JP2003269147A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of restraining adhesion of a reducer to a wall surface in an exhaust passage. <P>SOLUTION: This exhaust emission control device is characterized by disposing an exhaust throttle valve 20 between a reducer addition valve 21 and a catalyst converter 50, and by comprising an electronic control unit 22 for controlling the throttle valve 20 to the closing side along with the addition of the reducer. By controlling the throttle valve 20 to the closing side along with the addition of the reducer, the flow velocity in the vicinity of the wall surface in the exhaust passage is increased to blow off the adhering reducer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device provided with an exhaust gas purification catalyst and a reducing agent supply device in an exhaust system of the internal combustion engine.

[0002]

2. Description of the Related Art As an exhaust emission control device of this type, there is one disclosed in, for example, Japanese Patent Application Laid-Open No. 6-200740. This device is a lean N that stores nitrogen oxides (NOx) in an exhaust passage of a diesel engine under an oxygen excess atmosphere.
The lean NOx catalyst is equipped with an Ox catalyst, and the lean NOx catalyst occludes nitrogen oxides (NOx) in the exhaust gas, and when the lean NOx catalyst's occluding efficiency of nitrogen oxides (NOx) decreases, the exhaust gas to the lean NOx catalyst is reduced. By reducing the flow rate and adding the reducing agent in liquid form into fine particles, nitrogen oxides (NOx) are released from the lean NOx catalyst and the released nitrogen oxides (NOx) are reduced and purified. That is, in this device, the supplied reducing agent is lean N
By burning due to the catalytic action of the Ox catalyst to consume oxygen in the exhaust gas and lowering the atmospheric oxygen concentration of the lean NOx catalyst, the nitrogen oxides (NOx) occluded from the lean NOx catalyst are released to reduce the reducing agent. It is reduced and purified by.

In the above-mentioned conventional exhaust gas purification apparatus, when the atmospheric oxygen concentration of the lean NOx catalyst is lowered to release the nitrogen oxides (NOx) stored from the lean NOx catalyst for reduction purification, the lean NOx catalyst consumes a small amount of reducing agent. In order to efficiently reduce and purify the NOx catalyst, an exhaust throttle valve and a reducing agent addition valve are installed in this order from the exhaust upstream side in the exhaust pipe upstream of the lean NOx catalyst. The reducing agent is added after the opening degree is reduced to reduce the flow rate of the exhaust gas, and the oxygen concentration of the exhaust gas flowing into the lean NOx catalyst is locally reduced by a small amount of the reducing agent as much as possible.

[0004]

SUMMARY OF THE INVENTION In the above conventional exhaust purification system, a reducing agent is added in order to reduce the atmospheric oxygen concentration of the lean NOx catalyst, which is an exhaust purification catalyst, so as to accelerate the reduction purification action of the lean NOx catalyst. Supply to lean NOx catalyst.

However, according to the earnest studies by the present inventors, various improvements have been found in the addition of the reducing agent to the above-mentioned exhaust purification catalyst.

First, since the reducing agent adheres to the inner wall surface of the exhaust passage in the exhaust gas downstream of the reducing agent addition valve, it is necessary to add an appropriate amount of the reducing agent required to promote the above-mentioned exhaust gas purification action. Nevertheless, the oxygen concentration of the exhaust gas may still show a high value. That is, the substantial amount of the reducing agent added may decrease, which may lead to a reduction in the exhaust gas purification rate.

Further, if the reducing agent is added in advance in anticipation of the reducing agent adhesion in relation to the adhesion of the reducing agent to the inner wall surface of the exhaust passage, the lowering of the lower exhaust gas purification rate can be avoided,
This will increase the consumption of reducing agents. In particular, when adding engine fuel (for example, light oil) as a reducing agent,
It leads to deterioration of fuel consumption.

Further, as the number of times the reducing agent is added increases,
Since the reducing agent attached to the inner wall surface of the exhaust passage gradually condenses into droplets, the reducing agent of the droplets sometimes becomes lean NO.
It may flow into the x-catalyst, locally raise the temperature of the lean NOx catalyst, and locally deteriorate the lean NOx catalyst.

The present invention has been made in view of the above technical background, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine capable of suppressing the adhesion of the reducing agent to the inner wall surface of the exhaust passage.

[0010]

In order to solve the above technical problems, the present invention has the following configuration.

