JP2006348905A - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED To suppress deterioration of exhaust emission during execution of regeneration control in an exhaust gas purification system for an internal combustion engine.
SOLUTION: In regeneration control for regenerating exhaust purification capability of an exhaust purification device, a reducing agent is supplied to an exhaust purification device provided downstream from the catalyst by supplying the reducing agent from the upstream side of the catalyst having an oxidation function. When supplying, the upper limit value of the reducing agent supply amount is corrected based on the temperature of the catalyst and the rate of increase of the intake air amount of the internal combustion engine (S109).
[Selection] Figure 2

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine including an exhaust gas purification device provided in an exhaust passage of the internal combustion engine and a catalyst having an oxidation function provided in an exhaust gas passage upstream of the exhaust gas purification device.

  An exhaust purification system for an internal combustion engine includes an exhaust purification device provided in an exhaust passage of the internal combustion engine, and a catalyst having an oxidation function provided in an exhaust passage upstream of the exhaust purification device. It has been. Here, examples of the exhaust purification device include a particulate filter (hereinafter simply referred to as a filter) carrying a catalyst having an oxidation function and an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst). The filter collects particulate matter (hereinafter referred to as PM) in the exhaust. Further, the NOx catalyst occludes NOx when the surrounding atmosphere is an oxidizing atmosphere, and reduces NOx occluded when the reducing atmosphere is a reducing atmosphere.

Patent Document 1 discloses an exhaust gas purification system for an internal combustion engine as described above, which includes a filter as an exhaust gas purification device and a NOx catalyst as a catalyst having an oxidation function. In this Patent Document 1, the PM collection state in the filter is detected based on the amount of change in the intake air amount of the internal combustion engine, and the reducing agent supply amount to the NOx catalyst is further detected based on the detected PM collection state. To control.
JP 2001-193440 A JP 2003-83029 A

  In an exhaust gas purification system for an internal combustion engine provided with an exhaust gas purification device provided in an exhaust gas passage of the internal combustion engine and a catalyst having an oxidation function provided in an exhaust gas passage upstream of the exhaust gas purification device, the exhaust gas purification device Regeneration control is performed to regenerate the exhaust gas purification ability. In this regeneration control, the temperature of the catalyst is raised to the activation temperature, and a reducing agent may be supplied to the catalyst and the exhaust purification device from the upstream side of the catalyst.

  When the reducing agent is supplied to the catalyst whose temperature has been raised to the activation temperature, the reducing agent is oxidized in the catalyst and heat of oxidation is generated. The exhaust gas flowing into the exhaust purification device is heated by the oxidation heat. Thereby, the temperature of the exhaust emission control device can be raised.

  Further, the reducing agent that has not been oxidized in the catalyst is supplied to the exhaust purification device. Thereby, for example, when the exhaust purification device is a filter carrying a catalyst having an oxidation function, the reducing agent is oxidized in the catalyst carried on the filter. Therefore, the temperature of the filter can be further increased, and as a result, the PM collected by the filter can be oxidized and removed. Further, when the exhaust purification device is a NOx catalyst, the temperature of the NOx catalyst can be raised, and the ambient atmosphere can be made a reducing atmosphere. As a result, the SOx stored in the NOx catalyst can be reduced.

  However, in the regeneration control, if an excessive amount of reducing agent is supplied to the exhaust purification device without being oxidized by the catalyst, a part of the reducing agent is not oxidized or used for the reduction reaction. There is a risk of being discharged outside through the device. As a result, exhaust emission may be deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of suppressing deterioration of exhaust emission during execution of regeneration control in an exhaust purification system of an internal combustion engine. .

