JP2009275666A - Emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for an emission control device of an internal combustion engine capable of distributing a reducing agent over a wide area. <P>SOLUTION: The emission control device includes a reducing agent injection device for injecting a reducing agent to supply the reducing agent to a catalyst provided at an intermediate part of an exhaust passage of the internal combustion engine, and a determination means for determining at least one of injection timing and the injection pressure of the reducing agent from the reducing agent injection device according to a flow rate of exhaust gas so that the reducing agent injected from the reducing agent injection device is brought into a predetermined state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

There are known techniques for purifying NOx, increasing the temperature of the catalyst, and regenerating the filter by adding a reducing agent to the catalyst provided in the exhaust passage of the internal combustion engine. Further, a technique is known that includes an addition valve that injects urea water into the exhaust, and a static mixer that uniformly disperses the urea water in the exhaust by colliding the urea water downstream of the addition valve. (For example, refer to Patent Document 1).
Special table 2001-516635 gazette JP 2006-90149 A

  However, since the position where the reducing agent flows changes depending on the flow rate of the exhaust gas, the urea water may not collide with the position where the urea water can be dispersed most in the static mixer. For example, if the flow rate of exhaust gas is large, urea water injected from the addition valve flows on the downstream side of the exhaust flow before reaching the static mixer. Flowing. On the other hand, when the flow rate of the exhaust gas is small, urea water flows in the vicinity of the wall surface of the exhaust pipe on the side facing the addition valve. For this reason, if the urea water does not collide with the center of the static mixer, it may be difficult to uniformly distribute the urea water in the exhaust gas.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of dispersing a reducing agent in a wider range in an exhaust purification device for an internal combustion engine.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
A reducing agent injection device for injecting the reducing agent to supply the reducing agent to a catalyst provided in the middle of the exhaust passage of the internal combustion engine;
Determining means for determining at least one of the injection timing or injection pressure of the reducing agent from the reducing agent injection device according to the flow rate of exhaust gas so that the reducing agent injected from the reducing agent injection device is in a constant state; ,
It is characterized by providing.

  The reducing agent injection device injects a reducing agent containing at least a liquid. The trajectory through which the injected reducing agent flows changes depending on the flow rate of the exhaust gas. Here, “the reducing agent is in a constant state” means that even if the flow rate of the exhaust gas changes, at least one of the locus of the reducing agent, the dispersion range, the traveling direction, or the arrival position becomes substantially the same. To do. Further, the reducing agent may pass through a target position.

By the way, the exhaust does not flow at a constant flow rate but constantly changes. That is, since the flow rate of the exhaust gas near the reducing agent injection device changes, the position where the reducing agent flows changes depending on the injection timing of the reducing agent. For example, when the flow rate of the exhaust gas is large, the spray range is close to the wall surface on the reducing agent injection device side. On the other hand, if the injection timing is determined according to the flow rate of the exhaust gas, the reducing agent can be circulated to a desired position. In other words, the reducing agent is injected at a time when the flow rate of the exhaust gas causes the reducing agent to flow to a desired position. Thus, the reducing agent can be brought into a constant state by changing the injection timing of the reducing agent.

  Even if the injection pressure of the reducing agent is changed, the position where the reducing agent flows changes. Here, the greater the exhaust gas flow rate, the greater the force to flow the reducing agent downstream, and the smaller the exhaust gas flow rate, the easier the reducing agent goes straight in the injection direction. That is, if the injection flow of the reducing agent is increased as the flow rate of the exhaust gas is increased, the reducing agent can be prevented from flowing downstream, so that the reducing agent can be circulated to a desired position. Thus, the reducing agent can be brought into a constant state by changing the injection pressure of the reducing agent.

  That is, by changing the injection timing or injection pressure of the reducing agent, the reducing agent can be injected to a position where it can be most dispersed, so that the reducing agent can be dispersed in a wider range.

In the present invention, it further comprises pulsation estimating means for measuring or estimating the flow rate of the exhaust gas near the reducing agent injection device, the flow rate of the exhaust gas changing due to the pulsation wave,
The determining means can determine when the flow rate of the exhaust gas obtained by the pulsation estimating means is closest to a predetermined value as the reducing agent injection timing.

