JP2007120455A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for suppressing occurrence of troubles in the operating condition of an internal combustion engine even in the case that a part of fuel added from a fuel adding device to the exhaust system of the internal combustion engine is carried with exhaust due to exhaust recirculation to the intake system of the internal combustion engine. <P>SOLUTION: When it is detected that a part of fuel added from a fuel adding valve 28 to the inside of the exhaust branch pipe 18 of the internal combustion engine 1 is circulated through an EGR passage 25 and carried to an exhaust branch pipe 8, a cylinder injection amount is controlled to be reduced according to an amount of carried added fuel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  As a technique for reducing the amount of nitrogen oxides (hereinafter referred to as “NOx”) released from the internal combustion engine into the atmosphere, an exhaust gas recirculation (hereinafter referred to as “EGR”) device and an NOx storage reduction catalyst (hereinafter referred to as “NOX”). 2. Description of the Related Art Exhaust gas purification systems equipped with “NOx catalyst” are known.

  In such an exhaust purification system, a part of a reducing agent (hereinafter referred to as “added fuel”) such as fuel added to the exhaust branch pipe of the internal combustion engine in order to reduce and purify NOx occluded in the NOx catalyst, The exhaust gas may be transported to the intake system of the internal combustion engine together with exhaust gas by EGR (hereinafter referred to as “EGR gas”).

  In this case, excess fuel is supplied to the cylinders of the internal combustion engine, which may cause problems such as torque fluctuations and pre-ignition.

On the other hand, paying attention to the fuel addition device in the exhaust branch pipe, the exhaust outlet for EGR, and the positional relationship of the cylinders, the exhaust exhausted during the exhaust stroke of the plurality of cylinders may flow in the direction of the exhaust outlet. When the exhaust stroke is performed in a cylinder located at a certain location, the fuel addition by the fuel addition device is prohibited to suppress the addition fuel from being conveyed to the intake system together with the EGR gas. An exhaust purification system has been developed by the present applicant (see Patent Document 1).
JP 2005-16495 A JP 2000-38950 A JP-A-7-279718

  In the above exhaust purification system, it is desirable to reduce the amount of added fuel to the intake system as much as possible by appropriately designing the installation mode of the fuel addition device and exhaust outlet, the shape of the exhaust branch pipe, etc. It may be difficult to completely prevent the added fuel from being transported to the intake system due to restrictions such as the above.

  The present invention has been made in view of such circumstances, and even when the fuel added to the exhaust system of the internal combustion engine is transported to the intake system of the internal combustion engine together with the EGR gas, the operation state of the internal combustion engine is defective. It aims at providing the technique which suppresses that generation | occurrence | production occurs.

  In order to achieve the above object, according to the present invention, when the fuel added to the exhaust system of the internal combustion engine is transported together with the EGR gas to the intake system of the internal combustion engine, the fuel of the internal combustion engine depends on the amount of fuel transported. The greatest feature is to reduce the injection amount.

More specifically, the exhaust gas purification system for an internal combustion engine of the present invention is
A fuel supply device for supplying fuel to a cylinder of the internal combustion engine;
A fuel addition device for adding fuel into the exhaust branch pipe of the internal combustion engine;
An exhaust gas recirculation device for recirculating a part of the exhaust gas flowing through the exhaust branch pipe to the intake system of the internal combustion engine;
Detecting means for detecting that the fuel added from the fuel adding device is conveyed to the intake system together with exhaust by the exhaust gas recirculation device;
Estimating means for estimating an amount of fuel conveyed to the intake system together with exhaust by the exhaust gas recirculation device;
Control means for reducing the amount of fuel supplied from the fuel supply device in accordance with the estimated amount of the estimating means;
It is characterized by providing.

  In an exhaust purification system including a fuel addition device and an exhaust gas recirculation device, fuel added from the fuel addition device to the exhaust system of the internal combustion engine may be transported together with EGR gas to the intake system of the internal combustion engine.

  Therefore, in the exhaust purification system of the present invention, when the added fuel is transferred to the intake system by the exhaust gas recirculation device, the amount of fuel supplied by the fuel supply device is controlled to decrease according to the amount of added fuel transferred. .

