JP2006152875A - Catalyst heating system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To rapidly heating a catalyst while suppressing the deterioration of exhaust emission in a catalyst heating system of an internal combustion engine for increasing the temperature of the catalyst with oxidation function installed in the exhaust passage of the internal combustion engine. <P>SOLUTION: When unburned fuel is supplied to the catalyst to heat the temperature of the catalyst with the oxidation function installed in the exhaust passage of the internal combustion engine, a catalyst temperature rising rate is calculated. In a time period from the start of supply of the unburned fuel to the catalyst to a time point when the temperature rise rate of the catalyst first reaches a prescribed temperature rise rate or higher, the supplied amount of the unburned fuel per unit time to the catalyst is controlled based on the sucked amount of air of the internal combustion engine (S103). After a time point when the temperature rise rate of the catalyst is changed first to the prescribed temperature rise rate or higher, the supplied amount of the unburned fuel per unit time to the catalyst is controlled based on the sucked amount of air of the internal combustion engine and the temperature of the catalyst (S105). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a catalyst temperature raising system for an internal combustion engine that raises the temperature of a catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine.

  As a catalyst temperature raising system for an internal combustion engine that raises the temperature of a catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine, a technique for raising the temperature of the catalyst by executing sub fuel injection in addition to main fuel injection in the internal combustion engine It has been known.

  In such a catalyst temperature raising system for an internal combustion engine, for example, by performing sub fuel injection at the timing when the injected fuel burns in the cylinder, the exhaust temperature is raised, thereby raising the catalyst to the activation temperature. Let warm. After the temperature of the catalyst rises to the activation temperature, the injected fuel is not burned in the cylinder, and the sub-fuel injection is performed at the timing when the cylinder is discharged in the unburned state. There is one that is supplied to a catalyst and raises the temperature of the catalyst to a target temperature higher than the activation temperature by oxidation heat generated when the unburned fuel is oxidized by the catalyst (see, for example, Patent Document 1).

Further, when the catalyst having an oxidation function is supported on a particulate filter (hereinafter simply referred to as a filter) that collects particulate matter (hereinafter referred to as PM) in the exhaust gas, or upstream of the filter When the temperature of the catalyst is raised and the temperature of the filter is raised by the catalyst temperature raising system of the internal combustion engine as described above, the technology for oxidizing and removing the PM deposited on the filter is provided. It is known (for example, refer to Patent Document 2).
JP 2004-183506 A JP-A-7-259533 JP 2002-332899 A

  In a catalyst temperature raising system for an internal combustion engine that raises the temperature of a catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine, when the catalyst is in an active state, the temperature of the catalyst is further increased in order to further raise the temperature of the catalyst. In some cases, unburned fuel is supplied to the catalyst from the side.

  At this time, the temperature of the catalyst can be raised more quickly by increasing the amount of unburned fuel supplied to the catalyst per unit time. However, if the amount of unburned fuel supplied to the catalyst increases excessively, the amount of unburned fuel that is released into the atmosphere without being oxidized in the catalyst may increase, leading to deterioration in exhaust emission.

  The present invention has been made in view of the above problems, and suppresses deterioration of exhaust emission in a catalyst temperature rising system for an internal combustion engine that raises the temperature of a catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine. However, it is an object of the present invention to provide a technique capable of quickly raising the temperature of the catalyst.

In the present invention, when the unburned fuel is supplied to the catalyst having an oxidation function provided in the exhaust passage of the internal combustion engine to increase the temperature, the temperature increase rate of the catalyst is calculated. The amount of unburned fuel supplied to the catalyst per unit time after the start of the supply of unburned fuel to the catalyst until the point when the temperature rise rate of the catalyst first exceeds the specified temperature rise rate Is controlled based on the intake air amount of the internal combustion engine, and after the time when the temperature increase rate of the catalyst first changes to a specified temperature increase rate or more, the amount of unburned fuel supplied to the catalyst per unit time is reduced. Control based on the amount of intake air and the temperature of the catalyst.

More specifically, the catalyst temperature raising system for an internal combustion engine according to the present invention is:
In a catalyst temperature raising system for an internal combustion engine that raises the temperature of a catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine,
Unburned fuel supply means for supplying unburned fuel to the catalyst from the upstream side of the catalyst when the temperature of the catalyst is raised when the catalyst is in an active state;
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
Catalyst temperature detecting means for detecting the temperature of the catalyst;
A catalyst temperature increase rate calculating means for calculating a catalyst temperature increase rate that is a temperature increase amount of the catalyst per specified time when unburned fuel is supplied to the catalyst by the unburned fuel supply means;
Unburned fuel supply amount control means for controlling the supply amount of unburned fuel per unit time by the unburned fuel supply means,
In the unburned fuel supply amount control means, after the unburned fuel supply means starts supplying unburned fuel, the catalyst temperature increase rate calculated by the catalyst temperature increase rate calculating means is the first specified temperature increase rate. Until this time, the amount of unburned fuel supplied by the unburned fuel supply means per unit time is controlled based on the amount of intake air detected by the intake air amount detection means, and the catalyst temperature rises. After the time when the catalyst temperature increase rate calculated by the rate calculation means first becomes equal to or higher than the specified temperature increase rate, the intake air amount detected by the intake air amount detection means and the catalyst temperature detection means are detected. The supply amount of unburned fuel per unit time by the unburned fuel supply means is controlled based on the temperature of the catalyst.

  Here, the unburned fuel supply means is, for example, a sub fuel injection (hereinafter, referred to as “sub fuel injection”) performed at a timing at which fuel injected in the internal combustion engine is discharged from the cylinder in an unburned state without mainly burning in the cylinder. (Referred to as post fuel injection), or by adding exhaust fuel that is performed by adding fuel into the exhaust gas in the exhaust passage upstream of the catalyst, the unburned fuel is supplied to the catalyst from the upstream side of the catalyst. Supply.

