JP2008088926A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine with a NOx catalyst and a filter in an exhaust passage, for minimizing the worsening of fuel economy with the execution of filter regeneration control and NOx reduction control. <P>SOLUTION: The exhaust emission control system calculates a degree of suppressing the worsening of fuel economy with the execution of filter regeneration control due to a reduction of an EGR gas amount introduced into an intake system for the internal combustion engine and a degree of accelerating the worsening of fuel economy with the execution of NOx reduction control. It executes a reduction of the EGR gas amount when the degree of suppressing the worsening of fuel economy with the execution of the filter regeneration control is higher than the degree of accelerating the worsening of fuel economy with the execution of NOx reduction control. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine including an NOx storage reduction catalyst and a particulate filter provided in an exhaust passage.

In an exhaust gas purification system for an internal combustion engine provided with an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) provided in an exhaust passage, NOx reduction control is performed to reduce NOx stored in the NOx catalyst. . In NOx reduction control, by supplying fuel into the exhaust, the air-fuel ratio of the exhaust flowing into the NOx catalyst is lowered to an air-fuel ratio at which NOx can be reduced.

  Also, an exhaust gas purification system for an internal combustion engine provided with a particulate filter (hereinafter simply referred to as a filter) provided in an exhaust passage for collecting particulate matter (hereinafter referred to as PM) in the exhaust gas. In this case, filter regeneration control is performed to remove PM collected by the filter. In the filter regeneration control, fuel is supplied to exhaust gas, so that the fuel is supplied to a catalyst having an oxidation function provided on the upstream side of the filter or carried by the filter to oxidize the fuel. Then, the temperature of the filter is raised to a temperature at which PM can be oxidized by the oxidation heat generated by oxidizing the fuel.

Moreover, PM trapped by the filter, even if the filter regeneration control as described above is not performed in some cases be oxidized by NO ₂ in the exhaust. In Patent Document 1, when the exhaust gas purification system includes an EGR device, the amount of EGR gas introduced into the intake system of the internal combustion engine is reduced when the amount of collected PM in the filter exceeds a predetermined amount. The technology to be described is described. When the EGR gas is decreased, NOx in the exhaust gas increases. This is the NOx includes a NO _2, when the NO ₂ is increased oxidation of the PM by the NO ₂ is promoted.
JP 2002-70535 A JP 2003-120392 A JP 2005-90319 A JP 2002-97930 A Japan Society of Invention and Innovation Public Technique No. 2002-2190

In an exhaust gas purification system for an internal combustion engine provided with an NOx catalyst and a filter provided in an exhaust passage, the amount of NOx discharged from the internal combustion engine is increased by increasing the EGR gas amount when filter regeneration control is not being executed. Thus, when the oxidation of PM by NO ₂ is promoted, the amount of PM trapped in the filter is difficult to increase. That is, the period during which the collected amount of PM in the filter reaches the threshold value for starting execution of filter regeneration control becomes longer. Thereby, it is possible to lengthen the regeneration stop period, which is a period from when the execution of the filter regeneration control is stopped until the next execution of the filter regeneration control is started. For this reason, it is possible to suppress the deterioration of fuel consumption associated with the execution of the filter regeneration control.

However, when NOx discharged from the internal combustion engine is increased, the amount of NOx stored in the NOx catalyst is likely to increase. In this case, in order to suppress the amount of NOx that flows out without being stored in the NOx catalyst, a reduction stop period that is a period from when the execution of the NOx reduction control is stopped until the next execution of the NOx reduction control is started. Need to be shortened or the execution period of the NOx reduction control must be extended. For this reason, there is a concern that the deterioration of fuel consumption accompanying the execution of the NOx reduction control may be promoted.

  The present invention has been made in view of the above problems, and in an exhaust gas purification system for an internal combustion engine provided with a NOx catalyst and a filter provided in an exhaust passage, the fuel consumption associated with execution of filter regeneration control and NOx reduction control is improved. It aims at providing the technique which can suppress deterioration as much as possible.

  The present invention calculates the degree of suppression of fuel deterioration associated with the execution of filter regeneration control by reducing the amount of EGR gas introduced into the intake system of the internal combustion engine and the degree of promotion of fuel consumption deterioration associated with the execution of NOx reduction control. To do. Then, the EGR gas amount is reduced when the suppression degree of the deterioration of the fuel consumption accompanying the execution of the filter regeneration control is larger than the promotion degree of the deterioration of the fuel consumption accompanying the execution of the NOx reduction control.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
Fuel supply means for supplying fuel into the exhaust gas upstream of the NOx storage reduction catalyst and the particulate filter;
NOx reduction control for reducing the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst by supplying fuel into the exhaust gas by the fuel supply means, thereby reducing NOx stored in the NOx storage reduction catalyst NOx reduction means for performing
A filter that performs filter regeneration control that raises the temperature of the particulate filter by supplying fuel into the exhaust gas by the fuel supply means, and thereby oxidizes and removes the particulate matter collected by the particulate filter. Reproduction means;
An EGR device that introduces at least part of the exhaust gas flowing through the exhaust passage into the intake system of the internal combustion engine as EGR gas;
When filter regeneration control is not being executed by the filter regeneration means, the amount of EGR gas introduced into the intake system of the internal combustion engine by the EGR device is decreased to increase NOx in the exhaust, thereby EGR gas reducing means for promoting oxidation of particulate matter collected by the particulate filter with NO ₂ ;
A suppression degree calculation means for calculating a suppression degree of deterioration of fuel consumption due to execution of filter regeneration control by reducing the amount of EGR gas by the EGR gas reduction means;
An enhancement degree calculation means for calculating an enhancement degree of fuel consumption deterioration associated with execution of NOx reduction control by reducing the amount of EGR gas by the EGR gas reduction means;
When the suppression degree of the deterioration of the fuel consumption accompanying the execution of the filter regeneration control calculated by the suppression degree calculation means is larger than the promotion degree of the deterioration of the fuel consumption accompanying the execution of the NOx reduction control calculated by the promotion degree calculation means. The amount of EGR gas is reduced by the EGR gas reducing means.

  According to the present invention, when the degree of suppression of deterioration of fuel consumption due to execution of filter regeneration control is greater than the degree of promotion of reduction in fuel consumption, that is, when the amount of EGR gas is decreased, the amount of EGR gas is not decreased. When the overall fuel efficiency is improved as compared with the case, the EGR gas is reduced. Thereby, the deterioration of the fuel consumption accompanying execution of filter regeneration control and NOx reduction control can be suppressed as much as possible.

