JP2009041453A - Exhaust emission purifier for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission purifier for an internal combustion engine restraining torque decline of the internal combustion engine even if an EGR gas is introduced to an air intake path while executing a rich spike. <P>SOLUTION: The exhaust emission purifier for an internal combustion engine comprises: a filter 41 whose function is regenerated by rich spike; a fuel addition valve 12 for injecting a fuel into the exhaust path upstream of the filter 41; and a low pressure EGR path 31 for guiding a part of the exhaust gas as EGR gas from the exhaust path downstream of the filter 41 into an air intake path 4. In the case predetermined regeneration conditions are satisfied, a fuel is injected from the fuel addition valve 12 for executing rich spike to the filter 41. In the case where predetermined regeneration conditions are satisfied and the EGR gas is introduced into the air intake path 4 via the low pressure EGR path 31, a fuel is injected from the fuel addition valve 12 so that a part of the fuel injected from the fuel addition valve 12 is guided into a cylinder 2 with the exhaust gas flowing backward into the cylinder 2 while executing rich spike. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine that includes a fuel addition valve that injects fuel into an exhaust passage, and an EGR passage that connects an exhaust passage downstream of the fuel addition valve and an intake passage.

  There is known an internal combustion engine provided with a filter carrying an NOx storage reduction catalyst downstream of a turbine of a turbocharger, and having an EGR passage that takes out exhaust gas from the downstream of the filter and introduces it upstream of a compressor of the turbocharger. (See Patent Document 1). In addition, there is Patent Document 2 as a prior art document related to the present invention.

JP-A-2005-76456 JP-A-6-50134

  As is well known, the NOx storage reduction catalyst stores nitrogen oxides (NOx) when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and makes the exhaust air-fuel ratio richer than the stoichiometric or stoichiometric air-fuel ratio. Then, it is known that the stored NOx is reduced and purified in the presence of fuel as a reducing agent. In the case where the exhaust gas is taken out from the downstream side of the NOx storage reduction catalyst and recirculated to the intake passage as in the internal combustion engine of Patent Document 1, the NOx stored in the NOx storage reduction catalyst is reduced while the exhaust gas is recirculated. When a rich spike is executed to add fuel to the exhaust to make the exhaust air-fuel ratio richer than the stoichiometric air-fuel ratio, when the exhaust whose air-fuel ratio is richer than the stoichiometric air-fuel ratio is recirculated to the intake passage, Oxygen concentration decreases. When the intake air with the reduced oxygen concentration is sucked into the cylinder, the ignition delay is increased, and the torque of the internal combustion engine may be reduced.

  Therefore, an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can suppress a decrease in torque of the internal combustion engine even when EGR gas is introduced into the intake passage during a rich spike.

  An exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage, and an exhaust gas purification means whose function is regenerated by a rich spike that temporarily sets the air-fuel ratio of exhaust gas to a richer side than the stoichiometric air-fuel ratio, and the exhaust gas purification device A fuel addition means for injecting fuel into an exhaust passage upstream of the means, an EGR passage for leading part of the exhaust gas from the exhaust passage downstream of the exhaust purification means to the intake passage as EGR gas, and a predetermined regeneration condition is satisfied In addition, the rich spike execution means for injecting fuel from the fuel addition means so that the rich spike is executed to the exhaust purification means, the rich spike execution means, Execution of the rich spike when the predetermined regeneration condition is satisfied and EGR gas is guided to the intake passage through the EGR passage And a torque drop suppression means for injecting fuel from the fuel addition means so that a part of the fuel injected from the fuel addition means is guided into the cylinder together with exhaust gas flowing back into the cylinder of the internal combustion engine. Thus, the above-described problem is solved (claim 1).

  According to the exhaust emission control device of the present invention, a part of the fuel injected from the fuel addition means is introduced into the cylinder, so that the torque of the internal combustion engine can be increased by this fuel. Therefore, even if the intake air with a low oxygen concentration flows into the cylinder and the ignition delay increases, the torque reduction of the internal combustion engine can be suppressed. The fuel introduced into the cylinder changes the air-fuel ratio of the exhaust discharged from the cylinder to the rich side, so that it is also used for the regeneration of the function of the exhaust purification means, which is the original purpose. Therefore, it is possible to suppress a decrease in torque of the internal combustion engine without consuming fuel wastefully.

