JP2008038806A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of recovering sulfur poisoning of a storage reduction-type NOx catalyst in an exhaust emission control device of an internal combustion engine, even when load of the internal combustion engine is low. <P>SOLUTION: In the exhaust emission control device of the internal combustion engine having a plurality of cylinders, and being capable of performing a cylinder cut-off operation for cutting off the number of cylinders to be combusted, the device includes the storage reduction-type NOx catalyst storing NOx and reducing the stored NOx by a reducing agent, a means for recovering sulfur poisoning performing the cylinder cut-off operation when performing recovering sulfur poisoning of the storage reduction-type NOx catalyst (S103). By the cylinder cut-off operation, in a cylinder in which fuel is combusted, a fuel supply rate increases and combustion gas with high temperature and a low air-fuel ratio is discharged, thereby a temperature fall of the storage reduction-type NOx catalyst can be reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. This NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the NOx occluded when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present.

  By the way, the sulfur component contained in the fuel is occluded in the NOx catalyst in the same manner as NOx. The sulfur component occluded in this way is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning. Since the NOx purification rate of the NOx catalyst is reduced by this sulfur poisoning, it is necessary to perform a sulfur poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This sulfur poisoning recovery process is performed by raising the temperature of the NOx catalyst and flowing exhaust gas having a stoichiometric or rich air-fuel ratio to the NOx catalyst.

  Here, in the V-type engine, when sulfur poisoning is recovered, control is performed so that the air-fuel ratio to the cylinder of one bank is made rich or the stoichiometric air-fuel ratio and the air-fuel ratio to the cylinder of the other bank is made lean. A technique is known (for example, refer to Patent Document 1).

According to this technique, an unburned substance is generated in the exhaust gas from the cylinder of one bank, and the sulfur component released from the NOx storage reduction catalyst is reduced by the unburned substance. At this time, the lean operation of the other bank suppresses the fuel consumption of the entire internal combustion engine, and the sulfur poisoning recovery process can be performed while suppressing the fuel consumption of the entire internal combustion engine.
Japanese Patent Laid-Open No. 9-291814 JP-A-8-61052 JP-A-8-189388

However, recovery from sulfur poisoning requires high temperatures and low air-fuel ratios, and the NOx catalyst atmosphere must be maintained in this state for several minutes. Here, when the load on the internal combustion engine is low, the temperature of the exhaust gas discharged from the internal combustion engine is low and the air-fuel ratio of the exhaust gas becomes lean. Under such operating conditions, recovery from sulfur poisoning had to be abandoned.

Further, even if the sulfur poisoning recovery is started in a state where the load of the internal combustion engine is relatively high, it becomes difficult to continue the sulfur poisoning recovery if the load becomes low on the way. If the sulfur poisoning recovery process is stopped in such a case, it is necessary to perform the sulfur poisoning recovery process again, so that the amount of fuel consumption increases and the fuel consumption deteriorates. Furthermore, if the sulfur poisoning recovery process cannot be executed for a long period of time, the NOx purification rate will decrease.

The present invention has been made in view of the above problems, and in an exhaust purification device for an internal combustion engine, even when the load on the internal combustion engine is low, the sulfur poisoning of the NOx storage reduction catalyst is recovered. The purpose is to provide technology that can be used.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
In an exhaust emission control device for an internal combustion engine that has a plurality of cylinders and is capable of performing a reduced-cylinder operation that reduces a cylinder that burns fuel,
A NOx storage reduction catalyst in which NOx is stored and NOx stored is reduced by a reducing agent;
Sulfur poisoning recovery means for performing the reduced cylinder operation when performing sulfur poisoning recovery of the NOx storage reduction catalyst;
It is characterized by providing.

  Here, the internal combustion engine burns fuel in all cylinders (all cylinder operation), or stops combustion of fuel in any cylinder and burns fuel in the remaining cylinders (reduced cylinder operation). It is a possible internal combustion engine.