  As a result, it is possible to suppress the total amount of fuel supplied to the cylinder from becoming excessive, and to suppress the occurrence of air-fuel ratio disturbance and torque fluctuation. As a result, even when the added fuel is transferred to the intake system of the internal combustion engine by the exhaust gas recirculation device, it is possible to suppress the occurrence of problems in the operating state of the internal combustion engine.

  In the exhaust purification system of the present invention, the amount of fuel added by the exhaust gas recirculation device is estimated by the estimating means. As a method for estimating the amount of the added fuel conveyed, a method for estimating based on the EGR rate and the amount of fuel added can be exemplified. This is because the proportion of the fuel transferred from the fuel addition device to the intake system has a positive correlation with the EGR rate. Here, the EGR rate represents the ratio of the amount of EGR gas to the sum of the amount of exhaust gas recirculated to the intake system of the internal combustion engine (hereinafter referred to as “EGR gas amount”) and the amount of intake air.

  In the exhaust purification system of the present invention, the reduction control is performed only when the transport of the added fuel by the exhaust gas recirculation device is detected. This is because the added fuel may not be transferred to the intake system even when the fuel is added by the fuel addition device. In the exhaust purification system of the present invention, since the reduction control is not performed in such a case, the fuel supply amount to the cylinder is suppressed from becoming excessive.

  As a method for detecting the conveyance of the added fuel to the intake system, the amount of fuel contained in the EGR gas is larger than usual, or the amount of fuel contained in the exhaust downstream of the exhaust branch pipe is larger than usual. In a case where the amount of the added fuel is small, a method of determining that a part of the added fuel is conveyed to the intake system by the exhaust gas recirculation device can be exemplified.

  Further, it may be determined whether or not the added fuel is conveyed to the intake system from the positional relationship among the fuel addition device in the exhaust branch pipe, the exhaust outlet for EGR, and the cylinder in the exhaust stroke. At that time, it may be experimentally determined in advance which cylinder is in the exhaust stroke and the fuel is transferred to the intake system.

  By the way, since it takes a certain amount of time for the EGR gas to reach the intake system from the exhaust branch pipe, it takes a similar amount of time for the added fuel of the fuel addition device to reach the intake system of the internal combustion engine. Become.

  Therefore, it is preferable that the timing when the reduction control is executed is determined in consideration of the time required for the added fuel to reach the intake system after the fuel addition by the fuel addition device is started.

  Therefore, in the exhaust purification system of the present invention, the time when the reduction control is performed may be determined according to the flow rate of the EGR gas. This is because the EGR gas flow rate and the time required for the added fuel to reach the intake system have a negative correlation.

  Thereby, the reduction control can be performed in synchronization with the timing at which the fuel supplied to the cylinder actually starts to increase. As a result, it is possible to more reliably suppress fluctuations in the fuel supply amount to the cylinder.

  Since the added fuel immediately after the fuel addition from the fuel adding device is locally unevenly distributed in the exhaust branch pipe, the added fuel conveyed to the intake system of the internal combustion engine together with the EGR gas gradually increases. Accordingly, the amount of added fuel flowing into the cylinder does not increase rapidly but gradually increases. Also, when the fuel addition from the fuel addition device is stopped, the amount of added fuel sucked into the cylinder gradually decreases and returns to the normal fuel supply amount.

  Therefore, in the exhaust purification system of the present invention, the in-cylinder injection amount may be gradually increased or decreased at the start and end of the reduction control. Thereby, the fluctuation | variation by the conveyance of the addition fuel of the fuel quantity supplied to a cylinder can be suppressed more reliably. As a result, even when the added fuel is conveyed, it is possible to suppress the occurrence of problems in the operating state of the internal combustion engine.

  According to the present invention, even when a part of the fuel added from the fuel addition device to the exhaust system of the internal combustion engine is transported together with the EGR gas to the intake system of the internal combustion engine, a malfunction occurs in the operation state of the internal combustion engine. It becomes possible to suppress.

  The best mode for carrying out an exhaust purification system for an internal combustion engine according to the present invention will be described below with reference to the drawings.

  FIG. 1 schematically shows an embodiment of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders 2. The internal combustion engine 1 includes a fuel injection valve 3 that directly injects fuel into a combustion chamber (not shown) of each cylinder 2.

  An intake branch pipe 8 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown). In the middle of the intake pipe 9 connected to the intake branch pipe 8, a compressor housing 15a of a turbocharger 15 that operates using exhaust energy as a drive source is provided. An air flow meter 11 is provided upstream of the compressor housing 15a.

