JP4816573B2 - EGR system for internal combustion engine - Google Patents

Description

  The present invention relates to an EGR system for an internal combustion engine.

  As a technique for reducing the NOx emission amount from the internal combustion engine, a technique is known in which a part of the exhaust gas is introduced into the intake system as EGR gas and returned to the internal combustion engine. In addition, in an internal combustion engine equipped with a turbocharger, an HPL device that returns a part of the exhaust gas to the internal combustion engine via an HPL passage that connects an exhaust passage upstream from the turbine of the turbocharger and an intake passage downstream from the compressor of the turbocharger. And an LPL device that returns a part of the exhaust gas to the internal combustion engine via an LPL passage that connects an exhaust passage downstream from the turbine and an intake passage upstream from the compressor, and an HPL device according to the operating state of the internal combustion engine There is also known a technique for making it possible to perform EGR in a wider range of operation by using or switching between and an LPL device (see, for example, Patent Document 1).

Further, a technique is known in which an exhaust purification catalyst having oxidizing ability is disposed in the middle of an exhaust passage to oxidize HC and PM in the exhaust to purify the exhaust.
JP 2004-150319 A Japanese Patent Laid-Open No. 2004-162675 JP 2005-264821 A

When the exhaust gas purification catalyst is disposed on the EGR gas flow path, PM and HC in the EGR gas undergo an oxidation reaction in the exhaust gas purification catalyst, so that O ₂ in the EGR gas is consumed and CO ₂ is generated. The Therefore, the O ₂ concentration and CO ₂ concentration in the EGR gas at the time of flowing into the internal combustion engine are different from the O ₂ concentration and CO ₂ concentration in the burned gas at the time of exhaust from the internal combustion engine. there is a possibility. Therefore, the control target value of the EGR gas amount is obtained by calculating the CO ₂ concentration in the burned gas according to the operating state of the internal combustion engine and the variation in the CO ₂ concentration caused by CO ₂ generated in the exhaust purification catalyst. It is preferable to determine in consideration.

The amount of CO ₂ produced in the exhaust purification catalyst correlates with the temperature of the exhaust purification catalyst, the temperature of the exhaust purification catalyst correlates with the temperature of the exhaust gas flowing into the exhaust purification catalyst, and the exhaust temperature depends on the operating state of the internal combustion engine. Correlate. Therefore, contribution to the CO ₂ concentration of the EGR gas by the CO ₂ produced in the exhaust purification catalyst can be determined in accordance with the operating state of the internal combustion engine.

By the way, because of the heat capacity of the exhaust purification catalyst itself, depending on the material constituting the exhaust purification catalyst, the capacity of the exhaust purification catalyst, etc., the time constant related to the change in the catalyst temperature with respect to the change in the operating state of the internal combustion engine is There is a tendency to be longer than the time constant related to the change of the exhaust temperature with respect to the change of the engine operating state. Therefore, the temperature change of the exhaust purification catalyst may be delayed with respect to the change in the operating state of the internal combustion engine. For example, when the operating state of an internal combustion engine changes from a high load to a low load, the exhaust temperature changes from a high temperature to a low temperature with a relatively fast response as the operating state changes, whereas the exhaust purification catalyst temperature It is maintained at a high temperature for a while. Then, after a steady operation for a certain period in the low load operation state, the standard catalyst temperature is reached in the low load operation state. During the transition period of such a catalyst temperature change, the actual catalyst temperature is higher than the standard catalyst temperature corresponding to the current operation state (in this case, the low load operation state). Therefore, more PM and HC than expected are oxidized in the exhaust purification catalyst, and the CO ₂ concentration in the EGR gas becomes higher than expected. Therefore, the amount of CO ₂ in the in-cylinder gas of the internal combustion engine is excessively larger than expected, and there is a risk of causing poor combustion such as misfire or increasing the amount of unburned fuel discharged.

  The present invention has been made in view of such problems, and in an EGR system having an exhaust purification catalyst on the EGR gas flow path, combustion failure and emission during a transition in which the operating state of the internal combustion engine changes are considered. It aims at providing the technology which suppresses deterioration.

In order to achieve the above object, an EGR system for an internal combustion engine of the present invention includes an EGR means for returning a part of exhaust gas to the internal combustion engine as EGR gas via an EGR passage connecting the exhaust passage and the intake passage of the internal combustion engine,
An exhaust purification catalyst that is provided on the flow path of the EGR gas that is returned to the internal combustion engine by the EGR means and has an oxidizing ability;
Catalyst temperature acquisition means for acquiring the temperature of the exhaust purification catalyst;
(A) The exhaust purification catalyst assumed when the internal combustion engine in which the temperature (actual catalyst temperature) acquired by the catalyst temperature acquisition means is determined according to the operating state of the internal combustion engine is steadily operated for a certain period in the operating state . The catalyst transient condition is higher than the temperature (standard catalyst temperature), and
(B) When a catalyst activity condition is established in which the temperature (actual catalyst temperature) acquired by the catalyst temperature acquisition means is higher than a predetermined activation temperature of the exhaust purification catalyst,
Correction means for correcting the amount of EGR gas returned to the internal combustion engine by the EGR means to an amount smaller than a predetermined amount of EGR gas (standard EGR gas amount) according to the operating state of the internal combustion engine;
It is characterized by providing.

  Here, the standard catalyst temperature is the temperature of the exhaust purification catalyst when the internal combustion engine is in steady operation, and is determined for each operating state of the internal combustion engine.

  Further, as a case where the catalyst transient condition is satisfied, for example, a case where the operating state of the internal combustion engine changes from a high load to a low load can be exemplified. In this case, as described above, the operating state of the internal combustion engine is reduced from a high load to a low temperature due to the difference in the time constant of the temperature change with respect to the change in the operating state of the internal combustion engine between the exhaust purification catalyst temperature and the exhaust gas temperature. Even when the load is changed, the temperature of the exhaust purification catalyst does not immediately decrease, but is maintained at a high temperature for a while. Therefore, the actual catalyst temperature is higher than the standard catalyst temperature corresponding to the low load operation state for a certain period after the operation state of the internal combustion engine is changed from the high load to the low load.

The predetermined activation temperature is a lower limit value of the temperature of the exhaust purification catalyst necessary for the PM or HC oxidation reaction to occur in the exhaust purification catalyst. That is, when the temperature of the exhaust purification catalyst is lower than the activation temperature, no oxidation reaction occurs even if PM or HC passes through the exhaust purification catalyst. On the other hand, when the temperature of the exhaust purification catalyst is higher than the activation temperature, the oxidation reaction occurs when PM or HC passes through the exhaust purification catalyst, consuming O ₂ in the EGR gas and generating CO _2. As the O ₂ concentration in the gas decreases, the CO ₂ concentration increases.

In the situation where the catalyst transient condition and the catalyst activation condition are satisfied, according to the present invention, the CO ₂ concentration in the EGR gas supplied to the internal combustion engine is a standard CO ₂ concentration according to the operating state of the internal combustion engine. Even if it becomes higher, since the amount of EGR gas returned to the internal combustion engine is made smaller than the standard EGR gas amount, it is suppressed that the CO ₂ concentration in the in-cylinder gas of the internal combustion engine becomes excessively larger than expected. . Therefore, it is possible to suppress the occurrence of a combustion failure such as misfire or the increase in the amount of unburned fuel emission and the deterioration of emissions.

The means for correcting the amount of EGR gas to be reduced with respect to the standard EGR gas amount by the correcting means includes an EGR valve that is provided in the EGR passage and adjusts the amount of EGR gas flowing through the EGR passage. When the transient condition and the catalyst activation condition are satisfied, means for correcting the opening degree of the EGR valve to a closing side opening degree from a predetermined opening degree (standard EGR valve opening degree) according to the operating state of the internal combustion engine is adopted. can do.

As a result, the amount of EGR gas flowing through the EGR passage decreases from the normal time, so that the amount of EGR gas returned to the internal combustion engine can be reduced with respect to the standard EGR gas amount. Therefore, even when the CO ₂ concentration in the EGR gas becomes higher than expected due to the oxidation reaction of PM or HC in the exhaust purification catalyst, the amount of CO ₂ in the in-cylinder gas is suppressed from being excessively increased. Thus, poor combustion such as misfire can be suppressed.

As means for correcting the decrease in the EGR gas amount with respect to the standard EGR gas amount by the correcting means, the EGR rate of the intake air of the internal combustion engine is determined in accordance with the operating state of the internal combustion engine when the catalyst transient condition and the catalyst activation condition are satisfied. It is also possible to employ means for correcting the value to a value lower than a predetermined EGR rate (standard EGR rate).

  Here, the EGR rate is a ratio of the EGR gas amount to the total gas amount sucked into the cylinder. If the gas amount sucked into the cylinder is Gcyl and the EGR gas amount is Gegr, the EGR rate = Calculated as Gegr / Gcyl. Here, if the intake air amount (fresh air amount) is Ga, Gcyl = Ga + Gegr, and therefore, EGR rate = (Gcyl−Ga) / Gcyl can also be calculated. In the EGR control, a target EGR rate is set according to the operating state of the internal combustion engine, and an EGR valve, a throttle valve, an exhaust throttle valve, a nozzle vane in a VN turbo, etc., so that the actual EGR rate becomes the target EGR rate. Various EGR gas metering means are feedback-controlled.

According to the above configuration, when the catalyst transient condition and the catalyst activation condition are satisfied, the EGR control is executed after the target EGR rate is corrected to a value lower than the standard EGR rate. Therefore, even when the CO ₂ concentration in the EGR gas becomes higher than expected due to the oxidation reaction of PM or HC in the exhaust purification catalyst, the amount of CO ₂ in the in-cylinder gas is suppressed from being excessively increased. Monkey. Further, by correcting the target EGR rate, EGR gas may be caused by some cause (for example, change in engine warm-up state, change in operating state, change in internal state of EGR passage, intake passage, exhaust passage, etc.). Even when the flow rate characteristics of the intake air change as compared with the time of adaptation, the reduction correction of the EGR gas amount by the various EGR gas amount metering means as described above can be performed with high accuracy. Therefore, it is possible to more reliably suppress a combustion failure such as misfire when the catalyst transient condition and the catalyst activation condition are satisfied.

In each of the above configurations, the correction amount by the correction means may be determined based on the amount of CO ₂ generated in the exhaust purification catalyst.

Thus, when the catalyst transient condition and the catalyst activation condition are satisfied, the increase in CO ₂ in the cylinder gas of the internal combustion engine caused by CO ₂ generated in the exhaust purification catalyst is offset, It is possible to obtain a correction amount that brings the CO ₂ concentration close to the concentration at the normal time when the catalyst transient condition or the catalyst activation condition is not satisfied. Therefore, combustion failure such as misfire and deterioration of emission when the catalyst transient condition and the catalyst activation condition are satisfied can be more reliably suppressed.

Here, the amount of CO ₂ produced in the exhaust purification catalyst may be estimated based on the operating state of the internal combustion engine.

Although the amount of CO ₂ produced in the exhaust purification catalyst is considered to correlate with various factors, it can be considered that these factors basically correlate with the operating state of the internal combustion engine. Thus, if to estimate the amount of CO ₂ in the exhaust purification catalyst based on the operating state of the internal combustion engine, it is possible to bring the CO ₂ concentration of more accurately cylinder interior gas to the normal CO ₂ concentration at the time of .

The relationship between the operating state of the internal combustion engine and the amount of CO ₂ generated in the exhaust purification catalyst is determined according to one or a plurality of physical quantities (for example, the rotational speed and the load) representative of the operating state of the internal combustion engine, for example, through experiments or adaptation work. It can be obtained in advance as a map or function for determining the amount of CO ₂ produced in the purification catalyst. If two types of maps are prepared and used properly according to the situation, when the catalyst transient condition and the catalyst activation condition are satisfied, and at the normal time when at least one of the catalyst transient condition and the catalyst activation condition is not satisfied, The present invention can be realized with a simple configuration.

Further, a map for determining the correction amount of the EGR gas amount, the EGR valve opening degree, and the EGR rate according to the operation state of the internal combustion engine in consideration of the CO ₂ generation amount in the exhaust purification catalyst estimated in this way, It may have a function.

Further, the amount of CO ₂ generated in the exhaust purification catalyst when the catalyst transient condition and the catalyst activation condition are satisfied correlates with the chemical reaction rate of the oxidation reaction of PM or HC in the exhaust purification catalyst. This chemical reaction rate increases as the difference between the actual catalyst temperature and the standard catalyst temperature increases, and therefore the amount of CO ₂ produced in the exhaust purification catalyst tends to increase. Further, the amount of CO ₂ generated in the exhaust purification catalyst correlates with the amount of PM or HC passing through the exhaust purification catalyst. When the flow rate of EGR gas passing through the exhaust purification catalyst or the amount of PM or HC in the EGR gas increases, the amount of PM or HC used for the oxidation reaction in the exhaust purification catalyst increases. There is a tendency for the amount of CO ₂ produced to increase. The amount of CO ₂ produced in the exhaust purification catalyst is also correlated with the capacity (volume) of the exhaust purification catalyst. If the capacity of the exhaust purification catalyst is large, the opportunity for oxidation reaction of PM and HC in the exhaust purification catalyst increases, so that the amount of CO ₂ generated in the exhaust purification catalyst tends to increase.