The present invention comprises an internal combustion engine comprising an exhaust gas purification catalyst arranged in an exhaust passage, and a reducing agent supply means arranged upstream of the exhaust purification catalyst in the exhaust passage and adding a reducing agent into the exhaust passage. In the engine, an exhaust throttle valve is arranged between the reducing agent addition valve and the exhaust purification catalyst, and an exhaust throttle valve control means for controlling the exhaust throttle valve to the closing side in accordance with the addition of the reducing agent is provided. Characterize.

In the present invention thus constructed, the exhaust throttle valve is provided between the reducing agent addition valve and the exhaust purification catalyst, and the exhaust throttle valve is controlled to the closing side as the reducing agent is added. Therefore, by controlling the exhaust throttle valve to the closing side, the flow velocity near the inner wall surface of the exhaust passage is locally increased, and atomization of the reducing agent already attached is promoted. Further, the adhesion of the reducing agent to the inner wall surface of the exhaust passage is also suppressed.

In the above description, "to control the exhaust throttle valve to the closing side with the addition of the reducing agent" means that the reducing agent is actually added or that the reducing agent may be added. In the above, the intention is to control the exhaust throttle valve to the closing side, and it does not matter whether or not the reducing agent is actually added when controlling the exhaust throttle valve. Further, the exhaust purification catalyst means all exhaust purification catalysts whose exhaust purification action is restored by addition of a reducing agent.

Further, the exhaust throttle valve control means may control the exhaust throttle valve to the closing side according to the integrated value of the reducing agent addition amount.

In this configuration, the exhaust throttle valve is controlled to the closing side when the added amount of the reducing agent reaches the integrated value. That is,
When the reducing agent adheres to the inner wall surface of the exhaust passage to some extent, the exhaust throttle valve is controlled to promote atomization of the reducing agent adhered to the inner wall surface of the exhaust passage. Therefore, it is possible to reduce the execution frequency of the exhaust throttle control that causes a change in the engine output.

Further, the exhaust gas temperature detecting means for measuring or estimating the exhaust gas temperature near the exhaust throttle valve is provided, and the exhaust throttle valve control means controls the exhaust throttle valve to the closing side according to the exhaust gas temperature. You may.

In this structure, the exhaust gas temperature detecting means measures or estimates the exhaust gas temperature, and the exhaust throttle valve is controlled according to the exhaust gas temperature. That is, the reducing agent is
The lower the exhaust gas temperature, the easier it becomes to adhere to the inner wall surface of the exhaust passage. Therefore, in this configuration, the exhaust throttle valve is controlled to the closing side in such a situation.

Further, even if the exhaust throttle valve control means can change the opening degree and / or the closing time of the exhaust throttle valve according to at least one of the integrated value of the reducing agent addition amount and the exhaust gas temperature. Good.

In this configuration, the opening and / or the closing time correlated with the control of the exhaust throttle valve is controlled in accordance with at least one of the integrated value of the reducing agent addition amount and the exhaust gas temperature. The optimum opening and closing time can be obtained according to

Further, the exhaust throttle valve control means includes a differential pressure sensor for measuring a differential pressure between the upstream and downstream of the exhaust throttle valve, and the exhaust throttle valve is controlled by the differential pressure sensor so that the differential pressure becomes constant. You may control.

In this configuration, the differential pressure generated by the closing control of the exhaust throttle valve is detected by the differential pressure sensor, and the differential pressure is fed back to the closing control of the exhaust throttle valve. That is, the differential pressure generated between the upstream side and the downstream side of the exhaust throttle valve is maintained constant, and the fluctuation of the engine output due to the abrupt change of the exhaust gas flow rate during the control of the exhaust throttle valve is suppressed.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a preferred embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described. Note that the structure of the exhaust purification catalyst shown below is merely one embodiment of the present invention, and the details thereof can be changed according to various specifications of the internal combustion engine.

First, in the present embodiment, an exhaust purification system is constructed by providing the exhaust system of the lean-burn internal combustion engine 1 represented by a diesel engine or the like with the catalytic converter 50 and the reducing agent supply device.

The catalytic converter 50 includes a casing and various exhaust purification catalysts 50 provided in the casing.
It is provided with a and 50b and has an exhaust gas purification action for purifying harmful substances in the exhaust gas discharged from the engine body 1. More specifically, a casing is disposed downstream of the turbine housing of the internal combustion engine 1, and an exhaust gas purification catalyst is arranged in the casing in the order of an exhaust reduction NOx catalyst 50a and a particulate filter (hereinafter simply referred to as a filter) 50b from the exhaust upstream side. Is built in.