In the present invention, the filter regeneration means may execute filter regeneration control when the amount of PM collected in the filter reaches a predetermined amount. In this case, the PM emission amount calculating means for calculating a PM emission amount is the amount of PM emitted per unit time from the internal combustion engine, the NO ₂ inflow is the amount of NO ₂ which flows per unit filter time and nO ₂ inflow amount calculating means for output, is calculated on the basis of continuous PM oxidation amount is the amount of PM filter regeneration control is oxidized per unit time in the filter in a state of not being executed removed nO ₂ inflow A continuous PM oxidation amount calculating means, and a regeneration stop period that is a period from when the execution of the filter regeneration control is stopped until the next execution of the filter regeneration control is started. A regeneration stop period calculating means for calculating based on the oxidation amount.

Based on the amount of EGR gas, the amount of NOx discharged from the internal combustion engine per unit time can be calculated. Then, the NO ₂ inflow amount can be calculated based on the amount of NOx discharged per unit time. Further, the larger the NO ₂ inflow amount, the more the oxidation of PM by NO ₂ in the filter is promoted. Therefore, the continuous PM oxidation amount can be calculated based on the NO ₂ inflow amount.

  Moreover, the increase amount per unit time of the PM collection amount in the filter can be calculated based on the PM discharge amount and the continuous PM oxidation amount. Therefore, based on the predetermined collection amount, the PM discharge amount, and the continuous PM oxidation amount, the regeneration stop period that is the time until the PM collection amount in the filter reaches the predetermined collection amount can be calculated.

  Further, when the filter regeneration control is executed, the fuel consumption increases as compared with the case where the filter regeneration control is not executed. Therefore, in the above case, there is further provided an increase rate calculating means for calculating an increase rate during regeneration, which is a ratio of the fuel consumption when the filter regeneration control is executed by the filter regeneration means to the fuel consumption when the filter regeneration control is not executed. You may prepare. The increase rate calculating means includes a filter regeneration control execution period (hereinafter referred to as a regeneration execution period), fuel consumption per unit time during the regeneration execution period, a regeneration stop period calculated by the regeneration stop period calculating means, a regeneration The regeneration increase rate can be calculated based on the fuel consumption per unit time during the stop period.

As described above, when the amount of EGR gas is reduced by the EGR gas reduction means, the oxidation stop period is prolonged because the oxidation of PM by NO ₂ is promoted. In this case, the regeneration increase rate is reduced as compared with the case where the amount of EGR gas is not reduced. Therefore, the suppression degree calculation means decreases the degree of suppression of the deterioration of fuel consumption accompanying the execution of the filter regeneration control by reducing the amount of EGR gas by the EGR gas reduction means, and reduces the amount of EGR gas by the EGR gas reduction means. The increase rate during regeneration in the case may be calculated as a decrease rate relative to the increase rate during regeneration when the amount of EGR gas is not decreased.

  In the present invention, when the NOx reduction means uses the NOx reduction control execution period (hereinafter referred to as the reduction execution period) as the predetermined reduction execution period and the EGR gas reduction means does not reduce the amount of EGR gas, NOx A reduction stop period that is a period from when the execution of the reduction control is stopped until the next execution of the NOx reduction control is started may be set as a reference reduction stop period.

When the amount of EGR gas is reduced by the EGR gas reducing means, the NOx occlusion amount in the NOx catalyst is likely to increase. Therefore, when the amount of EGR gas is reduced by the EGR gas reducing means, the amount of NOx that flows out without being stored in the NOx catalyst (that is, NOx that flows out without being reduced) (hereinafter referred to as NOx outflow amount). In order to make the reduction execution period equal to the case where the amount of EGR gas is not reduced while keeping the reduction execution period as the predetermined reduction execution period, it is necessary to shorten the reduction stop period. Therefore, in the above case, when the amount of EGR gas is reduced by the EGR gas reduction means, the NOx increase reduction stop period, which is a reduction stop period in which the NOx outflow amount is equivalent to the case where the amount of EGR gas is not reduced. NOx increase reduction stop period calculation means for calculating the reduction stop period change when the EGR gas amount is reduced by the EGR gas reduction means to change the reduction stop period from the reference reduction stop period to the NOx increase reduction stop period And a means.

  Further, when the NOx reduction control is executed, the fuel consumption increases as compared with the case where the NOx reduction control is not executed. Therefore, in the above case, the ratio of the difference between the fuel consumption amount when the NOx reduction control is executed by the NOx reduction means and the fuel consumption amount when the NOx reduction control is not executed to the fuel consumption amount when the NOx reduction control is not executed. An increase ratio calculation means for calculating an increase ratio at the time of reduction may be further provided. The increase ratio calculation means includes the total amount of fuel supplied by the fuel supply means during the predetermined reduction execution period, the fuel consumption at the internal combustion engine during the predetermined reduction execution period, and the fuel consumption at the internal combustion engine during the reduction stop period. Based on the amount, an increase ratio at the time of reduction can be calculated.

  In the above, when the amount of EGR gas is reduced by the EGR gas reduction means, the reduction stop period is shortened so that the amount of NOx flowing out without being stored in the NOx catalyst is equivalent to the case where the amount of EGR gas is not reduced. Is done. In this case, the reduction increase rate ratio is increased as compared with the case where the amount of EGR gas is not decreased. Therefore, the degree-of-assistance calculation means reduces the degree of enhancement of fuel consumption accompanying the execution of NOx reduction control by reducing the amount of EGR gas by the EGR gas reduction means, and reduces the amount of EGR gas by the EGR gas reduction means. It may be calculated as a difference between the reduction increase ratio in the case and the reduction increase ratio in the case where the amount of EGR gas is not decreased.

  In the present invention, the NOx reduction means sets the reduction stop period as the predetermined reduction stop period, and sets the reduction execution period when the EGR gas reduction means does not decrease the amount of EGR gas as the reference reduction execution period. Also good.

  In order to make the NOx outflow amount equal to the case where the amount of EGR gas is not decreased while the reduction stop period is set to the predetermined reduction stop period when the amount of EGR gas is reduced by the EGR gas reduction means, the reduction is executed. It is necessary to extend the period. Therefore, in the above case, when the amount of EGR gas is reduced by the EGR gas reduction means, the NOx increase reduction execution period is a reduction execution period in which the NOx outflow amount is equivalent to the case where the amount of EGR gas is not reduced. NOx increase reduction execution period calculation means for calculating the reduction execution period change when the amount of EGR gas is reduced by the EGR gas reduction means and the reduction execution period is changed from the reference reduction execution period to the NOx increase reduction execution period And a means.

