JPH1181991A - Exhaust gas purifying device in engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying device in an engine, which supplies HC desorbed from an HC adsorbing catalyst to a NOx catalyst for reducing NOx in an oxygen excessive atmosphere so as to enhance to compression ratio of NOx, and which can stably ensure a volume of HC adsorbed to the HC adsorbing catalyst. SOLUTION: In a condition in which an HC adsorbing catalyst can adsorb HC (S2), if it is determined that an HC adsorbing volume (a) is less than a normal value a0 in the HC adsorbing catalyst (S7), an HC increasing means for increasing the volume of HC at the inlet of the HC adsorbing catalyst is energized (S9) so as to adsorb the HC by the normal volume a0. As the HC increasing means, a means for injecting fuel during scavenging stroke or the like, a means for retarding the fuel injection timing, a means of weakening swirl in a combustion chamber or a means for lowering the air excess ratio of combustion mixture is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly to an exhaust gas purifying apparatus suitable for purifying nitrogen oxides in a diesel engine.

[0002]

2. Description of the Related Art As a conventional exhaust purification device for a diesel engine, a NOx catalyst is provided by desorbing HC adsorbed on an HC adsorbent and supplying it as a reducing agent to a NOx catalyst capable of reducing NOx in an oxygen-excess atmosphere. Atmosphere H
There is known a configuration in which the C / NOx ratio is increased to improve the NOx purification rate (see Japanese Patent Application Laid-Open No. 4-27706).

[0003]

However, according to the above-mentioned conventional exhaust gas purifying apparatus, when the HC adsorbed by the HC adsorbent is used up, the HC / NOx ratio in the NOx catalyst atmosphere is reduced, and the NOx conversion is performed. There was a problem that the rate decreased. For example, if the operating conditions under which HC is desorbed from the HC adsorbent continue for a long time, desorption proceeds and the amount of adsorbed HC decreases, and if there is no opportunity to sufficiently recover the adsorbed amount thereafter, the reduction agent as In some cases, the HC / NOx ratio in the NOx catalyst atmosphere is reduced due to the shortage of HC, and the NOx reduction performance may be reduced.

[0004] The present invention has been made in view of such conventional problems, and by allowing HC as a reducing agent to be positively adsorbed on an HC adsorbent as necessary, the desorption conditions can be improved. Accordingly, it is an object of the present invention to provide an exhaust gas purification device that can suppress a decrease in the HC / NOx ratio in the NOx catalyst atmosphere and can maintain the NOx purification performance.

[0005]

According to the first aspect of the present invention, N is capable of purifying NOx in exhaust gas in an excess oxygen state.
An engine having an Ox catalyst, an HC adsorbent for adsorbing HC in exhaust gas on the upstream side of the NOx catalyst, and supplying HC desorbed from the HC adsorbent to the downstream NOx catalyst as a reducing agent. In the exhaust gas purifying apparatus, the H
C under the condition that the C adsorbent adsorbs HC,
When it is determined that the amount of HC adsorbed on the C adsorbent is smaller than the specified amount, the amount of HC in the exhaust gas flowing into the HC adsorbent is increased.

According to such a configuration, the HC adsorbent adsorbs HC in a low temperature state and desorbs HC in a high temperature (active state). However, a desired amount of adsorption can be obtained under conditions for adsorbing HC. If not, the amount of HC in the exhaust gas is positively increased to ensure the amount of HC adsorbed on the HC adsorbent. Then, when the desorption condition is satisfied, HC adsorbed as necessary and sufficiently is desorbed and supplied as a reducing agent to the downstream NOx catalyst, so that the NOx purification rate of the NOx catalyst is improved.

[0007] The HC adsorbent may be one having only HC adsorption performance, or may be an HC adsorption catalyst having catalytic performance together with HC adsorption performance. The invention according to claim 2 is configured as shown in FIG. FIG.
In NOx catalyst, the NOx catalyst
The HC adsorbent is disposed upstream of the NOx catalyst and adsorbs HC in the exhaust gas. The HC adsorbent removes the HC desorbed from the HC adsorbent to the downstream NOx catalyst by a reducing agent. It is a composition supplied as.

On the other hand, the adsorption / desorption condition discriminating means comprises the H
The adsorption / desorption conditions of the C adsorbent are determined, and the adsorption amount detecting means detects the amount of HC adsorbed on the HC adsorbent.
Further, it is a means for increasing HC and means for increasing the amount of HC in the exhaust gas flowing into the HC adsorbent. And H
The C increase control means controls the adsorption / desorption condition by the HC
When the adsorption condition of the adsorbent is determined and the amount of HC adsorption detected by the adsorption amount detecting means is smaller than a specified amount, the HC increasing means is operated.

With this configuration, it is detected that the HC adsorbent is in a condition for adsorbing HC (low temperature state, inactive state), and it is determined that the HC adsorption amount at that time is smaller than the specified amount. In some cases, by operating the HC increasing means, the amount of HC in the exhaust gas flowing into the HC adsorbent increases, so that the amount of HC adsorbed on the HC adsorbent is positively increased.

