JP2008121571A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control temperature of a filter during execution of filter regeneration control to more favorable temperature. <P>SOLUTION: After the execution of the filter regenerating control is started, the execution of the filter regenerating control is stopped when a difference between CO<SB>2</SB>concentration in an inflow side and CO<SB>2</SB>concentration in an outflow side comes to or blow a prescribed concentration difference. When a prescribed condition is satisfied and PM collection quantity becomes prescribed collection quantity or over, the temperature of the filter is gradually increased at a prescribed speed until the difference between the CO<SB>2</SB>concentration in the inflow side and the CO<SB>2</SB>concentration in the outflow side comes to or below the prescribed concentration difference. The temperature of the filter when the difference between the CO<SB>2</SB>concentration in the inflow side and the CO<SB>2</SB>concentration in the outflow side comes maximum during the period is set as a target temperature for the next filter regenerating control. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

    The present invention relates to an exhaust gas purification system for an internal combustion engine provided with a particulate filter that is provided in an exhaust passage and collects particulate matter in exhaust gas.

  A technique is known in which a particulate filter (hereinafter simply referred to as a filter) is provided in an exhaust passage in order to collect particulate matter (hereinafter referred to as PM) contained in the exhaust gas of an internal combustion engine.

In Patent Document 1, in an exhaust gas purification system for an internal combustion engine equipped with such a filter, in order to burn PM collected by the filter, combustion air is sent to the inlet side of the filter and the combustion air is heated. Techniques to do this are disclosed. In this Patent Document 1, it is a condition that the difference in the CO ₂ concentration of the gas at the outlet side of the filter before PM combustion is started and when PM combustion is being performed is smaller than a predetermined determination value. It is described that heating of the combustion air is stopped.
JP 2004-339996 A

  In an exhaust gas purification system for an internal combustion engine equipped with a filter, filter regeneration control is performed in which PM is oxidized and removed by raising the temperature of the filter. In the filter regeneration control, if the temperature of the filter is excessively increased, the filter 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 controlling the temperature of a filter at the time of execution of filter regeneration control to a more suitable temperature.

In the present invention, after the execution of the filter regeneration control is started, the execution of the filter regeneration control is stopped when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes a predetermined concentration difference or less. Then, when a predetermined condition is satisfied and the PM trapping amount is equal to or greater than the predetermined trapping amount, the filter is predetermined until the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes equal to or less than the predetermined concentration difference. The temperature is gradually raised at a speed, and the temperature of the filter when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration reaches the maximum value is set as the target temperature in the next filter regeneration control.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
A particulate filter provided in the exhaust passage for collecting particulate matter in the exhaust;
PM collection amount calculating means for calculating a PM collection amount that is a collection amount of particulate matter in the particulate filter;
Filter regeneration control that oxidizes and removes the particulate matter collected by the particulate filter by raising the temperature of the particulate filter to a target temperature when the amount of collected PM exceeds a predetermined amount Filter regeneration means to be executed;
Inflow-side CO ₂ concentration detection means for detecting the inflow side the CO ₂ concentration is the CO ₂ concentration of the exhaust gas flowing into the particulate filter,
And the outflow side the CO ₂ concentration detection means for detecting the outflow side the CO ₂ concentration is the CO ₂ concentration of the exhaust gas flowing out from the particulate filter,
After execution of the filter regeneration control is started by the filter regeneration means, the inflow side CO ₂
A reproduction stop means the difference between the density and the outflow side the CO ₂ concentration stops the execution of the filter regeneration control when it becomes less than a predetermined density difference,
The particulates until the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes equal to or less than the predetermined concentration difference when the predetermined condition is satisfied and the PM collection amount becomes equal to or greater than the predetermined capture amount. The temperature of the filter is gradually raised at a predetermined speed, and the temperature of the particulate filter when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration reaches the maximum value during this period is set as the target in the next filter regeneration control. It is characterized by temperature.

  Here, the predetermined collection amount is a PM collection amount which is a threshold value for starting execution of the filter regeneration control, and is a value determined in advance by an experiment or the like.

When PM collected by the filter is oxidized by executing the filter regeneration control, the outflow side CO ₂ concentration becomes higher than the inflow side CO ₂ concentration. When the oxidation of the collected PM ends, that is, when the removal of the PM from the filter is completed, the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes zero or a value near zero.

