JP4665830B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention includes an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst, and a pre-stage catalyst that is provided in an exhaust passage upstream of the exhaust purification device and has an oxidation function. The present invention relates to an exhaust gas purification system for an internal combustion engine.

  In an exhaust system of an internal combustion engine, an exhaust purification device provided in an exhaust passage of the internal combustion engine and including a catalyst, and a pre-stage catalyst provided in an exhaust passage upstream of the exhaust purification device and having an oxidation function The thing equipped with these is known. In such a configuration, there is a case where the reducing agent is supplied to the exhaust gas purification device by supplying the reducing agent into the exhaust gas upstream of the upstream catalyst in order to recover the performance of the exhaust gas purification device.

  In this case, the reducing agent supplied into the exhaust is oxidized in the pre-stage catalyst before reaching the exhaust purification device.

Further, Patent Document 1 discloses that HC in the exhaust is oxidized in the catalyst based on the difference between the exhaust temperature upstream of the catalyst provided in the exhaust passage of the internal combustion engine and the exhaust temperature downstream of the catalyst. A technique is disclosed in which the amount of generated heat is estimated and the catalyst is determined to be in a deteriorated state when the estimated amount of generated heat is smaller than a determination value.
JP 2003-106140 A

  The present invention includes an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst, and a pre-stage catalyst that is provided in an exhaust passage upstream of the exhaust purification device and has an oxidation function. In the exhaust gas purification system for an internal combustion engine, when the reducing agent is supplied to the exhaust gas purification device in order to restore the performance of the exhaust gas purification device, the amount of the reducing agent actually supplied to the exhaust gas purification device is more preferably controlled. It aims at providing the technology which can be done.

  The present invention calculates a reducing agent oxidation amount, which is the amount of reducing agent oxidized in the preceding catalyst at the time of execution of reducing agent supply, and based on the difference between the reducing agent oxidation amount and the reducing agent supply amount, A reducing agent reaching amount, which is an amount of the reducing agent reaching the purification device, is calculated. Then, the reducing agent supply method and / or the reducing agent supply amount are controlled so that the reducing agent reaching amount becomes the target supply amount.

More specifically, according to the exhaust gas purification system for an internal combustion engine according to the present invention,
An exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst;
A pre-stage catalyst provided in the exhaust passage upstream of the exhaust purification device and having an oxidation function;
Inflow exhaust gas temperature detection means for detecting an inflow exhaust gas temperature that is the temperature of the exhaust gas flowing into the front catalyst,
A pre-catalyst temperature detecting means for detecting the temperature of the pre-catalyst;
Reducing agent supply means for supplying the reducing agent to the exhaust purification device by supplying the reducing agent into the exhaust upstream of the preceding catalyst when recovering the performance of the exhaust purification device;
When the reducing agent is supplied by the reducing agent supply means, a reducing agent oxidation amount, which is the amount of reducing agent oxidized by the preceding catalyst based on the difference between the inflow exhaust gas temperature and the temperature of the preceding catalyst. A reducing agent oxidation amount calculating means for calculating;
Based on the difference between the supply amount of the reducing agent supplied into the exhaust gas by the reducing agent supply means and the reducing agent oxidation amount calculated by the reducing agent oxidation amount calculation means, the amount of the reducing agent that has reached the exhaust purification device A reducing agent reaching amount calculating means for calculating a reducing agent reaching amount that is an amount,
The reducing agent supply unit is controlled so that the reducing agent arrival amount calculated by the reduction arrival amount calculation unit becomes a target supply amount when the reducing agent supply unit executes the reducing agent supply.

  When the reducing agent is oxidized in the pre-stage catalyst, the temperature of the pre-stage catalyst rises due to the heat of oxidation. Therefore, the reducing agent oxidation amount at the upstream catalyst can be calculated from the difference between the inflow exhaust gas temperature and the temperature of the upstream catalyst.

  Further, from the difference between the reducing agent supply amount supplied by the reducing agent supply means and the reducing agent oxidation amount at the pre-stage catalyst, the reducing agent arrival amount reaching the exhaust purification device, that is, actually supplied to the exhaust purification catalyst. The supply amount of the reducing agent can be calculated.

  And according to this invention, a reducing agent supply means is controlled so that the reducing agent arrival amount becomes the target supply amount. Thereby, the supply amount of the reducing agent actually supplied to the exhaust gas purification device can be controlled to the target supply amount with higher accuracy.

  In the present invention, the amount of reducing agent that reaches the exhaust emission control device may be controlled by controlling the amount of reducing agent supplied from the reducing agent supply means. Further, the amount of reducing agent that reaches the exhaust gas purification device may be controlled by controlling the method of supplying the reducing agent by the reducing agent supply means.