  When unburned fuel is supplied to the catalyst by the unburned fuel supply means, the temperature of the catalyst rises due to oxidation heat generated when the unburned fuel is oxidized by the catalyst. In the present invention, the catalyst temperature increase rate, which is the temperature increase amount of the catalyst per specified time, is calculated by the catalyst temperature increase rate calculating means.

  At this time, the oxidation of the unburned fuel is difficult to be promoted since the temperature of the catalyst is relatively low until a certain period of time elapses after the supply of unburned fuel is started. Therefore, the catalyst temperature increase rate is a relatively low value. When a certain amount of time elapses after the supply of unburned fuel is started and the temperature of the catalyst rises, oxidation of the unburned fuel is easily promoted. Therefore, the catalyst temperature increase rate is a relatively high value. That is, at the point of time when the state where the oxidation of the unburned fuel is difficult to promote is changed to the state where the oxidation of the unburned fuel is easily promoted, the change in the catalyst temperature increase rate at which the catalyst temperature increase rate changes to the specified temperature increase rate or more. A point arises.

  Here, the specified temperature increase rate is a threshold value of the catalyst temperature increase rate at which it can be determined that the state in which the oxidation of unburned fuel in the catalyst is hardly promoted to the state in which the oxidation of unburned fuel in the catalyst is easily promoted. Also good. In addition, after the start of the supply of the unburned fuel by the unburned fuel supply means, if the catalyst temperature increase rate becomes equal to or higher than the specified temperature increase rate, the catalyst temperature increase rate is lower than the specified temperature increase rate after that point. Even in this case, the oxidation of the unburned fuel in the catalyst is easily promoted.

  Further, when it is difficult to promote the oxidation of unburned fuel in the catalyst, if the amount of unburned fuel supplied from the unburned fuel supply means (hereinafter simply referred to as supplied unburned fuel) is the same, the catalyst will oxidize. The amount of unburned fuel (hereinafter simply referred to as discharged unburned fuel) that is released into the atmosphere without increasing increases as the intake air amount of the internal combustion engine increases.

  That is, as the intake air amount of the internal combustion engine increases, the flow rate of exhaust gas passing through the catalyst (hereinafter simply referred to as exhaust flow rate) increases. Even if the oxidation of the unburned fuel in the catalyst is difficult to promote, if the exhaust flow rate is small to some extent, at least a part of the supplied unburned fuel adheres to the catalyst without being oxidized in the catalyst. Therefore, the smaller the exhaust flow rate, the more the amount of unburned fuel that is released is suppressed. However, as the intake air amount of the internal combustion engine increases, that is, as the exhaust flow rate increases, the unburned fuel in the exhaust becomes less likely to adhere to the catalyst. The amount will decrease. Therefore, as the intake air amount of the internal combustion engine increases, the ratio of the released unburned fuel amount to the supplied unburned fuel amount increases.

  On the other hand, when oxidation of unburned fuel in the catalyst is easily promoted, if the amount of supplied unburned fuel is the same, the amount of released unburned fuel increases as the intake air amount of the internal combustion engine increases, and the temperature of the catalyst increases. The higher the value, the lower.

  That is, even when the oxidation of unburned fuel in the catalyst is easily promoted, the unburned fuel that passes through the catalyst without being oxidized in the catalyst increases as the exhaust gas flow rate increases. Will do. However, in this case, the higher the temperature of the catalyst, the more the oxidation of unburned fuel in the catalyst is promoted. Therefore, the ratio of the amount of unburned fuel released to the amount of unburned fuel supplied decreases as the temperature of the catalyst increases.

  Therefore, in the present invention, from the start of the supply of unburned fuel by the unburned fuel supply means, until the catalyst temperature increase rate calculated by the catalyst temperature increase rate calculation means first exceeds the specified temperature increase rate. In other words, when the oxidation of unburned fuel in the catalyst is difficult to promote, the amount of unburned fuel supplied per unit time is controlled based on the intake air amount of the internal combustion engine. At this time, the larger the intake air amount of the internal combustion engine, the smaller the amount of unburned fuel supplied per unit time.

  Then, after the time when the catalyst temperature increase rate calculated by the catalyst temperature increase rate calculating means first becomes equal to or higher than the specified temperature increase rate, that is, when the oxidation of unburned fuel in the catalyst is easily promoted, the intake of the internal combustion engine The amount of unburned fuel supplied per unit time is controlled based on the amount of air and the temperature of the catalyst. At this time, the amount of supplied unburned fuel per unit time decreases as the intake air amount of the internal combustion engine increases, and the amount of supplied unburned fuel per unit time increases as the catalyst temperature increases.

  According to such control of the amount of unburned fuel supplied, when unburned fuel is supplied to the catalyst to raise the temperature of the catalyst, the amount of unburned fuel released is suppressed and the amount of unburned fuel to the catalyst per unit time is suppressed. Fuel supply can be increased as much as possible. Therefore, according to the present invention, the temperature of the catalyst can be raised more rapidly while suppressing the deterioration of exhaust emission.

  In the present invention, the specified time when the catalyst temperature increase rate is calculated by the catalyst temperature increase rate calculating means is determined when the calculated catalyst temperature increase rate is equal to or greater than the specified temperature increase rate. It is a time when it can be determined that the cause is a change from a state in which oxidation is hardly promoted to a state in which oxidation of unburned fuel in the catalyst is easily promoted.

In the present invention, when the exhaust throttle valve further provided in the exhaust passage downstream from the catalyst is further provided, the catalyst temperature increase rate is first increased by the specified temperature after the supply of unburned fuel by the unburned fuel supply means is started. The exhaust throttle valve may be in a closed state until the time when the rate becomes equal to or higher than the rate, and the exhaust throttle valve may be opened after the time when the catalyst temperature increase rate first exceeds the specified temperature increase rate.

  Here, the closed state of the exhaust throttle valve means that the flow rate of the exhaust is throttled by controlling the exhaust throttle valve in the valve closing direction. Further, opening the exhaust throttle valve means that the exhaust throttle valve has a larger opening than when the exhaust throttle valve is closed, and includes a case where the exhaust throttle valve is fully opened. .

