JP5365261B2 - Method and system for controlling exhaust gas recirculation in an internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress NOx generation quantity while suppressing soot quantity discharged to the outside. <P>SOLUTION: This invention relates to a method for controlling exhaust gas recirculation of a compression ignition type internal combustion engine 10 including a low pressure EGR passage 18 providing communication between an exhaust gas passage 12 at a downstream side of a turbine 20a of a turbocharger 20 and an intake air passage 14 at an upstream side of a compressor 20b, a high pressure EGR passage 16 providing communication between the exhaust gas passage at an upstream side of the turbine and the intake air passage at a downstream of the compressor, and a particulate filter 22 collecting soot in exhaust gas. When load of the internal combustion engine reduces under a condition where exhaust gas is recirculated by the low pressure EGR passage, a first process for recirculating exhaust gas under a condition where distribution ratio of recirculation quantity of the low pressure EGR passage and recirculation quantity of the high pressure EGR passage to whole total recirculation quantity is a prescribed first distribution rate is executed if soot collection capacity of the filter is low, and a second process for recirculating exhaust gas at second distribution ratio having higher ratio of recirculation quantity by the high pressure EGR passage than the first distribution ratio is executed if soot collection capacity is high. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method and system for controlling exhaust gas recirculation in an internal combustion engine that controls the amount of exhaust gas recirculated from the exhaust passage to the intake passage to adjust the oxygen concentration in the combustion chamber of the internal combustion engine and suppress the generation of NOx. Belongs to the field of exhaust purification technology.

  Conventionally, a method is known in which a part of exhaust gas is recirculated from the exhaust passage to the intake passage via the EGR passage, thereby reducing the amount of oxygen in the combustion chamber to a minimum amount that can achieve the required output of the engine. ing. This suppresses generation of NOx caused by excessively high temperature and high pressure in the combustion chamber due to combustion of oxygen more than necessary.

  In such a method, when the engine is provided with an exhaust turbocharger, such as the engine described in Patent Document 1, the compressor of the supercharger is connected from the exhaust passage on the downstream side of the turbine of the supercharger. The low-pressure EGR passage that recirculates the low-pressure exhaust gas by communicating with the upstream intake passage and the high-pressure exhaust gas that recirculates from the exhaust passage on the upstream side of the turbine to the intake passage on the downstream side of the compressor. And a high pressure EGR passage. Each EGR passage is provided with an EGR valve that adjusts the recirculation amount (EGR amount).

  In the case of such an engine, the temperature of the recirculated exhaust gas is lower than that of the high-pressure EGR passage in order to ensure a sufficient amount of oxygen in the combustion chamber when the load is high (the amount of oxygen is large because the gas density is high). A low pressure EGR passage is used.

  On the other hand, when the load is low, the amount of oxygen in the combustion chamber can be smaller than when the load is high, so the temperature of the recirculated exhaust gas is higher than that of the low-pressure EGR passage (the amount of oxygen is low because the gas density is low). An EGR passage is used.

  In any load, the EGR valve is controlled so that the EGR amount decreases when the engine speed increases, that is, when the required oxygen amount increases.

  As described above, the high pressure EGR passage and the low pressure EGR passage are selectively used according to the operating state of the engine, and the EGR amount of each passage is adjusted, thereby suppressing the generation of NOx while achieving the engine output request.

JP 2006-336547 A

  By the way, when the low pressure EGR passage and the high pressure EGR passage are provided as in the engine described in Patent Document 1, if the load on the engine is reduced while the exhaust gas is recirculated through the low pressure EGR passage, the low pressure EGR The EGR valve is controlled so that the amount of EGR through the passage increases (so that the amount of oxygen in the combustion chamber decreases). However, since it is a long path from the position of the low pressure EGR passage where the EGR valve is provided to the combustion chamber, the amount of oxygen in the combustion chamber decreases after the engine load decreases. As a result, the oxygen concentration in the combustion chamber temporarily becomes excessive from the time when the engine load is reduced until the amount of oxygen corresponding to the reduced load value is reached, and the amount corresponding to the excess oxygen. NOx is generated.

  Accordingly, the present invention recirculates the low-pressure exhaust gas by communicating the exhaust turbocharger and the exhaust passage on the downstream side of the turbine of the turbocharger with the intake passage on the upstream side of the compressor of the turbocharger. In an engine having a low-pressure EGR passage and a high-pressure EGR passage that recirculates high-pressure exhaust gas through communication between an exhaust passage upstream of the turbine and an intake passage downstream of the compressor, exhaust gas is recirculated through the low-pressure EGR passage. It is an object to immediately reduce the oxygen concentration in the combustion chamber and suppress the generation of NOx when the load of the engine is reduced in a state where the engine is running.