According to the third aspect of the present invention, the adsorbing / desorbing condition judging means judges the adsorbing / desorbing condition of the HC adsorbent from the operating condition of the engine. According to this configuration, since the exhaust gas temperature is estimated from operating conditions such as the engine load and the engine speed, it is possible to estimate whether the temperature condition is such that the HC adsorbent performs adsorption or desorption. become.

According to a fourth aspect of the present invention, there is provided an exhaust gas temperature detecting means for detecting the temperature of the exhaust gas flowing into the HC adsorbent, and the adsorbing / desorbing condition judging means is provided based on the detection result of the exhaust gas temperature detecting means. In this configuration, the conditions for adsorption and desorption of the HC adsorbent are determined. According to such a configuration, HC
By directly detecting the exhaust gas temperature flowing into the adsorbent,
It is determined whether the temperature condition is such that the HC adsorbent performs adsorption or desorption.

In the invention described in claim 5, the adsorption amount detecting means calculates a desorption amount and an adsorption amount per unit time of the HC adsorbent from the operating conditions of the engine, and calculates the adsorbed amount of the HC adsorbent. It was configured to detect the HC adsorption amount. According to this configuration, the amount of adsorption to the HC adsorbent and the amount of desorption from the HC adsorbent are respectively calculated from engine operating conditions such as engine load and engine speed, and under the adsorption conditions, the calculated adsorption amount is integrated. In addition, under the desorption conditions, the adsorption amount (HC remaining amount) at that time is calculated by sequentially subtracting the calculated desorption amount from the adsorption amount up to that time.

[0013] In the invention described in claim 6, the adsorption amount detecting means calculates the desorption amount and the adsorption amount per unit time of the HC adsorbent from the operating conditions of the engine and the temperature of the HC adsorbent. Then, the configuration is such that the HC adsorption amount in the HC adsorbent is detected. With this configuration, the amount of adsorption and the amount of desorption are calculated based on the engine operating conditions and the temperature of the HC adsorbent at that time, and the total amount of adsorption and the remaining amount of HC are calculated.

According to a seventh aspect of the present invention, the HC increasing means increases the amount of HC discharged from the engine by injecting fuel separately from normal fuel injection. According to such a configuration, in addition to fuel injection for normal combustion, by injecting fuel in, for example, a scavenging stroke of a diesel engine, unburned HC discharged from the engine is increased, and thus the HC adsorbent To increase the amount of HC in the exhaust gas flowing into the exhaust gas.

In the invention described in claim 8, the HC increasing means is configured to increase HC discharged from the engine by delaying the fuel injection timing. According to this configuration, the fuel injection timing is retarded (retarded) from the normal timing that is optimal for combustion, so that the unburned HC discharged from the engine is increased, and therefore, the fuel flows into the HC adsorbent. Increase the amount of HC in the exhaust gas.

According to the ninth aspect of the present invention, a swirl control valve for adjusting the intensity of the swirl generated in the combustion chamber is provided, and the HC increasing means weakens the swirl by the swirl control valve to thereby discharge the engine from the engine. HC
Is increased. According to this configuration, the amount of fuel adhering to the inner wall of the combustion chamber is increased by reducing the strength of the swirl adjusted by the swirl control valve, so that the amount of HC discharged as unburned HC is increased. .

According to a tenth aspect of the present invention, the HC increasing means increases the amount of HC discharged from the engine by reducing the excess air ratio of the combustion mixture. According to such a configuration, the excess air ratio of the combustion air-fuel mixture is forcibly reduced to a level lower than normal, thereby deteriorating the combustion.
To increase the amount of HC discharged from the engine.

According to the eleventh aspect of the invention, there is provided an intake throttle valve and an exhaust gas recirculation device, wherein the HC increasing means controls the opening degree of the intake throttle valve and the amount of exhaust gas recirculated by the exhaust gas recirculation device, thereby reducing combustion. The configuration is such that the excess air ratio of the air-fuel mixture is reduced to increase HC discharged from the engine. According to such a configuration, for example, by reducing the amount of exhaust gas recirculation in the exhaust gas recirculation device and reducing the opening of the intake throttle valve, the excess air ratio of the combustion air-fuel mixture is reduced. The amount of HC discharged from the fuel cell.

According to the twelfth aspect of the present invention, the deterioration diagnosing means for diagnosing the deterioration of the HC adsorbent, and
When the deterioration state of the C adsorbent is determined, the HC increasing means is operated when the desorption condition is determined by the adsorption / desorption condition determining means instead of the HC increase control means. HC increase control means.

According to this configuration, when it is determined that the HC adsorbent has deteriorated and the HC adsorption performance has decreased,
Even if the amount of HC is increased under the adsorption condition, the desired adsorption cannot be performed.
Therefore, instead of supplying the HC desorbed from the HC adsorbent to the NOx catalyst, the HC increased by the HC increasing means is directly supplied to the NOx catalyst to reduce the NOx catalyst. To secure HC as an agent.

[0021]

According to the first and second aspects of the present invention, HC
When the amount of HC adsorbed by the adsorbent is small, the amount of adsorption can be positively increased, so that the amount of HC desorbed from the HC adsorbent and supplied to the NOx catalyst as a reducing agent is stably secured. Therefore, there is an effect that the NOx purification rate of the NOx catalyst can be kept high.

