JP4867573B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  A particulate filter (hereinafter referred to as a filter) that collects particulate matter (hereinafter referred to as PM) in the exhaust discharged from the internal combustion engine is provided in the exhaust passage. A process for raising the temperature of the filter and removing PM collected by the filter by oxidation (hereinafter referred to as filter regeneration process) is performed on the filter.

And in the filter regeneration process, in order to suppress the excessive temperature rise of the filter, a technique for increasing the exhaust flow rate by increasing the engine speed is known (see Patent Document 1).
JP 2004-204774 A JP 2005-201060 A JP 2006-029239 A JP-A-2005-090274 JP 2001-073856 A

  When the exhaust gas flow rate is increased in the filter regeneration process, the excessive temperature rise of the filter can be suppressed. Here, when the fuel supply for the filter regeneration process is performed by post-injection into the cylinder of the internal combustion engine, the cycle intake air amount per cycle (hereinafter referred to as the cycle intake air amount) of the internal combustion engine is set. Accordingly, the post injection amount is determined. Therefore, if the cycle intake air amount increases when the exhaust flow rate is increased, the post-injection amount increases and the fuel adhering to the cylinder inner wall enters the engine oil, causing oil dilution. May end up.

  An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine using fuel injected into a cylinder of the internal combustion engine to supply fuel to the catalyst while suppressing excessive temperature rise of the filter when the filter regeneration means is implemented. It is to provide a technique for suppressing oil dilution.

In the present invention, the following configuration is adopted. That is,
A filter that is disposed in an exhaust passage of an internal combustion engine and collects particulate matter in the exhaust gas passing through the exhaust passage;
A catalyst having an oxidation function for increasing the temperature of the filter by oxidation reaction heat generated by supplying fuel;
Separately from the fuel for the output of the internal combustion engine, fuel is supplied to the catalyst by injecting into the cylinder of the internal combustion engine an amount of fuel according to the amount of cycle intake air per cycle of the internal combustion engine. Fuel supply means,
Filter regeneration means for raising the temperature of the filter and oxidizing and removing particulate matter collected by the filter by supplying fuel to the catalyst by the fuel supply means;
Control means for reducing the amount of cycle intake air while maintaining the engine speed of the internal combustion engine as the filter regeneration means progresses and the amount of particulate matter collected in the filter decreases.
An exhaust emission control device for an internal combustion engine, comprising:

If the exhaust gas flow rate is increased when the filter regeneration means is implemented, the excessive temperature rise of the filter can be suppressed. Here, when fuel supply for implementing the filter regeneration means is performed by post-injection (sub-injection) to the internal combustion engine, the post-injection amount depends on the cycle intake air amount per cycle of the internal combustion engine. It has been decided. Therefore, if the cycle intake air amount increases when the exhaust flow rate is increased, the post-injection amount increases and the fuel adhering to the cylinder inner wall enters the engine oil, causing oil dilution. May end up. Oil dilution increases the frictional resistance of the movable mechanism in the cylinder, and adversely affects the operating performance and reliability of the internal combustion engine.

  On the other hand, if the cycle intake air amount is reduced to suppress oil dilution, the post injection amount can be reduced, so that oil dilution can be suppressed, but overheating of the filter cannot be suppressed.

  That is, the suppression of oil dilution and the suppression of overheating of the filter are in a trade-off relationship.

  However, when the exhaust flow rate is decreased, the degree of suppression of oil dilution differs between the case where the engine flow rate is decreased and the exhaust flow rate is decreased, and the case where the cycle intake air amount is decreased and the exhaust flow rate is decreased. . That is, oil dilution can be suppressed when the exhaust air flow rate is decreased by decreasing the cycle intake air amount.

  This is because the degree of increase in the oil dilution with respect to the increase in the post injection amount caused by the increase in the cycle intake air amount is not linear but increases exponentially. For this reason, conversely, the degree of suppression of oil dilution with respect to the decrease in the post injection amount caused by the decrease in the cycle intake air amount increases exponentially.

  Therefore, in the present invention, as the filter regeneration means progresses and the accumulated amount of PM collected by the filter decreases, the cycle intake air amount is reduced while maintaining the engine speed of the internal combustion engine. .

  According to this configuration, when the filter regeneration means progresses and the accumulated amount of PM trapped in the filter decreases, the exhaust flow rate for suppressing the excessive temperature rise of the filter may be reduced. The cycle intake air amount is decreased while maintaining the engine speed of the engine.