  In the above case, based on the total amount of fuel supplied by the fuel supply means during the reduction execution period, the fuel consumption in the internal combustion engine during the reduction execution period, and the fuel consumption in the internal combustion engine during the predetermined reduction stop period Further, an increase ratio calculating means for calculating the increase ratio at the time of reduction may be further provided.

  In the above, when the amount of EGR gas is reduced by the EGR gas reduction means, the reduction execution period is extended so that the amount of outflow NOx is equal to the case where the amount of EGR gas is not reduced. In this case, as in the case where the reduction stop period described above is shortened, the reduction increase rate ratio is increased as compared with the case where the amount of EGR gas is not reduced. Therefore, also in this case, the degree-of-assistance calculation means determines the degree of promotion of deterioration in fuel consumption accompanying the execution of NOx reduction control by reducing the amount of EGR gas by the EGR gas reduction means, and the amount of EGR gas by the EGR gas reduction means. It may be calculated as a difference between the reduction increase ratio when the amount is reduced and the reduction increase ratio when the amount of EGR gas is not reduced.

  According to the present invention, it is possible to suppress as much as possible the deterioration of fuel consumption associated with the execution of filter regeneration control and NOx reduction 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 intake / exhaust system thereof>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 for directly injecting fuel into the cylinder 2.

  An intake manifold 5 and an exhaust manifold 7 are connected to the internal combustion engine 1. One end of an intake passage 4 is connected to the intake manifold 5. One end of an exhaust passage 6 is connected to the exhaust manifold 7. The exhaust manifold 7 is provided with a fuel addition valve 14 for adding fuel to the exhaust. In this embodiment, the fuel addition valve 14 corresponds to the fuel addition means according to the present invention.

  A compressor 8 a of a turbocharger (supercharger) 8 is installed in the intake passage 4. A turbine 8 b of a turbocharger 8 is installed in the exhaust passage 6.

  An air flow meter 18 is provided upstream of the compressor 8 a in the intake passage 4. A NOx catalyst 9 is provided downstream of the turbine 8b in the exhaust passage 6. Further, a filter 10 that collects PM in the exhaust gas is provided downstream of the NOx catalyst 9 in the exhaust passage 6. An air-fuel ratio sensor 15 that detects the air-fuel ratio of the exhaust is provided upstream of the NOx catalyst 9 in the exhaust passage 6. An upstream temperature sensor 16 and a downstream temperature sensor 17 for detecting the temperature of the exhaust gas are provided downstream of the NOx catalyst 9 and upstream of the filter 10 and downstream of the filter 10 in the exhaust passage 6. .

  The internal combustion engine 1 according to this embodiment includes an EGR device 11 that introduces at least a part of exhaust gas into the intake system as EGR gas. The EGR device 11 includes an EGR passage 12 having one end connected to the exhaust manifold 7 and the other end connected to the intake manifold 5. EGR gas is introduced from the exhaust manifold 7 into the intake manifold 5 through the EGR passage 12. The EGR passage 12 is provided with an EGR valve 13 that controls the amount of EGR gas introduced into the intake manifold 5.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 20. An air flow meter 18, an air-fuel ratio sensor 15, an upstream temperature sensor 16, and a downstream temperature sensor 17 are electrically connected to the ECU 20. These output signals are input to the ECU 20. The ECU 20 estimates the temperature of the NOx catalyst 9 based on the detected value of the upstream temperature sensor 16 and estimates the temperature of the filter 10 based on the detected value of the downstream temperature sensor 17.

  In addition, the fuel injection valve 3, the fuel addition valve 14, and the EGR valve 13 are electrically connected to the ECU 20. These are controlled by the ECU 20.

<NOx reduction control and filter regeneration control>
In this embodiment, NOx reduction control is performed to reduce NOx stored in the NOx catalyst 9. In the NOx reduction control, NO is added by adding fuel into the exhaust from the fuel addition valve 14.
The air-fuel ratio of the exhaust gas flowing into the x catalyst 9 is lowered and controlled to the target air-fuel ratio. Here, the target air-fuel ratio is a value equal to or less than a threshold value at which NOx stored in the NOx catalyst 9 can be reduced. The target air-fuel ratio is determined in advance by experiments or the like.

  In the present embodiment, when NOx reduction control is executed, a reduction execution period that is an execution period of the NOx reduction control is set as a predetermined reduction execution period Δtca. In addition, during the predetermined reduction execution period Δtca, fuel addition by the fuel addition valve 14 is executed a plurality of times with the fuel addition amount per time being the unit addition amount Qaddu. The number of fuel additions during the predetermined reduction execution period Δtca is defined as the predetermined addition number na.

  Further, in this embodiment, filter regeneration control is performed to remove PM collected by the filter 10. In the filter regeneration control, fuel is added to the exhaust gas from the fuel addition valve 14 to supply the fuel to the NOx catalyst 9 for oxidation. Thereby, the temperature of the filter 10 is raised by raising the temperature of the exhaust gas and controlled to the target temperature. Here, the target temperature is a value equal to or higher than a threshold value at which PM collected by the filter 10 can be oxidized and removed. The target temperature is determined in advance by experiments or the like.

  The filter regeneration control is executed when the amount of collected PM in the filter 10 reaches a predetermined amount of collection Fpmx.

  As described above, in the NOx reduction control and the filter regeneration control, the fuel addition to the exhaust gas by the fuel addition valve 14 is performed. Therefore, when these controls are executed, the fuel consumption increases compared to when these controls are not executed. That is, there is a possibility that the execution of these controls is accompanied by deterioration of fuel consumption.

<EGR gas amount control>
In the present embodiment, EGR gas is introduced into the intake manifold 5 by the EGR device 11 for the purpose of reducing NOx in the exhaust gas. The amount of EGR gas introduced into the intake manifold 5 is normally controlled based on the operating state of the internal combustion engine 1. The amount of EGR gas set based on the operating state of the internal combustion engine 1 is referred to as a reference EGR gas amount Qgbase.

However, the NOx in the exhaust gas includes a NO _2, when the temperature of the exhaust gas flowing into the filter 10 is high is PM is oxidized by even the NO ₂ in a state in which filter regeneration control is not being executed the filter 10 Removed from.