  Here, when the reduced-cylinder operation is performed, no torque is generated from a cylinder that stops the combustion of fuel (hereinafter referred to as a stopped cylinder), and therefore the torque generated from the entire internal combustion engine is reduced. In contrast, by increasing the torque generated in the cylinder burning the fuel (hereinafter referred to as the combustion cylinder), it is possible to eliminate the decrease in the torque of the entire internal combustion engine. By supplying more fuel to the combustion cylinder, the torque generated in the combustion cylinder can be increased. That is, the reduction in torque of the stopped cylinder can be supplemented by the combustion cylinder. For example, when the torque of the internal combustion engine as a whole is reduced by performing the reduced cylinder operation, the driver depresses the accelerator pedal, so that the amount of fuel supplied to the combustion cylinder is increased.

  In this way, by supplying more fuel to the combustion cylinder, the air-fuel ratio in the combustion cylinder is lowered and the combustion temperature is raised. That is, the air-fuel ratio and temperature of the exhaust can be brought close to a state suitable for sulfur poisoning recovery. Thereby, since the driving | operation area | region which can perform recovery | restoration of sulfur poisoning can be expanded, the deterioration of a fuel consumption can be suppressed.

The sulfur poisoning recovery means includes a number of reduced cylinders so that the temperature of the exhaust gas discharged from the internal combustion engine and the air-fuel ratio of the exhaust gas are in a state necessary for recovery of sulfur poisoning of the NOx storage reduction catalyst. May be determined.

In the present invention, the internal combustion engine is a V-type 8-cylinder internal combustion engine that performs continuous combustion at least once at intervals of 90 degrees of crank angle.
The sulfur poisoning recovery means can stop the combustion in half of the cylinders so that combustion is performed at intervals of 180 degrees of crank angle when recovery from sulfur poisoning is performed.

  A large displacement engine such as a V-type 8-cylinder internal combustion engine is often used at a lower load because the maximum generated torque is larger than that of a small displacement engine. Therefore, it is often operated with a lean air-fuel ratio. Therefore, it is often more difficult for a large displacement engine to perform a sulfur poisoning recovery process than a small displacement engine.

  Here, in a V-type 8-cylinder internal combustion engine that continuously burns at least once at crank angle intervals of 90 degrees, stable operation is possible even if fuel combustion is stopped every other cylinder. That is, even if combustion is performed every other cylinder, fuel can be combusted at equal intervals, so that the operation state is stabilized. That is, by performing combustion at intervals of a crank angle of 180 degrees, it is possible to easily achieve a high temperature and a low air-fuel ratio when recovering sulfur poisoning. Thereby, even if it is a large displacement engine, a sulfur poisoning recovery process can be implemented at the time of low load. In addition, even in an internal combustion engine other than the V-type 8-cylinder, stable operation is possible as in the case of the V-type 8-cylinder as long as fuel can be burned at equal intervals.

  In the present invention, a variable valve mechanism that can keep the exhaust valve closed is further provided, and when the sulfur poisoning recovery is performed by the sulfur poisoning recovery means, fuel combustion is stopped. The cylinder exhaust valve can remain closed.

When the exhaust valve is opened and closed as usual in the stopped cylinder, air that is not burned is discharged into the exhaust passage. When such air is mixed with the exhaust from the combustion cylinder, the air-fuel ratio of the exhaust from the combustion cylinder is increased. That is, since the air-fuel ratio of the exhaust gas that has been reduced by the combustion cylinder is increased by the exhaust gas from the stopped cylinder, the air-fuel ratio of the exhaust gas that reaches the NOx storage reduction catalyst becomes high. Further, since the exhaust from the stopped cylinder is not combusted, the temperature is low. Therefore, the exhaust from the stopped cylinder lowers the temperature of the exhaust that reaches the NOx storage reduction catalyst.