Considering such characteristics, the amount of CO ₂ produced in the exhaust purification catalyst is
Exhaust gas assumed when the internal combustion engine determined according to the temperature (actual catalyst temperature) acquired by the catalyst temperature acquisition means and the operating state of the internal combustion engine is steadily operated for a certain period in that operating state. Difference from purification catalyst temperature (standard catalyst temperature)
The flow rate of EGR gas passing through the exhaust purification catalyst,
The amount of PM in the EGR gas passing through the exhaust purification catalyst,
The amount of HC in the EGR gas passing through the exhaust purification catalyst,
The volume of the exhaust purification catalyst;
You may estimate based on at least one of these. In this way, the CO ₂ concentration of cylinder interior gas when the catalyst transient conditions and catalytic activity condition is satisfied, more precisely can be brought close to the CO ₂ concentration in the normal, deterioration of combustion failure and emission more It can be surely suppressed.

The idea of the present invention
A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
HPL means for returning a part of the exhaust gas as HPL gas to the internal combustion engine via an HPL passage connecting an exhaust passage upstream from the turbine and an intake passage downstream from the compressor;
LPL means for returning a part of the exhaust gas as LPL gas to the internal combustion engine via an LPL passage connecting an exhaust passage downstream from the turbine and an intake passage upstream from the compressor;
An LPL catalyst provided in the exhaust passage downstream from the connection location of the HPL passage and upstream from the connection location of the LPL passage;
LPL catalyst temperature acquisition means for acquiring the temperature of the LPL catalyst;
A case where the present invention is applied to an EGR system of an internal combustion engine equipped with the above will be described.

  In the EGR control in the EGR system having both the HPL means and the LPL means, together with the EGR rate and the EGR gas amount, all EGR gases for realizing the EGR rate and the EGR gas amount (returned to the internal combustion engine by the HPL means and the LPL means). The ratio between the HPL gas and the LPL gas in the exhaust gas) is controlled.

  For example, when the internal combustion engine is in a low load and low rotation operation state, the HPL gas ratio is set to 100% (that is, EGR is performed using only the HPL means), and the operation state of the internal combustion engine is changed from the high load side to the high rotation side. As the ratio changes, the HPL gas ratio is lowered and the LPL gas ratio is increased (that is, EGR is performed using both the HPL means and the LPL means), and when the internal combustion engine is operating at a high load or high speed, EGR control in which the ratio is set to 100% (that is, EGR is performed using only the LPL means) can be considered.

By the way, as described above, the amount of CO ₂ generated in the exhaust purification catalyst when the catalyst transient condition and the catalyst activation condition are satisfied correlates with the amount of exhaust gas passing through the exhaust purification catalyst, and passes through the exhaust purification catalyst. As the amount of exhaust gas increases, the amount of CO ₂ produced in the exhaust purification catalyst tends to increase. Therefore, in the EGR system in which the exhaust purification catalyst (LPL catalyst) is arranged on the LPL gas flow path as in the above configuration, the correction means includes:
(A) An LPL catalyst assumed when an internal combustion engine in which the temperature (actual LPL catalyst temperature) acquired by the LPL catalyst temperature acquisition means is determined according to the operating state of the internal combustion engine is steadily operated for a certain period of time in the operating state An LPL catalyst transient condition higher than the temperature (standard LPL catalyst temperature), and
(B) When the LPL catalyst activation condition in which the temperature (actual LPL catalyst temperature) acquired by the LPL catalyst temperature acquisition means is higher than the predetermined LPL catalyst activation temperature of the LPL catalyst is satisfied, the ratio of the HPL gas in the total EGR gas (HPL ratio) may be made higher than a predetermined ratio (standard HPL ratio) according to the operating state of the internal combustion engine.

By doing so, when the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied, the HPL ratio is increased, and conversely, the LPL gas ratio is decreased. Therefore, the amount of LPL gas passing through the LPL catalyst is reduced as compared with the normal time when the LPL catalyst transient condition or the LPL catalyst activation condition is not satisfied. Therefore, the amount of CO ₂ generated in the LPL catalyst is reduced, and it is possible to suppress an excessive increase in the CO ₂ concentration in the EGR gas supplied to the internal combustion engine.

At this time, even if the LPL ratio is low, CO ₂ is generated in the LPL catalyst as long as the LPL gas ratio is not zero. Therefore, since the CO ₂ concentration in the LPL gas is higher than normal, it is preferable to correct the amount of LPL gas by applying the correction in the general EGR system described above to the LPL-EGR system. That is, it is preferable to correct the amount of LPL gas by reducing the amount of opening of the LPL valve provided in the LPL passage. Even in the case of performing correction for these LPL-EGR systems, the LPL ratio is reduced from the normal time according to the above configuration, so that a large amount of CO ₂ is suppressed from being generated in the LPL catalyst. Therefore, the correction amount related to the correction for the LPL-EGR system can be made smaller than usual. Thereby, it is possible to suppress the deterioration of the exhaust performance due to the variation caused by the estimation of the CO ₂ generation amount in the LPL catalyst and the correction of the LPL valve opening.

  In the above configuration, an EGR system further provided with an HPL catalyst having an oxidizing ability provided in the middle of the HPL passage, that is, an exhaust purification catalyst on the EGR gas flow path in both the HPL-EGR system and the LPL-EGR system A case where the present invention is applied to an EGR system provided with the above will be described.

In such an EGR system, in addition to the case where the above-described LPL catalyst transient condition and LPL catalyst activation condition are satisfied, the CO ₂ concentration in the EGR gas can be higher than usual.
(C) HPL catalyst assumed when the internal combustion engine in which the temperature (actual HPL catalyst temperature) acquired by the HPL catalyst temperature acquisition means is determined according to the operating state of the internal combustion engine is steadily operated for a certain period of time in the operating state And (d) the temperature (actual HPL catalyst temperature) acquired by the HPL catalyst temperature acquisition means is higher than the predetermined HPL catalyst activation temperature of the HPL catalyst. The case where high HPL catalyst activity conditions are satisfied is considered.

When the LPL catalyst transient condition, the LPL catalyst activation condition, the HPL catalyst transient condition, and the HPL catalyst activation condition are satisfied, both of the LPL catalyst and the HPL catalyst may generate more CO ₂ than usual.

In such a case, in the EGR system of the present invention, the ratio of EGR gas flowing through the EGR path in which the exhaust purification catalyst having the larger amount of CO ₂ produced by the LPL catalyst and the HPL catalyst is provided, You may make it correct | amend the ratio of the said EGR gas in all the EGR gas so that it may become lower than the standard ratio determined according to the driving | running state of an internal combustion engine.

That is, in the above configuration,
HPL catalyst temperature acquisition means for acquiring the temperature of the HPL catalyst;
LPLCO ₂ production amount estimation means for estimating the amount of CO ₂ produced in the LPL catalyst;
HPLCO ₂ production amount estimation means for estimating the amount of CO ₂ produced in the HPL catalyst;
Further comprising
When the LPL catalyst transient condition, the LPL catalyst activation condition, the HPL catalyst transient condition, and the HPL catalyst activation condition are satisfied,
(A) when the amount of CO ₂ estimated by the LPLCO ₂ generation amount estimation means is larger than the amount of CO ₂ estimated by the HPLCO ₂ generation amount estimation means, the internal combustion ratio of HPL gas in the total EGR gas higher than the predetermined ratio corresponding to the operating state of the engine (standard HPL ratio), (B) CO where the amount of CO ₂ estimated by the LPLCO ₂ generation amount estimation means is estimated by the HPLCO ₂ generation amount estimation means _When the amount is less than or equal to ₂ , the ratio of the LPL gas in the total EGR gas may be higher than a predetermined ratio (standard LPL ratio) corresponding to the operating state of the internal combustion engine.

By doing so, when the amount of CO ₂ produced in the LPL catalyst is larger than the amount of CO ₂ produced in the HPL catalyst, the amount of LPL gas passing through the LPL catalyst is reduced compared to the normal time. An excessive increase in the concentration of CO ₂ in the EGR gas supplied to the internal combustion engine is suppressed. On the other hand, if the amount of CO ₂ produced in HPL catalyst is greater than the amount of CO ₂ produced in LPL catalyst, the amount of HPL gas passing through the HPL catalyst is reduced from normal supply to the internal combustion engine An excessive increase in the concentration of CO ₂ in the EGR gas is suppressed.

Therefore, according to the above configuration, even if the LPL catalyst transient condition, the LPL catalyst activation condition, the HPL catalyst transient condition, and the HPL catalyst activation condition are satisfied, the amount of CO ₂ generated in the exhaust purification catalyst is reduced as much as possible. It is possible to suppress the combustion failure and the emission deterioration.

As described above, the amount of CO ₂ produced in the exhaust purification catalyst is the difference between the actual catalyst temperature and the standard catalyst temperature, the amount of exhaust passing through the exhaust purification catalyst, the volume of the exhaust purification catalyst, and the PM passing through the exhaust purification catalyst. It depends on the amount of HC. Therefore, the LPLCO ₂ production amount estimation means and the HPLCO ₂ production amount estimation means may estimate the CO ₂ production amount in the LPL catalyst and the HPL catalyst based on these physical quantities.

In the EGR system having each configuration described above, when the catalyst transient condition and the catalyst activation condition are satisfied, the PM 2 or HC in the EGR gas that passes through the exhaust purification catalyst undergoes an oxidation reaction to cause CO ₂ in the EGR gas. Even when the concentration is higher than normal, the amount of EGR gas returned to the internal combustion engine is corrected to be lower than normal, thereby suppressing the CO ₂ concentration in the cylinder gas from becoming excessively high. Is intended.

  On the other hand, when the catalyst transient condition and the catalyst activation condition are satisfied, the catalyst transient is reduced by lowering the temperature of the exhaust purification catalyst or by suppressing the temperature of the exhaust purification catalyst from being further increased. You may make it implement | achieve as soon as possible the condition where conditions and catalyst activation conditions are not satisfied. Therefore, in the EGR system of the present invention, when the catalyst transient condition and the catalyst activation condition are satisfied, the exhaust gas purification is controlled by controlling the heat transfer between the exhaust gas purification catalyst and the EGR gas passing through the exhaust gas purification catalyst. The temperature of the catalyst was controlled.

  That is, in the EGR system having the HPL means and the LPL means as described above and further having the LPL catalyst in the LPL-EGR system, the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied, and When the exhaust gas temperature is lower than the actual LPL catalyst temperature, the amount of exhaust gas passing through the LPL catalyst is increased, and heat exchange is actively performed between the high temperature LPL catalyst and the low temperature exhaust gas. The temperature was lowered.

More specifically,
A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
HPL means for returning a part of the exhaust gas as HPL gas to the internal combustion engine via an HPL passage connecting an exhaust passage upstream from the turbine and an intake passage downstream from the compressor;
LPL means for returning a part of the exhaust gas as LPL gas to the internal combustion engine via an LPL passage connecting an exhaust passage downstream from the turbine and an intake passage upstream from the compressor;
An LPL catalyst provided in the exhaust passage downstream from the connection location of the HPL passage and upstream from the connection location of the LPL passage;
LPL catalyst temperature acquisition means for acquiring the temperature of the LPL catalyst;
Exhaust temperature acquisition means for acquiring the temperature of the exhaust discharged from the internal combustion engine;
In the configuration with
(A) An LPL catalyst assumed when an internal combustion engine in which the temperature (actual LPL catalyst temperature) acquired by the LPL catalyst temperature acquisition means is determined according to the operating state of the internal combustion engine is steadily operated for a certain period of time in the operating state LPL catalyst transient conditions higher than the temperature of (standard LPL catalyst temperature),
(B) LPL catalyst activation conditions in which the temperature (actual LPL catalyst temperature) acquired by the LPL catalyst temperature acquisition means is higher than a predetermined activation temperature of the LPL catalyst, and
(C) LPL exhaust low temperature condition in which the temperature acquired by the exhaust temperature acquisition means is lower than the temperature (actual LPL catalyst temperature) acquired by the LPL catalyst temperature acquisition means,
If the above holds, the amount of exhaust gas passing through the LPL catalyst may be made larger than a predetermined amount (standard LPL catalyst passing gas amount) according to the operating state of the internal combustion engine.

By doing so, since a large amount of low-temperature exhaust gas passes through the LPL catalyst, heat is transferred from the LPL catalyst to the low-temperature exhaust gas, and the temperature decrease of the LPL catalyst can be promoted. As a result, the actual LPL catalyst temperature can be quickly brought close to the standard LPL catalyst temperature. As described above, the amount of CO ₂ generated in the exhaust purification catalyst tends to increase as the difference between the actual catalyst temperature and the standard catalyst temperature increases. Therefore, the difference between the actual LPL catalyst temperature and the standard LPL catalyst temperature due to the above configuration. If it becomes small quickly, the production amount of CO _{2 in} the LPL catalyst can be rapidly reduced. Therefore, it is possible to suppress an excessive increase in the amount of CO ₂ in the cylinder gas of the internal combustion engine.

  On the other hand, if the exhaust gas temperature from the internal combustion engine is higher than the actual LPL catalyst temperature, whether to reduce the amount of exhaust gas that passes through the LPL catalyst and prevent the temperature of the LPL catalyst from further rising due to high-temperature exhaust gas Alternatively, the intake air amount is increased to lower the exhaust temperature, and the temperature rise of the LPL catalyst is suppressed.