Therefore, to reduce the amount of the EGR gas when the filter regeneration control is not being performed, increasing the NOx discharged from the internal combustion engine 1, there are cases where the oxidation of PM by NO ₂ is promoted. In this case, the amount of collected PM in the filter 10 is difficult to increase. That is, the period until the amount of collected PM in the filter 10 reaches the predetermined amount of collection Fpmx becomes longer. Therefore, the regeneration stop period that is a period from when the execution of the filter regeneration control is stopped to when the next execution of the filter regeneration control is started becomes longer. As a result, it is possible to suppress the deterioration of fuel consumption associated with the execution of the filter regeneration control.

  However, if the amount of NOx discharged from the internal combustion engine 1 is increased by decreasing the amount of EGR gas, the amount of NOx stored in the NOx catalyst 9 is likely to increase. In this case, in order to make the NOx outflow amount, which is the amount of NOx flowing out without being stored in the NOx catalyst, equal to the case where the amount of EGR gas is not reduced, the next NOx after the execution of the NOx reduction control is stopped. It is necessary to shorten the reduction stop period, which is a period until execution of the reduction control is started. If the reduction stop period is shortened, deterioration of fuel consumption accompanying NOx reduction control is promoted.

  Therefore, in this embodiment, when the amount of EGR gas is reduced below the reference EGR gas amount Qgbase, the degree of suppression of deterioration in fuel consumption associated with execution of filter regeneration control is reduced by the deterioration in fuel consumption associated with execution of NOx reduction control. Only when the degree of promotion is greater, the EGR gas is reduced.

  Hereinafter, a method of calculating the degree of suppression of deterioration of fuel consumption accompanying execution of filter regeneration control and the degree of promotion of deterioration of fuel consumption accompanying execution of NOx reduction control when the amount of EGR gas is reduced will be described.

  First, the calculation method of the suppression degree of the deterioration of the fuel consumption accompanying execution of filter regeneration control is demonstrated based on the flowchart shown in FIG. This flow is stored in advance in the ECU 20 and is executed by the ECU 20.

  As described above, when the filter regeneration control is executed, the fuel consumption increases compared to when the filter regeneration control is not executed. Here, the ratio of the fuel consumption when the filter regeneration control is executed to the fuel consumption when the filter regeneration control is not executed is defined as an increase rate during regeneration.

  When the deterioration of the fuel consumption accompanying the execution of the filter regeneration control is suppressed by reducing the amount of EGR gas from the reference EGR gas amount Qgbase, the increase rate during regeneration is decreased. Therefore, in this embodiment, the degree of suppression of deterioration in fuel consumption due to the execution of filter regeneration control is determined based on the amount of EGR gas at the regeneration increase rate when the amount of EGR gas is reduced below the reference EGR gas amount Qgbase. This is calculated as a decrease rate with respect to the regeneration increase rate when the EGR gas amount is Qgbase (hereinafter referred to as regeneration increase rate decrease rate).

  In this flow, in S101, the ECU 20 calculates a PM emission amount Qpme, which is the amount of PM discharged from the internal combustion engine 1 per unit time based on the operating state of the internal combustion engine 1. The relationship between the operating state of the internal combustion engine 1 and the PM emission amount Qpme is obtained through experiments or the like and stored in the ECU 20 in advance.

  Next, the ECU 20 determines in step S102 the amount of NOx discharged from the internal combustion engine 1 per unit time at the current time, that is, when the amount of EGR gas is the reference EGR gas amount Qgbase (hereinafter simply referred to as NOx emission amount). A reference NOx emission amount Qnoxbase is calculated. The relationship between the amount of EGR gas and the NOx emission amount is obtained through experiments or the like and stored in advance in the ECU 20.

In the present embodiment, a portion of the NO contained in the NOx discharged from the internal combustion engine 1 is converted to NO ₂ in the NOx catalyst 9. Therefore, in S103, the ECU 10 calculates the conversion rate Rc from NO to NO ₂ based on the temperature of the NOx catalyst 9. The relationship between the conversion rate Rc and the temperature of the NOx catalyst 9 is obtained through experiments or the like and is stored in the ECU 20 in advance.

Next, in S104, the ECU 20 presents the amount of NO ₂ flowing into the filter 10 per unit time at the present time based on the reference NOx emission amount Qnoxbase, the ratio of NO and NO ₂ in NOx, and the conversion rate Rc. A reference NO ₂ inflow amount Qno ₂ base (hereinafter simply referred to as NO ₂ inflow amount) is calculated. Note that the ratios of NO and NO _{2 in} NOx are obtained through experiments and the like and stored in the ECU 20 in advance.

Here, the amount of PM oxidized and removed per unit time by NO ₂ when the filter regeneration control is not executed is defined as the continuous PM oxidation amount. In step S105, the ECU 20 calculates a reference continuous PM oxidation amount Qpmobase, which is the current continuous PM oxidation amount, based on the reference NO ₂ inflow amount Qno ₂ base and the temperature of the filter 10. The relationship between the continuous PM oxidation amount, the NO ₂ inflow amount, and the temperature of the filter 10 is obtained by experiments or the like and stored in the ECU 20 in advance.

  Next, in S106, the ECU 20 calculates an increase amount of NOx emission amount (hereinafter simply referred to as NOx increase amount) ΔQnox when the amount of EGR gas is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga. .

Next, in S107, the ECU ₂₀ determines the NO ₂ inflow amount when the NOx emission amount increases by the NOx increase amount ΔQnox based on the NOx increase amount ΔQnox, the ratio of NO and NO ₂ in NOx, and the conversion rate Rc. ΔQno ₂ (hereinafter simply referred to as “NO ₂ increase amount”) is calculated.

Then, ECU 20, at S108, NO ₂ inflow is NO ₂ increase the continuous PM oxidation increment ΔQpmo is an increase amount of the continuous PM oxidation amount in the case of increased NO ₂ increase DerutaQno ₂ minutes DerutaQno ₂ and the filter 10 Based on the temperature of

Next, in S109, the ECU 20 calculates a reference regeneration stop period Δtf_s0, which is a regeneration stop period at the present time, based on the following equation (1).
Δtf_s0 = Fpmx / (Qpme−Qpmobase) (1)
(Fpmx: predetermined collection amount)
In the above formula (1), Qpme−Qpmobase is an increase amount per unit time of the amount of PM collected in the filter 10 at the current time. Therefore, the reference reproduction stop period Δtf_s0 can be calculated by the above equation (1).

Next, in S110, the ECU 20 sets the NOx increase regeneration stop period Δtf_s1, which is a regeneration stop period when the EGR gas amount is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga, based on the following equation (2). calculate.
Δtf_s1 = Fpmx / (Qpme−Qpmobase−ΔQpmo) (2)
In the above formula (2), Qpme-Qpmobase-ΔQpmo is an increase amount per unit time of the amount of PM collected in the filter 10 when the EGR gas amount is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga. Therefore, the NOx increase regeneration stop period Δtf_s1 can be calculated by the above equation (2). The NOx increase regeneration stop period Δtf_s1 calculated in this way is longer than the reference regeneration stop period Δtf_s0.