  As described above, since the exhaust gas flow rate is reduced by reducing the cycle intake air amount, the post injection amount is reduced due to the reduction of the cycle intake air amount, and the degree of suppression of oil dilution can be increased exponentially.

  Therefore, when implementing the filter regeneration means, it is possible to suppress oil dilution by the fuel injected into the cylinder of the internal combustion engine in order to supply the fuel to the catalyst while suppressing the excessive temperature rise of the filter.

  The fuel supply means is configured to inject fuel into a cylinder of the internal combustion engine by sub-injection after the main injection is performed, which is different from the main injection for the output of the internal combustion engine. The means may retard the sub-injection timing as the cycle intake air amount is decreased.

  When the amount of cycle intake air is reduced, the in-cylinder temperature of the internal combustion engine rises, and post-injection (sub-injection) fuel is likely to burn. According to this configuration, the post injection is performed after the in-cylinder temperature of the internal combustion engine has decreased by retarding the post injection timing. As a result, post-injected fuel can be supplied to the catalyst without burning in the cylinder of the internal combustion engine.

When the intake air pressure of the internal combustion engine decreases below a predetermined value due to a decrease in the cycle intake air amount, the control means stops reducing the cycle intake air amount, and the engine of the internal combustion engine It is good to reduce the rotation speed.

  Here, the predetermined value is a threshold intake pressure at which if the intake pressure of the internal combustion engine falls below this, the intake pressure to the internal combustion engine is insufficient and the internal combustion engine misfires.

  According to this configuration, the intake pressure of the internal combustion engine can be ensured to the minimum necessary, and misfire of the internal combustion engine can be suppressed.

  According to the present invention, in the exhaust gas purification apparatus for an internal combustion engine, when the filter regeneration means is implemented, the oil by the fuel injected into the cylinder of the internal combustion engine in order to supply the fuel to the catalyst while suppressing the excessive temperature rise of the filter Dilution can be suppressed.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and its intake / exhaust system.

  An internal combustion engine 1 shown in FIG. 1 is a diesel engine for driving a vehicle. 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 cylinder 2 is provided with a fuel injection valve 6 that directly injects fuel into the combustion chamber.

  The opening of the intake port 4 to the combustion chamber is opened and closed by the intake valve 7, and the opening of the exhaust port 5 to the combustion chamber is opened and closed by the exhaust valve 8. The intake port 4 is connected to the intake passage 9, and the exhaust port 5 is connected to the exhaust passage 10. The intake passage 9 is provided with an intake throttle valve 11 for adjusting the amount of external intake air (hereinafter referred to as fresh air) introduced into the cylinder 2.

  A filter 12 that collects PM in the exhaust is disposed in the middle of the exhaust passage 10. The filter 12 is a wall flow type filter made of a porous base material, and carries an oxidation catalyst typified by platinum (Pt) as a catalyst having an oxidation function. Note that the oxidation catalyst is not carried by the filter 12 and may be separately provided in the exhaust passage 10 on the upstream side of the filter 12, for example. The filter 12 may carry a NOx occlusion material represented by potassium (K) or cesium (Cs).

  The internal combustion engine 1 also includes an EGR device 13 that introduces a portion of the exhaust gas flowing through the exhaust passage 10 into the intake passage 9 as EGR gas. The EGR device 13 has an EGR passage 14 that connects the intake passage 9 and the exhaust passage 10. The connection portion of the EGR passage 14 with the exhaust passage 10 is located in the exhaust passage 10 upstream of the filter 12. The connection portion of the EGR passage 14 with the intake passage 9 is located in the intake passage 9 downstream of the intake throttle valve 11. The EGR passage 14 is provided with an EGR valve 15 that adjusts the amount of EGR gas introduced into the cylinder 2.

The internal combustion engine 1 configured as described above is provided with an ECU 16 that is an electronic control unit. An accelerator opening sensor 17 and a crank position sensor 18 are electrically connected to the ECU 16. The accelerator opening sensor 17 detects the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted. The crank position sensor 18 detects the crank angle of the crankshaft of the internal combustion engine 1. These output values are input to the ECU 16. And ECU
16 estimates the engine load of the internal combustion engine 1 based on the detection value of the accelerator opening sensor 17, and calculates the engine speed N of the internal combustion engine 1 based on the detection value of the crank position sensor 18.