  When supplying a reducing agent to the exhaust purification device in order to restore the performance of the exhaust purification device, if the supply amount of the reducing agent actually supplied to the exhaust purification device is relatively small, the supply amount of the reducing agent is increased. Along with this, the recovery rate increases.

  However, when the supply amount of the reducing agent exceeds a certain level, the recovery rate of the performance of the exhaust gas purification device reaches the upper limit value, and even when an additional amount of reducing agent is supplied, the recovery rate does not increase.

  Therefore, in the present invention, the target supply amount may be a value in the vicinity of the lower limit value of the reducing agent amount at which the recovery rate of the performance of the exhaust purification device is in the vicinity of the upper limit value.

  As a result, the performance of the exhaust emission control device can be restored as much as possible, and the amount of reducing agent supplied from the reducing agent supply means can be suppressed.

  According to the present invention, an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst, a pre-stage catalyst that is provided in an exhaust passage upstream of the exhaust purification device and has an oxidation function, In the exhaust gas purification system for an internal combustion engine having the above, when the reducing agent is supplied to the exhaust gas purification device so as to restore the performance of the exhaust gas purification device, the amount of the reducing agent actually supplied to the exhaust gas purification device is more suitable Can be controlled.

  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 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. The exhaust passage 2 is provided with an oxidation catalyst 4 and an NOx storage reduction catalyst 5 (hereinafter simply referred to as NOx catalyst 5).

  The NOx catalyst 5 is a catalyst that stores NOx in the exhaust when the ambient atmosphere is an oxidizing atmosphere and reduces the NOx that is stored when the ambient atmosphere is a reducing atmosphere. The NOx catalyst 5 is provided downstream of the oxidation catalyst 4 in the exhaust passage 2. In this embodiment, the oxidation catalyst 4 corresponds to the pre-stage catalyst according to the present invention, and the NOx catalyst corresponds to the exhaust purification device according to the present invention. The pre-stage catalyst may be a catalyst having an oxidation function. For example, the oxidation catalyst 4 may be a NOx catalyst, and the NOx catalyst 5 may be a particulate filter carrying a NOx catalyst.

  A fuel addition valve 6 is provided in the exhaust passage 2 upstream of the oxidation catalyst 4 to add fuel as a reducing agent into the exhaust.

  Further, a first temperature sensor 8 and a second temperature sensor 9 for detecting the temperature of the exhaust gas are provided upstream of the oxidation catalyst 4 in the exhaust passage 2 and between the oxidation catalyst 4 and the NOx catalyst 5, 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. A first temperature sensor 8 and a second temperature sensor 9 are electrically connected to the ECU 10. These output signals are input to the ECU 10. The ECU 10 estimates the temperature of the oxidation catalyst 4 based on the output value of the second temperature sensor 9.

  Further, the fuel addition valve 6 is electrically connected to the ECU 10. This is controlled by the ECU 10.

<NOx reduction control>
In this embodiment, NOx reduction control is performed to reduce the NOx stored in the NOx catalyst 5 and restore the NOx storage capability of the NOx catalyst 5. The NOx reduction control according to this embodiment is executed by intermittently adding fuel from the fuel addition valve 6 when the temperature of the NOx catalyst 5 is the activation temperature. By adding fuel from the fuel addition valve 6, the fuel is supplied to the NOx catalyst 5 via the oxidation catalyst 4. As a result, the air-fuel ratio of the ambient atmosphere of the NOx catalyst 5 decreases and the ambient atmosphere becomes a reducing atmosphere, so that NOx stored in the NOx catalyst 5 is reduced. Further, by intermittently adding fuel from the fuel addition valve 6, it is possible to suppress an excessive increase in temperature of the oxidation catalyst 4 or the NOx catalyst 5.

  Further, as described above, the fuel added from the fuel addition valve 6 is supplied to the oxidation catalyst 4 before reaching the NOx catalyst 5. Therefore, at least a part of the fuel added from the fuel addition valve 6 is oxidized in the oxidation catalyst 4. Therefore, the amount of fuel reached, which is the amount of fuel actually supplied to the NOx catalyst 5, becomes smaller than the amount of fuel added from the fuel addition valve 6. Therefore, in this embodiment, the amount of fuel added from the fuel addition valve 6 is controlled so that the amount of fuel reached becomes the target supply amount.

  Here, the relationship between the amount of fuel actually supplied to the NOx catalyst 5 and the NOx reduction rate when the NOx reduction control is executed will be described with reference to FIG. Here, the NOx reduction rate is a value indicating the ratio of the amount of NOx to be reduced to the amount of NOx stored in the NOx catalyst 5. In FIG. 2, the vertical axis represents the NOx reduction rate, and represents the amount of fuel actually supplied to the NOx catalyst 5.