  Next, in S111, the ECU 20 calculates a fuel consumption amount Qff per unit time during execution of the filter regeneration control. This fuel consumption amount Qff includes the fuel injection amount from the fuel injection valve 3 and the fuel addition amount from the fuel addition valve 14. The fuel addition amount from the fuel addition valve 14 is set based on the difference between the current temperature of the filter 10 and the target temperature and the intake air amount of the internal combustion engine 1.

  Next, in S112, the ECU 20 calculates a regeneration execution period Δtf that is an execution period of the filter regeneration control control. This regeneration execution period Δtf is a period during which PM collected by the filter 10 can be sufficiently oxidized and removed, and is calculated based on the operating state of the internal combustion engine 1 and the intake air amount.

As described above, in this embodiment, the filter regeneration control is executed when the amount of PM collected in the filter 10 reaches the predetermined amount of collection Fpmx. Therefore, regardless of the amount of EGR gas when the filter regeneration control is not executed, the fuel consumption amount Qff and the regeneration execution period Δtf are constant values.

  Next, in S113, the ECU 20 determines the fuel consumption amount Qfbase per unit time when the fuel addition by the fuel addition valve 14 is not performed (that is, when neither the filter regeneration control nor the NOx reduction control is executed). Calculation is based on the operating state of the engine 1.

Next, in S114, the ECU 20 calculates the regeneration increase rate Ki0 based on the following equation (3).
Ki0 = (Qff × Δtf + Qfbase × Δtf_s0) / ((Δtf + Δtf_s0) × Qfbase) (3)
In the above equation (3), Qff × Δtf is the total fuel consumption during the execution period of the filter regeneration control. Qfbase × Δtf_s0 is the total fuel consumption during the regeneration stop period. (Δtf + Δtf_s0) × Qfbase is the total fuel during the regeneration execution period and the regeneration stop period when it is assumed that the filter regeneration control is not performed even during the regeneration execution period (that is, the fuel addition by the fuel addition valve 14 is not performed). It is consumption. Therefore, the reproduction increase rate Ki0 can be calculated by the above equation (3).

Next, in S115, the ECU 20 calculates a regeneration increase rate Ki1 when the amount of EGR gas is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga based on the following equation (4).
Ki1 = (Qff × Δtf + Qfbase × Δtf_s1) / ((Δtf + Δtf_s1) × Qfbase) (4)
The above equation (4) is obtained by replacing Δtf_s0 in the above equation (3) with Δtf_s1. Therefore, the reproduction increase rate Ki1 can be calculated by the above equation (4). Ki1 is a smaller value than Ki0.

Next, in S116, the ECU 20 calculates the regeneration increase rate decrease rate RKi (unit:%) based on the following equation (5).
RKi = 100 × (Ki0 / Ki1-1) (5)

  Next, a method for calculating the degree of promotion of deterioration in fuel consumption accompanying the execution of NOx reduction control will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 20 and is executed by the ECU 20.

  As described above, when the NOx reduction control is executed, the fuel consumption increases as compared with the case where the NOx reduction control is not executed. Here, the difference between the fuel consumption amount when the NOx reduction control is executed and the fuel consumption amount when the NOx reduction control is not executed is referred to as an increase amount during reduction. Then, the ratio of the increase amount during reduction to the fuel consumption amount when the NOx reduction control is not executed is defined as the increase ratio during reduction.

  When the deterioration of fuel consumption accompanying the execution of the NOx reduction control is promoted by reducing the amount of EGR gas from the reference EGR gas amount Qgbase, the reduction increase rate ratio increases. Therefore, in this embodiment, the degree of promotion of deterioration in fuel consumption due to the execution of NOx reduction control is calculated by reducing the ratio of increase during reduction and the amount of EGR gas when the amount of EGR gas is reduced below the reference EGR gas amount Qgbase. It is calculated as a difference from the reduction rate increase rate ratio (hereinafter referred to as a reduction rate increase rate increase amount) when the reference EGR gas amount is Qgbase.

In this flow, the ECU 20 determines in step S201 the reference NOx emission amount Qnox that is the NOx emission amount at the present time, that is, when the amount of EGR gas is the reference EGR gas amount Qgbase.
Calculate base.

  Here, a period from when the execution of the NOx reduction control is stopped until the next execution of the NOx reduction control is referred to as a reduction stop period. Further, the ratio of the amount of NOx occluded in the NOx catalyst 9 during the reduction stop period (that is, the amount of NOx reduced during execution of the NOx reduction control) to the NOx emission amount is the NOx occlusion rate (= NOx occlusion amount / NOx). Emission amount).

  In S202, the ECU 20 calculates a reference NOx storage rate Rcebase, which is a NOx storage rate when the reduction stop period is set to the reference reduction stop period Δtc_s0, based on the reference NOx emission amount Qnoxbase. Here, the reference reduction stop period Δtc_s0 is a reduction stop period that is determined so that the NOx outflow amount falls within the allowable range when the EGR gas amount is controlled to the reference EGR gas amount Qgbase. The reference reduction stop period Δtc_s0 may be a predetermined constant value or may be set based on the operating state of the internal combustion engine 1.

  Next, in S203, the ECU 20 calculates a NOx increase amount ΔQnox when the EGR gas amount is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga.

Next, in S204, even when the EGR gas amount is decreased from the reference EGR gas amount Qgbase by the predetermined decrease amount ΔQga, the ECU 20 sets the NOx outflow amount to the same amount as when the EGR gas amount is the reference EGR gas amount Qgbase. The required NOx occlusion rate Rcedem, which is the NOx occlusion rate required to do this, is calculated based on the following equation (6).
Rcedem = 1− (Qnoxbase × (1−Rcebase)) / (Qnoxbase + ΔQnox) (6)
In the above equation (6), Qnoxbase × (1-Rcebase) is the NOx occlusion amount per unit time when the NOx emission amount is the reference NOx emission amount Qnoxbase, and Qnoxbase + ΔQnox is the EGR gas amount and the reference EGR gas amount Qgbase. Is the NOx emission amount when it is reduced by the predetermined reduction amount ΔQga. Therefore, the required NOx occlusion rate Rcedem can be calculated by the above equation (6).

