JP2006250036A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique by which the saturation of a purifying ability of a purifying catalyst can be suppressed when used on high grounds in an exhaust emission control device for an internal combustion engine equipped with the purifying catalyst having NO<SB>x</SB>occlusion ability and/or PM trapping ability. <P>SOLUTION: The exhaust emission control device for an internal combustion engine for causing the internal combustion engine to perform a low temperature combustion operation when sulfur poisoning is eliminated or the PM trapping ability is regenerated of a filter having the NO<SB>x</SB>occlusion ability and/or the PM trapping ability is characterized in that, by further narrowing the performing region of the low temperature combustion operation as the altitude of the service space becomes higher, elimination of sulfur poisoning or regeneration of the PM trapping ability can be performed while suppressing overheating of the purifying catalyst. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an exhaust purification technology for an internal combustion engine provided with a purification catalyst having NO _x storage ability and / or PM collection ability.

As an exhaust gas purification device for an internal combustion engine, when the oxygen concentration of the exhaust gas is high, NO _x in the exhaust gas is occluded (absorbed), and when the oxygen concentration of the exhaust gas is low, the occluded reduction type that releases and purifies the stored NO _x the NO _x catalyst and, those with purifying catalyst such as a particulate filter for trapping particulate (PM) in the exhaust gas are known.

An exhaust purification system of an internal combustion engine as described above, the PM regeneration treatment or the like for reproducing the SO _x regeneration process and PM trapping ability of the particulate filter for causing the eliminating sulfur poisoning of the storage-reduction the NO _x catalyst It is necessary to do it appropriately.

One way to perform the SO _x regeneration process and the PM regeneration processing, there is known a method for low temperature combustion operating an internal combustion engine (e.g., see Patent Document 1).
JP 2003-120373 A JP 2001-349230 A JP 2003-120365 A

During the execution of the SO _x regeneration process and the PM regeneration process as described above, the balance between the amount of heat generated by the purification reaction of SO _x and PM in the purification catalyst and the amount of heat taken away from the purification catalyst by the exhaust gas passing through the purification catalyst is In order to balance appropriately, overheating and overcooling of the purification catalyst are suppressed.

  However, when the internal combustion engine is used at a high altitude (high altitude), the exhaust density also decreases as the air density decreases, so the amount of heat transferred from the purification catalyst to the exhaust may be too small. There is.

When SO _x amount of heat transferred from the purifying catalyst during execution of the regeneration process and the PM regeneration processing to the exhaust is too small, there is a possibility to induce deterioration purifying catalyst is overheated. In contrast, a method of inhibiting the execution of the SO _x regeneration process and the PM regeneration processing is also contemplated in the highland, the internal combustion engine when a period used at high altitude increases, the purification catalyst purification ability of the exhaust Emissions; saturated It can lead to deterioration.

The present invention has been made in view of the above-described circumstances, and an object of the present invention is to purify at the time of high altitude use in an exhaust gas purification apparatus for an internal combustion engine provided with a purification catalyst having NO _x storage ability and / or PM collection ability. An object of the present invention is to provide a technology capable of suppressing saturation of the purification capacity of a catalyst.

In order to solve the above-described problems, the present invention eliminates sulfur poisoning of a purification catalyst having NO _x storage capacity and / or PM collection capacity or regenerates PM collection capacity at low temperature combustion operation. In the exhaust gas purification device of the internal combustion engine to be used, it is possible to eliminate sulfur poisoning and regenerate the PM trapping ability while suppressing the overheating of the purification catalyst by narrowing the execution region of the low temperature combustion operation as the altitude of use increases. It is characterized by that.

  Specifically, an exhaust emission control device for an internal combustion engine according to the present invention includes an altitude detection means for detecting an altitude at a place where the internal combustion engine is used, and an engine capable of low-temperature combustion operation as the altitude detected by the altitude detection means increases. Limiting means for lowering the upper limit of the load.

When the internal combustion engine is operated at low temperature combustion, the balance between the amount of heat generated by the purification reaction of SO _x and PM in the purification catalyst and the amount of heat taken away from the purification catalyst by the exhaust gas passing through the purification catalyst is appropriately balanced. The purification catalyst is maintained at a desired target temperature range.

  However, when the internal combustion engine is used at a high altitude (high altitude) and the low-temperature combustion operation is performed as usual (similar to the flat ground), the internal combustion engine is prevented from deteriorating in combustion stability due to lack of oxygen. It is necessary to correct the target air-fuel ratio to the lean side. In such a case, in order to raise the temperature of the purification catalyst to a desired high temperature range, it is necessary to increase the amount of additives such as fuel separately supplied to the purification catalyst. For this reason, the amount of heat taken away from the purification catalyst by the exhaust gas is reduced, and the amount of reaction heat generated in the purification catalyst is increased. As a result, the purification catalyst is likely to overheat.

