JP2017227172A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable quick purge processing superior in environmental performance.SOLUTION: An exhaust emission control device for an engine 2, which controls a rich air-fuel ratio accompanying post injection from a cylinder fuel injection valve 3 and a purge time to enable S purge control to remove sulfur components adsorbed to a NOx occlusion reduction catalyst 11, includes an engine control unit 30 for, when executing S purge, making the rich air-fuel ratio in the S purge control lower as the deterioration degree of the NOx occlusion reduction catalyst 11 is higher if the engine 2 is in a high-load operating condition, and making the purge time shorter as the deterioration degree of the NOx occlusion reduction catalyst 11 is higher if the engine 2 is in a low-load operating condition.SELECTED DRAWING: Figure 1

Description

  The present invention relates to purge control of an exhaust purification device for an internal combustion engine.

The exhaust passage of the internal combustion engine is provided with an exhaust purification device for purifying the exhaust. For example, in order to purify NOx (nitrogen oxides) in the exhaust gas of an internal combustion engine, exhaust purification catalysts such as NOx occlusion reduction catalysts have been developed.
The NOx storage reduction catalyst is configured, for example, by supporting a NOx storage agent on a carrier containing a noble metal, and has a function of capturing NOx under a lean air-fuel ratio atmosphere (oxidizing atmosphere). Then, by performing NOx purge that makes the exhaust rich air-fuel ratio by fuel injection control of the internal combustion engine or the like, the trapped NOx is released and reduced by reacting with HC and CO in the exhaust.

However, the NOx occlusion reduction catalyst occludes NOx in the exhaust and adsorbs sulfur in the exhaust. Therefore, in order to remove sulfur adsorbed on the NOx storage reduction catalyst, it is necessary to perform an S purge that makes the exhaust gas a rich air-fuel ratio by fuel injection control of the internal combustion engine and the like and raises the temperature of the exhaust gas flowing into the NOx storage reduction catalyst. Is done according to.
Further, in Patent Document 1, in NOx purge, the exhaust air-fuel ratio is periodically switched between lean and rich, and this rich time is changed based on the degree of deterioration of the catalyst, thereby reducing fuel consumption and unburned fuel. A technique for suppressing the emission of gas is disclosed.

Japanese Patent No. 2836523

By the way, in the S purge, the sulfur component adsorbed by the NOx storage reduction catalyst is discharged as sulfur dioxide (SO ₂ ) or hydrogen sulfide (H ₂ S). It is desirable to suppress.
Therefore, the S purge not only enables efficient purging with reduced fuel consumption by controlling based on the degree of deterioration of the catalyst as in the above-mentioned NOx purge of Patent Document 1, but also allows rapid and sulfurization. There is a demand to suppress the discharge of hydrogen.

  The present invention has been made to solve such problems, and in an internal combustion engine having an exhaust purification catalyst in an exhaust passage, it is possible to quickly perform S purge with excellent environmental performance by suppressing discharge of hydrogen sulfide. An object of the present invention is to provide an exhaust emission control device.

  In order to achieve the above object, in the exhaust emission control device for an internal combustion engine according to claim 1, an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine for storing nitrogen oxides in the exhaust, and fuel injection of the internal combustion engine The post-injection executed after the main injection by the means is controlled so that the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst is set to a predetermined rich air-fuel ratio, and the sulfur component adsorbed on the exhaust purification catalyst is removed from the exhaust purification catalyst. A purge control unit that performs purge control to be removed from the engine, an operation state detection unit that detects an operation state of the internal combustion engine, and a deterioration degree estimation unit that estimates a deterioration degree of the exhaust purification catalyst. The section is configured to change either the rich air-fuel ratio in the purge control or the time for the rich air-fuel ratio in the purge control based on the deterioration degree. .

