JP3632587B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
The exhaust gas of an internal combustion engine, particularly a diesel engine, contains harmful particulates mainly composed of carbon, and it is desired to reduce particulate emissions into the atmosphere. Therefore, it has been proposed to arrange a particulate filter as a filter for collecting particulates in the exhaust system of a diesel engine. Since such a particulate filter has a large exhaust resistance as the amount of particulate collection increases, it is necessary to regenerate the particulate filter itself by burning the collected particulate.
[0003]
When the exhaust gas becomes a high temperature of about 600 ° C. or higher as in the engine high load high speed operation, the particulates spontaneously ignite and burn, so that the particulate filter can be regenerated. However, there is no guarantee that such engine high-load high-speed operation is frequently performed. Generally, a heater or an oxidation catalyst is arranged in the particulate filter, and the heater is operated at the regeneration time, or A regeneration process such as supplying unburned fuel to the oxidation catalyst is performed.
[0004]
Therefore, it is necessary to determine the regeneration time of the particulate filter, but if the determined regeneration time is too early, regeneration processing will be performed unnecessarily, such as an increase in battery size or a large amount of fuel consumption. A problem occurs. Also, if the determined regeneration time is too late, the exhaust resistance of the engine exhaust system becomes very large and the engine output is reduced.
[0005]
Thus, it is desired to accurately determine the regeneration timing of the particulate filter. For example, it has been proposed to determine the regeneration timing based on the fact that the particulate collection amount increases as the vehicle travel distance increases. However, the particulate collection amount depends on the driving state during a predetermined travel distance. Due to differences, this method cannot determine the exact playback time.
[0006]
In addition, pressure sensors are arranged upstream and downstream of the particulate filter, and the regeneration time is determined based on the fact that the differential pressure detected by these two pressure sensors increases as the particulate collection amount increases. It has also been proposed to judge, but this method is also less preferred because the pressure sensor is expensive and the pressure sensor itself has a relatively large measurement error.
[0007]
In order to determine the regeneration timing of the particulate filter relatively inexpensively, JP-A-3-41112 discloses a measurement based on the fact that the amount of fresh intake air decreases as the amount of particulate collection increases. It has been proposed to determine the regeneration timing of the particulate filter by comparing the amount of fresh intake air with a reference value for each engine operating state.
[0008]
[Problems to be solved by the invention]
In determining the regeneration timing of the particulate filter based on the intake fresh air amount, it is important that the intake fresh air amount is stable, and only when the engine is in a specific operating state such as during steady operation or engine deceleration. The playback time cannot be determined. As a result, the determination interval becomes longer, and the regeneration time may not be determined even though a large amount of the particulates are collected in the particulate filter.
[0009]
Accordingly, an object of the present invention is to provide a new intake system for an exhaust gas purification apparatus for an internal combustion engine that performs regeneration processing of the particulate filter by judging the regeneration timing of the particulate filter disposed in the engine exhaust system based on the amount of fresh intake air. This is to prevent a large amount of particulates from being collected by the particulate filter even if the judgment interval of the regeneration timing based on the volume is extended.
[0010]
[Means for Solving the Problems]
The exhaust gas purification apparatus for an internal combustion engine according to the first aspect of the present invention determines the regeneration timing of the particulate filter based on the particulate filter disposed in the engine exhaust system and the amount of exhaust particulate discharged from the cylinder. First determining means, second judging means for judging the regeneration timing of the particulate filter based on the amount of fresh air taken into the engine intake system, and regeneration means for regenerating the particulate filter, When it is determined by at least one of the first determination means and the second determination means that the particulate filter is at the regeneration timing, the regeneration filter reproduces the particulate filter.The internal combustion engine is in an engine operating state with an exhaust gas recirculation passage communicating the upstream side of the particulate filter of the engine exhaust system and the engine intake system, and an exhaust gas amount recirculated through the exhaust gas recirculation passage. A control valve for controlling to an optimum value in accordance with the fuel flow rate, and the second determining means is configured to control the particulate based on the fresh air amount after the control valve is opened to a set opening degree at the time of fuel cut. Determine when to play a filterIt is characterized by that.
[0012]
Claims2The exhaust gas purification apparatus for an internal combustion engine according to claim 1 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the first determination means and the second determination means are for capturing particulates in the particulate filter. The regeneration time is determined after estimating the collection amount, and the particulate collection amount estimated by the first determination means is greater than the particulate collection amount estimated at the same time by the second determination means. When it falls below a set value, it is determined that at least one of the internal combustion engine and the regeneration means is abnormal.
[0013]
Claims3The exhaust gas purification apparatus for an internal combustion engine according to claim 1 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the first determination means considers the amount of particulate removed by oxidation on the particulate filter. Then, the regeneration time of the particulate filter is determined.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view showing an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. In the figure, 1 is an engine body, 2 is an engine intake system, and 3 is an engine exhaust system. In the engine intake system 2, a throttle valve 4 is arranged upstream of the intake manifold 2 a connected to each cylinder, and in order to detect the amount of fresh air taken into the engine intake system 2 upstream of the throttle valve 4. The air flow meter 5 is arranged. The upstream side of the air flow meter 5 communicates with the atmosphere via an air cleaner. In the present embodiment, the throttle valve 4 is not mechanically driven in conjunction with the accelerator pedal, but can be freely set by a step motor or the like.
[0015]
On the other hand, in the engine exhaust system 3, a particulate filter 6 is disposed downstream of the exhaust manifold 3a connected to each cylinder. The downstream side of the particulate filter 6 communicates with the atmosphere via a catalytic converter and a silencer.
[0016]
Between the intake manifold 2a and the throttle valve 4 in the engine intake system and between the exhaust manifold 3a and the particulate filter 6 in the engine exhaust system are communicated by an exhaust gas recirculation passage 7, and the exhaust gas recirculation passage 7 Is provided with a control valve 7a for controlling the amount of exhaust gas to be recirculated to an optimum amount according to the engine operating state.