  When the exhaust throttle valve is closed, the pressure in the exhaust passage on the upstream side of the exhaust throttle valve increases compared to when the exhaust throttle valve is opened. Therefore, for example, when unburned fuel is supplied to the catalyst by post fuel injection, if the exhaust throttle valve is closed, the fuel injected by the post fuel injection becomes difficult to be discharged from the internal combustion engine. As a result, part of the supplied unburned fuel tends to remain in the cylinder. In addition, in the case where unburned fuel is supplied to the catalyst by adding exhaust fuel in the exhaust passage, if the exhaust throttle valve is closed, a part of the supplied unburned fuel added by adding the exhaust fuel flows backward. It becomes easy to flow into the cylinder. The unburned fuel remaining or flowing into the cylinder is burned in the cylinder. Therefore, if the exhaust throttle valve is closed when unburned fuel is being supplied to the catalyst by the unburned fuel supply means, it is actually supplied to the catalyst compared to when the exhaust throttle valve is opened. Less unburned fuel.

  Therefore, when it is difficult to promote the oxidation of the unburned fuel in the catalyst, that is, from the start of the supply of the unburned fuel by the unburned fuel supply means until the time when the catalyst temperature increase rate first exceeds the specified temperature increase rate. In the meantime, by closing the exhaust throttle valve, for example, even if there is a variation in the amount of unburned fuel supplied by the unburned fuel supply means, the amount of released unburned fuel can be further suppressed. I can do it.

  On the other hand, when the exhaust throttle valve is opened, the exhaust flow rate is increased compared to when the exhaust throttle valve is closed. Therefore, if the exhaust throttle valve is closed when unburned fuel is being supplied to the catalyst by the unburned fuel supply means, the unburned fuel is more quickly compared to when the exhaust throttle valve is open. Will be supplied to the catalyst.

  Therefore, when the oxidation of unburned fuel in the catalyst is likely to be promoted, that is, after the catalyst temperature increase rate first exceeds the specified temperature increase rate, the exhaust throttle valve is opened to open the catalyst. It becomes possible to raise the temperature more quickly. In this case, it is preferable that the exhaust throttle valve is fully opened.

  Therefore, according to the control of the exhaust throttle valve as described above, the temperature of the catalyst can be raised more quickly while suppressing the deterioration of exhaust emission.

  In the present invention, the catalyst is in a state of being supported by a filter, and further includes an exhaust throttle valve provided in an exhaust passage on the downstream side of the filter. In the case where the specified temperature increase rate is set, when the unburned fuel is being supplied by the unburned fuel supply means, the second specified rate in which the temperature increase rate of the catalyst is higher than the first specified temperature increase rate. When the temperature rise rate becomes equal to or higher than the temperature increase rate, the supply of unburned fuel by the unburned fuel supply means may be stopped, the opening of the exhaust throttle valve may be increased, or the exhaust throttle valve may be fully opened.

When the catalyst is supported on the filter, the temperature of the filter increases as the temperature of the catalyst increases. When the temperature of the filter rises to a certain level, the oxidation of PM deposited on the filter is promoted, and the temperature of the filter and the catalyst further rises due to the oxidation heat of PM. At this time, the rate of temperature increase of the catalyst and the filter increases as the amount of PM accumulated in the filter increases.

  Here, the second specified temperature increase rate is a value by which it can be determined that the temperature increase rate of the catalyst and the filter has increased excessively because the PM accumulation amount in the filter is excessively large. If the temperature increase rate of the catalyst is equal to or higher than the second specified temperature increase rate, the second specified temperature increase rate is determined by the oxidation heat of PM when the catalyst temperature rise by supplying unburned fuel is continued. It may be a threshold value of a temperature increase rate at which it can be determined that there is a risk that the filter will overheat.

  Therefore, in the present invention, when the unburned fuel is being supplied by the unburned fuel supply means, when the temperature increase rate of the catalyst becomes equal to or higher than the second specified temperature increase rate, that is, the filter is excessive. When it can be determined that there is a risk of temperature rise, stop the supply of unburned fuel from the unburned fuel supply means, increase the opening of the exhaust throttle valve, or leave the exhaust throttle valve fully open. good.

  When the opening of the exhaust throttle valve is increased, the exhaust flow rate increases, so that the amount of heat removed from the filter by the exhaust (hereinafter simply referred to as the amount of heat removed) increases. Further, when the exhaust throttle valve is fully opened, the amount of heat taken away can be increased as much as possible. Therefore, by stopping the supply of unburned fuel from the unburned fuel supply means and controlling the exhaust throttle valve, it is possible to suppress the excessive temperature rise of the filter.

  As described above, when the temperature of the catalyst is raised again by supplying unburned fuel to the catalyst after stopping the supply of unburned fuel by the unburned fuel supply means, the exhaust throttle valve is closed. However, the supply of unburned fuel from the unburned fuel supply means may be started.

  In this case, when the supply of unburned fuel by the unburned fuel supply means is started, the temperature of the catalyst may be lowered to a temperature at which oxidation of the unburned fuel is difficult to be promoted. Therefore, when the supply of unburned fuel by the unburned fuel supply means is started to raise the temperature of the catalyst again, the exhaust throttle valve is closed. Thereby, as above-mentioned, the amount of emitted unburned fuel can be suppressed.

  Therefore, according to the above control, it is possible to suppress the deterioration of the emission even when the temperature of the catalyst is raised again.

  Further, when the exhaust throttle valve is closed, the pressure in the exhaust passage increases, so that the oxidation of PM deposited on the filter is easily promoted. Therefore, the amount of PM deposited on the filter can be reduced more quickly. If the PM accumulation amount in the filter is reduced to a certain amount, the temperature increase rate of the catalyst and the filter can be increased while suppressing the excessive temperature increase of the filter.

