JP2005061367A - Emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an emission control system of an internal combustion engine, in which the oxidation ability possessed by an emission control catalyst is surely estimated to make the temperature of the emission control catalyst surely reach a target temperature, and suppress the supplied fuel into the air from emitting. <P>SOLUTION: The emission control system of the internal combustion engine has the emission control catalyst 17, being a catalyst possessing the oxidation ability for oxidizing the material contained in the exhaust gas , and indicating characteristics which fall in the oxidation ability as the exhaust gas increases in the oxidation concentration. The oxidation ability of the emission control catalyst 17 is estimated based on the oxidation concentration of the exhaust gas to control a supply of fuel into the emission control catalyst 17 and the oxidation concentration of the exhaust gas, based on the estimated oxidation ability. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust purification system that purifies exhaust discharged from an internal combustion engine.

  An exhaust purification catalyst is provided in the exhaust passage of the internal combustion engine for the purpose of removing NOx, HC, etc. contained in the exhaust discharged from the internal combustion engine and purifying the exhaust. As this exhaust purification catalyst, a selective reduction type NOx purification catalyst that purifies exhaust by selectively reducing NOx in exhaust in a reducing atmosphere, or an occlusion reduction that purifies exhaust by storing and reducing NOx in exhaust. In addition to the type NOx purification catalyst, a three-way catalyst or the like can be used. Further, particulate matter in the exhaust gas is collected by a filter or the like on which the NOx storage reduction catalyst is supported, and release of the particulate matter to the atmosphere is suppressed.

  Here, in order for these exhaust purification catalysts to fully perform the catalytic function for exhaust purification, the temperature of the exhaust purification catalyst needs to be equal to or higher than a predetermined temperature (hereinafter referred to as “active temperature”). It is said. Therefore, in order to make the temperature of the exhaust purification catalyst equal to or higher than the activation temperature, a technique for injecting fuel corresponding to the oxygen concentration in the exhaust into the combustion chamber in the exhaust stroke and supplying it to the downstream exhaust purification catalyst (for example, Patent Document 1). And a technology for determining the amount of fuel to be supplied to the exhaust purification catalyst based on the NOx concentration difference between the upstream side and the downstream side of the exhaust purification catalyst (see, for example, Patent Document 2). . When fuel is supplied to the exhaust purification catalyst, the fuel is oxidized according to the oxidizing ability of the exhaust purification catalyst, and the temperature of the exhaust purification catalyst rises due to the oxidation heat generated there.

  In addition, in the filter carrying the NOx storage reduction catalyst, in order to oxidize and remove the collected particulate matter, fuel is supplied to the NOx storage reduction catalyst and the filter, and the heat of oxidation generated in the filter causes A technique for increasing the temperature is known (see, for example, Patent Document 3).

As described above, by utilizing the oxidation ability of the exhaust purification catalyst, the temperature of the exhaust purification catalyst or the temperature of the filter on which the exhaust purification catalyst is supported is increased by the oxidation heat in the oxidation reaction of the fuel supplied to the exhaust purification catalyst. It is possible to make it.
JP-A-11-264333 Japanese Patent Laid-Open No. 10-259713 JP 2002-38930 A JP-A-6-129238 JP-A-5-312026

  Here, in order to raise the temperature of the exhaust purification catalyst to a target temperature, for example, the activation temperature described above, an appropriate amount of fuel is supplied at an appropriate time according to the oxidation ability of the exhaust purification catalyst. Need to supply.

However, since it is difficult to accurately estimate the oxidizing ability of the exhaust purification catalyst, the fuel is not oxidized and released to the atmosphere unless fuel is supplied to the exhaust purification catalyst at an appropriate time. In addition, when the amount of fuel supplied to the exhaust purification catalyst is small, it becomes difficult to reliably raise the temperature of the exhaust purification catalyst to the target temperature, while on the other hand, the amount of fuel supplied to the exhaust purification catalyst is large. In some cases, the supplied fuel may be released to the atmosphere without being oxidized in the exhaust purification catalyst.

  In the present invention, in view of the above-described problems, by more reliably estimating the oxidation ability of the exhaust purification catalyst, the temperature of the exhaust purification catalyst can be reliably reached by the target temperature, and the supplied fuel can be returned to the atmosphere. It is an object of the present invention to provide an exhaust gas purification system for an internal combustion engine that suppresses the release of gas.

  In order to solve the above-described problems, the present invention focuses on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst. This is because the exhaust purification catalyst has a characteristic that the oxidizing ability of the exhaust purification catalyst varies greatly depending on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst, that is, the oxygen concentration of the atmosphere in which the substance constituting the exhaust purification catalyst is placed. Furthermore, the oxidizing power of the exhaust purification catalyst with respect to the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst shows different characteristics depending on the substances constituting the exhaust purification catalyst.

  Here, the oxidation ability of the exhaust purification catalyst with respect to the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst shows a characteristic that decreases as the oxygen concentration of the exhaust gas increases, and the oxygen concentration of the exhaust gas increases. And exhibiting an increasing characteristic.

  Therefore, first, in the exhaust gas purification system of the internal combustion engine provided with the exhaust gas purification catalyst exhibiting the former characteristic, that is, the oxidation ability that is provided in the exhaust passage of the internal combustion engine and oxidizes the substance contained in the exhaust gas flowing through the exhaust passage. In an exhaust gas purification system for an internal combustion engine having an exhaust purification catalyst having a characteristic that the oxidation ability of the catalyst decreases as the oxygen concentration of the exhaust gas increases, the oxygen concentration of exhaust gas flowing into the exhaust purification catalyst Oxygen concentration acquisition means for detecting or estimating the amount of fuel, fuel supply means for supplying fuel to the exhaust purification catalyst, and the oxidizing ability of the exhaust purification catalyst based on the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means And fuel supply control means for controlling the supply of fuel to the exhaust purification catalyst by the fuel supply means based on the estimated oxidation ability .

  An exhaust purification catalyst is a catalyst that is provided in an exhaust passage of an internal combustion engine and has an oxidizing ability to oxidize substances contained in exhaust flowing through the exhaust passage, and the oxidizing ability of the catalyst increases as the oxygen concentration of the exhaust increases. It is assumed that noble metal such as platinum that exhibits oxidizing ability and alkali metal that exhibits NOx storage characteristics and the like are constituents of the exhaust purification catalyst as factors that indicate the characteristics of the exhaust purification.

  That is, when the exhaust purification catalyst includes an alkali metal as a constituent component, oxygen in the exhaust is attracted to the alkali metal in the same manner as NOx, so that oxygen is adsorbed on the surface of the noble metal near the alkali metal. That is, it can be considered that the oxygen poisoning causes the surface of the noble metal to be covered with oxygen, and the efficiency of oxidation ability, which is the catalytic action of the noble metal, is reduced. Examples of the exhaust purification catalyst containing an alkali metal include the NOx storage reduction type NOx catalyst for storing and reducing NOx described above, and a three-way catalyst containing an alkali metal.

In an exhaust purification catalyst exhibiting such characteristics, the oxygen concentration of the exhaust is a major factor that determines the oxidation ability of the exhaust purification catalyst. Accordingly, it is possible to more accurately estimate the oxidizing ability of the exhaust purification catalyst based on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst. Then, by supplying an appropriate amount of fuel corresponding to the estimated oxidation ability of the exhaust purification catalyst to the exhaust purification catalyst at an appropriate time, the temperature of the exhaust purification catalyst is more reliably increased to the target temperature. It is possible to suppress the release of fuel into the atmosphere. The oxygen concentration of the exhaust gas can be estimated from the operating state such as the engine load and engine speed of the internal combustion engine, in addition to being detected by an oxygen concentration sensor provided in the exhaust passage through which the exhaust gas flows.

  Here, as control of fuel supply to the exhaust purification catalyst by the fuel supply control means, the higher the exhaust gas oxygen concentration detected or estimated by the oxygen concentration acquisition means, the higher the exhaust gas concentration to the exhaust purification catalyst by the fuel supply means. The fuel supply amount is decreased, and conversely, the fuel supply amount to the exhaust purification catalyst is increased by the fuel supply unit as the exhaust oxygen concentration detected or estimated by the oxygen concentration acquisition unit decreases. Is mentioned.

  That is, by supplying an amount of fuel in accordance with the transition of the oxidizing ability with respect to the oxygen concentration of the exhaust gas possessed by the exhaust purification catalyst to the exhaust purification catalyst from the fuel supply means, the supplied fuel is made to depend on the oxidizing ability of the exhaust purification catalyst. It is efficiently oxidized, and the temperature of the exhaust purification catalyst is more reliably raised to the target temperature, and the release of fuel into the atmosphere can be suppressed.

  Note that, in the exhaust purification catalyst exhibiting the above-described oxidation ability characteristics, the oxidation ability of the exhaust purification catalyst may be significantly reduced depending on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst. Even in such a case, if fuel is supplied to the exhaust purification catalyst in order to increase the temperature of the exhaust purification catalyst, it becomes difficult to avoid the release of fuel to the atmosphere.

  Therefore, in the exhaust gas purification system of the internal combustion engine, when the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means exceeds a predetermined oxygen concentration, the supply of fuel to the exhaust purification catalyst is prohibited. . Here, the predetermined oxygen concentration is the oxygen concentration of exhaust gas in which the oxidizing ability of the exhaust purification catalyst is remarkably lowered and it becomes difficult to suppress the release of fuel to the atmosphere. Can be determined by

  Thus, when the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst exceeds a predetermined oxygen concentration, the temperature of the exhaust purification catalyst is not increased by the fuel supply to the exhaust purification catalyst. In such a case, the temperature of the exhaust gas purification catalyst is raised by raising the temperature of the exhaust gas flowing into the exhaust gas purification catalyst by shifting the fuel injection timing to the retard side or the like.

  Here, as described above, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst can be cited as a factor that determines the oxidation ability of the exhaust purification catalyst. However, as another factor that determines the oxidation ability of the exhaust purification catalyst. There is a temperature of the exhaust purification catalyst. That is, as the temperature of the exhaust purification catalyst rises, the oxidizing ability of the exhaust purification catalyst also increases, and unless the temperature of the exhaust purification catalyst reaches the activation temperature, the oxidation by the exhaust purification catalyst is not performed efficiently. The oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst and the temperature of the exhaust purification catalyst are correlated with each other and reflected in the oxidizing ability of the exhaust purification catalyst.