According to the third aspect of the present invention, there is an effect that the desorption / adsorption conditions of the HC adsorbent can be easily detected from the operating conditions of the engine. According to the fourth aspect of the present invention, there is an effect that the desorption / adsorption conditions of the HC adsorbent can be accurately detected by directly detecting the exhaust gas temperature flowing into the HC adsorbent.

According to the fifth aspect of the present invention, it is possible to accurately estimate the amount of adsorbed HC (the remaining amount of HC) on the HC adsorbent in consideration of the difference between the amount of adsorbed HC and the amount of desorbed HC depending on the engine operating conditions. is there. According to the sixth aspect of the present invention, H depends on engine operating conditions and the temperature of the HC adsorbent.
In consideration of the difference between the amount of C adsorbed and the amount of desorbed C, there is an effect that the amount of adsorption (remaining HC) on the HC adsorbent can be more accurately estimated.

According to the present invention, unburned HC discharged from the engine is increased by fuel injection performed separately from normal fuel injection, and HC can be positively adsorbed by the HC adsorbent. This has the effect. According to the eighth aspect of the invention, the unburned HC discharged from the engine is increased by retarding the fuel injection timing more than usual, and the HC adsorbent can positively adsorb HC. is there.

According to the ninth aspect of the present invention, the amount of fuel adhering to the inner wall of the combustion chamber is increased by forcibly reducing the strength of the swirl, thereby increasing the unburned HC discharged from the engine. Accordingly, there is an effect that HC can be positively adsorbed on the HC adsorbent. According to the tenth aspect of the present invention, the unburned HC discharged from the engine is increased by forcibly reducing the excess air ratio of the combustion air-fuel mixture and deteriorating the combustibility, and HC is positively added to the HC adsorbent. There is an effect that it can be made to adsorb | suck effectively.

According to the eleventh aspect of the present invention, the excess air ratio of the combustion mixture can be forcibly reduced by controlling the opening degree of the intake throttle valve and the exhaust gas recirculation amount, and the exhaust gas is discharged from the engine. Increase unburned HC and add H to HC adsorbent
There is an effect that C can be positively adsorbed. According to the invention as set forth in claim 12, even if the HC adsorbent deteriorates and the HC adsorbing performance decreases, instead of the HC desorbed from the HC adsorbent, the HC adsorbent is directly used as a reducing agent for the NOx catalyst. There is an effect that HC can be supplied and the NOx purification performance of the NOx catalyst can be maintained.

[0027]

Embodiments of the present invention will be described below. FIG. 2 is a system configuration diagram of the engine according to the first embodiment. In FIG. 2, a diesel engine 101 is provided with an exhaust purification
2 is provided with an HC adsorption catalyst 201 and a NOx catalyst 202 interposed in a catalyst case 203 located in the second position.

The engine 101 is provided with a common rail type fuel injection device 107 capable of injecting fuel at an arbitrary time as a fuel injection device, and an engine control unit (engine C / U) incorporating a microcomputer. Reference numeral 106 controls the fuel injection amount and the injection timing of the common rail type fuel injection device 107 based on an engine rotation signal, an accelerator opening signal, and the like from an engine rotation sensor and an accelerator opening sensor (not shown).

The fuel injection device may be provided with a unit injector. The HC adsorption catalyst 2
As shown in FIG. 3, 01 (HC adsorbent) adsorbs HC in exhaust gas at a low temperature and starts desorption of the adsorbed HC when the temperature exceeds a predetermined temperature T ′ (specific value of the adsorption catalyst). Having. And at high temperature (HC adsorption catalyst active state)
, The HC desorbed from the HC adsorption catalyst 201
Is supplied as a reducing agent to the NOx catalyst 202 on the downstream side, so that HC / N
The Ox ratio increases, and the NOx conversion efficiency of the NOx catalyst 202 is improved.

However, if the amount of HC adsorbed on the HC adsorption catalyst 201 is small and the amount of HC desorbed and supplied to the NOx catalyst 202 on the downstream side is small, the HC / NOx ratio in the atmosphere of the NOx catalyst 202 decreases, and the NOx Will result in a reduction in the reduction processing performance. Therefore, in the present invention, when it is determined that the amount of adsorbed HC is small in a temperature range in which HC can be adsorbed by the HC adsorption catalyst 201 (low load operation region), the amount of HC discharged from the engine 101 by the HC increasing means is reduced. By increasing the amount, HC is positively adsorbed on the HC adsorption catalyst 201.

Here, as the HC increasing means, apart from the main injection (normal fuel injection), during the scavenging stroke, near the bottom dead center after the main injection or immediately after the main injection, a common rail type fuel is supplied between 360 ° ATDC. As a configuration in which fuel is injected from the injection device 107, the amount of HC discharged from the engine 101 is increased, and HC is positively adsorbed on the HC adsorption catalyst 201 (HC increase control means).