More specifically, in the above configuration,
(A) Transient conditions of the LPL catalyst,
(B) the LPL catalyst activation condition, and (c) an LPL exhaust high temperature condition in which the temperature acquired by the exhaust temperature acquisition means is higher than the temperature (actual LPL catalyst temperature) acquired by the LPL catalyst temperature acquisition means,
If
(A) The amount of exhaust gas passing through the LPL catalyst is made smaller than a predetermined amount (standard LPL catalyst passing gas amount) according to the operating state of the internal combustion engine, or
(B) The intake air amount may be made larger than a predetermined amount (standard intake air amount) according to the operating state of the internal combustion engine.

By making the amount of exhaust gas passing through the LPL catalyst smaller than the standard LPL catalyst passing gas amount, further temperature increase of the LPL catalyst due to high temperature exhaust gas passing through the LPL catalyst can be suppressed. Therefore, it is possible to suppress an increase in the amount of CO ₂ generated in the LPL catalyst, and it is possible to suppress an excessive increase in the CO ₂ concentration in the in-cylinder gas of the internal combustion engine. Also, by increasing the intake air amount from the standard intake air amount, the amount of gas supplied into the cylinder increases under the condition that the amount of heat input (fuel injection amount) is constant, so the temperature of the exhaust gas decreases. To do. Therefore, the state of the internal combustion engine can be quickly shifted to a state where the LPL exhaust gas high temperature condition is not satisfied, and an increase in the temperature of the LPL catalyst can be suppressed. As a means for increasing the intake air amount, for example, the opening degree of the throttle valve that controls the intake air amount is increased, or the nozzle vane that changes the flow rate characteristic of the turbine in the configuration having the variable capacity turbocharger is closed. It is possible to adopt means for

  Further, in the EGR system having the HPL means and the LPL means as described above and further having the HPL catalyst in the HPL-EGR system, the HPL catalyst transient condition and the HPL catalyst activation condition are satisfied, and When the exhaust gas temperature is lower than the actual HPL catalyst temperature, the amount of exhaust gas passing through the HPL catalyst is increased, and heat exchange is actively performed between the high-temperature HPL catalyst and the low-temperature exhaust gas. The temperature was lowered.

More specifically,
A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
HPL means for returning a part of the exhaust gas as HPL gas to the internal combustion engine via an HPL passage connecting an exhaust passage upstream from the turbine and an intake passage downstream from the compressor;
LPL means for returning a part of the exhaust gas as LPL gas to the internal combustion engine via an LPL passage connecting an exhaust passage downstream from the turbine and an intake passage upstream from the compressor;
An HPL catalyst provided in the middle of the HPL passage and having oxidation ability;
HPL catalyst temperature acquisition means for acquiring the temperature of the HPL catalyst;
Exhaust temperature acquisition means for acquiring the temperature of the exhaust discharged from the internal combustion engine;
In the configuration with
(A) An HPL catalyst assumed when an internal combustion engine in which the temperature (actual HPL catalyst temperature) acquired by the HPL catalyst temperature acquisition means is determined according to the operating state of the internal combustion engine is steadily operated for a certain period in the operating state. HPL catalyst transient conditions higher than the temperature of (standard HPL catalyst temperature),
(B) HPL catalyst activation conditions in which the temperature (actual HPL catalyst temperature) acquired by the HPL catalyst temperature acquisition means is higher than a predetermined activation temperature of the HPL catalyst, and
(C) HPL exhaust low temperature condition where the temperature acquired by the exhaust temperature acquisition means is lower than the temperature (actual HPL catalyst temperature) acquired by the HPL catalyst temperature acquisition means;
If the above holds, the amount of exhaust gas passing through the HPL catalyst may be made larger than a predetermined amount (standard HPL catalyst passing gas amount) according to the operating state of the internal combustion engine.

By doing so, since a large amount of low-temperature exhaust gas passes through the HPL catalyst, heat is transferred from the HPL catalyst to the low-temperature exhaust gas, and the temperature decrease of the HPL catalyst can be promoted. As a result, the actual HPL catalyst temperature can be quickly brought close to the standard HPL catalyst temperature. As described above, the amount of CO ₂ generated in the exhaust purification catalyst tends to increase as the difference between the actual catalyst temperature and the standard catalyst temperature increases. Therefore, the difference between the actual HPL catalyst temperature and the standard HPL catalyst temperature due to the above configuration. If it becomes small quickly, the production amount of CO _{2 in} the HPL catalyst can be rapidly reduced. Therefore, it is possible to suppress an excessive increase in the amount of CO ₂ in the cylinder gas of the internal combustion engine.

  On the other hand, if the exhaust gas temperature from the internal combustion engine is higher than the actual HPL catalyst temperature, the amount of exhaust gas that passes through the HPL catalyst is reduced to prevent the temperature of the HPL catalyst from further rising due to high-temperature exhaust gas. Alternatively, it is necessary to increase the intake air amount to lower the exhaust temperature to suppress the temperature rise of the HPL catalyst.

More specifically, in the above configuration,
(B) the HPL catalyst transient condition;
(B) the HPL catalyst activity condition;
(C) HPL exhaust high temperature condition in which the temperature acquired by the exhaust temperature acquisition means is higher than the temperature acquired by the HPL catalyst temperature acquisition means (actual HPL catalyst temperature);
If
(A) The amount of exhaust gas passing through the HPL catalyst is made smaller than a predetermined amount (standard HPL catalyst passage gas amount) according to the operating state of the internal combustion engine, or
(B) The intake air amount may be made larger than a predetermined amount (standard intake air amount) according to the operating state of the internal combustion engine.

By making the amount of exhaust gas passing through the HPL catalyst smaller than the standard HPL catalyst passing gas amount, further increase in temperature of the HPL catalyst due to high temperature exhaust gas passing through the HPL catalyst can be suppressed. Therefore, it is possible to suppress an increase in the amount of CO ₂ generated in the HPL catalyst, and it is possible to suppress an excessive increase in the CO ₂ concentration in the in-cylinder gas of the internal combustion engine. Also, by increasing the intake air amount from the standard intake air amount, the amount of gas supplied into the cylinder increases under the condition that the amount of heat input (fuel injection amount) is constant, so the temperature of the exhaust gas decreases. To do. Therefore, the state of the internal combustion engine can be quickly shifted to a state where the HPL exhaust high temperature condition is not satisfied, and an increase in the temperature of the HPL catalyst can be suppressed. As a means for increasing the intake air amount, for example, the opening degree of the throttle valve that controls the intake air amount is increased, or the nozzle vane that changes the flow rate characteristic of the turbine in the configuration having the variable capacity turbocharger is closed. It is possible to adopt means for

According to the present invention, in an EGR system having an exhaust purification catalyst on the EGR gas flow path, it is possible to suppress poor combustion and deterioration of emissions at the time of transition when the operating state of the internal combustion engine changes.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram schematically showing a schematic configuration of an internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system. The internal combustion engine 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

  The intake ports (not shown) of the respective cylinders 2 gather in the intake manifold 17 and communicate with the intake passage 3. An EGR passage 63 described later is connected to the intake passage 3. A throttle valve 62 for adjusting the amount of fresh air flowing into the intake passage 3 is disposed in the intake passage 3 upstream from the connection point of the EGR passage 63. An air flow meter 7 that measures the amount of intake air is provided in the intake passage 3 upstream of the throttle valve 62. Hereinafter, the intake passage 3 and the intake manifold 17 may be collectively referred to as an intake system.

  The exhaust ports (not shown) of the respective cylinders 2 are gathered in the exhaust manifold 18 and communicate with the exhaust passage 4. The exhaust manifold 18 is provided with an exhaust temperature sensor 21 that measures the temperature of exhaust discharged from the internal combustion engine 1. An exhaust purification catalyst 65 is disposed in the exhaust passage 4. The exhaust purification catalyst 65 has an oxidizing ability, and promotes an oxidation-reduction reaction between HC and PM in the inflowing exhaust gas and oxygen when the catalyst temperature is higher than a predetermined activation temperature. The exhaust purification catalyst 65 may include other exhaust purification devices, for example, a filter that collects PM in the exhaust, a NOx storage reduction catalyst, and the like. The exhaust purification catalyst 65 is provided with a catalyst temperature sensor 64 for measuring the catalyst temperature. In this embodiment, the catalyst temperature sensor 64 corresponds to the catalyst temperature acquisition means in the present invention. An EGR passage 63 is connected to the exhaust passage 4 downstream of the exhaust purification catalyst 65. Hereinafter, the exhaust passage 4 and the exhaust manifold 18 may be collectively referred to as an exhaust system.

  The internal combustion engine 1 is provided with an EGR device 61 that guides part of the exhaust gas flowing through the exhaust passage 4 to the intake passage 3 as EGR gas and returns it to the internal combustion engine 1. The EGR device 61 has an EGR passage 63 that connects the exhaust passage 4 downstream of the exhaust purification catalyst 65 and the intake passage 3 downstream of the throttle valve 62, and a part of the exhaust is taken into the intake passage via the EGR passage 63. 3 is allowed to flow. The EGR passage 63 is provided with an EGR valve 60 that can change the flow area of the EGR passage 63 and adjust the amount of EGR gas flowing through the EGR passage 63. The amount of EGR gas can be adjusted by adjusting the opening degree of the EGR valve 60.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 20 that controls the internal combustion engine 1. The ECU 20 is a microcomputer provided with a CPU, a ROM, a RAM, an input / output port, and the like. In addition to the air flow meter 7, the exhaust gas temperature sensor 21, and the catalyst temperature sensor 64 described above, the ECU 20 includes a water temperature sensor 14 that outputs an electric signal corresponding to the temperature of the cooling water circulating through the water jacket of the internal combustion engine 1, and an accelerator pedal A sensor such as an accelerator opening sensor 15 that outputs an electric signal corresponding to the operation amount and a crank position sensor 16 that outputs a pulse signal each time the crankshaft of the internal combustion engine 1 rotates by a predetermined angle (for example, 10 °) are electrically connected. The output signals from the sensors are connected to the ECU 20. The ECU 20 is electrically connected to devices such as a throttle valve 62 and an EGR valve 60, and these devices are controlled by a control signal output from the ECU 20.

  ECU20 acquires the driving | running state of the internal combustion engine 1, and a driver | operator's request | requirement based on the signal input from each said sensor. For example, the ECU 20 calculates the engine speed based on the signal input from the crank position sensor 16 and calculates the requested engine load based on the signal input from the accelerator opening sensor 15. Then, fuel injection and EGR are controlled by controlling each of the above devices in accordance with the calculated engine load and engine speed.

  The target values such as EGR gas amount, EGR valve opening, or EGR rate are adapted so that the emission and fuel consumption performance of the internal combustion engine 1 such as NOx, smoke, HC, etc., achieve a predetermined regulation value or a desired target value. Is stored in the ROM of the ECU 20. The ECU 20 acquires the operating state of the internal combustion engine 1, reads these target values corresponding to the acquired operating state, and controls the opening degree of the EGR valve 60 to the target opening degree, or the actual EGR rate and EGR gas. EGR control is performed by feedback controlling the EGR valve 60 and the throttle valve 62 so that the amount matches the target value.

By the way, as described above, when the temperature of the exhaust purification catalyst 65 becomes higher than the activation temperature, an oxidation reaction of PM or HC in the exhaust flowing into the exhaust purification catalyst 65 occurs. Thereby, O ₂ in the exhaust gas flowing into the exhaust purification catalyst 65 is consumed and CO ₂ is generated. Therefore, the O ₂ concentration in the exhaust gas decreases and the CO ₂ concentration increases. In the case of the present embodiment, the exhaust purification catalyst 65 is arranged on the EGR gas flow path, so that the O ₂ concentration and the CO ₂ concentration in the EGR gas at the time of flowing into the internal combustion engine 1 are from the internal combustion engine 1. There is a possibility that the O ₂ concentration or the CO ₂ concentration in the burned gas at the time of discharge becomes a different concentration. Therefore, the target value of the EGR gas amount of the above, the variation of the CO ₂ concentration due the CO ₂ concentration in the burnt gas in accordance with the operating state of the internal combustion engine 1, the CO ₂ produced in the exhaust purification catalyst 65 It is determined in consideration of minutes.

The amount of CO ₂ produced in the exhaust purification catalyst 65 correlates with the temperature of the exhaust purification catalyst 65, the temperature of the exhaust purification catalyst 65 correlates with the temperature of the exhaust gas flowing into the exhaust purification catalyst 65, and the exhaust temperature is the internal combustion engine. Correlate with the driving state of 1. Therefore, contribution to the CO ₂ concentration of the EGR gas by the CO ₂ produced in the exhaust purification catalyst 65 can be determined in accordance with the operating condition of the internal combustion engine 1.