  Here, the predetermined density difference is a threshold value with which it can be determined that the oxidation of PM has ended in the filter, and is determined in advance by experiments or the like.

Therefore, after the execution of the filter regeneration control is started, the filter regeneration control is stopped when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes equal to or smaller than the predetermined concentration difference, thereby causing the filter to Execution of filter regeneration control can be stopped when removal of the collected PM is completed. Thereby, it can suppress that the execution period of filter regeneration control becomes excessively long.

Further, in the present invention, when a predetermined condition is satisfied and the PM collection amount is equal to or greater than the predetermined collection amount, a difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration is equal to or less than the predetermined concentration difference. The particulate filter is gradually heated at a predetermined speed until

  Here, when the predetermined condition is satisfied, it is normal that a predetermined time has elapsed since the target temperature in the filter regeneration control was previously set or the target temperature in the filter regeneration control was previously set. For example, the filter regeneration control may be executed a predetermined number of times.

Further, PM contains SOF (soluble organic component) and Soot (soot), and SOF is more easily oxidized than Soot. Therefore, when the temperature of the filter is gradually raised so that the oxidation of PM is not accelerated rapidly, the oxidation of SOF is first promoted and then the oxidation of Soot is promoted. In this case, the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration while the temperature of the filter is raised reaches the first peak when the oxidation of SOF is most promoted (the inflow side at this time). The difference between the CO ₂ concentration and the outflow side CO ₂ concentration is referred to as the first peak value), and after that, once it drops below the first peak value, the second peak appears when the oxidation of Soot is most promoted. (The difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration at this time is referred to as a second peak value), and the second peak value is larger than the first peak value.

Here, the predetermined speed means that the first peak value and the second peak value as described above are generated in the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration while the temperature of the filter is raised. The rate of temperature increase. This predetermined speed can be determined in advance by experiments or the like.

The more the PM contained in the exhaust gas is less oxidized (that is, the more difficult it is to oxidize SOF and Soot), the more the temperature of the filter is raised to a higher temperature in order to oxidize PM collected in the filter. It is necessary to let In this case, the temperature at which the first peak value and the second peak value in the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration are higher. However, even in such a case, the temperature at which the second peak value that is the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration when oxidation of the soot that is difficult to oxidize is most promoted occurs. If the temperature of the filter is raised to a level, it is possible to oxidize the PM collected by the filter. That is, the temperature of the filter when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes the maximum value is the minimum value of the temperature at which the PM trapped in the filter can be completely oxidized. Become.

Therefore, in the present invention, the temperature of the filter when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes the maximum value when the temperature of the filter is gradually raised at a predetermined speed as described above is set next time. The target temperature in the filter regeneration control.

  Thereby, in filter regeneration control, it is possible to sufficiently remove PM collected by the filter while suppressing an excessive increase in the temperature of the filter. That is, the filter temperature at the time of executing the filter regeneration control can be controlled to a more suitable temperature.

In the present invention, the PM collection amount calculation means may be a first PM collection amount calculation means, and in addition to the first PM collection amount calculation means, a second PM collection amount calculation means may be further provided. In this case, the first PM trapping amount calculation means has a map showing the relationship between the operating state of the internal combustion engine and the PM trapping amount, and calculates the PM trapping amount based on the map. Further, the second PM collection amount calculating means is based on a history of the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration from the start of the execution of the filter regeneration control to the stop thereof. Thus, the PM collection amount at the time when the execution of the filter regeneration control is started is calculated.

During the execution of the filter regeneration control, the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration increases as the amount of PM to be oxidized increases. Therefore, oxidation is performed during the execution of the filter regeneration control based on the history of the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration from when the execution of the filter regeneration control is started until the execution is stopped. The amount of PM collected, that is, the amount of PM collected at the time when execution of the filter regeneration control is started can be calculated.

As described above, the second PM trapped amount calculation means starts executing the filter regeneration control based on the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration that are generated when the PM is actually oxidized in the filter. Calculate the amount of PM collected at the time of being. Therefore, the amount of PM trapped at the time when execution of the filter regeneration control is started can be calculated with higher accuracy.

  Therefore, in the above case, based on the PM collection amount calculated by the second PM collection amount calculation means, the PM collection amount for the operating state of the internal combustion engine in the map of the first PM collection amount calculation means is corrected. Correction means may be further provided.