  The present invention provides a regenerative control for regenerating the exhaust purification capacity of an exhaust purification device, by supplying a reducing agent from an upstream side of a catalyst having an oxidizing function, thereby supplying the reducing agent to an exhaust purification device provided downstream of the catalyst. When supplying, the upper limit value of the reducing agent supply amount is corrected based on the catalyst temperature and the rate of increase of the intake air amount of the internal combustion engine.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
An exhaust purification device provided in the exhaust passage of the internal combustion engine;
A catalyst having an oxidation function provided in the exhaust passage upstream of the exhaust purification device;
Catalyst temperature detecting means for detecting the temperature of the catalyst;
An increase rate calculating means for calculating an intake air amount increase rate that is an increase amount per unit time of the intake air amount of the internal combustion engine;
The catalyst is heated up to the activation temperature, and regeneration control is performed to regenerate the exhaust purification capability of the exhaust purification device by supplying a reducing agent to the catalyst and the exhaust purification device from the upstream side of the catalyst. Playback control execution means;
Correction means for correcting a reducing agent supply amount when supplying the reducing agent to the catalyst and the exhaust gas purification device in the regeneration control,
The correction means reduces the upper limit supply amount, which is the upper limit value of the reducing agent supply amount, as the temperature of the catalyst decreases, and decreases the upper limit supply amount as the intake air amount increase rate increases. To do.

  In the present invention, when the reducing agent is supplied to the catalyst and the exhaust emission control device in the regeneration control, the upper limit supply amount is corrected by the correcting means.

  Here, when the reducing agent is supplied from the upstream side of the catalyst to the catalyst and the exhaust purification device, the reducing agent is less likely to be oxidized in the catalyst as the temperature of the catalyst is lower. Therefore, the reducing agent is easily supplied to the exhaust purification device. On the other hand, the higher the intake air amount increase rate, the higher the increase amount per unit time of the exhaust flow rate through the catalyst and the filter (hereinafter referred to as the exhaust flow rate increase rate). The higher the exhaust flow rate increase rate, the easier the reducing agent passes through the catalyst. Therefore, the reducing agent is easily supplied to the exhaust purification device. Further, the higher the exhaust gas flow rate increase rate, the easier the reducing agent passes through the filter.

  Therefore, the correction means corrects the upper limit supply amount to a smaller amount as the catalyst temperature is lower. Also, the upper limit supply amount is corrected to a smaller amount as the intake air amount increase rate is higher.

  According to this, it can suppress that the reducing agent supply quantity to an exhaust gas purification apparatus becomes an excessive quantity. That is, the amount of reducing agent that passes through the filter and is released to the outside can be suppressed. Therefore, it is possible to suppress the deterioration of exhaust emission during the execution of regeneration control.

  In the present invention, the correction means may have an upper limit supply amount setting means for setting the upper limit supply amount. In this case, the upper limit supply amount setting means sets the upper limit supply amount to a smaller amount as the catalyst temperature is lower. Further, the higher the intake air amount increase rate, the lower the upper limit supply amount is set.

  Thereby, the lower the catalyst temperature, the lower the upper limit supply amount can be corrected, and the higher the intake air amount increase rate, the lower the upper limit supply amount can be corrected.

  With the exhaust gas purification system for an internal combustion engine according to the present invention, it is possible to suppress the deterioration of exhaust emission during the execution of regeneration control.

  Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Schematic configuration of internal combustion engine and its intake / exhaust system>
Here, the case where the present invention is applied to a diesel engine for driving a vehicle will be described as an example. 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. An intake passage 3 and an exhaust passage 2 are connected to the internal combustion engine 1. An air flow meter 7 is provided in the intake passage 3.

  On the other hand, the exhaust passage 2 is provided with a particulate filter 4 (hereinafter simply referred to as a filter 4) that collects PM in the exhaust. The filter 4 carries an oxidation catalyst. An oxidation catalyst 5 is provided in the exhaust passage 2 upstream of the filter 4. The oxidation catalyst and the oxidation catalyst 5 carried by the filter 4 may be any catalyst having an oxidation function, and may be, for example, a NOx catalyst. In this embodiment, the filter 4 constitutes the exhaust gas purification apparatus according to the present invention, and the oxidation catalyst 5 constitutes the catalyst according to the present invention.