In order to solve the above-described problem, an invention according to claim 1 is directed to an exhaust turbocharger including a turbine disposed in an exhaust passage and a compressor disposed in an intake passage, and an exhaust gas downstream of the turbine. A low pressure EGR passage that communicates a passage with an intake passage upstream of the compressor, a high pressure EGR passage that communicates an exhaust passage upstream of the turbine and an intake passage downstream of the compressor, and the low pressure EGR passage. A low pressure EGR amount adjusting means provided for adjusting the recirculation amount of the exhaust gas passing through the passage; and a high pressure EGR amount adjusting means provided in the high pressure EGR passage for adjusting the recirculation amount of the exhaust gas passing through the passage. A method of controlling exhaust gas recirculation of a compression ignition internal combustion engine having a particulate filter provided in an exhaust passage and collecting soot in exhaust gas,
An oxygen concentration control step of controlling at least one of the low pressure EGR amount adjusting means and the high pressure EGR amount adjusting means to control the oxygen concentration in the combustion chamber to a concentration corresponding to the load of the internal combustion engine;
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
As the oxygen concentration control step,
When the particulate collection capacity of the particulate filter is lower than the predetermined collection capacity, the distribution ratio of the recirculation amount by the low pressure EGR passage and the recirculation amount by the high pressure EGR passage to the total exhaust gas recirculation amount is a predetermined ratio. Performing a first step of recirculating exhaust gas at a first distribution ratio;
When the soot collection capacity of the particulate filter is higher than a predetermined collection capacity, a second step of recirculating the exhaust gas at a second distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than the first distribution ratio is performed. As well as
When the first step is executed as the oxygen concentration control step, at the start of the execution of the first step, the total exhaust gas recirculation amount based on the load value to be decreased is temporarily increased and corrected according to the increase correction. The EGR amount adjusting means is controlled .

The invention according to claim 2 is a method for controlling exhaust gas recirculation of an internal combustion engine according to claim 1,
In the case where a NOx treatment device that suppresses the discharge of NOx to the outside by treating NOx in the exhaust gas is provided,
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
When the particulate collection capacity of the particulate filter is lower than the predetermined collection capacity and the NOx treatment capacity of the NOx treatment device is lower than the predetermined treatment capacity, the oxygen concentration control step is more than the first distribution ratio. Performing a third step of recirculating the exhaust gas at a third distribution ratio in which the ratio of the recirculation amount by the high-pressure EGR passage is high;
At the same time, a fuel injection control process for increasing the number of fuel split injections is performed.

On the other hand, the invention according to claim 3 is an exhaust turbocharger comprising a turbine disposed in an exhaust passage and a compressor disposed in an intake passage, an exhaust passage downstream of the turbine, and an upstream side of the compressor A low pressure EGR passage that communicates with the intake passage of the engine, a high pressure EGR passage that communicates an exhaust passage on the upstream side of the turbine and an intake passage on the downstream side of the compressor, and the low pressure EGR passage. A low pressure EGR amount adjusting means for adjusting a recirculation amount of exhaust gas, a high pressure EGR amount adjusting means for adjusting a recirculation amount of exhaust gas passing through the high pressure EGR passage, and provided in the exhaust passage. A system for controlling exhaust gas recirculation of a compression ignition type internal combustion engine having a particulate filter that collects soot in exhaust gas,
Oxygen concentration control means for controlling at least one of the low pressure EGR amount adjusting means and the high pressure EGR amount adjusting means to control the oxygen concentration in the combustion chamber to a concentration corresponding to the load of the internal combustion engine;
A soot collection ability detecting means for detecting soot collection ability of the particulate filter,
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
The oxygen concentration control means is
When the soot collection capacity of the particulate filter detected by the soot collection capacity detection means is lower than a predetermined collection capacity, the recirculation quantity through the low pressure EGR passage and the recirculation quantity through the high pressure EGR passage with respect to the total exhaust gas recirculation quantity The first control is performed to recirculate the exhaust gas at a first distribution ratio in which the distribution ratio is a predetermined ratio;
When the soot collection capacity of the particulate filter detected by the soot collection capacity detecting means is higher than the predetermined collection capacity, the ratio of the reflux amount by the high pressure EGR passage is higher than the first distribution ratio. While executing the second control to recirculate the exhaust gas ,
When the oxygen concentration control means executes the first control, at the start of the execution of the first control, the total exhaust gas recirculation amount based on the load value to be decreased is temporarily increased and corrected according to the increase correction. The EGR amount adjusting means is controlled .

The invention according to claim 4 is a system for controlling exhaust gas recirculation of the internal combustion engine according to claim 3 ,
A NOx treatment device that suppresses discharge of the NOx to the outside by treating NOx in the exhaust gas;
NOx processing capacity detecting means for detecting the processing capacity of the NOx processing device;
Fuel injection control means for controlling fuel injection into the combustion chamber,
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
The soot collection capability of the particulate filter detected by the soot collection capability detection means is lower than the predetermined collection capability, and the NOx treatment capability of the NOx treatment device detected by the NOx treatment capability detection means is lower than the predetermined treatment capability. In this case, the oxygen concentration control means executes a third control for recirculating the exhaust gas at a third distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than the first distribution ratio,
In addition, the fuel injection control means increases the number of fuel split injections.

  According to the first aspect of the present invention, when the load of the internal combustion engine decreases while the exhaust gas is recirculated through the low pressure EGR passage, the high pressure EGR passage is used together with the low pressure EGR passage. The distance from the high pressure EGR amount adjusting means provided in the high pressure EGR passage to the combustion chamber is shorter than the distance from the low pressure EGR amount adjusting means provided in the low pressure EGR passage to the combustion chamber. At the same time, the amount of exhaust gas supplied to the combustion chamber can be increased, in other words, the oxygen concentration in the combustion chamber can be decreased. As a result, immediately after the load of the internal combustion engine is reduced, excess oxygen in the combustion chamber is suppressed, and generation of NOx is suppressed.

  Further, when the particulate collection capacity of the particulate filter is lower than the predetermined collection capacity, the distribution ratio of the recirculation amount by the low pressure EGR passage and the recirculation amount by the high pressure EGR passage to the total exhaust gas recirculation amount is a predetermined ratio. On the other hand, if the distribution ratio is higher than the predetermined collection capacity, the exhaust gas is recirculated at a second distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than that in the first distribution ratio.