  Thereby, the amount of PM trapped with respect to the operating state of the internal combustion engine on the map can be made more accurate. Therefore, it becomes possible to calculate the PM collection amount more accurately by the first PM collection amount calculation means. As a result, the next filter regeneration control can be executed at a more suitable time.

  In the present invention, the filter regeneration means may execute the filter regeneration control after the operation of the internal combustion engine is stopped after the PM collection amount becomes equal to or greater than the predetermined collection amount.

From the internal combustion engine, not only PM but also fuel components such as HC and CO are discharged together with the exhaust gas. When the filter regeneration control is executed, these fuel components in the exhaust gas may be oxidized in the filter. In this case, the oxidation of these fuel components may affect the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration.

According to the above, the filter regeneration control is executed in a state where the fuel component is not discharged from the internal combustion engine. For this reason, it is possible to suppress the oxidation of the fuel component in the filter from affecting the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration during the execution of the filter regeneration control. Therefore, the execution stop timing of the filter regeneration control in the present invention can be made more suitable.

  According to the present invention, the temperature of the filter at the time of executing the filter regeneration control can be controlled to a more suitable temperature.

<Schematic configuration of intake and exhaust system of internal combustion engine>
Here, a 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 intake / exhaust system of an internal combustion engine 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 11 is provided in the intake passage 3. The exhaust passage 2 is provided with a filter 5 that collects PM in the exhaust. An oxidation catalyst 4 is provided as an upstream catalyst in the exhaust passage 2 upstream of the filter 5. In this embodiment, the pre-stage catalyst may be a catalyst having an oxidation function, and a catalyst such as a three-way catalyst or an occlusion reduction type NOx catalyst may be provided in place of the oxidation catalyst 4.

A fuel addition valve 6 for adding fuel to the exhaust gas is provided in the exhaust passage 2 upstream of the oxidation catalyst 4. The filter 5 is provided with a temperature sensor 7 that detects the temperature of the filter 5. Further, an upstream CO ₂ concentration sensor 8 that detects the CO ₂ concentration (inflow side CO ₂ concentration) of the exhaust gas flowing into the filter 5 is provided in the exhaust passage 2 downstream from the oxidation catalyst 4 and upstream from the filter 5. It has been. A downstream CO ₂ concentration sensor 9 that detects the CO ₂ concentration (outflow side CO ₂ concentration) of the exhaust gas flowing out from the filter 5 is provided in the exhaust passage 2 downstream of the filter 5. In the present embodiment, the upstream CO ₂ concentration sensor 8 and the downstream CO ₂ concentration sensor 9 correspond to the inflow side CO ₂ concentration detection means and the outflow side CO ₂ concentration detection means according to the present invention, respectively.

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 electrically connected to an air flow meter 11 and a temperature sensor 7, an upstream CO ₂ concentration sensor 8, a downstream CO ₂ concentration sensor 9, and a crank position sensor 12 that detects the crank angle of the internal combustion engine 1. These output signals are input to the ECU 10. The ECU 10 calculates the rotational speed of the internal combustion engine 1 based on the output signal of the crank position sensor 12.

  Further, the ECU 10 is electrically connected to the fuel addition valve 6 and the fuel injection valve of the internal combustion engine 1. These are controlled by the ECU 10.

<Filter regeneration control>
In this embodiment, filter regeneration control is performed to remove PM collected by the filter 5. In the filter regeneration control, fuel is added to the exhaust by the fuel addition valve 6. The added fuel is supplied to the oxidation catalyst 4 and is oxidized in the oxidation catalyst 4. The exhaust gas is heated by the oxidation heat generated at this time, and the filter 5 is heated by the exhaust gas. The temperature of the filter 5 is controlled to the target temperature by controlling the amount of fuel added from the fuel addition valve 6.

  This filter regeneration control is executed when the amount of PM collected in the filter 5 is equal to or greater than a predetermined amount of collection. The ECU 10 stores a map indicating the relationship between the operating state of the internal combustion engine 1 (fuel injection amount, engine speed, intake air amount, etc.) and the amount of PM trapped in the filter 5. The ECU 10 calculates the amount of PM trapped in the filter 5 based on this map.