  Therefore, according to the above control, when the temperature of the catalyst is raised again, the temperature of the catalyst can be raised more quickly while suppressing the excessive temperature rise of the filter. In addition, the temperature of the filter can be raised more quickly.

  In the present invention, when raising the temperature of the catalyst, the temperature of the catalyst may be raised to a predetermined target temperature. The target temperature varies depending on the type of catalyst, the purpose of raising the temperature of the catalyst, and the like. In this case, according to the present invention, the catalyst can be raised to the target temperature in a shorter time while suppressing the deterioration of the exhaust emission.

According to the present invention, in a catalyst temperature raising system for an internal combustion engine that raises the temperature of a catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine, the temperature of the catalyst is raised more quickly while suppressing deterioration of exhaust emission. I can do it.

  Embodiments of a catalyst temperature raising system for an internal combustion engine according to the present invention will be described below with reference to the drawings.

<Schematic configuration of internal combustion engine and intake / exhaust system thereof>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. A piston 3 is slidably provided in the cylinder 2 of the internal combustion engine 1. An intake port 4 and an exhaust port 5 are connected to the combustion chamber in the upper part of the cylinder 2. The openings of the intake port 4 and the exhaust port 5 to the combustion chamber are opened and closed by an intake valve 6 and an exhaust valve 7, respectively. The intake port 4 and the exhaust port 5 are connected to an intake passage 8 and an exhaust passage 9, respectively. The cylinder 2 is provided with a fuel injection valve 10 that directly injects fuel into the cylinder 2.

  The intake passage 8 is provided with an air flow meter 16 that outputs an electrical signal corresponding to the intake air amount, and a throttle valve 17 that controls the intake air amount. The exhaust passage 9 is provided with a filter 11 that collects PM in the exhaust, and an oxidation catalyst 12 is provided upstream of the filter 11.

  Further, in the exhaust passage 9, an upstream side exhaust temperature sensor 13 that outputs an electrical signal corresponding to the exhaust temperature and a downstream side exhaust are provided upstream of the oxidation catalyst 12, downstream of the oxidation catalyst 12 and upstream of the filter. A temperature sensor 14 is provided. Further, an exhaust throttle valve 15 for controlling the exhaust flow rate is provided downstream of the filter 11 in the exhaust passage 9. The oxidation catalyst 12 only needs to have an oxidation function, and may be, for example, an NOx storage reduction catalyst.

    The internal combustion engine 1 configured as described above is provided with an ECU 20 for controlling the internal combustion engine 1. Various sensors such as an air flow meter 16, an upstream exhaust temperature sensor 13, and a downstream exhaust temperature sensor 14 are electrically connected to the ECU 20. Output signals from various sensors are input to the ECU 20. The ECU 20 estimates the temperature of the oxidation catalyst 12 based on the output values of the upstream side exhaust temperature sensor 13 and / or the downstream side exhaust temperature sensor 14. In addition, the fuel injection valve 10, the throttle valve 17, and the exhaust throttle valve 15 are electrically connected to the ECU 20. These are controlled by the ECU 20.

<Catalyst temperature rise control>
Next, catalyst temperature raising control when raising the temperature of the oxidation catalyst 12 according to the present embodiment will be described. In this embodiment, the catalyst temperature increase control is executed when the PM deposited on the filter 11 is oxidized and removed. That is, the temperature of the oxidation catalyst 12 is raised by executing the catalyst temperature rise control, and thereby the temperature of the exhaust gas flowing into the filter 11 is raised to a temperature at which the PM can be oxidized and removed. Raise to.

  In the catalyst temperature increase control according to the present embodiment, when the temperature of the oxidation catalyst 12 is lower than the lower limit value T1 of the activation temperature, the temperature of the oxidation catalyst 12 is increased by increasing the temperature of the exhaust discharged from the internal combustion engine 1. Let

When the temperature of the oxidation catalyst 12 becomes the activation temperature and the oxidation catalyst 12 becomes active, the post-fuel injection is executed in the internal combustion engine 1 to supply unburned fuel to the oxidation catalyst 12 and The temperature of the catalyst 12 is raised to the target temperature Tt.

  Here, the target temperature Tt is a temperature at which the temperature of the filter 11 becomes a temperature at which PM can be oxidized and removed if the temperature of the oxidation catalyst 12 reaches the target temperature Tt, and is determined in advance by experiments or the like. Value.

<Temperature change of oxidation catalyst during post fuel injection>
Here, the temperature change of the oxidation catalyst 12 when post fuel injection is executed in the internal combustion engine 1, that is, when unburned fuel is supplied to the oxidation catalyst 12, will be described with reference to FIG. In FIG. 2A, the vertical axis represents the post fuel injection amount per unit time (hereinafter referred to as unit post fuel injection amount), and the horizontal axis represents time. In FIG. 2B, the vertical axis represents the temperature of the oxidation catalyst 12, and the horizontal axis represents time. Here, a case where the unit post fuel injection amount is set to a constant amount as shown in FIG. 2 will be described.

  Here, as shown in FIG. 2, post fuel injection is started in the internal combustion engine 1 when the temperature of the oxidation catalyst 12 reaches the lower limit value T1 of the activation temperature. However, since the temperature of the oxidation catalyst 12 is relatively low until the elapse of a certain time after the start of the post fuel injection, the oxidation of the unburned fuel is hardly promoted. Therefore, the catalyst temperature increase rate, which is the temperature increase amount of the oxidation catalyst 12 every specified time, is a relatively low value. When a certain amount of time has elapsed after the start of post fuel injection and the temperature of the oxidation catalyst 12 rises, the oxidation of unburned fuel is easily promoted. Therefore, the catalyst temperature increase rate is a relatively high value. That is, at the point of time when the state where the oxidation of the unburned fuel is difficult to promote is changed to the state where the oxidation of the unburned fuel is easily promoted, as shown by the point P in FIG. A change point of the catalyst temperature increase rate that changes to the specified temperature increase rate Ru1 or more occurs.