  Further, the fuel injection valve 6, the intake throttle valve 11, and the EGR valve 15 are electrically connected to the ECU 16. These are controlled by the ECU 16.

  Exhaust gas discharged from the internal combustion engine 1 as described above contains PM such as soot, and PM in the exhaust gas is collected by the filter 12 and is prevented from being diffused into the atmosphere. ing.

  However, when the amount of PM collected by the filter 12 increases, the back pressure in the exhaust passage 10 on the upstream side of the filter 12 increases, leading to a decrease in the output of the internal combustion engine 1. May affect.

  For this reason, in this embodiment, the amount of accumulated PM collected by the filter 12 is estimated, and when the estimated amount of accumulated PM reaches a predetermined amount or more, the filter regeneration for oxidizing and removing the PM collected from the filter 12 is performed. Perform the process. The filter regeneration process corresponds to the filter regeneration means of the present invention.

  In the filter regeneration process in the present embodiment, in addition to the main injection for the output of the normal internal combustion engine 1, post injection is performed as sub-injection from the fuel injection valve 6 in the expansion stroke or exhaust stroke of the internal combustion engine 1. As a result, the fuel injected into the cylinder 2 passes through the exhaust port 5 in which the exhaust valve 8 is open, and further reaches the filter 12 disposed in the exhaust passage 10 to supply the fuel to the filter 12. To do. Then, the fuel is oxidized in the oxidation catalyst carried on the filter 12, the temperature of the filter 12 is increased by the oxidation reaction heat at that time, and the PM collected on the filter 12 is oxidized and removed. Note that the post injection in this embodiment corresponds to the fuel supply means of the present invention.

  Here, in the filter regeneration process, for example, when the vehicle is in an idling state, if the exhaust flow rate Ga that removes heat from the filter 12 is small, the filter 12 may overheat and melt. Therefore, at the start of the filter regeneration process, the exhaust gas flow rate Ga is increased in order to suppress overheating of the filter 12. The exhaust gas flow rate Ga is increased by, for example, controlling the EGR valve 15 to the closed side to decrease the EGR gas amount or increasing the engine speed N of the internal combustion engine 1.

  In the present embodiment, fuel supply for performing the filter regeneration process is performed by post injection to the internal combustion engine 1. In such a case, the post injection amount is determined according to the cycle intake air amount Gn per cycle of the internal combustion engine 1. For this reason, when the cycle intake air amount Gn is increased when the exhaust gas flow rate Ga is increased, the post injection amount is increased, and the fuel adhering to the inner wall surface of the cylinder 2 is mixed into the engine oil to dilute the oil. May occur. Oil dilution increases the frictional resistance of the movable mechanism in the cylinder 2 and adversely affects the operation performance and reliability of the internal combustion engine 1.

  On the other hand, if the cycle intake air amount Gn is reduced in order to suppress oil dilution, the post injection amount can be reduced, so that oil dilution can be suppressed, but overheating of the filter 12 cannot be suppressed.

  That is, suppression of oil dilution and suppression of overheating of the filter 12 are in a trade-off relationship.

  However, when the exhaust flow rate Ga is decreased, the oil dilution is performed when the engine flow rate N is decreased by decreasing the engine speed N and when the exhaust flow rate Ga is decreased by decreasing the cycle intake air amount Gn. The degree of suppression is different. That is, oil dilution can be suppressed when the exhaust air flow rate Ga is decreased by decreasing the cycle intake air amount Gn.

  This is because the degree of increase in the oil dilution with respect to the increase in the post injection amount caused by the increase in the cycle intake air amount Gn increases not exponentially but exponentially. For this reason, conversely, the degree of suppression of oil dilution with respect to the decrease in the post injection amount caused by the decrease in the cycle intake air amount Gn increases exponentially.

  Therefore, in the present embodiment, as the filter regeneration process proceeds and the amount of accumulated PM collected by the filter 12 decreases, the cycle intake air amount Gn is reduced while maintaining the engine speed N of the internal combustion engine 1. Control to decrease.