  That is, when the particulate filter can sufficiently collect the soot generated by recirculating the exhaust gas through the high-pressure EGR passage (soot generated by the local rich portion of the spray mixture due to insufficient oxygen amount), Increase the amount of recirculation through the EGR passage. On the other hand, when the particulate filter cannot sufficiently collect soot, the amount of reflux in the high pressure EGR passage is reduced.

According to the present invention, when the load of the internal combustion engine is reduced while the exhaust gas is recirculated through the low pressure EGR passage, the exhaust gas flow rate according to the first distribution ratio is reduced when the first step is performed. At the start of recirculation, the total exhaust gas recirculation amount based on the load value to be decreased is temporarily increased and corrected, and the low-pressure EGR amount adjusting means is controlled in accordance with the increase correction. Immediately after the decrease in the load, an increase in the amount of NOx generated is suppressed. Thereby, generation | occurrence | production of NOx can be suppressed, suppressing the soot discharged | emitted by external air.

  According to the second aspect of the present invention, when the NOx treatment device that suppresses the discharge of NOx to the outside by treating the NOx in the exhaust gas is provided, the exhaust gas is sent through the low pressure EGR passage. When the load of the internal combustion engine is reduced in a recirculating state, when the soot collection capacity of the particulate filter is lower than the predetermined collection capacity and the NOx treatment capacity of the NOx treatment device is lower than the predetermined treatment capacity, The exhaust gas is recirculated at a third distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than the first distribution ratio. At the same time, the number of fuel split injections is increased.

  Even if the processing capacity of the NOx processing device is low, the amount of recirculation through the high-pressure EGR passage is large, that is, the oxygen concentration in the combustion chamber is reduced, so that the generation of NOx is suppressed. As a result, the amount of NOx discharged to the outside is suppressed.

At this time, if the particulate filter has a low ability to collect soot, there is a concern that the particulate filter will burn abnormally due to excessive accumulation of soot, but this problem is incomplete by increasing the number of fuel split injections. By suppressing the combustion, the amount of soot generated is suppressed, which is solved. As a result, it is possible to prevent the particulate filter from burning abnormally even if the amount of recirculation through the high-pressure EGR passage is large and the particulate filter has a low trapping ability.

On the other hand, according to the third aspect of the present invention, when the load of the internal combustion engine decreases while exhaust gas is recirculated through the low pressure EGR passage, the high pressure EGR passage is used together with the low pressure EGR passage. The distance from the high pressure EGR amount adjusting means provided in the high pressure EGR passage to the combustion chamber is shorter than the distance from the low pressure EGR amount adjusting means provided in the low pressure EGR passage to the combustion chamber. At the same time, the amount of exhaust gas supplied to the combustion chamber can be increased, in other words, the oxygen concentration in the combustion chamber can be decreased. As a result, immediately after the load of the internal combustion engine is reduced, excess oxygen in the combustion chamber is suppressed, and generation of NOx is suppressed.

  Further, when the particulate collection capacity of the particulate filter is lower than the predetermined collection capacity, the distribution ratio of the recirculation amount by the low pressure EGR passage and the recirculation amount by the high pressure EGR passage to the total exhaust gas recirculation amount is a predetermined ratio. On the other hand, if the distribution ratio is higher than the predetermined collection capacity, the exhaust gas is recirculated at a second distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than that in the first distribution ratio.

  That is, when the particulate filter can sufficiently collect the soot generated by recirculating the exhaust gas through the high-pressure EGR passage (soot generated by the local rich portion of the spray mixture due to insufficient oxygen amount), Increase the amount of recirculation through the EGR passage. On the other hand, when the particulate filter cannot sufficiently collect soot, the amount of reflux in the high pressure EGR passage is reduced.

According to the present invention, when the load of the internal combustion engine is reduced while the exhaust gas is recirculated in the low pressure EGR passage, the exhaust gas distribution according to the first distribution ratio is performed when the first control is executed. At the start of recirculation, the total exhaust gas recirculation amount based on the load value to be decreased is temporarily increased and corrected, and the low-pressure EGR amount adjusting means is controlled in accordance with the increase correction. Immediately after the decrease in the load, an increase in the amount of NOx generated is suppressed. Thereby, generation | occurrence | production of NOx can be suppressed, suppressing the soot discharged | emitted by external air.

According to the fourth aspect of the present invention, when the NOx treatment device that suppresses the discharge of NOx to the outside by treating the NOx in the gas is provided, the exhaust gas is discharged through the low pressure EGR passage. When the load of the internal combustion engine is reduced in a recirculating state, when the soot collection capacity of the particulate filter is lower than the predetermined collection capacity and the NOx treatment capacity of the NOx treatment device is lower than the predetermined treatment capacity, The exhaust gas is recirculated at a third distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than the first distribution ratio. At the same time, the number of fuel split injections is increased.

  Even if the processing capacity of the NOx processing device is low, the amount of recirculation through the high-pressure EGR passage is large, that is, the oxygen concentration in the combustion chamber is reduced, so that the generation of NOx is suppressed. As a result, the amount of NOx discharged to the outside is suppressed.

At this time, if the particulate filter has a low ability to collect soot, there is a concern that the particulate filter will burn abnormally due to excessive accumulation of soot, but this problem is incomplete by increasing the number of fuel split injections. By suppressing the combustion, the amount of soot generated is suppressed, which is solved. As a result, it is possible to prevent the particulate filter from burning abnormally even if the amount of recirculation through the high-pressure EGR passage is large and the particulate filter has a low trapping ability.