The amount of HC adsorbed on the HC adsorption catalyst 201 is shown in a map showing the characteristics of the amount of HC desorbed per unit time shown in FIG. 4 and a map showing the characteristics of the amount of HC adsorbed per unit time shown in FIG. Is calculated based on the operating conditions of the engine. That is, in the adsorption area, the H
The adsorption amount a1 searched based on the intake air amount Q (a value representative of the engine load) and the engine speed Ne from the C adsorption amount map is integrated, and in the desorption region, the intake air amount from the HC desorption amount map is calculated. Quantity Q (engine load) and rotation speed N
The remaining adsorption amount is calculated by sequentially subtracting the desorption amount d1 retrieved based on e from the adsorption amount up to that time (adsorption amount detecting means).

When the amount of adsorption is smaller than the predetermined amount a0, the amount of adsorption is actively increased by actively supplying HC to the HC adsorption catalyst 201 by the HC increasing means in the adsorption region. , The amount of desorption at the time of shifting to the desorption region is secured, and the HC / NOx ratio in the atmosphere of the NOx catalyst 202 is increased. On the other hand, the adsorption amount is a predetermined amount a
When the amount is larger than 0 and when the amount of adsorption reaches the predetermined amount a0 by the operation of the HC increasing means, a necessary and sufficient amount of HC /
It is determined that the HC desorption amount that can secure the NOx ratio can be obtained, and the active supply of HC to the HC adsorption catalyst 201 by operating the HC increasing means is not performed.

The state of the HC adsorption control in the first embodiment will be described with reference to the flowchart of FIG. S
In step 1, the operating conditions of the engine 101 (intake air amount Q, engine speed Ne) are read. In S2 (adsorption / desorption condition detection means), the operating condition of the engine 101 is determined as follows: the HC adsorption catalyst 201 performs the adsorption of HC (adsorption area) or the adsorbed HC desorption area (desorption). Remote area).

In the case of the desorption region, the process proceeds to S3, where the HC desorption amount d1 per unit time according to the operating state is calculated from the HC desorption map shown in FIG. In S4, the HC adsorption amount (remaining amount) in the HC adsorption catalyst 201 is calculated by subtracting the desorption amount d1 obtained in S13 from the total adsorption amount (total deposition amount) a. In S5, it is determined whether or not the result of subtracting the desorption amount d1 from the total adsorption amount a exceeds 0,
If the result of the subtraction is 0 or less, the process proceeds to S6, in which the total adsorption amount a is set to 0, and the calculation of the total adsorption amount a to a negative value is avoided.

On the other hand, when it is determined in S2 that the area is the suction area, the process proceeds to S7. In S7, it is determined whether or not the total suction amount a is equal to or more than the specified suction amount a0. When the total adsorption amount a is equal to or more than the specified adsorption amount a0, the process proceeds to S8, where H
C Increase means is stopped. When the total adsorption amount a is less than the specified adsorption amount a0, the process proceeds to S9, and the HC increasing means is operated (HC increasing control means). .

In S10, the adsorption amount al is detected from the HC adsorption amount map per unit time shown in FIG. 5, and this is sequentially added to the total adsorption amount a, thereby increasing and updating the total adsorption amount a. Incidentally, the above-mentioned steps S3 to S6 and S10 correspond to the adsorption amount detecting means. Next, a second embodiment of the present invention will be described.

The system configuration of the second embodiment is the same as that of the first embodiment shown in FIG. 2, and the second embodiment will be described below with reference to FIG. Since the catalyst has thermal inertia, high temperature → low temperature or low temperature →
Even if the ambient temperature (exhaust temperature) changes to a high temperature, the temperature of the HC adsorption catalyst 201 does not immediately follow the change in the ambient temperature and exhibit the adsorption / desorption characteristic corresponding to the ambient temperature. In a stable steady state, the amount of adsorption and desorption of HC can be accurately estimated from the operating conditions of the engine, but an error occurs transiently.

Therefore, in the second embodiment, the exhaust gas temperature is calculated from the operating state of the engine 101, and the temperature of the HC adsorption catalyst 201 is calculated from the history of the exhaust gas temperature. The HC adsorption / desorption coefficient is read from the maps shown in FIGS. 7 and 8 based on the calculated temperature of the catalyst 201 and the engine speed Ne, and the coefficient and the HC adsorption / desorption coefficients shown in FIGS. The amount of HC adsorbed on the catalyst 201 is calculated from the amount of adsorption and desorption obtained from the separation map.

The second embodiment having the above configuration will be described in detail with reference to the flowchart of FIG. In S21, the engine 1
01 (intake air amount Q, engine speed Ne)
Read. In S22, the exhaust temperature is calculated from the operating conditions of the engine 101, and the temperature of the HC adsorption catalyst 201 is calculated from the exhaust temperature, the exhaust flow rate per unit time (corresponding to the intake air amount), the surface area of the catalyst, and the heat transfer coefficient.

In S23, it is determined from the temperature of the HC adsorption catalyst 201 calculated in S22 whether the region is an adsorption region or a desorption region.
If it is determined in S23 that the region is the desorption region, the process proceeds to S24
Then, based on the HC desorption map corresponding to the engine operating conditions (intake air amount, engine speed) shown in FIG. 4 and the HC desorption coefficient map shown in FIG. 7 corresponding to the catalyst temperature and the engine speed. Then, the HC desorption amount d1 per unit time according to the operating state and the catalyst temperature is calculated. Specifically, the HC desorption amount corresponding to the engine operating condition retrieved from the HC desorption map of FIG. 4 is multiplied by the HC desorption coefficient corresponding to the catalyst temperature retrieved from the HC desorption coefficient map of FIG. Thus, the HC desorption amount d1 is calculated.