[0017]
The exhaust gas recirculation passage 7 is provided with an exhaust cooler 7b for cooling the recirculated exhaust gas in order to allow a large amount of exhaust gas to be recirculated. Further, a turbocharger turbine 8 a is provided between the connection portion of the exhaust gas recirculation passage 7 in the engine exhaust system 3 and the particulate filter 6, and between the throttle valve 4 and the air flow meter in the engine intake system 2. Is provided with a turbocharger compressor 8b. Further, the engine intake system 2 is provided with an intake air cooler 2b that cools fresh air so that a large amount of fresh air can be introduced into the cylinder.
[0018]
The particulate filter 6 is a porous material particulate filter made of a porous material such as ceramic. This particulate filter has a plurality of axial spaces subdivided by a plurality of partition walls extending in the longitudinal direction. In two adjacent axial spaces, one is on the exhaust upstream side, and the other is on the exhaust downstream side. Is closed by a closing material such as ceramic. Thus, two adjacent axial spaces serve as trap passages for exhaust gas flowing from the exhaust upstream side to flow to the exhaust downstream side through the partition walls, and the partition walls made of the porous material serve as trap walls for exhaust gas passage. When it comes to collecting particulates.
[0019]
The particulate filter 6 may be, for example, a metal fiber particulate filter composed of a heat-resistant metal fiber nonwoven fabric and a heat-resistant metal corrugated sheet. In this particulate filter, two non-woven fabrics and two corrugated plates are stacked in the thickness direction and wound spirally, and a plurality of axial spaces are formed by the non-woven fabric and the corrugated plates. Is. As a heat-resistant metal fiber constituting the nonwoven fabric and a heat-resistant metal constituting the corrugated sheet, for example, Fe-Cr-Al alloy or Ni-Cr-Al alloy can be used. The two non-woven fabrics are welded continuously in a spiral form with one surface in close contact with each other at the exhaust upstream side end, and in a spiral form with the other surface in close contact with each other at the exhaust downstream side end. Welded continuously. Thus, the two axially adjacent spaces in the radial direction serve as trap passages for exhaust gas flowing from the exhaust upstream side to flow to the exhaust downstream side through any nonwoven fabric, and the nonwoven fabric serves as a trap wall and passes exhaust gas. Particulates are collected at the time.
[0020]
When a large amount of particulates are collected by such a particulate filter 6, in order to increase the exhaust resistance and greatly reduce the engine output, the particulates are reduced when an appropriate amount of particulates is collected. It is necessary to burn and regenerate the particulate filter itself.
[0021]
As a means for this purpose, in this embodiment, a heater is arranged in the particulate filter, and it is necessary to determine the regeneration time for operating the heater. Further, as a regeneration means for the particulate filter, an oxidation catalyst or the like may be disposed in the particulate filter, and unburned fuel or the like may be supplied to the oxidation catalyst at the regeneration timing.
[0022]
The determination of the regeneration time is not preferable whether it is too early or too late, and it is necessary to accurately determine that an appropriate amount of particulates has been collected. In the present embodiment, the control device 20 determines the regeneration time according to the flowcharts shown in FIGS. 2 and 3, and operates the regeneration means.
[0023]
First, in step 101, an exhaust particulate amount pm discharged from the cylinder per unit time (execution interval of this flowchart) is calculated. The amount of discharged particulate varies depending on the engine type, but if the engine type is determined, it becomes a function of the current required torque TQ and the engine speed N. FIG. 4A shows the exhaust particulate amount pm of the internal combustion engine shown in FIG. 1, and each curve pm1, pm2, pm3, pm4, pm5 shows the equal exhaust particulate amount (pm1 <pm2 <pm3). <Pm4 <pm5). In the example shown in FIG. 4A, the exhaust particulate amount pm increases as the required torque TQ increases. The exhaust particulate quantity pm shown in FIG. 4A may be mapped as shown in FIG. 4B as a function of the required torque TQ and the engine speed N.
[0024]
Next, in step 102, assuming that almost all of the discharged particulates are collected by the particulate filter 6, the discharged particulate amount pm is integrated to calculate the particulate collected amount PM1. In general, the size of the particulate filter is larger than the size of the particulate. In practice, a part of the exhausted particulate is not collected in the particulate filter and is not collected in the atmosphere. Will be released. Therefore, a predetermined coefficient may be multiplied in order to exclude the amount not collected from the discharged particulate quantity pm calculated in step 101, and this may be integrated in step 102. On the particulate filter, even when the filter temperature is low, the particulate is slightly reduced in oxidation. For this purpose, a predetermined coefficient may be multiplied from the exhausted particulate pm to remove the amount of oxidation reduction on the particulate filter, and this may be integrated in step 102. In particular, when an active oxygen release agent is supported on a particulate filter, the amount of particulate reduction due to oxidation is extremely large. It is necessary to judge the amount collected.
[0025]
In step 103, it is determined whether or not the particulate collection amount PM1 accumulated in this way is equal to or greater than the set collection amount A. When this determination is affirmed, it is determined that the particulate filter 6 is at the regeneration timing, and the routine proceeds to step 104 where the regeneration means is operated to perform the regeneration processing of the particulate filter 6. In step 105, it is determined whether or not the elapsed time t from the start of the playback process is equal to or greater than the predetermined time t1, and when this determination is negative, the playback process is continued. On the other hand, if the regeneration process is performed only for the predetermined time t1, the regeneration is completed and the routine proceeds to step 106, where the particulate collection amount PM1 is set to zero.
[0026]
Next, in step 107, it is determined whether or not the accelerator pedal depression amount L is 0, that is, whether or not the accelerator pedal is released. When this determination is affirmative, it is determined in step 108 whether or not the fuel injection amount Q is zero. When this determination is affirmative, in step 109, the throttle valve 4 is set to a fully open or nearly open position, and in step 110, the control valve 7a is set to a fully open or nearly fully open position.
[0027]
Next, at step 111, an intake air amount reference value Gn ′ that should be taken into each cylinder is calculated based on the current engine speed, and the intake air amount reference value Gn ′ and the actual new amount detected by the air flow meter 5 are calculated. A difference ΔGn from the volume Gn is calculated. In calculating the intake air amount reference value Gn ′, the reference value Gn ′ for each engine speed may be mapped.
