JP2007218140A - Exhaust emission control device and exhaust emission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit clogging of an addition injector adding fuel to exhaust gas. <P>SOLUTION: ECU 20 estimates NOx quantity absorbed by an storage reduction type NOx catalyst from a history of a operation condition of an engine, and makes fuel injected from the addition injector 17 for a predetermined period of time when the estimated NOx quantity reaches a predetermined value. Adding timing is controlled to complete addition of fuel at completion timing when exhaust in a specific cylinder in which the addition injector 17 is arranged in an exhaust path thereof is completed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine and an exhaust gas purification method therefor.

  An exhaust gas recirculation device is used to reduce NOx (nitrogen oxide) discharged from an internal combustion engine such as a gasoline engine. The exhaust gas recirculation device returns a part of the exhaust gas to the intake side to lower the combustion temperature in the cylinder and reduce the amount of NOx generated. However, the exhaust gas recirculation device alone cannot meet the exhaust gas regulations, and therefore, for example, nitrogen oxides in the exhaust gas are removed by using an NOx storage reduction catalyst together. Similarly, PM (exhaust gas particulate matter) is also removed by a filter or the like in order to comply with future exhaust gas regulations.

  Since a gasoline engine or the like is in a lean combustion state during normal operation, NOx is continuously adsorbed on the NOx storage reduction catalyst, and as a result, the NOx adsorption capacity of the NOx catalyst is saturated. Therefore, fuel is added to the exhaust gas to reduce the oxygen concentration of the exhaust gas, and NOx stored in the NOx storage reduction catalyst is released to recover the NOx adsorption capacity.

  In Patent Document 1, when fuel is added to the exhaust gas by the addition nozzle, the addition nozzle is arranged on the side opposite to the exhaust suction port of the exhaust gas recirculation device so that the added fuel amount does not enter the exhaust gas recirculation device. It is described to do.

Japanese Patent Application Laid-Open No. H10-228561 describes as a problem to suppress the generation of deposits at the tip of an injection nozzle that adds fuel to exhaust gas. In paragraph 0066 of Patent Document 2, when the crankshaft rotates by a predetermined crank angle θA from the compression top dead center TDC of the fourth cylinder, fuel injection is started from the injection nozzle, and the compression top dead center TDC of the third cylinder is started. That the fuel injection is temporarily stopped when the crankshaft is rotated by a predetermined crank angle θB, and the fuel injection is started again when the crankshaft is rotated by the predetermined crank angle θA from the compression top dead center TDC of the fourth cylinder. Has been. As described above, by stopping the fuel injection during the exhaust period of the third cylinder, the injected fuel adheres to the soot in the exhaust gas to increase the particle size. It is prevented that deposits are generated in the injection hole by moving in the direction of the injection nozzle by the exhaust.
JP 2001-280125 A JP 2003-201836 A

  The invention of Patent Document 1 does not control the fuel addition timing of the addition nozzle. The invention of Patent Document 2 controls the fuel injection timing of the injection nozzle, but the fuel is injected even after the exhaust of the fourth cylinder provided with the injection nozzle is completed. The fuel concentration remaining in the vicinity of the injection nozzle cannot be lowered.

  The subject of this invention is suppressing the clogging of the addition injector which adds a fuel to exhaust gas.

  The exhaust emission control device of the present invention has an exhaust manifold connected to an exhaust port of each cylinder of a multi-cylinder internal combustion engine, an exhaust path of an exhaust port of a specific cylinder among the multi-cylinders, or in the vicinity of the exhaust port. And an addition injector for adding fuel and other reducing agents to the exhaust, an exhaust purification means for removing a specific component of exhaust exhausted from the exhaust manifold and collecting exhaust gas particulate matter, and the addition injector Control means for controlling the addition timing of the addition injector such that the addition of fuel is completed within the exhaust period of the specific cylinder arranged in the exhaust path.

  According to the present invention, since the addition of fuel and other reducing agents is completed within the exhaust period of the specific cylinder in which the additive injector is disposed in the exhaust path, the fuel and other reducing agents injected from the additive injector are It is possible to reduce the amount of fuel and other reducing agents that are sufficiently scavenged by the exhaust of a specific cylinder and blown back to the vicinity of the addition injector by the exhaust of other cylinders. Thereby, it can suppress that fuel and other reducing agents adhere to the jet outlet of an addition injector, and a jet nozzle is blocked.