In step S25, the calculated HC desorption amount d1 is subtracted from the total HC adsorption amount (total HC accumulation amount) a.
The HC adsorption amount (remaining amount) of the HC adsorption catalyst 201 is calculated.
In S26, it is determined whether or not the result of subtracting the desorption amount d1 from the total adsorption amount a exceeds 0. If the subtraction result is 0 or less, the process proceeds to S27, where the total adsorption amount a To 0
To avoid calculating the total amount of adsorption a to a negative value.

On the other hand, when it is determined in S23 that the area is the suction area, the process proceeds to S28. In S28, the total adsorption amount a
Is greater than or equal to the specified adsorption amount a0. When the total adsorption amount a is equal to or greater than the specified adsorption amount a0, the process proceeds to S29, and the HC increasing means (fuel injection in a scavenging stroke or the like) is stopped. When the total adsorption amount a is less than the specified adsorption amount a0, the process proceeds to S30, and the HC increasing means is operated.

At S31, an HC adsorption map corresponding to the engine operating conditions (intake air amount, engine speed) shown in FIG. 5 and H corresponding to the catalyst temperature and the engine speed shown in FIG.
Based on the C adsorption coefficient map, the HC adsorption amount a1 per unit time according to the operating state and the actual catalyst temperature is calculated, and this is added to the total adsorption amount a. More specifically, the calculation of the adsorption amount a1 is performed based on the HC adsorption amount corresponding to the engine operating condition retrieved from the HC adsorption map shown in FIG. 5 and the HC adsorption amount corresponding to the catalyst temperature retrieved from the HC adsorption coefficient map shown in FIG. This is performed by multiplying the coefficients.

FIG. 10 is a diagram showing a system configuration according to the third embodiment. The HC adsorption catalyst 201 is different from the system configuration shown in FIG. 2 which is common to the first and second embodiments. The only difference is that a temperature sensor 103 as exhaust temperature detecting means is provided on the upstream side of. In the second embodiment, the exhaust gas temperature is estimated and calculated from the operating conditions of the engine. In the third embodiment, the exhaust gas temperature is directly detected by the temperature sensor 103. Thus, this makes it possible to accurately measure the exhaust gas temperature at the inlet of the catalyst, and to thereby estimate the catalyst temperature without being affected by the outside air temperature and calculate the HC adsorption / desorption amount with high accuracy.

Next, according to the flowchart of FIG.
A third embodiment having the above configuration will be described in detail. In S41, the operating conditions of the engine 101 are read. In S42, the temperature of the HC adsorption catalyst 201 is calculated from the exhaust gas temperature detected by the temperature sensor 103, the exhaust gas flow per unit time, the surface area of the catalyst, and the heat transfer coefficient.

In S43, it is determined from the temperature of the HC adsorption catalyst 201 calculated in S42 whether the region is an adsorption region or a desorption region.
If it is determined in S43 that the region is the detached region, the process proceeds to S44
To H in the same manner as in S24.
The C desorption amount d1 is calculated. In S45, the HC adsorption catalyst 201 is determined based on the total adsorption amount a and the HC desorption amount d1.
The HC adsorption amount (remaining amount) is calculated.

In steps S46 and S47, processing is performed to prevent the total adsorption amount a from being calculated to a negative value.
On the other hand, when it is determined in S43 that the area is the suction area, the process proceeds to S48. In S48, it is determined whether or not the total adsorption amount a is equal to or more than the specified adsorption amount a0. When the total adsorption amount a is equal to or more than the specified adsorption amount a0, the process proceeds to S49, where HC
The increasing means (fuel injection in a scavenging stroke or the like) is stopped.

When the total adsorption amount a is less than the specified adsorption amount a0, the routine proceeds to S50, where the HC increasing means is operated. In S51, similarly to S31, the HC adsorption amount a1
Is calculated and added to the total amount of adsorption a to update the total amount of adsorption a. FIG. 12 is a diagram showing a system configuration according to the fourth embodiment. In contrast to the system configuration according to the third embodiment shown in FIG. The only difference is that a temperature sensor 104 is provided.

According to such a configuration, the inlet temperature and the outlet temperature of the catalyst 201 can be measured separately, and the activity (desorption state) of the catalyst can be determined with higher accuracy from the catalyst inlet / outlet temperature. As for the inlet / outlet temperature of the HC catalyst 201, the outlet temperature is higher than the inlet temperature in the activated state of the catalyst, but as shown in FIG. 13, when the activity is lowered due to deterioration, the difference ΔT between the inlet and outlet exhaust temperatures becomes smaller.

Therefore, as shown in FIG. 14, a reference value of the temperature difference ΔT is set in each operation state, and when the actual temperature difference ΔT falls below this reference value, it is determined that the catalyst has deteriorated. Can be determined. When it is estimated that the HC adsorbing catalyst 201 is deteriorated and the HC adsorbing performance is degraded, the reducing agent HC is supplied to the NOx catalyst 202 by the HC increasing means under the desorption condition, so that the adsorbing catalyst 201 is depleted. Of the NOx catalyst 202 even after the
Ox purification performance can be maintained.