  An exhaust branch pipe 18 is connected to the internal combustion engine 1, and the exhaust branch pipe 18 and the intake branch pipe 8 recirculate part of the exhaust gas flowing through the exhaust branch pipe 18 to the intake branch pipe 8. Communication is made via a passage 25. The EGR passage 25 is connected to the exhaust branch pipe 18 by an exhaust outlet 25 a formed in the exhaust branch pipe 18.

In the middle of the EGR passage 25, an EGR flow rate adjustment valve 26, which is constituted by an electromagnetic valve or the like and changes the flow rate of exhaust gas (hereinafter referred to as "EGR gas") flowing through the EGR passage 25 in accordance with the magnitude of the applied voltage. Is provided. An EGR cooler 27 that cools the EGR gas is provided upstream of the EGR flow rate adjustment valve 26. An EGR cooler pre-catalyst 29 that purifies EGR gas is provided upstream of the EGR cooler 27. EG upstream of the EGR cooler pre-catalyst 29
An air-fuel ratio sensor 4 for detecting the air-fuel ratio of R gas is provided.

  In the EGR device configured as described above, when the EGR flow rate adjustment valve 26 is opened, the EGR passage 25 is in a conductive state, and a part of the exhaust gas flowing through the exhaust branch pipe 18 is passed from the exhaust outlet 25a to the EGR passage. 25, and is guided to the intake branch pipe 8 through the pre-EGR cooler catalyst 29 and the EGR cooler 27.

  The EGR gas recirculated to the intake branch pipe 8 is mixed with fresh air flowing from the upstream side of the intake branch pipe 8, and is guided to the combustion chamber of each cylinder 2.

  Each branch pipe of the exhaust branch pipe 18 communicates with the combustion chamber of each cylinder 2 through an exhaust port. The exhaust branch pipe 18 is connected to the turbine housing 15 b of the turbocharger 15 via the collecting portion 16. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 communicates with the atmosphere downstream.

  An NOx storage reduction catalyst 20 (hereinafter referred to as “NOx catalyst”) is provided in the middle of the exhaust pipe 19.

  The NOx catalyst 20 stores NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and releases the stored NOx when the oxygen concentration of the inflowing exhaust gas decreases. At that time, if a reducing component such as fuel is present in the exhaust, the released NOx is reduced and purified.

  A fuel addition valve 28 is provided in the exhaust branch pipe 18 so that the injection hole faces the exhaust branch pipe 18. The fuel as the reducing agent added from the fuel addition valve 28 into the exhaust branch pipe 18 reduces the oxygen concentration of the exhaust gas flowing through the exhaust branch pipe 18 and reaches the NOx catalyst 20 via the exhaust pipe 19. . Thereby, NOx occluded in the NOx catalyst 20 can be appropriately released and reduced from the NOx catalyst 20.

  The internal combustion engine 1 is provided with a crank position sensor 33 that outputs an electrical signal corresponding to the rotational position of the crankshaft.

  The fuel injection valve 3, the EGR flow rate adjustment valve 26, and the fuel addition valve 28 are electrically connected to the ECU 35, respectively, and controlled by a control signal output from the ECU 35. The air-fuel ratio sensor 4, the air flow meter 11, and the crank position sensor 33 are electrically connected to the ECU 35, and output signals thereof are input to the ECU 35. The ECU 35 controls the operating state of the internal combustion engine 1 based on the signals input from the sensors, and performs fuel injection amount reduction control that is the gist of the present invention.

  In the exhaust purification system configured as described above, when the EGR flow rate adjustment valve 26 is opened and EGR is being performed, the flow of exhaust gas flowing into the exhaust outlet 25a is present in the exhaust branch pipe 18. It is formed.

  At this time, if fuel is added from the fuel addition valve 28, a part of the added fuel may be conveyed to the intake branch pipe 8 through the EGR passage 25 together with the exhaust gas flowing into the exhaust outlet 25 a.

  In this case, since an extra fuel that is not assumed is supplied to the cylinder 2, when a normal amount of fuel is injected into the cylinder 2 from the fuel injection valve 3, the total amount of fuel supplied to the cylinder 2. (Hereinafter referred to as “in-cylinder fuel supply amount”) becomes excessive, and torque fluctuations and premature combustion may occur.

