JP2007270703A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

An exhaust emission control device for an internal combustion engine capable of promoting evaporation and dispersion of fuel added to an exhaust passage.
The present invention is applied to an engine 1 having an exhaust passage 13 having two exhaust ports 5 connected to one cylinder 2 and joined at a joining portion 20, and disposed in an exhaust passage downstream of the joining portion 20. In the exhaust gas purification apparatus for an internal combustion engine, comprising the NOx storage reduction catalyst 15 and the fuel addition valve 19 for adding fuel to the exhaust passage downstream of the merging portion 20 and upstream of the storage reduction NOx catalyst 15 In the merging portion 20, one branch passage 5a of the two exhaust ports 5 swirls the exhaust flow in the exhaust passage 15 downstream of the merging portion 20 by the exhaust A flowing in from one branch passage 5a. It is connected to the other branch passage 5b so that the swirl flow S is formed.
[Selection] Figure 2

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  An exhaust passage is connected to each of the two exhaust valve openings that open to the combustion chamber, causing a difference in the flow rate of the exhaust gas flowing through the two exhaust passages, and the merge of the two exhaust passages due to the difference in the exhaust flow rate There is known an exhaust gas purifying device that causes a disturbance in the exhaust flow of a part (see Patent Document 1). In addition, Patent Documents 2 to 5 exist as prior art documents related to the present invention.

JP 2000-110644 A JP 2000-282920 A JP 2001-65333 A JP 2002-213233 A JP 2003-184544 A

  In the conventional apparatus, the exhaust gas is agitated in the merge portion, but it is difficult to maintain the disturbance of the exhaust gas due to the agitation to the exhaust passage after the merge portion. Therefore, when a fuel addition valve for adding fuel to the exhaust passage is provided in the exhaust passage after the junction, the fuel added from the fuel addition valve does not evaporate and disperse, and the exhaust gas such as the exhaust purification catalyst is exhausted. There is a risk of reaching the purification means.

  Accordingly, an object of the present invention is to provide an exhaust purification device for an internal combustion engine capable of promoting the evaporation and dispersion of the fuel added to the exhaust passage.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to an internal combustion engine having an exhaust passage that is connected to one cylinder and has two branch passages that join at a joining portion, and the exhaust gas downstream from the joining portion. In the exhaust gas purification apparatus for an internal combustion engine, comprising: an exhaust gas purification unit disposed in a passage; and a fuel addition unit that adds fuel to an exhaust gas passage downstream from the merging portion and upstream from the exhaust gas purification unit. In the section, one of the two branch passages swirls the exhaust flow in the exhaust passage downstream of the joining portion by the exhaust gas flowing in from the one branch passage to form a swirling flow As described above, the above-described problem is solved by being connected to the other branch passage.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, a swirl flow (hereinafter sometimes referred to as a swirl flow) is formed in the exhaust passage downstream from the joining portion, and is added by this swirl flow. The fuel and the exhaust gas can be agitated to promote the evaporation and dispersion of the fuel.

  In one form of the exhaust emission control device of the present invention, the one branch passage is configured such that exhaust flows from the one branch passage in a tangential direction of a cross section that crosses the flow direction of the other branch passage at the junction. It may be connected to the other branch passage (claim 2). By connecting in this way, a swirl flow can be formed in the other branch passage by the exhaust gas flowing from one branch passage into the other branch passage. Therefore, a swirl flow can be formed in the exhaust passage after the junction.

  In one form of the exhaust emission control device of the present invention, a flow rate adjusting valve that is provided in the other branch passage and adjusts the flow rate of the exhaust gas flowing through the other branch passage, and according to the operating state of the internal combustion engine, And an operation control means for controlling the operation of the flow rate adjusting valve (claim 3). When the flow rate adjustment valve is closed and the flow rate of the exhaust gas flowing through the other branch passage is reduced, the exhaust gas discharged from one branch passage increases, so that a strong swirl flow can be formed in the exhaust passage. On the other hand, when the flow rate adjusting valve is opened, exhaust gas is also discharged from the other branch passage, so that pump loss (pumping loss) of the internal combustion engine can be suppressed. According to this aspect, since the flow rate of the exhaust gas flowing through the other branch passage is adjusted according to the operating state of the internal combustion engine, the evaporation of the fuel added to the exhaust passage and the pump loss of the internal combustion engine can be suppressed. A swirl flow can be appropriately formed so as to promote dispersion.

  In one form of the exhaust gas purification apparatus of the present invention, the operation control means controls the operation of the flow rate adjusting valve so that the flow rate of the exhaust gas flowing through the other branch passage decreases when the fuel addition means adds fuel. (Claim 4). Thus, by controlling the flow rate adjusting valve so that a strong swirl flow is formed when fuel is added, the added fuel can be quickly evaporated and dispersed.