1 is a schematic configuration diagram of a diesel engine and an intake / exhaust system thereof according to an embodiment of the present invention. It is the schematic of the control system containing the control apparatus of the diesel engine which concerns on one Embodiment of this invention. It is a figure which shows the map for determining the EGR channel | path to be used based on an engine speed and an engine load . It is a figure which shows the time chart of the some control performed when an engine load reduces in a low voltage | pressure EGR area | region, and the time chart when not performing this control. It is a figure for demonstrating the change rate and deviation for carrying out the increase correction | amendment of the recirculation amount of exhaust gas temporarily. It is a figure which shows the map for determining the increase correction amount of recirculation | reflux amount based on change rate. It is a figure which shows the map for determining the increase correction amount of the recirculation | reflux amount based on a deviation. It is a figure which shows the time chart for demonstrating division | segmentation injection. It is a figure which shows the flow of control which concerns on one Embodiment. It is a figure which shows the flow of control which concerns on other embodiment. It is a figure which shows the flow of control which concerns on the reference example of this invention .

  Embodiments of the present invention will be described below.

  FIG. 1 schematically shows the configuration of a diesel engine and its intake and exhaust system according to an embodiment of the present invention. FIG. 2 shows a control system of the diesel engine.

  A diesel engine 10 shown in FIG. 1 is an engine in which a part of exhaust gas is recirculated from an exhaust passage 12 to an intake passage 14, and a high pressure EGR passage 16 and a low pressure EGR passage 18 are provided to recirculate the exhaust gas. Is provided.

  The diesel engine 10 includes an exhaust turbocharger 20, and a turbine 20 a is disposed in the exhaust passage 12 and a compressor 20 b is disposed in the intake passage 14.

  The high pressure EGR passage 16 communicates the exhaust passage 12 portion on the upstream side of the turbine 20a of the turbocharger 20 and the intake passage 14 portion on the downstream side of the compressor 20b. The high-pressure EGR passage 16 is provided with a high-pressure EGR valve 16 a that adjusts the recirculation amount (EGR amount) of exhaust gas that passes through the passage 16.

  The low pressure EGR passage 18 communicates the exhaust passage 12 portion on the downstream side of the turbine 20a of the turbocharger 20 and the intake passage 14 portion on the upstream side of the compressor 20b. Further, the low pressure EGR passage 18 is provided with a low pressure EGR valve 18a for adjusting the EGR amount of the exhaust gas passing through the passage 18, and an EGR cooler 18b for cooling the recirculated exhaust gas.

  Further, the diesel engine 10 has a patty that collects soot in the exhaust gas in the exhaust passage 12, specifically, in the exhaust passage 12 portion between the turbine 20 a of the turbocharger 20 and the low-pressure EGR passage 18. A lean NOx trap catalyst (hereinafter referred to as “NOx”) that treats (traps) NOx in the exhaust gas to the curative filter 22 and the exhaust passage 12 downstream of the low-pressure EGR passage 18 to suppress NOx emission to the outside. 24).

  Further, the diesel engine 10 includes an intercooler 26 that cools the intake air in an intake passage 14 portion between the compressor 20b of the turbocharger 20 and the high-pressure EGR passage 16, and an air cleaner 28 that cleans the intake air. The intake passage 14 is provided upstream of the low pressure EGR passage 18.

  Furthermore, the diesel engine 10 includes a negative pressure adjusting valve 30 in a portion of the intake passage 14 between the low pressure EGR passage 18 and the air cleaner 28 and a portion of the intake passage 14 between the high pressure EGR passage 16 and the intercooler 26. And a throttle valve 32.

  The negative pressure adjustment valve 30 is a valve that adjusts the pressure on the upstream side of the compressor 20b in the intake passage 14, and controls the inflow of outside air into the intake passage 14 by controlling the opening amount. When the opening amount of the negative pressure adjusting valve 30 is adjusted, the negative pressure in the intake passage 14 between the valve 30 and the compressor 20b is adjusted, and the negative pressure is adjusted so that the intake air is sucked from the exhaust passage 12 via the low pressure EGR passage 18. The amount of exhaust gas flowing toward the passage 14 is adjusted.

  As shown in FIG. 2, the control device 50 of the diesel engine 10 includes an accelerator opening sensor 52 (this opening amount corresponds to the load of the diesel engine 10) that detects an accelerator pedal depression amount of the occupant, and a diesel engine. From an engine speed sensor 54 that detects the number of rotations of 10, a filter upstream pressure sensor 56 that detects pressure upstream of the particulate filter 22, and a filter downstream pressure sensor 58 that detects pressure downstream of the filter 58. Based on this signal, various controls are executed for the high pressure EGR valve 16a, the low pressure EGR valve 18a, and the combustion injection nozzle 10b.

  First, the control device 50 is configured to return to the combustion chamber 10a of the diesel engine 10 based on signals from the engine speed sensor 54 and the accelerator opening sensor 52, that is, based on the engine speed N and the engine load L. The EGR amount (the sum of the EGR amount by the high pressure EGR passage 16 and the EGR amount by the low pressure EGR passage 18) is determined.

  Specifically, the total EGR amount is determined by the map shown in FIG. When the engine speed N exceeds the specified speed Np, the control device 50 does not recirculate the exhaust gas to the combustion chamber 10a of the diesel engine 10 (closes the high pressure EGR valve 16a and the low pressure EGR valve 18a). This is because if the exhaust gas is recirculated to the combustion chamber 10a when the engine speed exceeds Np, the amount of oxygen in the combustion chamber 10a decreases, combustion weakens, and output at that speed cannot be achieved.