FIG. 15 is a flowchart showing the control contents of the fourth embodiment. In S61, the engine 10
The first operating condition (intake air amount Q, engine speed Ne) is read. In S62, the deterioration state of the HC adsorption catalyst 201 is determined by determining the catalyst deterioration flag.

If the catalyst deterioration flag is OFF and no catalyst deterioration has occurred, the routine proceeds to S63, where the temperature sensor 1
From 03, the inlet exhaust temperature T of the HC adsorption catalyst 201 is detected, and it is determined whether the temperature T is higher than the HC desorption start temperature T1. If the inlet exhaust gas temperature T is higher than the HC desorption start temperature T1, the process proceeds to S64, where it is assumed that the inlet exhaust gas temperature T = catalyst temperature, and the HC desorption map and the diagram shown in FIG. The HC desorption amount per unit time according to the operating state of the engine and the temperature of the HC adsorption catalyst 201 is calculated with reference to the HC desorption coefficient map corresponding to the catalyst temperature shown in FIG.

The catalyst temperature may be calculated from the inlet exhaust gas temperature T, the exhaust gas flow rate, the surface area of the catalyst, and the heat conduction coefficient. In S65, the desorption amount calculated in S64 is subtracted from the total adsorption amount a so far. In S66, it is determined whether or not the total suction amount a as a result of the subtraction processing exceeds 0. If the total suction amount a is not more than 0, the total suction amount a is reset to 0 in S67.

In step S68, the deterioration of the catalyst 201 is determined based on the catalyst entrance / exit temperature while the HC adsorption catalyst 201 does not adsorb HC. As shown in FIG. 12, when the catalyst outlet temperature exceeds the activation temperature T2, the catalyst outlet temperature becomes higher than the inlet temperature. However, as the deterioration proceeds, the difference between the inlet and outlet temperatures becomes smaller. The deterioration of the catalyst is determined from the difference ΔT (deterioration diagnosis means).

Specifically, a reference temperature difference ΔT corresponding to the engine operating conditions retrieved from the map shown in FIG.
When the measured value is smaller than the reference value, it is determined that the HC adsorption catalyst 201 has deteriorated, and a catalyst deterioration flag is set in S69. In S63, the exhaust gas temperature T at the inlet of the HC adsorption catalyst 201 becomes H
When it is determined that the temperature is lower than the C desorption start temperature T1, that is,
If it is in the adsorption region, the process proceeds to S70, and it is determined whether the HC adsorption amount a of the HC adsorption catalyst 201 is equal to or more than the specified adsorption amount a0.

If the HC adsorption amount a is equal to or greater than the specified adsorption amount a0, the HC increasing means is stopped in S71. On the other hand, H
When the C adsorption amount a is equal to or more than the specified adsorption amount a0, S7
In step 2, the HC increasing means for supplying HC to the HC adsorption catalyst 201 by operating fuel injection during the scavenging stroke is operated.

In step S73, referring to the HC adsorption amount map per unit time shown in FIG. 5 and the adsorption coefficient map corresponding to the catalyst temperature shown in FIG. 8, the adsorption amount a1 corresponding to the operating state of the engine and the catalyst temperature is determined. Is calculated, and the total amount of adsorption a is increased and updated based on the amount of adsorption a1. When the catalyst deterioration flag is on in S62 and the deterioration of the HC adsorption catalyst 201 is determined, the process proceeds to S74, and the temperature sensor 1
It is determined whether or not the catalyst inlet temperature T detected at 03 is equal to or higher than the desorption start temperature T1.

When the temperature is equal to or higher than the desorption start temperature T1, the process proceeds to S75, in which the HC increasing means is operated (deterioration-time HC increase control means). When the temperature is lower than the desorption start temperature T1, the process proceeds to S76. The HC increasing means (fuel injection in a scavenging stroke or the like) is stopped. That is, if the HC adsorption / desorption performance deteriorates due to the deterioration of the HC adsorption catalyst 201, a sufficient amount of HC is supplied to the NOx catalyst 202 under a normal condition even under the condition in which HC desorption is performed. Since it cannot be supplied as a reducing agent, at the time of deterioration, instead of supplying HC desorbed from the HC adsorption catalyst 201, HC discharged from the engine by the HC increasing means is directly supplied to the NOx catalyst 202, The HC / NOx ratio in the catalyst 202 is increased.

FIG. 16 is a diagram showing a system configuration according to the fifth embodiment of the present invention.
As a means for increasing HC, the amount of HC discharged from the engine is increased by retarding the normal injection timing, so that HC
Although HC is positively adsorbed to the adsorption catalyst 201, the increase in HC due to the delay of the injection timing can be performed not only by the common rail type fuel injection device but also by the distribution type fuel injection device. FIG. 16 shows the fuel injection device 10.
Reference numeral 7 denotes a distribution type fuel injection device.