  “Near the reducing agent injection device” can be a range in which the position where the reducing agent circulates changes according to the change in the flow rate of the exhaust gas at that position. Moreover, it is good also as a range which changes the advancing direction of a reducing agent according to the flow volume of the exhaust_gas | exhaustion in that position changing. Further, when the flow rate of the exhaust gas at that position changes, the range in which the reducing agent spraying range changes accordingly may be used. The spray range is not a range in which the reducing agent flows on the exhaust flow, but a range in which the reducing agent reaches due to momentum when injected from the reducing agent injection device.

  Here, pulsation waves are generated in the exhaust passage by opening and closing the exhaust valve. Then, the flow rate of the exhaust gas changes due to this pulsating wave. That is, since the flow rate of the exhaust gas near the reducing agent injection device is changed by the pulsating wave, the position where the reducing agent flows changes depending on the injection timing of the reducing agent. Further, the pulsation wave changes depending on the opening / closing timing of the exhaust valve, and the pulsation state of the exhaust in the vicinity where the reducing agent injection device injects the reducing agent is affected by these. Further, the time until the pulsation reaches the reducing agent injection device is affected by the length of the exhaust pipe from the exhaust valve to the reducing agent injection device. The pulsation estimating means can estimate the flow rate of the exhaust gas that changes due to the pulsating wave in consideration of these points. Further, a map can be created in advance in association with the operating state of the internal combustion engine, and the exhaust gas flow rate can be estimated based on the map.

  And if a reducing agent is injected when the flow volume of the exhaust gas which changes with a pulsation wave is the closest to a predetermined value, a reducing agent can be distribute | circulated to a desired position. That is, the predetermined value can be a flow rate of exhaust gas that allows the reducing agent to flow to a target position. This predetermined value may have a certain range. And, “when closest” means that the flow rate of exhaust gas that changes due to exhaust pulsation may not reach a predetermined value. In such a case, the reducing agent is injected when it approaches the predetermined value. This is to make it happen. This “closest time” includes a time when the value is a predetermined value.

  Thus, if the reducing agent is injected when the flow rate of the exhaust gas that changes due to pulsation is closest to a predetermined value, it is possible to determine the optimal injection pressure or injection timing according to the operating state at that time.

In the present invention, further comprising a dispersing device that is provided in the exhaust passage downstream of the reducing agent injection device and causes the reducing agent to collide and disperse the reducing agent in the exhaust gas,
The determining means may determine the time when the reducing agent injected from the reducing agent injection device is at a flow rate of exhaust gas that collides with the center of the dispersing device as the reducing agent injection timing.

  Here, when the reducing agent collides with the dispersing device, the reducing agent is reflected and scattered in a wide range. Thereby, dispersion | distribution and atomization of a reducing agent are accelerated | stimulated. Then, by causing the reducing agent injected from the reducing agent injection device to collide with the center of the dispersing device, most of the reducing agent directly collides with the dispersing device. Note that the collision with the center includes that at least a part of the reducing agent collides with the center. Further, the central axis of the trajectory through which the reducing agent flows may pass through the center of the dispersing device.

  That is, since most of the reducing agent injected from the reducing agent injection device collides with the dispersing device vigorously, it is possible to prevent the reducing agent from adhering to the wall surface of the exhaust passage and to further promote the dispersion of the reducing agent. it can. For example, a static mixer can be used as the dispersing device. Further, the flow rate of the exhaust gas such that the reducing agent injected from the reducing agent injection device collides with the center of the dispersion device becomes the predetermined value.

In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine according to the present invention may employ the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
A reducing agent injection device for injecting the reducing agent to supply the reducing agent to a catalyst provided in the middle of the exhaust passage of the internal combustion engine;
Flow rate estimating means for detecting or estimating the flow rate of the exhaust gas near the reducing agent injection device;
Pressure changing means for increasing the pressure of the reducing agent to be injected from the reducing agent injection device, when the flow rate obtained by the flow rate estimating means is high, rather than when the flow rate is low,
It is good also as providing.

  When the injection pressure of the reducing agent is changed, the position where the reducing agent flows changes. Here, the greater the exhaust gas flow rate, the greater the force to flow the reducing agent downstream. Therefore, the higher the exhaust gas flow rate, the higher the reducing agent injection pressure, the more the reducing agent flows downstream. Can be suppressed. For this reason, a reducing agent can be distribute | circulated to a desired position.

  As described above, if the reducing agent can be circulated to a desired position, the reducing agent can be prevented from adhering to the wall surface of the exhaust passage, so that the reducing agent can be dispersed in a wider range. Note that the reducing agent injection pressure may be changed stepwise according to the flow rate of the exhaust gas, or may be changed steplessly.