On the other hand, if the exhaust valve of the stop cylinder is kept closed, air is not discharged from the stop cylinder to the exhaust passage, so that the exhaust at higher temperature and lower air-fuel ratio reaches the NOx storage reduction catalyst. be able to. That is, it becomes possible to recover sulfur poisoning at a lower load.

  In the present invention, the sulfur poisoning recovery means can perform the reduced-cylinder operation when the load of the internal combustion engine becomes a first threshold value or less.

  The first threshold is an operating state in which the air-fuel ratio of the exhaust gas becomes higher or the temperature of the exhaust gas becomes lower as the sulfur poisoning recovery becomes more difficult unless the reduced-cylinder operation is performed. In other words, by reducing the cylinder operation when recovery from sulfur poisoning becomes difficult, it is possible to prevent the air-fuel ratio of the exhaust from excessively decreasing and the temperature of the exhaust from excessively increasing when the load is high. it can.

  In the present invention, the sulfur poisoning recovery means performs the reduced cylinder operation when the load of the internal combustion engine becomes equal to or higher than a second threshold value higher than the first threshold value during the reduced cylinder operation. Can be canceled.

  The reason why the second threshold value is set higher than the first threshold value is that the temperature of the exhaust gas is lowered when switching from the reduced-cylinder operation to the all-cylinder operation. Therefore, the exhaust gas temperature at this time is higher than the temperature necessary for sulfur poisoning recovery. This is to suppress the lowering. Further, if the operation is switched to the all-cylinder operation due to an increase in the load, it is possible to suppress an excessive decrease in the air-fuel ratio of the exhaust when the load is high or an excessive increase in the temperature of the exhaust.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention can recover sulfur poisoning of the NOx storage reduction catalyst even when the load on the internal combustion engine is low.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its exhaust system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 is a V-type 8-cylinder four-cycle diesel engine. The internal combustion engine 1 is combusted in one of the cylinders every 90 degrees of crank angle.

The internal combustion engine 1 includes a right bank 2 and a left bank 3. Each of the right bank 2 and the left bank 3 includes four cylinders 4. The right bank 2 includes cylinders 1, 3, 5, and 7 (represented by # 1, # 3, # 5, and # 7, respectively), and the left bank 3 includes 2,
4, 6, and 8 cylinders (represented by # 2, # 4, # 6, and # 8, respectively) are provided. A right exhaust manifold 5 connected to each cylinder 4 of the right bank 2 is connected to the right bank 2. Further, a left exhaust manifold 6 connected to each cylinder 4 of the left bank 3 is connected to the left bank 3. The right exhaust manifold 5 is connected to the right exhaust pipe 7, and the left exhaust manifold 6 is connected to the left exhaust pipe 8.

A right storage reduction type NOx catalyst 9 (hereinafter referred to as a right NOx catalyst 9) is provided in the middle of the right exhaust pipe 7, and a left storage reduction type NOx catalyst 10 (hereinafter, left) is provided in the middle of the left exhaust pipe 8. NOx catalyst 10) is provided. The right NOx catalyst 9 and the left NOx catalyst 10 occlude NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and store the NOx when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present. Has the function of reducing

  Further, the internal combustion engine 1 is provided with a variable valve mechanism 11 that can be stopped while the exhaust valve 15 provided in each cylinder 4 is closed.

  The internal combustion engine 1 configured as described above is provided with an ECU 13 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 13 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the above sensors, the ECU 13 outputs a signal corresponding to the crank angle of the internal combustion engine 1 and outputs an electric signal corresponding to the amount by which the driver depresses the accelerator pedal 16 to detect the engine load. The accelerator opening sensor 17 is connected via electric wiring, and these output signals are input to the ECU 13. The load on the internal combustion engine 1 is detected by the accelerator opening sensor 17.

  On the other hand, the variable valve mechanism 11 is connected to the ECU 13 via electric wiring, and the variable valve mechanism 11 is controlled by the ECU 13.