Preferably, the purge control unit may change the rich air-fuel ratio based on the degree of deterioration when the load of the internal combustion engine is equal to or greater than a predetermined value.
Preferably, the purge control unit may decrease the rich air-fuel ratio as the deterioration degree increases when the load of the internal combustion engine is equal to or greater than the predetermined value.
Preferably, the purge control unit may change a time for the rich air-fuel ratio based on the degree of deterioration when the load of the internal combustion engine is less than a predetermined value.

  Preferably, the purge control unit may reduce the time for the rich air-fuel ratio as the deterioration degree increases when the load of the internal combustion engine is less than the predetermined value.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, the rich air-fuel ratio and the rich air-fuel ratio at the time of purge control are controlled based on the deterioration degree of the exhaust purification catalyst. It is possible to appropriately set the time for the fuel ratio or the rich air-fuel ratio to suppress the fuel consumption in the purge control and reduce the execution time of the purge control. Further, when the exhaust purification catalyst is not deteriorated, the sulfur component in the catalyst can be completely released as compared with the conventional control.

  Further, by selecting either the rich air-fuel ratio or the rich air-fuel ratio as the control target for the degree of deterioration based on the operating status of the internal combustion engine, purge control suitable for the exhaust state that changes depending on the operating status of the internal combustion engine This makes it possible to suppress the sulfur component adsorbed on the exhaust purification catalyst from being discharged as hydrogen sulfide, thereby enabling purge control with excellent environmental performance.

1 is a schematic configuration diagram of an intake / exhaust system of an engine in an embodiment of the present invention. It is a flowchart which shows the S purge control procedure in an engine control unit. It is a graph which shows the relationship between the deterioration degree of the NOx storage reduction catalyst in S purge, and a total fuel injection amount.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an intake / exhaust system of a diesel engine (an internal combustion engine: hereinafter referred to as an engine 2) to which an exhaust emission control device 1 of the present invention is applied.
The engine 2 is mounted on a vehicle as a travel drive source, and is a multi-cylinder direct injection type engine. In FIG. 1, only one cylinder is illustrated in a simplified manner. The engine 2 is configured such that fuel can be injected into the combustion chamber 4 of each cylinder from an in-cylinder fuel injection valve 3 (fuel injection means) provided in each cylinder at an arbitrary injection timing and injection amount.

An electronic control throttle valve 6 for adjusting the flow rate of fresh air is provided in the intake passage 5 of the engine 2.
In the exhaust passage 10 of the engine 2, a NOx occlusion reduction catalyst 11 (exhaust purification catalyst) and a diesel particulate filter 12 are provided in order from the engine 2 toward the downstream. The NOx storage reduction catalyst 11 and the diesel particulate filter 12 are disposed in the vicinity of the exhaust port 13 of the engine 2.

  The NOx occlusion reduction catalyst 11 is configured, for example, by supporting a NOx occlusion agent such as barium (Ba) or potassium (K) on a carrier containing a noble metal such as platinum (Pt) or palladium (Pd). While trapping NOx (nitrogen oxide) under a lean air-fuel ratio atmosphere (oxidizing atmosphere), the trapped NOx is released under a rich air-fuel ratio atmosphere (reducing atmosphere) and reacted with HC and CO in the exhaust. Have the function of reducing

The diesel particulate filter 12 has a function of, for example, closing the upstream side and the downstream side of the honeycomb carrier passage with plugs alternately and collecting PM in the exhaust gas, and further has a porous structure that forms the passage. It is formed by supporting a catalytic noble metal such as platinum (Pt), palladium (Pd), rhodium (Rh) on the quality wall.
Further, the engine 2 is provided with a rotation speed sensor 20 that detects the rotation speed of the engine 2. An air flow sensor 21 that detects an intake air flow rate is provided in the intake passage 5 of the engine 2.