By the way, due to the heat capacity of the exhaust purification catalyst 65, the time constant related to the change in the catalyst temperature accompanying the change in the operating state of the internal combustion engine 1 depends on the material constituting the exhaust purification catalyst 65 and the capacity of the exhaust purification catalyst 65. Tends to be longer than the time constant related to the change in the exhaust temperature accompanying the change in the operating state of the internal combustion engine 1. Therefore, the temperature change of the exhaust purification catalyst 65 may be delayed with respect to the change in the operating state of the internal combustion engine 1. For example, when the operating state of the internal combustion engine 1 changes from a high load to a low load, the exhaust temperature changes with a relatively fast response from a high temperature to a low temperature as the operating state changes. The temperature is maintained at a high temperature for a while. Then, after a steady operation for a certain period in the low load operation state, the standard catalyst temperature is reached in the low load operation state. During the transition period of the temperature change of the exhaust purification catalyst 65, the actual catalyst temperature is higher than the standard catalyst temperature assumed in the current operation state (in this case, the low load operation state). . Therefore, it is considered that the amount of CO ₂ produced in the exhaust purification catalyst 65 is larger than the standard amount of CO ₂ produced in accordance with the operating state of the internal combustion engine 1. Therefore, when the target value of the EGR gas amount is immediately changed according to the change in the operating state of the internal combustion engine 1, EGR gas having a higher CO ₂ concentration than expected is supplied to the internal combustion engine 1, and the cylinder There is a possibility that the CO ₂ concentration in the internal gas becomes excessively higher than expected, leading to combustion failure such as misfire and deterioration of emission.

Therefore, in the EGR system according to the present embodiment,
(A) a catalyst transient condition in which the temperature (actual catalyst temperature) Tcat acquired by the catalyst temperature sensor 64 is higher than the standard catalyst temperature (standard catalyst temperature) Tst determined according to the operating state of the internal combustion engine 1;
(B) a catalyst activation condition in which the actual catalyst temperature Tcat is higher than a predetermined activation temperature Tcr of the exhaust purification catalyst 65;
When both of the above conditions are satisfied, the amount of EGR gas returned to the internal combustion engine 1 by the EGR device 61 is smaller than the standard EGR gas amount (standard EGR gas amount) determined according to the operating state of the internal combustion engine 1. It was corrected to.

Here, the standard catalyst temperature Tst is the temperature of the exhaust purification catalyst 65 when the internal combustion engine 1 is in steady operation, and is determined in advance by experiments, adaptation work, or the like as the temperature according to the operating state of the internal combustion engine 1. . When the catalyst transient condition is satisfied, that is, when the actual catalyst temperature Tcat> the standard catalyst temperature Tst is satisfied, a transient state in which the operation state of the internal combustion engine 1 changes from a high load to a low load as described above can be exemplified. The activation temperature Tcr is a lower limit value of the catalyst temperature required for the PM purification reaction to occur in the exhaust purification catalyst 65, and is obtained in advance by experiments or the like. When the actual catalyst temperature Tcat is lower than the activation temperature Tcr, that is, when the catalyst activation condition is not satisfied, the oxidation reaction does not occur even if PM or HC passes through the exhaust purification catalyst 65. Therefore, the CO ₂ concentration in the EGR gas does not become excessively higher than the standard CO ₂ concentration assumed from the operating state of the internal combustion engine 1. On the contrary, when the actual catalyst temperature Tcat is higher than the activation temperature Tcr, that is, when the catalyst activation condition is satisfied, the oxidation reaction occurs when PM or HC passes through the exhaust purification catalyst 65, and O ₂ in the EGR gas is consumed. At the same time, since CO ₂ is generated, the CO ₂ concentration in the EGR gas increases and may be higher than the standard CO ₂ concentration assumed from the operating state of the internal combustion engine 1.

According to the EGR system of the present embodiment having the above-described configuration, the CO in the EGR gas supplied to the internal combustion engine 1 when such catalyst transient conditions and catalyst activation conditions are satisfied (hereinafter referred to as catalyst transient conditions). _{Even when the 2} concentration is higher than the standard CO ₂ concentration according to the operating state of the internal combustion engine 1, the amount of EGR gas returned to the internal combustion engine is made smaller than the standard EGR gas amount. It is suppressed that the CO ₂ concentration in the internal gas becomes higher than expected. Therefore, it is possible to suppress the combustion failure and the deterioration of emission during a transition from a high load to a low load where the catalyst transient condition and the catalyst activation condition may be satisfied.

In the present embodiment, in order to reduce the EGR gas amount from the standard EGR gas amount, the opening degree of the EGR valve 60 is made larger than the standard opening degree (standard EGR valve opening degree) determined according to the operating state of the internal combustion engine 1. A means for correcting the opening on the closing side was adopted. Specifically, when the standard EGR valve opening degree Pegbse determined in advance according to the operation state of the internal combustion engine 1 and finally the target EGR valve opening degree Pegfin when the ECU 20 controls the EGR valve 60, The target EGR valve opening degree is set to Pegfin ← Pegbse + Pegcat during the catalyst transient when the catalyst transient condition and the catalyst activation condition are satisfied. Here, Pegcat is a correction amount for the opening degree of the EGR valve, and in the present embodiment, it is corrected to the opening degree on the closing side, so Pegcat <0. As a result, the amount of EGR gas flowing through the EGR passage 61 is reduced from the normal time, and the amount of EGR gas returned to the internal combustion engine 1 is reduced from the standard EGR gas amount. Therefore, when the catalyst transients catalyst transient conditions and catalytic activity condition is satisfied, in a case where the CO ₂ concentration in EGR gas becomes darker than normal also have CO ₂ concentration of the in-cylinder gas of an internal combustion engine 1 It is suppressed that it becomes too high.

Here, the standard EGR valve opening degree Pegbse, which is the EGR valve opening degree at the normal time, is determined as a map determined for each operation state (rotation speed and load) of the internal combustion engine 1 by the adaptation work as described above. Stored in ROM. In this embodiment, the correction amount Pegcat for the EGR valve opening at the time of catalyst transition is also determined in advance through experiments and adaptations that can maintain the CO ₂ concentration in the in-cylinder gas at an appropriate range during catalyst transition. It is calculated | required by work and is memorize | stored in ROM of ECU20 as a map or a function according to the driving | running state of the internal combustion engine 1. FIG.

  FIG. 2A is a diagram showing the relationship between the rotational speed of the internal combustion engine 1, the standard EGR valve opening degree Pegbse, the correction amount Pegcat, and the corrected EGR valve opening degree Pegbse + Pegcat. The horizontal axis represents the rotational speed of the internal combustion engine 1, and the vertical axis represents the EGR valve opening. The solid line represents the standard EGR valve opening degree Pegbse, and the broken line represents the corrected EGR valve opening degree Pegbse + Pegcat. FIG. 2B is a diagram showing the relationship between the load of the internal combustion engine 1, the standard EGR valve opening degree Pegbse, the correction amount Pegcat, and the corrected EGR valve opening degree Pegbse + Pegcat. The horizontal axis represents the load of the internal combustion engine 1, and the vertical axis represents the EGR valve opening. The solid line represents the standard EGR valve opening degree Pegbse, and the broken line represents the corrected EGR valve opening degree Pegbse + Pegcat. The final target EGR valve opening degree Pegfin is calculated from a contribution correlated with the rotation speed shown in the map of FIG. 2A and a contribution correlated with the load shown in the map of FIG. Is done.

As shown in FIG. 2, the map includes the relationship between the rotational speed and load of the internal combustion engine 1 and the correction amount Pegcat as a map, and depending on whether or not the catalyst transient condition and the catalyst activation condition are satisfied (solid line). And EGR control by switching between the map and the catalyst transient map (broken line), the EGR reduction control during the catalyst transient according to the present embodiment can be performed in consideration of the operating state of the internal combustion engine 1, It is possible to more reliably suppress the CO ₂ concentration in the in-cylinder gas of the internal combustion engine 1 from being excessively higher than the normal concentration.

  Hereinafter, the EGR reduction control during catalyst transition according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a routine of EGR reduction control at the time of catalyst transition according to the present embodiment. This routine is repeatedly executed by the ECU 20 every predetermined time while the internal combustion engine 1 is operating.

  First, in step S100, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, load, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the output values from the sensors described above.

  Next, in step S101, the ECU 20 determines whether or not a catalyst transient condition is satisfied. Specifically, the actual catalyst temperature Tcat is acquired based on the measured value by the catalyst temperature sensor 64, and the standard catalyst temperature Tst corresponding to the operating state of the internal combustion engine 1 acquired in step S100 is read, and Tcat> Tst is established. It is determined whether or not. If an affirmative determination is made in step S101, the ECU 20 proceeds to step S102. On the other hand, if a negative determination is made in step S101, the ECU 20 proceeds to step S104.

  In step S102, the ECU 20 determines whether the catalyst activation condition is satisfied. Specifically, the actual catalyst temperature Tcat acquired in step S101 is compared with the activation temperature Tcr of the exhaust purification catalyst 65 to determine whether or not Tcat> Tcr is satisfied. If an affirmative determination is made in step S102, the ECU 20 proceeds to step S103. On the other hand, if a negative determination is made in step S102, the ECU 20 proceeds to step S104.

  In step S103, the ECU 20 sets, as the target opening degree Pegfin of the EGR valve 60, the standard EGR valve opening degree Pegbse obtained in step S100 according to the operating state of the internal combustion engine 1 to Pegbse + Pegcat corrected by the correction amount Pegcat.

  In step S104, the ECU 20 sets the target opening degree Pegfin of the EGR valve 60 to the standard EGR valve opening degree Pegbse corresponding to the operating state of the internal combustion engine 1 acquired in step S100.

  In this embodiment, the ECU 20 that executes the above routine corresponds to the correcting means in the present invention.

  Next, a second embodiment of the present invention will be described. The schematic configuration of the internal combustion engine to which the EGR system according to the second embodiment is applied and its intake and exhaust systems is the same as that of the first embodiment. Below, description is abbreviate | omitted about the component same or equivalent to Example 1, and the name and code | symbol used in Example 1 are used.

  In Example 2, in order to reduce the amount of EGR gas returned to the internal combustion engine 1 by the EGR device 61 when the catalyst transient condition and the catalyst activation condition are satisfied, the target value of the EGR rate is set according to the operating state of the internal combustion engine 1. A means for correcting to a value lower than the standard EGR rate (standard EGR rate) determined by the

Specifically, when the standard EGR rate Egrbse determined in advance according to the operation state of the internal combustion engine 1 and finally the target EGR rate Egrtrg used for the EGR control by the ECU 20, the catalyst transient condition and the catalyst activation condition are set. At the time of catalyst transition where is satisfied, the target EGR rate is set to Egrtrg ← Egrbs + Egrcat. Here, Egrcat is a correction amount of the EGR rate, and in the case of the present embodiment, the EGR rate is corrected to a low value, so Egrcat <0. As a result, the EGR valve 60 opening, the throttle valve 62 opening, and the VN turbo are set so that the EGR rate is lower than the normal EGR rate during the catalyst transient when the catalyst transient condition and the catalyst activation condition are satisfied. In the case of the provided structure, the opening degree of the nozzle vane and the like are feedback-controlled. Accordingly, when the CO ₂ concentration in EGR gas becomes darker than normal also, it is prevented that the CO ₂ concentration of the in-cylinder gas of an internal combustion engine 1 becomes excessively high.

  Further, according to the present embodiment, the target EGR rate is corrected, so that some cause (for example, change in engine warm-up state, change in operation state, EGR passage 63, intake passage 3, exhaust state 4) Even when the flow characteristics of EGR gas or intake air change from the time of adaptation due to change, etc., the EGR gas amount is corrected accurately by the EGR gas amount metering means such as the EGR valve 60 and the throttle valve 62. be able to.

In this embodiment, the correction amount Egrcat for the EGR rate at the time of catalyst transition is determined based on the amount of CO ₂ generated in the exhaust purification catalyst 65 when the catalyst transient condition and the catalyst activation condition are satisfied. Specifically, the increase in CO ₂ in the in-cylinder gas of the internal combustion engine 1 caused by CO ₂ generated in the exhaust purification catalyst 65 at the time of catalyst transition when the catalyst transient condition and the catalyst activation condition are satisfied is offset, The correction amount Egrcat for the EGR rate is obtained so that the CO ₂ concentration in the in-cylinder gas matches the concentration at the normal time.

Here, the amount of CO ₂ generated in the exhaust purification catalyst 65 during the catalyst transition correlates with various factors. For example, it correlates with the chemical reaction rate of the oxidation reaction of PM or HC in the exhaust purification catalyst 65. The chemical reaction rate increases as the temperature difference ΔT = Tcat−Tst between the actual catalyst temperature Tcat and the standard catalyst temperature Tst increases. Therefore, the amount of CO ₂ generated in the exhaust purification catalyst 65 tends to increase as the temperature difference ΔT increases. Further, the amount of CO ₂ generated in the exhaust purification catalyst 65 correlates with the amount of PM or HC passing through the exhaust purification catalyst 65. When the flow rate of EGR gas passing through the exhaust purification catalyst 65 or the amount of PM or HC in the EGR gas increases, the amount of PM or HC used for the oxidation reaction in the exhaust purification catalyst 65 increases. There is a tendency for the amount of CO ₂ produced in the catalyst 65 to increase. Further, the amount of CO ₂ produced in the exhaust purification catalyst also correlates with the capacity of the exhaust purification catalyst 65. If the capacity of the exhaust purification catalyst 65 is large, the chance of PM oxidation reaction of HC in the exhaust purification catalyst 65 increases, so that the amount of CO ₂ generated in the exhaust purification catalyst 65 tends to increase.