  In one form of the exhaust emission control device of the present invention, the fuel addition means may be provided in an exhaust manifold. The fuel addition means may be provided around the outlet of the exhaust port of the cylinder. By providing the fuel addition means at such a position, a part of the fuel injected from the fuel addition means can be guided into the cylinder together with the exhaust gas.

  In one form of the exhaust emission control device of the present invention, the return timing when the exhaust gas whose air-fuel ratio is set to the richer side than the stoichiometric air-fuel ratio by execution of rich spike returns to the cylinder via the EGR passage and the intake passage. The torque reduction suppression means further includes a rich-spike when the predetermined regeneration condition is satisfied and EGR gas is guided to the intake passage via the EGR passage. In this rich spike, the timing at which a part of the fuel injected from the fuel addition means is introduced into the cylinder together with the exhaust gas is synchronized with the return timing of the rich spike executed before the rich spike. (Claim 4). The oxygen concentration of the intake air decreases at the return time when the exhaust gas whose air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio returns to the cylinder due to the rich spike executed previously. Therefore, by synchronizing the time when the fuel is introduced into the cylinder together with the exhaust gas and the previously executed rich spike return time, the torque reduction of the internal combustion engine can be more appropriately suppressed.

  In one form of the exhaust emission control device of the present invention, the exhaust purification device further includes a variable valve mechanism capable of changing a closing timing of the exhaust valve of the cylinder, wherein the torque reduction suppressing means satisfies the predetermined regeneration condition, and When EGR gas is guided to the intake passage through the EGR passage, the variable valve mechanism is controlled to retard the closing timing of the exhaust valve so that the exhaust gas flows back into the cylinder. (Claim 5). Thus, by retarding the valve closing timing of the exhaust valve, the exhaust gas can surely flow back into the cylinder, so that a part of the fuel injected from the fuel addition means can be more reliably guided into the cylinder. it can.

  In this embodiment, the variable valve mechanism can change the closing timing of the intake valve of the cylinder, and the torque reduction suppressing means satisfies the predetermined regeneration condition and the EGR passage through the EGR passage. When the gas is guided to the intake passage, the valve closing timing of the intake valve may be changed so as to promote the back flow of the exhaust gas into the cylinder by controlling the variable valve mechanism. Item 6). In this case, a part of the fuel injected from the fuel addition means can be more reliably guided into the cylinder. In order to promote the backflow of the exhaust, for example, when the piston is moving from the top dead center to the bottom dead center, the intake valve may be closed and the exhaust valve may be opened. In this case, since the inflow of the intake air from the intake passage into the cylinder is blocked, the back flow of the exhaust from the exhaust passage into the cylinder can be promoted.

  In one form of the exhaust emission control device of the present invention having a variable valve mechanism, the present invention further comprises an EGR rate acquisition means for acquiring an EGR rate that is a ratio of EGR gas in the intake air sucked into the cylinder, and the torque reduction The suppression means includes an injection period for injecting fuel from the fuel addition means so that the amount of fuel introduced into the cylinder together with exhaust gas is adjusted according to the EGR rate acquired by the EGR rate acquisition means, and the exhaust valve At least one of the valve closing timings may be changed (Claim 7). As is well known, since the oxygen concentration of the intake air changes according to the EGR rate, the torque of the internal combustion engine also changes according to the EGR rate. In this embodiment, since the amount of fuel introduced into the cylinder together with the exhaust gas is adjusted according to the EGR rate, an appropriate amount of fuel can be introduced into the cylinder with respect to a change in the torque of the internal combustion engine. Therefore, the torque reduction of the internal combustion engine can be appropriately suppressed.

  In this embodiment, the torque reduction suppressing means is configured to increase the amount of fuel introduced into the cylinder by exhaust gas flowing back into the cylinder as the EGR rate acquired by the EGR rate acquiring means increases. At least one of the injection period during which fuel is injected from the exhaust valve and the closing timing of the exhaust valve may be changed (Claim 8). The higher the EGR rate, the lower the oxygen concentration in the intake air, and the lower the torque of the internal combustion engine. Thus, by increasing the amount of fuel introduced into the cylinder together with the exhaust gas as the EGR rate is higher in this way, it is possible to appropriately suppress the torque reduction of the internal combustion engine.