  On the other hand, if the upper limit of the engine load capable of low-temperature combustion operation is lowered as the altitude of the place where the internal combustion engine is used becomes higher, the engine operating range in which low-temperature combustion operation can be performed becomes narrow, but the excessive temperature rise of the purification catalyst is suppressed. In addition, it is possible to eliminate sulfur poisoning and regenerate the PM trapping ability.

  As a result, even if the use period (operating time) of the internal combustion engine at high altitude is long, the purification ability of the purification catalyst is hardly saturated, and it is possible to suppress the deterioration of exhaust emission.

  In the present invention, the limiting means may limit the low-temperature combustion operation execution area to the idle operation area when the altitude detected by the altitude detection means exceeds a predetermined value. When the internal combustion engine is in an idle operation state, the amount of heat contained in the exhaust gas of the internal combustion engine is reduced (because the exhaust temperature is lowered). For this reason, even if the altitude is relatively high, it is possible to eliminate sulfur poisoning and regenerate the PM trapping ability while suppressing the excessive temperature rise of the purification catalyst.

In the present invention, the regeneration control means may increase the target temperature at the time of executing the low temperature combustion operation stepwise. In this case, since SO _x or PM occluded or collected by the purification catalyst becomes difficult to react at the same time, it is easy to suppress the excessive temperature rise of the purification catalyst and also suppress the generation amount of sulfur sulfide (H ₂ S). It becomes possible.

  In the present invention, the altitude detection means may detect altitude itself, such as a radio altimeter that emits radio waves and measures the reflection time from the ground surface, and detects changes in atmospheric pressure. There may be.

According to the present invention, in an exhaust gas purification apparatus for an internal combustion engine provided with a purification catalyst having NO _x storage ability and / or PM collection ability, excessive temperature rise of the purification catalyst is suppressed when the internal combustion engine is used at high altitude. In addition, it is possible to eliminate sulfur poisoning and regenerate the PM trapping ability.

  As a result, even when the internal combustion engine is used at a high altitude, the purification ability of the purification catalyst becomes difficult to saturate, and it becomes possible to suppress the deterioration of exhaust emission.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

  First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine). The internal combustion engine 1 has a plurality of cylinders 2, and each cylinder 2 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  An intake passage 4 is connected to the internal combustion engine 1. A compressor 50 of a centrifugal supercharger (turbocharger) 5 is disposed in the intake passage 4. An intake air cooler (intercooler) 6 is disposed in the intake passage 4 downstream of the compressor 50. An intake throttle valve 13 is disposed in the intake passage 4 downstream of the intercooler 6.

  An exhaust passage 7 is connected to the internal combustion engine 1. A turbine 51 of the turbocharger 5 is disposed in the middle of the exhaust passage 7. A filter 8 as a purification catalyst of the present invention is disposed in the exhaust passage 7 downstream from the turbine 51. The filter 8 is a particulate filter carrier that collects PM in the exhaust, and the NOx storage reduction catalyst is supported on the carrier.

  In the exhaust passage 7 upstream from the turbine 51, a fuel addition valve 9 for adding fuel to the exhaust flowing in the exhaust passage 7 is disposed. An exhaust temperature sensor 10 is disposed in the exhaust passage 7 downstream of the filter 8.

  The intake passage 4 downstream of the intake throttle valve 13 and the exhaust passage 7 upstream of the turbine 51 are connected by an EGR passage 11. In the middle of the EGR passage 11, an EGR cooler 12 and an EGR valve 13 are arranged.

  The internal combustion engine 1 configured as described above is provided with an ECU 14. The ECU 14 is an arithmetic and logic circuit that includes a CPU, ROM, RAM, backup RAM, and the like.

  The ECU 14 is electrically connected to various sensors such as the atmospheric pressure sensor 15 in addition to the exhaust gas temperature sensor 10 described above, and can input output signals of various sensors. The ECU 14 is electrically connected to the fuel injection valve 3, the fuel addition valve 9, the intake throttle valve 13, the EGR valve 15, and the like, and can electrically control them.

  The ECU 14 executes SOx regeneration processing, which is the gist of the present invention, in addition to known control such as fuel injection control based on the output signals of various sensors. Hereinafter, the SOx regeneration process will be specifically described.

  The sulfur poisoning of the NOx storage reduction catalyst is eliminated when the NOx storage reduction catalyst is exposed to a high temperature and rich atmosphere of approximately 600 ° C. or higher. As a method for bringing the NOx storage reduction catalyst into a high temperature and rich atmosphere, a method of operating the internal combustion engine 1 at low temperature combustion is known.