In the present embodiment, the EGR rate correction amount Egrcat is determined in consideration of the correlation between the amount of CO ₂ produced in the exhaust purification catalyst 65 and various physical amounts. FIG. 4 is a diagram showing the relationship between the temperature difference ΔT between the actual catalyst temperature Tcat and the standard catalyst temperature Tst, and the EGR rate correction amount Egrcat. The horizontal axis of FIG. 4 represents the temperature difference ΔT, and the vertical axis represents the magnitude (absolute value) of the EGR rate correction amount Egrcat. Since Egrcat is a negative value, the EGR rate is corrected to a smaller value as the value increases in the vertical axis direction in FIG. Further, a solid line A in FIG. 4 indicates that the flow rate of EGR gas passing through the exhaust purification catalyst 65 is relatively large, the amount of PM or HC passing through the exhaust purification catalyst 65 is relatively large, or the exhaust purification catalyst 65. The relationship between the temperature difference ΔT and the magnitude of the correction amount Egrcat when the capacity (size) is relatively large is shown. 4 indicates that the flow rate of EGR gas passing through the exhaust purification catalyst 65 is relatively small, the amount of PM or HC passing through the exhaust purification catalyst 65 is relatively small, or the exhaust purification catalyst. This shows the relationship between the temperature difference ΔT and the correction amount Egrcat when the capacity (size) of 65 is relatively small.

As shown in FIG. 4, in this embodiment, the magnitude of the EGR rate correction amount Egrcat increases as the temperature difference ΔT increases, and the correction amount Egrcat increases as the flow rate of EGR gas passing through the exhaust purification catalyst 65 increases. The correction amount Egrcat increases as the amount of PM or HC passing through the exhaust purification catalyst 65 increases, and the correction amount Egrcat increases as the capacity of the exhaust purification catalyst 65 increases. As a result, it is possible to determine the correction amount of the EGR rate in consideration of the variation of the CO ₂ generation amount according to the state of the exhaust purification catalyst 65, so that the CO ₂ concentration in the EGR gas during the catalyst transition is higher than usual. Even in a situation where it is high, it is possible to more reliably suppress the CO ₂ concentration in the cylinder gas of the internal combustion engine 1 from becoming excessively higher than usual.

  As shown in FIG. 4, when the temperature difference ΔT is larger than a certain level, the magnitude of the EGR rate correction amount Egrcat is set to a constant value. This is because the amount of PM and HC in the EGR gas becomes very small when the temperature difference ΔT becomes larger than a certain level, and the oxidation reaction of PM and HC in the exhaust purification catalyst 65 does not take place.

  Hereinafter, the EGR reduction control during catalyst transition according to the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing a routine of EGR reduction control at the time of catalyst transition according to the present embodiment. This routine is repeatedly executed by the ECU 20 every predetermined time while the internal combustion engine 1 is operating.

  First, in step S200, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, load, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the output values from the sensors described above.

  Next, in step S201, the ECU 20 determines whether the catalyst transient condition is satisfied. Specifically, the actual catalyst temperature Tcat is acquired based on the measured value by the catalyst temperature sensor 64, and the standard catalyst temperature Tst corresponding to the operating state of the internal combustion engine 1 acquired in step S200 is read, and Tcat> Tst is established. It is determined whether or not. If an affirmative determination is made in step S201, the ECU 20 proceeds to step S202. On the other hand, if a negative determination is made in step S201, the ECU 20 proceeds to step S204.

In step S202, the ECU 20 determines whether the catalyst activation condition is satisfied. Specifically, the actual catalyst temperature Tcat acquired in step S201 is compared with the activation temperature Tcr of the exhaust purification catalyst 65, and it is determined whether or not Tcat> Tcr is satisfied. If an affirmative determination is made in step S202, the ECU 20 proceeds to step S203. On the other hand, if a negative determination is made in step S202, the ECU 20 proceeds to step S204.

  In step S203, the ECU 20 sets the standard EGR rate Egrbs according to the operation state of the internal combustion engine 1 acquired in step S200 to Egrbs + Egrcat corrected by the correction amount Egrcat as the target EGR rate Egrtrg.

  In step S204, the ECU 20 sets the target EGR rate Egrtrg to the standard EGR rate Egrbs according to the operating state of the internal combustion engine 1 acquired in step S200.

  In this embodiment, the ECU 20 that executes the above routine corresponds to the correcting means in the present invention. The correction amount of the EGR valve opening in the first embodiment may be set according to the state of the exhaust purification catalyst 65 (difference between the actual catalyst temperature and the standard catalyst temperature, etc.) as in this embodiment.

  Next, Embodiment 3 of the present invention will be described. FIG. 6 is a diagram showing a schematic configuration of an internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system. Detailed descriptions of the components common to the first embodiment are omitted, and the names and symbols used in the first embodiment are used.

  The intake ports (not shown) of the respective cylinders 2 gather in the intake manifold 17 and communicate with the intake passage 3. An HPL passage 41, which will be described later, is connected in the vicinity of the connection portion between the intake manifold 17 and the intake passage 3. A second throttle valve 9 that adjusts the amount of intake air flowing through the intake passage 3 is disposed in the intake passage 3 upstream from the connection location of the HPL passage 41. An intercooler 8 for cooling the intake air is disposed in the intake passage 3 upstream of the second throttle valve 9. A compressor 11 of a turbocharger 13 is disposed in the intake passage 3 upstream from the intercooler 8. An LPL passage 31 described later is connected to the intake passage 3 upstream of the compressor 11. A first throttle valve 6 that adjusts the amount of fresh air flowing into the intake passage 3 is disposed in the intake pipe 3 upstream of the connection point of the LPL passage 31. An air flow meter 7 that measures the amount of fresh air flowing into the intake passage 3 is provided in the intake passage 3 upstream of the first throttle valve 6. An air cleaner (not shown) is connected to the intake passage 3 further upstream. Hereinafter, the intake passage 3, the intake manifold 17, the intercooler 8, the compressor 11, and the like arranged in these may be collectively referred to as “intake system”.

  In the intake system configured as described above, the air from which dust or dust has been removed through the air cleaner flows into the intake passage 3. The air flowing into the intake passage 3 is pressurized after passing through the compressor 11 and then cooled through the intercooler 8 and is also introduced into the intake passage 3 by the LPL device 30 and the HPL device 40 described later. The gas flows into the intake manifold 17 while being mixed with gas, and is distributed to the intake port of each cylinder 2 through each branch pipe of the intake manifold 17. The intake air distributed to the intake port is drawn into the combustion chamber of each cylinder 2 when an intake valve (not shown) is opened.

The exhaust ports (not shown) of the respective cylinders 2 are gathered in the exhaust manifold 18 and communicate with the exhaust passage 4. The exhaust manifold 18 is provided with an exhaust temperature sensor 21 that measures the temperature of exhaust discharged from the internal combustion engine 1. An HPL passage 41 is connected in the vicinity of the connection portion between the exhaust manifold 18 and the exhaust passage 4. A turbine 12 of the turbocharger 13 is disposed in the exhaust passage 4 downstream from the connection location of the HPL passage 41. The turbocharger 13 is a variable capacity turbocharger including a nozzle vane 5 that makes the flow area of exhaust gas passing through the turbine 12 variable. An LPL catalyst 34 is disposed in the exhaust passage 4 downstream from the turbine 12. The LPL catalyst 34 has an oxidizing ability, and promotes an oxidation-reduction reaction between HC and PM in the inflowing exhaust gas and oxygen when the catalyst temperature is higher than a predetermined LPL catalyst activation temperature. Note that the LPL catalyst 34 may be configured to include other exhaust purification devices, such as a filter that collects PM in the exhaust, a NOx storage reduction catalyst, and the like. The LPL catalyst 34 is provided with an LPL catalyst temperature sensor 35 that measures the temperature of the LPL catalyst 34. An exhaust throttle valve 19 that adjusts the amount of exhaust flowing through the exhaust passage 4 is disposed in the exhaust passage 4 downstream of the LPL catalyst 34. An LPL passage 31 is connected to the exhaust passage 4 downstream from the exhaust throttle valve 19. Hereinafter, the exhaust passage 4, the exhaust manifold 18, and the turbine 12, the LPL catalyst 34, and the like arranged in these may be collectively referred to as “exhaust system”.

  In the exhaust system configured as described above, the burned gas burned in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust manifold 18 through the exhaust port and flows into the exhaust passage 4. Exhaust gas flowing into the exhaust passage 4 is driven to rotate the turbine 13 and then purified of harmful substances such as PM contained in the LPL catalyst 34 and released into the atmosphere. A part of the exhaust gas is guided to the intake passage 3 as EGR gas by the LPL device 30 and / or the HPL device 40 described later.

  The internal combustion engine 1 includes an HPL device 40 that guides a part of the exhaust gas flowing through the exhaust passage 4 upstream from the turbine 12 to the intake passage 3 downstream from the compressor 11 and returns the exhaust gas to the internal combustion engine 1. The HPL device 40 includes an HPL passage 41 that connects the exhaust passage 4 upstream of the turbine 12 and the intake passage 3 downstream of the second throttle valve 9, and intakes a part of the exhaust through the HPL passage 41. It flows into the passage 3. The exhaust gas returned to the internal combustion engine 1 by the HPL device 40 is hereinafter referred to as “HPL gas”. An HPL valve 42 that changes the flow area of the HPL passage 41 is disposed in the HPL passage 41. The amount of HPL gas flowing through the HPL passage 41 is adjusted by adjusting the opening degree of the HPL valve 42.

  The internal combustion engine 1 is provided with an LPL device 30 that guides a part of the exhaust gas flowing through the exhaust passage 4 downstream from the turbine 12 to the intake passage 3 upstream from the compressor 11 and returns the exhaust gas to the internal combustion engine 1. The LPL device 30 has an LPL passage 31 that connects the exhaust passage 4 downstream from the exhaust throttle valve 19 and the intake passage 3 upstream from the compressor 11, and a part of the exhaust is taken into the intake passage via the LPL passage 31. 3 is allowed to flow. The exhaust gas returned to the internal combustion engine 1 by the LPL device 30 is hereinafter referred to as “LPL gas”. An LPL cooler 33 for cooling the LPL gas is disposed in the middle of the LPL passage 31. An LPL valve 32 that changes the flow area of the LPL passage 31 is disposed in the LPL passage 31 on the downstream side (the intake passage 3 side) of the LPL cooler 33. By adjusting the opening degree of the LPL valve 32, the amount of LPL gas flowing through the LPL passage 31 is adjusted.

  When EGR is performed by the HPL device 40 and / or the LPL device 30 configured in this manner, an incombustible and endothermic inert gas component such as water or carbon dioxide is mixed in the intake air, so that the combustion chamber As a result, the combustion temperature of the fuel decreases, and the amount of NOx generated decreases.

The internal combustion engine 1 is provided with an electronic control unit (ECU) 20 that controls the internal combustion engine 1. The ECU 20 is a microcomputer provided with a CPU, a ROM, a RAM, an input / output port, and the like. In addition to the air flow meter 7 described above, the ECU 20 outputs a water temperature sensor 14 that outputs an electric signal corresponding to the temperature of the cooling water circulating in the water jacket of the internal combustion engine 1, and an electric signal corresponding to the operation amount of the accelerator pedal. A sensor such as an accelerator opening sensor 15 and a crank position sensor 16 that outputs a pulse signal each time the crankshaft of the internal combustion engine 1 rotates by a predetermined angle (for example, 10 °) are electrically connected. E
Input to CU20. The ECU 20 is electrically connected to devices such as the first throttle valve 6, the second throttle valve 9, the nozzle vane 5, the exhaust throttle valve 19, the LPL valve 32, and the HPL valve 42, and a control signal output from the ECU 20. Are used to control these devices.

  ECU20 acquires the driving | running state of the internal combustion engine 1, and a driver | operator's request | requirement based on the signal input from each said sensor. For example, the ECU 20 calculates the engine speed based on the signal input from the crank position sensor 16 and calculates the requested engine load based on the signal input from the accelerator opening sensor 15. Then, fuel injection and EGR are controlled by controlling each of the above devices in accordance with the calculated engine load and engine speed.

  Here, basic EGR control performed in the EGR system of the present embodiment will be described.

  As shown in FIG. 7, in the EGR system of this embodiment, EGR is performed by using or switching the HPL device 40 and the LPL device 30 in accordance with the operating state of the internal combustion engine 1. In FIG. 7, the horizontal axis represents the rotational speed of the internal combustion engine 1, and the vertical axis represents the load of the internal combustion engine 1. As shown in FIG. 7, in the EGR control of the present embodiment, when the operating state of the internal combustion engine 1 is low load and low rotation, EGR is performed mainly by the HPL device 40, and the HPL device increases as the engine load or the engine speed increases. The amount of EGR (HPL gas amount) performed by the engine 40 is decreased and the amount of EGR (LPL gas amount) performed by the LPL device 30 is increased. When the operating state of the internal combustion engine 1 is high load or high rotation side, the LPL EGR is performed by the device 30.

  In FIG. 7, an area indicated by “HPL” represents an operating state area where EGR is performed mainly by the HPL device 40. This region is hereinafter referred to as an HPL region. An area indicated by “LPL” represents an operating state area where EGR is performed mainly by the LPL device 30. This region is hereinafter referred to as an LPL region. A medium load or medium rotation region represented by “MIX” between the HPL region and the LPL region represents a region where EGR is performed by using the HPL device 40 and the LPL device 30 together. This area is hereinafter referred to as a MIX area. As described above, in the MIX region, the control is performed to decrease the amount of HPL gas and increase the amount of LPL gas as the operation state becomes higher or higher. In other words, the HPL gas ratio (HPL ratio) in the total EGR gas is lowered and the LPL gas ratio (LPL ratio) in the total EGR gas is increased as the load increases or the rotation speed increases.