  In one form of the exhaust emission control device of the present invention, the exhaust purification device further comprises exhaust temperature acquisition means for acquiring the temperature of exhaust gas, and exhaust gas flow rate acquisition means for acquiring the flow rate of exhaust gas, wherein the operation control means acquires the exhaust gas temperature. The operation of the flow rate adjusting valve may be controlled based on at least one of the exhaust temperature acquired by the means or the exhaust flow rate acquired by the exhaust flow rate acquiring means. The evaporation and dispersion of the fuel added to the exhaust passage are affected by the exhaust temperature and the exhaust flow rate. Therefore, by controlling the flow rate adjustment valve based on at least one of the exhaust temperature and the exhaust flow rate, fuel evaporation and dispersion can be further promoted while suppressing pump loss of the internal combustion engine.

  In this embodiment, the flow rate of the exhaust gas flowing through the other branch passage increases as the exhaust gas temperature acquired by the exhaust gas temperature acquisition unit increases or the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit increases. The operation of the flow rate adjusting valve may be controlled such that the flow rate increases. When the exhaust gas temperature is high, the atmosphere temperature is high without closing the flow rate adjusting valve and forming a strong swirling flow, so that evaporation of the added fuel is promoted. When the exhaust gas flow rate is large, the exhaust gas flow rate flowing from one branch passage into the other branch passage increases, so that a strong swirling flow is formed in the exhaust passage after the merging portion without closing the flow rate adjusting valve. Therefore, in such a case, the flow rate adjustment valve is opened to suppress pump loss.

  In one form of the exhaust emission control device of the present invention, the exhaust gas purification device includes evaporability acquisition means for acquiring easiness of evaporation of fuel added to the exhaust passage from the fuel addition means, and the operation control means includes the evaporability The operation of the flow rate adjusting valve may be controlled in accordance with the easiness of evaporation of the fuel acquired by the acquiring means. In this way, by controlling the operation of the flow rate adjustment valve according to the ease of fuel evaporation (hereinafter referred to as evaporability), it is possible to suppress pump loss while properly evaporating the fuel. Hereinafter, in the present invention, it is described that evaporability is easy and that evaporability is good, and that evaporation is difficult is described as poor evaporability.

  In this embodiment, the operation control means controls the operation of the flow rate adjusting valve so that the flow rate of the exhaust gas flowing through the other branch passage decreases as the fuel added from the fuel addition means hardly evaporates. (Claim 8). According to this aspect, when the fuel evaporability is poor, that is, when it is difficult for the fuel to evaporate, the flow rate of the exhaust gas flowing through the other branch passage is reduced, so that a strong swirling flow is formed in the exhaust passage and the fuel evaporates. And dispersion is promoted. On the other hand, when the fuel evaporability is good, that is, when the fuel evaporates easily, the flow rate of the exhaust gas flowing through the other branch passage is increased, so that the pump loss of the internal combustion engine can be suppressed while appropriately evaporating and dispersing the fuel. it can.

  In one form of the exhaust emission control device of the present invention, an exhaust valve provided in each of the two branch passages to open and close the branch passage with respect to the cylinder, and the exhaust valves can be independently opened and closed. The variable valve mechanism and the variable valve mechanism are controlled so that the other branch passage is closed with respect to the cylinder by an exhaust valve that opens and closes the other branch passage when fuel is added by the fuel addition means. And an operation control means for performing the operation (claim 9). According to this aspect, since the exhaust gas is not discharged from the other branch passage when the fuel is added, the flow rate of the exhaust gas discharged from the one branch passage can be increased. Therefore, a strong swirl flow can be formed in the exhaust passage by the exhaust discharged from one branch passage, and evaporation and dispersion of the added fuel can be promoted. Further, in this embodiment, since the flow rate of the exhaust gas flowing through the other branch passage is adjusted by the exhaust valve, it is not necessary to provide a valve or the like in the other branch passage. Therefore, the pump loss of the internal combustion engine can be suppressed.

  As described above, according to the present invention, since the swirl flow is formed in the exhaust passage downstream of the joining portion, the evaporation and dispersion of the fuel added to the exhaust passage are promoted by the swirl flow. Therefore, exhaust gas emission can be improved by supplying sufficiently gasified and diffused fuel to the exhaust gas purification means. Also, by controlling the operation of the flow rate adjusting valve provided in the other branch passage in order to adjust the strength of the swirl flow according to the exhaust temperature, the exhaust flow rate, or the fuel evaporability, the pump loss of the internal combustion engine It is possible to promote the evaporation and dispersion of the fuel added to the exhaust passage while suppressing the above.