  Further, the torque reduction suppressing means may control the variable valve mechanism so that the closing timing of the exhaust valve is delayed as the EGR rate acquired by the EGR rate acquiring means is higher. ). By delaying the closing timing of the exhaust valve, it is possible to lengthen the time for the exhaust to flow back into the cylinder, so that more fuel injected from the fuel addition means can be introduced into the cylinder. Therefore, the lowering of the exhaust valve closing timing is delayed as the EGR rate is higher in this manner, whereby the torque reduction of the internal combustion engine can be appropriately suppressed.

  As described above, according to the exhaust gas purification apparatus of the present invention, when the predetermined regeneration condition is satisfied and the EGR gas is led to the intake passage through the EGR passage, it is injected from the fuel addition means. Since a part of the fuel is introduced into the cylinder, a reduction in torque of the internal combustion engine can be suppressed by this fuel.

  FIG. 1 shows an example of an internal combustion engine in which an exhaust emission control device according to one embodiment of the present invention is incorporated. An internal combustion engine (hereinafter also referred to as an engine) 1 in FIG. 1 is a diesel engine mounted as a driving power source in a vehicle, and an engine body provided with a plurality (four in FIG. 1) of cylinders 2. 3 and an intake passage 4 and an exhaust passage 5 connected to the respective cylinders 2. As shown in FIG. 1, the cylinders 2 are distinguished from each other by attaching cylinder numbers # 1 to # 4 from one end to the other end in the arrangement direction. In the intake passage 4, an air filter 6 for intake air filtration, an air flow meter 7 for outputting a signal corresponding to the intake air amount, a first throttle valve 8 for adjusting the intake air amount, a compressor 9a of a turbocharger 9, an intake air An intercooler 10 for cooling the air and a second throttle valve 11 for adjusting the intake air amount are provided. The exhaust passage 5 includes a fuel addition valve 12 as fuel addition means for injecting fuel into the exhaust passage 5, a turbine 9 b of the turbocharger 9, a first exhaust purification device 13 for purifying exhaust, and a flow of the exhaust passage 5. An exhaust throttle valve 14 capable of changing the road cross-sectional area, a bypass passage 15 that bypasses the exhaust throttle valve 14 to guide the exhaust downstream, and a second exhaust purification device 16 for purifying the exhaust are provided.

  As shown in FIG. 1, the fuel addition valve 12 is provided in the exhaust manifold 5 a that forms a part of the exhaust passage 5. Further, as shown in FIG. 2, the fuel addition valve 12 is provided around the outlet of the exhaust port 25 of the # 1 cylinder 2. By providing the fuel addition valve 12 at such a position, when the exhaust gas is flowing back into the # 1 cylinder 2, fuel is injected from the fuel addition valve 12 so that a part of the fuel is exhausted together with the exhaust gas # 1. Can flow into the cylinder 2. The bypass passage 15 is provided with a pressure adjusting valve 17 that opens when the pressure in the exhaust passage between the first exhaust purification device 13 and the exhaust throttle valve 14 exceeds a predetermined pressure. Further, as shown in FIG. 1, each cylinder 2 is provided with an injector 18 for injecting fuel into the cylinder 2. Each injector 18 is connected to a common rail 19 in which high-pressure fuel supplied to the injector 18 is stored.

  FIG. 2 is an enlarged view of the cylinder 2 of # 1. Although illustration is omitted, the same applies to the cylinders # 2 to # 4. As shown in FIG. 2, a piston 20 connected to a crankshaft (not shown) via a connecting rod 21 is inserted into the cylinder 2 in a reciprocable manner, and a combustion chamber 22 is formed in the cylinder 2. An intake port 23 that opens into the combustion chamber 22 and forms part of the intake passage 4 is opened and closed by an intake valve 24, and an exhaust port 25 that forms part of the exhaust passage 5 is opened and closed by an exhaust valve 26. Each opening / closing drive of the intake valve 24 and the exhaust valve 26 is performed by a variable valve mechanism 27 that can change the closing timing of the intake valve 24 and the exhaust valve 26. As such a variable valve mechanism 27, for example, an electromagnetic drive mechanism that opens and closes an exhaust valve with an electromagnetic coil is provided.