  Therefore, the fuel supply control means controls the fuel supply to the exhaust purification catalyst based on the temperature of the exhaust purification catalyst, and the fuel supply control means based on the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means. The temperature of the exhaust purification catalyst at which fuel supply to the exhaust purification catalyst by the supply means is started is determined.

  That is, in order to start the fuel supply to the exhaust purification catalyst, it is necessary that the temperature of the exhaust purification catalyst be equal to or higher than the activation temperature at which the oxidation ability is efficiently exhibited. However, in the exhaust purification catalyst showing the characteristics of the oxidizing ability with respect to the oxygen concentration of the exhaust gas up to the above, the temperature at which the oxidizing ability of the exhaust purification catalyst is efficiently exhibited by the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst. The range, that is, the range of the activation temperature varies.

  As the oxygen concentration of the exhaust gas increases, the oxidizing ability of the exhaust gas purification catalyst decreases. Therefore, when the oxygen concentration of the exhaust gas flowing into the exhaust gas purification catalyst increases, the activation temperature range shifts to the high temperature side. Therefore, in such a case, it is necessary to shift the temperature of the exhaust purification catalyst that starts the supply of fuel to the exhaust purification catalyst to the high temperature side. By doing so, the fuel supplied to the exhaust purification catalyst is oxidized more efficiently, and the release of the fuel into the atmosphere can be more reliably suppressed.

  Further, in the exhaust purification catalyst showing the characteristics of the oxidizing ability with respect to the oxygen concentration of the exhaust gas described above, the fuel is supplied to the exhaust purification catalyst when the temperature of the exhaust purification catalyst is raised by the generated oxidation heat. The oxidation efficiency of the exhaust purification catalyst also varies depending on the molecular weight of the fuel. For example, depending on the exhaust purification catalyst, the oxidation efficiency of the exhaust purification catalyst may decrease as the molecular weight of the supplied fuel increases. This is because the surface area of noble metals in an oxygen-poisoned state is narrowed, so that the contact between the fuel and the noble metal becomes difficult as the molecular weight of the fuel increases, and as a result, the oxidation of the fuel becomes difficult. It is done. Therefore, when the supplied fuel has a large molecular weight, if the same amount of fuel as the low molecular weight fuel is supplied to the exhaust purification catalyst, the supplied fuel is released to the atmosphere as the oxidation efficiency of the exhaust purification catalyst decreases. There is a risk.

  Here, as means for supplying fuel to the exhaust purification catalyst, means for leaving unburned component fuel in the exhaust gas by adjusting combustion conditions such as fuel injection timing, fuel injection amount, ignition timing, etc. in the internal combustion engine; A means for directly adding fuel to the exhaust gas flowing through the exhaust passage can be exemplified. The fuel supplied to the exhaust purification catalyst by the former is exposed to a high-temperature atmosphere in the combustion chamber, so that the molecular weight thereof is relatively small. On the other hand, the molecular weight of the fuel supplied to the exhaust purification catalyst by the latter is smaller than that of the former. growing. Therefore, in order to raise the temperature of the exhaust purification catalyst, the former fuel supply is preferable. However, since the fuel supply has some influence on the output of the internal combustion engine, it is difficult to always supply or supply a large amount of fuel. . Therefore, in order to quickly raise the temperature of the exhaust purification catalyst, the latter fuel supply is required.

  Therefore, in the exhaust gas purification system of the internal combustion engine, when the fuel supply means has a fuel addition means for adding fuel to the exhaust gas flowing into the exhaust purification catalyst, the fuel supply control means includes the oxygen concentration Based on the oxygen concentration of the exhaust detected or estimated by the acquiring means, the fuel addition start timing to the exhaust by the fuel adding means is determined.

  In the fuel supplied by the fuel addition means in which the molecular weight of the fuel is relatively large, the oxidation efficiency by the exhaust purification catalyst is relatively low. Therefore, an appropriate time, that is, a time when the added fuel is efficiently oxidized is determined based on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst. For example, the oxidation efficiency of the fuel having a large molecular weight is increased by adding the fuel at a time when the oxygen concentration of the exhaust gas is maintained at a higher oxidizing ability of the exhaust purification catalyst. By doing so, the fuel supplied to the exhaust purification catalyst is oxidized more efficiently, and the release of the fuel into the atmosphere can be more reliably suppressed.

  Therefore, at a time before the fuel addition start time determined by the fuel supply control means, fuel is supplied to the exhaust purification catalyst by adjusting the combustion conditions of the internal combustion engine, and is determined by the fuel supply control means. At a time later than the fuel addition start time, fuel is supplied to the exhaust purification catalyst by starting fuel addition to the exhaust by the fuel addition means.

As a result, the fuel having a relatively low molecular weight is supplied to the exhaust purification catalyst before the fuel addition start time, and the fuel with a relatively high molecular weight is exhausted after the fuel addition start time. Since it is supplied to the purification catalyst, the temperature of the exhaust purification catalyst can be raised more quickly to the target temperature, and the release of fuel into the atmosphere can be suppressed.

  Further, as described above, as a factor that determines the oxidation ability of the exhaust purification catalyst, in addition to the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst, the temperature of the exhaust purification catalyst can be cited. As the molecular weight of the fuel supplied to the exhaust purification catalyst increases, the oxidation efficiency of the exhaust purification catalyst decreases. Therefore, in the exhaust gas purification system of the internal combustion engine, the fuel supply control means starts the fuel addition to the exhaust gas by the fuel addition means based on the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means The temperature of the exhaust purification catalyst is calculated, and when the temperature of the exhaust purification catalyst exceeds the temperature calculated by the fuel supply control means, the fuel addition start timing to the exhaust gas by the fuel addition means is set.

  As a result, even if the temperature of the exhaust purification catalyst reaches the activation temperature, if the temperature is relatively low, the oxidation efficiency for the low molecular weight fuel is high, but the oxidation efficiency for the high molecular weight fuel is low. Therefore, in such a case, it is not preferable to add fuel to the exhaust, which is a supply of fuel having a high molecular weight. Therefore, the temperature of the exhaust purification catalyst that exhibits the oxidation performance of the exhaust purification catalyst that maintains the oxidation efficiency for fuel with a large molecular weight is maintained to a certain level, is calculated from the oxygen concentration of the exhaust, and the temperature of the exhaust purification catalyst is When the calculated temperature is exceeded, fuel is added to the exhaust. As the oxygen concentration in the exhaust gas becomes higher, the oxidizing ability of the exhaust gas purification catalyst decreases, so that the temperature of the exhaust gas purification catalyst for starting the addition of fuel to the exhaust gas shifts to the high temperature side. As a result, fuel can be supplied at a more appropriate time, and the supplied fuel can be more reliably suppressed from being released into the atmosphere.

  In the exhaust gas purification system for an internal combustion engine described above, the amount of fuel supplied to the exhaust gas purification catalyst is controlled based on the oxygen concentration of the exhaust gas flowing into the exhaust gas purification catalyst. 1 shows an exhaust purification system of an internal combustion engine having control of the oxygen concentration of exhaust gas flowing into the exhaust purification catalyst when fuel is supplied to the catalyst.

  Therefore, the catalyst is provided in the exhaust passage of the internal combustion engine and has an oxidizing ability to oxidize substances contained in the exhaust flowing through the exhaust passage, and the oxidizing ability of the catalyst decreases as the oxygen concentration of the exhaust increases. In an exhaust purification system of an internal combustion engine having an exhaust purification catalyst exhibiting characteristics, a fuel supply means for supplying fuel to the exhaust purification catalyst, and when the fuel is supplied to the exhaust purification catalyst by the fuel supply means, the exhaust purification catalyst Oxygen concentration control means for reducing the oxygen concentration of the exhaust gas flowing into the exhaust gas.

  The oxidation ability of the exhaust purification catalyst with respect to the oxygen concentration of the exhaust is as described above. Therefore, in an exhaust gas purification system for an internal combustion engine having an exhaust gas purification catalyst exhibiting this characteristic, the oxidizing ability of the exhaust gas purification catalyst decreases as the oxygen concentration of the exhaust gas increases. Therefore, instead of the amount of fuel supplied to the exhaust purification catalyst, the oxygen concentration itself of the exhaust flowing into the exhaust purification catalyst is controlled so as to be an oxygen concentration at which the oxidation ability of the exhaust purification catalyst can be efficiently exhibited. That is, in order to oxidize the supplied fuel efficiently, the oxygen concentration in the exhaust gas is reduced. As a result, the oxidation heat of the fuel supplied to the exhaust purification catalyst makes it possible to raise the temperature of the exhaust purification catalyst to the target temperature more reliably and to suppress the release of the fuel to the atmosphere. .

Here, in order to control the oxygen concentration of the exhaust, if the combustion conditions in the combustion chamber, for example, the intake air amount or the EGR amount are controlled, the engine output of the internal combustion engine fluctuates or the stability of combustion in the combustion chamber is hindered. There is a risk of doing. Therefore, the exhaust gas purification system of the internal combustion engine further includes oxygen concentration acquisition means for detecting or estimating the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst, and the oxygen concentration control means is detected by the oxygen concentration acquisition means. Alternatively, when the estimated oxygen concentration of the exhaust gas exceeds a predetermined concentration, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst is reduced. As a result, the oxygen concentration in the exhaust gas is reduced only when a predetermined condition is satisfied. Therefore, the engine output of the internal combustion engine may fluctuate or the stability of combustion in the combustion chamber may be hindered. Less. Further, the intake air amount and the EGR amount may be controlled only in the operation region of the internal combustion engine where there is little possibility of fluctuations in the output of the internal combustion engine by changing the intake air amount and the EGR amount.

  Further, the air-fuel ratio of the exhaust may be controlled when reducing the oxygen concentration of the exhaust. That is, to reduce the oxygen concentration of the exhaust, the air-fuel ratio of the exhaust may be shifted to the rich side. By doing so, it becomes possible to simultaneously control the amount of fuel supplied to the exhaust purification catalyst and the oxygen concentration of the exhaust. At this time, in the exhaust purification catalyst showing the characteristics of the oxidation ability with respect to the oxygen concentration of the exhaust gas described above, the oxidation ability of the exhaust purification catalyst is more efficiently exhibited when the air-fuel ratio is almost stoichiometric.