  The low-temperature combustion operation of the internal combustion engine 1 is realized by increasing the EGR gas amount. When EGR gas is mixed into the intake air of the internal combustion engine 1, the combustion temperature in the cylinder 2 is lowered, and the amount of NOx generated can be suppressed. At that time, if the ratio of the EGR gas contained in the intake air becomes higher than a predetermined ratio, the amount of soot generated increases abruptly, so that normal EGR control is performed at a ratio lower than the predetermined ratio.

By the way, when the EGR gas ratio is further increased from the predetermined ratio, soot is reduced again, and finally soot is hardly generated. This is presumably because the combustion temperature in the cylinder 2 is lower than the temperature at which hydrocarbons (HC) can become soot.

  The hydrocarbon (HC) whose growth has stopped before reaching soot is easily oxidized by the oxidation ability of the NOx storage reduction catalyst supported on the filter 8, so that the filter 8 generates the heat of oxidation reaction of the hydrocarbon (HC). In response, the temperature rises. Further, as described above, when the EGR gas ratio is increased, the amount of fresh air contained in the intake air is reduced, so that the atmosphere of the intake and exhaust becomes rich.

  Therefore, when the internal combustion engine 1 is operated at low temperature combustion, the emission amount of particulates (PM) represented by soot is suppressed, and the filter 8 can be made a high temperature and rich atmosphere.

  Note that even if the amount of EGR gas is increased to perform low-temperature combustion operation when the internal combustion engine 1 is operating at a high load, the amount of fuel provided for combustion in the cylinder 2 increases and at the same time the combustion temperature increases. It becomes difficult to keep hydrogen (HC) in the state before reaching the soot. Therefore, the low-temperature combustion operation as described above is preferably performed when the internal combustion engine 1 is not in a high load operation state (in other words, when the internal combustion engine 1 is in a medium / low load operation state).

  In order to eliminate sulfur poisoning of the NOx storage reduction catalyst when the internal combustion engine 1 is in a high load operation state, fuel is post-injected from the fuel injection valve 3 or fuel is added into the exhaust gas from the fuel addition valve 9. The filter 8 may be heated and exposed to a rich atmosphere.

When the SOx regeneration treatment is performed by a method as described above, the amount of heat generated by the oxidation-reduction reaction of hydrocarbons (HC) and SO _x in the filter 8, from the filter 8 by the exhaust passing through the filter 8 Since the balance with the amount of heat taken is appropriately balanced, overheating of the filter 8 is prevented.

However, when the internal combustion engine 1 according to the present embodiment is used at high altitude (for example, when a vehicle on which the internal combustion engine 1 is mounted travels on high altitude), the heat capacity of the exhaust gas decreases due to the decrease in air density. There is a possibility that the balance of heat amount as described above may not be balanced. That is, for the amount of heat generated by the oxidation-reduction reaction of hydrocarbons (HC) and SO _x in the filter 8, amount of heat removed from the filter 8 by the exhaust gas passing through the filter 8 may become too small.

  If the balance of heat quantity is not balanced in this way, the filter 8 may overheat and induce thermal degradation or the like of the NOx storage reduction catalyst. This tendency becomes more prominent as the altitude is higher and the exhaust gas temperature is higher (that is, the load on the internal combustion engine 1 is higher).

  Therefore, in the SOx regeneration process in the present embodiment, the ECU 14 determines the altitude of the place where the internal combustion engine 1 is used based on the output signal of the atmospheric pressure sensor 15, and the determined altitude is the altitude of the flat ground (the atmospheric pressure is When the altitude determined is higher than a predetermined amount (for example, 1000 m) higher than the altitude of approximately 1 atm, the SOx regeneration process execution region, in other words, the low temperature combustion operation execution region is narrowed.

  Specifically, as shown in FIG. 2, the ECU 14 limits the upper limit value of the engine load (fuel injection amount) and the upper limit value of the engine speed that can execute the low temperature combustion operation to be lower as the altitude is higher. For example, in the example of FIG. 2, when the altitude is in a range from flat ground to 1000 m, the engine load and the engine speed are set as usual.

When the altitude is in the range of 1000 to 3000 m, the upper limit value of the engine load is set lower as the altitude is higher within the range of Qmax 1000 to Qmax 3000 in the figure, and the upper limit value of the engine speed is Within the range from Nemax 1000 to Nemax 3000, the higher the altitude, the lower the setting.