  The additive injector may be provided directly in the exhaust port, or may be provided in the vicinity of the exhaust port as long as the material added by the additive injector is sufficiently scavenged by the exhaust of a specific cylinder.

  In the exhaust emission control device of the present invention, the control means controls the addition timing of the addition injector so that the addition of fuel or other reducing agent is completed a predetermined crank rotation angle before the exhaust timing of the specific cylinder. To do.

  With this configuration, the exhaust can be performed for a predetermined time even after the addition is completed. As a result, the remaining fuel and other reducing agents in the vicinity of the addition injector can be sufficiently scavenged, so that the remaining fuel and other reducing agents can adhere to the injection port of the addition injector and clog the injection port. Can be suppressed.

  In the exhaust emission control device of the present invention, the control means sets a timing at which an exhaust flow rate equal to or higher than a predetermined value is obtained as an addition end timing based on data indicating a relationship between the exhaust flow rate of the specific cylinder and the crank rotation angle.

  With this configuration, when the exhaust flow rate of a specific cylinder is greater than or equal to a predetermined value can be set as the addition end timing, the injected fuel and other reducing agents can be sufficiently scavenged by the exhaust of the specific cylinder. It is possible to suppress clogging of the injection port of the additive injector.

In the exhaust emission control device of the present invention, the control means starts adding fuel and other reducing agents before the exhaust of the specific cylinder is started.
By controlling the addition start timing in this manner, injection can be performed for a sufficient period of time, so that a sufficient amount of fuel or other reducing agent can be injected from the addition injector.

  According to the present invention, the fuel and other reducing agent injected from the additive injector can be sufficiently scavenged by the exhaust of the specific cylinder, so that the injection port of the injection injector can be prevented from being clogged.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an internal combustion engine according to an embodiment. FIG. 1 shows a 4-cylinder diesel engine and an exhaust purification device.

  1, the engine 11 has four cylinders 12a to 12d, exhaust ports 13a to 13d of the cylinders 12a to 12d, and fuel injection valves 14a to 14d for injecting fuel into the combustion chambers. In the following description, the first cylinder 12a, the second cylinder 12b, the third cylinder 12c, and the fourth cylinder 12d are referred to in order from the rightmost cylinder as viewed from the front of FIG.

  An exhaust manifold 15 is connected to the exhaust ports 13 a to 13 d of the cylinders 12 a to 12 d of the engine 11, and an exhaust collecting pipe 16 is connected to the exhaust port of the exhaust manifold 15. An addition injector 17 for adding fuel (or other reducing agent) to the exhaust gas is disposed in the exhaust path of the exhaust port 13d of the fourth cylinder 12d. Fuel is supplied to the addition injector 17 from the fuel pump 18 through the fuel pipe 19. The additive injector 17 serves to regenerate an NOx storage reduction catalyst described later by injecting fuel. The fuel addition timing of the addition injector 17 is controlled by an engine control electronic control unit (hereinafter referred to as ECU) 20.

  The exhaust outlet side of the exhaust collecting pipe 16 is connected to the turbine 21b of the turbocharger 21, and the turbine 21b is driven by the exhaust gas discharged from the exhaust collecting pipe 16 to drive the compressor 21a connected to the turbine 21b. While increasing the pressure of the intake air, the exhaust gas is discharged to the exhaust pipe 22. A filter 23 made of an NOx storage reduction catalyst or the like is connected to the exhaust pipe 22.

  The NOx storage reduction catalyst absorbs NOx in the exhaust gas when the oxygen concentration of the inflowing exhaust gas is equal to or higher than a predetermined value, and releases the absorbed NOx when the oxygen concentration of the exhaust gas becomes lower than a predetermined value. ing. The NOx storage reduction catalyst needs to remove the sulfur oxide because the NOx purification rate is lowered by the sulfur oxide generated by burning the sulfur content of the fuel. Sulfur oxide is removed by setting the temperature of the NOx storage reduction catalyst to a predetermined temperature that is significantly higher than the NOx release / reduction and setting the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to the stoichiometric air-fuel ratio. Thus, the purification ability of the catalyst can be recovered.