  Here, FIG. 2 is a diagram showing a combustion order of each cylinder 4 of the internal combustion engine 1. In the right bank 2, combustion is performed in the order of the first, seventh, third, and fifth cylinders, and in the left bank 3, combustion is performed in the order of the second, fourth, sixth, and eighth cylinders. And as a whole internal combustion engine 1, combustion is performed in the order of cylinders 1, 2, 7, 3, 4, 5, 6, and 8.

  In this embodiment, when the sulfur poisoning recovery process is performed and the load on the internal combustion engine 1 is lower than the predetermined load, the reduced-cylinder operation is performed. That is, combustion is performed at intervals of crank angles of 180 degrees, which are performed at intervals of crank angles of 90 degrees. Specifically, the combustion is stopped by burning the fuel in the first, seventh, fourth, and sixth cylinders and stopping the supply of fuel in the second, third, fifth, and eighth cylinders. Alternatively, the combustion is stopped by burning the fuel in the second, third, fifth, and eighth cylinders and stopping the supply of fuel in the first, seventh, fourth, and sixth cylinders.

  In the present embodiment, the following controls (1) to (4) are performed.

(1) When the internal combustion engine 1 becomes a low load during the sulfur poisoning recovery process The low load referred to here means that the exhaust gas air-fuel ratio becomes so high that the sulfur poisoning recovery becomes difficult unless the reduced cylinder operation is performed. Or the exhaust temperature is lowered. The load that becomes this threshold value (hereinafter referred to as the first threshold value) is obtained in advance through experiments or the like. Then, by stopping the combustion of the fuel in the half cylinder 4, the fuel is burned at an interval of 180 degrees in the crank angle.

As a result, the temperature of the exhaust gas can be raised, so that a decrease in the temperature of the right NOx catalyst 9 and the left NOx catalyst 10 can be suppressed even when the load is low. Moreover, since the amount of fuel supplied per cylinder is increased, the air-fuel ratio of the exhaust can be lowered. Therefore, even if the internal combustion engine 1 shifts from a high load to a low load during the sulfur poisoning recovery process, the sulfur poisoning recovery process can be continued.

(2) When the internal combustion engine 1 takes off the low load during the sulfur poisoning recovery process If the reduced cylinder operation is continued in such a case, the air-fuel ratio of the exhaust becomes excessively rich or the temperature of the exhaust is excessive. All cylinder operation is performed because the internal combustion engine torque does not increase. However, switching to the all-cylinder operation is performed when the load of the internal combustion engine 1 becomes equal to or higher than a second threshold value that is higher than the first threshold value.

  Here, when switching to all-cylinder operation, the air-fuel ratio of the exhaust gas decreases. Therefore, if switching to all-cylinder operation at the first threshold value, the temperature required for sulfur poisoning recovery may not be obtained. For this reason, the operation is switched to the all-cylinder operation after the second threshold value is higher than the first threshold value. This second threshold value is obtained in advance by experiments or the like as a load that can continuously perform sulfur poisoning recovery when switching from reduced cylinder operation to full cylinder operation.

(3) When it becomes necessary to perform sulfur poisoning recovery processing when the internal combustion engine 1 is operated at the low load Here, when it is necessary to perform sulfur poisoning recovery processing, for example, right NOx This is a case where the amount of the sulfur component occluded in the catalyst 9 or the left NOx catalyst 10 exceeds a specified amount. Right N
The amount of the sulfur component occluded in the Ox catalyst 9 or the left NOx catalyst 10 can be obtained from the fuel consumption, the output signal from the NOx sensor, the travel distance of the vehicle, and the like.

  Even in such a case, the combustion of the fuel is stopped in the half cylinders 4 and the combustion is performed at intervals of 180 degrees of the crank angle. As a result, the temperature of the exhaust gas can be raised, so that the temperatures of the right NOx catalyst 9 and the left NOx catalyst 10 can be raised. Moreover, since the amount of fuel supplied per cylinder is increased, the air-fuel ratio of the exhaust can be lowered. Therefore, even when the internal combustion engine 1 is operated at a low load, the sulfur poisoning recovery process can be executed.

