KR100629205B1 - Exhaust gas cleaning device for engine - Google Patents

Abstract

An object of the present invention is to prevent overheating of the catalyst due to the rich spike operation when the rich spike control and the S purge operation are performed efficiently.

To this end, the NOx storage catalyst 42 installed in the exhaust passage 40 of the engine 20 and the exhaust gas oil supplying the reducing agent component including HC during the rich spike operation or the S purge operation are added to the exhaust passage 40. The injector 41 and the rich spike operation for controlling the air-fuel ratio to the rich side are performed at predetermined times, and the HC component is added to the NOx storage catalyst 42 and the NOx storage catalyst 42 is heated above the S purge temperature T. And a catalyst temperature measuring sensor 101 for measuring the temperature of the NOx storage catalyst 42, and a control unit 100 for performing an S purge operation for removing sulfur content stored therein. The operating cycle of the rich spike operation is controlled based on the deviation from the S purge temperature T with respect to the temperature measured by 101).

Engine, Flue Gas Purifier

Description

EXHAUST GAS CLEANING DEVICE FOR ENGINE}

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows the structure of the exhaust-gas purification apparatus of the engine by one Embodiment of this invention.

2 is a diagram showing a relationship between a supply temperature of CO and HC per unit time and a catalyst temperature;

3 is a diagram showing the relationship between the rich spike period, the rich spike period, and the amount of CO and HC supplied per unit time;

Fig. 4 shows the timing of the rich spike signal in the exhaust gas purifying apparatus of the same engine, the timing of the S purge signal for performing the S purge operation, the amount of CO and HC supplied in the exhaust pipe, and the catalyst temperature (catalyst outlet). Explanatory drawing showing time change of gas temperature),

Fig. 5 shows the timing of the rich spike signal in the exhaust gas purifying apparatus of the same engine, the timing of the S purge signal for performing the S purge operation, the amount of CO and HC supplied in the exhaust pipe, and the catalyst temperature (catalyst outlet gas temperature). An explanatory diagram showing a time change of

6 shows the timing of the rich spike signal in the conventional exhaust gas purifier, the timing of the S purge signal for performing the S purge operation, the amount of CO and HC supplied in the exhaust pipe, and the catalyst temperature (catalyst outlet gas temperature). Explanatory diagram showing time change.

[Description of the code]

10: engine system 20: diesel engine

30: intake pipe 40: exhaust pipe

41: injector with exhaust gas oil 42: NOx storage catalyst

50: EGR piping 52: EGR valve

60: supercharger 100: control unit

101: catalytic temperature measurement sensor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an engine having an exhaust purification function for purifying harmful components contained in exhaust gas of an internal combustion engine.

2. Description of the Related Art [0002] An exhaust gas purifying apparatus is known in which a NOx storage catalyst is installed in an exhaust pipe of an engine. The exhaust gas purifier using such a NOx catalyst supplies a reducing agent such as light oil to the exhaust upstream side of the NOx reduction catalyst in order to release and reduce the NOx occluded. It is necessary to periodically perform a rich spike that lowers the value to 1 or less (for example, once per minute). Specifically, λ is reduced by controlling the engine intake system, post injection, or the like, and fuel is injected into the exhaust pipe upstream of the catalyst to reach rich spikes.

Moreover, when performing rich spikes, the technique of changing the grade of lean combustion and the grade of rich combustion according to a catalyst temperature is known (for example, refer patent document 1).

On the other hand, in the NOx storage catalyst, sulfur poisoning is caused by sulfur content in fuel. In order to remove this sulfur, it is necessary to carry out the S purge operation of discharge | emission for removing sulfur content regularly (for example, once every 5000 km run) for about 1 minute. S purge operation requires a catalyst temperature of, for example, 600 ° C. (S purge temperature) or more. For this reason, the technique of raising the temperature of a NOx storage catalyst by adding light oil to exhaust pipe or supplying HC by post injection etc. is known (for example, refer patent document 1).

[Patent Document 1] Japanese Patent Application Laid-Open No. 11-270382

The exhaust gas purification device of the engine described above has the following problems. The graphs H1 to H4 in FIG. 6 are timings of the rich spike signals for performing the rich spike operation in the exhaust gas purifying apparatus, timings of the S purge signals for performing the S purge operation, CO supplied to the exhaust pipe, It is a graph which shows the time change of HC supply amount and catalyst temperature (catalyst outlet gas temperature).

As can be seen from the graphs H1 and H2, since the rich spike control and the S purge control are performed independently, the rich spike operation and the S purge operation are simultaneously performed. Since both the rich spike operation and the S purge operation are caused by HC supply by addition of exhaust gas oil or post injection, the HC supply to the catalyst may be excessive depending on the timing, resulting in excessive heating of the catalyst.