Therefore, the nitrogen oxide and sulfur oxide adsorbed by the NOx storage reduction catalyst can be removed by controlling the fuel addition period of the addition injector 17 and the number of repetitions thereof.
An exhaust gas recirculation pipe 24 for returning a part of the exhaust gas to the intake side is connected to an exhaust port on the right end side (as viewed from the front of FIG. 1) of the exhaust manifold 15. An exhaust gas recirculation cooler 25 for cooling the exhaust gas and an exhaust gas recirculation valve 26 for controlling the exhaust gas flow rate are provided in the middle of the exhaust gas recirculation pipe 24.

  A filter 28 is connected to the input side of the intake pipe 27, and the compressor 21a of the turbocharger 21 described above is connected to the downstream side thereof. The intake air boosted by the compressor 21 a is cooled by the intercooler 29 and supplied to the intake manifold 31 through the intake throttle valve 30. The intake manifold 31 is also supplied with exhaust gas circulated by the exhaust gas recirculation pipe 24.

  Although not shown in the figure, the ECU 20 executes a calculation process such as an engine load and an engine speed, a fuel injection control process of the engine 11, a control of the intake throttle valve 30, an addition timing control process of the addition injector 17, and the like. It has a ROM that stores a program and data indicating the crank angle at the start and end of exhaust of each cylinder.

  The ECU 20 calculates the engine load and the engine speed based on a signal indicating the accelerator depression angle output from the accelerator opening sensor 32, a signal output every time the crankshaft rotates by a certain angle from the crank angle sensor 33, and the like. To do. Further, the engine operating state is determined based on the engine load and the engine speed. Then, the NOx amount absorbed by the NOx storage reduction catalyst is estimated from the history of the engine operating state, and when the estimated NOx amount reaches a predetermined value, fuel is injected from the addition injector 17 for a predetermined period to store the NOx storage reduction type. Nitrogen oxide adsorbed on the catalyst is reduced. The ECU 20 finishes the addition of the fuel from the addition injector 17 at a predetermined time before the end timing when the specific cylinder (fourth cylinder 12d) in which the addition injector 17 is disposed in the exhaust path ends the exhaust or the end timing of the exhaust. So that the addition timing is controlled.

The exhaust manifold 15, the exhaust recirculation pipe 24, the filter 23, the CPU of the ECU 20, and the like are collectively referred to as an exhaust purification device.
Hereinafter, the addition timing control process in the ECU 20 will be described with reference to the flowchart of FIG. The following processing is executed by a CPU (not shown) of the ECU 20.

  First, it is determined whether or not the addition condition is satisfied (FIG. 2, S11). The CPU of the ECU 20 calculates the engine load and the engine speed from the signal indicating the accelerator depression angle and the signal indicating the change in the crank rotation angle, and determines the operating state of the engine. Then, the NOx amount adsorbed on the NOx storage reduction catalyst is estimated from the history of the operating state of the engine, and it is determined whether or not the addition condition is satisfied based on whether or not the adsorption amount has reached a predetermined value. If the addition condition is not satisfied (S11, NO), the process is terminated there.

When the addition condition is satisfied (S11, YES), the addition start timing is calculated (S12). The calculation of the addition start timing is performed as follows, for example.
The exhaust start timing and end timing of each cylinder and the fuel addition period required to restore the characteristics of the NOx storage reduction catalyst are stored in advance in a ROM or the like, and the CPU of the ECU 20 controls the addition injector 17 to the exhaust path. The start timing and end timing of the exhaust of a specific cylinder arranged in the engine are acquired from the ROM, and the timing before the exhaust timing of the specific cylinder or a predetermined time before the end of exhaust is set as the fuel addition end timing To do.

  Specifically, a current crank rotation angle (hereinafter referred to as a crank angle) is calculated from a change in the crank rotation angle detected by the crank angle sensor 33, and a specific cylinder (implementation) in which the addition injector 17 is disposed from the ROM. In this embodiment, the crank angle at which exhaust of the fourth cylinder 12d) ends is acquired, and the crank angle at which exhaust of that cylinder ends or the crank angle before the crank angle at which exhaust ends ends is calculated as the addition end timing. . Then, the crank angle before the required addition period is calculated based on the addition end timing, and the calculated crank angle is set as the addition start timing.