  When the NOx reduction control is executed and the amount of fuel actually supplied to the NOx catalyst 5 is relatively small, the NOx reduction rate increases as the amount of fuel increases. However, as shown in FIG. 2, when the amount of fuel actually supplied to the NOx catalyst 5 exceeds a certain amount, the NOx reduction rate reaches the upper limit value, and even if more fuel is supplied, the NOx reduction rate is increased. It will not rise.

  Therefore, in the NOx reduction control according to this embodiment, the target supply amount, which is the target value of the reached fuel amount, is set in a range near the lower limit value of the fuel amount where the NOx reduction rate is in the vicinity of the upper limit value (indicated by A in FIG. 2). Set to a value within the range.

<NOx reduction control routine>
Hereinafter, the routine for NOx reduction 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 repeated at a predetermined interval.

  In this routine, the ECU 10 first determines in S101 whether or not an execution condition for NOx reduction control is satisfied. Here, the execution condition of the NOx reduction control is exemplified when the estimated value of the NOx occlusion amount in the NOx catalyst 5 is equal to or higher than the threshold value for executing the NOx reduction control and the temperatures of the oxidation catalyst 4 and the NOx catalyst 5 are at the activation temperature. I can do it. If an affirmative determination is made in S101, the ECU 10 proceeds to S102, and if a negative determination is made, the execution of this routine is once terminated.

  In S <b> 102, the ECU 10 performs reference fuel when fuel addition by the fuel addition valve 6 is performed based on the intake air amount, the fuel injection amount in the internal combustion engine 1, the inflow exhaust gas temperature detected by the first temperature sensor 8, and the like. The addition amount Qfbase is calculated. This reference fuel addition amount Qfbase is a fuel addition amount that is predicted to reach the target supply amount Qfnt when the fuel addition valve 6 and the oxidation catalyst 4 are in the initial state.

  Next, the ECU 10 proceeds to S103 and executes fuel addition by the fuel addition valve 6 with the fuel addition amount Qfi as the reference fuel addition amount Qfbase.

  However, even if the fuel addition is executed with the fuel addition amount Qfi as the reference fuel addition amount Qfbase, the target fuel amount Qfn reaching the NOx catalyst 5 due to manufacturing errors or deterioration of the fuel addition valve 6 or the oxidation catalyst 4 is the target. There is a possibility that it may be larger or smaller than the supply amount Qfnt. Therefore, in this routine, the fuel addition amount Qfi is corrected by the following method.

  The ECU 10 proceeds to S104 after S103. In S104, the ECU 10 calculates the temperature difference ΔTgc by subtracting the inflow exhaust gas temperature from the temperature of the oxidation catalyst 4 estimated from the detection value of the second temperature sensor 9.

  Here, if the operating state of the internal combustion engine 1 is in a steady state, the inflow exhaust gas temperature is substantially constant, but since the fuel addition by the fuel addition valve 6 is performed intermittently, the temperature of the oxidation catalyst 4 varies. That is, when the fuel added from the fuel addition valve 6 reaches the oxidation catalyst 4, the temperature of the oxidation catalyst 4 rises, and when the fuel does not reach the oxidation catalyst 4, the temperature of the oxidation catalyst 4 is Descend. Therefore, in S104, the ECU 10 stores the history of the temperature difference ΔTgc while intermittent fuel addition by the fuel addition valve 6 is being executed.

Next, the ECU 10 proceeds to S105, and calculates an oxidized fuel amount Qfo, which is the amount of fuel oxidized in the oxidation catalyst 4, based on the stored history of the temperature difference ΔTgc. here,
It can be determined that the greater the temperature difference ΔTgc, the greater the amount of oxidized fuel Qfo.

  Next, the ECU 10 proceeds to S106, and calculates the fuel amount Qfn that reaches the NOx catalyst 5 by subtracting the oxidized fuel amount Qfo from the reference fuel addition amount Qfbase.

  Next, the ECU 10 proceeds to S107, and determines whether or not the reached fuel amount Qfn calculated in S105 is smaller than the target supply amount Qfnt. If an affirmative determination is made in S107, the ECU 10 proceeds to S108, and if a negative determination is made, the ECU 10 proceeds to S109.

  In S108, the ECU 10 increases and corrects the fuel addition amount Qfi from the fuel addition valve 6 so that the reached fuel amount Qfn becomes the target supply amount Qfnt. Thereafter, the ECU 10 once terminates execution of this routine.

  On the other hand, in S109, the ECU 10 determines whether or not the reached fuel amount Qfn calculated in S105 is larger than the target supply amount Qfnt. If an affirmative determination is made in S109, the ECU 10 proceeds to S110. On the other hand, if a negative determination is made in S109, the ECU 10 once ends the execution of this routine. In this case, the fuel addition amount Qfi from the fuel addition valve 6 is maintained at the reference fuel addition amount Qfbase.