  The exhaust passage 2 is provided with a differential pressure sensor 11 that outputs an electrical signal corresponding to the pressure difference in the exhaust passage 2 before and after the filter 4. Further, a temperature sensor 13 that outputs an electrical signal corresponding to the temperature of the exhaust gas is provided downstream of the oxidation catalyst 5 and upstream of the filter 4 in the exhaust passage 2.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 10 includes a vehicle equipped with an air flow meter 7, a differential pressure sensor 11, a temperature sensor 13, a crank position sensor 14 that outputs an electrical signal corresponding to the rotation angle of the crankshaft of the internal combustion engine 1, and the internal combustion engine 1. An accelerator opening sensor 15 that outputs an electric signal corresponding to the accelerator opening is electrically connected. These output signals are input to the ECU 10.

  The ECU 10 estimates the amount of PM collected in the filter 4 based on the detection value of the differential pressure sensor 11. Further, the ECU 10 calculates the rotation speed of the internal combustion engine 1 based on the detection value of the crank position sensor 14 and calculates the load of the internal combustion engine 1 based on the detection value of the accelerator opening sensor 15. Further, the ECU 10 estimates the temperature of the oxidation catalyst 5 based on the detected value of the temperature sensor 13.

  In addition, a fuel injection valve of the internal combustion engine 1 is electrically connected to the ECU 10. The fuel injection valve is controlled by the ECU 10.

<Filter regeneration control>
In the present embodiment, when the amount of PM collected in the filter 4 becomes equal to or greater than the first specified amount of collection, filter regeneration control is started to oxidize and remove PM. Here, the first specified trapping amount is an amount smaller than the trapping amount that excessively affects the operating state of the internal combustion engine 1, and the filter 4 overheats when PM is oxidized. The amount is less than the amount collected. The first specified collection amount is determined in advance by experiments or the like. In this embodiment, the filter regeneration control corresponds to the regeneration control according to the present invention.

  In the filter regeneration control according to the present embodiment, exhaust gas temperature raising control is performed to raise the temperature of exhaust gas exhausted from the internal combustion engine 1 (hereinafter referred to as engine exhaust gas). The temperature of the oxidation catalyst 5 and the filter 4 rises with the temperature rise of the engine exhaust exhaust gas by the exhaust gas temperature raising control. Thereby, the temperature of the oxidation catalyst 5 is raised to the activation temperature. As the exhaust gas temperature raising control, control for retarding the main fuel injection timing in the internal combustion engine 1 can be exemplified.

  Further, in the filter regeneration control according to the present embodiment, in order to supply fuel as a reducing agent to the oxidation catalyst 5 and the filter 4 that have been activated, the auxiliary fuel injection is executed at a time after the main fuel injection in the internal combustion engine 1. Is done. This auxiliary fuel injection is executed at a timing such that at least a part of the fuel injected by the auxiliary fuel injection is discharged from the internal combustion engine 1 in an unburned state.

  When fuel is supplied to the oxidation catalyst 5 by executing the auxiliary fuel injection, the fuel is oxidized in the oxidation catalyst 5, and the exhaust gas flowing into the filter 4 is heated by the oxidation heat at that time. Along with this, the temperature of the filter 4 further increases.

  Further, in this embodiment, a part of the fuel supplied to the oxidation catalyst 5 by executing the sub fuel injection passes through the oxidation catalyst 5 without being oxidized in the oxidation catalyst 5. The fuel that has passed through the oxidation catalyst 5 is supplied to the filter 4. The fuel supplied to the filter 4 is oxidized by the oxidation catalyst supported on the filter 4. At this time, the temperature of the filter 4 further increases due to the oxidation heat.

  By such filter regeneration control, the temperature of the filter 4 is controlled to the specified filter temperature. Here, the specified filter temperature is a temperature at which collected PM can be oxidized and removed, and a temperature at which deterioration of the filter 4 can be suppressed. This prescribed filter temperature is determined in advance by experiments or the like. Thereby, PM is oxidized and removed.