  The control target values of the HPL gas amount and the LPL gas amount corresponding to each operation state are the NOx generation amount, smoke generation amount, HC generation amount, fuel consumption rate, etc. when the internal combustion engine 1 is in steady operation in the operation state. Various characteristics relating to the engine performance and the exhaust performance are determined in advance by an adaptation operation so as to achieve a predetermined regulation value and a desired target value, and are stored in the ROM of the ECU 20. Based on the acquired engine operating state, the ECU 20 reads the control target value of the HPL gas amount and the LPL gas amount corresponding to the operating state from the ROM, and the amount of exhaust gas returned to the combustion chamber by the HPL device 40 and the LPL device 30 is determined. The opening degree of the HPL valve 42, the LPL valve 32, the first throttle valve 6, the second throttle valve 9, the exhaust throttle valve 19, the nozzle vane 5, etc. is controlled so that the respective control target values are obtained.

In the EGR system of the present embodiment, since the LPL catalyst 34 is disposed on the LPL gas flow path, a problem similar to that described in the first embodiment occurs at the time of transition when the operating state of the internal combustion engine 1 changes. there's a possibility that. That is, the time constant related to the temperature change of the LPL catalyst 34 accompanying the change in the operating state of the internal combustion engine 1 due to the heat capacity of the LPL catalyst 34 is the time constant related to the change in the exhaust temperature accompanying the change of the operating state of the internal combustion engine 1. There is a tendency to be longer. Therefore, the temperature change of the LPL catalyst 34 may be delayed with respect to the change in the operating state of the internal combustion engine 1. For example, during a transition in which the operation state of the internal combustion engine 1 changes from a high load to a low load, the actual temperature of the LPL catalyst 34 is the standard LPL catalyst 34 temperature assumed in the current operation state of the internal combustion engine 1. There may be a higher transition period. In this case, the amount of CO ₂ produced in the LPL catalyst 34 is considered greater than the amount of standard CO ₂ which is assumed in the current operating state of the internal combustion engine 1. Therefore, when the target value of the LPL gas amount is immediately changed according to the operating state of the internal combustion engine 1, the LPL gas having a higher CO ₂ concentration than expected is supplied to the internal combustion engine 1, and the in-cylinder gas There is a risk that the CO ₂ concentration in the inside becomes excessively higher than expected, leading to poor combustion and worsening of emissions.

Here, as described above, the amount of CO ₂ generated in the exhaust purification catalyst is correlated with the flow rate of the exhaust gas that passes through the exhaust purification catalyst, and the exhaust gas purification increases as the amount of exhaust gas that passes through the exhaust purification catalyst increases. There is a tendency for the amount of CO ₂ produced in the catalyst to increase. In view of this characteristic, in the EGR system according to the present embodiment,
(A) The temperature (actual LPL catalyst temperature) TcatL acquired by the LPL catalyst temperature sensor 35 is higher than the standard LPL catalyst 34 temperature (standard LPL catalyst temperature) TstL determined according to the operating state of the internal combustion engine 1. LPL catalyst transient conditions;
(B) LPL catalyst activation conditions in which the actual LPL catalyst temperature TcatL is higher than the activation temperature TcrL of the LPL catalyst 34;
When both of these hold true, the ratio of HPL gas in all EGR gases is corrected to a value higher than a standard ratio (standard HPL ratio) determined according to the operating state of the internal combustion engine 1.

Here, the standard LPL catalyst temperature TstL is the temperature of the LPL catalyst 34 when the internal combustion engine 1 is in steady operation, and is determined in advance by experiments and fitting operations as a temperature according to the operating state of the internal combustion engine 1. When the LPL catalyst transient condition is satisfied, that is, when the actual LPL catalyst temperature TcatL> the standard LPL catalyst temperature TstL, the operating state of the internal combustion engine 1 changes from a high load to a low load as described in the first embodiment. A transient state can be illustrated. The activation temperature TcrL is a lower limit value of the temperature of the LPL catalyst 34 that is necessary for the PM or HC oxidation reaction to occur in the LPL catalyst 34, and is obtained in advance through experiments or the like. When the actual LPL catalyst temperature TcatL is lower than the activation temperature TcrL, that is, when the LPL catalyst activation condition is not satisfied, the oxidation reaction does not occur even if PM or HC passes through the LPL catalyst 34. Therefore, the CO ₂ concentration in the LPL gas does not become excessively higher than the standard CO ₂ concentration assumed from the operating state of the internal combustion engine 1. Conversely, when the actual LPL catalyst temperature TcatL is higher than the activation temperature TcrL, that is, when the LPL catalyst activation condition is satisfied, an oxidation reaction occurs when PM or HC passes through the LPL catalyst 34, and O ₂ in the LPL gas is reduced. Since CO ₂ is generated as it is consumed, the CO ₂ concentration in the LPL gas increases and may be higher than the standard CO ₂ concentration assumed from the operating state of the internal combustion engine 1.

According to the EGR system of the present embodiment having the above-described configuration, when the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied, the ratio of the HPL gas in the total EGR gas is increased. The ratio of LPL gas becomes low. Therefore, the amount of LPL gas passing through the LPL catalyst 34 is reduced as compared with the normal time when the LPL catalyst transient condition or the LPL catalyst activation condition is not satisfied. Therefore, the amount of CO ₂ generated in the LPL catalyst 34 is reduced, and the CO ₂ concentration in the EGR gas supplied to the internal combustion engine 1 can be suppressed from becoming excessively high.

Here, the correction amount of the HPL ratio increase correction (or the LPL ratio decrease correction) during the LPL catalyst transition depends on the operating state of the internal combustion engine 1 like the correction amount in the EGR reduction control according to the first embodiment. The map may be obtained by conforming work or experiment, or the state of the LPL catalyst 34 (temperature difference between the actual LPL catalyst temperature and the standard LPL catalyst temperature, the flow rate of the LPL gas passing through the LPL catalyst 34, the LPL catalyst 34 It is also possible to estimate the amount of CO ₂ produced in the LPL catalyst 34 based on the amount of PM or HC passing through, the capacity of the LPL catalyst 34, etc., and to calculate the amount in consideration of this CO ₂ production amount.

According to this embodiment, since the amount of EGR gas (LPL gas amount) in the LPL-EGR path that may change the CO ₂ concentration in the exhaust gas due to the passage of the exhaust gas is reduced, the exhaust purification catalyst. The amount of CO ₂ generated in can be reduced. Therefore, as in the first embodiment, although it is necessary to reduce the total EGR gas amount, HPL gas amount, or LPL gas amount in consideration of the amount of CO ₂ generated in the LPL catalyst 34, the magnitude of the correction amount is large. Can be reduced. Thereby, the estimation calculation of the CO ₂ generation amount accompanying the decrease correction of the total EGR gas amount, the HPL gas amount, or the LPL gas amount, the HPL valve 42, the LPL valve 32, the first throttle valve 6, the second throttle valve 9, the nozzle vane. 5. It is possible to suppress the deterioration of emissions caused by errors and variations occurring in the opening degree control of the exhaust throttle valve 19 and the like.

  Hereinafter, EGR reduction control during catalyst transition according to the present embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing a routine of EGR reduction control at the time of catalyst transition according to the present embodiment. This routine is repeatedly executed by the ECU 20 every predetermined time while the internal combustion engine 1 is operating.

  First, in step S300, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, load, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the output values from the sensors described above.

  Next, in step S301, the ECU 20 determines whether or not the LPL catalyst transient condition is satisfied. Specifically, the actual LPL catalyst temperature TcatL is acquired based on the measured value by the LPL catalyst temperature sensor 35, and the standard LPL catalyst temperature TstL corresponding to the operating state of the internal combustion engine 1 acquired in step S300 is read, and TcatL> It is determined whether TstL is established. If an affirmative determination is made in step S301, the ECU 20 proceeds to step S302. On the other hand, if a negative determination is made in step S301, the ECU 20 proceeds to step S304.

  In step S302, the ECU 20 determines whether the LPL catalyst activation condition is satisfied. Specifically, the actual LPL catalyst temperature TcatL acquired in step S301 is compared with the activation temperature TcrL of the LPL catalyst 34 to determine whether TcatL> TcrL is satisfied. If an affirmative determination is made in step S302, the ECU 20 proceeds to step S303. On the other hand, if a negative determination is made in step S302, the ECU 20 proceeds to step S304.

  In step S303, the ECU 20 corrects the HPL ratio to a value higher than the standard HPL ratio corresponding to the operating state of the internal combustion engine 1 acquired in step S300, and responds to the operating state of the internal combustion engine 1 acquired in step S300. Correct to a value lower than the standard LPL ratio.

  In step S304, the ECU 20 performs normal control. That is, the HPL ratio is set to the standard HPL ratio, and the LPL ratio is set to the standard LPL ratio.

Next, a fourth embodiment of the present invention will be described. FIG. 9 is a diagram showing a schematic configuration of an internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system. The difference between the configuration of this embodiment and the configuration of Embodiment 3 is that, in this embodiment, in addition to the configuration of Embodiment 3, an HPL catalyst 44 is further disposed in the middle of the HPL passage 41. The HPL catalyst 44 has an oxidizing ability, and promotes a redox reaction between HC and PM in the inflowing exhaust gas and oxygen when the catalyst temperature is higher than a predetermined HPL catalyst activation temperature. The HPL catalyst 44 may include other exhaust purification devices, such as a filter that collects PM in the exhaust, a NOx storage reduction catalyst, and the like. The HPL catalyst 44 is provided with an HPL catalyst temperature sensor 45 that measures the temperature of the HPL catalyst 44.

In the EGR system of the present embodiment, since the HPL catalyst 44 is further arranged on the HPL gas flow path in addition to the configuration of the third embodiment, the same problem as described for the LPL catalyst 34 in the third embodiment is caused. It may occur in the HPL catalyst 44. That is, the time constant related to the temperature change of the HPL catalyst 44 accompanying the change in the operating state of the internal combustion engine 1 due to the heat capacity of the HPL catalyst 44 is the time constant related to the change in the exhaust temperature accompanying the change of the operating state of the internal combustion engine 1. There is a tendency to be longer. Therefore, the temperature change of the HPL catalyst 44 may be delayed with respect to the change in the operating state of the internal combustion engine 1. For example, during a transition in which the operating state of the internal combustion engine 1 changes from a high load to a low load, the actual temperature of the HPL catalyst 44 is the standard HPL catalyst 44 temperature assumed in the current operating state of the internal combustion engine 1. There may be a higher transition period. In this case, the amount of CO ₂ produced in HPL catalyst 44 is considered greater than the amount of standard CO ₂ which is assumed in the current operating state of the internal combustion engine 1. Therefore, when the target value of the HPL gas amount is immediately changed according to the operating state of the internal combustion engine 1, the LPL gas having a higher CO ₂ concentration than expected is supplied to the internal combustion engine 1, and the in-cylinder gas There is a risk that the CO ₂ concentration in the inside becomes excessively higher than expected, leading to poor combustion and worsening of emissions.

As described above, the amount of CO ₂ produced in the exhaust purification catalyst is correlated with the flow rate of exhaust gas passing through the exhaust purification catalyst, and the amount of exhaust passing through the exhaust purification catalyst increases as the amount of exhaust passing through the exhaust purification catalyst increases. The tendency for the amount of CO ₂ to increase to be increased is the tendency to be observed at any time in the HPL catalyst 44 as in the LPL catalyst 34. Therefore, as in the case of Example 3,
(C) The temperature (actual HPL catalyst temperature) TcatH acquired by the HPL catalyst temperature sensor 45 is higher than the temperature (standard HPL catalyst temperature) TstH of the standard HPL catalyst 44 determined according to the operating state of the internal combustion engine 1. HPL catalyst transient conditions;
(D) HPL catalyst activation conditions in which the actual HPL catalyst temperature TcatH is higher than the activation temperature TcrH of the HPL catalyst 44;
If both of the above hold, it is preferable to correct the ratio of the LPL gas in all the EGR gases to a value higher than a standard ratio (standard LPL ratio) determined according to the operating state of the internal combustion engine 1.

Here, the standard HPL catalyst temperature TstH is the temperature of the HPL catalyst 44 when the internal combustion engine 1 is in steady operation, and is determined in advance by experiments and adaptation operations as a temperature according to the operating state of the internal combustion engine 1. When the HPL catalyst transient condition is satisfied, that is, when the actual HPL catalyst temperature TcatH> the standard HPL catalyst temperature TstH is satisfied, as described in the first embodiment, the operation state of the internal combustion engine 1 changes from a high load to a low load. A transient state can be illustrated. The activation temperature TcrH is a reduction value of the temperature of the HPL catalyst 44 necessary for the PM or HC oxidation reaction to occur in the HPL catalyst 44, and is obtained in advance by experiments or the like. When the actual HPL catalyst temperature TcatH is lower than the activation temperature TcrH, that is, when the HPL catalyst activation condition is not satisfied, the oxidation reaction does not occur even if PM or HC passes through the HPL catalyst 44. Therefore, the CO ₂ concentration in the HPL gas does not become excessively higher than the standard CO ₂ concentration assumed from the operating state of the internal combustion engine 1. On the contrary, when the actual HPL catalyst temperature TcatH is higher than the activation temperature TcrH, that is, when the HPL catalyst activation condition is satisfied, an oxidation reaction occurs when PM or HC passes through the HPL catalyst 44, and O ₂ in the HPL gas is reduced. Since CO ₂ is generated as it is consumed, the CO ₂ concentration in the HPL gas increases and may be higher than the standard CO ₂ concentration assumed from the operating state of the internal combustion engine 1.