The exhaust passage 10 of the engine 2 is provided with an upstream air-fuel ratio sensor 22 for detecting the exhaust air-fuel ratio and an upstream exhaust temperature sensor 23 for detecting the exhaust temperature on the upstream side of the NOx storage reduction catalyst 11. A downstream air-fuel ratio sensor 24 that detects the exhaust air-fuel ratio is provided in the exhaust passage downstream of the diesel particulate filter 12.
The engine control unit 30 (purge control unit, deterioration degree estimation unit, operation state detection unit) includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a timer, a central processing unit (CPU), and the like. The detection information of various sensors such as a rotational speed sensor 20, an air flow sensor 21, an upstream air-fuel ratio sensor 22, an upstream exhaust gas temperature sensor 23, a downstream air-fuel ratio sensor 24, and other information such as the accelerator operation amount of the vehicle, etc. The vehicle operation information is input, and the fuel injection amount and fuel injection timing from the in-cylinder fuel injection valve 3 and the opening degree of the electronic control throttle valve 6 are calculated based on the various information to control the operation of the various devices. By doing so, operation control of the engine 2 is performed.

  Further, the engine control unit 30 lowers the exhaust air-fuel ratio by post injection executed after main injection, thereby reducing the exhaust air-fuel ratio by NOx purge for removing NOx stored in the NOx storage reduction catalyst 11 and post-injection. At the same time, the unburned fuel is discharged into the exhaust passage, burned (oxidized) in the exhaust passage and the NOx storage reduction catalyst 11, and the temperature of the NOx storage reduction catalyst 11 is raised, so that the sulfur stored in the NOx storage reduction catalyst 11. S purge (purge control in the present invention) for removing components is possible.

The fuel injection by the in-cylinder fuel injection valve 3 is repeatedly performed every predetermined time, and the fuel injection amount is controlled by controlling the duty ratio.
Next, S purge control in the engine of this embodiment will be described with reference to FIGS. FIG. 2 is a flowchart showing the S purge control procedure executed in the engine control unit 30. FIG. 3 is a graph showing the relationship between the degree of deterioration of the NOx storage reduction catalyst 11 and the total fuel injection amount in the S purge.

The control of this embodiment is performed, for example, every elapse of a predetermined time during engine operation.
First, in step S10, the S poisoning amount of the NOx storage reduction catalyst 11 is estimated. The S poisoning amount is an adsorption amount of the sulfur component in the exhaust gas at the NOx storage reduction catalyst 11, and can be estimated based on, for example, the accumulated operation time of the engine 2 from the previous S purge, the accumulated amount of the fuel injection amount, or the like. Good. The control in this step corresponds to the deterioration degree estimation unit of the present invention. Then, the process proceeds to step S20.

In step S20, it is determined whether S purge is necessary. If the S poisoning amount estimated in step S10 exceeds the threshold set in the vicinity of the allowable value, it is determined that S purge is necessary, and the process proceeds to step S30. If the S poisoning amount is less than or equal to the threshold value, it is determined that S purge is not necessary, and this routine is terminated.
In step S30, the deterioration estimation for obtaining the deterioration degree (catalyst deterioration degree) of the NOx storage reduction catalyst 11 is performed. What is necessary is just to obtain | require the deterioration degree of the NOx storage reduction catalyst 11 based on engine operation integration time, integration driving distance, etc., for example. Alternatively, as described in, for example, Japanese Patent Application Laid-Open No. 2012-036762, post-injection is performed, and the degree of deterioration of the NOx storage reduction catalyst 11 is obtained based on the change state of the air-fuel ratio on the downstream side of the NOx storage reduction catalyst 11. And may be used when estimating deterioration at the next engine start. Then, the process proceeds to step S40.

  In step S40, it is determined whether or not the engine load P is equal to or greater than a predetermined value P1. The predetermined value P1 is a threshold value that is appropriately set for switching, for example, a high load that prioritizes drivability and a low load that prioritizes exhaust purification performance. If the engine load P is greater than or equal to the predetermined value P1, the process proceeds to step S50. If the engine load P is less than the predetermined value P1, the process proceeds to step S60. The engine load P is always obtained from the accelerator operation amount or the like in the engine control unit 30, and the function of calculating the engine load P in the engine control unit 30 corresponds to the operating state detection unit of the present invention.