<Execution stop control of filter regeneration control>
Here, the routine of the stop control of the 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 repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, the ECU 10 first determines whether or not the filter regeneration control is being executed in S101. When an affirmative determination is made in S101, the ECU 10 proceeds to S102, and when a negative determination is made, the execution of this routine is once terminated.

When PM is oxidized in the filter 5 during execution of the filter regeneration control, the outflow side CO ₂ concentration becomes higher than the inflow side CO ₂ concentration. When the oxidation of the collected PM ends, the difference between the outflow side CO ₂ concentration and the inflow side CO ₂ concentration becomes zero or a value near zero.

Therefore, in S102, it calculates the CO ₂ concentration difference ΔRg by subtracting the inflow side CO ₂ concentration from the outflow side the CO ₂ concentration.

Next, the ECU 10 proceeds to S103, and determines whether or not the CO ₂ concentration difference ΔRg is equal to or less than a predetermined concentration difference ΔRg0. Here, the predetermined concentration difference ΔRg0 is a threshold value with which it is possible to determine that PM is not oxidized in the filter 5. If an affirmative determination is made in S103, the ECU 10 proceeds to S104. On the other hand, if a negative determination is made in S103, the ECU 10 once ends the execution of this routine. In this case, the execution of the filter regeneration control is continued.

  The ECU 10 that has proceeded to S104 stops the fuel addition by the fuel addition valve 6. That is, the execution of the filter regeneration control is stopped. Thereafter, the ECU 10 once terminates execution of this routine.

  According to this routine, the execution of the filter regeneration control can be stopped when the removal of the PM collected by the filter 5 is completed. Therefore, it is possible to prevent the execution period of the filter regeneration control from becoming excessively long. Thereby, deterioration of the filter 5 can be suppressed. Moreover, since it can suppress that the fuel addition amount from the fuel addition valve 6 increases excessively, the deterioration of a fuel consumption can be suppressed.

<Target temperature setting method>
Here, a method for setting the target temperature in the filter regeneration control according to the present embodiment will be described with reference to FIGS.

FIG. 3 shows a CO ₂ concentration difference ΔRg when the temperature Tf of the filter 5 is gradually increased at a predetermined speed vup when the temperature Tf of the filter 5 is increased to remove the PM collected by the filter 5. It is a figure which shows the change of. In FIG. 3, the horizontal axis represents the temperature Tf of the filter 5, and the vertical axis represents the CO ₂ concentration difference ΔRg. In FIG. 3, the solid line represents a case where PM collected by the filter 5 is relatively easy to oxidize, and the broken line represents that the PM collected by the filter 5 is relatively difficult to oxidize. It represents the case of things.

When PM starts to be oxidized by gradually increasing the temperature Tf of the filter 5 at a predetermined speed vup, the CO ₂ concentration difference ΔRg gradually increases. First, when the temperature Tf of the filter 5 reaches a temperature at which the oxidation of SOF in PM is most promoted, the CO ₂ concentration difference ΔRg becomes the first peak value P1. Thereafter, the CO ₂ concentration difference ΔRg once decreases from the first peak value P1, and starts to increase again when the temperature Tf of the filter 5 reaches a temperature at which the oxidation of Soot in PM is promoted. When the temperature Tf of the filter 5 reaches a temperature at which the soot oxidation is most promoted, the CO ₂ concentration difference ΔRg becomes the second peak value P2. At this time, the second peak value P2 is larger than the first peak value P1. Thereafter, even if the temperature Tf of the filter 5 further increases, the CO ₂ concentration difference ΔRg decreases. When the oxidation of the collected PM ends, the CO ₂ concentration difference ΔRg becomes equal to or less than the predetermined concentration difference ΔRg0. That is, the second peak value P2 is the maximum value of the CO ₂ concentration difference ΔRg while the temperature Tf of the filter 5 is gradually increased at the predetermined speed vup.

As described above, the second peak value P2 of the CO ₂ concentration difference ΔRg occurs when the temperature Tf of the filter 5 reaches a temperature at which the soot oxidation is most promoted. Accordingly, the filter 5 is increased to the temperature Tfp when the CO ₂ concentration difference ΔRg becomes the second peak value P2, that is, when the CO ₂ concentration difference ΔRg becomes the maximum value (hereinafter referred to as peak temperature) Tfp. When heated, the PM collected by the filter 5 can be oxidized. That is, the peak temperature Tfp is the lowest temperature at which the PM collected by the filter 5 can be oxidized.