In the present invention, further comprising a dispersing device that is provided in the exhaust passage downstream of the reducing agent injection device and causes the reducing agent to collide and disperse the reducing agent in the exhaust gas,
The pressure changing means can change the pressure so that the reducing agent injected from the reducing agent injection device collides with the center of the dispersing device.

  That is, since most of the reducing agent injected from the reducing agent injection device collides with the dispersing device vigorously, it is possible to prevent the reducing agent from adhering to the wall surface of the exhaust passage and to further promote the dispersion of the reducing agent. it can.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the reducing agent can be dispersed in a wider range.

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

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the exhaust gas purification system for an internal combustion engine according to this embodiment is applied and its intake / exhaust system. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. An air flow meter 4 that outputs a signal corresponding to the flow rate of the intake air flowing through the intake passage 2 is provided in the middle of the intake passage 2. The air flow meter 4 measures the intake air amount of the internal combustion engine 1.

  On the other hand, a catalyst 5 is provided in the middle of the exhaust passage 3. A reducing agent is supplied to the catalyst 5. Examples of the catalyst 5 include an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, an oxidation catalyst, and a three-way catalyst. Moreover, what supported the catalyst 5 in the particulate filter, or a thing provided with the particulate filter downstream of the catalyst 5 may be used.

  A reducing agent injection valve 6 that injects a reducing agent into the exhaust gas is attached to the exhaust passage 3 upstream of the catalyst 5. As the reducing agent, for example, fuel or urea can be used, and varies depending on the type of the catalyst 5. The reducing agent injection valve 6 is opened by a signal from the ECU 10 described later and injects fuel into the exhaust. In this embodiment, the reducing agent injection valve 6 corresponds to the reducing agent injection device in the present invention.

  A dispersion plate 7 is provided downstream of the reducing agent injection valve 6 for dispersing the reducing agent over a wide range by colliding with the reducing agent. The dispersion plate 7 is provided at a position where the reducing agent injected from the reducing agent injection valve 6 reaches directly. To reach directly means not to arrive after riding on the flow of exhaust, but to reach with momentum when injected from the reducing agent injection valve 6. For example, the dispersion plate 7 is a plate installed at a right angle to the flow direction of the exhaust gas, and a plate having a plurality of holes can be used. In this embodiment, the dispersion plate 7 corresponds to the dispersion device in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the above sensor, the ECU 10 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 11 by the driver, and an accelerator opening sensor 12 that can detect the engine load, and a crank position that detects the engine speed. Sensors 13 are connected via electrical wiring, and output signals from these various sensors are input to the ECU 10.

  On the other hand, the reducing agent injection valve 6 is connected to the ECU 10 through an electrical wiring, and the opening / closing timing of the reducing agent injection valve 6 is controlled by the ECU 10.

  In this embodiment, the pulsation wave of the exhaust gas is taken into consideration when determining the timing for injecting the reducing agent from the reducing agent injection valve 6. That is, the exhaust pulsation changes the flow rate of the exhaust gas per unit time near the reducing agent injection valve 6, so that the reducing agent is injected at an optimal time in the change. The optimum time is a time when the central axis of the reducing agent flowing in the exhaust passes through the center of the dispersion plate 7.

First, the flow rate of the exhaust gas in which the central axis of the trajectory through which the injected reducing agent flows collides with the center of the dispersion plate 7 is obtained in advance through experiments or the like as a target value and stored in the ECU 10. The time when the actual exhaust gas flow rate approaches the target value is taken as the reducing agent injection timing. This target value may have a certain range to be a target range. That is, the reducing agent passage position where the reducing agent can be dispersed in an equivalent range may be the center of the dispersion plate 7.

  Here, FIG. 2 is a diagram showing the transition of the flow rate of the exhaust gas near the reducing agent injection valve 6. (A) shows a case where the flow rate of the exhaust gas is relatively high, and (B) shows a case where the flow rate of the exhaust gas is relatively low. Ga1 is a lower limit value of the target range, and Ga2 is an upper limit value of the target range. That is, when the reducing agent is injected when the flow rate of the exhaust gas is not less than the lower limit value Ga1 and not more than the upper limit value Ga2, the central axis of the reducing agent passes through the center of the dispersion plate 7. In this embodiment, the pressure of the reducing agent injected from the reducing agent injection valve 6 is constant.