  Further, even if the exhaust air-fuel ratio is in a richer state than the stoichiometric state, the exhaust purification catalyst is maintained at a high level of oxidation ability, but since the amount of fuel supplied to the exhaust purification catalyst is large, The risk of being released into the atmosphere increases. Therefore, when the air-fuel ratio of the exhaust gas is in a rich state, the air-fuel ratio of the exhaust gas may be shifted until it becomes almost stoichiometric.

  Here, in the exhaust purification catalyst, the characteristic of the oxidizing ability with respect to the oxygen concentration of the exhaust is considered to be due to oxygen poisoning of the exhaust purification catalyst as described above. Therefore, when supplying the fuel to the exhaust purification catalyst, when the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst is substantially stoichiometric as described above, fuel supply to the exhaust purification catalyst is started by the fuel supply means. In a later predetermined period, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is made richer than the substantially stoichiometric air-fuel ratio.

  As a result, when the fuel is supplied to the exhaust purification catalyst and the temperature of the exhaust purification catalyst is raised to the target temperature, the air-fuel ratio of the exhaust becomes rich for a predetermined period. The adsorbed oxygen can be separated from the exhaust purification catalyst. As a result, oxygen poisoning of the exhaust purification catalyst is eliminated, so that the oxidation ability increases, and the temperature of the exhaust purification catalyst rises more efficiently by the supplied fuel. Here, the predetermined period is a period during which the air-fuel ratio of the exhaust gas is set to a rich air-fuel ratio sufficient for eliminating oxygen poisoning of the exhaust purification catalyst.

  The exhaust air-fuel ratio may be made rich at any time after the fuel supply to the exhaust purification catalyst is started, but the fuel is oxidized by the exhaust purification catalyst in a state where oxidation performance is higher. Therefore, immediately after the fuel supply to the exhaust gas purification catalyst is started, that is, before the air-fuel ratio of the exhaust gas is substantially stoichiometric, the air-fuel ratio of the exhaust gas is made rich for a predetermined period, and then is substantially stoichiometric. Is preferred. Thus, it is possible to remove the oxygen poisoning of the exhaust purification catalyst first, recover the oxidation ability of the exhaust purification catalyst, and efficiently raise the temperature of the exhaust purification catalyst.

  Here, as described above, the oxidation efficiency of the exhaust purification catalyst varies depending on the molecular weight of the fuel contained in the exhaust. Depending on the operating state of the internal combustion engine, the molecular weight of the fuel contained in the exhaust gas will fluctuate, and if fuel is supplied to the exhaust purification catalyst by adding fuel directly to the exhaust gas, the proportion of high molecular weight fuel in the exhaust gas will increase. As a result, the oxidation efficiency of the exhaust purification catalyst decreases, and the supplied fuel may be released to the atmosphere.

Therefore, the exhaust gas purification system for the internal combustion engine further includes molecular weight state estimation means for estimating the molecular weight state of the fuel contained in the exhaust gas flowing into the exhaust gas purification catalyst. The oxygen concentration control means is such that the molecular weight state estimating means estimates that the exhaust gas flowing into the exhaust purification catalyst contains a large amount of fuel having a large molecular weight, so that the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst To lower.

  That is, what is the molecular weight of the fuel contained in the exhaust gas flowing into the exhaust purification catalyst from the operating state of the internal combustion engine, the amount of fuel directly added to the exhaust gas, etc., that is, which fuel has a high molecular weight It is estimated how much fuel with low molecular weight is included. Since the oxidation efficiency of the exhaust purification catalyst decreases as the amount of fuel having a large molecular weight increases, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst is reduced in order to increase the oxidation efficiency of the exhaust purification catalyst as much as possible. . Note that the average molecular weight of the fuel contained in the exhaust gas may be estimated. In that case, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst may be lowered as the average molecular weight increases. As a result, the temperature of the exhaust purification catalyst can be more reliably increased to the target temperature, and the supplied fuel can be efficiently oxidized, whereby the release of the fuel into the outside air can be suppressed.

  Here, the specific structure of the exhaust purification catalyst showing the characteristics of the oxidation ability with respect to the oxygen concentration of the exhaust gas described above may be a catalyst containing at least a noble metal and an alkali metal. In the exhaust gas purification system for an internal combustion engine provided with the exhaust gas purification catalyst having such a configuration, an upper exhaust gas purification catalyst composed of at least a noble metal and an alkali metal is provided in the exhaust passage upstream of the exhaust gas purification catalyst. . That is, the same catalyst as that of the exhaust purification catalyst and exhibiting the characteristic of oxidizing ability with respect to the oxygen concentration of the exhaust is provided on the upstream side of the exhaust purification catalyst.

  As a result, even if the exhaust gas contains a large amount of oxygen, oxygen is adsorbed by the upper exhaust purification catalyst provided on the upstream side, so that the exhaust purification catalyst located on the downstream side has a lower oxygen concentration. Reach. As a result, it becomes possible to maintain the oxidation ability of the exhaust purification catalyst high. Further, the fuel contained in the exhaust gas is not oxidized in the upper exhaust purification catalyst in which the oxygen is adsorbed and the oxidation ability is reduced, but is oxidized by the exhaust purification catalyst that maintains the high oxidation ability. The temperature of the catalyst rises.

  The exhaust purification catalyst up to the above has been a catalyst exhibiting the characteristic that the oxidizing ability of the exhaust purification catalyst decreases as the oxygen concentration of the exhaust increases. Next, the exhaust purification catalyst increases as the oxygen concentration of the exhaust increases. In the catalyst showing the characteristic that the oxidation ability of the catalyst increases, the temperature rise control of the catalyst will be described.

  Therefore, a catalyst that is provided in the exhaust passage of the internal combustion engine and has an oxidizing ability to oxidize substances contained in the exhaust flowing through the exhaust passage, and the oxidizing ability of the catalyst increases as the oxygen concentration of the exhaust increases. An exhaust purification system for an internal combustion engine having an exhaust purification catalyst exhibiting characteristics, wherein the oxygen concentration acquisition means detects or estimates the oxygen concentration of exhaust flowing into the exhaust purification catalyst, and is detected or estimated by the oxygen concentration acquisition means The oxidation capacity estimation means for estimating the oxidation capacity of the exhaust purification catalyst based on the oxygen concentration of the exhaust gas, and the oxidation capacity of the exhaust purification catalyst estimated by the oxidation capacity estimation means decreases as the exhaust purification catalyst is reduced. Fuel supply control means for reducing the amount of fuel supplied to the inflowing exhaust gas.

  In the exhaust purification catalyst, it is assumed that the cause of the characteristics of the oxidizing ability with respect to the oxygen concentration of the exhaust gas described above is that the constituent components of the exhaust purification catalyst do not contain an alkali metal showing the characteristic of attracting oxygen. Therefore, an exhaust purification catalyst that uses a noble metal that exhibits oxidation ability as a constituent component but does not contain an alkali metal as its constituent component increases the amount of oxygen supplied to the oxidation reaction as the oxygen concentration in the exhaust gas increases. In addition, the oxidation ability of the exhaust purification catalyst exhibits a characteristic of increasing.

Therefore, in an exhaust gas purification system for an internal combustion engine having an exhaust gas purification catalyst exhibiting such characteristics, it is estimated that as the oxygen concentration of the exhaust gas becomes higher, the oxidation ability of the exhaust gas purification catalyst increases, while the oxygen concentration of the exhaust gas becomes lower. As a result, it is estimated that the oxidation capacity of the exhaust purification catalyst will decrease, and an appropriate amount of fuel corresponding to the estimated oxidation capacity of the exhaust purification catalyst will be supplied to the exhaust purification catalyst. The temperature of the fuel can be more reliably raised to the temperature, and the supplied fuel can be efficiently oxidized, so that the release of the fuel to the outside air can be suppressed.

  In addition, the exhaust purification catalyst that exhibits the above-described characteristics of the oxidizing ability with respect to the oxygen concentration of the exhaust gas increases the oxidation efficiency of the exhaust purification catalyst as the molecular weight of the fuel supplied to the exhaust purification catalyst increases. It also shows the characteristic that the oxidation efficiency of the exhaust purification catalyst decreases as the molecular weight of the fuel supplied to the catalyst decreases.

  Therefore, a catalyst that is provided in the exhaust passage of the internal combustion engine and has an oxidizing ability to oxidize substances contained in the exhaust flowing through the exhaust passage, and the oxidizing ability of the catalyst increases as the oxygen concentration of the exhaust increases. An exhaust purification system for an internal combustion engine having an exhaust purification catalyst exhibiting characteristics, wherein the molecular weight state estimation means for estimating the molecular weight state of fuel contained in the exhaust gas flowing into the exhaust purification catalyst, and the molecular weight state estimation means, And oxygen concentration control means for increasing the oxygen concentration of the exhaust gas flowing into the exhaust gas purification catalyst so that it is estimated that the exhaust gas flowing into the exhaust gas purification catalyst contains a larger amount of fuel having a small molecular weight.

  That is, the state of the molecular weight of the fuel contained in the exhaust gas flowing into the exhaust purification catalyst from the operating state of the internal combustion engine, the amount of fuel directly added to the exhaust gas, etc., that is, how much the low molecular weight fuel is Estimate how much fuel with high molecular weight is included. Since the oxidation efficiency of the exhaust purification catalyst decreases as the amount of fuel having a low molecular weight increases, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst is increased in order to increase the oxidation efficiency of the exhaust purification catalyst as much as possible. . Note that the average molecular weight of the fuel contained in the exhaust gas may be estimated. In that case, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst may be increased as the average molecular weight is smaller. As a result, the temperature of the exhaust purification catalyst can be more reliably increased to the target temperature, and the supplied fuel can be efficiently oxidized, whereby the release of the fuel into the outside air can be suppressed.

  By more reliably estimating the oxidation ability of the exhaust purification catalyst from the oxygen concentration in the exhaust, the exhaust purification catalyst temperature can be reliably reached at the target temperature, and the release of supplied fuel to the atmosphere is suppressed. It becomes possible to do.