  Returning to FIG. 1, the description will be continued. The exhaust passage 5 and the intake passage 4 are connected by a high pressure EGR passage 30 and a low pressure EGR passage 31. As shown in FIG. 1, the high-pressure EGR passage 30 connects the exhaust manifold 5 a of the # 4 cylinder 2 and the intake passage 4 downstream from the second throttle valve 11. That is, the high pressure EGR passage 30 connects the exhaust passage 5 upstream of the exhaust purification devices 13 and 16 and the fuel addition valve 12 to the intake passage 4. On the other hand, the low pressure EGR passage 31 connects the exhaust passage 5 downstream of the first exhaust purification device 13 and the intake passage 4 upstream of the compressor 9a. Therefore, the low pressure EGR passage 31 corresponds to the EGR passage of the present invention. The high pressure EGR passage 30 is provided with a high pressure EGR valve 32 that adjusts the flow rate of EGR gas (hereinafter sometimes referred to as high pressure EGR gas) recirculated to the intake passage 4 via the high pressure EGR passage 30. . In the low pressure EGR passage 31, the flow rate of an EGR cooler 33 for cooling the EGR gas and the EGR gas recirculated to the intake passage 4 through the low pressure EGR passage 31 (hereinafter sometimes referred to as “low pressure EGR gas”). A low pressure EGR valve 34 is provided for adjusting the pressure.

The first exhaust purification device 13 is provided with a three-way catalyst 40 and a filter 41, and the second exhaust purification device 16 is provided with an oxidation catalyst 42. The filter 41 has a base material (not shown) capable of collecting particulates in the exhaust, and the base material carries an NOx storage reduction type NOx catalyst material (hereinafter sometimes abbreviated as NOx catalyst). ing. The NOx catalyst carried on the filter 41 occludes NOx when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and stores NOx when the exhaust air-fuel ratio is richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. And is reduced to nitrogen (N ₂ ) in the presence of fuel as a reducing agent for purification. Since there is an upper limit for the amount of NOx that can be stored in the NOx catalyst, NOx reduction is performed at predetermined intervals to release NOx from the NOx catalyst and reduce it to N ₂ so that the stored NOx amount does not reach this upper limit. The exhaust purification performance of the NOx catalyst is maintained at a high level. This NOx reduction is performed by supplying a predetermined amount of fuel from the fuel addition valve 12 to the exhaust passage 5 and executing a rich spike that temporarily sets the air-fuel ratio of the exhaust to be richer than the stoichiometric air-fuel ratio. Therefore, the filter 41 corresponds to the exhaust gas purification means of the present invention. The NOx catalyst only needs to be able to hold NOx by the catalyst, and whether it is absorbed or adsorbed is not limited by occlusion terms. Further, the mode of NOx release is not limited.

  The rich spike control, that is, the operation of the fuel addition valve 12 is controlled by an engine control unit (ECU) 50. The ECU 50 is configured as a computer including a microprocessor and peripheral devices such as a ROM and a RAM necessary for the operation thereof, and refers to output signals from various sensors provided in the engine 1 so that the throttle valves 8, 11, This is a well-known computer unit that controls the injector 18 and the variable valve mechanism 27 and the like, thereby controlling the operating state of the engine 1. The ECU 50 calculates the amount of fuel to be supplied to each cylinder 2 based on, for example, the operating state of the engine 1, and controls the operation of each injector 18 so that the calculated amount of fuel is supplied to each cylinder 2. . Further, the ECU 50 calculates the amount of EGR gas to be introduced into the intake passage 4 via the EGR passages 30 and 31 based on the operating state of the engine 1, and the calculated amount of EGR gas is introduced into the intake passage 4. Thus, the opening degree of each EGR valve 32, 34 is controlled. The ECU 30 is connected with a crank angle sensor 51 that outputs a signal corresponding to the engine rotational speed (rotation speed) of the engine 1 and an A / F sensor 52 that outputs a signal corresponding to the air-fuel ratio of the exhaust as various sensors. ing. An air flow meter 7 is also connected to the ECU 30.