  Here, the first specified temperature increase rate Ru1 is a catalyst temperature increase rate at which it can be determined that the oxidation of the unburned fuel in the oxidation catalyst 12 is hardly promoted and the oxidation of the unburned fuel in the catalyst is easily accelerated. Is the threshold value. If the catalyst temperature increase rate once exceeds the first specified temperature increase rate Ru1 after the start of the post fuel injection, even if the catalyst temperature increase rate is lower than the first specified temperature increase rate Ru1 after that point, The oxidation of the unburned fuel in the oxidation catalyst 12 is in a state that is easily promoted.

  That is, from the start of the execution of post fuel injection to raise the temperature of the oxidation catalyst 12, until the time when the temperature increase rate of the oxidation catalyst 12 becomes a value equal to or higher than the first specified temperature increase rate Ru1 ((( The time before tp in b) is in a state where oxidation of unburned fuel is difficult to be promoted in the oxidation catalyst 12, and after the time when the temperature increase rate of the oxidation catalyst 12 becomes a value equal to or higher than the first specified temperature increase rate Ru1 ( It can be determined that the oxidation catalyst 12 is easily promoted to oxidize unburned fuel at the time after tp in FIG.

  In the present embodiment, the specified time for calculating the catalyst temperature increase rate is the oxidation time of the unburned fuel in the oxidation catalyst 12 when the calculated catalyst temperature increase rate is equal to or greater than the first specified temperature increase rate Ru1. It is a time when it can be determined that the cause is a change from a state where it is difficult to promote the oxidation to a state where the oxidation of the unburned fuel in the oxidation catalyst 12 is easily promoted.

<Unit post fuel injection amount control in catalyst temperature rise control>
Next, control of the unit post fuel injection amount in the catalyst temperature increase control will be described. When post-fuel injection is performed to supply unburned fuel to the oxidation catalyst 12, if oxidation of the unburned fuel is difficult to be promoted in the oxidation catalyst 12, the larger the intake air amount of the internal combustion engine 1, the more oxidation It becomes difficult for unburned fuel to adhere to the catalyst 12. Therefore, as the intake air amount of the internal combustion engine 1 increases, the ratio of the released unburned fuel amount to the post fuel injection amount increases.

  On the other hand, when post fuel injection is executed to supply unburned fuel to the oxidation catalyst 12, if the oxidation catalyst 12 is in a state where oxidation of unburned fuel is likely to be promoted, the intake air amount of the internal combustion engine 1 is large. The unburned fuel passes through the oxidation catalyst 12 without being oxidized in the oxidation catalyst 12. Therefore, the ratio of the amount of unburned fuel released to the post fuel injection amount increases as described above. However, in this case, the higher the temperature of the oxidation catalyst 12, the more the oxidation of unburned fuel in the oxidation catalyst 12 is promoted. Accordingly, the higher the temperature of the oxidation catalyst 12, the lower the ratio of the amount of unburned fuel released to the post fuel injection amount.

  Therefore, in this embodiment, when it is difficult to oxidize unburned fuel in the oxidation catalyst 12, the unit post fuel injection amount is controlled based on the intake air amount of the internal combustion engine 1. At this time, the larger the intake air amount of the internal combustion engine 1, the smaller the unit post fuel injection amount. When the oxidation of the unburned fuel is facilitated in the oxidation catalyst 12, the unit post fuel injection amount is controlled based on the intake air amount of the internal combustion engine 1 and the temperature of the oxidation catalyst 12. At this time, the unit post fuel injection amount decreases as the intake air amount of the internal combustion engine 1 increases, and the unit post fuel injection amount increases as the temperature of the oxidation catalyst 12 increases.

<Control routine for catalyst temperature rise control>
Hereinafter, the control routine of the catalyst temperature increase control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is executed every time the crankshaft rotates a specified crank angle during operation of the internal combustion engine 1.

  In this routine, first, in S101, the ECU 20 determines whether or not an estimated PM accumulation amount that is an estimated value of the PM accumulation amount in the filter 11 is equal to or greater than a specified PM accumulation amount Q1. Here, the prescribed PM accumulation amount Q1 is a threshold value of the PM accumulation amount that can be determined that the exhaust gas purification capacity of the filter 11 is excessively reduced, and is a value that is determined in advance by experiments or the like. Moreover, as a calculation method of the estimated PM accumulation amount, a method of calculating based on the integrated value of the fuel injection amount in the internal combustion engine 1 can be exemplified. If an affirmative determination is made in S101, the ECU 20 proceeds to S102, and if a negative determination is made, the ECU 20 ends the execution of this routine.

  In S102, the ECU 20 determines whether or not the temperature of the oxidation catalyst 12 is equal to or higher than the lower limit value T1 of the activation temperature. If an affirmative determination is made in S102, the ECU 20 proceeds to S103, and if a negative determination is made, the ECU 20 proceeds to S108.

  The ECU 20 that has proceeded to S108 executes exhaust gas temperature raising control for raising the temperature of the exhaust gas discharged from the internal combustion engine 1. Examples of the exhaust gas temperature raising control include control for increasing the engine load of the internal combustion engine 1 by reducing the opening of the exhaust throttle valve 15. After executing the exhaust gas temperature raising control in S107, the ECU 20 returns to S102.

  On the other hand, the ECU 20 that has proceeded to S103 calculates a unit post fuel injection amount based on the intake air amount of the internal combustion engine 1 at the present time. Then, post fuel injection is executed based on the calculated unit post fuel injection amount. Here, as shown in FIG. 4, a map 1 showing the relationship between the intake air amount of the internal combustion engine 1 and the unit post fuel injection amount is stored in the ECU 20 in advance, and the unit post fuel injection amount is calculated from the map 1. To do. In this map 1, the unit post fuel injection amount decreases as the intake air amount of the internal combustion engine 1 increases. After executing the post fuel injection in S103, the ECU 20 proceeds to S104.