  When engine speed N does not exceed Np and engine load L is low, control device 50 recirculates exhaust gas to combustion chamber 10a of diesel engine 10 only through high-pressure EGR passage 16 (closes low-pressure EGR valve 18a). On the other hand, when the engine load L is high, the exhaust gas is recirculated only through the low pressure EGR passage 18 (the high pressure EGR valve 16a is closed). When the engine load is in the meantime (in the transient region), the exhaust gas is recirculated through both EGR passages.

  Explaining, the exhaust gas recirculated to the combustion chamber 10a through the low-pressure EGR passage 18 is cooled by the EGR cooler 18b and the intercooler 26, and therefore, compared with the exhaust gas recirculated through the high-pressure EGR passage 16 Since the temperature is low, that is, the gas density is high, the amount of oxygen is large. Therefore, when the engine load L is a high load, in order to achieve an output at that load, that is, in order to increase the amount of oxygen in the combustion chamber 10a, the exhaust gas via the low pressure EGR passage 18 is supplied to the combustion chamber 10a. Reflux. On the other hand, when the engine load L is low, the amount of oxygen in the combustion chamber 10a may be smaller than that in the case of high load, and therefore the exhaust gas via the high-pressure EGR passage 16 is returned to the combustion chamber 10a.

  When the exhaust gas is recirculated through either the high pressure EGR passage 16 or the low pressure EGR passage 18, the controller 50 determines the total amount based on the engine speed N and the engine load L, that is, based on the output of the diesel engine 10. The amount of EGR is calculated. In other words, the minimum oxygen concentration in the combustion chamber 10a that can achieve the output is calculated. Then, the opening degree of the EGR valve 16a and / or 18a is controlled so that the calculated oxygen concentration is obtained. Thereby, the output of the required diesel engine 10 is ensured, suppressing generation | occurrence | production of NOx.

  Further, the control device 50 calculates the pressure difference between the upstream pressure and the downstream pressure of the particulate filter 22 based on the signals from the filter upstream pressure sensor 56 and the filter downstream pressure sensor 58, and based on the calculated pressure difference, The filter 22 is configured to calculate the amount of soot collected. Specifically, the relationship between the pressure difference and the amount of trapped soot is experimentally determined, and the amount of soot collected by the particulate filter 22 is calculated from the relationship and the calculated pressure difference.

  Further, the control device 50 calculates the total amount of NOx generated based on the history of changes in the signals from the engine speed sensor 54 and the accelerator opening sensor 52, that is, based on the history of changes in the output of the diesel engine 10. The remaining NOx treatable amount (processing capacity) of the NOx catalyst 24 is calculated as a result of processing the calculated total amount of NOx.

  Furthermore, the control device 50 performs the control according to the present invention when the engine load decreases in the low pressure EGR region shown in FIG. 3 (when the load decrease amount per unit time decreases beyond the specified amount), that is, the low pressure When the load on the diesel engine 10 decreases while exhaust gas is recirculated in the EGR passage 18, the following control is executed.

  To explain, when the load of the diesel engine 10 is reduced while the exhaust gas is recirculated in the low pressure EGR passage 18, the low pressure EGR valve is set so that the oxygen concentration value in the combustion chamber 10a corresponding to the load value of the reduction destination is reduced. Although the opening amount of 18a is increased, in this case, the oxygen concentration in the combustion chamber 10a actually falls behind the decrease in load. That is, as shown in the time chart of FIG. 4A, the actual value Cr of the oxygen concentration C in the combustion chamber 10a decreases with a delay from the target value Ct based on the engine load L. As shown in the figure, the amount of NOx generated temporarily increases immediately after the engine load L decreases, as shown in the figure.

  This occurs because the path from the low pressure EGR valve 18a to the combustion chamber 10a is long, so that the oxygen in the combustion chamber 10a becomes excessive by the amount of delay in the decrease in the oxygen concentration C in the combustion chamber 10a. Thus, immediately after the engine load decreases, the amount of NOx generated increases.

  As a countermeasure, when the engine load decreases in the low pressure EGR region, the control device 50 temporarily increases the opening amount of the high pressure EGR valve 16a or increases the total EGR amount of the exhaust gas based on the load value of the decrease destination. It is configured to temporarily correct the increase.

First, as shown in FIG. 4B, when the soot trapping amount of the particulate filter 22 is smaller than the specified amount as a condition (when soot trapping capacity is high), the control device 50 operates in the low pressure EGR region of FIG. When the engine load L decreases in the engine, the opening amount of the low pressure EGR valve 18a is increased so as to decrease to the oxygen concentration C in the combustion chamber 10a corresponding to the decreased load value (similar to FIG. 4A). The opening amount of the high pressure EGR valve 16a is temporarily increased (the EGR amount by the high pressure EGR passage 16 is temporarily increased) so that the actual value Cr and the target value Ct coincide with each other and the oxygen concentration C in the combustion chamber 10a decreases. To increase the amount.) That is, the value of the high pressure EGR passage 16 is temporarily increased in the ratio (distribution ratio) between the EGR amount by the low pressure EGR passage 18 and the EGR amount by the high pressure EGR passage 16 with respect to the total EGR amount. As a result, as shown in FIG. 4B, an increase in the amount of NOx generated can be suppressed immediately after the engine load decreases.