  Here, an embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention will be described based on the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an exhaust purification system of an internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 is a compression ignition internal combustion engine having at least one cylinder 2. Further, a fuel injection valve 4 for injecting fuel directly into the combustion chamber 3 of the cylinder 2 is provided.

  Next, an intake branch pipe 5 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 5 is connected to the combustion chamber 3 via an intake port 6. Here, the communication between the combustion chamber 3 and the intake port 6 is performed by opening and closing the intake valve 7. The intake branch pipe 5 is connected to the intake pipe 8. An air flow meter 9 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake pipe 8 is attached to the intake pipe 8. An intake throttle valve 10 for adjusting the flow rate of the intake air flowing through the intake pipe 8 is provided at a portion of the intake pipe 8 located immediately upstream of the intake branch pipe 5. The intake throttle valve 10 is provided with an intake throttle actuator 11 that is configured by a step motor or the like and that opens and closes the intake throttle valve 10.

  On the other hand, an exhaust branch pipe 13 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 13 is connected to the combustion chamber 3 via an exhaust port 14. Here, the communication between the combustion chamber 3 and the exhaust port 14 is performed by opening and closing the exhaust valve 15. The exhaust branch pipe 13 is further connected to an exhaust pipe 16, and an exhaust purification catalyst 17 for purifying exhaust exhausted from the internal combustion engine is provided in the middle of the exhaust pipe 16. The characteristics of the exhaust purification catalyst 17 will be described later. In addition, a recirculation passage 18 that recirculates a part of the exhaust discharged from the combustion chamber 3 from the exhaust branch pipe 13 to the intake branch pipe 5 and introduces it into the combustion chamber 3 communicates. An EGR cooler 19 that cools the recirculated exhaust gas (hereinafter referred to as “EGR gas”) and an EGR valve 20 that adjusts the flow rate of the EGR gas are provided in the recirculation passage 18. Further, the exhaust pipe 16 is provided with a fuel addition valve 12 for adding fuel to the exhaust gas flowing through the exhaust pipe.

  Here, the fuel injection valve 4, the fuel addition valve 12, the intake throttle valve 10, and the EGR valve 20 are opened and closed by a control signal from an electronic control unit (hereinafter referred to as an ECU: Electronic Control Unit) 30. That is, the fuel injection timing and the injection amount from the fuel injection valve 4 are controlled by a command from the ECU 30, and the engine output of the internal combustion engine 1 is controlled accordingly. Similarly, the amount of fuel added from the fuel addition valve 12 to the exhaust, the timing of addition, the amount of intake air flowing into the combustion chamber 3, the amount of EGR gas introduced into the combustion chamber 3, and the like are controlled.

  Further, an accelerator opening sensor 31 is electrically connected to the ECU 30. The ECU 30 receives a signal corresponding to the accelerator opening, and calculates an engine load and the like of the internal combustion engine 1 based on the signal. Further, the crank position sensor 32 is electrically connected to the ECU 30, and the ECU 30 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1 and calculates the engine rotational speed and the like of the internal combustion engine 1. Further, an upstream side exhaust temperature sensor 33 that detects the temperature of the exhaust gas flowing into the exhaust purification catalyst 17 is provided in the exhaust pipe 16 upstream of the exhaust purification catalyst 17 and is electrically connected to the ECU 30. The exhaust pipe 16 on the downstream side of the exhaust purification catalyst 17 is provided with a downstream exhaust temperature sensor 34 and an exhaust air / fuel ratio sensor 35 for detecting the temperature and air / fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst 17, respectively. And are electrically connected.

  Here, the above-described exhaust purification catalyst 17 is a catalyst having at least a noble metal and an alkali metal as constituent components, and the catalyst is supported on a filter. Therefore, the exhaust purification catalyst 17 stores NOx in the exhaust when the air-fuel ratio of the exhaust is lean, and reduces and releases the stored NOx when the air-fuel ratio of the exhaust becomes rich. Then, the NOx in the exhaust gas is purified. Furthermore, oxidation of fuel, carbon monoxide and the like in the exhaust is performed by the noble metal which is a constituent component of the exhaust purification catalyst 17. Further, particulate matter in the exhaust gas is collected by the filter on which the exhaust purification catalyst 17 is supported, so that release of the particulate matter to the atmosphere is suppressed.

  In order to exhibit such an exhaust purification function of the exhaust purification catalyst 17, the temperature of the exhaust purification catalyst 17 needs to be equal to or higher than the activation temperature. When the temperature of the exhaust purification catalyst 17 is lower than the activation temperature, it becomes difficult to efficiently purify NOx in the exhaust. Therefore, in order to efficiently purify the exhaust gas, it is necessary to quickly raise the temperature of the exhaust gas purification catalyst 17 to the activation temperature and maintain it at the activation temperature. Further, as the particulate matter is collected by the filter carrying the exhaust purification catalyst 17, the pressure in the exhaust pipe 16 increases and affects the combustion of fuel in the combustion chamber 3. Therefore, it is necessary to raise the temperature of the exhaust purification catalyst 17 every predetermined period to oxidize and remove the collected particulate matter.

  Accordingly, the temperature of the exhaust purification catalyst 17 is increased by utilizing the oxidation ability of the exhaust purification catalyst 17, that is, by the oxidation heat generated by supplying fuel to the exhaust purification catalyst 17 and oxidizing the fuel by the oxidation ability. Ascend or maintain.

  Here, the characteristics of the oxidizing ability of the exhaust purification catalyst 17 will be described with reference to FIGS. FIG. 2 is a graph showing the transition of the oxidizing ability of the exhaust purification catalyst 17 with respect to the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17. The horizontal axis of the graph represents the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17, and the oxygen concentration represented by the point S on the horizontal axis is when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 is in a stoichiometric state. Of oxygen concentration. The vertical axis of the graph indicates the HC oxidation rate that represents the oxidation ability of the exhaust purification catalyst 17. The HC oxidation rate is represented by the amount of fuel oxidized by the exhaust purification catalyst 17 with respect to the amount of fuel (HC) supplied to the exhaust purification catalyst 17. In FIG. 2, the temperature of the exhaust purification catalyst 17 is a constant temperature that has reached the activation temperature.

In FIG. 2, line L1 represents the transition of the HC oxidation rate when the molecular weight of the fuel supplied to the exhaust purification catalyst 17 is relatively high. In the present embodiment, the fuel is represented by C ₁₀ H _22. . A line L2 is a transition of the HC oxidation rate when the molecular weight of the fuel supplied to the exhaust purification catalyst 17 is relatively low. In the present embodiment, the fuel is represented by C ₃ H ₆ . Therefore, as the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17 increases, the HC oxidation rate of the exhaust purification catalyst 17 decreases. Even if the oxygen concentration of the exhaust gas is the same, the HC oxidation rate of the exhaust purification catalyst 17 decreases as the molecular weight of the fuel supplied to the exhaust purification catalyst 17 increases.

  The alkali metal constituting the exhaust purification catalyst 17 has an action of occluding NOx in the exhaust gas, that is, an action of attracting NOx, while also attracting oxygen in the exhaust gas. Therefore, the oxygen attracted by the alkali metal is adsorbed on the surface of the noble metal existing in the vicinity of the alkali metal to reduce the surface area of the noble metal, thereby reducing the oxidation effect by the noble metal. It can be considered that the oxygen poisoning state is one of the factors that reduce the HC oxidation rate, which is the oxidation ability of the exhaust purification catalyst 17. Even if the oxygen concentration of the exhaust gas is the same, the HC oxidation rate of the exhaust purification catalyst 17 varies depending on the molecular weight of the supplied fuel. For the noble metal whose surface area decreases as the molecular weight of the fuel increases. It is thought that it is difficult to contact efficiently. Therefore, the oxidation efficiency of the fuel decreases as the molecular weight of the fuel supplied to the exhaust gas purification catalyst 17 in the oxygen poisoning state increases.

  FIG. 3 is a graph showing the transition of the oxidizing ability of the exhaust purification catalyst 17 with respect to the temperature of the exhaust purification catalyst 17. The horizontal axis of the graph represents the temperature of the exhaust purification catalyst 17, and the vertical axis of the graph represents the HC oxidation rate that represents the oxidation ability of the exhaust purification catalyst 17. The HC oxidation rate is synonymous with the HC oxidation rate shown in FIG. In FIG. 3, the molecular weight of the fuel supplied to the exhaust purification catalyst 17 is the same.

  In FIG. 3, the line L3 indicates the transition of the oxidizing ability of the exhaust purification catalyst 17 when the oxygen concentration of the exhaust flowing into the exhaust purification catalyst 17 is high, for example, when the air-fuel ratio of the exhaust is a slightly lean air-fuel ratio. It is. Further, line L4 represents the transition of the oxidizing ability of the exhaust purification catalyst 17 when the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17 is low, for example, when the air fuel ratio of the exhaust gas is a stoichiometric air fuel ratio. As shown in FIG. 3, as the temperature of the exhaust purification catalyst 17 increases, the oxidation capacity of the exhaust purification catalyst 17 increases. However, the degree of increase in the oxidation capacity depends on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17. Is different. That is, as the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17 becomes higher, the rate of increase in oxidizing ability accompanying the temperature rise of the exhaust purification catalyst 17 becomes smaller.

As a result, the temperature of the exhaust purification catalyst 17 for determining that the exhaust purification catalyst 17 is in an active state varies depending on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17. For example, assuming that the active state of the exhaust purification catalyst 17 is a state in which an oxidation ability with an HC oxidation rate of the exhaust purification catalyst 17 equal to or greater than X (%) is obtained, the exhaust gas having an oxygen concentration in the line L3 flows into the exhaust purification catalyst 17. In some cases, it is necessary to raise the temperature of the exhaust purification catalyst 17 to Tst1. Line L4
When the exhaust gas having the oxygen concentration in the gas flows into the exhaust purification catalyst 17, the temperature of the exhaust purification catalyst 17 only needs to be raised to Tst0 (<Tst1).