[First embodiment]
1 and 2 show an embodiment of a diesel engine (hereinafter abbreviated as an engine) as an internal combustion engine in which the exhaust emission control device of the present invention is incorporated. The engine 1 is mounted on a vehicle as a driving power source, and is attached to a cylinder block 3 in which a plurality of (only one is shown in FIG. 1) cylinders 2 are formed, and an upper portion of the cylinder block 3. A cylinder head 6 having two intake ports 4 and two exhaust ports 5 (see FIG. 2) is provided for one cylinder 2. A crankshaft 7 is rotatably supported on the cylinder block 3. The piston 8 and the crankshaft 7 inserted so as to reciprocate in each cylinder 2 are connected via a connecting rod 9, and the reciprocating motion of each piston 8 is transmitted to the crankshaft 7 as rotational motion. . The cylinder head 6 is provided with an intake pipe 10 at a position corresponding to the intake port 4 and an exhaust pipe 11 at a position corresponding to the exhaust port 5. By providing the intake pipe 10 and the exhaust pipe 11 in this way, an intake passage 12 is formed by the intake pipe 10 and the intake port 4, and an exhaust passage 13 is formed by the exhaust port 5 and the exhaust pipe 11. The intake passage 12 is provided with an intake air amount sensor 14 that outputs a signal corresponding to the intake air amount of the engine 1. The exhaust passage 13 has an NOx storage reduction catalyst (hereinafter abbreviated as NOx catalyst) 15 as exhaust purification means, an exhaust temperature sensor 16 as exhaust temperature acquisition means for outputting a signal corresponding to the exhaust temperature, and exhaust gas. A / F sensors 17 and 18 are provided for outputting signals corresponding to the air-fuel ratio (A / F). A fuel addition valve 19 is provided as a fuel addition means in the exhaust passage 13 upstream of the NOx catalyst 15 and downstream of the junction 20 (see FIG. 2A).

  FIG. 2 is an enlarged view of the exhaust port 5 of the engine 1. 2A is a plan view of the exhaust port 5, and FIG. 2B is a cross-sectional view of the exhaust port 5 taken along the line IIb-IIb in FIG. 2A. In addition, arrows A, B, and S in FIGS. 2A and 2B indicate the flow of exhaust gas, respectively. As shown in FIG. 2A, the two exhaust ports 5 are connected from one exhaust port (hereinafter referred to as a swirl exhaust port) 5a to the other exhaust port (hereinafter referred to as a straight exhaust port). .) The merging section 20 joins the exhaust gas into 5b. As described above, the exhaust ports 5a and 5b correspond to the branch passages of the present invention by being connected to one cylinder 2 and joining at the joining portion 20. As shown in FIG. 2 (b), the swirl side exhaust port 5a is in the tangential direction of the cross section that crosses the flow direction of the straight side exhaust port 5b (direction of arrow B in FIG. 2 (a)) at the junction 20. It is connected to the straight side exhaust port 5b so that the exhaust flows from the swirl side exhaust port 5a. By connecting the two exhaust ports 5 in this way, the exhaust gas flowing in from the swirl side exhaust port 5a (arrow A in FIG. 2) is connected to the exhaust passage 13 downstream of the joining portion 20 as shown in FIGS. A swirl flow (swirl flow) indicated by an arrow S in 2 (b) can be formed.

  Returning to FIG. 1, the description will be continued. The cylinder head 6 is provided with an injector 22 so as to face the combustion chamber 21 formed in each cylinder 2. The cylinder head 6 is provided with an intake valve 23 and an exhaust valve 24 that open and close between the combustion chamber 21 and the intake port 4 and the exhaust port 5, respectively. The intake valve 23 and the exhaust valve 24 are opened and closed by a valve mechanism 25. Since these configurations and operations may be the same as those of a well-known engine, detailed description thereof is omitted.

The NOx catalyst 15 has the property of storing NOx when the exhaust air-fuel ratio is lean and releasing the stored NOx when the exhaust air-fuel ratio is rich or reducing and reducing it to nitrogen (N ₂ ). is doing. Since there is an upper limit for the amount of NOx that can be stored in the NOx catalyst 15, NOx reduction for releasing NOx from the NOx catalyst 15 and reducing it to N ₂ so that the stored NOx amount does not reach this upper limit is performed at a predetermined interval. To maintain the exhaust purification performance of the NOx catalyst 15 at a high level. The NOx catalyst 15 is poisoned by sulfur oxide (SOx) contained in the exhaust gas. Therefore, the temperature of the NOx catalyst 15 is raised to a temperature range in which sulfur (S) is released from the NOx catalyst 15 and the exhaust air / fuel ratio is stoichiometrically rich or rich to recover S poisoning. S playback is performed. The fuel addition valve 19 adds a fuel to the exhaust passage 13 to generate a reducing atmosphere necessary when performing NOx reduction and S regeneration. Hereinafter, NOx reduction and S regeneration may be collectively described as function regeneration processing.