  In this case, although the amount of EGR by the high pressure EGR passage 16 is increased (by reducing the amount of oxygen in the combustion chamber 10a), the local rich portion of the spray mixture is generated and the amount of soot generated is increased. Since the soot generated by the particulate filter 22 is collected, the amount of soot discharged to the outside is suppressed.

On the other hand, when the soot trapping amount of the particulate filter 22 is larger than the specified amount as a condition (soot trapping capability is low) and the remaining NOx treatable amount of the NOx catalyst 24 is large (NOx processing capability is high), When the engine load L decreases in the low pressure EGR region, the control device 50 does not delay the load L to the oxygen concentration C in the combustion chamber 10a corresponding to the decreased load value, as shown in FIG. In order to decrease, the opening amount of the low pressure EGR valve 18a is increased while temporarily increasing the amount. In other words, the exhaust gas total EGR amount based on the load value to be decreased is temporarily increased and corrected, and the low pressure EGR valve 18a is controlled accordingly.

  The increase correction amount of the total EGR amount of the exhaust gas is determined based on the change rate ΔCt of the target value Ct of the oxygen concentration C calculated based on the engine load L and the deviation D between the target value Ct and the actual value Cr. Is done. Specifically, a map showing the relationship between the change rate ΔCt and the increase correction amount Ea as shown in FIG. 6 and a map showing the relationship between the deviation D and the increase correction amount ELa as shown in FIG. 7 are experimental. The total EGR amount of the exhaust gas is corrected to increase based on these two maps, the change rate ΔCt and the deviation D.

  In this case, the delay in decreasing the oxygen concentration C in the combustion chamber 10a (the delay in the actual value Ct with respect to the target value Cr of the oxygen concentration C) due to the increase correction of the total EGR amount of the exhaust gas is the increase in FIG. Although it is shorter than the case without correction, it is longer than that in FIG. Immediately after the engine load L decreases, the amount of increase in the NOx generation amount is smaller than that in the case of FIG. 4A, but is larger than that in FIG. 4B. This is because, as shown in FIG. 1, the distance from the low pressure EGR valve 18a to the combustion chamber 10a is longer than the distance from the high pressure EGR valve 16a to the combustion chamber 10a.

Furthermore, as a condition, when the soot collection amount of the particulate filter 22 is larger than the specified amount (soot collection capability is low) and the remaining NOx treatable amount of the NOx catalyst 24 is small (NOx treatment capability is low), As shown in FIG. 4D, the control device 50 performs the same control as in FIG. 4B on the high pressure EGR valve 16a and the low pressure EGR valve 18a, and also divides the fuel. Increase the number of injections.

  FIG. 8 shows the relationship between the divided fuel injection, the amount of heat generated therewith, and the piston stroke.

  As shown in FIG. 8, the control device 50 controls the fuel injection nozzle 10b to divide one fuel injection into main injection and sub-injection, and execute the sub-injection at the latter stage of combustion by the main injection. (Sub-injection combustion is started before the amount of heat generated by main-injection combustion becomes zero), and the occurrence of incomplete combustion is suppressed, that is, the generation of soot due to incomplete combustion is suppressed. Thereby, even if the particulate collection capacity of the particulate filter 22 is low, the amount of soot discharged to the outside is suppressed.

  From here, the flow of control for determining which of the controls shown in FIGS. 4B to 4D is executed will be described with reference to the flow shown in FIG.

  First, the flow shown in FIG. 9 is the low pressure EGR region in step S100, the decrease amount ΔL per unit time of the engine load is larger than the specified amount in step S110, and the oxygen concentration C in the combustion chamber 10b in step S120. This is started by detecting that the deviation D between the actual value Cr and the target value Ct is larger than the specified value, that is, that the engine load has decreased in the low pressure EGR region.

  In step S <b> 130, the control device 50 determines whether or not the amount of soot collected by the particulate filter 22 is less than a specified amount. If not, the process proceeds to step S140. Otherwise, the process proceeds to step S150.

  In step S140, the control device 50 increases the opening amount of the high-pressure EGR valve 16a and increases the EGR amount by the high-pressure EGR passage 16 (see FIG. 4B).

  On the other hand, if it is determined in step S130 that the amount of soot trapped by the particulate filter 22 is large, in step S150, the controller 50 determines whether or not the remaining processing capacity of the NOx catalyst 24 is greater than the specified capacity, that is, the remaining NOx. It is determined whether or not the processable amount is greater than the prescribed amount. If larger, the process proceeds to step S160. Otherwise, the process proceeds to step S170.

  In step S160, the control device 50 corrects the opening amount of the low pressure EGR valve 18a by increasing (see FIG. 4C).

  On the other hand, if it is determined in step S150 that the processing capacity of the NOx catalyst 24 is small, in step S170, the controller 50 increases the opening amount of the high pressure EGR valve 16a, increases the EGR amount by the high pressure EGR passage 16, and increases the fuel. Increase the number of split injections.

  In step S180, the control device 50 determines whether or not the deviation D between the actual value Cr of the oxygen concentration C in the combustion chamber 10b and the target value Ct is substantially zero. If almost zero, the process proceeds to step S190. Otherwise, the process returns to step S130.

  In step S190, the control device 50 resets the control to the normal low pressure EGR region. Then proceed to return and return to start.

  According to this embodiment, when the load of the diesel engine 10 decreases in the low pressure EGR region, the oxygen concentration in the combustion chamber 10a can be immediately reduced. This suppresses an increase in the amount of NOx generated immediately after the load decreases. Further, it can be executed in consideration of the state of the particulate filter 22 and the NOx catalyst 23, that is, the amount of soot and NOx discharged to the outside is suppressed.