(4) When recovery from sulfur poisoning is completed when the internal combustion engine 1 is operated at the low load In such a case, it is not necessary to continue the reduced-cylinder operation, so immediately switch to the all-cylinder operation. .

  Next, the flow of the sulfur poisoning recovery process in the present embodiment will be described. FIG. 3 is a flowchart showing a flow of the sulfur poisoning recovery process in the present embodiment. This routine is repeatedly executed every predetermined time.

In step S101, it is determined whether it is necessary to perform sulfur poisoning recovery processing of the right NOx catalyst 9 or the left NOx catalyst 10. As described above, the determination is made based on whether or not the amount of the sulfur component stored in the right NOx catalyst 9 or the left NOx catalyst 10 exceeds a specified amount.

  If an affirmative determination is made in step S101, the routine proceeds to step S102, where sulfur poisoning is recovered. On the other hand, if a negative determination is made, it is not necessary to perform sulfur poisoning recovery, so this routine is temporarily terminated.

In step S102, it is determined whether or not the load of the internal combustion engine 1 is equal to or less than the first threshold value. That is, in this step, it is determined whether or not a reduced-cylinder operation is necessary to recover sulfur poisoning.

  If an affirmative determination is made in step S102, the process proceeds to step S103 to perform a reduced-cylinder operation, whereas if a negative determination is made, the process proceeds to step S107 to perform an all-cylinder operation.

  In step S103, sulfur poisoning recovery is performed in the reduced cylinder operation. At the same time, the exhaust valve of the cylinder 4 where combustion is not performed is kept closed. In this embodiment, the ECU 13 that performs the sulfur poisoning recovery while performing the reduced cylinder operation in step S103 corresponds to the sulfur poisoning recovery means in the present invention.

  In step S104, it is determined whether or not the load of the internal combustion engine 1 is equal to or greater than a second threshold value. That is, when the sulfur poisoning recovery is performed in the reduced-cylinder operation, it is determined whether the load on the internal combustion engine 1 has increased and the need for the reduced-cylinder operation has been eliminated.

  If an affirmative determination is made in step S104, the process proceeds to step S107 to switch to all-cylinder operation. On the other hand, if a negative determination is made, the process proceeds to step S105 and sulfur poisoning recovery is continued in the reduced cylinder operation.

  In step S105, it is determined whether recovery from sulfur poisoning has been completed. For example, when the sulfur poisoning recovery is performed over a predetermined time, it is determined that the sulfur poisoning recovery is completed.

  If an affirmative determination is made in step S105, the process proceeds to step S106. On the other hand, if a negative determination is made, the process returns to step S104, and sulfur poisoning recovery is continued in the reduced cylinder operation.

  In step S106, the sulfur poisoning recovery process ends, and all cylinder operation is performed. When the reduced-cylinder operation is performed, the opening / closing of the exhaust valve 15 of the cylinder 4 that has not been combusted is resumed.

  In step S107, sulfur poisoning recovery is performed in all cylinder operation. In the case of switching from the reduced-cylinder operation, the opening / closing of the exhaust valve 15 of the cylinder 4 in which combustion has not been performed is resumed.

  In step S108, it is determined whether or not the load of the internal combustion engine 1 is equal to or less than a first threshold value. In this step, processing similar to that in step S102 is performed.

  If an affirmative determination is made in step S108, the process proceeds to step S103, and sulfur poisoning recovery is performed by the reduced cylinder operation. On the other hand, if a negative determination is made, the process proceeds to step S109 and continues to sulfur poisoning in the all cylinder operation. Recovery is done.

  In step S109, it is determined whether or not the recovery from sulfur poisoning has been completed. In this step, processing similar to that in step S105 is performed.