  In step S50, the rich depth in the S purge is set based on the degree of deterioration of the NOx storage reduction catalyst 11 estimated in step S30. The rich depth is the target air-fuel ratio on the richest side of the exhaust during the S purge, and the rich depth is controlled by controlling the duty ratio of the fuel injected in a pulse form from the in-cylinder fuel injection valve 3. . Then, as the degree of deterioration increases, the rich depth is set smaller. In this step, the purge time (the total time required for the rich air-fuel ratio in one purge control) is constant regardless of the degree of deterioration. Then, the process proceeds to step S70.

In step S60, the purge time in the S purge is set based on the degree of deterioration of the NOx storage reduction catalyst 11 estimated in step S30. Specifically, the purge time is set shorter as the degree of deterioration increases. In this step, the rich depth is constant regardless of the degree of deterioration. Then, the process proceeds to step S70.
In step S70, the S purge is executed with the rich depth and purge time set in step S50 or step S60. As shown by the solid line in FIG. 3, the total fuel injection amount in the S purge (the total value of the post injection amount in one S purge) is stored in NOx regardless of whether the rich depth or the purge time is controlled. It decreases as the degree of deterioration of the reduction catalyst 11 increases. Then, this routine ends.

  As described above, in the present embodiment, when the S purge is performed, the rich depth or the purge time is changed based on the degree of deterioration of the NOx storage reduction catalyst 11. In the NOx occlusion reduction catalyst 11, when the degree of deterioration is small, the NOx occlusion material and the sulfur component are firmly bonded, so that the sulfur component is not easily released even when the S purge is executed. Therefore, when the degree of deterioration is small, the conventional control in which the total fuel injection amount is made constant regardless of the degree of deterioration as shown by the broken line in FIG. 3 by increasing the rich depth or extending the purge time. As a result, the total fuel injection amount can be increased, and the sulfur component can be sufficiently released from the NOx storage reduction catalyst 11. When the degree of deterioration is small, the total fuel consumption when the S purge is performed can be suppressed by reducing the rich depth or shortening the purge time.

Further, in the present embodiment, based on the engine operating state at the time of the S purge, the rich depth or the purge time is changed based on the degree of deterioration of the NOx storage reduction catalyst 11.
When the engine load is a high load equal to or greater than the predetermined value P1, the rich depth is set large when the deterioration degree is small, and the rich depth is set small as the deterioration degree increases. As a result, when the degree of deterioration is small, it is difficult to release the sulfur component when the S purge is performed, but the fuel injection amount per unit time in the post injection is increased to promote the release of the sulfur component. The performance of the NOx occlusion reduction catalyst 11 can be recovered quickly and sufficiently. When the degree of deterioration is large, the sulfur component is easily released when the S purge is performed. Therefore, the fuel injection amount per unit time in the post injection is reduced to suppress the reduction in fuel consumption in the S purge. In addition, slip gas due to excessive S purge can be reduced. At high loads, even if the degree of deterioration is small, the purge time is not lengthened. Therefore, the S purge is terminated quickly, the influence on the engine output due to the execution of the S purge is suppressed in a short time, and drivability is improved. be able to. Further, since the exhaust air-fuel ratio is on the rich side at the time of high load, the exhaust air-fuel ratio can be easily made rich on the S purge and the sulfur component can be discharged quickly.

  On the other hand, at a low load where the engine load is less than the predetermined value P1, the purge time is set longer when the degree of deterioration is small, and the purge time is set shorter as the degree of deterioration increases. As a result, when the degree of deterioration is small, it is difficult to release the sulfur component when the S purge is performed, but it is possible to release the sulfur component sufficiently by setting a long purge time, and storing NOx. The performance of the reduction catalyst 11 can be recovered. When the degree of deterioration is large, the sulfur component is likely to be released when the S purge is performed. Therefore, the reduction in fuel consumption due to the S purge can be suppressed by shortening the purge time.