  Then, after the start of the filter regeneration control, when the amount of collected PM in the filter 4 decreases to the second specified amount or less, the execution of the filter regeneration control is stopped. Here, the second specified trapping amount is a threshold amount that can be determined to take some time before the PM trapping amount becomes the first specified trapping amount Q1 again, that is, the PM trapping amount is sufficient. It is an amount that becomes a threshold value that can be judged to have decreased. This second specified trapping amount is also a predetermined amount by experiment or the like.

<Setting of upper limit injection amount in filter regeneration control>
When sub fuel injection is executed in the filter regeneration control, a reference injection amount that is a reference value of the sub fuel injection amount is calculated based on the intake air amount of the internal combustion engine 1 and the temperature of the oxidation catalyst 5. This reference injection amount is an amount by which the temperature of the filter 4 can be controlled to the specified filter temperature if the operating state of the internal combustion engine 1 is a steady operating state.

Here, when the operation state of the internal combustion engine 1 becomes a transient operation state in which the intake air amount increases due to an acceleration request or the like, the exhaust gas flow rate flowing through the oxidation catalyst 5 and the filter 4 also increases. And when sub fuel injection is performed when the operation state of the internal combustion engine 1 is in such a transient operation state,
The oxidation catalyst 5 is less likely to be oxidized than when the internal combustion engine 1 is in a steady operation state. In addition, the fuel is hardly oxidized even in the oxidation catalyst supported on the filter 4. That is, the fuel easily passes through the oxidation catalyst 5 and the filter 4.

  Therefore, when the sub fuel injection is executed with the reference injection amount as the sub fuel injection amount when the operation state of the internal combustion engine 1 is in the transient operation state as described above, the amount of fuel supplied to the filter 4 is an excessive amount. There is a risk of becoming. That is, the amount of fuel that passes through the filter 4 and is discharged to the outside may be excessive. Therefore, in this embodiment, the upper limit injection amount that is the upper limit value of the sub fuel injection amount is set based on the temperature of the oxidation catalyst 5 and the intake air amount increase rate when the sub fuel injection is executed.

  When the auxiliary fuel injection is executed, the lower the temperature of the oxidation catalyst 5, the less the fuel is oxidized in the oxidation catalyst 5. Therefore, fuel is easily supplied to the filter 4. On the other hand, the higher the intake air amount increase rate, the higher the exhaust flow rate increase rate. The higher the exhaust flow rate increase rate, the easier the fuel passes through the oxidation catalyst 5. Therefore, fuel is easily supplied to the filter 4. Further, the higher the exhaust gas flow rate increase rate, the easier the fuel passes through the filter 4.

  Therefore, in this embodiment, the upper limit injection amount is set to a smaller amount as the temperature of the oxidation catalyst 5 is lower. Further, the upper limit injection amount is set to a smaller amount as the intake air amount increase rate is higher.

<Control routine for filter regeneration control>
Next, a control routine for filter regeneration 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 10 and is executed at regular intervals during the operation of the internal combustion engine 1.

  In this routine, first, in S101, the ECU 10 determines whether or not the PM collection amount Qpm in the filter 4 is equal to or greater than the first specified collection amount Q1. When an affirmative determination is made in S101, the ECU 10 proceeds to S102, and when a negative determination is made, the ECU 10 once ends the execution of this routine.

  In S102, the ECU 10 performs the exhaust gas temperature raising control described above.

  Next, the ECU 10 determines whether or not the temperature Tc of the oxidation catalyst 5 is equal to or higher than the lower limit value Tc0 of the activation temperature. If an affirmative determination is made in S103, the ECU 10 proceeds to S104. If a negative determination is made, the ECU 10 repeats S103.

  The ECU 10 having advanced to S104 calculates the reference injection amount Qfsbase based on the current intake air amount of the internal combustion engine 1 and the temperature Tc of the oxidation catalyst 5.

  Next, the ECU 10 proceeds to S105 and determines whether or not the accelerator opening has increased. That is, it is determined whether or not the operating state of the internal combustion engine 1 shifts to a transient operating state in which the intake air amount increases. If an affirmative determination is made in S105, the ECU 10 proceeds to S106, and if a negative determination is made, the ECU 10 proceeds to S114.