[0028]
As the particulate collection amount to the particulate filter 6 increases, the exhaust resistance increases and the intake fresh air amount decreases, and the difference ΔGn calculated in step 111 represents the current particulate collection amount. Yes. In step 112, the difference ΔGn is converted into the particulate collection amount PM2.
[0029]
In the estimation of the particulate collection amount based on the intake air amount as described above, it is necessary that the intake air amount is stable, and this estimation is possible even during steady operation. However, in the internal combustion engine having the exhaust gas recirculation passage 7 as in this embodiment, when calculating the intake air amount reference value, the control valve 7a is closed to stop the exhaust gas recirculation, or at least the control is performed. It is necessary to fix the valve 7a at a predetermined opening, and the amount of recirculated exhaust gas may not be suitable for the current operation, and exhaust emission or combustion will deteriorate.
[0030]
In this flowchart, during the engine operation including the steady operation, the judgment of step 107 or step 108 is denied, and the estimation of the particulate collection amount is not performed, and the judgment of step 107 and step 108 is performed. When the result is affirmative, that is, the particulate collection amount is estimated only when the fuel cut is intended to decelerate the engine. At the time of fuel cut, in addition to the intake air amount being stable, as a matter of course, since combustion is not performed, there is no particular problem whether the control valve 7a is closed or opened. .
[0031]
However, since the reference value itself becomes smaller when the engine decelerates, even if the actual intake fresh air amount becomes 80% of the reference value due to the collection of particulates, there is a slight difference, and the particulates are accurately In order to estimate the amount collected, it is necessary to measure the amount of intake air very accurately.
[0032]
In the present embodiment, the present invention is not limited, but the throttle valve 4 is increased to the fully open vicinity during engine deceleration to increase the intake fresh air amount and the reference value. As long as the fuel is cut, there is no particular problem even if the amount of fresh intake air is increased. Thus, even if there are some errors in the measurement of the amount of intake air, a relatively accurate estimation of the amount of particulate collection is possible. Is possible.
[0033]
Moreover, although this invention is not limited, in this embodiment, the control valve of the exhaust gas recirculation passage 7 is further fully opened at the time of engine deceleration. If particulates are not collected in the particulate filter 6, the downstream side of the throttle valve 4 of the engine intake system 2 and the upstream side of the particulate filter 6 of the engine exhaust system 6 have substantially the same pressure. Therefore, even if a small amount of gas passes through the exhaust gas recirculation passage 7, the reference value Gn ′ is substantially equal to the actual intake fresh air amount Gn and is calculated in step 111. The difference ΔGn is almost zero, and the particulate collection amount PM2 calculated in step 112 is zero.
[0034]
However, when the particulate matter is collected in the particulate filter 6 and the exhaust resistance increases, the pressure on the upstream side of the particulate filter 6 in the engine exhaust system 6 increases, and passes through the exhaust gas recirculation passage 7 and passes through the engine intake system. The gas begins to recirculate and the amount increases as the particulate collection increases. As a result, the actual intake fresh air amount decreases with an increase in the exhaust resistance of the particulate filter 6 and also decreases with this recirculated gas amount.
[0035]
In this way, when an appropriate amount of particulates is collected in the particulate filter 6, a more significant difference occurs between the reference value Gn ′ and the actual intake fresh air amount Gn. Thereby, the difference ΔGn calculated in step 111 becomes relatively large, and the particulate collection amount can be accurately estimated even if there is some measurement error.
[0036]
In the present embodiment, the particulate collection amount is estimated based on the difference ΔGn between the reference value Gn ′ and the actual intake fresh air amount Gn. Of course, the actual intake fresh air amount Gn and the reference value Gn ′ are estimated. The ratio Gn / Gn ′ is also a value representing the particulate collection amount, and the particulate collection amount may be estimated based on this value. This value is 1 when the collected amount is 0, and decreases as the collected amount increases.
[0037]
In step 113, the difference between the particulate collection amount PM2 estimated based on the intake fresh air amount in step 112 and the particulate collection amount PM1 calculated by integrating the exhaust particulate amount pm in step 102 is a predetermined value. It is determined whether or not it is greater than or equal to B. When this determination is negative, there is no significant difference between the particulate collection amount PM2 estimated based on the intake fresh air amount and the particulate collection amount PM1 estimated based on the exhaust particulate amount, and the step Proceeding to step 118, it is determined whether or not the particulate collection amount PM2 with high reliability, which is estimated by the actual intake air amount, is equal to or larger than the set collection amount A used in step 103. When this determination is negative, in step 119, the particulate collection amount PM1 based on the discharged particulate amount pm is replaced with an accurate particulate collection amount PM2, and the process ends.
[0038]
On the other hand, when the determination in step 113 is affirmative, that is, the difference between the accurate particulate collection amount PM2 estimated based on the intake fresh air amount and the particulate collection amount PM1 estimated based on the exhaust particulate amount. When is large, it is considered that the particulate collection amount PM1 is inaccurate.
[0039]
In step 114, it is determined whether the particulate collection amount PM1 is currently 0, that is, it is determined in step 106 whether the regeneration process has been completed. When this determination is affirmative, although the regeneration process should be finished, the particulate filter 6 remains, and the heater provided in the particulate filter 6 is normal. Or the oxidation catalyst carried on the particulate filter 6 has deteriorated and the unburned fuel or the like could not be burned sufficiently. In step 115, the particulate filter is regenerated. Judged to be defective. By notifying the driver of this, the regeneration means of the particulate filter 6 can be repaired at an early stage.
[0040]
Next, in step 116, as a temporary measure until the regeneration means is repaired, the duration of the regeneration process in step 105 and step 121 described later is changed from a predetermined time t1 to a time t2 longer than that, and after step 118. Perform the process.
[0041]
Further, when the determination in step 114 is negative, the exhaust particulate quantity pm estimated by the engine operating state is smaller than the actual, for example, an abnormality in the fuel injection system in which fuel is injected more than intended. Or, it may be an abnormality of the exhaust gas recirculation system in which the exhaust gas is recirculated more than intended, and it is determined in step 117 that the engine is abnormal. By notifying the driver of this, the engine can be repaired at an early stage. Next, the processing after step 118 is performed.