  Although the present invention has been described with reference to the above-described embodiment, the present invention is not limited to this.

For example, in the case of the above-described embodiment, the control related to the time chart shown in FIG. 4C is performed when the load of the diesel engine 10 decreases in the low pressure EGR region, and the total EGR amount of the exhaust gas based on the load value of the reduction destination. the temporarily and increasing correction, although temporarily increase correction of the opening degree of the low-pressure EGR valve 18a according to the increase correction, therewith, the dose may be increased to opening degree of the high-pressure EGR valve 18a. However, since the total EGR amount of the exhaust gas is corrected to increase, if the opening amount of the high pressure EGR valve 18a is excessively increased, the oxygen concentration in the combustion chamber 10a is greatly reduced, and soot is generated in large quantities.

  In addition, as shown in FIG. 9, the control of the above-described embodiment is for the diesel engine 10 that can divide and inject fuel into the combustion chamber 10a in consideration of the processing capacity of the NOx catalyst 24, but includes a NOx catalyst. The present invention is also applicable to diesel engines that do not execute split injection.

In this case, the control flow is similar to the flow shown in FIG. 9 differs from the flow shown in FIG. 9 in that there is no step (S150) for determining the processing capacity of the NOx catalyst 24 and step (S170) for increasing the opening amount of the high-pressure EGR valve 16a and executing sub-injection. Is a point.

  The flow shown in FIG. 10 will be described. This flow is the low pressure EGR region in step S300, the reduction amount ΔL per unit time of the engine load is larger than the specified amount in step S310, and the oxygen in the combustion chamber in step S320. The process is started by detecting that the deviation D between the actual value Cr of the concentration C and the target value Ct is larger than the specified value, that is, that the engine load has decreased in the low pressure EGR region.

  In step S330, the control device determines whether or not the amount of soot collected by the particulate filter is less than a specified amount. If not, the process proceeds to step S340. Otherwise, the process proceeds to step S350.

  In step S340, the control device increases the opening amount of the high pressure EGR valve, and increases the EGR amount through the high pressure EGR passage.

On the other hand, if it is determined in step S330 that the particulate filter has a large amount of soot trapped, in step S350, the control device increases and corrects the opening amount of the low pressure EGR valve.
In step S360, the control device determines whether or not the deviation D between the actual value Cr of the oxygen concentration C in the combustion chamber and the target value Ct is substantially zero. If almost zero, the process proceeds to step S370. Otherwise, the process returns to step S330.

  In step S370, the control device resets the control to the normal low pressure EGR region. Then proceed to return and return to start.

Furthermore, in a diesel engine that does not have a NOx catalyst and can perform split injection, if you want to suppress NOx as much as possible even at the expense of some fuel consumption, as a reference example of the present invention, instead of increasing the opening amount of the low pressure EGR valve, While increasing the opening amount of the EGR valve, the secondary injection may be executed.

  In this case, the control flow is similar to the flow shown in FIG. The difference from the flow shown in FIG. 9 is that there is no step (S150) for determining the processing capacity of the NOx catalyst 24 and step (S160) for correcting the opening amount of the low pressure EGR valve 18a.

  The flow shown in FIG. 11 will be described. This flow is the low pressure EGR region in step S500, the reduction amount ΔL per unit time of the engine load is larger than the specified amount in step S510, and the oxygen in the combustion chamber in step S520. The process is started by detecting that the deviation D between the actual value Cr of the concentration C and the target value Ct is larger than the specified value, that is, that the engine load has decreased in the low pressure EGR region.

  In step S530, the control device determines whether or not the amount of soot collected by the particulate filter is less than a specified amount. If not, the process proceeds to step S540. Otherwise, the process proceeds to step S550.

  In step S540, the control device increases the opening amount of the high pressure EGR valve, and increases the EGR amount through the high pressure EGR passage.

On the other hand, if it is determined in step S530 that the amount of soot trapped by the particulate filter is large, in step S550, the control device increases the opening amount of the high-pressure EGR valve and executes sub-injection.
In step S560, the control device determines whether or not the deviation D between the actual value Cr of the oxygen concentration C in the combustion chamber and the target value Ct is substantially zero. If almost zero, the process proceeds to step S570. Otherwise, the process returns to step S530.

  In step S570, the control device resets the control to the normal low pressure EGR region. Then proceed to return and return to start.

  As described above, the present invention communicates an exhaust turbocharger and a low-pressure exhaust gas by communicating the exhaust passage on the downstream side of the turbine of the turbocharger with the intake passage on the upstream side of the compressor of the turbocharger. In an engine having a low-pressure EGR passage that recirculates gas and a high-pressure EGR passage that recirculates high-pressure exhaust gas through an exhaust passage on the upstream side of the turbine and an intake passage on the downstream side of the compressor, exhaust gas in the low-pressure EGR passage When the engine load is reduced while the engine is recirculating, the oxygen concentration in the combustion chamber can be immediately reduced to suppress the generation of NOx. Therefore, it may be suitably used in the field of vehicles equipped with diesel engines.