  The operation of the fuel addition valve 19 is controlled by an engine control unit (ECU) 30. The ECU 30 is a well-known computer unit that controls the operating state of the engine 1. The ECU 30 controls the operation of the fuel addition valve 19 so that, for example, NOx reduction is performed at a predetermined interval with respect to the NOx catalyst 15. In addition, the ECU 30 controls, for example, fuel injection to the engine 1 so that the operating state of the engine 1 is appropriately controlled. Note that the ECU 30 provides various physical quantities or state quantity detection means to be referred to in these controls as intake air quantity sensor 14, exhaust temperature sensor 16, A / F sensors 17 and 18, and phase of crankshaft 7 ( A crank angle sensor 31 that outputs a signal corresponding to the crank angle) and a water temperature sensor 32 that outputs a signal corresponding to the cooling water temperature of the engine 1 are connected.

  In this embodiment, since a swirl flow can be formed in the exhaust passage 13 downstream from the merging portion 20, evaporation and dispersion of fuel added from the fuel addition valve 19 to the exhaust passage 13 are promoted by this swirl flow, Fuel that is sufficiently gasified can be supplied to the NOx catalyst 15. Therefore, the function regeneration process of the NOx catalyst 15 can be appropriately performed, and the exhaust purification performance of the NOx catalyst 15 can be maintained in a high state. Further, since the fuel can be prevented from adhering to the end face of the NOx catalyst 15, clogging of the end face of the NOx catalyst 15 can be suppressed.

[Second form]
A second embodiment of the present invention will be described with reference to FIGS. FIG. 3 shows a main part of the engine 1 in which the exhaust emission control device according to the second embodiment of the present invention is incorporated. 3A is a plan view of the exhaust port 5 of the engine 1, and FIG. 3B is a cross-sectional view of the exhaust port 5 taken along line IIIb-IIIb in FIG. 3A. As shown in FIG. 3A, in this embodiment, an exhaust swirl control valve (hereinafter abbreviated as exhaust SCV) as a flow rate adjusting valve for adjusting the flow rate of the exhaust gas flowing through the exhaust port 5b is connected to the straight exhaust port 5b. This is different from the first embodiment in that 40 is provided. Other parts are the same as those in the first embodiment. Therefore, the same reference numerals are given to the portions common to the first embodiment described above in FIG. 3, and the description thereof is omitted.

  When the exhaust SCV 40 is closed, the flow rate of the exhaust gas discharged from the straight side exhaust port 5b can be decreased and the flow rate of the exhaust gas discharged from the swirl side exhaust port 5a can be increased. A strong swirl flow can be formed in the exhaust passage 13 by the exhaust gas. That is, the strength of the swirl flow formed in the exhaust passage 13 can be controlled by opening and closing the exhaust SCV 40.

  The exhaust SCV 40 is controlled by the ECU 30 executing the exhaust SCV operation control routine of FIG. 4 at a predetermined cycle while the engine 1 is operating. In the control routine of FIG. 4, the ECU 30 first obtains the rotational speed of the engine 1, the amount of fuel injected from the injector 22 into the combustion chamber 21, the coolant temperature of the engine 1, etc. in step S <b> 11 and refers to these information. The operating state of the engine 1 is acquired. These pieces of information are acquired with reference to output signals of the crank angle sensor 31 and the water temperature sensor 32, for example. In the next step S12, the ECU 30 refers to the acquired operating state of the engine 1 and determines whether or not the addition of fuel to the exhaust passage 13 is requested. For example, it is determined that the addition of fuel is required when the function regeneration process of the NOx catalyst 15 is performed. The ECU 30 estimates the integrated value of the NOx amount stored in the NOx catalyst 15 with reference to the fuel amount injected from the injector 15 and the intake air amount in a routine (not shown) different from this control routine. When it is determined that the integrated value exceeds a predetermined allowable upper limit value, NOx reduction of the NOx catalyst 15 is performed. The ECU 30 also estimates the integrated value of the amount of S poisoned by the NOx catalyst 15 with reference to the fuel injection amount from the injector 22, and the integrated value of the S amount is equal to or greater than a predetermined allowable amount. If it is determined, S reproduction is performed.