  When the altitude exceeds 3000 m, the upper limit value of the engine load is limited to Qmax3000 and the upper limit value of the engine load is limited to Nemax3000. Here, Qmax 3000 and Nemax 3000 are set to be equal to the load and engine speed when the internal combustion engine 1 is in the idling operation state. For this reason, when the altitude exceeds 3000 m, the low-temperature combustion operation is executed only when the internal combustion engine 1 is in the idle operation state.

  As in the example shown in FIG. 2, when the engine load capable of performing the low temperature combustion operation and the upper limit value of the engine speed are lowered in inverse proportion to the change in altitude, the feasible region of the low temperature combustion operation becomes higher as the altitude increases. Narrow. That is, the execution region of the low-temperature combustion operation is performed only in a region where the load and the engine speed are lower as the altitude is higher.

  The excessive temperature rise of the filter 8 due to the low temperature combustion operation is more likely to occur as the altitude is higher and the engine load is higher, but the upper limit value of the engine load capable of performing the low temperature combustion operation is inversely proportional to the increase in altitude. If the temperature is lowered, it becomes difficult for the filter 8 to overheat due to the low temperature combustion operation.

  Therefore, according to the SOx regeneration process in the present embodiment, the engine operation region in which the low temperature combustion operation can be performed becomes narrower as the altitude becomes higher, but the sulfur poisoning can be eliminated while suppressing the excessive temperature rise of the filter 8. it can. Therefore, even if the period of use (operating time) of the internal combustion engine 1 at a high altitude is long, the purifying ability of the filter 8 (in this case, the NOx occlusion ability of the NOx storage reduction catalyst) is not easily saturated. As a result, deterioration of exhaust emission is suppressed.

  Further, even when the altitude exceeds 3000 m, it is possible to eliminate sulfur poisoning while suppressing the excessive temperature rise of the filter 8 by limiting the execution region of the low temperature combustion operation to the idle operation region. It becomes.

  In the present embodiment, the low temperature combustion operation is taken as an example of the execution method of the SOx regeneration process. However, by post-injecting fuel from the fuel injection valve 3 or adding fuel into the exhaust gas from the fuel addition valve 9. Also in the method of performing the SOx regeneration process, the same effect as that of the present embodiment can be obtained by narrowing the operation region in which post injection can be performed or the operation region in which fuel can be added to exhaust gas depending on altitude.

  In the SOx regeneration process, the ratio of EGR gas (the opening degree of the EGR valve 13) is feedback controlled so that the temperature of the filter 8 (the output signal of the exhaust temperature sensor 10 in the example of FIG. 1) becomes a desired target temperature. However, the target temperature at that time may be increased stepwise.

  For example, the ECU 14 may set the target temperature at the initial stage of execution of the SOx regeneration process to be lower than the normal target temperature (for example, the target temperature on flat ground), and the target temperature becomes higher as the SOx regeneration process execution time becomes longer. .

Since SOx stored in the NOx storage reduction catalyst has a different temperature range that can be purified depending on the individual storage states, the SOx stored in the NOx storage reduction catalyst is all at once when the target temperature is increased stepwise as described above. It is difficult to cause a purification reaction. As a result, it becomes easy to suppress the excessive temperature rise of the filter 8 and it is also possible to suppress the generation amount of sulfur sulfide (H ₂ S) per unit time.

  In the present embodiment, the example in which the SOx regeneration process executable region of the filter 8 is narrowed as the altitude increases is described. However, the PM regeneration process executable region of the filter 8 may be narrowed as the altitude increases. .

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. It is a figure which shows the relationship between the driving | operation area | region which can perform SOx reproduction | regeneration processing, and altitude.

Explanation of symbols

1 ... Internal combustion engine 8 ... Filter (Purification catalyst)
11 .... EGR
12 .... EGR cooler 13 .... EGR valve 14 .... ECU
15 .... Atmospheric pressure sensor (altitude detection means)

Claims (3)

A purification catalyst having NO _x storage ability and / or PM collection ability, and the purification catalyst is operated at a low temperature when the sulfur poisoning of the purification catalyst is eliminated or when the PM collection ability is regenerated. In an exhaust gas purification apparatus for an internal combustion engine comprising a regeneration control means for raising the temperature to a temperature,
Altitude detecting means for detecting the altitude of the place where the internal combustion engine is used;
Limiting means for lowering the upper limit of the engine load capable of low-temperature combustion operation, as the altitude detected by the altitude detecting means becomes higher,
An exhaust emission control device for an internal combustion engine, comprising: 2. The internal combustion engine according to claim 1, wherein the limiting means limits the low-temperature combustion operation execution area to an idle operation area when the altitude detected by the altitude detection means exceeds a predetermined value. Exhaust purification device. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the regeneration control means raises the target temperature at the time of executing the low temperature combustion operation in a stepwise manner.

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