  As shown in FIG. 1, in the engine 1, the exhaust outlet of the low pressure EGR passage 21 is provided in the exhaust passage 5 downstream of the fuel addition valve 12, so that the low pressure EGR gas is introduced into the intake passage 4. When the rich spike is executed while the engine is in operation, the exhaust gas whose air-fuel ratio is richer than the stoichiometric air-fuel ratio is introduced into the intake passage 4 as low pressure EGR gas. In this case, the oxygen concentration of the intake air sucked into the cylinder 2 decreases, the air-fuel ratio of the air-fuel mixture in the cylinder 2 changes to the rich side, and the ignition delay increases. Therefore, the torque of the engine 1 is reduced. Therefore, the ECU 50 delays the valve closing timing of the exhaust valve 26 to reduce the exhaust gas to the cylinder 2 when the low pressure EGR gas whose air-fuel ratio is richer than the stoichiometric air-fuel ratio is sucked into the cylinder 2 and the oxygen concentration of the intake air decreases. The fuel is injected back from the fuel addition valve 12 and a part of the fuel is introduced into the cylinder 2 by exhaust gas that flows back into the cylinder 2. As a result, the amount of fuel combusted in the cylinder 2 is increased, and the torque reduction of the engine 1 is suppressed. Hereinafter, this control may be referred to as torque reduction suppression control. On the other hand, when the low pressure EGR gas is not introduced into the intake passage 4, the oxygen concentration of the intake air does not fluctuate greatly, and thus it is necessary to introduce a part of the fuel injected from the fuel addition valve 12 into the cylinder 2. Absent. Therefore, in such a case, after the exhaust valve 26 of each cylinder 2 is closed, fuel is injected from the fuel addition valve 12 to perform rich spike. Hereinafter, this control may be referred to as normal addition control.

  FIG. 3 shows a fuel addition control routine that the ECU 50 repeatedly executes at predetermined intervals during operation of the engine 1 in order to control the rich spike. By executing this control routine, the ECU 50 functions as rich spike execution means of the present invention. In the control routine of FIG. 3, the ECU 50 first acquires the operating state of the engine 1 in step S11. As the operating state of the engine 1, for example, the rotational speed of the engine 1, the intake air amount, the amount of fuel injected into each cylinder 2, and the like are acquired.

  In the next step S12, the ECU 30 determines whether or not a predetermined regeneration condition for executing NOx reduction is satisfied. The predetermined regeneration condition is determined to be satisfied when, for example, the NOx amount stored in the NOx catalyst after the previous NOx reduction is estimated and the estimated NOx amount is equal to or greater than a predetermined determination value. Since the estimation of the amount of NOx stored in the NOx catalyst may be performed by a known estimation method, the description is omitted. The determination value is used to determine whether it is necessary to perform NOx reduction. For example, a value lower than the upper limit value of the amount of NOx that can be stored in the NOx catalyst is set. If it is determined that the predetermined regeneration condition is not satisfied, the current control routine is terminated.

  On the other hand, if it is determined that the predetermined regeneration condition is satisfied, the process proceeds to step S13, where the ECU 50 determines whether low-pressure EGR gas is introduced into the intake passage 4. This determination is made based on the opening degree of the low pressure EGR valve 34, and it is determined that the low pressure EGR gas is being introduced while the low pressure EGR valve 34 is open. If it is determined that the low-pressure EGR gas has not been introduced, the process proceeds to step S14, where the ECU 50 executes the rich spike by the normal addition control. Thereafter, the current control routine is terminated.