[0042]
If it is determined in step 118 that the accurately estimated particulate collection amount PM2 is greater than or equal to the set collection amount A, the process proceeds to step 120 and the regeneration means is operated. Next, at step 121, it is determined whether or not the elapsed time t from the start of the playback process has reached a predetermined time t1, and the playback process is continued until this determination is affirmed. Next, in step 122, the particulate collection amount PM1 used in step 102 is set to 0, and the process is ended. If it is determined in step 115 that the regeneration means is defective, the predetermined time is changed to a long time t2, and the lack of heat generation of the heater is compensated by extending the energization time, and the oxidation catalyst is deteriorated. Is compensated by extending the supply time of the unburned fuel, so that the particulates collected by the particulate filter can be almost completely burned out.
[0043]
However, the extension of the regeneration process time is only a provisional measure, and both the heater energization time extension and the unburned fuel supply time extension are not preferable. Further, the regeneration cannot be dealt with by extension of the regeneration time such as disconnection of the heater. In any case, if it is determined in step 115 that the reproduction is abnormal, it is necessary to repair the reproducing means at an early stage.
[0044]
Estimating the amount of particulate collection based on the actual intake fresh air volume is accurate, but the intake fresh air volume must be stable, and it must be in a specific operating state such as during steady state operation or engine deceleration. It is possible to estimate the amount of particulate collection only at this time. As a result, the estimation interval may be prolonged only by estimating the particulate collection amount, and the regeneration time may not be determined even though a large amount of particulates is collected in the particulate filter.
[0045]
In this flowchart, the first judgment means for estimating the particulate collection amount based on the exhausted particulate quantity exhausted from the cylinder and judging the regeneration timing of the particulate filter, and the new air amount taken into the engine intake system And determining the regeneration time of the particulate filter by estimating the particulate collection amount based on the particulate filter, and the particulate filter is at the regeneration time by at least one of the first determination means and the second determination means. When the judgment is made, the particulate filter is reproduced by the reproducing means.
[0046]
As a result, the exhausted particulate amount per unit time itself is an estimated value based on the engine operating state, and therefore the estimated particulate collection amount using the integrated value is not so accurate. Since the determination of the regeneration time of the particulate filter by the first determination means is always performed irrespective of the engine operating state in addition to the determination of the regeneration time of the particulate filter by the second determination means, Even if the judgment interval of the regeneration time by the judging means is extended, if the regeneration time is judged by the first judging means, the particulate filter is regenerated and a large amount of particulates is collected in the particulate filter. There is no.
[0047]
FIG. 5 is a plan view showing a surrounding structure of a particulate filter 6 'different from the particulate filter described above, and FIG. 6 is a side view thereof. In this surrounding structure, the switching unit 9 connected to the downstream side of the exhaust manifold 3a via the exhaust pipe 3b, the particulate filter 6 ′, one side of the particulate filter 6 ′ and the switching unit 9 are connected. A first connection portion 3 d, a second connection portion 3 e that connects the other side of the particulate filter 6 ′ and the switching portion 9, and an exhaust passage 3 c on the downstream side of the switching portion 9 are provided. The switching unit 9 includes a valve body 9 a that can block the exhaust flow in the switching unit 9. At one blocking position of the valve body 9a, the upstream side in the switching unit 9 is communicated with the first connection part 3d and the downstream side in the switching unit 9 is communicated with the second connection part 3e. As indicated by the arrows, the flow proceeds from one side of the particulate filter 6 'to the other side.
[0048]
FIG. 7 shows the other blocking position of the valve body 9a. In this blocking position, the upstream side in the switching unit 9 is communicated with the second connection portion 3e and the downstream side in the switching unit 9 is communicated with the first connection portion 3d, and the exhaust gas is as shown by arrows in FIG. , Flows from the other side of the particulate filter 6 ′ to one side. Thus, by switching the valve body 9a, the direction of the exhaust gas flowing into the particulate filter 6 ′ can be reversed, that is, the exhaust upstream side and the exhaust downstream side of the particulate filter 6 ′ can be reversed. It becomes possible.
[0049]
In this way, the surrounding structure of the particulate filter can reverse the exhaust upstream side and the exhaust downstream side of the particulate filter with a very simple configuration. Further, in the particulate filter, a large opening area is required in order to facilitate the inflow of exhaust gas. However, the structure around the particulate filter does not deteriorate the vehicle mountability, and FIGS. As shown in FIG. 2, a particulate filter having a large opening area can be used.
[0050]
FIG. 8 shows the structure of the particulate filter 6 '. In FIG. 8, (A) is a front view of the particulate filter 6 ', and (B) is a side sectional view. As shown in these drawings, the particulate filter 6 ′ has an oblong front shape, and is, for example, a wall flow type having a honeycomb structure formed of a porous material such as cordierite. It has a number of axial spaces subdivided by partition walls 54 extending in the axial direction. In two adjacent axial spaces, one is closed on the exhaust downstream side by the plugs 52 and 53, and the other is closed on the exhaust upstream side. In this way, one of the two adjacent axial spaces becomes the exhaust gas inflow passage 50 and the other becomes the outflow passage 51, and the exhaust gas always passes through the partition wall 54 as shown by an arrow in FIG. 8B. The particulates in the exhaust gas are very small compared to the size of the pores of the partition wall 54, but collide with the exhaust upstream surface of the partition wall 54 and the pore surface in the partition wall 54. Be collected. Thus, each partition wall 54 functions as a collecting wall for collecting particulates. In this particulate filter 6 ′, in order to oxidize and remove the collected particulates, alumina or the like is used on both side surfaces of the partition wall 54, and preferably on the pore surface in the partition wall 54, as described below. An active oxygen release agent and a noble metal catalyst are supported.
[0051]
The active oxygen release agent is an agent that promotes oxidation of particulates by releasing active oxygen. Preferably, oxygen is taken in and retained when excess oxygen is present in the surroundings, and the oxygen concentration in the surroundings is increased. When lowered, the retained oxygen is released in the form of active oxygen.
[0052]
As this noble metal catalyst, platinum Pt is usually used, and as active oxygen release agents, alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, and rubidium Rb, barium Ba, calcium Ca, and strontium Sr are used. At least one selected from such alkaline earth metals, lanthanum La, rare earths such as yttrium Y, and transition metals is used.