  Therefore, as shown in FIGS. 2 and 3, the oxidizing ability of the exhaust purification catalyst 17 varies depending on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17, so that the supplied fuel is efficient depending on the oxygen concentration of the exhaust gas. It is not always oxidized. The degree of the temperature increase of the exhaust purification catalyst 17 varies depending on the oxygen concentration of the exhaust. Therefore, it may be difficult to raise the temperature of the exhaust purification catalyst 17 to a target temperature, or the supplied fuel may be released to the atmosphere without being oxidized. Therefore, when the temperature of the exhaust purification catalyst 17 is raised by supplying fuel to the exhaust purification catalyst 17 in consideration of the above-described characteristics of the oxidizing ability of the exhaust purification catalyst 17, the temperature of the exhaust purification catalyst 17 is increased to the target temperature. The fuel supply control for more reliably avoiding the release of fuel to the atmosphere will be described below.

  FIG. 4 shows the fuel supply control to the exhaust purification catalyst 17 (exhaust purification catalyst temperature rise control) for increasing the temperature of the exhaust purification catalyst 17 to a target temperature and more reliably avoiding the release of fuel to the atmosphere. It is a flowchart of. The control is executed by the ECU 30.

  First, in S101, the oxygen concentration De of exhaust flowing into the exhaust purification catalyst 17 is estimated from the operating state of the internal combustion engine 1. For example, from the ratio of the amount of air provided for combustion in the combustion chamber 3 and the amount of fuel obtained from the opening of the intake throttle valve 10, the opening of the EGR valve 20, and the fuel injection amount from the fuel injection valve 4, etc. The oxygen concentration De of the exhaust gas to be discharged is estimated. At this time, a map in which the opening degree of the intake throttle valve 10 is used as a parameter and the output is the oxygen concentration De of the exhaust gas is stored in a memory in the ECU 30, and the oxygen concentration De of the exhaust gas is estimated by accessing the memory. To do. When the process of S101 ends, the process proceeds to S102.

  In S102, the temperature Tst of the exhaust purification catalyst 17 at which fuel supply to the exhaust purification catalyst 17 is started is calculated based on the oxygen concentration De of the exhaust estimated in S101. As shown in FIG. 3, the degree of increase in the oxidation ability accompanying the temperature increase of the exhaust purification catalyst 17 varies depending on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17. Therefore, the temperature of the exhaust purification catalyst 17 that serves as a reference for starting fuel supply to the exhaust purification catalyst 17 when the oxidizing ability of the exhaust purification catalyst 17 is increased to such an extent that the supplied fuel can be efficiently oxidized. Tst is calculated.

  Here, the fuel supply to the exhaust purification catalyst 17 is first performed by adjusting the combustion conditions of the internal combustion engine 1 (performed in S110 described later). Specifically, in the expansion stroke or the exhaust stroke after the fuel injection in the vicinity of the compression stroke top dead center from the fuel injection valve 4 that greatly contributes to the engine output of the internal combustion engine 1, the fuel is injected from the fuel injection valve 4 into the combustion chamber 3. (Hereinafter, the fuel injection is referred to as “post-injection”). Since the fuel injected by the post-injection is exposed to the high-temperature combustion gas in the combustion chamber 3, the fuel having a relatively small molecular weight is supplied to the exhaust purification catalyst 17. Therefore, for example, Tst0 or Tst1 in FIG. 3 is calculated as Tst based on the oxygen concentration of the exhaust gas. When the process of S102 ends, the process proceeds to S103.

In S103, the temperature of the exhaust purification catalyst 17 is estimated from the exhaust temperature flowing into the exhaust purification catalyst 17 detected from the upstream side exhaust temperature sensor 33, and the estimated temperature of the exhaust purification catalyst 17 is calculated in S102. It is determined whether or not it is greater than Tst. That is, it is determined whether or not the temperature of the exhaust purification catalyst 17 can be increased by starting the fuel supply to the exhaust purification catalyst 17. If it is determined in S103 that the exhaust temperature is higher than Tst, it means that the temperature of the exhaust purification catalyst 17 has risen to such an extent that the supplied fuel can be efficiently oxidized, and the process proceeds to S105, Thereafter, fuel supply to the exhaust purification catalyst 17 is started. In S103, if it is determined that the exhaust temperature is equal to or lower than Tst, it means that the temperature of the exhaust purification catalyst 17 has not increased to such an extent that the supplied fuel can be efficiently oxidized, Purification catalyst 17
The fuel supply is not performed, and the process proceeds to S104.

  When the process proceeds from S103 to S104, the temperature of the exhaust purification catalyst 17 is increased by increasing the temperature of the exhaust itself flowing into the exhaust purification catalyst 17 in S104. For example, the exhaust gas temperature is raised by retarding the fuel injection from the fuel injection valve 4 in the vicinity of the compression top dead center. When the process of S104 ends, the processes after S101 are performed again.

  When the process proceeds from S103 to S105, the oxygen concentration De of the exhaust gas flowing into the exhaust purification catalyst 17 is estimated from the operating state of the internal combustion engine 1 in S105, similarly to S101 described above. When the process of S105 ends, the process proceeds to S106.

  In S106, based on the oxygen concentration De of the exhaust estimated in S105, in the fuel supply to the exhaust purification catalyst 17, the addition of the fuel from the fuel addition valve 12, which is the supply of fuel having a large molecular weight, is started. The temperature Tast is calculated. As described in the processing of S <b> 102, the degree of increase in oxidation ability accompanying the temperature increase of the exhaust purification catalyst 17 varies depending on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17. Further, as the molecular weight of the supplied fuel increases, the oxidation efficiency of the exhaust purification catalyst 17 decreases. Therefore, in order to perform addition to the exhaust gas by the fuel addition valve 12, the temperature of the exhaust purification catalyst 17 is set to a temperature at which the oxidation ability of the exhaust purification catalyst 17 becomes an oxidation ability that can efficiently oxidize a fuel having a large molecular weight. There is a need to. Therefore, since the oxidation efficiency by the exhaust purification catalyst 17 becomes sufficient, the value of Tast increases as the oxygen concentration De of the exhaust increases. If the exhaust gas oxygen concentration De estimated in S101 is the same as the exhaust gas oxygen concentration De estimated in S105, the relationship Tst <Tast is established. When the process of S106 ends, the process proceeds to S107.

  In S107, the temperature of the exhaust purification catalyst 17 is estimated from the exhaust temperature flowing into the exhaust purification catalyst 17 detected from the upstream side exhaust temperature sensor 33, and the estimated temperature of the exhaust purification catalyst 17 is calculated in S106. It is determined whether it is greater than Tast. That is, it is determined whether or not fuel can be added to the exhaust gas from the fuel addition valve 12. If it is determined in S107 that the exhaust temperature is higher than Tast, it means that the temperature of the exhaust purification catalyst 17 has risen to such an extent that fuel with a high molecular weight can be efficiently oxidized, and the process proceeds to S111. Thereafter, fuel is added to the exhaust gas from the fuel addition valve 12. If it is determined in S107 that the exhaust temperature is equal to or lower than Tast, it means that the temperature of the exhaust purification catalyst 17 has not risen to such an extent that fuel with a high molecular weight can be oxidized efficiently. The fuel is not added to the exhaust from the addition valve 12, and the process proceeds to S108 in order to supply a fuel having a low molecular weight.

  When the process proceeds from S107 to S108 and thereafter, in S108 to S110, the fuel having a low molecular weight is supplied to the exhaust purification catalyst 17. In S108, the oxygen concentration De of the exhaust gas flowing into the exhaust purification catalyst 17 is estimated from the operating state of the internal combustion engine 1 as in S101 described above. When the process of S108 ends, the process proceeds to S109.

  In S109, the oxidation ability of the exhaust purification catalyst 17 is estimated based on the exhaust oxygen concentration De estimated in S108. That is, the current oxidizing ability of the exhaust purification catalyst 17 is estimated based on the characteristics of the oxidizing ability with respect to the oxygen concentration of the exhaust gas indicated by the line L2 in FIG. 2 and the oxygen concentration De of the exhaust gas. When the process of S109 ends, the process proceeds to S110.

In S110, the combustion conditions of the internal combustion engine 1 are adjusted so that an amount of fuel corresponding to the oxidation ability of the exhaust purification catalyst 17 estimated in S109 is supplied to the exhaust purification catalyst 17. That is, as the oxidizing ability of the exhaust purification catalyst 17 is higher, a larger amount of fuel can be oxidized, so that the amount of fuel supplied to the exhaust purification catalyst 17 is increased. The fuel supply to the exhaust purification catalyst 17 is performed by, for example, the above-described post-injection. When the process of S110 ends, the processes after S107 are performed again.

  Next, when the process proceeds from S107 to S111 and thereafter, in S111 to S113, the fuel having a high molecular weight is supplied to the exhaust purification catalyst 17. In S111, the oxygen concentration De of the exhaust gas flowing into the exhaust purification catalyst 17 is estimated from the operating state of the internal combustion engine 1 as in S101 described above. When the process of S111 ends, the process proceeds to S112.

  In S112, the oxidizing ability of the exhaust purification catalyst 17 is estimated based on the oxygen concentration De of the exhaust estimated in S111. That is, the current oxidation ability of the exhaust purification catalyst 17 is estimated based on the characteristics of the oxidation ability with respect to the oxygen concentration of the exhaust gas indicated by the line L1 in FIG. 2 and the oxygen concentration De of the exhaust gas. When the process of S112 ends, the process proceeds to S113.

  In S113, the fuel addition valve 12 is controlled so as to supply the exhaust purification catalyst 17 with an amount of fuel corresponding to the oxidation ability of the exhaust purification catalyst 17 estimated in S112. That is, as the oxidizing ability of the exhaust purification catalyst 17 is higher, a larger amount of fuel can be oxidized. Therefore, the amount of fuel added to the exhaust from the fuel addition valve 12 is increased. When the process of S113 ends, the process proceeds to S114.

  In S114, the temperature of the exhaust purification catalyst 17 is estimated from the exhaust temperature flowing into the exhaust purification catalyst 17 detected from the upstream side exhaust temperature sensor 33, and the estimated temperature of the exhaust purification catalyst 17 is higher than the target temperature. It is determined whether or not. If it is determined in S114 that the exhaust temperature is higher than the target temperature, this control is terminated. In S114, when it is determined that the exhaust temperature is equal to or lower than the target temperature, the processing after S111 is performed again.