  In S104, the ECU 20 determines whether or not the catalyst temperature increase rate is equal to or higher than the first specified temperature increase rate RU1. If an affirmative determination is made in S104, the ECU 20 proceeds to S105, and if a negative determination is made, the ECU 20 returns to S103.

  In step S105, the ECU 20 calculates a unit post fuel injection amount based on the current intake air amount of the internal combustion engine 1 and the current temperature of the oxidation catalyst 12. Then, post fuel injection is executed based on the calculated unit post fuel injection amount. Here, as shown in FIG. 4, a map 2 showing the relationship between the intake air amount of the internal combustion engine 1 and the temperature of the oxidation catalyst 12 and the unit post fuel injection amount is stored in the ECU 20 in advance. The post fuel injection amount is calculated. In this map 2, the unit post fuel injection amount decreases as the intake air amount of the internal combustion engine 1 increases, and the unit post fuel injection amount increases as the temperature of the oxidation catalyst 12 increases. In S105, after the post fuel injection is executed, the ECU 20 proceeds to S106.

  In S106, the ECU 20 determines whether or not the temperature of the oxidation catalyst 12 is equal to or higher than the target temperature Tt. If an affirmative determination is made in S105, the ECU 20 proceeds to S107, and if a negative determination is made, the ECU 20 returns to S105.

  In S107, the ECU 20 starts executing the oxidation catalyst temperature maintenance control so as to maintain the temperature of the oxidation catalyst 12 at the target temperature Tt. In the oxidation catalyst temperature maintenance control, the unit post fuel injection amount may be controlled based on the detection value of the downstream side exhaust temperature sensor 14 or the like. In S107, after starting execution of the oxidation catalyst temperature maintenance control, the ECU 20 ends the execution of this routine.

  According to the control routine described above, the oxidation of the unburned fuel is accelerated in the oxidation catalyst 12 from the time when the post fuel injection is started until the time when the catalyst temperature increase rate first exceeds the specified temperature increase rate RU1. When it is difficult to do this, the unit post fuel injection amount is controlled based on the intake air amount of the internal combustion engine 1. At this time, the unit post fuel injection amount decreases as the intake air amount of the internal combustion engine 1 increases.

  And from the time when the catalyst temperature increase rate first becomes equal to or higher than the specified temperature increase rate RU1 until the temperature of the oxidation catalyst 12 reaches the target temperature Tt, that is, the oxidation of the unburned fuel is easily promoted in the oxidation catalyst 12. At this time, the unit post fuel injection amount is controlled based on the intake air amount of the internal combustion engine 1 and the temperature of the oxidation catalyst 12. At this time, the unit post fuel injection amount decreases as the intake air amount of the internal combustion engine 1 increases, and the unit post fuel injection amount increases as the temperature of the oxidation catalyst 12 increases.

  Therefore, according to this embodiment, when supplying unburned fuel to the oxidation catalyst 12 to raise the temperature of the oxidation catalyst 12 to the target temperature Tt, the unit post fuel injection amount is suppressed while suppressing the amount of unburned fuel released. Can be increased as much as possible. As a result, it is possible to raise the temperature of the catalyst more quickly while suppressing the deterioration of exhaust emission, and thus it is possible to raise the temperature of the oxidation catalyst 12 to the target temperature Tt in a shorter time.

  In this embodiment, the case where unburned fuel is supplied to the oxidation catalyst 12 by post fuel injection in the internal combustion engine 1 has been described. However, a fuel addition valve is provided in the exhaust passage 9 upstream of the oxidation catalyst 12, The unburned fuel may be supplied to the oxidation catalyst 12 by adding fuel into the exhaust gas from the fuel addition valve. In this case, the control of the unit post fuel injection amount according to this embodiment is applied to the control of the fuel addition amount from the fuel addition valve.

  Further, the catalyst temperature increase control according to this embodiment may be applied when the oxidation catalyst 12 or the filter 11 is replaced with an NOx storage reduction catalyst and the SOx stored in the NOx storage reduction catalyst is reduced.

  Since the schematic configuration of the internal combustion engine and the intake / exhaust system thereof according to the present embodiment is the same as that of the first embodiment, the description thereof is omitted.

<Control of exhaust throttle valve in catalyst temperature rise control>
In the catalyst temperature increase control according to the present embodiment, in addition to the control of the unit post fuel injection amount as in the first embodiment, the control of the exhaust throttle valve 15 is executed.

  FIG. 5 is a diagram showing the relationship between the unit post fuel injection amount and the released fuel injection amount when post fuel injection is executed when the temperature of the oxidation catalyst 12 is the lower limit value T1 of the activation temperature. In FIG. 5, a solid line a indicates a case where post fuel injection is performed with the exhaust throttle valve 15 fully open, and a broken line b indicates a case where post fuel injection is performed with the exhaust throttle valve 15 closed. ing. In FIG. 5, the horizontal axis represents the unit post fuel injection amount, and the vertical axis represents the released fuel injection amount. Note that the time when the temperature of the oxidation catalyst 12 is the lower limit value T1 of the activation temperature corresponds to the time when the start of post fuel injection in the catalyst temperature increase control is started. That is, in this case, it is difficult for the oxidation catalyst 12 to promote oxidation of unburned fuel.

  When the exhaust throttle valve 15 is closed, the pressure in the exhaust passage 9 on the downstream side of the exhaust throttle valve 15 is increased as compared with when the exhaust throttle valve 15 is fully opened. The remaining fuel tends to remain in the cylinder 2 of the internal combustion engine 1. Therefore, the amount of unburned fuel actually supplied to the oxidation catalyst 12 is reduced. As a result, as shown in FIG. 5, when the oxidation catalyst 12 is in a state where oxidation of unburnt fuel is difficult to promote, if the exhaust throttle valve 15 is closed when performing post fuel injection, the exhaust Compared to when the throttle valve 15 is fully open, the amount of released unburned fuel can be further suppressed.