  On the other hand, in this embodiment, when it is detected that a part of the added fuel is transported to the intake branch pipe 8 together with the EGR gas, the amount of fuel transported to the intake branch pipe 8 (hereinafter referred to as “transport amount”). The amount of fuel injected from the fuel injection valve 3 into the cylinder 2 (hereinafter referred to as “in-cylinder injection amount”) is controlled to be reduced according to the estimated amount.

  Hereinafter, the reduction control of the in-cylinder injection amount performed by the ECU 35 will be described based on the flowchart of FIG. The flowchart of FIG. 2 is a flowchart showing a routine for performing the reduction control of the in-cylinder injection amount, and this routine is repeatedly executed by the ECU 35 every predetermined period.

  First, in step S201, the ECU 35 determines whether or not the NOx storage amount M of the NOx catalyst 20 is larger than a predetermined reference storage amount M0. That is, the ECU 35 determines whether or not fuel should be added to the NOx catalyst 20 by the fuel addition valve 28.

  The reference storage amount M0 is determined based on the upper limit amount of the NOx storage amount at which the NOx storage capacity of the NOx catalyst 20 is not saturated. As a method of estimating or detecting the NOx occlusion amount M, a method of estimating based on the history of the operating state of the internal combustion engine 1 stored in the ECU 35 can be exemplified.

  If an affirmative determination is made in step S201, the ECU 35 executes the processing from step S202 onward in order to perform fuel addition. On the other hand, if a negative determination is made in step S201, the ECU 35 determines that it is not necessary to add fuel, and ends the execution of this routine.

  The fuel addition is performed in order to change the ambient atmosphere of the NOx catalyst 20 to a reducing atmosphere and to supply fuel as a reducing agent into the exhaust around the NOx catalyst. Since the air-fuel ratio of the exhaust gas flowing through the NOx catalyst 20 changes depending on the operating state of the internal combustion engine 1, the amount of fuel added to make the ambient atmosphere of the NOx catalyst 20 a reducing atmosphere depends on the operation of the internal combustion engine 1. It is preferable to be determined according to the state.

  Therefore, in this embodiment, in steps S202 to S203, the engine speed Ne and the in-cylinder injection amount Qf are detected as the operating state of the internal combustion engine 1, and the fuel addition valve is used with the engine speed Ne and the in-cylinder injection amount Qf as parameters. 28 fuel addition amount Qad is calculated.

  Specifically, the ECU 35 first stores the detection signal from the crank position sensor 33 as the engine speed Ne in step S202, and reads the in-cylinder injection amount Qf from the control signal for the fuel injection valve 3. Subsequently, in step S203, the ECU 35 calculates the fuel addition amount Qad based on a function or map using the engine speed Ne and the in-cylinder injection amount Qf as parameters. This function or map is obtained in advance by experiments and stored in the ROM of the ECU 35.

  In step S204, the ECU 35 outputs a control signal to the fuel addition valve 28 to perform fuel addition at the fuel addition amount Qad calculated in step S203, and starts fuel addition.

  In step S205, the ECU 35 starts a timer counter t that counts an elapsed time from the start of fuel addition in step S204.

In step S <b> 206, the ECU 35 determines whether the fuel added into the exhaust branch pipe 18 by the fuel addition valve 28 circulates through the EGR passage 25 together with the EGR gas and is conveyed to the intake branch pipe 8. Specifically, when the detected value A / F of the air-fuel ratio sensor 4 provided in the EGR passage 25 is lower than a predetermined reference air-fuel ratio A / F0, it is determined that the added fuel is conveyed to the intake branch pipe 8. Like to do.

  This is because when the added fuel is conveyed to the intake branch pipe 8, the air-fuel ratio of the EGR gas is substantially equal to the air-fuel ratio of the exhaust discharged from the internal combustion engine 1, whereas the added fuel is in the intake branch pipe 8. This is because the air-fuel ratio of the EGR gas decreases because the amount of fuel contained in the EGR gas increases when the EGR gas is being conveyed.

  The reference air-fuel ratio A / F0 may be a fixed value, but may be a variable value that is changed according to the operating state of the internal combustion engine 1. This is because the air-fuel ratio of the EGR gas when the added fuel is not conveyed to the intake branch pipe 8 is substantially equal to the air-fuel ratio of the exhaust discharged from the internal combustion engine 1, and the air-fuel ratio of the exhaust of the internal combustion engine 1 is It is because it changes according to the driving state.