The fifth embodiment is different from the main injection shown in the first to fourth embodiments in that the HC injection means for injecting fuel during a scavenging stroke or the like is provided with a retardation of the injection timing by H.
The only difference is that the C increasing means is used, and the present invention can be applied to any of the first to fourth embodiments. For example, when applied to the first embodiment, in the flowchart of FIG. 6, it is determined in S7 that the HC adsorption amount a is less than the specified amount a0, and when the process proceeds to S9, the injection timing is retarded. so,
The amount of HC discharged from the engine 101 is increased,
Active increase of HC adsorbed on the adsorption catalyst 201 is aimed at. When the HC adsorption amount a becomes equal to or more than the specified amount a0,
Proceeding to S8, the retard of the injection timing is stopped, and the injection is returned to the normal injection timing.

S28 to S30 of FIG. 9 and S48 to S48 of FIG.
In S50 and S70 to S72 in FIG. 15, similarly, the retard control of the injection timing can be used as the HC increasing means. FIG. 17 is a system configuration diagram showing the sixth embodiment of the present invention. In the system configuration shown in FIG.
The intake port includes a swirl control valve 108 driven to be opened and closed by an actuator, and the control of the swirl control valve 108 realizes an HC increasing means.

That is, it is determined that the amount of HC adsorbed on the HC adsorption catalyst 201 is smaller than the specified amount in the adsorption region overlapping the low-load, low-rotation region where the swirl control valve 108 should generate a strong swirl. Sometimes, the swirl is forcibly weakened (swirl control valve 1
08 opening) to increase the combustion chamber (cavity)
The fuel injected from the injection nozzle adheres to the inner wall of the combustion chamber and is discharged as unburned HC.

The sixth embodiment is also applicable to any of the first to fourth embodiments. For example,
When applied to the first embodiment, in the flowchart of FIG. 6, it is determined in S7 that the HC adsorption amount a is less than the specified amount a0, and when the process proceeds to S9, the swirl control valve 10
The swirl is weakened by opening the opening degree of the opening 8 more than usual, and the amount of HC emission from the engine is increased. When the HC adsorption amount a becomes equal to or greater than the specified amount a0, the process proceeds to S8, in which the control for weakening the swirl is stopped, and the swirl control valve 108 is controlled to a normal opening.

S28 to S30 in FIG. 9 and S48 to S30 in FIG.
Similarly in S50 and S70 to S72 in FIG. 15, the control for weakening the swirl can be used as the HC increasing means. FIG. 18 is a system configuration diagram showing a seventh embodiment of the present invention. In the system configuration shown in FIG. 18, an EGR passage 109 for communicating the exhaust passage 102 with the intake manifold, An exhaust gas recirculation device including an EGR valve 110 interposed and driven to open and close by an actuator is provided, and an intake throttle valve 105 driven to be opened and closed by an actuator is provided between the intake manifold and the air cleaner 111.

The EGR valve 110 and the intake throttle valve 105, which are opened and closed by actuators, respectively.
By controlling the degree of opening, the HC increasing means is realized. Specifically, in the adsorption region (low load region), the EGR valve 110 is slightly closed at the same time as the intake throttle valve 105 to reduce the excess air ratio. Is reduced to deteriorate combustion and increase unburned HC.

The seventh embodiment is also applicable to any of the first to fourth embodiments. For example,
When applied to the first embodiment, in the flowchart of FIG. 6, it is determined in S7 that the HC adsorption amount a is less than the specified amount a0, and when the process proceeds to S9, the EGR valve 110 is simultaneously operated with the intake throttle valve 105. A little, the excess air ratio is lowered to worsen the combustion, the unburned HC is increased,
HC is positively adsorbed on the adsorption catalyst 201. When the HC adsorption amount a becomes equal to or more than the specified amount a0, the process proceeds to S8, in which the opening control of the EGR valve 110 and the intake throttle valve 105 is stopped (the throttled opening is opened).

S28 to S30 in FIG. 9 and S48 to S48 in FIG.
Similarly in S50 and S70 to S72 in FIG. 15, the control to increase the unburned HC by worsening the combustion by closing the intake throttle valve 105 and the EGR valve 110 can be used as the HC increasing means.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an exhaust emission control device according to a second embodiment of the present invention.

FIG. 2 is a system configuration diagram according to the first embodiment.

FIG. 3 is a view showing HC desorption characteristics of an HC adsorption catalyst.

FIG. 4 is a diagram showing an HC desorption amount detection map in which desorption amounts are stored in accordance with engine operating conditions.

FIG. 5 is a diagram showing an HC adsorption amount detection map in which the amount of adsorption is stored according to operating conditions of the engine.

FIG. 6 is a flowchart showing control contents according to the first embodiment;

FIG. 7 is a view showing an HC desorption coefficient map in which an HC desorption coefficient is stored according to an engine speed Ne and a catalyst inlet temperature.

FIG. 8 is a view showing an HC adsorption coefficient map in which an HC adsorption coefficient is stored according to an engine speed Ne and a catalyst inlet temperature.

FIG. 9 is a flowchart illustrating control contents according to the second embodiment.

FIG. 10 is a system configuration diagram according to a third embodiment.

FIG. 11 is a flowchart illustrating control contents according to the third embodiment.

FIG. 12 is a system configuration diagram according to a fourth embodiment.

FIG. 13 is a diagram illustrating a relationship between catalyst deterioration and a difference ΔT between catalyst inlet / outlet temperatures.