For this reason, it is thought that HC supply will not become excessive by reducing CO and HC supply amount at the time of S purge operation, On the contrary, there existed a problem that the time to reach S purge temperature became long, or S purge temperature did not reach. .

Here, an object of the present invention is to provide an exhaust gas purifying apparatus for an engine capable of efficiently performing rich spike control and S purge operation and preventing overheating of the catalyst due to rich spike operation.

In order to solve the said subject and achieve the objective, the exhaust gas purification apparatus of the engine of this invention is comprised as follows.

(1) a catalyst installed in the exhaust passage of the engine to occlude NOx in the exhaust gas flowing into the exhaust passage and to reduce NOx when the air-fuel ratio of the exhaust gas becomes rich, and a reducing agent component containing HC in the exhaust passage; A rich spike control unit for supplying a reducing agent supplying unit, a rich spike control unit operating the reducing agent supply unit to temporarily control the air-fuel ratio to the rich side at a predetermined time, and adding a HC component to the catalyst and heating the catalyst at a predetermined temperature An S purge control unit for determining the need and unnecessary S purge operation for removing the sulfur content stored in the catalyst, and a catalyst temperature measuring sensor for measuring the temperature of the catalyst, and the S purge control unit has determined that S purge is necessary. In this case, the rich spike control unit measures the temperature measured by the catalyst temperature measuring sensor. To about based on the deviation from the predetermined temperature characterized by controlling the operation period of the rich-spike operation.

(2) An exhaust gas purifying apparatus for an engine according to (1), wherein the cycle is shortened as the deviation is large.

(3) a catalyst installed in the exhaust passage of the engine to occlude NOx in the exhaust gas flowing into the exhaust passage and to reduce NOx when the air-fuel ratio of the exhaust gas becomes rich, and a reducing agent component containing HC in the exhaust passage; A reducing spike control unit for supplying the reducing agent supplying unit, a rich spike operation for controlling the air-fuel ratio to the rich side temporarily by operating the reducing agent supplying unit every predetermined time, and adding a HC component to the catalyst and heating the catalyst at a predetermined temperature The S purge control unit for determining the need and unnecessary S purge operation for removing the sulfur content occupied by the catalyst, and a catalyst temperature measuring sensor for measuring the temperature of the catalyst, have been determined to be necessary by the S purge control unit. In this case, the rich spike control unit controls the temperature measured by the catalyst temperature measuring sensor. The operation period of the rich spike operation is controlled based on the deviation from the predetermined temperature.

(4) An exhaust gas purifying apparatus for the engine according to (3), wherein the cycle is lengthened as the deviation is large.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the configuration of an exhaust gas purifying apparatus 10 of an engine according to an embodiment of the present invention. Fig. 2 is a diagram showing the relationship between CO and HC supply amount per unit time and catalyst temperature. Fig. 3 is a rich spike. A graph showing the relationship between the period, the rich spike period, and the amount of CO and HC supply per unit time, and the graphs G1 to G4 of FIG. 4 are timings of the rich spike signals and the S purge operation for performing the rich spike operation in the exhaust gas purifier. Is a graph showing the timing of the S purge signal, the amount of CO and HC supplied to the exhaust pipe, and the time change of the catalyst temperature (catalyst outlet gas temperature).

The engine system 10 includes a diesel engine 20. An intake pipe 30 is connected to the intake side of the diesel engine 20, and an exhaust pipe 40 is connected to the exhaust side. In addition, the exhaust side of the diesel engine 20 and the intake pipe 30 are connected to the EGR pipe 50 which returns the exhaust gas (EGR gas) to the intake pipe 30. In addition, in FIG. 3, 60 is a supercharger and 100 is a control apparatus.

The intake pipe 30 is connected to the air flow sensor 31, the compressor 61 of the supercharger 60, the intercooler 32, the intake throttle 33, and the connection portion 34 of the EGR pipe 50 from the intake side. Is installed.

The exhaust pipe 40 includes a turbine 62 of the supercharger 60 from the diesel engine 20 side, an exhaust gas oil addition injector 41 for supplying light oil into the exhaust pipe 40, and a NOx storage catalyst 42. It is installed. The NOx storage catalyst 42 occludes NOx in exhaust gas flowing into the exhaust pipe 40, and reduces the NOx occluded when the exhaust gas becomes rich.

The EGR pipe 50 is provided with an EGR cooler 51 for cooling the exhaust gas from the exhaust pipe 40 side, and an EGR valve 52 for adjusting the flow rate of the exhaust gas.

The controller 100 is connected to the output of the catalyst temperature measuring sensor 101 disposed at the outlet side of the NOx storage catalyst 42 of the exhaust pipe 40, and the catalyst temperature of the NOx storage catalyst 42 is always fed back. .