Next, the addition of fuel is started at the addition start timing obtained by the above calculation (S13).
Next, when the fuel injection starts from the addition injector 17 and the addition end timing is reached, the addition ends (S14).

Here, the fuel addition timing of the embodiment and the conventional fuel addition timing will be described with reference to FIG.
FIG. 3 shows the fuel concentration in the vicinity of the addition injector 17 and the exhaust start timing of a specific cylinder in the control method of the addition timing of the embodiment in which the fuel addition end timing is synchronized with the exhaust end timing of the fourth cylinder 12d. It is the figure which compared the fuel concentration of the addition injector 17 vicinity in the control method of the conventional addition timing which synchronized the addition start timing of the fuel.

  The vertical axis in FIG. 3 indicates the fuel fraction in the vicinity of the injector 17, and the horizontal axis indicates the crank angle. The characteristic indicated by the solid line in FIG. 3 indicates the fuel concentration fraction in the vicinity of the addition injector 17 when the addition timing control of the embodiment is performed, and the characteristic indicated by the dotted line is the addition when the conventional addition timing control is performed. The fuel concentration fraction in the vicinity of the injector 17 is shown. Further, the portion surrounded by the letters “˜cylinder exhaust” described in the middle of FIG. 3 represents the opening timing of the exhaust valve of the cylinder.

  Now, when the addition injector 17 is disposed in the exhaust path of the exhaust port 13d of the fourth cylinder 12d, in the addition timing control method of the embodiment, the crank angle at which the exhaust of the fourth cylinder 12d ends (FIG. 3). 1440 deg) is set as the addition end timing, and it is necessary to release a predetermined fuel addition period (NOx adsorbed by the NOx storage reduction catalyst) with reference to the crank angle at which the exhaust of the fourth cylinder 12d ends. The crank angle (900 deg in FIG. 3) before the fuel addition period) is obtained, and the crank angle is set as the addition start timing.

In this case, the maximum fuel fraction in the vicinity of the addition injector 17 is about 3.5% (weight percent).
On the other hand, in the conventional addition timing control method, the fuel addition is started at the crank angle at which the exhaust of the fourth cylinder 12d is started, and the addition is terminated when a predetermined fuel addition period elapses. is doing.

  In this case, as shown by a dotted line in FIG. 3, the maximum fuel fraction in the vicinity of the addition injector 17 is 0.1, and this value is 0.035 when the addition timing control of the embodiment is performed. It is much larger than that. This is because fuel is added even after the exhaust of the fourth cylinder 12d is completed, so that the fuel injected by the exhaust gas exhausted from the other cylinders (the second cylinder and the first cylinder in FIG. 3). Is presumed to be blown back in the vicinity of the addition injector 17.

  Therefore, by controlling the addition timing so that the addition of fuel is completed at the exhaust end timing of the fourth cylinder 12d in which the addition injector 17 is disposed in the exhaust path, the exhaust from the addition injector 17 is caused by the exhaust of the fourth cylinder 12d. Most of the injected fuel can be scavenged. As a result, the amount of fuel blown back to the vicinity of the addition injector 17 by the exhaust of the other cylinders can be greatly reduced, so that the blown back fuel adheres to the exhaust port of the addition injector 17 and the exhaust port is clogged. Can be suppressed.

FIG. 4 is a diagram showing a simulation result showing a change in the exhaust flow rate with respect to the crank angle of the fourth cylinder 12d. The vertical axis in FIG. 4 indicates the exhaust flow rate, and the horizontal axis indicates the crank angle.
The exhaust flow rate of the fourth cylinder 12d has a peak value of about 0.032 (kg / s) at the start of exhaust, and immediately after that, after the flow rate has decreased to almost 0, the flow rate increases again, and the exhaust angle ends near a crank angle of 1440 deg. The exhaust gas flow rate is close to zero.

  Therefore, even if the addition end timing is set in synchronization with the exhaust end timing of the fourth cylinder 12d, the fuel injected from the addition injector 17 can be sufficiently scavenged, but the exhaust flow rate before a predetermined time before the exhaust end timing is reduced. It is preferable to set the fuel addition end timing when the crank angle is greater than 0 or greater than or equal to a predetermined value from the viewpoint of surely scavenging the injected fuel.