10 Internal combustion engine (diesel engine)
12 Exhaust passage 14 Intake passage 16 High pressure EGR passage 18 Low pressure EGR passage 20 Turbocharger 20a Turbine 20b Compressor

Claims (4)

An exhaust turbocharger comprising a turbine disposed in the exhaust passage and a compressor disposed in the intake passage; a low-pressure EGR passage communicating the exhaust passage downstream of the turbine and the intake passage upstream of the compressor; A high-pressure EGR passage that communicates an exhaust passage on the upstream side of the turbine with an intake passage on the downstream side of the compressor, and a low-pressure EGR that is provided in the low-pressure EGR passage and adjusts the recirculation amount of the exhaust gas that passes through the passage. An amount adjusting means; a high pressure EGR amount adjusting means provided in the high pressure EGR passage for adjusting a recirculation amount of exhaust gas passing through the passage; and a particulate matter provided in the exhaust passage for collecting soot in the exhaust gas. A method for controlling exhaust gas recirculation of a compression ignition internal combustion engine having a filter,
An oxygen concentration control step of controlling at least one of the low pressure EGR amount adjusting means and the high pressure EGR amount adjusting means to control the oxygen concentration in the combustion chamber to a concentration corresponding to the load of the internal combustion engine;
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
As the oxygen concentration control step,
When the particulate collection capacity of the particulate filter is lower than the predetermined collection capacity, the distribution ratio of the recirculation amount by the low pressure EGR passage and the recirculation amount by the high pressure EGR passage to the total exhaust gas recirculation amount is a predetermined ratio. Performing a first step of recirculating exhaust gas at a first distribution ratio;
When the soot collection capacity of the particulate filter is higher than a predetermined collection capacity, a second step of recirculating the exhaust gas at a second distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than the first distribution ratio is performed. As well as
When the first step is executed as the oxygen concentration control step, at the start of the execution of the first step, the total exhaust gas recirculation amount based on the load value to be decreased is temporarily increased and corrected according to the increase correction. A method for controlling exhaust gas recirculation of an internal combustion engine, comprising controlling an EGR amount adjusting means . A method for controlling exhaust gas recirculation of an internal combustion engine according to claim 1,
In the case where a NOx treatment device that suppresses the discharge of NOx to the outside by treating NOx in the exhaust gas is provided,
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
When the particulate collection capacity of the particulate filter is lower than the predetermined collection capacity and the NOx treatment capacity of the NOx treatment device is lower than the predetermined treatment capacity, the oxygen concentration control step is more than the first distribution ratio. Performing a third step of recirculating the exhaust gas at a third distribution ratio in which the ratio of the recirculation amount by the high-pressure EGR passage is high;
A method for controlling exhaust gas recirculation of an internal combustion engine, wherein a fuel injection control step of increasing the number of fuel split injections is executed. An exhaust turbocharger comprising a turbine disposed in the exhaust passage and a compressor disposed in the intake passage; a low-pressure EGR passage communicating the exhaust passage downstream of the turbine and the intake passage upstream of the compressor; A high-pressure EGR passage that communicates an exhaust passage on the upstream side of the turbine with an intake passage on the downstream side of the compressor, and a low-pressure EGR that is provided in the low-pressure EGR passage and adjusts the recirculation amount of the exhaust gas that passes through the passage. An amount adjusting means; a high pressure EGR amount adjusting means provided in the high pressure EGR passage for adjusting a recirculation amount of exhaust gas passing through the passage; and a particulate matter provided in the exhaust passage for collecting soot in the exhaust gas. A system for controlling exhaust gas recirculation of a compression ignition internal combustion engine having a filter,
Oxygen concentration control means for controlling at least one of the low pressure EGR amount adjusting means and the high pressure EGR amount adjusting means to control the oxygen concentration in the combustion chamber to a concentration corresponding to the load of the internal combustion engine;
A soot collection ability detecting means for detecting soot collection ability of the particulate filter,
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
The oxygen concentration control means is
When the soot collection capacity of the particulate filter detected by the soot collection capacity detection means is lower than a predetermined collection capacity, the recirculation quantity through the low pressure EGR passage and the recirculation quantity through the high pressure EGR passage with respect to the total exhaust gas recirculation quantity The first control is performed to recirculate the exhaust gas at a first distribution ratio in which the distribution ratio is a predetermined ratio;
When the soot collection capacity of the particulate filter detected by the soot collection capacity detecting means is higher than the predetermined collection capacity, the ratio of the reflux amount by the high pressure EGR passage is higher than the first distribution ratio. While executing the second control to recirculate the exhaust gas,
When the oxygen concentration control means executes the first control, at the start of the execution of the first control, the total exhaust gas recirculation amount based on the load value to be decreased is temporarily increased and corrected according to the increase correction. A system for controlling exhaust gas recirculation of an internal combustion engine, which controls an EGR amount adjusting means . A system for controlling exhaust gas recirculation of an internal combustion engine according to claim 3,
A NOx treatment device that suppresses discharge of the NOx to the outside by treating NOx in the exhaust gas;
NOx processing capacity detecting means for detecting the processing capacity of the NOx processing device;
Fuel injection control means for controlling fuel injection into the combustion chamber,
When the load of the internal combustion engine decreases while the exhaust gas is recirculated in the low pressure EGR passage,
The soot collection capability of the particulate filter detected by the soot collection capability detection means is lower than the predetermined collection capability, and the NOx treatment capability of the NOx treatment device detected by the NOx treatment capability detection means is lower than the predetermined treatment capability. In this case, the oxygen concentration control means executes a third control for recirculating the exhaust gas at a third distribution ratio in which the ratio of the recirculation amount through the high-pressure EGR passage is higher than the first distribution ratio,
A system for controlling exhaust gas recirculation in an internal combustion engine , wherein the fuel injection control means increases the number of fuel split injections .

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