The NOx storage reduction catalyst 50a is a representative example of a lean NOx catalyst provided in the exhaust system of a lean-burn internal combustion engine, and has an exhaust gas purification function for mainly purifying nitrogen oxides (NOx) in the exhaust gas. is doing.

More specifically, when the oxygen concentration of the exhaust gas is high, nitrogen oxides (NOx) in the exhaust gas are stored, and when the oxygen concentration of the exhaust gas is low, that is, the exhaust gas flowing into the NOx storage reduction catalyst. By reacting the stored nitrogen oxides (NOx) with the unburned fuel components (CO, HC) contained in the exhaust gas when the air-fuel ratio of the gas is low, harmless nitrogen (N ₂ ) It has the ability to purify exhaust gas.

The structure is, for example, alumina (Al
² O ³ ) as a carrier, and potassium (K), sodium (Na), lithium (Li), cesium (Cs) on the carrier.
Alkali metal such as, or alkaline earth such as barium (Ba), calcium (Ca) or lanthanum (L
a), at least one selected from rare earths such as yttrium (Y), and a noble metal such as platinum (Pt).

Incidentally, to give a supplementary explanation of the above-mentioned exhaust gas purification action, in the lean-burn internal combustion engine 1, combustion is usually performed in an oxygen excess atmosphere. Therefore, the oxygen concentration of the exhaust gas discharged along with the combustion hardly decreases until the reduction / release action is promoted, and the unburned fuel components (CO, HC) contained in the exhaust gas are also reduced. Very few.

Therefore, in this embodiment, the engine fuel (HC) that is a reducing agent is injected and supplied into the exhaust gas to promote the reduction of the oxygen concentration, and the hydrocarbon (HC) that is an unburned fuel component is exhausted. It is replenished in the gas to promote the above-mentioned exhaust gas purification action. The supply of the reducing agent at the time of purification is performed by a reducing agent supply device described later.
In the present embodiment, the reducing agent adding device constitutes the reducing agent supply means according to the present invention. The description of the reducing agent supply device will be given later. The catalytic converter 50 has a structure without the NOx storage reduction catalyst, that is, the filter 5
It is also applicable to 0b only.

The one filter 50b is a type of exhaust gas purification catalyst that oxidizes and burns particulates such as soot contained in the exhaust gas by the action of a catalytic substance. More specifically, a filter base material 58 carrying an activated oxygen releasing agent as a catalyst substance is provided, and the fine particles collected on the filter base material 58 are oxidatively burned by the oxidizing power of the activated oxygen for purification (removal). )
It has a function of purifying exhaust gas.

As shown in FIG. 2, the filter substrate 58 has a honeycomb shape formed of a porous material such as cordierite and has a plurality of channels 55 and 56 extending in parallel with each other. ing. More specifically, an exhaust gas inflow passage 55 whose downstream end is closed by a plug 55a,
Exhaust gas outflow passage 5 whose upstream end is closed by a plug 56a
6 and the exhaust gas inflow passage 55 and the exhaust gas outflow passage 56 are provided with a filter base 58 through a thin partition wall 57.
Are arranged side by side in the vertical and horizontal directions.

Further, in the surface of the wall 57 and the pores inside,
A carrier layer formed of alumina (Al ² O ³ ) or the like is provided. On the carrier, in addition to a precious metal catalyst such as platinum (Pt), if excess oxygen exists in the surroundings, the excess oxygen is occluded and When the oxygen concentration decreases, an active oxygen releasing agent that releases the stored oxygen in the form of active oxygen is carried.

As the active oxygen releasing agent, alkali metals such as potassium (K), sodium (Na), lithium (Li), cesium (Cs) and rubidium (Rb), barium (Ba), calcium (Ca). ), At least one selected from alkaline earth metals such as strontium (Sr), rare earths such as lanthanum (La) and yttrium (Y), and transition metals such as cerium (Ce) and tin (Sn). Should be used.

Also, preferably, an alkali metal or alkaline earth metal having a higher ionization tendency than calcium (Ca), that is, potassium (K), lithium (Li), cesium (Cs), rubidium (Rb), barium (Ba). ),
It is preferable to use strontium (Sr) or the like.