  By the way, when the exhaust gas flow rate increases, the lower limit value of the fluctuating exhaust gas flow rate becomes larger than the upper limit value Ga2 of the target range, so that the exhaust gas flow rate does not fall within the target range. In such a case, the time when the flow rate of the exhaust gas becomes the smallest is the reducing agent injection timing. That is, the time when the difference between the flow rate of the exhaust gas and the upper limit value Ga2 of the target range becomes the smallest is set as the reducing agent injection timing. This time is indicated by “injection” in FIG.

  On the other hand, when the flow rate of exhaust gas decreases, the upper limit value of the fluctuating exhaust gas flow rate becomes smaller than the lower limit value Ga1 of the target range, so that the exhaust gas flow rate does not fall within the target range. In such a case, the time when the flow rate of the exhaust gas is maximized is set as the reducing agent injection timing. That is, the time when the difference between the lower limit value Ga1 of the target range and the flow rate of the exhaust gas becomes the smallest is set as the reducing agent injection timing. This time is indicated by “injection” in FIG.

  In other words, the time when the pulsation is closest to the target range is set as the reducing agent injection timing. It should be noted that instead of injecting the reducing agent every time it approaches the target range, it is sufficient to inject only when it is necessary to inject the reducing agent.

  If there is a time when the fluctuating exhaust gas flow rate falls within the target range, this time is taken as the reducing agent injection time.

  Since the exhaust pulsation is generated by opening and closing the exhaust valve, it changes according to the engine speed. Therefore, the frequency and amplitude of the pulsation are obtained in advance through experiments or the like in association with the engine speed, and are mapped and stored in the ECU 10. Further, the relationship shown in FIG. 2 may be obtained in advance by experiments or the like and mapped.

  The average value of the flow rate of the exhaust gas that changes due to exhaust pulsation can be obtained based on the intake air amount obtained by the air flow meter 4 and the fuel supply amount into the cylinder. That is, the actual exhaust gas flow rate can be calculated in consideration of the average value and the pulsation amplitude and frequency. In this embodiment, for example, the ECU 10 that estimates the flow rate of exhaust gas based on the engine speed corresponds to the pulsation estimating means in the present invention.

  FIG. 3 is a flowchart showing a flow for determining the injection timing of the reducing agent according to the present embodiment. This routine is repeatedly executed every predetermined time when there is a request to supply the reducing agent to the catalyst 5.

In step S101, the ECU 10 determines whether the exhaust gas flow rate Ga is less than the lower limit value GA1 or greater than the upper limit value GA2. The exhaust gas flow rate Ga here is an average value not considering exhaust pulsation. When the exhaust gas flow rate Ga is not less than the lower limit GA1 and not more than the upper limit GA2, the central axis of the reducing agent injected from the reducing agent injection valve 6 collides with the center of the dispersion plate 7. That is, the reducing agent can collide with the center of the dispersion plate 7 without considering the exhaust pulsation. The lower limit value GA1 and the upper limit value GA2 are obtained in advance by experiments or the like and stored in the ECU 10.

  If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, the process proceeds to step S106 and the reducing agent is injected at a normal time. The normal time is a time determined without considering exhaust pulsation. In this case, the reducing agent is injected immediately when there is a request to supply the reducing agent.

  In step S102, the ECU 10 reads an amplitude map of exhaust pulsation. In other words, how much the flow rate of the exhaust gas changes is obtained by an experiment in advance in association with the engine speed, for example, and is mapped.

  In step S103, the ECU 10 determines whether or not there is a time when the exhaust gas flow rate Ga is greater than or equal to the lower limit GA1 and within the upper limit GA2 if the exhaust pulsation amplitude ΔGa is considered. That is, it is determined whether or not the exhaust gas flow rate Ga may be greater than or equal to the lower limit GA1 and within the upper limit GA2 when the amplitude ΔGa read in step S102 is increased or decreased.

  If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process proceeds to step S105.

  In step S104, the ECU 10 determines, as the reducing agent injection timing, the time closest to the range in which the exhaust gas flow rate fluctuating due to pulsation is not less than the lower limit GA1 and not more than the upper limit GA2. That is, even when exhaust pulsation is taken into account, there is no time when the flow rate of the exhaust gas is not less than the lower limit value GA1 and not more than the upper limit value GA2, so the time closest to this time is set as the injection timing of the reducing agent. Specifically, when exhaust pulsation occurs at a flow rate less than the lower limit GA1, the time when the exhaust flow rate is the highest is the injection timing of the reducing agent. Further, when exhaust pulsation occurs at a flow rate higher than the upper limit GA2, the time when the exhaust gas flow rate is the smallest is set as the reducing agent injection timing.