  According to this control, when fuel is supplied to the exhaust purification catalyst 17 in order to increase the temperature of the exhaust purification catalyst 17, the fuel supply start timing is determined based on the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17. . Furthermore, the supply start timing of each fuel is determined based on the oxygen concentration of the exhaust gas according to the molecular weight of the supplied fuel. Even when the fuel is supplied, an amount of fuel corresponding to the oxidizing ability of the exhaust purification catalyst 17 is supplied to the exhaust purification catalyst 17 based on the oxygen concentration of the exhaust. As a result, the temperature of the exhaust purification catalyst 17 is more reliably raised to the target temperature, and an appropriate amount of fuel is supplied in accordance with the oxidizing ability of the exhaust purification catalyst 17, so that the supplied fuel is efficient. Thus, it is possible to more reliably suppress the release of fuel to the atmosphere.

  In this control, the amount of fuel supplied to the exhaust purification catalyst 17 is increased or decreased according to the oxidation ability of the exhaust purification catalyst 17 estimated based on the oxygen concentration of the exhaust flowing into the exhaust purification catalyst 17. However, when the oxygen concentration of the exhaust gas exceeds a predetermined oxygen concentration, the fuel supply itself to the exhaust purification catalyst 17 may be interrupted. In particular, when fuel is added to the exhaust gas by the fuel addition valve 12, the molecular weight of the fuel is relatively large. Therefore, when the oxygen concentration of the exhaust gas is increased, the exhaust gas purification is performed as indicated by the line L1 in FIG. The oxidation ability of the catalyst 17 is significantly reduced. Therefore, the fuel supply itself may be interrupted in order to more reliably suppress the release of fuel to the atmosphere. It should be noted that the predetermined oxygen concentration serving as a reference for interrupting the fuel supply may be determined based on the characteristics of the oxidizing ability with respect to the oxygen concentration of the exhaust gas of the exhaust purification catalyst 17.

  In the exhaust purification system of the internal combustion engine 1 shown in FIG. 1, a single exhaust purification catalyst 17 is placed in the exhaust pipe 16 as a catalyst for exhaust purification. Therefore, the exhaust pipe 16 upstream of the exhaust purification catalyst 17 is further connected to the exhaust purification catalyst 17 in series so that the exhaust gas purification catalyst 17 has the same oxidation ability characteristic with respect to the oxygen concentration of the exhaust gas as at least. An upper exhaust purification catalyst which is a catalyst having noble metal and alkali metal as constituent components is provided.

As a result, even when the exhaust gas contains a large amount of oxygen, oxygen is adsorbed by the upper exhaust purification catalyst provided on the upstream side, so that the exhaust purification catalyst located on the downstream side has a relatively low oxygen concentration. Exhaust reaches. As a result, it becomes possible to maintain the oxidizing ability of the downstream side exhaust purification catalyst 17 high. Further, the fuel contained in the exhaust is not oxidized in the upper exhaust purification catalyst in which the oxygen is adsorbed and the oxidation ability is reduced, but is oxidized by the exhaust purification catalyst 17 that maintains the oxidation ability high. As a result, the temperature of the exhaust purification catalyst 17 can be efficiently increased, and the release of fuel to the atmosphere can be suppressed.

  Next, a second embodiment of the temperature rise control of the exhaust purification catalyst 17 in the internal combustion engine 1 and the exhaust purification system of the internal combustion engine 1 shown in FIG. 1 will be described based on FIG. FIG. 5 is a flowchart of the exhaust purification catalyst temperature raising control. The control is executed by the ECU 30.

  First, in S201, supply of fuel to the exhaust purification catalyst 17 is started. By adjusting the combustion conditions of the internal combustion engine 1 as indicated by S110 in FIG. 4 or by adding fuel to the exhaust from the fuel addition valve 12 as indicated by S113 in the same figure, these are simultaneously performed. By doing so, fuel is supplied to the exhaust purification catalyst 17. When the process of S201 ends, the process proceeds to S202.

  In S202, the oxygen concentration De of the exhaust gas flowing into the exhaust purification catalyst 17 is estimated from the operating state of the internal combustion engine 1 in the same manner as S101 in FIG. When the process of S202 ends, the process proceeds to S203.

  In S203, it is determined whether or not the exhaust oxygen concentration De estimated in S202 is greater than a predetermined oxygen concentration De0. Here, the predetermined oxygen concentration De0 is a threshold value for determining the degree of reduction in the oxidation ability of the exhaust purification catalyst 17. That is, when the oxygen concentration De of the exhaust gas is larger than De0, it means that the oxidation ability of the exhaust purification catalyst 17 is lowered and it is difficult to efficiently oxidize the supplied fuel. The predetermined oxygen concentration De0 may be varied in accordance with the amount of fuel supplied in S201, and is a value at which the oxidizing ability of the exhaust purification catalyst 17 is efficient as represented by the concentration S in FIG. It may be fixed to. If it is determined in S203 that the oxygen concentration De of the exhaust gas is greater than the predetermined oxygen concentration De0, the process proceeds to S204. On the other hand, if it is determined in S203 that the oxygen concentration De of the exhaust gas is equal to or lower than the predetermined oxygen concentration De0, the process proceeds to S206.

  In S204, the state of the molecular weight of the fuel contained in the exhaust flowing into the exhaust purification catalyst 17 is estimated. For example, in the fuel supplied in S201, the ratio of the amount of high molecular weight fuel added to the exhaust gas by the fuel addition valve 12 and the amount of low molecular weight fuel supplied by adjusting the combustion conditions of the internal combustion engine 1 Is estimated from the operating state of the internal combustion engine 1 and the amount of fuel added from the fuel addition valve 12. When the process of S204 ends, the process proceeds to S205.

  In S205, based on the molecular weight state of the fuel in the exhaust gas estimated in S204, the oxygen concentration of the exhaust gas flowing into the exhaust gas purification catalyst 17 is exhibited by the oxidizing ability of the exhaust gas purification catalyst 17 necessary for the oxidation of the supplied fuel. The opening degree of the EGR valve 20 is adjusted so that the oxygen concentration is adjusted. That is, as the amount of fuel supplied increases, the oxidizing ability of the exhaust purification catalyst 17 is required. Therefore, the opening degree of the EGR valve 20 is increased to reduce the oxygen concentration of the exhaust. Furthermore, as shown in FIG. 2, the oxidizing ability of the exhaust purification catalyst 17 varies depending on the molecular weight of the supplied fuel. Therefore, in S204, when the exhaust gas contains a large amount of fuel with a high molecular weight, the EGR valve 20 is used to reduce the oxygen concentration of the exhaust gas more than when the exhaust gas contains a large amount of fuel with a low molecular weight. Increase the opening of. Preferably, when the oxygen concentration of the exhaust gas is set to the same oxygen concentration (concentration S in FIG. 2) as when the air-fuel ratio of the exhaust gas is in a stoichiometric state, the oxidizing ability of the exhaust purification catalyst 17 can be maintained high. Become. When the processing of S205 ends, the process proceeds to S206.

  In S206, the temperature of the exhaust purification catalyst 17 is estimated from the exhaust temperature flowing into the exhaust purification catalyst 17 detected from the upstream side exhaust temperature sensor 33, and the estimated temperature of the exhaust purification catalyst 17 is higher than the target temperature. It is determined whether or not. If it is determined in S206 that the exhaust temperature is higher than the target temperature, this control is terminated. In S206, when it is determined that the exhaust temperature is equal to or lower than the target temperature, the processing from S202 is performed again.

  According to this control, when the fuel is supplied to the exhaust purification catalyst 17 in order to increase the temperature of the exhaust purification catalyst 17, the exhaust purification catalyst 17 exhibits the oxidizing ability necessary for the oxidation of the supplied fuel. The oxygen concentration is adjusted. As a result, the temperature of the exhaust purification catalyst 17 is more reliably increased to the target temperature, and the supplied fuel is efficiently oxidized, thereby more reliably suppressing the fuel from being released into the atmosphere. Is possible.

  When the opening degree of the EGR valve 20 is adjusted, the combustion condition of the fuel in the combustion chamber 3 fluctuates. Therefore, depending on the operating state of the internal combustion engine 1, the engine output fluctuates or the fuel combustion becomes unstable. There is a risk that. However, in this control, when the oxygen concentration De of the exhaust gas is less than or equal to the predetermined oxygen concentration De0 in S203, the opening degree of the EGR valve 20 is not adjusted, so the engine output and combustion of the internal combustion engine 1 are not adjusted. It becomes possible to avoid fluctuations in stability as much as possible. Furthermore, this control may not be performed when the opening of the EGR valve 20 is adjusted to cause fluctuations in the engine output and combustion stability of the internal combustion engine 1.

  In S205 of this control, the oxidation concentration of the exhaust gas flowing into the exhaust purification catalyst 17 is adjusted by adjusting the opening degree of the EGR valve 20. However, instead of the EGR valve 20, the opening degree of the intake throttle valve 10 is changed. The oxygen concentration of the exhaust gas may be adjusted by adjusting.

  Next, a third embodiment of the temperature rise control of the exhaust purification catalyst 17 in the internal combustion engine 1 and the exhaust purification system of the internal combustion engine 1 shown in FIG. 1 will be described based on FIG. FIG. 6 is a flowchart of the exhaust purification catalyst temperature raising control. The control is executed by the ECU 30.

  First, in S301, the timer Tr is started. When the process of S301 ends, the process proceeds to S302.

  In S302, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 is set to a rich air-fuel ratio. The control of the air-fuel ratio of the exhaust is performed by controlling the amount of fuel added to the exhaust from the fuel addition valve 12 based on the air-fuel ratio signal obtained from the exhaust air-fuel ratio sensor 35. When the process of S302 ends, the process proceeds to S303.

  In S303, it is determined whether or not the value of the timer Tr is greater than a predetermined time T0. When it is determined that the value of the timer Tr is greater than the predetermined time T0, the process proceeds to S304, and when it is determined that the value of the timer Tr is equal to or less than the predetermined time T0, the processes after S302 are performed again.

  In S304, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 is set to the air-fuel ratio in the vicinity of the stoichiometry. When the process of S305 ends, the process proceeds to S305.

  In S305, the temperature of the exhaust purification catalyst 17 is estimated from the exhaust temperature flowing into the exhaust purification catalyst 17 detected from the upstream side exhaust temperature sensor 33, and the estimated temperature of the exhaust purification catalyst 17 is higher than the target temperature. It is determined whether or not. If it is determined in S305 that the exhaust temperature is higher than the target temperature, this control is terminated. In S305, if it is determined that the exhaust temperature is equal to or lower than the target temperature, the processing from S304 is performed again.

