value DTM1 for determining deterioration is set in accordance with the average exhaust amount during the adsorption period, so that the exhaust amount (that is, the operating condition (engine ) Determined from the load and the number of rotations) can be accurately determined.

In the fourth embodiment, the average exhaust amount is not directly detected, but the average value of the output of the air flow meter for measuring the intake air amount of the engine is used.

In each of the first, second and third embodiments, the difference DTM between the variables TM2MAX and TM1MAX and the reference value DTM
Although the deterioration judgment is performed by comparing with the variable TM1
The ratio of MAX and TM2MAX, that is, R = TM2MAX
/ TM1MAX, and by comparing this ratio R with a reference value DTM2 obtained in advance through experiments, R <DTM
2, when the adsorbent deteriorated, and R ≧ DT
In the case of M2, another embodiment (fifth embodiment) for determining that deterioration has not occurred is considered. In this case, the fourth
As described above in the embodiment, the upstream temperature T1,
Since the timing at which the downstream portion temperature T2 reaches a peak changes in accordance with the displacement during the adsorption period, the variables TM2MAX and T
The ratio of M1MAX becomes a constant value without being affected by the displacement during the adsorption period (TM2MAX only depending on the degree of deterioration of the adsorbent).
And the ratio of TM1MAX changes). That is, in the fifth embodiment, the reference value DTM2 may be a fixed value.
It is not necessary to set the DTM2 in a table corresponding to the displacement during the adsorption period. This makes it possible to determine the deterioration of the adsorbent with the same accuracy as in the first, second, and third embodiments. Thus, the memory capacity can be reduced.

When the ratio between the variables TM1MAX and TM2MAX is R2 = TM1MAX / TM2MAX,
By comparing the ratio R2 with a reference value DTM3 obtained in advance through experiments, it is determined that the adsorbent has deteriorated when R2 ≧ DTM3, and that no deterioration has occurred when R2 <DTM3. Not even.

In the embodiment, the case where the adsorbent is provided in the bypass passage has been described. However, even in the case where the adsorbent is provided in the middle of the main exhaust pipe in an exhaust system having no bypass passage, the adsorbent is not used. Since the internal temperature peak occurs due to heat, the deterioration determination of the adsorbent according to the present invention can be performed.

[Brief description of the drawings]

FIG. 1 is a control system diagram of a first embodiment.

FIG. 2 is a waveform diagram showing changes in upstream and downstream temperatures of the adsorbent when the temperature of exhaust gas flowing into the adsorbent under the adsorption conditions is substantially equal to the temperature of the adsorbent.

FIG. 3 is a waveform chart showing changes in upstream and downstream temperatures of the adsorbent when the temperature of exhaust gas flowing into the adsorbent under the adsorption conditions is different from the temperature of the adsorbent.

FIG. 4 is a flowchart for explaining a deterioration determination of an adsorbent.

FIG. 5 is a flowchart illustrating the setting of a deterioration determination permission flag.

FIG. 6 is a flowchart for explaining the determination of deterioration of an adsorbent according to the second embodiment.

FIG. 7 is a characteristic diagram of a reference value DTM1 according to a fourth embodiment.

FIG. 8 is a diagram corresponding to the claims of the first invention.

FIG. 9 is a diagram corresponding to claims of the second invention.

FIG. 10 is a diagram corresponding to claims of the third invention.

[Explanation of symbols]

 2 exhaust pipe 5 adsorbent 11 control unit 12 exhaust temperature sensor 13 upstream temperature sensor 14 downstream temperature sensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Keiji Okada 2 Nissan Motor Co., Ltd., Takaracho, Kanagawa-ku, Yokohama, Kanagawa

Claims (9)

[Claims] An adsorbent for adsorbing HC discharged from the engine when the engine is at a low temperature; sensors for detecting internal temperatures of an upstream portion and a downstream portion of the adsorbent; and conditions for adsorbing the HC by the adsorbent. Means for determining whether or not the adsorbent is present, and means for measuring the peak occurrence time of the output of each of the temperature sensors under the adsorption condition based on the determination result. Means for deciding whether or not a deterioration has occurred in the HC adsorbent of the engine. 2. An adsorbent for adsorbing HC discharged from the engine when the temperature of the engine is low, a sensor for detecting internal temperatures of an upstream portion and a downstream portion of the adsorbent, and outputs of these temperature sensors differentiated with time. Means for determining whether or not the adsorbent is in a condition for adsorbing the HC, and means for measuring a peak occurrence time of a time differential value of the output of each of the temperature sensors when the condition is in an adsorption condition based on the determination result. And a means for judging whether or not the adsorbent has deteriorated based on a comparison of the two peak occurrence times. 3. An adsorbent for adsorbing HC discharged from the engine when the engine temperature is low, a sensor for detecting an internal temperature of an upstream portion and a downstream portion of the adsorbent, and an output of each of the temperature sensors differentiated with time. Means for determining whether the adsorbent is in a condition for adsorbing the HC, means for determining whether the difference between the inlet exhaust gas temperature of the adsorbent and the upstream temperature is equal to or less than a predetermined value. And the peak generation timing of each temperature sensor output when the difference between the inlet exhaust gas temperature of the adsorbent and the upstream portion temperature is equal to or less than a predetermined value under the adsorption condition from these determination results, Means for measuring the peak occurrence time of the time differential value of each temperature sensor output when the difference between the inlet exhaust gas temperature of the adsorbent and the upstream temperature exceeds a predetermined value; When the difference between the inlet exhaust gas temperature of the adsorbent and the upstream portion temperature is equal to or less than a predetermined value, a comparison between two peak occurrence times of the temperature sensor output is performed. Means for determining whether the adsorbent has deteriorated by comparing two peak occurrence times of the time derivative of the temperature sensor output when the difference between the exhaust gas temperature and the upstream temperature exceeds a predetermined value. An HC sorbent deterioration diagnosis device for an engine, comprising: 4. The engine HC according to claim 1, wherein the peak occurrence time of each of the temperature sensor outputs is a time from a suction start timing to a timing at which the temperature sensor output reaches a peak. Adsorbent deterioration diagnosis device. 5. The peak generation time of the time differential value of each temperature sensor output is the time from the adsorption start timing to the timing at which the time differential value of the temperature sensor output reaches a peak. Or the degradation diagnostic device of HC adsorbent of the engine according to 3. 6. The deterioration determining means determines that the adsorbent has deteriorated when the time difference between the two peak occurrence times is smaller than a reference value by comparing the time difference between the two peak occurrence times with a reference value. The means according to any one of claims 1 to 5, further comprising means for judging that the adsorbent has not deteriorated when the time difference between the two peak occurrence times is equal to or greater than a reference value. Deterioration diagnosis device for HC adsorbent of engine. 7. The HC adsorbent deterioration diagnosis apparatus for an engine according to claim 6, wherein the reference value is a value corresponding to an exhaust amount during the HC adsorption period. 8. A comparison between the two peak occurrence times is made by the second
6. The HC adsorbent deterioration diagnosis device according to claim 1, wherein the comparison is made between a ratio of two peak occurrence times and a reference value. 9. The engine according to claim 1, wherein the determination of the deterioration is stopped when the desorption of HC from the adsorbent has not been completed during the previous operation. Degradation diagnostic device for HC adsorbent.