  The ECU 10 having proceeded to S106 calculates the required main fuel injection amount Qfm from the accelerator opening.

Next, the ECU 10 proceeds to S107, and calculates the maximum value Gamax of the intake air amount when the requested main fuel injection amount Qfm is the main fuel injection amount. Here, first, the maximum engine speed Nmax of the internal combustion engine 1 when the required main fuel injection amount Qfm is set as the main fuel injection amount is calculated. The relationship between the main fuel injection amount and the maximum rotational speed Nmax can be obtained in advance by experiments or the like. Then, the maximum value Gamax of the intake air amount is calculated based on the requested main fuel injection amount Qfm and the maximum rotation speed Nmax. In the present embodiment, the relationship between the required main fuel injection amount Qfm, the maximum rotation speed Nmax, and the maximum value Gamax of the intake air amount is stored in advance in the ECU 10 as a map. The maximum value Gamax of the intake air amount is calculated from this map.

  Next, the ECU 10 proceeds to S108 and calculates an intake air amount increase rate RGa. Here, the amount of increase in the intake air amount is obtained by subtracting the intake air amount at the present time from the maximum value Gamax of the intake air amount, that is, the intake air amount before the main fuel injection amount increases to the required main fuel injection amount Qfm. ΔGa is calculated. Then, the intake air amount increase rate RGa is calculated by dividing the increase amount ΔGa of the intake air amount by the time Δt required for the current rotational speed of the internal combustion engine 1 to rise to the maximum rotational speed Nmax.

  Next, the ECU 10 proceeds to S109, calculates the upper limit injection amount Qfsmax based on the temperature Tc of the oxidation catalyst 5 and the intake air amount increase rate RGa, and sets this upper limit injection amount Qfsmax as the upper limit value of the auxiliary fuel injection amount. . In the present embodiment, as shown in FIG. 3, a map showing the relationship among the temperature Tc of the oxidation catalyst 5, the intake air amount increase rate RGa, and the upper limit fuel injection amount Qfamax is stored in the ECU 10 in advance. The upper limit injection amount Qfsmax is calculated from this map. In this map, the upper limit injection amount Qfsmax is smaller as the temperature Tc of the oxidation catalyst 5 is lower. Further, the higher the intake air amount increase rate RGa, the smaller the upper limit injection amount Qfsmax.

  Next, the ECU 10 proceeds to S110, and determines whether or not the reference injection amount Qfsbase is larger than the upper limit injection amount Qfsmax. If an affirmative determination is made in S110, the ECU 10 proceeds to S111. If a negative determination is made, the ECU 10 proceeds to S114.

  The ECU 10 that has proceeded to S111 executes the auxiliary fuel injection with the upper limit injection amount Qfsmax as the auxiliary fuel injection amount. Thereafter, the ECU 10 proceeds to S112.

  On the other hand, the ECU 10 that has proceeded to S114 executes the auxiliary fuel injection with the reference injection amount Qfsbase as the auxiliary fuel injection amount. Thereafter, the ECU 10 proceeds to S112.

  In S112, the ECU 10 determines whether or not the PM collection amount in the filter 4 has decreased to the second specified collection amount Q2 or less. If an affirmative determination is made in S112, the ECU 10 proceeds to S113, and if a negative determination is made, the ECU 10 proceeds to S104.

  In S113, the ECU 10 stops the exhaust gas temperature raising control and the auxiliary fuel injection. That is, the execution of the filter regeneration control is stopped. Thereafter, the ECU 10 temporarily stops the execution of this routine.

  According to the control routine described above, when the auxiliary fuel injection is performed in the filter regeneration control and the operating state of the internal combustion engine 1 is in a transient operating state in which the intake air amount increases, the upper limit injection amount Qfsmax is Is set.

  The upper limit injection amount Qfsmax is set to a smaller amount as the temperature Tc of the oxidation catalyst 5 is lower and as the intake air amount increase rate RGa is higher.