In the engine system 10 configured as described above, the S purge operation is performed in the following operation. That is, during normal engine operation, the rich spike operation is performed at predetermined intervals, and is performed by the control of combustion of the engine and the addition of light oil containing HC into the exhaust pipe 40 from the exhaust light oil addition injector 41. At this time, when the S purge operation is required, the NOx storage catalyst 42 is heated by supplying HC from the exhaust gas oil addition injector 41 in the exhaust pipe 40. At this time, when the catalyst temperature does not reach the S purge temperature T, the rich spike operation is controlled as the direction in which the temperature increase rate increases, that is, the cycle of the rich spike operation (M in FIG. 4) is shortened.

When the catalyst temperature reaches the S purge temperature T, the rich spike operation is returned to the original interval. For this reason, catalyst temperature changes before and after S purge temperature T, and it does not become over temperature. Moreover, when catalyst temperature is higher than S purge temperature T, you may control so that a rich spike period may be lengthened. In addition, when the S purge operation ends and returns to the normal engine operation, the rich spike operation returns to the normal cycle.

As described above, in the engine system 10 according to the present embodiment, when the S purge operation is started, the HC spike is increased by shortening the rich spike cycle by a large deviation of the catalyst temperature with respect to the S purge temperature T. In a short time, the catalyst temperature can be controlled to reach the S purge temperature (T).

As can be seen from Figs. 2 and 3, the shorter the rich spike period means that the supply amount of CO and HC per unit time increases, and as a result, the temperature increase of the catalyst can be increased. For this reason, while performing rich spikes, the sulfur content stored in the NOx storage catalyst 42 by the S purge operation can be smoothly removed, and overheating can be prevented.

The graphs L1 to L4 in FIG. 5 are the timings of the rich spike signals for performing the rich spike operation in the exhaust gas purifying apparatus according to the modification of the engine system 10, and the timings of the S purge signals for performing the S purge operation. Is a graph showing the change in the amount of CO and HC supplied to the exhaust pipe and the time change of the catalyst temperature (catalyst outlet gas temperature).

In the above-described example, the period of the rich spike operation is adjusted, but in the present modification, the rich spike period (time during which rich spikes are performed per one time) is adjusted. That is, the rich spike operation | movement of predetermined period and a fixed period is performed during normal engine operation. At this time, when the S purge operation is requested, the temperature of the NOx storage catalyst 42 is increased by supplying HC into the exhaust pipe 40. At this time, when the catalyst temperature does not reach the S purge temperature T, the rich spike operation is controlled as the direction in which the temperature increase rate increases, i.e., the duration of the rich spike operation (N in FIG. 5) becomes long. .

When the catalyst temperature reaches the S purge temperature T, the rich spike period returns to its original length. For this reason, catalyst temperature changes before and after S purge temperature T, and it does not become over temperature. In addition, when the catalyst temperature is higher than the S purge temperature T, it may be controlled to shorten the rich spike period. In addition, when the S purge operation ends and returns to normal engine operation, the rich spike period returns to the normal length. Also in this modification, the same effects as in the case of controlling the rich spike period described above can be obtained.

In addition, this invention is not limited to the said embodiment. For example, in the above example, either the rich spike period or the rich spike period is controlled, but both may be controlled at the same time. In addition, of course, various deformation | transformation is possible in the range which does not deviate from the summary of this invention.

According to the present invention, the rich spike control and the S purge operation can be performed efficiently, and the overheating of the catalyst due to the rich spike operation can be prevented.

Claims (5)

A catalyst installed in the exhaust passage of the engine to occlude NOx in the exhaust gas flowing into the exhaust passage and to reduce the NOx when the air-fuel ratio of the exhaust gas becomes rich; A reducing agent supply unit supplying a reducing agent component including HC in the exhaust passage; A rich spike control unit which performs the rich spike operation for temporarily controlling the air-fuel ratio to the rich side by operating the reducing agent supply unit; An S purge control unit which adds an HC component to the catalyst and determines the necessity and unnecessaryness of an S purge operation for removing sulfur content stored in the catalyst by heating at a predetermined temperature or more; And And a catalyst temperature measuring sensor for measuring the temperature of the catalyst: When the S purge control unit determines that the S purge is necessary, the rich spike control unit changes the shape of the rich spike operation based on a deviation from the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor. The exhaust gas purification device of the engine, characterized in that. The method of claim 1, And the rich spike control unit controls an operation cycle of the rich spike operation based on a deviation from the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor. The method of claim 2, The exhaust gas purifier of the engine, characterized in that the cycle is shortened as the deviation is increased. The method of claim 1, And the rich spike control unit controls the operation period of the rich spike operation based on a deviation from the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor. The method of claim 4, wherein The exhaust gas purifying apparatus of the engine characterized by lengthening the said period as said deviation becomes large.

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