  Here, FIG. 7 shows the transition of the air-fuel ratio of the exhaust gas adjusted by this control. The horizontal axis in FIG. 7 indicates time, and the vertical axis indicates the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17. Note that the air-fuel ratio of the exhaust when this control is executed is A1, and A1 is a lean air-fuel ratio as shown in FIG. By executing this control, the air-fuel ratio of the exhaust gas changes from the lean air-fuel ratio A1 to the rich air-fuel ratio A2, and the state where the exhaust air-fuel ratio is A2 is maintained for a time T0. Thereafter, the air-fuel ratio of the exhaust is set to an air-fuel ratio in the vicinity of stoichiometric A0.

  As a result, first, in the temperature raising control of the exhaust purification catalyst 17, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 is first made rich so that oxygen poisoning of the exhaust purification catalyst 17 is eliminated. As a result, the oxidizing ability of the exhaust purification catalyst 17 increases, and the supplied fuel is oxidized more efficiently. Therefore, it is preferable that the time T0 is a time sufficient for eliminating the oxygen poisoning of the exhaust purification catalyst 17. In order to eliminate oxygen poisoning of the exhaust purification catalyst 17 more efficiently, hydrogen or carbon monoxide as a reducing agent may be supplied to the exhaust purification catalyst 17 at the same time. Thereafter, the air-fuel ratio of the exhaust gas becomes an air-fuel ratio in the vicinity of the stoichiometric ratio, so that fuel is supplied in a state where the exhaust purification catalyst 17 has a high oxidizing ability, so that the temperature of the exhaust purification catalyst 17 reaches the target temperature. It becomes possible to further suppress the release of fuel into the atmosphere and the deterioration of fuel consumption due to excessive fuel supply.

  Next, a fourth embodiment of the temperature rise control of the exhaust purification catalyst 17 in the internal combustion engine 1 and the exhaust purification system of the internal combustion engine 1 shown in FIG. 1 will be described. In the above-described embodiments, the fuel supply to the exhaust purification catalyst 17 and the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17 are controlled based on the oxidizing ability of the exhaust purification catalyst 17.

  Therefore, in the present embodiment, the supply of fuel to the exhaust purification catalyst 17 and the oxygen concentration of the exhaust are further controlled in consideration of catalyst deterioration of the exhaust purification catalyst 17. First, the degree of catalyst deterioration of the exhaust purification catalyst 17 is estimated from the exhaust temperatures detected by the upstream side exhaust temperature sensor 33 and the downstream side exhaust temperature sensor 34. For example, when the amount of fuel added to the exhaust from the fuel addition valve 12 is Q, when the temperature of the exhaust gas is essentially increased by ΔT1 by the exhaust purification catalyst 17, it is detected by the upstream side exhaust temperature sensor 33 and the downstream side exhaust temperature sensor 34. If the difference in exhaust gas temperature is ΔT2 (ΔT2 <ΔT1), it is considered that the catalytic function of the exhaust purification catalyst 17 is deteriorated by an amount corresponding to ΔT1−ΔT2. When the catalytic function of the exhaust purification catalyst 17 deteriorates, its oxidizing ability decreases.

  Therefore, based on the decrease ΔT1-ΔT2 in the temperature increase of the exhaust purification catalyst 17, the oxidation ability of the exhaust purification catalyst 17 or the parameter related to the oxidation ability in the above-described embodiments is corrected. For example, when the exhaust purification catalyst 17 has deteriorated, its oxidizing ability is lowered, and therefore, correction for reducing the amount of fuel supply according to the oxidizing ability is performed. That is, as the decrease ΔT2-ΔT1 in the temperature increase of the exhaust purification catalyst 17 increases, the amount of fuel supplied according to the oxidizing ability of the exhaust purification catalyst 17 is further reduced.

  When the exhaust purification catalyst 17 has deteriorated, the fuel supply start temperature Tst, which is the temperature of the exhaust purification catalyst 17 at which fuel supply to the exhaust purification catalyst 17 is started, or the exhaust gas from the fuel addition valve 12 to the exhaust. The value of the fuel addition start temperature Tast, which is the temperature of the exhaust purification catalyst 17 at which fuel addition starts, may be increased as the degree of catalyst deterioration increases. Furthermore, when the oxidation capacity of the exhaust purification catalyst 17 is controlled by adjusting the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 17, the exhaust gas becomes more exhausted as the degree of catalyst deterioration of the exhaust purification catalyst 17 increases. In order to reduce the oxygen concentration, the opening of the EGR valve 20 may be increased, or the opening of the intake throttle valve 10 may be decreased.

  By correcting the oxidizing ability of the exhaust purification catalyst 17 as described above, it is possible to more appropriately supply fuel to the exhaust purification catalyst 17 and control the oxygen concentration of the exhaust, and thus the temperature of the exhaust purification catalyst 17 can be further increased. It is possible to reliably increase the target temperature and more reliably suppress the release of fuel to the atmosphere.

  In the above-described embodiment, in the exhaust purification system of the internal combustion engine 1 shown in FIG. 1, the exhaust purification catalyst 17 for purifying the exhaust is composed of at least a noble metal and an alkali metal as described above. The catalyst exhibits a characteristic that the oxidation ability of the exhaust gas that flows into the exhaust purification catalyst 17 decreases as the oxygen concentration of the exhaust gas increases. Here, in the present embodiment, instead of the exhaust purification catalyst 17 exhibiting the characteristics, the internal combustion engine 1 that uses the exhaust purification catalyst 21 that is a catalyst having a noble metal as a constituent component and not an alkali metal as a constituent component. 1 shows an exhaust purification system.

  Since the exhaust purification catalyst 21 does not contain an alkali metal as a constituent component, the precious metal as a constituent component is less likely to cause oxygen poisoning than the exhaust purification catalyst 17. Therefore, unlike the case of the exhaust purification catalyst 17, the characteristics of the oxidation ability of the exhaust purification catalyst 21 show the characteristic that the oxidation ability of the catalyst increases as the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 21 increases. This is because the precious metal that is a component is less likely to be in an oxygen-poisoned state, so that the more oxygen is present in the exhaust, the more actively the oxidation of the fuel supplied to the exhaust purification catalyst 18 is considered. It is done.

  Therefore, when the temperature of the exhaust purification catalyst 21 is increased by supplying fuel, the characteristics of the oxidizing ability exhibited by the exhaust purification catalyst 21 are taken into consideration. FIG. 8 shows a graph of the transition of the oxidizing ability of the exhaust purification catalyst 21 with respect to the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 21. The horizontal axis of the graph indicates the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 21, and the oxygen concentration represented by the point S on the horizontal axis indicates that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 21 is in a stoichiometric state. Of oxygen concentration. Further, the vertical axis of the graph indicates the HC oxidation rate representing the oxidation ability of the exhaust purification catalyst 21. Here, the HC oxidation rate is synonymous with the HC oxidation rate in FIG. In FIG. 8, the temperature of the exhaust purification catalyst 21 is a constant temperature that reaches the activation temperature.

In FIG. 8, a line L5 is a transition of the HC oxidation rate when the molecular weight of the fuel supplied to the exhaust purification catalyst 21 is relatively large. In the present embodiment, the fuel is represented by C ₁₀ H _22. . The line L6 is the transition of the HC oxidation rate when the molecular weight of the fuel supplied to the exhaust purification catalyst 21 is relatively low. In the present embodiment, the fuel is represented by C ₃ H ₆ . Accordingly, as the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 21 increases, the HC oxidation rate of the exhaust purification catalyst 21 increases. Even if the oxygen concentration of the exhaust gas is the same, the HC oxidation rate of the exhaust purification catalyst 21 increases as the molecular weight of the fuel supplied to the exhaust purification catalyst 21 increases.

Therefore, when the fuel is supplied to the exhaust purification catalyst 21 to increase the temperature of the exhaust purification catalyst 21 by utilizing its oxidizing ability, the characteristics shown in FIG. 8 are considered. For example, similarly to S101 in FIG. 4, the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 21 from the operating state of the internal combustion engine 1 is estimated. Next, based on the estimated oxygen concentration of the exhaust gas and the transition of the oxidation ability of the exhaust purification catalyst 21 shown in FIG. 8, the oxidation ability exhibited by the exhaust purification catalyst 21 at the time of supplying fuel is estimated. Then, an amount of fuel corresponding to the estimated oxidation ability of the exhaust purification catalyst 21 is supplied to the exhaust purification catalyst 21. That is, when the oxygen concentration of the exhaust gas is high, the oxidizing ability of the exhaust gas purification catalyst 21 increases. Accordingly, the amount of fuel supplied to the exhaust gas purification catalyst 21 is increased accordingly, and the exhaust gas purification concentration decreases as the exhaust gas oxygen concentration decreases. Since the oxidizing ability of the catalyst 21 is lowered, the amount of fuel supplied to the exhaust purification catalyst 21 is reduced accordingly. By supplying such fuel to the exhaust purification catalyst 21, the temperature of the exhaust purification catalyst 21 is more reliably raised to the target temperature, and the supplied fuel is released by the exhaust purification catalyst 21 into the atmosphere without being oxidized. It can be suppressed.

  As shown in FIG. 8, the oxidation efficiency of the fuel by the exhaust purification catalyst 21 also varies depending on the molecular weight of the fuel supplied to the exhaust purification catalyst 21. Therefore, when the oxygen concentration of the exhaust gas is the same, if the molecular weight of the fuel supplied to the exhaust gas purification catalyst 21 is large, for example, the fuel is added to the exhaust gas by the fuel addition valve 12 so that the fuel is supplied to the exhaust gas purification catalyst 21. In the case of supply, when the molecular weight of the fuel is small, for example, by adjusting the combustion conditions of the internal combustion engine 1, the amount of supplied fuel is increased compared to the case of supplying fuel to the exhaust purification catalyst 21. May be.