Next, in S205, the ECU 20 calculates a NOx occlusion rate increase rate Rup, which is a ratio of the required NOx occlusion rate Rcedem to the reference NOx occlusion rate Rcebase, based on the following equation (7).
Rup = Rcedem / Rcebase (7)

  In this embodiment, the NOx occlusion rate can be increased by shortening the reduction stop period. Therefore, in this embodiment, when the amount of EGR gas is reduced, the NOx occlusion rate is increased to the required NOx occlusion rate Rcedem by shortening the reduction stop period from the reference reduction stop period Δtc_s0.

  Therefore, in S206, the ECU 20 calculates a correction coefficient α for correcting the reduction stop period based on the NOx occlusion rate increase rate Rup. The correction coefficient α is a correction coefficient for shortening the reference reduction stop period Δtc_s0 to the NOx increase reduction stop period Δtc_s1. Here, the NOx increase reduction stop period Δtc_s1 is a reduction stop that makes it possible to set the NOx storage rate to the required NOx storage rate Rcedem when the EGR gas amount is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga. It is a period. The relationship between the correction coefficient α and the NOx occlusion rate increase rate Rup is obtained through experiments and stored in the ECU 20 in advance.

Next, in S207, the ECU 20 calculates the NOx increase reduction stop period Δtc_s1 based on the following equation (8).
Δtc_s1 = Δtc_s0 × α (8)

  In the present embodiment, when the reduction of the EGR gas amount is executed, the ECU 20 changes the reduction stop period from the reference reduction stop period Δtc_s0 to the NOx increase reduction stop period Δtc_s1 calculated by the above equation (8).

  Next, in S208, the ECU 20 determines the fuel consumption amount Qfbase per unit time when the fuel addition by the fuel addition valve 14 is not performed (that is, when neither the filter regeneration control nor the NOx reduction control is executed). Calculation is based on the operating state of the engine 1.

Next, in S209, the ECU 20 calculates the current increase ratio Rred0 (unit:%) based on the following equation (9).
Rred0 = 100 × ((Qaddu × na + Qfbase × (Δtca + Δtc_s0)) / Qfbase × (Δtca + Δtc_s0))-1) (9)
(Qaddu: unit addition amount, na: predetermined number of additions, Δtca: predetermined reduction execution period)
In the above equation (9), Qaddu × na is the total amount of fuel added from the fuel addition valve 14 during the reduction execution period, and Qfbase × (Δtca + Δtc_s0) is the internal combustion engine 1 during the reduction execution period and the reduction stop period. Total fuel consumption. Accordingly, the reduction increase ratio Rred0 can be calculated by the above equation (9).

Next, in S210, the ECU 20 calculates the reduction increase ratio Rred1 (unit:%) when the amount of EGR gas is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga based on the following equation (10). calculate.
Rred1 = 100 × ((Qaddu × na + Qfbase × (Δtca + Δtc_s1)) / (Qfbase × (Δtca + Δtc_s1))-1) (10)
The above equation (10) is obtained by replacing Δtc_s0 in the above equation (9) with Δtc_s1. Accordingly, the reduction increase ratio Rred1 can be calculated by the above equation (10). Also, Rred1 is a larger value than Rred0.

Next, in S211, the ECU 20 calculates a reduction increase ratio increase amount ΔRred based on the following equation (11).
ΔRred = Rred1-Rred0 (11)

  Next, an EGR gas amount control routine according to this embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is executed by the ECU 20. This routine is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

In this routine, first, in S301, the ECU 10 determines whether or not the temperature Tgin of the exhaust gas flowing into the filter 10 is equal to or higher than a predetermined exhaust gas temperature Ta. Here, the predetermined exhaust temperature Ta is a temperature at which it can be determined that the oxidation of PM by NO ₂ in the filter 10 is promoted when NOx discharged from the internal combustion engine 1 is increased by decreasing the amount of EGR gas. It is a threshold value. The predetermined exhaust temperature Ta is determined in advance by experiments or the like. If an affirmative determination is made in S301, the ECU 20 proceeds to S302, and if a negative determination is made, the ECU 20 once ends the execution of this routine.

  In S302, the ECU 20 calculates the regeneration increase rate decrease rate RKi and the reduction increase ratio increase ΔRred by the above-described method.

  Next, the ECU 10 proceeds to S303, and determines whether or not the regeneration increase rate decrease rate RKi is larger than the reduction increase rate ratio increase amount ΔRred. If an affirmative determination is made in S303, the ECU 20 proceeds to S304, and if a negative determination is made, the ECU 20 proceeds to S306.

  The ECU 20 having proceeded to S304 executes a reduction in EGR gas. That is, the amount of EGR gas is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga. As a result, the NOx discharged from the internal combustion engine 1 increases, and the oxidation of PM in the filter 10 is promoted. Therefore, the regeneration stop period becomes longer than the reference regeneration stop period Δtf_s0 and becomes the regeneration stop period Δtf_s1 when NOx increases.

  Next, the ECU 20 proceeds to S305 and shortens the reduction stop period from the reference reduction stop period Δtc_s0 to the NOx increase reduction stop period Δtc_s1. Thereafter, the ECU 20 once terminates execution of this routine.

  On the other hand, the ECU 20 having proceeded to S306 controls the amount of EGR gas to the reference EGR gas amount Qgbase.

  Next, the ECU 20 proceeds to S307 and controls the reduction stop period to the reference reduction stop period Δtc_s0. Thereafter, the ECU 20 once terminates execution of this routine.

  According to the routine described above, the amount of EGR gas is reduced only when the regeneration increase rate decrease rate RKi is larger than the reduction increase rate ratio increase amount ΔRred. In other words, when the amount of EGR gas is reduced below the reference EGR gas amount Qgbase, the degree of suppression of fuel consumption deterioration associated with execution of filter regeneration control is greater than the degree of promotion of fuel consumption deterioration associated with execution of NOx reduction control. Only in some cases is the EGR gas reduced.

  Therefore, according to the present embodiment, it is possible to suppress as much as possible the deterioration of fuel consumption associated with the execution of the filter regeneration control and the NOx reduction control.

<Modification>
Next, a modification of the present embodiment will be described. In the above, when the amount of EGR gas is reduced below the reference EGR gas amount Qgbase, the NOx occlusion rate is increased to the required NOx occlusion rate Rcedem by shortening the reduction stop period. However, the NOx occlusion rate can also be increased by extending the reduction execution period while keeping the reduction stop period constant and increasing the number of times of fuel addition from the fuel addition valve 14 during the reduction execution period. .