Since the intake air amount is small at low load, the air-fuel ratio in the NOx occlusion reduction catalyst 11 is unlikely to change to the lean side due to the oxygen occlusion performance of the NOx occlusion reduction catalyst 11 when performing the S purge. In the S purge, the amount of oxygen in the NOx storage reduction catalyst 11 becomes small, and the sulfur component adsorbed on the NOx storage reduction catalyst 11 tends to flow out as hydrogen sulfide (H ₂ S). Therefore, when the S purge is executed in a low engine load state, the purge time is changed with respect to the degree of deterioration without increasing the rich depth, thereby suppressing the discharge of hydrogen sulfide from the NOx storage reduction catalyst 11. S purge with excellent environmental performance is possible.

  In addition, this invention is not limited to the said embodiment. For example, in the above embodiment, the rich depth is increased as the degree of deterioration of the NOx storage reduction catalyst 11 increases in the high load state of the engine 2, and the deterioration of the NOx storage reduction catalyst 11 in the low load state of the engine 2. Although the purge time is increased as the degree increases, the control may be executed only in one of the high load state and the low load state of the engine 2.

Further, the control of the rich depth or the purge time based on the degree of deterioration of the NOx storage reduction catalyst 11 may be changed in stages, or may be controlled so as to change within a range of the degree of deterioration set as appropriate. .
In the present invention, either one of the rich depth and the purge time in the S purge control is selected as a control target based on the operating state of the engine, and the selected control target is controlled based on the degree of deterioration of the NOx storage reduction catalyst. Any change method for each control object based on the degree of deterioration may be set as appropriate.

  The present invention can be widely applied to an engine that includes an NOx storage reduction catalyst in an exhaust passage as an exhaust purification device and performs S purge.

2 Engine (Internal combustion engine)
3 In-cylinder fuel injection valve (fuel injection means)
11 NOx storage reduction catalyst (exhaust gas purification catalyst)
30 Engine control unit (purge control unit, degradation level estimation unit, operating state detection unit)

Claims (5)

An exhaust purification catalyst that is provided in the exhaust passage of the internal combustion engine and stores nitrogen oxides in the exhaust;
Sulfur adsorbed on the exhaust purification catalyst by controlling post injection executed after main injection by the fuel injection means of the internal combustion engine so that the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst becomes a predetermined rich air-fuel ratio A purge control unit for performing purge control to remove components from the exhaust purification catalyst;
An operating state detector for detecting an operating state of the internal combustion engine;
A deterioration degree estimation unit for estimating the deterioration degree of the exhaust purification catalyst,
The purge control unit changes, based on the deterioration degree, one of the rich air-fuel ratio and the time required for the rich air-fuel ratio in the purge control based on the operating state. Exhaust purification device.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the purge control unit changes the rich air-fuel ratio based on the degree of deterioration when a load of the internal combustion engine is a predetermined value or more.   3. The internal combustion engine according to claim 2, wherein the purge control unit reduces the rich air-fuel ratio as the deterioration degree increases when the load of the internal combustion engine is equal to or greater than the predetermined value. Exhaust purification device.   4. The purge control unit according to claim 1, wherein when the load on the internal combustion engine is less than a predetermined value, the purge control unit changes a time period during which the rich air-fuel ratio is set based on the degree of deterioration. The exhaust gas purification apparatus for an internal combustion engine according to the item.   5. The purge control unit according to claim 4, wherein when the load of the internal combustion engine is less than the predetermined value, the purge control unit decreases the time for the rich air-fuel ratio as the deterioration degree increases. An exhaust purification device for an internal combustion engine.

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