  When an affirmative determination is made in step S206, the ECU 35 executes a control for reducing the in-cylinder injection amount after step S207. On the other hand, if a negative determination is made in step S206, the ECU 35 proceeds to step S218, stops the timer counter t, resets the timer counter t to 0, and ends the execution of this routine.

  In steps S207 to S210, the ECU 35 estimates the amount of added fuel transferred to the intake branch pipe 8 of the internal combustion engine 1, and calculates a reduction control amount for the in-cylinder injection amount.

  First, in steps S207 and S208, the ECU 35 calculates an EGR rate R. Specifically, the ECU 35 detects the intake air amount Ga by the air flow meter 11, and calculates the EGR gas flow rate Ge and the EGR rate R based on the detected values. The EGR gas flow rate Ge may be estimated based on the differential pressure between the exhaust pressure and the intake pressure. The EGR rate R is calculated by calculating Ge / (Ge + Ga).

  In step S209, the ECU 35 calculates the conveyance rate k of the added fuel. The transport rate k of the added fuel represents the proportion of the fuel added by the fuel addition valve 28 that flows through the EGR passage 25 together with the EGR gas and is transported to the intake branch pipe 8.

  The conveyance rate k of the added fuel depends on the EGR rate R. FIG. 3 is a graph showing the relationship between the EGR rate R and the added fuel conveyance rate k. The horizontal axis in FIG. 3 represents the EGR rate R, and the vertical axis represents the transport rate k of the added fuel. As shown in FIG. 3, as the EGR rate R increases, the conveyance rate k of the added fuel increases.

  This is because the added fuel flows into the exhaust outlet 25a by the flow of the EGR gas formed in the exhaust branch pipe 18 and is transported to the intake branch pipe 8 together with the EGR gas, so that the added fuel increases as the EGR gas flow rate Ge increases. This is because the transport rate k tends to increase.

  The relationship between the EGR rate R and the added fuel transfer rate k is obtained in advance by experiments and recorded in the ROM of the ECU 35 as a map or a function. In step S209, the ECU 35 calculates the added fuel conveyance rate k according to the EGR rate R calculated in step S208 based on this map or function.

  In step S210, the ECU 35 calculates a reduction control amount Qk with respect to the in-cylinder injection amount. Specifically, the added fuel transfer amount Qk is estimated by calculating the product of the added fuel amount Qad calculated in step S203 and the added fuel transfer rate k calculated in step S209. Amount.

  Since the increase amount of the in-cylinder fuel supply amount due to the addition fuel being conveyed to the intake branch pipe 8 is substantially equal to the addition fuel conveyance amount Qk, the amount corresponding to the addition fuel conveyance amount Qk is reduced from the in-cylinder injection amount. Thus, the in-cylinder fuel supply amount can be made substantially equal to the initial in-cylinder injection amount Qf.

  Thereby, even when the added fuel is conveyed, it is possible to suppress the in-cylinder fuel supply amount from becoming excessive, and it is possible to suppress the occurrence of a malfunction in the operating state of the internal combustion engine 1.

  In step S211, the ECU 35 determines the timing for starting the reduction control for the in-cylinder injection amount. Specifically, the ECU 35 calculates a delay time Td from when fuel addition is started until the cylinder fuel supply amount actually starts to increase.

  The delay time Td is the time required for the added fuel to flow through the EGR passage 25 and reach the intake branch pipe 8. Since the added fuel is conveyed to the intake branch pipe 8 together with the EGR gas, the delay time Td is substantially equal to the time required for the EGR gas to flow through the EGR passage 25 and reach the exhaust branch pipe 8, and the EGR gas flow rate Ge It changes depending on.

  FIG. 4 is a diagram showing the relationship between the EGR gas flow rate Ge and the delay time Td. The horizontal axis in FIG. 4 represents the EGR gas flow rate Ge, and the vertical axis represents the delay time Td. As shown in FIG. 4, the EGR gas flow rate Ge and the delay time Td have a negative correlation.

  This is because, as the EGR gas flow rate Ge increases, the time required for the EGR gas to reach the intake branch pipe 8 from the exhaust branch pipe 18 becomes shorter. This is because the intake branch pipe 8 is reached.