In the filter 50b thus constructed, the exhaust gas first flows in the order of the exhaust gas inflow passage 55, the partition wall 57, and the exhaust gas outflow passage 56 (arrow a in FIG. 2), soot contained in the exhaust gas, etc. The fine particles are collected on the surface and inside of the partition wall 57 while passing through the partition wall 57. The fine particles collected in the partition wall 57 are separated from each other by the partition wall 57.
The oxygen concentration of the exhaust gas flowing into the (filter substrate) is changed a plurality of times to be oxidized by activated oxygen, which is finally burned out and removed from the filter substrate 58 without emitting a bright flame. In the present embodiment, instead of the particulate filter 50b carrying the active oxygen releasing agent, a filter carrying a NOx catalyst or a NOx storage agent, or a monolith carrier carrying a NOx catalyst or a NOx storage agent may be applied. Good.

Further, in this embodiment, the filter 50b is used.
When changing the oxygen concentration of the exhaust gas flowing into the
Similarly to the NOx storage reduction catalyst 50a, the reducing agent supply means injects and supplies the engine fuel (hydrocarbon: HC) as the reducing agent into the exhaust gas to change the oxygen concentration of the exhaust gas. That is, in the present embodiment, the catalytic converter 5 having the NOx storage reduction catalyst 50a and the filter 50b built therein.
By arranging 0 in the exhaust pipe 11, fine particles such as nitrogen oxides (NOx) and soot contained in the exhaust gas are purified.

Subsequently, the above-mentioned storage reduction type NOx catalyst 5
0a and the reducing agent supply device that promotes the exhaust gas purification action of the filter 50b will be described.

The reducing agent supply device includes a reducing agent addition valve 21 attached to the exhaust pipe 11 upstream of the catalytic converter 50, and an electronic control unit 2 provided in the control system of the internal combustion engine 1.
It is composed of 2 etc.

The reducing agent addition valve 21 is an electric type on-off valve, and under the reducing agent supply program prepared in the electronic control unit 22, an appropriate amount of the reducing agent is injected and supplied into the exhaust gas at an appropriate timing. is doing. Also, the reducing agent addition valve 21
Is connected to the fuel supply system of the internal combustion engine and supplies the engine fuel supplied from the combustion supply system to the catalytic converter 50 as a reducing agent.

Further, the electronic control unit 22 outputs the output of the air-fuel ratio sensor provided downstream of the catalytic converter 50 and the outputs of the exhaust gas temperature sensors 24a and 24b provided upstream and downstream of the filter 50b. Further, the reducing agent supply amount and the supplying timing of the reducing agent are calculated based on various engine operating histories that change according to the engine operation, and the reducing agent addition valve 2 is calculated based on the calculated supplying amount and supply timing.
The opening and closing of 1 is controlled. The electronic control unit 22
Then, in the valve opening control of the reducing agent addition valve 21, a predetermined amount of reducing agent is supplied to the exhaust purification catalyst by performing a plurality of supply operations (valve opening operation) in one supply process. .

As described above, in the present embodiment, the reducing agent supply means injects and supplies the engine fuel, which is a reducing agent, into the exhaust gas, and promotes the exhaust gas purification action of the above-described storage reduction NOx catalyst 50a and the filter 50b. ing.

An oxidation catalytic converter (not shown) is provided downstream of the catalytic converter 50 to purify unburned fuel components (HC, CO) in the exhaust gas that has flowed without being purified by the catalytic converter 50. Good.

Further, in the present embodiment, the exhaust throttle valve 20 is provided downstream of the reducing agent addition valve 21 in the exhaust gas, which is entangled with the above-mentioned reducing agent supply device. That is, the exhaust throttle valve 20 is provided between the reducing agent addition valve 21 and the catalytic converter 50.

The exhaust throttle valve 20 is a butterfly valve provided between the reducing agent addition valve 21 and the catalytic converter 50, and its opening / closing control is processed by the electronic control unit 22. More specifically, a control amount for obtaining a flow velocity suitable for blowing off the reducing agent adhering to the inner wall surface of the exhaust passage is calculated, and the exhaust throttle valve 20 is controlled to an optimum opening degree. Next,
By controlling the exhaust throttle valve 20 to the closing side, the flow velocity in the vicinity of the exhaust throttle valve 20 increases and promotes atomization of the reducing agent adhering to the inner wall surface of the exhaust passage as the reducing agent is added. In addition, the added reducing agent is suppressed from adhering to the inner wall surface of the exhaust passage.