  If it is determined that fuel addition to the exhaust passage 13 is requested, the process proceeds to step S13, and the ECU 30 closes the exhaust SCV 40. In the subsequent step S14, the ECU 30 determines whether or not the addition of fuel to the exhaust passage 13 has been completed. Whether or not the addition of fuel has ended is determined by, for example, an integrated value of the amount of fuel added from the fuel addition valve 19 to the exhaust passage 13. The ECU 30 determines that the addition of the fuel to the exhaust passage 13 is completed when the integrated value of the fuel amount exceeds the fuel amount necessary for performing the function regeneration process of the NOx catalyst 15.

  If it is determined that the fuel addition to the exhaust passage 13 has been completed, or if it is determined in step S12 that the fuel addition to the exhaust passage 13 is not requested, the process proceeds to step S15, and the ECU 30 opens the exhaust SCV 40. Thereafter, the current control routine is terminated. On the other hand, when it is determined that the fuel addition to the exhaust passage 13 has not ended, the process proceeds to step S16, and the ECU 30 closes the exhaust SCV 40. Thereafter, the current control routine is terminated.

  According to the above embodiment, since the exhaust SCV 40 is closed when fuel is added to the exhaust passage 13, even when the flow rate of exhaust discharged from the cylinder 2 is small, a strong swirl flow is formed in the exhaust passage 13 and added. The evaporation and dispersion of fuel can be promoted. Therefore, the fuel can be gasified more reliably and supplied to the NOx catalyst 15. Further, since the exhaust SCV 40 is open at times other than the time of fuel addition, the exhaust is discharged from both the swirl side exhaust port 5a and the straight side exhaust port 5b. Therefore, the pump loss of the engine 1 can be suppressed. The ECU 30 functions as an operation control means of the present invention by executing the control routine of FIG. 4 and controlling the operation of the exhaust SCV 40.

  FIG. 5 shows a modification of the exhaust SCV operation control routine. In FIG. 5, the same processes as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted. The control routine of FIG. 5 is repeatedly executed at a predetermined cycle during operation of the engine 1.

  In the control routine of FIG. 5, the ECU 30 first obtains the operating state of the engine 1 in step S11, and then obtains the temperature of exhaust gas discharged from the engine 1 and the flow rate of exhaust gas in step S21. The exhaust temperature is acquired with reference to an output signal of the exhaust temperature sensor 16, for example. The exhaust flow rate can be estimated based on the output signal of the intake air amount sensor 14, for example. By estimating the exhaust flow rate in this way, the ECU 30 functions as the exhaust flow rate acquisition means of the present invention. In the next step S22, the ECU 30 calculates a target opening (hereinafter, abbreviated as a target SCV opening) AngSCV_trg of the exhaust SCV 40 based on the exhaust temperature and the exhaust flow rate of the engine 1. For example, the target SCV opening AngSCV_trg may be specified by storing in advance a map in which the exhaust temperature and the exhaust flow rate of the engine 1 are associated with the target SCV opening AngSCV_trg in the ROM provided in the ECU 30 and using this map. Good. FIG. 6 shows an example of a map in which the exhaust temperature and the exhaust flow rate are associated with the target SCV opening AngSCV_trg. In addition, the numerical value of 0-1 in the map of FIG. 6 has shown the opening degree of the exhaust SCV40. In this map, 0 indicates fully open and 1 indicates fully closed. As shown in FIG. 6, in this map, the target SCV opening AngSCV_trg is set to a smaller value as the exhaust gas temperature is higher and the exhaust gas flow rate is higher. That is, as the exhaust temperature is higher and the exhaust flow rate is higher, the exhaust SCV 40 is opened, and the flow rate of the exhaust gas flowing through the straight-side exhaust port 5b is increased.

  In step S12, the ECU 30 determines whether or not fuel addition to the exhaust passage 13 is requested. If it is determined that fuel addition is requested, the process proceeds to step S23, where the ECU 30 adjusts the opening AngSCV of the exhaust SCV 40 to the calculated target SCV opening AngSCV_trg. In the subsequent step S14, the ECU 30 determines whether or not the addition of fuel to the exhaust passage 13 has been completed.

  If it is determined that the fuel addition to the exhaust passage 13 has been completed, or if it is determined in step S12 that the fuel addition to the exhaust passage 13 is not requested, the process proceeds to step S24, where the ECU 30 fully opens the exhaust SCV 40. . Thereafter, the current control routine is terminated. On the other hand, if it is determined that the fuel addition to the exhaust passage 13 has not ended, the process proceeds to step S25, where the ECU 30 maintains the opening degree AngSCV of the exhaust SCV 40 at the target SCV opening degree AngSCV_trg. Thereafter, the current control routine is terminated.