  Therefore, in this modification, the reduction stop period is set to a predetermined reduction stop period Δtc_sa. When the amount of EGR gas is reduced below the reference EGR gas amount Qgbase, the NOx occlusion rate is increased to the required NOx occlusion rate Rcedem by extending the reduction execution period. In this embodiment, the fuel addition amount from the fuel addition valve 14 in the NOx reduction control is a unit addition amount Qaddu, and the number of additions is changed according to the reduction execution period.

  Hereinafter, a method for calculating the degree of promotion of deterioration in fuel consumption associated with execution of NOx reduction control according to the present modification will be described based on the flowchart shown in FIG. Also in this modified example, the degree of promotion of deterioration of fuel consumption due to the execution of NOx reduction control is calculated as an increase amount increase during reduction. This flow is stored in advance in the ECU 20 and is executed by the ECU 20. Here, only parts different from the flowchart shown in FIG. 3 will be described.

In this flow, in S402, the ECU 20 calculates a reference NOx storage rate Rcebase, which is a NOx storage rate when the reduction execution period is the reference reduction execution period Δtc0, based on the reference NOx emission amount Qnoxbase. Here, the reference reduction execution period Δtc0 is a reduction execution period that is determined such that the NOx outflow amount falls within the allowable range when the EGR gas amount is controlled to the reference EGR gas amount Qgbase. The reference reduction execution period Δtc0 may be a predetermined constant value, or may be set based on the operating state of the internal combustion engine 1. The number of additions from the fuel addition valve 14 during the reference reduction execution period Δtc0 is defined as a reference addition number n0.

  In S406, the ECU 20 calculates a correction coefficient β for correcting the reduction execution period based on the NOx occlusion rate increase rate Rup. The correction coefficient β is a correction coefficient for extending the reference reduction execution period Δtc0 to the NOx increase reduction execution period Δtc1. Here, during the NOx increase reduction execution period Δtc1, the NOx occlusion rate when the EGR gas amount is reduced from the reference EGR gas amount Qgbase by the predetermined decrease amount ΔQga can be set to the required NOx occlusion rate Rcedem. It is a period. The relationship between the correction coefficient β and the NOx occlusion rate increase rate Rup is obtained through experiments and stored in the ECU 20 in advance.

Next, in S407, the ECU 20 calculates a NOx increase reduction execution period Δtc1 based on the following equation (11).
Δtc1 = Δtc0 × β (11)

  In this modification, when the reduction of the EGR gas amount is executed, the ECU 20 changes the reduction execution period from the reference reduction execution period Δtc0 to the NOx increase reduction execution period Δtc1 calculated by the above equation (11). Accordingly, the number of fuel additions from the fuel addition valve 14 during the reduction execution period also increases from the reference addition number n0 to the NOx increase addition number n1.

In step S409, the ECU 20 calculates the current increase ratio Rred0 (unit:%) based on the following equation (12).
Rred0 = 100 × ((Qaddu × n0 + Qfbase × (Δtc0 + Δtc_sa)) / Qfbase × (Δtc0 + Δtc_sa))-1) (12)
(Qaddu: unit addition amount, n0: reference addition number, Δtc_sa: predetermined reduction stop period)
In the above equation (12), Qaddu × n0 is the total amount of fuel added from the fuel addition valve 14 during the reduction execution period, and Qfbase × (Δtc0 + Δtc_sa) is the internal combustion engine 1 in the reduction execution period and the reduction stop period. Total fuel consumption. Accordingly, the reduction increase ratio Rred0 can be calculated by the above equation (12).

Next, in S410, the ECU 20 calculates the reduction increase ratio Rred1 (unit:%) when the amount of EGR gas is decreased from the reference EGR gas amount Qgbase by a predetermined decrease amount ΔQga based on the following equation (13). calculate.
Rred1 = 100 × ((Qaddu × n1 + Qfbase × (Δtc1 + Δtc_sa)) / (Qfbase × (Δtc1 + Δtc_sa))-1) (13)
In the above equation (13), n0 in the above equation (12) is replaced with n1, and Δtc0 is replaced with Δtc1. Accordingly, the reduction increase ratio Rred1 can be calculated by the above equation (12). Also in this case, Rred1 is larger than Rred.

  Then, in the same manner as the flowchart shown in FIG. 3, in S211, the reduction increase rate increase amount ΔRred is calculated. Also in the present modification, the amount of EGR gas is reduced only when the regeneration increase rate decrease rate RKi is greater than the reduction increase rate ratio increase amount ΔRred.

In this embodiment, when the amount of EGR gas is decreased by the predetermined decrease amount ΔQga, the decrease in the EGR gas is executed when the regeneration increase rate decrease rate RKi becomes larger than the reduction increase rate ratio increase amount ΔRred. . However, the EGR gas decrease may be executed by calculating the decrease amount of the EGR gas such that the regeneration increase rate decrease rate RKi is larger than the reduction increase ratio increase amount ΔRred.

  In this embodiment, instead of fuel addition from the fuel addition valve 14, the fuel injection valve 3 performs sub fuel injection at a time later than the main fuel injection, so that fuel can be supplied into the exhaust gas. Good.

Alternatively, the NOx catalyst 9 may be supported on the filter 10. Further, in addition to the NOx catalyst 9, a catalyst having an oxidation function such as a three-way catalyst or an oxidation catalyst may be provided in the exhaust passage 6 upstream of the filter 10 as a pre-stage catalyst. In this case, NO contained in the NOx in the exhaust gas is also converted into NO ₂ in the pre-stage catalyst.

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 flow for calculating the increase rate decrease rate at the time of reproduction | regeneration which concerns on an Example. The flowchart which shows the flow for calculating the increase amount increase ratio at the time of a reduction | restoration which concerns on an Example. The flowchart which shows the routine of EGR gas amount control which concerns on an Example. The flowchart which shows the flow for calculating the increase amount increase ratio at the time of reduction | restoration which concerns on the modification of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Intake passage 5 ... Intake manifold 6 ... Exhaust passage 7 ... Exhaust manifold 9 ... Particulate filter 10 ... Occlusion reduction type NOx catalyst 11 ... EGR device 12, EGR passage 13, EGR valve 14, Fuel addition valve 15, Air-fuel ratio sensor 16, Upstream temperature sensor 17, Downstream temperature sensor 18, Airflow meter 20, ECU

Claims (4)