Here, the control amount of the exhaust throttle valve 20 may be the opening degree of the exhaust throttle valve 20, the closing time of the exhaust throttle valve 20, or both. The opening degree of the exhaust throttle valve 20 is set from a two-dimensional map showing the relationship between the engine speed, the integrated value of the reducing agent addition amount, and the opening degree of the exhaust throttle valve 20, as shown in FIG.

The two-dimensional map will be described here.
The flow velocity for blowing off the reducing agent adhering to the inner wall surface of the exhaust passage can be controlled by adjusting the opening degree of the exhaust throttle valve 20. That is, in order to increase the flow velocity for blowing off the reducing agent, the opening degree of the exhaust throttle valve 20 is controlled to the closed side, and to reduce the flow rate, the opening degree of the exhaust throttle valve 20 is controlled to the open side.

The flow velocity for blowing off the reducing agent is
Integrated value of reducing agent added to the exhaust passage and exhaust throttle valve 2
There is a correlation with the flow velocity in the exhaust passage before the zero valve closing control. That is, if the integrated value of the added amount of the reducing agent is small, the flow velocity required to blow off the reducing agent may be slow, and the opening degree of the exhaust throttle valve 20 may be controlled slightly to the closing side, or Fully open. On the other hand, if the integrated value of the added amount of the reducing agent is large, the flow velocity required to blow off the reducing agent becomes high, and the opening degree of the exhaust throttle valve 20 must be largely controlled to the closing side.

Further, when the engine speed is high, the flow rate of exhaust gas flowing through the exhaust passage is large, so that the flow velocity in the exhaust passage is high. Therefore, in order to obtain the flow velocity required to blow off the reducing agent, the opening degree of the exhaust throttle valve 20 may be controlled slightly to the closing side or may be in the fully opened state. On the other hand, if the engine speed is low, the flow rate through the exhaust passage is low. Therefore, in order to obtain the flow velocity required to blow off the reducing agent, the opening degree of the exhaust throttle valve 20 has to be largely controlled to the fully closed side.

That is, the opening degree of the exhaust throttle valve 20 is
It can be set from a two-dimensional map of the engine speed, the integrated value of the reducing agent addition amount, and the opening degree of the exhaust throttle valve 20 as shown in FIG. This two-dimensional map can be grasped by various preliminary experiments. Such a two-dimensional map is
It is stored in advance in the ROM provided in the electronic control unit 22.

On the other hand, there is also a situation in which the flow velocity on the inner wall surface of the exhaust passage cannot be kept constant even after the opening of the exhaust throttle valve 20 is set to the predetermined opening by the above control. That is, since the exhaust gas flow rate fluctuates due to changes in operating conditions, it may be necessary to slightly correct the exhaust throttle valve 20 to a predetermined opening degree. At that time, the differential pressure sensor 2
3 is used to control the pressure difference generated between the upstream side and the downstream side of the exhaust throttle valve 20 so as to be kept constant,
The opening degree of the exhaust throttle valve 20 can be appropriately controlled with respect to the fluctuation of the exhaust flow rate.

Further, when the exhaust throttle valve 20 is suddenly controlled to the closing side at one time, the pressure in the exhaust passage between the exhaust throttle valve 20 and the internal combustion engine becomes too high, which may cause a torque shock. At this time, by using the differential pressure sensor 23, it is possible to control the exhaust throttle valve 20 while suppressing the torque shock by maintaining a constant differential pressure between the upstream side and the downstream side of the exhaust throttle valve 20.

Next, based on the above contents, the control of the exhaust throttle valve 20 will be described with reference to the processing routine shown in FIG. It should be noted that in the present embodiment, the exhaust throttle valve control means according to the present invention is configured by the electronic control unit 22 and various sensors required to execute the following processing routine.

First, the electronic control unit 22 reads the operating condition of the internal combustion engine from various sensors (step 110) and determines whether or not the reducing agent should be added (step 120).

In step 120, the reducing agent should be added in addition to the above-mentioned situation in which the exhaust gas purification action is promoted, when temperature raising control is required to raise the temperature of the exhaust gas purification catalyst, and in the SOx of the filter 50b. SO to recover poisoning
x When the poisoning recovery control is requested, it is determined that the reducing agent should be added. Further, the reducing agent addition request is output when, for example, the number of miles traveled, the traveling time, and the like satisfy the predetermined conditions among the driving conditions read in step 110.