  In step S105, the ECU 10 determines the timing when the value obtained by increasing or decreasing the exhaust gas pulsation amplitude ΔGa to the exhaust gas flow rate Ga is not less than the lower limit GA1 and not more than the upper limit GA2 as the reducing agent injection timing. That is, since there is a time when the flow rate of the exhaust gas is not less than the lower limit GA1 and not more than the upper limit GA2 due to exhaust pulsation, this time is set as the injection timing of the reducing agent.

  In this way, it is possible to determine the most appropriate reducing agent injection timing in the current operating state. Thereby, since many reducing agents can collide with the dispersion | distribution board 7, this reducing agent can be disperse | distributed to the wide range in exhaust_gas | exhaustion. In this embodiment, the ECU 10 that processes the flow shown in FIG. 3 corresponds to the determining means in the present invention.

As described above, according to this embodiment, the reducing agent can be dispersed in a wide range, so that the temperature in the catalyst 5 or the particulate filter can be made uniform. Further, since the reducing agent can be supplied to the entire catalyst 5, for example, the NOx purification ability can be further enhanced.

  Note that the shape of the dispersion plate 7 employed in this embodiment is merely an example, and other shapes can be employed. In the present embodiment, the dispersion plate 7 is installed so as to be perpendicular to the flow of exhaust, but it may be installed at an angle to the flow of exhaust.

In the present embodiment, the dispersion plate 7 is provided. However, even when the dispersion plate 7 is not provided, the reducing agent can be dispersed in a wider range. For example, by determining the injection timing of the reducing agent so that the reducing agent flows through the central axis of the exhaust passage, it is possible to disperse the reducing agent in a wide range while preventing the reducing agent from adhering to the exhaust passage 3. .

  In this embodiment, the injection pressure of the reducing agent is changed according to the flow rate of the exhaust gas. Since other devices are the same as those in the first embodiment, description thereof is omitted.

  When the injection pressure of the reducing agent is changed, the position where the reducing agent flows changes. For example, when the exhaust gas flow rate is the same, the higher the injection pressure of the reducing agent, the closer the position where the reducing agent circulates is in the injection direction from the reducing agent injection valve 6. That is, since the momentum of the reducing agent is increased, the amount of the reducing agent that flows downstream is reduced. Therefore, the higher the injection pressure of the reducing agent, the closer the position where the reducing agent circulates is to the wall surface facing the wall surface on the side of the exhaust passage 3 where the reducing agent injection valve 6 is provided. Further, the lower the injection pressure of the reducing agent, the closer the position where the reducing agent flows is closer to the wall surface of the exhaust passage 3 on the side where the reducing agent injection valve 6 is provided.

  On the other hand, when the injection pressure of the reducing agent is the same, the position where the reducing agent flows is closer to the injection direction from the reducing agent injection valve 6 as the flow rate of the exhaust gas is smaller. That is, as the flow rate of exhaust gas increases, the amount of reducing agent that flows downstream increases. Therefore, the smaller the flow rate of the exhaust, the closer the position where the reducing agent flows is to the wall surface facing the wall surface of the exhaust passage 3 on the side where the reducing agent injection valve 6 is provided. Further, as the flow rate of the exhaust gas increases, the position where the reducing agent flows is closer to the wall surface of the exhaust passage 3 on the side where the reducing agent injection valve 6 is provided.

  Therefore, in this embodiment, the reducing agent injection pressure is increased as the exhaust gas flow rate is increased, and the reducing agent injection pressure is decreased as the exhaust gas flow rate is decreased. In this case, the flow rate of the exhaust gas may be divided into a plurality of regions, and the injection pressure of the reducing agent may be changed stepwise. Further, it may be changed gradually (steplessly) according to the flow rate of the exhaust gas.

  That is, as the flow rate of exhaust gas increases, the reducing agent is more likely to flow downstream. Therefore, the reducing agent is prevented from flowing downstream by increasing the injection pressure of the reducing agent. That is, as the flow rate of exhaust gas increases, the reducing agent collides with a position that is shifted from the center of the dispersion plate 7 and close to the reducing agent injection valve 6. A reducing agent collides with the center of the plate 7.

  In addition, the smaller the exhaust gas flow rate, the easier it is for the reducing agent to go straight, so the reducing agent injection pressure is lowered so that the reducing agent flows downstream by the exhaust gas. That is, as the flow rate of exhaust gas decreases, the reducing agent collides with a position that is displaced from the center of the dispersion plate 7 and far from the reducing agent injection valve 6. A reducing agent collides with the center of the plate 7.