  When the exhaust temperature is high, the evaporation of fuel can be promoted by the exhaust heat without forming a strong swirl flow. When the exhaust flow rate is large, the exhaust passage 13 is strong even if the exhaust SCV 40 is not closed because the flow rate of the exhaust gas discharged from the swirl side exhaust port 5a is large without reducing the flow rate discharged from the straight side exhaust port 5b. A swirl flow can be formed. Therefore, in the control routine of FIG. 5, the exhaust SCV 40 is opened to suppress the pump loss of the engine 1 as the exhaust temperature is higher or the exhaust flow rate is higher. Thus, by adjusting the opening degree of the exhaust SCV 40 based on the exhaust temperature and the exhaust flow rate, it is possible to promote evaporation and dispersion of the added fuel while suppressing pump loss during fuel addition. Note that the target SCV opening AngSCV_trg need not be referred to both the exhaust temperature and the exhaust flow rate. The target SCV opening AngSCV_trg may be set with reference to one of the exhaust temperature and the exhaust flow rate.

  FIG. 7 shows another modification of the exhaust SCV operation control routine. In FIG. 7, the same processes as those in FIGS. 4 and 5 are denoted by the same reference numerals, and the description thereof is omitted. The control routine of FIG. 7 is also repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 7, the ECU 30 performs the same processing as the control routine of FIG. 5 until the calculation of the target SCV opening AngSCV_trg in step S22. In the subsequent step S31, the ECU 30 acquires fuel evaporability. The evaporability of the fuel is acquired based on, for example, the exhaust air / fuel ratio detected by the A / F sensors 17 and 18. The A / F sensors 17 and 18 do not react to the fuel present in the liquid state in the exhaust gas, but react only to the gasified fuel. Therefore, when the difference between the output signal of the A / F sensor 17 and the output signal of the A / F sensor 18 (hereinafter abbreviated as an air-fuel ratio difference) is small, the fuel in the exhaust gas reaches the NOx catalyst 15 before reaching the NOx catalyst 15. Since it is considered that the fuel is almost gasified, it can be determined that the fuel is easily evaporated, that is, the fuel is easily evaporated. On the other hand, when the air-fuel ratio difference is large, it is considered that the fuel reaches the NOx catalyst 15 in a liquid state and is gasified in the NOx catalyst 15, so that it can be determined that the fuel is difficult to evaporate, that is, the fuel evaporability is poor. . At this time, the evaporability of the fuel may be acquired, for example, as a temperature at which 90% of the fuel evaporates, a so-called 90% distillation temperature. The 90% distillation temperature of the fuel may be specified by storing in advance a map in which the air-fuel ratio difference, the exhaust temperature, and the 90% distillation temperature are associated with each other in a ROM provided in the ECU 30, for example. The 90% distillation temperature is so low that the fuel evaporability is good, that is, the fuel is easy to evaporate, and the fuel evaporativity is bad, ie, the fuel is difficult to evaporate.

  In the next step S32, the ECU 30 calculates a coefficient (hereinafter abbreviated as a correction coefficient) CV_Fuel for correcting the target SCV opening AngSCV_trg. The correction coefficient CV_Fuel may be specified by storing a map in which a 90% distillation temperature and a correction coefficient are associated with each other in advance in a ROM provided in the ECU 30, for example. FIG. 8 shows an example of a map in which the 90% distillation temperature of the fuel is associated with the correction coefficient. As shown in FIG. 8, in this map, the higher the 90% distillation temperature, that is, the harder the fuel evaporates, the larger the correction coefficient is set. In subsequent step S33, the ECU 30 multiplies the target SCV opening AngSCV_trg by the correction coefficient CV_Fuel to calculate a corrected target SCV opening AngSCV_trg. In this correction, the target SCV opening AngSCV_trg is set to a larger value as the fuel is less likely to evaporate. That is, the exhaust SCV 40 is closed as the fuel is less likely to evaporate. When a value larger than 1 is calculated as the corrected target SCV opening AngSCV_trg, 1 is set to the target SCV opening AngSCV_trg. Thereafter, the process proceeds to step S12. Thereafter, the ECU 30 performs the same processing as that of the control routine of FIG. 5, and then ends the current control routine.

  In the control routine of FIG. 7, the exhaust SCV 40 is closed and the swirl flow formed in the exhaust passage 13 is strengthened so that the fuel evaporability is poor, that is, the fuel hardly evaporates. Therefore, evaporation and dispersion of the added fuel can be promoted. On the other hand, since the fuel evaporability is good, that is, correction is made so that the exhaust SCV 40 can be opened as the fuel evaporates more easily, the pump loss during fuel addition can be further suppressed. Note that the ECU 30 functions as the evaporation amount acquisition means of the present invention by executing step S31 of FIG. 7 and acquiring the fuel evaporation.