Here, when PM (that is, SOF or Soot) is relatively difficult to oxidize, when the temperature Tf of the filter 5 is increased at a predetermined speed, as shown by the broken line in FIG. The temperature Tf of the filter 5 at which the first peak value P1 and the second peak value P2 of the CO ₂ concentration difference ΔRg are generated is higher than that in the case of being easily oxidized. That is, the peak temperature Tfp becomes a higher value. However, even in such a case, if the temperature of the filter 5 is raised to the peak temperature Tfp, the PM collected by the filter 5 can be oxidized.

Incidentally, when suddenly increasing the temperature Tf of the filter 5 to remove the PM trapped in the filter 5, since the oxidation of SOF oxidation of Soot is rapidly promoted, first to the CO ₂ concentration difference ΔRg The peak value P1 and the second peak value P2 are difficult to appear. The predetermined speed vup when the temperature of the filter 5 is gradually raised as described above is that the CO ₂ concentration difference ΔRg is changed to the first peak value P1 and the second peak value as described above while the temperature of the filter 5 is raised. The speed is such that the peak value P2 occurs. Such a predetermined speed vup can be obtained in advance by experiments or the like.

Therefore, in this embodiment, when the PM collection amount becomes equal to or greater than the predetermined collection amount in a state where the predetermined condition is satisfied, the filter is performed at the predetermined speed vup until the CO ₂ concentration difference ΔRg becomes equal to or less than the predetermined concentration difference ΔRg0. 5 is raised. During this time, the peak temperature Tfp is detected, and the peak temperature Tfp is set as the target temperature for the next execution of the filter regeneration control.

  Hereinafter, a routine for setting the target temperature Tft in the 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 repeatedly executed at predetermined intervals.

In this routine, first, the ECU 10 determines whether or not a predetermined condition is satisfied in S201. Here, as a predetermined condition, normal filter regeneration is performed when a predetermined time has elapsed since the target temperature Tft in the filter regeneration control was previously set or when the target temperature Tft in the filter regeneration control was previously set. A case where the control has been executed a predetermined number of times can be exemplified. If an affirmative determination is made in S101, the ECU 10 proceeds to S202, and if a negative determination is made, the ECU 10 once ends the execution of this routine.

  The ECU 10 having proceeded to S202 determines whether or not the PM collection amount Qpm in the filter 5 is equal to or greater than a predetermined collection amount Qpm0. If an affirmative determination is made in S202, the ECU 10 proceeds to S203, and if a negative determination is made, the ECU 10 once ends the execution of this routine.

In step S203, the ECU 10 starts adding fuel from the fuel addition valve 6 so that the temperature of the filter 5 is increased at a predetermined speed vup (for example, 20 to 30 ° C./min). 5 starts the temperature increase. The ECU 10 stores a history of changes in the CO ₂ concentration difference ΔRg while raising the temperature of the filter 5.

Next, the ECU 10 proceeds to S204, and calculates the CO ₂ concentration difference ΔRg by subtracting the inflow side CO ₂ concentration from the outflow side CO ₂ concentration.

Next, the ECU 10 proceeds to S205, and determines whether or not the CO ₂ concentration difference ΔRg is equal to or less than a predetermined concentration difference ΔRg0. If an affirmative determination is made in S205, the ECU 10 proceeds to S206. If a negative determination is made, the ECU 10 returns to S204.

  In step S206, the ECU 10 stops the fuel addition by the fuel addition valve 6 and stops the temperature of the filter 5 from rising.

  Next, the ECU 10 proceeds to S207 and detects a peak temperature Tfp while the filter 5 is being heated.

  Next, the ECU 10 proceeds to S208, and sets the peak temperature Tfp detected in S207 as the target temperature Tft in the next filter regeneration control. Thereafter, the ECU 10 once terminates execution of this routine.

  According to the present embodiment, the target temperature Tft of the filter 5 in the filter regeneration control actually sets the PM regardless of whether the PM collected by the filter 5 is easily oxidized or hardly oxidized. Is set to the peak temperature Tfp, which is the lowest temperature that can be fully oxidized. Thereby, at the time of execution of filter regeneration control, it is possible to sufficiently remove PM collected by the filter 5 while suppressing an excessive increase in the temperature of the filter 5. That is, the temperature of the filter 5 at the time of executing the filter regeneration control can be controlled to a more suitable temperature.