  FIG. 4 is a flowchart illustrating a flow for determining the injection pressure of the reducing agent according to the present embodiment. This routine is repeatedly executed every predetermined time when there is a request to supply the reducing agent to the catalyst 5.

  In step S201, the ECU 10 acquires the flow rate of the exhaust. The exhaust gas flow rate here may be an average value of the exhaust gas flow rate in the first embodiment, or may be an exhaust gas flow rate that varies due to pulsation. That is, in this embodiment, the reducing agent injection timing can be determined according to the average value of the exhaust gas flow rate, and the reducing agent injection timing can also be determined according to the exhaust gas flow rate that varies due to pulsation. . In this embodiment, the ECU 10 that processes step S201 corresponds to the flow rate estimating means in the present invention.

  In step S202, the ECU 10 determines the reducing agent injection pressure in accordance with the flow rate of the exhaust gas. For example, the relationship between the flow rate of the exhaust gas and the injection pressure of the reducing agent is obtained in advance through experiments or the like and mapped and stored in the ECU 10. In this embodiment, the ECU 10 that processes step S202 corresponds to the pressure changing means in the present invention.

  In this way, the reducing agent can collide with the center of the dispersion plate 7, so that the reducing agent can be dispersed in a wider range.

As described above, according to this embodiment, the reducing agent can be dispersed in a wide range, so that the temperature in the catalyst 5 or the particulate filter can be made uniform. Further, since the reducing agent can be supplied to the entire catalyst 5, for example, the NOx purification ability can be further enhanced.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification system of the internal combustion engine which concerns on an Example, and its intake / exhaust system. It is the figure which showed transition of the flow volume of the exhaust gas near a reducing agent injection valve. FIG. 2A shows a case where the flow rate of exhaust gas is relatively high, and FIG. 2B shows a case where the flow rate of exhaust gas is relatively low. 3 is a flowchart illustrating a flow for determining the injection timing of the reducing agent according to the first embodiment. 10 is a flowchart showing a flow for determining the injection timing of the reducing agent according to the second embodiment.

Explanation of symbols

1 Internal combustion engine 2 Intake passage 3 Exhaust passage 4 Air flow meter 5 Catalyst 6 Reducing agent injection valve 7 Dispersion plate 10 ECU
11 Accelerator pedal 12 Accelerator opening sensor 13 Crank position sensor

Claims (5)

A reducing agent injection device for injecting the reducing agent to supply the reducing agent to a catalyst provided in the middle of the exhaust passage of the internal combustion engine;
Determining means for determining at least one of the injection timing or injection pressure of the reducing agent from the reducing agent injection device according to the flow rate of exhaust gas so that the reducing agent injected from the reducing agent injection device is in a constant state; ,
An exhaust emission control device for an internal combustion engine, comprising: Pulsation estimating means for measuring or estimating the flow rate of the exhaust gas in the vicinity of the reducing agent injection device, the flow rate of the exhaust gas changing due to the pulsation wave;
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the determining unit determines when the flow rate of the exhaust gas obtained by the pulsation estimating unit is closest to a predetermined value as an injection timing of the reducing agent. A dispersion device provided in an exhaust passage downstream of the reducing agent injection device and causing the reducing agent to collide and disperse the reducing agent in the exhaust;
2. The determination unit according to claim 1, wherein the determining unit determines a time when the reducing agent injected from the reducing agent injection device has a flow rate of exhaust gas that collides with a center of the dispersing device as an injection timing of the reducing agent. An exhaust gas purification apparatus for an internal combustion engine as described. A reducing agent injection device for injecting the reducing agent to supply the reducing agent to a catalyst provided in the middle of the exhaust passage of the internal combustion engine;
Flow rate estimating means for detecting or estimating the flow rate of the exhaust gas near the reducing agent injection device;
Pressure changing means for increasing the pressure of the reducing agent to be injected from the reducing agent injection device, when the flow rate obtained by the flow rate estimating means is high, rather than when the flow rate is low,
An exhaust emission control device for an internal combustion engine, comprising: A dispersion device provided in an exhaust passage downstream of the reducing agent injection device and causing the reducing agent to collide and disperse the reducing agent in the exhaust;
5. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the pressure changing means changes the pressure so that the reducing agent injected from the reducing agent injection device collides with the center of the dispersing device.

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