  On the other hand, if it is determined that the low pressure EGR gas has been introduced into the intake passage 4, the process proceeds to step S15, where the ECU 50 returns the exhaust in which the air-fuel ratio is set to the richer side than the stoichiometric air-fuel ratio due to the rich spike into the cylinder 2. The return time that is the time until is specified. Here, exhaust gas whose air-fuel ratio is set to a richer side than the stoichiometric air-fuel ratio due to the rich spike from the time of execution of the rich spike passes through the exhaust passage 5, the low pressure EGR passage 31, and the intake passage 4 once. The time until returning to the cylinder 2 is specified as the return time. The exhaust movement time from the fuel addition valve 12 to the exhaust outlet of the low pressure EGR passage 31 is, for example, the amount of intake air, the amount of fuel injected into each cylinder 2, the number of revolutions of the engine 1, and the piping that forms the exhaust passage 5. This can be estimated based on the cross-sectional area of the channel. Further, the time for the exhaust gas to pass through the low pressure EGR passage 31 can be estimated based on the flow rate of the low pressure EGR gas, the opening degree of the low pressure EGR valve 34, the flow path cross-sectional area of the pipe forming the low pressure EGR passage 31, and the like. The travel time of the exhaust gas from the exhaust inlet of the low pressure EGR passage 31 to the cylinder 2 can be estimated based on the intake air amount, the flow rate of the low pressure EGR gas, and the like. Therefore, the return timing is such that the exhaust travel time from the fuel addition valve 12 to the exhaust outlet of the low pressure EGR passage 31, the time during which exhaust passes through the low pressure EGR passage 31, and the exhaust introduction port of the low pressure EGR passage 31 to the cylinder 2 It is specified based on the total time of exhaust movement time until. The method for specifying the return time is not limited to this method. For example, if the exhaust gas whose air-fuel ratio is richer than the stoichiometric air-fuel ratio is sucked into the cylinder 2, the torque of the engine 1 decreases. Time may be measured and a regression time may be specified based on this measured time. By executing this process, the ECU 50 functions as the return time specifying means of the present invention.

  In the next step S16, the ECU 50 retards the closing timing of the exhaust valve 26 so that a part of the fuel injected from the fuel addition valve 12 is introduced into the # 1 cylinder 2 at the specified return timing. Torque reduction suppression control is executed by injecting fuel from the fuel addition valve 12. Thus, by injecting fuel from the fuel addition valve 12, the return time and the rich spike execution time can be synchronized. Thereafter, the current control routine is terminated. By executing this process, the ECU 50 functions as a torque reduction suppressing means of the present invention.

  As described above, when the rich spike is executed when the low pressure EGR gas is being introduced into the intake passage 4, torque recovery control is executed, and a part of the fuel injected from the fuel addition valve 12 is introduced into the cylinder 2. The torque reduction of the engine 1 can be suppressed. Since the fuel introduced into the cylinder 2 changes the air-fuel ratio of the exhaust gas discharged from the cylinder 2 to the rich side, it is also used for the rich spike that is the original purpose. Therefore, a reduction in torque of the engine 1 can be suppressed without wastefully consuming fuel.

  In the torque reduction suppression control, the valve closing timing of the intake valve 24 may be changed so that the backflow of the exhaust gas into the cylinder 2 is promoted. For example, by closing the intake valve 24 when the piston 20 is moving from the top dead center to the bottom dead center, the intake air flow from the intake passage 4 into the cylinder 2 is blocked and the exhaust passage 5 is connected to the cylinder. The backflow of the exhaust gas into the inside 2 can be promoted.

In the torque reduction suppression control, the exhaust valve 26 is adjusted so that the amount of fuel flowing into the cylinder 2 together with the exhaust gas is adjusted based on the EGR rate that is the ratio of EGR gas in the intake air sucked into the cylinder 2. The valve closing time may be changed. The oxygen concentration O2 in the cylinder 2 can be expressed by the following equation (1). Note that the constant φ in the equation (1) is an equivalence ratio.
O2 = 0.21 × (1-EGR rate × φ) (1)
When the exhaust gas having an air-fuel ratio richer than the stoichiometric air-fuel ratio is introduced into the intake air due to the rich spike, the equivalence ratio φ is 1, so the oxygen concentration in the cylinder 2 is determined according to the EGR rate. In this case, since the oxygen concentration in the cylinder 2 decreases as the EGR rate increases, the torque of the engine 1 further decreases. Therefore, it is necessary to introduce more fuel into the cylinder 2 together with the exhaust gas as the EGR rate is higher. The amount of fuel flowing into the cylinder 2 together with the exhaust can be adjusted, for example, at the closing timing of the exhaust valve 26. As the closing timing of the exhaust valve 26 is delayed, the time during which the exhaust gas flows back into the cylinder 2 becomes longer, so that more fuel can be introduced into the cylinder 2 together with the exhaust gas. Therefore, the ECU 50 estimates the EGR rate based on, for example, the opening degree of the high pressure EGR valve 32, the opening degree of the low pressure EGR valve 34, and the intake air amount, and the exhaust valve at the time of torque reduction suppression control according to the estimated EGR rate. 26 valve closing timing is set. Thus, by estimating an EGR rate, ECU50 functions as an EGR rate acquisition means of the present invention. The valve closing timing of the exhaust valve 26 may be set with reference to the relationship between the EGR rate and the valve closing timing of the exhaust valve 26 shown in FIG. The relationship shown in FIG. 4 is obtained in advance by experiments or the like and stored in the ROM of the ECU 50 as a map.