[0053]
In this case, as the active oxygen release agent, 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, and strontium Sr are used. preferable.
[0054]
Next, how the collected particulates are oxidized and removed by such a particulate filter carrying an active oxygen release agent will be described by taking platinum Pt and potassium K as an example. The same particulate removal action can be performed using other noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals.
[0055]
In a diesel engine, combustion is usually performed under excess air, and therefore the exhaust gas contains a large amount of excess air. That is, when the ratio of air and fuel supplied to the engine intake system and the combustion chamber is referred to as the air-fuel ratio of the exhaust gas, the air-fuel ratio is lean. Further, since NO is generated in the combustion chamber, the exhaust gas contains NO. The fuel also contains sulfur S, which reacts with oxygen in the combustion chamber to react with SO.₂  It becomes. Therefore, in the exhaust gas, SO₂  It is included. Therefore excess oxygen, NO and SO₂  The exhaust gas containing the gas flows into the exhaust upstream side of the particulate filter 6 '.
[0056]
FIGS. 9A and 9B schematically show enlarged views of the exhaust gas contact surface of the particulate filter 6 ′. 9A and 9B, reference numeral 60 indicates platinum Pt particles, and reference numeral 61 indicates an active oxygen release agent containing potassium K.
[0057]
As described above, since a large amount of excess oxygen is contained in the exhaust gas, when the exhaust gas comes into contact with the exhaust gas contact surface of the particulate filter, as shown in FIG.₂  Is O₂ ⁻Or O^2-It adheres to the surface of platinum Pt. On the other hand, NO in the exhaust gas is O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂  (2NO + O₂  → 2NO₂  ). Then the generated NO₂  A part of N is oxidized on platinum Pt and absorbed in the active oxygen release agent 61, and combined with potassium K, nitrate ion NO as shown in FIG.₃ ⁻Diffused into the active oxygen release agent 61 in the form of potassium nitrate KNO₃  Is generated. In this way, harmful NO contained in the exhaust gas_X  Can be absorbed by the particulate filter 6 ', and the amount released to the atmosphere can be greatly reduced.
[0058]
On the other hand, as described above, the exhaust gas contains SO.₂  Is also included, this SO₂  Is absorbed into the active oxygen release agent 61 by the same mechanism as NO. That is, as described above, oxygen O₂  Is O₂ ⁻Or O^2-Is attached to the surface of platinum Pt in the form of SO₂  Is O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with SO₃  It becomes. The generated SO₃  Is partly oxidized on platinum Pt while being absorbed in the active oxygen release agent 61 and combined with potassium K, sulfate ions SO.₄ ^2-  Diffused into the active oxygen release agent 61 in the form of potassium sulfate K₂SO₄Is generated. In this way, potassium nitrate KNO is contained in the active oxygen release catalyst 61.₃  And potassium sulfate K₂SO₄Is generated.
[0059]
Particulates in the exhaust gas adhere to the surface of the active oxygen release agent 61 carried by the particulate filter, as indicated by 62 in FIG. 9B. At this time, the oxygen concentration at the contact surface between the particulate 62 and the active oxygen release agent 61 decreases. When the oxygen concentration is lowered, a difference in concentration occurs between the active oxygen release agent 61 having a high oxygen concentration, and therefore oxygen in the active oxygen release agent 61 is brought into contact with the particulate 62 and the active oxygen release agent 61. Try to move towards. As a result, potassium nitrate KNO formed in the active oxygen release agent 61₃  Is decomposed into potassium K, oxygen O, and NO, oxygen O goes to the contact surface between the particulate 62 and the active oxygen release agent 61, and NO is released from the active oxygen release agent 61 to the outside. NO released to the outside is oxidized on the platinum Pt on the downstream side, and is again absorbed in the active oxygen release agent 61.
[0060]
On the other hand, potassium sulfate K formed in the active oxygen release agent 61 at this time₂SO₄Also potassium K, oxygen O and SO₂  The oxygen O is directed to the contact surface between the particulate 62 and the active oxygen release agent 61, and SO₂  Is released from the active oxygen release agent 61 to the outside. SO released to the outside₂  Is oxidized on the platinum Pt on the downstream side and is absorbed again into the active oxygen release agent 61. However, potassium sulfate K₂SO₄Is stabilized, potassium nitrate KNO₃  It is difficult to release active oxygen compared to.
[0061]
On the other hand, the oxygen O toward the contact surface between the particulate 62 and the active oxygen release agent 61 is potassium nitrate KNO.₃  And potassium sulfate K₂SO₄It is oxygen decomposed from a compound such as Oxygen O decomposed from the compound has high energy and has extremely high activity. Therefore, the oxygen directed toward the contact surface between the particulate 62 and the active oxygen release agent 61 is active oxygen O. When these active oxygen O comes into contact with the particulate 62, the particulate 62 is oxidized without emitting a luminous flame.
[0062]
By the way, since platinum Pt and the active oxygen release agent 61 are activated as the temperature of the particulate filter increases, the amount of active oxygen O released from the active oxygen release agent 61 per unit time increases as the temperature of the particulate filter increases. To do. Therefore, the amount of fine particles that can be removed by oxidation without emitting a luminous flame per unit time on the particulate filter increases as the temperature of the particulate filter increases.
[0063]
The solid line in FIG. 10 indicates the amount G of fine particles that can be removed by oxidation without emitting a bright flame per unit time. In FIG. 10, the horizontal axis represents the temperature TF of the particulate filter. When the discharged particulate pm discharged from the combustion chamber per unit time is smaller than the amount G of fine particles that can be removed by oxidation, that is, in the region I in FIG. 10, all the particulate discharged from the combustion chamber is collected by the particulate filter. As soon as it is done, the particulate filter can be oxidized and removed without emitting a bright flame in a short time.
[0064]
On the other hand, when the discharged particulate amount pm is larger than the fine particle amount G that can be removed by oxidation, that is, in the region II in FIG. 10, the amount of active oxygen is insufficient to oxidize all the particulates. 11A to 11C show the state of particulate oxidation in such a case.