  Further, when the exhaust throttle valve 15 is fully opened, the exhaust flow rate is increased compared to when the exhaust throttle valve 15 is closed, so that the fuel injected by the post fuel injection enters the oxidation catalyst 12 more quickly. Will be supplied. Therefore, when the oxidation catalyst 12 is in a state where the oxidation of unburned fuel is easily promoted, the exhaust throttle valve 15 is closed when the exhaust throttle valve 15 is fully opened when the post fuel injection is performed. Compared to the case, it is possible to raise the temperature of the oxidation catalyst 12 more quickly.

<Control routine for catalyst temperature rise control>
Hereinafter, the control routine of the catalyst temperature increase control according to the present embodiment will be described based on the flowchart shown in FIG. Note that this routine differs from the control routine for catalyst temperature increase control according to Embodiment 1 described above only in that S201 and S202 are added, and the other steps are the same. Therefore, only S201 and S202 will be described here. This routine is stored in advance in the ECU 20 and is executed every time the crankshaft rotates a specified crank angle during operation of the internal combustion engine 1.

  In this routine, if an affirmative determination is made in S102, the ECU 20 proceeds to S201. The ECU 20 having proceeded to S201 closes the exhaust throttle valve 15 and then proceeds to S103.

  In this routine, if an affirmative determination is made in S104, the ECU 20 proceeds to S202. In step S202, the ECU 20 fully opens the exhaust throttle valve 15, and then proceeds to step S105.

According to the control routine described above, the oxidation of the unburned fuel is accelerated in the oxidation catalyst 12 from the time when the post fuel injection is started until the time when the catalyst temperature increase rate first exceeds the specified temperature increase rate RU1. When it is difficult to do this, the exhaust throttle valve 15 is controlled to be closed.

  And from the time when the catalyst temperature increase rate first becomes equal to or higher than the specified temperature increase rate RU1 until the temperature of the oxidation catalyst 12 reaches the target temperature Tt, that is, the oxidation of the unburned fuel is easily promoted in the oxidation catalyst 12. At this time, the exhaust throttle valve 15 is controlled to be fully opened.

  Therefore, according to the present embodiment, the temperature of the catalyst can be raised more quickly while suppressing the deterioration of exhaust emission.

  FIG. 7 is a diagram showing a schematic configuration of the internal combustion engine and its intake / exhaust system according to the present embodiment. In this embodiment, the oxidation catalyst 12 is not provided in the exhaust passage 9 upstream of the filter 11 but is supported by the filter 11. Since the other configuration is the same as that of the first embodiment described above, the same reference numeral is given to the same configuration, and the description thereof is omitted. Further, in the present embodiment, the catalyst temperature increase control similar to that in the above-described embodiment 2 is performed.

<Filter overheating suppression control during post fuel injection>
In the catalyst temperature increase control according to this embodiment, as described above, when the estimated PM accumulation amount in the filter 11 is determined to be equal to or greater than the specified PM accumulation amount Q1, and the temperature of the oxidation catalyst 12 is the activation temperature. The post fuel injection is executed when the value is equal to or greater than the lower limit value T1.

  However, an error may occur between the estimated PM deposition amount and the actual PM deposition amount. When the actual PM accumulation amount is larger than the estimated PM accumulation amount, for example, when the unit post fuel injection amount is increased because the specified temperature rise inflection point P is detected, the temperature increase rate of the filter May rise excessively, and as a result, the filter 11 may overheat.

  Therefore, in this embodiment, the filter overtemperature suppression control that suppresses the excessive temperature increase of the filter when the post fuel injection is performed is executed. Hereinafter, the control routine of the filter overheating suppression control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is executed every time the crankshaft rotates a specified crank angle during operation of the internal combustion engine 1.

  In this routine, the ECU 20 first determines in step S301 whether post fuel injection is being performed. If an affirmative determination is made in S301, the ECU 20 proceeds to S302, and if a negative determination is made, the ECU 20 once ends the execution of this routine.

  In S302, the ECU 20 determines whether or not the catalyst temperature increase rate is equal to or higher than the second specified temperature increase rate Ru2. Here, the second specified temperature increase rate Ru2 is a value by which it can be determined that the temperature increase rates of the oxidation catalyst 12 and the filter 11 have increased excessively because the PM accumulation amount in the filter 11 is excessively large. When the rate is equal to or higher than the second specified temperature increase rate Ru2, if the temperature of the oxidation catalyst 12 is continuously increased by post fuel injection, it is possible to determine that the filter 11 may be excessively heated due to the oxidation heat of PM. The rate threshold. The second specified temperature increase rate Ru2 is higher than the first specified temperature increase rate Ru1. If an affirmative determination is made in S302, the ECU 20 proceeds to S303, and if a negative determination is made, the ECU 20 once ends the execution of this routine.

  In S303, the ECU 20 stops the post fuel injection. By stopping the post fuel injection, the supply of unburned fuel to the oxidation catalyst 12 can be stopped.

Next, the ECU 20 proceeds to S304 and increases the opening of the exhaust throttle valve 15. Here, it is preferable that the exhaust throttle valve 15 is fully opened. At this time, if the exhaust throttle valve 15 is already fully open, the fully open state is maintained.

  When the opening degree of the exhaust throttle valve 15 is increased, the amount of heat taken away increases because the exhaust flow rate increases. Further, when the opening of the exhaust throttle valve 15 is fully opened, the amount of heat taken away from the filter 11 can be increased as much as possible. Therefore, by stopping the post fuel injection and controlling the exhaust throttle valve 15 as described above, the excessive temperature rise of the filter 11 can be suppressed.

  Next, the ECU 20 proceeds to S305 and determines whether or not the temperature of the oxidation catalyst 12 is equal to or lower than a specified temperature T2. Here, the specified temperature T2 is a temperature at which the oxidation of unburned fuel is difficult to be promoted although it is not less than the lower limit value T1 of the activation temperature. When the temperature of the oxidation catalyst 12 becomes equal to or lower than the specified temperature T2, it can be determined that there is almost no possibility that the filter 11 will overheat even if post fuel injection is performed again. If an affirmative determination is made in S305, the ECU 20 proceeds to S306, and if a negative determination is made, the ECU 20 repeats S305.