  Note that when the normal filter regeneration control is executed, the temperature of the filter 5 may be raised to the target temperature Tf as soon as possible.

<Correction of map>
In the present embodiment, the PM collection amount Qpm in the filter 5 is calculated based on a map indicating the relationship between the operating state of the internal combustion engine 1 stored in the ECU 10 and the PM collection amount in the filter 5. The filter regeneration control is executed when the calculated PM collection amount Qpm becomes equal to or greater than the predetermined collection amount Qpm0. Here, correction of the map according to the present embodiment will be described.

As described above, during execution of the filter regeneration control, the CO ₂ concentration difference ΔRg is generated by the oxidation of PM in the filter 5. In this embodiment, after the execution of the filter regeneration control is started, the execution of the filter regeneration control is stopped when the CO ₂ concentration difference ΔRg becomes equal to or smaller than the predetermined concentration difference ΔRg0. Therefore, the amount of PM oxidized in the filter 5 during execution of the filter regeneration control can be calculated based on the history of the CO ₂ concentration difference ΔRg from the start of execution of the filter regeneration control to the stop of the execution. . The amount of PM oxidized in the filter 5 during the execution of the filter regeneration control is the amount of PM collected when the execution of the filter regeneration control is started.

Therefore, in this embodiment, the amount of collected PM at the time when the execution of the filter regeneration control is started is calculated based on the history of the CO ₂ concentration difference ΔRg from the start of the execution of the filter regeneration control to the stop of the execution. To do. If the PM collection amount calculated in this way is different from the PM collection amount at the start of execution of the filter regeneration control calculated based on the map, the PM trapping with respect to the operating state of the internal combustion engine 1 in the map is performed. Correct the collection. That is, even if the amount of PM collected at the start of execution of the filter regeneration control at this time is calculated based on the map, it is recorded in the history of the CO ₂ concentration difference ΔRg from the start of execution of the filter regeneration control to the stop of execution. The map is corrected so as to be the same as the value calculated based on it.

The CO ₂ concentration difference ΔRg generated during the execution of the filter regeneration control is caused by the actual oxidation of PM in the filter 5. Therefore, by calculating the PM collection amount at the start of execution of the filter regeneration control based on the CO ₂ concentration difference ΔRg, the PM collection amount can be calculated more accurately. Therefore, by correcting the map as described above, the amount of PM trapped with respect to the operating state of the internal combustion engine 1 in the map can be made more accurate. As a result, the next filter regeneration control can be executed at a more suitable time.

In the filter regeneration control according to the present embodiment, instead of fuel addition by the fuel addition valve 6, the sub-fuel injection is executed in the internal combustion engine 1 at a time later than the main fuel injection, whereby the oxidation catalyst 4 is Fuel may be supplied. Further, the temperature of the filter 5 may be raised using a heater, a microwave heating device, or the like without supplying the fuel to the oxidation catalyst 4. In this case, during the execution of the filter regeneration control, the fuel added from the fuel addition valve 6 does not flow into the filter 5 and is not oxidized, so that the influence on the CO ₂ concentration difference ΔRg due to the oxidation of the fuel is suppressed. I can do it. Therefore, it is possible to improve the calculation accuracy of the PM collection amount at the start of execution of the filter regeneration control based on the CO ₂ concentration difference ΔRg.

In this embodiment, the upstream CO ₂ concentration sensor 8 detects the inflow side CO ₂ concentration, but it is based on the intake air amount, the fuel injection amount in the internal combustion engine 1, the fuel addition amount from the fuel addition valve 6, and the like. Thus, the inflow side CO ₂ concentration may be estimated. Further, instead of the upstream CO ₂ concentration sensor 8, when the CO ₂ concentration sensor for detecting a CO ₂ concentration of the intake air in the intake passage 3 is provided, the inflow-side using the detection value of the CO ₂ concentration sensor The CO ₂ concentration may be estimated. In these cases, ECU 10 performing the inflow side CO ₂ concentration estimated to correspond to the inlet side CO ₂ concentration detector according to the present invention.