  Thus, by changing the valve closing timing of the exhaust valve 26 according to the EGR rate, it is possible to appropriately suppress the torque reduction of the engine 1 and to reduce the fluctuation range of the torque of the engine 1.

  The parameter for adjusting the amount of fuel that flows into the cylinder 2 together with the exhaust is not limited to the closing timing of the exhaust valve 26. For example, the amount of fuel that flows into the cylinder 2 together with the exhaust gas may be adjusted by changing the start timing and end timing of the injection period in which fuel is injected from the fuel addition valve 12. For example, by increasing the start time of the injection period as the EGR rate is higher, the time at which fuel begins to flow into the cylinder 2 together with the exhaust gas can be advanced. Therefore, more fuel can flow into the cylinder 2 together with the exhaust gas. Further, the end time of the injection period may be delayed as the EGR rate is higher. In this case, since the time over which the valve opening period during which the exhaust valve is open and the injection period overlap can be lengthened, more fuel can be caused to flow into the cylinder 2 together with the exhaust gas. Further, both the closing timing of the exhaust valve 26 and the start timing and end timing of the injection period may be changed according to the EGR rate.

  This invention is not limited to the form mentioned above, It can implement with a various form. For example, the internal combustion engine to which the present invention is applied is not limited to a diesel engine, and may be applied to various internal combustion engines using gasoline or other fuels. The exhaust purification device may be provided with an exhaust purification catalyst in which a NOx storage reduction catalyst is supported on a carrier instead of a filter in which an NOx storage reduction catalyst material is supported. In addition, the exhaust purification device may be provided with various exhaust purification means whose function is regenerated by a rich spike that temporarily sets the air-fuel ratio of the exhaust to be richer than the stoichiometric air-fuel ratio. The variable valve mechanism of the internal combustion engine to which the present invention is applied is not limited to an electromagnetic drive mechanism. Any valve-operating mechanism that can change the closing timing of the exhaust valve of each cylinder may be used. For example, a valve-operating mechanism that drives a cam for opening / closing the exhaust valve with an electric motor may be used.

  The position where the fuel addition valve is provided is not limited to the above-described form. An exhaust addition valve may be provided at various positions where a part of the fuel injected from the fuel addition valve flows into the cylinder together with the exhaust that flows back into the cylinder. Further, the fuel addition valve may be provided around the exhaust port outlet of other cylinders without being limited to the periphery of the exhaust port outlet of the # 1 cylinder. However, in this case, a fuel addition valve is provided at a position away from the exhaust outlet of the high pressure EGR passage to prevent fuel injected from the fuel addition valve from being introduced into the intake passage via the high pressure EGR passage. Further, the fuel addition valve may be provided between the exhaust port outlets of the two cylinders, for example, between the exhaust port outlet of the # 1 cylinder and the exhaust port outlet of the # 2 cylinder. In this case, the fuel injected from the fuel addition valve can be introduced into the two cylinders. Therefore, it is possible to suppress a decrease in torque in these two cylinders.