FIG. 14 is a view showing a map in which a reference value of a difference ΔT between catalyst inlet / outlet temperatures is stored.

FIG. 15 is a flowchart illustrating control contents according to the fourth embodiment.

FIG. 16 is a system configuration diagram showing a fifth embodiment.

FIG. 17 is a system configuration diagram showing a sixth embodiment.

FIG. 18 is a system configuration diagram showing a seventh embodiment.

[Explanation of symbols]

 101 engine 102 exhaust passage 103, 104 temperature sensor 105 intake throttle valve 106 engine control unit 107 fuel injection device 108 swirl control valve 109 EGR valve 110 EGR passage 111 air cleaner 201 HC adsorption catalyst 202 NOx catalyst 203 catalyst case

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02B 31/00 F02B 31/00 L F02D 21/08 301 F02D 21/08 301A 41/04 310 41/04 310Z 41/40 41 / 40 DF 43/00 301 43/00 301N 301K F02M 25/07 570 F02M 25/07 570B

Claims (12)

[Claims] An NOx catalyst capable of purifying NOx in exhaust gas in an excess oxygen state is provided, and an HC adsorbent for adsorbing HC in exhaust gas is provided upstream of the NOx catalyst, and desorbed from the HC adsorbent. In the exhaust gas purifying apparatus for an engine configured to supply the reduced HC to the NOx catalyst on the downstream side as a reducing agent, the condition is that the HC adsorbent adsorbs HC,
An exhaust gas purifying apparatus for an engine, wherein when it is determined that the amount of HC adsorbed on the HC adsorbent is smaller than a specified amount, the amount of HC in the exhaust gas flowing into the HC adsorbent is increased. 2. An NOx catalyst capable of purifying NOx in exhaust gas in an excess oxygen state, and an HC adsorbent disposed upstream of the NOx catalyst for adsorbing HC in the exhaust gas. An exhaust / purification device for an engine configured to supply the separated HC as a reducing agent to a downstream NOx catalyst, wherein an adsorption / desorption condition determining means for determining an adsorption / desorption condition of the HC adsorbent; Adsorption amount detecting means for detecting the amount of HC adsorbed to the fuel cell; HC increasing means for increasing the amount of HC in the exhaust gas flowing into the HC adsorbent; HC determined and detected by the adsorption amount detecting means.
An exhaust gas purification device for an engine, comprising: HC increase control means for operating the HC increase means when the amount of adsorption is smaller than a prescribed amount. 3. An exhaust gas purifying apparatus for an engine according to claim 2, wherein said adsorption / desorption condition judging means judges the adsorption / desorption condition of said HC adsorbent from the operating condition of the engine. 4. An exhaust gas temperature detecting means for detecting an exhaust gas temperature flowing into the HC adsorbent, wherein the adsorbing / desorbing condition determining means detects the temperature of the HC adsorbing material based on a detection result of the exhaust temperature detecting means. 3. The exhaust gas purifying apparatus for an engine according to claim 2, wherein conditions for adsorption and desorption are determined. 5. The adsorption amount detecting means calculates a desorption amount and an adsorption amount per unit time of the HC adsorbent from an operating condition of an engine, and detects the HC adsorption amount in the HC adsorbent. 5. The method according to claim 2, wherein
An exhaust gas purification device for an engine according to any one of the above. 6. The HC adsorbing means calculates an amount of desorption and an amount of adsorbed per unit time of the HC adsorbent from the operating conditions of the engine and the temperature of the HC adsorbent, respectively, and calculates the amount of adsorbed HC. The exhaust gas purification device for an engine according to any one of claims 2 to 4, wherein an amount of HC adsorbed on the material is detected. 7. The method according to claim 2, wherein the HC increasing means increases the amount of HC discharged from the engine by injecting fuel separately from normal fuel injection. An exhaust gas purifying device for an engine according to the above. 8. The engine according to claim 2, wherein the HC increasing means increases HC discharged from the engine by delaying fuel injection timing. Exhaust purification equipment. 9. A swirl control valve for adjusting the intensity of swirl generated in the combustion chamber, wherein the HC increasing means weakens the swirl by the swirl control valve to increase HC exhausted from the engine. The exhaust gas purification device for an engine according to any one of claims 2 to 6, wherein: 10. The HC exhausted from the engine by reducing the excess air ratio of the combustion mixture by the HC increasing means.
The exhaust gas purifying apparatus for an engine according to any one of claims 2 to 6, wherein the value is increased. 11. An excess air ratio of a combustion mixture, comprising an intake throttle valve and an exhaust gas recirculation device, wherein the HC increasing means controls an opening degree of the intake throttle valve and an amount of exhaust gas recirculated by the exhaust gas recirculation device. 11. The exhaust gas purifying apparatus for an engine according to claim 10, wherein the exhaust gas is reduced to increase HC discharged from the engine. 12. A deterioration diagnosing means for diagnosing deterioration of the HC adsorbent, and when the deterioration diagnosing means determines the deterioration state of the HC adsorbent, the adsorption / desorption is performed in place of the HC increase control means. When the desorption condition is determined by the desorption condition determining means,
The exhaust gas purifying apparatus for an engine according to any one of claims 2 to 11, further comprising: a deterioration-time HC increasing control means for operating the C increasing means.