According to this, it can suppress that the fuel supply amount to the filter 4 becomes an excessive amount. That is, the amount of fuel that passes through the filter 4 and is discharged to the outside can be suppressed. Accordingly, it is possible to suppress the deterioration of exhaust emission during the execution of the filter regeneration control.

<Modification>
Next, as a modification of the present embodiment, a case where a NOx catalyst is provided instead of the filter 4 will be described. In such a case, SOx poisoning regeneration control is performed to reduce SOx stored in the NOx catalyst. In this case, the NOx catalyst constitutes the exhaust purification device according to the present invention. The SOx regeneration control corresponds to the regeneration control according to the present invention.

  Also in the SOx poisoning regeneration control, the exhaust gas temperature raising control and the auxiliary fuel injection are executed as in the filter regeneration control. With these controls, the temperature of the NOx catalyst is raised, and fuel is supplied as a reducing agent to the NOx catalyst by sub fuel injection. As a result, the atmosphere around the NOx catalyst becomes a reducing atmosphere, and SOx is reduced.

  Also in this SOx poisoning regeneration control, when the sub fuel injection is executed when the operation state of the internal combustion engine 1 is in a transient operation state in which the intake air amount increases, the fuel passes through the oxidation catalyst 5 and the NOx catalyst and is externally Easily released.

  Therefore, also in the SOx poisoning regeneration control, the upper limit value of the auxiliary fuel injection amount is set by the same method as in the filter regeneration control. Thereby, it can suppress that the amount of fuel supply to the NOx catalyst becomes an excessive amount. That is, the amount of fuel that passes through the NOx catalyst and is released to the outside can be suppressed. Therefore, it is possible to suppress deterioration of exhaust emission during execution of SOx poisoning regeneration control.

  In this embodiment, the case where fuel is supplied to the oxidation catalyst 5 and the filter 4 (or NOx catalyst) by executing sub fuel injection in the internal combustion engine 1 has been described. However, the exhaust gas upstream of the oxidation catalyst 5 is explained. A fuel addition valve may be provided in the passage 2 and fuel may be added from the fuel addition valve instead of the auxiliary fuel injection. In this case, the upper limit value of the fuel addition amount by the fuel addition valve is set by the same method as the upper limit injection amount.

The figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its intake / exhaust system. The flowchart which shows the control routine of filter reproduction | regeneration control. The map which shows the relationship between the temperature of an oxidation catalyst, the intake air amount increase rate, and the upper limit fuel injection amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 4 ... Particulate filter 5 ... Oxidation catalyst 7 ... Air flow meter 10 ... ECU
11 .... Differential pressure sensor 13 ... Temperature sensor 14 ... Crank position sensor 15 ... Accelerator position sensor

Claims (2)

An exhaust purification device provided in the exhaust passage of the internal combustion engine;
A catalyst having an oxidation function provided in the exhaust passage upstream of the exhaust purification device;
Catalyst temperature detecting means for detecting the temperature of the catalyst;
An increase rate calculating means for calculating an intake air amount increase rate that is an increase amount per unit time of the intake air amount of the internal combustion engine;
The catalyst is heated up to the activation temperature, and regeneration control is performed to regenerate the exhaust purification capability of the exhaust purification device by supplying a reducing agent to the catalyst and the exhaust purification device from the upstream side of the catalyst. Playback control execution means;
Correction means for correcting a reducing agent supply amount when supplying the reducing agent to the catalyst and the exhaust gas purification device in the regeneration control,
The correction means reduces the upper limit supply amount, which is the upper limit value of the reducing agent supply amount, as the temperature of the catalyst decreases, and decreases the upper limit supply amount as the intake air amount increase rate increases. An exhaust purification system for an internal combustion engine. The correction means has an upper limit supply amount setting means for setting the upper limit supply amount;
The upper limit supply amount setting means sets the upper limit supply amount to a smaller amount as the temperature of the catalyst is lower, and sets the upper limit supply amount to a smaller amount as the intake air amount increase rate is higher. The exhaust gas purification system for an internal combustion engine according to claim 1.

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