Further, a configuration in which a catalyst having an oxidation function such as the oxidation catalyst 4 is supported on the filter 5 may be adopted. In such a configuration, PM is oxidized by a catalyst (hereinafter referred to as a supported catalyst) supported on the filter 5 in the filter 5 when the filter regeneration control is executed. In this case, the PM becomes difficult to be oxidized as the supported catalyst progresses. That is, the higher the degree of deterioration of the supported catalyst, the higher the target temperature Tft of the filter 5 in the filter regeneration control needs to be. Even in such a case, according to the method for setting the target temperature Tft of the filter regeneration control according to the above-described embodiment, the peak temperature that is the lowest value of the temperature at which PM can be actually oxidized can be obtained. Tfp is detected, and the peak temperature Tfp is the target temperature T of the filter 5
Set to ft. Therefore, according to this embodiment, the target temperature Tft of the filter 5 in the filter regeneration control is set to the peak temperature Tfp regardless of the degree of deterioration of the supported catalyst. Therefore, when the filter regeneration control is executed, PM trapped in the filter 5 can be sufficiently removed while suppressing an excessive increase in the temperature of the filter 5 and the supported catalyst.

<Modification>
Here, a modification of the present embodiment will be described. FIG. 5 is a diagram showing a schematic configuration of an intake / exhaust system of an internal combustion engine according to this modification. In this modification, an electric heater 13 for heating the filter 5 is provided. The electric heater 13 is electrically connected to the ECU 10 and its operation is controlled by the ECU 10. The other configuration is the same as the configuration shown in FIG.

  In this modification, the filter regeneration control is performed by heating the filter 5 with the electric heater 13 after the operation of the internal combustion engine 1 is stopped after the PM collection amount in the filter 5 becomes equal to or greater than the predetermined collection amount. Execute by that.

After the operation of the internal combustion engine 1 is stopped, the exhaust does not flow into the filter 5, that is, the fuel component does not flow into the filter 5. Therefore, when the filter regeneration control is performed after the internal combustion engine 1 is stopped, it is suppressed that the fuel component is oxidized in the filter 5 during the execution of the filter regeneration control, thereby affecting the CO ₂ concentration difference ΔRg. Further, by raising the temperature of the filter 5 by the electric heater 13, it is possible to suppress the influence of the fuel added from the fuel addition valve 6 from being oxidized and affecting the CO ₂ concentration difference ΔRg.

Therefore, when the filter regeneration control is executed after the operation of the internal combustion engine 1 is stopped, it becomes possible to more accurately determine the time point at which the removal of PM collected by the filter 5 is completed by the CO ₂ concentration difference ΔRg. Therefore, by executing the execution stop control of the filter regeneration control as described above, the execution of the filter regeneration control can be stopped at a more suitable time.

In the present modification, the method for setting the target temperature Tft in the above-described filter regeneration control is also executed after the operation of the internal combustion engine 1 is stopped. In this case, for the above reason, the correlation between the oxidation amount of PM and the CO ₂ concentration difference ΔRg during execution of the filter regeneration control becomes higher. Therefore, the target temperature Tft can be set to a more suitable value by setting the target temperature Tft in the filter regeneration control by the above method after the operation of the internal combustion engine 1 is stopped.

Also in this modified example, the map indicating the relationship between the operation state of the internal combustion engine 1 and the amount of PM trapped in the filter 5 is corrected. The filter regeneration control is executed after the operation of the internal combustion engine 1 is stopped, and the PM collection amount at the start of the filter regeneration control is calculated based on the history of the CO ₂ concentration difference ΔRg at this time. Can be calculated with higher accuracy. Therefore, by correcting the map based on the PM collection amount calculated in this way, the PM collection amount with respect to the operating state of the internal combustion engine 1 in the map can be made more accurate.

  In this modification, as shown in FIG. 6, an electric heater 14 that superheats the oxidation catalyst 4 is provided in place of the electric heater 13 and the secondary air is disposed in the exhaust passage 2 upstream of the fuel addition valve 6. A secondary air supply device 15 may be provided. The electric heater 14 and the secondary air supply device 15 are electrically connected to the ECU 10, and their operation is controlled by the ECU 10.