  The characteristic of FIG. 4 showing the change in the exhaust flow rate with respect to the crank angle is considered to change depending on the shape of the exhaust manifold 15, the shape of the exhaust passage, etc. Therefore, a crank angle that provides a desired exhaust flow rate is added according to individual design conditions. What is necessary is just to set as an end timing.

  According to the above-described embodiment, the addition timing is controlled so that the addition of fuel is completed at the end of exhausting a specific cylinder in which the addition injector 17 is disposed in the exhaust path or a predetermined time before the end of exhausting. Thus, the fuel injected from the addition injector 17 is sufficiently scavenged by the exhaust of a specific cylinder, and the fuel blown back to the vicinity of the addition injector 17 by the exhaust of other cylinders can be greatly reduced. As a result, it is possible to prevent the added fuel from remaining in the vicinity of the added injector 17 and the fuel from adhering to the injection port and clogging the injection port.

The present invention is not limited to the embodiment described above, and may be configured as follows, for example.
(1) The present invention can be applied not only to a four-cylinder internal combustion engine but also to an engine having another number of cylinders. Further, the addition is not limited to the case of synchronizing with the end of exhaust of the fourth cylinder, and the addition may be terminated a predetermined time before the end of exhaust of the cylinder disposed in the exhaust path or at the end.
(2) The addition timing may be controlled based not only on the crank angle of the engine but also on other data such as time data indicating the exhaust timing of the cylinder and sensor detection data.
(3) Instead of the NOx storage reduction catalyst, the present invention can also be applied to, for example, PM (particulate matter) regeneration or S (sulfur) regeneration in an exhaust purification device equipped with a DPF (diesel particulate filter). In addition, an additive injector to which a reducing agent other than fuel is added can also be applied.

It is a figure which shows the structure of the internal combustion engine of embodiment. It is a flowchart which shows a fuel addition timing control process. It is a figure which shows the fuel concentration of the addition injector vicinity. It is a figure which shows the relationship between the exhaust flow volume of a 4th cylinder, and a crank angle.

Explanation of symbols

11 Engine 12a-12d 1st-4th cylinder 13a-13d Exhaust port 15 Exhaust manifold 16 Exhaust collecting pipe 17 Addition injector 18 Fuel pump 20 ECU
22 exhaust pipe 23 filter 24 exhaust recirculation pipe

Claims (6)

An exhaust manifold connected to the exhaust port of each cylinder of a multi-cylinder internal combustion engine;
An addition injector that is disposed in the exhaust path of an exhaust port of a specific cylinder of the multi-cylinder or in the vicinity of the exhaust port and adds fuel or other reducing agent to the exhaust,
Exhaust purification means for removing specific components of exhaust exhausted from the exhaust manifold and collecting exhaust gas particulate matter;
An exhaust emission control device comprising control means for controlling the addition timing of the addition injector so that the addition of fuel or other reducing agent is completed within the exhaust period of the specific cylinder in which the addition injector is disposed in the exhaust path. .   2. The exhaust gas purification according to claim 1, wherein the control means controls the addition timing of the addition injector so that the addition of fuel or other reducing agent is completed before a predetermined crank rotation angle from the exhaust end timing of the specific cylinder. apparatus.   3. The exhaust gas purification according to claim 1, wherein the control unit sets a timing at which an exhaust gas flow rate equal to or higher than a predetermined value is obtained as an addition end timing based on data indicating a relationship between an exhaust gas flow rate of the specific cylinder and a crank rotation angle. apparatus.   The exhaust purification device according to claim 1, 2 or 3, wherein the catalyst is an NOx storage reduction catalyst.   The exhaust emission control device according to claim 1 or 2, wherein the control means starts addition of fuel or other reducing agent before the exhaust of the specific cylinder is started. An exhaust gas purification method for an exhaust gas purification apparatus having an addition injector that is disposed in an exhaust path of an exhaust port of a specific cylinder in a multi-cylinder internal combustion engine and adds fuel or other reducing agent to exhaust gas,
An exhaust purification method for controlling the addition timing of the addition injector so that the addition of fuel or other reducing agent is completed within the exhaust period of the specific cylinder in which the addition injector is disposed in the exhaust path.

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