  In S110, the ECU 10 corrects the fuel addition amount Qfi from the fuel addition valve 6 so as to decrease so that the reached fuel amount Qfn becomes the target supply amount Qfnt. Thereafter, the ECU 10 once terminates execution of this routine.

  According to the routine described above, the fuel amount Qfn that is actually supplied to the NOx catalyst 5 is calculated by performing fuel addition from the fuel addition valve 6. Then, the fuel addition amount Qfi from the fuel addition valve 6 is controlled so that the reached fuel amount Qfn becomes the target supply amount Qfnt.

  Therefore, when the NOx reduction control is executed, the amount of fuel actually supplied to the NOx catalyst 5 (reached fuel amount Qfn) can be controlled to the target supply amount Qfnt with higher accuracy. As a result, the NOx stored in the NOx catalyst 5 can be reduced as much as possible, and the amount of fuel added from the fuel addition valve 6 when the NOx reduction control is executed can be suppressed.

  In the above routine, the reached fuel amount Qfn is controlled to the target supply amount Qfnt by controlling the fuel addition amount Qfi from the fuel addition valve 6. In this embodiment, instead of this, the reached fuel amount Qfn may be controlled to the target supply amount Qfnt by controlling the fuel addition method by the fuel addition valve 6.

  For example, the reached fuel amount Qfn can be increased by lengthening the fuel addition interval when fuel is intermittently added from the fuel addition valve 6, and the reached fuel amount Qfn can be increased by shortening the fuel addition interval. Can be reduced. Further, the amount of fuel reached Qfn can be increased by increasing the amount of fuel added per fuel addition at the time of intermittently adding fuel from the fuel addition valve 6, and the amount per fuel addition can be increased. By reducing the fuel addition amount, the reached fuel amount Qfn can be reduced.

  In addition, in the NOx reduction control according to the present embodiment, instead of fuel addition by the fuel addition valve 6, fuel is supplied into the exhaust gas by executing sub fuel injection in the internal combustion engine 1 during the exhaust stroke, and the fuel May be supplied to the NOx catalyst 5.

  In the present embodiment, the case where the present invention is applied at the time of executing the NOx reduction control has been described as an example. However, the present invention is performed at the time of performing the so-called SOx poisoning recovery control that reduces the SOx stored in the NOx catalyst 5. May be applied. In this case, when the SOx poisoning recovery control is executed, the amount of fuel actually supplied to the NOx catalyst 5 can be controlled to a more suitable amount.

  Further, when a particulate filter carrying a NOx catalyst is provided in place of the NOx catalyst 5, the present invention can be applied to filter regeneration control for removing particulate matter collected on the particulate filter. Good. In this case, when the filter regeneration control is executed, the amount of fuel actually supplied to the particulate filter can be controlled to a more suitable amount.

The figure which shows schematic structure of the intake / exhaust system of the internal combustion engine which concerns on an Example. The figure which shows the relationship between the supply amount of the fuel actually supplied to a NOx catalyst, and a NOx reduction rate. The flowchart which shows the routine of NOx reduction control which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Intake passage 4 ... Oxidation catalyst 5 ... NOx storage reduction catalyst 6 ... Fuel addition valve 8 ... First temperature sensor 9・ ・ Second temperature sensor 10 ・ ・ ECU

Claims (2)

An exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst;
A pre-stage catalyst provided in the exhaust passage upstream of the exhaust purification device and having an oxidation function;
Inflow exhaust gas temperature detection means for detecting an inflow exhaust gas temperature that is the temperature of the exhaust gas flowing into the front catalyst,
A pre-catalyst temperature detecting means for detecting the temperature of the pre-catalyst;
Reducing agent supply means for supplying the reducing agent to the exhaust purification device by supplying the reducing agent into the exhaust upstream of the upstream catalyst when recovering the performance of the exhaust purification device;
When the reducing agent is supplied by the reducing agent supply means, the reducing agent oxidation amount, which is the amount of reducing agent oxidized by the preceding catalyst, based on the difference between the inflow exhaust gas temperature and the temperature of the preceding catalyst. A reducing agent oxidation amount calculating means for calculating;
Based on the difference between the supply amount of the reducing agent supplied into the exhaust gas by the reducing agent supply means and the reducing agent oxidation amount calculated by the reducing agent oxidation amount calculation means, the amount of the reducing agent that has reached the exhaust purification device A reducing agent reaching amount calculating means for calculating a reducing agent reaching amount that is an amount,
An internal combustion engine characterized by controlling the reducing agent supply means so that the reducing agent arrival amount calculated by the reduction arrival amount calculating means becomes a target supply amount when the reducing agent supply means executes the reducing agent supply. Engine exhaust purification system.   2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the target supply amount is a value in the vicinity of a lower limit value of a reducing agent amount at which a performance recovery rate of the exhaust gas purification apparatus is in the vicinity of an upper limit value.

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