  FIG. 2 shows a time chart during the filter regeneration process in the present embodiment. Immediately after the start of the filter regeneration process, the exhaust gas flow rate Ga is increased. As the filter regeneration process progresses and the PM accumulation amount collected by the filter 12 decreases, that is, as the filter regeneration process elapses over time, the filter 12 increases excessively as the PM accumulation amount decreases. Since it becomes difficult to warm, the exhaust flow rate Ga can be decreased. For this reason, in order to reduce the exhaust gas flow rate Ga, the cycle intake air amount Gn is reduced as the filter regeneration process elapses. The method of reducing the cycle intake air amount Gn is performed by controlling the intake throttle valve 11 to the closed side. As shown in FIG. 2, while the cycle intake air amount Gn is being decreased, the engine speed N of the internal combustion engine 1 maintains the speed at the start of the filter regeneration process.

  That is, in this embodiment, the filter regeneration process proceeds and the amount of PM accumulated in the filter 12 decreases, and the exhaust gas flow Ga for suppressing the excessive temperature rise of the filter 12 may be reduced. In this case, the cycle intake air amount Gn is decreased while maintaining the engine speed N of the internal combustion engine 1.

  As described above, since the exhaust gas flow rate Ga is reduced by reducing the cycle intake air amount Gn, the post injection amount is reduced due to the decrease in the cycle intake air amount Gn, and the degree of suppression of oil dilution is increased exponentially. Can do.

  Accordingly, during the filter regeneration process, it is possible to suppress oil dilution by post-injected fuel injected into the cylinder 2 of the internal combustion engine 1 in order to supply fuel to the filter 12 while suppressing excessive temperature rise of the filter 12.

  Further, as shown in FIG. 2, as the cycle intake air amount Gn is decreased, the post injection timing is retarded and the post injection delay amount is increased.

  When the cycle intake air amount Gn is decreased, the in-cylinder temperature of the internal combustion engine 1 rises, and the post-injected fuel becomes easy to burn. Therefore, as the cycle intake air amount Gn is decreased, the post injection retard amount is increased, so that the post injection is performed after the in-cylinder temperature of the internal combustion engine 1 is lowered. Thereby, the post-injected fuel can be supplied to the filter 12 without burning in the cylinder 2 of the internal combustion engine 1.

When the intake air pressure of the internal combustion engine 1 decreases to a predetermined value or less due to the decrease of the cycle intake air amount Gn, the decrease of the cycle intake air amount Gn is stopped, and the engine speed N of the internal combustion engine 1 is stopped. Reduce. Here, the predetermined value is a threshold intake pressure at which if the intake pressure of the internal combustion engine 1 falls below this value, the intake pressure to the internal combustion engine 1 is insufficient and the internal combustion engine 1 misfires.

  That is, when the cycle intake air amount is reduced to the limit intake air amount such that the intake pressure of the internal combustion engine 1 decreases as the internal combustion engine 1 misfires (time t1 in FIG. 2), the cycle intake air amount Gn is set to Stop decreasing and keep it at that value. The exhaust flow rate Ga after t1 is reduced by reducing the engine speed N of the internal combustion engine 1. Since the cycle intake air amount Gn is maintained at the value at the time t1 after t1, the post injection amount, the post injection delay amount, and the like are maintained at the values at the time t1.

  In this way, when the cycle intake air amount Gn decreases to the limit intake air amount, the reduction of the cycle intake air amount Gn is stopped, so that the necessary minimum intake pressure of the internal combustion engine 1 can be ensured and the misfire of the internal combustion engine 1 can be ensured. Can be suppressed.

  Here, the control routine for performing the filter regeneration processing of the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 16 and is a routine that is periodically executed. The ECU 16 that performs the control shown in FIG. 3 corresponds to the control means of the present invention.

  In step S101, first, the ECU 16 refers to the vehicle travel history, the operation history of the internal combustion engine 1, and the like to determine whether or not the filter regeneration process is required.

  Specifically, the PM accumulation amount is estimated with reference to the travel distance of the vehicle, the exhaust gas flow rate Ga flowing into the filter 12 and the like, and when the PM accumulation amount has reached the threshold value at which the filter regeneration process should be started, the filter It is determined that the reproduction process is required.

  If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  Subsequently, in step S102, the ECU 16 establishes a filter regeneration process start flag to start the filter regeneration process. Thereby, the filter regeneration process is started.

  Subsequently, in step S103, the ECU 16 increases the exhaust gas flow rate Ga with the start of the filter regeneration process. Specifically, the exhaust gas flow rate Ga is increased by controlling the EGR valve 11 to the closed side to decrease the EGR gas amount or increasing the engine speed N of the internal combustion engine 1.