  In the above-described form, the execution time of the rich spike is controlled so that the execution time of this rich spike and the return time of the previous rich spike are synchronized. It is also possible to synchronize with the return time corresponding to the rich spike executed at the same time. In each of the above-described embodiments, the return time is defined as the return time to the cylinder via the exhaust passage, the low pressure EGR passage, and the intake passage once. The return time is defined as the return time to the cylinder via these two or more times. The present invention may be implemented as

The figure which shows an example of the internal combustion engine in which the exhaust gas purification apparatus which concerns on one form of this invention was integrated. The figure which expands and shows the cylinder of # 1 of FIG. The flowchart which shows the fuel addition control routine which ECU of FIG. 1 performs. The figure which shows an example of the relationship between an EGR rate and the valve closing timing of an exhaust valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 4 Intake passage 5 Exhaust passage 5a Exhaust manifold 12 Fuel addition valve (fuel addition means)
24 Intake valve 25 Exhaust port 26 Exhaust valve 27 Variable valve mechanism 31 Low pressure EGR passage (EGR passage)
41 Filter (exhaust gas purification means)
50 engine control unit (rich spike execution means, torque drop suppression means, return timing identification means, EGR rate acquisition means)

Claims (9)

Exhaust purification means provided in the exhaust passage, whose function is regenerated by a rich spike that temporarily sets the air-fuel ratio of the exhaust to be richer than the stoichiometric air-fuel ratio, and fuel is injected into the exhaust passage upstream of the exhaust purification means A fuel addition means, an EGR passage for leading part of the exhaust gas from the exhaust passage downstream of the exhaust purification means to the intake passage as EGR gas, and the rich spike with respect to the exhaust purification means when a predetermined regeneration condition is satisfied. An exhaust purification device for an internal combustion engine, comprising: rich spike execution means for injecting fuel from the fuel addition means so that
The rich spike execution means is injected from the fuel addition means during execution of the rich spike when the predetermined regeneration condition is satisfied and EGR gas is guided to the intake passage through the EGR passage. An internal combustion engine comprising: a torque reduction suppressing means for injecting fuel from the fuel adding means so that a part of the fuel is introduced into the cylinder together with exhaust gas flowing back into the cylinder of the internal combustion engine. Exhaust purification device.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the fuel addition means is provided in an exhaust manifold.   The exhaust purification device for an internal combustion engine according to claim 1, wherein the fuel addition means is provided around an outlet of an exhaust port of the cylinder. Regression timing specifying means for specifying the return timing when the exhaust gas whose air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio by execution of rich spike returns to the cylinder via the EGR passage and the intake passage is further provided,
When the predetermined regeneration condition is satisfied and the EGR gas is guided to the intake passage through the EGR passage, the torque reduction suppressing means determines the execution time of the rich spike in the fuel addition means in the rich spike. The time when a part of the fuel injected from the fuel is introduced into the cylinder together with the exhaust gas and the return time of the rich spike executed before the rich spike are adjusted to be synchronized with each other. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3. A variable valve mechanism capable of changing the closing timing of the exhaust valve of the cylinder;
When the predetermined regeneration condition is satisfied and the EGR gas is guided to the intake passage via the EGR passage, the torque reduction suppressing means controls the variable valve mechanism to exhaust the exhaust gas into the cylinder. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the valve closing timing of the exhaust valve is retarded so that a reverse flow of the exhaust gas occurs. The variable valve mechanism can change the closing timing of the intake valve of the cylinder,
When the predetermined regeneration condition is satisfied and the EGR gas is guided to the intake passage through the EGR passage, the torque reduction suppressing means controls the variable valve mechanism to enter the cylinder. 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the closing timing of the intake valve is changed so that the backflow of the exhaust gas is promoted. EGR rate acquisition means for acquiring an EGR rate that is a ratio of EGR gas in the intake air sucked into the cylinder;
The torque reduction suppressing means includes an injection period for injecting fuel from the fuel adding means so that an amount of fuel introduced into the cylinder together with exhaust gas is adjusted according to the EGR rate acquired by the EGR rate acquiring means, and The exhaust emission control device for an internal combustion engine according to claim 5 or 6, wherein at least one of the closing timings of the exhaust valves is changed.   The torque reduction suppression means injects fuel from the fuel addition means such that the higher the EGR rate acquired by the EGR rate acquisition means, the greater the amount of fuel guided into the cylinder by the exhaust gas flowing back into the cylinder. The exhaust emission control device for an internal combustion engine according to claim 7, wherein at least one of an injection period to be performed and a closing timing of the exhaust valve is changed.   The torque reduction suppression unit controls the variable valve mechanism so that the closing timing of the exhaust valve is delayed as the EGR rate acquired by the EGR rate acquisition unit increases. An exhaust gas purification apparatus for an internal combustion engine as described.

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