Further, when the exhaust purification catalyst is arranged in both the HPL gas flow path and the LPL gas flow path as in the configuration of the present embodiment, (b) the LPL catalyst transient condition described in the third embodiment. And (b) the LPL catalyst activation condition, and (c) the HPL catalyst transient condition and (d) the HPL catalyst activation condition are all satisfied. In such a case, both the CO ₂ concentration in the HPL gas and the CO ₂ concentration in the LPL gas may be higher than the standard CO ₂ concentration assumed from the operating state of the internal combustion engine 1.

In such a case, in the EGR system according to the present embodiment, the ratio of EGR gas passing through the catalyst with the smaller amount of CO ₂ produced by the LPL catalyst 34 and the HPL catalyst 44 is determined as the operation of the internal combustion engine 1. Higher than the standard ratio determined according to the situation. That is, when the LPL catalyst transient condition, the LPL catalyst activation condition, the HPL catalyst transient condition, and the HPL catalyst activation condition are satisfied,
(A) When the amount of CO ₂ generated in the LPL catalyst 34 (DCO2L) is larger than the amount of CO ₂ generated in the HPL catalyst 44 (DCO2H), the ratio of the HPL gas in the total EGR gas is set to the internal combustion engine 1. Higher than the standard ratio (standard HPL ratio) determined according to the operating state of
(B) When the amount of CO ₂ produced in the LPL catalyst 34 (DCO2L) is less than or equal to the amount of CO ₂ produced in the HPL catalyst 44 (DCO2H), the ratio of the LPL gas in the total EGR gas is set to the internal combustion engine 1 Higher than the standard ratio (standard LPL ratio) determined according to the operating state.

By doing so, the amount of EGR gas in the EGR path, which may generate more CO ₂ when exhaust passes, is reduced, so that the total amount of CO ₂ generated in the LPL catalyst 34 and the HPL catalyst 44 is reduced. Can be reduced. Therefore, as in the first embodiment, it is necessary to correct the total EGR gas amount, the LPL gas amount, or the HPL gas amount in consideration of the amount of CO ₂ generated in the LPL catalyst 34 and the HPL catalyst 44. The magnitude of the quantity can be reduced. Thereby, the estimation calculation of the CO ₂ generation amount accompanying the decrease correction of the total EGR gas amount, the LPL gas amount, or the HPL gas amount, the HPL valve 42, the LPL valve 32, the first throttle valve 6, the second throttle valve 9, the nozzle vane. 5. It is possible to suppress the deterioration of emissions caused by errors and variations occurring in the opening degree control of the exhaust throttle valve 19 and the like.

Here, and amount of CO ₂ generated in the LPL catalyst 34, the amount of CO ₂ generated in HPL catalyst 44 has a correlation with the amount of CO ₂ that occurs in the exhaust purification catalyst as described in Example 2 It can be estimated based on various physical quantities. For example, the temperature difference ΔTH between the actual HPL catalyst temperature TcatH and the standard HPL catalyst temperature TstH, the flow rate of HPL gas passing through the HPL catalyst 44, the amount of PM and HC passing through the HPL catalyst 44, the capacity and material of the HPL catalyst 44, etc. And the amount of CO ₂ generated in the HPL catalyst 44 are obtained in advance by experiments or the like, stored in the ROM of the ECU 20 in the form of a map or function, and based on this, the CO generated in the HPL catalyst 44 is stored. The quantity of ₂ can be estimated. The same applies to the LPL catalyst 34.

  Hereinafter, EGR reduction control during catalyst transition according to the present embodiment will be described with reference to FIG. FIG. 10 is a flowchart showing a routine of EGR reduction control at the time of catalyst transition according to the present embodiment. This routine is repeatedly executed by the ECU 20 every predetermined time while the internal combustion engine 1 is operating.

  First, in step S400, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, load, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the output values from the sensors described above.

Next, in step S401, the ECU 20 determines whether or not the LPL catalyst transient condition is satisfied. Specifically, the actual LPL catalyst temperature TcatL is acquired based on the measured value by the LPL catalyst temperature sensor 35, and the standard LPL catalyst temperature TstL corresponding to the operating state of the internal combustion engine 1 acquired in step S400 is read, and TcatL> It is determined whether TstL is established. If an affirmative determination is made in step S401, the ECU 20 proceeds to step S402. On the other hand, if a negative determination is made in step S401, the ECU 20 once ends the execution of this routine.

  In step S402, the ECU 20 determines whether or not the LPL catalyst activation condition is satisfied. Specifically, the actual LPL catalyst temperature TcatL acquired in step S401 is compared with the activation temperature TcrL of the LPL catalyst 34 to determine whether TcatL> TcrL is satisfied. If an affirmative determination is made in step S402, the ECU 20 proceeds to step S403. On the other hand, if a negative determination is made in step S402, the ECU 20 once ends the execution of this routine.

  In step S403, the ECU 20 determines whether an HPL catalyst transient condition is satisfied. Specifically, the actual HPL catalyst temperature TcatH is acquired based on the measured value by the HPL catalyst temperature sensor 45, and the standard HPL catalyst temperature TstH corresponding to the operating state of the internal combustion engine 1 acquired in step S400 is read, and TcatH> It is determined whether TstH is established. If an affirmative determination is made in step S403, the ECU 20 proceeds to step S404. On the other hand, if a negative determination is made in step S403, the ECU 20 once ends the execution of this routine.

  In step S404, the ECU 20 determines whether the HPL catalyst activation condition is satisfied. Specifically, the actual HPL catalyst temperature TcatH acquired in step S403 is compared with the activation temperature TcrH of the HPL catalyst 44 to determine whether TcatH> TcrH is satisfied. If an affirmative determination is made in step S404, the ECU 20 proceeds to step S405. On the other hand, if a negative determination is made in step S404, the ECU 20 once ends the execution of this routine.

In step S405, ECU 20 estimates the amount of produced CO ₂ DCO2H in HPL catalyst 44, and a CO ₂ generation amount DCO2L in LPL catalytic 34.

In step S406, the ECU 20 determines whether or not the CO ₂ generation amount DCO2L in the LPL catalyst 34 estimated in step S405 is larger than the CO ₂ generation amount DCO2H in the HPL catalyst 44. If an affirmative determination is made in step S406, the ECU 20 proceeds to step S407. On the other hand, if a negative determination is made in step S406, the ECU 20 proceeds to step S408.

  In step S407, the ECU 20 increases the ratio of the HPL gas in all the EGR gases to be higher than the standard HPL ratio, and lowers the ratio of the LPL gas to be lower than the standard LPL ratio.

  In step S408, the ECU 20 lowers the ratio of the HPL gas in all the EGR gases from the standard HPL ratio, and increases the ratio of the LPL gas from the standard LPL ratio.

In the present embodiment, the ECU 20 that executes step S405 corresponds to the LPLCO ₂ generation amount estimation means and the HPLCO ₂ generation amount estimation means in the present invention.

Next, a fifth embodiment of the present invention will be described. Since the schematic configuration of the internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system is the same as that of the third embodiment, the detailed description is omitted and the names and symbols used in the third embodiment are used.

In the EGR system according to the present embodiment, when the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied for the LPL catalyst 34, the temperature of the LPL catalyst 34 is increased by lowering the temperature of the LPL catalyst 34 or more. By suppressing this, the situation where the LPL catalyst transient condition or the LPL catalyst activation condition is not satisfied is realized as early as possible. Specifically, LPL catalyst transient conditions and LPL catalyst activation conditions are satisfied, and an LPL exhaust low temperature condition in which the exhaust temperature Tex acquired based on the output value from the exhaust temperature sensor 21 is lower than the actual LPL catalyst temperature TcatL is satisfied. In this case, the amount of exhaust gas passing through the LPL catalyst 34 is increased from a standard amount (standard LPL catalyst passing gas amount) determined according to the operating state of the internal combustion engine 1. As a result, heat exchange is actively performed between the low-temperature exhaust gas and the high-temperature LPL catalyst 34, and the temperature of the LPL catalyst 34 can be quickly brought close to the standard LPL catalyst temperature. As described above, the amount of CO ₂ generated in the LPL catalyst 34 tends to increase as the temperature difference between the actual LPL catalyst temperature and the standard LPL catalyst temperature increases. If the difference from the LPL catalyst temperature is quickly reduced, the amount of CO ₂ produced in the LPL catalyst 34 can be quickly reduced. Therefore, it is possible to suppress an excessive increase in the amount of CO ₂ in the in-cylinder gas of the internal combustion engine 1.

On the other hand, when the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied, and the LPL exhaust gas high temperature condition in which the exhaust temperature Tex acquired based on the output value from the exhaust temperature sensor 21 is higher than the actual LPL catalyst temperature TcatL is satisfied. Has reduced the amount of exhaust gas passing through the LPL catalyst 34 from the standard LPL passage gas amount. Thereby, it is possible to prevent the LPL catalyst 34 from being further heated by the high temperature exhaust gas. Therefore, an increase in the amount of CO ₂ generated in the LPL catalyst 34 can be suppressed, and an excessive increase in the CO ₂ concentration in the in-cylinder gas of the internal combustion engine 1 can be suppressed.

  Thus, according to the present embodiment, the LPL catalyst 34 can be shortened or suppressed from excessively extending the period in which the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied. It is possible to suppress poor combustion and worsening of emissions.

  When the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied, and the LPL exhaust gas high temperature condition in which the exhaust temperature Tex acquired based on the output value from the exhaust temperature sensor 21 is higher than the actual LPL catalyst temperature TcatL is satisfied. The intake air amount may be larger than a standard intake air amount (standard intake air amount) determined according to the operating state of the internal combustion engine 1. In this case, since the amount of gas supplied into the cylinder increases under the condition that the amount of heat input (fuel injection amount) is constant, the temperature of the exhaust gas decreases. Therefore, the state of the internal combustion engine 1 can be promptly shifted to a state where the LPL exhaust high temperature condition is not satisfied, and an increase in the temperature of the LPL catalyst 34 can be suppressed. As a means for increasing the intake air amount, for example, a means for correcting the opening of the first throttle valve 6 to the opening on the open side or correcting the opening of the nozzle vane 5 to the opening on the closing side can be employed. .

Further, in this embodiment, by controlling the heat exchange between the LPL catalyst 34 and the exhaust gas passing through the LPL catalyst 34, the period in which the LPL catalyst transient condition and the LPL catalyst activation condition are satisfied is shortened or the period is prevented from being lengthened. However, this EGR control can be similarly applied to the HPL catalyst 44. That is, when the HPL catalyst transient condition and the HPL catalyst activation condition are satisfied, and the HPL exhaust low temperature condition in which the exhaust temperature Tex acquired by the exhaust temperature sensor 21 is lower than the actual HPL catalyst temperature TcatH is satisfied, the HPL catalyst 44 is satisfied. By increasing the amount of exhaust gas passing through the standard amount (standard HPL catalyst passage gas amount) determined according to the operating state of the internal combustion engine 1, the temperature drop of the HPL catalyst 44 can be promoted. As a result, the actual HPL catalyst temperature can be quickly brought close to the standard HPL catalyst temperature. Further, when the HPL catalyst transient condition and the HPL catalyst activation condition are satisfied, and the HPL exhaust high temperature condition where the exhaust temperature Tex is higher than the actual HPL catalyst temperature TcatH is satisfied, the amount of exhaust gas passing through the HPL catalyst 44 is standardized. By making the amount less than the amount of gas passing through the HPL catalyst or making the amount of intake air larger than the standard amount of intake air, the temperature rise of the HPL catalyst 44 can be often improved. Thereby, it can suppress that the period when HPL catalyst transient conditions and HPL catalyst activation conditions are satisfied becomes long.

  Hereinafter, EGR control according to the present embodiment will be described with reference to FIG. FIG. 11 is a flowchart showing an EGR control routine according to the present embodiment. This routine is repeatedly executed by the ECU 20 every predetermined time while the internal combustion engine 1 is operating.

  First, in step S500, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, load, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the output values from the sensors described above.

  Next, in step S501, the ECU 20 acquires the exhaust gas temperature Tex. Specifically, the exhaust temperature sensor 21 measures the temperature of the exhaust gas in the exhaust manifold 18.

  In step S502, the ECU 20 determines whether or not the LPL catalyst transient condition is satisfied. Specifically, the actual LPL catalyst temperature TcatL is acquired based on the measured value by the LPL catalyst temperature sensor 35, and the standard LPL catalyst temperature TstL corresponding to the operating state of the internal combustion engine 1 acquired in step S500 is read, and TcatL> It is determined whether TstL is established. If an affirmative determination is made in step S502, the ECU 20 proceeds to step S503. On the other hand, if a negative determination is made in step S502, the ECU 20 once ends the execution of this routine.