The above-mentioned temperature raising control is well known in which a reducing agent is supplied to the exhaust purification catalyst and the exhaust purification catalyst is forcibly heated by the heat of reaction between the reducing agent and the catalyst substance carried on the filter 50b. Control. On the other hand, SOx poisoning recovery control is performed on the basis of sulfur oxide (SO
x) is a control for recovering (eliminating) a decrease in exhaust gas purification rate of the filter 50b, that is, "SOx poisoning" caused by the occlusion of the filter 50b.
After the temperature is raised to 0 ° C. or higher, a reducing agent is supplied to promote thermal decomposition and release of sulfur oxide (SOx) that causes SOx poisoning.

Subsequently, the electronic control unit 22 determines whether or not to control the exhaust throttle valve 20 to the closing side in response to the establishment of the determination result that the reducing agent should be added in the determination of step 120. A determination is made based on the integrated value of the amount (step 130).

That is, the reducing agent adhering to the inner wall surface of the exhaust passage gradually increases in response to repeated injections of the reducing agent, and eventually becomes droplets which flow into the catalytic converter 50 and flow into the filter 5.
Although it causes deterioration such as 0b, the amount of the adhesion can be roughly grasped by the integrated value of the reducing agents added so far. Therefore, in the present embodiment, the presence or absence of exhaust throttle control is determined according to the integrated value of the reducing agent addition amount. More specifically, a predetermined integrated value (R), which serves as a criterion for determining whether or not the amount of the reducing agent attached reaches the allowable amount, is set, and the integrated value of the reducing agent addition amount reaches the predetermined integrated value (R). Therefore, it is determined that the exhaust throttle control should be performed. It should be noted that the predetermined integrated value (R) corresponding to the criterion can be grasped by various preliminary experiments carried out in consideration of the shape of the addition valve, the injection pressure, etc., which are correlated with the adhesion of the reducing agent.

Subsequently, in the electronic control unit 22, when the addition amount of the reducing agent reaches the predetermined integrated value (R),
The exhaust throttle valve 20 is controlled to the closing side to increase the flow velocity near the inner wall surface of the exhaust passage (step 140). That is, in this step 140, by controlling the exhaust throttle valve 20 to the closing side, the flow velocity near the inner wall surface of the exhaust passage is increased, and the reducing material that has already adhered is blown off while being promoted. Therefore, the attached reducing agent is separated from the inner wall surface of the exhaust passage before becoming a droplet. Then, this processing routine is once ended.

On the other hand, when it is determined in step 120 that the reducing agent should not be added, it can be considered that the reducing agent is not added, and the routine is temporarily terminated without passing through step 130. Further, even if the addition amount of the reducing agent has not reached the predetermined integrated value (R) in step 130, it can be considered that the attached amount of the reducing agent is within the allowable amount, and the processing routine does not pass through step 140. Ends once.

As described above, in the exhaust gas purifying apparatus according to the present embodiment, the exhaust throttle valve 20 is controlled to the closing side as the reducing agent is added, and the flow velocity near the inner wall surface of the exhaust passage is forcibly increased, Blows off while promoting atomization of the reducing agent that has adhered to the inner wall surface of the exhaust passage. Therefore, the reducing agent whose atomization has been promoted flows into the catalytic converter 50, so that deterioration of the catalytic converter 50 due to the inflow of the reducing agent in droplets is prevented.

Further, since the exhaust throttling control for blowing off the reducing agent is carried out in the situation where the reducing agent should be added,
The blown-off reducing agent effectively acts to promote the exhaust gas purifying action and the like, and thus wasteful consumption of the reducing agent can be prevented.

The above-described processing routine is merely an embodiment of the present invention, and the details thereof can be changed as desired. Hereinafter, the modified example will be described with reference to FIGS. 6 to 8. It should be noted that, in the flowcharts shown below, the description of the same parts as those of the above-described processing routine will be omitted.

First, in the processing routine shown in FIG. 6 as the first embodiment, in determining whether or not to control the exhaust throttle valve 20 to the closing side, a flow for determining whether or not exhaust throttle valve control is performed based on the exhaust gas temperature. Changed to. That is, when the exhaust gas temperature is low, the temperature of the exhaust passage inner wall surface is also low,
The added reducing agent is rapidly cooled on the inner wall surface of the exhaust passage and tends to adhere to the inner wall surface of the exhaust passage. Therefore, in the first embodiment, the exhaust throttle valve 20 is controlled in association with the exhaust gas temperature.