After the operation of the internal combustion engine 1 is stopped, the exhaust does not flow into the exhaust passage 2. Therefore, in the configuration shown in FIG. 6, when the filter regeneration control is performed after the internal combustion engine 1 is stopped, the oxidation catalyst 4 is heated to the activation temperature by the electric heater, and the secondary air supply device enters the secondary in the exhaust passage 2. Supply air. Then, fuel addition by the fuel addition valve 6 is executed.

In this case, since the fuel is added by the fuel addition valve 6, the added fuel may flow into the filter 5. However, similarly to the above, the fuel component discharged from the internal combustion engine 1 is suppressed from flowing into the filter 5 and being oxidized during the execution of the filter regeneration control. Accordingly, even when the filter regeneration control is executed after the operation of the internal combustion engine 1 is stopped with the configuration shown in FIG. 6, the filter regeneration control is performed as compared with the case where the filter regeneration control is executed during the operation of the internal combustion engine 1. The correlation between the oxidation amount of PM and the CO ₂ concentration difference ΔRg during execution of the above can be made higher.

The figure which shows schematic structure of the intake / exhaust system of the internal combustion engine which concerns on an Example. The flowchart which shows the routine of the execution stop control of the filter regeneration control which concerns on an Example. Graph showing changes in CO ₂ concentration difference when the temperature was gradually increased to the filter at a predetermined speed. The flowchart which shows the routine for setting the target temperature in the filter reproduction | regeneration control which concerns on an Example. The figure which shows schematic structure of the intake / exhaust system of the internal combustion engine which concerns on the modification of an Example. The figure which shows schematic structure of the intake / exhaust system of the internal combustion engine which concerns on the modification of an Example.

Explanation of symbols

1 ... internal combustion engine 2 ... exhaust passage 4 ... oxidizing catalyst 5 ... particulate filter 6 ... fuel addition valve 7 ... temperature sensor 8 ... upstream CO ₂ concentration sensor 9,・ ・ Downstream CO ₂ concentration sensor 10 ・ ・ ECU
11. Air flow meter 12 Crank position sensor 13 Electric heater 14 Electric heater 15 Secondary air supply device

Claims (3)

A particulate filter provided in the exhaust passage for collecting particulate matter in the exhaust;
PM collection amount calculating means for calculating a PM collection amount that is a collection amount of particulate matter in the particulate filter;
Filter regeneration control that oxidizes and removes the particulate matter collected by the particulate filter by raising the temperature of the particulate filter to a target temperature when the amount of collected PM exceeds a predetermined amount Filter regeneration means to be executed;
Inflow-side CO ₂ concentration detection means for detecting the inflow side the CO ₂ concentration is the CO ₂ concentration of the exhaust gas flowing into the particulate filter,
And the outflow side the CO ₂ concentration detection means for detecting the outflow side the CO ₂ concentration is the CO ₂ concentration of the exhaust gas flowing out from the particulate filter,
After the start of the filter regeneration control by the filter regeneration means, the regeneration stop for stopping the execution of the filter regeneration control when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes a predetermined concentration difference or less. Means,
The particulates until the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration becomes equal to or less than the predetermined concentration difference when the predetermined condition is satisfied and the PM collection amount becomes equal to or greater than the predetermined capture amount. The temperature of the filter is gradually raised at a predetermined speed, and the temperature of the particulate filter when the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration reaches the maximum value during this period is set as the target in the next filter regeneration control. An exhaust gas purification system for an internal combustion engine, characterized by having a temperature. The PM collection amount calculation means is the first PM collection amount calculation means,
The first PM collection amount calculating means has a map showing the relationship between the operating state of the internal combustion engine and the PM collection amount, and calculates the PM collection amount based on the map,
The execution of the filter regeneration control is started based on the history of the difference between the inflow side CO ₂ concentration and the outflow side CO ₂ concentration after the execution of the filter regeneration control is stopped until the execution is stopped. A second PM collection amount calculating means for calculating a PM collection amount at a time point;
Correction means for correcting the PM trapping amount for the operating state of the internal combustion engine in the map based on the PM trapping amount calculated by the second PM trapping amount calculating unit;
The exhaust gas purification system for an internal combustion engine according to claim 1, further comprising: The filter regeneration means executes filter regeneration control after the operation of the internal combustion engine is stopped after the PM collection amount becomes equal to or greater than the predetermined collection amount. Exhaust gas purification system for internal combustion engines.

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