  In step S503, the ECU 20 determines whether or not the LPL catalyst activation condition is satisfied. Specifically, the actual LPL catalyst temperature TcatL acquired in step S502 is compared with the activation temperature TcrL of the LPL catalyst 34 to determine whether TcatL> TcrL is satisfied. If an affirmative determination is made in step S503, the ECU 20 proceeds to step S504. On the other hand, if a negative determination is made in step S503, the ECU 20 once ends the execution of this routine.

  In step S504, the ECU 20 determines whether or not the LPL exhaust low temperature condition is satisfied. Specifically, the actual LPL catalyst temperature TcatL acquired in step S502 is compared with the exhaust gas temperature Tex acquired in step S501, and it is determined whether or not TcatL> Tex is satisfied. If an affirmative determination is made in step S504, the ECU 20 proceeds to step S505. On the other hand, if a negative determination is made in step S504, the ECU 20 proceeds to step S506.

  In step S505, the ECU 20 performs correction to increase the LPL catalyst passage gas amount from the standard LPL catalyst passage gas amount.

  In step S506, the ECU 20 performs correction to reduce the LPL catalyst passage gas amount from the standard LPL catalyst passage gas amount.

  In the above routine, in step S506, correction for increasing the intake air amount from the standard intake air amount may be performed. Further, as described above, the EGR control can be similarly applied to the HPL catalyst. In this embodiment, the ECU 20 that executes step S501 corresponds to the exhaust gas temperature acquisition means in the present invention.

  Each of the above-described embodiments is an example for explaining the present invention, and various modifications can be made to the above-described embodiments without departing from the spirit of the present invention. Moreover, it is also possible to implement the present invention by combining the above embodiments.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an EGR system according to a first embodiment is applied, and an intake system and an exhaust system thereof. FIG. 2A is a diagram showing the relationship between the rotational speed of the internal combustion engine 1 in the EGR reduction control of the first embodiment, the standard EGR valve opening, the correction amount, and the corrected EGR valve opening. FIG. 2B is a diagram illustrating a relationship between the load of the internal combustion engine 1 in the EGR reduction control of the first embodiment, the standard EGR valve opening, the correction amount, and the corrected EGR valve opening. 4 is a flowchart illustrating a routine of EGR reduction control according to the first embodiment. It is a figure which shows the relationship between the temperature difference of the actual catalyst temperature and standard catalyst temperature in EGR reduction | decrease control of Example 2, and the correction amount of an EGR rate. 7 is a flowchart illustrating a routine for EGR reduction control according to a second embodiment. It is a figure which shows schematic structure of the internal combustion engine to which the EGR system of Example 3 is applied, its intake system, and an exhaust system. It is a figure which shows the basic EGR control map in the EGR system of Example 3. FIG. 12 is a flowchart illustrating a routine for EGR reduction control according to a third embodiment. FIG. 6 is a diagram showing a schematic configuration of an internal combustion engine to which an EGR system of a fourth embodiment is applied and its intake system and exhaust system. 12 is a flowchart illustrating a routine for EGR reduction control according to a fourth embodiment. 10 is a flowchart illustrating a routine for EGR control according to a fifth embodiment.

Explanation of symbols

1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Nozzle vane 6 First throttle valve 7 Air flow meter 8 Intercooler 9 Second throttle valve 10 LPL catalyst 11 Compressor 12 Turbine 13 Turbocharger 14 Water temperature sensor 15 Accelerator opening sensor 16 Crank position Sensor 17 Intake manifold 18 Exhaust manifold 19 Exhaust throttle valve 20 ECU
21 Exhaust temperature sensor 30 LPL device 31 LPL passage 32 LPL valve 33 LPL cooler 35 LPL catalyst temperature sensor 40 HPL device 41 HPL passage 42 HPL valve 44 HPL catalyst 45 HPL catalyst temperature sensor 60 EGR valve 61 EGR device 62 Throttle valve 63 EGR passage 64 Catalyst temperature sensor 65 Exhaust gas purification catalyst

Claims (12)

EGR means for returning a part of the exhaust gas as EGR gas to the internal combustion engine through an EGR passage connecting the exhaust passage and the intake passage of the internal combustion engine;
An exhaust purification catalyst that is provided on the flow path of the EGR gas that is returned to the internal combustion engine by the EGR means and has an oxidizing ability;
Catalyst temperature acquisition means for acquiring the temperature of the exhaust purification catalyst;
(A) A catalyst transient higher than the temperature of the exhaust purification catalyst assumed when the internal combustion engine in which the temperature acquired by the catalyst temperature acquisition means is determined in accordance with the operating state of the internal combustion engine is steadily operated for a certain period in that operating state. Conditions and
(B) a catalyst activation condition in which the temperature acquired by the catalyst temperature acquisition means is higher than a predetermined activation temperature of the exhaust purification catalyst;
When the following holds, the correction means for correcting the amount of EGR gas returned to the internal combustion engine by the EGR means to an amount smaller than a predetermined amount of EGR gas according to the operating state of the internal combustion engine;
An EGR system for an internal combustion engine comprising: In claim 1,
An EGR valve that is provided in the EGR passage and adjusts the amount of EGR gas flowing through the EGR passage;
The correction means corrects the opening degree of the EGR valve from a predetermined opening degree according to an operating state of the internal combustion engine to a closing side opening degree when the catalyst transient condition and the catalyst activation condition are satisfied. EGR system. In claim 1,
The correction means corrects the EGR rate of the intake air of the internal combustion engine to a value lower than a predetermined EGR rate according to the operating state of the internal combustion engine when the catalyst transient condition and the catalyst activation condition are satisfied. . In any one of Claims 1-3,
An EGR system for an internal combustion engine that determines a correction amount by the correction means based on an amount of CO ₂ generated in the exhaust purification catalyst. In claim 4,
An EGR system for an internal combustion engine that estimates an amount of CO ₂ produced in the exhaust purification catalyst based on an operating state of the internal combustion engine. In claim 4,
The amount of CO ₂ produced in the exhaust purification catalyst,
The difference between the temperature acquired by the catalyst temperature acquisition means and the temperature of the exhaust purification catalyst assumed when the internal combustion engine determined according to the operation state of the internal combustion engine is in a steady operation for a certain period in the operation state ;
The flow rate of EGR gas passing through the exhaust purification catalyst,
The amount of PM in the EGR gas passing through the exhaust purification catalyst,
The amount of HC in the EGR gas passing through the exhaust purification catalyst,
The volume of the exhaust purification catalyst;
An EGR system for an internal combustion engine that estimates based on at least one of the following. A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
HPL means for returning a part of the exhaust gas as HPL gas to the internal combustion engine via an HPL passage connecting an exhaust passage upstream from the turbine and an intake passage downstream from the compressor;
LPL means for returning a part of the exhaust gas as LPL gas to the internal combustion engine via an LPL passage connecting an exhaust passage downstream from the turbine and an intake passage upstream from the compressor;
An LPL catalyst provided in the exhaust passage downstream from the connection location of the HPL passage and upstream from the connection location of the LPL passage;
LPL catalyst temperature acquisition means for acquiring the temperature of the LPL catalyst;
(A) An LPL catalyst whose temperature acquired by the LPL catalyst temperature acquisition means is higher than the temperature of the LPL catalyst assumed when the internal combustion engine in which the temperature is determined according to the operating state of the internal combustion engine is steadily operated in the operating state for a certain period of time. Transient conditions, and
(B) an LPL catalyst activation condition in which the temperature acquired by the LPL catalyst temperature acquisition means is higher than a predetermined activation temperature of the LPL catalyst;
When the above holds, the correction means for making the ratio of the HPL gas in the total EGR gas returned to the internal combustion engine by the HPL means and the LPL means higher than a predetermined ratio according to the operating state of the internal combustion engine,
An EGR system for an internal combustion engine comprising: In claim 7,
An HPL catalyst provided in the middle of the HPL passage and having oxidation ability;
HPL catalyst temperature acquisition means for acquiring the temperature of the HPL catalyst;
LPLCO ₂ production amount estimation means for estimating the amount of CO ₂ produced in the LPL catalyst;
HPLCO ₂ production amount estimation means for estimating the amount of CO ₂ produced in the HPL catalyst;
Further comprising
The correction means includes
(A) Transient conditions of the LPL catalyst,
(B) the LPL catalytic activity condition;
(C) An HPL catalyst whose temperature acquired by the HPL catalyst temperature acquisition means is higher than the temperature of the HPL catalyst assumed when the internal combustion engine in which the internal combustion engine is steadily operated for a certain period of time in the operating state. Transient conditions, and
(D) HPL catalyst activation conditions in which the temperature acquired by the HPL catalyst temperature acquisition means is higher than a predetermined activation temperature of the HPL catalyst;
If
(A) when said LPLCO ₂ generation amount of CO ₂ estimated by the generation amount estimation means is larger than the amount of CO ₂ estimated by the HPLCO ₂ generation amount estimation means, the ratio of HPL gas in the total EGR gas Higher than a predetermined ratio according to the operating state of the internal combustion engine,
(B) said LPLCO ₂ when the amount of the amount estimated CO ₂ estimated by means of the following production of CO ₂ estimated by the HPLCO ₂ generation amount estimation means, the ratio of LPL gas in the total EGR gas An EGR system for an internal combustion engine in which the engine is higher than a predetermined ratio according to the operating state of the internal combustion engine. A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
HPL means for returning a part of the exhaust gas as HPL gas to the internal combustion engine via an HPL passage connecting an exhaust passage upstream from the turbine and an intake passage downstream from the compressor;
LPL means for returning a part of the exhaust gas as LPL gas to the internal combustion engine via an LPL passage connecting an exhaust passage downstream from the turbine and an intake passage upstream from the compressor;
An LPL catalyst provided in the exhaust passage downstream from the connection location of the HPL passage and upstream from the connection location of the LPL passage;
LPL catalyst temperature acquisition means for acquiring the temperature of the LPL catalyst;
Exhaust temperature acquisition means for acquiring the temperature of the exhaust discharged from the internal combustion engine;
(A) An LPL catalyst whose temperature acquired by the LPL catalyst temperature acquisition means is higher than the temperature of the LPL catalyst assumed when the internal combustion engine in which the temperature is determined according to the operating state of the internal combustion engine is steadily operated in the operating state for a certain period of time. Transient conditions,
(B) LPL catalyst activation conditions in which the temperature acquired by the LPL catalyst temperature acquisition means is higher than a predetermined activation temperature of the LPL catalyst, and
(C) LPL exhaust low temperature condition in which the temperature acquired by the exhaust temperature acquisition means is lower than the temperature acquired by the LPL catalyst temperature acquisition means;
Is established, the internal combustion engine EGR system increases the amount of exhaust gas passing through the LPL catalyst from a predetermined amount according to the operating state of the internal combustion engine. In claim 9,
(A) Transient conditions of the LPL catalyst,
(B) the LPL catalyst activity condition, and
(C) LPL exhaust gas high temperature condition in which the temperature acquired by the exhaust temperature acquisition means is higher than the temperature acquired by the LPL catalyst temperature acquisition means;
If
(A) the amount of exhaust gas passing through the LPL catalyst is less than a predetermined amount corresponding to the operating state of the internal combustion engine, or
(B) An EGR system for an internal combustion engine that increases the intake air amount from a predetermined amount according to the operating state of the internal combustion engine. A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
HPL means for returning a part of the exhaust gas as HPL gas to the internal combustion engine via an HPL passage connecting an exhaust passage upstream from the turbine and an intake passage downstream from the compressor;
LPL means for returning a part of the exhaust gas as LPL gas to the internal combustion engine via an LPL passage connecting an exhaust passage downstream from the turbine and an intake passage upstream from the compressor;
An HPL catalyst provided in the middle of the HPL passage and having oxidation ability;
HPL catalyst temperature acquisition means for acquiring the temperature of the HPL catalyst;
Exhaust temperature acquisition means for acquiring the temperature of the exhaust discharged from the internal combustion engine;
(A) The HPL catalyst whose temperature acquired by the HPL catalyst temperature acquisition means is higher than the temperature of the HPL catalyst assumed when the internal combustion engine in which the internal combustion engine is steadily operated for a certain period in the operating state Transient conditions,
(B) HPL catalyst activation conditions in which the temperature acquired by the HPL catalyst temperature acquisition means is higher than a predetermined activation temperature of the HPL catalyst, and
(C) HPL exhaust low temperature condition in which the temperature acquired by the exhaust temperature acquisition means is lower than the temperature acquired by the HPL catalyst temperature acquisition means;
Is established, the internal combustion engine EGR system increases the amount of exhaust gas passing through the HPL catalyst from a predetermined amount according to the operating state of the internal combustion engine. In claim 11,
(B) the HPL catalyst transient condition;
(B) the HPL catalyst activity condition, and
(C) HPL exhaust gas high temperature condition in which the temperature acquired by the exhaust gas temperature acquisition unit is higher than the temperature acquired by the HPL catalyst temperature acquisition unit;
If
(A) the amount of exhaust gas passing through the HPL catalyst is made smaller than a predetermined amount corresponding to the operating state of the internal combustion engine, or
(B) An EGR system for an internal combustion engine that increases the intake air amount from a predetermined amount according to the operating state of the internal combustion engine.

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