[0065]
That is, when the amount of active oxygen is insufficient to oxidize all the particulates, if the particulates 62 adhere on the active oxygen release agent 61 as shown in FIG. Particulates that are only oxidized and not fully oxidized remain on the exhaust upstream side of the particulate filter. Next, when the state where the amount of active oxygen is insufficient continues, the particulate portion that has not been oxidized from one to the next remains on the exhaust upstream surface, and as a result, as shown in FIG. The exhaust upstream surface is covered with the residual particulate portion 63.
[0066]
Such residual particulate portion 63 gradually changes to a carbonaceous material that is difficult to oxidize, and when the exhaust upstream surface is covered with the residual particulate portion 63, NO and SO by platinum Pt.₂  The active oxygen release action by the active oxygen release agent 61 is suppressed. Accordingly, the residual particulate portion 63 can be gradually oxidized over time, but another particulate 64 is placed on the residual particulate portion 63 from the next to the next as shown in FIG. In other words, when the particulates are deposited in a laminated form, these particulates are separated from the platinum Pt and the active oxygen release agent. It is not oxidized. Therefore, further particulates are deposited on the particulate 64 one after another. That is, when the state in which the discharged particulate amount pm is larger than the oxidizable and removable fine particle amount G continues, the particulates are deposited in a laminated manner on the particulate filter.
[0067]
In this way, in the region I in FIG. 10, the particulates are oxidized on the particulate filter within a short time without emitting a bright flame, and in the region II in FIG. 10, the particulates are deposited on the particulate filter in a stacked manner. To do. Therefore, if the relationship between the discharged particulate amount pm and the oxidizable and removable fine particle amount G is in the region I, it is possible to prevent the accumulation of particulates on the particulate filter. However, this is not always realized, and particulates may accumulate on the particulate filter.
[0068]
When such a particulate filter 6 ′ is used, in the flowchart shown in FIGS. 2 and 3 described above, in step 102, the amount of fine particles that can be removed by oxidation based on the discharged particulate pm and the current particulate filter temperature TF. The difference from G is integrated. Of course, when the amount G of fine particles that can be removed by oxidation is larger and the difference is a negative value, zero is added, but if the particulate collection amount PM1 has a value at this point, That is, if the discharged particulate amount pm has exceeded the oxidizable and removable fine particle amount G so far and the particulates remain on the particulate filter, the residual particulates are oxidized and removed by the margin of the oxidizable and removable fine particle amount G. Therefore, a negative value may be added.
[0069]
The regeneration processing that is performed when the particulate collection amount PM1 calculated in this way or the particulate collection amount PM2 estimated based on the intake fresh air amount is equal to or greater than the set collection amount A is, for example, the air-fuel ratio of the exhaust gas. Is to make it rich. When the oxygen concentration in the exhaust gas is lowered in this way, the active oxygen O is released from the active oxygen release agent 61 to the outside at once, and the particulates deposited by the active oxygen O released at once are burned and removed at once without generating a bright flame. Can be made.
[0070]
In order to make the air-fuel ratio of the exhaust gas rich, fuel injection into the cylinder in the exhaust stroke, fuel injection upstream of the particulate filter 6 'in the engine exhaust system, or the like can be used. In particular, when a reducing agent such as unburned fuel is supplied to the particulate filter 6 ′, this reducing agent uses oxygen in the exhaust gas by an oxidation catalyst such as platinum Pt carried on the particulate filter 6 ′. And burn. In this way, the oxygen concentration in the exhaust gas decreases, and the particulate filter temperature TF rises due to the combustion heat of the reducing agent, and the amount G of the fine particles that can be removed by oxidation increases, and the residual particulates are removed by oxidation. It is advantageous.
[0071]
As a regeneration means for the particulate filter 6 ′, a heater may be disposed in the particulate filter 6 ′, and the temperature of the particulate filter 6 ′ may be simply increased to increase the amount of particulates that can be removed by oxidation. Further, the particulate filter 6 'may be heated by raising the exhaust gas temperature by retarding the ignition timing or retarding the fuel injection timing.
[0072]
In this embodiment, as described above, the exhaust upstream side and the exhaust downstream side of the particulate filter 6 'can be easily reversed, and this may be implemented as a regeneration means. Before the particulate collection amount adversely affects the vehicle running, for example, when the particulates are accumulated to the extent shown in FIG. If it is determined that the regeneration time is reached, the valve body 9a is switched to the other blocking position as a regeneration process. In the wall flow type particulate filter, the particulates collide with the exhaust upstream surface of the partition wall 54 where the exhaust gas mainly collides and the exhaust gas flow facing surface in the pores, that is, one of the collection surfaces of the partition wall 54. If the active oxygen released from one of the collecting surfaces is insufficient with respect to the collected particulates, all remains without being oxidized and removed.
[0073]
If the exhaust upstream side and the exhaust downstream side of the particulate filter are reversed by switching the valve body 9a, there is no further particulate accumulation on the particulates that accumulate on one of the collecting surfaces of the partition wall. The residual and deposited particulates are gradually oxidized and removed by the active oxygen released from one of the collecting surfaces. In particular, the particulates remaining and depositing in the pores of the partition walls are easily broken and fragmented by the exhaust gas flow in the reverse direction, as shown in FIG. Move downstream.
[0074]
As a result, many of the finely divided particulates are dispersed in the pores of the partition walls, and are often oxidized and removed by direct contact with the active oxygen release agent supported on the inner surface of the pores of the partition walls. Become. In this way, by supporting the active oxygen release agent in the pores of the partition walls, the residual particulates can be remarkably easily oxidized and removed. Further, in addition to this oxidation removal, the other collection surface of the partition wall 54 that has become upstream due to the backflow of the exhaust gas, that is, the exhaust upstream surface of the partition wall 54 where the exhaust gas mainly collides and the inside of the pores On the exhaust gas flow facing surface (which is on the side opposite to the one collecting surface), new particulates in the exhaust gas adhere and are oxidized and removed by the active oxygen released from the active oxygen release agent. . A part of the active oxygen released from the active oxygen release agent during the oxidation removal moves to the downstream side together with the exhaust gas, and the remaining particulates are oxidized and removed by the backflow of the exhaust gas.