  The relationship between the EGR gas flow rate Ge and the delay time Td is obtained in advance by experiments, and is stored in the ROM of the ECU 35 as a function or map using the EGR gas flow rate Ge as a parameter. In step S211, the ECU 35 calculates a delay time Td corresponding to the EGR gas flow rate Ge detected in step S207 based on this function or map.

  In step S212, the ECU 35 determines whether or not the elapsed time since the start of fuel addition has exceeded the delay time Td obtained in step S211. Specifically, the ECU 35 determines whether or not the current value of the timer counter t is greater than the delay time Td. The ECU 35 repeatedly executes step S212 until an affirmative determination is made.

  If an affirmative determination is made in step S212, the ECU 35 proceeds to step S213, and starts a reduction control for the in-cylinder injection amount. Specifically, the ECU 35 subtracts a reduction control amount Qk for the in-cylinder injection amount calculated in step S210 from the initial in-cylinder injection amount Qf detected in step S202, thereby correcting the in-cylinder injection amount Qf ′ ( = Qf-Qk). Then, the ECU 35 controls the fuel injection valve 3 to reduce the in-cylinder injection amount from the initial in-cylinder injection amount Qf to the corrected in-cylinder injection amount Qf ′.

  At this time, the ECU 35 controls to reduce the in-cylinder injection amount from the initial in-cylinder injection amount Qf to the corrected in-cylinder injection amount Qf ′ over a predetermined time interval ΔT. This is because the added fuel conveyed to the intake branch pipe 8 together with the EGR gas gradually increases, and the in-cylinder fuel supply amount also gradually increases. Accordingly, the in-cylinder fuel supply amount can be more reliably suppressed from being excessively reduced by gradually reducing the in-cylinder injection amount reduction control. The time interval ΔT is obtained in advance by experiments.

In step S214, the ECU 35 determines whether fuel addition should be stopped.
Specifically, it is determined whether or not the current value of the timer counter t is greater than the fuel addition time Tg. The fuel addition time Tg is the time required from the start of fuel addition to release and reduce NOx occluded in the NOx catalyst 20 until the NOx occlusion capacity sufficiently recovers, and is obtained in advance by experiments.

  The ECU 35 repeatedly executes step S214 until an affirmative determination is made. If an affirmative determination is made in step S214, the ECU 35 proceeds to step S215, and outputs a control signal to the fuel addition valve 28 to stop fuel addition.

  Subsequently, in step S216, the ECU 35 determines whether or not the reduction control for the in-cylinder injection amount started in step S213 should be stopped. Specifically, it is determined whether or not the current value of the timer counter t is greater than the sum Td + Tg of the delay time Td and the fuel addition time Tg.

  This is because the in-cylinder fuel is actually stopped after the fuel addition is stopped by a mechanism similar to that in which a time lag has occurred since the start of fuel addition until the in-cylinder fuel supply amount actually starts to increase. This is because there is a time lag until the supply amount starts to return to the original amount.

  The delay time Td calculated in step S211 may be substituted for the delay time from when the fuel addition is stopped until the amount of fuel added to the intake branch pipe 8 becomes almost negligible.

  The ECU 35 repeatedly executes step S216 until an affirmative determination is made.

  If an affirmative determination is made in step S216, the ECU 35 proceeds to step S217, and stops the reduction control for the in-cylinder injection amount. Specifically, the ECU 35 controls the fuel injection valve 3 to increase the in-cylinder injection amount from the corrected in-cylinder injection amount Qf ′ to the initial in-cylinder injection amount Qf.

  At this time, the ECU 35 performs an increase control on the in-cylinder injection amount over a predetermined time interval ΔT, similarly to the control executed in step S213.

  In step S218, the ECU 35 stops the timer counter t and resets the timer counter t to 0, and ends the execution of this routine.

FIG. 5 shows changes over time in the fuel addition amount, the in-cylinder injection amount, the transport amount of the added fuel, and the in-cylinder fuel supply amount when the ECU 35 executes the reduction control routine for the in-cylinder injection amount as described above. FIG. In FIG. 5, the horizontal axis of FIGS. I to IV represents time, the vertical axis of FIG. I is the fuel addition amount, the vertical axis of FIG. II is the in-cylinder injection amount, the vertical axis of FIG. The vertical axis in FIG. IV represents the in-cylinder fuel supply amount.