An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
Fuel supply means for supplying fuel into the exhaust gas upstream of the NOx storage reduction catalyst and the particulate filter;
NOx reduction control for reducing the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst by supplying fuel into the exhaust gas by the fuel supply means, thereby reducing NOx stored in the NOx storage reduction catalyst NOx reduction means for performing
A filter that performs filter regeneration control that raises the temperature of the particulate filter by supplying fuel into the exhaust gas by the fuel supply means, and thereby oxidizes and removes the particulate matter collected by the particulate filter. Reproduction means;
An EGR device that introduces at least part of the exhaust gas flowing through the exhaust passage into the intake system of the internal combustion engine as EGR gas;
When filter regeneration control is not being executed by the filter regeneration means, the amount of EGR gas introduced into the intake system of the internal combustion engine by the EGR device is decreased to increase NOx in the exhaust, thereby EGR gas reducing means for promoting oxidation of particulate matter collected by the particulate filter with NO ₂ ;
A suppression degree calculation means for calculating a suppression degree of deterioration of fuel consumption due to execution of filter regeneration control by reducing the amount of EGR gas by the EGR gas reduction means;
An enhancement degree calculation means for calculating an enhancement degree of fuel consumption deterioration associated with execution of NOx reduction control by reducing the amount of EGR gas by the EGR gas reduction means;
When the suppression degree of the deterioration of the fuel consumption accompanying the execution of the filter regeneration control calculated by the suppression degree calculation means is larger than the promotion degree of the deterioration of the fuel consumption accompanying the execution of the NOx reduction control calculated by the promotion degree calculation means. An exhaust gas purification system for an internal combustion engine, characterized in that the amount of EGR gas is reduced by the EGR gas reduction means. The filter regeneration means executes filter regeneration control when the amount of particulate matter collected in the particulate filter reaches a predetermined amount;
PM emission amount calculating means for calculating a PM emission amount that is an amount of particulate matter discharged per unit time from the internal combustion engine;
And NO ₂ inflow amount calculating means for calculating the NO ₂ inflow is the amount of NO ₂ which flows per unit time in the particulate filter,
Continuous PM oxidation amount calculation that calculates a continuous PM oxidation amount that is an amount of particulate matter oxidized and removed per unit time in the particulate filter in a state where filter regeneration control is not executed based on the NO ₂ inflow amount Means,
Regeneration for calculating a regeneration stop period, which is a period from when execution of filter regeneration control is stopped until execution of the next filter regeneration control is started, based on the predetermined collection amount, PM discharge amount, and continuous PM oxidation amount A suspension period calculation means;
The increase rate during regeneration, which is the ratio of the fuel consumption when the filter regeneration control is executed by the filter regeneration means to the fuel consumption when the filter regeneration control is not executed, is determined as the execution period of the filter regeneration control and the execution of the filter regeneration control. An increase rate calculating means for calculating based on the fuel consumption per unit time during the period, the regeneration stop period, and the fuel consumption per unit time during the regeneration stop period,
The degree-of-suppression calculation means reduces the degree of suppression of deterioration in fuel consumption accompanying the execution of filter regeneration control by reducing the amount of EGR gas by the EGR gas reduction means, and reduces the amount of EGR gas by the EGR gas reduction means. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the increase rate at the time of regeneration in the case of occurrence is calculated as a decrease rate with respect to the increase rate at the time of regeneration when the amount of EGR gas is not decreased. When the NOx reduction means sets the execution period of NOx reduction control as a predetermined reduction execution period and does not reduce the amount of EGR gas by the EGR gas reduction means, the NOx reduction control is stopped after the execution of the NOx reduction control is stopped. A reduction stop period that is a period until execution of the reduction control is started is set as a reference reduction stop period,
A reduction stop period in which when the amount of EGR gas is reduced by the EGR gas reducing means, the amount of NOx that flows out without being stored in the NOx storage reduction catalyst is equivalent to the case where the amount of EGR gas is not reduced. NOx increase reduction stop period calculating means for calculating the NOx increase reduction stop period,
A reduction stop period changing means for changing the reduction stop period from a reference reduction stop period to a NOx increase reduction stop period when the amount of EGR gas is reduced by the EGR gas reduction means;
Increase during reduction, which is the ratio of the difference between the fuel consumption when NOx reduction control is executed by the NOx reduction means and the fuel consumption when NOx reduction control is not executed to the fuel consumption when NOx reduction control is not executed The ratio of the total amount of fuel supplied by the fuel supply means during the predetermined reduction execution period, the fuel consumption in the internal combustion engine during the predetermined reduction execution period, and the fuel in the internal combustion engine during the reduction stop period An increase ratio calculation means for calculating based on consumption,
The degree-of-assistance calculation means reduces the degree of enhancement of fuel consumption accompanying the execution of NOx reduction control by reducing the amount of EGR gas by the EGR gas reduction means, and reduces the amount of EGR gas by the EGR gas reduction means. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust purification system of the internal combustion engine is calculated as a difference between a reduction increase ratio in the case of reduction and a reduction increase ratio in the case of not reducing the amount of EGR gas. The NOx reduction means sets a reduction stop period, which is a period from when execution of NOx reduction control is stopped to when execution of the next NOx reduction control is started, to a predetermined reduction stop period, and by the EGR gas reduction means The NOx reduction control execution period when the amount of EGR gas is not decreased is set as a reference reduction execution period,
NOx reduction control in which when the amount of EGR gas is reduced by the EGR gas reduction means, the amount of NOx flowing out without being stored in the NOx storage reduction catalyst is equivalent to the case where the amount of EGR gas is not reduced. NOx increase reduction execution period calculation means for calculating a NOx increase reduction execution period that is an execution period of
A reduction execution period changing means for changing the execution period of the NOx reduction control from the reference reduction execution period to the NOx increase reduction execution period when the amount of EGR gas is reduced by the EGR gas reduction means;
Increase during reduction, which is the ratio of the difference between the fuel consumption when NOx reduction control is executed by the NOx reduction means and the fuel consumption when NOx reduction control is not executed to the fuel consumption when NOx reduction control is not executed The ratio of the total amount of fuel supplied by the fuel supply means during the execution period of NOx reduction control, the amount of fuel consumed by the internal combustion engine during the execution period of NOx reduction control, and the internal combustion engine during the predetermined reduction stop period An increase ratio calculating means for calculating based on fuel consumption in the engine,
The degree-of-assistance calculation means reduces the degree of enhancement of fuel consumption accompanying the execution of NOx reduction control by reducing the amount of EGR gas by the EGR gas reduction means, and reduces the amount of EGR gas by the EGR gas reduction means. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust purification system of the internal combustion engine is calculated as a difference between a reduction increase ratio in the case of reduction and a reduction increase ratio in the case of not reducing the amount of EGR gas.

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