  Subsequently, in step S104, the ECU 16 decreases the cycle intake air amount Gn in order to decrease the exhaust gas flow rate Ga in accordance with the progress of the filter regeneration process. At this time, the engine speed N of the internal combustion engine 1 is maintained at the value at the start of the filter regeneration process. Further, the post injection retard amount is increased as the cycle intake air amount Gn is decreased.

  Here, since the PM removal amount is calculated by multiplying the elapsed time from the start of the normal filter regeneration processing to the present time and the temperature of the filter 12, the reduction amount of the cycle intake air amount Gn is equal to PM. This is based on the amount of remaining PM estimated from the removal amount. Then, the closing amount of the intake throttle valve 11 is obtained from a map or the like obtained in advance showing the relationship between the PM accumulation amount and the closing amount of the intake throttle valve 11, and cycle suction is performed by controlling the intake throttle valve 11 to the closed side. The air amount Gn is decreased.

Further, the post injection delay amount is controlled so as to increase based on a map obtained in advance showing the relationship between the post injection delay amount and the closing amount of the intake throttle valve 11.

  In step S105, the ECU 16 determines whether or not the cycle intake air amount Gn is equal to or less than a limit value. Here, the limit value is a limit intake air amount such that the intake air pressure of the internal combustion engine 1 decreases as the internal combustion engine 1 misfires if the intake air amount is less than the limit value. The time point when the cycle intake air amount Gn reaches this limit value is the time point t1 shown in FIG.

  If an affirmative determination is made in step S105, the process proceeds to step S106. On the other hand, if a negative determination is made, a loop is returned to step S105.

  In step S106, the ECU 16 reduces the engine speed N of the internal combustion engine 1 in order to reduce the exhaust gas flow rate Ga in accordance with the degree of progress of the filter regeneration process. At this time, the cycle intake air amount Gn and the post injection retard amount are maintained at the values at the time t1.

  Subsequently, in step S107, the ECU 16 determines whether or not the filter regeneration process has been completed. Here, since the PM removal amount is calculated as described above, it is determined that the filter regeneration process has been completed when the remaining PM accumulation amount estimated from the PM removal amount becomes zero.

  If an affirmative determination is made in step S107, this routine is once ended. On the other hand, if a negative determination is made, a loop is returned to step S106.

  As described above, in this routine, during the filter regeneration process, post injection that is injected into the cylinder 2 of the internal combustion engine in order to supply fuel to the filter 12 while suppressing excessive temperature rise of the filter 12 is performed. Oil dilution with fuel can be suppressed.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.

1 is a diagram illustrating an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1. FIG. 6 is a time chart during a filter regeneration process according to the first embodiment. 6 is a flowchart illustrating a routine of filter regeneration processing according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Piston 4 Intake port 5 Exhaust port 6 Fuel injection valve 7 Intake valve 8 Exhaust valve 9 Intake passage 9 Exhaust passage 10 Exhaust passage 11 Intake throttle valve 12 Filter 13 EGR device 14 EGR passage 15 EGR valve 16 ECU
17 Accelerator opening sensor 18 Crank position sensor Ga Exhaust flow rate Gn Cycle intake air amount N Engine speed

Claims (3)

A filter that is disposed in an exhaust passage of an internal combustion engine and collects particulate matter in the exhaust gas passing through the exhaust passage;
A catalyst having an oxidation function for increasing the temperature of the filter by oxidation reaction heat generated by supplying fuel;
Separately from the fuel for the output of the internal combustion engine, fuel is supplied to the catalyst by injecting into the cylinder of the internal combustion engine an amount of fuel according to the amount of cycle intake air per cycle of the internal combustion engine. Fuel supply means,
Filter regeneration means for raising the temperature of the filter and oxidizing and removing particulate matter collected by the filter by supplying fuel to the catalyst by the fuel supply means;
Control means for reducing the amount of cycle intake air while maintaining the engine speed of the internal combustion engine as the filter regeneration means progresses and the amount of particulate matter collected in the filter decreases.
An exhaust emission control device for an internal combustion engine, comprising: The fuel supply means is configured to inject fuel into a cylinder of the internal combustion engine by sub-injection after the main injection is performed, which is different from the main injection for output of the internal combustion engine.
2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the control means retards the timing of the sub-injection as the cycle intake air amount is decreased.   When the intake air pressure of the internal combustion engine decreases below a predetermined value due to a decrease in the cycle intake air amount, the control means stops reducing the cycle intake air amount, and the engine of the internal combustion engine The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the rotational speed is reduced.

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