  In S306, the ECU 20 closes the exhaust throttle valve 15.

  Next, the ECU 20 proceeds to S307 and starts re-execution of post fuel injection. At this time, since the oxidation of the unburned fuel in the oxidation catalyst 12 is hardly promoted, the unit post fuel injection amount is calculated from the map 1 shown in FIG. 4 as described above. After starting the re-execution of the post fuel injection, the ECU 20 once ends the execution of this routine.

  According to the control routine described above, excessive temperature rise of the filter 11 can be suppressed.

  Further, after the post fuel injection is temporarily stopped, the exhaust throttle valve 15 is closed when the re-execution of the post fuel injection is started in order to raise the temperature of the oxidation catalyst 12 again. The amount can be suppressed. Accordingly, even when the temperature of the oxidation catalyst 12 is raised again, it is possible to suppress the deterioration of the emission.

  Further, when the exhaust throttle valve 15 is in the closed state, the pressure in the exhaust passage 9 increases, so that the oxidation of PM deposited on the filter 11 is easily promoted. Therefore, the PM accumulation amount in the filter 11 can be reduced more quickly. If the PM accumulation amount in the filter 11 is reduced to a certain amount, the temperature increase rate of the oxidation catalyst 12 and the filter 11 can be increased while suppressing the excessive temperature rise of the filter 11.

  Accordingly, when the temperature of the oxidation catalyst 12 is raised again by closing the exhaust throttle valve 15 at the start of re-execution of post fuel injection, the oxidation catalyst 12 and the filter are suppressed while suppressing excessive temperature rise of the filter 11. 11 can be heated more quickly.

The schematic block diagram of the internal combustion engine which concerns on Example 1 and 2 of this invention, and its intake-exhaust system. The figure for demonstrating the temperature change of the oxidation catalyst when post fuel injection is performed. The flowchart which shows the control routine of the catalyst temperature rising control which concerns on Example 1 of this invention. The figure which shows the maps 1 and 2 for calculating unit post fuel-injection amount. Map 1 is a map showing the relationship between the intake air amount of the internal combustion engine and the unit post fuel injection amount. Map 2 is a map showing the relationship between the intake air amount of the internal combustion engine, the temperature of the oxidation catalyst, and the unit post fuel injection amount. The figure which shows the relationship between unit post fuel injection amount and discharge | release fuel injection amount in the case of performing post fuel injection when the temperature of an oxidation catalyst is the lower limit of activation temperature. The flowchart which shows the control routine of the catalyst temperature rising control which concerns on Example 2 of this invention. The schematic block diagram of the internal combustion engine which concerns on Example 3 of this invention, and its intake-exhaust system. The flowchart which shows the control routine of the filter overheating suppression control which concerns on Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 9 ... Exhaust passage 10 ... Fuel injection valve 11 ... Particulate filter 12 ... Oxidation catalyst 13 ... Upstream exhaust temperature sensor 14 ... Downstream exhaust temperature sensor 15..Exhaust throttle valve 16..Air flow meter 17..Throttle valve 20..ECU

Claims (3)

In a catalyst temperature raising system for an internal combustion engine that raises the temperature of a catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine,
Unburned fuel supply means for supplying unburned fuel to the catalyst from the upstream side of the catalyst when the temperature of the catalyst is raised when the catalyst is in an active state;
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
Catalyst temperature detecting means for detecting the temperature of the catalyst;
A catalyst temperature increase rate calculating means for calculating a catalyst temperature increase rate that is a temperature increase amount of the catalyst per specified time when unburned fuel is supplied to the catalyst by the unburned fuel supply means;
Unburned fuel supply amount control means for controlling the supply amount of unburned fuel per unit time by the unburned fuel supply means,
In the unburned fuel supply amount control means, after the unburned fuel supply means starts supplying unburned fuel, the catalyst temperature increase rate calculated by the catalyst temperature increase rate calculating means is the first specified temperature increase rate. Until this time, the amount of unburned fuel supplied by the unburned fuel supply means per unit time is controlled based on the amount of intake air detected by the intake air amount detection means, and the catalyst temperature rises. After the time when the catalyst temperature increase rate calculated by the rate calculation means first becomes equal to or higher than the specified temperature increase rate, the intake air amount detected by the intake air amount detection means and the catalyst temperature detection means are detected. A catalyst temperature raising system for an internal combustion engine, wherein the amount of unburned fuel supplied by the unburned fuel supply means per unit time is controlled based on the temperature of the catalyst. An exhaust throttle valve provided in the exhaust passage downstream of the catalyst;
From the start of the supply of unburned fuel by the unburned fuel supply means until the time when the catalyst temperature increase rate calculated by the catalyst temperature increase rate calculation means first becomes equal to or higher than the specified temperature increase rate, The exhaust throttle valve is closed, and the exhaust throttle valve is opened after the catalyst temperature increase rate calculated by the catalyst temperature increase rate calculating means first exceeds the specified temperature increase rate. The catalyst temperature raising system for an internal combustion engine according to claim 1. The catalyst is in a state of being supported by a particulate filter that collects particulate matter in the exhaust,
An exhaust throttle valve provided in the exhaust passage downstream of the particulate filter;
The specified temperature increase rate as the first specified temperature increase rate,
When unburned fuel is supplied by the unburned fuel supply means, the temperature increase rate of the catalyst is equal to or higher than the second specified temperature increase rate higher than the first specified temperature increase rate. When the supply of unburned fuel by the unburned fuel supply means is stopped, the opening of the exhaust throttle valve is increased, or the exhaust throttle valve is fully opened,
Thereafter, when the temperature of the catalyst is raised again by supplying unburned fuel to the catalyst, supply of unburned fuel by the unburned fuel supply means is started while the exhaust throttle valve is closed. The catalyst temperature raising system for an internal combustion engine according to claim 1.

Images