[0075]
That is, the residual particulates on one collecting surface in the partition wall are not only for the active oxygen released from this collecting surface, but also for the oxidation removal of the particulates on the other collecting surface of the partition wall by the backflow of exhaust gas. The remaining active oxygen used comes with the exhaust gas. Thereby, by reversing the exhaust upstream side and the exhaust downstream side of the particulate filter and alternately using one collection surface and the other collection surface of the particulate filter partition for collecting particulates, Even if particulates are collected to some extent on one collection surface of the particulate filter partition during reverse rotation, in addition to the arrival of active oxygen to the residual collection particulates due to the backflow of exhaust gas, Furthermore, since the particulates are not collected, the residual particulates are gradually oxidized and removed. In this way, the remaining particulates on the other collecting surface that currently collects the particulates, the remaining particulates on one collecting surface until the valve body 9a is switched again due to the regeneration timing due to the remaining collected particulates. The curate can be sufficiently oxidized and removed.
[0076]
Of course, if the air-fuel ratio of the exhaust gas is made rich at the time of reversal between the exhaust upstream side and the exhaust downstream side of this particulate filter, or immediately after that, the other particulates of the particulate filter partition walls do not remain. Since the active oxygen is easily released on the collecting surface as compared with one of the collecting surfaces, the residual particulates can be more reliably oxidized and removed by the active oxygen released in a larger amount.
[0077]
By the way, calcium Ca in the exhaust gas is SO.₃  In the presence of calcium sulfate CaSO₄  Is generated. This calcium sulfate CaSO₄  Is called ash and is difficult to oxidize and remove. Accordingly, in order to prevent clogging of the particulate filter due to the ash, when an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca is used as the active oxygen release agent 61, for example, potassium K, the release of active oxygen is performed. SO diffused in the agent 61₃  Binds potassium K and potassium sulfate K₂SO₄Calcium Ca is SO₃  It passes through the partition wall of the catalytic converter without being coupled with the. Therefore, the particulate filter is not clogged by ash. Thus, as described above, as the active oxygen release agent 61, 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, strontium Sr is used. Is preferred.
[0078]
Further, even if the particulate filter carries only a noble metal such as platinum Pt, NO retained on the surface of platinum Pt.₂  Or SO₃  Active oxygen can be released from However, in this case, the solid line indicating the amount G of fine particles that can be removed by oxidation moves slightly to the right as compared with the solid line shown in FIG.
[0079]
Moreover, NO in exhaust gas as an active oxygen release agent_X  NO used for purification_X  It is also possible to use an occlusion reduction catalyst. In this case, the stored NO_X  And SO_X  In order to release the exhaust gas, it is necessary to at least temporarily enrich the air-fuel ratio of the exhaust gas, and this enrichment control may be used as a regeneration means for the particulate filter.
[0080]
Incidentally, in FIG. 10, the amount G of fine particles that can be removed by oxidation is shown as a function of only the temperature TF of the particulate filter 6 ′, but this amount of fine particles G that can be removed by oxidation is actually the oxygen concentration in the exhaust gas, the exhaust gas. NO inside_x  It is also a function of the concentration, the unburned HC concentration in the exhaust gas, the degree of oxidization of fine particles, the space velocity of the exhaust gas flow in the particulate filter 6 ', the exhaust gas pressure, and the like. Therefore, it is preferable to calculate the amount G of fine particles that can be removed by oxidation in consideration of the influence of all the above-mentioned factors including the temperature TF of the particulate filter 6 '.
[0081]
However, among these factors, the temperature TF of the particulate filter 6 'has the largest influence on the amount G of fine particles that can be removed by oxidation, and the relatively large influences are the oxygen concentration in the exhaust gas and NO._X  Concentration. FIG. 13A shows a change in the particulate amount G that can be removed by oxidation when the temperature TF of the particulate filter 6 ′ and the oxygen in the exhaust gas change, and FIG. 13B shows the change in the particulate filter 6 ′. Temperature TF and NO in exhaust gas_x  A change in the amount G of fine particles that can be removed by oxidation when the concentration changes is shown. In FIGS. 13A and 13B, the broken lines indicate the oxygen concentration and NO in the exhaust gas._X  This shows the case where the concentration is a reference value. In FIG.₂  ]₁  When the oxygen concentration in the exhaust gas is higher than the reference value, [O₂  ]₂  [O₂  ]₁  FIG. 13B shows a case where the oxidation concentration is higher than that in FIG. 13B.₁  Is NO in the exhaust gas than the reference value_X  [NO] when the concentration is high₂  [NO]₁  More than NO_X  Each shows a high concentration.
[0082]
As the concentration of oxygen in the exhaust gas increases, the amount G of fine particles that can be removed by oxidation alone increases, but the amount of oxygen taken into the active oxygen release agent 61 further increases, so that the active oxygen released from the active oxygen release agent 61 also increases. Increase. Accordingly, as shown in FIG. 13A, the amount G of fine particles that can be removed by oxidation increases as the oxygen concentration in the exhaust gas increases.
[0083]
On the other hand, NO in the exhaust gas is oxidized on the surface of platinum Pt as described above, and NO.₂  It becomes. NO generated in this way₂  Is absorbed in the active oxygen release agent 61 and the remaining NO₂  Detaches from the surface of platinum Pt to the outside. At this time, the particulate is NO₂  Contact with the catalyst promotes the oxidation reaction. Therefore, as shown in FIG. 13B, NO in the exhaust gas_X  As the concentration increases, the amount G of fine particles that can be removed by oxidation increases. However, this NO₂  Particulate oxidation promotion effect due to NO occurs only when the exhaust gas temperature is between about 250 ° C. and about 450 ° C. Therefore, as shown in FIG. 13B, NO in the exhaust gas_X  As the concentration increases, the amount G of fine particles that can be removed by oxidation increases when the temperature TF of the particulate filter 22 is between about 250 ° C. and 450 ° C.
[0084]
As described above, the amount G of fine particles that can be removed by oxidation is preferably calculated in consideration of all the factors that affect the amount of fine particles G that can be removed by oxidation. In addition to the temperature TF of the filter 6 ', the oxygen concentration and NO in the exhaust gas that have a relatively large effect_X  If the amount G of fine particles that can be removed by oxidation is calculated based on the concentration, the integrated value pm used in step 102 in the above-described flowchart can be calculated more accurately.