  Further, the oxidizing ability of the exhaust purification catalyst 21 also varies depending on the oxygen concentration of the inflowing exhaust gas. Therefore, the oxygen concentration of the exhaust may be adjusted according to the fuel supplied to the exhaust purification catalyst 21. Therefore, the molecular weight state of the fuel in the exhaust gas flowing into the exhaust purification catalyst 21 is estimated, and the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst 21 is supplied based on the estimated molecular weight state of the fuel in the exhaust gas. The opening degree of the EGR valve 20 and the opening degree of the intake throttle valve 10 are adjusted so as to obtain an oxygen concentration at which the oxidizing ability of the exhaust purification catalyst 21 required for the oxidation of fuel is exhibited.

  That is, as the amount of fuel supplied increases, the oxidizing ability of the exhaust purification catalyst 21 is required, so the oxygen concentration of the exhaust increases. Further, as shown in FIG. 8, the oxidizing ability of the exhaust purification catalyst 21 varies depending on the molecular weight of the supplied fuel. Therefore, when the estimated molecular weight state of the fuel in the exhaust gas is a state in which a lot of fuel having a low molecular weight is contained in the exhaust gas, compared to a case in which the exhaust gas contains a large amount of fuel having a high molecular weight. In order to further increase the oxygen concentration of the exhaust gas, the opening degree of the EGR valve 20 is reduced or the opening degree of the intake throttle valve 10 is increased.

  As a result, when the fuel is supplied to the exhaust purification catalyst 21 in order to increase the temperature of the exhaust purification catalyst 21, the exhaust purification catalyst 21 exerts the oxidizing ability necessary for the oxidation of the supplied fuel so that the oxygen of the exhaust The density is adjusted. As a result, the temperature of the exhaust purification catalyst 21 is more reliably increased to the target temperature, and the supplied fuel is efficiently oxidized, thereby more reliably suppressing the fuel from being released into the atmosphere. Is possible.

1 is a block diagram showing a schematic configuration of an exhaust purification system for an internal combustion engine and a control system of the exhaust purification system according to an embodiment of the present invention. 6 is a graph showing a transition of the oxidation ability of the exhaust purification catalyst with respect to the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst of the exhaust purification catalyst in the exhaust purification system of the internal combustion engine according to the embodiment of the present invention. 4 is a graph showing a transition of the oxidation ability of the exhaust purification catalyst with respect to the temperature of the exhaust purification catalyst in the exhaust purification system of the internal combustion engine according to the embodiment of the present invention. 5 is a first control flowchart for performing temperature increase control of the exhaust purification catalyst in the exhaust purification system of the internal combustion engine according to the embodiment of the present invention. 6 is a second control flowchart for performing temperature increase control of the exhaust purification catalyst in the exhaust purification system of the internal combustion engine according to the embodiment of the present invention. 7 is a third control flowchart for performing temperature increase control of an exhaust purification catalyst in the exhaust purification system of the internal combustion engine according to the embodiment of the present invention. In the exhaust gas purification system for an internal combustion engine according to the embodiment of the present invention, the transition of the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst when the floor temperature control of the exhaust gas purification catalyst shown in the third control flowchart is performed is shown. It is a graph. 6 is a graph showing a transition of the oxidation ability of the exhaust purification catalyst with respect to the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst of the exhaust purification catalyst in the exhaust purification system of the internal combustion engine according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Combustion chamber 4 ... Fuel injection valve 10 ... Intake throttle valve 12 ... Fuel addition valve 17 ... Exhaust gas purification catalyst 20 ...・ EGR valve 21 ・ ・ ・ ・ Exhaust gas purification catalyst 30 ・ ・ ・ ・ ECU
31 ... Accelerator opening sensor 32 ... Crank position sensor 33 ... Upstream exhaust temperature sensor 34 ... Downstream exhaust temperature sensor 35 ... Exhaust air / fuel ratio sensor

Claims (17)

A catalyst that is provided in an exhaust passage of an internal combustion engine and has an oxidizing ability to oxidize substances contained in exhaust flowing through the exhaust passage, and has a characteristic that the oxidizing ability of the catalyst decreases as the oxygen concentration of the exhaust increases. An exhaust purification catalyst shown,
Oxygen concentration acquisition means for detecting or estimating the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst;
Fuel supply means for supplying fuel to the exhaust purification catalyst;
The oxidation ability of the exhaust purification catalyst is estimated based on the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means, and the fuel to the exhaust purification catalyst by the fuel supply means is based on the estimated oxidation ability An exhaust purification system for an internal combustion engine, comprising: a fuel supply control means for controlling the supply of the internal combustion engine. The fuel supply control means reduces the amount of fuel supplied to the exhaust purification catalyst by the fuel supply means as the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means increases. The exhaust gas purification system for an internal combustion engine according to claim 1. The fuel supply control means prohibits the fuel supply means from supplying fuel to the exhaust purification catalyst when the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means exceeds a predetermined oxygen concentration. The exhaust gas purification system for an internal combustion engine according to claim 2, wherein the exhaust gas purification system is an internal combustion engine. The fuel supply control means controls the fuel supply to the exhaust purification catalyst based on the temperature of the exhaust purification catalyst, and the fuel supply means based on the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the temperature of the exhaust gas purification catalyst at which fuel supply to the exhaust gas purification catalyst is started is determined. The fuel supply means has fuel addition means for adding fuel to the exhaust gas flowing into the exhaust purification catalyst,
The fuel supply control means determines the fuel addition start time to the exhaust gas by the fuel addition means based on the oxygen concentration of the exhaust gas detected or estimated by the oxygen concentration acquisition means. Exhaust gas purification system for internal combustion engines. In the time before the fuel addition start time determined by the fuel supply control means, fuel is supplied to the exhaust purification catalyst by adjusting the combustion conditions of the internal combustion engine,
The fuel is supplied to the exhaust purification catalyst by starting the fuel addition to the exhaust gas by the fuel addition means at a time after the fuel addition start time determined by the fuel supply control means. Item 6. An exhaust gas purification system for an internal combustion engine according to Item 5. The fuel supply control means calculates the temperature of the exhaust purification catalyst that starts adding fuel to the exhaust gas by the fuel addition means based on the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquisition means;
7. The fuel addition start time to the exhaust gas by the fuel addition unit is set when the temperature of the exhaust purification catalyst exceeds the temperature calculated by the fuel supply control unit. Exhaust gas purification system for internal combustion engines. A catalyst that is provided in an exhaust passage of an internal combustion engine and has an oxidizing ability to oxidize substances contained in exhaust flowing through the exhaust passage, and has a characteristic that the oxidizing ability of the catalyst decreases as the oxygen concentration of the exhaust increases. An exhaust purification catalyst shown,
Fuel supply means for supplying fuel to the exhaust purification catalyst;
An exhaust gas purification system for an internal combustion engine, comprising: oxygen concentration control means for reducing the oxygen concentration of exhaust gas flowing into the exhaust gas purification catalyst when fuel is supplied to the exhaust gas purification catalyst by the fuel supply means. Oxygen concentration acquisition means for detecting or estimating the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst,
The oxygen concentration control means reduces the oxygen concentration of exhaust flowing into the exhaust purification catalyst when the oxygen concentration of exhaust detected or estimated by the oxygen concentration acquisition means exceeds a predetermined concentration. The exhaust gas purification system for an internal combustion engine according to claim 8. The oxygen concentration control means, when supplying fuel to the exhaust purification catalyst by the fuel supply means, makes the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a substantially stoichiometric air-fuel ratio. The exhaust purification system for an internal combustion engine according to claim 8. The oxygen concentration control means makes the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst richer than the substantially stoichiometric air-fuel ratio in a predetermined period after the fuel supply means starts supplying fuel to the exhaust purification catalyst. The exhaust gas purification system for an internal combustion engine according to claim 10, wherein the air-fuel ratio is in a state. A molecular weight state estimating means for estimating a molecular weight state of fuel contained in the exhaust gas flowing into the exhaust purification catalyst;
The oxygen concentration control means increases the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst as the molecular weight state estimation means estimates that the exhaust gas flowing into the exhaust purification catalyst contains a larger amount of fuel having a higher molecular weight. 9. The exhaust gas purification system for an internal combustion engine according to claim 8, wherein the exhaust gas purification system is reduced. The exhaust purification system for an internal combustion engine according to any one of claims 1 to 12, wherein the exhaust purification catalyst is a catalyst composed of at least a noble metal and an alkali metal. The exhaust purification catalyst is a catalyst composed of at least a noble metal and an alkali metal,
The exhaust gas purification catalyst according to any one of claims 1 to 12, further comprising an upper exhaust gas purification catalyst that is provided in an exhaust passage upstream of the exhaust gas purification catalyst and includes at least a noble metal and an alkali metal. An exhaust purification system for an internal combustion engine. A catalyst which is provided in an exhaust passage of an internal combustion engine and has an oxidizing ability to oxidize substances contained in exhaust flowing through the exhaust passage, and has a characteristic that the oxidizing ability of the catalyst increases as the oxygen concentration of the exhaust increases. An exhaust purification catalyst shown,
Oxygen concentration acquisition means for detecting or estimating the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst;
Oxidizing capacity estimating means for estimating the oxidizing capacity of the exhaust purification catalyst based on the oxygen concentration of the exhaust detected or estimated by the oxygen concentration acquiring means;
Exhaust gas purification of an internal combustion engine, comprising: fuel supply control means for reducing the amount of fuel supplied to the exhaust gas flowing into the exhaust gas purification catalyst as the oxidation capacity of the exhaust gas purification catalyst estimated by the oxidation capacity estimation means decreases system. A catalyst which is provided in an exhaust passage of an internal combustion engine and has an oxidizing ability to oxidize substances contained in exhaust flowing through the exhaust passage, and has a characteristic that the oxidizing ability of the catalyst increases as the oxygen concentration of the exhaust increases. An exhaust purification catalyst shown,
A molecular weight state estimating means for estimating a molecular weight state of fuel contained in the exhaust gas flowing into the exhaust purification catalyst;
Oxygen concentration control means for increasing the oxygen concentration of the exhaust gas flowing into the exhaust purification catalyst so that the exhaust gas flowing into the exhaust purification catalyst is estimated to contain a large amount of low molecular weight fuel by the molecular weight state estimation means; An exhaust gas purification system for an internal combustion engine, comprising: 17. The exhaust gas purification system for an internal combustion engine according to claim 15 or 16, wherein the exhaust gas purification catalyst is a catalyst having a noble metal as a constituent component and not an alkali metal as a constituent component.

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