  If an affirmative determination is made in step S109, the process proceeds to step S106, where the sulfur poisoning recovery process is completed. On the other hand, if a negative determination is made, the process returns to step S108, and sulfur poisoning recovery is continued in all cylinder operation. It is.

As described above, according to this embodiment, when the sulfur poisoning recovery is necessary and the internal combustion engine 1 is operated at a low load, the reduced-cylinder operation is performed, so that the air-fuel ratio of the exhaust gas is reduced. Can be reduced and the temperature of the exhaust gas can be raised, so that sulfur poisoning can be recovered. Thereby, since the operation range which can perform sulfur poisoning recovery can be expanded, sulfur poisoning recovery can be performed under various traveling conditions. In addition, since the amount of fuel consumed in the sulfur poisoning recovery process can be reduced, fuel efficiency can be improved.

  Further, in a V-type 8-cylinder internal combustion engine that performs combustion at least once at intervals of 90 degrees of crank angle, combustion is performed at intervals of 180 degrees of crank angle when performing a reduced cylinder operation, so that the internal combustion engine is stably operated. be able to. Note that not only the V-type 8-cylinder but also an internal combustion engine having other arrangements of cylinders can reduce the air-fuel ratio of the exhaust and raise the temperature of the exhaust by performing the reduced-cylinder operation. Further, even in an internal combustion engine having other arrangements of cylinders, stable operation is possible by burning fuel at equal intervals.

  Further, when performing the reduced-cylinder operation, the exhaust valve of the cylinder 4 where combustion is not performed is kept closed by the variable valve mechanism 11, so the air-fuel ratio of the exhaust is exhausted by the air discharged from the cylinder where combustion is not performed. Can be prevented from rising or the temperature of the exhaust gas can be lowered.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. It is the figure which showed the combustion order of each cylinder of an internal combustion engine. It is the flowchart which showed the flow of the sulfur poisoning recovery process in an Example.

Explanation of symbols

1 Internal combustion engine 2 Right bank 3 Left bank 4 Cylinder 5 Right exhaust manifold 6 Left exhaust manifold 7 Right exhaust pipe 8 Left exhaust pipe 9 Right NOx catalyst 10 Left NOx catalyst 11 Variable valve mechanism 13 ECU
14 Crank position sensor 15 Exhaust valve 16 Accelerator pedal 17 Accelerator opening sensor

Claims (5)

In an exhaust emission control device for an internal combustion engine that has a plurality of cylinders and is capable of performing a reduced-cylinder operation that reduces a cylinder that burns fuel,
A NOx storage reduction catalyst in which NOx is stored and NOx stored is reduced by a reducing agent;
Sulfur poisoning recovery means for performing the reduced cylinder operation when performing sulfur poisoning recovery of the NOx storage reduction catalyst;
An exhaust emission control device for an internal combustion engine, comprising: The internal combustion engine is a V-type 8-cylinder internal combustion engine that performs continuous combustion at least once at intervals of 90 degrees in crank angle,
2. The internal combustion engine according to claim 1, wherein the sulfur poisoning recovery means stops combustion in half of the cylinders so that combustion is performed at intervals of a crank angle of 180 degrees when performing sulfur poisoning recovery. Exhaust purification device.   A variable valve mechanism capable of keeping the exhaust valve closed; and when the sulfur poisoning recovery is performed by the sulfur poisoning recovery means, The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the exhaust gas purification apparatus is kept closed.   The exhaust purification of an internal combustion engine according to any one of claims 1 to 3, wherein the sulfur poisoning recovery means performs the reduced-cylinder operation when a load of the internal combustion engine becomes a first threshold value or less. apparatus.   The sulfur poisoning recovery means stops the reduced-cylinder operation when the load of the internal combustion engine becomes equal to or higher than a second threshold value that is higher than the first threshold value during the reduced-cylinder operation. The exhaust emission control device for an internal combustion engine according to claim 4.

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