Here, the exhaust gas temperature in this embodiment is the temperature detected by the exhaust gas temperature sensor 24a mounted on the upstream side of the filter 50b, that is, the filter 50b.
The temperature of the exhaust gas flowing into That is, the temperature of the exhaust gas on the inner wall surface of the exhaust passage is estimated as the temperature of the exhaust gas flowing into the filter 50b.

First, the electronic control unit 22 determines whether or not to control the exhaust throttle valve 20 to the closing side in accordance with the determination result that the reducing agent should be added in the determination in step 120, depending on the exhaust gas temperature. Judgment based on step 23
0). That is, in step 230, the adhering condition of the reducing agent is determined using the predetermined temperature (T) as a threshold in order to determine whether or not the injected reducing agent is likely to adhere to the inner wall surface of the exhaust passage. It should be noted that the predetermined temperature (T) corresponding to the criterion can be grasped by various preliminary experiments carried out in consideration of the reducing agent addition amount and the like.

Subsequently, in the electronic control unit 22, the exhaust gas temperature has not yet reached the predetermined temperature (T), and it is considered that the reducing agent is easily attached, and the exhaust throttle valve 20 is closed. Is controlled to increase the flow velocity near the inner wall surface of the exhaust passage (step 140). That is, in this step 140, by controlling the exhaust throttle valve 20 to the closing side, the flow velocity near the inner wall surface of the exhaust passage is increased, and the reducing agent already adhering is blown off while being promoted. Therefore, the attached reducing agent is separated from the inner wall surface of the exhaust passage before becoming a droplet.

Further, when the exhaust gas temperature reaches the predetermined temperature (T) in step 230, it can be considered that the reducing agent is hard to adhere, and this processing routine is once ended without passing through step 140.

A second embodiment will be described with reference to the processing routine shown in FIG. In the present embodiment, in determining whether or not to control the exhaust throttle valve 20 to the closing side, the above-described embodiments are combined, and further, after the exhaust throttle control is performed, the exhaust throttle valve 20 is set to the normal opening degree. It is added with control to return.

That is, in the electronic control unit 22, the integrated value of the reducing agent addition amount reaches the predetermined integrated value (R) in response to the establishment of the determination result that the reducing agent should be added in step 320 (step 330). ), And the exhaust gas temperature has not reached the predetermined temperature (T) (step 340).
Accordingly, the exhaust throttle valve 20 is controlled to the closing side. In this embodiment, the determination based on the integrated value of the reducing agent is performed in step 330 and then the determination is performed in step 340 based on the exhaust gas temperature.
It is also possible to switch the order of 0s. That is, the determination based on the integrated value of the reducing agent may be performed after the determination based on the exhaust gas temperature.

Then, in the electronic control unit 22, after controlling the exhaust throttle valve 20 to the closing side (step 350),
It is determined whether or not the valve closing time has passed a predetermined time (step 360). That is, in step 360, it is determined whether or not the reducing agent adhering to the inner wall surface of the exhaust passage is sufficiently blown off, based on the predetermined time. It should be noted that the predetermined time corresponding to the determination standard can be grasped by various preliminary experiments carried out in consideration of the reducing agent addition amount, the exhaust gas temperature, etc., which are correlated with the reducing agent adhesion.

Then, the electronic control unit 22 considers that the blowing of the reducing agent adhering to the inner wall surface of the exhaust passage has ended after the elapse of a predetermined time after the control of the exhaust throttle valve 20, and the exhaust throttle valve 20 To the normal opening degree (step 370). Then, this processing routine is once ended.

Further, when the predetermined time has not yet passed, it is considered that the reducing agent adhering to the inner wall surface of the exhaust passage is not sufficiently blown off, and the exhaust throttle valve 20 is continuously maintained on the closed side to exhaust the exhaust passage. Maintains the blowing-off of the reducing agent adhering to the inner wall surface.

Subsequently, in the third embodiment, instead of the process of step 350 of the second embodiment shown in FIG. 7, the optimum opening degree and / or closing time of the exhaust throttle valve 20 at each time is calculated. The exhaust throttle valve 2 according to the calculated value
0 is changed to a process of controlling to the closing side, and a process of determining whether or not the control amount of the exhaust throttle valve 20 has reached the control amount (opening degree, closing time) set on the electronic control unit 22. Was added (see FIG. 8).