In FIG. 5, the time point at which fuel addition by the fuel addition valve 28 is started is set as the origin of time t (FIGS. I and A). Therefore, the time t represented by the horizontal axis in FIG. 5 is equal to the value of the timer counter t in the above routine.

After the start of fuel addition (FIGS. I and A), after the delay time Td has elapsed (t = Td), the added fuel actually starts to be conveyed to the intake branch pipe 8 of the internal combustion engine (FIGS. III and B1). Reduction control with respect to the in-cylinder injection amount is started (FIG. II, B2). Thereafter, the transport amount of the added fuel gradually increases to reach Qk (FIG. III, C1), and the in-cylinder injection amount is controlled to gradually decrease from Qf to Qf ′ accordingly (FIG. II, C2).

After the fuel addition time Tg has elapsed since the start of fuel addition (t = Tg), the fuel addition is stopped (FIGS. I and D). After the delay time Td elapses after the fuel addition is stopped (t = Td + Tg), the amount of the added fuel conveyed to the intake branch pipe 8 starts to decrease (FIG. III, E1), and correspondingly decreases with respect to the in-cylinder injection amount. Control is stopped (Fig. II, E2). Thereafter, the transport amount of the added fuel gradually decreases to zero (FIG. III, F1), and the in-cylinder injection amount is gradually increased from Qf ′ to Qf accordingly (FIG. II, F2).

  In this way, the in-cylinder injection amount is controlled to decrease in accordance with the amount of fuel added, so that the in-cylinder fuel supply amount is maintained at the original Qf (FIG. IV).

  As described above, the ECU 35 executes the reduction control routine for the in-cylinder injection amount, thereby realizing the detection means, estimation means, and control means according to the present invention. As a result, even when a part of the added fuel is transferred to the intake system of the internal combustion engine 1, it is possible to suppress the occurrence of problems in the operating state of the internal combustion engine 1.

  The embodiment described above is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in C2 and F2 in FIG. 5, the reduction control is performed so that the change in the in-cylinder injection amount is smooth, but the reduction control is performed so that the in-cylinder injection amount gradually changes in a stepped manner. However, the various effects peculiar to the present invention as described above are not lost.

1 is a diagram showing a schematic configuration of an internal combustion engine in an embodiment of the present invention. It is a flowchart which shows the weight reduction control routine in the Example of this invention. It is a figure which shows the relationship between the EGR rate in the Example of this invention, and the conveyance rate of an addition fuel. It is a figure which shows the relationship between the EGR gas flow volume and delay time in the Example of this invention. It is a figure which shows the time change of the fuel addition amount, in-cylinder injection amount, the conveyance amount of addition fuel, and the in-cylinder fuel supply amount when the reduction control routine in the Example of this invention is performed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Air-fuel ratio sensor 8 ... Intake branch pipe 9 ... Intake pipe 11 ... Air flow meter 15 ... Turbocharger 15a ... compressor housing 15b ... turbine housing 16 ... collecting part 18 ... exhaust branch pipe 19 ... exhaust pipe 20 ... NOx catalyst 25 ... EGR passage 25a ... exhaust outlet 26 ... EGR flow rate adjustment valve 27 ... EGR cooler 28 ... Fuel addition valve 29 ... EGR cooler pre-catalyst 33 ... Crank position sensor 35 ... ECU

Claims (3)

A fuel supply device for supplying fuel to a cylinder of the internal combustion engine;
A fuel addition device for adding fuel into the exhaust branch pipe of the internal combustion engine;
An exhaust gas recirculation device for recirculating a part of the exhaust gas flowing through the exhaust branch pipe to the intake system of the internal combustion engine;
Detecting means for detecting that the fuel added from the fuel adding device is conveyed to the intake system together with exhaust by the exhaust gas recirculation device;
Estimating means for estimating an amount of fuel conveyed to the intake system together with exhaust by the exhaust gas recirculation device;
Control means for reducing the amount of fuel supplied from the fuel supply device in accordance with the estimated amount of the estimating means;
An exhaust gas purification system for an internal combustion engine, comprising:   2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the control means determines an execution timing of the reduction control in accordance with a flow rate of exhaust gas recirculated to the intake system by the exhaust gas recirculation device. 3. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the control means gradually increases or decreases the fuel supplied from the fuel supply device at the start and end of the reduction control.

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