[0085]
Specifically, as shown in FIGS. 14A to 14F, oxidation at each temperature TF (200 ° C., 250 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C.) of the particulate filter 6 ′. The amount G of the fine particles that can be removed is the oxygen concentration [O₂  ] And NO in exhaust gas_x  It is mapped as a function of concentration [NO], and the temperature TF, oxidation concentration [O] of each particulate filter 6 '₂  ] And NO_x  The amount G of fine particles that can be removed by oxidation according to the concentration [NO] can be calculated from the maps shown in FIGS. 14A to 14F by proportional distribution.
[0086]
The oxygen concentration in the exhaust gas [O₂  ] And NO_x  Concentration [NO] is measured by oxygen concentration sensor and NO_X  It can be detected using a density sensor. However, the oxygen concentration in the exhaust gas [O₂  ] As a function of the required torque TQ and the engine speed N as shown in FIG._X  The concentration [NO] is also mapped as a function of the required torque TQ and the engine speed N as shown in FIG. 15B. From these maps, the oxygen concentration [O₂  ] And NO_X  The concentration [NO] may be calculated.
[0087]
As a regeneration process when the active oxygen releasing agent is carried on the particulate filter, when the temperature of the particulate filter is increased by supplying a reducing agent such as unburned fuel and energizing the heater, In step 121, such reproduction processing is performed for a predetermined time t1 or t2, thereby completing the reproduction. However, regeneration should be completed when the amount G of particulates that can be removed by oxidation based on the temperature of the heated particulate filter exceeds the calculated or estimated particulate collection amount PM1 or PM2. The regeneration process such as the supply of the reducing agent and the energization of the heater may be stopped.
[0088]
【The invention's effect】
As described above, the exhaust gas purification apparatus for an internal combustion engine according to the present invention includes the first determination means for determining the regeneration timing of the particulate filter based on the amount of exhaust particulate discharged from the cylinder, and the fresh air introduced into the engine intake system. A second judging means for judging the regeneration timing of the particulate filter based on the amount; and a reproducing means for regenerating the particulate filter, wherein the particulate filter is operated by at least one of the first judging means and the second judging means. When it is determined that it is the reproduction time, the particulate filter is reproduced by the reproducing means.
[0089]
The internal combustion engine has an exhaust gas recirculation passage that connects the upstream side of the particulate filter of the engine exhaust system and the engine intake system, and the amount of exhaust gas that is recirculated through the exhaust gas recirculation passage according to the engine operating state. A control valve for controlling to a value,The second judgment means isBased on the amount of fresh air after opening the control valve to the set opening at the time of fuel cutAlthough accurate judgment is possible to judge the regeneration time of the particulate filterThe secondIf only two determination means are used, the determination interval may be prolonged and a large amount of particulates may be collected in the particulate filter. However, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, in addition to the second determination means, the first determination means determines the regeneration timing of the particulate filter regardless of the specific engine operating state based on the exhaust particulate amount. In order to regenerate the particulate filter, even if this judgment is somewhat inaccurate, a large amount of particulates will not be collected in the particulate filter.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
FIG. 2 is a part of a flowchart for determining a reproduction time.
FIG. 3 is the remaining part of the flowchart of FIG. 2;
FIG. 4 is a diagram showing an amount of discharged particulates.
FIG. 5 is a plan view showing a surrounding structure of another particulate filter.
6 is a side view of FIG. 5. FIG.
7 is a view showing another blocking position of the valve body in the switching portion different from FIG.
FIG. 8 is a diagram illustrating a structure of a particulate filter.
FIG. 9 is a diagram for explaining the oxidizing action of particulates.
FIG. 10 is a graph showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of the particulate filter.
FIG. 11 is a diagram for explaining a particulate deposition action.
FIG. 12 is an enlarged cross-sectional view of a partition wall of a particulate filter.
FIG. 13 is a diagram showing the amount of fine particles that can be removed by oxidation.
FIG. 14 is a diagram showing a map of the amount of fine particles that can be removed by oxidation.
FIG. 15 shows oxygen concentration and NO in exhaust gas._X  It is a figure which shows the map of a density | concentration.
[Explanation of symbols]
1 ... Engine body
2 ... Engine intake system
3 ... Engine exhaust system
4 ... Throttle valve
5 ... Air flow meter
6 ... Particulate filter
7 ... Exhaust gas recirculation passage
7a ... Control valve
20 ... Control device

Claims (3)

A particulate filter disposed in the engine exhaust system, first determination means for determining the regeneration timing of the particulate filter based on the amount of exhaust particulate discharged from the cylinder, and the amount of fresh air taken into the engine intake system Based on the second judgment means for judging the regeneration timing of the particulate filter and the regeneration means for regenerating the particulate filter, and the particulate judgment is performed by at least one of the first judgment means and the second judgment means. When it is determined that the curative filter is in the regeneration period, the particulate filter is regenerated by the regeneration means, and the internal combustion engine exhausts the exhaust gas communicating with the upstream side of the particulate filter of the engine exhaust system and the engine intake system. Recirculation through recirculation passage and exhaust gas recirculation passage A control valve for controlling the amount of gas to an optimum value according to the engine operating state, and the second judging means opens the new valve after opening the control valve to a set opening at the time of fuel cut. An exhaust gas purification apparatus for an internal combustion engine, wherein the regeneration time of the particulate filter is determined based on an air volume . The first determination means and the second determination means determine the regeneration time after estimating the amount of particulate collection in the particulate filter, and the particulate collection estimated by the first determination means. It is determined that at least one of the internal combustion engine and the regeneration means is abnormal when the collected amount is lower than a set value or more than the particulate collection amount estimated at the same time by the second judging means. The exhaust emission control device for an internal combustion engine according to claim 1. 2. The exhaust gas purification of an internal combustion engine according to claim 1, wherein the first determination unit determines a regeneration timing of the particulate filter in consideration of an amount of particulate removed by oxidation on the particulate filter. apparatus.

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