[Third embodiment]
9 and 10 show the engine 1 in which the exhaust emission control device according to the third embodiment of the present invention is incorporated. FIG. 10 shows a perspective view of the cylinder 2 of FIG. 9 and 10 that are the same as those in FIG. 1 described above are denoted by the same reference numerals, and description thereof is omitted. The engine 1 includes a variable valve mechanism 50 capable of controlling the opening / closing operation of the exhaust valve 24 independently of the operating state of the engine 1. The variable valve mechanism 50 can open and close the two exhaust valves 24 provided in each cylinder 2 independently. That is, the variable valve mechanism 50 can synchronize the opening and closing operations of the two exhaust valves 24, and for example, one of the two exhaust valves 24 is maintained in a state in which the exhaust port 5 is closed. The other exhaust valve 24 can be opened as it is. The variable valve mechanism 50 is controlled by the ECU 30. FIG. 11 shows an exhaust valve operation control routine that the ECU 30 repeatedly executes at a predetermined cycle during operation of the engine 1 in order to control the variable valve mechanism 50. In FIG. 11, the same processes as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted.

  In the control routine of FIG. 11, the ECU 30 performs the same process as in FIG. 4 until the process of determining whether or not the addition of fuel to the exhaust passage 13 is requested (the process of step S12). If it is determined that fuel addition to the exhaust passage 13 is required, the process proceeds to step S41, where the ECU 30 controls the variable valve mechanism 50 to open and close the straight-side exhaust port 5b shown in FIG. , Abbreviated as a straight side exhaust valve) 24b is stopped in a state where the straight side exhaust port 5b is closed (closed state). That is, the straight-side exhaust valve 24b is stopped so that the exhaust is not discharged from the straight-side exhaust port 5b. In the subsequent step S14, the ECU 30 determines whether or not the addition of fuel to the exhaust passage 13 has been completed.

  If it is determined that fuel addition to the exhaust passage 13 has been completed, or if it is determined in step S12 that fuel addition to the exhaust passage 13 has not been requested, the process proceeds to step S42, where the ECU 30 sets the variable valve mechanism 50. By controlling, the operation of the straight side exhaust valve 24b is returned to the normal operation that opens and closes according to the operating state of the engine 1. Thereafter, the current control routine is terminated. On the other hand, if it is determined that the fuel addition to the exhaust passage 13 has not ended, the process proceeds to step S43, and the ECU 30 maintains the closed state of the straight side exhaust valve 24b. Thereafter, the current control routine is terminated.

  According to the above embodiment, when the fuel is added to the exhaust passage 13, the straight-side exhaust valve 24b is maintained in the closed state, so that the exhaust discharged from the swirl-side exhaust port 5a causes the exhaust passage 13 to enter the exhaust passage 13. A strong swirl flow can be formed. Therefore, the evaporation and dispersion of the fuel added to the exhaust passage 13 can be promoted by the swirl flow, and the exhaust emission of the engine 1 can be improved. In this embodiment, since the flow rate of the exhaust gas flowing through the straight side exhaust port 5b is adjusted by the straight side exhaust valve 24b, the strength of the swirl flow can be controlled without arranging a valve or the like in the straight side exhaust port 5b. . Therefore, the pump loss of the engine 1 during normal operation can be reduced as compared with the case where a valve or the like is disposed in the straight-side exhaust port 5b.

  The present invention is not limited to the above-described embodiments, and may be implemented in various forms. For example, the present invention is not limited to a diesel engine, and may be applied to various internal combustion engines that use gasoline or other fuels. The branch passage of the present invention is not limited to the exhaust port. For example, when two exhaust flows discharged from one cylinder are joined in the exhaust manifold, the exhaust passage including the exhaust manifold up to the joining portion corresponds to the branch passage.

  The exhaust purification means disposed in the exhaust passage is not limited to the NOx storage reduction catalyst. A particulate filter, a particulate filter on which an oxidation catalyst is supported, or a particulate filter on which an NOx storage reduction catalyst is supported may be disposed. When these particulate filters (hereinafter abbreviated as filters) are arranged, PM regeneration is performed by adding fuel to the exhaust passage, raising the temperature of the filter, and oxidizing and removing particulate matter (PM) deposited on the filter. Are implemented periodically. Therefore, by applying the present invention, it is possible to supply the gas sufficiently fueled to the filter and raise the temperature of the filter quickly and substantially uniformly.