That is, in the third embodiment, the exhaust throttle valve 2
It is possible to change not only 0 to the closing side but also an appropriate opening degree and closing time according to the occasion.

The details of the processing routine shown in FIG. 8 will be described below.

First, similarly to the second embodiment, in the electronic control unit 22, the integrated value of the reducing agent addition amount reaches the predetermined integrated value (R) (step 330), and the exhaust gas temperature is set to the predetermined temperature (T). ) Is not reached (step 340), the opening degree of the exhaust throttle valve 20 and the closing time are set to, for example,
While calculating using the map shown in FIG. 3, etc., the exhaust throttle valve 20 is controlled in accordance with the calculated value (step 45).
0).

Next, in step S460, the electronic control unit 22 controls the exhaust throttle valve 20 and then, when the opening degree and the closing time reach the calculated value (control value) for control, the appropriate opening degree is received. It is assumed that the exhaust throttle valve 20 is controlled to the normal opening degree (step 370),
This processing routine is once ended.

In step 460, when the actual control amount (opening degree, closing time) has not reached the calculated value for control, it is considered that the reducing agent is not sufficiently blown off, and the exhaust throttle valve continues. The opening degree of 20 and the opening time are changed according to the calculated value at each time. As described above, in the third embodiment, not only is the exhaust throttle valve 20 closed,
Change to the optimum opening and closing time according to the occasion.

[0079]

As described above, according to the present invention, it is possible to provide an exhaust gas purification apparatus for an internal combustion engine capable of suppressing the adhesion of the reducing agent to the inner wall surface of the exhaust passage.

[Brief description of drawings]

FIG. 1 is a schematic structural diagram of an internal combustion engine according to the present embodiment.

FIG. 2 is a diagram showing an internal structure of a particulate filter according to the present embodiment.

FIG. 3 is a two-dimensional map showing the relationship between the integrated value of the engine speed, the reducing agent addition amount, and the opening degree of the exhaust throttle valve.

FIG. 4 is a schematic configuration diagram of exhaust throttle valve control using a differential pressure sensor.

FIG. 5 is a flowchart showing a processing routine of an exhaust throttle valve control program according to the present embodiment.

FIG. 6 is a flowchart showing a processing routine of an exhaust throttle valve control program according to the first embodiment.

FIG. 7 is a flowchart showing a processing routine of an exhaust throttle valve control program according to the second embodiment.

FIG. 8 is a flowchart showing a processing routine of an exhaust throttle valve control program according to a third embodiment.

[Explanation of symbols]

1 Internal combustion engine 11 exhaust pipe 20 Exhaust throttle valve 21 Reductant addition valve 22 Electronic control unit 23 Differential pressure sensor 24a, 24b Exhaust gas temperature sensor 50 catalytic converter 50a Storage reduction type NOx catalyst 50b particulate filter 55 Exhaust gas inflow passage 55a stopper 56 Exhaust gas outflow passage 56a stopper 57 partitions 58 Filter base material

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Claims (5)

[Claims] 1. An exhaust purification catalyst disposed in an exhaust passage,
Is arranged upstream of the exhaust purification catalyst in the exhaust passage,
In an internal combustion engine provided with a reducing agent supply means for adding a reducing agent into the exhaust passage, an exhaust throttle valve is arranged between the reducing agent supply means and the exhaust purification catalyst, and the reducing agent is added as the reducing agent is added. An exhaust emission control device for an internal combustion engine, comprising exhaust throttle valve control means for controlling the exhaust throttle valve to a closed side. 2. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the exhaust throttle valve control means controls the exhaust throttle valve to a closing side in accordance with an integrated value of the reducing agent addition amount. . 3. An exhaust gas temperature detecting means for measuring or estimating an exhaust gas temperature near the exhaust throttle valve, wherein the exhaust throttle valve control means closes the exhaust throttle valve according to the exhaust gas temperature. The exhaust emission control device for an internal combustion engine according to claim 1, which is controlled. 4. The exhaust throttle valve control means is capable of changing the opening degree and / or closing time of the exhaust throttle valve according to at least one of the integrated value of the reducing agent addition amount and the exhaust gas temperature. The exhaust emission control device for an internal combustion engine according to claim 1, characterized in that 5. The exhaust throttle valve control means includes a differential pressure sensor for measuring a differential pressure between an upstream side and a downstream side of the exhaust throttle valve, and the exhaust throttle valve so that the differential pressure becomes constant by the differential pressure sensor. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 4, wherein