The figure which shows one form of the diesel engine in which the exhaust gas purification apparatus of this invention was integrated. FIG. 2 is an enlarged view showing an exhaust port of the engine of FIG. 1, wherein (a) is a plan view of the exhaust port, and (b) is a cross-sectional view of the exhaust port taken along line IIb-IIb of (a). It is a figure which shows the principal part of the engine in which the exhaust gas purification apparatus which concerns on the 2nd form of this invention is integrated, (a) is a top view of an engine exhaust port, (b) is in the IIIb-IIIb line | wire of (a). The figure which shows the cross section of an exhaust port. 7 is a flowchart showing an exhaust SCV operation control routine executed by the ECU. 7 is a flowchart showing a modification of the exhaust SCV operation control routine. The figure which shows an example of the map which matched exhaust temperature and exhaust flow volume, and the target SCV opening. 7 is a flowchart showing another modification of the exhaust SCV operation control routine. The figure which shows an example of the map which matched 90% distillation temperature of fuel, and the correction coefficient. The figure which shows the engine incorporating the exhaust gas purification apparatus which concerns on the 3rd form of this invention. The perspective view of a cylinder. The flowchart which shows the exhaust valve operation control routine which ECU performs.

Explanation of symbols

1 Diesel engine (internal combustion engine)
2 Cylinder 5 Exhaust port (branch passage)
13 Exhaust passage 15 NOx storage reduction catalyst (exhaust purification means)
16 Exhaust temperature sensor (exhaust temperature acquisition means)
19 Fuel addition valve (fuel addition means)
20 merging section 24 exhaust valve 30 engine control unit (operation control means, exhaust flow rate acquisition means, evaporability acquisition means)
40 Exhaust swirl control valve (flow adjustment valve)
50 Variable valve mechanism

Claims (9)

Exhaust purification means applied to an internal combustion engine having an exhaust passage that is connected to one cylinder and has two branch passages that join at a joining portion, and disposed in an exhaust passage downstream from the joining portion; In an internal combustion engine exhaust purification device comprising: a fuel addition means for adding fuel to an exhaust passage downstream from a merging portion and upstream from the exhaust purification means,
In the merging portion, one of the two branch passages swirls the exhaust flow in the exhaust passage downstream of the merging portion by the exhaust gas flowing in from the one branch passage to form a swirling flow. The exhaust gas purification apparatus for an internal combustion engine is connected to the other branch passage as described above.   The one branch passage is connected to the other branch passage so that exhaust flows from the one branch passage in a tangential direction of a cross section crossing the flow direction of the other branch passage at the junction. The exhaust gas purification apparatus for an internal combustion engine according to claim 1.   A flow rate adjusting valve provided in the other branch passage for adjusting the flow rate of the exhaust gas flowing through the other branch passage; and an operation control means for controlling the operation of the flow rate adjusting valve in accordance with an operating state of the internal combustion engine; The exhaust emission control device for an internal combustion engine according to claim 1 or 2, characterized by comprising:   The said operation control means controls the operation | movement of the said flow regulating valve so that the flow volume of the exhaust_gas | exhaustion which distribute | circulates the said other branch passage at the time of the fuel addition by the said fuel addition means may decrease. Exhaust gas purification device for internal combustion engine. Exhaust temperature acquisition means for acquiring the temperature of the exhaust, and exhaust flow rate acquisition means for acquiring the flow rate of the exhaust,
4. The operation control unit controls the operation of the flow rate adjusting valve based on at least one of an exhaust temperature acquired by the exhaust temperature acquisition unit or an exhaust flow rate acquired by the exhaust flow rate acquisition unit. Or the exhaust gas purification apparatus for an internal combustion engine according to 4.   The operation control means may increase the flow rate of the exhaust gas flowing through the other branch passage as the exhaust gas temperature acquired by the exhaust gas temperature acquisition means is higher or as the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition means is higher. 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the operation of the flow rate adjusting valve is controlled. Evaporability acquisition means for acquiring easiness of evaporation of fuel added to the exhaust passage from the fuel addition means,
The said operation control means controls operation | movement of the said flow regulating valve according to the easiness of the evaporation of the fuel which the said evaporability acquisition means acquired, The any one of Claims 3-6 characterized by the above-mentioned. Exhaust gas purification device for internal combustion engine.   The operation control means controls the operation of the flow rate adjusting valve so that the flow rate of the exhaust gas flowing through the other branch passage decreases as the fuel added from the fuel addition means hardly evaporates. An exhaust emission control device for an internal combustion engine according to claim 7.   An exhaust valve provided in each of the two branch passages to open and close the branch passage with respect to the cylinder; a variable valve mechanism capable of independently opening and closing the exhaust valves; and fuel by the fuel addition means And an operation control means for controlling the operation of the variable valve mechanism so that the other branch passage is closed with respect to the cylinder by an exhaust valve that opens and closes the other branch passage. The exhaust emission control device for an internal combustion engine according to claim 1 or 2.

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